Fluid pressure control device

Abstract

To provide a fluid pressure control device which prevents quick acceleration of a cylinder.SOLUTION: A load holding mechanism 20 has: a switching valve 22 which is operated in conjunction with a control valve 6 by a pilot pressure supplied through a pilot control valve 9 and switches an operation of an operate check valve 21; and a relief valve 41 which opens when a pressure in a load side pressure chamber 2a reaches a predetermined pressure. The switching valve 22 has: a spring chamber 54 in which a biasing member 36 for biasing a spool 56 in a valve closing direction is housed; a drain chamber 51 provided at the opposite side of the spring chamber 54 across the spool 56; a drain passage 76 which is connected to the relief valve 41 and connected to at least one of the drain chamber 51 and the spring chamber 54; a pressure guide passage 90 which connects the drain passage 76 with the downstream side of the spool 56; and a check valve 91 which is provided at the pressure guide passage 90 and only allows flow of a working fluid from the drain passage 76 to the downstream side of the spool 56.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] The fluid pressure control device described in Patent Document 1 includes a relief valve that opens when the pressure in the load side pressure chamber of the cylinder reaches a predetermined pressure, a relief discharge passage that guides the relief fluid discharged from the relief valve to a tank, and a drain passage that communicates the drain chamber and the spring chamber of the switching valve with the relief discharge passage.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] In the fluid pressure control device disclosed in Patent Document 1, when the relief valve opens while the operator is extending the cylinder by lever operation, the relief fluid is discharged to the tank through the relief discharge passage, but also flows into the drain chamber and the spring chamber through the drain passage, and the spool of the switching valve moves in the closing direction, and there is a possibility that the extension speed of the cylinder intended by the operator cannot be obtained. In such a case, if the operator operates the lever to increase the pilot pressure acting on the spool in order to obtain the intended extension speed, the spool moves in the opening direction, and the working fluid flows vigorously to the downstream side of the spool where the pressure has decreased due to the movement of the spool in the closing direction, and the cylinder accelerates suddenly temporarily.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a fluid pressure control device that prevents sudden acceleration of a cylinder.

Means for Solving the Problem

[0006] The present invention is a fluid pressure control device that controls the telescopic operation of a cylinder for driving a load, and includes a control valve that controls the supply of working fluid from a fluid pressure supply source to the cylinder, a pilot control valve that controls the pilot pressure led from a pilot pressure supply source to the control valve, a main passage that connects a load side pressure chamber of the cylinder where a load pressure due to the load acts when the control valve is in the neutral position and the control valve, and a load holding mechanism provided in the main passage. The load holding mechanism includes 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 according to the back pressure, a switching valve that operates in conjunction with the control valve by a pilot pressure led through the pilot control valve to switch the operation of the operate check valve, and a relief valve that opens when the pressure in the load side pressure chamber reaches a predetermined pressure. The switching valve has a pilot chamber to which a pilot pressure is led through the pilot control valve, a spool that moves according to the pilot pressure in the pilot chamber, a spring chamber that houses a biasing member that biases the spool in the valve closing direction, a drain chamber provided on the side opposite to the spring chamber with the spool interposed therebetween, a drain passage that is connected to the relief valve and at least one of the drain chamber and the spring chamber, a pressure guiding passage that connects the drain passage and the downstream side of the spool, and a check valve provided in the pressure guiding passage that allows only the flow of working fluid from the drain passage to the downstream side of the spool.

[0007] Further, the present invention is characterized in that the switching valve further has a piston that receives a pilot pressure on its back surface and applies a thrust against the biasing force of the biasing member to the spool, and the drain chamber is partitioned by the spool and the piston.

[0008] Further, the present invention is characterized in that the pilot chamber and the drain chamber are common, and a throttle that imparts resistance to the passing working fluid is provided in the passage of the drain passage that connects the drain chamber and the spring chamber.

[0009] In these inventions, a check valve that allows only the flow of the working fluid from the drain passage to the downstream side of the spool is provided in the pressure guiding passage that connects the drain passage and the downstream side of the spool. Therefore, when the relief valve opens while the operator is operating the cylinder in a direction to contract the load side pressure chamber by lever operation, the relief fluid is guided to the downstream side of the spool through the pressure guiding passage. Thus, rapid acceleration of the cylinder can be prevented.

Effects of the Invention

[0010] According to the present invention, rapid acceleration of the cylinder can be prevented.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0012] Hereinafter, with reference to the drawings, a fluid pressure control device according to an embodiment of the present invention will be described.

[0013] The hydraulic control device controls the operation of hydraulic working equipment such as a hydraulic excavator. In this embodiment, a hydraulic control device 100 that controls the telescopic operation of a cylinder 2 that drives an arm (load) 1 of the hydraulic excavator shown in FIG. 1 will be described. Hereinafter, the case where hydraulic oil is used as the working fluid of the cylinder 2 will be described, but for example, a water-soluble alternative fluid or the like may be used instead of the hydraulic oil.

[0014] First, referring to FIG. 2, the hydraulic circuit of the hydraulic control device 100 will be described.

[0015] The cylinder 2 includes a cylindrical cylinder tube 2c, a piston 2d that is slidably inserted into the cylinder tube 2c and divides the inside of the cylinder tube 2c into a rod side chamber 2a and a rodless side chamber 2b, and one end is connected to the piston 2d, and the other end extends outside the cylinder tube 2c and is connected to the arm 1. a rod 2e.

[0016] The hydraulic excavator is equipped with a power source such as an engine or an electric motor, and the power drives a pump 4 as a fluid pressure supply source and a pilot pump 5 as a pilot pressure supply source.

[0017] 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 led from the pilot pump 5 to the control valve 6.

[0018] The control valve 6 is connected to the rod side chamber 2a of the cylinder 2 by a first main passage 7, and the control valve 6 is connected to the rodless side chamber 2b of the cylinder 2 by a second main passage 8.

[0019] The control valve 6 operates by the pilot pressure led from the pilot pump 5 through the pilot control valve 9 to the pilot chambers 6a and 6b as the operator of the hydraulic excavator manually operates the operation lever 10.

[0020] Specifically, when pilot pressure is introduced into the pilot chamber 6a, the control valve 6 switches to position 6A, hydraulic oil is supplied from the pump 4 to the rod-side chamber 2a through the first main passage 7, and the 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 arrow 80 shown in Fig. 1.

[0021] On the other hand, when pilot pressure is introduced into the pilot chamber 6b, the control valve 6 switches to position 6B, hydraulic oil is supplied from the pump 4 to the anti-rod-side chamber 2b through the second main passage 8, and the 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 extends, and the arm 1 descends in the direction of arrow 81 shown in Fig. 1.

[0022] When no pilot pressure is introduced into the pilot chambers 6a and 6b, the control valve 6 assumes position 6C, the supply and discharge of hydraulic oil to and from the cylinder 2 are blocked, and the arm 1 remains stationary.

[0023] In this way, the control valve 6 has three positions: the contraction position 6A for contracting the cylinder 2, the extension position 6B for extending the cylinder 2, and the neutral position 6C for holding the load of the cylinder 2. It switches the supply and discharge of hydraulic oil to and from the cylinder 2 to control the telescopic movement of the cylinder 2.

[0024] Here, as shown in Fig. 1, when the control valve 6 is switched to the neutral position 6C to stop the movement of the arm 1 with the bucket 13 lifted, a force in the extending direction acts on the cylinder 2 due to the self-weight of the bucket 13 and the 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 where load pressure acts when the control valve 6 is in the neutral position 6C.

[0025] A load holding mechanism 20 is provided in a first main passage 7 connected to a 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. 1.

[0026] In the cylinder 15 that drives the boom 14 (see FIG. 1), since the anti-rod side chamber 15b becomes the load side pressure chamber, when the 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.

[0027] The load holding mechanism 20 includes an operate 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 a pilot pressure guided through the pilot control valve 9 to switch the operation of the operate check valve 21.

[0028] The operate check valve 21 has a valve body 24 that opens and closes the first main passage 7, a seat portion 28 on which the valve body 24 seats, a back pressure chamber 25 facing the back of the valve body 24, and a passage 26 formed in the valve body 24 that constantly guides the working oil in the rod side chamber 2a to the back pressure chamber 25. A throttle 26a that imparts resistance to the passing working oil is provided in the passage 26.

[0029] The first main passage 7 has a cylinder side first main passage 7a that connects the rod side chamber 2a and the operate check valve 21, and a control valve side first main passage 7b that connects the operate check valve 21 and the control valve 6.

[0030] A first pressure receiving surface 24a on which the pressure in the control valve side first main passage 7b acts and a second pressure receiving surface 24b on which the pressure in the rod side chamber 2a acts through the cylinder side first main passage 7a are formed on the valve body 24.

[0031] A spring 27 as a biasing member that biases the valve body 24 in the valve 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 the direction of seating the valve body 24 on the seat portion 28.

[0032] When the valve body 24 is seated on the sheet portion 28, the operation 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. That is, the operation check valve 21 prevents the leakage of hydraulic oil in the rod side chamber 2a, holds the load pressure, and holds the stop state of the arm 1.

[0033] The switching valve 22 has a pilot chamber 23 into which a pilot pressure is introduced through the pilot control valve 9, a spool 56 (see FIG. 3) that moves according to the pilot pressure in the pilot chamber 23, a spring chamber 54 that houses a spring 36 as a biasing member that biases the spool 56 in the valve closing direction, a drain chamber 51 provided on the side opposite to the spring chamber 54 with the spool 56 interposed therebetween, and a drain passage 76 that connects the spring chamber 54 and the drain chamber 51 to the tank T.

[0034] 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 first main passage 7b on the control valve side by bypassing the operation check valve 21. The back pressure passage 31 is a passage for guiding the hydraulic oil in the back pressure chamber 25 to the first main passage 7b on the control valve side. 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 first main passage 7b on the control valve side.

[0035] The switching valve 22 switches the communication between the bypass passage 30 and the back pressure passage 31 with respect to the downstream passage 38, and controls the flow of the hydraulic oil in the first main passage 7 that becomes the meter out side when the cylinder 2 is extended.

[0036] 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 has three positions: a blocking position 22A, a first communication position 22B, and a second communication position 22C.

[0037] When the pilot pressure is introduced into the pilot chamber 6b of the control valve 6, at the same time, the pilot pressure is also introduced into the pilot chamber 23. That is, when the control valve 6 is switched to the extended position 6B, the switching valve 22 is also switched to the first communication position 22B or the second communication position 22C.

[0038] Specifically, when the pilot pressure is not introduced into the pilot chamber 23, the switching valve 22 maintains the cutoff position 22A by the biasing force of the spring 36. In the cutoff position 22A, both the first supply port 32 and the second supply port 33 are cutoff.

[0039] When the pilot pressure of not less than the first predetermined pressure and less than the second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 is switched to the first communication position 22B. In the first communication position 22B, the first supply port 32 communicates with the discharge port 34. Thereby, the hydraulic oil in the rod-side chamber 2a is guided from the bypass passage 30 through the switching valve 22 to the downstream passage 38. That is, the hydraulic oil in the rod-side chamber 2a bypasses the operate check valve 21 and is guided to the first main passage 7b on the control valve side. At this time, resistance is imparted to the flow of the hydraulic oil by the throttle 37. The second supply port 33 remains cutoff.

[0040] When the pilot pressure of not less than the second predetermined pressure is introduced into the pilot chamber 23, the switching valve 22 is switched 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. Thereby, the hydraulic oil in the back-pressure chamber 25 is guided 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 guided to the first main passage 7b on the control valve side and is discharged from the control valve 6 to the tank T. Thereby, a differential pressure is generated before and after the throttle 26a, and the pressure in the back-pressure chamber 25 is reduced. Therefore, the force in the valve closing direction acting on the valve body 24 is reduced, the valve body 24 is separated from the seat portion 28, and the function of the operate check valve 21 as a check valve is released.

[0041] 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, allowing the passage of hydraulic oil and discharging the hydraulic oil in the rod side chamber 2a. The relief valve 41 is provided in a relief passage 40 that branches off from upstream of the switching valve 22 in the bypass passage 30. The relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the drain passage 76. Note that the relief passage 40 may be provided to branch off from the cylinder side first main passage 7a, or may be directly connected to the rod side chamber 2a.

[0042] The drain passage 76 has a first drain passage 76a connected to the drain chamber 51, a second drain passage 76b connected to the spring chamber 54, a third drain passage 76c connected to the relief valve 41, and a fourth drain passage 76d connecting the first drain passage 76a, the second drain passage 76b, and the third drain passage 76c. The first drain passage 76a and the second drain passage 76b are provided to communicate directly.

[0043] The drain chamber 51 communicates with the third drain passage 76c downstream of the relief valve 41 through the first drain passage 76a and the fourth drain passage 76d. The spring chamber 54 communicates with the third drain passage 76c downstream of the relief valve 41 through the second drain passage 76b and the fourth drain passage 76d. The third drain passage 76c communicates with a drain port 86 that opens to the outer surface of the body 60 (see FIG. 3) of the load holding mechanism 20. The drain port 86 is connected to the tank T through a pipe 55 (see FIG. 2). In this way, the relief pressure oil discharged from the relief valve 41 and the drain of the drain chamber 51 and the spring chamber 54 are discharged to the tank T through the drain port 86 and the pipe 55. Since both the drain chamber 51 and the spring chamber 54 provided on both sides of the spool 56 of the switching valve 22 communicate with the tank T, when the switching valve 22 is in the cutoff position 22A, atmospheric pressure acts on both ends of the spool 56, preventing a situation where the spool 56 moves unintentionally.

[0044] 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.

[0045] Next, with reference mainly to FIG. 3, the switching valve 22 will be described in detail. FIG. 3 is a cross-sectional view of the load holding mechanism 20, showing a state in which pilot pressure is not introduced into the pilot chamber 23 and the switching valve 22 is in the shut-off position 22A. In FIG. 3, those denoted by the same reference numerals as those shown in FIG. 2 have the same configuration as the configuration shown in FIG. 2.

[0046] The switching valve 22 is incorporated into the 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. A spool 56 is slidably incorporated into the sleeve 61.

[0047] On the side of one end face 56a of the spool 56, a spring chamber 54 is partitioned by a cap 57. The spring chamber 54 is connected to the second drain passage 76b through a notch 61a formed in the end face of the sleeve 61. The hydraulic oil that has leaked into the spring chamber 54 is discharged from the second drain passage 76b to the tank T.

[0048] An annular first spring receiving member 45 whose end face abuts against one end face 56a of the spool 56 and a pin portion 56c protruding from one end face 56a of the spool 56 is inserted into the hollow portion, and a second spring receiving member 46 disposed near the bottom of the cap 57 are accommodated in the spring chamber 54. The spring 36 is interposed in a compressed state between the first spring receiving member 45 and the second spring receiving member 46, and biases the spool 56 in the valve closing direction via the first spring receiving member 45.

[0049] The axial position of the second spring receiving member 46 in the spring chamber 54 is set by the tip of an adjustment bolt 47 that penetrates and is screwed into the bottom of the cap 57 and abuts against the back surface of the second spring receiving member 46. By screwing in the adjustment bolt 47, the second spring receiving member 46 moves in a direction approaching the first spring receiving member 45. Therefore, by adjusting the screwing amount of the adjustment bolt 47, the initial spring load of the spring 36 can be adjusted. The adjustment bolt 47 is fixed by a nut 48.

[0050] A pilot chamber 23 is defined laterally of the other end face 56b of the spool 56. The pilot chamber 23 is defined by a piston hole 60b formed in communication with the spool hole 60a and a cap 58 closing the piston hole 60b. Pilot pressure is introduced into the pilot chamber 23 through a pilot passage 52 formed in the body 60. A piston 50 that receives pilot pressure on its back face and applies a thrust force against the biasing force of the spring 36 to the spool 56 is slidably accommodated within the pilot chamber 23.

[0051] A drain chamber 51 is defined within the piston hole 60b by the spool 56 and the piston 50. The drain chamber 51 is connected to a first drain passage 76a. The hydraulic oil that has leaked into the drain chamber 51 is discharged from the first drain passage 76a to the tank T.

[0052] The piston 50 has a sliding portion 50a whose outer peripheral surface slides along the inner peripheral surface of the piston hole 60b, a tip portion 50b formed with a smaller diameter compared to the sliding portion 50a and facing the other end face 56b of the spool 56, and a base end portion 50c formed with a smaller diameter compared to the sliding portion 50a and facing the tip end face of the cap 58.

[0053] When pilot pressure oil is supplied into the pilot chamber 23 through the pilot passage 52, pilot pressure acts on the back face of the base end portion 50c and the annular back face of the sliding portion 50a. As a result, the piston 50 advances, and the tip portion 50b abuts against the other end face 56b of the spool 56 to move the spool 56. In this way, the spool 56 receives the thrust force of the piston 50 generated based on the pilot pressure acting on the back face of the piston 50 and moves against the biasing force of the spring 36. Even when the back face of the base end portion 50c abuts against the tip end face of the cap 58, the base end portion 50c has a smaller diameter compared to the sliding portion 50a, and since pilot pressure acts on the annular back face of the sliding portion 50a, the piston 50 can advance.

[0054] One end of the piston 50 faces the pilot chamber 23, and the other end faces the drain chamber 51 connected to the tank T. Therefore, the thrust of the piston 50 generated based on the pilot pressure in the pilot chamber 23 is efficiently transmitted to the spool 56.

[0055] The spool 56 stops at a position where the biasing force of the spring 36 acting on one end face 56a and the thrust of the piston 50 acting on the other end face 56b are balanced, and the switching position of the switching valve 22 is set at the stop position of the spool 56.

[0056] Three ports, i.e., 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), are formed in the sleeve 61.

[0057] The outer peripheral surface of the spool 56 is partially cut out in an annular shape, and the first pressure chamber 64, the second pressure chamber 65, the third pressure chamber 66, and the fourth pressure chamber 67 are formed by the cut-out portion and the inner peripheral surface of the sleeve 61.

[0058] The first pressure chamber 64 is always in communication with the discharge port 34.

[0059] The third pressure chamber 66 is always in communication with the first supply port 32. A plurality of throttles 37 that communicate the third pressure chamber 66 and the second pressure chamber 65 are formed on the outer peripheral surface of the land portion 72 of the spool 56 when the spool 56 moves against the biasing force of the spring 36.

[0060] The fourth pressure chamber 67 is always in communication with the second pressure chamber 65 through a pressure guiding passage 68 formed axially in the spool 56.

[0061] When the pilot pressure is not introduced into the pilot chamber 23, the poppet valve 70 formed on the spool 56 is pressed against the valve seat 71 formed on the inner periphery of the sleeve 61 by the biasing force of the spring 36, and the communication between the second pressure chamber 65 and the first pressure chamber 64 is blocked. Accordingly, the communication between the first supply port 32 and the discharge port 34 is blocked. Thereby, the hydraulic oil in the rod side chamber 2a does not leak to the discharge port 34. This state corresponds to the blocking position 22A of the switching valve 22. In a state where the poppet valve 70 is seated on the valve seat 71 by the biasing force of the spring 36, since there is a slight gap between the end face of the first spring receiving member 45 and the end face of the sleeve 61, the poppet valve 70 is surely seated on the valve seat 71 by the biasing force of the spring 36.

[0062] When the pilot pressure is introduced into the pilot chamber 23 and the thrust of the piston 50 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. Thereby, the poppet valve 70 separates from the valve seat 71, and the third pressure chamber 66 and the second pressure chamber 65 communicate with each other through the plurality of throttles 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. By the communication between the first supply port 32 and the discharge port 34, the hydraulic oil in the rod side chamber 2a is guided to the downstream passage 38 (see FIG. 2) through the throttle 37. This state corresponds to the first communication position 22B of the switching valve 22.

[0063] When the pilot pressure introduced into the pilot chamber 23 increases, the spool 56 further moves against the biasing force of the spring 36, and the fourth pressure chamber 67 communicates with the second supply port 33. Thereby, the second supply port 33 communicates with the discharge port 34 through the fourth pressure chamber 67, the pressure guiding passage 68, the second pressure chamber 65, and the first pressure chamber 64. By the communication between the second supply port 33 and the discharge port 34, the hydraulic oil in the back pressure chamber 25 is guided to the downstream passage 38 (see FIG. 2) by bypassing the throttle 37. This state corresponds to the second communication position 22C of the switching valve 22.

[0064] Next, with reference to FIGS. 2 and 3, the operation of the hydraulic control device 100 will be described.

[0065] When the control valve 6 is in the neutral position 6C, the hydraulic oil discharged from the pump 4 is not supplied to the cylinder 2. At this time, since no pilot pressure is introduced into the pilot chamber 23 of the switching valve 22, the switching valve 22 is in the blocked position 22A.

[0066] For this reason, the back pressure chamber 25 of the operate check valve 21 is maintained at the pressure of the rod side chamber 2a. Here, since the pressure receiving area in the valve closing direction of the valve body 24 (the area of the back surface of the valve body 24) is larger than the area of the second pressure receiving surface 24b which is the pressure receiving area in the valve opening direction, due to the load acting on the back surface of the valve body 24 by the pressure of the back pressure chamber 25 and the biasing force of the spring 27, the valve body 24 is seated on the seat portion 28. In this way, the operate check valve 21 prevents the leakage of the hydraulic oil in the rod side chamber 2a and maintains the stopped state of the arm 1.

[0067] When the operation 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 contracted position 6A by an amount corresponding to the pilot pressure. When the control valve 6 switches to the contracted position 6A, the discharge pressure of the pump 4 acts on the first pressure receiving surface 24a of the operate check valve 21. At this time, since the switching valve 22 is in the blocked position 22A without pilot pressure being introduced into the pilot chamber 23, the back pressure chamber 25 of the operate 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 larger than the total load of the load acting on the back surface of the valve body 24 by the pressure of the back pressure chamber 25 and the biasing force of the spring 27, the valve body 24 separates from the seat portion 28. When the operate check valve 21 opens in this way, the hydraulic oil discharged from the pump 4 is supplied to the rod side chamber 2a, and the cylinder 2 contracts. As a result, the arm 1 rises in the direction of the arrow 80 shown in FIG. 1.

[0068] When the operation lever 10 is operated and pilot pressure is led from the pilot control valve 9 to the pilot chamber 6b of the control valve 6, the control valve 6 switches to the extended position 6B by an amount corresponding to the pilot pressure. At the same time, since pilot pressure is also led to the pilot chamber 23, the switching valve 22 switches to the first communication position 22B or the second communication position 22C according to the supplied pilot pressure.

[0069] When the pilot pressure led to the pilot chamber 23 is equal to or higher than the first predetermined pressure and lower than the second predetermined pressure, the switching valve 22 switches to the first communication position 22B. In this case, since the communication between the second supply port 33 and the discharge port 34 is blocked, the back pressure chamber 25 of the operate check valve 21 is maintained at the pressure of the rod side chamber 2a, and the operate check valve 21 maintains a closed state.

[0070] On the other hand, since the first supply port 32 communicates with the discharge port 34, the hydraulic oil in the rod side chamber 2a is led from the bypass passage 30 through the throttle 37 to the downstream passage 38, and is discharged from the control valve side first main passage 7b through the control valve 6 to the tank T. Further, since 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 81 shown in FIG. 1.

[0071] Here, the switching valve 22 is mainly switched to the first communication position 22B when performing a crane operation of lowering the conveyed object attached to the bucket 13 to the target position. In the crane operation, it is necessary to extend the cylinder 2 at a low speed and lower the arm 1 slowly in the direction of the arrow 81. Therefore, the pilot pressure led to the pilot chamber 6b of the control valve 6 is small, and the control valve 6 is only slightly switched to the extended position 6B. For this reason, the pilot pressure led to the pilot chamber 23 of the switching valve 22 is also small, becoming equal to or higher than the first predetermined pressure and lower than the second predetermined pressure, and the switching valve 22 only switches to the first communication position 22B. Therefore, the hydraulic oil in the rod side chamber 2a passes through the throttle 37 and is discharged, and the arm 1 descends at a low speed suitable for the crane operation.

[0072] Also, when the switching valve 22 is in the first communication position 22B, even if a situation occurs where the operating oil leaks to the outside due to a rupture or the like in the control valve side first main passage 7b, the flow rate of the operating oil discharged from the rod side chamber 2a is restricted by the throttle 37. Therefore, the falling speed of the bucket 13 is suppressed. This function is called metering control. For this reason, before the bucket 13 falls to the ground, the switching valve 22 can be switched to the shut-off position 22A, and the sudden fall of the bucket 13 can be prevented.

[0073] Thus, the throttle 37 is for suppressing the descending speed of the cylinder 2 when the operate check valve 21 is closed and for suppressing the falling speed of the bucket 13 when the control valve side first main passage 7b ruptures.

[0074] When the pilot pressure guided to the pilot chamber 23 is equal to or higher than the second predetermined pressure, the switching valve 22 switches to the second communication position 22C. In this case, since the second supply port 33 communicates with the discharge port 34, the operating oil in the back pressure chamber 25 of the operate check valve 21 is bypassed from the back pressure passage 31 through the throttle 37 and guided to the downstream passage 38, and is discharged from the control valve side first main passage 7b through the control valve 6 to the tank T. As a result, a differential pressure is generated before and after the throttle 26a, and the pressure in the back pressure chamber 25 decreases. Therefore, the force in the valve closing direction acting on the valve body 24 decreases, the valve body 24 separates from the seat portion 28, and the function of the operate check valve 21 as a check valve is released.

[0075] Thus, the operate check valve 21 allows the flow of the operating oil from the control valve 6 to the rod side chamber 2a, while operating to allow the flow of the operating oil from the rod side chamber 2a to the control valve 6 according to the back pressure, which is the pressure in the back pressure chamber 25.

[0076] When the operation check valve 21 opens, the hydraulic oil in the rod side chamber 2a is discharged to the tank T through the first main passage 7, so the cylinder 2 extends quickly. That is, when the switching valve 22 is switched to the second communication position 22C, the flow rate of the hydraulic oil discharged from the rod side chamber 2a increases, so the flow rate of the hydraulic oil supplied to the counter rod side chamber 2b increases, and the extension speed of the cylinder 2 becomes faster. As a result, the arm 1 quickly descends in the direction of arrow 81.

[0077] The switching valve 22 is switched to the second communication position 22C when performing excavation work or the like. The pilot pressure led to the pilot chamber 6b of the control valve 6 is large, and the control valve 6 is largely switched to the extension position 6B. For this reason, the pilot pressure led to the pilot chamber 23 of the switching valve 22 is also large and becomes equal to or higher than the second predetermined pressure, so the switching valve 22 is switched to the second communication position 22C.

[0078] Here, when the operator operates the operation lever 10 to lead the pilot pressure to the pilot chamber 23 and move the spool 56 in the opening direction to extend the cylinder 2, and the pressure in the rod side chamber 2a rises and the relief valve 41 opens, the relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the third drain passage 76c, while it is also led to the drain chamber 51 and the spring chamber 54 through the first drain passage 76a and the second drain passage 76b. When the relief pressure oil is led to the drain chamber 51, the piston 50 may move away from the spool 56. In this case, since the thrust of the piston 50 generated by the pilot pressure is not transmitted to the spool 56, the spool 56 moves in the closing direction by the biasing force of the spring 36. As a result, although the operator operates the operation lever 10 and the pilot pressure is led to the pilot chamber 6b and the pilot chamber 23, the extension speed of the cylinder 2 intended by the operator cannot be obtained.

[0079] On the other hand, even if the spool 56 moves in the closing direction, since pilot pressure is introduced into the pilot chamber 6b of the control valve 6, the downstream passage 38 and the first main passage 7b on the control valve side, which are downstream of the spool 56, are in a state of communicating with the tank T through the control valve 6. Therefore, the hydraulic oil inside the downstream passage 38 and the first main passage 7b on the control valve side is discharged to the tank T, and the pressure decreases. The hydraulic oil in the downstream passage 38 and the first main passage 7b on the control valve side may flow into the tank T due to its own weight, resulting in a negative pressure inside the downstream passage 38 and the first main passage 7b on the control valve side.

[0080] In such a situation, when the operator operates the operation lever 10 to increase the pilot pressure acting on the spool 56 in order to obtain the intended extension speed, the spool 56 moves in the opening direction again. At this time, due to the movement of the spool 56 in the closing direction, hydraulic oil rushes into the downstream passage 38 and the first main passage 7b on the downstream side of the spool 56 where the pressure has decreased, and the cylinder 2 temporarily accelerates rapidly in the extension direction.

[0081] As a countermeasure, in the present embodiment, as shown in FIGS. 2 and 3, the switching valve 22 has a pilot pressure passage 90 connecting the drain passage 76 and the downstream side of the spool 56, and a check valve 91 provided in the pilot pressure passage 90 that allows only the flow of hydraulic oil from the drain passage 76 to the downstream side of the spool 56. This will be described in detail below.

[0082] In this embodiment, one end of the pressure guiding passage 90 is connected to the second drain passage 76b via the spring chamber 54, and the other end is connected to the downstream passage 38. One end of the pressure guiding passage 90 is connected to the spring chamber 54 through a notch 61a formed in the end face of the sleeve 61. The configuration in which one end of the pressure guiding passage 90 is connected to the second drain passage 76b via the spring chamber 54 is not limited, and it may be directly connected to the second drain passage 76b without passing through the spring chamber 54, or may be connected to the first drain passage 76a, the third drain passage 76c, or the fourth drain passage 76d. Further, the other end of the pressure guiding passage 90 may be configured to be connected to the downstream side of the spool 56, and may be connected to the control valve side first main passage 7b.

[0083] As shown in FIG. 3, the check valve 91 includes a poppet valve 92 movably accommodated in the pressure guiding passage 90, a valve seat 93 formed in the pressure guiding passage 90, a plug 94 that seals an opening of the pressure guiding passage 90 that opens to the outer surface of the body 60, a spring 95 that is compressed and accommodated between the poppet valve 92 and the plug 94 and biases the poppet valve 92 toward the valve seat 93 as a biasing member, and an annular seal member 96 provided on the outer peripheral surface of the plug 94.

[0084] When the pressure in the drain passage 76 becomes higher than the pressure in the downstream passage 38, the poppet valve 92 moves against the biasing force of the spring 95 to open the valve. Thereby, the flow of the hydraulic oil from the drain passage 76 through the pressure guiding passage 90 to the downstream passage 38 is allowed. On the other hand, when the pressure in the downstream passage 38 is higher than the pressure in the drain passage 76, the poppet valve 92 seats on the valve seat 93 and closes the valve due to the biasing force of the spring 95, so that the flow of the hydraulic oil from the downstream passage 38 through the pressure guiding passage 90 to the drain passage 76 is blocked. Note that the check valve 91 is not limited to the poppet type, and may be of the ball type, or may be an operate check valve that opens with the upstream pressure as a pilot pressure.

[0085] Since the switching valve 22 has the pressure guiding passage 90 and the check valve 91, the following operational effects are achieved.

[0086] When the operator operates the operation lever 10 to introduce pilot pressure into the pilot chamber 23 and move the spool 56 in the opening direction, and the pressure in the rod-side chamber 2a increases and the relief valve 41 opens while the cylinder 2 is in the extended state, as described above, the spool 56 moves in the closing direction. At this time, since the downstream passage 38 on the downstream side of the spool 56 communicates with the tank T through the control valve 6, the pressure decreases. And when the pressure in the drain passage 76 becomes higher than the pressure in the downstream passage 38, the check valve 91 opens, and hydraulic oil is guided from the drain passage 76 to the downstream passage 38 through the pressure guiding passage 90. As a result, the pressure in the drain passage 76 decreases, and the pressures in the drain chamber 51 and the spring chamber 54 also decrease. Also, since hydraulic oil is guided to the downstream side of the spool 56 from the drain passage 76 through the pressure guiding passage 90, the pressure drop in the downstream passage 38 and the first main passage 7b on the control valve side is suppressed.

[0087] Therefore, when the spool 56 moves in the closing direction and the operator operates the operation lever 10 to increase the pilot pressure acting on the spool 56 in order to obtain the intended extension speed, due to the pressure drop in the drain chamber 51 and the spring chamber 54, the spool 56 smoothly moves in the opening direction, so that the operator can quickly obtain the intended extension speed. Also, since the pressure drop in the downstream passage 38 and the first main passage 7b on the control valve side is suppressed, when the spool 56 moves in the opening direction, it is prevented that hydraulic oil flows vigorously to the downstream side of the spool 56 and the cylinder 2 accelerates suddenly in the extension direction temporarily. Furthermore, by suppressing the pressure drop in the downstream passage 38 and the first main passage 7b on the control valve side, it is prevented that the downstream passage 38 and the first main passage 7b on the control valve side become negative pressure, and the occurrence of cavitation is prevented, so the responsiveness when the operation lever 10 is operated is improved.

[0088] According to the above first embodiment, the following effects are achieved.

[0089] A check valve 91 that allows only the flow of hydraulic oil from the drain passage 76 to the downstream side of the spool 56 is provided in the pressure guiding passage 90 that connects the drain passage 76 and the downstream side of the spool 56. Therefore, even when the relief valve 41 opens while the operator is extending the cylinder 2 by operating the lever, the relief pressure oil is guided to the downstream side of the spool 56 through the pressure guiding passage 90. As a result, the pressure in the drain passage 76 decreases, and the pressures in the drain chamber 51 and the spring chamber 54 also decrease. In addition, the pressure drop on the downstream side of the spool 56 is suppressed. Thus, even when the operator operates the operation lever 10 to increase the pilot pressure acting on the spool 56 in order to obtain the intended extension speed when the relief valve 41 opens and the spool 56 moves in the closing direction, a sudden acceleration of the cylinder 2 can be prevented.

[0090] The modification examples of the above embodiment will be described below. The following modification examples are also within the scope of the present invention, and it is also possible to combine the following modification examples with the configuration of the above embodiment or to combine the following modification examples with each other.

[0091] (1) The drain passage 76 is not limited to the configuration as in the above embodiment. For example, as shown in FIG. 4, the fourth drain passage 76d may not be provided, and the first drain passage 76a and the second drain passage 76b may be directly connected to the third drain passage 76c. Further, as shown in FIG. 5, the first drain passage 76a and the third drain passage 76c may be connected, while the second drain passage 76b may be provided independently. In this configuration, the pressure guiding passage 90 is connected to the drain passage 76 having the first drain passage 76a and the third drain passage 76c. Further, as shown in FIG. 6, the second drain passage 76b and the third drain passage 76c may be connected, while the first drain passage 76a may be provided independently. In this configuration, the pressure guiding passage 90 is connected to the drain passage 76 having the second drain passage 76b and the third drain passage 76c. That is, the pressure guiding passage 90 is connected to the relief valve 41 and is also connected to the drain passage 76 that is connected to at least one of the drain chamber 51 and the spring chamber 54.

[0092] (2) Referring to FIGS. 7 and 8, a modified example of the above embodiment will be described. FIG. 7 is a hydraulic circuit diagram of the hydraulic control device 101 according to this modified example, and FIG. 8 is a cross-sectional view of the load holding mechanism 20 of the hydraulic control device 101 according to this modified example. In FIGS. 7 and 8, components having the same functions as those in the above embodiment are denoted by the same reference numerals as in the above embodiment, and the description thereof will be omitted. In this modified example, the piston 50 of the above embodiment is not provided, and the pilot chamber 23 and the drain chamber 51 are provided as a common space.

[0093] In the drain passage 76, an orifice 97 as a throttle that imparts resistance to the working oil passing therethrough is provided in the passage connecting the drain chamber 51 and the spring chamber 54. Specifically, in this modified example, a first drain passage 76a connected to the drain chamber 51 and a second drain passage 76b connected to the spring chamber 54 are connected, and the orifice 97 is provided in the connected passage. Thereby, when the working oil is guided to the pilot chamber 23 through the pilot passage 52, the pressure on the upstream side of the orifice 97 acts on the pilot chamber 23, and the pressure on the downstream side of the orifice 97 acts on the drain chamber 51. Therefore, the spool 56 moves due to the balance between the load due to the differential pressure across the orifice 97 and the biasing force of the spring 36.

[0094] When the operator operates the operation lever 10 to introduce the pilot pressure into the pilot chamber 23 and move the spool 56 in the opening direction, and the pressure in the rod side chamber 2a increases and the relief valve 41 opens while the cylinder 2 is in the extended operation state, the relief pressure oil discharged from the relief valve 41 is guided to the drain chamber 51 and the spring chamber 54. In this modified example, since the piston 50 is not provided, the thrust of the spool 56 generated by the pilot pressure does not decrease due to the relief pressure oil guided to the drain chamber 51. However, since a closing force acts on the spool 56 due to the relief pressure oil guided to the spring chamber 54, a closing force acts on the spool 56 as in the above embodiment. Therefore, also in this modified example, the pressure guiding passage 90 and the check valve 91 exhibit the same effects as those in the above embodiment.

[0095] (3) A modified example of the form shown in FIGS. 7 and 8 is shown in FIG. 9. As shown in FIG. 9, the drain passage 76 may be configured such that a first drain passage 76a connected to the drain chamber 51 is not provided, and a third drain passage 76c connected to the relief valve 41 and a second drain passage 76b connected to the spring chamber 54 are connected. Also in this modified example, the pressure guiding passage 90 and the check valve 91 exhibit the same operational effects as those in the above-described embodiment.

[0096] Hereinafter, the configuration, operation, and effects of the embodiment of the present invention will be collectively described.

[0097] A fluid pressure control device 100 that controls the telescopic operation of a cylinder 2 driving a load 1 includes a control valve 6 that controls the supply of working fluid from a fluid pressure supply source 4 to the cylinder 2, a pilot control valve 9 that controls the pilot pressure led from a pilot pressure supply source 5 to the control valve 6, a main passage 7b that connects a load side pressure chamber 2a of the cylinder 2 where a load pressure due to the load 1 acts when the control valve 6 is in a neutral position 6C and the control valve 6, and a load holding mechanism 20 provided in the main passage 7b. The load holding mechanism 20 includes an operate check valve 21 that allows the flow of working fluid from the control valve 6 to the load side pressure chamber 2a while allowing the flow of working fluid from the load side pressure chamber 2a to the control valve 6 according to the back pressure, a switching valve 22 that operates in conjunction with the control valve 6 by a pilot pressure led through the pilot control valve 9 to switch the operation of the operate check valve 21, and a relief valve 41 that opens when the pressure in the load side pressure chamber 2a reaches a predetermined pressure. The switching valve 22 includes a pilot chamber 23 to which a pilot pressure is led through the pilot control valve 9, a spool 56 that moves according to the pilot pressure in the pilot chamber 23, a spring chamber 54 that houses a biasing member 36 that biases the spool 56 in a valve closing direction, a drain chamber 51 provided on the side opposite to the spring chamber 54 with the spool 56 interposed therebetween, a drain passage 76 that is connected to the relief valve 41 and is connected to at least one of the drain chamber 51 and the spring chamber 54, a pressure guiding passage 90 that connects the drain passage 76 and the downstream side of the spool 56, and a check valve 91 provided in the pressure guiding passage 90 that allows only the flow of working fluid from the drain passage 76 to the downstream side of the spool 56.

[0098] Further, the switching valve 22 further includes a piston 50 that receives a pilot pressure on its back surface and applies a thrust to the spool 56 against the biasing force of the biasing member 36, and the drain chamber 51 is partitioned by the spool 56 and the piston 50.

[0099] Also, the pilot chamber 23 and the drain chamber 51 are common, and a throttle 97 that imparts resistance to the passing working fluid is provided in a passage of the drain passage 76 that connects the drain chamber 51 and the spring chamber 54.

[0100] In these configurations, a check valve 91 that allows only the flow of the working fluid from the drain passage 76 to the downstream side of the spool 56 is provided in the pressure guiding passage 90 that connects the drain passage 76 and the downstream side of the spool 56. Therefore, when the relief valve 41 opens while the operator is operating the cylinder 2 in a direction to contract the load side pressure chamber 2a by lever operation, the relief fluid is guided to the downstream side of the spool 56 through the pressure guiding passage 90. Thus, rapid acceleration of the cylinder 2 can be prevented.

[0101] As described above, the embodiments of the present invention have been explained. However, the above embodiments merely show a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

Explanation of Reference Numerals

[0102] 1 ··· Arm (Load), 2 ··· Cylinder, 2a ··· Rod Side Pressure Chamber (Load Side Pressure Chamber), 4 ··· Pump (Fluid Pressure Supply Source), 5 ··· Pilot Pump (Pilot Pressure Supply Source), 6 ··· Control Valve, 7b ··· Control Valve Side First Main Passage (Main Passage), 9 ··· Pilot Control Valve, 20 ··· Load Holding Mechanism, 21 ··· Operate Check Valve, 22 ··· Changeover Valve, 23 ··· Pilot Chamber, 38 ··· Downstream Passage, 41 ··· Relief Valve, 50 ··· Piston, 51 ··· Drain Chamber, 54 ··· Spring Chamber, 56 ··· Spool, 76 ··· Drain Passage, 76a ··· First Drain Passage, 76b ··· Second Drain Passage, 76c ··· Third Drain Passage, 76d ··· Fourth Drain Passage, 90 ··· Pressure Guiding Passage, 91 ··· Check Valve, 97 ··· Orifice (Throttle)

Claims

1. A hydraulic control device for controlling the telescopic operation of a cylinder that drives a load, comprising: a control valve for controlling the supply of working fluid from a hydraulic pressure source to the cylinder; a pilot control valve for controlling the pilot pressure led from a pilot pressure source to the control valve; a main passage connecting the load side pressure chamber of the cylinder where a load pressure due to the load acts when the control valve is in the neutral position and the control valve; a load holding mechanism provided in the main passage; and the load holding mechanism includes: 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 according to the back pressure; a switching valve that operates in conjunction with the control valve by a pilot pressure led through the pilot control valve and switches the operation of the operate check valve; a relief valve that opens when the pressure in the load side pressure chamber reaches a predetermined pressure; and the switching valve includes: a pilot chamber to which a pilot pressure is led through the pilot control valve; a spool that moves according to the pilot pressure in the pilot chamber; a spring chamber that houses a biasing member that biases the spool in the valve closing direction; a drain chamber provided on the side opposite to the spring chamber with the spool interposed therebetween; a drain passage that is connected to the relief valve and is connected to at least one of the drain chamber and the spring chamber; a pilot pressure passage that connects the drain passage and the downstream side of the spool; and a check valve provided in the pilot pressure passage that allows only the flow of working fluid from the drain passage to the downstream side of the spool. A hydraulic control device characterized by this.

2. The switching valve further has a piston that receives a pilot pressure on its back surface and applies a thrust to the spool against the biasing force of the biasing member, and the drain chamber is partitioned by the spool and the piston. The hydraulic control device according to Claim 1, characterized by this.

3. The pilot chamber and the drain chamber are common, and in the drain passage, a throttle for imparting resistance to the passing working fluid is provided in the passage connecting the drain chamber and the spring chamber. The hydraulic control device according to Claim 1, characterized by this.

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