Abstract
Power steering variable displacement pump (VDP) is a fuel efficient and cost effective steering technology that has been applied to small vehicles. However, vehicle marketability performance associated with this technology must be improved to satisfactory levels before it can be used in large and heavy vehicles. For this reason, a study is conducted on the potential application of the VDP technology to a sport utility vehicle with an emphasis on improving noise performance. First, the problem areas in noise are identified through a vehicle operational study that compares vehicle noise characteristics between a VDP prototype and a constant displacement pump (CDP). Second, an effective method is developed for evaluating the source noise characteristics of power steering pumps, and a strong correlation is established between the measured characteristics of the pump unit and a subjective judgment of vehicle noise performance. Through this evaluation, the source noise characteristics of the VDP is analyzed, contributory harmonic orders are clarified, and design measures for improving the VDP characteristics are implemented. Third, based on the improved source noise characteristics, the noise attenuation characteristics of the steering system are optimized by means of a pulsation transmission loss concept. Finally, significant reduction in vehicle noise levels at the VDP dominant harmonic frequencies is confirmed by objective measurement and subjective evaluation. Overall, fuel efficiency benefits and vehicle steering performance are confirmed, and satisfactory results are achieved in reducing both noise and fuel consumption without affecting vehicle dynamics.
Keywords: fuel efficiency, noise, vibration, cost, steering