Control unit for electric motor and vehicle steering system including the same

#This application claims priority to Japanese Patent Application No. 2012-041868 filed on Feb. 28, 2012 the disclosure of which, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.

#1. Field of the Invention

#The invention relates to a control unit for an electric motor, and a vehicle steering system including the same.

#The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

#FIG. 1 is a view showing the schematic configuration of a vehicle steering system;

#FIG. 2 is a perspective view of an EPS actuator;

#Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings.

#As shown in FIG. 1, in a vehicle steering system 1, a steering shaft 3 to which a steering wheel 2 is fixed is connected to a rack shaft 5 via a rack and pinion mechanism 4. With this configuration, rotation of the steering shaft 3 generated in response to a steering operation is converted into a linear motion of the rack shaft 5 by the rack and pinion mechanism 4. The steering shaft 3 is formed by connecting a column shaft 8, an intermediate shaft 9, and a pinion shaft 10 to each other. The linear motion of the rack shaft 5 generated in accordance with the rotation of the steering shaft 3 is transmitted to knuckles (not shown) via tie rods 11 connected to respective ends of the rack shaft 5. As a result, the steering angle of steered wheels 12, that is, the traveling direction of a vehicle is changed.

#Further, the vehicle steering system 1 includes an EPS actuator (steering effort assisting device) 13 that supplies a steering system with an assist force for assisting a steering operation. The vehicle steering system 1 according to the present embodiment is configured as a so-called column-type electric power steering device in which the column shaft 8 is rotated. In the vehicle steering system 1, an electric motor 14 that serves as a driving source for the EPS actuator 13 is connected to the column shaft 8 via a speed reduction mechanism 15 that includes a worm gear and a worm wheel so as to drive the column shaft 8. The speed of rotation transmitted from the electric motor 14 is reduced by the speed reduction mechanism 15 and the rotation with a reduced speed is transmitted to the column shaft 8. In this way, motor torque is supplied to the steering system as the assist force.