clutch its types design construction & working with new technology

Clutch its types Design construction & working with latest technology

1. Power transmission:

The power developed by the engine in automobiles should be transmitted to the road wheel efficiently. The power transmission system basically needs a clutch to transmit the power from the engine to the remaining parts of the transmission. The power transmission system is different for different types of vehicles.

In case of two wheelers with gears the power is transmitted from the clutch to the gearbox and then transmitted to the wheels by means of chain drive or gear drive. In case of non-geared two wheelers the power is transmitted from the clutch directly to the wheels through the chain drive / gear drive or sometimes through the variation mechanism.

In case of LMVs and HTVs the power transmission consists of clutch and gearbox as the common features. In the conventional (front engine rear wheel drive) the power is transmitted from gearbox to road wheels by means of universal joint, propeller shaft, sliding joint, differential and half shaft. In case of front engine front wheel drive transaxle is commonly used. In this case the gear box is arranged transversely and power transmission may not be provided with propeller shaft and bevel gear arrangement. This type of arrangement is compact and also contains less number of moving parts. In the case of four wheel drive, the arrangement is similar to conventional power transmission with transfer gear box or transfer case as the additional features. The transfer gear box transmits the power to both the axles uniformly.

Power transmission

1. Clutch

A clutch is a mechanism which enables the rotary motion of one shaft to be transmitted at will to second shaft, whose axis is coincident with that of first.

· Clutch is located between engine and gear box. When the clutch is engaged, the power flows from the engine to the rear wheels through the transmission system and the vehicle moves.

· When the clutch is disengaged, the power is not transmitted to the rear wheels and the vehicle stops, while the engine is still running.

Clutch is disengaged when:-

a) Starting the engine.

b) Shifting the gears.

c) Idling the engine.

clutch Assembly

1. Functions of a clutch

· To permit engagement or disengagement of a gear when the vehicle is stationary and the engine is running.

· To transmit the engine power to the road wheels smoothly without shock to the transmission system while setting the wheel in motion.

· To permit the engaging of gears when the vehicle is in motion without damaging the gear wheels.

2. Principle of Operation of a Clutch:-

The clutch principle is based on friction. When two friction surfaces are brought in contact with each other and pressed they are united due to friction between them. If one is revolved the other will also revolve. The friction between the two surfaces depends upon-

i. Area of the surface.

ii. Pressure applied upon them.

iii. Coefficient of friction of the surface materials

iv. Here, one surface is considered as driving member and the other as driven member.

The driving member of a clutch is the flywheel mounted on the crankshaft, the driven member is the pressure plate mounted on the transmission shaft. Friction surfaces (clutch plates) are between the two members (driving and driven). On the engagement of the clutch, the engine is connected to the transmission (gear box) and the power flows from the engine to the rear wheels through the transmission system. When the clutch is disengaged by pressing a clutch pedal, the engine is disconnected from the transmission and consequently the power does not flow to the rear wheels while the engine is still running.

Principle of Friction Clutch

1. Friction clutch

In these types of clutches, friction force is used to engage and disengage the clutch. A friction plate is inserted between the driving member and the driven member of clutch. When the driver releases the clutch pedal, the driven member and driving member of clutch, comes in contact with each other. A friction force works between these two parts. So when the driving member revolves, it makes revolve the driven member of clutch and the clutch is in engage position.

5.1.) Single plate clutch:

In the single plate clutch a flywheel is fixed to the engine shaft and a pressure plate is attached to the gear box shaft. This pressure plate is free to move on the spindle of the shaft. A friction plate is situated between the flywheel and pressure plate. Some springs are inserted into compressed position between these plates. When the clutch pedal releases then the pressure plate exerts a force on the friction plate due to spring action. So clutch is in engage position. When the driver pushes the clutch pedal it due to mechanism it serves as the disengagement of clutch.

5.2 Working of single Plate clutch

A single plate friction clutch consisting of a clutch disk between the flywheel and a pressure plate. Both the pressure plate and the flywheel rotate with the engine crankshaft or the driving shaft. Both sides of clutch disc are faced with friction material.

· The clutch disc is mounted on the hub which is free to move axially along the splines of the driven shaft but not turntable towards the transmission input shaft.

· The pressure plate pushes the clutch plate towards the flywheel by a set of strong springs which are arranged radially inside the body.

· The three levers (also known as release levers or fingers) are carried on pivots suspended from the case of the body.

· These are arranged in such a manner so that the pressure plate moves away from the flywheel by the inward movement of a thrust bearing.

· The bearing is mounted upon a forked shaft and moves forward when the clutch pedal is pressed.

Single Plate Clutch

Parts of single plate clutch

Single Plate Clutch Advantages & Disadvantages

5.3 Advantages:

· Simple and inexpensive and need little maintenance.

· Gear changing is easier than the cone clutch because the pedal movement is less.

· It is more reliable because it does not suffer from disadvantages of binding of cone.

5.4 Disadvantages:

· The springs have to be more stiff hence greater force required to disengage.

5.5 Single Plate Clutch Applications

· Single plate clutches are used where large radial space is available such as: trucks, buses, cars etc.

· As sufficient surface area is available for the heat dissipation in such clutches, no cooling oil is required. Therefore, single plate clutches are dry type.

5.6 Design details of single plate clutch

R2 = inner radius of friction surface.

R1= outer radius of friction surface.

P= intensity of pressure normal to friction surface.

Consider a different element at radius R & of width dr. Then axial load on the differential element is.

dW= p x dA

Ø Total axial load on the clutch.

ʃ pr x dr equation-1

And total torque transmitted.

T=ʃ μ (p2pi rdr) x r =

[T=W x r] equation-2

Pr = constant (uniform rate of wear)

i) Uniform pressure intensity

W= from equation-1

From equation-2

T= μ /3 (R1³- R2³) multiply (R1²- R2²) to numerator & denominator

= [2/3 μ (R1³- R2³)/ (R1²- R2²)]

p (R1²- R2²)

=2/3 μ W (R1³- R2³)/ (R1²- R2²) [W=

= μ W R [R=2/3(R1³- R2³)/ (R1²- R2²)]

ii) Uniform rate of wear

W=2

from equation-1

T= μ /3 (R1²- R2²) from equation-2

T= μ/2 (R1- R2) [

r (R1- R2)]

T= μ W [(R1- R2)/2] effective mean radius R= (R1- R2)/2

T= μ W R equation-3

Now in an actual single plate clutch, there are 2 pairs of friction surfaces

Equation 3 modified as

T= 2μ W R

Ø Design & Calculation of single plate clutch

P1 – Friction pad inner diameter

P2 – Friction pad thickness

P3 – Friction facing thickness

Ri – Inner radius of clutch disc in meters

Ro – Outer radius of the clutch disc in meters

N – Speed of engine in rpm = 3750 rpm

ωr – angular velocity in rad/s

P max – clamping pressure in MPa

Ø Mathematical Calculations

The material considered for the friction pad is Kevlar 49 Aramid. Uniform Wear Theory is considered for calculations, and accordingly, the intensity of the pressure is inversely proportional to the radius of friction plate.

𝑅 =𝑅𝑖+𝑅𝑜 /2= 0.1𝑚

In general, the frictional torque acting on the clutch plate is given by

𝑇 = 𝑁 ×μ ×W ×R

In general, the frictional torque acting on the clutch plate is given by 𝑊 = 3000𝑁

𝑃 ×𝑟 = 𝐶 (𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡)

Axial force on the clutch pad,

𝑊 = 2𝜋×𝐶 × (𝑅𝑜 −𝑅𝑖)

𝐶 = 0.0119𝑁𝑚

The maximum pressure occurs at the inner radius and the minimum pressure at the outer radius.

In general, the frictional torque acting on the clutch plate is given by

𝑃𝑚𝑖𝑛 =𝐶 𝑅𝑜= 0.0994 𝑀𝑝𝑎

𝑃𝑚𝑎𝑥 =𝐶 𝑅𝑖 = 0.1492 𝑀𝑝𝑎

Here, we consider the maximum pressure value obtained in the Finite Element Analysis of the clutch plate.

Ø Thermal Analysis

T – Temperature of the disc in Celsius

T1 – Limiting temperature of the material in Celsius = 150ºC

µ - Coefficient of friction of the material = 0.4

k – Thermal conductivity of the material in Watts per meter Kelvin

h – Heat transfer coefficient of the material.in Watts per sq. meters per Kelvin.

q – Heat energy generated in watts

qf – heat flux in W/m2

t – Slip time in seconds = 0.5s

A – Area of a friction pad = 0.000931m2

4.2 Mathematical Calculations

𝜔𝑟 =2×𝜋×𝑁/ 60= 392.6𝑟𝑎𝑑/𝑠

𝑞 = 𝜇 ×𝑃𝑚𝑎𝑥 ×𝜔𝑟 = 23.4375 𝑊

𝑞𝑓 =𝑞 𝐴

= 25155𝑊/𝑚2

6.) Multi plate clutch:

A multi-plate clutch is a type of clutch in which the multiple clutch plates are used to make frictional contact with the flywheel of the engine in order to transmit power between the engine shaft and the transmission shaft of an automobile vehicle. A multi-plate clutch is used in automobiles and in machinery where high torque output is required. In bikes and scooter multi-plate clutch is used due to the limitation of compact gearbox used in bikes and scooter.

Multi plate clutch

6.1 Multi Plate Clutch Working

Multiplate plate clutch working

· During clutch engagement, spring pressure forces the pressure plate towards engine flywheel. This causes the friction plates and the steel driven plates to be held together.

· Friction locks them together tightly. Then the clutch basket, drive plates, driven plates, clutch hub and the gearbox input shaft all spin together as one unit.

· Now power flows from the clutch basket through the plates to the inner clutch hub and into the main shaft of the transmission.

· The clutch gets released or disengaged when the clutch pedal is pressed. This causes the clutch pressure plate to be moved away from the drive and driven plates, overcoming the clutch spring force.

· This movement of the pressure plate, relieves the spring pressure holding the drive and driven plates together. Then the plates float away from each other and slip axially.

· Thus, the clutch shaft speed reduces slowly. Finally, the clutch shaft stops rotating. Power is no longer transferred into the transmission gearbox.

6.2 Multi Plate Clutch Advantages & Disadvantages

Advantages:

· Increase the amount of torque to be transmitted.

· Decrease the pedal effort to operate the clutch.

· Decrease the weight of the clutch.

· Decrease the moment of inertia of the clutch.

· Increase in better acceleration.

Disadvantages:

· Heavy.

· Too expensive.

6.3 Multi Plate Clutch Applications

· Multi plate clutches are wet type.

· Multi plate clutches are used where compact construction is required, e.g. scooters and motorcycles.

6.4 Design details of Multiplate clutch

If n= total number of friction plate in the Multiplate clutch, then, number of pairs of contact surfaces = (n-1).

T= (n-1) μ W R equation-1

Accordingly,

i.) For uniform pressure intensity,

T = (n-1) 2/3 μ W (R1³- R2³)/ (R1²- R2²) equation-2

ii.) For uniform rate of wear,

T= (n-1) μ W [(R1+ R2)/2] equation-3

6. Cone clutch

A simple cone clutch is shown in figure. Cone clutch consists of an inner cup attached to driving shaft and follower cone. Follower cone is movable; it can axially slide over the driven member. The inner side of the driver cup exactly fits the outer surface of the cone. The slope of the cone is made small, that help to give higher normal forces. The recommended angle of slope is between 8-15 degree. According to the allowable normal pressure and coefficient of friction required the contact face of the driven member is lined with material like leather, asbestos, wood, etc. The clutch engaged by bringing two cone surfaces together in contact. A spring is provided on the drive shaft to hold the face of clutch in touch by producing required axial force. A forked lever is used to disengagement of the clutch.

6.5 Advantages of Cone Clutch:

1. Small axial force is required to keep the clutch engaged.

2. Simple design.

3. For a given dimension, the torque transmitted by cone clutch is higher than that of a single plate clutch.

6.6 Disadvantages of Cone Clutch:

1. One pair of friction surface only.

2. The tendency to grab.

3. The small cone angle causes some reluctance in disengagement.

6.7 Design of cone clutch

r₂ = inner radius of friction surface.

r₁= outer radius of friction surface.

Consider a different element at radius r & of width ds as shown. Then area of this differential element dA is given by.

dA dA =

Then normal load on differential element is

dp = pdA = 2

Where p is the intensity of pressure normal to friction surfaces

Axial load on the differential element is.

dW =dP sinϴ = 2

dr sinϴ/sinϴ =

equation-1

Total Axial load on the clutch

r₂

W=ʃ dW from equation-1

r₁

r₂

ʃ pr x dr equation-2

r₁

And total torque transmitted.

r₂ r₂

T=ʃ μ

.r =

/sinϴ [T=W x dp] equation-3

r₁ r₁

r₂

equation-4

r₁

From equation 2 & 4 can be integrated by considering.

1. Uniform pressure intensity P=constant. This condition is experienced when the two friction surfaces are perfectly contacting each other.

2. Uniform rate of wear. Wear depends upon the intensity of pressure p and velocity of rubbing which further depends upon r. thus uniform rate of ware pr=constant.

1. Uniform pressure intensity

Equation 3 can be written as

r₂ r₂

ʃ r dr = 2

[r/2] equation-2

r₁ r₁

(r₂²- r₁²) equation-5

This is independent of the cone angle.

From equation-4

r₂

from equation-4

r₁

(r₂³- r₁³) equation-4

(r₂³- r₁³)/ (r₂²- r₁²)] x [

(r₂²- r₁²)] substituting from equation-5

T=μWR R=

(r₂³- r₁³)/ (r₂²- r₁²)]

i.) Uniform rate of wear

r₂

W=2

∫dr =2

(r₂-r₁) equqtion-5 from equation-1

r₁

r₂

r₁

(r₂²- r₁²)] equation-4

= [2

(r₂–r₁)] [μ/2sinϴ (r₂-r₁)]

T= μ W/2sinϴ [(r₂+r₁)] substituting from equation-5

T= μ W R R= (r₂+r₁)/2sinϴ R=Effective mean radius

Application of Cone Clutch:

Cone Clutches are used in specialist transmissions in racing, rallying, or in extreme off-road or other industrial applications.

Ø Formulae of single , multi & cone clutch

Sr.no	Type of clutch	Uniform pressure Theory	Uniform wear theory
1	Single plate clutch	T= 2/3 μ W (R1³- R2³)/ (R1²- R2²)	T=1/2 μ W [(R1+R2)]
2	Multi plate clutch	T= n 2/3 μ W (R1³- R2³)/ (R1²- R2²)	T=n 1/2 μ W [(R1+R2)]
3	Cone clutch	T= 2/3 μ W (R1³- R2³)/ (R1²- R2²) x cosecα	T= 1/2 μ W [(R1+R2)]cosecα

Power transmission by single plate clutch is given by.

P = ω T P=2

NT/60 watt

Where N= speed of driving shaft.

· Centrifugal clutch:

Principle:

All friction clutch works on same principle. In centrifugal clutch the initial force which are used to engage the clutch is achieve by centrifugal action or centrifugal force. This centrifugal force automatically engage the clutch at a predefine speed and disengage it when the engine slow down below a limit.

7.1 Construction

Centrifugal clutch

Spider or Guide:

Spider or guide is works as one of the pressure plate of simple clutch. It is connected to the driving shaft of engine. It is called guide way because it hold the shoe and guide its movement. The initial position of shoe in the guide is controlled by the springs.

Drum:

Drum act like the pressure plate of a simple clutch. It is connected with the driven member and rotates with it. Drum does not directly connect with the guide or shoe.

Shoe:

Shoe is major part of centrifugal clutch. It acts like engaging member of guide and drum during running condition. When the driving shaft rotates, it makes rotate the shoe which is free to move in guide. Due to rotation a centrifugal action works on it which forces it outward and connects with drum.

Springs:

Springs are controlling element of this type of clutch. Each shoe require one spring. The shoe is connected with the guide through these springs. It holds the shoe at its initial position unlit driving member achieves the required speed at which the centrifugal force can overcome spring force. If we want to change the engaging speed of the clutch, we simply change these springs with higher spring.

Friction Lining:

The outer face of the shoe which is going to connect with drum is equipped with friction lining. These lining play the same role which friction plate play in simple clutch. It is used to transmit torque from driving member to driven member and also avoid direct contact of shoe through drum which reduces wear and tear of shoe.

7.2 Working:

· At the initial condition when the engine is off the shoe are not connected with the drum.

· As the engine start, the Spider or Guide attached with engine shaft start to rotate.

· The shoe connected with the spider also rotate with it and felt some centrifugal action.

· This centrifugal force makes shoe to slide in the direction of circumference.

· At low speed, the centrifugal force is too low to overcome the spring force which tends to bind the shoe inside the guide.

· As the speed increases the shoe move outside and make a contact with drum. The friction lining between shoe and drum start to transfer torque from engine to drum.

· Now the drum start to rotate and as the speed of engine increase, it will increase the centrifugal force and also the efficiency of torque transmission through centrifugal action.

· When the engine speed decrease, will decrease the centrifugal action which remove the contact of drum and shoe and disengage the clutch.

· Thus this is an automatically speed operated clutch. The operating speed of clutch can be maintained by replacing spring.

7.3 Advantages:

· It is low in price.

· Easy to operate.

· It doesn’t require any separate control mechanism like clutch pedal etc.

· The engaging speed can be preciously controlled by selecting springs.

· It is used for automating transmission in which the driver first select gear and then press the accelerator pedal.

· It requires less maintenance.

7.4 Disadvantages:

· Power transmission is limited due to slippage.

· It cannot used to transmit high amount of torque.

· The power transmission or speed regulation is totally depended on controlling speed.

· Overheating problem due to quick engagement during running condition.

7.5 Application:

· It is used in chain saw, lawn mower etc.

· It is used in textile industries.

7.6 Design of centrifugal clutch

In the designing of centrifugal clutch it is required to determine the weight of the shoe,size of the shoe & dimensions of the sprig. The following procedure may be adopted or the design of a centrifugal clutch.

7.2 Mass of the shoes

Consider one shoe of a centrifugal clutch

Let m= mass of each shoe

N= no of shoes

r= distance 0f centre of gravity of the shoe from the centre of the spider.

R= inside radius of the pulley rim

N= running speed of the pulley in r.p.m

ω= angular running speed of the pulley in rad/sec =2

N/60 rad/s

ω₁=angular speed at which the engagement begins to take place and

μ = coefficient of friction between the shoe & rim.

We know that the centrifugal force acting on each shoe at the running speed.

P_c = mrω²

Since the speed at which the engagement begins to take place is generally taken as 3/4^th of the running speed therefore the inward force on each shoe exerted by the spring is given by.

P_s =m ω₁²r = m(3/4 ω)² r =( 9/16) mω² r

Net outward radial Force (i.e. centrifugal force with which the shoe presses against the rim at the running speed

= P_c- P_s = mrω² - ( 9/16) mω² r = 7/16 m r ω²

And the frictional force acting tangentially on each shoe

F= μ (P_c- P_s)

Frictional torque acting on each shoe

F x R = μ (P_c- P_s) x R

And Total frictional torque transmitted,

T= μ (P_c- P_s) x R x n

T= n F R [F=μ (P_c- P_s) ]

From this expression the mass of the shoes (m) may be evaluated.

· Size of the shoes

Let l = contact length of the shoes

b= width of the shoes

R = contact radius of the shoes. It is same as the inside radius off the rim of the pulley.

ϴ= angle subtended by the shoe at the centre of the spider in radians and

P = intensity of pressure exerted on the shoe. In order to ensure reasonable life, it may be taken as 0.1 N/mm²

We know that ϴ= I/R or I= ϴ R =

Area of contact of the shoe

= l. b

And the force with which the shoe presses against the rim

= A x p = l.b.p

Since the force with which the shoe presses against the rim at the running speed is (P_c- P_s) therefore

l.b.p =P_c - P_s

From this expression the width of shoe (b) may be obtained.

· Dimensions of the spring

We have discussed above that the load on the spring is given by

P_s = (9/16) x mrω²

The dimensions of the spring may be obtained as usual.

8 Semi-centrifugal clutch

8.1 Construction details of semi centrifugal clutch:

· Three hinged and weighted levers and three clutch Springs alternately arranged at equal space on the Pressure plate (only one lever and clutch spring shown in figure)

· Fly wheel is fitted to engine crank shaft

· Clutch plate is mounted on the splines of the clutch shaft

· Pressure plate is freely supported on clutch shaft

Semi-centrifugal clutch

8.2 Working of Semi centrifugal clutch

Clutch engaged

· Clutch springs exerts pressure on pressure plate at low engine speeds

· At high speeds the centrifugal force developed by rotation of weighted levers

Exerts pressure on pressure plate

· Pressure plate applies pressure on clutch plate

· Clutch plate firmly rotates in between fly wheel and pressure plate

· Clutch shaft rotates along with clutch plate

Clutch disengage

· As Driver presses the clutch pedal, pressure plate moves back against the force of

The springs

· Clutch plate also moves back on splines of clutch shaft

· Clutch plate speed reduces slowly and finally stops

8.3 Advantages of semi centrifugal clutch:

· Less stiff clutch springs are used as they operate only at low speeds

· Driver will not get strained in operating the clutch

Disadvantages of centrifugal clutch

· automatically disengaging at low engine speeds

· Only at high speeds, centrifugal force is sufficient to keep the clutch in engaged position

Used in

· Vauxhall car (foreign car)

8 Clutch Operating Linkage

The clutch unit is a rigid part of the flywheel and hence the crankshaft assembly. It is therefore subjected to the engine and transmission vibrations such as rocking, shaking and pitching. The clutch foot-pedal assembly, on the other hand, is attached to the body structure. As a result, this may be subjected to slight bump and rebound movements of the body. For smooth operation of the clutch without any jerks, some sort of flexible linkage system must be incorporated, which does not interfere with the clutch adjustment, is compact, needs very little maintenance, has a long working life, is simple, and is reasonably cheap. The three basic methods of transmitting movement and force to the clutch from the foot pedal are

9.1 Mechanical Operation.

· Rod-operated Linkage

As the clutch pedal is pressed, it pivots about the mounting bracket and the withdrawal rod pulls back or forwards according to the arrangement. Consequently the withdrawal lever rotates the fork-arm about the cross-shaft and pushes the thrust-bearing saddle against the clutch release-plate. This causes the movement of the release levers towards the flywheel, so that they pivot about the eyebolt pins, withdrawing the pressure-plate from the driven-plate thereby interrupting the drive.

9.2 Cable-operated Linkage

Cable linkage is a popular and effective method of transferring movement from the pedal to the clutch. The cable assembly uses an inner multi-strand steel-wire core and an outer cable sheath of a spiral wound flexible sleeve normally with nylon end-pieces. This plastic sleeve provides very good rubbing wear properties without requiring in general any lubrication. Also the inside of the sleeve may be lined with anti-friction material such as Polytetra fluorethylene (PTFE) plastic to minimise any slip-stick friction.

9.2 Hydraulically-operated Linkage

A more convenient way to transmit force and movement is by hydraulic linkage in which the fluid is forced through a flexible plastic pipeline, spun between the foot-pedal and the clutch bell-housing. A master-cylinder, mounted on the bulkhead and a push-rod joining the clutch-pedal to the sliding piston, provides the control of the clutch action. A slave cylinder unit containing the piston is installed on an extension formed on the bell-housing flange. The slave piston relays the slightest movement to the fork-lever through the slave pushrod. The thrust bearing assembly is fixed to one end of the fork lever, and a spherical pivot is installed slightly in from this end.

The master-cylinder piston pushes a continuous column of fluid through the pipeline when the clutch pedal is pressed down. This causes the displacement of an equal volume of fluid into the

slave-cylinder due to which the piston moves out and tilts the fork lever. This causes the thrust bearing to defect the release-fingers so that the driven-plate is slipped.

Master cylinder slave cylinder
Driven-plate wear, in this system, is compensated by the slave return-spring and piston automatically moves to take up the increased fork-lever tilt. The hydraulic actuating mechanisms are independent of frictional wear unlike cables due to application of large leverage. This system is particularly suitable for heavy-duty vehicles such as on large trucks.

9.4 Vacuum-operated Clutch

In this type of clutch, engine intake manifold vacuum is used for disengaging the clutch. It uses a vacuum reservoir connected to the intake manifold through a non-return valve. It has a vacuum cylinder and piston, the rod side of the piston is opened to the atmosphere. The solenoid valve is operated when the switch is closed so that the circuit is complete. The switch is mounted on the gear lever so that when the gear lever is operated to change the gear, the switch is also closed.

Vacuum clutch

In the normal position the valve rod is in the bottom position of the valve (shown dotted in and the switch is open. At this stage, the pressure on both sides of the piston in the vacuum cylinder is atmospheric. When the switch is closed due to the operation of gear change lever, the solenoid coil is energized and the valve rod is pulled up. This action opens the passage between the reservoir and the vacuum cylinder, so that a pressure differential acts on the piston of the vacuum cylinder. As a consequence the piston moves in the forward direction, causing the operation of linkage to disengage the clutch.

9 Electromagnetic Clutch

Construction

Rotor:

Rotor is a major part of this clutch witch is connected directly to the driving shaft or engine shaft. It continuously rotates along with the driving shaft.

Winding or Coil:

Winding coil is situated behind the rotor and remains in stationary position during clutch working. It is shown in figure. A high voltage DC supply is connected with this winding which transfer a high voltage current into this winding and convert it into electromagnet.

Armature:

Armature is situated at front of the rotor. It is connected to the hub or pressure plated with the help or rivet or bolted joint.

Hub:

Hub or pressure plate is bolted with the gear shaft or driven shaft and rotates with it. It is situated after the armature.

Friction Plate:

Friction plate is inserted between armature and rotor according to the requirement.

Supply unit:

Supply unit consist clutch switch, battery, wire etc.

10.1 Working:

· The electromagnetic clutch working can be summarized into following points.

· In the initial condition the clutch is in disengage position. There is an air gap between rotor and hub.

· First the engine starts which makes rotate the rotor connected with the engine shaft.

· A DC battery supplies DC current into the clutch winding.

· This high voltage DC current converts this winding into an electromagnet which attract armature towards it.

· This armature force friction plate towards the rotor and make rotate the hub.

· Thus the hub rotate and the rotor transmit 100% torque during engage position.

· When the clutch switch / pedal is pressed, the battery stops the supply in winding which remove the electromagnetic force, thus the clutch is in disengage position.

10.2 Advantages:

· No linkage is required to operate the clutch. So it can be installed any remote location.

· It can be used to achieve automatic transmission.

· Easy to operate.

· Less wear and tear at contact point.

10.3Disadvantages:

· This clutch operating temperature is limited by the temperature rating of the insulating material.

· High initial Cost.

11. Cable type clutch linkage

A cable-type clutch linkage is simple, lightweight and is the most common linkage on newer cars today. Normally, a cable connects the pivot of the clutch pedal directly to the release fork. This simple design is flexible, compact, and eliminates nearly the entire wearing pivot points found in a shaft and lever linkage. There is one downside to this type of setup: cables will gradually stretch and can break due to excessive wear and electrolysis.

On a typical installation, one end of the cable is connected to the clutch pedal and a spring is attached to the pedal assembly to keep the pedal in the "up" position. The other end of the cable is connected to the clutch release fork with a fitting that allows for free-play adjustments. When the clutch pedal is depressed, the cable pulls the clutch fork, causing the release bearing to move forward against the pressure plate.

Commonly found in mid- and rear-engine vehicles, a hydraulic clutch linkage is basically a mini hydraulic brake system. A master cylinder is attached to the clutch pedal by an actuator rod, and the slave cylinder is connected to the master cylinder by high-pressure tubing. The slave cylinder is normally attached to a bracket next to the bell housing, so that it can move the clutch release fork directly.

Cable type clutch linkage

11.1The advantages of cable clutch

· Because the cable clutch system has so few pivot points, there are fewer parts that will sustain damage through ordinary wear and tear. There’s a lot going on mechanically when it comes to getting your vehicle in and out of gear and the simpler the system, the lower the likelihood of developing problems.

11.2 The disadvantages of cable clutch

· The only downside to a cable clutch is that if you own your car for a long time, the cables will eventually wear and stretch, and could even break. If the cable wears or stretches, you may find it difficult to put your car in gear. If it breaks, you won’t be able to shift at all.

12. Wet Clutches

It is in most cases multi plates clutch. It has 5-10 metal disks connected to "bell" (engine side) by splines on the outer side, and similar number of friction material covered metal disks connected to "outgoing shaft" (by splines in centre of disks). They are mounted in enclosed housing, filled with ATF oil, and rotate with engine. From "shaft" side is mounted hydraulic cylinder, which press plate’s together when clutch drive. It rotates together with clutch bell, and has oil pressure feeding through shaft. It is simple explanation of its construction.

12.1Wet Clutch (Multi-plate Clutch)

Working

The clutch has 2 modes of operation- engagement and disengagement. During the engagement mode, the plates are squeezed together and the transmission fluid present between the plates is pushed out. Torque is then transmitted through the clutch and to the corresponding gear set. The engagement process takes place in three stages.

· Hydrodynamic stage

· Contact stage

· Locked up stage

· During the hydrodynamic stage, the plates are separated from each other and are filled with a film of fluid. As a result of which torque is not developed through frictional contact but in contrast it is developed due to the viscous torque transfer through the automotive transmission fluid (ATF). The plates now start moving closer to each other and the fluid film begins to shrink.

· The contact stage is said to occur when the plates are squeezed further towards each other. Few contact points are said to be formed and these are known as asperity points. Torque is slowly transferred through these asperity points which increase gradually and hydrodynamic torque consequently begins to decrease. There is a slip or relative velocity between the plates at this stage due to which there is an increase in the temperature of the plates.

· The final stage is the locked up stage where in the torque is entirely transmitted through frictional contact only. The steel and friction plates are completely in contact with each other and hence rotate at the same speed. The transmission fluid in between the plates is completely squeezed out. The presence of grooves in the plates plays a major role in guiding the fluid and hence plays a role in the torque capacity and heat flow. The disengagement mode also called as the open clutch condition is when the friction disc and the steel plate are separated from each other and are rotating at different speeds. Hence a relative velocity exists between the two. A hydrodynamic torque is developed during such a situation. This is caused because of the shearing effects of the viscous fluid and the torque developed is referred to as drag torque. The drag torque mainly depends on the viscosity of the fluid and also depends on the presence of air bubbles trapped between the plates.

12.2 Drag torque physics of wet clutch

Two discs at certain distance apart from each other are considered with a fluid filled between them. One of the discs is stationary while the other is moving. The fluid present within them will offer an internal resistance to the motion of the plate in the form of a shearing force. This shearing force due to the viscous effect of the fluid is termed as drag torque and is also known as drag loss.

The drag torque leads to a loss in power in the transmission. For an automatic transmission, it contributes as much as 20% to the entire transmission losses. The drag torque in a clutch is said to be influenced by the following parameters.

· Drag torque increases with an increase in the number of discs used in a clutch pack

· Drag torque decreases with an increase in clearance between two consecutive discs.

· Drag torque decreases with a decrease in lubrication flow rate.

· Drag Torque increases with a decrease in temperature. Temperature plays a major role and with a change in temperature, the viscosity and density of the fluid also changes.

· Drag torque increases with an increase in the radius of the discs.

Typical drag torque behaviour can be as shown as follows.

Drag torque in a wet clutch is plotted against the relative speed of the plates. It is divided into three regions- region I, region II and region III. Initially, there is a linear increase in drag torque with relative speed up to a particular speed (critical speed). This is because drag toque is proportional to the relative speed and there is a full film of oil that exists between the discs. This corresponds to the region I. The region II can be seen as region of decreasing drag torque and as the speed increased the drag torque decreased further. This is attributed to the fact that earlier in region I, centrifugal effect was quite low and surface tension forces predominated. The surface tension forces were responsible in keeping full film of oil between the plates as much as possible. But as the speed increased, the centrifugal forces dominated and as a result of which small air pockets were formed near the outer diameter of the discs. These air pockets gradually became bigger as the relative speed increased. This consequently led to the oil film diminishing and resulted in a decrease in drag torque.

Finally region III causes an increase in drag torque with increase in relative speed. This is explained by the fact that fluid forms a mist between the clutch plates. This was seen in many visual experiments.

12.3 Wet Clutch-

Advantages:

· Lesser heat will be generated.

· Friction produced will be lesser.

· Minimal slipping during shifts.

· High torque capacity

· Low weight, easy packaging

· No noise or vibrations (Good NVH characteristics)

· Long life

· High energy density

· Low drag Torque to reduce fuel cost

Disadvantages:

· Harder to maintain.

· Difficult to clean.

12.4 Nissans Intelligent dual clutch control technology

Ø Dual Clutch Technology Functionality hybrids.

In a hybrid system, the motor supports the engine, improving driving performance and fuel consumption by regenerating with the motor and storing energy in the battery, using this to drive like an EV and for accelerating.
The one-motor two-clutch hybrid system can separate the engine from the drive train as necessary. It can utilize the engine and motor as power sources, from running just on the motor to using both motor and engine for full acceleration, achieving a more efficient drive as per the situation. During regeneration and electric-mode driving, the engine is completely disconnected from the drive-train, resulting in zero loss from engine friction.

System of 2 Clutch hybrid cars

· Nissan replaced an existing 7-speed automatic transmission’s torque converter with a motor and two clutches in a compact configuration. Using a one-motor system to drive the wheels and regenerate electricity allows for a reduction in the number of parts and a lighter weight.

· The two clutches transfer energy mechanically to the engine and motor. While being efficient and with little energy loss compared to a normal torque converter, the system also has intuitive and responsive acceleration. Through integrated control of this system and transmission using high-level control technology it achieves a drive that responds to a range of driving conditions.

· The hybrid car lithium-ion battery can discharge high currents in a short time. In this way, the proportion of running the motor increases, and it is possible to recover braking energy frequently. Being able to use electricity effectively means the consumption of gasoline fuel decreases and contributes accordingly to better mileage.

13. Difference between Dry & Wet clutch

Dry clutch	Wet clutch
A dry clutch is a clutch which does not have oil present between the clutch plates	Physical oil is present between the plates of the clutch
The sound in dry clutch is more as compared to wet clutch and goes on increasing as the clutch goes on wearing out.	The sound level is net clutch is less as compared to dry clutch or it is taken up by the oil present between the plates
Wear and tear is more in dry clutch	Wear and tear is less in wet clutch
Maintenance cost is high	Maintenance cost is low
The life is less as compared to wet clutch	The life is more as compared to wet clutch
The dust which is collected by wear and tear of the plates is in the cover of the clutch casing.	The dust is removed by the oil filter present in the clutch casing.

13. Main Parts of clutch:-

Main parts of clutch

The clutch assembly consists of many small parts but following are the major parts

1. Flywheel – The flywheel, mounted on the crankshaft, keeps on running as long as the engine keeps running. The flywheel is equipped with friction surface OR a friction disc is bolted to outer side of flywheel.

Flywheel

2. Friction discs – Single OR multiple (as per requirement) discs lined with friction material having high coefficient of friction are mounted on the drive shaft.
3. Pressure plate – Another friction disc is bolted to pressure plate. The pressure plate is mounted on the splined hub.

pressure plate

4. Spring & release levers – The spring used are diaphragm springs which moves friction disc back & forth. The spring is retracted with the help of levers.

5. Piolet bearing:-A pilot bearing supports the engine side of the input shaft. The pilot bearing used on Toyota vehicles is a ball bearing located in a bore in the end of the crankshaft. The pilot bearing only turns when the clutch is disengaged.

6. Clutch cover Assembly: - The clutch cover assembly is bolted to the flywheel and provides the pressure needed to hold the clutch disc to the flywheel for proper power transmission. It is important that the assembly be well balanced and able to radiate the heat generated when the clutch disc is engaged.

Toyota uses two types of clutch cover assemblies:

• Diaphragm spring

• Diaphragm Spring Turnover (DST)

clutch cover

13.1 Diaphragm Spring Turnover

The Diaphragm Spring Turnover (DST) type of clutch cover assembly differs from the conventional type only in construction. The DST cover does not use a separate pivot stud to connect the diaphragm spring to the cover. The cover is shaped so that the pivot points are part of the clutch cover. Since the retracting springs have been eliminated, the strap springs are used to disengage the pressure plate from the clutch disc. The diaphragm spring fingers are chrome plated in the area where the release bearing rides to help eliminate wear and noise. With this design, the clutch cover gives optimum release performance and is lightweight.

Diaphragm Spring Turnover

13.2 Self-Centering Release Bearing

A self centering release bearing is used to prevent noise caused by the release bearing pressing unevenly on the diaphragm spring. This noise occurs when the centerline between the crankshaft, clutch cover assembly, transaxle input shaft and release bearing is not the same. It is used on transaxles because the input shaft does not fit into a pilot bearing in the crankshaft like a transmission input shaft does. The transaxle input shaft is supported by bearings in the case. The self centering release bearing automatically compensates for this by aligning itself with the centerline of the diaphragm spring. This helps prevent noise associated with clutch disengagement.

Self-Centering Release Bearing

The hub of the self centering release bearing is made of pressed steel. The bearing is not pressed onto the hub as with the conventional release bearing. A rubber seat, resin seat, bearing, and wave washer are secured to the hub with a snap ring. The inner diameter of the release bearing is 1 to 2mm greater than the outer diameter of the hub. This clearance allows the release bearing to move and self center to avoid wear.

Self-Centering Release Bearing

13.3 Requirement of a good friction lining:

§ High co-efficient of friction.

§ Good wearing properties.

§ Cheap and easy to manufacture.

§ High resistance to heat.

.4 Clutch Friction Material:

§ Organic

§ Heavy- duty organic

§ Cermaics

§ Kevler

§ Feramic

§ FeramAlloy Facing

1. Organ

Organic facings are typically made from phenolic resins, friction modifiers like metallic powder or metal oxides, and compounded rubber. These facings come in two types:

Ø Molded Facings:-which are very affordable but lack strength.

Ø Woven Facings: - which include fiberglass yarn woven into the material to increase strength.

As you can see, woven organic facings are much stronger than Molded facings, which translate to better life and performance.

Woven organic friction materials are commonly used in OEM applications, as they offer a good combination of smooth engagement, wear resistance, and strength.

2. Heavy- duty organic

· Heavy-duty organic clutch facings are similar to normal organic clutches in terms of engagement smoothness, but with more temperature resistance and durability.

· Heavy-duty organic clutch facings feature more metallic content, which boosts heat resistance and reduces fade.

· This gives these clutches resistance to temperatures as high as 700°F, at least for short periods, as well as increased burst strength.

3. Ceramics

· Ceramic clutch facings are made from a mixture of copper, iron, tin bronze, silicon dioxide, and/or graphite. The material is sintered or brazed onto a backing plate, and then often riveted to the main clutch plate.

· Ceramic clutch facings can withstand considerable heat - they can operate without fading at temperatures up to 1,000°F. This heat resistance makes them ideal for racing.

· Finally, it's important to note that the ratio of static to dynamic friction is quite high for ceramic clutches. This means that ceramic clutch engagement can be abrupt.

4. Kevlar

· Kevlar and Twaron are trademarked names for para-aramid fibers that are often used to make clutch discs. Kevlar and Twaron have two key benefits: longevity and smooth engagement.

· In terms of longevity, Kevlar and Twaron facings last 2-3 times longer than organic facings, all things being equal. Additionally, these fibers have a low static-to-dynamic friction coefficient, making them an ideal choice for applications where smooth engagement is essential (such as off-road driving, rock crawling, etc.).

· While Kevlar facings require higher clamping pressures than most materials – and have a long break-in period (1,000 miles) - their durability makes them a great choice for vehicles with stock or slightly modified engines.

5. Feramic

· With a high coefficient of friction and a high static-to-dynamic ratio, most feramic clutch facings are strictly for racing applications where quick lock-up is most important.

· Feramic facings are made from a combination of steel, silicon dioxide, tin bronze, and graphite. Feramic facings can be full across the face or they can be buttons.

· A special type of feramic clutch facing - known as a carbotic facing - is used in truck applications, offering ceramic-like temperature resistance with smoother engagement.

6. FeramAlloy Facing

· A newer material, FeramAlloy facings are likely to replace ceramic facings. FeramAlloy offers similar levels of wear and temperature resistance compared to ceramics, but with a much better static to dynamic ratio (and therefore smoother engagement).

· FeramAlloy facings also have less "chatter" than ceramic facings.

· Phoenix Friction is one of the first clutch manufacturers to begin offering FeramAlloy facings for use on heavy-duty applications (diesel trucks, commercial trucking, etc.).

13.5 Clutch Friction material Table

Type	μ Range	Fade temp (⁰F)	Best use
Woven organic	0.25-0.3	600	Daily driver
HD organic	0.25-0.3	700	Most street performance, Towing & hauling application
Kevlar	0.35-0.37	500	Longevity, off-roading
Carbotic	0.45-0.48	750	Heavy-duty hauling &towing commercial Trucking
Ceramic	0.4-0.6	1000	Racing
Feramic	0.5-0.55	1000	Racing/Agriculture
FeramAlloy	0.4-0.6	1000	Heavy duty hauling &Towing, commercial Trucking

14. Symptoms of a failing clutch

Hard to select gears
Engine RPM increasing with no increase in vehicle speed
Burning smell from vehicle
Clutch pedal not returning
Unable to depress clutch pedal
Shudder or vibration when changing gears

14.1 Preliminary clutch inspection

A thorough inspection of all clutch-operating components should be done before disassembly. The first step is to inspect mechanical, cable or hydraulic linkages for specified clutch pedal free-play. Second, since they may affect smooth clutch engagement or magnify a minor chatter condition, always make sure that the engine and transmission mounting and torque-absorbing components aren’t oil-saturated, broken or worn out.

Third, inspect the clutch pedal lever bushings for excessive wear and inspect the vehicle’s firewall for excessive distortion when the clutch pedal is depressed. In some cases, a factory reinforcement kit may be required to restore full travel to the clutch pedal assembly.

Next, make sure that clutch pedal travel isn’t limited by an improper pushrod or linkage adjustment or by an extra-thick floor mat lying under the pedal. Last, inspect hydraulic linkages for fluid level, fluid condition and external leakage.

14.2 How to Adjust a Clutch

Self-Adjusting Clutch

The self-adjusting clutch is one of the two types of clutch-adjustment testing methods, and it is the easier of the two.

Step 1 – Lift up the Clutch Pedal

With your car engine running and your parking brake engaged, slip one foot beneath the clutch pedal and lift it upward toward you.

Step 2 – Depress the Pedal

Then, test it by depressing the pedal and putting your car in gear. Make note of the distance your clutch has to move downward before you can change gears.

Step 3 – Test the Pedal

To give it a fair test, try putting it into low forward gear, then second forward and finally third forward. Make note of how much you need to depress the clutch pedal before it disengages the clutch and allows you to put the car into gear without grinding any of the gears. Be sure the clutch pedal doesn't come up too high before it disengages the clutch.

14.3 Manual Clutch Adjustment

Step 1 – Get into the Proper Position

With your engine turned off and your hand brake engaged, get into a position in the front seat where you will be able to see behind the car's dashboard on the driver's side. If necessary, get into position outside the car with the door open. Lower yourself so that your head is partially under the dashboard.

Step 2 – Push the Clutch Pedal and Locate the Hook

With one hand, push the clutch pedal toward the floorboard and hold it there. Next, locate a large hook-like object on the clutch assembly. It should be near the top of the clutch shaft.

Step 3 – Pull the Hook Upward

As you continue to put pressure on the clutch pedal, pull up on the hook-like object until you hear it click once. Then, release your pressure on it.

Step 4 – Test the Clutch

Next, test the clutch. Climb back onto the seat and start the engine. Keeping one foot on the brake pedal, push the clutch pedal downward toward the floor with your foot and adjust your gearshift lever to put your car in gear as you did in the first test. If the clutch pedal isn't working properly, you can replace it yourself in a few steps, too.

14.4 Clutch overhauling

14.5 Clutch removal

Remove the engine first.
Mark the flywheel and the clutch cover for later reassembly. Use something like a sharp punch. I've known some people to use paint.
Remove the bolts securing the clutch cover one turn at a time Do this diagonally opposite one another rather than working directly around the cover. This will help ensure that heavy spring pressure will not warp the clutch cover.
Once the spring pressure has been relieved, remove each bolt.
Now remove the clutch.

14.6 Disassembling of Clutch

· Drain all of the fluids out of your engine and transmission.

· Remove the engine and transmission from the car.

· Remove the bolts holding the transmission to the engine, and slide the transmission off of the clutch. Some transmissions require a bit of force.

· The exposed surface of the clutch is the pressure plate; you need to remove this to disassemble the unit. Lock the engine, and then take out all of the bolts on the edge of the pressure plate.

· Pull the pressure plate off the flywheel; normally pressure plates have pins in them, so this might require a little bit of prying. Once the pressure plate is removed, the clutch disk should simply fall off.

· At this movement clutch is disassemble.

14.7 Inspection of clutch components

Experienced technicians know the importance of visually inspecting each clutch component as it is disassembled. This helps determine if a part failed earlier than it should have, and helps locate any condition that needs correcting before the clutch is reassembled.

During disassembly, the flywheel, clutch cover assembly, clutch disc, release bearing and pilot bearing should be checked to determine if they were the cause of the failure. During each phase of reassembly, remember to check for proper clearances and operation. This ensures that any faulty parts or assemblies can be corrected early in the reassembly process.

14.8 Fly wheel inspection

The flywheel must have a flat surface to prevent chatter, and the proper surface finish to provide the necessary coefficient of friction. The wear of the friction surface is usually concave. The new flat clutch disc will not seat completely against a worn flywheel. This can cause premature clutch wear, chatter or even clutch disc failure. Grooves, heat checks, and warping can occur if there is excessive slippage,

The flywheel should be checked for excessive runout if there is vibration or an odd wear pattern at the hub of the disc or clutch cover release levers.

Flywheel axial runout:

· With the dial indicator mounted with the measuring stem pointing directly toward the flywheel, adjust the indicator to read zero.

· While observing the dial indicator, rotate the flywheel; to eliminate crankshaft end play, maintain an even pressure during rotation.

· The amount of axial runout is indicated by the variation in reading .If the flywheel is to be removed.

· Place index marks at the crankshaft flange for faster alignment during reassembly. Inspect the starter ring gear teeth. If damaged, replace either the starter ring gear or flywheel.

14.9 Clutch cover assembly inspection

A used clutch cover assembly should be visually inspected for cover distortion and friction surface damage. The friction surface of the clutch cover assembly tends to polish or glaze from normal use. Excessive slippage can cause grooves, heat checks, and warping.

Set the clutch cover on the flywheel. The flywheel and clutch cover mounting points should meet evenly and completely. Inspect for gaps, as they indicate a distorted clutch cover. Additionally, inspect the clutch diaphragm for wear at the contact surface with the release bearing. Clutch diaphragm wear occurs at the contact point with the release bearing. Measure the width and depth of the wear to determine if it is within tolerable limits.

Clutch disc inspection

Always check a used clutch disc for facing thickness, damper spring condition, hub spline wear, and warpage or axial runout by measuring the height of the facing surface above the rivets. The minimum depth should be 0.012 in. (0.3mm). The hub splines and damper springs should be visually checked for rust and shiny worn areas, and broken or missing springs.

Disc warpage is checked by completing an axial runout check. The disc is rotated while watching for wobbling (runout) of the facing surfaces. More than 0.031 in. (0.8mm) is excessive, and the disc should be replaced.

Axial runout check

Disc warpage can also be checked by setting the disc against the flywheel. The disc facing should make even contact all around the flywheel.

14.10 Release bearing inspection

Release bearings are checked by feeling for roughness and visually checked for obvious wear. They are normally replaced with the disc and clutch cover.

On self-adjusting release bearings, also check that the selfcentering system is not sticking.

14.11 Clutch pedal adjustment

Normal service for a clutch includes checking the mechanical linkage systems for clutch pedal height and free play, and checking the hydraulic systems fluid levels.

To check for clutch pedal height, measure the distance from the vehicle floor (asphalt sheet under the carpet) to the top of the clutch pedal. Refer to the appropriate repair manual for vehicle specifications.

Clutch height adjustment

If the clutch pedal requires a height adjustment, it is adjusted using the pedal height adjust point. Always adjust clutch pedal height before adjusting clutch pedal free play.

To check and adjust clutch pedal free play, push the clutch pedal downward by hand until all play is removed and resistance is felt. The distance from this point to the pedal top position is free play.

Clutch Free play adjustment

Free play travel that is less than specifications indicates the need for adjustment of the push rod. Too little free play may result in the clutch master cylinder compensating port being blocked, preventing the return of fluid. This will result in difficulty in bleeding the hydraulic circuit and may also cause the clutch to slip as under hood temperatures cause fluid to expand pushing the release cylinder piston and release bearing.

Clutch pedal adjustment

To check the clutch release point:

· Pull the parking brake lever and install the wheel stopper.

· Start and idle the engine.

· Place the transmission in high gear and slowly engage the clutch.

· When the clutch begins to engage (tachometer speed begins to drop), this is the release point.

· Measure the stroke from the release point to the full stroke end position.

· Standard distance: 0.98 in. (25mm) or more (from pedal stroke end position to release point).

· If the distance is not as specified, perform the following checks:

· Check pedal height.

· Check push rod play and pedal free play.

· Bleed clutch line.

· Check clutch cover and disc.

Clutch release point

· Preventive maintenance :- check pedal free play, check fluid levels, and perform necessary adjustments to ensure correct system operation.

· Problem diagnosis: - determine the cause of a concern in order to specify appropriate repair procedures.

· Repair: - perform appropriate repair or component replacement tasks to attain proper vehicle operation.

14.12 Clutch slippage

· This section describes normal maintenance, adjustments, and diagnostic procedures for common clutch system concerns.

· Start the vehicle and warm up the engine to normal operating temperature, block the wheels, and apply the parking brake.

· Shift the transmission into the highest gear and release the clutch pedal in a smooth, normal motion. If the clutch is engaging correctly, the engine should stall immediately. A delay in engine stalling indicates slow engagement and a slipping clutch condition.

14.13 Clutch chatter

· Clutch chatter is caused by a clutch that grabs and slips repeatedly, eventually marring the clutch cover pressure plate and flywheel surfaces. A grabbing or chattering clutch produces a severe vibration while engaging the clutch and the vehicle is accelerated from a stop. The vibration can be felt as well as heard and may transfer to the vehicle body cause secondary noise.

· Clutch chatter may be caused by oil or grease on the clutch disc, glazed, loose or broken disc facings, worn torsion dampers, bent or distorted clutch disc, a loose clutch cover, missing flywheel dowel pins, or excessive flywheel runout. Hot spots on the flywheel or pressure plate can cause the clutch disc to be clamped unevenly resulting in chatter.

· Influences outside of the clutch assembly may cause chattering such as; broken engine or transmission mounts, worn or damaged constant velocity (CV) axle joint or universal joints. Wear in the joints or loose motor mounts can cause the clutch to slip after initial engagement while the clutch pedal is released and the component reaches the end of its play. The abrupt change in rotational speed feeds back to the clutch causing slippage.

14.14 Clutch drag

Clutch drag is a condition where the clutch does not release completely. Symptoms can include hard shifting into gear from neutral and gear clash. A clutch spins down test checks for complete clutch disengagement. The clutch disc, input shaft and transmission gears should come to a complete stop within a few seconds after disengaging the clutch.

Checking clutch spin down:

· Start the vehicle and warm up the engine and transmission to operating temperature.

· With the transmission in neutral and the engine running at idle speed, push in the clutch pedal, wait nine seconds, and shift the transmission into reverse.

· Gear clash or grinding indicates a clutch that hasn’t completely released.

14.15 Clutch judder:

Clutch judder is most noticeable when setting off from a standstill. It manifests itself as a strong vibration when you release the clutch to get the car moving from rest. If you notice clutch judder, it is an indication that the clutch assembly including the flywheel might need replacement.

14.16 Clutch chatter

Clutch chatter is best described as a stutter or vibration as the clutch is released. It is most noticeable when starting out from a complete stop. Clutch chatter is the most difficult clutch problem to diagnose and repair.

Clutch related Chatter problems

Disc

Clutch Disc related Contamination: Oil on the disc from an engine or transmission leak
Torsion Spring Escaped: usually caused by “popping” the clutch or attempting to push start the car

Pressure Plate Distorted

Pressure Plate Related Warped friction plate: Usually due to excessive heat build-up. Can be caused by excessively slipping the clutch
Warped Diaphram Spring: Defective part
Uneven Coil Spring Pressures: Defective part. Very few of this style clutch made today

Release Bearing

Release Bearing Related Damaged or Worn Release Bearing: Usually on very high mileage cars, or can result from extended operation with a defective pressure plate
Grooved release bearing guide
Worn bearing retainer .

15. Fluid flywheel

Fluid flywheel

A liquid coupling is used to transmit engine turning effort (torque) to a clutch and transmission. The coupling is always a major part of the engine flywheel assembly. As such it is sometime called a fluid flywheel.

One of the shells is fixed to the crankshaft of the engine and the other to the clutch/gearbox shaft. The two shells are mounted very close, with their open ends facing each other, so that they can be turned independently without touching. Housing surrounds both units to make a closed assembly. About 80% of the interior of the assembly is filled with oil.

15.1 Working of fluid flywheel

The driving unit, called impeller, is linked to the engine crankshaft. When the engine throttle is opened, the oil in the impeller starts moving. Due to the force of the rotating, trapped oil impinges on the fins of the driven unit called runner and causes it to move. In this way, the moving liquid transmits the engine power to the clutch driving plat or to any other unit to which the runner is attached. This happens without any metal contact.

In the actual units, the runner speed becomes almost equal to that of the impeller only under the best operating conditions, when the efficiency of liquid coupling is highest. But usually the runner speed is less than that of the impeller. The (speed) lag of the runner behind the impeller is known as slip. This (speed) slip varies with many factors such as engine speed, vehicle speed and engine and vehicle load.

Fluid Flywheel

15.2 Direction of fluid flow

Imagine tubes A & B filled with fluid, A at N „rpm‟ & B at n „rpm‟.

• Let outer end C of A closed with diaphragm.

• Let outer end D of B closed with diaphragm.

• Let pressure exerted at C = pa

• Let pressure exerted at D = pb

• Therefore pa α N2 & pb α n2

• Therefore N > n, pa > pb

• So if diaphragm is removed fluid flows from E to F.

• pa > pb so fluid circulate between impeller & runner.

• Thus because of difference in speed between impeller & runner, fluid circulates between impeller & runner.

At K- fluid particle at radius r

· Rotates in a circle of radius r and angular speed of N.

· So linear speed = 2πr n

· Therefore K.E at K = ½ w/g (2

r)²

· Similarly K.E. at L = ½ w/g (2

R) ²

· Hence K.E. at L > at K. So K.E of fluid is increased.

· K.E. at M = ½ w/g (2

R) ²

· K.E. at M < K.E. at L (so some fluid lost)

· K.E.s at N = ½ w/g (2

r)²

· K.E. at N < K.E. at M

· So fluid K.E is transferred to runner.

· Thus mechanical energy is transferred due to change in K.E of rotating fluid.

15.3 Construction of Fluid Flywheel

A fluid Flywheel consists of three components, plus the hydraulic fluid:

· The housing, also known as the shell (which must have an oil-tight seal around the drive shafts), contains the fluid and turbines.

Two turbines (fan like components):

· One connected to the input shaft; known as the pump or impeller, primary wheel input turbine

· The other connected to the output shaft, known as the turbine, output turbine, secondary wheel or runner

Construction of fluid Flywheel

15.4 Power transmission of Fluid Flywheel.

Fluid drive flywheel cannot achive 100% effficiency, but it has much appreaciated effficiency of 98%. The equation for fluid flywheel coupling & slip is discussed below.

Efficiency of fluid coupling = power at output/power at input.

η = (power transmitted to driven shat)/(power available to the driving shaft)

Power at any shaft = 2

NT/60

Sustituting this value in efficiency equation, Here “A” stands for diving shaft “B” stand for driven shaft.

η = N_B T_B/N_A T_A

But the torque transmission is same T_A=T_B

Then efficiency η = N_B/N_A

15.5 FLUID USED IN FLUID FLYWHEEL

Servo Super Multi grade Oils are blended from highly refined base stocks and balanced additive package containing shear stable VI improver, metallic detergent dispersant and anti-oxidant. These oils are formulated to meet lubrication requirements of both gasoline and diesel engines. Servo Super Multi-grade Oils are red in colour and suitable for all seasons. Mineral oils having low viscosity are used as working fluid SAE 10, SAE 10w; oils are used in Fluid coupling

15.6 Design of fluid flywheel

Specific charge of the working place is taken as, q

Speed of shaft np

Pump head (Hp) = ϼ ((P* η) ^1/2/ np)

Shaft speed (m rad/s).

Discharge flow = P*η / P*G*Hp

Velocity of meridian component = √ (2 * g *Hp)

Inlet and outlet areas of impeller= Q/ cm

Diameter of turbine = √ (g *Hp/ ω² (1 - m²))

Impeller inlet & outlet width = Q/ 2* 3.14 *re

No of blade on impeller Z1

No of blade on turbine Z2= Z1+2

Torque calculation of Fluid Flywheel

Torque = force due to mass X radial distance of force application

= F X R Where, F= force due mass = mg. R = distance of force application

Therefore Torque = F R = m*g*R

Power transmitted= 2*π * N* T/60

15.7 Variation of Efficiency with speed ratio

· When starting from rest, efficiency = 0 i.e. both output speed and output are zero.

· Efficiency = 0 when the load is removed, runner is allowed to race.

· As the runner gains speed, efficiency increases.

· Max value of efficiency at design point (arbitrarily set).

· Max efficiency is of 85% to 90% based on 1. No of stages 2. No of blades 3. Refinement of blades 4. Blades entrance & exit angles

· At a certain speed ratio, coupling point output torque = input torque.

15.8 Variation of torque with speed ratio

· Output torque is max when starting α 1/ N2

· T.C of cars has stall – torque ratio of 2.0 & 2.5.

· Possible to get high torque ratios, but not practical, since is low, trouble of overheating.

· Reducing gear is used for high ratios

· Another reason for moderate stall torque – its efficiency as F.C decreases further .i.e. for high torque ratio vanes have to be curved sharply.

· Single stage T.C – 2 to 4 • Two stage T.C – 3 to 5.

· Three stage T.C – 4.5 to 6

15.9 Properties of working fluids

· It should have high density.

· It should have optimum viscosity. If low viscosity fluid is used, sealing is difficult & leakage takes place. If highly viscous fluid is used slip will be more.

· It should have low co-efficient expansion.

· It must have good heat transferable properties.

· It must have good lubricating properties.

· It must be readily available & cheaper.

· It must be non- corrosion.

15.10 Slip

· Slip is the ratio of the different of speeds of rotation of the impeller & runner. To the speed of rotation of impeller and expressed in percentage. Speed of runner always lags behind that of impeller

· Percentage slip = (N-n/N)*100 where runner speed n=0, slip = 100% Torque is not transmitted When N = n, slip = 0 , Torque is fully transmitted

15.11Application of Fluid Flywheel:

1. Used For industrial application where heavy starting torque or inertia is needed under constant cyclic Loading.

2. Automobile: Mainly used in automobile sector in semi-Automatic or Fully Automatic Transmission system:-In automotive applications, the pump typically is connected to the flywheel of the engine in fact, the coupling’s enclosure may be part of the flywheel proper, and thus is turned by the engine’s crankshaft. The turbine is connected to the input shaft of the transmission. While the transmission is in gear, as engine speed increases torque is transferred from the engine to the input shaft by the motion of the fluid, propelling the vehicle. In this regard, the behaviour of the fluid coupling strongly resembles that of a mechanical clutch driving a manual transmission.

3. Aeronautical applications

15.12 Advantages of Fluid Flywheel

· Controlled start up speed without shock loading of power transmission system.

· There is no mechanical contact between driving shaft and driven shaft (or between pump wheel and turbine wheel). Hence there is no frictional wearing of them.

· Power transmission is smooth. Motor or engine starts unloaded.

· Fluid coupling can dampen shock loads. Fluid coupling can run smoothly even in extreme conditions.

· The power transmission is free from vibration. There is no chance of vibration noises when power transmitted from vibrating engine to the driven shaft by using a fluid coupling. Fluid coupling can be used in both vertical and horizontal application.

· In case of overloading, it can disengage from driver by automatically draining the oil filled by blowing of fusible plug

· The maximum torque can be adjusted by varying the amount of oil filled in the casing.

15.13 Disadvantages of fluid flywheel

· There is always slip. There is always slight dierence in speed of pump wheel & turbine wheel

· The fluid filled in casing must be compatible with coupling component, it directly affects the transmission behavior of the fluid flywheel.

· Fluid coupling cannot develop torque when the driving shaft and driven shat are rotating in same angular velocity.

· Under stalling condition, the coupling dissipates energy as heat it may lead to damage.

16. Torque converter

A torque converter is a type of fluid coupling which is used to transfer rotating power from the engine of a vehicle to the transmission. It takes place of mechanical clutch in an automatic transmission. The main function of it is to allow the load to be isolated from the main power source. It sits in between the engine and transmission. It has the same function as the clutch in manual transmission. As the clutch separates the engine from the load when it stops, in the same way it also isolates the engine from load and keep engine running when vehicle stops.

16.1 Its main functions are:

1. It transfers the power from engine to the transmission input shaft.
2. It drives the front pump of the transmission.
3. It isolates the engine from the load when the vehicle is stationary.
4. It multiplies the torque of the engine and transmits it to the transmission. It almost doubles the output torque.

16.2 Construction of torque converter

1. Impeller or Pump

The impeller is connected to the housing and the housing connected to the engine shaft. It has curved and angled vanes. It rotates with the engine speed and consists of automatic transmission fluid. When it rotates with the engine, the centrifugal force makes the fluid move outward. The blades of the impeller are designed in such a way that it directs the fluid towards the turbine blades. It acts as centrifugal pump which sucks the fluid from the automatic transmission and delivers it to the turbine.

2. Stator:

The stator is located in between the impeller and turbine. The main function of the stator is to give direction to the returning fluid from the turbine, so that the fluid enters to the impeller in the direction of its rotation. As the fluid enters in the direction of the impeller, it multiplies the torque. So stator helps in the torque multiplication by changing the direction of the fluid and allows it to enter in the direction of the impeller rotation. The stator changes the direction of fluid almost up to 90 degree. The stator is mounted with a one way clutch that allows rotating it in one direction and preventing its rotation in other direction. Turbine is connected to the transmission system of the vehicle. And the stator is placed in between the impeller and turbine.

stator

Torque converter

3. Turbine

Turbine is connected to the input shaft of the automatic transmission. It is present at the engine side. It also consists of curved and angled blades. The blades of the turbine are designed in such a way that it can change the direction of the fluid completely that strikes on its blades. It is the change in the direction of the fluid that forces the blades to move in the direction of the impeller. As the turbine rotates the input shaft of the transmission also rotates and made the vehicle to move. The turbine is also has a lock up clutch at its back. The lock up clutch comes into play when the torque converter achieves coupling point. the lockup eliminates the loses and improves the efficiency of the converter.

16.3 Working of Torque Converter

It has three stages of operations

1. Stall: During stall (stop) condition of the vehicle, the engine is applying power to the impeller but the turbine cannot rotate. This happens, when the vehicle is stationary and driver has kept his foot on the brake paddle to prevent it from moving. During this condition maximum multiplication of torque takes place. As the driver removes its foot from the brake paddle and presses the accelerator paddle, the impeller starts moving faster and this set the turbine to move. At this situation, there is a larger difference between the pump and turbine speed. The impeller speed is much greater than the turbine speed.

2. Acceleration: During acceleration, the turbine speed keeps on increasing, but still there is large difference between the impeller and turbine speed. As the speed of the turbine increases the torque multiplication reduces. During acceleration of the vehicle the torque multiplication is less than that is achieved during stall condition.

3. Coupling: It is a situation when the turbine achieved approximately 90 percent speed of the impeller and this point is called coupling point. The torque multiplication seizes and becomes zero and the torque converter behaves just like a simple fluid coupling. At the coupling point the lock up clutch come into play and locks the turbine to the impeller of the converter. This puts the turbine and impeller to move with the same speed. Lock up clutch engages only when coupling point is achieved. During coupling the stator also starts to rotate in the direction of the impeller and turbine rotation.

16.4 Fluid Flow in torque converter

For the turbine of the torque converter: (i) the high energy flow from the pump enters axially and is turned toward the inward radial direction, the flow also has tangential velocities, (ii) the pressure on the blades (flow energy) is absorbed by the turbine blades and the flow energy (pressure on the blade) is converted into turbine rotation, and (iii) the flow is made to exit the turbine in the axial direction. The function of the stator is to redirect the flow from the turbine exit to the inlet of the pump. The flow at the turbine exit has a strong negative tangential velocity (opposite to the pump rotation). The stator causes the flow to have a zero or positive tangential incidence in to the pump. Due to the closed-loop interaction of the pump, turbine, and stator, the flow field in the torque converter is highly three-dimensional, unsteady and turbulent

The speed ratio (SR), for a fluid coupling (and torque converter) is generally defined as:

SR=ω t / ω p,

Where,

ω t = turbine angular speed; ωp = pump angular speed.

And torque ratio (TR), is defined as:

TR= τt / τp

Where, τt Torque of the turbine, τp Torque of the pump.

The efficiency of the torque converter is:

ε = Pt / Pp. = (ωt / ωp) • (τt / τp ) =SR • TR (1.3)

Where Pt =output turbine shaft power, Pp = input pump shaft power.

For a conventional fluid coupling consisting of a pump and a turbine,

neglecting the mechanical losses

τt = τp

That is, the output torque always has to be equal to the input torque (TR=1). If equation (1.3) is rewritten with TR=1, it gives ε = SR.

K factor (Also known as capacity factor) is defined as:

K= N/√ T.

K= K factor (Capacity factor).

Units are radians/second/√ (newton-meters) i.e. (rad/s/(N*m)^0.5)

Where N= pump speed (rpm) and T= pump Torque

And in another way, capacity factor is defined as:

C = 1/ K²

C = Capacity factor.

Units are newton-meters/ (radians/second) 2 i.e. (N*m/ (rad/s)^2)

Where torque converter consist of stator so

Where τs is the torque for the stator

τp = τs + τt i.e. τp - τt = τs

16.5 Problems in Torque converter

· Overheating: If the temperature gauge seems to overheat, it would mean that the torque converter is not working correctly. In general, overheating is possibly the most common sign of problems in a torque converter because a drop in the fluid pressure would make the transmission to overheat. In fact, this would also be the sign of the malfunctioning solenoid or low levels of fluid, so remember to check it first.

· Transmission slipping: An issue of the torque converter will usually show itself quite rapidly since the fluid could not be controlled properly. If too much or not enough amount of fluid is passed onto the transmission, then it could make the gears to slip and you would usually feel the loss in acceleration. In addition, you would also see a sudden decrease in the fuel economy of the car. Ineffective or low fluid could also be the reason, so you have to examine the fluid if any slipping happen.

· Shuddering: If your car start to shudder at the speed from 30 to 45 miles per hour, it would mean that a torque converter is happening. In fact, it would usually feel like going over a bump or rough road and you would certainly notice if it occurs.

· Dirty fluid: After checking the fluid, if there are a lot of black substance, it would either mean that your torque converter or transmission are damaged. In this situation, you need to change a fluid first, then start the vehicle for a short time, and check it again.

· High stall speed: A malfunctioning torque converter would take a transmission more time to engage your engine, leading to greater than usual stall speed. You could do test for stall speed to find out any problems in the torque converter, but you would have to understand the torque converter and the specifications of the engine’s stall speed first.

· Strange noises: Any foreign noises such as revving or clicking sounds would indicate a problem in the torque converter.

16.6 Advantages

· It produces the maximum torque as compared with the vehicle equipped with clutch.

· It removes the clutch pedal.

· It makes the job of driving a vehicle easier.

16.7Disadvantages

· Its fuel efficiency is low as compared with the vehicle with manual transmission.

16.8Application

· The torque converter is used in the vehicle that is equipped with the automatic transmission. It is also used in industrial power transmission such as conveyer drives, winches, drilling rigs, almost all modern forklifts, construction equipment, and railway locomotives.

· It is used in marine propulsion systems.

16.9Difference between Fluid Flywheel & Torque converter

· Fluid Flywheel is shown in the figure.

· It consists of two members the driving and driven member as shown. The driving member is attached to the engine and the driven member to the transmission shaft.

· The two members do not have any direct contact.

· Torque converter is as shown in the figure.

· The construction is very similar to that of the fluid flywheel expect for an additional stationary member called stator.

· All the members have blades or vanes of specific shape.

· Even though the construction is similar, the operation is not.

· The fluid flywheel transmits the same torque as given as given to it by the engine shaft whereas the torque converter increases the torque in the ratio of 2:1 or 3:1.

· Thus the torque converter serves the same purpose as that of the gearbox whereas the fluid flywheel merely acts as a hydraulic coupling transmitting the same torque and power as that of the engine input.