Work machine

Abstract

A work machine includes: a hydraulic pump configured to change a discharge amount of hydraulic oil based on a differential pressure between a pump discharge pressure and a load sensing pressure corresponding to a load pressure input via a signal flow path; a first travel motor configured to be driven by the hydraulic oil supplied from the hydraulic pump; a second travel motor configured to be driven by the hydraulic oil supplied from the hydraulic pump; a work implement cylinder configured to be driven by the hydraulic oil supplied from the hydraulic pump; a first travel control valve configured to control a flow rate and a direction of the hydraulic oil supplied from the hydraulic pump to the first travel motor;a second travel control valve configured to control a flow rate and direction of hydraulic oil supplied from the hydraulic pump to the second travel motor; a work implement control valve configured to control a flow rate and direction of hydraulic oil supplied from the hydraulic pump to the work implement cylinder; a first pressure compensation valve connected to the signal flow path via a first inlet flow path, the first pressure compensation valve configured to compensate for a differential pressure across the first travel control valve based on the load sensing pressure; a second pressure compensation valve connected to the signal flow path via a second inlet flow path, the second pressure compensation valve configured to compensate for a differential pressure across the second travel control valve based on the load sensing pressure;a bypass flow path configured to bypass at least a portion of the second inlet flow path; a travel communication valve disposed on a coupling flow path coupling the first travel operation valve and the second travel operation valve; a temperature sensor configured to detect a hydraulic oil temperature indicative of a temperature of the hydraulic oil; and a controller configured to adjust a stroke of the travel communication valve based on detection data from the temperature sensor in a state where both the first travel operation valve and the second travel operation valve are disposed in a neutral position.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a work machine. STATE OF THE ART

[0002] In technical fields related to work machines, a work machine including a load sensing control circuit, such as a work machine disclosed in Patent Document 1, is known. In a load sensing system, the discharge amount of hydraulic oil from a hydraulic pump is adjusted based on a differential pressure between a discharge pressure of the hydraulic oil from the hydraulic pump and a load sensing pressure (LS pressure) corresponding to a load pressure of a hydraulic actuator. In addition, an LS loss characteristic is known in which the LS pressure decreases as the load pressure increases. List of citationsPatent literature

[0003] Patent Document 1: JP 2006-336730 A SUMMARY OF THE INVENTIONTechnical Problem

[0004] In the load sensing system, an LS drop amount is set through an LS input throttle, which indicates the amount of load pressure reduction. As the temperature of the hydraulic oil changes, the viscosity of the hydraulic oil changes. As a result, the LS drop amount may fluctuate. If the LS drop amount fluctuates, a suitable LS pressure may not be achieved. If the suitable LS pressure is not achieved, the operability of the work equipment may deteriorate. For example, the operating amount of a work lever and the operating speed of the work equipment may not match, or a work equipment search may occur.

[0005] An object of the present disclosure is to suppress deterioration of the operability of working devices. Solution to the problem

[0006] According to the present invention, there is provided a work machine including: a hydraulic pump configured to change a discharge amount of hydraulic oil based on a differential pressure between a pump discharge pressure and a load sensing pressure corresponding to a load pressure input via a signal flow path; a first travel motor configured to be driven by the hydraulic oil supplied from the hydraulic pump; a second travel motor configured to be driven by the hydraulic oil supplied from the hydraulic pump; a work implement cylinder configured to be driven by the hydraulic oil supplied from the hydraulic pump; a first travel control valve configured to control a flow rate and a direction of the hydraulic oil supplied from the hydraulic pump to the first travel motor;a second travel control valve configured to control a flow rate and direction of hydraulic oil supplied from the hydraulic pump to the second travel motor; a work implement control valve configured to control a flow rate and direction of hydraulic oil supplied from the hydraulic pump to the work implement cylinder; a first pressure compensation valve connected to the signal flow path via a first inlet flow path, the first pressure compensation valve configured to compensate for a differential pressure across the first travel control valve based on the load sensing pressure; a second pressure compensation valve connected to the signal flow path via a second inlet flow path, the second pressure compensation valve configured to compensate for a differential pressure across the second travel control valve based on the load sensing pressure;a bypass flow path configured to bypass at least a portion of the second inlet flow path; a travel communication valve disposed on a coupling flow path coupling the first travel operation valve and the second travel operation valve; a temperature sensor configured to detect a hydraulic oil temperature indicative of a temperature of the hydraulic oil; and a controller configured to adjust a stroke of the travel communication valve based on detection data from the temperature sensor in a state where both the first travel operation valve and the second travel operation valve are disposed in a neutral position. Advantageous effects of the invention

[0007] According to the present disclosure, deterioration of the operability of working equipment is suppressed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view illustrating a work machine according to a first embodiment. Fig. 2 is a diagram illustrating a hydraulic system of the working machine according to the first embodiment. Fig. 3 is an enlarged view of a part of the hydraulic system according to the first embodiment. Fig. 4 is a block diagram schematically illustrating the hydraulic system according to the first embodiment. Fig. 5 is a diagram showing a relationship between a load pressure and a differential pressure according to the first embodiment. Fig. 6 is a diagram illustrating an operation of a driving communication valve according to the first embodiment. Fig. 7 is a diagram illustrating an operation of the travel communication valve according to the first embodiment. Fig. 8 is a diagram schematically illustrating the driving communication valve according to the first embodiment. Fig. 9 is a diagram schematically illustrating a spool of the travel communication valve according to the first embodiment. Fig. 10 is a diagram schematically illustrating an operation of the travel communication valve according to the first embodiment. Fig. 11 is a diagram showing table data indicating a relationship between a hydraulic oil temperature, a target lift amount, and an opening area of the travel communication valve according to the first embodiment. Fig. 12 is a flowchart illustrating a control method of the hydraulic system according to the first embodiment. Fig. 13 is a flowchart illustrating a control method of the hydraulic system according to a second embodiment. Fig. 14 is a flowchart illustrating a control method of the hydraulic system according to a third embodiment. Fig. 15 is a diagram showing table data indicating a relationship between a pump discharge pressure, a target lift amount, and an opening area of a travel communication valve according to the third embodiment. DESCRIPTION OF EMBODIMENTS

[0008] Embodiments of the disclosure will be described below with reference to the drawings, but the disclosure is not limited to the embodiments. Components of the embodiments described below can be combined arbitrarily. Furthermore, in some cases, some components may not be used. First embodimentWorking machine

[0009] A first embodiment is described. Fig. 1 is a perspective view illustrating a work machine 1 according to the present embodiment. The work machine 1 is operated on a construction site. In the present embodiment, the work machine 1 is a hydraulic excavator. In the following description, the work machine 1 will be appropriately referred to as a hydraulic excavator 1. The hydraulic excavator 1 includes a traveling body 2, a rotating body 3, a working implement 4, a working implement cylinder 5, and a control device 6. The traveling body 2 travels while supporting the rotating body 3. The traveling body 2 includes a pair of crawler tracks 2A. The crawler tracks 2A are rotated by a traveling motor. The crawler tracks 2A are rotated, and thereby the traveling body 2 travels. The rotating body 3 is supported by the traveling body 2. The rotating body 3 is provided with a cab. The working implement 4 is attached to the rotating body 3.The work tool 4 includes a boom 4A, an arm 4B, and a bucket 4C. The work tool cylinder 5 operates the work tool 4. The work tool cylinder 5 is a hydraulic cylinder. The work tool 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. hydraulic system

[0010] Fig. 2 is a diagram illustrating a hydraulic system 10 of the hydraulic excavator 1 according to the present embodiment. Fig. 3 is an enlarged view of a part of the hydraulic system 10 according to the present embodiment. Fig. Figure 4 is a block diagram schematically illustrating the hydraulic system 10 according to the present embodiment. The hydraulic system 10 includes a load sensing control circuit.

[0011] The hydraulic system 10 includes a hydraulic pump 11, a hydraulic oil tank 12, a travel motor 7, a travel motor 8, the implement cylinder 5, a travel control valve 13, a travel control valve 14, an implement control valve 15, a pressure compensation unit 16 with a pressure compensation valve 16S, a pressure compensation unit 17 with a pressure compensation valve 17S, a pressure compensation unit 18 with 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.

[0012] The hydraulic pump 11 is a variable-displacement hydraulic pump. An outlet port of the hydraulic pump 11 is connected to a pump flow path 19. The hydraulic pump 11 changes a discharge amount of hydraulic oil based on a differential pressure between a pump discharge pressure and a load sensing pressure (LS pressure) corresponding to a load pressure input via a signal flow path 22. The pump discharge pressure refers to the pressure of the hydraulic oil discharged from the discharge port of the hydraulic pump 11.

[0013] As in Fig. 2 and Fig. 3, the travel motor 7 is a hydraulic motor driven by the hydraulic oil supplied from the hydraulic pump 11. The travel motor 7 rotates the left crawler belt 2A. The travel control valve 13 controls the flow rate and a direction of the hydraulic oil supplied from the hydraulic pump 11 to the travel motor 7. The travel control valve 13 includes 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 outlet port of the hydraulic pump 11 via the pump flow path 19. The second port 13B is connected to one port 7A of the travel motor 7. The third port 13C is connected to another port 7B of the travel motor 7. The fourth port 13D is connected to an input port 16A of the pressure compensating valve 16S.The fifth port 13E is connected to an output port 16B of the pressure relief valve 16S. The fifth port 13E is connected to the travel communication valve 26 via a coupling flow path 20. Both the sixth port 13F and the seventh port 13G are connected to the hydraulic oil tank 12 via a tank flow path 21.

[0014] As in Fig. As illustrated in Figure 4, the hydraulic excavator 1 includes a travel lever 31. The travel lever 31 is arranged in the cabin of the rotating body 3. The travel lever 31 is operated by an operator. Pilot ports are provided at both end portions of the travel control valve 13. Based on an operation amount of the travel lever 31, pilot pressures are input to the pilot ports of the travel control valve 13. As shown in Fig. 2 and Fig. As illustrated in Fig. 3, in a state where the pilot pressures are not input, the travel control valve 13 is arranged in a neutral position N in which the hydraulic oil is not supplied to the travel motor 7. The pilot pressure is input to the pilot port at one end portion of the travel control valve 13, and thus the travel control valve 13 is arranged in a forward position F to cause the traveling body 2 to travel forward. When the travel control valve 13 is in the forward position F, the hydraulic oil flows from the hydraulic pump 11 into the port 7A of the travel motor 7 via the first port 13A, an inlet throttle 13M, the fourth port 13D, the pressure compensation valve 16S, the fifth port 13E and the second port 13B. The hydraulic oil flowing from the port 7B of the travel motor 7 is sent to the hydraulic oil tank 12 via the third port 13C, the sixth port 13F and the tank flow path 21.The pilot pressure is input to the pilot port at the other end portion of the travel control valve 13, and thus the travel control valve 13 is arranged in a reverse position R to cause the traveling body 2 to travel backward. When the travel control valve 13 is in the reverse position R, the hydraulic oil from the hydraulic pump 11 flows into the port 7B of the travel motor 7 via the first port 13A, an inlet throttle 13N, the fourth port 13D, the pressure relief valve 16S, the fifth port 13E, and the third port 13C. The hydraulic oil flowing from the port 7A of the travel motor 7 is sent to the hydraulic oil tank 12 via the second port 13B, the seventh port 13G, and the tank flow path 21.

[0015] As in Fig. 2 and Fig. 3, the travel motor 8 is a hydraulic motor driven by the hydraulic oil supplied from the hydraulic pump 11. The travel motor 8 rotates the right crawler belt 2A. The travel control valve 14 controls a flow rate and direction of the hydraulic oil supplied from the hydraulic pump 11 to the travel motor 8. The travel control valve 14 includes 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 outlet port of the hydraulic pump 11 via the pump flow path 19. The second port 14B is connected to one port 8A of the travel motor 8. The third port 14C is connected to another port 8B of the travel motor 8. The fourth port 14D is connected to an input port 17A of the pressure compensation valve 17S.The fifth port 14E is connected to an output port 17B of the pressure relief valve 17S. The fifth port 14E is connected to the travel communication valve 26 via the coupling flow path 20. Both the sixth port 14F and the seventh port 14G are connected to the hydraulic oil tank 12 via the tank flow path 21.

[0016] Based on the operating amount of the travel lever 31, pilot pressures are input into pilot ports of the travel control valve 14. As shown in Fig. 2 and Fig. As illustrated in Fig. 3, in a state where the pilot pressures are not input, the travel control valve 14 is arranged in a neutral position N in which the hydraulic oil is not supplied to the travel motor 8. The pilot pressure is input to the pilot port at one end portion of the travel control valve 14, and thus the travel control valve 14 is arranged in a forward position F to cause the traveling body 2 to travel forward. When the travel control valve 14 is in the forward position F, the hydraulic oil flows from the hydraulic pump 11 into the port 8A of the travel motor 8 via the first port 14A, an inlet throttle 14M, the fourth port 14D, the pressure compensation valve 17S, the fifth port 14E and the second port 14B. The hydraulic oil flowing from the port 8B of the travel motor 8 is sent to the hydraulic oil tank 12 via the third port 14C, the sixth port 14F and the tank flow path 21.The pilot pressure is input to the pilot port at the other end portion of the travel control valve 14, and thus the travel control valve 14 is arranged in a reverse position R to cause the traveling body 2 to travel backward. When the travel control valve 14 is in the reverse position R, the hydraulic oil from the hydraulic pump 11 flows into the port 8B of the travel motor 8 via the first port 14A, an inlet throttle 14N, the fourth port 14D, the pressure relief valve 17S, the fifth port 14E, and the third port 14C. The hydraulic oil flowing from the port 8A of the travel motor 8 is sent to the hydraulic oil tank 12 via the second port 14B, the seventh port 14G, and the tank flow path 21.

[0017] As in Fig. 2 and Fig. 3, the work implement cylinder 5 is a hydraulic cylinder driven by the hydraulic oil supplied from the hydraulic pump 11. The work implement control valve 15 controls a flow rate and direction of the hydraulic oil supplied from the hydraulic pump 11 to the work implement cylinder 5. The work implement control valve 15 includes 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 outlet port of the hydraulic pump 11 via the pump flow path 19. The second port 15B is connected to a port 50A of the work implement cylinder 5. The third port 15C is connected to another port 50B of the work implement cylinder 5. The fourth port 13D is connected to an input port 18A of the pressure compensation valve 18S.The fifth port 15E is connected to an output port 18B of the pressure compensating valve 18S. Both the sixth port 15F and the seventh port 15G are connected to the hydraulic oil tank 12 via the tank flow path 21.

[0018] As in Fig. As shown in Figure 4, the hydraulic excavator 1 includes a working lever 32. The working lever 32 is arranged in the cab of the rotating body 3. The working lever 32 is operated by the operator. Pilot pressures are input to both end portions of the working tool operating valve 15. Pilot ports are provided at both end portions of the working tool operating valve 15. Based on an operating amount of the working lever 32, the pilot pressures are input to the pilot ports of the working tool operating valve 15. As shown in Fig. 2 and Fig. 3, in a state where the pilot pressures are not input, the work implement operating valve 15 is arranged in a neutral position N in which the hydraulic oil is not supplied to the work implement cylinder 5. The pilot pressure is input to the pilot port at one end portion of the work implement operating valve 15, and thus the work implement operating valve 15 is arranged in an extension position U for extending the work implement cylinder 5. When the work implement operating valve 15 is in the extension position U, the hydraulic oil from the hydraulic pump 11 flows into the port 50A of the work implement cylinder 5 via the first port 15A, an inlet throttle 15M, the fourth port 15D, the pressure relief valve 18S, the fifth port 15E, and the second port 15B.The hydraulic oil flowing from the port 50B of the working implement cylinder 5 is sent to the hydraulic oil tank 12 via the third port 15C, the sixth port 15F, and the tank flow path 21. The pilot pressure is input to the pilot port at the other end portion of the working implement operating valve 15, and thus the working implement operating valve 15 is arranged in a retraction position D for retracting the working implement cylinder 5. When the work implement operating valve 15 is in the retract position D, the hydraulic oil flows from the hydraulic pump 11 into the port 50B of the work implement cylinder 5 via the first port 15A, an inlet throttle 15N, the fourth port 15D, the pressure compensating valve 18S, the fifth port 15E, and the third port 15C. The hydraulic oil flowing from the port 50A of the work implement cylinder 5 is sent to the hydraulic oil tank 12 via the second port 15B, the seventh port 15G, and the tank flow path 21.

[0019] The pressure compensation unit 16 includes the pressure compensation valve 16S, an inlet flow path 16C connecting the output port 16B of the pressure compensation valve 16S and the signal flow path 22, a check valve 16D disposed on the inlet flow path 16C, and a charge detection input throttle 16E (LS input throttle) disposed on the inlet flow path 16C. The pressure compensation valve 16S is connected to the signal flow path 22 via the inlet flow path 16C. The pressure compensation valve 16S compensates for a differential pressure across the travel control valve 13 based on an LS pressure input from the signal flow path 22. The pressure compensation valve 16S receives the LS pressure input from the signal flow path 22 to a pilot port of the pressure compensation valve 16S and operates to keep the differential pressure across the travel control valve 13 constant.The pressure equalization valve 16S moves between a fully open position A and a fully closed position B.

[0020] The pressure compensation unit 17 includes the pressure compensation valve 17S, an inlet flow path 17C connecting the output port 17B of the pressure compensation valve 17S and the signal flow path 22, a check valve 17D disposed on the inlet flow path 17C, and a charge detection input throttle 17E (LS input throttle) disposed on the inlet flow path 17C. The pressure compensation unit 17 also includes a bypass flow path 17F bypassing at least a portion of the inlet flow path 17C, and a bypass throttle 17G disposed on the bypass flow path 17F. The pressure compensation valve 17S is connected to the signal flow path 22 via the inlet flow path 17C. The pressure compensation valve 17S compensates for a differential pressure across the travel control valve 14 based on the LS pressure input from the signal flow path 22.The pressure compensating valve 17S receives the LS pressure input from the signal flow path 22 to a pilot port of the pressure compensating valve 17S and operates to maintain a constant differential pressure across the travel control valve 14. The pressure compensating valve 17S moves between a fully open position A and a fully closed position B.

[0021] The pressure compensation unit 18 includes the pressure compensation valve 18S, an inlet flow path 18C connecting the input port 18A of the pressure compensation valve 18S and the signal flow path 22, a check valve 18D disposed on the inlet flow path 18C, and a charge detection input throttle 18E (LS input throttle) disposed on the inlet flow path 18C. The pressure compensation valve 18S is connected to the signal flow path 22 via the inlet flow path 18C. The pressure compensation valve 18S compensates for a differential pressure across the implement control valve 15 based on the LS pressure input from the signal flow path 22. The pressure compensation valve 18S receives the LS pressure input from the signal flow path 22 to a pilot port of the pressure compensation valve 18S and operates to maintain the differential pressure across the implement control valve 15 constant.The pressure equalization valve 18S moves between a fully open position A and a fully closed position B.

[0022] A pressure corresponding to the highest load pressure from a load pressure of the travel motor 7, a load pressure of the travel motor 8 and a load pressure of the working device cylinder 5 is called LS pressure P LS to the signal flow path 22. Part of the hydraulic oil supplied to the signal flow path 22 is sent to the hydraulic oil tank 12 via a throttle 23. The LS pressure P LS , which is led to the signal flow path 22, is also led to the LS valve 24.

[0023] As in Fig. 2, the LS valve 24 adjusts the discharge amount of hydraulic oil discharged from the hydraulic pump 11 based on a differential pressure between a pump discharge pressure P P and the LS pressure P LSwhich was input from the signal flow path 22. The servo piston 25 is connected to the hydraulic pump 11. The LS valve 24 adjusts the discharge amount of hydraulic oil from the hydraulic pump 11 via the servo piston 25. The LS valve 24 moves to a neutral position N, a low differential pressure position L, and a high differential pressure position H. When the differential pressure between the pump discharge pressure P P and the LS pressure P LSacting on the LS valve 24 is low, the LS valve 24 moves to the low differential pressure position L. When the LS valve 24 is in the low differential pressure position L, the hydraulic oil of the servo piston 25 is sent to the hydraulic oil tank 12 and the servo piston 25 moves in an increasing direction Ya to increase the capacity of the hydraulic pump 11. The capacity of the hydraulic pump 11 increases and thus the discharge amount of hydraulic oil from the hydraulic pump 11 increases. When the differential pressure between the pump discharge pressure P P and the LS pressure P LSacting on the LS valve 24 is high, the LS valve 24 moves to the high differential pressure position H. When the LS valve 24 is in the high differential pressure position H, a portion of the hydraulic oil discharged from the hydraulic pump 11 is introduced into the servo piston 25, and the servo piston 25 moves in a decreasing direction Yb to reduce the capacity of the hydraulic pump 11. The capacity of the hydraulic pump 11 decreases, and thus the discharge amount of hydraulic oil from the hydraulic pump 11 decreases.

[0024] The travel communication valve 26 is arranged on the coupling flow path 20. The coupling flow path 20 connects the fifth port 13E of the travel control valve 13 to the fifth port 14E of the travel control valve 14. A spool of the travel communication valve 26 moves between an open position V, in which the flow of hydraulic oil between the travel control valve 13 and the travel control valve 14 is permitted, and a closed position W, in which the flow of hydraulic oil between the travel control valve 13 and the travel control valve 14 is blocked. An electromagnetic valve 33 is connected to the travel communication valve 26. The control device 6 can move the spool of the travel communication valve 26 to the open position V and the closed position W by controlling the electromagnetic valve 33. The control device 6 controls the travel communication valve 26 based on an operating state of the travel lever 31.When the travel lever 31 is operated to make the hydraulic excavator 1 travel straight, the control device 6 moves the spool of the travel communication valve 26 to the open position V. Even when the travel lever 31 is operated to make the hydraulic excavator 1 travel straight, for example, the rotational speed of the travel motor 7 and the rotational speed of the travel motor 8 may be different due to a manufacturing defect or the like in at least one of the travel motor 7 and the travel motor 8. The spool of the travel communication valve 26 moves to the open position V when the hydraulic excavator 1 travels straight, and thus, a difference between the load pressure of the travel motor 7 and the load pressure of the travel motor 8 decreases. Accordingly, the hydraulic excavator 1 can travel straight appropriately. 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 vehicle 2 means that the vehicle 2 changes its direction of travel (travels around a curve).

[0025] The bypass flow path 17F is provided to suppress a reduction in the traveling speed of the traveling body 2 when the working device 4 is operated in a state where the traveling body 2 is traveling. When the working device operation valve 15 is activated so that the working device cylinder 5 operates, a phenomenon may occur in which the flow rate of the hydraulic oil supplied to the traveling motor 7 and the traveling motor 8 decreases and the traveling speed of the traveling body 2 decreases. When the working device 4 is operated in a state where the traveling body 2 is traveling, the load pressure of the working device 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 working device cylinder 5 is higher than the load pressures of the traveling motor 7 and the traveling motor 8, the high LS pressure P LS, which corresponds to the load pressure of the working device cylinder 5, which is the highest pressure, is input to each of the pressure compensating valve 16S and the pressure compensating valve 17S and is also input to the LS valve 24. When the LS pressure P LS from the signal flow path 22 into the pressure compensating unit 17, at least a portion of the hydraulic oil flowing from the signal flow path 22 into the pressure compensating unit 17 can flow through the bypass flow path 17F. As a result, the pressure in the signal flow path 22 and the pressure acting from the signal flow path 22 on the pilot port of the pressure compensating valve 17S decrease. Therefore, a decrease in the flow rate of the hydraulic oil supplied to the travel motor 8 is suppressed. Thus, a decrease in the travel speed of the traveling body 2 is suppressed.

[0026] The temperature sensor 27 detects a hydraulic oil temperature, which indicates 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.

[0027] The pressure sensor 28 detects the pressure of the hydraulic oil. In the present embodiment, the pressure sensor 28 detects the pump outlet pressure P P , which indicates the pressure of the hydraulic oil discharged from the outlet port of the hydraulic pump 11. Adjusting the LS pressure

[0028] Fig. Fig. 5 is a diagram showing a relationship between a load pressure and a differential pressure according to the present embodiment. In a load detection system, the discharge amount of hydraulic oil discharged from the hydraulic pump 11 is determined based on the differential pressure between the pump discharge pressure P P and the LS pressure P LS, which corresponds to the load pressure P L of a hydraulic actuator. Generally, in the load sensing system, the discharge amount of hydraulic oil discharged from the hydraulic pump 11 is adjusted by activating the LS valve 24 so that the pump discharge pressure P P is higher by a predetermined differential pressure than the LS pressure P LS That is, as by a line La in Fig. 5, the discharge amount of hydraulic oil discharged from the hydraulic pump 11 is adjusted so that a value [P P - P LS] becomes constant.

[0029] In the present embodiment, the LS pressure P LS , which corresponds to the load pressure P L corresponds to, is output from the LS input throttle 16E, the LS input throttle 17E and the LS input throttle 18E. In the following description, the differential pressure [P L - P LS] between the load pressure P L and the LS pressure P LSappropriately referred to as LS waste amount. As shown by a line Lb in Fig. 5, a LS waste amount [P P - P LS ] when the load pressure P L increases. If the LS waste amount [P L -P LS ] increases, the LS waste amount [P L -P LS ] and a differential pressure [P P -P L ] above the implement control valve 15 decreases by the constant value [P P -P LS ] indicated by the line La, so that the flow rate of the hydraulic oil flowing through the implement control valve 15 decreases. When the flow rate of the hydraulic oil flowing through the implement control valve 15 decreases, the operating speed of the implement 4 decreases. In the hydraulic system 10, adjustment is made by the LS input throttles (16E, 17E, 18E) so that the appropriate LS drop amount [P L -P LS] is obtained. Due to the appropriate LS waste amount [P L -P LS ] a property is obtained which consists in that the operating speed of the working device 4 decreases slightly when the load pressure P L increases, thereby achieving a favorable operability of the working device 4.

[0030] As in Fig. 3, in the present embodiment, the LS input reactor 16E, the LS input reactor 17E, and the LS input reactor 18E are each fixed reactors. An opening area of each of the LS input reactor 16E, the LS input reactor 17E, and the LS input reactor 18E does not change. Each of the LS input reactor 16E, the LS input reactor 17E, and the input reactor 18E is optimized (selected) to achieve the desired LS drop amount [P L -P LS ] to obtain.

[0031] When the temperature of the hydraulic oil changes, the viscosity of the hydraulic oil changes. Therefore, when the hydraulic oil temperature changes, the LS drop amount [P L -P LS ] fluctuate, and the appropriate LS pressure P LS may not be obtained. For example, when the temperature of the hydraulic oil becomes high, the viscosity of the hydraulic oil may decrease, the hydraulic oil may leak from a gap between a valve body and a spool of each of the travel control valve 13 and the travel control valve 14, the flow rate of the hydraulic oil flowing through the LS input throttle may increase, and the LS drop amount [P L -P LS ] can increase. As shown by a line Lc in Fig. 5, even at the same load pressure P L , if the LS waste amount [P L -P LS ] increases, the differential pressure [P P -P L ] across the valve. If the differential pressure [PP - P L ] across the implement control valve 15 decreases, the operating speed of the implement 4 may decrease. When the hydraulic oil temperature becomes low, the LS drop amount [P L - P LS] and the differential pressure [P P - P L ] above the valve increases even at the same load pressure P L . If the differential pressure [P P - P L ] above the implement control valve 15 increases, the operating speed of the implement 4 may increase or a search of the implement 4 may occur. That is, when the LS drop amount [P L - P LS] fluctuates according to the hydraulic oil temperature, the operability of the working device 4 may deteriorate. For example, the operating amount of the working lever 32 and the operating speed of the working device 4 may not match, or a search of the working device 4 may occur.

[0032] In the present embodiment, the control device 6 adjusts a stroke of the traveling communication valve 26 based on the hydraulic oil temperature when the working machine 4 is operated in a state where the traveling body 2 is stopped, so that the LS drop amount [P L - P LS] for the load pressure P Lof the working implement cylinder 5 does not fluctuate greatly. That is, when the working implement operation valve 15 is activated in a state where 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 detection data from the temperature sensor 27. An opening area of the travel communication valve 26 is adjusted by adjusting the stroke of the travel communication valve 26. Based on the hydraulic oil temperature, the stroke of the travel communication valve 26 is changed and the opening area of the travel communication valve 26 is changed. Thus, a fluctuation in the LS drop amount [P L - P LS] suppressed. Therefore, even if the hydraulic oil temperature changes, the desired LS pressure P LS be obtained.

[0033] Fig. 6 and Fig. 7 are diagrams each illustrating an operation of the travel communication valve 26 according to the present embodiment. Fig. 6 illustrates a state of the travel communication valve 26 when the hydraulic oil temperature is low. Fig. 7 illustrates a state of the travel communication valve 26 when the hydraulic oil temperature is high.

[0034] As in Fig. 6, when the hydraulic oil temperature is low, the control device 6 moves the spool of the travel communication valve 26 based on the detection data of the Fig. 2 to the open position V. That is, as the hydraulic oil temperature decreases, the control device 6 increases the opening area of the travel communication valve 26. Both the travel operation valve 13 and the travel operation valve 14 are in the neutral position N. The work implement 4 is operating, and therefore, the load pressure of the work implement cylinder 5 is input to the signal flow path 22. The hydraulic oil in the signal flow path 22 flows into the bypass flow path 17F via the inlet flow path 17C. The hydraulic oil flowing into the bypass flow path 17F flows into the fifth port 14E.

[0035] Although the travel operation valve 14 is in the neutral position N, the hydraulic oil flowing into the fifth port 14E is supplied to the sixth port 14F. The travel operation valve 14 is a spool valve. Generally, a small gap is provided between a valve body and a spool to allow the spool to slide smoothly. Due to this gap, a small amount of hydraulic oil leaks even when the travel operation valve 14 is in the neutral position N. Therefore, the hydraulic oil is supplied from the fifth port 14E to the sixth port 14F. Since the spool of the travel communication valve 26 is in the open position V, at least a portion of the hydraulic oil supplied from the inlet flow path 17C to the bypass flow path 17F is sent to the travel operation valve 13 via the travel communication valve 26. The hydraulic oil sent to the travel operation valve 13 flows into the fifth port 13E.The hydraulic oil flowing into the fifth port 13E is fed to the sixth port 13F (leaks there).

[0036] At least a portion of the hydraulic oil supplied from the fifth port 14E to the sixth port 14F is sent to the hydraulic oil tank 12 via the tank flow path 21. The hydraulic oil discharged from the fifth port 13E to the sixth port 13F is also sent to the hydraulic oil tank 12 via the tank flow path 21. That is, when the spool of the travel communication valve 26 is in the open position V, the hydraulic oil flows out from both the travel control valve 13 and the travel control valve 14. The outflow of the hydraulic oil creates an LS drop characteristic.

[0037] As in Fig. 7, when the hydraulic oil temperature is high, the control device 6 moves the spool of the travel communication valve 26 based on the detection data of the Fig. 2 to the closed position W. That is, as the hydraulic oil temperature increases, the control device 6 reduces the opening area of the travel communication valve 26. Both the travel operation valve 13 and the travel operation valve 14 are in the neutral position N. The work implement 4 is operating, and therefore, the load pressure of the work implement cylinder 5 is input to the signal flow path 22. The hydraulic oil in the signal flow path 22 flows into the bypass flow path 17F via the inlet flow path 17C. The hydraulic oil flowing into the bypass flow path 17F flows into the fifth port 14E.

[0038] The hydraulic oil flowing into the fifth port 14E leaks into the sixth port 14F. At least a portion of the hydraulic oil supplied from the fifth port 14E to the sixth port 14F is sent to the hydraulic oil tank 12 via the tank flow path 21. Since the spool of the travel communication valve 26 is in the closed position W, the hydraulic oil 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, the hydraulic oil flows out of the travel operation valve 14, but the hydraulic oil does not flow out of the travel operation valve 13.

[0039] Although the flow out of the hydraulic oil causes the LS drop property, this LS drop amount is smaller than the LS drop amount [P L - P LS]when the spool of the travel communication valve 26 is arranged in the open position V.

[0040] That is, when the hydraulic oil temperature is low, the hydraulic oil flows from each of the travel control valve 13 and the travel control valve 14 to the hydraulic oil tank 12.

[0041] When the hydraulic oil temperature is high, the hydraulic oil flows from the travel control valve 14 into the hydraulic oil tank 12, and the hydraulic oil does not flow from the travel control valve 13 into the hydraulic oil tank 12. When the hydraulic oil temperature is high, an increase in the LS drop amount [P L - P LS] suppressed. The control device 6 can detect a fluctuation in the LS drop amount [P L - P LS] by increasing the opening area of the travel communication valve 26 as the hydraulic oil temperature decreases and reducing the opening area of the travel communication valve 26 as the hydraulic oil temperature increases. Since a fluctuation in the LS drop amount [P L - P LS] suppressed, the desired LS pressure P LS even when the hydraulic oil temperature changes. Travel communication valve

[0042] Fig. 8 is a diagram schematically illustrating the driving communication valve 26 according to the present embodiment. As shown in Fig. As illustrated in Figure 8, the travel communication valve 26 includes a valve body 34 and a spool 35 movable within the valve body 34. The valve body 34 has an annular recess 36 and an annular recess 37. Both the annular recess 36 and the annular recess 37 are arranged to surround the spool 35. An inlet port 38 for the hydraulic oil is provided at an inner peripheral portion of the annular recess 36, and an outlet port 39 for the hydraulic oil is provided at an inner peripheral portion of the annular recess 37.

[0043] Fig. 9 is a diagram schematically illustrating the spool 35 of the travel communication valve 26 according to the present embodiment. The spool 35 includes a small-diameter rod portion 40, a large-diameter rod portion 41 connected to a right end portion of the small-diameter rod portion 40, and a large-diameter rod portion 42 connected to a left end portion of the small-diameter rod portion 40. An outer diameter of the small-diameter rod portion 40 is smaller than an outer diameter of the large-diameter rod portion 41 and an outer diameter of the large-diameter rod portion 42. A cutout portion 43 is formed at a left end portion of an outer peripheral surface of the large-diameter rod portion 41.In the following description, a region of the outer peripheral surface of the large-diameter rod portion 41 to the right of a right end portion 43A of the cutout portion 43 is appropriately referred to as a land surface 44.

[0044] Fig. 10 is a diagram schematically illustrating an operation of the travel communication valve 26 according to the embodiment. Fig. 10(A) illustrates the state in which the spool 35 is arranged in the open position V. When the spool 35 is arranged in the open position V, the right end portion of the small-diameter rod portion 40 and the left end portion of the large-diameter rod portion 41 face the inlet port 38. The hydraulic oil from the inlet port 38 flows around an outer peripheral surface of the small-diameter rod portion 40 and the outer peripheral surface of the large-diameter rod portion 41 including the cutout portion 43. In the Fig. In the state illustrated in Figure 10(A), the opening of the travel communication valve 26 through which the hydraulic oil flows is formed around the outer peripheral surface of the small-diameter rod portion 40 and the cutout portion 43 of the large-diameter rod portion 41. Note that the opening area of the travel communication valve 26 is maximized when the length of the small-diameter rod portion 40 facing the annular recess 36 is maximized.

[0045] Fig. 10(B) illustrates a state in which the slider 35 is moved relative to the Fig. 10(A). The slide 35 moves to the left, and thus the cutout portion 43 and the land surface 44 of the large-diameter rod portion 41 face the inlet port 38. In the position shown in Fig. In the state illustrated in Fig. 10(B), the opening of the travel communication valve 26 through which the hydraulic oil flows is formed around the cutout portion 43 of the large-diameter rod portion 41. The opening area of the travel communication valve 26 in the state shown in Fig. 10(B) is smaller than the opening area of the driving communication valve 26 in the state shown in Fig. 10(A) illustrated condition.

[0046] Fig. 10(C) illustrates a state in which the slider 35 is moved relative to the Fig. 10(B). The slider 35 moves to the left, and thus a position of the right end portion 43A of the cutout portion 43 coincides with a position of a left end portion of the inlet port 38. The small-diameter rod portion 40 and the cutout portion 43 do not face the inlet port 38, and the land surface 44 of the large-diameter rod portion 41 faces the entire inlet port 38. In the position shown in Fig. 10(C), the opening of the travel communication valve 26 through which the hydraulic oil flows is formed around the land surface 44 of the large-diameter rod portion 41. In the state shown in Fig. 10(C), the hydraulic oil guided from the inlet portion 38 to the land surface 44 leaks from a gap between the large-diameter rod portion 41 and the valve body 34 and then flows to the outlet port 39. In the following description, a position of the spool 35 at which a position of the right end portion 43A of the cutout portion 43 of the large-diameter rod portion 41 and a position of the left end portion of the annular recess 36 coincide is appropriately referred to as a cutout opening closed position X. The flow rate of the hydraulic oil guided in the Fig. 10(C) is smaller than the flow rate of the hydraulic oil flowing through the travel communication valve 26 in the state illustrated in Fig. 10(B) flows through the driving communication valve 26.

[0047] Fig. 10(D) illustrates a state in which the slider 35 is moved relative to the Fig. 10(C). The spool 35 moves to the left, thereby forming a gap 45 between the land surface 44 of the large-diameter rod portion 41 and an inner peripheral surface of the valve body 34. The hydraulic oil from the inlet port 38 flows into the gap 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 oil flows encloses the gap 45. The flow rate of the hydraulic oil leaking from the gap 45 decreases with increasing length Ld of the gap 45. The length Ld of the gap 45 in the Fig. 10(D) is longer than the length Ld of the gap opening 45 in the state shown in Fig. 10(C). The flow rate of the hydraulic oil flowing in the Fig. 10(D) is smaller than the flow rate of the hydraulic oil flowing through the travel communication valve 26 in the state illustrated in Fig. 10(C) flows through the driving communication valve 26.

[0048] Fig. 10(E) shows a state in which the slider 35 moves to the closed position W to the left of the Fig. 10(D). The closed position W is a position in which the spool 35 has reached a stroke end in a state in which the land surface 44 of the large-diameter rod portion 41 faces the entire annular recess 36. The length Ld of the gap opening 45 when the spool 35 is arranged in the closed position W is longer than the length Ld of the gap opening 45 in the state shown in Fig. 10(D). The flow rate of the hydraulic oil exiting from the gap opening 45 in the state shown in Fig. 10(E) is smaller than the flow rate of the hydraulic oil exiting from the gap opening 45 in the state shown in Fig. 10(D). In the present embodiment, when the spool 35 is placed in the closed position W, the flow rate of the hydraulic oil flowing through the travel communication valve 26 is minimized.

[0049] In this way, the opening of the travel communication valve 26 through which the hydraulic oil flows includes a cutout opening formed around the small-diameter rod portion 40 and the cutout 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 in a first movement range between the open position V and the cutout-opening-closed position X, the hydraulic oil flows from the inlet port 38 into the cutout opening formed around the small-diameter rod portion 40 and the cutout portion 43 provided on the large-diameter rod portion 41 and flows out of the outlet port 39. The opening area decreases as the stroke of the spool 35 increases to the left.When the spool 35 moves in a second movement range between the cutout-opening closed position X and the closed position W, the hydraulic oil flows from the inlet port 38 into the gap 45 formed between the land surface 44 of the large-diameter rod portion 41 and the inner peripheral surface of the valve body 34, exits the gap 45, and then flows out of the outlet port 39. The flow rate of the hydraulic oil exiting the gap 45 decreases as the stroke of the spool 35 increases to the left.In the present embodiment, adjusting the stroke of the travel communication valve 26 includes changing a position of the spool 35 in the first moving range between the open position V and the cutout opening closed position X and changing the position of the spool 35 in the second moving range between the cutout opening closed position X and the closed position W.

[0050] Fig. Fig. 11 is a graph showing a relationship between the hydraulic oil temperature, a target lift 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 Fig. As shown in Figure 11, a number of specified temperatures T1, T2, T3 and T4 are defined for the hydraulic oil temperature. Fig. According to the table data shown in Figure 11, the specified temperature T2 is higher than the specified temperature T1, the specified temperature T3 is higher than the specified temperature T1, the specified temperature T4 is higher than the specified temperature T2, and the specified temperature T4 is higher than the specified temperature T3. When the travel communication valve 26 is in the fully open state and the hydraulic oil temperature gradually increases from a low temperature and reaches the specified temperature T2, the travel communication valve 26 begins to close. The opening area of the travel communication valve 26 gradually decreases at temperatures between the specified temperature T2 and the specified temperature T4, and at the specified temperature T4, the travel communication valve 26 is in the fully closed state.When the travel communication valve 26 is in the fully closed state and the hydraulic oil temperature gradually decreases from a high temperature to the specified temperature T3, the travel communication valve 26 begins to open. The opening area of the travel communication valve 26 gradually increases at temperatures between the specified temperature T3 and the specified temperature T1, and at the specified temperature T1, the travel communication valve 26 is in the fully open state. Based on the table data, the control device 6 fully opens the travel communication valve 26 when the hydraulic oil temperature is equal to or lower than the specified temperature T1, which is a first temperature threshold, and fully closes the travel communication valve 26 when the hydraulic oil temperature is equal to or higher than the specified temperature T4, which is a second temperature threshold.The fully closed state of the travel communication valve 26 refers to a state in which 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 a state in which the spool 35 has reached the closed position W.

[0051] As shown by the correlation data on the left side of the graph in Fig. 11, in the first movement range between the open position V and the cutout-opening-closed position X, the opening area of the travel communication valve 26 increases as the stroke amount of the spool 35 decreases. This increases the flow rate of the hydraulic oil flowing through the travel communication valve 26. In the first movement range, the opening area of the travel communication valve 26 decreases as the stroke amount of the spool 35 increases. This decreases the flow rate of the hydraulic oil flowing through the travel communication valve 26. In the second movement range between the cutout-opening-closed position X and the closed position W, the length Ld of the gap opening 45 of the Fig. 10(D) when the stroke amount of the spool 35 decreases. This increases the flow rate of the hydraulic oil flowing through the travel communication valve 26. In the second movement range, the length Ld of the gap opening 45 of the Fig. 10(D) increases as the lift amount of the spool 35 increases. This decreases the flow rate of the hydraulic oil flowing through the travel communication valve 26. In both the first and second movement ranges, the control device 6 can adjust the flow rate of the hydraulic oil flowing through the travel communication valve 26 by controlling the lift amount of the spool 35.

[0052] Please note that the specified temperature T1 and the specified temperature T2 may be the same. The specified temperature T1 and the specified temperature T3 may be the same. The specified temperature T2 and the specified temperature T4 may be the same. The specified temperature T3 and the specified temperature T4 may be the same. Control procedures

[0053] Fig. 12 is a flowchart illustrating a control method of the hydraulic system 10 according to the present embodiment. The control device 6 detects the operation amount of the travel lever 31 (step SA1). The control device 6 determines whether the hydraulic excavator 1 is traveling based on the operation amount of the travel lever 31 (step SA2). If it is determined in step SA2 that the hydraulic excavator 1 is traveling (Yes in step SA2), the control device 6 determines whether the traveling body 2 is steered based on the operation amount of the travel lever 31 (step SA3).

[0054] If it is determined in step SA3 that the traveling body 2 is being steered (Yes in step SA3), the control device 6 outputs a command current to the electromagnetic valve 33 to fully close the traveling communication valve 26 (step SA4). As a result of the command current being output to the electromagnetic valve 33, the spool 35 of the traveling communication valve 26 is placed in the closed position W, and the traveling communication valve 26 is fully closed (step SA5). The traveling communication valve 26 is fully closed, and thus the traveling body 2 can be stably steered.

[0055] If it is determined in step SA3 that the traveling body 2 is not steered (No in step SA3), the control device 6 outputs a command current to the electromagnetic valve 33 to fully open the traveling communication valve 26 (step SA6). As a result of the command current being output to the electromagnetic valve 33, the spool 35 of the traveling communication valve 26 is placed in the open position V, and the traveling communication valve 26 is fully opened (step SA7). Since the traveling communication valve 26 is fully opened as described above, the difference between the load pressure of the traveling motor 7 and the load pressure of the traveling motor 8 becomes small, so the traveling body 2 can travel straight stably.

[0056] If it is determined in step SA2 that the hydraulic excavator 1 is not traveling (No in step SA2), the LS drop control is started (step SA8). The control device 6 detects the hydraulic oil temperature. That is, the control device 6 acquires the detection data from the temperature sensor 27 (step SA9).

[0057] The control device 6 determines the target lift amount of the spool 35 of the travel communication valve 26 based on the hydraulic oil temperature (step SA10). In the present embodiment, the control device 6 determines the target lift amount of the spool of the travel communication valve 26 based on the table data indicating the relationship between the hydraulic oil temperature and the target lift amount, which is described with reference to Fig. 11. The table data is predefined. The lift amount of the spool of the travel communication valve 26 and the opening area of the travel communication valve 26 exhibit a negative correlation. As the lift amount increases, the opening area becomes smaller; as the lift amount decreases, the opening area becomes larger.

[0058] The control device 6 determines the target lift amount based on the detection data from the temperature sensor 27 and the table data, and then outputs a command current to the electromagnetic valve 33 based on the target lift amount (step SA11). As a result of the command current being output to the electromagnetic valve 33, the travel communication valve 26 performs a lift, and the opening area of the travel communication valve 26 is adjusted (step SA12). By adjusting the opening area of the travel communication valve 26, a fluctuation in the LS drop amount [P L - P LS] suppressed. Effects

[0059] As described above, in the present embodiment, the stroke of the travel communication valve 26 is adjusted based on the hydraulic oil temperature. Therefore, even with a change in the hydraulic oil temperature, a large fluctuation in the LS drop amount [P L - P LS] suppressed. Since a fluctuation in the LS waste amount [P L - P LS] is suppressed, the appropriate LS pressure P LS receive.

[0060] This suppresses a deterioration in the operability of the working device 4. Second embodiment

[0061] A second embodiment will be described. In the following description, components identical or equivalent to those of the above-described embodiment are denoted by the same reference numerals, and their descriptions will be simplified or omitted.

[0062] Fig. 13 is a flowchart illustrating a control method of the hydraulic system 10 according to the present embodiment. Since steps SB1 to SB7 are the same as those described with reference to Fig. 12 described steps SA1 to SA7, their description is omitted.

[0063] In step SB8, the control device 6 detects the operation amount of the work lever 32 (step SB8). The control device 6 determines whether the work implement 4 is operating based on the operation amount of the work lever 32 (step SB9). If it is determined in step SB9 that the work implement 4 is not operating (No in step SB9), the control device 6 performs the processing of step SB6 and the processing of step SB7. When the travel motor 7, the travel motor 8, and the work implement cylinder 5 are not operating, the travel communication valve 26 is fully open.In a case where a pilot pressure is input to a pilot port of the travel communication valve 26 when a command current is input to the electromagnetic valve 33 and the travel communication valve 26 is fully closed, and the travel communication valve 26 is fully opened by a spring force when the command current is not input to the electromagnetic valve 33, the pilot pressure is prevented from being input to the travel communication valve 26 when the travel motor 7, the travel motor 8, and the work machine cylinder 5 are not operating, thereby suppressing leakage of pilot oil in a pilot circuit. This suppresses deterioration of fuel consumption of the hydraulic excavator 1.

[0064] If it is determined in step SB9 that the working device 4 is operating (Yes in step SB9), the LS drop control is started (step SB10). The control device 6 detects the hydraulic oil temperature (step SB11). The control device 6 determines the target lift amount of the travel communication valve 26 based on the detection data from the temperature sensor 27 and the values determined with reference to Fig. 10 (step SB12). After determining the target lift amount, the control device 6 outputs a command current to the electromagnetic valve 33 based on the target lift amount (step SB13). As a result of the output of the command current to the electromagnetic valve 33, the spool 35 of the travel communication valve 26 performs a stroke, and the opening area of the travel communication valve 26 is adjusted (step SB14). By adjusting the opening area of the travel communication valve 26, a fluctuation in the LS drop amount [P L- P LS] suppressed. Third embodiment

[0065] A third embodiment will be described. In the following description, components identical or equivalent to those of the above-described embodiment are denoted by the same reference numerals, and their descriptions will be simplified or omitted.

[0066] Fig. 14 is a flowchart illustrating a control method of the hydraulic system 10 according to the present embodiment. Since steps SC1 to SC7 are the same as those described with reference to Fig. 12 described steps SA1 to SA7, their description is omitted.

[0067] If it is determined in step SC2 that the hydraulic excavator 1 is not traveling (No in step SC2), the LS drop control is started (step SC8).

[0068] The control device 6 detects the hydraulic oil temperature and the pump outlet pressure PP . That is, the control device 6 acquires the detection data from the temperature sensor 27 and the 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 determines the target lift amount of the travel communication valve 26 based on the hydraulic oil temperature and the pump discharge pressure P P (Step SC10).

[0069] The control device 6 determines a first candidate value for the target lift amount of the travel communication valve 26 based on the detection data from the temperature sensor 27 and the values obtained with reference to Fig. 11. Further, the control device 6 determines a second candidate value for the target lift amount of the travel communication valve 26 based on the table data that shows a predetermined relationship between the pump outlet pressure P P and the target stroke amount.

[0070] Fig. 15 is a graph showing a relationship between the pump outlet pressure P P , the target lift amount and the opening area of the travel communication valve 26 according to the present embodiment. As can be seen from the table data on the right side of the graph in Fig. 15 are for the pump outlet pressure P P a variety of specified pressures P1, P2, P3 and P4 are defined. In the Fig. 15, the specified pressure P2 is higher than the specified pressure P1, the specified pressure P3 is higher than the specified pressure P1, the specified pressure P4 is higher than the specified pressure P2, and the specified pressure P4 is higher than the specified pressure P3. When the travel communication valve 26 is in the fully open state and the pump outlet pressure P P from a low pressure gradually increases and reaches the specified pressure P2, the travel communication valve 26 begins to close. The opening area of the travel communication valve 26 gradually decreases at pressures between the specified pressure P2 and the specified pressure P4, and the travel communication valve 26 is in the fully closed state at the specified pressure P4. When the travel communication valve 26 is in the fully closed state and the pump outlet pressure P Pfrom a high pressure gradually decreases and reaches the specified pressure T3, the travel communication valve 26 begins to open. The opening area of the travel communication valve 26 gradually increases at pressures between the specified pressure P3 and the specified pressure P1, and at the specified pressure P1, the travel communication valve 26 is in the fully open state. Based on the table data, the control device 6 fully opens the travel communication valve 26 when the pump outlet pressure P P is equal to or lower than the specified pressure P1, which is a first pressure threshold, and closes the travel communication valve 26 completely when the pump outlet pressure P Pis equal to or higher than the specified pressure P4, which is a second pressure threshold. The fully closed state of the travel communication valve 26 refers to a state in which the spool of the travel communication valve 26 has reached the stroke end. The state in which the spool 35 has reached the stroke end is a state in which the spool 35 has reached the closed position W.

[0071] As shown by the correlation data on the left side of the graph in Fig. 15, in the first movement range between the open position V and the cutout opening-closed position X, the opening area of the travel communication valve 26 increases as the stroke amount of the spool 35 decreases. This increases the flow rate of the hydraulic oil flowing through the travel communication valve 26. In the first movement range, the opening area of the travel communication valve 26 decreases as the stroke amount of the spool 35 increases. This decreases the flow rate of the hydraulic oil flowing through the travel communication valve 26. In the second movement range between the cutout opening-closed position X and the closed position W, the length Ld of the gap opening 45 of the Fig. 10(D) when the stroke amount of the spool 35 decreases. This increases the flow rate of the hydraulic oil flowing through the travel communication valve 26. In the second movement range, the length Ld of the gap opening 45 of the Fig. 10(D) increases as the lift amount of the spool 35 increases. This decreases the flow rate of the hydraulic oil flowing through the travel communication valve 26. In both the first and second movement ranges, the control device 6 can adjust the flow rate of the hydraulic oil flowing through the travel communication valve 26 by controlling the lift amount of the spool 35.

[0072] Please note that the specified pressure P1 and the specified pressure P2 can be equal to each other. The specified pressure P1 and the specified pressure P3 can be equal to each other. The specified pressure P2 and the specified pressure P4 can be equal to each other. The specified pressure P3 and the specified pressure P4 can be equal to each other.

[0073] The control device 6 determines the second candidate value for the target stroke amount based on the detection data from the pressure sensor 28 and the values determined with reference to Fig. 15 described table data. In Fig. 14, the control device 6 sets a smaller one of the first candidate value determined based on the hydraulic oil temperature and the second candidate value determined based on the pump outlet pressure P Pis determined as the target lift amount. After determining the target lift amount, the control device 6 outputs a command current to the electromagnetic valve 33 based on the target lift amount (step SC11). As a result of the output of the command current to the electromagnetic valve 33, the travel communication valve 26 performs a lift, and the opening area of the travel communication valve 26 is adjusted (step SC12). By adjusting the opening area of the travel communication valve 26, a fluctuation in the LS drop amount [P L - P LS] suppressed.

[0074] In a case where a pilot pressure is input to the pilot port of the travel communication valve 26 when the command current is input to the electromagnetic valve 33 and the travel communication valve 26 is fully closed, and the travel communication valve 26 is fully opened by a spring force when the command current is not input to the electromagnetic valve 33, the pilot pressure is prevented from being input to the travel communication valve 26 when the pump discharge pressure P P is low and the influence of a fluctuation in the LS waste amount [P L - P LS] is small, thereby suppressing leakage of pilot oil in the pilot circuit. This suppresses deterioration of the operability of the hydraulic excavator 1 and deterioration of fuel consumption. List of reference symbols

[0075] 1 Hydraulic excavator, 2 Travel body, 2A Crawler track, 3 Rotating body, 4 Working device, 4A Boom, 4B Arm, 4C Bucket, 5 Working device cylinder, 5A Boom cylinder, 5B Arm cylinder, 5C Bucket cylinder, 6 Control device, 7 Travel motor (first travel motor), 7A connection, 7B connection, 8 Travel motor (second travel motor), 8A connection, 8B connection, 10 Hydraulic system, 11 Hydraulic pump, 12 Hydraulic oil tank, 13 Travel control valve (first travel control valve), 13A First connection, 13B Second connection, 13C Third connection, 13D Fourth connection, 13E Fifth connection, 13F Sixth connection, 13G Seventh connection, 13M Inlet throttle, 13N Inlet throttle, 14 Travel control valve (second travel control valve), 14A First connection, 14B Second port, 14C Third port, 14D Fourth port, 14E Fifth port, 14F Sixth port, 14G Seventh port, 14M Inlet throttle, 14N Inlet throttle, 15 Implement control valve, 15A First port, 15B Second port, 15C Third port,15D Fourth port, 15E Fifth port, 15F Sixth port, 15G Seventh port, 15M Inlet throttle, 15N Inlet throttle, 16 Pressure balance unit, 16A Inlet port, 16B Outlet port, 16C Inlet flow path, 16D Check valve, 16E Charge sense inlet throttle (LS inlet throttle), 16S Pressure balance valve (first pressure balance valve), 17 Pressure balance unit, 17A Inlet port, 17B Outlet port, 17C Inlet flow path, 17D Check valve, 17E Charge sense inlet throttle (LS inlet throttle), 17F Bypass flow path, 17G Bypass throttle, 17S Pressure balance valve (second pressure balance valve), 18 Pressure balance unit, 18A Inlet port, 18B Output port, 18C Input flow path, 18D Check valve, 18E Charge sense input throttle (LS input throttle), 18S Pressure equalization valve, 19 Pump flow path, 20 Coupling flow path, 21 Tank flow path, 22 Signal flow path, 23 Throttle, 24 Charge sense valve (LS valve),25 Servo piston, 26 Travel communication valve, 27 Temperature sensor, 28 Pressure sensor, 31 Travel lever, 32 Working lever, 33 Solenoid valve, 34 Valve body, 35 Spool, 36 Annular recess, 37 Annular recess, 38 Inlet port, 39 Outlet port, 40 Small diameter rod section, 41 Large diameter rod section, 42 Large diameter rod section, 43 Cutout section, 43A right end section, 44 Land surface, 45 Gap opening, 50A port, 50B port, A Fully open position, B Fully closed position, D Retreat 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 PPump outlet pressure, R Reverse position, U Extended position, Ya Increase direction, Yb Decrease direction, V Open position, W Closed position, X Cutout opening-closed position QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2006-336730 A

[0003]

Claims

[1] Work machine, comprising: a hydraulic pump configured to change a discharge amount of hydraulic oil based on a differential pressure between a pump discharge pressure and a load sensing pressure corresponding to a load pressure input via a signal flow path; a first travel motor configured to be driven by the hydraulic oil supplied from the hydraulic pump; a second travel motor configured to be driven by the hydraulic oil supplied from the hydraulic pump; a working implement cylinder configured to be driven by the hydraulic oil supplied from the hydraulic pump; a first travel control valve configured to control a flow rate and a direction of hydraulic oil supplied from the hydraulic pump to the first travel motor; a second travel control valve configured to control a flow rate and a direction of hydraulic oil supplied from the hydraulic pump to the second travel motor; a work implement control valve configured to control a flow rate and a direction of hydraulic oil supplied from the hydraulic pump to the work implement cylinder; a first pressure compensation valve connected to the signal flow path via a first inlet flow path, the first pressure compensation valve configured to compensate for a differential pressure across the first travel control valve based on the load sensing pressure; a second pressure compensation valve connected to the signal flow path via a second inlet flow path, the second pressure compensation valve configured to compensate for a differential pressure across the second travel control valve based on the load sensing pressure; a bypass flow path configured to bypass at least a portion of the second inlet flow path; a travel communication valve arranged on a coupling flow path that couples the first travel control valve and the second travel control valve; a temperature sensor configured to detect a hydraulic oil temperature indicative of a temperature of the hydraulic oil; and a control device configured to adjust a stroke of the travel communication valve based on detection data from the temperature sensor in a state where both the first travel operation valve and the second travel operation valve are arranged in a neutral position. [2] Working machine according to claim 1, wherein an opening range of the driving communication valve is adjusted by adjusting the stroke of the driving communication valve and the control device increases the opening area when the temperature of the hydraulic oil decreases and decreases the opening area when the temperature of the hydraulic oil increases. [3] The work machine according to claim 1, wherein the control device fully opens the travel communication valve when the hydraulic oil temperature is equal to or less than a first temperature threshold, and fully closes the travel communication valve when the hydraulic oil temperature is equal to or greater than a second temperature threshold. [4] Working machine according to claim 1, comprising: a pressure sensor configured to detect the pump outlet pressure, wherein the control device adjusts the stroke of the driving communication valve based on the detection data of the temperature sensor and the detection data of the pressure sensor. [5] The work machine of claim 4, wherein the controller fully opens the travel communication valve when the pump outlet pressure is equal to or less than a first pressure threshold, and fully closes the travel communication valve when the pump outlet pressure is equal to or greater than a second pressure threshold. [6] The work machine according to claim 1, wherein the control device adjusts the stroke of the travel communication valve when the work implement control valve is activated. [7] Working machine according to claim 1, wherein the driving communication valve includes a valve body and a slide movable in the valve body, the slide valve includes a small diameter rod section and a large diameter rod section connected to the small diameter rod section, an opening of the travel communication valve through which the hydraulic oil flows, a cutout opening formed around the small-diameter rod portion and around a cutout 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 in a first range of motion in which the hydraulic oil flows from an inlet port of the valve body into the cutout opening, and in a second range of motion in which the hydraulic oil flows from the inlet port into the gap opening, and adjusting the stroke of the travel communication valve includes changing a position of the spool in the first range of motion and changing the position of the spool in the second range of motion.

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