| 摘要 |
PURPOSE:To improve the traveling performance by using the device in synchronous engagement type and permitting the speed change operation only when the car speed is lower than a standard value and permitting a hydraulic circuit to be unloaded, thus permitting the speed change during traveling. CONSTITUTION:A hydraulic circuit 10 for traveling drive is equipped with a hydraulic pump 11 driven by a prime mover 1, hydraulic motor 12 for traveling, traveling selector valve 13 which controls the normal and reverse revolution and stop of the hydraulic motor 12, unload valve 14, retarding valve 15, and a relief valve 16. The unload valve 14 is a hydraulic pilot selector valve and connected with a hydraulic source 3 and a tank 4 through a selector valve 2 for unloading, and when the selector valve 2 is at the position (a), the unload valve is at the position (a) and cuts off the both of the inlet and outlet ports of the hydraulic motor 12, and when the selector valve 2 is switched to the position (b), the unload valve 14 is switched to the position (b), and communicates to the inlet and outlet ports of the hydraulic motor 12.
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