Fluid pressure control device

Abstract

A load holding mechanism 20 has a switch valve (22) that switches operation of an operation check valve (21). The switch valve (22) is provided in a first drain passage (76a) connected to a pilot chamber (23), and has a gas release valve (80) for discharging gas from the pilot chamber (23) to the drain side. The gas release valve (80) has a valve body (82) that opens and closes a passage (81). When a pilot pressure supply source (5) is stopped, the valve body (82) is brought into contact with a first seat portion (81b) by a bias force of a biasing member (83), and blocks the passage (81). When the pilot pressure supply source (5) is driven and a pilot pressure of the pilot chamber (23) is less than a predetermined pressure lower than a pilot pressure at which a spool (56) moves, the valve body (82) moves against the bias force of the biasing member (83) and separates from the first seat portion (81b) to allow a flow of fluid from the pilot chamber (23) to the drain side.

Description

Fluid Pressure Control Device

[0001] The present invention relates to a fluid pressure control device.

[0002] Japanese Patent Application Laid-Open Publication No. 2010-101400 discloses a fluid pressure control device for controlling the operation of work equipment, which includes a control valve that switches the supply and discharge of hydraulic oil to and from a cylinder to control the extension and contraction movement of the cylinder, and a load holding mechanism that is installed in a main passage that connects the load side pressure chamber of the cylinder to the control valve.

[0003] The load holding mechanism includes a pilot operated check valve and a meter-out control valve that operates in response to pilot pressure to switch the operation of the pilot operated check valve. The meter-out control valve includes a spool, a pilot chamber to which the pilot pressure is introduced, and a piston that is slidably accommodated in the pilot chamber and receives the pilot pressure to move the spool.

[0004] In this type of fluid pressure control device, a drain chamber communicating with a tank is defined between the spool and the piston so that the thrust of the piston is efficiently transmitted to the spool when pilot pressure is introduced into the pilot chamber.

[0005] An annular gap is provided between the piston and the housing to allow air to be discharged from the pilot chamber to the drain chamber. When the work equipment is stopped, the air on the drain chamber side moves to the pilot chamber side through the annular gap between the piston and the housing. When the work equipment is started, the air that has moved to the pilot chamber side delays the increase in pilot pressure in the pilot chamber in response to the operator's input operation, and the increase in pilot pressure in the pilot chamber is completed only after the air on the pilot chamber side has been discharged to the drain chamber through the annular gap between the piston and the housing.

[0006] In this way, the gas on the pilot chamber side causes a delay in response to input operations by the operator when starting up the work equipment.

[0007] The present invention aims to prevent the movement of gas from the drain side to the pilot chamber side and to suppress response delays caused by the influence of the gas.

[0008] According to one aspect of the present invention, there is provided a fluid pressure control device for controlling the extension and retraction of a cylinder that drives a load, the fluid pressure control device comprising: a control valve that controls the supply of working fluid to the cylinder; a pilot control valve that controls the pilot pressure introduced to the control valve from a pilot pressure supply source; a main passage that connects the control valve to a load-side pressure chamber of the cylinder on which a load pressure due to a load acts when the control valve is in a neutral position; and a load holding mechanism provided in the main passage, wherein the load holding mechanism comprises an operate check valve that allows the flow of working fluid from the control valve to the load-side pressure chamber, while allowing the flow of working fluid from the load-side pressure chamber to the control valve in accordance with a back pressure; and a switching valve that operates in conjunction with the control valve by the pilot pressure introduced through the pilot control valve and switches the operation of the operate check valve, and the switching valve controls the pilot control valve. the pilot chamber into which pilot pressure is introduced through a valve, a spool that moves in response to the pilot pressure in the pilot chamber, a drain passage connected to the pilot chamber, and a gas vent valve provided in the drain passage for discharging gas from the pilot chamber to the drain side, the gas vent valve having a passage provided between the pilot chamber side and the drain side, a valve body that opens and closes the passage, and a biasing member that biases the valve body, and when the pilot pressure supply source is stopped, the valve body comes into contact with a first seat portion by the biasing force of the biasing member to block the passage, and when the pilot pressure supply source is driven and the pilot pressure in the pilot chamber is less than a predetermined pressure that is lower than the pilot pressure at which the spool moves, the valve body moves against the biasing force of the biasing member and away from the first seat, allowing fluid to flow from the pilot chamber to the drain side.

[0009] FIG. 1 is a diagram showing a part of a hydraulic excavator. FIG. 2 is a fluid pressure circuit diagram of a fluid pressure control device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a load holding mechanism of a fluid pressure control device according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of the periphery of a gas vent valve. FIG. 5 is a graph showing the relationship between the pilot pressure in a pilot chamber and the flow rate of air flowing from the pilot chamber to the drain side. FIG. 6 is a cross-sectional view of the periphery of a gas vent valve in a load holding mechanism of a fluid pressure control device according to a modified embodiment of the present invention.

[0010] Hereinafter, a fluid pressure control device according to an embodiment of the present invention will be described with reference to the drawings.

[0011] A fluid pressure control device controls the operation of hydraulic work equipment such as a hydraulic excavator. In this embodiment, a hydraulic control device 100 will be described that controls the extension and retraction of a cylinder 2 that drives an arm (load) 1 of a hydraulic excavator shown in FIGS. 1 and 2 . The fluid pressure control device may also control the extension and retraction of a lift cylinder mounted on a forklift or the like. In the following, a case will be described in which hydraulic oil is used as the working fluid for the cylinder 2, but instead of hydraulic oil, for example, a water-soluble substitute liquid or the like may be used.

[0012] First, the hydraulic circuit of the hydraulic control device 100 will be described with reference to Fig. 2. The cylinder 2 includes a cylindrical cylinder tube 2c, a piston 2d slidably inserted into the cylinder tube 2c and dividing the interior of the cylinder tube 2c into a rod-side chamber 2a and an anti-rod-side chamber 2b, and a rod 2e having one end connected to the piston 2d and the other end extending outside the cylinder tube 2c and connected to the arm 1.

[0013] The hydraulic excavator is equipped with a power source such as an engine or an electric motor, and the power from the engine drives a pump 4 serving as a fluid pressure supply source and a pilot pump 5 serving as a pilot pressure supply source. The pilot pump 5 may be eliminated, and the pump 4 may also be used as the pilot pressure supply source. In other words, the pump 4 may be used as both the fluid pressure supply source and the pilot pressure supply source.

[0014] The hydraulic control device 100 includes a control valve 6 that controls the supply of hydraulic oil from the pump 4 to the cylinder 2 , and a pilot control valve 9 that controls the pilot pressure guided from the pilot pump 5 to the control valve 6 .

[0015] The control valve 6 and the rod side chamber 2 a of the cylinder 2 are connected by a first main passage 7 , and the control valve 6 and the anti-rod side chamber 2 b of the cylinder 2 are connected by a second main passage 8 .

[0016] The control valve 6 is operated by a pilot pressure that is guided from the pilot pump 5 through the pilot control valve 9 to the pilot chambers 6 a and 6 b when the operator of the hydraulic excavator manually operates the control lever 10 .

[0017] Specifically, when pilot pressure is introduced into the pilot chamber 6a, the control valve 6 switches to position 6A, and hydraulic oil is supplied from the pump 4 to the rod side chamber 2a through the first main passage 7, while hydraulic oil in the anti-rod side chamber 2b is discharged to the tank T through the second main passage 8. As a result, the cylinder 2 contracts, and the arm 1 rises in the direction of the arrow 18 shown in FIG.

[0018] On the other hand, when pilot pressure is introduced into the pilot chamber 6b, the control valve 6 switches to position 6B, and hydraulic oil is supplied from the pump 4 to the anti-rod side chamber 2b through the second main passage 8, while hydraulic oil in the rod side chamber 2a is discharged to the tank T through the first main passage 7. As a result, the cylinder 2 is extended, and the arm 1 moves down in the direction of arrow 19 shown in FIG.

[0019] When no pilot pressure is introduced into the pilot chambers 6a and 6b, the control valve 6 is in position 6C, the supply and discharge of hydraulic oil to the cylinder 2 is cut off, and the arm 1 remains stopped.

[0020] In this way, the control valve 6 has three positions: a contraction position 6A for contracting the cylinder 2, an extension position 6B for extending the cylinder 2, and a neutral position 6C for holding the load on the cylinder 2. The control valve 6 switches the supply and discharge of hydraulic oil in the cylinder 2 and controls the extension and retraction of the cylinder 2.

[0021] 1, when the control valve 6 is switched to the neutral position 6C to stop the movement of the arm 1 while the bucket 13 is lifted, a force acts on the cylinder 2 in the extending direction due to the weight of the bucket 13, arm 1, etc. In this way, in the cylinder 2 that drives the arm 1, the rod-side chamber 2a becomes a load-side pressure chamber to which load pressure acts when the control valve 6 is in the neutral position 6C.

[0022] A load holding mechanism 20 is provided in the first main passage 7 connected to the rod side chamber 2a, which is a load side pressure chamber. The load holding mechanism 20 holds the load pressure in the rod side chamber 2a when the control valve 6 is in the neutral position 6C, and is fixed to the surface of the cylinder 2 as shown in FIG.

[0023] In the cylinder 15 that drives the boom 14 (see FIG. 1), the anti-rod side chamber 15b serves as a load side pressure chamber, and therefore, when a load holding mechanism 20 is provided on the boom 14, the load holding mechanism 20 is provided in the main passage connected to the anti-rod side chamber 15b.

[0024] The load holding mechanism 20 has an operated check valve 21 provided in the first main passage 7, and a switching valve 22 that operates in conjunction with the control valve 6 by pilot pressure guided through the pilot control valve 9, and switches the operation of the operated check valve 21.

[0025] The operated check valve 21 has a valve element 24 that opens and closes the first main passage 7, a seat portion 28 on which the valve element 24 sits, a back pressure chamber 25 facing the back surface of the valve element 24, and a passage 26 formed in the valve element 24 that constantly guides the hydraulic oil in the rod-side chamber 2a to the back pressure chamber 25. A throttle 26a is provided in the passage 26 to apply resistance to the hydraulic oil passing through it.

[0026] The first main passage 7 has a cylinder-side first main passage 7 a connecting the rod-side chamber 2 a and the operated check valve 21 , and a control-valve-side first main passage 7 b connecting the operated check valve 21 and the control valve 6 .

[0027] The valve body 24 is formed with a first pressure-receiving surface 24a on which the pressure of the control valve side first main passage 7b acts, and a second pressure-receiving surface 24b on which the pressure of the rod side chamber 2a acts through the cylinder side first main passage 7a.

[0028] A spring 27 serving as a biasing member that biases the valve body 24 in the closing direction is accommodated in the back pressure chamber 25. The pressure in the back pressure chamber 25 and the biasing force of the spring 27 act in a direction that causes the valve body 24 to seat on the seat portion 28.

[0029] When the valve element 24 is seated on the seat portion 28, the operate check valve 21 functions as a check valve that blocks the flow of hydraulic oil from the rod side chamber 2a to the control valve 6. In other words, the operate check valve 21 prevents leakage of hydraulic oil from the rod side chamber 2a, maintains the load pressure, and maintains the stopped state of the arm 1.

[0030] The switching valve 22 has a pilot chamber 23 to which pilot pressure is introduced via the pilot control valve 9, a spool 56 (see Figure 3) that moves according to the pilot pressure in the pilot chamber 23, a spring 36 as a biasing member that biases the spool 56 in the closing direction, a spring chamber 54 (see Figure 3) that accommodates the spring 36, and a drain passage 76 connected to the pilot chamber 23 and the spring chamber 54.

[0031] A bypass passage 30 and a back pressure passage 31 are connected to the upstream side of the switching valve 22, and a downstream passage 38 is connected to the downstream side of the switching valve 22. The bypass passage 30 is a passage for guiding the hydraulic oil in the rod side chamber 2a to the control valve-side first main passage 7b, bypassing the operated check valve 21. The back pressure passage 31 is a passage for guiding the hydraulic oil in the back pressure chamber 25 to the control valve-side first main passage 7b. The downstream passage 38 is a passage for guiding the hydraulic oil from the bypass passage 30 and the back pressure passage 31 to the control valve-side first main passage 7b.

[0032] The switching valve 22 switches the communication between the bypass passage 30 and the back pressure passage 31 and the downstream passage 38, and controls the flow of hydraulic oil in the first main passage 7, which is on the meter-out side when the cylinder 2 is extended.

[0033] The switching valve 22 has three ports: a first supply port 32 communicating with the bypass passage 30, a second supply port 33 communicating with the back pressure passage 31, and a discharge port 34 communicating with the downstream passage 38. The switching valve 22 also has three positions: a shutoff position 22A, a first communicating position 22B, and a second communicating position 22C.

[0034] When the pilot pressure is introduced into the pilot chamber 6b of the control valve 6, the pilot pressure is also introduced into the pilot chamber 23. In other words, when the control valve 6 is switched to the extension position 6B, the switching valve 22 is also switched to the first communication position 22B or the second communication position 22C.

[0035] Specifically, when no pilot pressure is introduced into the pilot chamber 23, the switching valve 22 is maintained in the shutoff position 22A by the biasing force of the spring 36. In the shutoff position 22A, both the first supply port 32 and the second supply port 33 are shut off.

[0036] When a pilot pressure equal to or greater than a first predetermined pressure and less than a second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 switches to the first communication position 22B. In the first communication position 22B, the first supply port 32 communicates with the discharge port 34. As a result, the hydraulic oil in the rod-side chamber 2a is introduced from the bypass passage 30 through the switching valve 22 to the downstream passage 38. In other words, the hydraulic oil in the rod-side chamber 2a bypasses the operated check valve 21 and is introduced into the control-valve-side first main passage 7b. At this time, resistance is applied to the flow of hydraulic oil by the orifice 37. The second supply port 33 remains blocked.

[0037] When a pilot pressure equal to or greater than the second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 switches to the second communication position 22C. In the second communication position 22C, the first supply port 32 communicates with the discharge port 34, and the second supply port 33 also communicates with the discharge port 34. As a result, the hydraulic oil in the back pressure chamber 25 is introduced from the back pressure passage 31 through the switching valve 22 to the downstream passage 38. At this time, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37 and is introduced into the control valve-side first main passage 7b, and is discharged from the control valve 6 to the tank T. As a result, a pressure difference occurs across the throttle 26a, and the pressure in the back pressure chamber 25 decreases. As a result, the force acting on the valve element 24 in the closing direction decreases, the valve element 24 moves away from the seat portion 28, and the function of the operated check valve 21 as a check valve is released.

[0038] The load holding mechanism 20 has a relief valve 41 that opens when the pressure in the rod-side chamber 2a reaches a predetermined pressure, and discharges the hydraulic oil in the rod-side chamber 2a to the tank T. The relief valve 41 is provided in a relief passage 40 that branches off from the bypass passage 30 upstream of the switching valve 22. The relief passage 40 may be provided by branching off from the cylinder-side first main passage 7a, or may be directly connected to the rod-side chamber 2a.

[0039] The drain passage 76 has a first drain passage 76a connected to the pilot chamber 23, a second drain passage 76b connected to the spring chamber 54, and a joint drain passage 76c formed by the joining of the first drain passage 76a and the second drain passage 76b. The joint drain passage 76c communicates with a drain port 77 that opens on the outer surface of the body 60 (see FIG. 3) of the load holding mechanism 20. The drain port 77 is connected to the tank T through a drain hose 78.

[0040] A relief valve 43 that opens when the pressure in the control valve side first main passage 7b reaches a predetermined pressure is connected to the control valve side first main passage 7b. A relief valve 44 that opens when the pressure in the second main passage 8 reaches a predetermined pressure is connected to the second main passage 8. The relief valves 43 and 44 are provided to release high pressures that are generated in the rod side chamber 2a and the anti-rod side chamber 2b of the cylinder 2, respectively, when a large external force is applied to the arm 1.

[0041] Next, the switching valve 22 will be described in detail, mainly with reference to Fig. 3. Fig. 3 is a cross-sectional view of the load holding mechanism 20, showing a state in which pilot pressure is not introduced to the pilot chamber 23 and the switching valve 22 is in the shut-off position 22A. In Fig. 3, components that are assigned the same reference numerals as those shown in Fig. 2 have the same configuration as those shown in Fig. 2.

[0042] The switching valve 22 is incorporated into a body 60 of the load holding mechanism 20. A spool hole 60a is formed in the body 60, and a substantially cylindrical sleeve 61 is inserted into the spool hole 60a. The spool 56 is slidably incorporated into the sleeve 61.

[0043] A spring chamber 54 is defined by a cap 57 on the side of one end surface 56a of the spool 56. The spring chamber 54 is connected to a second drain passage 76b through a notch 61a formed in the end surface of the sleeve 61. Hydraulic oil that leaks into the spring chamber 54 is drained from the second drain passage 76b to the tank T.

[0044] The spring chamber 54 accommodates an annular first spring bearing member 45, the end face of which abuts against one end face 56a of the spool 56 and into whose hollow portion a pin portion 56c formed to protrude from the one end face 56a of the spool 56 is inserted, and a second spring bearing member 46 disposed near the bottom of the cap 57. The spring 36 is interposed in a compressed state between the first spring bearing member 45 and the second spring bearing member 46, and biases the spool 56 in the closing direction via the first spring bearing member 45.

[0045] A pilot chamber 23 is defined to the side of the other end surface 56b of the spool 56. The pilot chamber 23 is defined by a pilot hole 60b formed in communication with a spool hole 60a of the body 60, a cap 58 closing the pilot hole 60b, and the other end surface 56b of the spool 56. A pilot passage 52 formed in the body 60 is connected to the pilot chamber 23, and pilot pressure oil (pilot fluid) is guided through the pilot passage 52. The pilot pressure of the pilot chamber 23 acts on the other end surface 56b of the spool 56, causing the spool 56 to move against the biasing force of the spring 36. The spool 56 stops at a position where the biasing force of the spring 36 acting on the one end surface 56a and the load due to the pilot pressure acting on the other end surface 56b are balanced, and the switching position of the switching valve 22 is set at the stop position of the spool 56.

[0046] A first drain passage 76a formed in the body 60 is also connected to the pilot chamber 23. A gas vent valve 80 is provided in the first drain passage 76a to discharge air from the pilot chamber 23 to the drain side (tank T side). When the pilot pressure in the pilot chamber 23 exceeds a predetermined pressure, the gas vent valve 80 blocks the flow of pilot pressure oil from the pilot chamber 23 to the drain side, and therefore does not adversely affect the operation of the spool 56. The gas vent valve 80 will be described in detail later. Note that the gas vent valve 80 is not shown in FIG. 2.

[0047] The sleeve 61 has three ports formed therein: a first supply port 32 communicating with the bypass passage 30 (see FIG. 2), a second supply port 33 communicating with the back pressure passage 31 (see FIG. 2), and a discharge port 34 communicating with the downstream passage 38 (see FIG. 2).

[0048] The outer peripheral surface of the spool 56 is partially cut out in an annular shape, and the cut out portion and the inner peripheral surface of the sleeve 61 form a first pressure chamber 64, a second pressure chamber 65, a third pressure chamber 66, and a fourth pressure chamber 67.

[0049] The first pressure chamber 64 is constantly connected to the exhaust port 34. The third pressure chamber 66 is constantly connected to the first supply port 32. A plurality of orifices 37 are formed on the outer peripheral surface of the land portion 72 of the spool 56, which communicate between the third pressure chamber 66 and the second pressure chamber 65 as the spool 56 moves against the biasing force of the spring 36. The fourth pressure chamber 67 is constantly connected to the second pressure chamber 65 through a pressure introducing passage 68 formed in the spool 56 in the axial direction.

[0050] When the operating lever 10 is not operated and pilot pressure is not introduced into the pilot chamber 23, the biasing force of the spring 36 presses the poppet valve 70 formed in the spool 56 against a valve seat 71 formed on the inner periphery of the sleeve 61, blocking communication between the second pressure chamber 65 and the first pressure chamber 64. Therefore, communication between the first supply port 32 and the discharge port 34 is blocked. As a result, hydraulic oil in the rod-side chamber 2a does not leak into the discharge port 34. This state corresponds to the blocked position 22A of the switching valve 22. When the poppet valve 70 is seated on the valve seat 71 by the biasing force of the spring 36, a small gap exists between the end face of the first spring bearing member 45 and the end face of the sleeve 61, so the poppet valve 70 is reliably seated against the valve seat 71 by the biasing force of the spring 36.

[0051] When the operating lever 10 is operated to introduce pilot pressure into the pilot chamber 23, and the load of the pilot pressure acting on the spool 56 becomes greater than the biasing force of the spring 36, the spool 56 moves against the biasing force of the spring 36. As a result, the poppet valve 70 moves away from the valve seat 71, and the third pressure chamber 66 and the second pressure chamber 65 communicate with each other through the multiple orifices 37. Therefore, the first supply port 32 communicates with the discharge port 34 through the third pressure chamber 66, the second pressure chamber 65, and the first pressure chamber 64. Due to the communication between the first supply port 32 and the discharge port 34, the hydraulic oil in the rod-side chamber 2a is introduced to the downstream passage 38 (see FIG. 2 ) through the orifices 37. This state corresponds to the first communicating position 22B of the switching valve 22.

[0052] When the pilot pressure introduced into the pilot chamber 23 increases, the spool 56 moves further against the biasing force of the spring 36, and the second supply port 33 communicates with the fourth pressure chamber 67. As a result, the second supply port 33 communicates with the discharge port 34 through the fourth pressure chamber 67, the pressure introducing passage 68, the second pressure chamber 65, and the first pressure chamber 64. Due to the communication between the second supply port 33 and the discharge port 34, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37 and is introduced to the downstream passage 38 (see FIG. 2 ). This state corresponds to the second communication position 22C of the switching valve 22.

[0053] Next, the operation of the hydraulic control device 100 will be described with reference to FIGS.

[0054] When the control valve 6 is in the neutral position 6C, the hydraulic oil discharged by the pump 4 is not supplied to the cylinder 2. At this time, no pilot pressure is introduced into the pilot chamber 23 of the switching valve 22, so the switching valve 22 is in the shut-off position 22A.

[0055] As a result, the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the rod side chamber 2a. Here, the pressure receiving area of ​​the valve element 24 in the closing direction (the area of ​​the back surface of the valve element 24) is larger than the area of ​​the second pressure receiving surface 24b, which is the pressure receiving area in the opening direction, so the load acting on the back surface of the valve element 24 due to the pressure in the back pressure chamber 25 and the biasing force of the spring 27 cause the valve element 24 to be seated on the seat portion 28. In this way, the operated check valve 21 prevents leakage of hydraulic oil from the rod side chamber 2a, and the stopped state of the arm 1 is maintained.

[0056] When the operating lever 10 is operated and pilot pressure is introduced from the pilot control valve 9 to the pilot chamber 6a of the control valve 6, the control valve 6 switches to the retracted position 6A by an amount corresponding to the pilot pressure. When the control valve 6 switches to the retracted position 6A, the discharge pressure of the pump 4 acts on the first pressure-receiving surface 24a of the operated check valve 21. At this time, the switching valve 22 is in the shut-off position 22A without introducing pilot pressure to the pilot chamber 23, so the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the rod-side chamber 2a. When the load acting on the first pressure-receiving surface 24a becomes greater than the total load of the load acting on the back surface of the valve disc 24 due to the pressure in the back pressure chamber 25 and the biasing force of the spring 27, the valve disc 24 moves away from the seat portion 28. When the operated check valve 21 opens in this manner, hydraulic oil discharged from the pump 4 is supplied to the rod-side chamber 2a, and the cylinder 2 retracts. As a result, the arm 1 moves up in the direction of the arrow 18 shown in FIG.

[0057] When the operating lever 10 is operated and pilot pressure is introduced from the pilot control valve 9 to the pilot chamber 6b of the control valve 6, the control valve 6 switches to the extension position 6B by an amount corresponding to the pilot pressure. At the same time, pilot pressure is also introduced to the pilot chamber 23, so the switching valve 22 switches to the first communication position 22B or the second communication position 22C depending on the supplied pilot pressure.

[0058] When the pilot pressure introduced into the pilot chamber 23 is equal to or greater than the first predetermined pressure and less than the second predetermined pressure, the switching valve 22 switches to the first communication position 22B. In this case, communication between the second supply port 33 and the discharge port 34 is blocked, so the back pressure chamber 25 of the operated check valve 21 is maintained at the pressure of the rod side chamber 2a, and the operated check valve 21 maintains its closed state.

[0059] On the other hand, because the first supply port 32 communicates with the discharge port 34, the hydraulic oil in the rod-side chamber 2a is guided from the bypass passage 30 through the throttle 37 to the downstream passage 38, and is then discharged from the control valve-side first main passage 7b through the control valve 6 to the tank T. In addition, because the hydraulic oil discharged from the pump 4 is supplied to the anti-rod-side chamber 2b, the cylinder 2 extends. As a result, the arm 1 descends in the direction of the arrow 19 shown in FIG. 1 .

[0060] Here, the switching valve 22 is switched to the first communication position 22B mainly when performing crane work to lower an object attached to the bucket 13 to a target position. During crane work, it is necessary to extend the cylinder 2 at a low speed to slowly lower the arm 1 in the direction of arrow 19. Therefore, the pilot pressure introduced to the pilot chamber 6b of the control valve 6 is small, and the control valve 6 is only switched slightly to the extended position 6B. For this reason, the pilot pressure introduced to the pilot chamber 23 of the switching valve 22 is also small, and is equal to or greater than the first predetermined pressure and less than the second predetermined pressure, and the switching valve 22 is only switched to the first communication position 22B. Therefore, the hydraulic oil in the rod-side chamber 2a is discharged through the orifice 37, and the arm 1 is lowered at a low speed suitable for crane work.

[0061] Furthermore, when selector valve 22 is in first communicating position 22B, even if a situation occurs in which control valve side first main passage 7b ruptures or the like and hydraulic oil leaks to the outside, the flow rate of hydraulic oil discharged from rod side chamber 2a is limited by orifice 37, thereby suppressing the falling speed of bucket 13. For this reason, selector valve 22 can be switched to shut-off position 22A before bucket 13 falls to the ground, preventing bucket 13 from falling suddenly.

[0062] In this way, the throttle 37 serves to suppress the descending speed of the cylinder 2 when the operated check valve 21 is closed, and also to suppress the falling speed of the bucket 13 when the control valve side first main passage 7b bursts.

[0063] When the pilot pressure introduced into the pilot chamber 23 is equal to or higher than the second predetermined pressure, the switching valve 22 is switched to the second communication position 22C. In this case, the second supply port 33 is connected to the discharge port 34, so that the hydraulic oil in the back pressure chamber 25 of the operated check valve 21 is introduced from the back pressure passage 31 to the downstream passage 38, bypassing the throttle 37, and is then discharged from the control valve-side first main passage 7b through the control valve 6 to the tank T. This generates a pressure difference across the throttle 26a, reducing the pressure in the back pressure chamber 25. This reduces the force acting on the valve element 24 in the closing direction, causing the valve element 24 to move away from the seat portion 28, and the function of the operated check valve 21 as a check valve is released.

[0064] In this way, the operated check valve 21 allows the flow of hydraulic oil from the control valve 6 to the rod side chamber 2a, while also operating to allow the flow of hydraulic oil from the rod side chamber 2a to the control valve 6 in accordance with the back pressure, which is the pressure in the back pressure chamber 25.

[0065] When the operate check valve 21 opens, the hydraulic oil in the rod side chamber 2a passes through the first main passage 7 and is discharged to the tank T, causing the cylinder 2 to quickly extend. In other words, when the switching valve 22 is switched to the second communicating position 22C, the flow rate of hydraulic oil discharged from the rod side chamber 2a increases, causing the flow rate of hydraulic oil supplied to the anti-rod side chamber 2b to increase, thereby increasing the extension speed of the cylinder 2. As a result, the arm 1 quickly descends in the direction of arrow 19.

[0066] The switching valve 22 is switched to the second communication position 22C when excavation work or the like is being performed, and the pilot pressure introduced to the pilot chamber 6b of the control valve 6 is large, so that the control valve 6 is switched largely to the extension position 6B. Therefore, the pilot pressure introduced to the pilot chamber 23 of the switching valve 22 is also large and exceeds the second predetermined pressure, so that the switching valve 22 is switched to the second communication position 22C.

[0067] Next, the gas vent valve 80 will be described mainly with reference to Figure 4. Figure 4 is a cross-sectional view of the area around the gas vent valve 80. Below, a case will be described in which the gas vent valve 80 discharges air from the pilot chamber 23 to the drain chamber 51, but what is discharged by the gas vent valve 80 is not limited to air and may be other gases.

[0068] Conventional hydraulic control devices have had a problem in that, when the hydraulic excavator is stopped, air on the drain side moves toward the pilot chamber 23. Specifically, when the hydraulic excavator is stopped, hydraulic oil in the pilot chamber 23 and the pilot passage 52 flows down into the tank T due to gravity, creating negative pressure in the pilot chamber 23 and the pilot passage 52. As a result, air that has been sucked from the tank T into the combined drain passage 76c and the first drain passage 76a moves toward the pilot chamber 23 and the pilot passage 52. Furthermore, as shown in FIG. 1 , the load holding mechanism 20 provided in the cylinder 2 that drives the arm 1 is located at the highest position in the hydraulic excavator. Therefore, when the hydraulic excavator is stopped for a long period of time, air accumulates in the first drain passage 76a, the second drain passage 76b, the combined drain passage 76c, and the drain hose 78. The accumulated air moves toward the pilot chamber 23 and the pilot passage 52.

[0069] If air moves from the drain side to the pilot chamber 23 side in this way, when the hydraulic excavator starts from a stopped state, the increase in pilot pressure in the pilot chamber 23 in response to input operations by the operator is delayed due to the influence of the air that has moved to the pilot chamber 23 side. In this way, the air on the pilot chamber 23 side causes a delay in the response of the cylinder 2 to input operations by the operator when the hydraulic excavator starts.

[0070] To address this issue, in this embodiment, the gas vent valve 80 provided in the first drain passage 76a discharges air from the pilot chamber 23 to the drain side and blocks the flow of air from the drain side to the pilot chamber 23. This will be described in detail below.

[0071] The gas vent valve 80 has a housing 90, a passage 81 formed in the housing 90 and extending between the pilot chamber 23 side and the drain side, a valve element 82 that opens and closes the passage 81, and a spring 83 that serves as a biasing member that biases the valve element 82. The passage 81 is formed to pass through the housing 90 along the longitudinal direction of the first drain passage 76a. The valve element 82 is a sphere and is provided midway through the passage 81. The spring 83 is provided in a compressed state between the valve element 82 and the housing 90.

[0072] The passage 81 has a valve element accommodating portion 81a that accommodates the valve element 82. The inner diameter of the valve element accommodating portion 81a is larger than the outer diameter of the valve element 82. The inner diameter of the passage 81 other than the valve element accommodating portion 81a is smaller than the outer diameter of the valve element 82. One end of the spring 83 is accommodated in the valve element accommodating portion 81a and contacts the valve element 82, while the other end is provided outside the valve element accommodating portion 81a and contacts a step 90a formed on the housing 90. As a result, the valve element accommodating portion 81a is formed with an annular first seat portion 81b with which the valve element 82 contacts due to the biasing force of the spring 83, and a second seat portion 81c with which the valve element 82 contacts due to the pressure in the pilot chamber 23. The valve element 82 moves between the first seat portion 81b and the second seat portion 81c within the valve element accommodating portion 81a.

[0073] The housing 90 includes a first housing 91 mounted in the first drain passage 76a and a second housing 92 attached to the first housing 91. A hole 91a is formed in the end surface of the first housing 91 facing the pilot chamber 23, and the second housing 92 is attached to the hole 91a. An O-ring 99 serving as a seal member is provided between the inner surface of the first drain passage 76a and the outer peripheral surface of the first housing 91 to prevent leakage of pilot pressure oil therebetween. Instead of providing the O-ring 99, the first housing 91 may be press-fitted into the first drain passage 76a. Furthermore, an O-ring 98 serving as a seal member is provided between the outer peripheral surface of the second housing 92 and the inner peripheral surface of the hole 91a to prevent leakage of pilot pressure oil therebetween. Instead of providing the O-ring 98, the second housing 92 may be press-fitted into the hole 91a. The first housing 91 may be formed integrally with the body 60.

[0074] The second housing 92 is formed with a small diameter hole 92a that communicates with the pilot chamber 23, and a large diameter hole 92b that communicates with the small diameter hole 92a and has a larger inner diameter than the small diameter hole 92a. The small diameter hole 92a and the large diameter hole 92b form part of the passage 81. The large diameter hole 92b defines the valve body accommodating portion 81a. A step formed between the small diameter hole 92a and the large diameter hole 92b forms a first seat portion 81b. The opening edge of the passage 81 formed on the bottom surface of the hole 91a forms a second seat portion 81c.

[0075] When installing the gas vent valve 80 in the first drain passage 76a, first, with the valve body 82 housed in the large diameter hole 92b of the second housing 92, the second housing 92 is inserted into the hole 91a of the first housing 91 so that the spring 83 is interposed between the valve body 82 and the step 90a. Then, the integrated first and second housings 91 and 92 are installed in the first drain passage 76a.

[0076] Next, the operation and function of the gas vent valve 80 will be described.

[0077] When the power source mounted on the hydraulic excavator is in a stopped state and the pilot pump 5 is stopped, the pilot pressure in the pilot chamber 23 is zero, so the valve element 82 comes into contact with the first seat portion 81b by the biasing force of the spring 83, blocking the passage 81 (the state shown in FIG. 4 ). As a result, even when the hydraulic excavator is stopped, the movement of air from the drain side to the pilot chamber 23 side through the passage 81 is prevented.

[0078] On the other hand, when the power source mounted on the hydraulic excavator is in operation and the pilot pump 5 is driven, the valve element 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b. At this time, the valve element 82 does not contact the second seat portion 81c when the pilot pressure in the pilot chamber 23 is below a predetermined pressure, but contacts the second seat portion 81c when the pilot pressure in the pilot chamber 23 is equal to or higher than the predetermined pressure. This will be described in more detail with reference to Figure 5. Figure 5 is a graph showing the relationship between the pilot pressure in the pilot chamber 23 and the flow rate of air flowing from the pilot chamber 23 to the drain side.

[0079] When the pilot pump 5 is operating and the operator is not operating the control lever 10, the pilot pressure oil discharged from the pilot pump 5 is discharged to the tank T through the pilot control valve 9 and is hardly introduced into the pilot chamber 23. However, even in this state, when the pilot pump 5 is operating, a minimum pilot pressure, specifically, a pilot pressure of approximately 0.05 to 0.2 MPa, acts on the pilot passage 52 and the pilot chamber 23. In this state, the valve element 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b, but does not contact the second seat portion 81c. In other words, the valve element 82 is positioned between the first seat portion 81b and the second seat portion 81c due to the balance between the pilot pressure in the pilot chamber 23 and the biasing force of the spring 83. This state occurs when the pilot pressure in the pilot chamber 23 is below a predetermined pressure. 5, air is permitted to flow from the pilot chamber 23 to the drain side through the passage 81, and the air on the pilot chamber 23 side is discharged to the drain side. Therefore, when the hydraulic excavator is started from a stopped state, the air on the pilot chamber 23 side is naturally discharged to the drain side before the operator operates the control lever 10, and therefore, when the operator starts to operate the control lever 10, a delay in the response of the cylinder 2 to the operation is suppressed.

[0080] When the operator operates the operating lever 10 to perform work, a pilot pressure of 0.3 MPa or more acts on the pilot chamber 23. In this state, the valve element 82 moves against the biasing force of the spring 83 and contacts the second seat portion 81c. This state occurs when the pilot pressure in the pilot chamber 23 is equal to or greater than a predetermined pressure. In this state, as shown in FIG. 5 , the flow of air from the pilot chamber 23 to the drain side through the passage 81 is blocked, and the flow of pilot pressure oil is also blocked. Therefore, the desired pilot pressure acts on the pilot chamber 23, and the movement of the piston 50 allows the spool 56 to move, so the passage 81 does not adversely affect the operation of the cylinder 2.

[0081] The predetermined pressure, which is the pilot pressure at which the valve element 82 contacts the second seat portion 81c, is set to a pressure lower than the pilot pressure at which the spool 56 moves, and is approximately 0.3 PMa in this embodiment. This predetermined pressure is set depending on the capacity of the pilot pump 5, the inner diameter and length of the pilot passage 52, etc. The initial load of the spring 83 is set so that the valve element 82 contacts the second seat portion 81c at a pressure equal to or higher than the predetermined pressure.

[0082] As described above, the gas vent valve 80 prevents air from moving from the drain side to the pilot chamber 23 side when the pilot pump 5 is stopped, and when the pilot pump 5 is driven, the air on the pilot chamber 23 side is naturally discharged to the drain side before the operator operates the control lever 10, thereby suppressing a delay in the response of the cylinder 2 to the operator's input operation. Furthermore, when the operator operates the control lever 10, the flow of pilot pressure oil from the pilot chamber 23 to the drain side is blocked, so the gas vent valve 80 does not adversely affect the operation of the switching valve 22 and the cylinder 2.

[0083] When the hydraulic excavator is started from a stopped state, the operator may operate the control lever 10 to bleed air from the pilot chamber 23 to the drain side through the passage 81. In this case, however, it is necessary to operate the control lever 10 so that the valve element 82 does not come into contact with the second seat portion 81c (in this embodiment, so that the pilot pressure in the pilot chamber 23 does not exceed 0.3 MPa). In other words, it is necessary to operate the control lever 10 so that the spool 56 does not move.

[0084] According to the above embodiment, the following effects are achieved.

[0085] When the pilot pump 5 is stopped, the valve element 82 of the gas vent valve 80 comes into contact with the first seat portion 81b due to the biasing force of the spring 83 to block the passage 81, thereby preventing the movement of air from the drain side to the pilot chamber 23 side. Furthermore, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is lower than a predetermined pressure, the valve element 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b, allowing air to flow from the pilot chamber 23 to the drain side, so that air on the pilot chamber 23 side is discharged to the drain side, and a response delay of the cylinder 2 due to the influence of air is suppressed.

[0086] In addition, when the operator operates the operating lever 10, the flow of pilot pressure oil from the pilot chamber 23 to the drain side through the passage 81 is blocked, so the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

[0087] <Modification 1> A modification of the above embodiment will be described below with reference to Fig. 6. Fig. 6 is a view corresponding to Fig. 4 and is a cross-sectional view of the periphery of the gas vent valve 80. In Fig. 6, components having the same functions as those in the above embodiment are denoted by the same reference numerals. In this modification, the configuration of the gas vent valve 80 differs from that of the above embodiment.

[0088] In this modified example, when the pilot pump 5 is stopped, the valve element 82 comes into contact with the first seat portion 81b due to the biasing force of the spring 83, blocking the passage 81 and preventing air from moving from the drain side to the pilot chamber 23 side. Furthermore, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is lower than a predetermined pressure, the valve element 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b, allowing air to flow from the pilot chamber 23 to the drain side. Therefore, air on the pilot chamber 23 side is discharged to the drain side, and a response delay of the cylinder 2 due to the influence of air is suppressed. In this respect, this modified example is the same as the above embodiment.

[0089] However, in the gas vent valve 80 of this modified example, even when the pilot pressure in the pilot chamber 23 is equal to or higher than the predetermined pressure, the valve element 82 moves against the biasing force of the spring 83 but does not come into contact with the second seat portion 81c (see FIG. 4), and does not block the flow of pilot pressure oil from the pilot chamber 23 to the drain side through the passage 81. This is because, unlike the above embodiment, the entire spring 83 is accommodated in the valve element accommodating portion 81a. Specifically, the spring 83 is provided in a compressed state between the valve element 82 and the bottom surface of the hole 91a formed in the first housing 91.

[0090] In this modified example, even when the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure, the valve element 82 does not come into contact with the second seat portion 81c (see FIG. 4), and therefore allows the flow of pilot pressure oil from the pilot chamber 23 to the drain side through the passage 81. However, the gas vent valve 80 has an orifice 85 that is provided in the passage 81 and serves as a throttle that applies resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain side. Therefore, when the operator operates the control lever 10, the orifice 85 applies resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain side, and the desired pilot pressure acts on the pilot chamber 23, so that the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

[0091] In this modification, the orifice 85 is formed in the second housing 92. However, the position where the orifice 85 is formed is not limited as long as the orifice 85 is provided in the passage 81. For example, the orifice 85 may be provided in the passage 81 of the first housing 91.

[0092] <Modification 2> In the above embodiment and Modification 1, a configuration in which a piston is not provided in the pilot chamber 23 has been described. However, a piston (not shown) may be slidably housed in the pilot chamber 23. In this configuration, the pilot chamber 23 is defined between the cap 58 and the piston, and a drain chamber is defined between the piston and the spool 56. The piston receives pilot pressure from the pilot chamber 23 and applies a thrust to the spool 56 that counters the biasing force of the spring 36. In Modification 2, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is less than a predetermined pressure, the air in the pilot chamber 23 flows through the gap between the outer peripheral surface of the piston and the inner peripheral surface of the pilot hole 60b and is then discharged to the drain side through the gas vent valve 80.

[0093] The configuration, operation, and effects of the embodiment of the present invention will be described below.

[0094] A hydraulic control device (100) (fluid pressure control device) for controlling the expansion and contraction operation of a cylinder (2) that drives a load (1) includes a control valve (6) that controls the supply of working fluid from a pump (4) (fluid pressure supply source) to the cylinder (2), a pilot control valve (9) that controls the pilot pressure introduced to the control valve (6) from a pilot pump (5) (pilot pressure supply source), a main passage (7) that connects the control valve (6) to a load-side pressure chamber (2a) of the cylinder (2) on which a load pressure from the load (1) acts when the control valve (6) is in a neutral position (6C), and a load holding mechanism (20) provided in the main passage (7). The load holding mechanism (20) has an operate check valve (21) that allows the working fluid to flow from the control valve (6) to the load-side pressure chamber (2a) and also allows the working fluid to flow from the load-side pressure chamber (2a) to the control valve (6) in accordance with a back pressure, and a switching valve (22) that operates in conjunction with the control valve (6) by the pilot pressure introduced through the pilot control valve (9) and switches the operation of the operate check valve (21). the spool 56 moves in response to the pilot pressure in the pilot chamber 23; a first drain passage 76 a (drain passage) connected to the pilot chamber 23; and a gas vent valve 80 provided in the first drain passage 76 a for discharging air (gas) from the pilot chamber 23 to the drain side. The gas vent valve 80 has a passage 81 provided between the pilot chamber 23 side and the drain side, a valve element 82 for opening and closing the passage 81, and a spring 83 (biasing member) for biasing the valve element 82. When the pilot pump 5 is stopped, the biasing force of the spring 83 causes the valve element 82 to come into contact with a first seat portion 81 b to block the passage 81. When the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is less than a predetermined pressure that is lower than the pilot pressure at which the spool 56 moves, the valve element 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81 b, allowing the flow of fluid from the pilot chamber 23 to the drain side.

[0095] In this configuration, a gas vent valve 80 for discharging air from the pilot chamber 23 to the drain side is provided in the first drain passage 76a, and when the pilot pump 5 is stopped, the valve element 82 of the gas vent valve 80 comes into contact with the first seat portion 81b by the biasing force of the spring 83 to block the passage 81, thereby preventing air from moving from the drain side to the pilot chamber 23 side. Furthermore, when the pilot pump 5 is driven and the pilot pressure in the pilot chamber 23 is lower than a predetermined pressure, the valve element 82 moves against the biasing force of the spring 83 and separates from the first seat portion 81b, allowing fluid to flow from the pilot chamber 23 to the drain side. This allows air on the pilot chamber 23 side to be discharged to the drain side, thereby suppressing a response delay of the cylinder 2 caused by the influence of air. Therefore, the movement of air from the drain side to the pilot chamber 23 side can be prevented and a response delay caused by the influence of air can be suppressed.

[0096] Furthermore, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure, the valve body 82 moves against the biasing force of the spring 83 and contacts the second seat portion 81c, blocking the passage 81 and blocking the flow of pilot pressure oil from the pilot chamber 23 to the drain side.

[0097] In this configuration, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure, the valve body 82 blocks the flow of pilot pressure oil from the pilot chamber 23 to the drain side through the passage 81, so that the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

[0098] Furthermore, the valve element 82 allows the flow of pilot pressure oil from the pilot chamber 23 to the drain side even when the pilot pressure in the pilot chamber 23 is equal to or higher than the predetermined pressure, and the gas vent valve 80 further has an orifice 85 (restriction) that is provided in the passage 81 and applies resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain side.

[0099] In this configuration, when the pilot pump 5 is operating and the pilot pressure in the pilot chamber 23 is equal to or higher than a predetermined pressure, the orifice 85 provides resistance to the flow of pilot pressure oil from the pilot chamber 23 to the drain side, so the gas vent valve 80 does not adversely affect the operation of the cylinder 2.

[0100] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0101] This application claims priority based on Japanese Patent Application No. 2022-41677, filed with the Japan Patent Office on March 16, 2022, the entire contents of which are incorporated herein by reference.

Claims

1. A fluid pressure control device that controls the extension and contraction operation of a cylinder that drives a load, a control valve for controlling the supply of hydraulic fluid to the cylinder; a pilot control valve for controlling a pilot pressure introduced from a pilot pressure supply source to the control valve; a main passage connecting the control valve to a load-side pressure chamber of the cylinder to which a load pressure due to a load acts when the control valve is in a neutral position; a load retaining mechanism provided in the main passage, The load holding mechanism includes: an operated check valve that allows the flow of hydraulic fluid from the control valve to the load side pressure chamber, and also allows the flow of hydraulic fluid from the load side pressure chamber to the control valve in response to a back pressure; a switching valve that operates in conjunction with the control valve by a pilot pressure introduced through the pilot control valve and switches the operation of the operated check valve; The switching valve is a pilot chamber to which a pilot pressure is introduced through the pilot control valve; A spool that moves in response to the pilot pressure in the pilot chamber; A drain passage connected to the pilot chamber; a gas vent valve provided in the drain passage for discharging gas from the pilot chamber to the drain side, The gas vent valve is A passage provided between the pilot chamber side and the drain side; a valve body for opening and closing the passage; a biasing member that biases the valve body, The initial load of the biasing member is set so that, when the pilot pressure supply source is stopped, the valve body comes into contact with the first seat portion by the biasing force of the biasing member to block the passage, and, when the pilot pressure supply source is driven and the pilot pressure in the pilot chamber is less than a predetermined pressure lower than the pilot pressure at which the spool moves, the valve body moves against the biasing force of the biasing member and separates from the first seat portion to allow the flow of fluid from the pilot chamber to the drain side. Fluid pressure control device.

2. The fluid pressure control device according to claim 1, When the pilot pressure supply source is driven and the pilot pressure in the pilot chamber is equal to or higher than a predetermined pressure, the valve body moves against the biasing force of the biasing member to come into contact with the second seat portion, blocking the passage and blocking the flow of pilot fluid from the pilot chamber to the drain side. Fluid pressure control device.

3. The fluid pressure control device according to claim 1, the valve body allows the pilot fluid to flow from the pilot chamber to the drain side even when the pilot pressure in the pilot chamber is equal to or higher than the predetermined pressure, The gas vent valve further has a throttle provided in the passage for providing resistance to the flow of pilot fluid from the pilot chamber to the drain side. Fluid pressure control device.