Clutch is a mechanism, which is used for the engagement and disengagement of the power transmission from driving shaft to driven shaft. A clutch is used for control the power transmission. Clutch is placed between the engine and the transmission. At the time of engagement of clutch, the power flows from the engine to the rear wheel. When the clutch is disengaged, the power does not flow from the engine to rear wheel, but engine is still working.
PRINCIPLES OF WORKING
Clutch is simply work on the principle of friction. When two friction surfaces, one is rotating come in contact with non rotating surface. As a result both the surface becomes rotated. This rotation is depends upon the friction area of the surface, pressure applied on surface and co-efficient of friction of the surface and material of the surface.
Material used in clutch
There are lots of material used in steel, aluminium, cotton fabrics, polymers, vegetable fibres, fibre glass and asbestos.
In this type steel, iron and copper has 30 to 65% of the total material of clutch.
It have organic and in organic material like glass, rubber, carbon and Kevlar. This material has coefficient friction is between 00.33 and 0.40.
These materials have high copper content with organic material.
TYPES OF FRICTION MATERIALS
The friction materials of the clutch plate are generally of three types.
MILL BOARD TYPEIt includes asbestos sheets treated with different types of impregnates. They are cheap as well as quite satisfactory in operation.
They are made from a matrix of asbestos fibre and starch or other suitable binding materials. It has only one disadvantage, these type pf friction materials is that each clutch facing has to be moulded separately.
This further divided in two types.
1. Laminated type: - This type of friction material is prepared by holding one layer over the other with a binder between them.
2. Solid woven: - The cloth is woven just to the required thickness.
The most common friction materials follows are
1. Leather- Co-efficient of friction 0.27
2. Cork- Co-efficient of friction 0.32
3. Fabric- Co-efficient of friction 0.40
4. Asbestos - Co-efficient of friction 0.20
5. Reybestos and Ferodo - Co-efficient of friction 0.20
QUALITY OF CLUTCHES
The following point, which have to present in good Quality of clutch
- It should be maintain vehicle dynamic balancing at high speed.
- Clutches have the capacity to wear high heat dissipation at the time of engagement of power.
- Clutch should be easy in operating for the driver.
- It should avoid the sudden jerks at the time of gradual engagement.
- Clutch should be vibration resistance
- Free pedal play it should have free pedal play in order to reduce effective clamping load on the carbon thrust bearing and wear on it.
- The size of the clutch should be small, so it has occupied minimum space.
- It should be Skill to transmit max. torque of the engine.
- The driven member of the clutch should be light in weight, so that it will not continue to rotate for any kind length of time after the clutch has been disengaged.
MAIN PARTS OF A CLUTCH
The driving members consist of a fly wheel mounted on the engine crankshaft.
The driven member consists of a disc or plate, which also called the clutch plate. It is free to slide horizontally on the splines of the clutch shaft.
It consists of a foot pedal, linkage and release or throw-out bearing, release levers and the springs necessary to insure the proper operation of the clutch.
Properties of Good clutch lining
- Good wearing properties.
- High co-efficient of friction.
- Cheap and easy to manufacture.
- Good binder in it.
- High resistance to heat.
Types of Clutches
1. Friction clutch
1.1. Single plate clutch
This is the most common type of clutch used in vehicles. It consists of only one clutch plate mounted on the splines of the clutch shaft. The pressure plate is bolted to the fly wheel through clutch springs and free to slide on the clutch shaft when the clutch pedal is operated.
1.2. Multi-plate clutch
It consists of a number of clutch plates, instead of only one clutch plate as in the case of single plate clutch. The number of plates are increased the friction on the surface. Due to this, it increases the capacity of the clutch to transmit torque.
When the clutch is operated in an oil bath, it is called as wet clutch. It generally used conjunction within, or as a part of the automatic transmission.
When the clutch is operated dry, it is called as dry clutch.
1.3. Cone clutch
It consists of friction surfaces in the form of cones. The male cone is mounted on the splined clutch shaft and the female cone present on the engine shaft. It has friction surface on its conical surfaces. One of the disadvantages of this clutch, if the angle of cone is made smaller than 20*, the male cone tends to bind within the female cone and it becomes difficult to disengage the clutch. On the basis of construction it further divided in two parts.
- External cone
- Internal cone
2. Centrifugal clutch
To keep clutch in engaged position, it used centrifugal force on the place of spring force. It also does not require clutch pedal for operating the clutch. It operates automatically depending upon the engine speed.
3. Semi-centrifugal clutch
This type of clutch is used both kinds of forces, spring force as well as centrifugal force. The springs are used to transmit the torque at normal speeds and centrifugal force is used to transmit the torque at high speeds.
4. Conical spring clutch or Diaphragm clutch
It consist of a diaphragm on conical spring which produce pressure on the pressure plate for engagement of the clutch. The spring is mounted on pressure plates by the following two types.
- Tapered finger type
- Crown spring type
The advantage of this type of clutch is it has no need of release levers, the spring itself act as a series of levers.
5. Positive clutch-Dog and spline clutch
This type of clutch is used to lock two shafts together by using the two set of internal splines. It slides on to a splined shaft with smaller diameter splines. The other bigger diameter splines mash with the external dog clutch, having teeth on the driving shaft.
6. Hydraulic clutch
This kind of clutch is operated by oil pressure. It consists of a cylinder together with piston, control valve, pump, accumulator and oil reservoir. The clutch linkage is connected to the piston and pump is operated by the engine. The oil from the reservoir is pumped into the accumulator tank and it connected to the cylinder through the control valve and the control valve is electrically controlled by a switch in the gear lever.
7. Electro-magnetic clutch
In this type of clutch flywheel consists of electrical winding. When the electrical current passes through the winding with the help of battery or dynamo. It produce an electromagnetic field, pull the pressure plate, hence the clutch is engaged and when the power supply is cut-off the clutch is disengaged.
It is operated in the same way as the hydraulic clutch. There is only difference is that it is operated by vacuum instead of oil pressure.
9. Over-running clutch or free-wheel unit
In this type of the driven shaft take turn freely at certain conditions. When the driven shaft rotates faster than the drive shaft, the free wheel clutch help to disengagement of power transmission between them.
Troubles In Clutches And Their Causes
1. Slipping clutch
When the clutch in engaged position, the bearing surfaces of flywheel, clutch plate and pressure plate are slip one over the other, this called the slipping the clutch.
- Worn linings
- Greasy or oil facings
- Incorrect pedal adjustment
- Weak pressure springs
- Bending pedal mechanism
- Improperly installed linings
- Lack of free play in clutch pedal
2. Grabbing and chattering clutch
when clutch do not engage smoothly or vehicle vibrate at the time of engagement, it is called Grabbing and chattering clutch.
- Loose engine supports.
- Badly turned engine
- Tight splines on the driven shaft
- Misalignment of the linkage
- Grease or oil on lining
- Damaged pressure plate or flywheel
- Hardness due to dirt and wear
3. Rapid wear of linings
The linings of clutch plate may wear out rapidly.
- Pressure plates not fitted correctly
- Incorrect alignment of the linkage
- Weak or broken pressure springs
- Engagement of the clutch at high speeds
4. Dragging clutch
When the pedal is thrown out to disengage the clutch, the driver plate does not stop rotating.
- Improper release of lever adjustment
- Misalignment of clutch housing
- Loose and worn linkage
- Splines are too tightly connected
- Free pedal play is too much
5. Clutch noise
At the time of engagement of the clutch
- Poor alignment between the clutch or transmission house and the engine
- Worn splines on the clutch shaft
At the time of disengagement of clutch
- Bearing of the clutch is worn or dry
- Loose release fork mounting
- Bearings are too tight or binding not proper
- Pilot bearing worn or dry in the flywheel
CLUTCH USED IN THE AUTOMOBILES NOW A DAYS
Royal Enfield, Bullet, Vijay Deluxe, Lambretta scooter, Kawasaki Ninja and More.
SINGLE DRY PLATE
Dodge Fargo model (27.94 cm dia.)
Ashok Leyland Commet (33 cm dia.)
Hindustan ambassador Mark II (20.32 cm dia.)
Premier Padmini (`18.40cm dia.) and Premier President (`180.40cm dia.)
Fiat 1100 (`18.40cm dia.)
Jeep CJ-3B (`21.60 cm dia.)