| 摘要 |
PURPOSE:To avoid any possibility of being incurred into a very dangerous state by constituting a steering shaft so as to be set to a fail-safe mode which restores it to a neutral position, in the case where travel of a spool valve is detected and it has moved abnormally. CONSTITUTION:A rear-wheel steering mechanism 171 is provided with a cylinder chamber 92 installed around a steering shaft 80 supported on a housing 12 shiftably in the axial direction, and a piston 84 partitioning off this cylinder chamber 92 into a first cylinder chamber 94 and a second cylinder chamber 95, and pressure oil for steering rear wheels is fed to either of the first cylinder chamber 94 or second cylinder chamber 95 by means of an axial movement of a spool valve 60 for a spool valve mechanism 148. In this case, there is provided a travel detecting means 69 which detects the extent of axial travel and generates a position signal, whereby the position signal is compared with a reference signal, and when the spool valve shows an abnormal movement, each pressure of both these cylinder chambers 94, 95 is equalized and thereby the steering shaft 80 is reset to the neutral position by a fail-safe mechanism 149. |
