| 摘要 |
PURPOSE:To eliminate generation of a residual pressure in an oil path so as to contrive miniaturization of an oil hydraulic pump by discharging operating oil, delivered from the oil hydraulic pump when a rear wheel is not steered, directly to a drain tank through an under lap formed in a direction switching valve. CONSTITUTION:A hydraulic control unit 11, controlled in accordance with a vehicle running condition by an electronic control unit ECU, controls a power cylinder 20 to change a direction of a rear wheel, and the unit 11 has a direction switching valve 13. Here, two operating oil supply ports 18R, 18L, operating oil feed ports 21R, 21L and an operating oil discharge port 22 are formed in a housing 16 of the direction switching valve 13, and grooves 23R, 23L are formed in an internal peripheral surface of the housing 16 between each operating oil supply port 18R, 18L and the discharge port 22. On the other hand, land parts 24R, 24L are formed in a location corresponding to the grooves 23R, 23L, in a neutral position, in a spool 17, and each land part 24R, 24L and shoulder parts 23RK, 23LK of the grooves 23R, 23L serve as an under lap so as to form a space S at neutral time of the spool 17. |
