Systematic Approach to Attenuate NVH Issues in Hydraulic Steering Gear

In commercial vehicles, Hydraulic Power Assisted Steering (HPAS) gear plays a crucial role in enhancing steering performance by providing hydraulic assistance. The HPAS gear comprises a Directional Control Valve (DCV) assembly, where the input shaft and recirculation units are integrated. The valve system which is known for the heart of the HPAS gear, operates under high-pressure conditions. In the DCV, the input shaft is equipped with bearings to support side loads exerted by the system, and a valve component is freely assembled to minimize friction caused by these side loads. The complexity of the floating valve design results in the less slot volume, leading to cavitation and vibrational noise. While this noise is typically suppressed in internal combustion (IC) engine-powered vehicles, its implementation in electric vehicles (EVs) has led to pronounced audible noise, dominating the system. Experimental vibration analysis of the steering gear reveals both low and high-frequency vibrations, indicating the presence of hiss and low-frequency vibration noise. To address these noise concerns in EV applications, a systematic approach has been undertaken, and a new design has been proposed and experimentally analyzed. This paper presents a detailed analysis of noise issues and provides tuning strategies for higher NVH requirements to enhance the performance of HPAS gear in various applications. Keywords: Noise, Input Shaft, Steering Gear, NVH, EV Applications