APTE 5501 VEHICLE
Power & Transmission
Clutches
An Overview Presentation
Relevant Chapters in H. Heizler
“ Advanced Vehicle Technology
Chapters 2 & 4
In Bosch H/Book 5th Ed pg 590
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
What Are The Common Types Of
Clutches?
MECHANICAL
ELECTRO-MAGNETIC
HYDRO-DYNAMIC
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 ClutchesPositive 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 ClutchesPositive Engagement // Contd
 Or it can be an over-running
clutch, which has several
forms/ applications like:
 One-way clutch or freewheeling 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
Mechanical Clutches- Positive
Engagement // Contd
 Another form of freewheeling 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.
Simple Sprag freewheel clutch
Mechanical Clutches- Positive
Engagement // Contd
 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 .
Simple Backstop assembly in a conveyor
Mechanical Clutches- Positive
Engagement // Contd
 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
Frictional Engagement
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.
Frictional Engagement
Disc/ Plate Clutch
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
Dry Disc Clutch
BASIC ASSEMBLY COMPONENTS
FLYWHEEL FACE
CLUTCH DISC
PRESSURE PLATE ASSEMBLY ( Clutch
Cover)
CLUTCH RELEASE MECHANISM
( Release Bearing, Fork & Attachment,
Cable/Hydraulic Release, Pedal)
The clutch components including the release mechanism
Source: Toyota, May’s
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 DUALMASS FLYWHEEL?
WHAT ADVANTAGE IT
HAS
Single Mass Flywheel
Source: www.roadraceengineering.com
Dual Mass Flywheel
Source: Federal Mogul
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..
PRESSURE PLATE
ASSEMBLY
CONFIGURATION
• SINGLE PLATE / DUAL
OR MULTI PLATE
• COIL SPRINGS /
DIAPHRAGM SPRING
• PUSH RELEASE / PULL
RELEASE
MATERIALS 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 systems
Source : May’s
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 Engagement
Wet 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 Engagement
Centrifugal 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 gocarts, moped drives, chainsaws, line
trimmers. May exist in other applications
like some automatic transmissions lock-up
converters.
Exploded view of a centrifugal clutch
Source: www.dansmc.com
Frictional Engagement
Cone Clutch
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 clutch
Source: www.tb-training.co.uk
VISCOUS 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





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 clutch
Source: Ogura Industrial Corp.
ELECTRO-MAGNETIC CLUTCH
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).
Sectional View of Magnetic Powder Clutch
Source: LIEDTKE Antriebstechnik GmbH &
Co.
Hydrodynamic Clutches
This 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 steadystate running.
Top fig: Sectional view of a fluid coupling,
Bottom: view of Drive/Driven members
Source: www.autotran.us
Hydrodynamic Clutches
2. 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 converter
Source: www.dolphintransmissions.com
Torque transmitted from
Clutch
As 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.
Force , Torque & Coefficient of Friction
During operation there is some pressure operating over the face of the clutch plate given F = pA.
p= hydraulic pressure and A = the surface area
It 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.
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
Analysing common Clutch Problems:
Clutch Slip
Clutch spin or drag
Clutch Chatter or grab
Class Activity
1. Group Discussion
2. Class Activity