Neutral Valve Structure

Abstract

There is provided a neutral valve structure applied to at least one of a pair of operation fluid lines in an HST, including: a valve body slidable 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; and a biasing member for urging the valve body toward the releasing position on one side of the axis line direction. The valve body includes: 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; and 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. The closing-side pressure-receiving portion has a receiving pressure area larger than that of the releasing-side pressure-receiving portion.

1 - 7 . (canceled) 
   
   
       8 . A neutral valve structure applied to a port block in which a pair of first and second operation passages configuring at least parts of the pair of operation fluid lines in the HST are formed substantially parallel with each other,
 the port block including:   a linear installation passage intersecting with the first and second operation passages and having first and second ends respectively near to the first and second operation passages, both of the first and second ends opened at the outer surface;   a drain passage fluidly connected to the installation passage between the first and second operation passages;   a first releasing passage having a first end fluidly connected to the installation passage between the first operation passage and the drain passage and a second end fluidly connected to a low-pressure area;   a second releasing passage having a first end fluidly connected to the installation passage between the second operation passage and the drain passage and a second end fluidly connected to the low-pressure area;   a first neutral valve inserted into the installation passage from the first end and switching fluid-connection or fluid-disconnection between the first operation passage and the first releasing passage according to the hydraulic pressure of the first operation passage; and   a second neutral valve inserted into the installation passage from the second end and switching fluid-connection or fluid-disconnection between the second operation passage and the second releasing passage according to the hydraulic pressure of the second operation passage,   each of the first and second neutral valves including:
 a valve body inserted into the installation passage in a slidable manner along the axis line direction so as to straddle the corresponding operation passage, the valve body capable of taking a releasing position on one side of the axis line direction where the corresponding operation passage and the corresponding releasing passage are fluidly connected to each other and a closing position on the other side of the axis line direction where the corresponding operation passage and the corresponding releasing passage are fluidly disconnected to each other; 
 a biasing member having a tip end engaged to the valve body so as to urge the valve body toward the releasing position on one side of the axis line direction; and 
 a lid member engaging a base end of the biasing member and defining a spring chamber for accommodating the biasing member between the valve body and the lid member, 
   the valve body including:
 a closing-side pressure-receiving portion for receiving the hydraulic pressure of the corresponding operation oil passage 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; 
 a releasing-side pressure-receiving portion for receiving the hydraulic pressure of the corresponding operation oil passage so as to press the valve body toward the releasing position on one side of the axis line direction along with the biasing member, the releasing-side pressure-receiving portion having a receiving pressure area smaller than that of the closing-side pressure-receiving portion; and 
 an axis line hole for fluidly connecting the corresponding spring chamber and the drain passage. 
   
   
   
       9 . (canceled) 
   
   
       10 . (canceled) 
   
   
       11 . A neutral valve structure applied to a port block in which a pair of first and second operation passages configuring at least parts of a pair of operation fluid lines in the HST are formed,
 the port block including:   a first releasing passage having a first end fluidly connected to the first operation passage and a second end fluidly connected to a low-pressure area; and   a first neutral valve inserted into the first operation passage and switching fluid-connection or fluid-disconnection between the first operation passage and the first releasing passage according to the hydraulic pressure of the first operation passage,   the first neutral valve including:
 a valve body inserted into the first operation passage in a slidable manner along the axis line direction, the valve body capable of taking a releasing position on one side of the axis line direction where the first operation passage and the first releasing passage are fluidly connected to each other and a closing position on the other side of the axis line direction where the first operation passage and the first releasing passage are fluidly disconnected to each other; 
 a biasing member having a tip end engaged to the valve body so as to urge the valve body toward the releasing position on one side of the axis line direction; and 
 a lid member engaging a base end of the biasing member and defining the spring chamber for accommodating the biasing member between the valve body and the lid member, 
   the valve body including:
 a closing-side pressure-receiving portion for receiving the hydraulic pressure of the first operation passage 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; and 
 a releasing-side pressure-receiving portion for receiving the hydraulic pressure of the first operation passage so as to press the valve body toward the releasing position on one side of the axis line direction along with the biasing member, the releasing-side pressure-receiving portion having a receiving pressure area smaller than that of the closing-side pressure-receiving portion. 
   
   
   
       12 . The neutral valve structure according to  claim 11 , wherein
 the port block further includes:
 a second releasing passage having a first end fluidly connected to the second operation passage and a second end fluidly connected to the low-pressure area; and 
 a second neutral valve inserted into the second operation passage and switching fluid-connection or fluid-disconnection between the second operation passage and the second releasing passage according to the hydraulic pressure of the second operation passage, 
   the second neutral valve including:
 a valve body inserted into the second operation passage in a slidable manner along the axis line direction, the valve body capable of taking a releasing position on one side of the axis line direction where the second operation passage and the second releasing passage are fluidly connected and a closing position on the other side of the axis line direction where the second operation passage and the second releasing passage are fluidly disconnected to each other; 
 a biasing member having a tip end locked to the valve body so as to urge the valve body toward the releasing position on one side of the axis line direction; and 
 a lid member engaging a base end of the biasing member and defining a spring chamber for accommodating the biasing member between the valve body and the lid member, 
   the valve body including:
 a closing-side pressure-receiving portion for receiving the hydraulic pressure of the second operation passage 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; and 
 a releasing-side pressure-receiving portion for receiving the hydraulic pressure of the first operation passage so as to press the valve body toward the releasing position on one side of the axis line direction along with the biasing member, the releasing-side pressure-receiving portion having a receiving pressure area smaller than that of the closing-side pressure-receiving portion. 
   
   
   
       13 . The neutral valve structure according to  claim 11 , wherein the valve body is provided with an orifice located between the corresponding operation passage and the corresponding releasing passage. 
   
   
       14 - 16 . (canceled)