Reduction of vehicle power assisted steering noise

Introduction: To achieve low levels of noise and vibration in the interior of a vehicle, the noise levels from major sources such as the engine and transmission have been greatly reduced in recent years. Unfortunately, this has meant that the noise from ancillary components has become relatively more prominent. One such component is the power assisted steering (PAS) system, the noise from which is a problem on nearly all vehicles. This paper reports an investigation into the moaning noise produced when the steering wheel is turned at idle, commonly known as PAS moan. The major factors involved in PAS moan are: the transmission of structure-borne and air-borne noise through the vehicle; the transmission of pressure ripples in the hydraulic circuit of the PAS system; and the generation of flow ripples at the PAS pump. In section 3 the results of a study into the reduction of PAS moan is reported. Section 3.1 outlines the experimental set-up and measurement technique. Section 3.2 reports on the effect on vehicle interior noise of the installation of the of the PAS system. Section 3.3 reports on the influence of tuning hoses in the PAS hydraulic circuit and section 3.4 gives an assessment of the reduction in interior noise due to a modification of the power steering pump. The findings outlined in this paper are part of more detailed study into power steering noise reported in reference [1].