Reducing the Fluid-Borne Noise of Variable-Displacement Vane Pump for Automotive Hydraulic Power Steering System

In an automotive hydraulic power steering system a variable-displacement vane pump, which is equipped with a control de vice for adjusting the eccentricity of the cam ring appropriately according to the pump rotational speed (ie., vehicle speed), has gradually begun to be used for energy saving in place of a fixed-displacement vane pump. However, fluid-borne noise radiated 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 presents development research of a quieter (low-fluid-borne noise level) variable-displacement vane pump for HPS systems. First, it is indicated based on both the measurements and simulation analysis of pump source flow ripple that the excessive increase of fluid borne noise produced by existing variable-displacement vane pumps is mainly caused by vane bounce occurring in the trapping sections near dead centers, which is difficult to prevent when conventional cylindrical (completely round profile) cam ring is used Next, a new cam ring profile for preventing vane bounce called the “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 the bench test circuit The proposed cam ring is found to be able to reduce fluid-borne noise at least to the level of a fixed pump. The newly developed types of pumps have already been put into practice in several kinds of automobiles.