brakes new rev2
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What are Hydraulics?
Moving something by means of a liquid(water or oil) under pressure.
Pressure (psi) = F1/A1 = F2/A2
http://www.ph.utexas.edu/~itiq/iq/303K/ch15/15.2.3.jpg
What is the MAof this lift if
A2 = 4 X A1
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Pneumatic Tools
Moving something by means ofcompressed air
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How do hydraulic brakes work?
The hydraulic fluid doesnot compress verymuch. Whenpressurized the forceget transmittedthroughout the system.
The brake fluid musthave a very high boilingpoint and not freeze incold driving conditions.
http://auto.howstuffworks.com/brake3.htm Click for animation!
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Using leverage and hydraulics, the brakingforce gets multiplied.
This lever multiplies the forceon the first cylinder by four.
The diameter of the brakecylinder is 3 times largerthan the pedal cylinder. Thisis nine times larger in area.This multiplies the force
another nine times(although pressure is thesame throughout). Thetradeoff is that the brakepiston only travels 1/9 the
distance of the first pedalcylinder.
Applied Force is increased 36 times.
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Disk Brakes
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http://auto.howstuffworks.com/drum-brake1.htm
Click to animate!
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http://auto.howstuffworks.com/master-brake1.htmClick for animation!
A more modern braking system uses a master cylinder with two pistonsto ensure a fluid leak can be isolated to one of the wheels.
http://auto.howstuffworks.com/master-brake1.htmhttp://auto.howstuffworks.com/master-brake1.htmhttp://auto.howstuffworks.com/master-brake1.htmhttp://auto.howstuffworks.com/master-brake1.htm -
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http://auto.howstuffworks.com/power-brake2.htm
More force isRequired to operateDisk brakes.Power brakes areUsed to increase
Forces on theMaster cylinder.
http://auto.howstuffworks.com/power-brake2.htmhttp://auto.howstuffworks.com/power-brake2.htmhttp://auto.howstuffworks.com/power-brake2.htmhttp://auto.howstuffworks.com/power-brake2.htm -
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What do brakes really do?
They stop the wheels, not the car.
If the car stops without crashing the
brakes absorb most of the kinetic energyof the car, turning that energy into HEAT
High performance brakes must quickly
shed the heat that is generated. Effective braking is determined by the
contact the wheels have with the road.
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Drum brakes tend to have heat build upinside the rotating drum.
The rotor and brake pads used in diskbrake systems are exposed to the outsideair, making cooling easier.
Drum brakes are less expensive and haveimproved, so many cars still have diskbrakes in the front and drum brakes in the
rear.
See article at:http://www.edmunds.com/ownership/techcenter/articles/43857/article.html
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What is Friction?
An invisible force that resists motion when twosurfaces in contact try to move relative to oneanother.
Frictionis a force which causes the motionbetween two surfaces to be reduced.
Because of friction people used to believe beforeGalileo and Newton that forces were always
needed to keep something in motion.
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Static Friction two surfaces at rest withrespect to each other
There are two types of Friction:1. Static Friction
2. Kinetic (sliding) Friction
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Tire at bottom is not moving relative to the road. Static friction
between tire and road is what controls the car.
Speed of tire at top is 2X speed of the car.
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Tire tread, road, and driving conditionsdetermine the coefficient of friction.A bald tire on a dry roads has a muchhigher friction coefficient than on a wetroad.
http://hyperphysics.phy-astr.gsu.edu
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Breakaway Point
Max. Static Frictional Force
Kinetic Friction is constant.
http://www.lightandmatter.com
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Kinetic FrictionStatic Friction
FStatic> FKinetic is the friction coefficient
Static friction willcounteract any applied
force up to a certainthreshold at which frictionis overcome and theobject begins to slide.
Once in motion, kineticfriction resists motion.
Static Friction dependson how squishedtogether the two
surfaces are.
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Anti-lock braking systems
ABS keeps the tires from skidding as long as thedriver keeps the brake pedal down.
When slamming on the brakes, wheels can stopspinning much faster than a car can stop.Wheels have less kinetic energy than the car.
When a wheel stops rolling it is called lock up.When this happens the car must now skidbecause the wheels are not turning.
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Kinetic (sliding) friction is much less than staticfriction.
Once a car skids, the tires lose grip with theroad and the driver loses control.
Skidding results in reduced friction between tiresand road.
Lower frictional forces reduces control. Drivermight not be able to turn the car, or car may
spin out if one wheel is skidding and the othersare not.
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Safer only when used properly.
ABS functions only when brakes are notpumped. ABS creates pedal chatter whichmeans ABS is working.
ABS doesnt mean you will stop quicker.
However control of the car is maintained,because skidding is avoided.
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The ABS controller (computer)
Ensures that the tires slows down at the samerate as the car, but keeps the tires forces just
under the point where sliding would occurjust under Fstatic-max
This maximizes the braking power.
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http://www.youtube.com/watch?v=uq4DDMMoomU
Demo of conventional brakes vs. ABS:
http://www.youtube.com/watch?v=uq4DDMMoomUhttp://www.youtube.com/watch?v=uq4DDMMoomU -
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How is this done?
The system uses a computer to monitorthe speed of each wheel. When it detects
that one or more wheels are turningslower than the remaining wheels, thecomputer sends a signal to momentarilyremove and reapply the pressure to the
affected wheels to allow them to continueturning. This "pumping" of the brakesoccurs at ten or more times a second.http://www.familycar.com/brakes.htm
Th t i t f l t i
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The system consists of an electroniccontrol unit, a hydraulic actuator*, andwheel speed sensors at each wheel.
* An actuator is a device in a car that uses electricity to do some sort ofmechanical movement- Such as power door locks or a remote trunk opener.
In this case the actuator releases pressure in the brakes to pulse thebrakes.
http://www.aa1car.com/library/abs1.htm
Information from wheel speedsensors is fed to the controller.
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If the controller determines that one tire is
rotating more slowly than the other tires, thecontroller sends a signal to the wheels actuator tolower the brake fluid pressure to prevent skidding.
www.lake-link.com
Solenoid valve closes,preventing more fluid
from getting to the brake.It then is reopened, thuspumping the brake.
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Do ABS brakes work in the snow oron icy roads?
What is the primary advantage ofABS brakes?
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Heat what a waste!!!Regenerative brakingabsorbs some of the carskinetic energy to generateelectricity instead ofproducing wasteful heat.
The electric motor operates like agenerator during braking.
This puts energy back into thebattery.
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http://www.youtube.com/watch?v=F19qeag-o_I
How a Parallel Hybrid car works
http://www.youtube.com/watch?v=F19qeag-o_Ihttp://www.youtube.com/watch?v=F19qeag-o_Ihttp://www.youtube.com/watch?v=F19qeag-o_Ihttp://www.youtube.com/watch?v=F19qeag-o_I -
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What are benefits ofRegenerative Breaking?
Have wheels turn a generator connected to abattery to capture some of the Kinetic Energy of
the Car Allows the Pruis to use a much smaller gas
engine since high power demands can besupplemented by electric motor and battery.
Transfer unwanted KE into Potential Energy tobe converted back into KE at a later time.
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How the battery and engine worktogether is determined by a
microcontroller
Scenarios:
All the engine power is not needed, so excess engineenergy is used to charge the battery
Engine power is not sufficient, so battery operates anelectric motor boosting power
Unwanted Kinetic Energy is used in braking to chargebattery Car only needs low power provided by electric motor,
then gas engine stays off. While at rest, all systems are off; no idle waste.
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Scenario 1
Engine charges a low battery This happens if battery is low, usually at the beginning of a trip
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Scenario 2
When waiting at lights, engine andelectric motor are off no idling
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Scenario 3
Engine power exceeds cars demand, therefore engineturns generator.
Generator (i.e. electric motor) charges the battery
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Scenario 4
Energy demand can be satisfied by battery only
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Scenario 5 When braking, wheels turn generator that in turn charge the battery.
This also happens sometimes when coasting.
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Scenario 6
Engine only energy demand equals that of gas engine.
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Scenario 7
Engine and Battery working in consort to drive wheels
Demand exceeds power of gas engine
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Hybrid Benefits
Low emissions
Car performs well under most cases with a much
smaller engine, due to reliance on the batteryand electric motor for boosts in power
Very sophisticated embedded microcontrollersthat manage energy demands
Captures excess energy of motor and duringbreaking
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Flywheel Storage System(FES)
Another technique for storing unwantedKE of the car
Energy is transferred to a flywheel as KE.
Flywheel turns freely and independently ofuntil KE is needed again to propel the car.
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Thought question.
What are some reasons the Prius mightget better mileage in stop and go
conditions than on the highway?
http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.consumerenergycenter.org/transportation/consumer_tips/vehicle_energy_losses.html
Good sources of information.
l
http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.consumerenergycenter.org/transportation/consumer_tips/vehicle_energy_losses.htmlhttp://www.consumerenergycenter.org/transportation/consumer_tips/vehicle_energy_losses.htmlhttp://www.consumerenergycenter.org/transportation/consumer_tips/vehicle_energy_losses.htmlhttp://www.consumerenergycenter.org/transportation/consumer_tips/vehicle_energy_losses.htmlhttp://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/ -
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http://www.consumerenergycenter.org
Losses in Conventional Car
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Typical Car
PriusSimulator