Development of a Quieter Variable-Displacement Vane Pump for Automotive Hydraulic Power Steering System

Abstract

In an automotive hydraulic power steering system a variable-displacement vane pump that is equipped with a control device for adjusting the eccentricity of the cam ring and thus pump delivery flow rate according to the pump rotational speed (i.e. vehicle speed) is gradually being used for energy saving in place of a fixed-displacement vane pump. However, fluid-borne noise radiating into the passenger compartment has greatly increased following this replacement, and, therefore, countermeasures to reduce pump source flow ripple have been required more than anything else to further spread its usage. This paper reports on development research of a quieter (low fluid-borne noise level) varia-ble-displacement vane pump for HPS systems. First, it is indicated based on both experimental measurements and sim-ulation analysis of pump source flow ripple that the excessive increase of fluid-borne noise produced by existing varia-ble-displacement vane pumps equipped with a cylindrical cam ring is mainly caused by vane bounce occurring in the trapping sections near the bottom dead center, which is difficult to prevent when a conventional cylindrical (completely round profile) cam ring is used. Next, a new cam ring profile for preventing vane bounce called a “modified profile cam ring” is proposed and its effectiveness is examined by noise tests in the passenger compartment of a real car as well as measurements of pump source flow ripple in a bench test circuit. The proposed cam ring is found to be successful in reducing fluid-borne noise to at least the level of a fixed pump. The newly developed types of pumps have already been put into practice in several kinds of automobiles.