The following types of dry friction clutches will be described here :-

1. Cone clutch
2. Single plate clutch
3. Multi plate clutch

1. Cone clutch :-
  • In this type the contact surfaces are in the form of cones.
  • In the engaged position, the male cone is fully inside the female cone so that the friction surfaces are in complete contact.
  • This is done by means of springs which keeps the male on cone pressed all the time.
  • When the clutch is engaged, the torque is transmitted from the engine via the flywheel and the male cone to the splined gearbox shaft.
  • For disengaging the clutch the male cone is pulled out by means of the lever system operated through the clutch pedal thereby separating the contact surfaces.

Advantages :-

The only advantage of the cone clutch is that the normal force acting on the contact surfaces in this case is larger than the axial force, as compared to the simple single plate clutch in which the normal force acting on the contact surfaces is equal to the axial force.

 Disadvantages :-

This type of clutch is practically obsolete because of certain inherent disadvantages :-

(i). If the angle of cone is made smaller than about 20° the male cone tends to bind or join the female cone and it becomes difficult to disengage the clutch.
     

(ii). A small amount of wear on the cone surface results in a considerable amount of the axial movement of the male cone for which it will be difficult to allow.



2. Single plate clutch :-


  • Friction plate is held between the flywheel and the pressure plate.
  • They are springs (the number may vary, depending upon design) arranged circumferentially, which provide axial force to keep the clutch in engage position.
  • The friction plate is mounted on a hub which is splined from inside and is thus free to slide over the gearbox shaft.
  • Friction facing is attached to the friction plate on both sides to provide two annular friction surfaces for the transmission of power.
  • A pedal is provided to pull the pressure plate against the spring force whenever it is required to be disengaged. Ordinarily it remains in engaged position.
  • When the clutch pedal is pressed, the pressure plate is moved to the right against the force of the spring.
  • This is achieved by means of a suitable linkage and a thrust bearing.
  • With this movement of the pressure plate, the friction plate is released and clutch is disengaged.
  • In actual practice the construction of the clutch differs.
  • The pressure plate, springs, the release lever and the cover form a sub assembly, called the cover assembly which can be mounted directly to the engine block, of course, placing the clutch plate is between the flywheel and the pressure plate with the clutch shaft is inserted in.

 Advantages :-

1. With the single plate clutch, gear changing is easier than with the cone clutch, because the pedal movement is less in this case.

2. In thus not suffer from disadvantages of cone clutch that is binding of cones etc and hence it is more reliable.

 Disadvantage :-

  • As compared to cone clutch, the springs have to be more stiff and this means greater force required to be applied by the driver while disengaging.
  • The single plate clutches used in various vehicles manufactured in India have been shown in figure.
  • Referring figure in the assembled position release lever (2) rest against the centre opening of the cover spring (1).
  • There is an eyebolt nut (7), which causes the strut (9) to pull the pressure plate against the springs, thus holding together the Assembly.
  • When the cover is bolted onto the flywheel, the pressure plate is further pushed back against the springs, causing them to be compressed further, which relaxes the release lever.
  • Anti rattle springs (3) serve to prevent the undesirable noise due to release levers when the clutch is in the engage position.

 3. Multi plate clutch :-

  • The multi plate clutch is an extension of single plate clutch where the number of frictional and metal plates is increased.
  • The increase in the number of friction surfaces obviously increases capacity of the clutch to transmit torque, the size remaining the fixed.
  • Alternatively, the overall diameter of the clutch is reduced for the same torque transmission as a single plate clutch.
  • This type of clutch is, therefore used in some heavy transport vehicles and racing cars where high torque is to be transmitted.
  • Besides, this finds application in case of scooters and motorcycles, where space available is limited.
  • The construction is similar to that of single plate type except that all the frictional plates in this case are in two sets that is one set of plates slides in the grooves on the flywheel and the other one slides on spines on the pressure plate hub. Alternate plates belong to each set.