JP2015105686A - Hydraulic work machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic work machine in which energy of return oil during deceleration of a hydraulic actuator is regenerated, and the occurrence of cavitation on a suction side is prevented with simple structure.SOLUTION: A hydraulic work machine includes: a supply line from a control valve 51 to a hydraulic actuator 44; a return line from the hydraulic actuator 44 to the control valve 51; a back-pressure holding line 58 separate from the return line; a back-pressure holding valve 60 generating back pressure in the back-pressure holding line 58; brake valves 62A, 62B; lines 64A, 64B for anti-cavitation; a regenerative motor 68; a primary regenerative line 70 and a secondary regenerative line 72 on the upstream side and the downstream side of the regenerative motor, respectively; and regeneration switching devices 74A, 74B, 76, 78. The secondary regenerative line 72 introduces the hydraulic oil discharged from the regenerative motor 68 to the back-pressure holding line 58.

Description

  The present invention relates to a hydraulic working machine such as a hydraulic excavator having an energy regeneration function.

  2. Description of the Related Art Conventionally, a hydraulic working machine such as a hydraulic excavator has a function of regenerating energy of a hydraulic actuator included in the working machine. Specifically, Patent Document 1 discloses a work machine including an engine, a hydraulic actuator, and a regenerative motor connected to the engine, and the regenerative motor is rotated by oil discharged from the hydraulic actuator. An apparatus that assists the engine by causing the engine to be operated is disclosed. This working machine will be described with reference to FIGS. FIG. 2 shows an outline of a hydraulic excavator which is a working machine described in Patent Document 1, and FIG. 3 shows a hydraulic circuit mounted thereon. The hydraulic circuit provided in the said hydraulic working machine is shown.

  The hydraulic excavator shown in FIG. 2 includes a lower traveling body 1, an upper revolving body 2 mounted on the lower traveling body 1 so as to be able to swivel about an axis X perpendicular to the ground, and a excavation attachment 3. Are a boom 4, an arm 5, a bucket 6, a boom cylinder 7 for raising and lowering the boom 4, an arm cylinder 8 for rotating the arm 5 with respect to the boom 4, and a bucket cylinder 9 for rotating the bucket 6 with respect to the arm 5. Is provided.

  The hydraulic circuit shown in FIG. 3 includes a hydraulic pump 10 driven by an engine 11, a turning motor 12 for turning the upper turning body 2, a control valve 13 for controlling the turning motor 12, a right turn and Left-turn pipes 14 and 15, right and left brake relief valves 16 and 17, right and left anti-cavitation check valves 18 and 19, and a regenerative circuit 20 are provided.

  The control valve 13 is provided between the hydraulic pump 10 and the tank T and the turning motor 12, and is composed of a hydraulic switching valve that is switched by a pilot pressure from a remote control valve (not shown). The control valve 13 operates to switch the flow path for supplying and discharging the hydraulic oil to and from the swing motor 12, thereby enabling control of rotation / stop switching, rotation direction, and rotation speed of the swing motor 12. . Specifically, the control valve 13 maintains the neutral position 13a shown when the remote control valve is not operated, and when the remote control valve is operated, the control valve 13 moves from the neutral position 13a to the right turn position 13b with a stroke corresponding to the operation amount. Alternatively, the valve is opened to the left turn position 13c. The right and left turning pipelines 14 and 15 are piped to connect the control valve 13 and the right turning and left turning ports 12a and 12b of the turning motor 12, respectively.

  At the neutral position 13a, the control valve 13 blocks the right and left turning conduits 14 and 15 from the hydraulic pump 10 to prevent the turning motor 12 from rotating, while the right turning position 13b or the left turning position. At the position 13c, the hydraulic pump 10 is connected to the right turning pipeline 14 or the left turning pipeline 15, and thereby the turning motor 12 is rotated clockwise or counterclockwise to rotate the upper swing body 2 clockwise or counterclockwise. .

  The relief valves 16 and 17 are respectively interposed between the right and left turning pipelines 14 and 15 and the tank line 30 connected to the tank T, and the pressure of the corresponding pipeline 14 or 15 is set to the set pressure. When it becomes above, the valve is opened and the pipe line 14 or 15 is communicated with the tank T. The check valves 18 and 19 are arranged in parallel with the relief valves 16 and 17, respectively, and are interposed between the right turn pipeline 14 and the left turn pipeline 15 and the tank line 30. Each check valve 18, 19 allows the flow of hydraulic oil from the tank line 30 to the right and left turning pipelines 14, 15, while allowing the right turning pipeline 14 and the left turning pipeline 15 to connect to the tank line. Block the flow of hydraulic oil to 30.

  The regenerative circuit 20 includes a regenerative motor 21, a regenerative switching valve 22, a right turn regeneration line 23 that branches from the left turn pipeline 15, and a left turn that branches from the right turn pipeline 14. A regeneration line 24 and a regeneration tank line 25 communicating with the tank T are provided.

  The regenerative motor 21 is a variable displacement hydraulic motor, and is connected to the output shaft of the engine 11 together with the hydraulic pump 10. The regenerative motor 21 is provided in the regenerative tank line 25 and is rotated by the hydraulic oil (return oil) flowing toward the tank T through the regenerative tank line 25, whereby the hydraulic motor 10 by the engine 11 is rotated. Assist driving.

  The regeneration switching valve 22 is interposed between the regeneration lines 23 and 24 and the regeneration tank line 25. The regenerative switching valve 22 is configured by, for example, a three-position electromagnetic switching valve that can be switched and controlled by a controller (not shown), and has a neutral position 22a, a right turning regenerative position 22b, and a left turning regenerative position 22c. The regeneration switching valve 22 blocks both regeneration lines 23 and 24 from the regeneration tank line 25 at the neutral position 22a, and the right turn regeneration line 23 at the regeneration tank at the regeneration position 22b for turning right. The left turn regeneration line 24 is connected to the regeneration tank line 25 at the left turn regeneration position 22c.

  In this circuit, for example, when the control valve 13 returns from the right turning position 13b to the neutral position 13a, the turning motor 12 and both turning pipelines 14 and 15 are blocked from the pump 10 and the tank T. And the return of oil from the turning motor 12 to the tank T are prevented. On the other hand, since the swing motor 12 tries to continue to rotate in the direction corresponding to the right turn due to the inertia of the upper swing body 2, the pressure is applied to the left turn pipeline 15 corresponding to the discharge side pipeline, that is, the meter-out pipeline. stand. Then, when the pressure reaches the set pressure of the left relief valve 17, the left relief valve 17 is opened, and hydraulic oil in the left turning pipeline 15 is allowed to flow into the tank line 30. Accordingly, a braking force corresponding to the set pressure of the left relief valve 17 acts on the turning motor 12.

  On the other hand, when the right turning pipeline 14 of the turning motor 12 tends to have a negative pressure, the hydraulic oil in the tank T is sucked up from the tank line 30 to the right turning pipeline 14 via the right check valve 18. Cavitation is prevented. That is, the anti-cavitation hydraulic oil as indicated by the black arrow in FIG. 3 is automatically supplied to the right turning pipeline 14.

  Further, at the time of this right turn deceleration, the regenerative switching valve 22 is switched to the right turn side regenerative position 22b, whereby hydraulic oil discharged from the left turn port 12b of the turn motor 12 is supplied to the right turn side regenerative line. 23 and regenerative motor 21 through regenerative tank line 25. By introducing the hydraulic oil, the regenerative motor 21 rotates to assist the drive of the hydraulic motor 10 by the engine 11. In this way, the regenerative motor 21 converts the energy of the hydraulic oil discharged from the turning motor 12 into rotational energy, that is, regenerates.

JP 2003-120616 A

  In the circuit shown in FIG. 3, since the hydraulic oil in the tank is sucked up as the anti-cavitation hydraulic oil by the negative pressure of the pipe line on the inlet side of the swing motor 12, the pressure on the inlet side may not be sufficiently increased. That is, there is a possibility that cavitation is not sufficiently prevented.

  As means for solving this inconvenience, the above-mentioned patent document 1 introduces and stores a part of the return oil discharged from the swing motor into the accumulator, and operates for anti-cavitation from the accumulator to the suction side of the swing motor at the time of turning deceleration. Although a technique for supplying oil is disclosed, this technique requires an accumulator for anti-cavitation and a plurality of switching valves associated therewith, and it is inevitable that the structure is complicated and the cost is increased. Further, since a part of the return oil is used for rotational driving of the regenerative motor, there is a possibility that the anti-cavitation hydraulic oil to be replenished from the accumulator to the suction side of the swing motor is insufficient.

  The present invention provides a hydraulic working machine provided with a hydraulic actuator such as a hydraulic motor as means for solving the above-mentioned problems, and while regenerating the energy of the return oil during deceleration of the hydraulic actuator, An object of the present invention is to provide a device that can more reliably prevent the occurrence of cavitation on the suction side with a simple structure.

  The hydraulic working machine provided by the present invention includes an engine, a hydraulic pump that discharges hydraulic oil when driven by the engine, an inlet port that receives supply of hydraulic oil discharged from the hydraulic pump, and discharges the hydraulic oil A hydraulic actuator that has an outlet port to be driven and is driven by the supply of the hydraulic oil, and a drive stop that is interposed between the hydraulic pump and the hydraulic actuator and blocks the hydraulic actuator from the hydraulic pump and the tank Switching between a position and a driving position that forms a flow path that allows the hydraulic oil to be supplied from the hydraulic pump to the inlet port of the hydraulic actuator and discharged from the outlet port of the hydraulic actuator to the tank. Possible control valves and inlet ports of the control valve and the hydraulic actuator A return line connecting the control valve and the outlet port of the hydraulic actuator, and hydraulic oil discharged from the hydraulic actuator via a path different from the return line to the tank as return oil A back pressure holding line for returning, a back pressure holding valve that is interposed between the back pressure holding line and the tank, and generates a constant back pressure in the back pressure holding line, the hydraulic actuator, and the back pressure A brake valve interposed between the holding line and communicating the outlet side to the back pressure holding line while generating a brake pressure on the outlet side of the hydraulic actuator when the control valve is in the drive stop position; The hydraulic oil flowing through the back pressure holding line when the control valve is in the drive stop position is used for anti-cavitation. An anti-cavitation line that allows the oil to be supplied to the inlet side of the hydraulic actuator as a moving oil, and a regenerative motor that is connected to the output shaft of the engine and rotates by receiving the supply of the return oil to assist the engine And a regenerative primary line that branches from the return line and is discharged from the hydraulic actuator to the inlet of the regenerative motor, and hydraulic oil that is discharged from the outlet of the regenerative motor to the back pressure holding line. A regenerative secondary line to be introduced, and a regenerative switching device that can be switched between a regenerative permissible state that communicates with the regenerative primary line and a regenerative blocking state that shuts off, and that switches to the regenerative permissible state when the hydraulic actuator is decelerated. Prepare.

  According to this hydraulic working machine, the combination of the back pressure holding valve and the regenerative secondary line makes it possible to reliably prevent cavitation on the suction side of the hydraulic actuator while performing efficient regeneration.

  First, as a basic deceleration operation of this hydraulic work machine, when the control valve is switched from its drive position to the drive stop position, the brake valve generates brake pressure on the outlet side of the hydraulic actuator while The hydraulic actuator is decelerated by releasing a part of the discharged hydraulic oil to the back pressure holding line, and the hydraulic oil in the back pressure holding line is supplied to the inlet side, that is, the suction side of the hydraulic actuator through the anti-cavitation line. As a result, the pressure on the suction side is maintained at least at the back pressure or a pressure close thereto, thereby preventing cavitation on the suction side.

  Further, during this deceleration, the regenerative switching device switches to the regenerative allowable state, so that the hydraulic oil that is part of the return oil discharged from the outlet of the hydraulic actuator and has a relatively high pressure upstream of the brake valve. Is introduced into the regenerative motor through the regenerative primary line, and the energy of the return oil is regenerated with high efficiency by turning the regenerative motor. In addition, the hydraulic oil discharged from the regenerative motor, i.e., the return oil that contributed to the rotation of the regenerative motor is reduced to the back pressure holding line, i.e., the upstream line of the back pressure holding valve, through the regenerative secondary line. The hydraulic oil that has contributed to the rotation of the regenerative motor as well as the hydraulic oil that has passed through the brake valve can be supplied to the inlet side of the hydraulic actuator as anti-cavitation hydraulic oil. That is, almost all of the return oil discharged from the hydraulic actuator can be replenished as anti-cavitation hydraulic fluid to the inlet side of the hydraulic actuator, thereby eliminating the shortage of anti-cavitation hydraulic fluid. Therefore, prevention of cavitation becomes more reliable.

  Further, the back pressure holding valve is a check valve with a spring, for example, and opens when the pressure of the back pressure holding line is equal to or higher than the set pressure, and the hydraulic oil from the back pressure holding line to the tank is opened. A simple valve such as a valve that allows the flow of hydraulic oil from the tank to the back pressure holding line while permitting the flow can be used.

  As described above, according to the present invention, a hydraulic working machine including a hydraulic actuator such as a hydraulic motor has a simple structure for generating cavitation on the suction side of the hydraulic actuator when the hydraulic actuator is decelerated. What can be more reliably prevented is provided.

1 is a hydraulic circuit diagram showing a main part of a hydraulic excavator according to an embodiment of the present invention. 1 is a schematic side view of a hydraulic excavator to which the present invention is applied. It is a circuit block diagram which shows a prior art.

  An embodiment of the present invention will be described with reference to FIGS.

  In this embodiment, the present invention is applied to the hydraulic excavator shown in FIG. 3 and includes the components shown in FIG. That is, the hydraulic excavator includes, as main components, an engine 40, a first hydraulic pump 41, a second hydraulic pump 42, a plurality of hydraulic actuators including a swing motor 44, and control valves 46 to 48, 50 to. 52, a remote control valve 54, a first motor line 56A, a second motor line 56B, a back pressure holding line 58, a back pressure holding valve 60, and first and second relief valves 62A that function as brake valves. 62B, first and second anti-cavitation lines 64A and 64B, a regeneration circuit CR, and a regeneration switching device.

  The first hydraulic pump 41 and the second hydraulic pump 42 are both connected to the output shaft of the engine 40 and are driven by the engine 40 to discharge hydraulic oil. Center bypass lines 43A and 43B are connected to the discharge ports of the first hydraulic pump 41 and the second hydraulic pump 42, respectively. These center bypass lines 43A and 43B all reach the tank T.

  Each of the control valves 46 to 48 and 50 to 52 operates so as to perform switching between supply of hydraulic oil to the corresponding hydraulic actuator and discharge of hydraulic oil from the hydraulic actuator. Among these, the control valves 46 to 48 are disposed along the center bypass line 43A, and the control valves 50 to 52 are disposed along the center bypass line 43B. Each of the control valves 46 to 48 has a neutral position for opening the center bypass line 43A and a drive position for supplying hydraulic oil flowing through the center bypass line 43A to the corresponding actuator. Similarly, each of the control valves 50 to 52 has a neutral position for opening the center bypass line 43B and a drive position for supplying hydraulic oil flowing through the center bypass line 43B to the corresponding actuator.

  The turning motor 44 is one of the plurality of hydraulic actuators, and is a hydraulic motor for turning the upper turning body 2 shown in FIG. Specifically, the turning motor 44 has a first port 44a and a second port 44b, and when one of the ports 44a and 44b is supplied with hydraulic oil, it rotates in a direction corresponding to the port. Then, the upper swing body 2 is swung in the same direction and the hydraulic oil is discharged from the other port.

  The control valve 51 among the control valves 46 to 48 and 50 to 52 corresponds to the turning motor 44. The control valve 51 is interposed between the swing motor 44 and the hydraulic pump 42. The first motor line 56A connects the control valve 51 to the first port 44a of the swing motor 44, and the second motor line 56B connects the control valve 51 to the second port 44b of the swing motor 44.

  The control valve 51 is composed of a three-position pilot type hydraulic switching valve having a pair of pilot ports, and has a neutral position 51a which is a drive stop position, a first drive position 51b, and a second drive position 51c. . At the neutral position 51a, the control valve 51 blocks both the ports 44a and 44b of the swing motor 44 from the hydraulic pump 42 and the tank T, thereby preventing the swing motor 44 from being driven. At the first drive position 51b, the control valve 51 forms an oil passage that allows hydraulic oil to be supplied from the hydraulic pump 42 to the first port 44a of the swing motor 44 through the first motor line 56A. In addition, an oil passage that allows the hydraulic oil to be discharged from the second port 44b of the swing motor 44 to the tank T through the second motor line 56B is formed, and thereby the swing motor 44 is moved in a first direction (for example, The upper swing body 2 is swung in the direction by rotating in the left direction. Similarly, the control valve 51 allows the hydraulic oil to be supplied from the hydraulic pump 42 to the second port 44b of the swing motor 44 through the second motor line 56B at the second drive position 51c. And an oil passage that allows the hydraulic oil to be discharged from the first port 44a of the swing motor 44 to the tank T through the first motor line 56A. The upper turning body 2 is turned in the direction (for example, the right direction) to rotate.

  The remote control valve 54 is operated to switch the position of the control valve 51 to drive or stop the turning motor 44. The remote control valve 54 has an operation lever and a remote control valve main body. The remote control valve main body does not output pilot pressure when the operation lever is not operated from the neutral position, whereby the control valve 51 maintains the neutral position 51a. On the other hand, when the operation lever is operated to either the left or right side from the neutral position, the remote control valve main body operates with respect to the pilot port corresponding to the operation direction of the operation lever of both pilot ports of the control valve 51. A pilot pressure of a magnitude corresponding to the operation amount of is supplied. As a result, the control valve 51 operates to the drive position corresponding to the pilot port to which the pilot pressure is supplied among the first and second drive positions 51b and 51c, by the stroke corresponding to the pilot pressure.

  The back pressure holding line 58 is a conduit for returning hydraulic oil discharged from the turning motor 44 to the tank T as return oil through a path different from the return line 56B or 56A. The back pressure holding valve 60 is interposed between the back pressure holding line 58 and the tank T, and generates a certain back pressure in the back pressure holding line 58. Specifically, the back pressure holding valve 60 according to this embodiment is configured by a simple check valve with a spring, and the flow of hydraulic oil from the tank T to the back pressure holding line 58 is blocked, and the back pressure holding line 58 is blocked. With respect to the flow of hydraulic oil from the tank T to the tank T, the valve is opened only when the pressure in the back pressure holding line 58 becomes equal to or higher than a certain spring pressure. Allow hydraulic oil to flow to T. Therefore, the back pressure holding valve 60 can generate a back pressure corresponding to the spring pressure in the back pressure holding line 58.

  The first relief valve 62A and the second relief valve 62B are interposed between the second motor line 56B and the first motor line 56A and the back pressure holding line 58, respectively, and a control valve 51 as will be described later. It functions as a brake valve when the turning motor 44 is decelerated by returning to the neutral position 51a. Specifically, the first relief valve 62A is opened only when the primary pressure, that is, the pressure in the second motor line 56B is equal to or higher than the set pressure given to the first relief valve 62A, and the second relief valve 62A is opened. The inflow of hydraulic oil from the motor line 56B to the back pressure holding line 58 is allowed. Similarly, the second relief valve 62B opens only when the primary pressure, that is, the pressure in the first motor line 56A is equal to or higher than the set pressure given to the second relief valve 62B, and the first motor The inflow of hydraulic oil from the line 56A to the back pressure holding line 58 is allowed.

  In the first and second anti-cavitation lines 64A and 64B, the hydraulic oil flowing through the back pressure holding line 58 when the control valve 51 is in the neutral position 51a is used as the anti-cavitation hydraulic oil. 2 is a conduit for allowing the motor lines 56A and 56B to be supplied respectively. Specifically, the first anti-cavitation line 64A is interposed between the first motor line 56A and the back pressure holding line 58 and is directed from the back pressure holding line 58 toward the first motor line 56A. The first check valve 66A that allows the flow of hydraulic oil only is included. Similarly, the second anti-cavitation line 64B is interposed between the second motor line 56B and the back pressure holding line 58, and in a direction from the back pressure holding line 58 toward the second motor line 56B. A second check valve 66B that only allows the flow of hydraulic oil is included.

  The regenerative circuit CR is a circuit for recovering the energy of the return oil discharged from the swing motor 44 as regenerative energy and reducing it to assist driving the hydraulic pumps 41 and 42 by the engine 40. The regenerative circuit CR according to this embodiment includes a regenerative motor 68, a regenerative primary line 70, and a regenerative secondary line 72.

  The regenerative motor 68 is connected to the output shaft of the engine 40 and rotates by receiving the supply of the return oil to assist the engine 40. Specifically, the regenerative motor 68 has an inlet that receives supply of return oil discharged from the turning motor 44 and an outlet that discharges the return oil, and receives the supply of return oil, thereby the engine. The motor 40 rotates in a direction that assists in driving the hydraulic pumps 41 and 42.

  The regenerative primary line 70 is a conduit for introducing return oil discharged from the swing motor 44 to the inlet of the regenerative motor 68, and includes a first branch line 70a, a second branch line 70b, and a shuttle valve. 71 and an introduction line 70c. The first and second branch lines 70a and 70b branch from the first motor line 54A and the second motor line 54B, respectively, and are connected to a pair of inlets of the shuttle valve 71, respectively. The shuttle valve 71 selects a high-pressure hydraulic oil introduced from each inlet and discharges it from the outlet. The introduction line 70 c connects the outlet of the shuttle valve 71 and the inlet of the regenerative motor 68, and introduces hydraulic oil discharged from the outlet of the shuttle valve 71 to the inlet of the regenerative motor 68.

  The regeneration secondary line 72 is a pipe line provided on the outlet side of the regeneration motor 68. As its feature, the regenerative secondary line 72 connects the outlet and the back pressure holding line 58 so that the hydraulic oil discharged from the outlet of the regenerative motor 68 is introduced into the back pressure holding line 58. .

  The regeneration switching device is a device for turning on and off regeneration by the regeneration circuit CR, and can be switched between a regeneration permission state in which the regeneration primary line 70 is communicated and a regeneration prevention state in which the regeneration primary line 70 is shut off. When the vehicle decelerates, it switches to the regeneration permission state. The regenerative switching device according to this embodiment includes a detection unit that detects whether or not the turning motor 44 is in a decelerating state, a switching unit that switches between opening and closing the regenerative primary line 70, and the switching unit. A control unit for controlling.

  More specifically, the regenerative switching device according to this embodiment includes pressure sensors 74A and 74B that constitute the detection unit, a regenerative switching valve 76 that constitutes the switching unit, and a controller 78 that constitutes the control unit. .

  The pressure sensors 74A and 74B detect pressures in the first and second motor lines 56A and 56B, respectively. Specifically, a detection signal corresponding to the pressure is generated and input to the controller 78. The controller 78 determines whether or not the swing motor 44 is in a decelerating state based on the pressure detected by the pressure sensors 74A and 74B and the rotation direction of the swing motor 44, and determines that it is in a decelerating state. The switching of the regenerative switching valve 76 is controlled so that the regenerative primary line 70 is opened only when the regenerative primary line 70 is opened.

  The regeneration switching valve 76 is provided in the middle of the introduction line 70 c in the regeneration primary line 70, and has an open position 76 a that opens the introduction line 70 c and a close position 76 b that blocks the regeneration primary line 70. The regenerative switching valve 76 can be constituted by a two-position electromagnetic switching valve having a solenoid 77 as shown in FIG. 1, for example, and only when an electric signal is input to the solenoid 77. The closing position 76b is switched to the opening position 76a.

  The regeneration switching device according to the present invention is not limited to that shown in FIG. For example, the switching unit of the regeneration switching device may determine the deceleration of the turning based on the operation of the operation lever of the remote control valve 54. Further, in place of the regenerative switching valve 76 and the shuttle valve 71, a three-position switching valve having a combined function, that is, a blocking position for blocking the first and second branch lines 70a, 70b from the regenerative motor 68, There may be provided a switching valve having first and second opening positions that selectively communicate the first and second branch lines 70a and 70b with the regenerative motor 68, respectively.

  Next, the operation of this circuit will be described.

  When the operation lever of the remote control valve 54 is operated in a state where the engine 40 is operating and the hydraulic pumps 41 and 42 are operating, and the control valve 51 is switched to, for example, the first drive position 51b, the hydraulic pump 42 is operated. The hydraulic oil discharged from the engine is supplied to the first port 44a of the swing motor 44 via the control valve 51 and the first motor line 56A, thereby rotating the swing motor 44 in the first direction. The turning motor 44 discharges hydraulic oil from the second port 44b, and this hydraulic oil is returned to the tank T via the second motor line 56B and the control valve 51 as return oil. At this time, the controller 78 of the regenerative switching device keeps the regenerative switching valve 76 at the closed position 76 b and prevents the hydraulic oil from flowing into the regenerative motor 68.

  When the operation lever is returned to the neutral position from this state, and thereby the control valve 51 returns to the neutral position 51a, the control valve 51 connects the first motor line 56A and the second motor line 56B together with the hydraulic pump 42 and the tank T. Thus, the supply of hydraulic oil from the hydraulic pump 42 to the swing motor 44 is blocked.

  At this time, the swing motor 44 continues to rotate due to the moment of inertia of the upper swing body 2, and hydraulic oil is output from the second port 44b to the second motor line 56B. Since the second motor line 56B is cut off from the tank, the pressure in the second motor line 56B increases as the hydraulic oil is discharged. When this pressure reaches the set pressure of the first relief valve 62A, the first relief valve 62A is opened to allow the hydraulic oil to flow out from the second motor line 56B to the back pressure holding line 58. . Therefore, the first relief valve 62A maintains the pressure in the second motor line 56B at a pressure corresponding to the set pressure of the first relief valve 62A, and applies this pressure to the brake motor 44 as a brake pressure.

  On the other hand, in the first motor line 56A, which is a conduit on the suction side of the swing motor 44, the suction of the hydraulic oil by the rotation of the swing motor 44 is continued even though the hydraulic oil is not supplied to the first motor line 56A. Therefore, the pressure of the first motor line 56A decreases. However, when this pressure falls below the pressure in the back pressure holding line 58 held by the back pressure holding valve 60, that is, the back pressure, the back pressure holding line 58 passes through the first anti-cavitation line 64 (in other words, Then, anti-cavitation hydraulic fluid is supplied to the first motor line 56A by the back pressure (from the first relief valve 62A through the back pressure holding line 58 and the first anti-cavitation line 64A). The pressure in the motor line 56A is maintained at least at the back pressure or a pressure close thereto, so that cavitation in the first motor line 56 is prevented.

  Further, in the regenerative switching device, the controller 78 determines that the turning is being decelerated based on the pressures detected by the pressure sensors 74A and 74B, and inputs a command signal to the solenoid 77 of the regenerative switching valve 76 to input the regenerative switching valve. 76 is switched to the open position 76a. Thereby, the regeneration oil energy is regenerated by the regeneration circuit CR. Specifically, the return oil flowing through the second motor line 56B flows into the inlet of the regenerative motor 68 via the second branch line 70b, the shuttle valve 71, and the introduction line 70c, and rotates the regenerative motor 68. Thereby, the energy of the return oil is converted into the rotational energy of the regenerative motor 68 and used for assisting the driving of the hydraulic pumps 41 and 42 by the engine 40.

  Further, as a characteristic of this circuit, the return oil after contributing to the rotation of the regenerative motor 68, that is, the return oil discharged from the outlet of the regenerative motor 68, passes through the regenerative secondary line 72 and the back pressure holding line 58. That is, it is introduced into the upstream line of the back pressure holding valve 60. As a result, the return oil used for the rotation of the regenerative motor 68 can also be used as the anti-cavitation hydraulic oil. That is, in this circuit, the hydraulic oil discharged from the turning motor 44 is divided into the first relief valve 62A (or the second relief valve 62B) and the regenerative motor 68, but any hydraulic oil flows into the back pressure holding line 58. Therefore, when the back pressure holding valve 60 is closed, almost all of the hydraulic oil discharged from the turning motor 44 is used as anti-cavitation hydraulic oil via the back pressure holding line 58. Become. Therefore, the occurrence of cavitation due to the lack of anti-cavitation hydraulic oil can be prevented more reliably.

  In addition, this effect is a simple configuration of a combination of a back pressure holding valve 60 that holds the back pressure of the back pressure holding line 58 and a regenerative secondary line 72 that returns the return oil from the regenerative motor 68 to the upstream side thereof. Can be obtained at Therefore, both good regeneration and prevention of cavitation can be achieved without requiring an accumulator and a complicated switching valve associated therewith as in the prior art. Further, the back pressure holding valve 60 can be constituted by a simple valve such as a check valve with a spring as shown in FIG.

  In the present invention, the hydraulic actuator to be regenerated is not limited to a swing motor. For example, the present invention can be effectively applied to the case where the energy of the return oil discharged from the boom cylinder 7 is regenerated when the boom 4 of the hydraulic shovel boom 4 shown in FIG. 2 is decelerated.

  The work machine to which the present invention is applied is not limited to a hydraulic excavator. The present invention can be applied to various hydraulic work machines including a hydraulic actuator to be decelerated.

CR regenerative circuit T tank 40 engine 42 hydraulic pump 44 swing motor 44a inlet port 44b outlet port 51 control valve 51a neutral position (swing stop position)
51b, 51c Drive position 56A First motor line 56B Second motor line 58 Back pressure holding line 60 Back pressure holding valve 62A First relief valve 62B Second relief valve 64A First anti-cavitation line 64B Second anti-cavitation motor line 68 Regenerative motor 70 Regenerative primary line 72 Regenerative secondary line 74A, 74B Pressure sensor 76 Regenerative switching valve 78 Controller

Claims (2)

A hydraulic working machine,
Engine,
A hydraulic pump that discharges hydraulic oil by being driven by the engine;
A hydraulic actuator having an inlet port for receiving a supply of hydraulic oil discharged from the hydraulic pump and an outlet port for discharging the hydraulic oil; and driven by receiving the supply of the hydraulic oil;
A drive stop position that is interposed between the hydraulic pump and the hydraulic actuator and blocks the hydraulic actuator from the hydraulic pump and tank, supply of hydraulic oil from the hydraulic pump to the inlet port of the hydraulic actuator, and the hydraulic actuator A control valve that can be switched to a drive position that forms a flow path that allows discharge of hydraulic oil from the outlet port of the tank to the tank;
A supply line connecting the control valve and the inlet port of the hydraulic actuator;
A return line connecting the control valve and the outlet port of the hydraulic actuator;
A back pressure holding line for returning hydraulic oil discharged from the hydraulic actuator to the tank as return oil in a path different from the return line;
A back pressure holding valve that is interposed between the back pressure holding line and the tank and generates a constant back pressure in the back pressure holding line;
It is interposed between the hydraulic actuator and the back pressure holding line, and when the control valve is in the driving stop position, the outlet side is connected to the back pressure holding line while generating brake pressure on the outlet side of the hydraulic actuator. A brake valve communicating with the
An anti-cavitation line that allows hydraulic oil flowing through the back pressure holding line to be supplied to the inlet side of the hydraulic actuator as anti-cavitation hydraulic oil when the control valve is in the drive stop position;
A regenerative motor connected to the output shaft of the engine and rotating by receiving the supply of the return oil to assist the engine;
A regenerative primary line for branching from the return line and introducing return oil discharged from the hydraulic actuator to the inlet of the regenerative motor;
A regenerative secondary line for introducing hydraulic oil discharged from the outlet of the regenerative motor into the back pressure holding line;
A hydraulic work machine comprising: a regenerative switching device that can be switched between a regenerative permission state that communicates the regenerative primary line and a regenerative inhibition state that blocks the regenerative primary line, and that switches to the regenerative permission state when the hydraulic actuator is decelerated. 2. The hydraulic working machine according to claim 1, wherein the back pressure holding valve is a check valve with a spring to which a set pressure is applied, and opens when the pressure in the back pressure holding line is equal to or higher than the set pressure. A hydraulic working machine that is a valve that permits the flow of hydraulic oil from the back pressure holding line to the tank while blocking the flow of hydraulic oil from the tank to the back pressure holding line.

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