| 摘要 |
<p>A crawler tractor has an engine-driven transmission for supplying motive power to the left and right crawler tracks through spring-applied fluid-released left and right steering clutches and also has spring-applied fluid-released track brakes. A hydraulic steering clutch and brake control system is provided and includes left and right manually operable steering levers for the clutches and a single foot-operated brake pedal. The control system further includes a single pump for supplying hydraulic fluid to the steering clutches and to the brake actuators for the brakes. A steering valve, having a flow divider therein, receives fluid from the pump and is responsive to actuation of the steering levers to supply fluid to release the steering clutches. The steering valve also continually directs fluid to a pilot operated shuttle valve which is responsive to operation of the steering clutches to direct operating fluid to the brake actuators to effect brake release for that track whose clutch is engaged. A combined pressure relief valve, brake valve and brake inhibitor valve is provided and operates in response to the brake pedal and is also responsive to fluid pressure in the tractor transmission. The control system operates so that actuation of either steering lever from neutral effects fluid release of its associated steering clutch, whereupon depression of the single brake pedal will then operate the combined valve to effect spring application of the brake for that track whose clutch is released. If both steering levers are in neutral and transmission fluid pressure drops below a predetermined value, as during reverse shifting to change direction of tractor travel, the combined valve effects automatic spring-application of both brakes, without loss of fluid pressure necessary for control of the steering clutches.</p> |
