1. Field of the Invention
This invention relates generally to clutches, and more particularly to centrifugal clutches.
2. Description of the Prior Art
Centrifugal clutches are well known in the art. In essence, these devices, sometimes known as frictional contact axial clutches, utilize mating frictional members to transfer torque from an input housing to an output shaft This is accomplished by harnessing the effects of centrifugal force upon radially translatable elements to generate axial movement and ultimately axial thrust. This axial thrust is applied upon an input housing frictional member which, by interacting with an output shaft frictional member, effectively transmits the input housing torque to the output, or driven shaft.
In this type of axial clutch, the radially translatable elements are simple weights which surround the output shaft. Typically these weights are radially spring biased away from the input housing and against the output shaft. During operation, as the angular velocity of the input housing increases, likewise the centrifugal force developed by each of these weights increases. When the centrifugal force associated with each weight exceeds the preload force developed in each of the weight springs, these weights begin to move radially outwardly. These weights are commonly designed with a slanted surface such that continued outward radial movement of the weights will result in corresponding axial movement of a pressure plate which has a coacting slanted surface abutting the slanted surface of the weights. As the weights translate radially outwardly, the pressure plate continues translating axially compressing a series of clutch rings which are fixedly attached within the input housing. These clutch rings have disposed therebetween the peripheral edges of clutch disks, the disks themselves being splined to the output, or driven shaft. When the axial force applied by the pressure plate develops a sufficiently large frictional force between the clutch rings and the clutch disks so as to preclude slippage therebetween, the clutch becomes engaged and the output shaft commences rotation. The input housing angular velocity at which this engagement occurs is often referred to as the clutch "engagement speed."
While this most basic machine is well known and has widespread application, it nonetheless has several drawbacks. First, since the vehicle through which torque is transmitted in this machine is friction, frictional wear is an inherent disadvantage. Consequently, the operating characteristics of the clutch are transient, and will therefore change with time. Specifically, wear between the clutch rings and the clutch disks results in an ever-increasing clutch engagement speed. The engagement speed increases because the pressure plate must continually travel a further axial distance to generate the non-slip condition between clutch disks and clutch plates to account for the material lost from each to frictional contact. The traditional centrifugal clutch is lacking in that there is no mechanism with which to easily adjust axially the pressure plate and coacting weights to account for this frictional wear. Second, should one wish to selectively adjust the clutch engagement speed, the weight/spring combination of the clutch must be varied, and hence, the weights, springs, or both must be removed and replaced with substitutes.
For both of these scenarios the traditional clutch assembly must inevitably be disassembled. To correct a worn clutch, the clutch rings, clutch plates, or both must be replaced. And, to selectively change the engagement speed of the clutch, the weights, springs, or both must be replaced. It is desirable, then, for a centrifugal clutch to have some means by which one can externally adjust the clutch to both 1) account for frictional wear, and 2) selectively change the clutch engagement speed, but without having to disassemble the clutch assembly.
It has therefore been one object of the present invention to provide a centrifugal clutch with means for effecting fine tuning adjustments to account for the change in engagement speed due to frictional wear of the clutch rings and disks, thereby maintaining a constant engagement speed.
Another object of the present invention has been to provide a centrifugal clutch with external means for selectively adjusting the clutch engagement speed.
Yet another object of the present invention has been to provide a centrifugal clutch wherein replacing the weights and springs therein to change the engagement speed is more easily facilitated.