A New Degree of Freedom for Variable Axial Piston Pumps with Valve Plate Rotation

Abstract

Conventionally, variable axial piston machines vary displacement by adjusting the length of the piston stroke, which can be done by adjusting the angle of the swash plate in swash plate machines or the angle of the cylinder block in bent axis machines. Another possibility to achieve variable displacement is to rotate the valve plate and thus adjust the effective use of the piston stroke. An advantage of this method is that it only requires small forces and is easier to control in comparison to conventional displacement adjustment.

This idea is not new, and the concept was studied decades ago, but unfortunately, cavitation and high pressure peaks in the bridge between the kidneys hindered a successful implementation of valve plate rotation.

Using a double pump with opposing pistons offers the potential to overcome these obstacles, as the displacement can be adjusted by joint rotation of both valve plates, and the effective bridge angles can be adjusted by relative rotation of the valve plates. This paper presents a methodology to optimise valve plate kidney angles for a double pump with rotating valve plates. Optimisation results for exemplary sets of operating points are presented. At high setting ratios, power losses and flow pulsations can be reduced. The risk of cavitation and high pressure peaks can be eliminated, but at the expense of cross-porting and increased losses at low setting ratios and high speeds.