MULTI-PLATE CLUTCH: CONSTRUCTION, TYPES AND WORKING PRINCIPLE

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 motor-cycles 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.
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.
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 end plate 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.
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 this 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.
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:
• The multi-plate clutches ultimately increases the capacity of the torque transmission of the vehicle.
• The second advantage of such clutches is that they reduce the moment of inertia of the clutch system.
The only downside of the multi-plate clutch system is that they give rise to more heat as they consist of a large number of the frictional plates.

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