Variable speed accessory drive

Abstract

The accessories of a prime mover (such as an engine) are automatically maintained at a more constant speed with varying prime mover speed using a flat belt driving a variable diameter pulley wherein a fixed diameter pulley attached to the variable diameter pulley is used to drive another belt coupled to the accessories. The variable diameter pulley assembly includes a shaft and a pair of pulley sheaves each having a pair of relatively movably guideway disks with belt engaging elements extending between the pulley sheaves. Mutual angular changes between the guideway disks causes a corresponding change in the effective diameter of the pulley assembly. A speed responsive actuator assembly is employed and includes a housing with at least a pair of springs. The actuator assembly is positioned by a balance of forces including the centrifugal force of the belt drive elements, the compression force of the actuator springs, and the forces due to the belt. One side of the actuator assembly is connected in a preferred embodiment to the outer guideway disks and hence to the shaft while the inner guideway disks are connected to the other side of the actuator assembly. As the engine speed increases, the belt engaging elements move out to a larger radius because of their centrifugal force which increases with the square of the speed. Since the pulley driven at engine speed is normally of fixed diameter, an increased variable pulley diameter causes the variable pulley speed to decrease relative to the engine speed.