APTE 5501 VEHICLE APTE 5501 VEHICLE Power & TransmissionPower & Transmission

ClutchesClutches

An Overview Presentation

Relevant Chapters in H. Heizler “ Advanced Vehicle Technology

Chapters 2 & 4In Bosch H/Book 5th Ed pg 590

3 Key Questions Here:3 Key Questions Here:

• What Is The Purpose Of A Clutch?

1 To allow the driver to operate the engine in its most efficient speed range - nominally 2000 - 3500 RPM, providing an operating speed range of 1500 RPM (Except when moving off from standstill. During this transition mode the engine must briefly operate outside of its designed speed range.)

2. Allows driver to select a suitable gear ratio to increase engine torque (torque multiplication) to match an increased load requirement. (Change down to a lower gear - a higher numerical gear ratio.)

Major Types of Clutches Major Types of Clutches What Are The Common Types Of Clutches?

MECHANICAL

ELECTRO-MAGNETIC

HYDRO-DYNAMIC

Major Types of Clutches Major Types of Clutches What Materials Are Clutches Made Of?

•A coefficient of friction that remains stable with temperature change•Excellent thermal conductivity•Good wear resistance•Resistance to thermal fatigue•Good high temperature strength•A uniform coefficient of friction over the surface

Mechanical Clutches- Mechanical Clutches- Positive EngagementPositive Engagement

• Designed as a binary device either engaged or disengaged. There are different designs & applications for positive engagement clutches. They can either transmit torque flow in one-way or two-way.

• A common 2-way Positive Engagement Clutch is the as dog clutch ( alternative name is jaw or tooth clutch). This type operates by sliding a toothed hub along a shaft to engage with matching teeth on a gear wheel or another shaft , as shown.

Dog Clutch

Mechanical Clutches- Mechanical Clutches- Positive Engagement // Positive Engagement // ContdContd

Or it can be an over-running clutch, which has several forms/ applications like:

One-way clutch or free-wheeling clutch. Here , torque is transmitted only if the rollers are dragged to wedge between the inner and outer receways. Drive is interrupted when input torque direction is reversed so that rollers will shift towards the stop edge in inner race. A simple application is the free-wheel built in the bicycle wheel sprocket assembly. Cyclist as a result can "freewheel" down hills.

Simple roller-wedge freewheel clutch

Another form of free-wheeling clutch is the sprag clutch, as shown. The sprag element either wedges ( rotates counter-clockwise) to couple the inner and outer raceways, or slips against both races during decouple( rotates clock-wise) when the torque input direction reverses or if the driven part rotates faster than driving part. Sprag elements sit in an array and supporting springs maintain their peripheral positioning.

Mechanical Clutches- Positive Mechanical Clutches- Positive Engagement // Engagement // ContdContd

Simple Sprag freewheel clutch

Another application of overrunning clutches in escalators and inclined conveyors, where in case of drive breakdown, the assembly will self brake to make sure the escalator will not slide downward under gravity. This is called a “ Backstop”. In this configuration the outer race is made stationary and inner race which contains the rollers cavities is coupled to the drive shaft, as shown .

Mechanical Clutches- Positive Mechanical Clutches- Positive Engagement // Engagement // ContdContd

Simple Backstop assembly in a conveyor

Another application of one-way clutch in overrunning setup. The figure shows how the one-way clutch couples the starter motor to the IC, during starting. When engine starts and picks up,then the clutch will decouple to protect starter from overrunning beyond its design speed.

Application of overrunning clutch in a starting system

Mechanical Clutches- Positive Mechanical Clutches- Positive Engagement // Engagement // ContdContd

Also binary devices, either engaged or disengaged. Power flow is transmitted by friction between driving and driven components. This clutch family subdivides into:• Disc/plate clutch.•Centrifugal clutch.•Cone clutch.•Viscous silicone clutch.

Mechanical Clutches Mechanical Clutches Frictional EngagementFrictional Engagement

This type comprises of dual or multi interfacing between a fibrous friction material facing and a hard metal facing. Can be DRY interfacing or WET interfacing.

Dry Plate Clutch ( left: single disc/pressure plate, right: double disc/ pressure plate)

Wet Multi Plate Clutch

Frictional EngagementFrictional EngagementDisc/ Plate ClutchDisc/ Plate Clutch

Dry Disc ClutchDry Disc Clutch

The clutch components including the release mechanism Source: Toyota, May’s

BASIC ASSEMBLY COMPONENTSFLYWHEEL FACE CLUTCH DISCPRESSURE PLATE ASSEMBLY ( Clutch Cover)CLUTCH RELEASE MECHANISM( Release Bearing, Fork & Attachment, Cable/Hydraulic Release, Pedal)

Dry Disc Clutch// contd..Dry Disc Clutch// contd..FLYWHEEL • MADE OF CAST IRON/

ALLOY METAL• SURFACE CONDITION• PILOT BEARING• SINGLE / DUAL-MASS

FLYWHEELS, WHAT IS THE DIFFERENCE?

• WHAT IS THE APPLICATION OF DUAL-MASS FLYWHEEL? WHAT ADVANTAGE IT HAS

Single Mass FlywheelSource: www.roadraceengineering.com

Dual Mass FlywheelSource: Federal Mogul

Dry Disc Clutch//contd..Dry Disc Clutch//contd..

CLUTCH DISC• ASSEMBLY OF METAL AND

COMPOSITE COMPONENTS HELD TOGETHER BY RIVETS AND DOWELS

• DESIGN FACTORS, LETS THINK OF THEM AND DISCUSS!

• TORQUE TRANSMITTED• SLIP AND WEAR RESISTANCE• KINDNESS TO IRON SURFACES• DISSIPATION OF HEAT • EXPELTION OF SEPATATING

DEBRIS• ROTATION DIRECTION• TORSIONAL OSCILLATION

DAMPENING• RIGIDITY• SIMPLICITY OF REPAIR

A clutch disc assembly Source : Toyota, May’s

Dry Disc Clutch//contd..Dry Disc Clutch//contd..PRESSURE PLATE

ASSEMBLY

CONFIGURATION• SINGLE PLATE / DUAL

OR MULTI PLATE• COIL SPRINGS /

DIAPHRAGM SPRING• PUSH RELEASE / PULL

RELEASEMATERIALS USED?• CAST IRON FOR

PRESSURE PLATES• SPRING STEEL FOR

SPRINGS

A pressure-plate assembly Source : Toyota, May’s

Pull type and push-type clutch release systemsSource : May’s

Dry Disc Clutch//contd..Dry Disc Clutch//contd..

Clutch Release Mechanisms:•Can be cable/ rod mechanism.•Can be hydro-mechanical, employing master and slave cylinders using brake fluid.•Can be pneumatically operated, like in commercial vehicles transmissions.

Cable clutch release Source: Ed May’s

Hydro-mechanical clutch release Source: Ed May’s

Frictional EngagementFrictional EngagementWet Multiplate ClutchWet Multiplate Clutch

This clutch type is an assembly of alternating steel plates set and steel-lined plates set. One set is splined to the driving component, while the other set is splined to the driven component. The assembly may be engaged by a piston actuated by hydraulic pressure which opposes the disengagement force of return spring(s)

Applications: Motorcycles clutch, automatic transmissions clutches, etc. A wet multiplate clutch assembly.

Source: Howstuff Works

Frictional EngagementFrictional Engagement

Centrifugal ClutchCentrifugal Clutch This type of clutches operates by the centrifugal effect. The engine or motor rotates a plate fitted with clutch shoes that are pulled inward by return springs.

The clutch remains disengaged as long as the engine/ motor speed is below the threshold speed when the centrifugal outward force acting on the rotating shoes overcomes the spring tension force. Then the frictional lining on the shoes catches on the driven drum and torque is transmitted across the clutch.

Common applications: low to medium torque transmission in general like go-carts, moped drives, chainsaws, line trimmers. May exist in other applications like some automatic transmissions lock-up converters.

Exploded view of a centrifugal clutchSource: www.dansmc.com

This clutch type is made of a conical profiled disc and a mating drum. A suitable mechanism slides the disc a splined shaft to engage against the conical drum. Usually, frictional material is layered on the conical disc periphery, or the disc or its periphery is made of soft metal like bronze or brass which grabs well to cast ion drum.

Applications : low to medium torque transmissions like small marine outboard engines. Adopted in the manual gearbox synchronisers to bring speeds of the mainshaft and the selected gear wheel very close during engagement.

Illustration of a simple cone clutchSource: www.tb-training.co.uk

Frictional EngagementFrictional Engagement

Cone ClutchCone Clutch

VISCOUS COUPLING CLUTCHVISCOUS COUPLING CLUTCH

This clutch type makes advantage of the change of properties of silicone fluid with temperature. Unlike all fluids, silicon becomes more viscous with temperature rise due to shear between the coupling multiplates when their respective speeds differ very much. Therefore, the “thickened” silicone will bond between the plates to bring them at same speed.

Applications: Viscous coupling for full-time all wheel drives, viscous limited slip differentials, engine cooling fan clutch

Illustration: Cut-away view of viscous LSD top, and detailed drawing bottom Source: www.arstechnica.de/

ELECTRO-MAGNETIC CLUTCH ELECTRO-MAGNETIC CLUTCH

Mainly a Binary Clutching Device, either engaged or released.

Application in operating compressors for car air conditioning or to compress air for commercial chassis systems ( Brake/ Suspension ..etc)

Advantage: Simple construction, operates through electric/electronic control.

Disadvantage: Limitation on peak torque to be transmitted, electric power continuous consumption while engaged.

On the other hand, another type of electro-magnetic clutch is developed for traction applications, and is named the “ Magnetic Powder” clutch. This type can produce a coupling rate that is variably controllable by excitation level infinitely from 0% ( released) to 100 % ( fully engaged).

Simple construction of an electro-magnetic clutchSource: Ogura Industrial Corp.

ELECTRO-MAGNETIC CLUTCH ELECTRO-MAGNETIC CLUTCH

Sectional View of Magnetic Powder ClutchSource: LIEDTKE Antriebstechnik GmbH & Co.

On the other hand, another type of electro-magnetic clutch is developed for traction applications, and is named the “ Magnetic Powder” clutch. This type can produce a coupling rate that is variably controllable by excitation level infinitely from 0% ( released) to 100 % ( fully engaged).

Hydrodynamic ClutchesHydrodynamic ClutchesThis family subdivides into 2 common designs:1. Fluid Coupling: As shown is made of 2 torus wheels fitted with vanes and the whole housing is filled with a hydraulic fluid ( e.g. automatic trans. Fluid).Fluid couplings are usually used in shock-less start-up drives, as they prevent heavy starting load to hit motor/engine. There will be a lot of slippage between driven and driving members upon start-up and transient running, but they will eventually approach full coupling on steady-state running.

Top fig: Sectional view of a fluid coupling, Bottom: view of Drive/Driven members

Source: www.autotran.us

Hydrodynamic ClutchesHydrodynamic Clutches2. The Torque Converter. This is the other type of hydrodynamic clutch family. As shown on right, it is similar to the fluid coupling, except that instead of 2 major members for the coupling case, here we got 3 members; the impeller ( or pump), the turbine, and the stator with its oneway clutch and stationary support.

Torque converter features multiplication of input torque in stall-condition ( i.e. when excessive resistance load applied on output turbine shaft that will slow it behind the impeller). The disadvantage is the slippage that takes place at top revolution speed, because of the fluid as the energy transmission media.

A sectional view of a 3 elements torque converterSource: www.dolphintransmissions.com

Torque transmitted from ClutchTorque transmitted from ClutchAs we have seen from the previous slides that the clutch system an important system in the vehicle – without the clutch system - vehicle will not be able to transmit the power output via the transmission then to the final drives to the wheels.If we look at the clutch plate – it is design to withstand maximum engine torque, torsional vibration, sudden change in engine rotation etc.

During operation there is some pressure operating over the face of the clutch plate -given F = pA. p= hydraulic pressure and A = the surface areaIt is also noted that the frictional force on the face of the clutch is simply the normal force (F) times the coefficient of friction force materials (μ).

The clutches friction forces are used to transmit torque.

Therefore: Frictional torque (Ft) = friction force X effective radius.

Where “Pa “ is the applied pressure where “D” is the large diameter of the clutch plate

and where as “d” is the smaller diameter.

Force , Torque & Coefficient of Friction

To determine the Frictional Force: Ff =

We can also use this formula to determine the frictional force on the surface of the clutch:

Torque transmitted

)n

Refer example on hand out

Clutch spin or drag

Analysing common Clutch Problems:Clutch Slip

Clutch Chatter or grab

Class Activity

1. Group Discussion

2. Class Activity