Abstract: An electric power steering device provided with two belleville springs for suppressing the axial movement of a worm rotated by a steering-assisting electric motor and having shaft portions at its both end portions, and limiting members for limiting the deflection amounts of the two belleville springs. The limiting members are respectively disposed at portions along the outer circumferences of the shaft portions at both end portions of the worm, the respective inner circumferential portions of the two belleville springs are formed into flat portions, the outer circumferential portions thereof are respectively formed into tapered portions having a taper shape, and the limiting members are made contact with the flat portions, thereby limiting the deflection amounts of the tapered portions. Hence, the limiting members can be provided without increasing the size of the worm serving as a small gear.

Abstract: A gearing radius of a worm wheel is set corresponding to a neighborhood region of a steering neutral position, in such a way as to be relatively large. Thus, backlash is made to be relatively small. This prevents noises from being produced when an automobile travels straight on a bad road. Conversely, the backlash is set corresponding to most of regions of steering angles, which are within the remaining region thereof, in such a manner as to be relatively large. Thus, increase in resistance torque is suppressed. This is realized by a simple configuration in which a bias portion is provided in a part of the profile of teeth. In a case where power is transmitted from an electric motor by a worm shaft and a worm wheel during a steering operation, noises are hard to be produced even when the automobile travels on a bad road.

Abstract: An electric power steering device provided with two belleville springs for suppressing the axial movement of a worm rotated by a steering-assisting electric motor and having shaft portions at its both end portions, and limiting members for limiting the deflection amounts of the two belleville springs. The limiting members are respectively disposed at portions along the outer circumferences of the shaft portions at both end portions of the worm, the respective inner circumferential portions of the two belleville springs are formed into flat portions, the outer circumferential portions thereof are respectively formed into tapered portions having a taper shape, and the limiting members are made contact with the flat portions, thereby limiting the deflection amounts of the tapered portions. Hence, the limiting members can be provided without increasing the size of the worm serving as a small gear.

Abstract: A gearing radius of a worm wheel is set corresponding to a neighborhood region of a steering neutral position, in such a way as to be relatively large. Thus, backlash is made to be relatively small. This prevents noises from being produced when an automobile travels straight on a bad road. Conversely, the backlash is set corresponding to most of regions of steering angles, which are within the remaining region thereof, in such a manner as to be relatively large. Thus, increase in resistance torque is suppressed. This is realized by a simple configuration in which a bias portion is provided in a part of the profile of teeth. In a case where power is transmitted from an electric motor by a worm shaft and a worm wheel during a steering operation, noises are hard to be produced even when the automobile travels on a bad road.