JP4918001B2 - Fluid pressure control device - Google Patents

Description

  The present invention relates to a fluid pressure control device that controls a hydraulic working device such as a hydraulic excavator.

  As a hydraulic control device for controlling a hydraulic working device, Patent Document 1 discloses a cylinder that expands and contracts by hydraulic oil supplied from a pump and drives a load, and switches between supply and discharge of a working fluid to the cylinder and controls expansion and contraction of the cylinder. A control valve is disclosed that includes a control valve and a load holding mechanism that is interposed between a load side pressure chamber of a cylinder on which a load pressure acts when the control valve is in a shut-off position and the control valve.

  The load holding mechanism includes a pilot check valve and a pilot switching valve that switches operation of the pilot check valve.

The spool position of the control valve and the pilot switching valve is switched by the pilot pressure supplied from the pilot valve.
JP 2004-132411 A

  In the hydraulic control device described in Patent Document 1, in the initial stage of supplying the pilot pressure to the control valve and the pilot switching valve to lower the load from the load holding state where the control valve is in the shut-off position, the load holding mechanism The pilot switching valve opens with the control valve closed.

  As a result, the high pressure in the load side pressure chamber acts on the passage from the pilot switching valve to the control valve, and the hydraulic pressure in the passage rapidly increases. When the hydraulic pressure in the passage changes abruptly, a strong impact is generated on the hydraulic working equipment.

  The present invention has been made in view of the above-described problems, and an object thereof is to alleviate an impact generated when a load is lowered from a load holding state.

The present invention includes a cylinder that expands and contracts by a working fluid supplied from a pump, drives a load, switches a supply and discharge of the working fluid to and from the cylinder, and controls the expansion and contraction operation of the cylinder. A pilot valve operated by a pilot, a main passage connecting the load side pressure chamber of the cylinder to which the load pressure due to a load acts when the control valve is in a shut-off position, and the control valve, and the main passage is interposed A load holding mechanism, wherein the load holding mechanism allows the flow of working fluid from the control valve to the load side pressure chamber, and the pressure in the load side pressure chamber is restricted by a throttle passage. An operation check valve that allows the flow of working fluid from the load side pressure chamber to the control valve in accordance with the pressure of the back pressure chamber that is always guided through A bypass passage for guiding the working fluid in the load side pressure chamber to the main passage by bypassing the operation check valve; a back pressure passage for guiding the working fluid in the back pressure chamber to the main passage; the bypass passage; It is installed in the back pressure passage and operates in conjunction with the control valve by the pilot pressure from the pilot valve. When the load is increased, the flow is interrupted, and when the load is decreased, the working fluid on the meter-out side A meter-out control valve for controlling the flow of the valve, and the meter-out control valve is moved by the pilot pressure and switches the communication of the main passage with respect to the bypass passage and the back pressure passage, and the spool When pilot pressure does not act on the formed valve body and the spool, the valve body is pushed by the biasing force of the spring. A valve seat vignetting by holding the load pressure of the load-side pressure chamber between the valve body, the initial communication between the bypass passage and the main passage, suppressing the increase ratio of the opening area with respect to the amount of movement of the spool An opening area restraining means for switching between the bypass passage and the main passage before the control valve opens when the control valve switches from a shut-off position for holding the load to a position for lowering the load. And an increase in pressure in the main passage is suppressed by the opening area suppression means.

  According to the present invention, when the control valve switches from the shut-off position where the load is held to the position where the load is lowered, the pressure increase in the main passage is suppressed by the opening area suppression means of the meter-out control valve. Therefore, the change of the hydraulic pressure in the main passage can be suppressed and the generation of a strong impact can be prevented.

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

  The fluid pressure control device controls the operation of a hydraulic working device such as a hydraulic excavator. In this embodiment, the fluid pressure control device controls the expansion and contraction operation of the cylinder 2 that drives the arm (load) 1 of the hydraulic excavator shown in FIG. The case where it does is demonstrated.

  First, the hydraulic circuit of the hydraulic control device will be described with reference to FIG. FIG. 2 is a hydraulic circuit diagram of the hydraulic control device.

  The cylinder 2 is defined as a rod-side pressure chamber 2a and an anti-rod-side pressure chamber 2b by a piston rod 3 that moves slidably in the cylinder 2.

  An engine (not shown) is mounted on the hydraulic excavator, and a pump 4 and a pilot pump 5 which are hydraulic sources are connected to the engine.

  The working oil (working fluid) discharged from the pump 4 is supplied to a control valve 6 that switches between supplying and discharging the working fluid to and from the cylinder 2.

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

  The control valve 6 is operated by the pilot pressure supplied from the pilot pump 5 to the pilot chambers 6 a and 6 b through the pilot valve 9 when the crew of the excavator manually operates the operation lever 10.

  Specifically, when the pilot pressure is supplied to the pilot chamber 6a, the control valve 6 is switched to the position a, and hydraulic oil is supplied from the pump 4 to the rod side pressure chamber 2a via the first main passage 7. At the same time, the hydraulic oil in the anti-rod side pressure chamber 2 b is discharged to the tank T through the second main passage 8. As a result, the cylinder 2 contracts and the arm 1 moves up in the direction of the arrow 80 shown in FIG.

  When the pilot pressure is supplied to the pilot chamber 6b, the control valve 6 is switched to the position b, and the hydraulic oil is supplied from the pump 4 to the anti-rod side pressure chamber 2b through the second main passage 8. At the same time, the hydraulic oil in the rod side pressure chamber 2 a is discharged to the tank T through the first main passage 7. Thereby, 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 supplied to the pilot chambers 6a and 6b, the control valve 6 is switched to the position c, the supply of hydraulic oil to the cylinder 2 is shut off, and the arm 1 is kept stopped.

  Thus, the control valve 6 includes three switching positions: a contracted position a for contracting the cylinder 2, an extending position b for extending the cylinder 2, and a blocking position c for holding the load of the cylinder 2.

  Here, as shown in FIG. 1, when the control valve 6 is switched to the shut-off position c and the movement of the arm 1 is stopped in the state where the bucket 13 is lifted, the weight of the bucket 13 and the arm 1 etc. A force in the extending direction acts. Thus, in the cylinder 2 that drives the arm 1, the rod-side pressure chamber 2 a becomes a load-side pressure chamber in which the load pressure acts when the control valve 6 is in the cutoff position c.

  In the cylinder 15 that drives the boom 14, the non-rod side pressure chamber 15b is a load side pressure chamber.

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

  The load holding mechanism 20 includes an operation check valve 21 interposed in the first main passage 7 and the hydraulic oil in the first main passage 7 on the meter-out side when the cylinder 2 is extended and the arm 1 is lowered. And a meter-out control valve 22 for controlling the flow.

  The operation check valve 21 is a valve body 24 that opens and closes the first main passage 7, a back pressure chamber 25 defined on the back surface of the valve body 24, and hydraulic oil in the rod side pressure chamber 2 a that is formed in the valve body 24. A throttle passage 26 that always leads to the back pressure chamber 25 is provided.

  The first main passage 7 is connected to the cylinder side first main passage 7 a that connects the rod side pressure chamber 2 a and the operation check valve 21 by the valve body 24, and the control valve side first that connects the operation check valve 21 and the control valve 6. It is divided into a main passage 7b.

  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 on the rod side pressure chamber 2a acts through the cylinder side first main passage 7a. And are formed.

  A spring 27 that urges the valve body 24 in the valve closing direction is accommodated in the back pressure chamber 25. Thus, the pressure in the back pressure chamber 25 and the urging force of the spring 27 act so that the valve body 24 is seated on the valve seat 28.

  The state in which the valve body 24 is seated on the valve seat 28 is a state in which the operation check valve 21 is functioning as a check valve that blocks the flow of hydraulic oil from the rod side pressure chamber 2a to the control valve 6. is there. That is, the operation check valve 21 prevents the hydraulic oil in the rod side pressure chamber 2a from leaking, maintains the load pressure, and maintains the arm 1 in a stopped state.

  In addition, the load holding mechanism 20 bypasses the operating check valve 21 to the first main passage 7 by bypassing the hydraulic oil in the rod side pressure chamber 2a and the hydraulic fluid in the back pressure chamber 25 to the first main passage. And a back pressure passage 31 leading to 7.

  The meter-out control valve 22 is interposed in the bypass passage 30 and the back pressure passage 31, and operates in conjunction with the control valve 6 by the pilot pressure supplied to the pilot chamber 22a through the pilot valve 9. The communication of the control valve side first main passage 7b with respect to the passage 31 is switched.

  The meter-out control valve 22 includes three supply 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 control valve side first main passage 7b. Provide a port.

  Further, the meter-out control valve 22 has three switching positions, that is, a cutoff position x, a first communication position y, and a second communication position z.

  The pilot pressure of the same pressure is simultaneously supplied to the pilot chamber 22a when the pilot pressure is supplied to the pilot chamber 6b of the control valve 6. That is, when the control valve 6 is switched to the extended position b, the meter-out control valve 22 is also switched to the first communication position y or the second communication position z.

  More specifically, when the pilot pressure is not supplied to the pilot chamber 22a, the meter-out control valve 22 maintains the cutoff position x by the urging force of the spring 36. At the blocking position x, both the first supply port 32 and the second supply port 33 are blocked.

  When a pilot pressure less than a predetermined pressure is supplied to the pilot chamber 22a, the meter-out control valve 22 is switched to the first communication position y. In the first communication position y, the first supply port 32 communicates with the discharge port 34. Thus, the hydraulic oil in the rod side pressure chamber 2a is guided from the bypass passage 30 to the control valve side first main passage 7b. At this time, the throttle 37 gives resistance to the flow of hydraulic oil. In addition, the 2nd supply port 33 maintains the state interrupted | blocked.

  When a pilot pressure higher than a predetermined pressure is supplied to the pilot chamber 22a, the meter-out control valve 22 is switched to the second communication position z. At the second communication position z, the first supply port 32 communicates with the discharge port 34 and the second supply port 33 communicates with the discharge port 34. Thus, the hydraulic oil in the back pressure chamber 25 is guided from the back pressure passage 31 to the control valve side first main passage 7b.

  A relief passage 40 is branched and connected upstream of the meter-out control valve 22 in the bypass passage 30, and allows the hydraulic oil to pass through the relief passage 40 when the pressure of the hydraulic oil in the bypass passage 30 reaches a predetermined pressure. An allowable sub-relief valve 41 is interposed. An orifice 42 is provided downstream of the sub relief valve 41. The pressure on the upstream side of the orifice 42 is guided to the pilot chamber 22a, and the pressure on the downstream side is discharged to the tank T. When the pressure on the upstream side of the orifice 42 is led to the pilot chamber 22a, the meter-out control valve 22 is set to be switched to the first communication position y or the second communication position z by the pressure.

  The first relief valve 43 is connected to the control valve side first main passage 7 b, and the second relief valve 44 is connected to the second main passage 8. The first relief valve 43 and the second relief valve 44 are for releasing the high pressure generated in the rod side pressure chamber 2a and the non-rod side pressure chamber 2b of the cylinder 2 when a large external force is applied to the arm 1.

  Next, the configuration of the load holding mechanism 20 will be specifically described mainly with reference to FIGS. 3 and 4. FIG. 3 is a cross-sectional view of the load holding mechanism 20 in the hydraulic control device, and FIG. 4 is an enlarged cross-sectional view of the main part of the meter-out control valve 22. 3 and 4, the same reference numerals as those shown in FIG. 2 denote the same components as those shown in FIG.

  The load holding mechanism 20 includes a first body 50 in which the operation check valve 21 is incorporated, and a second body 51 in which the meter-out control valve 22 and the sub relief valve 41 are incorporated.

  A sliding hole 52 is formed in the first body 50, and the valve body 24 is slidably incorporated in the sliding hole 52. The valve body 24 has a first pressure receiving surface 24a on which the pressure of the control valve side first main passage 7b communicating with the control valve 6 acts, and a pressure of the cylinder side first main passage 7a communicating with the rod side pressure chamber 2a. The acting second pressure receiving surface 24b is formed.

  The opening end of the sliding hole 52 is closed by a spring receiving member 53, and a back pressure chamber 25 is defined between the spring receiving member 53 and the valve body 24. A spring 27 that urges the valve body 24 in the valve closing direction is accommodated in the back pressure chamber 25. The valve body 24 is formed with a throttle passage 26 that constantly guides the hydraulic oil in the rod side pressure chamber 2 a to the back pressure chamber 25. Thereby, the pressure of the back pressure chamber 25 acts on the back surface of the valve body 24, and a force in the valve closing direction acts on the valve body 24.

  With the pressure of the back pressure chamber 25 and the urging force of the spring 27, when the valve body 24 is seated on the valve seat 28, the communication between the cylinder side first main passage 7a and the control valve side first main passage 7b is blocked. The

  The first body 50 is formed with a bypass passage 30 that communicates with the cylinder-side first main passage 7a and that guides the hydraulic oil in the rod-side pressure chamber 2a.

  A spool hole 55 is formed in the second body 51, and a substantially cylindrical sleeve 61 is inserted into the inner periphery of the spool hole 55. A spool 56 of the meter-out control valve 22 is slidably incorporated in the inner periphery of the sleeve 61.

  One open end of the spool hole 55 is closed by a cap 57, and a spring 36 that biases one end of the spool 56 is accommodated in the spring chamber 54 defined by the cap 57. The spring chamber 54 communicates with the tank T via a passage (not shown).

  The other open end of the spool hole 55 is closed by a cap 58, and a piston 59 is slidably accommodated in the cap 58. The front end of the piston 59 faces the other end of the spool 56, and a pilot chamber 22a into which pilot pressure is guided is defined on the back surface of the piston 59. The spool 56 moves due to a balance between the biasing force of the spring 36 acting on one end and the pilot pressure acting on the other end via the piston 59, and the switching position of the meter-out control valve 22 is set.

  The sleeve 61 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 control valve side first main passage 7b. It is formed.

  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 cutout portion and the inner peripheral surface of the sleeve 61, A 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 and is always in communication with the second pressure chamber 65 by a plurality of throttles 37 formed in a groove shape on the outer periphery of the land portion 72 of the spool 56. Accordingly, the hydraulic oil in the rod side pressure chamber 2 a is always guided to the second pressure chamber 65 through the bypass passage 30, the first supply port 32, the third pressure chamber 66, and the throttle 37.

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

  When pilot pressure is not supplied to the pilot chamber 22a, the valve body 70 formed on the spool 56 is pressed against the valve seat 71 formed on the inner periphery of the sleeve 61 by the urging force of the spring 36, and the first pressure chamber Communication between 64 and the second pressure chamber 65 is blocked. Therefore, the communication between the first supply port 32 and the discharge port 34 is blocked. Thus, the hydraulic oil in the rod side pressure chamber 2a does not leak to the discharge port 34, and the load pressure in the rod side pressure chamber 2a is held by the valve body 70. This state corresponds to the cutoff position x of the meter-out control valve 22.

  When the pilot pressure is supplied to the pilot chamber 22 a and the thrust of the piston 59 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. . Accordingly, the valve body 70 is separated from the valve seat 71, the first pressure chamber 64 and the second pressure chamber 65 are communicated, and the first supply port 32 is communicated with the discharge port 34. Due to the communication between the first supply port 32 and the discharge port 34, the hydraulic oil in the rod side pressure chamber 2 a is guided to the control valve side first main passage 7 b through the throttle 37. This state corresponds to the first communication position y of the meter-out control valve 22.

  When the pilot pressure supplied to the pilot chamber 22a increases, the spool 56 further moves against the urging force of the spring 36, and the fourth pressure chamber 67 communicates with the second supply port 33. As a result, the second supply port 33 communicates with the discharge port 34 via the fourth pressure chamber 67, the pressure guide 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 control valve side first main passage 7b. This state corresponds to the second communication position z of the meter-out control valve 22.

  A valve assembly chamber 75 communicating with the first supply port 32 is formed in the second body 51, and the sub relief valve 41 is accommodated in the valve assembly chamber 75.

  The sub relief valve 41 is housed in the valve assembly chamber 75, and the first supply port 32 is connected to the first discharge passage 76 and the second discharge passage 77 by the valve opening operation of the sub relief valve 41. The first discharge passage 76 is connected to the pilot chamber 22a, and the second discharge passage 77 is connected to the tank T. The second discharge passage 77 is provided with an orifice 42 that provides resistance to the passing hydraulic fluid. As described above, in the hydraulic oil discharged by the sub relief valve 41, the pressure upstream of the orifice 42 is guided to the pilot chamber 22a, and the pressure downstream of the orifice 42 is guided to the tank T. Therefore, when the sub-relief valve 41 is opened, the spool 56 moves in a direction in which the spring 36 is compressed, and the meter-out control valve 22 is switched to the first communication position y or the second communication position z.

  Next, the operation of the hydraulic control device will be described.

  When the control valve 6 is in the cutoff position c, the hydraulic oil discharged from the pump 4 is not supplied to the cylinder 2. At this time, since pilot pressure is not supplied to the pilot chamber 22a of the meter-out control valve 22, the meter-out control valve 22 is also in the cutoff position x.

  For this reason, the back pressure chamber 25 of the operation check valve 21 is maintained at the pressure of the rod side pressure chamber 2a. Here, 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 that is the pressure receiving area in the valve opening direction. The urging force of the spring 27 causes the valve body 24 to be seated on the valve seat 28. As described above, the operation check valve 21 prevents the hydraulic oil in the rod-side pressure chamber 2a from leaking, and the arm 1 is kept stopped.

  When the pilot pressure is supplied from the pilot valve 9 to the pilot chamber 6a of the control valve 6 by operating the operation lever 10, the control valve 6 is switched to the contracted position a by an amount corresponding to the pilot pressure. When the control valve 6 is switched to the contracted position a, the pressure of the hydraulic oil discharged from the pump 4 acts on the first pressure receiving surface 24a of the operation check valve 21. At this time, since the pilot pressure is not supplied to the pilot chamber 22a and the meter-out control valve 22 is in the cutoff position x, the back pressure chamber 25 of the operation check valve 21 is maintained at the pressure of the rod side pressure chamber 2a. Is done. Therefore, 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 due to the pressure of the back pressure chamber 25 and the urging force of the spring 27, the valve The body 24 leaves the valve seat 28. When the operation check valve 21 is opened in this manner, the hydraulic oil discharged from the pump 4 is supplied to the rod side pressure chamber 2a, and the cylinder 2 contracts. As a result, the arm 1 rises in the direction of the arrow 80 shown in FIG.

  When the pilot pressure is supplied from the pilot valve 9 to the pilot chamber 6b of the control valve 6 by operating the operation lever 10, the control valve 6 is switched to the extended position b by an amount corresponding to the pilot pressure. At the same time, since the pilot pressure is supplied to the pilot chamber 22a, the meter-out control valve 22 switches to the first communication position y or the second communication position z according to the supplied pilot pressure.

  When the pilot pressure supplied to the pilot chamber 22a is less than a predetermined pressure, the meter-out control valve 22 is switched to the first communication position y. 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 operation check valve 21 is maintained at the pressure of the rod side pressure chamber 2a, and the operation check valve 21 is The valve is closed. Thereby, the communication between the cylinder side first main passage 7a and the control valve side first main passage 7b is blocked.

  However, since the first supply port 32 communicates with the discharge port 34, the hydraulic oil in the rod side pressure chamber 2a is led from the bypass passage 30 to the control valve side first main passage 7b via the throttle 37, and the control valve 6 is discharged into the tank T. Further, since the hydraulic oil discharged from the pump 4 is supplied to the non-rod side pressure chamber 2b, the cylinder 2 extends. As a result, the arm 1 is lowered in the direction of the arrow 81 shown in FIG.

  Here, the meter-out control valve 22 is switched to the first communication position y mainly when a crane operation is performed to lower the conveyed product attached to the bucket 13 to a target position. In the crane operation, the control valve 6 is only slightly switched to the extended position b in order to slowly lower the arm 1 in the direction of the arrow 81. For this reason, the pressure supplied to the pilot chamber 6b of the control valve 6 is small, the pilot pressure supplied to the pilot chamber 22a of the meter-out control valve 22 is less than a predetermined pressure, and the meter-out control valve 22 reaches the one communication position y. Only switch. Therefore, the hydraulic oil in the rod side pressure chamber 2a is discharged through the throttle 37, and the arm 1 descends at a low speed suitable for crane work.

  Further, when the meter-out control valve 22 is in the first communication position y, the rod-side pressure chamber is not affected even if the control valve-side first main passage 7b ruptures and the hydraulic fluid leaks to the outside. Since the flow rate of the hydraulic oil discharged from 2a is regulated by the throttle 37, the falling speed of the bucket 13 becomes slow. For this reason, before the bucket 13 falls to the ground, the meter-out control valve 22 can be switched to the cutoff position x, and the bucket 13 can be prevented from falling.

  As described above, the throttle 37 is for suppressing the descending speed of the cylinder 2 when the operation check valve 21 is closed, and suppressing the falling speed of the bucket 13 when the control valve side first main passage 7b is ruptured. .

  When the pilot pressure supplied to the pilot chamber 22a is equal to or higher than a predetermined pressure, the meter-out control valve 22 is switched to the second communication position z. 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 guided from the back pressure passage 31 to the control valve side first main passage 7b, and is controlled. It is discharged from the valve 6 to the tank T. As a result, a differential pressure is generated before and after the throttle passage 26, and the pressure in the back pressure chamber 25 is reduced, so that the force in the valve opening direction acting on the valve body 24 is greater than the force in the valve closing direction, The valve body 24 is separated from the valve seat 28, and the function of the operation check valve 21 as a check valve is released.

  In this way, the operation check valve 21 allows the flow of hydraulic oil from the control valve 6 to the rod side pressure chamber 2a, and from the rod side pressure chamber 2a to the control valve 6 according to the pressure of the back pressure chamber 25. Operates to allow hydraulic fluid flow.

  When the operation check valve 21 is opened, the hydraulic oil in the rod side pressure chamber 2a passes through the first main passage 7 and is discharged to the tank T, so that the cylinder 2 extends quickly. That is, when the meter-out control valve 22 is switched to the second communication position z, the flow rate of the hydraulic oil discharged from the rod side pressure chamber 2a is large, so the flow rate of the hydraulic oil supplied to the non-rod side pressure chamber 2b is large. Thus, the extension speed of the cylinder 2 is increased. As a result, the arm 1 quickly descends in the direction of the arrow 81.

  As described above, the meter-out control valve 22 is switched to the second communication position z when excavation work or the like is performed, and the control valve 6 is largely switched to the extended position b. For this reason, the pressure supplied to the pilot chamber 6b of the control valve 6 is large, the pilot pressure supplied to the pilot chamber 22a of the meter-out control valve 22 exceeds a predetermined pressure, and the meter-out control valve 22 is in the second communication position z. Switch to.

  When a large external force is applied to the arm 1 when the control valve 6 is set to the cutoff position c and the movement of the arm 1 is stopped, the rod-side pressure chamber 2a of the cylinder 2 or the anti-rod-side pressure is applied. The pressure in the chamber 2b increases. When the pressure in the rod side pressure chamber 2a reaches a predetermined pressure, the sub-relief valve 41 is opened, and the hydraulic oil in the rod side pressure chamber 2a is discharged through the orifice 42. Then, the pressure on the upstream side of the orifice 42 is guided to the pilot chamber 22a of the meter-out control valve 22, and the pressure on the downstream side is discharged to the tank T. Therefore, the meter-out control valve 22 is in the first communication position y or the second position. It switches to the communication position z, and the cylinder side first main passage 7a and the control valve side first main passage 7b communicate with each other. Thereby, the high pressure in the rod side pressure chamber 2 a is discharged to the tank T through the first relief valve 43.

  Further, when the pressure in the counter rod side pressure chamber 2b reaches a predetermined pressure, the second relief valve 44 opens, and the high pressure in the counter rod side pressure chamber 2b passes through the second relief valve 44 to the tank. Discharged to T.

  As described above, the meter-out control valve 22 operates in conjunction with the control valve 6 by the pilot pressure. When the arm 1 is raised, the meter-out control valve 22 is set to the cutoff position x to cut off the flow of hydraulic oil. Is lowered to the first communication position y or the second communication position z to control the flow of hydraulic oil in the first main passage 7 on the meter-out side.

  Next, meter-out control by the meter-out control valve 22 when the arm 1 is lowered will be described in detail. FIG. 5A is a graph showing the opening areas of the control valve 6 and the meter-out control valve 22 with respect to the pilot pressure when the arm 1 is lowered from the held state. FIG. 5B is a graph showing the pressure in the cylinder side first main passage 7a and the control valve side first main passage 7b with respect to the pilot pressure when the arm 1 is lowered from the state in which the arm 1 is held. In FIG. 5A, after switching to the second communication position z in the opening area of the meter-out control valve 22, the total opening area including the opening area of the operation check valve 21 is shown. Further, the opening area of the meter-out control valve 22 is an area through which hydraulic oil opened by the valve body 70 can pass.

  Since the same pilot pressure is supplied to the pilot chamber 6b of the control valve 6 and the pilot chamber 22a of the meter-out control valve 22, switching timing between the control valve 6 and the meter-out control valve 22 is provided for each. It is set by adjusting the urging force of the spring to be adjusted.

  When the arm 1 is lowered, that is, when the cylinder 2 is extended, the meter-out control valve 22 is operated when the meter-out control valve 22 is switched after the control valve 6 is switched to the extended position b. Since the cylinder 2 does not operate until the start of the operation, the lever operation feeling of the crew changes as compared with a hydraulic excavator in which the load holding mechanism 20 is not mounted, and the crew feels uncomfortable.

  Therefore, the switching timing of the control valve 6 and the meter-out control valve 22 during the extension operation of the cylinder 2 is as follows. As shown in FIG. 5A, the meter-out control valve 22 is first switched to the first communication position y. The control valve 6 is set so that the meter-out control valve 22 starts to switch to the extended position b before switching to the second communication position z. Furthermore, the initial opening degree of the valve body 70 when the meter-out control valve 22 is switched to the first communication position y is set so as to be greatly opened with a minute stroke of the meter-out control valve 22.

  Thus, when the meter-out control valve 22 precedes the control valve 6 and opens at a large opening, the meter-out control valve 22 causes inconvenience to the extension operation of the cylinder 2 by the control valve 6. There is nothing.

  However, when the meter-out control valve 22 precedes the control valve 6 and opens with a large opening, the meter-out control valve 22 is initially controlled to start switching from the cutoff position x to the first communication position y. When the valve 6 is closed, the high-pressure hydraulic oil in the rod-side pressure chamber 2 a flows into the control valve-side first main passage 7 b through the bypass passage 30.

  When the meter-out control valve 22 is in the shut-off position x, the control valve side first main passage 7b is in a low pressure state because the pressure in the rod side pressure chamber 2a does not act on the control valve side first main passage 7b. It is.

  Accordingly, at the initial stage when the meter-out control valve 22 starts to switch from the shut-off position x to the first communication position y, the high pressure in the rod-side pressure chamber 2a passes through the bypass passage 30 and the control valve-side first main passage 7b in the low pressure state. The pressure in the control valve side first main passage 7b increases abruptly. When the pressure in the control valve side first main passage 7b changes abruptly, a strong impact is generated in the hydraulic excavator.

  As a countermeasure against this, the meter-out control valve 22 has an opening area suppression means that suppresses an increase rate of the opening area with respect to the movement amount of the spool 56 at the initial stage of communication between the bypass passage 30 and the control valve side first main passage 7b. Provided. Below, an opening area suppression means is demonstrated with reference to FIG.

  As shown in FIG. 4, as the opening area suppression means, the seat surface of the valve seat 71 on which the valve body 70 is seated against the tapered outer peripheral surface of the valve body 70 formed on the spool 56 of the meter-out control valve 22. Is formed in a tapered shape having a small angle difference.

  In this way, the valve body 70 and the valve seat 71 are formed in a tapered shape having a predetermined angular difference, so that the meter-out control valve 22 starts to switch from the cutoff position x to the first communication position y, that is, When the valve body 70 is separated from the valve seat 71, the opening area of the valve body 70 gradually increases with respect to the movement amount (pilot pressure) of the spool 56, as indicated by reference numeral 85 in FIG. become. Thus, when the hydraulic oil in the rod side pressure chamber 2a flows into the control valve side first main passage 7b, the pressure in the control valve side first main passage 7b is as shown by reference numeral 86 in FIG. Since it rises slowly, the change in the pressure of the control valve side first main passage 7b is suppressed, and the impact generated in the hydraulic excavator can be prevented.

  Further, since the valve body 70 and the valve seat 71 are formed in a tapered shape having a predetermined angular difference, the valve body 70 and the valve seat 71 are in contact with each other at one place on the circumference, so that the sealing performance is improved. Keeps good.

Below, the other form of an opening area suppression means is demonstrated.
(1) As an opening area suppressing means, as shown in FIG. 6, a flat portion 70a parallel to the axial direction of the spool 56 is formed on the tapered outer peripheral surface of the valve body 70, and a flat portion 70a is formed on the valve seat 71. The opposing flat part 71a parallel to is formed.

  When the meter-out control valve 22 is at the shut-off position x, the first pressure chamber 64 and the second pressure chamber 65 are brought into contact with the tapered portion 70b of the valve body 70 by the end of the opposed flat portion of the valve seat 71. Is disconnected.

Then, at the initial stage when the meter-out control valve 22 starts to switch from the shut-off position x to the first communication position y, the valve body 70 moves while the flat portion 70a slides in parallel with the opposed flat portion 71a of the valve seat 71. . While the flat portion 70a of the valve body 70 and the opposed flat portion 71a of the valve seat 71 are opposed to each other, the opening area of the valve body 70 with respect to the movement amount of the spool 56 increases slowly. Thereby, when the hydraulic oil in the rod side pressure chamber 2a flows into the control valve side first main passage 7b, the pressure in the control valve side first main passage 7b rises slowly.
(2) The opening area suppression means is not formed in the valve body 70 but is formed in the land portion 72 that separates the second pressure chamber 65 and the third pressure chamber 66.

  As shown in FIG. 7, the groove-shaped throttle 37 formed on the outer periphery of the land portion 72 is formed in parallel to the axial direction of the spool 56, does not penetrate to the second pressure chamber 65, and the meter-out control valve 22 In the case of the blocking position x, it is formed so as to be closed by an annular closing portion 90 formed on the inner periphery of the sleeve 61. The throttle 37 is formed so that the closing by the closing portion 90 is released at the same time that the valve body 70 is separated from the valve seat 71.

  At the initial stage when the meter-out control valve 22 starts to switch from the shut-off position x to the first communication position y, the closing of the throttle 37 by the closing portion 90 is released at the same time as the valve body 70 moves away from the valve seat 71. As the spool 56 moves, the opening area of the throttle 37 with respect to the second pressure chamber 65 increases. As a result, the opening area of the valve body 70 also increases slowly. Thereby, when the hydraulic oil in the rod side pressure chamber 2a flows into the control valve side first main passage 7b, the pressure in the control valve side first main passage 7b rises slowly.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  The present invention can be applied to a hydraulic control device of a hydraulic excavator.

It is a figure which shows a hydraulic shovel part. 1 is a hydraulic circuit diagram of a hydraulic control device according to an embodiment of the present invention. It is sectional drawing of the load holding mechanism in the hydraulic control apparatus of embodiment of this invention. It is a principal part expanded sectional view of the meter-out control valve in the hydraulic control apparatus of embodiment of this invention. (A) It is a graph which shows the opening area of the control valve with respect to pilot pressure and the meter-out control valve in the case of lowering from the state which hold | maintained the arm. (B) It is a graph which shows the pressure of the cylinder side 1st main channel | path and control valve side 1st main channel | path with respect to the pilot pressure in the case of lowering from the state which hold | maintained the arm. It is sectional drawing which shows the other form of the opening area suppression means in a meter out control valve. It is sectional drawing which shows the other form of the opening area suppression means in a meter out control valve.

Explanation of symbols

1 Arm (load)
2 Cylinder 2a Rod side pressure chamber 2b Non-rod side pressure chamber (load side pressure chamber)
3 Piston rod 4 Pump 6 Control valves 6a, 6b Pilot chamber 7 First main passage 7a Cylinder side first main passage 7b Control valve side first main passage 8 Second main passage 9 Pilot valve 20 Load holding mechanism 21 Operate check valve 22 Meter-out control valve 22a Pilot chamber 24 Valve body 24a First pressure receiving surface 24b Second pressure receiving surface 25 Back pressure chamber 26 Throttle passage 27 Spring 30 Bypass passage 31 Back pressure passage 32 First supply port 33 Second supply port 34 Discharge port 36 Spring 37 Restriction 54 Spring chamber 55 Spool hole 56 Spool 59 Piston 61 Sleeve 64 First pressure chamber 65 Second pressure chamber 66 Third pressure chamber 67 Fourth pressure chamber 68 Pressure guiding passage 70 Valve body 71 Valve seat

Claims (4)

A cylinder that expands and contracts by a working fluid supplied from a pump and drives a load;
A control valve that switches the supply and discharge of the working fluid to and from the cylinder and controls the expansion and contraction of the cylinder;
A pilot valve that pilot-operates the control valve with a pilot pressure;
A main passage that connects the control valve with a load side pressure chamber of the cylinder on which a load pressure due to a load acts when the control valve is in a shut-off position;
In a fluid pressure control device comprising a load holding mechanism interposed in the main passage,
The load holding mechanism is
The flow of the working fluid from the control valve to the load side pressure chamber is allowed, and the pressure of the load side pressure chamber is controlled from the load side pressure chamber according to the pressure of the back pressure chamber that is always guided through the throttle passage. An operation check valve that allows the flow of working fluid to the control valve;
A bypass passage that bypasses the operation check valve and leads the working fluid in the load side pressure chamber to the main passage;
A back pressure passage for guiding the working fluid of the back pressure chamber to the main passage;
It is interposed in the bypass passage and the back pressure passage, and operates in conjunction with the control valve by the pilot pressure by the pilot valve. When the load is increased, the flow is interrupted, and when the load is decreased, the meter A meter-out control valve for controlling the flow of the working fluid on the out side,
The meter-out control valve is
A spool that moves by the pilot pressure and switches communication of the main passage with respect to the bypass passage and the back pressure passage;
A valve body formed on the spool;
When pilot pressure is not acting on the spool, the valve body is pressed by the urging force of a spring to hold the load pressure of the load side pressure chamber with the valve body, and
An opening area suppression means for suppressing an increase rate of the opening area with respect to the movement amount of the spool at an initial stage of communication between the bypass passage and the main passage;
When the control valve switches from the shut-off position for holding the load to the position for lowering the load, the bypass passage and the main passage communicate with each other before the control valve opens, and the opening area suppression means The fluid pressure control device according to claim 1, wherein an increase in pressure in the main passage is suppressed. Before SL as the opening area restraining means, the fluid pressure control apparatus according to claim 1, characterized in that it is formed in a tapered shape with the valve locus predetermined angular difference between the valve body. Prior Symbol opening area suppressing means,
A flat portion formed on the tapered outer peripheral surface of the valve body and parallel to the axial direction of the spool;
The fluid pressure control device according to claim 1, wherein the fluid pressure control device is configured by an opposing flat portion formed on the valve seat and parallel to the flat portion. The spool is formed in a groove shape on the outer periphery thereof in parallel with the axial direction of the spool, and provides resistance to the flow of the working fluid from the bypass passage to the main passage, and when the operation check valve is closed. A throttle for suppressing the lowering speed of the cylinder at
The opening area suppressing means is
Fluid of claim 1 wherein the valve body is characterized in that said bypass passage remote from the valve seat and the main passage is configured at the same time as the communication, the clogging of the aperture the the closing portion is released Pressure control device.

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