Hydraulic system for work machine

Abstract

A hydraulic system for a work machine includes an operation member, a prime mover, a hydraulic pump driven by the prime mover, the hydraulic pump configured to output an operation fluid, a first temperature sensor to measure a temperature of the operation fluid, a first fluid tube connected to the hydraulic pump, an operation valve connected to the first fluid tube, the operation valve configured to control, in accordance with an operation extent of the operation member, a pressure of the outputted operation fluid, a hydraulic apparatus driven by the operation fluid outputted from the operation valve, a second hydraulic tube connecting the operation valve to the hydraulic apparatus, a discharge fluid tube to discharge the operation fluid included in the second fluid tube; and an actuation valve disposed on the discharge fluid tube, the actuation valve configured to control an aperture of the actuation valve based on the temperature.

What is claimed is: 
     
         1 . A hydraulic system for a work machine comprising:
 an operation member;   a hydraulic pump to output an operation fluid;   a first fluid tube connected to the hydraulic pump;   an operation valve disposed on the first fluid tube, the operation valve being configured to control, in accordance with an operation extent of the operation member, a pressure of the operation fluid to be outputted;   a hydraulic apparatus to be driven by the operation fluid outputted from the operation valve;   a second hydraulic tube connecting the operation valve to the hydraulic apparatus;   an actuation valve disposed on the first fluid tube between the operation valve and the hydraulic pump;   a third fluid tube connecting the second fluid tube to an intermediate section of the first fluid tube between the operation valve and the actuation valve; and   a check valve disposed on the third fluid tube, the check valve being configured to supply the operation fluid from the second fluid tube to the first fluid tube and block the operation fluid flowing from the first fluid tube to the second fluid tube.   
     
     
         2 . The hydraulic system according to  claim 1 , comprising
 a throttle disposed between the operation valve and a portion of the second fluid tube, the portion being connected to the third fluid.   
     
     
         3 . A hydraulic system for a work machine comprising:
 an operation member to be moved to one direction and to the other direction;   a hydraulic pump to output an operation fluid;   a first fluid tube connected to the hydraulic pump;   a first operation valve connected to the first fluid tube, the first operation valve being configured to control, in accordance with the movement to the one direction of the operation member, a pressure of the operation fluid to be outputted;   a second operation valve connected to the first fluid tube, the first operation valve being configured to control, in accordance with the movement to the other direction of the operation member, a pressure of the operation fluid to be outputted;   a hydraulic apparatus to be driven by the operation fluid outputted from the first operation valve or from the second operation valve; and   a pressure changer to differentiate a pressure of the operation fluid that is supplied from the first operation valve to the hydraulic apparatus when the operation member is moved to the one direction from a pressure of the operation fluid that is supplied from the second operation valve to the hydraulic apparatus when the operation member is moved to the other direction.   
     
     
         4 . A hydraulic system for a work machine comprising:
 an operation member to be moved to a first direction and to a second direction perpendicular to the first direction;   a hydraulic pump to output an operation fluid;   a first fluid tube connected to the hydraulic pump;   a first operation valve connected to the first fluid tube, the first operation valve being configured to control, in accordance with the movement to one direction in the first direction of the operation member, a pressure of the operation fluid to be outputted;   a second operation valve connected to the first fluid tube, the first operation valve being configured to control, in accordance with the movement to the other direction in the first direction of the operation member, a pressure of the operation fluid to be outputted;   a third operation valve connected to the first fluid tube, the first operation valve being configured to control, in accordance with the movement to one direction in the second direction of the operation member, a pressure of the operation fluid to be outputted;   a fourth operation valve connected to the first fluid tube, the first operation valve being configured to control, in accordance with the movement to the other direction in the second direction of the operation member, a pressure of the operation fluid to be outputted;   a hydraulic apparatus to be driven by the operation fluid outputted from at least one of the first operation valve, the second operation valve, the third operation valve, and the fourth operation valve; and   a pressure changer to differentiate a pressure of the operation fluid that is supplied from the first operation valve or the second operation valve to the hydraulic apparatus when the operation member is moved to the first direction from a pressure of the operation fluid that is supplied from the third operation valve or the fourth operation valve to the hydraulic apparatus when the operation member is moved to the second direction.   
     
     
         5 . The hydraulic system according to  claim 4 ,
 wherein the hydraulic apparatus is a travel device to travel forward, backward, rightward, and leftward,   the first operation valve is a valve to output the operation fluid for the forward traveling to the travel device,   the second operation valve is a valve to output the operation fluid for the backward traveling to the travel device,   the third operation valve is a valve to output the operation fluid for the rightward traveling to the travel device, and   the fourth operation valve is a valve to output the operation fluid for the leftward traveling to the travel device.   
     
     
         6 . The hydraulic system according to  claim 5 ,
 wherein the pressure changer includes
 a first variable relief valve connected to the first operation valve, the first variable relief valve having a pressure-receiving portion to receive the pressure outputted from the third operation valve, and 
 a second variable relief valve connected to the second operation valve, the first variable relief valve having a pressure-receiving portion to receive the pressure outputted from the fourth operation valve. 
   
     
     
         7 . A hydraulic system for a work machine comprising:
 a hydraulic pump to output an operation fluid;   a first hydraulic fluid connected to the hydraulic pump;   a travel device to be activated by the operation fluid;
 a first operation device connected to the travel device, including a first operation member to be moved to one direction and to the other direction, 
 a first operation valve connected to the first fluid tube, the first operation valve being configured to control, in accordance with the movement to the one direction of the first operation member, a pressure of the operation fluid, and 
 a second operation valve connected to the first fluid tube, the first operation valve being configured to control, in accordance with the movement to the other direction of the first operation member, the pressure of the operation fluid; 
   a second operation device connected to the travel device, the second operation device being other than the first operation device, including
 a second operation member to be moved to one direction and to the other direction, 
 a third operation valve connected to the first fluid tube, the third operation valve being configured to control, in accordance with the movement to the one direction of the second operation member, the pressure of the operation fluid, and 
 a fourth operation valve connected to the first fluid tube, the fourth operation valve being configured to control, in accordance with the movement to the other direction of the second operation member, the pressure of the operation fluid; 
   a first select valve including
 an output port to output higher any one of the pressure of the operation fluid outputted from the first operation valve and the pressure of the operation fluid outputted from the third operation valve; 
   a second select valve including
 an output port to output higher any one of the pressure of the operation fluid outputted from the second operation valve and the pressure of the operation fluid outputted from the fourth operation valve; 
   a third select valve including
 an output port to output higher any one of the pressure of the operation fluid outputted from the output port of the first operation valve and the pressure of the operation fluid outputted from the output port of the second operation valve; 
   a fourth fluid tube connected to the output port of the third select valve; and   a brake device connected to the fourth fluid tube, the brake device to release a braking state of the travel device when the pressure of the operation fluid is applied to the brake device.   
     
     
         8 . The hydraulic system according to  claim 7 , comprising:
 a fifth fluid tube connected to an intermediate portion of the fourth fluid tube; and   a switch valve connected to the fifth fluid tube, the switch valve being configured to be switched to discharge the operation fluid included in the fifth fluid tube.   
     
     
         9 . The hydraulic system according to  claim 7 , comprising
 a first check valve disposed on the fourth fluid tube, the first check valve being configured to supply the operation fluid from the third select valve to the brake device and block the operation fluid flowing from the brake device to the third select valve.   
     
     
         10 . The hydraulic system according to  claim 9 , comprising
 a second check valve to supply the operation fluid from a side of the first check valve to the switch valve and block the operation fluid flowing from the switch valve to the side of the first check valve.   
     
     
         11 . The hydraulic system according to  claim 7 , comprising
 a switch to switch the switch valve between a side to discharge the operation fluid included in the fourth fluid tube and a side not to discharge the operation fluid included in the fourth fluid tube.