| 摘要 |
PURPOSE:To take an effective measure to count fail-safe by a method wherein a DC motor-driven valve is used as a fail-safe valve, and based on a difference in the current value of the DC motor between a motor running period and a motor non-running period, failure in operation of the fail-safe valve is detected. CONSTITUTION:A rear wheel steering mechanism 6 is operated by a rotary shaft 20 through a steering ratio varying mechanism 8 in linkage with operation of a front wheel steering mechanism 4. The steering ratio varying mechanism 8 comprises a control rod 35 having the one end coupled to the spool valve of a control valve 27, a swing arm 38 having a base end pivotally supported at 37 to a U-shaped holder 36, and a connecting rod 41 for intercoupling the control rod 35 and the swing arm 38. A fail-safe mechanism 55 to open a hydraulic circuit during failure in operation of a rear wheel steering system is located in a hydraulic circuit for a power cylinder 24 of a rear wheel steering mechanism 6. In this case, based on the difference in a current value of a DC motor 59 for driving a fail safe valve 58 opened during detection of failure in operation, it is detected whether the valve 58 is normal or failed in operation. |
