JP6502813B2 - Fluid pressure control device - Google Patents

Description

  The present invention relates to a fluid pressure control device that controls the operation of a hydraulic work device.

  As a hydraulic control device for controlling the operation of hydraulic work equipment, Patent Document 1 discloses a cylinder device, a control valve for controlling the expansion and contraction operation of the cylinder device, and a load holding valve provided between the cylinder device and the control valve. , Is disclosed. The load holding valve includes a pilot check valve, a switching valve for releasing the check function of the pilot check valve, and a relief valve that opens when the load pressure of the bottom pressure chamber of the cylinder device increases.

  The switching valve includes a pilot chamber in which the pilot pressure is introduced, and a spool that moves by the pilot pressure in the pilot chamber. In the pilot chamber, the end of the spool is not directly exposed, but the end of the sub-spool provided adjacent to the spool is exposed.

  When the load pressure in the bottom pressure chamber of the cylinder device rises and the relief valve opens, a relief back pressure is generated on the upstream side of the orifice provided downstream of the relief valve, and the relief back pressure becomes the pilot chamber of the switching valve Led between the spool and the sub-spool. As a result, the spool moves to switch the switching valve, the check function of the pilot check valve is released, and the pressure in the bottom pressure chamber decreases.

Japanese Patent Laid-Open No. 2000-220603

  In the hydraulic control device disclosed in Patent Document 1, when the cylinder device is contracted, the pilot pressure is introduced to the pilot chamber of the switching valve by the operator of the hydraulic shovel manually operating the control lever. The pilot pressure acts on the sub-spool, and the sub-spool applies a thrust to the spool to open the spool, the check function of the pilot check valve is released, and the cylinder device contracts. On the other hand, when the load pressure in the bottom pressure chamber of the cylinder device rises and the relief valve opens, the relief back pressure generated on the upstream side of the orifice provided downstream of the relief valve is introduced between the spool and the sub spool It acts on the spool and thrust is applied to the spool. As described above, when the pilot pressure is introduced to the pilot chamber to move the spool by the operator's operation, the thrust is applied to the spool via the sub spool, while the relief back pressure is directly spooled when the relief valve is opened. Act on.

  Here, when the relief valve is opened in a state where the pilot pressure is introduced to the pilot chamber by the operation of the operator and the spool is open, the relief back pressure is introduced between the spool and the sub spool, so the sub spool And the thrust by the pilot pressure is not transmitted from the sub spool to the spool. When the pressure receiving area of the spool on which the relief back pressure acts is smaller than the pressure receiving area of the sub spool, the spool moves in the closing direction depending on the relief back pressure.

  Therefore, when the relief valve is opened while the operator operates the operation lever so as to contract the cylinder device, the spool moves in the closing direction, and the cylinder device intended by the operator Situations may occur where the rate of contraction can not be obtained.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fluid pressure control device which enables stable operation of a cylinder.

  A first invention is a fluid pressure control device for controlling the extension operation of a cylinder driving a load, wherein the load side pressure chamber and the control valve of the cylinder on which the load pressure by the load acts when the control valve is in the neutral position. And a load holding mechanism provided in the main passage, and the load holding mechanism allows the flow of the working fluid from the control valve to the load side pressure chamber, while the load holding mechanism allows the flow according to the back pressure. An operation check valve that allows the flow of working fluid from the load side pressure chamber to the control valve, and a switching valve that operates in conjunction with the control valve by the pilot pressure guided through the pilot control valve to switch the operation of the operation check valve And a relief valve that opens when the pressure in the load-side pressure chamber reaches a predetermined pressure, and a relief discharge passage that leads the relief fluid discharged from the relief valve to the tank. The switching valve relief discharges the piston that receives pilot pressure on the back and applies a thrust to the spool against the biasing force of the biasing member, the drain chamber separated by the spool and the piston, the drain chamber and the spring chamber And a drain passage communicating with the passage, wherein the relief fluid discharged from the relief valve is discharged to the tank through the relief discharge passage and does not operate the switching valve.

  In the first aspect of the invention, the relief fluid discharged from the relief valve is discharged to the tank through the relief discharge passage and does not operate the switching valve. Therefore, the operator is operating the operation lever so as to extend and retract the cylinder. Even when the relief valve is opened, the spool does not move in the closing direction, and the expansion and contraction speed of the cylinder intended by the operator can be obtained.

  A second aspect of the invention is characterized in that a throttle that provides resistance to fluid passing through the drain passage is provided.

  According to the second aspect of the invention, even when a surge pressure is generated in the relief discharge passage when the relief valve is opened, it is possible to suppress the propagation of the surge pressure to the spring chamber and the drain chamber. Therefore, malfunction of the spool can be prevented.

  A third aspect of the invention is characterized in that the relief valve has a larger discharge flow rate as compared with the case where the switching valve is switched by the discharged relief fluid to open the operation check valve.

  In the third invention, the relief valve is a large capacity type having a large discharge flow rate, so the degree of freedom in design is improved.

  According to the present invention, stable operation of the cylinder is possible.

It is a figure showing a part of hydraulic excavator. FIG. 1 is a hydraulic circuit diagram of a fluid pressure control device according to an embodiment of the present invention. It is a sectional view of the load maintenance mechanism of the fluid pressure control device concerning the embodiment of the present invention. It is a top view of the load maintenance mechanism of the fluid pressure control device concerning the embodiment of the present invention. It is a hydraulic circuit figure of the fluid pressure control device concerning the 1st modification of an embodiment of the present invention. It is a hydraulic circuit figure of the fluid pressure control device concerning the 2nd modification of an embodiment of the present invention. It is a hydraulic circuit figure of the fluid pressure control device concerning the 3rd modification of an embodiment of the present invention. It is a hydraulic circuit figure of the fluid pressure control device concerning the 4th modification of an embodiment of the present invention. It is a hydraulic circuit figure showing a comparative example of an embodiment of the present invention. It is sectional drawing which shows the comparative example of embodiment of this invention.

  A fluid pressure control device according to an embodiment of the present invention will be described with reference to the drawings.

  The fluid pressure control device controls the operation of a hydraulic working device such as a hydraulic shovel, and in the present embodiment, controls the extension and contraction operation of the cylinder 2 which drives the arm (load) 1 of the hydraulic shovel shown in FIG. The hydraulic control device will be described.

  First, the hydraulic circuit of the hydraulic control device will be described with reference to FIG.

  The cylinder 2 is connected to a cylindrical cylinder tube 2c, a piston 2d slidably inserted into the cylinder tube 2c and partitioning the inside of the cylinder tube 2c into a rod side chamber 2a and an opposite rod side chamber 2b, and one end connected to the piston 2d, And a rod 2e extending to the outside of the cylinder tube 2c and connected to the arm 1.

  An engine is mounted on the hydraulic shovel, and the power of the engine drives a pump 4 as a fluid pressure supply source and a pilot pump 5 as a pilot pressure supply source.

  The hydraulic control device includes a control valve 6 that controls the supply of hydraulic fluid from the pump 4 to the cylinder 2, and a pilot control valve 9 that controls a pilot pressure introduced from the pilot pump 5 to the control valve 6.

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

  The control valve 6 operates with a pilot pressure introduced from the pilot pump 5 to the pilot chambers 6a and 6b through the pilot control valve 9 as the operator of the hydraulic shovel manually operates the control lever 10.

  Specifically, when the pilot pressure is introduced to the pilot chamber 6a, the control valve 6 is switched to the position 6A, and the hydraulic fluid is supplied from the pump 4 to the rod side chamber 2a through the first main passage 7; The hydraulic oil in the opposite rod side chamber 2 b is discharged to the tank T through the second main passage 8. Thereby, the cylinder 2 is contracted and the arm 1 is lifted in the direction of the arrow 80 shown in FIG.

  On the other hand, when the pilot pressure is introduced to the pilot chamber 6b, the control valve 6 is switched to the position 6B, and the hydraulic fluid is supplied from the pump 4 to the opposite rod side chamber 2b through the second main passage 8 The hydraulic oil 2 a is discharged to the tank T through the first main passage 7. As a result, the cylinder 2 is extended and the arm 1 is lowered in the direction of the arrow 81 shown in FIG.

  When the pilot pressure is not led to the pilot chambers 6a and 6b, the control valve 6 is at the position 6C, the supply and discharge of hydraulic oil to the cylinder 2 is blocked, and the arm 1 is kept stopped.

  Thus, 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 of the cylinder 2. The hydraulic oil supply / discharge is switched to control the extension operation of the cylinder 2.

  Here, as shown in FIG. 1, when the control valve 6 is switched to the neutral position 6C and the movement of the arm 1 is stopped in a state where the bucket 13 is lifted, the cylinder 2 is moved by its own weight. The force in the direction of extension acts on the. Thus, in the cylinder 2 which drives the arm 1, the rod side chamber 2a becomes the load side pressure chamber on which the load pressure acts when the control valve 6 is at the neutral position 6C.

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

  In the cylinder 15 for driving the boom 14, since the opposite rod side chamber 15b is the load side pressure chamber, when the load holding mechanism 20 is provided on the boom 14, the load is applied to the main passage connected to the opposite rod side chamber 15b. A holding mechanism 20 is provided (see FIG. 1).

  The load holding mechanism 20 operates in conjunction with the control valve 6 by the operation check valve 21 provided in the first main passage 7 and the pilot pressure introduced to the pilot chamber 23 through the pilot control valve 9. And a switching valve 22 for switching the operation.

  The operation check valve 21 includes a valve body 24 for opening and closing the first main passage 7, a seat portion 28 on which the valve body 24 is seated, a back pressure chamber 25 defined on the back of the valve body 24, and the valve body 24. And a passage 26 for always guiding the hydraulic oil of the rod side chamber 2 a to the back pressure chamber 25. The passage 26 is provided with a stop 26a.

  The first main passage 7 has a cylinder side first main passage 7a connecting the rod side chamber 2a and the operation check valve 21, and a control valve side first main passage 7b connecting the operation check valve 21 and the control valve 6 .

  The valve body 24 has 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. It is formed.

  The back pressure chamber 25 accommodates a spring 27 as a biasing member that biases the valve body 24 in the valve closing direction. The pressure of 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.

  When the valve body 24 is seated on the seat portion 28, the operating check valve 21 functions as a check valve that shuts off the flow of hydraulic fluid from the rod side chamber 2a to the control valve 6. That is, the operation check valve 21 prevents the leakage of the hydraulic oil in the rod side chamber 2a, holds the load pressure, and holds the arm 1 in the stopped state.

  The load holding mechanism 20 further bypasses the hydraulic oil in the rod side chamber 2a to the control valve side first main passage 7b by bypassing the operation check valve 21, and the hydraulic oil in the back pressure chamber 25 on the control valve side. And a back pressure passage 31 leading to the first main passage 7b.

  The switching valve 22 is provided in the bypass passage 30 and the back pressure passage 31, switches communication between the bypass passage 30 and the back pressure passage 31 with the control valve side first main passage 7b, and extends the cylinder 2 when extending the cylinder 2 Control the flow of hydraulic oil in the first main passage 7.

  The switching valve 22 includes three ports of a first supply port 32 communicating with the bypass passage 30, a second supply port 33 communicating with the back pressure passage 31, and an exhaust port 34 communicating with the control valve side first main passage 7b. Have. Further, the switching valve 22 has three positions of a blocking position 22A, a first communication position 22B, and a second communication position 22C.

  When the pilot pressure is introduced to the pilot chamber 6 b of the control valve 6, the pilot pressure of the same pressure is simultaneously introduced to 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.

  Specifically, when the pilot pressure is not guided to the pilot chamber 23, the switching valve 22 maintains the shutoff position 22A by the biasing force of the spring 36. In the blocking position 22A, both the first supply port 32 and the second supply port 33 are blocked.

  When a pilot pressure equal to or more than the first predetermined pressure and less than the second predetermined pressure is introduced to 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. As a result, the hydraulic oil in the rod side chamber 2 a is led from the bypass passage 30 through the switching valve 22 to the control valve side first main passage 7 b. That is, the hydraulic oil in the rod side chamber 2a bypasses the operation check valve 21 and is led to the control valve side first main passage 7b. At this time, the restriction 37 applies resistance to the flow of the hydraulic oil. The second supply port 33 remains shut off.

  When a pilot pressure equal to or higher than the second predetermined pressure is introduced to the pilot chamber 23, the switching valve 22 switches to the second communication position 22C. In the second communication position 22 C, the first supply port 32 communicates with the discharge port 34, and the second supply port 33 also communicates with the discharge port 34. Thus, the hydraulic oil in the back pressure chamber 25 is led from the back pressure passage 31 through the switching valve 22 to the control valve side first main passage 7 b. At this time, the hydraulic oil in the back pressure chamber 25 bypasses the throttle 37 and is led to the control valve side first main passage 7 b and is discharged from 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 becomes smaller, so the force in the valve closing direction acting on the valve body 24 becomes smaller. Then, the function of the operation check valve 21 as a check valve is released.

  A relief passage 40 is branched and connected upstream of the switching valve 22 in the bypass passage 30. The relief passage 40 is provided with a relief valve 41 that opens when the pressure in the rod side chamber 2a reaches a predetermined pressure to allow the passage of the hydraulic oil and allows the hydraulic oil in the rod side chamber 2a to escape. The relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77 connecting the relief valve 41 and the tank T.

  Connected to the control valve side first main passage 7b is a relief valve 43 which opens when the pressure in the control valve side first main passage 7b reaches a predetermined pressure.

  Next, the switching valve 22 will be described in detail, mainly with reference to FIGS. 3 and 4. FIG. 3 is a cross-sectional view of the load holding mechanism 20 and shows a state in which the pilot pressure is not guided to the pilot chamber 23 and the switching valve 22 is in the blocking position 22A. FIG. 4 is a plan view of the load holding mechanism 20. As shown in FIG. In FIGS. 3 and 4, ones given the same reference numerals as the reference numerals shown in FIG. 2 have the same configurations as the configuration shown in FIG.

  The switching valve 22 is incorporated into the body 60. 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 in the sleeve 61.

  A spring chamber 54 is defined by a cap 57 on the side of one end surface 56 a of the spool 56. The spring chamber 54 is connected to the first drain passage 76 a through a notch 61 a formed on the end surface of the sleeve 61. The first drain passage 76 a is connected to the relief discharge passage 77. Therefore, the hydraulic oil leaking into the spring chamber 54 is discharged to the tank T through the first drain passage 76 a and the relief discharge passage 77.

  The spring chamber 54 accommodates a spring 36 as a biasing member for biasing the spool 56. Further, in the spring chamber 54, an annular first spring receiving member 45 in which an end face abuts on one end face 56a of the spool 56 and a pin portion 56c which is formed in a hollow portion to protrude on one end face 56a of the spool 56 is inserted. And a second spring receiving member 46 disposed in the vicinity of the bottom of the cap 57. The spring 36 is interposed between the first spring receiving member 45 and the second spring receiving member 46 in a compressed state, and biases the spool 56 in the valve closing direction via the first spring receiving member 45.

  The axial position of the second spring receiving member 46 in the spring chamber 54 is set by the tip of the adjustment bolt 47 passing through and screwing to the bottom of the cap 57 abutting on the back of the second spring receiving member 46 Be done. By screwing in the adjustment bolt 47, the second spring receiving member 46 moves in the 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.

  A pilot chamber 23 is defined on the side of the other end surface 56b of the spool 56 by a piston hole 60b formed in communication with the spool hole 60a and a cap 58 for closing the piston hole 60b. The pilot pressure is introduced to the pilot chamber 23 through a pilot passage 52 formed in the body 60. A piston 50 slidably received in the pilot chamber 23 receives a pilot pressure on its back surface and applies a thrust against the urging force of the spring 36 to the spool 56.

  The drain chamber 51 is partitioned by the spool 56 and the piston 50 in the piston hole 60 b. The drain chamber 51 is connected to the second drain passage 76 b, and the second drain passage 76 b is connected to the relief discharge passage 77. Therefore, the hydraulic oil leaking into the drain chamber 51 is discharged to the tank T through the second drain passage 76 b and the relief discharge passage 77.

  The piston 50 is formed to have a smaller diameter as compared with the sliding portion 50a whose outer peripheral surface slides along the inner peripheral surface of the piston hole 60b and the sliding portion 50a, and the tip end which faces the other end surface 56b of the spool 56 50 b and a proximal end 50 c which is smaller in diameter than the sliding portion 50 a and which faces the distal end surface of the cap 58.

  When pilot pressure oil is supplied into the pilot chamber 23 through the pilot passage 52, pilot pressure acts on the back surface of the proximal end 50c and the annular back surface of the sliding portion 50a. As a result, the piston 50 advances, and the leading end 50 b abuts on the other end surface 56 b of the spool 56 to move the spool 56. Thus, the spool 56 receives the thrust of the piston 50 generated based on the pilot pressure acting on the back surface of the piston 50, and moves against the biasing force of the spring 36. Even when the back surface of the proximal end 50c is in contact with the distal end surface of the cap 58, the proximal end 50c has a smaller diameter than the sliding portion 50a, and the pilot pressure is applied to the annular back surface of the sliding portion 50a. The piston 50 can be advanced because

  Since 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, the thrust of the piston 50 generated based on the pilot pressure of the pilot chamber 23 is efficiently spooled It is transmitted to 56.

  The drain chamber 51 and the spring chamber 54 respectively communicate with the relief discharge passage 77 through the first drain passage 76 a and the second drain passage 76 b. The relief discharge passage 77 is formed in communication with the drain port 53 opened on the outer surface of the body 60. The drain port 53 is connected to the tank T through a pipe 55 (see FIG. 2). Since the drain chamber 51 and the spring chamber 54 both communicate with the tank T, when the switching valve 22 is in the shutoff position 22A, atmospheric pressure acts on both ends of the spool 56, and the spool 56 moves unintentionally Such a situation is prevented.

  Thus, the relief pressure oil discharged from the relief valve 41 and the drain of the drain chamber 51 and the spring chamber 54 join together and are discharged to the tank T through the drain port 53 and the pipe 55.

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

  The sleeve 61 includes 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 the control valve side first main passage 7b. Three ports of the discharge port 34 communicating are formed.

  The outer peripheral surface of the spool 56 is partially cut out in an annular shape, and the cut 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 The fourth pressure chamber 67 is formed.

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

  The third pressure chamber 66 is always in communication with the first supply port 32. When the spool 56 moves against the biasing force of the spring 36, a plurality of throttles 37 communicating the third pressure chamber 66 with the second pressure chamber 65 are formed on the outer periphery of the land portion 72 of the spool 56. .

  The fourth pressure chamber 67 is always in communication with the second pressure chamber 65 through a pressure introduction passage 68 formed in the spool 56 in the axial direction.

  When the pilot pressure is not guided to the pilot chamber 23, the poppet valve 70 formed on the spool 56 by the biasing force of the spring 36 is pressed against the valve seat 71 formed on the inner periphery of the sleeve 61, and the second pressure is generated. The communication between the chamber 65 and the first pressure chamber 64 is cut off. Therefore, the communication between the first supply port 32 and the discharge port 34 is cut off. Thus, the hydraulic oil in the rod side chamber 2a does not leak to the discharge port 34. This state corresponds to the shutoff position 22A of the switching valve 22. In the state where the poppet valve 70 is seated on the valve seat 71 by the biasing force of the spring 36, a slight gap exists between the end face of the first spring receiving member 45 and the end face of the sleeve 61. The seat 71 is securely seated by the biasing force of the spring 36.

  When the pilot pressure is introduced to the pilot chamber 23 and the thrust of the piston 50 acting on the spool 56 becomes larger 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 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, so the first supply port 32 receives the third pressure chamber 66 and the second pressure. It communicates with the discharge port 34 through the chamber 65 and the first pressure chamber 64. The communication between the first supply port 32 and the discharge port 34 leads hydraulic oil in the rod side chamber 2 a to the control valve side first main passage 7 b through the throttle 37. This state corresponds to the first communication position 22 B of the switching valve 22.

  When the pilot pressure introduced to the pilot chamber 23 is increased, 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. Thus, 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. By 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 control valve side first main passage 7b. This state corresponds to the second communication position 22C of the switching valve 22.

  Next, the operation of the hydraulic control system will be described mainly with reference to FIGS. 2 and 3.

  When the control valve 6 is in the neutral position 6C, the hydraulic fluid discharged by the pump 4 is not supplied to the cylinder 2. At this time, since the pilot pressure is not guided to the pilot chamber 23 of the switching valve 22, the switching valve 22 is also in the state of the shutoff position 22A.

  For this reason, the back pressure chamber 25 of the operation 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 (area on 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, The valve body 24 is seated on the seat portion 28 by the load acting on the back surface of the valve body 24 and the biasing force of the spring 27. Thus, the leak of the hydraulic fluid in the rod side chamber 2a is prevented by the operation check valve 21, and the stopped state of the arm 1 is maintained.

  When the control 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 is switched to the contracted position 6 A, the discharge pressure of the pump 4 acts on the first pressure receiving surface 24 a of the operating check valve 21. At this time, since the switching valve 22 is in the state of the blocking position 22A because the pilot pressure is not guided to the pilot chamber 23, the back pressure chamber 25 of the operation check valve 21 is maintained at the pressure of the rod side chamber 2a. When the load acting on the first pressure receiving surface 24 a is larger than the total load of the load acting on the back surface of the valve body 24 due to the pressure of the back pressure chamber 25 and the biasing force of the spring 27, the valve body 24 Leave the seat 28. Thus, when the operation check valve 21 is opened, the hydraulic fluid discharged from the pump 4 is supplied to the rod side chamber 2a, and the cylinder 2 is contracted. Thereby, the arm 1 ascends in the direction of the arrow 80 shown in FIG.

  When the control 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 extended position 6B by an amount corresponding to the pilot pressure. At the same time, the 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 according to the supplied pilot pressure.

  When the pilot pressure introduced into the pilot chamber 23 is equal to or more than the first predetermined pressure and less than the second predetermined pressure, the switching valve 22 is switched to the first communication position 22B. In this case, since the communication between the second supply port 33 and the discharge port 34 is shut off, the back pressure chamber 25 of the operation check valve 21 is maintained at the pressure of the rod side chamber 2a, and the operation check valve 21 is closed. It becomes a state.

  On the other hand, since the first supply port 32 communicates with the discharge port 34, the hydraulic oil in the rod side chamber 2 a passes from the bypass passage 30 through the throttle 37 and is led to the control valve side first main passage 7 b. Is discharged to the tank T. Further, since the hydraulic oil discharged from the pump 4 is supplied to the opposite rod side chamber 2b, the cylinder 2 extends. Thereby, the arm 1 is lowered in the direction of the arrow 81 shown in FIG.

  Here, the switching valve 22 is switched to the first communication position 22B mainly when carrying out a crane operation to lower the transported object attached to the bucket 13 to a target position. In the crane operation, the cylinder 2 needs to be extended at a low speed to slowly lower the arm 1 in the direction of the arrow 81, so that the control valve 6 is only switched slightly to the extended position 6B. For this reason, the pilot pressure introduced to the pilot chamber 6b of the control valve 6 is small, and the pilot pressure introduced to the pilot chamber 23 of the switching valve 22 is equal to or greater than the first predetermined pressure and less than the second predetermined pressure. It only switches to position 22B. Therefore, the hydraulic oil in the rod side chamber 2a is discharged through the throttle 37 and the arm 1 descends at a low speed suitable for the crane operation.

  In addition, when the switching valve 22 is in the first communication position 22B, even if the control valve side first main passage 7b ruptures and the hydraulic oil leaks to the outside, it is discharged from the rod side chamber 2a. Since the flow rate of hydraulic fluid is limited by the throttle 37, 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 shutoff position 22A, and the rapid fall of the bucket 13 can be prevented.

  Thus, the throttle 37 is for suppressing the lowering speed of the cylinder 2 at the time of closing of the operation check valve 21 and for suppressing the falling speed of the bucket 13 at the time of rupture of the control valve side first main passage 7b. .

  When the pilot pressure introduced 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 hydraulic oil in the back pressure chamber 25 of the operation check valve 21 is led to the control valve side first main passage 7b through the back pressure passage 31 for control The valve 6 is discharged 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 becomes smaller, so the force in the valve closing direction acting on the valve body 24 becomes smaller and the valve body 24 separates from the seat portion 28 The function of the operation check valve 21 as a check valve is canceled.

  Thus, while the operation check valve 21 allows the flow of hydraulic fluid from the control valve 6 to the rod side chamber 2a, the flow of hydraulic fluid from the rod side chamber 2a to the control valve 6 according to the pressure of the back pressure chamber 25. Act to allow.

  When the operation check valve 21 is opened, the hydraulic oil in the rod side chamber 2a is discharged to the tank T through the first main passage 7, so that 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 opposite rod side chamber 2b increases. The extension speed is faster. Thereby, the arm 1 descends quickly in the direction of the arrow 81.

  The switching valve 22 is switched to the second communication position 22C when digging operation or the like is performed, and the control valve 6 is largely switched to the extension position 6B. Therefore, the pilot pressure guided to the pilot chamber 6b of the control valve 6 is large, the pilot pressure guided to the pilot chamber 23 of the switching valve 22 becomes equal to or higher than the second predetermined pressure, and the switching valve 22 switches to the second communication position 22C. .

  Next, the operation of the present embodiment will be described.

  First, with reference to FIGS. 9 and 10, a comparative example of the present embodiment will be described. 9 and 10, the same reference numerals as in FIGS. 2 and 3 denote the same components as in the above embodiment. In the comparative example shown in FIGS. 9 and 10, the relief passage 40 is provided with a relief valve 90 that opens when the pressure in the rod side chamber 2a reaches a predetermined pressure and releases the hydraulic oil in the rod side chamber 2a. An orifice 91 is provided in the relief discharge passage 77 connecting the relief valve 90 and the tank T. When the pressure of the rod side chamber 2a reaches a predetermined pressure and the relief valve 90 is opened, the relief pressure oil on the upstream side of the orifice 91 discharged from the relief valve 90 is guided to the drain chamber 51 through the second drain passage 76b. As a result, when the switching valve 22 is switched to the second communication position 22C, the operating check valve 21 is opened, and the pressure of the hydraulic oil in the rod side chamber 2a is reduced.

  In such a comparative example, the pilot pressure is introduced to the pilot chamber 23 by the operator's operation to move the spool 56 and the cylinder 2 is extended, the pressure in the rod side chamber 2a is increased, and the relief valve 90 is opened. In the case of the valve, the relief pressure oil on the upstream side of the orifice 91 discharged from the relief valve 90 is guided to the drain chamber 51. Since the relief back pressure on the upstream side of the orifice 91 introduced to the drain chamber 51 is larger than the pilot pressure introduced to the pilot chamber 23, the piston 50 moves in the direction away from the spool 56. Therefore, the thrust of the piston 50 generated by the pilot pressure is not transmitted to the spool 56. Further, since the pressure receiving area of the spool 56 on which the pressure of the drain chamber 51 acts is smaller than the pressure receiving area of the piston 50, depending on the magnitude of the relief back pressure on the upstream side of the orifice 91 led to the drain chamber 51, the spool 56 Can be moved in the closing direction by the biasing force of the spring 36.

  Thus, in the comparative example, when the relief valve 90 is opened while the operator is operating the operation lever so as to extend the cylinder 2, the spool 56 is moved in the closing direction. As a result, it may happen that the extension speed of the cylinder 2 intended by the operator can not be obtained.

  On the other hand, in the present embodiment, as shown in FIGS. 2 and 3, no orifice is provided in the relief discharge passage 77 connecting the relief valve 41 and the tank T. Therefore, the relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77, and no high pressure acts on the drain chamber 51. As described above, in the present embodiment, even if the relief valve 41 is opened, the operation of the switching valve 22 is not affected, and the relief pressure oil discharged from the relief valve 41 does not operate the switching valve 22. Specifically, when the relief valve 41 is opened, the relief pressure oil is slightly guided to the drain chamber 51 through the second drain passage 76b, but the relief pressure oil overcomes the thrust of the piston 50 generated by the pilot pressure. There is no pressure to move the piston 50 away from the spool 56. Therefore, according to the present embodiment, even if the relief valve 41 is opened while the operator is operating the operation lever so as to extend and move the cylinder 2, the spool 56 moves in the closing direction. The extension speed of the cylinder 2 intended by the operator can be obtained.

  As shown in FIG. 2, the relief discharge passage 77 communicates with the second drain port 86 opened on the outer surface of the body 60 through the passage 87. A pipe may be connected to the second drain port 86, and the second drain port 86 and the tank T may be connected via the pipe. According to this structure, the relief pressure oil discharged from the relief valve 41 is also discharged to the tank through the passage 87. Therefore, the flow rate of the relief pressure oil introduced to the drain chamber 51 can be reduced. However, in order to reduce piping connecting the body 60 of the load holding mechanism 20 and the tank T, piping is not connected to the second drain port 86, and the second drain port 86 is sealed by the plug 88 (see FIG. 4) It is preferable to do. Further, the drain port 53 is sealed by a plug, piping is connected to the second drain port 86, the relief pressure oil discharged from the relief valve 41 and the drain of the drain chamber 51 and the spring chamber 54 are the second drain port. It may be discharged to the tank T through 86.

  According to the above embodiment, the following effects can be obtained.

  The relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77 and does not operate the switching valve 22. Therefore, the operator is operating the operation lever so as to extend and retract the cylinder 2. Even when the relief valve 41 is opened, the spool 56 does not move in the closing direction, and the expansion and contraction speed of the cylinder 2 intended by the operator can be obtained. Thus, stable operation of the cylinder 2 is possible.

  Further, in the present embodiment, the relief pressure oil discharged from the relief valve 41 joins the drain of the drain chamber 51 and the spring chamber 54 and is discharged to the tank T through the drain port 53 and the pipe 55. Therefore, it is not necessary to provide a dedicated pipe for leading the relief pressure oil discharged from the relief valve 41 to the tank T, so the number of pipes can be reduced.

  In addition, since the relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77 and is hardly guided to the drain chamber 51, the relief back pressure pulsates when the relief valve 41 is opened. Even if the pulsation is transmitted to the spool 56, it is prevented. Therefore, the occurrence of vibration is suppressed.

  Further, the relief valve 90 of the comparative example in which the switching valve 22 is switched by the discharged relief pressure oil to open the operation check valve 21 drains the pressure for switching the spool 56 of the switching valve 22 to the second communication position 22C. In order to lead to the chamber 51, a small displacement relief valve with a small discharge flow rate is used. On the other hand, when the pressure of the rod side chamber 2a reaches a predetermined pressure, the relief valve 41 of the present embodiment opens to release the hydraulic oil of the rod side chamber 2a to the tank T and the pressure of the rod side chamber 2a. Since it is necessary to have a function to lower the pressure, a large capacity relief valve having a larger discharge flow rate as compared to the relief valve 90 of the comparative example is used. As described above, since the relief valve 41 of the present embodiment is of a large capacity type, the degree of freedom in design is improved. Further, since the relief valve 41 is of a large capacity type, the pressure in the rod side chamber 2a can be maintained at a predetermined pressure even when a surge pressure is generated such that the pressure in the rod side chamber 2a rapidly increases. Thus, damage to the cylinder 2 due to the surge pressure can be prevented.

  Next, a modification of the present embodiment will be described with reference to FIGS.

  In the first modification shown in FIG. 5, as a throttle that applies resistance to the hydraulic oil passing through each of the first drain passage 76a connected to the spring chamber 54 and the second drain passage 76b connected to the drain chamber 51. Orifices 82, 83 are provided. By providing the orifices 82 and 83 in the first drain passage 76a and the second drain passage 76b, the spring chamber 54 is formed even when a surge pressure is generated in the relief discharge passage 77 when the relief valve 41 is opened. Also, propagation of surge pressure to the drain chamber 51 can be suppressed. Therefore, malfunction of the spool 56 can be prevented.

  In the second and third modifications shown in FIGS. 6 and 7, the method of connecting the first drain passage 76a and the second drain passage 76b to the relief discharge passage 77 is different from the embodiment shown in FIGS. As described above, the method of connecting the first drain passage 76a and the second drain passage 76b to the relief discharge passage 77 is not limited to a specific configuration.

  In the fourth modification shown in FIG. 8, an orifice 84 as a throttle for applying resistance to hydraulic oil passing therethrough is provided in a combined drain passage 76 c where the first drain passage 76 a and the second drain passage 76 b join. By this configuration, only one orifice can be used to suppress the propagation of surge pressure.

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

  In this embodiment, the fluid pressure control device controls the expansion and contraction operation of the cylinder 2 driving the arm 1 and controls the supply of hydraulic fluid from the pump 4 to the cylinder 2 and the pilot pump 5 The pilot control valve 9 for controlling the pilot pressure guided to the valve 6 and the rod side pressure chamber 2a of the cylinder 2 on which the load pressure by the arm 1 acts when the control valve 6 is at the neutral position 6C are connected to the control valve 6 The load holding mechanism 20 includes a main passage 7 and a load holding mechanism 20 provided in the main passage 7. The load holding mechanism 20 allows the flow of hydraulic fluid from the control valve 6 to the rod side pressure chamber 2a, while responding to the back pressure. Operation check valve 21 which allows the flow of hydraulic fluid from rod-side pressure chamber 2a to control valve 6, and operates in conjunction with control valve 6 by the pilot pressure guided through pilot control valve 9 A switching valve 22 for switching the operation of the operation check valve 21, a relief valve 41 which opens when the pressure in the rod side pressure chamber 2a reaches a predetermined pressure, and a relief fluid discharged from the relief valve 41 as a tank The switching valve 22 includes a pilot chamber 23 to which a pilot pressure is guided through the pilot control valve 9, a spool 56 which moves according to the pilot pressure of the pilot chamber 23, and a spool 56. A spring chamber 54 in which a spring 36 urging in the valve closing direction is accommodated, a piston 50 for applying a thrust against the urging force of the spring 36 to the spool 56 under pilot pressure on the back, a spool 56 and a piston 50 The divided drain chamber 51, the drain chamber 51 and the spring chamber 54 are communicated with the relief discharge passage 77. That drain passage 76a, includes a 76 b, the relief pressure oil discharged from the relief valve 41 is discharged to the tank T not operate the switching valve 22 through the relief discharge passage 77.

  In this configuration, the relief pressure oil discharged from the relief valve 41 is discharged to the tank T through the relief discharge passage 77 and does not operate the switching valve 22, so the operator operates the operation lever so as to extend and retract the cylinder 2. Even when the relief valve 41 is opened during the operation, the spool 56 does not move in the closing direction, and the expansion and contraction speed of the cylinder 2 intended by the operator can be obtained. Thus, stable operation of the cylinder 2 is possible.

  Further, in the present embodiment, the drain passages 76a and 76b are provided with the throttles 82 and 83 for applying resistance to the hydraulic fluid passing therethrough.

  In this configuration, even when surge pressure is generated in the relief discharge passage 77 when the relief valve 41 is opened, propagation of the surge pressure to the spring chamber 54 and the drain chamber 51 can be suppressed. Therefore, malfunction of the spool 56 can be prevented.

  Further, in the present embodiment, the relief valve 41 has a larger discharge flow rate as compared with the case where the operation check valve 21 is opened by switching the switching valve 22 by the discharged relief pressure oil.

  In this configuration, since the relief valve 41 is of a large capacity type having a large discharge flow rate, the degree of freedom in design is improved.

  As mentioned above, although the embodiment of the present invention was described, the above-mentioned embodiment showed only a part of application example of the present invention, and in the meaning of limiting the technical scope of the present invention to the concrete composition of the above-mentioned embodiment. Absent.

Reference Signs List 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, 7 ... first main passage, 9 ... pilot control valve, 20 ... load holding mechanism, 21 ... operation check valve, 22 ... switching Valves 23, pilot chamber 41, relief valves 50, pistons 51, drain chambers 53, drain ports 54, spring chambers 56, spools 76a ... 1st drain passage, 76b ... 2nd drain passage, 77 ... relief relief passage, 82, 83, 84 ... orifice (throttle)

Claims (3)

A fluid pressure control device for controlling the extension operation of a cylinder driving a load, comprising:
A control valve that controls the supply of working fluid from a fluid pressure source 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 and the load side pressure chamber of the cylinder on which the load pressure by the load acts when the control valve is in the neutral position;
And a load holding mechanism provided in the main passage,
The load holding mechanism
An operation 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 a back pressure;
A switching valve that operates in conjunction with the control valve according to a pilot pressure guided through the pilot control valve, and switches operation of the operation check valve;
A relief valve that opens when the pressure in the load-side pressure chamber reaches a predetermined pressure;
And a relief discharge passage for guiding the relief fluid discharged from the relief valve to a tank,
The switching valve is
A pilot chamber in which a pilot pressure is introduced through the pilot control valve;
A spool that moves according to the pilot pressure in the pilot chamber;
A spring chamber containing a biasing member for biasing the spool in the valve closing direction;
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;
A drain chamber partitioned by the spool and the piston;
A drain passage communicating the drain chamber and the spring chamber with the relief discharge passage;
The relief fluid discharged from said relief valve is discharged to said tank through said relief discharge passage, and does not operate said switching valve.   The fluid pressure control device according to claim 1, wherein the drain passage is provided with a throttle that applies resistance to the fluid passing therethrough.   The fluid pressure control according to claim 1 or 2, wherein the relief valve has a larger discharge flow rate as compared with the case where the switching valve is switched by the discharged relief fluid to open the operation check valve. apparatus.

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