Patent ID: 7523610

Claim:
A neutral valve structure applied to at least one of a pair of operation fluid lines in an HST, comprising: (a) a port block formed with first and second operation passages that form at least parts of the pair of operation fluid lines and an installation passage; (b) a valve body inserted in the installation passage in a slidable manner in the axis line direction so as to take a closing position where the corresponding operation fluid line is liquid-tightly closed and a releasing position where the corresponding operation fluid line is released to a low-pressure area; (c) a biasing member inserted in the installation passage for urging the valve body toward the releasing position on one side of the axis line direction; (d) a lid member attached to the port block so as to close an opening end of the installation passage to engage a base end of the biasing member and define a spring chamber for accommodating the biasing member between the valve body and the lid member; and (e) the valve body including: (i) a closing-side pressure-receiving portion for receiving the hydraulic pressure of the corresponding operation fluid line so as to press the valve body toward the closing position on the other side of the axis line direction against the urging force of the biasing member; (ii) a releasing-side pressure-receiving portion for receiving the hydraulic pressure of the corresponding operation fluid line so as to press the valve body toward the releasing position on one side of the axis line direction along with the biasing member; and (iii) the closing-side pressure-receiving portion having a receiving pressure area larger than that of the releasing-side pressure-receiving portion; and (f) the lid member being threaded into the opening end of the installation passage so as to be position-adjustable with respect to the axis line direction of the valve body.