The cause of a noise, which was produced in a hydraulic power steering system during driving on a rough way, was analyzed by experiment and numerical simulation. The experiment using a vehicle indicated that the noise was caused by a pressure surge. A mathematical model was made based on the experimental results, and numerical simulation analysis was performed. From the analysis, measures to reduce the pressure surge were found, and such a characteristic of the pressure surge as to express the noise level was found. The mathematical model has made it possible to predict the noise level in a hydraulic power steering system using this characteristic of the pressure surge.
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