| 摘要 |
A prime mover (A) has an arm assembly (B) pivotally connected thereto. A cutting assembly (C) is operatively connected with the arm assembly to be positioned thereby. The arm assembly is connected to the tractor to pivot about both vertical and horizontal axes such that the cutting means is positionable fore-and-aft as well as up and down. A hydraulic control circuit (D) controls the position of the arm assembly. The control circuit includes a first through-rod-type hydraulic cylinder (60) which includes a piston (62) slidably disposed therein to divide the cylinder into two equidiameter chambers (64, 66). A through-rod (68) is connected with the piston and extends through both chambers of the cyylinder. The hydraulic cylinder and the piston rod each have the same diameter in both chambers such that as the piston moves, one of the chambers draws the same amount of fluid as the other chamber discharges. A unidirectional pressure relief valve (70) connects the two chambers to allow fluid to flow from one chamber to the other when the pressure differential therebetween exceeds a first preselected pressure, but blocks fluid flow in the opposite direction. This enables the arm assembly to break away in one direction. Additional through-rod-type hydraulic cylinders (80, 90) control the position of arms within the arm assembly and the position of the cutting apparatus. Additional one-way pressure relief valves (84, 94) are connected with the other hydraulic cylinders to allow the arm assembly and cutting assembly to break away.
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