Hydraulic system, construction machine, hydraulic control method, and computer storage medium

Abstract

The hydraulic system of the present application returns working oil discharged from an actuator to a tank via an oil cooler, and includes a throttle member, a flow path connecting the throttle member and the tank via the oil cooler, a discharge flow path connecting the throttle member and the tank, and a switching valve switching the flow direction of the working oil in accordance with a negative control pressure generated by the throttle member. When the negative control pressure generated by the throttle member is equal to or greater than a reference, the switching valve causes the working oil to flow to the flow path. When the negative control pressure is less than the reference, the switching valve blocks the inflow of the working oil from the throttle member to the flow path, and causes the working oil to flow to the discharge flow path.

Description

TECHNICAL FIELD

[0001] The present application relates to a hydraulic system for controlling back pressure of a negative control hydraulic system, a construction machine, a hydraulic control method, and a computer storage medium. BACKGROUND

[0002] There are many machines driven by hydraulic control, such as construction machines. There is a hydraulic system using a negative control system in a hydraulic system that drives a construction machine such as a hydraulic shovel. In a hydraulic system using negative control, a relief valve and a restriction member that becomes a resistance are provided at the most downstream of a center bypass route of the hydraulic system. The hydraulic system is controlled in such a manner that a detection signal based on a control pressure of the restriction member is fed back to a hydraulic pump, thereby increasing and decreasing a flow rate of working oil of the center bypass route.

[0003] For example, in a case where an operation part is located at a neutral position, a higher control pressure is generated at the restriction member. In a case where the operation part is in a working state, a lower control pressure is generated at the restriction member. The hydraulic system controls the flow rate with a negative characteristic. That is, the hydraulic system decreases the flow rate of working oil delivered from the hydraulic pump in a case where the control pressure of the restriction member is higher. The hydraulic system increases the flow rate of working oil delivered from the hydraulic pump in a case where the control pressure of the restriction member is lower.

[0004] Generally, working oil that has passed through the relief valve and the restriction member of the negative control is returned to a tank for accumulating working oil via a return line. At this time, if a large amount of working oil flows into the return line, the back pressure of the restriction member rises, and the pressure (control pressure) of the restriction member does not decrease sufficiently. In this case, in the hydraulic system, the flow rate of working oil delivered from the hydraulic pump is controlled to decrease. Therefore, a state in which the maximum flow rate of working oil is not ejected from the hydraulic pump can occur.

[0005] Prior art documents

[0006] Patent documents

[0007] Patent Literature 1: Japanese Patent Application Publication No. 2013-53498 SUMMARY

[0008] Problems to be solved by the invention

[0009] As a countermeasure against the state in which the back pressure of the negative control rises, there is a method in which the return line of the negative control is directly connected to the tank. However, according to this method, in a case where a lever of the operation part is located at a neutral position, there is a possibility that working oil is overheated without passing through an oil cooler connected to an upstream side of the tank.

[0010] The hydraulic system, construction machine, hydraulic control method, and program according to the present application are able to accurately control the discharge amount of a hydraulic pump and suppress overheating.

[0011] Solution to the problem

[0012] The hydraulic system according to the present application is a hydraulic system in which working oil discharged from an actuator is returned to a tank via an oil cooler, and is provided with: a throttle member; a flow path connecting the throttle member and the tank via the oil cooler; a discharge flow path connecting the throttle member and the tank; and a switching valve that switches the flow direction of the working oil in accordance with a negative control pressure generated by the throttle member, in a case where the negative control pressure generated by the throttle member is equal to or higher than a reference, the switching valve causes the working oil to flow to the flow path, and in a case where the negative control pressure is less than the reference, the switching valve blocks the inflow of the working oil from the throttle member to the flow path and causes the working oil to flow to the discharge flow path.

[0013] With this configuration, in a case where the negative control pressure (back pressure) is equal to or higher than the reference at the time of neutral of the operation section, for example, the switching valve causes the working oil to flow from the throttle member to the flow path and causes the working oil to flow to the oil cooler, thereby being able to suppress overheating. At the same time, it is possible to maintain the discharge amount in a normal state without the back pressure of the throttle member falling below the pressure of the maximum flow rate of the discharge hydraulic pump. In addition, in a case where the back pressure of the throttle member is less than the reference without generating overheating, it is possible to lower the back pressure of the throttle member by causing the working oil to directly return to the tank and to maintain the discharge amount of the hydraulic pump in a normal state.

[0014] The switching valve can be connected to the downstream side of the throttle member.

[0015] With this configuration, the switching valve is built into the pressure relief valve of the negative control, and thus it is possible to simplify the device structure.

[0016] The switching valve can be provided with: a first valve seat that, in a case where the negative control pressure is equal to or higher than the reference, causes the throttle member and the flow path to communicate, and that, in a case where the negative control pressure is less than the reference, blocks the communication between the throttle member and the discharge flow path; and a second valve seat that, in a case where the negative control pressure is equal to or higher than the reference, blocks the communication between the throttle member and the discharge flow path, and that, in a case where the negative control pressure is less than the reference, causes the throttle member and the discharge flow path to communicate.

[0017] This configuration allows the back pressure of the throttling element to drop below the control pressure of the maximum flow rate under negative control. Simultaneously, it enables the working oil to flow into the discharge path or flow path based on the negative control pressure conditions, thus suppressing overheating.

[0018] The construction machinery of one technical solution of the present invention can also be configured to have the hydraulic system described above.

[0019] In a hydraulic control method of one embodiment of the present invention, when the negative control pressure in the throttling device that generates negative control pressure is above a reference, the working oil is allowed to flow into the flow path connecting the throttling device and the oil cooler, which is connected to the upstream side of a tank where the working oil is stored. When the negative control pressure is below the reference, the inflow of the working oil into the flow path is blocked, and the working oil is allowed to flow into the discharge flow path connected to the tank.

[0020] This configuration allows the back pressure of the throttling element to drop below the control pressure of the maximum flow rate under negative control. Simultaneously, it enables the working oil to flow into the discharge path or flow path based on the negative control pressure conditions, thus suppressing overheating.

[0021] The program of one technical solution of the present invention causes a computer to perform the following processing: when the negative control pressure in the throttling device that generates negative control pressure is above a reference, the working oil is allowed to flow into the flow path connecting the throttling device and the oil cooler, which is connected to the upstream side of the tank where the working oil is stored; when the negative control pressure is below the reference, the inflow of the working oil into the flow path is blocked, and the working oil is allowed to flow into the discharge flow path connected to the tank.

[0022] This configuration allows the back pressure of the throttling element to drop below the control pressure of the maximum flow rate under negative control. Simultaneously, it enables the working oil to flow into the discharge path or flow path based on the negative control pressure conditions, thus suppressing overheating.

[0023] A hydraulic system according to one embodiment of the present invention comprises: a detection circuit for negative control, which is disposed downstream of the hydraulic circuit; a switching valve, which is disposed between the detection circuit and the tank; and a flow path that connects the switching valve to an oil cooler and connects to the tank via the oil cooler, the flow path having a confluence path connecting the detection circuit and the switching valve.

[0024] With this configuration, when the operating unit is neutral, and the negative control pressure (back pressure) is higher than the reference, the switching valve operates to allow the working oil to flow to the oil cooler, thereby suppressing overheating and allowing the working oil to flow from the throttling element to the flow path.

[0025] Effects of the invention

[0026] According to the present invention, the injection volume of the hydraulic pump can be accurately controlled, and overheating can be suppressed. Attached Figure Description

[0027] Figure 1 This is a diagram illustrating the structure of the construction machinery in an embodiment of the present invention.

[0028] Figure 2 This is a block diagram illustrating the structure of the hydraulic system of the construction machinery in an embodiment of the present invention.

[0029] Figure 3 This is a hydraulic circuit diagram of the back pressure switching valve in an embodiment of the present invention.

[0030] Figure 4A This is a cross-sectional view showing the structure of the back pressure switching valve in an embodiment of the present invention.

[0031] Figure 4B This is a cross-sectional view showing the structure of the back pressure switching valve in an embodiment of the present invention.

[0032] Figure 5 This is a block diagram illustrating the structure of the control device that drives the hydraulic system in the embodiments of the present invention.

[0033] Reference signs list

[0034] 1. Hydraulic system; 10. Hydraulic pump; 11. Pump 1; 12. Pump 2; 13. Oil cooler; 14. Check valve; 15. Tank; 20. Actuator; 31. First bypass flow path; 32. Second bypass flow path; 35. Flow path; 35A. Merging path; 36. Discharge flow path; 37. Flow path; 41. First supply flow path; 42. Second supply flow path; 45. Hydraulic circuit; 50. Directional valve; 60. Detection circuit; 61. First throttling element; 62. Second throttling element; 63. First pressure relief valve; 64. Second pressure relief valve; 68. Low-pressure selector valve ; 70. Back pressure switching valve; 71. Switching valve; 71a. Conical surface; 72. First valve seat; 73. Second valve seat; 74. Throttling orifice; 74a. Hole; 74b. Through hole; 75. Step; 76. Return spring; 77. Second valve seat; 77a. Conical surface; 78. Valve body; 80. Regulator; 100. Construction machinery; 101. Rotating body; 102. Traveling body; 103. Cab; 104. Boom; 105. Stick; 106. Bucket; 200. Control device; 210. Switching valve; 220. Detection unit; 230. Control unit. Detailed Implementation

[0035] Next, embodiments of the present invention will be described with reference to the accompanying drawings.

[0036] (Construction machinery)

[0037] like Figure 1 As shown, the construction machinery 100 is, for example, a hydraulic excavator. The construction machinery 100 includes a slewing body 101 and a traveling body 102. The slewing body 101 is mounted on the traveling body 102 in a rotatable manner. A hydraulic system 1 is provided on the slewing body 101.

[0038] The slewing body 101 includes: a cab 103 for an operator to ride in; a boom 104 having one end connected to the cab 103 in a swingable manner; a stick 105 having one end connected to the other end of the boom 104 (the end opposite to the cab 103, the top end) in a swingable manner; and a bucket 106 connected to the other end of the stick 105 (the other end opposite to the boom 104, the top end) in a swingable manner. A hydraulic system 1 is provided inside the cab 103. The cab 103, boom 104, stick 105, and bucket 106 are driven by working oil supplied from the hydraulic system 1.

[0039] (Hydraulic system)

[0040] like Figure 2 As shown, hydraulic system 1 is mounted on a hydraulic excavator. Hydraulic system 1 includes hydraulically driven actuators 20. Actuators 20 include multiple actuators 22, 21, 26, 23, 25, and 24 for driving the stick 105, boom 104, etc. Hydraulic system 1 includes a hydraulic pump 10 that supplies working oil to each actuator 22, 21, 26, 23, 25, and 24. Hydraulic pump 10 adjusts the flow rate of working oil supplied to each actuator 22, 21, 26, 23, 25, and 24. Actuators 20 include hydraulic cylinders and hydraulic motors.

[0041] The hydraulic system 1 includes a tank 15 for storing working oil and a hydraulic pump 10 for distributing the working oil stored in the tank 15 to various flow paths. The hydraulic system 1 includes a detection circuit 60 and a back pressure switching valve 70. An oil cooler 13 is connected upstream of the tank 15. A check valve 14 is connected upstream of the oil cooler 13. The check valve 14 prevents backflow of working oil to a position upstream of the check valve 14.

[0042] A directional valve 50 is provided between the hydraulic pump 10 and the actuator 20. The directional valve 50 controls the flow rate of the working oil supplied to the actuator 20. The directional valve 50 includes multiple directional valves 51 to 56 that drive each actuator 21 to 26.

[0043] In addition to the aforementioned structure, the hydraulic system 1 also includes an operating unit (not shown) and a regulator 80 for controlling the hydraulic pump 10. The operating unit outputs operating signals to each actuator 20. The operating signals output from the operating unit are input to the directional valve 50 and the regulator 80. The directional valve 50 is driven based on the input operating signals. The directional valve 50 includes multiple switching valves (spool valves). The multiple switching valves are neutral opening type switching valves. The regulator 80 adjusts the injection volume of the working oil injected from the hydraulic pump 10 based on the operating signals output from the operating unit.

[0044] The hydraulic pump 10 includes a first pump 11 and a second pump 12. The hydraulic pump 10 is driven by a prime mover (not shown) such as an engine. The hydraulic pump 10 is a pump that allows for variable volume of injected working oil. The first pump 11 is connected to a first bypass flow path 31 (center bypass path) and a first supply flow path 41. The second pump 12 is connected to a second bypass flow path 32 (center bypass path) and a second supply flow path 42.

[0045] The first bypass flow path 31 and the second bypass flow path 32 are bypass flow paths used to prevent the working oil supplied from the hydraulic pump 10 from being supplied to the actuator 20 and instead return it to the tank 15. The first supply flow path 41 and the second supply flow path 42 are flow paths that supply the working oil supplied from the hydraulic pump 10 to the actuator 20. The first supply flow path 41 and the second supply flow path 42 will be discussed later. The hydraulic pump 10, the oil cooler 13, the tank 15, the bypass flow paths 31 and 32, the flow path 35, the supply flow paths 41 and 42, the switching valve 50, etc., constitute the hydraulic circuit 45 that drives the actuator 20.

[0046] A detection circuit 60 is connected downstream of the first bypass flow path 31 and the second bypass flow path 32. The detection circuit 60 is a negative control detection circuit located downstream of the hydraulic circuit 45. The detection circuit 60 detects the negative control pressure.

[0047] The detection circuit 60 is connected to the flow path 35 (return line) for returning the working oil to the tank 15. A detailed description of the detection circuit 60 follows. The hydraulic system 1 performs negative control based on the detected value of the negative control pressure detected by the detection circuit 60, controlling the capacity (e.g., injection volume) of the hydraulic pump 10.

[0048] The detection circuit 60 includes a first pressure relief valve 63 connected to the downstream end of the first bypass flow path 31 and a first throttling element 61 that generates pressure P1. The downstream sides of the first pressure relief valve 63 and the first throttling element 61 are connected to the flow path 35.

[0049] The detection circuit 60 includes a second pressure relief valve 64 connected to the downstream end of the second bypass flow path 32 and a second throttling element 62 that generates pressure P2. The downstream sides of the second pressure relief valve 64 and the second throttling element 62 are connected to the flow path 35. The detection circuit 60 also includes a low-pressure selection valve 68 that selects the lower pressure of pressure P1 and pressure P2 and switches the flow path.

[0050] The first pressure relief valve 63 is a safety valve that opens the flow path 35 and discharges working oil to the tank 15 side (downstream side) when the pressure P1 of the first throttling element 61 exceeds the reference value. The first pressure relief valve 63 releases the first pressure relief pressure when the pressure of the working oil reaches the preset first pressure relief pressure, allowing the working oil to flow into the flow path 35.

[0051] The second pressure relief valve 64 is a safety valve that opens the flow path 35 and discharges the working oil from the downstream end of the second bypass flow path 32 to the tank 15 side without passing through the second bypass flow path 62 when the pressure P2 of the second throttling element 62, which is connected to the downstream end of the second bypass flow path 32, exceeds the reference value. The second pressure relief valve 64 releases the second pressure relief pressure when the pressure of the working oil reaches the preset second pressure relief pressure, allowing the working oil to flow into the flow path 35.

[0052] A back pressure switching valve 70 is provided between the detection circuit 60 and the flow path 35 to adjust the back pressure of the flow path 35. The back pressure switching valve 70 is connected to the flow path 35 and the discharge flow path 36, which is directly connected to the tank 15. The structure of the back pressure switching valve 70 will be described in detail below.

[0053] Flow path 35 is connected to tank 15. Flow path 35 is a return line that returns working oil to tank 15. Flow path 35 is connected to multiple directional valves 51 to 56 respectively. Flow path 35 connects the detection circuit 60 and the back pressure switching valve 70 at the confluence path 35A downstream of the detection circuit 60 and the back pressure switching valve 70.

[0054] Each actuator 21 to 26 is connected to the flow path 35. The flow path 35 is the flow path that returns the working oil discharged from each actuator 21 to 26 to the tank 15.

[0055] The working oil flowing into flow path 35 flows into oil cooler 13 via check valve 14. Oil cooler 13 is equipped with a heat exchanger. Oil cooler 13 lowers the temperature of the working oil flowing into it. The working oil, cooled by oil cooler 13, returns to tank 15. The working oil returned to tank 15 is then supplied to actuator 20 again by pumps 11 and 2.

[0056] Pump 11 directs working oil into the first supply path 41. The first supply path 41 supplies working oil from pump 11 to actuators 21-26. The first supply path 41 is connected to actuators 22, 24, 25, and 26. The first supply path 41 is connected to the upstream side of the first bypass path 31. The first supply path 41 also supplies working oil to directional valves 52, 54, 55, and 56.

[0057] The second supply flow path 42 is a flow path for supplying working oil injected from the second pump 12 to actuators 21, 23, 25, and 26. The second supply flow path 42 is connected to the upstream portion of the second bypass flow path 32. The second supply flow path 42 is also a flow path for supplying working oil to directional valves 51, 53, 55, and 56.

[0058] In addition, check valves are provided in each of the above-mentioned flow paths 41 and 42. The check valves prevent the working oil that has flowed into the directional valves 51, 53, 54, 55, and 56 from flowing back into each of the flow paths 41 and 42.

[0059] Directional control valves 51-56 are valves that adjust the flow rate of working oil supplied from hydraulic pump 10 to multiple actuators 21-26 and switch the flow direction of working oil relative to multiple actuators 21-26. Directional control valves 51-56 return the working oil discharged from actuators 21-26 to flow path 35 (tank 15).

[0060] Directional control valves 51-56 are positioned between hydraulic pump 10 and actuators 21-26. Each of directional control valves 51-56 has a spool valve. The spool valve switches the flow rate and direction of the working oil according to the stroke (position) of the spool valve core.

[0061] The directional valves 51 to 56 are: directional valve 51 for left-hand travel, directional valve 52 for right-hand travel, directional valve 53 for swing, directional valve 54 for boom, directional valve 55 for stick, and directional valve 56 for bucket.

[0062] The left-hand drive directional valve 51 and the rotary drive directional valve 53 are connected to the second bypass flow path 32 and the second supply flow path 42. The left-hand drive directional valve 51 and the rotary drive directional valve 53 are driven by working oil supplied from the second pump 12. The directional valve 53 is a valve that changes the flow rate and direction of the working oil flowing to the actuator 23. The right-hand drive directional valve 52 is connected to the first bypass flow path 31 and the first supply flow path 41. The right-hand drive directional valve 52 is driven by working oil supplied from the first pump 11.

[0063] The boom directional valve 54, the stick directional valve 55, and the bucket directional valve 56 are connected to the first bypass flow path 31 and the first supply flow path 41, and also to the second bypass flow path 32 and the second supply flow path 42. The boom directional valve 54, the stick directional valve 55, and the bucket directional valve 56 are driven by working oil supplied from the first pump 11 and the second pump 12. A detection circuit 60 is connected downstream of the first bypass flow path 31 and the second bypass flow path 32 connected to the directional valve 56.

[0064] The detection circuit 60 uses negative control to control the capacity of the hydraulic pump 10. The detection circuit 60 outputs the lower of the pressure P1 detected at the first throttling element 61 and the pressure P2 detected at the second throttling element 62 as pressure P (negative control pressure).

[0065] The first throttling element 61 is located at the downstream end of the first bypass flow path 31. The first throttling element 61 is formed such that the cross-sectional area of ​​the flow path is reduced relative to the first bypass flow path 31. The first throttling element 61 reduces the flow velocity of the working oil flowing from the first bypass flow path 31 to the first throttling element 61, thereby generating pressure P1. A detection unit (not shown) is provided in the first throttling element 61. The detection unit converts the pressure P1 into an electrical signal and outputs it.

[0066] The second throttling element 62 is located at the downstream end of the second bypass flow path 32. The second throttling element 62 is formed such that the cross-sectional area of ​​the flow path is reduced relative to the second bypass flow path 32. The second throttling element 62 reduces the flow velocity of the working oil flowing from the second bypass flow path 32 to the second throttling element 62, thereby generating pressure P2. A detection unit (not shown) is provided in the second throttling element 62. The detection unit converts the pressure P2 into an electrical signal and outputs it.

[0067] The low-pressure selector valve 68 selects and detects the lower of the pressure P1 detected at the first throttling element 61 and the pressure P2 detected at the second throttling element 62. The low-pressure selector valve 68 outputs the selected pressure P as the detected pressure value. The low-pressure selector valve 68 includes, for example, a shuttle valve. A detection unit (not shown) is provided in the low-pressure selector valve 68. In the detection unit, the pressure P is converted into hydraulic pressure, an electrical signal, etc., and output. The low-pressure selector valve 68 outputs the detected pressure P to the regulator 80 used for controlling the hydraulic pump 10.

[0068] The regulator 80 adjusts the injection volume of the hydraulic pump 10 based on the pressure P obtained from the low-pressure selector valve 68. The regulator 80 adjusts the injection volume of the hydraulic pump 10 to control it to a preset minimum when the operating lever of the operating unit is in a neutral position. That is, the regulator 80 minimizes the amount of working oil that returns to the tank 15 without performing any work when the operating unit is in a neutral position. Therefore, the regulator 80 adjusts the hydraulic pump 10 injection volume in a manner that decreases as the pressure P increases when the operating unit is in a neutral position. The regulator 80 also adjusts the hydraulic pump 10 injection volume in a manner that increases as the pressure P decreases when the operating unit is in operation.

[0069] The regulator 80 links the first pump 11 and the second pump 12. The regulator 80 controls the flow of working oil from the first pump 11 and the second pump 12 in such a way that the injection volume is the same.

[0070] In the detection circuit 60, the working oil that has passed through the first throttling element 61 and the second throttling element 62 returns to the tank 15 via the flow path 35. At this time, if the amount of working oil flowing into the flow path 35 (return oil) is greater than usual, the back pressure of the first throttling element 61 and the second throttling element 62 is maintained at a high level. If the back pressure of the first throttling element 61 and the second throttling element 62 is maintained at a high level, there is a possibility that the pressure P detected by the detection circuit 60 does not decrease. In this state, the regulator 80 continuously detects the high pressure P and therefore controls the flow by reducing the injection volume of the hydraulic pump 10. Therefore, there is a possibility that the hydraulic pump 10 is not supplying working oil at its maximum flow rate.

[0071] Therefore, the back pressure switching valve 70 connected to the detection circuit 60 switches according to the pressure P detected by the detection circuit 60, allowing the working oil to flow from the first throttling element 61 and the second throttling element 62 to the flow path 35 or blocking the flow.

[0072] like Figure 3 As shown, the upstream side of the back pressure switching valve 70 is connected to the flow path 37 on the downstream side of the first throttling element 61 and the second throttling element 62. The downstream side of the back pressure switching valve 70 is connected to the flow path 35 and the discharge flow path 36. The back pressure switching valve 70 includes a switching valve 71 that switches the flow path to either the flow path 35 or the discharge flow path 36.

[0073] When the negative control pressure detected at the first throttling element 61 and the second throttling element 62 is above the reference value, the back pressure switching valve 70 actuates the switching valve 71 to connect flow path 37 to flow path 35. In this case, the back pressure switching valve 70 allows working oil to flow from flow path 37 to flow path 35. The working oil flowing in flow path 35 flows into the oil cooler 13.

[0074] When the negative control pressure detected at the first throttling element 61 and the second throttling element 62 is less than the reference value, the back pressure switching valve 70 actuates the switching valve 71 to block the flow of working oil from flow path 37 to flow path 35. In this case, the back pressure switching valve 70 blocks the inflow of working oil to the oil cooler 13 and allows the working oil to flow from flow path 37 to the discharge flow path 36. The back pressure switching valve 70 allows the working oil to flow directly into the tank 15 without passing through the oil cooler 13.

[0075] Next, the structure of the back pressure switching valve 70 will be explained.

[0076] like Figure 4A As shown, the back pressure switching valve 70 includes a switching valve 71 formed in a cylindrical shape. The switching valve 71 is a check valve that switches the flow direction of the working oil passing through flow path 37 to either flow path 35 or discharge flow path 36. Flow path 35 is connected to flow path 37 at its downstream end in a direction orthogonal to flow path 37. Discharge flow path 36 is connected to flow path 37 at its downstream end in a straight line along flow path 37.

[0077] The switching valve 71 includes a valve body 78, a first valve seat 72, a second valve seat 77, and a throttling orifice 74.

[0078] The valve body 78 extends in the straight direction of the flow path 37.

[0079] A first valve seat 72 is formed on one end of the valve body 78. The first valve seat 72 is formed with a diameter larger than that of the valve body 78. The first valve seat 72 is cylindrical. The first valve seat 72 has a conical surface 71a formed by chamfering the corners.

[0080] When the negative control pressure is less than the reference pressure, the conical surface 71a of the first valve seat 72 abuts against the circular end of the flow path 37 (the boundary between flow path 37 and flow path 35). As a result, the switching valve 71 blocks the connection between flow path 37 and flow path 35. Figure 4B As shown, when the negative control pressure is above the reference level, the conical surface 71a of the first valve seat 72 separates from the circular end of the flow path, opening the inlet of the flow path 35. Thus, the switching valve 71 connects the flow path 37 and the flow path 35. With the flow path 37 and the flow path 35 connected, the switching valve 71 allows working oil to flow from the flow path 37 to the flow path 35.

[0081] The throttling orifice 74 has an orifice 74a and a through orifice 74b. The throttling orifice 74 is formed in such a way as to reduce the flow path of the working oil and thus generate resistance.

[0082] The orifice 74a sets one end of the switching valve 71 as one end, and extends along the axis of the switching valve 71 (the straight direction of the flow path 37) to the middle of the switching valve 71.

[0083] A through hole 74b communicates with the other end of hole 74a in the switching valve 71. The through hole 74b extends orthogonally to hole 74a. The through hole 74b opens on the side of the valve body 71a. A step 75 is formed on the side of the switching valve 71 (valve body 71a) with a diameter smaller than that of the switching valve 71.

[0084] The other end of the switching valve 71 is inserted into the return spring 76 that is hooked onto the step 75. A second valve seat 77 is formed on the other end of the valve body 71a. The second valve seat 77 has a conical surface 77a formed in a conical shape.

[0085] The conical surface 77a of the second valve seat 77 abuts against the circular end formed at the inlet of the discharge flow path 36. When the negative control pressure is above the reference level, the second valve seat 77 abuts against the circular inlet end of the discharge flow path 36. In this case, the second valve seat 77 blocks the communication between the discharge flow path 36 and the flow path 37. Figure 4A As shown, when the negative control pressure is less than the reference, the second valve seat 77 separates from the circular inlet of the discharge flow path 36. In this case, the second valve seat 77 opens the discharge flow path 36 and allows working oil to flow from the flow path 37 to the discharge flow path 36.

[0086] like Figure 4B As shown, the spring constant of the return spring 76 is adjusted so that the return spring 76 contracts when the negative control pressure is above the reference (when the resistance generated by the throttle orifice 74 is above a predetermined value). Figure 4A As shown, the spring constant of the return spring 76 is adjusted so that the return spring 76 does not contract when the negative control pressure is less than the reference (when the resistance generated by the throttle orifice 74 is less than the predetermined value).

[0087] Based on such a structure, such as Figure 4B As shown, for switching valve 71, when the negative control pressure is less than the reference pressure, the first valve seat 72 blocks the flow path 35, and the second valve seat 77 opens the discharge flow path 36. In this case, switching valve 71 allows working oil to flow from flow path 37 to discharge flow path 36. Figure 4A As shown, for the switching valve 71, when the negative control pressure is above the reference level, the return spring 76 contracts and the first valve seat 72 opens the flow path 35, and the second valve seat 77 blocks the discharge flow path 36. In this case, the switching valve 71 allows working oil to flow from the flow path 37 to the flow path 35.

[0088] Therefore, when the negative control pressure is above the reference level, the back pressure switching valve 70 allows the working oil to flow from the first throttling element 61 and the second throttling element 62 into the flow path 35. This reduces the back pressure of the first throttling element 61 and the second throttling element 62. The back pressure switching valve 70 allows the working oil to flow into the flow path 35, thereby lowering the temperature of the working oil in the oil cooler 13. As a result, overheating is suppressed, and the negative control pressure is reduced below the control pressure for maximum flow, allowing the hydraulic pump 10 to spray at its maximum flow rate.

[0089] When the negative control pressure is less than the reference value, the back pressure switching valve 70 allows the working oil to flow from the first throttling element 61 and the second throttling element 62 to the discharge flow path 36. The back pressure switching valve 70 also allows the working oil flowing in the flow path 37 to return directly to the tank 15. As a result, the back pressure of the first throttling element 61 and the second throttling element 62 is reduced. By allowing the working oil to flow to the discharge flow path 36, the back pressure switching valve 70 can reduce the negative control pressure below the control pressure of the maximum flow rate, thereby restoring the maximum flow rate of the hydraulic pump 10.

[0090] As described above, according to the hydraulic system 1, when the operating unit is neutral, if the negative control pressure (back pressure) detected by the detection circuit 60 is above the reference level, the working oil is allowed to flow from the throttling elements 61 and 62 to the oil cooler 13. This cools the working oil and suppresses overheating, and allows the negative control pressure to be reduced below the control pressure for maximum flow, thus enabling the hydraulic pump 10 to spray at its maximum flow rate.

[0091] According to hydraulic system 1, during operation of the operating unit, when the negative control pressure is less than the reference, the flow of working oil to oil cooler 13 is blocked. Therefore, the working oil returns directly to tank 15 without passing through oil cooler 13. As a result, the negative control pressure can be reduced below the control pressure for maximum flow, allowing hydraulic pump 10 to spray at maximum flow.

[0092] [Variation Example]

[0093] The hydraulic system of the aforementioned back pressure switching valve 70 can also be configured using a solenoid valve. The hydraulic control method for the back pressure switching valve 70 can also be electrically controlled by a control device.

[0094] The control device 200 includes, for example, a switching valve 210 that switches the flow path of the working oil; a detection unit 220 that detects the negative control pressure; and a control unit 230 that switches the flow path of the switching valve 210 based on the detection value detected by the detection unit 220. The switching valve 210 is an electrically controlled solenoid valve. The detection unit 220 is, for example, a pressure sensor provided in the flow path.

[0095] When the negative control pressure is above the reference level, the control unit 230 uses the switching valve 210 to allow the working oil to flow to the oil cooler 13. When the negative control pressure is below the reference level, the control unit 230 uses the switching valve 210 to block the flow of working oil to the oil cooler 13. In this case, the working oil flows to the tank 15 without passing through the oil cooler 13.

[0096] The aforementioned control units are implemented by processors such as CPUs (Central Processing Units) executing programs (software) stored in program memory. Some or all of these functional units can be implemented in hardware such as LSIs (Large Scale Integration), ASICs (Application Specific Integrated Circuits), and FPGAs (Field-Programmable Gate Arrays), or through a combination of software and hardware. Programs can be pre-stored on storage devices such as HDDs (Hard Disk Drives) and flash memory, or on removable storage media such as DVDs and CD-ROMs, and loaded into the storage unit via a drive mounted on the storage medium.

[0097] The present invention has been described above as one embodiment, but the present invention is not limited to the above embodiment and can be appropriately modified without departing from its spirit. For example, the example shown is that the throttle orifice 74 of the back pressure switching valve 70 is provided inside the switching valve 71, but it is not limited thereto, and the throttle orifice 74 may also be provided on the discharge flow path 36 side.

Claims

1. A hydraulic system in which working oil discharged from an actuator is returned to a tank via an oil cooler, wherein, This hydraulic system has the following features: Throttling device; A flow path that connects the throttling element and the tank via the oil cooler; The discharge path connects the throttling element and the tank; and A switching valve that switches the flow direction of the working oil based on the negative control pressure generated by the throttling element. When the negative control pressure generated by the throttling element is above a reference level, the switching valve allows the working oil to flow into the flow path. When the negative control pressure is less than the reference, the switching valve blocks the inflow of working oil from the throttling element into the flow path, and allows the working oil to flow into the discharge flow path.

2. The hydraulic system according to claim 1, wherein, The switching valve is connected to the downstream side of the throttling element.

3. The hydraulic system according to claim 1 or 2, wherein, The switching valve includes: The first valve seat, when the negative control pressure is above the reference, connects the throttling element and the flow path; when the negative control pressure is below the reference, the first valve seat blocks the connection between the throttling element and the discharge flow path. The second valve seat, when the negative control pressure is above the reference, blocks the connection between the throttling element and the discharge path; when the negative control pressure is below the reference, the second valve seat connects the throttling element and the discharge path.

4. A construction machine comprising the hydraulic system described in any one of claims 1 to 3.

5. A hydraulic control method, wherein, In this hydraulic control method, When the negative control pressure in the throttling device that generates negative control pressure is above a reference level, the working oil flows through the flow path connecting the throttling device and the oil cooler, which is connected to the upstream side of a tank where the working oil is stored. When the negative control pressure is less than the reference, the inflow of working oil into the flow path is blocked, and the working oil is allowed to flow into the discharge flow path connected to the tank.

6. A computer storage medium, readable, storing a program that causes a computer to perform the following processes: When the negative control pressure in the throttling device that generates negative control pressure is above a reference level, the working oil is allowed to flow into the flow path connecting the throttling device and the oil cooler, which is connected to the upstream side of the tank where the working oil is stored. When the negative control pressure is less than the reference, the inflow of working oil into the flow path is blocked, and the working oil is allowed to flow into the discharge flow path connected to the tank.

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