| 摘要 |
<P>PROBLEM TO BE SOLVED: To smoothly operate a ball screw mechanism against the load in the radial direction to be applied to a rack shaft of an electric power steering device. <P>SOLUTION: In an electric power steering device 1, a ball screw mechanism 4 performs the screw feed of a rack shaft 2 in the axial direction by the rotation of an electric motor 3. The ball screw mechanism 4 has a cylindrical ball nut 10 for covering the outer circumference of the rack shaft 2. Spiral grooves opposite to each other are formed in the outer circumference of the rack shaft 2 and the inner circumference of the ball nut 10. A large number of balls 13 are held between these spiral grooves. A pressure ring 31 is press-fitted in a center part of the ball nut 10 so that the clearance between the spiral groove and a ball 13 is smaller at the center part of the ball nut 10, and larger toward ends of the ball nut 10. The setting of this clearance enables the smooth screw feed of the rack shaft 2 which is deflection-deformed. <P>COPYRIGHT: (C)2011,JPO&INPIT |
