| 摘要 |
<p>A fully hydraulic steering system is provided with a steering valve, which sends out discharge pressure oil from a hydraulic pump in proportion to a control input of a handle, and a directional control valve, by which discharged pressure oil from the steering valve is changed over as pilot pressure and discharged pressure oil from the hydraulic pump is fed to a steering cylinder. Said directional control valve is so designed that a spool inserted into a spool hole of the valve body can be freely displaced from its neutral position to a first position, in which discharged pressure oil from the hydraulic pump is fed to one of oil chambers in the steering cylinder and pressure oil in the other oil chamber is allowed to flow into a tank, and to a second position, in which discharged pressure oil from the hydraulic pump is fed to the other oil chamber in the steering cylinder and pressure oil in the one of the chambers is allowed to flow into the tank. In this fully hydraulic steering system, a small diameter portion and a cut groove for the inflow of pressure oil from the steering cylinder into the tank are formed on the spool. Furthermore, the cut groove is so shaped that, when the spool is displaced from the neutral position toward the first position or the second position, the opening area thereof is increased until the spool is displaced to an intermediate position and is then decreased thereafter. <IMAGE></p> |
