| 摘要 |
PROBLEM TO BE SOLVED: To provide an electric power steering device which is small-sized and inexpensive. SOLUTION: In this electric power steering device, a steering assist torque which produced from a motor in accordance with a steering torque is transmitted through a gear type speed reduction mechanism to a steering system rack and pinion mechanism 32 including a pinion 32 and a rack 34, for steering steered wheels. The pinion 32 and the rack 34 are helical gears having a torsion angleθwhich is set in such a range that it does not exceed a friction angle of the helical gears. The tooth forms of the helical gears are set in such a way that the tooth face of at least one of the pair of gears is an arcuate surface having a substantial center located on the reference line thereof, and the tooth flank of at least the other one of the pair is an arcuate surface having a substantial center located on the reference line thereof.
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