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Multi-Plate Clutch: Construction

A multi-plate clutch is a type of clutch that transmits more power from the engine to the transmission shaft of an automobile vehicle and also, makes up for the torque loss due to slippage. Heavy machinery, commercial vehicles, special purpose military vehicles, racing cars, and bikes use this type of clutch. Scooters and motorcycles use multi-plate clutches due to limited space in their gearboxes. Multiple clutches consist of more than three discs or plates so that it is able to provide more torque output.

Multi-plate clutches are used in heavy vehicles with racing cars and motorcycles for transmitting high torque. As compared to single plate clutch, these are smooth and easy to operate due to their assembly of friction surface’s contact. It may be used where the space is very limited.
As the number of clutch plates is increased, the friction surfaces will be also increased. The increase in friction surface obviously increases the capacity of the clutch to transmit more torque for the same size. The multi-plate clutch of small size transmits approximately the same torque as a single plate clutch of twice the diameter.

The need for a Multi-plate clutch

The factors that determine the torque-transmitting capacity of a plate clutch are listed below.
1. The effective radius of the friction surfaces.
2. The coefficient of friction acting between the friction surfaces.
3. The number of friction surfaces.
4. The clamping force holding the friction surfaces together.
The clamping force acts between the friction surfaces and the friction characteristics of the lining materials. Clearly, there must be practical limitations to the extent these factors may be increased. Higher clamping forces can demand excessive driver effort to operate the clutch, while materials with higher friction values can tend to make a clutch fierce in engagement.

multi plate clutch Diagram — multi-plate clutch Diagram

Construction of a Multi-Plate Clutch

A typical clutch consists of the following parts:
• Clutch basket,
• Clutch hub or inner hub,
• Friction plates or drive plates,
• Steel plates or driven plates,
• pressure plates and clutch springs

Types of a Multi-plate clutch

1. Spring type Multi-Plate Clutch:

In this type of Multi-Plate Clutch, a cover is bolted to the flywheel. Multiple clutch plate is found on the cover. The outer plates of the clutch apply thrust on the inner plates with the help of clutch springs or thrust springs to form a drive, thereby engaging the plates. For the clutch disengagement, the mechanism withdraws the endplate to compress the springs and release the other plates. Old cars and bikes use this type of clutch.

2. Diaphragm type Multi-Plate Clutch:

Diaphragm type clutch is another version of the spring type multi-plate clutch. This type of clutch consists of a special crown-shaped finger type spring, that is why the name diaphragm type. It does not come with thrust springs or clutches. During engagement of the clutch, the diaphragm bears against the outer ring and during disengagement, the reaction load is bear by the inner ring. Modern bikes and cars use this type of clutch.

3. Hydraulic Operated or Automatic Transmission Clutch:

Automatic transmission vehicles use this type of clutch. A hydraulic device containing highly compressed fluid operating with the accelerated pedal is attached to the multi-plate clutch. The engagement and the disengagement of the clutch plates are received by the hydraulic device which is controlled with the accelerator pedal.

Working of a Multi-plate clutch

A multi-plate clutch system consists of the separator plates, pressure plates, diaphragm spring, flywheel, input shaft, etc. A separator plate is often known as the clutch discs.

multi disc clutch exploded — multi-disc clutch exploded

The input shaft is connected to the flywheel and this input shaft is joined with the engine. That means whenever the input shaft starts rotating, the flywheel starts rotating in the same direction as that of the input shaft. A flywheel has teeth which are always situated on its periphery. Two pressure plates are always separated by one separator plate. You may be thinking about the material which is used in forming these separator plates? Well, generally these separator plates are made of iron. A clutch plate has some rough lining on it. The asbestos material is used for producing this rough lining. So, when we press the clutch of our vehicle then, the spring gives pressure to the pressure plate at one end. This pressure is then applied to the separator as well as clutch plates. Due to this pressure, the clutch plate at the other end comes in contact with the flywheel and thus this pressure plate engages with the flywheel. So, the vehicle starts to accelerate. When the clutch pedal is in the rest position, the clutch plate is always engaged with the flywheel.

Why are multi-plate clutches used in motorcycles

Multi-plate Wet type clutch is most commonly used in a motorcycle because of following reasons-

1. The multi-plate clutch is very compact, occupies less space, and transmits more torque. In a motorcycle, space available to locate the clutch is small and the clutch is enclosed in a cover.
2. With multiple plates, surface strength and friction in the engaged clutch are increased.
3. Depending upon the power output of the engine and weight of two-wheeler, 4 to 8 sets of plates are required and assemble in a single cover.
4. The clutch plates and friction plates are immersed in an oil bath, hence known as a wet clutch, and operate smoothly.
5. Oil helps the clutch to run cool. Debris resulting from clutch wear can be drain easily with oil.
6. This type of clutch has more life and depends upon the quality of oil used.

Difference Between Single Plate Clutch and Multi-Plate Clutch :

Sr. no.	Single Plate clutch	Multi-plate clutch
1.	It consists of only one clutch plate.	It consists of two or more number of clutch plates.
2.	The number of pairs of friction surfaces in contact are two.	The number of pairs of friction surfaces in contact are more than two.
3.	It does not ensure smooth engagement.	It ensures a smooth and gradual engagement.
4.	It requires more space.	It requires less space.
5.	For the same power transmission, larger in size.	For the same power transmission, smaller in size.
6.	For the same size, torque transmission capacity is less.	For same size, torque transmission capacity is more.
7.	Frictional power loss is less.	Since it has number of friction plates instead of single, frictional power loss is more.
8.	Application- Trucks, Jeeps, cars etc.	Application- Two-wheelers, racing cars, some heavy-duty trucks.

Advantages of Multi-plate clutch :

So, above is the working of the multi-plate. Apart from its working, it is a time to take a brief glance at the advantages of the multi-plate clutch.

Hence, below are the benefits of this type of clutch:

Increased torque transmission capacity could be obtained.
The diameter is reduced as it has more friction surface which reduces the size of the clutch assembly.
It is highly reliable.
It is suitable for heavy vehicles.
Increase in better acceleration.
Decrease the weight of the clutch.
Decrease the pedal effort to operate the clutch.

Disadvantages Of Multi-plate Clutch :

The multi-plate clutch system is generating more heat as they consist of a large number of the frictional plates.
Multi-plate clutches are too expensive.

Application of Multi-plate Clutch :

It is used where the overall space required to accommodate the clutch is constrained such as in Scooters & motorbikes.
Multi-plate wet clutch used in Two-Wheeler where space is limited.
It is also used in racing cars where torque transmission criteria are maximum.
It is used in Heavy Transport vehicles and special purpose vehicles.
It is used in heavy vehicles for high torque transmission, where a single plate clutch of the same size is not sufficient to transmit such high torques.
A multi-plate dry clutch is used in heavy-duty transport vehicles for example tractor-trailer in which the requirement of power and torque is more or higher.

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