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7/23/2019 Clutch Gear Box-Final
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 1
CHAPTER 5
CLUTCH
5.1 Funct ion of a Clutch
The torque developed by the engine at starting speed is very low. Therefore, it is not
possible to start the engine under load. This requires that the transmission system
should provide a means of connecting and disconnecting the engine from rest of the
transmission system. Such an operation must be smooth and without shock to the
occupants of the vehicle.
Thus the two main functions of a clutch are:
1. To allow the engine to be separated from rest of the transmission system.
This is required when:
a) starting and running the engine at a sufficiently high speed to generate
sufficient power necessary for moving the vehicle from rest;
b) shifting the gears so that damage to gear teeth can be avoided; and
c) Stopping the vehicle after applying brakes.
2. The second function of the clutch is to allow the engine to take up the
driving load of the vehicle gradually and without shock.
Frict ion Surface
The following are the requirements of the friction mating surfaces used in clutches.
1. It must have good mechanical strength and thermal expansion to
withstand the torque and thermal stresses over a wide temperature range
without distortion, bell-mouthing or excessive expansion.
2. Its heat soak capacity and thermal conductivity should be sufficient.
3. Its structure and finish must provide a consistent mating surface under all
conditions of operation.
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 2
4. It must be hard enough to give a long wear life and resist scoring and
abrasion.
5. It must be cheap.
5.2 The main requirements of a c lutch :
1. It should be able to transmit maximum torque of the engine under all
conditions.(Torque transmission)
2. It should engage gradually to avoid sudden jerks.( Gradual Engagement)
3. It should be able to dissipate large amount of heat generated during clutch
operation.(Heat dissipation)
4. It should be dynamically balanced, particularly in the case of high speed
engine clutches.(Dynamic Balancing)
5. It should have suitable mechanism to damp vibrations and to eliminate noise
produced during power transmission.(Vibration Damping)
6. It should be as small as possible so that it will occupy minimum space.(Size)
7. It should be easy to operate requiring as little exertion as possible on the part
of the driver.(Ease of operation)
8. It should be made as light as possible so that it will continue to rotate for any
length of time after the clutch has been disengaged.
5.3 Method o f op erat ion of a Single Plate Clutch:
The movable parts of the clutch are pressed together by the thrust springs sothat the driven plate is trapped between the flywheel and the pressure plate. The
three components thus clamped together connect the engine to the primary shaft of
the gearbox. When the driver of the vehicle operates the clutch pedal the release
levers draw back the pressure plate, compressing the springs, thus separating the
flywheel, driven plate, and pressure plate hence disconnecting the drive.
As the pedal is released the pressure plate under the influence of the
expanding spring pressure, pushes the driven plate along the splines on the primary
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 3
shaft. As the clutch faces press closer together the slip between these faces is
gradually reduced, until the speed of the gearbox primary shaft corresponds to the
engine crankshaft speed .
Fig.5.1 Single Plate clutch i) Engaged ii) Disengaged
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 4
Fig.5.2 Single Plate Clutch
5.4 Semi-centr i fugal clutc h:
A semi-centrifugal clutch is used to transmit power from high-powered engines
where clutch disengagement requires appreciable and tiresome driver’s effort. The
transmission of power in such clutches is partly by the clutch springs and the rest by
centrifugal action of an extra weight provided in the system. The clutch springs
serve to transmit the torque up to normal speeds, while the centrifugal force assists
at speeds higher than the normal.
Construction: Construction of a semi-centrifugal clutch is shown in figure ‘a’.
Besides having a clutch plate, a pressure plate, and a splined shaft, it mainly
consists of (i) Compression spring (3 numbers), and (ii) Weighted levers (3
numbers). In this figure, only one compression spring and weighted lever are
shown.
The three weighted levers are hinged, and spaced at equal intervals on the periphery
of the clutch assembly. One suc h weighted lever hinged at B is shown in figure ‘b’.
This lever is hinged to pressure plate also through the needle bearing. The bearingcontains several needle rollers. The upper side A of the lever is weighted.
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 5
Working: In its operation at low engine speeds, the compression springs assist in
preventing the clutch slipping as the centrifugal effect upon the weighted upper side
is very small. But when the engine accelerates, the upper end tends to move
outwards under centrifugal action. It thus introduces a torque about hinge B which
causes a normal force over the pressure plate at the needle bearings (3 numbers).
Effect of normal force is to increase the pressure on the pressure plate which is
sufficient to prevent slip at full engine load since the centrifugal force Fc increases as
square of the speed N. Thus Fc is proportional to N 2 which is depicted in figure b
and c below.
Fig.5.3 Variation of force on Pressure Plate in Semi-Centrifugal Clutch
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 6
Fig.5.4 Semi-Centrifu gal Clutc h
5.5 Centr i fugal clu tches
Fig.5.6 Characteristics of Centrifugal clutch
Fig .5.5 a) Single Plate b) Multiplate Clutch
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 7
Fig.5.5 (b) Centrifugal clutch
The principle of these is shown in the simple arrangement in Fig. ( a ) above where a
single-plate clutch, of ordinary construction has its presser plate A actuated by the
‘centrifugal’ forces acting on masses B formed on the ends of bell -crank levers
pivoted on pins in the cover plate C. This arrangement has two principal drawbacks.
First, there would be some force acting on the presser plate whenever the clutch was
rotating and thus the clutch would never be completely disengaged. Secondly, if the
force P due to the centrifugal force CF were sufficient to engage the clutch fully at
say 1000 rev/min then it would become nine times as great at 3000 rev/min and it
would require nine times the force necessary with an ordinary clutch to produce
disengagement at that higher speed by pulling the presser plate back in the ordinary
way, and it is desirable to be able to disengage the clutch in that way.
The first drawback can be overcome by putting in springs D (shown dotted) which
apply a force Q opposing the force P. The centrifugal forces will then not give rise to
any pressure on the driven plate until they have increased sufficiently to overcome
the force Q and until then the clutch will be completely disengaged. By choosing the
magnitude of Q suitably, the commencement of the engagement can be made to
occur at any desired speed. Usually in motor car clutches at speed of about 500rev/min is chosen.
The second drawback can be overcome by modifying the construction as shown at
( b ) where the bell-crank levers press on a floating plate E between which and the
presser plate are placed springs F. These springs transmit the force P from the
floating plate to the presser plate. A stop G limits the outward motion of the masses
B and thus limits the amount the springs F can be compressed. The force that must
be applied to the presser plate in order to pull it back so as to disengage the clutch is
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 8
now limited to the difference between the force Q and the force exerted by the
springs F when the masses having come against the stops G) have compressed
them fully. This difference can be made to have any desired value.
5.6 The Fluid Flywh eel
The fluid flywheel shown in figure consists of a split housing which is rotated by the
engine. Inside this housing is a turbine, or driven rotor, which is connected by a
shaft to the gearbox.
Fluid Flywheel Characteristic.
Fig.5.6 Fluid Flywheel
The flywheel housing is divided up into a number of cells by means of radial vanes,
and these cells correspond to similar openings in the turbine. As the driving member
rotates, the fluid flows outwards under the action of centrifugal force, and circulates
from the flywheel to the turbine cells. Because the fluid is also being carried round
by the driving member, the fluid tends to rotate the turbine. The constantly
circulating fluid thus gains energy from the driving member and imparts this energy
to the turbine.
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 9
At maximum efficiency the amount of slip between the two rotating parts is only
about 2%, the slip being greater at lower speeds. Complete disconnection of the
drive is not possible with a fluid coupling, and it is not suitable for use with an
ordinary gearbox. It is generally used in conjunction with epicyclic gears to provide a
semi- or fully-automatic gearbox.
Advantages:
- Fluid flywheels require less attention than friction clutches and need no
adjustment.
- The drive is taken up smoothly,
- Torsional vibration of the crankshaft and the transmission are damped out,
- The fluid absorbs transmission shocks when braking or coasting down a hill
and
- The clutch pedal is eliminated.
5.7 GEAR BOX
Torque avai lable and torqu e requ ired by an automo bi le:
Fig.5.7 Torqu e Required and Avai lable
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 10
5.8 Transm ission Requirements
The primary duty of the transmission system is to provide a drive from the engine to
the rear wheel. The nature of the transmission system is greatly affected by the
characteristics of the power plant installed for propelling the vehicle.
Transmission requirements of a vehicle using conventional power plants:
The torque developed by the engine at the starting speed is very low.
Therefore, it is not possible to start the engine under load. This requires that
the transmission system should provide a means of connecting and
disconnecting the engine from rest of the transmission system. Such an
operation must be smooth and without shock to the occupants of the vehicle.
The engine should be able to start and propel the fully laden car up to a
gradient of at least 1 in 4. This roughly requires that the overall transmission
torque ratio should be about 10:1 for sports cars and 20:1 for small vehicles.
Since the final drive ratio varies from 3.5:1 to 5:1, it means that an additional
torque ratio of 3:1 to 4:1 is required to give an overall ratio to cope with themaximum gradients.
The transmission should allow the engine to run in the region of its maximum
power speed when the car is traveling at maximum speed. This means
matching of the maximum engine to the maximum vehicle speed.
It must allow transmission of maximum engine power continuously over as
large a speed range as possible to permit the fastest possible acceleration.
For obtaining good fuel economy the transmission system should give
automatically the highest possible torque ratio at steady running.
Thus an optimum transmission system would give a smooth start from the rest
and bridge the gap between the maximum speed and starting speed by suitable
gears so as to provide good acceleration and hill climbing consistent with fuel
economy over a wide speed range.
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 11
In addition to these, other transmission system requirements are:
- It should allow the power transmission at an angle of 90 degrees.
- It should allow the driven wheels to be driven at different speeds.
- It should permit relative movement between the frame mounted engine and
the spring supported axle.
5.9 Vehicle Resistances
Tract ive effort is defined as the force exerted by the driving wheel in a direction
parallel to the ground against the road resistance.
A moving vehicle has to overcome the following road resistances:
1. Rolling resistance,
2. Air resistance, and
3. Gradient resistance
1. Rolling Resistance:
Rolling resistance is defined as the resistance to rolling motion offered by
road over which the vehicle is moving. It is mainly the losses occurring due to
deformation of road and tyre and losses occurring due to dissipation of energy in
tyre. The main cause of the rolling resistance is the hysterics losses, the greater part
of which are converted into heat. Then factors which affect the rolling resistance are
speed and inflation pressure of the tyre, tyre design, etc. The effect of speed,
however, is quite small and the rolling resistance can for practical purposes, be
considered as independent of speed.
2. Air Resistance:
The vehicle while moving experiences aerodynamic drag the magnitude of which
depends upon the frontal area of the vehicle, shape and the speed of the vehicle.
This aerodynamic drag is called the air resistance and is given by
Air resistance = 212
d C AV
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 12
Where C d is the coefficient of drag, A the frontal area, is the density of air and V
the vehicle speed. Since the air resistance is proportional to the square of the
vehicle speed, it becomes quite significant for high speed vehicles and requires
careful study of the frontal area, its profile, and the surface finish, etc.
3. Gradient Resistance:
When a vehicle moves up a gradient, a part of its weight tries to pull it down. That
means a force equal to this pull must be supplied by the engine to overcome this
resistance which is referred to as gradient resistance.
The gradient resistance depends upon the weight of the vehicle and the steepness
or t he grade of the road. It is independent of the speed of the vehicle.
4. Total Resistanc e
The total resistance to the motion of the vehicle is thus given by
R t = R r + R a + R g
5.10 TYPES OF GEAR BOX
a. Sliding mesh type gear box,
b. Constant –mesh Type gear box:
- Dog clutch type,
- Synchromesh type.
- Automatic gear box,
- Overdrive,
c. Torque converter.
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 13
Figure 5.8 shows the method of engagement of gears in a sliding mesh and a
constant mesh gear box.
Figure 5.8.
Figure 5.9 Sliding mesh gear box with 4 forward and one reverse speed
.
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 14
Figure 5.10. A typical 3 forward and one reverse speed type sliding mesh type gear
box
a. Sl id ing m esh gear box: In a sliding mesh gear box the movement of the fork will
make the gears on the main shaft to slide on the splines provided on the shaft. This
will lead to one of the gears on the main shaft to engage with the corresponding
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 15
matching gear on the counter shaft (lay shaft) and thus receive the required power
and speed.
Fig.5.11 Sliding mesh type gear box
b.Constant –Mesh gear box : In the constant-mesh type gearbox all the gears are
all the time in constant mesh. It has three shafts, (like that in the sliding mesh gearbox) namely, primary shaft, main-shaft and the layshaft. The primary shaft which
carries the clutch is splined and carries a gear that meshes with the first gear on the
layshaft. The main shaft has a number of gears (in descending sizes) that mesh with
the gears on the layshaft. However, these gears, being on bushes or ball or roller
bearings, are free to move on the main shaft but they do not transmit torque in this
situation. The large layshaft gear is engaged with the primary shaft gear and other
layshaft gears are engaged with main shaft gears. A dog clutch splined to the
mainshaft provides means of locking the freely rotating main shaft gears to the main
shaft to allow a gear ratio change.
Fig.5.12 Constant mesh gear box
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 16
c. Synchrom esh Mechanisms
The purpose of the synchromesh mechanism is to bring to the same speed, the two
coupling members just before the actual coupling so that the gear teeth do not clash
and a smooth and silent coupling is obtained.
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 17
Figure 5.13 above shows the synchro-dog clutch principle.
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 18
Synchromesh Mechanisms
Figure5.14 below gives the exploded view of the synchro unit
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 19
When the synchromesh is disengaged, gears are running free on the main shaft and
the two gears to be engaged are running at different speeds. When the selector
lever is moved, the sliding sleeve and the sliding gear slide together because of the
pressure of the spring-loaded balls until the cones on the gears contact. Both gears
have now reached the same speed. As the selector lever is moved further, the
sliding gear cone is held against the high speed gear cone as shown in the extreme
right part of figure and the sliding sleeve presses the spring loaded balls and slides
over on to the high-speed gear, thereby, locking the sliding gear to it. Since at the
time of final engagement of the gears, both the gears are running at the same speed,
the meshing is quiet and clash-free.
5.11 TORQUE CONVERTER
Performance of a Torque Converter
Fig.5.15 Torque converter
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 20
Torque converters are similar in construction to the fluid flywheel, the main
difference being that the former has a reaction member or stator. This stator
produces a change of torque between the input and output shafts of the converter,
enabling an infinite number of speed and torque changes to be obtained to suit
varying conditions. If this conversion is multiplied by the ratio of an epicyclic gearbox,
the torque demands of a large-engine car are covered for all practical purpose.
A single stage three-element torque converter is shown in a simple form in
figure. The three elements are the impeller, stator, and turbine; other designs have
more elements and additional stages to improve the efficiency over a wide range,
and may have variable-angle stator-vanes.
Basically, the action of the torque converter is as follows. The stator, or
stationary member, redirects the flow of oil leaving the turbine outlets and, with the
stator as a fulcrum, boosts the action of the impeller. To improve the performance,
the blades of the turbine are curved and are fewer in number than the impeller to
overcome the effects of vane interference.
As the turbine speed increases the stator vanes would tend to impede the
return of oil to the impeller, and to prevent this, the stator is mounted on a one-wayclutch. Thus the stator can rotate in the same direction as the engine, together with
the turbine and impeller, but is held in the opposite direction and possesses similar
characteristics to the fluid flywheel, the speed ratio between the engine and output
shaft approaching 1:1.
Figure.5.16.Flow of fluid in torque converter (a) under low speed condition the stator deflects the fluid
flow back to the impeller (b) under high speed condition the stator free wheels and fluid flow is not
deflected.
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 21
4.12 Epicycl ic Gearbo x
Figure shows a simple epi-cyclic gearbox. In its simplest form it consists of three
elements: a sun gear, an
annulus (or ring gear) and a
carrier, the latter supporting
two or more planet wheels
which mesh with both sun
gear and annulus. The teeth
are constantly in mesh and
changes in ratio are made
by holding one of the three
components of the system and causing the others to rotate around it.
Action Arm ‘a’ S (Ts) P (Tp) A (T A)
Fix the arm and give +1
rev. to S0 1
S
P
T
T S S P
P A A
T T T
T T T
Fix the arm and give +x
rev. to S0 +x
S
P
T x
T S
A
T x
T
A
S
P
arm aCarrier
S
p
a
A
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 22
Give +y rev. to arm and
+x rev. to Sy Y + x
S
P
T y x
T
S
A
T y x
T
Sl.
No.
Reaction member
(member is fixed
to frame)
Driving member -
speed
Driven member -
speed
Type of output
1. Sun gear S
(x +y) = 0 or x =
-y
Speed of A = S
A
T y x
T
or S A
A
T T y
T
Speed of arm =
y
Speed
Reduction
2. Annulus A
S
A
T y x
T = 0 or
A
S
T x y
T
Speed of S = x + y
or S A
S
T T y
T
Speed of arm =
y
Speed
Reduction
3. Sun gear S
(x +y) = 0 or x =-y
Speed of arm = y
Speed of A =
S
A
T
y xT
or S A
A
T T y
T
Speedincrease
(Overdrive)
4. Annulus A
S
A
T
y xT
= 0 or
Speed of S = x + Speed
increase
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 23
A
S
T x y
T
Speed of arm = y y
or S A
S
T T y
T
(Overdrive)
5. Carrier arm a y =
0
Speed of Sun S = x +
y =x as y = 0
Speed of
Annulus A =
S
A
T y x
T
= S
A
T x
T
Reverse gear
speed
reduction
6. Carrier arm a y =
0
Speed of Annulus A =
S
A
T y x
T = S
A
T x
T
Speed of Sun S
= x +y = x as y =
0
Reverse gear
overdrive
A lay-shaft gear arrangement with a given set of parts can provide only two ratios buta given epicyclic train can provide six ratios depending upon which member is held
stationary for reaction and which is used for input. Brake bands are used to hold the
member of epicyclic gear train. Out of these six ratios two are reducing ratios, by
driving firstly from sun wheel to career and secondly from annulus to carrier. Another
two gear ratios are speed increasing ratios (overdrives) by driving firstly from carrier
to sun wheel and secondly from planet carrier to annulus. The rest of the two gear
ratios are reversing ratios-one giving speed reduction by driving from sun wheel to
annulus and the other giving a speed increase by driving from annulus to sun wheel.
If any two members are locked together the entire epicyclic gear train acts as a solid
shaft because locking two members locks up the whole system.
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5.13 THE OVERDRIVE MECHANISM
The overdrive permits the propeller to rotate faster in the top gear than the
primary shaft. Engine revolutions can be reduced by 20-25% so permitting high
cruising at lower engine revolutions. This in turn extends the life of the engine,
improves the fuel consumption, and reduces vibration and noise. When fitted to
intermediate gears it increases the ratios available, and ratios of the normal
reduction gears are altered to take advantages of the additional ratios.
Fig.5.16 Over drive mechanism
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Fig.5.16 Over drive mechanism
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 26
Generally an overdrive is fitted to top or third and top gear only. Over drives are
especially suited to high powered cars employing three speed gear boxes since in
order to produce flexible top gear performance a low gear final drive may be
necessary, resulting in the engine running faster at high speeds than is desirable.
The over drive may be operated manually or automatically; in the latter case it
comes to operation at a particular speed.
Typical over drive unit is shown in the figure. Epicyclic gears are normally used in the
over drive. During normal drive, the cone clutch locks the sun wheel to the annulus
and the entire assembly rotates, giving a direct drive through the one way clutch. To
bring the over drive into operation, the clone clutch is moved until it contacts the
stationary brake lining. Now the planet wheels and their carrier are driven round the
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Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 27
stationary sun wheel, the one way clutch is over run by the annulus and the output
shaft speed is increased.
Adv antages of epicyc l ic gear tra ins:
1. The epicyclic gear trains are very popular for automatic transmissions
because change from one ratio to another can be made without loosing any
traction as there is no axial engagement or disengagement of gear teeth or
dogs.
2. It is very compact compared to the layshaft gear train.
3. The loads coming to the gear teeth are lower because of being shared by at
least two (more usually three) tooth contact points.
4. The epicyclic gear box is inheritently quieter in operation.
5. By using several planet gears the loads on the bearings can be balanced; the
shaft bearings in a layshaft gear train are comparatively heavily loaded.
5.14 Free wheel mech anism :
The free-wheel assembly, or overrunning clutch, sprag clutch, or one-way clutch, is
an essential part of every overdrive. It transmits power only from the transmission
main shaft to the output shaft when the sun gear is unlocked, and releases the main
shaft from driving the output shaft when the planetary gears are in overdrive.
Figure A shows the construction and principles of operation of a typical free-wheelunit. One part consists of a hub with internal splines to connect it to the transmission
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shaft. The outside surface of the hub contains twelve cams so designed to hold
twelve rollers in a cage between them and the outer race. The outer race is splined
to the overdrive output shaft. When the hub is driven in the direction shown in figure,
(clockwise) the rollers ride up the cams and by their wedging action force the outer
race to follow the hub. This is the method of driving the output shaft in direct drive.
Figure B shows what happens when the outer race becomes the driving member.
The rollers move down the cams, to release the outer race from the hub, thus
allowing it to move independent of the hub, and so make the entire assembly act like
a roller bearing. In this way the unit runs free whenever power is being transmitted
through the planetary gears or whenever the engine slows down and the output shaft
starts to drive the transmission main shaft.
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 29
Prob lems o n clu tch
Single -plate clutch:
5.1 A motor car engine develops 5.9 b.KW at 2100 r.p.m. Find the suitable size
of clutch plate having friction linings riveted on both sides, to transmit the
power, under the following conditions:
a.) intensity of the pressure on the surface not to exceed 6.87 x 104 Pa,
b.) Slip torque and losses due to wear etc. is 35% of engine torque.
c.) Co-efficient of friction on contact surface is 0.3.
d.) Inside diameter of the friction plate is 0.55 times the outside diameter.
Solu t ion :
60000 60000 5.9
2 2 2100
w P
T N
= 26.84 N-m.
Taking account of the losses, the total torque is
T = 26.84 x 1.35 = 36.23 N-m.
We have, T = πµC (r 22 – r 1
2) 2
Or 36.23 = πx 0.3 x 6.87 x 104 x r 1
2
211
20.55
r r
= πx 4.122 x 104 3
1
11
0.303
r
or 3 3
1 4 4
36.23 0.303 1.22
4.122 10 0.697 10r m
or r 1 = 49.5 mm
and r 2 = 90 mm
Hence inside diameter = 99 mm
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Clutch & Gear Box
Prof Pradeep Kumar Shetty, Dept of Mech engg., MIT,Manipal 30
And outside diameter = 180 mm
5.2: In a gear box the clutch shaft pinion has 14 teeth and low gear main shaft
pinion 32 teeth. The corresponding layshaft pinions have 36 and 18 teeth. The
rear axle ratio is 3.7:1 and the effective radius of the rear tyre is 0.355 m.
calculate the car speed in the above arrangement at an engine speed of 2500
r.p.m.
Solu t ion :
Gear ratio =
Speed of clutch shaft
speed of main shaft
Teeth of layshaft pinion Teeth of mainshaft pinion
Teeth of clutch shaft pinion Teeth of lay shaft pinion
=36 32
14 18 = 4.57:1
The rear axle ratio is 3.7:1.
Hence overall gear ratio,
G = 4.57 x 3.7:1 = 16.92:1
Speed of the car ,2 2500 0.3552
/16.92 1000
Nr V km hr
G
= 19.8 Km/hr
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Exercise 5
1. What are the functions of Clutch?
2. What is the requirement of a clutch?
3. Explain with a neat sketch working of a Semi-centrifugal clutch.
4. With a neat sketch explain the working of Fluid flywheel.
5. Write a short note on i) Centrifugal clutch ii) Single plate clutch.
6. What are the requirements of Transmission? Explain
7. Define the terms i) Rolling resistance, ii) Air resistance, and iii) Gradient
resistance
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Clutch & Gear Box
8. Explain with a neat sketch of a Sliding Mesh gear box and show the diagram
of engaging gear 1st and 4th gear.
9. Explain with a neat sketch of a Constant Mesh gear box and show the
diagram of engaging gear 1st and Reverse gear gear.
10. Explain with a neat sketch of a Synchromesh Mesh gear box and show the
diagram of engaging gear 1st and 3rd gear.
11. Write a short note on i) Torque converter ii) Epicyclic gear box with a neat
sketch.
12. Explain with a neat sketch working of a Overdrive.
13. What are the advantages of epicyclic gear box?