TYPES OF CLUTCHES
There have been several kinds of clutches used on automotive vehicles. They are made to be used on vehicles ranging from small passenger cars to large tractors and tracked vehicles.
One way clutches are classified is by the type of spring used to hold the driving and driven members together. A few of these are single, diaphragm, and helical spring clutches.
In clutches where the diaphragm is used instead of coil springs, the diaphragm is a cone shaped of spring steel. The diaphragm is mounted between the cover and the pressure plate so that the diaphragm is nearly flat when the clutch is in the engaged position. The action of this type of spring is similar to that of the bottom of an ordinary oil can. The outer rim of the diaphragm is secured to the pressure plate and is pivoted on rings so that pressure applied at the inner section will cause the outer rim to move away from the flywheel. This draws the pressure plate away from the clutch disk, releasing or disengaging the clutch. When the pressure is released from the inner section, the oil can action of the diaphragm causes the inner section to move out and the movement of the outer rim forces the pressure plate against the clutch disk, engaging the clutch.
In single spring clutches, the pressure plate applies pressure to the clutch disk through an adjusting plate sleeve and a series of toggle levers. When the clutch release bearing moves forward it applies pressure to the lower portion of the toggle lever through the adjusting plate sleeve. This moves the toggle levers away from the pressure plate. The pressure plate is then pulled away from the clutch disk by springs. In this single spring, the pressure may be exerted by a single, large coil spring.
In helical spring clutches, a system of levers pivoted on the cover forces the pressure plate away from the driven disk and against the pressure springs when the clutch release bearing moves forward against the inner ends of the levers.
Automotive clutches are also classified by the number of plates or disks used in their construction.
The single plate clutch has one driven disk between the flywheel and the pressure plate. The flywheel is not considered to be a plate even though it acts as one of the driving surfaces.
A double plate clutch is different only in that another disk and plate have been added.
MULTIPLE-DISK CLUTCH
Driving disks have lugs similar to gear teeth around their outside edges. These mesh with internal splines in the clutch case, which is bolted to and rotates with the flywheel. The driven disks are carried on parallel pins, which are solidly set in the clutch spider. This construction permits movement of all the disks and the pressure plate to provide clearance between them. When the clutch is engaged, the spring moves the pressure plate forward, holding all the disks together firmly. This causes the clutch spider to revolve and turn the clutch shaft to which it is keyed. In multiple-disk clutches, the facings usually are attached to the driving disks. This reduces the weight of the driven disks and, consequently, their tendency to continue spinning after the clutch is released. Because of the considerable number of disks involved, the pressure plate has to move farther to separate the disks completely than it does in clutches having fewer driving and driven members. There is, therefore, less mechanical advantage on the clutch pedal, and a greater foot pressure is required to depress it.
In a wet-type clutch, the disks and the entire internal assembly run in an oil bath. The operation of this type of clutch is similar to that of the dry type, except that the friction surfaces are made of different materials, and the gradual engagement between the driving and driven members is caused by pressing the oil from between the disks. As the oil is eliminated, the friction increases.
Helical spring (semicentrifugal). Many passenger car clutches are of the semicentrifugal type, in which the pressure between the plates is increased as the speed of the clutch increases. This is accomplished by means of centrifugal weights built into the outer ends of the release levers so that the outward pull of centrifugal force is transformed into pressure on the plate. This construction permits the use of relatively light clutch springs, thus facilitating the depression of the clutch pedal for gear shifting. |