The Control Torque on the Swash Plate of an Axial-Piston Pump Utilizing Piston-Bore Springs

Abstract

This research begins by presenting a nontraditional pump design which utilizes a piston-bore spring. The piston-bore spring is included in this design for the purpose of holding the cylinder block against the valve plate and for forcing the pistons in the negative x-direction. By forcing the pistons in this direction, the piston-bore spring also assists in holding the slippers against the swash plate during the normal operation of the pump. Though these advantages of the design may be readily seen by inspection, it is not obvious how the control torque on the swash plate is effected by the piston-bore spring nor is it obvious how one would go about designing the spring to produce a favorable result. To clarify the benefit of this design, a mechanical analysis is conducted to describe the effect of the spring on the control torque itself. As a result of this analysis, a general equation which describes the swash-plate motion is presented. Within this equation, it may be seen that the spring force provides a restoring force on the swash plate which tends to stabilize the design. The piston-bore spring is also shown to be capable of eliminating the cross-over from a stroke increasing swash-plate torque to a stroke decreasing swash-plate torque. By eliminating this cross over, the backlash in the pump control (which is commonly observed in practice) can be prevented.