Clutch Lever Design Issues

Abstract

Clutches possessing levers are prevalent in the North American market of medium and heavy duty trucks. The purpose of this paper is to investigate dynamic and kinematic problems related to clutch levers. Clutch designers are primarily concerned with the effects of levers on clamp load in the engaged state of the clutch, but neglect or downplay, consequences of dynamic effects on the release properties of clutches. The paper focuses on the release aspect of levers although the clamp load is also considered. The research method used in this paper was based on mathematical modeling and simulation of engagement and release processes. Main issues studied include: ○ Lever ratio varies both during the bearing departure and with wear of the clutch. The lever ratio variation affects both the lift of the pressure plate and the clutch clamp load. The simulation model can be utilized to optimize both lever shape and lever positioning during the entire clutch life. ○ Deflections of levers and other internal actuation components affect not only the pressure plate lift but also engagement quality of the clutch. ○ Centrifugal forces acting on levers affect the clamp load, release load and stability of lever location during clutch operation. Inertia forces of levers can affect the strap function and increase or decrease the clutch lift. ○ Improvements in stability of lever positioning during release can minimize clutch hysteresis. Some numerical examples are presented in order to illustrate clutch performance improvements made possible by simple design changes of levers. The main objective of this paper is to study kinematic and dynamic issues affecting the internal actuation process of the clutch and, subsequently, to derive mathematical models of clutch lever functions during actuations. The ultimate goal is to integrate these models into clutch design practice in order to improve important clutch characteristics.