Multi Plate Clutch – Parts, Working, Advantages, Disadvantages, and Applications.

A clutch is an instrument which is used to engage and disengage the engine with the gearbox.
The clutch in which two or more than two clutch plates are used is called multi-plate clutch.
There are many plates in multi-plate clutch so that we can transfer maximum amount of torque.
Adding plates to cutch to create multi-plate clutch will increase the torque capacity of the clutch without increasing the spring strength or clutch diameter.
As the number of clutch plates is increased, the number if frictional surface will also be increased and hence the toque transmitting capacity of the clutch also increases.
The multi plate clutch of small size transmits almost double torque than a single plate clutch of twice the diameter.

Why a Multi Plate Clutch is needed:

The torque transmitting capacity of clutch depends on the factors given below:
i) Co-efficient of friction acting between the frictional surfaces.
ii) The radius of the frictional surface.
iii) Clamping force between the force holding the frictional surfaces together.
iv) The number of the frictional surface.

For factor (i), there is limit to which the coefficient of friction can be increased and de to high friction the clutch may become fierce while engaging.
For factor (ii), the radius cannot be increased much as the clutch has to be fixed inside a motor vehicle. So the size and radius of the clutch can not be increased very much.
For factor (iii), the clamping force cannot be increased much because higher clamping force may require excessive driver effort.
But factor (iv) can be easily increased by increasing the number of clutch plates and the torque transmitting capacity of the clutch can be increased easily without any loss. Because of this reason multi plate clutch was needed and invented.

Parts of multi plate clutch:

1) Input Shaft:
This input shaft is connected with engine crankshaft. It takes power from the engine. The other end of the input shaft is connected to the flywheel.

2) Flywheel:
As the flywheel is connected to the input shaft the flywheel also rotates when the input shaft rotates. Flywheel has teeth cut on its surface which get fixed on the teeth of pinion which rotates with the power from a battery and helps in self-starting.

3) Clutch Plates:
The clutch plate is a circular disc and friction lining is riveted on both side of the clutch plate. The friction lining is present on both sides of the clutch plate to increase the co-efficient of friction between the clutch plate and flywheel and between the clutch plates and separator plates. The friction lining is made up of either carbon fiber, sandwich bronze, or graphite. These clutch plates also have springs which are used used to absorb the damping while the clutch plate rotates.

4) Separator Plates:
A separator plate is used to separate two clutch plates from each other. These separator plates are also called steel discs as they are made up of steel. They are interlocked within the basket. These seperators are placed between two clutch plates. Generally these clutch plates are made of steel but in some cases, it is made of cast iron. It also has shape like circular disc.

5) Clutch pack:
The set of all clutch and separator plates is also referred to as a clutch pack.

5) Pressure Plate:
These plates are called pressure plates because it maintains pressure on the clutch plates and separator plates. This pressure plate is attached to the splined sleeves and these sleeves are attached to the pedal fulcrum. When the pedal is pressed, the sleeves is attached to the pedal fulcrum moves outward which in turn moves the pressure plate. These pressure plates apply the pressure to the clutch plates and separator plates so that the clutch plates and the separator plates are connected to each other as well as engaged with the flywheel. As the clutch plates and separator plates are connected due to pressure plate, the separator plates also rotate when the clutch plates rotate.

6) Diaphragm Spring:
Diaphragm spring is of convex shape and elevated at the top. The clamping force on the friction facing is provided by the diaphragm spring.

7) Cover Plate:
This cover plate is bolted with the flywheel and is used to cover the whole system of multi plate clutch.

Working:

Disengagment of clutch:
When the clutch pedal is pressed, the release bearing acts on the pressure plate diaphragm spring the center of the diaphragm spring is moved in the forward direction but the corners of the diaphragm spring which are connected to the pressure plates move in the backward direction and hence the pressure plates also move in the backward direction because the corners of the diaphragm spring are bolted with the pressure plate.
As the pressure plate moves backward, the pressure plate releases pressure from the clutch plates as well as the separator plates. As the pressure is released from the clutch and separator plates, the clutch plate is also disengaged from the flywheel and allows the flywheel to rotate freely without turning the clutch shaft. Hence, the clutch comes in a disengaged position.
As the clutch comes in a disengaged position, the engine is disengaged with the gearbox and there is no power transmission between the two.

Engagement of clutch:
When the clutch pedal is released, the pressure plates will again put the pressure on the clutch plates and separator plates, and the group of clutch plates and separator plates will again engage with the flywheel and the power of input shaft will be transmitted to the output shaft. Hence, the power transmission between the engine and the gearbox will start again.

Types of Multiple Plate Clutch:

1) Spring Type Multi Plate Clutch:
In spring type multi plate clutch, a cover is bolted to the the flywheel of the engine. Inside this cover the clutch plates, pressure plate, thrust bearing etc are present. Unlike the diaphragm clutch, thrust springs are used to move the clutch plates which pushes the clutch plates and create a contact between them and hence the clutch come in engaged position.

2) Diaphragm type multi plate clutch
In the diaphragm type multi plate clutch, diaphragm spring is used instead of thrust spring to push the pressure plate and bring the clutch in engaged condition. The diaphragm spring used in this clutch is crown shaped finger type spring. This diaphragm spring applies the pressure plate which further pushes the clutch plates for the enagement of clutch.

3) Hydraulic operated or Automatic Clutch:
Hydraulic Operated Clutch is used in modern vechiles with automatic transmission system. In this type of clutch, a hydraulic device is used instead of springs for the engagement and disengagement of clutch.
This hydraulic device contains highly compressed liquid and it is operated by acceleration pedal as it is used in automatic transmission.

Advantages of Multi Plate Clutch:

1) High torque transmission capacity.
2) Multi Plate Clutch has very compact size.
3) It decreases the weight of the clutch.
4) It is very much suitable for heavy vechiles.
5) It decreses the effort to put on pedals to operate the clutch.
6) It increases the acceleration.
7) It decreases the moment of inertia of the clutch.

Disadvantages:

1) It is very costly.
2)  This clutch heats up very quickly.

Applications Of Multi Plate Clutch:

1) Multi Plate clutch is used where the required space where the clutch needs to be installed is very less like in motorcycles and scooters.
2) It is also used in racing care where high acceleration is required and torque transmission criteria is maximum.
3) Used in heavy transport vechiles and special pupose vechiles.