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  Why double- disc clutches are more proper than single disc clutches?

Multi-plate Clutch

A multi-plate clutch has more than one driven plate. Although this type of clutch has been widely used on cars up to about 1930, the several advantages of the single-plate clutch, specifically its ability to completely disengage the drive has caused a very rare use of a multi-plate unit as a main transmission clutch installed between the engine and gear box. However, a multi-plate type of clutch finds a use in automatic gearboxes. In these gearboxes, a number of clutches hold the various gear elements, and as the clutch diameter in these units is limited, a multi-plate clutch is suitable.

Multi-plate Hydraulically Operated Automatic Transmission Clutches

Multi-plate clutches are extensively used along with band brakes in epicyclic compound gear trains of automatic transmission system to lock different stages of the gearing or gear carriers together, so that a combination of gear ratios are available. These clutches contain a pack of annular discs or plates, and alternative plates are circumferentially grooved internally and externally to match up with the splines in the input and output drive members respectively.

When these plates are pressed together, torque is transmitted from the input to the output members. These steel plates have either resented paper linings or with sintered bronze linings for transferring moderate or large torques respectively. The complete gear assembly is sub­merged in fluid, and hence the linings operate wet. These clutches are hydraulically operated by servo pistons either directly or indirectly through a lever disc spring, which multiplies the clamping load and also acts as a piston return spring.

For implements such as BCS728 which operate as a two wheel tractors in small scale lands, some criteria like weight, easy gear shift and torque have significant effects. Double- disc clutches can ensure you about all of them.

There are several significant advantages of a smaller diameter, multiple disc clutches over a larger diameter single disc unit.

Multi disc clutch advantages:

  1. Increase the amount of torque able to be transmitted.
  2. Decrease the pedal effort to operate the clutch.
  3. Decrease the weight of the clutch
  4. Decrease the M.O.I. (Moment of Inertia) of the clutch.

The amount of torque that a clutch transmits is critical to the ultimate performance of a vehicle.

Multi disc clutches increase the available torque capacity by 2 for twin disc and 3 for triple disc.

Torque Capacity is affected by 4 factors:

  1. Decreasing the diameter reduces torque capacity.
  2. A smaller diameter clutch has a smaller diaphragm, which usually means a lower clamping force
  3. Adding a second clutch disc doubles the torque capacity.
  4. Increasing the coefficient of friction of the clutch discs increases the torque capacity.
  5. If the multi disc clutch is correctly designed and engineered, the losses from the smaller diameter and lower clamp force are much less than the gain in coefficient of friction and extra disc(s), giving the torque increase.


Examples:

Diameter

Weight

No of Discs

Torque

9.0in/225mm

33.8lb/15.4kg

2

1010ft lbs/1365Nm

7.25in/185mm

26.6lb/12.1kg

3

984ft lbs/1330Nm

12.0in/300mm

46.0lb/21.0kg

1

781ft lbs/973Nm