| 摘要 |
A crawler tractor has an engine-driven fluid power shifted transmission for supplying motive power to left and right crawler tracks through spring-applied fluid-released left and right steering clutches and also has spring-applied fluid-released brake actuators for the track brakes. A hydraulic control system for steering and braking the tractor includes a combined steering and braking valve having a pair of lever operated valve spools, a shuttle valve, and a supplemental brake control valve operated by a single brake pedal. The combined steering and braking valve, which includes a flow divider, directs fluid from a pump to the brake actuators to maintain the brakes released when the valve spools are in neutral. When a lever operated valve spool is moved from neutral to some other position, the combined steering and braking valve directs fluid to disengage a clutch and causes the brake for the associated track to be applied. The combined steering and braking valve operates to regulate fluid pressure in the system and also operates to ensure that sufficient fluid pressure is available for clutch operation regardless of brake actuator demands. The shuttle valve is connected to the brake actuators and is responsive to the supplemental brake valve to apply either or both brakes when the supplemental brake valve is actuated either by the brake pedal or in response to a drop of fluid pressure in the power shift transmission. |
