Hydraulic system for work machine, and work machine

Abstract

A hydraulic system for a work machine includes a hydraulic pump to supply a pilot fluid, and a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure. The pilot pressure is a pressure of the pilot fluid supplied from the hydraulic pump. The hydraulic system includes a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions. The hydraulic system includes a pressure applying device to apply a second pilot pressure to the hydraulic switch valve. The second pilot pressure is lower than the first pilot pressure.

What is claimed is: 
     
       1. A hydraulic system for a work machine, comprising:
 a hydraulic pump to supply a pilot fluid; 
 a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure, the pilot pressure being a pressure of the pilot fluid supplied from the hydraulic pump; 
 a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions; and 
 a pressure applying device to apply a second pilot pressure to the hydraulic switch valve, the second pilot pressure being lower than the first pilot pressure, 
 wherein the pressure applying device includes
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve, 
 a fourthan other fluid tube connecting the hydraulic pump to the direction switch valve, and 
 a fourth throttle to set the pilot pressure in the direction switch valve to the second pilot pressure. 
 
 
     
     
       2. The hydraulic system according to  claim 1 , wherein
 the pressure applying device includes
 a first further fluid tube connecting the hydraulic pump to the hydraulic switch valve, and 
 a firstan other throttle to set the pilot pressure in the firstfurther fluid tube to the second pilot pressure. 
 
 
     
     
       3. The hydraulic system according to  claim 1 , comprising:
 a first check valve provided in the second fluid tube, the pilot fluid being to flow from the direction switch valve to the hydraulic switch valve through the first check valve, the pilot fluid being prevented from flowing from the hydraulic switch valve to the direction switch valve through the first check valve. 
 
     
     
       4. The hydraulic system according to  claim 3 , comprising:
 a coupler provided in the second fluid tube to couple an upper stream portion of the first check valve to a downstream portion of the first check valve; and 
 a fifthan other throttle provided in the coupler to reduce a speed at which the pilot fluid flows in the coupler. 
 
     
     
       5. The hydraulic system according to  claim 4 , wherein the coupler is a branched fluid tube to couple the upper stream portion of the first check valve to the downstream portion of the first check valve, the branched fluid tube being arranged to be in a parallel connection with the first check valve. 
     
     
       6. The hydraulic system according to  claim 1 , wherein the hydraulic switch valve includes a spool to be switched to a plurality of switch positions. 
     
     
       7. A work machine comprising the hydraulic system according to  claim 1 . 
     
     
       8. A hydraulic system for a work machine, comprising:
 a hydraulic pump to supply a pilot fluid; 
 a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure, the pilot pressure being a pressure of the pilot fluid supplied from the hydraulic pump; 
 a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions; and 
 a speed reducing device to reduce a speed of changing the pilot pressure to be changed to the first pilot pressure, 
 wherein the speed reducing device includes
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve, 
 a second throttle to reduce the pilot pressure in the second fluid tube, 
 a thirdan other fluid tube connecting the hydraulic switch valve to a tank to which the pilot fluid is to be discharged from the hydraulic switch valve, and 
 a thirdan other throttle to reduce an amount of the pilot fluid flowing in the thirdother fluid tube, 
 
 wherein the second throttle and the third other throttle reduce the speed of changing the pilot pressure. 
 
     
     
       9. The hydraulic system according to  claim 8 , comprising:
 a second check valve provided in the third other fluid tube, the pilot fluid being to flow from the hydraulic switch valve to the tank through the second check valve, the pilot fluid being prevented from flowing from the tank to the hydraulic switch valve through the second check valve. 
 
     
     
       10. A hydraulic system for a work machine, comprising:
 a hydraulic pump to supply a pilot fluid; 
 a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure, the pilot pressure being a pressure of the pilot fluid supplied from the hydraulic pump; 
 a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions; 
 a pressure applying device to apply a second pilot pressure to the hydraulic switch valve, the second pilot pressure being lower than the first pilot pressure; and 
 a speed reducing device to reduce a speed of changing the pilot pressure, the pilot pressure being to be applied to the hydraulic switch valve and to be changed to the first pilot pressure. 
 
     
     
       11. The hydraulic system according to  claim 10 , wherein
 the pressure applying device includes
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve, 
 a fourthan other fluid tube connecting the hydraulic pump to the direction switch valve, and 
 a fourth throttle to set the pilot pressure in the direction switch valve to the second pilot pressure. 
 
 
     
     
       12. The hydraulic system according to  claim 11 , comprising:
 a first check valve provided in the second fluid tube, the pilot fluid being to flow from the direction switch valve to the hydraulic switch valve through the first check valve, the pilot fluid being prevented from flowing from the hydraulic switch valve to the direction switch valve through the first check valve. 
 
     
     
       13. The hydraulic system according to  claim 12 , comprising:
 a coupler provided in the second fluid tube to couple an upper stream portion of the first check valve to a downstream portion of the first check valve; and 
 a fifthan other throttle provided in the coupler to reduce a speed at which the pilot fluid flows in the coupler. 
 
     
     
       14. The hydraulic system according to  claim 13 , wherein the coupler is a branched fluid tube to couple the upper stream portion of the first check valve to the downstream portion of the first check valve, the branched fluid tube being arranged to be in a parallel connection with the first check valve. 
     
     
       15. The hydraulic system according to  claim 10 , wherein
 the speed reducing device includes
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve, 
 a second throttle to reduce the pilot pressure in the second fluid tube, 
 a thirdan other fluid tube connecting the hydraulic switch valve to a tank to which the pilot fluid is to be discharged from the hydraulic switch valve, and 
 a thirdan other throttle to reduce an amount of the pilot fluid flowing in the thirdother fluid tube, 
 
 wherein the second throttle and the third other throttle reduce the speed of changing the pilot pressure. 
 
     
     
       16. The hydraulic system according to  claim 15 , comprising:
 a second check valve provided in the third other fluid tube, the pilot fluid being to flow from the hydraulic switch valve to the tank through the second check valve, the pilot fluid being prevented from flowing from the tank to the hydraulic switch valve through the second check valve. 
 
     
     
       17. A hydraulic system for a work machine, comprising:
 a hydraulic pump to supply a pilot fluid; 
 a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure, the pilot pressure being a pressure of the pilot fluid supplied from the hydraulic pump; 
 a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions; 
 a pressure applying device to apply a second pilot pressure to the hydraulic switch valve, the second pilot pressure being lower than the first pilot pressure; 
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve; 
 a fourthan other fluid tube connecting the hydraulic pump to the direction switch valve; and 
 a discharge fluid tube which is connected to the direction switch valve and through which the pilot fluid in the second fluid tube is to be introduced from the direction switch valve, 
 wherein the direction switch valve is switchable between a first position and a second position, the direction switch valve being switched to the first position such that the second fluid tube communicates with the discharge fluid tube to relieve the pilot fluid in the second fluid tube, the direction switch valve being switched to the second position such that the fourth other fluid tube communicates with the second fluid tube to apply the first pilot pressure to the hydraulic switch valve. 
 
     
     
       18. The hydraulic system according to  claim 17 , comprising:
 a pressure sensor to detect a pilot pressure in the second fluid tube; and 
 a controller to output a command to switch the direction switch valve to the first position when the pilot pressure detected by the pressure sensor is less than a third pilot pressure while the controller outputs a command to switch the direction switch valve to the second position. 
 
     
     
       19. The hydraulic system according to  claim 17 , comprising:
 a pressure sensor to detect a pilot pressure in the fourth other fluid tube; and 
 a controller to output a command to switch the direction switch valve to the first position when the pilot pressure detected by the pressure sensor is less than a third pilot pressure while the controller outputs a command to switch the direction switch valve to the second position. 
 
     
     
       20. The hydraulic system according to  claim 19 , wherein the controller is to output the command to switch the direction switch valve to the second position when the pilot pressure detected by the pressure sensor is equal to or more than the third pilot pressure while the controller outputs the command to switch the direction switch valve to the first position. 
     
     
       21. The hydraulic system according to  claim 19 , comprising:
 an operation member connected to the controller to be manipulated to operate the direction switch valve, 
 wherein the controller holds the direction switch valve at the first position even when the operation member is manipulated in order to switch the direction switch valve to the second position while the pilot pressure detected by the pressure sensor is less than the third pilot pressure. 
 
     
     
       22. The hydraulic system according to  claim 17 , comprising:
 a first pressure sensor to detect the pilot pressure in the second fluid tube; 
 a second pressure sensor to detect the pilot pressure in the fourth other fluid tube; and 
 a controller to output the command to switch the direction switch valve to the first position when the pilot pressure detected by the pressure sensor is less than a third pilot pressure while the controller outputs the command to switch the direction switch valve to the second position and to output the command to switch the direction switch valve to the second position when the pilot pressure detected by the pressure sensor is equal to or more than the third pilot pressure while the controller outputs the command to switch the direction switch valve to the first position. 
 
     
     
       23. A hydraulic system for a work machine, comprising:
 a hydraulic pump to supply a pilot fluid; 
 a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure, the pilot pressure being a pressure of the pilot fluid supplied from the hydraulic pump; 
 a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions; 
 a speed reducing device to reduce a speed of changing the pilot pressure to be changed to the first pilot pressure; 
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve; 
 a fourthan other fluid tube connecting the hydraulic pump to the direction switch valve; and 
 a discharge fluid tube which is connected to the direction switch valve and through which the pilot fluid in the second fluid tube is to be introduced from the direction switch valve, 
 wherein the direction switch valve is switchable between a first position and a second position, the direction switch valve being switched to the first position such that the second fluid tube communicates with the discharge fluid tube to relieve the pilot fluid in the second fluid tube, the direction switch valve being switched to the second position such that the fourth other fluid tube communicates with the second fluid tube to apply the first pilot pressure to the hydraulic switch valve. 
 
     
     
       24. A hydraulic system for a work machine, comprising:
 a hydraulic pump to supply a pilot fluid; 
 a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure, the pilot pressure being a pressure of the pilot fluid supplied from the hydraulic pump; 
 a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions; 
 a pressure applying device to apply a second pilot pressure to the hydraulic switch valve, the second pilot pressure being lower than the first pilot pressure; and 
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve, 
 wherein the direction switch valve is a proportional valve to change an aperture to change a pilot pressure that is a pressure of the pilot fluid flowing in the second fluid tube, 
 and wherein the pressure applying device is to set the aperture of the proportional valve to maintain the pilot pressure in the second fluid tube to be less than the first pilot pressure. 
 
     
     
       25. A hydraulic system for a work machine, comprising:
 a hydraulic pump to supply a pilot fluid; 
 a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure, the pilot pressure being a pressure of the pilot fluid supplied from the hydraulic pump; 
 a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions; 
 a speed reducing device to reduce a speed of changing the pilot pressure to be changed to the first pilot pressure; 
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve; and 
 a speed controller to control a speed of changing the pilot pressure to be changed to the first pilot pressure, 
 wherein the direction switch valve is a proportional valve to change an aperture to change the pilot pressure in the second fluid tube, 
 and wherein the speed controller includes the speed reducer reducing device to change a reduce the speed of changing the aperture of the proportional valve to reduce the speed of changing the pilot pressure to be changed to the first pilot pressure. 
 
     
     
       26. A hydraulic system for a work machine, comprising:
 a hydraulic pump to supply a pilot fluid; 
 a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure, the pilot pressure being a pressure of the pilot fluid supplied from the hydraulic pump; 
 a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions; 
 a speed reducing device to reduce a speed of changing the pilot pressure to be changed to the first pilot pressure; 
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve; and 
 a speed controller including the speed reducer reducing device to change a reduce the speed of changing the pilot pressure to be changed to the first pilot pressure; and 
 a first travel sensor to detect a travel speed, 
 wherein the direction switch valve is a proportional valve to change an aperture to change the pilot pressure in the second fluid tube, 
 wherein the speed controller is to set a speed of changing the aperture of the proportional valve to a first changing speed corresponding to a first speed when the travel speed is the first speed, and to set the speed of changing the aperture of the proportional valve to a second changing speed corresponding to a second speed when the travel speed is the second speed, 
 and wherein the first changing speed is lower than the second changing speed. 
 
     
     
       27. A hydraulic system for a work machine, comprising:
 a hydraulic pump to supply a pilot fluid; 
 a hydraulic switch valve to be switched to a plurality of switching positions based on a pilot pressure, the pilot pressure being a pressure of the pilot fluid supplied from the hydraulic pump; 
 a direction switch valve to apply a first pilot pressure to the hydraulic switch valve to switch the hydraulic switch valve into one of the plurality of switching positions; 
 a speed reducing device to reduce a speed of changing the pilot pressure to be changed to the first pilot pressure; 
 a second fluid tube connecting the direction switch valve to the hydraulic switch valve; 
 a speed controller including the speed reducer reducing device to change a reduce the speed of changing the pilot pressure to be changed to the first pilot pressure; and 
 a second travel sensor to detect an operation being in traveling and an operation being in non-travelinga travel detector to detect whether a travel speed is zero in a non-traveling state or the travel speed is greater than zero in a traveling state, 
 wherein the direction switch valve is a proportional valve to change an aperture to change the pilot pressure in the second fluid tube, 
 wherein the speed controller is to set a speed of changing the aperture of the proportional valve to a third changing speed corresponding to a state of the traveling state and to a fourth an other changing speed corresponding to a state of the non-traveling state, 
 and wherein the third changing speed is lower than the fourth other changing speed.