Working machinery

Abstract

To suppress the deterioration of the operability of a working machine.SOLUTION: A working machine comprises: a first traveling opening valve 13 for controlling a flow rate and a direction of a working fluid which is supplied to a first traveling motor 7; a second traveling operation valve 14 for controlling a flow rate and a direction of a working fluid which is supplied to a second traveling motor 8 from a hydraulic pump 11; a working fluid operation valve 15; a first pressure compensation valve of the first traveling operation valve 13 connected to a signal flow passage via a first introduction flow passage; a second pressure compensation valve of the second traveling operation valve 14 connected to the signal flow passage via a second introduction flow passage; a bypass flow passage bypassing at least a part of the second introduction flow passage; a traveling communication valve 26 arranged at a connecting flow passage 20 which connects the first traveling operation valve 13 and the second traveling operation valve 14; a temperature sensor 27 for detecting a working fluid temperature which indicates a temperature of the working fluid; and a control device 6 for adjusting a stroke of the traveling communication valve 26 on the basis of detection data of the temperature sensor 27 in a state that the first traveling operation valve 13 and the second traveling operation valve 14 are arranged in a neutral position.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to a work machine. [Background technology]

[0002] In the technical field related to working machinery, working machinery having a load sensing control circuit, such as that disclosed in Patent Document 1, is known. In a load sensing system, the amount of hydraulic fluid discharged from a hydraulic pump is adjusted based on the pressure difference between the discharge pressure of the hydraulic fluid from the hydraulic pump and the load sensing pressure (LS pressure) corresponding to the load pressure of the hydraulic actuator. Furthermore, an LS drop characteristic is known in which the LS pressure decreases as the load pressure increases. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2006-336730 [Overview of the project] [Problems that the invention aims to solve]

[0004] In load sensing systems, the LS drop amount, which indicates the amount of load pressure reduction, is set by the LS introduction throttling. When the temperature of the hydraulic fluid changes, the viscosity of the hydraulic fluid changes, which may cause the LS drop amount to fluctuate. If the LS drop amount fluctuates, it may not be possible to obtain the correct LS pressure. If the correct LS pressure is not obtained, the operability of the implement may deteriorate, for example, the amount of operation of the work lever and the operating speed of the implement may not match, or the implement may hunt.

[0005] This disclosure aims to suppress the deterioration of the operability of the work equipment. [Means for solving the problem]

[0006] According to this disclosure, a hydraulic pump that changes the discharge amount of hydraulic fluid based on the differential pressure between the pump discharge pressure and a load sensing pressure corresponding to the load pressure input via a signal path; a first travel motor driven by the hydraulic fluid supplied from the hydraulic pump; a second travel motor driven by the hydraulic fluid supplied from the hydraulic pump; a work machine cylinder driven by the hydraulic fluid supplied from the hydraulic pump; a first travel control valve that controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump to the first travel motor; a second travel control valve that controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump to the second travel motor; a work machine control valve that controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump to the work machine cylinder; and a first introduction valve A working machine is provided, comprising: a first pressure compensation valve connected to a signal channel via a flow path and compensating for the differential pressure across a first travel operating valve based on load sensing pressure; a second pressure compensation valve connected to a signal channel via a second introduction channel and compensating for the differential pressure across a second travel operating valve based on load sensing pressure; a bypass channel that bypasses at least a portion of the second introduction channel; a travel communication valve disposed in a connecting channel that connects the first travel operating valve and the second travel operating valve; a temperature sensor that detects the hydraulic oil temperature indicating the temperature of the hydraulic oil; and a control device that adjusts the stroke of the travel communication valve based on the detection data of the temperature sensor when the first travel operating valve and the second travel operating valve are each in a neutral position. [Effects of the Invention]

[0007] According to this disclosure, deterioration in the operability of the work equipment is suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a perspective view showing a work machine according to the first embodiment. [Figure 2] Figure 2 shows the hydraulic system of a work machine according to the first embodiment. [Figure 3] Figure 3 is an enlarged view of a part of the hydraulic system according to the first embodiment. [Figure 4] Figure 4 is a schematic block diagram showing the hydraulic system according to the first embodiment. [Figure 5] Figure 5 shows the relationship between load pressure and differential pressure according to the first embodiment. [Figure 6] Figure 6 shows the operation of the travel communication valve according to the first embodiment. [Figure 7] Figure 7 shows the operation of the travel communication valve according to the first embodiment. [Figure 8] Figure 8 is a schematic diagram showing a travel communication valve according to the first embodiment. [Figure 9] Figure 9 is a schematic diagram showing the spool of the travel communication valve according to the first embodiment. [Figure 10] Figure 10 is a schematic diagram showing the operation of the travel communication valve according to the first embodiment. [Figure 11] Figure 11 is a table showing the relationship between the hydraulic fluid temperature, the target stroke amount, and the opening area of ​​the travel communication valve according to the first embodiment. [Figure 12] Figure 12 is a flowchart showing a control method for a hydraulic system according to the first embodiment. [Figure 13] Figure 13 is a flowchart showing a control method for a hydraulic system according to the second embodiment. [Figure 14] Figure 14 is a flowchart showing a control method for a hydraulic system according to the third embodiment. [Figure 15] Figure 15 is a table showing the relationship between the pump discharge pressure, target stroke amount, and opening area of ​​the travel communication valve according to the third embodiment. [Modes for carrying out the invention]

[0009] The embodiments relating to this disclosure will be described below with reference to the drawings, but this disclosure is not limited to these embodiments. The components of the embodiments described below can be combined as appropriate. In addition, some components may not be used.

[0010] [First Embodiment] <Working machinery> A first embodiment will be described. Figure 1 is a perspective view showing a work machine 1 according to this embodiment. The work machine 1 operates at a work site. In this embodiment, the work machine 1 is a hydraulic excavator. In the following description, the work machine 1 will be referred to as hydraulic excavator 1 as appropriate. The hydraulic excavator 1 comprises a traveling body 2, a slewing body 3, a work implement 4, a work implement cylinder 5, and a control device 6. The traveling body 2 travels while supporting the slewing body 3. The traveling body 2 has a pair of tracks 2A. The tracks 2A are rotated by a travel motor. The traveling body 2 travels due to the rotation of the tracks 2A. The slewing body 3 is supported by the traveling body 2. A driver's cab is provided in the slewing body 3. The work implement 4 is attached to the slewing body 3. The work implement 4 includes a boom 4A, an arm 4B, and a bucket 4C. The work implement cylinder 5 operates the work implement 4. The work implement cylinder 5 is a hydraulic cylinder. The work equipment cylinder 5 includes a boom cylinder 5A, an arm cylinder 5B, and a bucket cylinder 5C. The control device 6 includes a computer system. The control device 6 controls the hydraulic excavator 1.

[0011] <Hydraulic System> Figure 2 shows the hydraulic system 10 of the hydraulic excavator 1 according to this embodiment. Figure 3 is an enlarged view of a part of the hydraulic system 10 according to this embodiment. Figure 4 is a schematic block diagram showing the hydraulic system 10 according to this embodiment. The hydraulic system 10 includes a load sensing control circuit.

[0012] The hydraulic system 10 includes a hydraulic pump 11, a hydraulic oil tank 12, a travel motor 7, a travel motor 8, a work machine cylinder 5, a travel operation valve 13, a travel operation valve 14, a work machine operation valve 15, a pressure compensation unit 16 having a pressure compensation valve 16S, a pressure compensation unit 17 having a pressure compensation valve 17S, a pressure compensation unit 18 having a pressure compensation valve 18S, a load sensing valve 24 (LS valve), a servo piston 25, a travel communication valve 26, a temperature sensor 27, and a pressure sensor 28.

[0013] The hydraulic pump 11 is a variable displacement hydraulic pump. The discharge port of the hydraulic pump 11 is connected to the pump flow path 19. The hydraulic pump 11 changes the discharge amount of hydraulic fluid based on the pressure difference between the pump discharge pressure and the load sensing pressure (LS pressure) corresponding to the load pressure input via the signal flow path 22. The pump discharge pressure refers to the pressure of the hydraulic fluid discharged from the discharge port of the hydraulic pump 11.

[0014] As shown in Figures 2 and 3, the travel motor 7 is a hydraulic motor driven by hydraulic fluid supplied from a hydraulic pump 11. The travel motor 7 rotates the left track 2A. The travel control valve 13 controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump 11 to the travel motor 7. The travel control valve 13 has a first port 13A, a second port 13B, a third port 13C, a fourth port 13D, a fifth port 13E, a sixth port 13F, and a seventh port 13G. The first port 13A is connected to the discharge port of the hydraulic pump 11 via a pump passage 19. The second port 13B is connected to one port 7A of the travel motor 7. The third port 13C is connected to the other port 7B of the travel motor 7. The fourth port 13D is connected to the input port 16A of the pressure compensation valve 16S. The fifth port 13E is connected to the output port 16B of the pressure compensation valve 16S. The fifth port 13E is connected to the travel communication valve 26 via the connecting passage 20. The sixth port 13F and the seventh port 13G are each connected to the hydraulic oil tank 12 via the tank passage 21.

[0015] As shown in Figure 4, the hydraulic excavator 1 is equipped with a travel lever 31. The travel lever 31 is located in the operator's cab of the slewing body 3. The travel lever 31 is operated by an operator. Pilot ports are provided at both ends of the travel control valve 13. Pilot pressure is input to the pilot ports of the travel control valve 13 based on the amount of operation of the travel lever 31. As shown in Figures 2 and 3, when no pilot pressure is input, the travel control valve 13 is located in a neutral position N where no hydraulic fluid is supplied to the travel motor 7. When pilot pressure is input to the pilot port at one end of the travel control valve 13, the travel control valve 13 is moved to a forward position F that moves the travel body 2 forward. When the travel control valve 13 is moved to the forward position F, hydraulic fluid from the hydraulic pump 11 flows into port 7A of the travel motor 7 via the first port 13A, meter-in throttle 13M, fourth port 13D, pressure compensation valve 16S, fifth port 13E, and second port 13B. The hydraulic fluid that flows out from port 7B of the travel motor 7 is sent to the hydraulic fluid tank 12 via the third port 13C, the sixth port 13F, and the tank passage 21. When pilot pressure is input to the pilot port at the other end of the travel control valve 13, the travel control valve 13 is positioned in the reverse position R, which moves the travel body 2 in reverse. When the travel control valve 13 is positioned in the reverse position R, hydraulic fluid from the hydraulic pump 11 flows into port 7B of the travel motor 7 via the first port 13A, the meter-in throttle 13N, the fourth port 13D, the pressure compensation valve 16S, the fifth port 13E, and the third port 13C. The hydraulic fluid that flows out from port 7A of the travel motor 7 is sent to the hydraulic fluid tank 12 via the second port 13B, the seventh port 13G, and the tank passage 21.

[0016] As shown in Figures 2 and 3, the travel motor 8 is a hydraulic motor driven by hydraulic fluid supplied from the hydraulic pump 11. The travel motor 8 rotates the right track 2A. The travel control valve 14 controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump 11 to the travel motor 8. The travel control valve 14 has a first port 14A, a second port 14B, a third port 14C, a fourth port 14D, a fifth port 14E, a sixth port 14F, and a seventh port 14G. The first port 14A is connected to the discharge port of the hydraulic pump 11 via the pump passage 19. The second port 14B is connected to one port 8A of the travel motor 8. The third port 14C is connected to the other port 8B of the travel motor 8. The fourth port 14D is connected to the input port 17A of the pressure compensation valve 17S. The fifth port 14E is connected to the output port 17B of the pressure compensation valve 17S. The fifth port 14E is connected to the travel communication valve 26 via the connecting passage 20. The sixth port 14F and the seventh port 14G are each connected to the hydraulic oil tank 12 via the tank passage 21.

[0017] Based on the amount of operation of the travel lever 31, pilot pressure is input to the pilot port of the travel control valve 14. As shown in Figures 2 and 3, when no pilot pressure is input, the travel control valve 14 is positioned in a neutral position N where no hydraulic fluid is supplied to the travel motor 8. When pilot pressure is input to the pilot port at one end of the travel control valve 14, the travel control valve 14 is positioned in a forward position F that moves the travel body 2 forward. When the travel control valve 14 is positioned in the forward position F, hydraulic fluid from the hydraulic pump 11 flows into port 8A of the travel motor 8 via the first port 14A, meter-in throttle 14M, fourth port 14D, pressure compensation valve 17S, fifth port 14E, and second port 14B. The hydraulic fluid that flows out from port 8B of the travel motor 8 is sent to the hydraulic fluid tank 12 via the third port 14C, sixth port 14F, and tank passage 21. When pilot pressure is input to the pilot port at the other end of the travel control valve 14, the travel control valve 14 is positioned in the reverse position R, which moves the travel body 2 in reverse. When the travel control valve 14 is positioned in the reverse position R, hydraulic fluid from the hydraulic pump 11 flows into port 8B of the travel motor 8 via the first port 14A, meter-in throttle 14N, fourth port 14D, pressure compensation valve 17S, fifth port 14E, and third port 14C. The hydraulic fluid that flows out of port 8A of the travel motor 8 is sent to the hydraulic fluid tank 12 via the second port 14B, seventh port 14G, and tank passage 21.

[0018] As shown in Figures 2 and 3, the work machine cylinder 5 is a hydraulic cylinder driven by hydraulic fluid supplied from a hydraulic pump 11. The work machine operating valve 15 controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump 11 to the work machine cylinder 5. The work machine operating valve 15 has a first port 15A, a second port 15B, a third port 15C, a fourth port 15D, a fifth port 15E, a sixth port 15F, and a seventh port 15G. The first port 15A is connected to the discharge port of the hydraulic pump 11 via a pump passage 19. The second port 15B is connected to one port 50A of the work machine cylinder 5. The third port 15C is connected to the other port 50B of the work machine cylinder 5. The fourth port 13D is connected to the input port 18A of the pressure compensation valve 18S. The fifth port 15E is connected to the output port 18B of the pressure compensation valve 18S. The sixth port 15F and the seventh port 15G are each connected to the hydraulic oil tank 12 via the tank passage 21.

[0019] As shown in Figure 4, the hydraulic excavator 1 is equipped with a work lever 32. The work lever 32 is located in the operator's cab of the slewing body 3. The work lever 32 is operated by an operator. Pilot pressure is input to both ends of the work implement control valve 15. Pilot ports are provided at both ends of the work implement control valve 15. Based on the amount of operation of the work lever 32, pilot pressure is input to the pilot ports of the work implement control valve 15. As shown in Figures 2 and 3, when no pilot pressure is input, the work implement control valve 15 is positioned in a neutral position N where no hydraulic fluid is supplied to the work implement cylinder 5. When pilot pressure is input to the pilot port at one end of the work implement control valve 15, the work implement control valve 15 is positioned in an extended position U that extends the work implement cylinder 5. When the implement control valve 15 is positioned in the extended position U, hydraulic fluid from the hydraulic pump 11 flows into port 50A of the implement cylinder 5 via the first port 15A, meter-in throttle 15M, fourth port 15D, pressure compensation valve 18S, fifth port 15E, and second port 15B. The hydraulic fluid that flows out from port 50B of the implement cylinder 5 is sent to the hydraulic fluid tank 12 via the third port 15C, sixth port 15F, and tank passage 21. When pilot pressure is input to the pilot port at the other end of the implement control valve 15, the implement control valve 15 is positioned in the shortened position D, which is retracted from the implement cylinder 5. When the work implement operating valve 15 is positioned in the shortened position D, hydraulic fluid from the hydraulic pump 11 flows into port 50B of the work implement cylinder 5 via the first port 15A, meter-in throttle 15N, fourth port 15D, pressure compensation valve 18S, fifth port 15E, and third port 15C. The hydraulic fluid that flows out of port 50A of the work implement cylinder 5 is sent to the hydraulic fluid tank 12 via the second port 15B, seventh port 15G, and tank passage 21.

[0020] The pressure compensation unit 16 includes a pressure compensation valve 16S, an introduction channel 16C connecting the output port 16B of the pressure compensation valve 16S to the signal channel 22, a check valve 16D located in the introduction channel 16C, and a load-sensing introduction throttle 16E (LS introduction throttle) located in the introduction channel 16C. The pressure compensation valve 16S is connected to the signal channel 22 via the introduction channel 16C. The pressure compensation valve 16S compensates for the differential pressure across the travel operation valve 13 based on the LS pressure input from the signal channel 22. The pressure compensation valve 16S receives the LS pressure input from the signal channel 22 to the pilot port of the pressure compensation valve 16S and operates to maintain a constant differential pressure across the travel operation valve 13. The pressure compensation valve 16S moves between a fully open position A and a fully closed position B.

[0021] The pressure compensation unit 17 includes a pressure compensation valve 17S, an inlet passage 17C connecting the output port 17B of the pressure compensation valve 17S to the signal passage 22, a check valve 17D located in the inlet passage 17C, and a load-sensing inlet throttle 17E (LS inlet throttle) located in the inlet passage 17C. The pressure compensation unit 17 also includes a bypass passage 17F that bypasses at least a portion of the inlet passage 17C, and a bypass throttle 17G located in the bypass passage 17F. The pressure compensation valve 17S is connected to the signal passage 22 via the inlet passage 17C. The pressure compensation valve 17S compensates for the differential pressure across the travel operation valve 14 based on the LS pressure input from the signal passage 22. The pressure compensation valve 17S receives the LS pressure input from the signal passage 22 to its pilot port and operates to maintain a constant differential pressure across the travel operation valve 14. The pressure compensation valve 17S moves between a fully open position A and a fully closed position B.

[0022] The pressure compensation unit 18 includes a pressure compensation valve 18S, an introduction channel 18C connecting the input port 18A of the pressure compensation valve 18S to the signal channel 22, a check valve 18D located in the introduction channel 18C, and a load-sensing introduction throttle 18E (LS introduction throttle) located in the introduction channel 18C. The pressure compensation valve 18S is connected to the signal channel 22 via the introduction channel 18C. The pressure compensation valve 18S compensates for the differential pressure across the work implement operating valve 15 based on the LS pressure input from the signal channel 22. The pressure compensation valve 18S receives the LS pressure input from the signal channel 22 to the pilot port of the pressure compensation valve 18S and operates to maintain a constant differential pressure across the work implement operating valve 15. The pressure compensation valve 18S moves between a fully open position A and a fully closed position B.

[0023] The pressure corresponding to the highest load pressure among the load pressure of the travel motor 7, the load pressure of the travel motor 8, and the load pressure of the work machine cylinder 5 is the LS pressure P. LS It is then guided to the signal channel 22. A portion of the hydraulic fluid guided to the signal channel 22 is sent to the hydraulic fluid tank 12 via the throttle 23. In addition, the LS pressure P guided to the signal channel 22 LS This is led to the LS valve 24.

[0024] As shown in Figure 2, the LS valve 24 controls the pump discharge pressure P P and the LS pressure P input from the signal channel 22 LS Based on the pressure difference, the amount of hydraulic fluid discharged from the hydraulic pump 11 is adjusted. The servo piston 25 is connected to the hydraulic pump 11. The LS valve 24 adjusts the amount of hydraulic fluid discharged from the hydraulic pump 11 via the servo piston 25. The LS valve 24 moves to a neutral position N, a low pressure difference position L, and a high pressure difference position H. Pump discharge pressure P acts on the LS valve 24. P and LS pressure P LS When the differential pressure is small, the LS valve 24 moves to the low differential pressure position L. When the LS valve 24 is positioned at the low differential pressure position L, the hydraulic fluid from the servo piston 25 is sent to the hydraulic fluid tank 12, and the servo piston 25 moves in the increasing direction Ya, which increases the capacity of the hydraulic pump 11. As the capacity of the hydraulic pump 11 increases, the amount of hydraulic fluid discharged from the hydraulic pump 11 increases. Pump discharge pressure P acting on the LS valve 24P and LS pressure P LS When the pressure difference is large, the LS valve 24 moves to the high pressure position H. When the LS valve 24 is positioned at the high pressure position H, a portion of the hydraulic fluid discharged from the hydraulic pump 11 is introduced to the servo piston 25, causing the servo piston 25 to move in the decreasing direction Yb, which reduces the capacity of the hydraulic pump 11. As the capacity of the hydraulic pump 11 decreases, the amount of hydraulic fluid discharged from the hydraulic pump 11 decreases.

[0025] The travel communication valve 26 is located in the connecting passage 20. The connecting passage 20 connects the fifth port 13E of the travel control valve 13 and the fifth port 14E of the travel control valve 14. The spool of the travel communication valve 26 moves between an open position V, which allows the flow of hydraulic fluid between the travel control valve 13 and the travel control valve 14, and a closed position W, which blocks the flow of hydraulic fluid between the travel control valve 13 and the travel control valve 14. A solenoid valve 33 is connected to the travel communication valve 26. The control device 6 can move the spool of the travel communication valve 26 between the open position V and the closed position W by controlling the solenoid valve 33. The control device 6 controls the travel communication valve 26 based on the operating state of the travel lever 31. When the travel lever 31 is operated so that the hydraulic excavator 1 moves in a straight line, the control device 6 moves the spool of the travel communication valve 26 to the open position V. For example, due to manufacturing tolerances in at least one of the travel motors 7 and 8, even if the travel lever 31 is operated to move the hydraulic excavator 1 in a straight line, there is a possibility that a difference may occur between the rotational speed of travel motor 7 and the rotational speed of travel motor 8. When the hydraulic excavator 1 moves in a straight line, the spool of the travel communication valve 26 moves to the open position V, which reduces the difference between the load pressure of travel motor 7 and the load pressure of travel motor 8. As a result, the hydraulic excavator 1 can move in a straight line properly. When the travel lever 31 is operated to steer the traveling body 2, the control device 6 moves the spool of the travel communication valve 26 to the closed position W. Steering the traveling body 2 means that the traveling body 2 changes its direction of travel (turns a curve).

[0026] The bypass flow passage 17F is provided to suppress a decrease in the traveling speed of the traveling body 2 when the work implement 4 is operated while the traveling body 2 is traveling. When the work implement operation valve 15 is actuated to operate the work implement cylinder 5, the flow rate of hydraulic oil supplied to the traveling motor 7 and the traveling motor 8 decreases, which may cause a phenomenon that the traveling speed of the traveling body 2 decreases. When the work implement 4 is operated while the traveling body 2 is traveling, the load pressure of the work implement cylinder 5 may be higher than the load pressures of the traveling motor 7 and the traveling motor 8. When the load pressure of the work implement cylinder 5 is higher than the load pressures of the traveling motor 7 and the traveling motor 8, a high LS pressure P corresponding to the load pressure of the work implement cylinder 5 which is the maximum pressure LS is input to each of the pressure compensation valve 16S and the pressure compensation valve 17S, and is also input to the LS valve 24. When the LS pressure P is input from the signal flow passage 22 to the pressure compensation unit 17 LS , at least a part of the hydraulic oil that has flowed into the pressure compensation unit 17 from the signal flow passage 22 can flow through the bypass flow passage 17F. As a result, the pressure in the signal flow passage 22 decreases, and the pressure acting on the pilot port of the pressure compensation valve 17S from the signal flow passage 22 decreases. Accordingly, a reduction in the flow rate of the hydraulic oil supplied to the traveling motor 8 is suppressed. This suppresses a decrease in the traveling speed of the traveling body 2.

[0027] The temperature sensor 27 detects a hydraulic oil temperature indicating the temperature of the hydraulic oil. In the present embodiment, the temperature sensor 27 detects the temperature of the hydraulic oil flowing from the hydraulic oil tank 12 into the hydraulic pump 11.

[0028] The pressure sensor 28 detects the pressure of the hydraulic oil. In the present embodiment, the pressure sensor 28 detects a pump discharge pressure P indicating the pressure of the hydraulic oil discharged from the discharge port of the hydraulic pump 11 P .

[0029] [Adjustment of LS pressure] FIG. 5 is a diagram showing the relationship between the load pressure P according to the present embodiment L and the differential pressure. In the load sensing system, the LS pressure P corresponding to the pump discharge pressure P P and the load pressure P of the hydraulic actuator L ​LS Based on the pressure difference, the amount of hydraulic fluid discharged from the hydraulic pump 11 is adjusted. Generally, in a load sensing system, the operation of the LS valve 24 adjusts the pump discharge pressure P P LS pressure P LS The discharge rate of the hydraulic fluid discharged from the hydraulic pump 11 is adjusted so that the pressure is higher by a predetermined differential pressure. That is, as shown by line La in Figure 5, the value [P P -P LS The discharge amount of hydraulic fluid discharged from the hydraulic pump 11 is adjusted so that [the value] remains constant.

[0030] In this embodiment, the load pressure P is controlled by the LS introduction aperture 16E, LS introduction aperture 17E, and LS introduction aperture 18E. L LS pressure P LS The output is as follows: In the following explanation, the load pressure P L and LS pressure P LS The differential pressure [P L -P LS This will be referred to as the LS drop amount as appropriate. As shown by line Lb in Figure 5, the load pressure P L As the value increases, the amount of LS drops [P L -P LS ] increases. LS drop amount [P L -P LS As ] increases, the constant value [P] shown by line La increases P -P LS ] of which, LS drop amount [P L -P LS ] increases, and the differential pressure across the work machine operating valve 15 [P P -P L As [P] decreases, the flow rate of hydraulic fluid passing through the work implement operating valve 15 decreases. When the flow rate of hydraulic fluid passing through the work implement operating valve 15 decreases, the operating speed of the work implement 4 decreases. In the hydraulic system 10, the LS introduction throttle (16E, 17E, 18E) controls the appropriate LS drop amount [P L -P LS It is adjusted so that ] is obtained. Appropriate LS drop amount [P L -P LS ] Due to the load pressure P LAs the pressure increases, the operating speed of the implement 4 decreases slightly, resulting in good operability of the implement 4.

[0031] As shown in Figure 3, in this embodiment, the LS introduction aperture 16E, LS introduction aperture 17E, and LS introduction aperture 18E are fixed apertures. The aperture area of ​​each of the LS introduction apertures 16E, LS introduction aperture 17E, and LS introduction aperture 18E does not change. The desired LS drop amount [P L -P LS The LS target aperture 16E, LS target aperture 17E, and LS target aperture 18E are each optimized (selected) so that the desired result is obtained.

[0032] When the hydraulic fluid temperature changes, the viscosity of the hydraulic fluid changes. Therefore, when the hydraulic fluid temperature changes, the LS drop amount [P L -P LS ] fluctuates, and the appropriate LS pressure P LS It may not be possible to obtain the desired result. For example, when the hydraulic fluid temperature rises, the viscosity of the hydraulic fluid decreases, causing the hydraulic fluid to leak from the gap between the valve body and spool of the travel operation valve 13 and the travel operation valve 14, increasing the flow rate through the LS introduction throttle, and the LS drop amount [P L -P LS ] may increase. As shown by line Lc in Figure 5, the same load pressure P L But LS drop amount [P L -P LS When ] increases, the differential pressure [P P -P L ] decreases. The differential pressure across the work machine operating valve 15 [P P -P L If ] decreases, the operating speed of the work implement 4 may decrease. When the hydraulic oil temperature is low, the same load pressure P L But LS drop amount [P L -P LS ] decreases, and the differential pressure [P P -P L ] increases. The differential pressure across the work machine operating valve 15 [P P -P LIf ] increases, the operating speed of work machine 4 may increase, or work machine 4 may hunt. In other words, LS drop amount [P L -P LS If the operating temperature fluctuates due to the hydraulic fluid temperature, the amount of operation of the work lever 32 and the operating speed of the work implement 4 may become mismatched, or the work implement 4 may hunt, potentially worsening the operability of the work implement 4.

[0033] In this embodiment, when the working implement 4 is operated while the traveling body 2 is stopped, the control device 6 controls the load pressure P of the working implement cylinder 5. L LS drop amount [P L -P LS To prevent large fluctuations in the LS drop amount [P], the stroke of the travel communication valve 26 is adjusted based on the hydraulic oil temperature. That is, when the travel operation valve 13 and the travel operation valve 14 are each in the neutral position N, the control device 6 adjusts the stroke of the travel communication valve 26 based on the detection data of the temperature sensor 27 when operating the work machine operation valve 15. By adjusting the stroke of the travel communication valve 26, the opening area of ​​the travel communication valve 26 is adjusted. By changing the stroke of the travel communication valve 26 and changing the opening area of ​​the travel communication valve 26 based on the hydraulic oil temperature, the LS drop amount [P] is adjusted. L -P LS The fluctuation of ] is suppressed. Therefore, even if the hydraulic fluid temperature changes, the desired LS pressure P LS You can obtain this.

[0034] Figures 6 and 7 show the operation of the travel communication valve 26 according to this embodiment. Figure 6 shows the state of the travel communication valve 26 when the hydraulic oil temperature is low. Figure 7 shows the state of the travel communication valve 26 when the hydraulic oil temperature is high.

[0035] As shown in Figure 6, when the hydraulic fluid temperature is low, the control device 6 moves the spool of the travel communication valve 26 to the open position V based on the detection data of the temperature sensor 27 shown in Figure 2. That is, the lower the hydraulic fluid temperature, the larger the opening area of ​​the travel communication valve 26 is made by the control device 6. The travel operation valves 13 and 14 are each positioned in the neutral position N. When the work machine 4 is operated, the load pressure of the work machine cylinder 5 is input to the signal channel 22. The hydraulic fluid in the signal channel 22 flows into the bypass channel 17F via the introduction channel 17C. The hydraulic fluid that has flowed into the bypass channel 17F flows into the fifth port 14E.

[0036] Although the travel control valve 14 is positioned in the neutral position N, the hydraulic fluid that flows into the fifth port 14E is supplied to the sixth port 14F. The travel control valve 14 is a spool valve. Generally, a small gap is provided between the valve body and the spool to allow for smooth sliding of the spool. Due to this gap, even when the travel control valve 14 is positioned in the neutral position N, a small amount of hydraulic fluid leaks out. Therefore, hydraulic fluid is supplied from the fifth port 14E to the sixth port 14F. Since the spool of the travel communication valve 26 is positioned in the open position V, at least a portion of the hydraulic fluid supplied from the introduction passage 17C to the bypass passage 17F is sent to the travel control valve 13 via the travel communication valve 26. The hydraulic fluid sent to the travel control valve 13 flows into the fifth port 13E. The hydraulic fluid that flows into the fifth port 13E is supplied (leaks) to the sixth port 13F.

[0037] At least a portion of the hydraulic fluid supplied from the 5th port 14E to the 6th port 14F is sent to the hydraulic fluid tank 12 via the tank passage 21. Also, any hydraulic fluid leaking from the 5th port 13E to the 6th port 13F is sent to the hydraulic fluid tank 12 via the tank passage 21. In other words, when the spool of the travel communication valve 26 is in the open position V, hydraulic fluid flows out from both the travel operation valve 13 and the travel operation valve 14. This leakage of hydraulic fluid causes an LS drop characteristic.

[0038] As shown in Figure 7, when the hydraulic fluid temperature is high, the control device 6 moves the spool of the travel communication valve 26 to the closed position W based on the detection data of the temperature sensor 27 shown in Figure 2. That is, the higher the hydraulic fluid temperature, the smaller the opening area of ​​the travel communication valve 26 is made by the control device 6. The travel operation valves 13 and 14 are each positioned in the neutral position N. When the work machine 4 is operated, the load pressure of the work machine cylinder 5 is input to the signal channel 22. The hydraulic fluid in the signal channel 22 flows into the bypass channel 17F via the introduction channel 17C. The hydraulic fluid that has flowed into the bypass channel 17F flows into the fifth port 14E.

[0039] The hydraulic fluid that flows into the fifth port 14E leaks into the sixth port 14F. At least a portion of the hydraulic fluid supplied from the fifth port 14E to the sixth port 14F is sent to the hydraulic fluid tank 12 via the tank passage 21. Since the spool of the travel communication valve 26 is in the closed position W, the hydraulic fluid supplied from the fifth port 14E to the sixth port 14F is not supplied to the travel operation valve 13. That is, when the spool of the travel communication valve 26 is in the closed position W, hydraulic fluid flows out from the travel operation valve 14, but not from the travel operation valve 13. Although the outflow of hydraulic fluid causes an LS drop characteristic, the amount of LS drop [P] when the spool of the travel communication valve 26 is in the open position V is... L -P LS It is smaller than ].

[0040] In other words, when the hydraulic fluid temperature is low, hydraulic fluid flows from both the travel control valve 13 and the travel control valve 14 into the hydraulic fluid tank 12. When the hydraulic fluid temperature is high, hydraulic fluid flows from the travel control valve 14 into the hydraulic fluid tank 12, but not from the travel control valve 13 into the hydraulic fluid tank 12. As a result, when the hydraulic fluid temperature is high, the LS drop amount [P L -P LS The increase in ] is suppressed. The control device 6 increases the opening area of ​​the travel communication valve 26 as the hydraulic oil temperature decreases, and decreases the opening area of ​​the travel communication valve 26 as the hydraulic oil temperature increases, thereby reducing the LS drop amount [P L -P LSThis can suppress fluctuations in LS drop amount [P L -P LS By suppressing fluctuations in ], the desired LS pressure P can be maintained even when the hydraulic fluid temperature changes. LS You can obtain this.

[0041] [Travel Communication Valve] Figure 8 is a schematic diagram showing a travel communication valve 26 according to this embodiment. As shown in Figure 8, the travel communication valve 26 has a valve body 34 and a spool 35 that is movable inside the valve body 34. The valve body 34 has an annular recess 36 and an annular recess 37. The annular recess 36 and the annular recess 37 are arranged to surround the spool 35. An inlet 38 for hydraulic fluid is provided on the inner circumference of the annular recess 36, and an outlet 39 for hydraulic fluid is provided on the inner circumference of the annular recess 37.

[0042] Figure 9 is a schematic diagram showing the spool 35 of the travel communication valve 26 according to this embodiment. The spool 35 has a small-diameter rod portion 40, a large-diameter rod portion 41 connected to the right end of the small-diameter rod portion 40, and a large-diameter rod portion 42 connected to the left end of the small-diameter rod portion 40. The outer diameter of the small-diameter rod portion 40 is smaller than the outer diameter of the large-diameter rod portion 41 and the outer shape of the large-diameter rod portion 42. A notch 43 is formed at the left end of the outer circumferential surface of the large-diameter rod portion 41. In the following description, the area of ​​the outer circumferential surface of the large-diameter rod portion 41 to the right of the right end 43A of the notch 43 will be appropriately referred to as the land surface 44.

[0043] Figure 10 is a schematic diagram showing the operation of the travel communication valve 26 according to the embodiment. Figure 10(A) shows the state in which the spool 35 is positioned in the open position V. When the spool 35 is positioned in the open position V, the right end of the small-diameter rod portion 40 and the left end of the large-diameter rod portion 41 face the inlet 38. The hydraulic fluid from the inlet 38 flows around the outer circumferential surface of the small-diameter rod portion 40 and around the outer circumferential surface of the large-diameter rod portion 41, including the notch 43. In the state shown in Figure 10(A), the opening of the travel communication valve 26 through which the hydraulic fluid flows is formed around the outer circumferential surface of the small-diameter rod portion 40 and around the notch 43 of the large-diameter rod portion 41. Note that when the length of the small-diameter rod portion 40 facing the annular recess 36 is maximized, the opening area of ​​the travel communication valve 26 is maximized.

[0044] Figure 10(B) shows the state in which the spool 35 has moved to the left of the position shown in Figure 10(A). As the spool 35 moves to the left, the notch 43 and land surface 44 of the large-diameter rod portion 41 face the inlet 38. In the state shown in Figure 10(B), the opening of the travel communication valve 26 through which the hydraulic fluid flows is formed around the notch 43 of the large-diameter rod portion 41. The opening area of ​​the travel communication valve 26 in the state shown in Figure 10(B) is smaller than the opening area of ​​the travel communication valve 26 in the state shown in Figure 10(A).

[0045] Figure 10(C) shows the state in which the spool 35 has moved to the left of the position shown in Figure 10(B). As the spool 35 moves to the left, the position of the right end 43A of the notch 43 coincides with the position of the left end of the inlet 38. The small-diameter rod portion 40 and the notch 43 no longer face the inlet 38, and the land surface 44 of the large-diameter rod portion 41 faces the entire inlet 38. In the state shown in Figure 10(C), the opening of the travel communication valve 26 through which the hydraulic fluid flows is formed around the land surface 44 of the large-diameter rod portion 41. In the state shown in Figure 10(C), the hydraulic fluid supplied from the inlet 38 to the land surface 44 leaks out through the gap between the large-diameter rod portion 41 and the valve body 34 and then flows to the outlet 39. In the following description, the position of the spool 35 where the position of the right end 43A of the notch 43 of the large-diameter rod portion 41 coincides with the position of the left end of the annular recess 36 will be appropriately referred to as the notch opening closed position X. The flow rate of hydraulic fluid through the travel communication valve 26 in the state shown in Figure 10(C) is less than the flow rate of hydraulic fluid through the travel communication valve 26 in the state shown in Figure 10(B).

[0046] Figure 10(D) shows the state where the spool 35 has moved to the left of the position shown in Figure 10(C). When the spool 35 moves to the left, a gap opening 45 is formed between the land surface 44 of the large-diameter rod portion 41 and the inner circumferential surface of the valve body 34. The hydraulic fluid from the inlet 38 flows into the gap opening 45 formed around the land surface 44 of the large-diameter rod portion 41. The opening of the travel communication valve 26 through which the hydraulic fluid flows includes the gap opening 45. The flow rate of hydraulic fluid leaking from the gap opening 45 decreases as the length Ld of the gap opening 45 increases. The length Ld of the gap opening 45 in the state shown in Figure 10(D) is longer than the length Ld of the gap opening 45 in the state shown in Figure 10(C). The flow rate of hydraulic fluid passing through the travel communication valve 26 in the state shown in Figure 10(D) is less than the flow rate of hydraulic fluid passing through the travel communication valve 26 in the state shown in Figure 10(C).

[0047] Figure 10(E) shows the state in which the spool 35 has moved to the closed position W, which is to the left of the position shown in Figure 10(D). The closed position W is the position in which the spool 35 has reached the stroke end with the land surface 44 of the large-diameter rod portion 41 facing the entire annular recess 36. The length Ld of the gap opening 45 when the spool 35 is in the closed position W is longer than the length Ld of the gap opening 45 in the state shown in Figure 10(D). The flow rate of hydraulic fluid leaking from the gap opening 45 in the state shown in Figure 10(E) is less than the flow rate of hydraulic fluid leaking from the gap opening 45 in the state shown in Figure 10(D). In this embodiment, when the spool 35 is in the closed position W, the flow rate of hydraulic fluid passing through the travel communication valve 26 is minimized.

[0048] Thus, the opening of the travel communication valve 26 through which the hydraulic fluid flows includes a notched opening formed around the small-diameter rod portion 40 and around the notched portion 43 provided on the large-diameter rod portion 41, and a gap opening formed between the large-diameter rod portion 41 and the valve body 34. When the spool 35 moves within a first range of motion between the open position V and the notched opening closed position X, the hydraulic fluid from the inlet 38 flows into the notched opening formed around the small-diameter rod portion 40 and around the notched portion 43 provided on the large-diameter rod portion 41, and flows out from the outlet 39. The opening area becomes smaller as the stroke amount to the left of the spool 35 increases. When the spool 35 moves within a second range of motion between the notched opening closed position X and the closed position W, the hydraulic fluid from the inlet 38 flows into the gap opening 45 formed between the land surface 44 of the large-diameter rod portion 41 and the inner circumferential surface of the valve body 34, leaks out of the gap opening 45, and then flows out from the outlet 39. The flow rate of hydraulic fluid leaking from the gap opening 45 decreases as the stroke amount of the spool 35 to the left increases. In this embodiment, adjusting the stroke of the travel communication valve 26 includes changing the position of the spool 35 in a first movement range between the open position V and the notched opening closed position X, and changing the position of the spool 35 in a second movement range between the notched opening closed position X and the closed position W.

[0049] Figure 11 is a diagram showing the relationship between the hydraulic fluid temperature, the target stroke amount, and the opening area of ​​the travel communication valve 26 according to the embodiment. As shown in the table data on the right side of the graph in Figure 11, multiple specified temperatures T1, T2, T3, and T4 are defined for the hydraulic fluid temperature. In the table data shown in Figure 11, specified temperature T2 is higher than specified temperature T1, specified temperature T3 is higher than specified temperature T1, specified temperature T4 is higher than specified temperature T2, and specified temperature T4 is higher than specified temperature T3. When the travel communication valve 26 is fully open and the hydraulic fluid temperature gradually rises from a low state to reach the specified temperature T2, the travel communication valve 26 begins to close. Between specified temperatures T2 and T4, the opening area of ​​the travel communication valve 26 gradually decreases, and at specified temperature T4 it becomes fully closed. Also, when the travel communication valve 26 is fully closed and the hydraulic fluid temperature gradually falls from a high state to reach the specified temperature T3, the travel communication valve 26 begins to open. Between the specified temperature T3 and the specified temperature T1, the opening area of ​​the travel communication valve 26 gradually increases, and at the specified temperature T1, it becomes fully open. Based on the table data, the control device 6 fully opens the travel communication valve 26 when the hydraulic oil temperature is below the first temperature threshold, the specified temperature T1, and fully closes the travel communication valve 26 when the hydraulic oil temperature is above the second temperature threshold, the specified temperature T4. The fully closed state of the travel communication valve 26 means that the spool 35 of the travel communication valve 26 has reached the stroke end. The state in which the spool 35 has reached the stroke end is the state in which the spool 35 has reached the closed position W.

[0050] As shown in the correlation data on the left side of the graph in Figure 11, in the first movement range between the open position V and the notched opening closed position X, the smaller the stroke amount of the spool 35, the larger the opening area of ​​the travel communication valve 26, and as a result, the flow rate of hydraulic fluid through the travel communication valve 26 increases. In the first movement range, the larger the stroke amount of the spool 35, the smaller the opening area of ​​the travel communication valve 26, and as a result, the flow rate of hydraulic fluid through the travel communication valve 26 decreases. In the second movement range between the notched opening closed position X and the closed position W, the smaller the stroke amount of the spool 35, the smaller the length Ld of the gap opening 45 of the travel communication valve 26 shown in Figure 10(D), and as a result, the flow rate of hydraulic fluid through the travel communication valve 26 increases. In the second movement range, the larger the stroke amount of the spool 35, the larger the length Ld of the gap opening 45 of the travel communication valve 26 shown in Figure 10(D), and as a result, the flow rate of hydraulic fluid through the travel communication valve 26 decreases. The control device 6 can adjust the flow rate of hydraulic fluid through the travel communication valve 26 by controlling the stroke amount of the spool 35 in each of the first and second movement ranges.

[0051] Note that the specified temperature T1 and specified temperature T2 may be equal. The specified temperature T1 and specified temperature T3 may be equal. The specified temperature T2 and specified temperature T4 may be equal. The specified temperature T3 and specified temperature T4 may be equal.

[0052] [Control Method] Figure 12 is a flowchart showing the control method for the hydraulic system 10 according to this embodiment. The control device 6 acquires the amount of operation of the travel lever 31 (step SA1). Based on the amount of operation of the travel lever 31, the control device 6 determines whether or not the hydraulic excavator 1 is moving (step SA2). If it is determined in step SA2 that the hydraulic excavator 1 is moving (step SA2: Yes), the control device 6 determines whether or not the vehicle 2 is steering based on the amount of operation of the travel lever 31 (step SA3).

[0053] In step SA3, if it is determined that the vehicle 2 is steering (step SA3: Yes), the control device 6 outputs a command current to the solenoid valve 33 so that the vehicle communication valve 26 is fully closed (step SA4). As a result of the command current being output to the solenoid valve 33, the spool 35 of the vehicle communication valve 26 is moved to the closed position W, and the vehicle communication valve 26 is fully closed (step SA5). With the vehicle communication valve 26 fully closed, the vehicle 2 can steer stably.

[0054] In step SA3, if it is determined that the vehicle 2 is not steering (step SA3: No), the control device 6 outputs a command current to the solenoid valve 33 so that the vehicle communication valve 26 opens fully (step SA6). When the command current is output to the solenoid valve 33, the spool 35 of the vehicle communication valve 26 is set to the open position V, and the vehicle communication valve 26 opens fully (step SA7). As described above, when the vehicle communication valve 26 opens fully, the difference between the load pressure of the vehicle motor 7 and the load pressure of the vehicle motor 8 becomes smaller, so that the vehicle 2 can move in a straight line stably.

[0055] In step SA2, if it is determined that the hydraulic excavator 1 is not moving (step SA2: No), LS drop control is started (step SA8). The control device 6 acquires the hydraulic fluid temperature. That is, the control device 6 acquires the detection data from the temperature sensor 27 (step SA9).

[0056] The control device 6 determines the target stroke amount of the spool 35 of the travel communication valve 26 based on the hydraulic fluid temperature (step SA10). In this embodiment, the control device 6 determines the target stroke amount of the spool of the travel communication valve 26 based on table data showing the relationship between hydraulic fluid temperature and target stroke amount, as explained with reference to Figure 11. The table data is predetermined. There is a negative correlation between the stroke amount of the spool of the travel communication valve 26 and the opening area of ​​the travel communication valve 26. The larger the stroke amount, the smaller the opening area, and the smaller the stroke amount, the larger the opening area.

[0057] The control device 6 determines the target stroke amount based on the detection data from the temperature sensor 27 and the table data, and then outputs a command current to the solenoid valve 33 based on the target stroke amount (step SA11). The output of the command current to the solenoid valve 33 causes the travel communication valve 26 to stroke, and the opening area of ​​the travel communication valve 26 is adjusted (step SA12). The adjustment of the opening area of ​​the travel communication valve 26 reduces the LS drop amount [P L -P LS The fluctuations in ] are suppressed.

[0058] [effect] As described above, in this embodiment, the stroke of the travel communication valve 26 is adjusted based on the hydraulic fluid temperature. Therefore, even if the hydraulic fluid temperature changes, the LS drop amount [P L -P LS Large fluctuations in ] are suppressed. LS drop amount [P L -P LS By suppressing fluctuations in ], the appropriate LS pressure P LS This is achieved. This suppresses the deterioration of the operability of the work implement 4.

[0059] [Second Embodiment] A second embodiment will now be described. In the following description, the same or equivalent components as those in the above-described embodiment will be denoted by the same reference numerals, and the descriptions of those components will be simplified or omitted.

[0060] Figure 13 is a flowchart showing the control method for the hydraulic system 10 according to this embodiment. Steps SB1 to SB7 are the same as steps SA1 to SA7 described with reference to Figure 12, so their description is omitted.

[0061] In step SB8, the control device 6 acquires the amount of operation of the work lever 32 (step SB8). Based on the amount of operation of the work lever 32, the control device 6 determines whether or not the work implement 4 is operating (step SB9). In step SB9, if it is determined that the work implement 4 is not operating (step SB9: No), the control device 6 performs the processes of step SB6 and step SB7. When the travel motor 7, travel motor 8, and work implement cylinder 5 are not operating, the travel communication valve 26 is fully open. When a command current is input to the solenoid valve 33, pilot pressure is input to the pilot port of the travel communication valve 26, causing the travel communication valve 26 to be fully closed, and when no command current is input to the solenoid valve 33, the travel communication valve 26 is fully opened by the force of the spring. By preventing pilot pressure from being input to the travel communication valve 26 when the travel motor 7, travel motor 8, and work implement cylinder 5 are not operating, pilot oil leakage in the pilot circuit is suppressed. This suppresses the deterioration of the fuel efficiency of the hydraulic excavator 1.

[0062] In step SB9, if it is determined that the work implement 4 is operating (step SB2: Yes), LS drop control is started (step SB10). The control device 6 acquires the hydraulic oil temperature (step SB11). Based on the detection data from the temperature sensor 27 and the table data explained with reference to Figure 10, the control device 6 determines the target stroke amount of the travel communication valve 26 (step SB12). After determining the target stroke amount, the control device 6 outputs a command current to the solenoid valve 33 based on the target stroke amount (step SB13). As a result of the command current being output to the solenoid valve 33, the spool 35 of the travel communication valve 26 strokes, and the opening area of ​​the travel communication valve 26 is adjusted (step SB14). As the opening area of ​​the travel communication valve 26 is adjusted, the LS drop amount [P L -P LS The fluctuations in ] are suppressed.

[0063] [Third Embodiment] The third embodiment will be described. In the following description, components that are the same as or equivalent to those in the above-described embodiment are denoted by the same reference numerals, and descriptions of such components are simplified or omitted.

[0064] FIG. 14 is a flowchart illustrating the control method for the hydraulic system 10 according to the present embodiment. Steps SC1 to SC7 are the same as steps SA1 to SA7 described with reference to FIG. 12, so descriptions thereof are omitted.

[0065] When it is determined in step SC2 that the hydraulic excavator 1 is not traveling (step SC2: No), LS drop control is started (step SC8).

[0066] The control device 6 acquires the hydraulic oil temperature and the pump discharge pressure P P . That is, the control device 6 acquires detection data from the temperature sensor 27 and detection data from the pressure sensor 28 (step SC9). In the present embodiment, the control device 6 adjusts the stroke of the travel communication valve 26 based on the detection data from the temperature sensor 27 and the detection data from the pressure sensor 28. That is, the control device 6, based on the hydraulic oil temperature and the pump discharge pressure P P , determines the target stroke amount of the travel communication valve 26 (step SC10).

[0067] The control device 6 determines the first candidate value for the target stroke amount of the travel communication valve 26 based on the detection data from the temperature sensor 27 and the table data described with reference to FIG. 11. Further, the control device 6 determines the second candidate value for the target stroke amount of the travel communication valve 26 based on pre-defined table data indicating the relationship between the pump discharge pressure P P and the target stroke amount.

[0068] FIG. 15 is a diagram illustrating the relationship among the pump discharge pressure P P , the target stroke amount, and the opening area of the travel communication valve 26. Like the table data shown on the right side of the graph in FIG. 15, the pump discharge pressure P PA plurality of predetermined pressures P1, P2, P3, P4 are defined. In the table data shown in FIG. 15, the predetermined pressure P2 is higher than the predetermined pressure P1, the predetermined pressure P3 is higher than the predetermined pressure P1, the predetermined pressure P4 is higher than the predetermined pressure P2, and the predetermined pressure P4 is higher than the predetermined pressure P3. When the travel communication valve 26 is in a fully open state, the pump discharge pressure P P gradually rises from a low state and reaches the predetermined pressure P2, the travel communication valve 26 starts to close. Between the predetermined pressure P2 and the predetermined pressure P4, the opening area of the travel communication valve 26 gradually decreases, and becomes a fully closed state at the predetermined pressure P4. Further, when the travel communication valve 26 is in a fully closed state, the pump discharge pressure P P gradually decreases from a high state and reaches the predetermined pressure P3, the travel communication valve 26 starts to open. Between the predetermined pressure P3 and the predetermined pressure P1, the opening area of the travel communication valve 26 gradually increases, and becomes a fully open state at the predetermined pressure P1. The control device 6, based on the table data, controls the pump discharge pressure P P to fully open the travel communication valve 26 when it is equal to or less than the predetermined pressure P1 which is the first pressure threshold, and the pump discharge pressure P P to fully close the travel communication valve 26 when it is equal to or higher than the predetermined pressure P4 which is the second pressure threshold. The state where the travel communication valve 26 is in the fully closed state refers to a state where the spool of the travel communication valve 26 has reached the stroke end. The state where the spool 35 has reached the stroke end is a state where the spool 35 has reached the closed position W.

[0069] As shown in the correlation data on the left side of the graph in Figure 15, in the first movement range between the open position V and the notched opening closed position X, the smaller the stroke amount of the spool 35, the larger the opening area of ​​the travel communication valve 26, and as a result, the flow rate of hydraulic fluid through the travel communication valve 26 increases. In the first movement range, the larger the stroke amount of the spool 35, the smaller the opening area of ​​the travel communication valve 26, and as a result, the flow rate of hydraulic fluid through the travel communication valve 26 decreases. In the second movement range between the notched opening closed position X and the closed position W, the smaller the stroke amount of the spool 35, the smaller the length Ld of the gap opening 45 of the travel communication valve 26 shown in Figure 10(D), and as a result, the flow rate of hydraulic fluid through the travel communication valve 26 increases. In the second movement range, the larger the stroke amount of the spool 35, the larger the length Ld of the gap opening 45 of the travel communication valve 26 shown in Figure 10(D), and as a result, the flow rate of hydraulic fluid through the travel communication valve 26 decreases. The control device 6 can adjust the flow rate of hydraulic fluid through the travel communication valve 26 by controlling the stroke amount of the spool 35 in each of the first and second movement ranges.

[0070] Note that the specified pressures P1 and P2 may be equal. The specified pressures P1 and P3 may be equal. The specified pressures P2 and P4 may be equal. The specified pressures P3 and P4 may be equal.

[0071] The control device 6 determines a second candidate value for the target stroke amount based on the detection data from the pressure sensor 28 and the table data described with reference to Figure 15. In Figure 14, the control device 6 determines the first candidate value based on the hydraulic fluid temperature and the pump discharge pressure P P The smaller of the second candidate value determined based on the above is set as the target stroke amount. After determining the target stroke amount, the control device 6 outputs a command current to the solenoid valve 33 based on the target stroke amount (step SC11). As a result of the command current being output to the solenoid valve 33, the travel communication valve 26 strokes, and the opening area of ​​the travel communication valve 26 is adjusted (step SC12). As the opening area of ​​the travel communication valve 26 is adjusted, the LS drop amount [P L -PLS The fluctuations in ] are suppressed.

[0072] When a command current is input to the solenoid valve 33, pilot pressure is input to the pilot port of the travel communication valve 26, causing the travel communication valve 26 to close completely. When no command current is input to the solenoid valve 33, the travel communication valve 26 opens completely due to the force of the spring. P Low LS drop amount [P L -P LS When the effect of fluctuations in [ ] is small, pilot pressure is not input to the travel communication valve 26, thereby suppressing pilot oil leakage in the pilot circuit. This suppresses deterioration of the operability and fuel efficiency of the hydraulic excavator 1. [Explanation of Symbols]

[0073] 1...Hydraulic excavator, 2...Traction unit, 2A...Tracks, 3...Slewing unit, 4...Work implement, 4A...Boom, 4B...Arm, 4C...Bucket, 5...Work implement cylinder, 5A...Boom cylinder, 5B...Arm cylinder, 5C...Bucket cylinder, 6...Control device, 7...Travel motor (1st travel motor), 7A...Port, 7B...Port, 8...Travel motor (2nd travel motor), 8A...Port, 8B...Port, 10...Hydraulic system, 11...Hydraulic pump, 12...Hydraulic oil tank, 13...Travel control valve (1st travel control valve), 13A...1st port, 13B...2nd port, 13C...3rd port, 13D ...Port 4, 13E...Port 5, 13F...Port 6, 13G...Port 7, 13M...Meter-in throttle, 13N...Meter-in throttle, 14...Travel control valve (2nd travel control valve), 14A...Port 1, 14B...Port 2, 14C...Port 3, 14D...Port 4, 14E...Port 5, 14F...Port 6, 14G...Port 7, 14M...Meter-in throttle, 14N...Meter-in throttle, 15...Work equipment control valve, 15A...Port 1, 15B...Port 2, 15C...Port 3, 15D...Port 4, 15E...Port 5, 15F...Port 6, 15G...Port 7 Port, 15M... Meter-in throttle, 15N... Meter-in throttle, 16... Pressure compensation section, 16A... Input port, 16B... Output port, 16C... Inlet channel, 16D... Check valve, 16E... Load sensing inlet throttle (LS inlet throttle), 16S... Pressure compensation valve (first pressure compensation valve), 17... Pressure compensation section, 17A... Input port, 17B... Output port, 17C... Inlet channel, 17D... Check valve, 17E... Load sensing inlet throttle (LS inlet throttle), 17F... Bypass channel, 17G... Bypass throttle, 17S... Pressure compensation valve (second pressure compensation valve), 18... Pressure compensation section, 18A... Input Port, 18B…Output port, 18C…Inlet channel, 18D…Check valve, 18E…Load sensing inlet throttle (LS inlet throttle), 18S…Pressure compensation valve, 19…Pump channel, 20…Connecting channel, 21…Tank channel, 22…Signal channel, 23…Throttle, 24…Load sensing valve (LS valve), 25…Servo piston, 26…Travel communication valve, 27…Temperature sensor, 28…Pressure sensor, 31…Travel lever, 32…Operating lever, 33…Solenoid valve, 34…Valve body, 35…Spool, 36…Annular recess, 37…Annular recess, 38…Inlet, 39…Outlet, 40…Small diameter rod section41...Large diameter rod section, 42...Large diameter rod section, 43...Notch section, 43A...Right end, 44...Land surface, 45...Gap opening, 50A...Port, 50B...Port, A...Fully open position, B...Fully closed position, D...Shortened position, F...Forward position, H...High differential pressure position, L...Low differential pressure position, La...Line, Lb...Line, Lc...Line, Ld...Length, N...Neutral position, P, L ...load pressure, P LS ...LS pressure, P P ...Pump discharge pressure, R...reverse position, U...extended position, Ya...increasing direction, Yb...decreasing direction, V...open position, W...closed position, X...notch opening closed position.

Claims

1. A hydraulic pump that changes the discharge rate of hydraulic fluid based on the differential pressure between the pump discharge pressure and the load sensing pressure corresponding to the load pressure input via the signal channel, A first travel motor driven by the hydraulic fluid supplied from the hydraulic pump, A second travel motor driven by the hydraulic fluid supplied from the hydraulic pump, A work machine cylinder driven by the hydraulic fluid supplied from the hydraulic pump, A first travel operation valve that controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump to the first travel motor, A second travel control valve controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump to the second travel motor, A work machine operating valve that controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump to the work machine cylinder, A first pressure compensation valve is connected to the signal path via a first introduction path and compensates for the differential pressure across the first travel operating valve based on the load sensing pressure, A second pressure compensation valve is connected to the signal path via a second introduction path and compensates for the differential pressure across the second travel control valve based on the load sensing pressure, A bypass channel that bypasses at least a portion of the second introduction channel, A travel communication valve is disposed in a connecting passage that connects the first travel operation valve and the second travel operation valve, A temperature sensor for detecting the hydraulic fluid temperature, which indicates the temperature of the hydraulic fluid, The system includes a control device that adjusts the stroke of the travel communication valve based on the temperature sensor detection data, while the first travel operating valve and the second travel operating valve are each in a neutral position. A type of machinery used for industrial work.

2. The opening area of ​​the travel communication valve is adjusted by adjusting the stroke of the travel communication valve. The control device increases the opening area as the hydraulic fluid temperature decreases, and decreases the opening area as the hydraulic fluid temperature increases. The work machine according to claim 1.

3. The control device fully opens the travel communication valve when the hydraulic oil temperature is below a first temperature threshold, and fully closes the travel communication valve when the hydraulic oil temperature is above a second temperature threshold. The work machine according to claim 1.

4. The system includes a pressure sensor for detecting the pump discharge pressure, The control device adjusts the stroke of the travel communication valve based on the detection data from the temperature sensor and the detection data from the pressure sensor. The work machine according to claim 1.

5. The control device fully opens the travel communication valve when the pump discharge pressure is below a first pressure threshold, and fully closes the travel communication valve when the pump discharge pressure is above a second pressure threshold. The work machine according to claim 4.

6. The control device adjusts the stroke of the travel communication valve when operating the work machine operating valve. The work machine according to claim 1.

7. The aforementioned travel communication valve comprises a valve body and a spool that is movable inside the valve body. The spool has a small-diameter rod portion and a large-diameter rod portion connected to the small-diameter rod portion. The opening of the travel communication valve through which the hydraulic fluid flows includes a notched opening formed around the small-diameter rod portion and around the notched portion provided on the large-diameter rod portion, and a gap opening formed between the large-diameter rod portion and the valve body. The spool moves within a first range of movement in which the hydraulic fluid from the inlet of the valve body flows into the notched opening, and within a second range of movement in which the hydraulic fluid from the inlet flows into the gap opening. Adjusting the stroke of the travel communication valve includes changing the position of the spool in the first range of movement and changing the position of the spool in the second range of movement. The work machine according to claim 1.

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