A research about contact stress of worm gear for EPS (Electric Power Steering)

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A research about contact stress of worm gear for EPS (Electric Power Steering)

Watanabe, Katsuji / Shimizu, Yauso

This paper describes the new worm gear for EPS (Electric Power Steering) and the effect of the reduction of the contact stress of the worm gear. In conjunction with recent trends in vehicles getting larger and tires gaining larger footprints, the EPS motor assist torque has increased considerably. This leads to the issue involving the enlargement of the external diameter of the worm gear and the worm wheel gear, which are reduction gears that boost motor torque. In order to address this issue, the authors examined single-threaded worm gears, and the fundamental factors that cause the enlargement of the external diameter of worm wheel from the standpoint of the mesh of the gear. To solve this problems, a new worm gear that addressed this issue is proposed. This new worm gear was examined concerning the contact stress in comparison to the conventional worm gear. The following results were obtained. (1) The conventional worm gear increases the contact stress toward the end of mesh, and the maximum value is calculated at the end of the mesh. (2) The proposed worm gear decreased the contact stress at the end of mesh and the maximum contact stress has been reduced with 12%. (3) During the durability test, conventional worm wheel surface damaged and surface the color turned yellow due to the heating at the end of mesh. (4) The proposed worm gear has no damage, and there was only a slight amount of creep evident on the surface of the teeth. The effectiveness of the proposed gear has been confirmed using an actual device.