Patent ID: 7500361

Claim:
A hydraulic pump unit of variable displacement type disposed away from a pair of hydraulic motor units which are capable of being independently arranged, the pump unit fluidly-connected to the pair of hydraulic motor units so as to change the outputs of the pair of hydraulic motor units in both forward and reverse rotation directions, comprising: a pair of first and second hydraulic pump bodies operatively rotated and driven by a driving source, a pump case surrounding the first and second hydraulic pump bodies, a pair of first and second capacity adjusting mechanisms for respectively changing capacities of the first and second hydraulic pump bodies, and a hydraulic servomechanism for transmitting an external input based on a manual operation to the first and second capacity adjusting mechanisms by utilizing a hydraulic force, wherein each of the first and second capacity adjusting mechanisms includes an output adjusting member for changing a reciprocating range of hydraulic pistons of the corresponding hydraulic pump body according to its tilting position, and a control shaft having a base end portion operatively connected to the output adjusting member so as to tilt the output adjusting member and a tip end portion accessible from outside of the pump case, the hydraulic servomechanism includes a servo piston case defining first and second piston accommodating chambers; first and second servo pistons respectively accommodated in a reciprocating manner in the first and second piston accommodating chambers, each of the first and second servo pistons dividing the corresponding piston accommodating chamber into a regular rotation oil chamber and a reverse rotation oil chamber; and first and second directional switching valves for changing corresponding passages fluidly connected to the corresponding regular rotation oil chambers and the corresponding reverse rotation oil chambers according to the external input, each of the first and second servo pistons is formed with an engaging groove on its outer peripheral surface, the engaging groove extending in a direction orthogonal to an axis line of the servo piston, the tip ends of the control shafts of the first and second capacity adjusting mechanisms extend outward from one end surface of the pump case, and the servo piston case is detachably connected to the one end surface of the pump case so that the tip ends of the control shafts of the first and second capacity adjusting mechanisms are operatively engaged into the engaging grooves of the first and second servo pistons, respectively.