JP2012229776A - Hydraulic circuit for raising/lowering boom cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic circuit with improved braking characteristics in cylinder load inversion, without valve loss or increase in size of a circuit configuration, so as to directly drive raising or lowering of a boom cylinder of a construction machine.SOLUTION: The hydraulic circuit for raising or lowering a boom cylinder includes a two-way rotary pump, a load cylinder in which two discharge openings of the pump and cylinder chambers are connected, and a safety valve containing a relief valve. It includes a spring centering type hydraulic pilot three-position switching valve which has a first position for connecting a tank with a second branch path from a flow channel between a rod side cylinder chamber and a second discharge opening of the pump by displacement due to oil pressure from a bottom side cylinder chamber, a second position which connects the tank, a first branch path from the flow channel between the bottom side cylinder chamber and the first discharge opening of the pump by displacement due to oil pressure from the rod-side cylinder chamber, and a third position located at the center for disconnecting branch paths and the tank.

Description

  The present invention relates to a hydraulic circuit that controls the lifting and lowering of a boom cylinder of a construction machine such as a heavy machine called an excavator.

  A heavy machine such as an excavator generally used as a construction machine is equipped with a swivel stage on a self-propelled vehicle that turns with a part of the hydraulic pressure converted from the power generated by the engine by a hydraulic generator. An operation cabin and a hydraulic operation boom pivotally supported by hydraulic pressure from a hydraulic pressure generator are installed. A drilling bucket is attached to the tip of the hydraulically operated boom via a hydraulically operated arm connected to the boom so as to bend and extend. The ground excavation work is performed by controlling the driving of.

  In the hydraulic pressure generator, the hydraulic pump is driven to rotate by the engine, and the generated fluid power is sent to the hydraulic cylinders of the respective parts, thereby enabling a high output work. In such a construction machine by hydraulic drive, since the driving power is large unlike other machines, there are many difficult problems for energy saving. Manufacturers can consider electrification first, but many hydraulic systems use a hydraulic pump to drive the hydraulic pump from a battery while maintaining the conventional circuit configuration for operating the working cylinder with a control valve. .

  In a hydraulic circuit of a hydraulic actuator, cylinder drive control is performed by directional control using a hydraulic servo valve that is most responsive and controllable. However, although the hydraulic servo valve has good response, it has a problem of high power consumption. In particular, a large amount of power is required to drive a boom having a load on the arm and bucket in the construction machine as described above. Therefore, in order to raise and lower the boom cylinder for raising and lowering the boom, a hydraulic actuator can be directly controlled without using a hydraulic servo valve by combining a recently developed AC servo motor that responds at high speed with a piston pump. A hydraulic circuit has been proposed (see, for example, Patent Documents 1 and 2).

  For example, as shown in FIG. 4, a simple hydraulic circuit in which a load cylinder 3 is simply connected to both outlet ports of a bidirectional rotary pump 9 that is driven by an AC servomotor 8 and can supply hydraulic pressure in both forward and reverse directions. It is done. That is, in this hydraulic control system, there is no control valve on the serial line between the pump discharge line and the cylinder, and the safety control system 13 and the self-priming valve 20 are substantially configured (see Patent Document 3).

  Usually, the safety valve 13 is composed of two relief valves that release the hydraulic pressure in the bottom cylinder chamber 6 and the rod cylinder chamber 7 of the load cylinder 3 when they exceed a predetermined set pressure. 20 is composed of two operated check valves that are opened by the pilot pressure from the supply hydraulic oil on the rod side and the bottom side, and the oil suction of the pump 9 is performed by the supply from the return line of the cylinder operation. The self-priming valve 20 compensates the excess and deficiency of the oil amount based on the cylinder cross-sectional area difference from the side. The safety valve 13 and the self-priming valve 20 do not need extra power or increase in circuit configuration, and do not affect the energy saving effect by direct drive of the hydraulic actuator.

Japanese Patent No. 3647319 Japanese Patent No. 3877901 JP 2006-329241 A

  However, when the boom cylinder of the construction machine is lifted and lowered by the hydraulic circuit as described above, if the cylinder load is reversed during the movement of the boom cylinder, the opening and closing of the operation check valve is also reversed, and the pressure in the circuit is suddenly increased. Depending on the load condition of the boom bucket, the cylinder pressure becomes an intermediate pressure and both operation check valves open at the same time. This makes it impossible to control the lifting and lowering of the boom cylinder. In addition, when such load reversal causes dynamic vibration, there is a limit to braking measures.

  For example, as a countermeasure, it may be possible to arrange a counter balance valve that incorporates a check valve with a spool that is kept at a set pressure by a spring. In this case, however, a valve loss occurs, resulting in energy saving. However, the advantage of directly controlling the hydraulic actuator by omitting the hydraulic servo valve is lost. In addition, the circuit configuration is increased due to the mounting of the valve, resulting in high costs.

  An object of the present invention is a hydraulic circuit that directly controls the lifting and lowering of a boom cylinder for construction machinery, and has improved hydraulic braking performance when reversing the cylinder load without causing valve loss or an increase in circuit configuration. It is to provide a circuit.

  The present invention has two discharge ports, and reverses the hydraulic oil in the tank from one of the two discharge ports that is selectively specified by the rotation direction by the rotational drive by the servo motor. A bi-directional rotary pump that sucks in through the stop valve and discharges from the other discharge port; a load cylinder in which the two discharge ports of the pump are connected to the bottom side cylinder chamber and the rod side cylinder chamber; In a boom cylinder elevating hydraulic circuit having a safety valve composed of two relief valves for releasing the hydraulic pressure from the rod side and the bottom side of the cylinder when a predetermined set pressure is exceeded, one discharge of the pump From the first branch path from the flow path connecting the outlet and the bottom side cylinder chamber and from the flow path connecting the other discharge port of the pump and the rod side cylinder chamber A hydraulic pilot switching valve for switching the connection state between the second branch path and the tank by a hydraulic displacement is provided. The switching valve is driven by a part of the hydraulic pressure from the bottom cylinder chamber when the boom cylinder is lowered. Displacement disconnects the connection between the first branch path and the tank and connects the second branch path and the tank so that an excess of the flow rate supplied from the pump to the rod side cylinder chamber with respect to the required flow rate is stored in the tank. A first position that forms a first connection circuit that leads to a position where the second branch passage and the tank are displaced by a partial pressure when the pressure in the rod side cylinder chamber rises in a boom ground state after the boom cylinder is lowered. And a second connection circuit that connects the first branch path and the tank to form a second connection circuit that guides the surplus flow rate of the return hydraulic oil from the bottom cylinder chamber to the tank. And a third position that disconnects the tank from both the first branch path and the second branch path at a central position between the first position and the second position. It is what.

  That is, the present invention is a spring centering-type hydraulic pilot three-position switching valve in place of an operation check valve that constitutes a conventional self-priming valve in a hydraulic circuit that directly controls the raising and lowering of a boom cylinder of a construction machine. It is equipped with. Therefore, even if there is no load on the bucket at the tip of the boom, the bottom cylinder chamber is always loaded by its own weight. Therefore, the hydraulic pressure from the bottom cylinder chamber causes the three-position switching valve to be in the first position. When the first connecting circuit is formed and the boom cylinder is raised in this state, the discharge hydraulic oil from the pump is supplied to the bottom side cylinder chamber as it is without returning to the tank, while the rod side cylinder chamber The return hydraulic fluid from the refrigerant flows back to the pump, and the insufficient flow rate due to the cylinder area difference between the bottom side and the rod side is sucked from the tank through the check valve and supplemented.

  Even if the boom cylinder is switched to the lower position, the three-position switching valve remains in the state of the first connection circuit according to the first position without being changed by the hydraulic pressure due to the load of its own weight as in the case of the upward movement, and is discharged from the bottom cylinder chamber. Thus, the discharge hydraulic oil from the pump that is recirculated to the pump and supplied to the rod side cylinder chamber does not require a total flow rate, and the excess amount is the second branch formed at the first position of the three-position switching valve. The tank is returned to the tank via a first connection circuit communicating the path and the tank.

  As described above, in the hydraulic circuit according to the present invention, even if the cylinder load is reversed, the pressure in the circuit that causes dynamic vibration unlike the conventional operation check valve is maintained stably without causing a sudden drop. Excellent braking performance is exhibited. Moreover, this improvement in braking performance has been realized by replacing the operating check valve with a spring centering type hydraulic pilot switching valve, which eliminates the need for extra power and valve loss and increases the circuit configuration. The energy saving merit of the direct drive hydraulic circuit is not impaired.

  Furthermore, in the hydraulic circuit of the present invention, even if the pressure in the rod side cylinder chamber rises in the boom grounding state when the boom cylinder is moved to the excavation process after the boom cylinder is lowered, the three positions are Since the switching valve is displaced to the second position to form a second connection circuit that connects the first branch path and the tank, the return hydraulic oil from the bottom cylinder chamber circulates to the pump and the excess flow rate is reduced to the tank. Return to. Therefore, in the conventional operation check valve, the pressure increase in the rod side cylinder chamber and the accompanying pressure decrease in the bottom side cylinder chamber cannot cope with the opening and closing, so that the excess flow cannot be returned well and the cylinder stops. Problems are avoided.

  In the boom cylinder lifting / lowering hydraulic circuit according to the present invention, a spring centering type hydraulic pilot 3 is used in place of the conventional self-priming valve composed of an operation check valve in an energy saving circuit that directly drives the load cylinder without the hydraulic servo valve. By disposing the position switching valve, the switching valve can maintain the same first connection circuit state in the first position even if the cylinder load is reversed without impairing the energy saving effect. The shortage of the hydraulic oil supply flow rate to the rod side cylinder chamber when the boom cylinder is raised can be supplemented by sucking from the tank, and when the pressure in the rod side cylinder chamber rises when excavating after the boom cylinder is lowered, the second position is reached. The second connection circuit state is formed by the change of the flow rate and the excess flow rate of the return hydraulic oil from the bottom cylinder chamber is increased. Can be returned to, can maintain good lifting operation of the boom cylinder is always satisfactorily compensate for the excess and deficiency of the hydraulic fluid flow.

It is a schematic block diagram of the hydraulic circuit for raising / lowering boom cylinder by one embodiment of this invention. FIG. 2 is a diagram showing a change over time with respect to each element during the lifting and lowering operation of the boom cylinder in the hydraulic circuit of FIG. 1, (a) is a piston position y (horizontal axis: time s, vertical axis: height m), (B) is bottom side cylinder chamber pressure Ph and rod side cylinder chamber pressure Pr (horizontal axis: time s, vertical axis: pressure bar), (c) is supply flow rate q1 to the bottom side cylinder chamber and rod side cylinder chamber. Supply flow rate q2 (horizontal axis: time s, vertical axis: flow rate L / min), (d) communicates with the tank via a three-position switching valve out of the flow rate supplied from the pump to the rod side cylinder chamber when descending The excess flow rate q3a (horizontal axis: time s, vertical axis: flow rate L / min) returning from the second branch path, (e) is the insufficient flow rate q3b drawn into the pump from the tank via the check valve when the boom cylinder is raised. (Horizontal axis: time s, vertical axis: flow rate L / min), (f) Discharge from the flop flow q (horizontal axis: time s, the vertical axis: flow rate L / min) is. FIG. 2 is a diagram showing a change over time with respect to each element when shifting from lowering the boom cylinder to excavation in the hydraulic circuit of FIG. 1, (a) is a piston position y (horizontal axis: time s, vertical axis: (Height m), (b) is bottom cylinder chamber pressure Ph and rod side cylinder chamber pressure Pr (horizontal axis: time s, vertical axis: pressure bar), (c) is the supply flow rate q1 to the bottom cylinder chamber. Supply flow rate q2 (horizontal axis: time s, vertical axis: flow rate L / min) to the rod side cylinder chamber, (d) is an excess flow rate q3a (returned from the second branch passage communicating with the tank via the 3-position switching valve). (Horizontal axis: time s, vertical axis: flow rate L / min), (e) shows surplus hydraulic oil returning from the bottom cylinder chamber through the first branch passage communicating with the tank through the three-position switching valve in the excavation state Partial flow q4a (horizontal axis: time s, vertical axis: flow rate L / min), (f) Insufficient flow q3b (horizontal axis: time s, vertical axis: flow rate L / min) sucked into the pump through the check valve, (g) is the discharge flow rate q from the pump (horizontal axis: time s, vertical axis) : Flow rate L / min). It is an example of the conventional boom cylinder raising / lowering hydraulic circuit.

  As an embodiment of the present invention, FIG. 1 shows a boom cylinder lifting / lowering hydraulic circuit of a construction machine. The substantial raising / lowering operation of the boom cylinder 1 in this hydraulic circuit is performed in accordance with the raising / lowering of the piston 5 and the rod 4 of the load cylinder 3 that supports the boom 2. That is, the load cylinder 3 includes an AC servo motor 8 driven by power from an engine mounted on the construction machine main body side, and a bidirectional rotary pump 9 having two discharge ports driven by the servo motor 8. Is partitioned into a bottom cylinder chamber 6 and a rod cylinder chamber 7 by a piston 5, and one first outlet 9 a of the two discharge ports of the pump 9 is connected to a bottom cylinder chamber by a first oil passage 11. 6, and the other second outlet 9 b is directly connected to the rod side cylinder chamber 7 by the second oil passage 12.

  Between the first oil passage 11 and the second oil passage 12, the hydraulic pressure in the rod side cylinder chamber 7 and the bottom side cylinder chamber 6 is relieved when exceeding a predetermined set pressure, respectively, as in the prior art. A safety valve 13 consisting of two relief valves is arranged.

  In the above basic configuration, when the boom cylinder 1 is lifted, the hydraulic oil is discharged from the first outlet 9a of the pump 9 by driving the rotation of the AC servo motor 8 in the forward direction, and the first oil passage The piston 5 and the rod 4 are raised by supplying the gas from the cylinder 11 into the bottom cylinder chamber 6. Accordingly, the return hydraulic oil discharged from the rod side cylinder chamber 7 is sucked from the second outlet 9b of the pump 9 through the second oil passage 12 and circulates.

  When the boom cylinder 1 is lowered, the rotation of the AC servo motor 8 is driven in the reverse direction to discharge the hydraulic oil from the second outlet 9b of the pump 9, and the rod side cylinder chamber 7 is discharged from the second oil passage 12. Then, the piston 5 and the rod 4 are lowered. Accordingly, the return hydraulic oil discharged from the bottom side cylinder chamber 6 is sucked from the first outlet 9a of the pump 9 through the first oil passage 11 and circulates. The first outlet 9a of the pump 9 can suck hydraulic oil from the tank 10 via the check valve CK1, and the second outlet 9b can suck hydraulic oil from the tank 10 via the check valve CK2.

  In this hydraulic circuit, too much or insufficient hydraulic oil flow occurs based on the difference between the cylinder cross-sectional area Ah on the bottom side and the cylinder cross-sectional area Ar on the rod side. Conventionally, as a self-priming valve for compensating for this, Instead of the operation check valve being arranged, in this hydraulic circuit, a spring centering type hydraulic pilot three-position switching valve 16 is arranged between the first oil passage 11 and the second oil passage 12.

  The switching valve 16 is provided between the port A of the first branch path 14 from the first oil path 11, the port B of the second branch path 15 from the second oil path 12, and the port T of the tank 10. The connection state is switched. Specifically, the first position 17 forms a first connection circuit that disconnects the port A and the tank port T of the first branch path 14 and connects the port B and the tank port T of the second branch path 15. And a second position 18 that forms a second connection circuit that disconnects the connection between the port B of the second branch 15 and the tank port T and connects the port A and the tank port T of the first branch 14. All ports are closed at the central position between the first value 17 and the second position 18 to disconnect the tank port T from both the port A of the first branch 14 and the port B of the second branch 15. It has three positions with the third position 19.

  The switching valve 16 is provided with springs at both ends, and a circuit state in which the connection between the ports A and B and the tank port T at the third position 19 is disconnected is maintained in a neutral state by both springs. When the switching valve 16 is displaced against the spring by the pilot pressure from the first oil passage 11, a first connection circuit is formed by the first position 17, and the spring is caused by the pilot pressure from the second oil passage 12. When the switching valve 16 is displaced against this, a second connection circuit by the second position 18 is formed. Note that the pilot pressure from the first and second oil passages to the switching valve 16 is controlled in pressure and flow rate through a throttle, respectively.

  In the hydraulic circuit having the above configuration, the operation of the switching valve 16 when the boom cylinder 1 is moved up and down will be described below. In FIG. 2, the time-dependent transition of each element in this raising / lowering operation | movement is shown as a diagram of (a)-(f), respectively. (A) piston position y (m), (b) bottom cylinder chamber pressure Ph and rod side cylinder chamber pressure Pr (bar), (c) supply flow rate q1 to bottom cylinder chamber 6 and The supply flow rate q2 (L / min) to the rod side cylinder chamber 7 and (d) show the first supply flow rate to the rod side cylinder chamber 7 at the time of lowering and communicated with the tank port T via the three-position switching valve 16. The excess flow q3a (L / min) returning from the bifurcated passage 15 and (e) show the shortage flow q3b (L / min), (f) sucked into the pump from the tank 10 via the check valve CK2 when the boom cylinder is raised. ) Indicates the discharge flow rate q (L / min) from the pump.

  First, as can be seen from the diagram (b), the pressure Ph in the bottom-side cylinder chamber 6 is always maintained at 40 bar and the pressure Pr in the rod-side cylinder chamber 7 does not increase over a series of lifting operation steps. Further, since there is always a load due to the weight of the boom bucket in the bottom side cylinder chamber 6 even when there is no load on the bucket, the switching valve 16 is first driven by the first position 17 by the pilot pressure from the first oil passage 11. A connection circuit is formed.

  If the boom cylinder 1 is raised in this state, the hydraulic oil flow rate q discharged from the first outlet 9a of the pump 9 becomes the supply flow rate q1 to the bottom side cylinder chamber 6 as it is, and is discharged from the rod side cylinder chamber 7. The flow rate q2 of the hydraulic oil is sucked from the second outlet 9b of the pump 9 and circulates at a flow rate corresponding to the cylinder cross-sectional area difference. Although the supply flow rate to the bottom side cylinder chamber 6 is insufficient with this recirculation suction flow rate, the pump 9 can suck the deficiency flow rate q3b from the tank 10 via the check valve CK2, and can supplement the deficiency.

  Even if the boom cylinder 1 is raised and then lowered, the switching valve 16 remains in the first connection circuit state at the first position 17 due to the same weight load, and is not different from that when the boom cylinder 1 is raised. In this descending step, the rotational direction of the pump 9 is reversed from that when it is raised, and the hydraulic oil flow rate q2 discharged from the second outlet 9b is supplied to the rod side cylinder chamber 7 and simultaneously discharged from the bottom side cylinder chamber 6. The hydraulic oil q1 is sucked from the first outlet 9a and circulated to the pump 9. However, since the total amount of the recirculation is not required for the lowering of the boom cylinder 1, the excess flow rate q 3 a is connected to the tank port T in the first connection circuit at the first position 17 of the switching valve 16. B is returned to the tank.

  As described above, in the present boom cylinder lifting / lowering hydraulic circuit including the hydraulic pilot three-position switching valve 16 as a self-priming valve, the switching valve 16 is displaced even if the load in the cylinder 3 is reversed while moving. Therefore, it is possible to maintain a state in which compensation for excess and deficiency of oil can be satisfactorily performed, and excellent braking performance is realized.

  Next, in the present hydraulic circuit, the operation of the switching valve 16 when the boom cylinder 1 is lowered to the excavation will be described below. In FIG. 3, the time-dependent transition of each element in this raising / lowering operation | movement is shown as a diagram of (a)-(g), respectively. (A) piston position y (m), (b) bottom cylinder chamber pressure Ph and rod side cylinder chamber pressure Pr (bar), (c) supply flow rate q1 to bottom cylinder chamber 6 and The supply flow rate q2 (L / min) to the rod side cylinder chamber 7 and (d) show the first supply flow rate to the rod side cylinder chamber 7 at the time of lowering and communicated with the tank port T via the three-position switching valve 16. The excess flow rate q3a (L / min) returning to the tank 10 from the 2-branch path 15 and (e) is a three-position switching valve of the hydraulic oil flow rate returning from the bottom cylinder chamber 6 to the tank 10 in the excavated state. The surplus flow rate q4a returning to the tank from the first branch passage 14 communicating with the tank port T via 16 is shown in (f) as the shortage flow rate q3b sucked into the pump from the tank 10 via the check valve CK2 when the boom cylinder is raised. Is (L / min) or (g) a pump? The discharge flow rate q (L / min) is shown.

  The switching valve 16 in the hydraulic circuit performs the same operation as in the state shown in FIG. 2 during the normal lifting process, but the boom cylinder 1 is further moved from the lowering state to the excavation state, that is, the diagram (a). When the piston height y at the position further falls below 0.2 m, the pressure Pr in the rod side cylinder chamber 7 rapidly increases. The switching valve 16 that has received the pilot pressure from the second oil passage 12 as the pressure rises is displaced against the spring, forms a second connection path by the second position 18, and the first branch path 14. Port A and tank port T are connected.

  Accordingly, the hydraulic oil flow rate q1 discharged from the bottom side cylinder chamber 6 does not return to the pump 9 as it is, and the surplus flow rate q4a returns from the first branch 14 to the tank 10 via the switching valve 16. .

  At this time, the lowering speed of the boom cylinder 1 increases by the reciprocal of the cylinder cross-sectional area ratio (Ar / Ah). This is because the second connection circuit in the excavation state is a state in which the discharge flow rate q from the pump 9 is supplied to the full rod side cylinder chamber 7. However, in the actual excavation state by the construction machine, there is no particular problem because the work is performed at a relatively low speed.

1: Boom cylinder 2: Boom 3: Load cylinder 4: Rod 5: Piston 6: Bottom side cylinder chamber 7: Rod side cylinder chamber 8: AC servo motor 9: Bidirectional rotary pump 9a: First outlet 9b: Second outlet CK1, CK2: Check valve 10: Tank 11: First oil passage 12: Second oil passage 13: Safety valve (relief valve)
14: 1st branch path 15: 2nd branch path 16: Hydraulic pilot 3 position switching valve 17: 1st position 18: 2nd position 19: 3rd position 20: Self-priming valve (operated check valve)

Claims (1)

It has two discharge ports, and the hydraulic oil in the tank is passed through a check valve from one of the two discharge ports selectively specified by the rotation direction by the rotational drive by the servo motor. A bidirectional rotary pump that suctions and discharges from the other discharge port, a load cylinder in which the two discharge ports of the pump are connected to the bottom side cylinder chamber and the rod side cylinder chamber, and the rod side of the load cylinder And a hydraulic circuit for raising and lowering the boom cylinder, including a safety valve composed of two relief valves for releasing the hydraulic pressure from the bottom side when the hydraulic pressure from the bottom side exceeds a predetermined set pressure,
A first branch path from a flow path connecting one discharge port of the pump and the bottom cylinder chamber and a second branch from a flow path connecting the other discharge port of the pump and the rod side cylinder chamber A hydraulic pilot switching valve for switching the connection state between the road and the tank by a hydraulic displacement.
The switching valve is displaced by a part of the hydraulic pressure from the bottom cylinder chamber when the boom cylinder descends, disconnecting the first branch path and the tank and connecting the second branch path and the tank to the pump. The first position for forming a first connection circuit for guiding the excess of the flow rate supplied from the cylinder to the rod side cylinder chamber to the tank to the tank, and the pressure of the rod side cylinder chamber in the grounded boom state after the boom cylinder is lowered Of the hydraulic fluid returned from the bottom side cylinder chamber, the first branch passage and the tank are connected by disconnecting the second branch passage and the tank by being displaced by the partial pressure when rising. Connection between the tank and both of the first branch path and the second branch path is performed at a second position that forms a second connection circuit that guides the surplus flow rate to the tank, and at a central position between the first position and the second position. And the third position, Boom cylinder elevating hydraulic circuit, which is a 3-position switching valve of the type spring centering with.

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