| 摘要 |
PURPOSE: To generate a good steering feeling by eliminating the blow-through phenomenon of a working oil associated with the inversion of the piston sliding direction, and generating a sufficient steering assist force with a high responsiveness at the reversal of the steering direction. CONSTITUTION: A seal groove 50 is formed at the periphery of a piston 1 which is borne by a ball screw shaft 3 and fitted in a cylinder chamber 2, and a backup ring 51 and seal ring 52 are wound in such a way as overlapped inside and outside in the seal groove 50 so that a sealing means 5 is formed. The backup ring 51 is put in resilient contact with the seal ring 52 in several (two) places across the width, and the seal ring 52 is pressed outward to the internal circumferential surface of the cylinder chamber 2, and the oil chambers S1, S2 on both sides are sealed liquid-tightly. A similar sealing means 6 is furnished on a seal ring 6a inside the piston 1, and a seal ring 62 is pressed inward by a backup ring 61 which is in resilient contact in two places across the width to the outside surface of the ball screw shaft 3 so that the oil chambers S1, S2 on both sides are sealed liquid-tightly.
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