Anti-lock braking systemFrom Wikipedia, the free encyclopedia

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An anti-lock braking system (ABS, from German: Antiblockiersystem) is a safety system that allows

the wheels on a motor vehicle to continue interacting tractively with the road surface as directed by driver

steering inputs while braking, preventing the wheels from locking up (that is, ceasing rotation) and therefore

avoiding skidding.

An ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery

surfaces for many drivers; however, on loose surfaces like gravel or snow-covered pavement, an ABS can

significantly increase braking distance, although still improving vehicle control.[1]

Since initial widespread use in production cars, anti-lock braking systems have evolved considerably.

Recent versions not only prevent wheel lock under braking, but also electronically control the front-to-rear

brake bias. This function, depending on its specific capabilities and implementation, is known as electronic

brakeforce distribution (EBD), traction control system, emergency brake assist, or electronic stability

control (ESC).

Operation

The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake).[9]

A typical ABS includes a central electronic control unit (ECU), four wheel speed sensors, and at least two hydraulic valves within the brake hydraulics. The ECU constantly monitors the rotational speed of each wheel; if it detects a wheel rotating significantly slower than the others, a condition indicative of impending wheel lock, it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel; the wheel then turns faster. Conversely, if the ECU detects a wheel turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied, slowing down the wheel. This process is repeated continuously and can be detected by the driver via brake pedal pulsation. Some anti-lock system can apply or release braking pressure 16 times per second.[10]

The ECU is programmed to disregard differences in wheel rotative speed below a critical threshold, because when the car is turning, the two wheels towards the center of the curve turn slower than the outer two. For this same reason, a differential is used in virtually all roadgoing vehicles.

If a fault develops in any part of the ABS, a warning light will usually be illuminated on the vehicle instrument panel, and the ABS will be disabled until the fault is rectified.

The modern ABS applies individual brake pressure to all four wheels through a control system of hub-mounted sensors and a dedicated micro-controller. ABS is offered or comes standard on most road vehicles produced today and is the foundation for ESC systems, which are rapidly increasing in popularity due to the vast reduction in price of vehicle electronics over the years.[11]

Modern electronic stability control (ESC or ESP) systems are an evolution of the ABS concept. Here, a minimum of two additional sensors are added to help the system work: these are a steering wheel angle sensor, and a gyroscopic sensor. The theory of operation is simple: when the gyroscopic sensor detects that the direction taken by the car does not coincide with what the steering wheel sensor reports, the ESC software will brake the necessary individual wheel(s) (up to three with the most sophisticated systems), so that the vehicle goes the way the driver intends. The steering wheel sensor also helps in the operation of Cornering Brake Control (CBC), since this will tell the ABS that wheels on the inside of the curve should brake more than wheels on the outside, and by how much.

The ABS equipment may also be used to implement a traction control system(TCS) on acceleration of the vehicle. If, when accelerating, the tire loses traction, the ABS controller can detect the situation and take suitable action so that traction is regained. More sophisticated versions of this can also control throttle levels and brakes simultaneously.

[edit]Components

There are four main components to an ABS: speed sensors, valves, a pump, and a controller.

Speed sensors

The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information.

ValvesThere is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:

In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.

In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.

In position three, the valve releases some of the pressure from the brake.

PumpSince the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.

ControllerThe controller is an ECU type unit in the car which receives information from each individual wheel speed sensor, in turn if a wheel loses traction the signal is sent to the controller, the controller will then limit the brakeforce (EBD) and activate the ABS modulator which actuates the braking valves on and off.

[edit]Use

There are many different variations and control algorithms for use in an ABS. One of the simpler systems works as follows:[10]

1. The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 km/h) under

ideal conditions, but a wheel that locks up could stop spinning in less than a second.

2. The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.

3. When the ABS system is in operation the driver will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. This pulsing also tells the driver that the ABS has been triggered. Some ABS systems can cycle up to 16 times per second.

[edit]Brake types

Anti-lock braking systems use different schemes depending on the type of brakes in use. They can be differentiated by the number of channels: that is, how many valves that are individually controlled—and the number of speed sensors.[10]

Four-channel, four-sensor ABSThis is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

Three-channel, four-sensor ABSThere is a speed sensor on all four wheels and a separate valve for each of the front wheels, but only one valve for both of the rear wheels.

Three-channel, three-sensor ABSThis scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front

wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle. This system provides individual control of the front wheels, so they can both achieve maximum braking force. The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness. This system is easy to identify, as there are no individual speed sensors for the rear wheels.

One-channel, one-sensor ABSThis system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle. This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness. This system is also easy to identify, as there are no individual speed sensors for any of the wheels.

[edit]Effectiveness

A 2003 Australian study by Monash University Accident Research Centre found that ABS:[1]

Reduced the risk of multiple vehicle crashes by 18 percent,

Reduced the risk of run-off-road crashes by 35 percent.

On high-traction surfaces such as bitumen, or concrete, many (though not all) ABS-equipped cars are able to attain braking distances better (i.e. shorter) than those that would be easily possible without the benefit of ABS. In real world conditions even an alert, skilled driver without ABS would find it difficult, even through the use of techniques like threshold braking, to match or improve on the performance of a typical driver with a modern ABS-equipped vehicle. ABS reduces

chances of crashing, and/or the severity of impact. The recommended technique for non-expert drivers in an ABS-equipped car, in a typical full-braking emergency, is to press the brake pedal as firmly as possible and, where appropriate, to steer around obstructions. In such situations, ABS will significantly reduce the chances of a skid and subsequent loss of control.

In gravel, sand and deep snow, ABS tends to increase braking distances. On these surfaces, locked wheels dig in and stop the vehicle more quickly. ABS prevents this from occurring. Some ABS calibrations reduce this problem by slowing the cycling time, thus letting the wheels repeatedly briefly lock and unlock. Some vehicle manufacturers provide an "off-road" button to turn ABS function off. The primary benefit of ABS on such surfaces is to increase the ability of the driver to maintain control of the car rather than go into a skid, though loss of control remains more likely on soft surfaces like gravel or slippery surfaces like snow or ice. On a very slippery surface such as sheet ice or gravel, it is possible to lock multiple wheels at once, and this can defeat ABS (which relies on comparing all four wheels, and detecting individual wheels skidding). Availability of ABS relieves most drivers from learning threshold braking.

A June 1999 National Highway Traffic Safety Administration (NHTSA) study found that ABS increased stopping distances on loose gravel by an average of 22 percent.[12]

According to the NHTSA,

"ABS works with your regular braking system by automatically pumping them. In vehicles not equipped with ABS, the driver has to manually pump the brakes to prevent wheel lockup. In vehicles equipped with ABS, your foot should remain firmly planted on the brake pedal, while ABS pumps the brakes for you so you can concentrate on steering to safety."

When activated, some earlier ABS systems caused the brake pedal to pulse noticeably. As most drivers rarely or never brake hard enough to cause brake lock-up, and a significant number rarely bother to read the car's manual,[citation needed] this may not be discovered until an emergency. When drivers do encounter an emergency that causes them to brake hard, and thus encounter this pulsing for the first time, many are believed to reduce pedal pressure, and thus lengthen braking distances, contributing to a higher level of accidents than the superior emergency stopping capabilities of ABS would otherwise promise. Some manufacturers have therefore implemented a brake assist system that determines that the driver is attempting a "panic stop" (by detecting that the brake pedal was depressed very fast, unlike a normal stop where the pedal pressure would usually be gradually increased, Some systems additionally monitor the rate at the accelerator was released)[citation needed] and the system automatically increases braking force where not enough pressure is applied. Hard or panic braking on bumpy surfaces, because of the bumps causing the speed of the wheel(s) to become erratic may also trigger the ABS. Nevertheless, ABS significantly improves

safety and control for drivers in most on-road situations.

Anti-lock brakes are the subject of some experiments centred around risk compensation theory, which asserts that drivers adapt to the safety benefit of ABS by driving more aggressively. In a Munich study, half a fleet of taxicabs was equipped with anti-lock brakes, while the other half had conventional brake systems. The crash rate was substantially the same for both types of cab, and Wilde concludes this was due to drivers of ABS-equipped cabs taking more risks, assuming that ABS would take care of them, while the non-ABS drivers drove more carefully since ABS would not be there to help in case of a dangerous situation.[13] A similar study was carried out in Oslo, with similar results.[citation needed]

[edit]

Diesel engineA diesel engine (also known as a compression-ignition engine) is an internal combustion

engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into

the combustion chamber. This is in contrast to spark-ignition engines such as a petrol

engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which uses

a spark plug to ignite an air-fuel mixture. The engine was developed by Rudolf Diesel in 1893.

The diesel engine has the highest thermal efficiency of any regular internal or external

combustion engine due to its very high compression ratio. Low-speed Diesel engines (as used in

ships and other applications where overall engine weight is relatively unimportant) often have a

thermal efficiency which exceeds 50 percent.[1][2] [3] [4]

Diesel engines are manufactured in two stroke and four stroke versions. They were originally used as

a more efficient replacement for stationary steam engines. Since the 1910s they have been used

insubmarines and ships. Use in locomotives, large trucks and electric generating plants followed later.

In the 1930s, they slowly began to be used in a few automobiles. Since the 1970s, the use of diesel

engines in larger on-road and off-road vehicles in the USA increased. As of 2007, about 50 percent of

all new car sales in Europe are diesel.[5]

The world's largest diesel engine is currently a Wärtsilä Sulzer RT96-C Common Rail marine diesel of

about 108,920 hp (81,220 kW) @ 102 rpm [6] output.[7

How diesel engines work

The diesel internal combustion engine differs from the gasoline powered Otto cycle by using highly

compressed, hot air to ignite the fuel rather than using a spark plug (compression ignition rather

than spark ignition).

In the true diesel engine, only air is initially introduced into the combustion chamber. The air is then

compressed with a compression ratio typically between 15:1 and 22:1 resulting in 40-bar (4.0 MPa;

580 psi) pressure compared to 8 to 14 bars (0.80 to 1.4 MPa) (about 200 psi) in the petrol engine.

This high compression heats the air to 550 °C (1,022 °F). At about the top of the compression stroke,

fuel is injected directly into the compressed air in the combustion chamber. This may be into a

(typically toroidal) void in the top of the piston or a pre-chamber depending upon the design of the

engine. The fuel injector ensures that the fuel is broken down into small droplets, and that the fuel is

distributed evenly. The heat of the compressed air vaporizes fuel from the surface of the droplets. The

vapour is then ignited by the heat from the compressed air in the combustion chamber, the droplets

continue to vaporise from their surfaces and burn, getting smaller, until all the fuel in the droplets has

been burnt. The start of vaporisation causes a delay period during ignition and the characteristic

diesel knocking sound as the vapor reaches ignition temperature and causes an abrupt increase in

pressure above the piston. The rapid expansion of combustion gases then drives the piston

downward, supplying power to the crankshaft.[25] Engines for scale-model aeroplanes use a variant of

the Diesel principle but premix fuel and air via a carburation system external to the combustion

chambers.

As well as the high level of compression allowing combustion to take place without a separate ignition

system, a high compression ratio greatly increases the engine's efficiency. Increasing the

compression ratio in a spark-ignition engine where fuel and air are mixed before entry to the cylinder

is limited by the need to prevent damaging pre-ignition. Since only air is compressed in a diesel

engine, and fuel is not introduced into the cylinder until shortly before top dead centre (TDC),

premature detonation is not an issue and compression ratios are much higher.

Major advantages

Diesel engines have several advantages over other internal combustion engines:

They burn less fuel than a petrol engine performing the same work, due to the engine's higher

temperature of combustion and greater expansion ratio.[1] Gasoline engines are typically 30

percent efficient while diesel engines can convert over 45 percent of the fuel energy into

mechanical energy.[27]

They have no high-tension electrical ignition system to attend to, resulting in high reliability and

easy adaptation to damp environments. The absence of coils, spark plug wires, etc., also

eliminates a source of radio frequency emissions which can interfere with navigation and

communication equipment, which is especially important in marine and aircraft applications.

They can deliver much more[quantify] of their rated power on a continuous basis than a petrol engine.

[citation needed]

The life of a diesel engine is generally about twice as long as that of a petrol engine[28] due to the

increased strength of parts used. Diesel fuel has better lubrication properties than petrol as well.

Diesel fuel is considered safer than petrol in many applications. Although diesel fuel will burn in

open air using a wick, it will not explode and does not release a large amount of flammable vapor.

The low vapor pressure of diesel is especially advantageous in marine applications, where the

accumulation of explosive fuel-air mixtures is a particular hazard. For the same reason, diesel

engines are immune to vapor lock.

For any given partial load the fuel efficiency (mass burned per energy produced) of a diesel

engine remains nearly constant, as opposed to petrol and turbine engines which use

proportionally more fuel with partial power outputs.[29][30][31][32]

They generate less waste heat in cooling and exhaust.[1]

Diesel engines can accept super- or turbo-charging pressure without any natural limit,

constrained only by the strength of engine components. This is unlike petrol engines, which

inevitably suffer detonation at higher pressure.

The carbon monoxide content of the exhaust is minimal, therefore diesel engines are used in

underground mines.[33]

Biodiesel  is an easily synthesized, non-petroleum-based fuel (through transesterification) which

can run directly in many diesel engines, while gasoline engines either need adaptation to

run synthetic fuels or else use them as an additive to gasoline (e.g., ethanol added to gasohol).

Mechanical and electronic injection

Many configurations of fuel injection have been used over the past century (1901–2000).

Most present day (2008) diesel engines make use of a camshaft, rotating at half crankshaft speed,

lifted mechanical single plunger high pressure fuel pump driven by the engine crankshaft. For each

cylinder, its plunger measures the amount of fuel and determines the timing of each injection. These

engines use injectors that are very precise spring-loaded valves that open and close at a specific fuel

pressure. For each cylinder a plunger pump is connected to an injector with a high pressure fuel line.

Fuel volume for each single combustion is controlled by a slanted groove in the plunger which rotates

only a few degrees releasing the pressure and is controlled by a mechanical governor, consisting of

weights rotating at engine speed constrained by springs and a lever. The injectors are held open by

the fuel pressure. On high speed engines the plunger pumps are together in one unit.[34] Each fuel line

should have the same length to obtain the same pressure delay.

A cheaper configuration on high speed engines with fewer than six cylinders is to use an axial-piston

distributor pump, consisting of one rotating pump plunger delivering fuel to a valve and line for each

cylinder (functionally analogous to points and distributor cap on an Otto engine).[26] This contrasts with

the more modern method of having a single fuel pump which supplies fuel constantly at high pressure

with a common rail (single fuel line common) to each injector. Each injector has a solenoidoperated by

an electronic control unit, resulting in more accurate control of injector opening times that depend on

other control conditions, such as engine speed and loading, and providing better engine performance

and fuel economy. This design is also mechanically simpler than the combined pump and valve

design, making it generally more reliable, and less loud, than its mechanical counterpart.

Both mechanical and electronic injection systems can be used in either direct or indirect

injection configurations.

Older diesel engines with mechanical injection pumps could be inadvertently run in reverse, albeit

very inefficiently, as witnessed by massive amounts of soot being ejected from the air intake. This was

often a consequence of push starting a vehicle using the wrong gear. Large ship diesels can run

either way.

Injection pumpFrom Wikipedia, the free encyclopedia

This article may require cleanup to meet Wikipedia's quality standards. (Consider using more specific clean up instructions.) Please improve this article if you can. The talk page may contain suggestions. (February 2008)

Injection pump for a 12-cylinder diesel engine

An Injection Pump is the device that pumps fuel into the cylinders of a diesel engine or less typically,

a gasoline engine. Traditionally, the pump is driven indirectly from the crankshaft by gears, chains or a

toothed belt (often the timing belt) that also drives the camshaft on overhead-cam engines ( OHC ). It

rotates at half crankshaft speed in a conventional four-stroke engine. Its timing is such that the fuel is

injected only very slightly before top dead centre of that cylinder's compression stroke. It is also common

for the pump belt on gasoline engines to be driven directly from the camshaft. In some systems injection

pressures can be as high as 200Mpa.

Contents

[hide]

1 Safety

2 Construction

3 New types

4 References

[edit]Safety

Because of the need for positive injection into a very high-pressure environment, the pump develops great

pressure—typically 15,000 psi (100 MPa) or more on newer systems. This is a good reason to take great

care when working on diesel systems; escaping fuel at this sort of pressure can easily penetrate skin and

clothes, and be injected into body tissues with medical consequences serious enough to

warrant amputation.[1]

[edit]Construction

Inline diesel injection pump

Earlier diesel pumps used an in-line layout with a series of cam-operated injection cylinders in a line, rather

like a miniature inline engine. The pistons have a constant stroke volume, and injection volume (ie,

throttling) is controlled by rotating the cylinders against a cut-off port that aligns with a helical slot in the

cylinder. When all the cylinders are rotated at once, they simultaneously vary their injection volume to

produce more or less power from the engine. Inline pumps still find favour on large multi-cylinder engines

such as those on trucks, construction plant, static engines and agricultural vehicles.

Distributor diesel injection pump

For use on cars and light trucks, the rotary pump or distributor pump was developed. It uses a single

injection cylinder driven from an axial cam plate, which injects into the individual fuel lines via a rotary

distribution valve. Later incarnations such as the Bosch VE pump vary the injection timing with crank speed

to allow greater power at high crank speeds, and smoother, more economical running at slower revs. Some

VE variants have a pressure-based system that allows the injection volume to increase over normal to

allow a turbocharger or supercharger equipped engine to develop more power under boost conditions.

Inline diesel metering pump

All injection pumps incorporate a governor to cut fuel supply if the crank speed endangers the engine - the

heavy moving parts of diesel engines do not tolerate overspeeding well, and catastrophic damage can

occur if they are over-revved.

ROTARY PUMP

General Description – An external view of atypical pump is shown in Fig. 1 and an internalsection in Fig. 2.The main rotating components are the driveshaft (1), distributor rotor (2), transfer pumpblades (5), and governor components (11).The drive shaft engages the distributor rotorin the hydraulic head. The drive end of therotor incorporates two pumping plungers.The plungers are actuated toward eachother simultaneously by an internal cam ringthrough rollers and shoes which are carried inslots at the drive end of the rotor. The numberof cam lobes normally equals the number ofengine cylinders.Fig. 1 — PumpFig. 2 — Sectional viewThe transfer pump at the rear of the rotor isthe postive displacement vane-type and isenclosed in the end cap. The end cap alsohouses the fuel inlet strainer and transfer pumppressure regulator. Transfer pump pressure isautomatically compensated for viscosity effectsdue to both temperature changes and variousfuel grades.The distributor rotor incorporates twocharging ports and a single axial bore with onedischarge port to serve all head outlets to theinjection tubings. The hydraulic head containsthe bore in which the rotor revolves, the meteringvalve bore, the charging ports and the headoutlet fittings. The high pressure injectiontubings leading to the nozzles are fastened tothese fittings.Distributor pumps contain their ownmechanical governor capable of close speedregulation. Both all-speed and min-max typesare available. The centrifugal force of the weightsin their retainer is transmitted through a sleeveto the governor arm and through a linkage tothe metering valve. The metering valve can beclosed to shut off fuel through the linkage by anindependently operated shut-off lever.Components:1. Drive Shaft2. Distributor Rotor3. Hydraulic Head4. Delivery Valve5. Transfer Pump6. Pressure Regulator7. Discharge Fitting8. Metering Valve9. Pumping Plungers10. Internal Cam Ring11. Governor12. Governor Weights13. Advance14. Drive Shaft Bushing15. Housing16. Rollers

4Regulating pistonInlet side Regulating slotRegulating springRegulatorThin plateOrifice

Spring Adjusting PlugDischarge sideFig. 3 — Transfer pump regulatorShoeThe automatic speed advance is a hydraulicmechanism which advances or retards thebeginning of fuel delivery from the pump. Thiscan respond to speed alone, or to a combinationof speed and load changes. A more detaileddescription of each pump area will be coveredin the following pages.Transfer pump pressure regulation – Refer toFig. 3 for the following description. Filtered, lowpressure fuel from an overhead tank or a liftpump passes through the transfer pump inletscreen. This vane-type pump consists of astationary liner and four spring loaded blades,which are carried in the rotor slots. Excess fuelis recirculated to the transfer pump inlet bymeans of the pressure regulator piston, spring,and ported sleeve. Fuel pressure from thetransfer pump forces the piston in the regulatorsleeve against the spring. The pressure curve iscontrolled by the pump displacement, springrate and preload, and regulating slotconfiguration. Therefore, pressure increaseswith speed.The transfer pump operates consistentlyover a wide viscosity range determined bydifferent grades of diesel fuels and also whenaffected by varying temperatures. A thin plateincorporating a sharp-edged orifice is located inthe spring adjusting plug. Flow through anorifice of this type is virtually unaffected byviscosity changes. An additional biasing pressureis exerted against the spring side of the pistonand is determined by the linear flow aroundthe regulating piston and the flow through theorifice. With cold or viscous fuels a reducedflow occurs through the piston and sleevePlungerRotorLeaf springclearance, and the additional biasing pressure isslight. With hot or low viscosity fuels theclearance flow increases and the pressure withinthe spring chamber increases. The regulatingspring and higher biasing pressure forcescombine to control the slot area. This controlmaintains a nearly constant transfer pumppressure over a broad range of fuel viscositiesand thus maintains stable automatic advanceoperation over various fuel types andtemperatures.Hydraulic head and rotor – Fig. 4 shows anexploded view of the rotor and the pumpingplungers. The cam rollers contact the innersurface of the cam ring form and push theplungers toward each other for injection. Theshoes act as tappets betweenthe rollers and plungers.

Cam rollerLeaf spring screwFig. 4 — Rotor and plungerRefer to Fig. 5. As the rotor revolves, its twoinlet passages register with the charging annulusports in the hydraulic head. Transfer pump fuelcontrolled by the metering valve opening, flowsinto the pumping chamber forcing the plungersapart. The plungers move outward for a distanceproportional to the amount of fuel required forthe next injection stroke. If only a small amountis admitted, as at idling, the plungers move outa short distance. If half-load is required,approximately half the pumping chamber isfilled. This process is known as inlet metering.5Full-load delivery is controlled by themaximum plunger travel. This plunger travel islimited by the leaf spring as it is contacted bythe edge of the shoes.Roller betweencam lobesPlunger Meteringvalve Circularfuel passageRotorLeafspringCamShoe Inletpassages ChargingpassageIransterpumpcam lobeCam RotorOutlet fittingDeliveryRoller contactsvalve Discharge portPumpingchamberFig. 5 — Plunger chargingRefer to Fig. 6. The leaf spring contacts twopoints near the outer ends of the rotor. As theadjusting screw is turned inward, the center ofthe leaf spring moves in and its ends extendoutward. This increases the maximum plungertravel. Turning the adjusting screw out has thereverse effect. The adjustment set point isretained by the screw head-to-leaf springCam ringLeaf springPlungersFig. 6 — Cam, plungers and leaf springfriction and the coating material on the screwthreads.As the rotor continues to revolve (Fig. 7),the inlet ports move out of registry and therotor discharge port indexes with one of thehead outlets. The rollers then contact opposingcam lobes which force the shoes inward againstthe plungers. At this point high pressure pumpingbegins. Further rotation of the rotor moves theFig. 7 — Plunger dischargingrollers along the cam ramps forcing the plungers

together. During the discharge stroke the fuelbetween the plungers is displaced into the axialpassage of the rotor through the delivery valveto the discharge port. The pressurized fuel thenpasses through the outlet fitting, enters theinjection tubing and opens the nozzle. Deliverycontinues until the rollers travel over the camnoses and begin to move outwardly. The pressurein the axial passage is then reduced, allowingthe nozzle to close.6

Common railCommon rail direct fuel injection is a modern variant of direct fuel injection system

for petrol and diesel engines.

Common rail fuel injector

On diesel engines, it features a high-pressure (over 1,000 bar/15,000 psi) fuel rail feeding

individual solenoid valves, as opposed to low-pressure fuel pump feeding unit injectors (Pumpe/Düse

or pump nozzles). Third-generation common rail diesels now feature piezoelectric injectors for

increased precision, with fuel pressures up to 1,800 bar/26,000 psi.

In gasoline engines, it is utilised in gasoline direct injection engine technology.

Principles

Solenoid or piezoelectric valves make possible fine electronic control over the fuel injection time and

quantity and the higher pressure that the common rail technology makes available provides better

fuel atomisation. In order to lower engine noise, the engine's electronic control unit can inject a small

amount of diesel just before the main injection event ("pilot" injection), thus reducing its explosiveness

and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold

starting and so on. Some advanced common rail fuel systems perform as many as five injections per

stroke.[6]

Common rail engines require very short (< 1 s) or no heating up time at all[citation needed] and produce

lower engine noise and emissions than older systems.

Diesel engines have historically used various forms of fuel injection. Two common types include the

unit injection system and the distributor/inline pump systems (See diesel engine and unit injector for

more information). While these older systems provided accurate fuel quantity and injection timing

control, they were limited by several factors:

They were cam driven and injection pressure was proportional to engine speed. This typically

meant that the highest injection pressure could only be achieved at the highest engine speed and

the maximum achievable injection pressure decreased as engine speed decreased. This

relationship is true with all pumps, even those used on common rail systems; with the unit or

distributor systems, however, the injection pressure is tied to the instantaneous pressure of a

single pumping event with no accumulator and thus the relationship is more prominent and

troublesome.

They were limited in the number and timing of injection events that could be commanded during a

single combustion event. While multiple injection events are possible with these older systems, it

is much more difficult and costly to achieve.

For the typical distributor/inline system, the start of injection occurred at a pre-determined

pressure (often referred to as: pop pressure) and ended at a pre-determined pressure. This

characteristic resulted from "dummy" injectors in the cylinder head which opened and closed at

pressures determined by the spring preload applied to the plunger in the injector. Once the

pressure in the injector reached a pre-determined level, the plunger would lift and injection would

start.

In common rail systems, a high pressure pump stores a reservoir of fuel at high pressure — up to and

above 2,000 bars (29,000 psi). The term "common rail" refers to the fact that all of the fuel injectors

are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel

is stored at high pressure. This accumulator supplies multiple fuel injectors with high pressure fuel.

This simplifies the purpose of the high pressure pump in that it only has to maintain a commanded

pressure at a target (either mechanically or electronically controlled). Thefuel injectors are typically

ECU-controlled. When the fuel injectors are electrically activated, a hydraulic valve (consisting of a

nozzle and plunger) is mechanically or hydraulically opened and fuel is sprayed into the cylinders at

the desired pressure. Since the fuel pressure energy is stored remotely and the injectors are

electrically actuated, the injection pressure at the start and end of injection is very near the pressure in

the accumulator (rail), thus producing a square injection rate. If the accumulator, pump and plumbing

are sized properly, the injection pressure and rate will be the same for each of the multiple injection

events.

Basic Engine Parts

The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. The engine described above has one cylinder. That is typical of most lawn mowers, but most cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed or boxer), as shown in the following figures.

Figure 2. Inline - The cylinders are arranged in a line in a single bank.

Figure 3. V - The cylinders are arranged in two banks set at an angle to one another.

Figure 4. Flat - The cylinders are arranged in two banks on opposite sides of the engine.Different configurations have different advantages and disadvantages in terms of smoothness, manufacturing cost and shape characteristics. These advantages and disadvantages make them more suitable for certain vehicles.

Let's look at some key engine parts in more detail.

Spark plug The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly.

Valves The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.

PistonA piston is a cylindrical piece of metal that moves up and down inside the cylinder.

Piston ringsPiston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes:

They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion.

They keep oil in the sump from leaking into the combustion area, where it would be burned and lost.Most cars that "burn oil" and have to have a quart added every 1,000 miles are burning it because the engine is old and the rings no longer seal things properly.

Connecting rodThe connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates.

Crankshaft The crankshaft turns the piston's up and down motion into circular motion just like a crank on a jack-in-the-box does.

Sump The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).

Next, we'll learn what can go wrong with engines.

Automotive batteryFrom Wikipedia, the free encyclopedia

12 V, 40 Ah Lead-acid car battery

An automotive battery is a type of rechargeable battery that supplies electric energy to an automobile.

[1] Usually this refers to an SLI battery (starting, lighting, ignition) to power the starter motor, the lights, and

the ignition system of a vehicle’s engine. An automotive battery may also be a traction battery used for the

main power source of an electric vehicle.

Automotive SLI batteries are usually lead-acid type, and are made of six galvanic cells in series to provide

a 12 volt system. Each cell provides 2.1 volts for a total of 12.6 volt at full charge. Heavy vehicles such as

highway trucks or tractors, often equipped with Diesel engines, may have two batteries in series for a 24

volt system, or may have parallel strings of batteries.

Lead-acid batteries are made up of plates of lead and separate plates of lead dioxide, which are

submerged into an electrolyte solution of about 35% sulfuric acid and 65% water.[2] This causes a chemical

reactionthat releases electrons, allowing them to flow through conductors to produce electricity. As the

battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface

to lead sulfate. When the battery is recharged, the chemical reaction is reversed: the lead sulfate reforms

into lead oxide and lead. With the plates restored to their original condition, the process may now be

repeated.

Battery recycling of automotive batteries reduces resources required for manufacture of new batteries and

diverts toxic lead from landfills or improper disposal.

Contents

[hide]

1 Types

2 Use and maintenance

o 2.1 Fluid level

o 2.2 Charge and discharge

o 2.3 Storage

o 2.4 Changing a battery

o 2.5 Freshness

3 Failure

4 Exploding batteries

5 Terms and ratings

6 Terminal voltage

7 See also

8 References

9 External links

[edit]Types

Lead-acid batteries for automotive use are made with slightly different construction techniques, depending

on the application of the battery. The "flooded cell" type, indicating liquid electrolyte, is typically inexpensive

and long-lasting, but requires more maintenance and can spill or leak. Flooded batteries are distinguished

by the removable caps that allow for the electrolyte to be tested and maintained.

More costly alternatives to flooded batteries are "Sealed" or "Valve regulated" battery of the absorbed glass

mat (AGM) type which uses a glass mat separator, and a "gel cell" uses fine powder to absorb and

immobilize the sulfuric acid electrolyte. These batteries are not serviceable (typically termed "maintenance-

free") and do not require replenishment of electrolyte under normal use. Both types of sealed batteries may

be used in vehicular applications where leakage is a concern. However, this article deals with the classic,

flooded-type of car battery.

The starting (cranking) or shallow cycle type is designed to deliver large bursts of power for a short time,

as is needed to start an engine. Once the engine is started, the battery is recharged by the engine-driven

charging system. Starting batteries are intended to have a low depth of discharge on each use. They are

constructed of many thin plates with thin separators between the plates, and may have a higher specific

gravity electrolyte to reduce internal resistance. [1]

The deep cycle (or motive) type is designed to continuously provide power for long periods of time (for

example in a trolling motor for a small boat, auxiliary power for a recreational vehicle, or traction power for

a golf cart or other battery electric vehicle). They can also be used to store energy from a photovoltaic array

or a small wind turbine. Deep-cycle batteries have fewer, thicker plates and are intended to have a greater

depth of discharge on each cycle, but will not provide as high a current on heavy loads. The thicker plates

survive a higher number of charge/discharge cycles. The specific energy is in the range of 30-40 watt-

hours per kilogram.[2] Some battery manufacturers claim their batteries are dual purpose (for both starting

and deep cycling). This may include "marine" type batteries that may be labeled "deep discharge", which is

slightly different than "deep cycle".

Some cars use more exotic starter batteries- the 2010 Porsche 911 GT3 RS offers a lithium-ion battery as

an option to save weight over a conventional lead-acid battery.[3]

[edit]Use and maintenance

[edit]Fluid level

Filling a (flooded lead-acid type) car battery with distilled water

Car batteries using lead-antimony plates would require regular watering to replace water lost due

to electrolysis on each charging cycle. By changing the alloying element to calcium, more recent designs

have lower water loss, unless overcharged. Modern car batteries have reduced maintenance requirements,

and may not provide caps for addition of water to the cells. Such batteries include extra electrolyte above

the plates to allow for losses during the battery life. If the battery has easily detachable caps then a top-up

with distilled water may be required from time to time. Prolonged overcharging or charging at excessively

high voltage causes some of the water in the electrolyte to be broken up into hydrogen and oxygen gases,

which escape from the cells. If the electrolyte liquid level drops too low, the plates are exposed to air, lose

capacity, and are damaged. The sulfuric acid in the battery normally does not require replacement since it

is not consumed even on overcharging. Impurities or additives in the water will reduce the life and

performance of the battery. Manufacturers usually recommend use of demineralized or distilled water,

since even potable tap water can contain high levels of minerals.

[edit]Charge and discharge

In normal automotive service the vehicle's charging system powers the vehicle's electrical systems and

restores charge used from the battery during engine cranking. When installing a new battery or recharging

a battery that has been accidentally discharged completely, one of several different methods can be used

to charge it. The most gentle of these is called trickle charging. Other methods include slow-charging and

quick-charging, the latter being the harshest.

The voltage regulator of the charge system does not measure the relative currents charging the battery and

for powering the car's loads. The charge system essentially provides a fixed voltage of typically 13.8 to 14.4

V (Volt), adjusted to ambient temperature, unless the alternator is at its current limit. A discharged battery

draws a high current of typically 20 to 40 A (Ampere). As the battery gets charged the charge current

typically decreases 2 A to 5 A. A high load results when multiple high-power systems such as ignition,

radiator fan, heater blowers, lights and entertainment system are running. In this case, the battery voltage

will decrease and the charge current as well.

Some manufacturers include a built-in hydrometer to show the state of charge of the battery. This acrylic

"eye" has a float immersed in the electrolyte. When the battery is charged, the specific gravity of the

electrolyte increases (since all the sulfate ions are in the electrolyte, not combined with the plates), and the

colored top of the float is visible in the window. When the battery is discharged (or if the electrolyte level is

too low), the float sinks and the window appears yellow (or black). The built-in hydrometer only checks the

state of charge of one cell and will not show faults in the other cells. In a non-sealed battery each of the

cells can be checked with a portable or hand-held hydrometer.

Jumper cable connected to battery post. Hydrometer window visible by jumper clamp. White powdery corrosion

products visible on top of battery. This BCI Group 24F battery claims 525 cold cranking amperes and 125 minutes

reserve capacity. A battery this size weighs about 20 kg (44 lbs).

In emergencies a vehicle can be jump started by the battery of another vehicle or by a portable battery

booster.

Whenever the car's charge system is inadequate to fully charge the battery, a battery charger can be used.

Simple chargers will not regulate the charge current and the user needs to stop the process or lower the

charge current to prevent excessive gassing of the battery. More elaborate chargers, in particular those

implementing the 3-step charge profile, also referred to as IUoU, charge the battery fully and safely in a

short time without requiring user intervention. Desulfating chargers are also commercially available for

charging all types of lead-acid batteries.

[edit]Storage

Batteries last longer when stored in a charged state. Leaving an automotive battery discharged will shorten

a battery's life or make it unusable if left for an extended period (usually over several

years); sulfationeventually becomes irreversible by normal charging. Batteries in storage may be monitored

and periodically charged, or attached to a "float" charger to retain their capacity. Batteries are prepared for

storage by charging and cleaning the posts deposits. Batteries are stored in a cool, dry environment for

best results since high temperatures increase the self discharge rate and plate corrosion.

[edit]Changing a battery

When changing a battery, battery manufacturers recommend disconnecting the ground connection first to

prevent accidental short-circuits between the battery terminal and the vehicle frame. A study by the

National Highway Traffic Safety Association estimated that in 1994 more than 2000 people were injured in

the United States while working with automobile batteries.

The majority of automotive lead-acid batteries are filled with the appropriate electrolyte solution at the

manufacturing plant, and shipped to the retailers ready to sell. Decades ago, this was not the case. The

retailer filled the battery, usually at the time of purchase, and charged the battery. This was a time-

consuming and potentially dangerous process. Care had to be taken when filling the battery with acid, as

acids are highly corrosive and can damage eyes, skin and mucous membranes. Fortunately, this is less of

a problem these days, and the need to fill a battery with acid usually only arises when purchasing a

motorcycle or ATV battery.

[edit]Freshness

Because of "sulfation", lead-acid batteries stored with electrolyte slowly deteriorate. Car batteries are date

coded to ensure installation within one year of manufacture. In the United States, the manufacturing date is

printed on a sticker. The date can be written in plain text or using an alphanumerical code. The first

character is a letter that specifies the month (A for January, B for February and so on).[4] The letter "I" is

skipped due to its potential to be mistaken for the number 1. The second character is a single digit that

indicates the year of manufacturing (for example, 6 for 2006). When first installing a newly purchased

battery a "top up" charge at a low rate with an external battery charger (available at auto parts stores) may

maximize battery life and minimize the load on the vehicle charging system.

[edit]Failure

Common battery faults include:

Shorted cell due to failure of the separator between the positive and negative plates

Shorted cell or cells due to build up of shed plate material below the plates of the cell

Broken internal connections due to corrosion

Broken plates due to vibration and corrosion

Low electrolyte level

Cracked or broken case

Broken terminals

Sulfation after prolonged disuse in a low or zero charged state

Corrosion at the battery terminals can prevent a car from starting due to electrical resistance. The white

powder sometimes found around the battery terminals is usually lead sulfate which is toxic by inhalation,

ingestion and skin contact. The corrosion is caused by an imperfect seal between the plastic battery case

and lead battery post allowing sulfuric acid to react with the lead battery posts. The corrosion process is

also expedited by over charging. Corrosion can also be caused by factors such as salt water, dirt, heat,

humidity, cracks in the battery casing or loose battery terminals. Inspection, cleaning and protection with a

light coating of dielectric grease are measures used to prevent corrosion of battery terminals.

Sulfation occurs when a battery is not fully charged. The longer it remains in a discharged state the harder

it is to overcome sulfation. This may be overcome with slow, low-current (trickle) charging. Sulfation is the

formation of large, non-conductive lead sulfate crystals on the plates; lead sulfate formation is part of each

cycle, but in the discharged condition the crystals become large and block passage of current through the

electrolyte.

The primary wear-out mechanism is the shedding of active material from the battery plates, which

accumulates at the bottom of the cells and which may eventually short-circuit the plates.

Early automotive batteries could sometimes be repaired by dismantling and replacing damaged separators,

plates, intercell connectors and other repairs. Modern battery cases do not facilitate such repairs; an

internal fault generally requires replacement of the entire unit. [1]

[edit]Exploding batteries

Car battery after explosion

Any lead-acid battery system when overcharged will produce hydrogen gas (gassing) by electrolysis of

water. If the rate of overcharge is small, the vents of each cell allow the dissipation of the gas. However, on

severe overcharge or if ventilation is inadequate, or the battery is faulty, a flammable concentration of

hydrogen may remain in the cell or in the battery enclosure. An internal spark can cause

a hydrogen and oxygen explosion, which will damage the battery and its surroundings and which will

disperse acid into the surroundings. Anyone close to the battery may be injured.

Sometimes the ends of a battery will be severely swollen, and when accompanied by the case being too

hot to touch, this usually indicates a malfunction in the charging system of the car. Reversing the positive

and negative leads will damage the battery. When severely overcharged, a lead-acid battery produces high

levels of hydrogen and the venting system built into the battery cannot handle the high level of gas, so the

pressure builds inside the battery, resulting in the swollen ends. An unregulated alternator can quickly ruin

a battery by excessive voltage. A swollen, hot battery is dangerous.

Persons handling car batteries should wear protective equipment (goggles, overalls, gloves) to avoid injury

by acid spills. Any open flame or electric sparks in the area also present a danger of ignition of any

hydrogen gas emanating from a battery.

BrakeFrom Wikipedia, the free encyclopedia

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (April 2010)

This article is about the vehicle component. For other uses, see Brake (disambiguation).

Disc brake on a motorcycle

A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this

article is dedicated to various types of vehicular brakes.

Most commonly brakes use friction to convert kinetic energy into heat, though other methods of energy

conversion may be employed. For example regenerative braking converts much of the energy to electrical

energy, which may be stored for later use. Other methods convert kinetic energy into potential energy in

such stored forms as pressurized air or pressurized oil. Still other braking methods even transformkinetic

energy into different forms, for example by transferring the energy to a rotating flywheel.

Brakes are generally applied to rotating axles or wheels, but may also take other forms such as the surface

of a moving fluid (flaps deployed into water or air). Some vehicles use a combination of braking

mechanisms, such as drag racing cars with both wheel brakes and a parachute, or airplanes with both

wheel brakes and drag flaps raised into the air during landing.

Since kinetic energy increases quadratically with velocity (K = mv2 / 2), an object traveling at 10 meters

per second has 100 times as much energy as one traveling at 1 meter per second, and consequently the

theoretical braking distance, when braking at the traction limit, is 100 times as long. In practice, fast

vehicles usually have significant air drag, and energy lost to air drag rises quickly with speed.

Almost all wheeled vehicles have a brake of some sort. Even baggage carts and shopping carts may have

them for use on a moving ramp. Most fixed-wing aircraft are fitted with wheel brakes on theundercarriage.

Some aircraft also feature air brakes designed to reduce their speed in flight. Notable examples

include gliders and some World War II-era aircraft, primarily some fighter aircraft and many dive

bombers of the era. These allow the aircraft to maintain a safe speed in a steep descent. The Saab B

17 dive bomber used the deployed undercarriage as an air brake.

Friction brakes on automobiles store braking heat in the drum brake or disc brake while braking then

conduct it to the air gradually. When traveling downhill some vehicles can use their engines to brake.

When the brake pedal is pushed a piston pushes the pad towards the brake disc which slows the wheel

down. On the brake drum it is similar as the cylinder pushes the brake shoes towards the drum which also

slows the wheel down.

Contents

[hide]

1 Types

2 Characteristics

o 2.1 Brake boost

3 Noise

4 Inefficiency

5 See also

6 References

7 External links

[edit]Types

Brakes may be broadly described as using friction, pumping, or electromagnetics. One brake may use

several principles: for example, a pump may pass fluid through an orifice to create friction:

Frictional brakes are most common and can be divided broadly into "shoe" or "pad" brakes, using an

explicit wear surface, and hydrodynamic brakes, such as parachutes, which use friction in a working

fluid and do not explicitly wear. Typically the term "friction brake" is used to mean pad/shoe brakes and

excludes hydrodynamic brakes, even though hydrodynamic brakes use friction.

Friction (pad/shoe) brakes are often rotating devices with a stationary pad and a rotating wear surface.

Common configurations include shoes that contract to rub on the outside of a rotating drum, such as

a band brake; a rotating drum with shoes that expand to rub the inside of a drum, commonly called a

"drum brake", although other drum configurations are possible; and pads that pinch a rotating disc,

commonly called a "disc brake". Other brake configurations are used, but less often. For

example, PCC trolley brakes include a flat shoe which is clamped to the rail with an electromagnet;

the Murphy brake pinches a rotating drum, and the Ausco Lambert disc brake uses a hollow disc (two

parallel discs with a structural bridge) with shoes that sit between the disc surfaces and expand

laterally.

Pumping brakes are often used where a pump is already part of the machinery. For example, an

internal-combustion piston motor can have the fuel supply stopped, and then internal pumping losses

of the engine create some braking. Some engines use a valve override called a Jake brake to greatly

increase pumping losses. Pumping brakes can dump energy as heat, or can be regenerative brakes

that recharge a pressure resivoir called an hydraulic accumulator.

Electromagnetic brakes are likewise often used where an electric motor is already part of the

machinery. For example, many hybrid gasoline/electric vehicles use the electric motor as a generator

to charge electric batteries and also as a regenerative brake. Some diesel/electric railroad locomotives

use the electric motors to generate electricity which is then sent to a resistor bank and dumped as

heat. Some vehicles, such as some transit buses, do not already have an electric motor but use a

secondary "retarder" brake that is effectively a generator with an internal short-circuit. Related types of

such a brake are eddy current brakes, and electro-mechanical brakes (which actually are magnetically

driven friction brakes, but nowadays are often just called “electromagnetic brakes” as well).

[edit]Characteristics

Brakes are often described according to several characteristics including:

Peak force – The peak force is the maximum decelerating effect that can be obtained. The peak force

is often greater than the traction limit of the tires, in which case the brake can cause a wheel skid.

Continuous power dissipation – Brakes typically get hot in use, and fail when the temperature gets

too high. The greatest amount of power (energy per unit time) that can be dissipated through the brake

without failure is the continuous power dissipation. Continuous power dissipation often depends on

e.g., the temperature and speed of ambient cooling air.

Fade – As a brake heats, it may become less effective, called brake fade. Some designs are inherently

prone to fade, while other designs are relatively immune. Further, use considerations, such as cooling,

often have a big effect on fade.

Smoothness – A brake that is grabby, pulses, has chatter, or otherwise exerts varying brake force

may lead to skids. For example, railroad wheels have little traction, and friction brakes without an anti-

skid mechanism often lead to skids, which increases maintenance costs and leads to a "thump thump"

feeling for riders inside.

Power – Brakes are often described as "powerful" when a small human application force leads to a

braking force that is higher than typical for other brakes in the same class. This notion of "powerful"

does not relate to continuous power dissipation, and may be confusing in that a brake may be

"powerful" and brake strongly with a gentle brake application, yet have lower (worse) peak force than a

less "powerful" brake.

Pedal feel – Brake pedal feel encompasses subjective perception of brake power output as a function

of pedal travel. Pedal travel is influenced by the fluid displacement of the brake and other factors.

Drag – Brakes have varied amount of drag in the off-brake condition depending on design of the

system to accommodate total system compliance and deformation that exists under braking with ability

to retract friction material from the rubbing surface in the off-brake condition.

Durability – Friction brakes have wear surfaces that must be renewed periodically. Wear surfaces

include the brake shoes or pads, and also the brake disc or drum. There may be tradeoffs, for example

a wear surface that generates high peak force may also wear quickly.

Weight – Brakes are often "added weight" in that they serve no other function. Further, brakes are

often mounted on wheels, and unsprung weight can significantly hurt traction in some circumstances.

"Weight" may mean the brake itself, or may include additional support structure.

Noise – Brakes usually create some minor noise when applied, but often create squeal or grinding

noises that are quite loud.

[edit]Brake boost

Most modern vehicles use a vacuum assisted brake system that greatly increases the force applied to the

vehicle's brakes by its operator.[1] This additional force is supplied by the vacuum generated by the running

engine, but this force is greatly reduced when the engine is running at full throttle and the available vacuum

is diminished.

Because of this, reports of unintended acceleration are often accompanied by complaints of failed or

weakened brakes, as the high-revving engine is unable to provide enough vacuum to power the brake

booster. This problem is exacerbated in vehicles equipped with automatic transmissions as the vehicle will

automatically downshift upon application of the brakes, thereby further elevating engine RPM and reducing

available braking power while increasing the engine's effective torque.

[edit]Noise

Brake lever on a horse-drawn hearse

Main article: Roadway noise

Although ideally a brake would convert all the kinetic energy into heat, in practice a significant amount may

be converted into acoustic energy instead, contributing to noise pollution.

For road vehicles, the noise produced varies significantly with tire construction, road surface, and the

magnitude of the deceleration.[2] Noise can be caused by different things. These are signs that there may

be issues with brakes wearing out over time.

[edit]Inefficiency

A significant amount of energy is always lost while braking, even with regenerative braking which is not

perfectly efficient. Therefore a good metric of efficient energy use while driving is to note how much one is

braking. If the majority of deceleration is from unavoidable friction instead of braking, one is squeezing out

most of the service from the vehicle. Minimizing brake use is one of the fuel economy-maximizing

behaviors.

While energy is always lost during a brake event, a secondary factor that influences efficiency is "off-brake

drag", or drag that occurs when the brake is not intentionally actuated. After a braking event, hydraulic

pressure drops in the system , allowing the brake caliper pistons to retract. However, this retraction must

accommodate all compliance in the system (under pressure) as well as thermal distortion of components

like the brake disc or the brake system will drag until the contact with the disc, for example, knocks the

pads and pistons back from the rubbing surface. During this time, there can be significant brake drag. This

brake drag can lead to significant parasitic power loss, thus impact fuel economy and vehicle performance.

Drum brakeFrom Wikipedia, the free encyclopedia

This article relies largely or entirely upon a single source. Please help improve this article by introducing appropriate citations to additional sources. (July 2008)

A drum brake with the drum removed as used on the rear wheel of a car or truck. Note that in this installation, a cable-

operated parking brake uses the service shoes.

A drum brake is a brake in which the friction is caused by a set of shoes or pads that press against a

rotating drum-shaped part called a brake drum.

The term "drum brake" usually means a brake in which shoes press on the inner surface of the drum.

When shoes press on the outside of the drum, it is usually called a clasp brake. Where the drum is pinched

between two shoes, similar to a conventional disk brake, it is sometimes called a "pinch drum brake",

although such brakes are relatively rare. A related type of brake uses a flexible belt or "band" wrapping

around the outside of a drum, called a band brake.

Components

The Drum Brake has a large number of components depending upon the type of vehicle, in which it is used. Some of the major components of the Drum brake are:

Back Plate Brake Drum Wheel cylinder Brake shoe Springs and pins

[edit]Back Plate

The Back Plate serves as the base on which all the components are assembled. It attaches to the axle and forms a solid surface for the wheel cylinder, brake shoes and assorted hardware. Since all the braking operations exert pressure on the back plate, it needs to be very strong and resistant to any wear and tear or corrosion. A good back plate hardly creates any problem. Apart from these parts, Lever for Emergency or Parking brake, and Automatic Brake-shoe adjuster are also present in the brakes of the recent years.

Back plate made in the pressing shop.

[edit]Brake Drum

The brake drum is generally made of a special type of cast iron. It is positioned very close to the brake shoe without actually touching it, and rotates with the wheel and axle. As the lining is pushed against the inner surface of the drum, friction heat can reach as high as 600 degrees F. The brake drum must be:

1. Accurately balanced.2. Sufficiently rigid.3. Resistant against wear.4. Highly heat-conductive.5. Lightweight.

[edit]Wheel Cylinder

One wheel cylinder is used for each wheel. Two pistons operate the shoes, one at each end of the wheel cylinder. When hydraulic pressure from the master cylinder acts upon the piston cup, the pistons are pushed toward the shoes, forcing them against the drum. When the brakes are not being applied, the piston is returned to its

original position by the force of the brake shoe return springs. The parts of the wheel cylinder are as follows:

Cut-away section of a wheel cylinder.

Piston Compression spring Dust cap Protective plug Bleed screw Self - locking screw.[edit]Brake shoe

Brake shoes are made of two pieces of sheet steel welded together. The friction material is attached to the Lining table either by adhesive bonding or riveting. The crescent shaped piece is called the Web and contains holes and slots in different shapes for return springs, hold-down hardware, parking brake linkage and self-adjusting components. All the application force of the wheel cylinder is applied through the web to the lining table and brake lining. The edge of the lining table generally has three “V" shaped notches or tabs on each side called Nibs. The nibs rest against the support pads of the backing plate to which the shoes are installed. Each brake assembly has two shoes, a primary and secondary. The primary shoe is located toward the front of the vehicle and has the lining positioned differently than the secondary shoe. Quite often the two shoes are interchangeable, so close inspection for any variation is important.

Brake shoe assembly

Linings must be resistant against heat and wear and have a high friction coefficient. This coefficient must be as unaffected as possible by fluctuations in temperature and humidity. Materials which make up the brake shoe include,

Friction modifiers, Powdered metal, Binders, Fillers and Curing agents.

Friction modifiers such as graphite and cashew nut shells, alter the friction coefficient. Powdered metals such as lead, zinc, brass, aluminium and other metals increase a material’s resistance to heat fade. Binders are the glues that hold the friction material together. Fillers are added to friction material in small quantities to accomplish specific purposes, such as rubber chips to reduce brake noise.

[edit]Springs and Pins

The various springs and accompanying components present in the drum brake are as follows,

Spring plate Retaining pin Lower return spring Holder pin Holder spring

The brakes are held against the backing plate by retaining clips and springs. The hold down spring is used to retain the brake shoe in

position in relation to the backing plate. During vehicle operation it keeps the brake shoe in position.

[edit]Automatic Brake Self Adjuster

This Adjuster consists of the following components

Sectional layout showing the push rods, Nut adjuster and Lever pawl.

Push rod male and female Nut adjuster Lever pawl

It is used to adjust the distance between the brake shoe and the drum automatically, in the case of brake shoe wear.

[edit]Working:

[edit]Normal Braking Operation

When you apply the brakes, brake fluid is forced under pressure from the Tandem Master Cylinder (TMC) into the wheel cylinder, which in turn pushes the brake shoes into contact with the machined surface on the inside of the drum. This rubbing action reduces the rotation of the brake drum, which is coupled to the wheel. Hence the speed of the vehicle is reduced. When the pressure is released, return springs pull the shoes back to their rest position.

[edit]Automatic Brake Self-Adjuster

As the brake linings wear, the shoes must travel a greater distance to reach the drum. When the distance reaches a certain point, a self-adjusting mechanism automatically reacts by adjusting the rest position of the shoes so that they are closer to the drum. Here, the adjusting lever rocks enough to advance the adjuster gear by one tooth. The adjuster has threads on it, like a bolt, so that it unscrews a little bit when it turns, lengthening to fill in the gap. When the brake shoes wear a little more, the adjuster can advance again, so it always keeps the shoes close to the drum.

[edit]Emergency Brake

The parking brake (emergency brake) system controls the brakes through a series of steel cables that are connected to either a hand lever or a foot pedal. The idea is that the system is fully mechanical and completely bypasses the hydraulic system so that the vehicle can be brought to a stop even if there is a total brake failure. Here the cable pulls on a lever mounted in the brake and is directly connected to the brake shoes. This has the effect of bypassing the wheel cylinder and controlling the brakes directly.

[edit]Self-applying characteristic

Drum brakes have a natural "self-applying" characteristic, better known as "self-energizing." [1] The rotation of the drum can drag either or both of the shoes into the friction surface, causing the brakes to bite harder, which increases the force holding them together. This increases the stopping power without any additional effort being expended by the driver, but it does make it harder for the driver to modulate the brake's sensitivity. It also makes the brake more sensitive to brake fade, as a decrease in brake friction also reduces the amount of brake assist.

Disc brakes exhibit no self-applying effect because the hydraulic pressure acting on the pads is perpendicular to the direction of rotation of the disc.[1] Disc brake systems usually have servo assistance ("Brake Booster") to lessen the driver's pedal effort, but some disc braked cars (notably race cars) and smaller brakes for motorcycles, etc., do not need to use servos.[1]

Note: In most designs, the "self applying" effect only occurs on one shoe. While this shoe is further forced into the drum surface by a moment due to friction, the opposite effect is happening on the other shoe. The friction force is trying to rotate it away from the drum. The forces are different on each brake shoe resulting in one shoe wearing faster. It is possible to design a two-shoe drum brake where both shoes are self-applying (having separate actuators and pivoted at opposite ends), but these are very uncommon in practice.

[edit]Drum brake designs

Rendering of a drum brake

Drum brakes are typically described as either leading/trailing or twin leading.[1]

Rear drum brakes are typically of a leading/trailing design(For Non Servo Systems), or [Primary/Secondary] (For Duo Servo Systems) the shoes being moved by a single double-acting hydraulic cylinder and hinged at the same point.[1] In this design, one of the brake shoes will always experience the self-applying effect, irrespective of whether the vehicle is moving forwards or backwards.[1] This is particularly useful on the rear brakes, where the parking brake (handbrake or footbrake) must exert enough force to stop the vehicle from travelling backwards and hold it on a slope. Provided the contact area of the brake shoes is large enough, which isn't always the case, the self-applying effect can securely hold a vehicle when the weight is transferred to the rear brakes due to the incline of a slope or the reverse direction of motion. A further advantage of using a single hydraulic cylinder on the rear is that the opposite pivot may be made in the form of a double lobed cam that is rotated by the action of the parking brake system.

Front drum brakes may be of either design in practice, but the twin leading design is more effective.[1] This design uses two actuating cylinders arranged so that both shoes will utilize the self-applying characteristic when the vehicle is moving forwards.[1] The brake shoes pivot at opposite points to each other.[1] This gives the maximum possible braking when moving forwards, but is not so effective when the vehicle is traveling in reverse.[1]

The optimum arrangement of twin leading front brakes with leading/trailing brakes on the rear allows for more braking force to be deployed at the front of the vehicle when it is moving forwards, with less at the rear. This helps to prevent the rear wheels locking up, but still provides adequate braking at the rear when it is needed.[1]

The brake drum itself is frequently made of cast iron, although some vehicles have used aluminum drums, particularly for front-wheel applications. Aluminum conducts heat better than cast iron, which improves heat dissipation and reduces fade. Aluminum drums are also lighter than iron drums, which reduces unsprung weight. Because aluminum wears more easily than iron, aluminum drums will frequently have an iron or steel liner on the inner surface of the drum, bonded or riveted to the aluminum outer shell.

[edit]Advantages

Drum brakes are used in most heavy duty trucks, some medium and light duty trucks, and few cars, dirt bikes, and ATV's. Drum brakes are often applied to the rear wheels since most of the stopping force is generated by the front brakes of the vehicle and therefore the heat generated in the rear is significantly less. Drum brakes allow simple incorporation of a parking brake. Drum brakes are also occasionally fitted as the parking (and emergency) brake even when the rear wheels use disk brakes as the main brakes. In this situation, a small drum is usually fitted within or as part of the brake disk also known as a banksia brake.

In hybrid vehicle applications, wear on braking systems is greatly reduced by energy recovering motor-generators (see regenerative braking), so some hybrid vehicles such as the GMC Yukon hybrid and Toyota Prius (except the third generation) use drum brakes.

Disc brakes rely on pliability of caliper seals and slight runout to release pads, leading to drag, fuel mileage loss, and disc scoring. Drum brake return springs give more positive action and, adjusted correctly, often have less drag when released.

Certain heavier duty drum brake systems compensate for load when determining wheel cylinder pressure; a feature unavailable when disks are employed. One such vehicle is the Jeep Comanche. The

Comanche can automatically send more pressure to the rear drums depending on the size of the load, whereas this would not be possible with disks.

Due to the fact that a drum brakes friction contact area is at the circumference of the brake, a drum brake can provide more braking force than an equal diameter disc brake. The increased friction contact area of drum brake shoes on the drum allows drum brake shoes to last longer than disc brake pads used in a brake system of similar dimensions and braking force. Drum brakes retain heat and are more complex than disc brakes but are often the more economical and powerful brake type to use in rear brake applications due to the low heat generation of rear brakes, a drum brakes self applying nature, large friction surface contact area, and long life wear characteristics(%life used/kW of braking power).

Although drum brakes are often the better choice for rear brake applications in all but the highest performance applications, vehicle manufactures are increasingly installing disc brake system at the rear wheels. This is due to the popularity rise of disc brakes after the introduction front ventilated disc brakes. Front ventilated disc brakes performed much better than the front drum brakes they replaced. The difference in front drum and disc brake performance caused car buyers to purchase cars that also had rear disc brakes. Additionally rear disc brakes are often associated with high performance race cars which has increase their popularity in street cars. Rear disc brakes in most applications are not ventilated and offer no performance advantage over drum brakes. Even when rear discs are ventilated, it is likely that the rear brakes will never benefit from the ventilation unless subjected to very high performance racing style driving.

[edit]As a tailshaft parking/emergency brake

Drum brakes have also been incorporated on the transmission tailshaft as parking brakes (e.g. Chryslers through 1956), with the an advantage that it is completely independent of the service brakes, but having a severe disadvantage in that when used with a bumper jack (common in that era) on the rear (without proper wheel blocks) the differential's action can allow the vehicle to roll off the jack.

[edit]Disadvantages

Drum brakes, like most other types, are designed to convert kinetic energy into heat by friction.[1] This heat is intended to be further transferred to atmosphere, but can just as easily transfer into other components of the braking system.

Brake drums have to be large to cope with the massive forces that are involved, and they must be able to absorb and dissipate a lot of heat. Heat transfer to atmosphere can be aided by incorporating cooling fins onto the drum. However, excessive heating can occur due to heavy or repeated braking, which can cause the drum to distort, leading to vibration under braking.

The other consequence of overheating is brake fade.[1] This is due to one of several processes or more usually an accumulation of all of them.

1. When the drums are heated by hard braking, the diameter of the drum increases slightly due to thermal expansion, this means the brakes shoes have to move farther and the brake pedal has to be depressed further.

2. The properties of the friction material can change if heated, resulting in less friction. This can be a much larger problem with drum brakes than disk brakes, since the shoes are inside the drum and not exposed to cooling ambient air. The loss of friction is usually only temporary and the material regains its efficiency when cooled,[1] but if the surface overheats to the point where it becomes glazed the reduction in braking efficiency is more permanent. Surface glazing can be worn away with further use of the brakes, but that takes time.

3. Excessive heating of the brake drums can cause the brake fluid to vaporize, which reduces the hydraulic pressure being applied to the brake shoes.[1] Therefore less retardation is achieved for a given amount of pressure on the pedal. The effect is worsened by poor maintenance. If the brake fluid is old and has absorbed moisture it thus has a lower boiling point and brake fade occurs sooner.[1]

Brake fade is not always due to the effects of overheating. If water gets between the friction surfaces and the drum, it acts as a lubricant

and reduces braking efficiency.[1] The water tends to stay there until it is heated sufficiently to vaporize, at which point braking efficiency is fully restored. All friction braking systems have a maximum theoretical rate of energy conversion. Once that rate has been reached, applying greater pedal pressure will not result in a change of this rate, and indeed the effects mentioned can substantially reduce it. Ultimately this is what brake fade is, regardless of the mechanism of its causes.

Disc brakes are not immune to any of these processes, but they deal with heat and water more effectively than drums.

Drum brakes can be grabby if the drum surface gets light rust or if the brake is cold and damp, giving the pad material greater friction. Grabbing can be so severe that the tires skid and continue to skid even when the pedal is released. Grab is the opposite of fade: when the pad friction goes up, the self-assisting nature of the brakes causes application force to go up. If the pad friction and self-amplification are high enough, the brake will stay on due to self-application even when the external application force is released.

Another disadvantage of drum brakes is their relative complexity. A person must have a general understanding of how drum brakes work and take simple steps to ensure the brakes are reassembled correctly when doing work on drum brakes. And, as a result of this increased complexity (compared to disk brakes), maintenance of drum brakes is generally more time-consuming. Also, the greater number of parts results in a greater number of failure modes compared to disk brakes. Springs can break from fatigue if not replaced along with worn brake shoes. And the drum and shoes can become damaged from scoring if various components (such as broken springs or self-adjusters) break and become loose inside the drum.[edit]

Disc brakeFrom Wikipedia, the free encyclopedia

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (June 2008)

Close-up of a disc brake on a car

On automobiles, disc brakes are often located within the wheel

The disc brake or disk brake is a device for slowing or stopping the rotation of a wheel while it is in

motion.

A brake disc (or rotor in U.S. English) is usually made of cast iron, but may in some cases be made of

composites such as reinforced carbon-carbon or ceramic matrix composites. This is connected to the

wheel and/or the axle. To stop the wheel, friction material in the form of brake pads (mounted on a device

called a brake caliper) is forced mechanically, hydraulically, pneumatically or electromagnetically against

both sides of the disc. Friction causes the disc and attached wheel to slow or stop. Brakes convert motion

to heat, and if the brakes get too hot, they become less effective, a phenomenon known as brake fade.

Discs

A cross-drilled disc on a modern motorcycle

The design of the disc varies somewhat. Some are simply solid cast iron, but others are hollowed out with fins or vanes joining together the disc's two contact surfaces (usually included as part of a casting process). The weight and power of the vehicle will determine the need for ventilated discs.[10] The "ventilated" disc design helps to dissipate the generated heat and is commonly used on the more-heavily-loaded front discs.

Many higher performance brakes have holes drilled through them. This is known as cross-drilling and was originally done in the 1960s on racing cars. For heat dissipation purposes, cross drilling is still used on some braking components, but is not favored for racing or other hard use as the holes are a source of stress cracks under severe conditions.

Discs may also be slotted, where shallow channels are machined into the disc to aid in removing dust and gas. Slotting is the preferred method in most racing environments to remove gas, water, and de-glaze brake pads. Some discs are both drilled and slotted. Slotted discs are generally not used on standard vehicles because they quickly wear down brake pads; however, this removal of material is beneficial to race vehicles since it keeps the pads soft and avoids vitrification of their surfaces.

As a way of avoiding thermal stress, cracking and warping of the disc these are sometimes mounted in a half loose way to the hub with coarse splines. This allows the disc to expand in a controlled symmetrical way and with less unwanted heat transfer to the hub.

On the road, drilled or slotted discs still have a positive effect in wet conditions because the holes or slots prevent a film of water building up between the disc and the pads. Crossdrilled discs may eventually crack at the holes due to metal fatigue. Cross-drilled brakes that are manufactured poorly or subjected to high stresses will crack much sooner and more severely.

[edit]On motorcycles

Motorcycle disc brakes have become increasingly sophisticated, partly through marketing. Their discs are usually drilled and occasionally slotted. Calipers have evolved from simple "single-pot" units to 2-, 4- and even 6-pot items. It is debatable whether the modern fashions of "radially-mounted calipers" and "wavy discs" significantly improve braking. Since (compared to cars) motorcycles have a higher centre of gravity:wheelbase ratio, they experience more weight transference when braking. A modern sports bike will typically have twin front discs of large diameter, but only a single rear disc that is very much smaller (or even a small rear drum brake). The front brake(s) provide most of the required deceleration; the rear brake serves mainly as to "balance" the motorcycle during braking. If too much braking force is applied to the rear brake, the rear wheel is liable to lock up; so motorcycles should not have oversize rear brakes.

[edit]On bicycles

See also: Bicycle brake#Disc brakes.

A mountain bike disc brake

Mountain bike disc brakes range from simple, mechanical (cable) systems, to expensive and powerful, 6-pot (piston) hydraulic disc systems, commonly used on downhill racing bikes. Improved technology has seen the creation of the first vented discs for use on

mountain bikes, similar to those on cars, introduced to help avoid heat fade on fast alpine descents. Although less common, discs are also used on road bicycles for all-weather cycling with predictable braking, although drums are sometimes preferred as harder to damage in crowded parking, where discs are sometimes bent. Most bicycle brake discs are made of stainless steel, although some lightweight discs are made of titanium or aluminium. Discs are thin, often about 2 mm. Some use a two-piece floating disc style, others use a floating caliper, others use pads that float in the caliper, and some use one moving pad that makes the caliper slide on its mounts, pulling the other pad into contact with the disc. Because the "motor" is small, an uncommon feature of bicycle brakes is pads that retract to eliminate residual drag when the brake is released. In contrast, most other brakes drag the pads lightly when released.

[edit]On other vehicles

Disc brakes are increasingly used on very large and heavy road vehicles, where previously large drum brakes were nearly universal. One reason is the disc's lack of self-assist makes brake force much more predictable, so peak brake force can be raised without more risk of braking-induced steering or jackknife on articulated vehicles. Another is disc brakes fade less when hot, and in a heavy vehicle air and rolling drag and engine braking are small parts of total braking force, so brakes are used harder than on lighter vehicles, and drum brake fade can occur in a single stop. For these reasons, a heavy truck with disc brakes can stop in about 120% the distance of a passenger car, but with drums stopping takes about 150% the distance.[14] In Europe, stopping distance regulations essentially require disc brakes for heavy vehicles. In the U.S., drums are allowed and are typically preferred for their lower purchase price, despite higher total lifetime cost and more frequent service intervals.

A railroad bogie and disc brakes

Yet larger discs are used for railroads and some airplanes. Passenger rail cars and light rail often use disc brakes outboard of the wheels, which helps ensure a free flow of cooling air. In contrast, some airplanes have the brake mounted with very little cooling and the brake gets quite hot in a stop, but this is acceptable as the maximum braking energy is very predictable.

For auto use, disc brake discs are commonly manufactured out of a material called grey iron. The SAE maintains a specification for the manufacture of grey iron for various applications. For normal car and light truck applications, the SAE specification is J431 G3000 (superseded to G10). This specification dictates the correct range of hardness, chemical composition, tensile strength, and other properties necessary for the intended use. Some racing cars and airplanes use brakes with carbon fiber discs and carbon fiber pads to reduce weight. Wear rates tend to be high, and braking may be poor or grabby until the brake is hot.[edit]

Suspension (vehicle)From Wikipedia, the free encyclopedia

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (April 2010)

The front suspension components of a Ford Model T.

The rear suspension on a truck: a leaf spring.

Part of car front suspension and steeringmechanism: tie rod, steering arm, king pin axis (using ball joints).

Van Diemen RF01 Racing Car Suspension.

Suspension is the term given to the system of springs, shock absorbers and linkages that connects

a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's

roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle

occupants comfortable and reasonably well isolated from road noise, bumps, and vibrations,etc. These

goals are generally at odds, so the tuning of suspensions involves finding the right compromise. It is

important for the suspension to keep the road wheel in contact with the road surface as much as possible,

because all the forces acting on the vehicle do so through the contact patches of the tires. The suspension

also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front

and rear suspension of a car may be different.

This article is primarily about four-wheeled (or more) vehicle suspension. For information on two-wheeled

vehicles' suspensions see the suspension (motorcycle), motorcycle fork, bicycle suspension, andbicycle

fork articles.

GEAR BOX

Automotive basics

The need for a transmission in an automobile is a consequence of the characteristics of the internal

combustion engine. Engines typically operate over a range of 600 to about 7000 revolutions per

minute (though this varies, and is typically less for diesel engines), while the car's wheels rotate

between 0 rpm and around 1800 rpm.

Furthermore, the engine provides its highest torque outputs approximately in the middle of its range,

while often the greatest torque is required when the vehicle is moving from rest or traveling slowly.

Therefore, a system that transforms the engine's output so that it can supply high torque at low

speeds, but also operate at highway speeds with the motor still operating within its limits, is required.

Transmissions perform this transformation.

Many transmissions and gears used in automotive and truck applications are contained in a cast

iron case, though more frequently aluminium is used for lower weight especially in cars. There are

usually three shafts: a mainshaft, a countershaft, and an idler shaft.

The mainshaft extends outside the case in both directions: the input shaft towards the engine, and the

output shaft towards the rear axle (on rear wheel drive cars- front wheel drives generally have the

engine and transmission mounted transversely, the differential being part of the transmission

assembly.) The shaft is suspended by the main bearings, and is split towards the input end. At the

point of the split, a pilot bearing holds the shafts together. The gears and clutches ride on the

mainshaft, the gears being free to turn relative to the mainshaft except when engaged by the clutches.

Types of automobile transmissions include manual, automatic or semi-automatic transmission.

[edit]Manual

A five-speed gearbox.

Main article: Manual transmission

Manual transmission come in two basic types:

a simple but rugged sliding-mesh or unsynchronized / non-synchronous system, where straight-

cut spur gear sets are spinning freely, and must be synchronized by the operator matching

engine revs to road speed, to avoid noisy and damaging "gear clash",

and the now common constant-mesh gearboxes which can include non-synchronised,

or synchronized / synchromesh systems, where diagonal cut helical (and sometimes double-

helical) gear sets are constantly "meshed" together, and a dog clutch is used for changing gears.

On synchromesh boxes, friction cones or "synchro-rings" are used in addition to the dog clutch.

The former type is commonly found in many forms of racing cars, older heavy-duty trucks, and some

agricultural equipment.

Manual transmissions are the most common type outside North America and Australia. They are

cheaper, lighter, usually give better performance, and fuel efficiency (although automatic

transmissions with torque converter lockup and advanced electronic controls can provide similar

results). It is customary for new drivers to learn, and be tested, on a car with a manual gear change.

In Malaysia and Denmark all cars used for testing (and because of that, virtually all those used for

instruction as well) have a manual transmission. In Japan, the

Philippines, Germany, Poland, Italy, Israel, the Netherlands, Belgium, New Zealand, Austria,Bulgaria,

the UK,[3][4] Ireland,[4] Sweden, Estonia, France, Spain, Switzerland, the Australian states of Victoria,

Western Australia and Queensland, Finland and Lithuania, a test pass using an automatic car does

not entitle the driver to use a manual car on the public road; a test with a manual car is required.[citation

needed] Manual transmissions are much more common than automatic transmissions

in Asia, Africa, South America and Europe.

Many manual transmissions include both synchronized and unsynchronized gearing; it is not

uncommon for the first/reverse gear to lack synchros. Those gears are meant to be shifted into only

when the vehicle is stopped.

Some manual transmissions have an extremely low ratio for first gear, which is referred to as a

"creeper gear" or "granny gear". Such gears are usually not synchronized. This feature is common on

pickup trucks tailored to trailer-towing, farming, or construction-site work. During normal on-road use,

the truck is usually driven without using the creeper gear at all, and second gear is used from a

standing start.

[edit]Non-synchronous

Main article: Non-synchronous transmissions

There are commercial applications engineered with designs taking into account that the gear shifting

will be done by an experienced operator. They are a manual transmission, but are known as non-

synchronized transmissions. Dependent on country of operation, many local, regional, and national

laws govern the operation of these types of vehicles (see Commercial Driver's License). This class

may include commercial, military, agricultural, or engineering vehicles. Some of these may use

combinations of types for multi-purpose functions. An example would be a power take-off (PTO) gear.

The non-synchronous transmission type requires an understanding of gear range, torque, engine

power, and multi-functional clutch and shifter functions. Also see Double-clutching, and Clutch-

brake sections of the main article.

[edit]Automatic

Main article: Automatic transmission

Epicyclic gearing or planetary gearing as used in an automatic transmission.

Most modern North American and Australian and many larger, high specification European and

Japanese cars have an automatic transmission that will select an appropriate gear ratio without any

operator intervention. They primarily use hydraulics to select gears, depending on pressure exerted

by fluid within the transmission assembly. Rather than using a clutch to engage the transmission, a

fluid flywheel, ortorque converter is placed in between the engine and transmission. It is possible for

the driver to control the number of gears in use or select reverse, though precise control of which gear

is in use may or may not be possible.

Automatic transmissions are easy to use. However, in the past, automatic transmissions of this type

have had a number of problems; they were complex and expensive, sometimes had reliability

problems (which sometimes caused more expenses in repair), have often been less fuel-efficient than

their manual counterparts (due to "slippage" in the torque converter), and their shift time was slower

than a manual making them uncompetitive for racing. With the advancement of modern automatic

transmissions this has changed.[citation needed]

Attempts to improve the fuel efficiency of automatic transmissions include the use of torque

converters which lock up beyond a certain speed, or in the higher gear ratios, eliminating power loss,

and overdrive gears which automatically actuate above certain speeds; in older transmissions both

technologies could sometimes become intrusive, when conditions are such that they repeatedly cut in

and out as speed and such load factors as grade or wind vary slightly. Current computerized

transmissions possess very complex programming to both maximize fuel efficiency and eliminate any

intrusiveness.[citation needed]

For certain applications, the slippage inherent in automatic transmissions can be advantageous; for

instance, in drag racing, the automatic transmission allows the car to be stopped with the engine at a

high rpm (the "stall speed") to allow for a very quick launch when the brakes are released; in fact, a

common modification is to increase the stall speed of the transmission. This is even more

advantageous for turbocharged engines, where the turbocharger needs to be kept spinning at high

rpm by a large flow of exhaust in order to keep the boost pressure up and eliminate the turbo lag that

occurs when the engine is idling and the throttle is suddenly opened.

[edit]Semi-automatic

Main article: Semi-automatic transmission

The creation of computer control also allowed for a sort of cross-breed transmission where the car

handles manipulation of the clutch automatically, but the driver can still select the gear manually if

desired. This is sometimes called a "clutchless manual," or "automated manual" transmission. Many

of these transmissions allow the driver to give full control to the computer. They are generally

designed using manual transmission "internals", and when used in passenger cars, have

synchromesh operated helical constant mesh gear sets.

Specific type of this transmission includes: Easytronic, and Geartronic.

A "dual-clutch" transmission uses two sets of internals which are alternately used, each with its own

clutch, so that only the clutches are used during the actual "gearchange".

Specific type of this transmission includes: Direct-Shift Gearbox.

There are also sequential transmissions which use the rotation of a drum to switch gears.[5

TurbochargerFrom Wikipedia, the free encyclopedia

"Turbo" redirects here. For other uses, see Turbo (disambiguation).

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (May 2010)

It has been suggested that Superturbocharging be merged into this article or section. (Discuss) Proposed since July 2011.

Cut-away view of an air foil bearing-supported turbocharger made by Mohawk Innovative Technology

A turbocharger, or turbo (colloquialism), is a centrifugal compressor powered by a turbine which is driven

by an engine's exhaust gases. Its benefit lies with the compressor increasing the pressure of air entering

the engine (forced induction) thus resulting in greater performance (for either, or both, power & efficiency).

They are popularly used with internal combustion engines(e.g. four-stroke engines like Otto

cycles and Diesel cycles). Turbochargers have also been found useful compounding external combustion

engines such as automotive fuel cells.[1]

Operating principle

This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (May 2010)

All naturally aspirated Otto and diesel cycle engines rely on the downward stroke of a piston to create

a low-pressure area (less than atmospheric pressure) above the piston in order to draw air through

the intake system. With the rare exception of tuned induction systems, most engines cannot inhale

their full displacement of atmospheric density air. The measure of this loss or inefficiency in four

stroke engines is called volumetric efficiency. If the density of the intake air above the piston is equal

to atmospheric, then the engine would have 100% volumetric efficiency. Unfortunately, most engines

fail to achieve this level of performance.

This loss of potential power is often compounded by the loss of density seen with elevated altitudes.

Thus, a natural use of the turbocharger is with aircraft engines. As an aircraft climbs to higher

altitudes the pressure of the surrounding air quickly falls off. At 5,486 m (18,000 ft) the air is at half the

pressure of sea level, which means that the engine will produce less than half-power at this altitude.

The objective of a turbocharger, just as that of a supercharger, is to improve an engine's volumetric

efficiency by increasing the intake density. The compressor draws in ambient air and compresses it

before it enters into the intake manifold at increased pressure. This results in a greater mass of air

entering the cylinders on each intake stroke. The power needed to spin the centrifugal compressor is

derived from the high pressure and temperature of the engine's exhaust gases. The turbine converts

the engine exhaust's potential pressure energy and kinetic velocity energy into rotational power, which

is in turn used to drive the compressor.

A turbocharger may also be used to increase fuel efficiency without any attempt to increase power. It

does this by recovering waste energy in the exhaust and feeding it back into the engine intake. By

using this otherwise wasted energy to increase the mass of air it becomes easier to ensure that all

fuel is burnt before being vented at the start of the exhaust stage. The increased temperature from the

higher pressure gives a higher Carnot efficiency.

The control of turbochargers is very complex and has changed dramatically over the 100 plus years of

its use. A great deal of this complexity stems directly from the control and performance requirements

of various engines with which it is used. In general, the turbocharger will accelerate in speed when the

turbine generates excess power and decelerates when the turbine generates deficient power. Aircraft,

industrial diesels, fuel cells and motor-sports are examples of the wide range of performance

requirements.

Turbo lag

All turbocharger applications can be roughly divided into 2 categories, those requiring rapid throttle

response and those that do not. This is the rough division between automotive applications and all

others (marine, aircraft, commercial automotive, industrial, locomotives). While important to varying

degrees, turbo lag is most problematic when rapid changes in engine performance are required.

Turbo lag is the time required to change speed and function effectively in response to a throttle

change. For example, this is noticed as a hesitation in throttle response when accelerating from idle

as compared to a naturally aspirated engine. Throttle lag may be noticeable under any driving

condition, yet becomes a significant issue under acceleration. This is symptomatic of the time needed

for the exhaust system working in concert with the turbine to generate enough extra power to

accelerate rapidly. A combination of inertia, friction and compressor load are the primary contributors

to turbo lag. By eliminating the turbine, the directly driven compressor in a supercharger does not

suffer from this problem.

Lag can be reduced in a number of ways:

1. by lowering the rotational inertia of the turbocharger; for example by using lighter, lower

radius parts to allow the spool-up to happen more quickly. Ceramic turbines are of benefit in

this regard and or billet compressor wheel.

2. by changing the aspect ratio of the turbine.

3. by increasing the upper-deck air pressure (compressor discharge) and improving

the wastegate response; this helps but there are cost increases and reliability disadvantages

that car manufacturers are not happy about.

4. by reducing bearing frictional losses; by using a foil bearing rather than a conventional oil

bearing. This reduces friction and contributes to faster acceleration of the turbo's rotating

assembly.

5. Variable-nozzle turbochargers (discussed below) greatly reduce lag.

6. by decreasing the volume of the upper-deck piping.

7. by using multiple turbos sequentially or in parallel.

Key components and installation

On the left, the brass oil drain connection. On the right are the braided oil supply line and water coolant line

connections.

Compressor impeller side with the cover removed.

Turbine side housing removed.

A wastegate installed next to the turbocharger.

The turbocharger has three main components. First, a turbine, which is almost always a radial inflow

turbine. Second, a compressor, which is almost always a centrifugal compressor. These first two

components are the primary flow path components.

Third, the center housing/hub rotating assembly (CHRA). Then, depending upon the exact installation

and application, numerous other parts, features and controls may be required.

[edit]Center housing and rotating assembly

[edit]Compressor

Impeller/diffuser/volute housing

Main article: Centrifugal compressor

Ported shroud/map width enhancement

Main article: Compressor map

The flow range of a turbocharger compressor can also be increased by allowing air to bleed from a

ring of holes or a circular groove around the compressor at a point slightly downstream of the

compressor inlet (but far nearer to the inlet than to the outlet).

The ported shroud is a performance enhancement which allows the compressor to operate at

significantly lower flows. It achieves this by forcing a simulation of impeller stall to occur continuously.

Allowing some air to escape at this location inhibits the onset of surge and widens the compressor

map. While peak efficiencies decrease, areas of high efficiency may notably increase in size.

Increases in compressor efficiency result in slightly cooler (more dense) intake air, which improves

power. In contrast to compressor exhaust blow off valves, which are electronically controlled, this is a

passive structure which is constantly open.

The ability of the compressor to accommodate high mass flows (high boost at low rpm) may also be

increased marginally (because near choke conditions the compressor draws air inward through the

bleed path). This technology is widely used by turbocharger manufacturers such as Honeywell Turbo

Technologies, Cummins Turbo Technologies, and GReddy. When implemented appropriately, it has a

reasonable impact on compressor map width while having little effect on the maximum efficiency

island.

Charge air cooler /Intercooler

Illustration of inter-cooler location.

For all practical situations, the act of compressing air increases the air's temperature along with

pressure. This temperature increase can cause a number of problems when not expected or when

installing a turbocharger on an engine not designed for forced induction. Excessive charge air

temperature can lead to detonation, which is extremely destructive to engines.

When a turbocharger is installed on an engine, it is common practice to fit the engine with

an intercooler (also known as a charge air cooler, or CAC), a type of heat exchanger which gives up

heat energy in the charge to the ambient air. To assure the intercooler's performance, it is common

practice to leak test the intercooler during routine service, particularly in trucks where a leaking

intercooler can result in a 20% reduction in fuel economy.

Fuel-air mixture ratio

Main article: Air-fuel ratio

In addition to the use of intercoolers, it is common practice to introduce extra fuel into the charge for

the sole purpose of cooling. The amount of extra fuel varies, but typically reduces the air-fuel ratio to

between 11 and 13, instead of the stoichiometric 14.7 (in gasoline engines). The extra fuel is not

burned, as there is insufficient oxygen to complete the chemical reaction, and instead undergoes a

phase change from vapor (liquid) to gas. This reaction absorbs heat (the latent heat of vaporization),

and the added mass of the extra fuel reduces the average kinetic energy of the charge and exhaust

gas. The gaseous hydrocarbons generated are oxidized to carbon dioxide, carbon monoxide, and

water in the catalytic converter.

A method of generally coping with this problem is in one of several ways. The most common one is to

add an intercooler or aftercooler somewhere in the air stream between the compressor outlet of the

turbocharger and the engine intake manifold. Intercoolers and aftercoolers are types of heat

exchangers allow the compressed air to give up some of its heat energy to the ambient air. In the

past, some aircraft featured anti-detonant injection for takeoff and climb phases of flight, which

performs the function of cooling the fuel/air charge before it reaches the cylinders.

In contrast, modern turbocharged aircraft usually forego any kind of temperature compensation,

because the turbochargers are generally small and the manifold pressures created by the

turbocharger are not very high. Thus the added weight, cost, and complexity of a charge cooling

system are considered to be unnecessary penalties. In those cases the turbocharger is limited by the

temperature at the compressor outlet, and the turbocharger and its controls are designed to prevent a

large enough temperature rise to cause detonation. Even so, in many cases the engines are designed

to run rich in order to use the evaporating fuel for charge cooling.

[edit]Turbine

The housings fitted around the compressor impeller and turbine collect and direct the gas flow through

the wheels as they spin. The size and shape can dictate some performance characteristics of the

overall turbocharger. Often the same basic turbocharger assembly will be available from the

manufacturer with multiple housing choices for the turbine and sometimes the compressor cover as

well. This allows the designer of the engine system to tailor the compromises between performance,

response, and efficiency to application or preference. Twin-scroll designs have two valve-operated

exhaust gas inlets, a smaller sharper angled one for quick response and a larger less angled one for

peak performance.

The turbine and impeller wheel sizes also dictate the amount of air or exhaust that can be flowed

through the system, and the relative efficiency at which they operate. Generally, the larger the turbine

wheel and compressor wheel, the larger the flow capacity. Measurements and shapes can vary, as

well as curvature and number of blades on the wheels. Variable geometry turbochargers are further

developments of these ideas.

The center hub rotating assembly (CHRA) houses the shaft which connects the compressor impeller

and turbine. It also must contain a bearing system to suspend the shaft, allowing it to rotate at very

high speed with minimal friction. For instance, in automotive applications the CHRA typically uses a

thrust bearing or ball bearing lubricated by a constant supply of pressurized engine oil. The CHRA

may also be considered "water cooled" by having an entry and exit point for engine coolant to be

cycled. Water cooled models allow engine coolant to be used to keep the lubricating oil cooler,

avoiding possible oil coking (the destructive distillation of the engine oil) from the extreme heat found

in the turbine. The development of air-foil bearings has removed this risk. Adaptation of turbochargers

on naturally aspirated internal combustion engines, either on petrol or diesel, can yield power

increases of 30% to 40%.

Variable geometry

Garrett variable-geometry turbocharger on DV6TED4 engine

Instead of using two turbochargers in different sizes, some engines use a single turbocharger,

called variable-geometry or variable-nozzle turbos; these turbos use a set of vanes in the exhaust

housing to maintain a constant gas velocity across the turbine, the same kind of control as used on

power plant turbines. Such turbochargers have minimal lag like a small conventional turbocharger and

can achieve full boost as low as 1,500 engine rpm, yet remain efficient as a large conventional

turbocharger at higher engine speeds. In many setups these turbos do not use a wastegate. The

vanes are controlled by a membrane identical to the one on a wastegate, but the mechanism operates

the variable vane system instead. These variable turbochargers are commonly used in diesel engines.

[7]

[edit]Wastegate

Main article: Wastegate

View of a turbocharger from the turbine exhaust side, showing the integral wastegate to the right

To manage the pressure of the air coming from the compressor (known as the "upper-deck air

pressure"), the engine's exhaust gas flow is regulated before it enters the turbine with

a wastegate that bypasses excess exhaust gas entering the turbocharger's turbine.[8] A wastegate is

the most common mechanical speed control system, and is often further augmented by an electronic

or manual boost controller. The main function of a wastegate is to allow some of the exhaust to

bypass the turbine when the set intake pressure is achieved. This regulates the rotational speed of

the turbine and thus the output of the compressor. The wastegate is opened and closed by the

compressed air from the turbo and can be raised by using a solenoid to regulate the pressure fed to

the wastegate membrane.[9] This solenoid can be controlled by Automatic Performance Control, the

engine's electronic control unit or a boost control computer.

Most modern automotive engines have wastegates that are internal to the turbocharger, although

some earlier engines (such as the Audi Inline-5 in the UrS4 and S6) have external wastegates.

External wastegates are more accurate and efficient than internal wastegates, but are far more

expensive, and thus are generally only found in racing cars (where precise control of turbo boost is a

necessity and any efficiency increase is welcomed).

Aircraft waste-gates and their operation are similar to automotive installations, however there are

notable differences as well. Even within aircraft applications there are 2 distinctions,

military/performance and non-performance.

[edit]Anti-surge/dump/blow off valves

Main article: Blowoff valve

A recirculating type anti-surge valve

Turbocharged engines operating at wide open throttle and high rpm require a large volume of air to

flow between the turbo and the inlet of the engine. When the throttle is closed compressed air will flow

to the throttle valve without an exit (i.e. the air has nowhere to go).

This causes a surge which can raise the pressure of the air to a level which can damage the turbo. If

the pressure rises high enough, a compressor stall will occur, where the stored pressurized air

decompresses backwards across the impeller and out the inlet. The reverse flow back across the

turbocharger causes the turbine shaft to reduce in speed more quickly than it would naturally, possibly

damaging the turbocharger. In order to prevent this from happening, a valve is fitted between the

turbo and inlet which vents off the excess air pressure. These are known as an anti-surge, diverter,

bypass, blow-off valve (BOV) or dump valve. It is basically a pressure relief valve, and is normally

operated by the vacuum in the intake manifold.

The primary use of this valve is to maintain the turbo spinning at a high speed. The air is usually

recycled back into the turbo inlet (diverter or bypass valves) but can also be vented to the atmosphere

(blow off valve). Recycling back into the turbocharger inlet is required on an engine that uses a mass-

airflow fuel injection system, because dumping the excessive air overboard downstream of the mass

airflow sensor will cause an excessively rich fuel mixture (this is because the mass-airflow sensor has

already accounted for the extra air which is no longer being used). Valves which recycle the air will

also shorten the time needed to re-spool the turbo after sudden engine deceleration, since the load on

the turbo when the valve is active is much lower than if the air charge is vented to atmosphere.

IntercoolerFrom Wikipedia, the free encyclopedia

For the Australian rock group, see Intercooler (band).

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (March 2009)

It has been suggested that Charge air cooler be merged into this article or section. (Discuss) Proposed since October 2009.

An intercooler (original UK term, sometimes aftercooler in US practice), or charge air cooler, is an air-to-

air or air-to-liquid heat exchange device used on turbocharged and supercharged (forced induction) internal

combustion engines to improve theirvolumetric efficiency by increasing intake air charge density through

nearly isobaric (constant pressure) cooling, which removes the heat of compression (i.e., the temperature

rise) that occurs in any gas when its pressure is raised or its unit mass per unit volume (density) is

increased. A decrease in intake air charge temperature sustains use of a more dense intake charge into

the engine, as a result of supercharging. The lowering of the intake charge air temperature also eliminates

the danger of pre-detonation (knock) of the fuel air charge prior to timed spark ignition. Thus preserving the

benefits of more fuel/air burn per engine cycle, increasing the output of the engine. Intercoolers increase

the efficiency of the induction system by reducing induction air heat created by the turbocharger and

promoting more thorough combustion. They also eliminate the need for using the wasteful method of

lowering intake charge temperature by the injection of excess fuel into the cylinders' air induction

chambers, to cool the intake air charge, prior to its flowing into the cylinders. This wasteful practice (when

intercoolers are not used) nearly eliminated the gain in engine efficiency from supercharging, but was

necessitated by the greater need to prevent at all costs the engine damage that pre-detonation engine

knocking causes.[1]

The inter prefix in the device name originates from historic compressor designs. In the past, aircraft

engines were built with charge air coolers that were installed between multiple stages of supercharging,

[citation needed] thus the designation of inter. Modernautomobile designs are technically

designated aftercoolers because of their placement at the end of supercharging chain. This term is now

considered archaic in modern automobile terminology since most forced induction vehicles have single-

stage superchargers or turbochargers although "aftercooler" is still in common use in the piston engined

aircraft industry. In a vehicle fitted with two-stage turbocharging, it is possible to have both an intercooler

(between the two turbocharger units) and an aftercooler (between the second-stage turbo and the engine).

The JCB Dieselmax land speed record-holding car is an example of such a system. In general, an

intercooler or aftercooler is said to be a charge air cooler.

Intercoolers can vary dramatically in size, shape and design, depending on the performance and space

requirements of the entire supercharger system. Common spatial designs are front mounted intercoolers

(FMIC), top mounted intercoolers (TMIC) and hybrid mount intercoolers (HMIC). Each type can be cooled

with an air-to-air system, air-to-liquid system, or a combination of both.

Exhaust systemFrom Wikipedia, the free encyclopedia

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (October 2007)

Exhaust manifold (chrome plated) on a car engine

Muffler and tail pipe on a car

An exhaust system is usually tubing used to guide reaction exhaust gases away from a

controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine

and includes one or more exhaust pipes. Depending on the overall system design, the exhaust gas may

flow through one or more of:

Cylinder head  and exhaust manifold

A turbocharger to increase engine power.

A catalytic converter to reduce air pollution.

A muffler (North America) / silencer (Europe), to reduce noise.

Catalytic converterFrom Wikipedia, the free encyclopedia

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Catalytic converter on a 1996 Dodge Ram Van

A catalytic converter (colloquially, "cat" or "catcon") is a device used to reduce the toxicity of exhaust

emissions from an internal combustion engine. Inside a catalytic converter, a catalyst stimulates a chemical

reaction in which noxious byproducts of combustion carbon monoxide, unburned hydrocarbons, and oxides

of nitrogen are converted to less-toxic or inert substances such as carbon dioxide, hydrogen, nitrogen and

oxygen.[1]

First widely introduced on series-production automobiles in the United States market for the 1975 model

year to comply with tightening U.S. Environmental Protection Agency regulations on auto exhaust

emissions, catalytic converters are still most commonly used in motor vehicle exhaust systems. Catalytic

converters are also used on generator sets, forklifts, mining equipment, trucks, buses, trains, airplanesand

other engine-equipped machines.

MufflerFrom Wikipedia, the free encyclopedia

This article is about the exhaust system component. For other uses, see Muffler (disambiguation).

This article may require cleanup to meet Wikipedia's quality standards. (Consider using more specific clean up instructions.) Please improve this article if you can. The talk page may contain suggestions. (July 2007)

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (March 2011)

This article may contain original research. Please improve it by verifying the claims made and adding references. Statements consisting only of original research may be removed. More details may be available on the talk page. (March 2011)

Muffler(silver) and exhaust pipe on aDucati 695 motorcycle

A muffler (or silencer in British English) is a device for reducing the amount of noise emitted by

the exhaust of an internal combustion engine. The muffler was originally invented by Milton O. Reeves.[1

Description

Dual tailpipes attached to a the muffler on a passenger car

Mufflers are typically installed along the exhaust pipe as part of the exhaust system of an internal

combustion engine. The muffler reduces exhaust noise by absorption—the exhaust is routed through

a series of passages and chambers lined with roving fiberglass wool—and/or resonating chambers

tuned to cause destructive interference wherein opposite sound waves cancel each other out,

and Catalytic converters also have a muffling effect.

Changing the muffler / mini-muffler / catalytic converter combination can change the sound of a car's

exhaust system considerably. Removing a vehicle's muffler or installing a less effective muffler than

the original can cause the vehicle to violate noise regulations. Nevertheless some vehicle owners

remove their car muffler in the belief it will improve performance, or just to make them louder.