| 摘要 |
PURPOSE:To improve stability and safety of a vehicle for its running, by fixing the steering ratio to a predetermined value mainly by an actuator while by a mechanical urging means only when the actuator is inoperative, when abnormality is generated in an electrical system. CONSTITUTION:A rear wheel steering mechanism generates auxiliary power of steering by pressure oil supplied to and discharged from right and left pressure oil chambers of a power cylinder 15. Here a solenoid valve 37, which is closed in the normal time, is mounted interposing between bypass passages 38 connecting the both pressure oil chambers, and said valve 37 is controlled by an electrical system fail-safe mechanism 34 in a controller 28. Said fail-safe mechanism 34, which sets the first fail mode resetting the rear wheel steering mechanism slowly to a predetermined position by driving a pulse motor 25 and the second fail mode resetting the steering mechanism faster than the first fail mode, is constituted so as to control the valve 37 after the above described modes are decided in a mode decision part 35 in accordance with a signal from a trouble condition detecting means 45. |
