JP2013044399A - Hydraulic drive system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic drive system for reducing energy loss in a charge pump.SOLUTION: In the hydraulic drive system 1, a hydraulic fluid passage 15 connects a main pump 10 with a hydraulic actuator 14, and constitutes a closed circuit. Check valves 44 and 45 are disposed between the main pump and the hydraulic actuator. A first hydraulic pressure adjustment unit 43 controls a hydraulic pressure in the hydraulic fluid passage not to exceed a predetermined first set pressure. A charge passage 35 is connected between the main pump and the check valves. The charge pump 28 discharges a hydraulic fluid to the charge passage. A second hydraulic pressure adjustment unit 42 is connected with the charge passage and controls a hydraulic pressure in the charge passage not to exceed a second set pressure smaller than the first set pressure. Passage opening and closing units 41a and 41b allow the hydraulic fluid to flow from the charge passage to the hydraulic fluid passage and inhibit the flow of the hydraulic fluid from the hydraulic fluid passage to the charge passage. An accumulator 38 is connected with the charge passage.

Description

  The present invention relates to a hydraulic drive system.

  Work machines such as hydraulic excavators and wheel loaders include hydraulic actuators such as hydraulic cylinders and hydraulic motors. The hydraulic oil discharged from the hydraulic pump is supplied to the hydraulic actuator via the hydraulic circuit. For example, Patent Document 1 proposes a work machine including a hydraulic closed circuit for supplying hydraulic oil to a hydraulic actuator. Since the hydraulic circuit is a closed circuit, the kinetic energy and potential energy of the member driven by the hydraulic actuator are regenerated. As a result, the fuel consumption of the prime mover that drives the hydraulic pump can be reduced.

  In many cases, a charge circuit is added to the hydraulic closed circuit. The charge circuit is provided to replenish hydraulic oil to the hydraulic closed circuit. The charge circuit has a charge pump and a charge flow path. The charge pump is usually a fixed capacity pump and is driven by a drive source such as an engine. The charge pump discharges hydraulic oil into the charge flow path. The charge flow path is connected to a hydraulic closed circuit. When the flow rate of the hydraulic oil supplied to the hydraulic pump is insufficient and the hydraulic pressure in the hydraulic closed circuit is lower than the hydraulic pressure in the charge channel, the hydraulic oil is supplied from the charge channel to the hydraulic closed circuit.

Special table 2009-511831

  The hydraulic closed circuit as described above may be provided with a check valve in order to prevent backflow of hydraulic oil. The check valve is disposed between the hydraulic pump and the hydraulic actuator in the hydraulic closed circuit. For example, when the hydraulic actuator is a boom cylinder of a hydraulic excavator, the check valve is disposed between the hydraulic pump and the boom cylinder in a hydraulic closed circuit. Since the boom cylinder is loaded with a bucket load or a load due to the weight of the work implement, a hydraulic pressure (hereinafter referred to as “the load”) is applied to the flow path between the boom cylinder and the check valve. It is called “holding pressure”). When hydraulic oil is supplied to the boom cylinder in this state, the hydraulic oil discharged from the hydraulic pump is first used to increase the hydraulic pressure in the flow path between the hydraulic pump and the check valve to a holding pressure. When the hydraulic pressure in the flow path between the hydraulic pump and the check valve becomes equal to or higher than the holding pressure, the check valve opens and hydraulic oil is supplied to the boom cylinder. As a result, the boom cylinder starts operating. There is no return oil from the boom cylinder to the hydraulic pump until the boom cylinder starts to operate, so all the hydraulic oil supplied to the hydraulic pump is supplied from the charge circuit. Therefore, the charge pump needs to have a capacity that can supply the flow rate of the hydraulic fluid at the time of such pressure increase. On the other hand, during the operation of the boom cylinder, the hydraulic pressure between the hydraulic pump and the boom cylinder has already reached the pressure required to drive the boom cylinder. For this reason, the charge pump only needs to be able to supply hydraulic oil having a flow rate smaller than the flow rate at the time of pressure increase described above. Therefore, if the capacity of the charge pump is set with reference to the above-described pressure increase, excess hydraulic fluid is generated during operation of the boom cylinder. The excess amount of hydraulic oil is discharged from the charge flow path to the hydraulic oil tank.

  The hydraulic excavator sometimes performs a so-called dumping operation. The dumping operation is an operation of loading excavated earth and sand on the loading platform of the dump truck. In the dump loading operation, the excavator excavates the earth and sand and loads it in the bucket, and then turns while raising the boom to the height of the loading platform of the dump truck stopped beside the excavator. Then, the excavator discharges the earth and sand of the bucket to the loading platform of the dump truck and returns to the original excavation position again. In such a one-cycle operation of the dumping operation, the time required for boosting the boom cylinder is much shorter than the time during which the boom cylinder is operating. For example, while the time during which the boom cylinder is operating is about 10 seconds, the time required for boosting the boom cylinder is about 0.1 seconds. Therefore, a large amount of hydraulic oil is wasted from the charge flow path, and energy for driving the charge pump is wasted.

  An object of the present invention is to provide a hydraulic drive system capable of reducing energy loss in a charge pump.

  The hydraulic drive system according to the first aspect of the present invention includes a main pump, a hydraulic actuator, a hydraulic oil flow path, a check valve, a first hydraulic pressure adjustment unit, a charge flow path, a charge pump, and a second pump. A hydraulic pressure adjusting unit, a channel opening / closing unit, and an accumulator are provided. The main pump discharges hydraulic oil. The hydraulic actuator is driven by hydraulic oil discharged from the main pump. The hydraulic oil flow path connects the main pump and the hydraulic actuator, and forms a closed circuit between the main pump and the hydraulic actuator. The check valve is disposed between the main pump and the hydraulic actuator in the hydraulic oil passage. The check valve allows the flow of hydraulic oil from the main pump to the hydraulic actuator. The check valve prohibits the flow of hydraulic oil from the hydraulic actuator to the main pump. The first hydraulic pressure adjustment unit adjusts the hydraulic pressure of the hydraulic fluid passage so that the hydraulic pressure of the hydraulic fluid passage does not exceed a predetermined first set pressure. The charge flow path is connected between the main pump and the check valve in the hydraulic oil flow path. The charge pump discharges hydraulic oil into the charge flow path. The second hydraulic pressure adjusting unit is connected to the charge flow path and adjusts the hydraulic pressure of the charge flow path so that the hydraulic pressure of the charge flow path does not exceed a second set pressure that is smaller than the first set pressure. The flow path opening / closing portion allows the flow of hydraulic oil from the charge flow path to the hydraulic oil flow path, and prohibits the flow of hydraulic oil from the hydraulic oil flow path to the charge flow path. The accumulator is connected to the charge channel.

  The hydraulic drive system according to the second aspect of the present invention is the hydraulic drive system according to the first aspect, and the main pump has a first pump port and a second pump port. The main pump is in a state where hydraulic oil is supplied to the second pump port and hydraulic oil is discharged from the first pump port, and in a state where the hydraulic oil is supplied to the first pump port and hydraulic oil is discharged from the second pump port And can be switched to. The hydraulic actuator has a first actuator port and a second actuator port. The hydraulic actuator is in a state in which hydraulic oil is supplied to the second actuator port and hydraulic oil is discharged from the first actuator port, and in a state in which hydraulic oil is supplied to the first actuator port and hydraulic oil is discharged from the second actuator port. And can be switched to. The hydraulic oil channel has a first channel and a second channel. The first flow path connects the first pump port and the first actuator port. The second flow path connects the second pump port and the second actuator port. The charge channel is connected to the first channel and the second channel.

  In the hydraulic drive system according to the first aspect of the present invention, the hydraulic oil can be sufficiently replenished to the hydraulic oil flow path by the hydraulic oil discharged from the charge pump during the operation of the hydraulic actuator. Further, when the pressure of the hydraulic fluid passage between the main pump and the check valve is increased to the holding pressure, the hydraulic fluid discharged from the charge pump and the hydraulic fluid stored in the accumulator together with the hydraulic fluid discharged to the hydraulic fluid passage. Hydraulic oil can be replenished. For this reason, a charge pump can be reduced in size compared with the case where hydraulic fluid is replenished to a hydraulic fluid flow path only with a charge pump. Thereby, energy loss in the charge pump can be reduced.

  In the hydraulic drive system according to the second aspect of the present invention, when the hydraulic pressure in the first flow path decreases, the hydraulic oil stored in the accumulator is discharged via the charge flow path together with the hydraulic oil discharged from the charge pump. The first channel is replenished. When the hydraulic pressure in the second flow path decreases, the hydraulic oil stored in the accumulator is replenished to the second flow path through the charge flow path together with the hydraulic oil discharged from the charge pump. For this reason, when the hydraulic actuator is driven in any direction, when the pressure of the hydraulic fluid passage between the main pump and the check valve is increased to the holding pressure, the hydraulic actuator is discharged together with the hydraulic fluid discharged from the charge pump. The hydraulic fluid stored in the accumulator can be replenished to the first flow path or the second flow path.

1 is a block diagram illustrating a configuration of a hydraulic drive system according to a first embodiment of the present invention. It is a block diagram which shows the structure of the hydraulic drive system which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the structure of the hydraulic drive system which concerns on other embodiment of this invention. It is a block diagram which shows the structure of the hydraulic drive system which concerns on other embodiment of this invention.

  Hereinafter, a hydraulic drive system according to an embodiment of the present invention will be described with reference to the drawings.

1. First Embodiment FIG. 1 is a block diagram showing a configuration of a hydraulic drive system 1 according to a first embodiment of the present invention. The hydraulic drive system 1 is mounted on a work machine such as a hydraulic excavator, a wheel loader, or a bulldozer. The hydraulic drive system 1 includes an engine 11, a main pump 10, a hydraulic actuator 14, a hydraulic oil passage 15, a passage switching valve 16, and a pump controller 24.

  The engine 11 drives the first hydraulic pump 12 and the second hydraulic pump 13. The engine 11 is, for example, a diesel engine, and the output of the engine 11 is controlled by adjusting the fuel injection amount from the fuel injection device 21. The fuel injection amount is adjusted by the fuel injection device 21 being controlled by the engine controller 22. The actual rotational speed of the engine 11 is detected by the rotational speed sensor 23, and the detection signal is input to the engine controller 22 and the pump controller 24, respectively.

  The main pump 10 is driven by the engine 11 and discharges hydraulic oil. The main pump 10 includes a first hydraulic pump 12 and a second hydraulic pump 13. The hydraulic oil discharged from the main pump 10 is supplied to the hydraulic actuator 14 via the flow path switching valve 16.

  The first hydraulic pump 12 is a variable displacement hydraulic pump. By controlling the tilt angle of the first hydraulic pump 12, the discharge flow rate of the first hydraulic pump 12 is controlled. The tilt angle of the first hydraulic pump 12 is controlled by the first pump flow rate control unit 25. The first pump flow control unit 25 controls the discharge flow rate of the first hydraulic pump 12 by controlling the tilt angle of the first hydraulic pump 12 based on the command signal from the pump controller 24. The first hydraulic pump 12 is a two-way discharge type hydraulic pump. Specifically, the first hydraulic pump 12 has a first pump port 12a and a second pump port 12b. The first hydraulic pump 12 can be switched between a first discharge state and a second discharge state. In the first discharge state, the first hydraulic pump 12 draws hydraulic oil from the second pump port 12b and discharges the hydraulic oil from the first pump port 12a. In the second discharge state, the first hydraulic pump 12 draws hydraulic oil from the first pump port 12a and discharges the hydraulic oil from the second pump port 12b.

  The second hydraulic pump 13 is a variable displacement hydraulic pump. By controlling the tilt angle of the second hydraulic pump 13, the discharge flow rate of the second hydraulic pump 13 is controlled. The tilt angle of the second hydraulic pump 13 is controlled by the second pump flow rate control unit 26. The second pump flow rate control unit 26 controls the discharge flow rate of the second hydraulic pump 13 by controlling the tilt angle of the second hydraulic pump 13 based on the command signal from the pump controller 24. The second hydraulic pump 13 is a two-way discharge type hydraulic pump. Specifically, the second hydraulic pump 13 has a first pump port 13a and a second pump port 13b. Similar to the first hydraulic pump 12, the second hydraulic pump 13 can be switched between a first discharge state and a second discharge state. In the first discharge state, the second hydraulic pump 13 draws hydraulic oil from the second pump port 13b and discharges the hydraulic oil from the first pump port 13a. In the second discharge state, the second hydraulic pump 13 sucks the hydraulic oil from the first pump port 13a and discharges the hydraulic oil from the second pump port 13b.

  The hydraulic actuator 14 is a hydraulic cylinder that is driven by hydraulic oil discharged from the first hydraulic pump 12 and the second hydraulic pump 13. The hydraulic actuator 14 drives a work machine such as a boom, an arm, or a bucket, for example. The hydraulic actuator 14 has a cylinder rod 14a and a cylinder tube 14b. The inside of the cylinder tube 14b is partitioned into a first chamber 14c and a second chamber 14d by a cylinder rod 14a. The hydraulic actuator 14 has a first actuator port 14e and a second actuator port 14f. The first actuator port 14e communicates with the first chamber 14c. The second actuator port 14f communicates with the second chamber 14d. The hydraulic actuator 14 is in a state where hydraulic oil is supplied to the second actuator port 14f and hydraulic oil is discharged from the first actuator port 14e, and hydraulic oil is supplied to the first actuator port 14e and hydraulic oil is supplied from the second actuator port 14f. Can be switched to a state in which is discharged. That is, the hydraulic actuator 14 expands and contracts by switching between supply and discharge of hydraulic oil to and from the first chamber 14c and the second chamber 14d. Specifically, the hydraulic oil is supplied to the first chamber 14c via the first actuator port 14e and discharged from the second chamber 14d via the second actuator port 14f. Stretch. Hydraulic oil is supplied to the second chamber 14d via the second actuator port 14f and discharged from the first chamber 14c via the first actuator port 14e, whereby the hydraulic actuator 14 contracts. The pressure receiving area in the first chamber 14c of the cylinder rod 14a is larger than the pressure receiving area in the second chamber 14d of the cylinder rod 14a. Therefore, when the hydraulic actuator 14 is extended, a larger amount of hydraulic oil than the hydraulic oil discharged from the second chamber 14d is supplied to the first chamber 14c. When the hydraulic actuator 14 is contracted, a larger amount of hydraulic oil than the hydraulic oil supplied to the second chamber 14d is discharged from the first chamber 14c.

  The hydraulic fluid passage 15 is connected to the first hydraulic pump 12, the second hydraulic pump 13, and the hydraulic actuator 14. The hydraulic oil flow path 15 has a first flow path 17 and a second flow path 18. The first flow path 17 connects the first pump port 12a of the first hydraulic pump 12 and the first actuator port 14e. The first flow path 17 connects the first pump port 13a of the second hydraulic pump 13 and the first actuator port 14e. The second flow path 18 connects the second pump port 12b of the first hydraulic pump 12 and the second actuator port 14f. The first flow path 17 includes a first actuator flow path 31 and a first pump flow path 33. The second flow path 18 includes a second actuator flow path 32 and a second pump flow path 34. The first actuator flow path 31 is connected to the first chamber 14c of the hydraulic actuator 14 via the first actuator port 14e. The second actuator flow path 32 is connected to the second chamber 14d of the hydraulic actuator 14 via the second actuator port 14f. The first pump flow path 33 supplies hydraulic oil to the first chamber 14 c of the hydraulic actuator 14 via the first actuator flow path 31, or the first chamber of the hydraulic actuator 14 via the first actuator flow path 31. 14c is a flow path for recovering hydraulic oil from 14c. The first pump flow path 33 is connected to the first pump port 12 a of the first hydraulic pump 12. The first pump flow path 33 is connected to the first pump port 13 a of the second hydraulic pump 13. Accordingly, the hydraulic oil from both the first hydraulic pump 12 and the second hydraulic pump 13 is supplied to the first pump flow path 33. The second pump flow path 34 supplies hydraulic oil to the second chamber 14 d of the hydraulic actuator 14 via the second actuator flow path 32, or the second chamber of the hydraulic actuator 14 via the second actuator flow path 32. 14d is a flow path for recovering hydraulic oil from 14d. The second pump flow path 34 is connected to the second pump port 12 b of the first hydraulic pump 12. The second pump port 13 b of the second hydraulic pump 13 is connected to the hydraulic oil tank 27. Accordingly, the hydraulic oil from the first hydraulic pump 12 is supplied to the second pump flow path 34. The hydraulic fluid passage 15 is closed between the main pump 10 and the hydraulic actuator 14 by the first pump passage 33, the first actuator passage 31, the second actuator passage 32, and the second pump passage 34. Is configured.

  The hydraulic oil passage 15 further has a relief passage 36. The relief flow path 36 is connected to the first pump flow path 33 via a check valve 41c. The check valve 41c is opened when the hydraulic pressure of the first pump flow path 33 becomes higher than the hydraulic pressure of the relief flow path 36. The relief flow path 36 is connected to the second pump flow path 34 via a check valve 41d. The check valve 41d is opened when the hydraulic pressure of the second pump flow path 34 becomes higher than the hydraulic pressure of the relief flow path 36. The relief flow path 36 is connected to the charge flow path 35 via a relief valve 43. The relief valve 43 maintains the pressure of the relief flow path 36 below a predetermined first set pressure. Therefore, the relief valve 43 adjusts the hydraulic pressure of the hydraulic fluid passage so that the hydraulic pressure of the first pump passage 33 and the second pump passage 34 does not exceed a predetermined first set pressure. The relief valve 43 corresponds to the first hydraulic pressure adjustment unit of the present invention.

  The hydraulic drive system 1 further includes a charge pump 28 and a charge flow path 35. The charge pump 28 is a hydraulic pump for replenishing hydraulic fluid to the first flow path 17 or the second flow path 18. The charge pump 28 is driven by the engine 11 to discharge hydraulic oil to the charge flow path 35. The charge pump 28 is a fixed displacement hydraulic pump. The charge channel 35 is connected to the first channel 17 and the second channel 18. The charge passage 35 is connected between the main pump 10 and the first check valve 44 in the hydraulic oil passage 15. Specifically, the charge flow path 35 is connected to the first pump flow path 33 via the check valve 41a. The check valve 41 a allows the flow of hydraulic oil from the charge flow path 35 to the first pump flow path 33 and prohibits the flow of hydraulic oil from the first pump flow path 33 to the charge flow path 35. The check valve 41a is opened when the hydraulic pressure of the first pump flow path 33 becomes lower than the hydraulic pressure of the charge flow path 35. In addition, the charge flow path 35 is connected between the main pump 10 and the second check valve 45 in the hydraulic oil flow path 15. Specifically, the charge flow path 35 is connected to the second pump flow path 34 via the check valve 41b. The check valve 41b allows the flow of hydraulic oil from the charge flow path 35 to the second pump flow path 34, and prohibits the flow of hydraulic oil from the second pump flow path 34 to the charge flow path 35. The check valve 41b is opened when the hydraulic pressure of the second pump flow path 34 becomes lower than the hydraulic pressure of the charge flow path 35. The check valve 41a and the check valve 41b correspond to the flow path opening / closing portion of the present invention.

  The charge flow path 35 is connected to the hydraulic oil tank 27 via a charge relief valve 42. The charge relief valve 42 adjusts the hydraulic pressure of the charge flow path 35 so that the hydraulic pressure of the charge flow path 35 does not exceed a predetermined second set pressure. The second set pressure is smaller than the first set pressure described above. When the hydraulic pressure of the first pump flow path 33 or the second pump flow path 34 becomes lower than the hydraulic pressure of the charge flow path 35, the hydraulic oil from the charge pump 28 passes through the charge flow path 35 and the first pump flow path 33 or the first pump flow path 34. 2 is supplied to the pump flow path 34. Thereby, the hydraulic pressure of the first pump flow path 33 and the second pump flow path 34 is maintained at a predetermined value or more. The charge relief valve 42 corresponds to the second hydraulic pressure adjustment unit of the present invention. An accumulator 38 is connected to the charge channel 35. The hydraulic oil passage 15 further has an adjustment passage 37. The adjustment channel 37 is connected to the charge channel 35.

  The flow path switching valve 16 is an electromagnetic control valve that is controlled based on a command signal from a pump controller 24 described later. The flow path switching valve 16 switches the connection of the flow paths based on a command signal from the pump controller 24. The flow path switching valve 16 is disposed between the main pump 10 and the hydraulic actuator 14 in the hydraulic oil flow path 15. The flow path switching valve 16 includes a first pump port 16a, a first cylinder port 16b, a first adjustment port 16c, and a first bypass port 16d. The first pump port 16 a is connected to the first pump flow path 33 via the first check valve 44. The first cylinder port 16 b is connected to the first actuator flow path 31. The first adjustment port 16 c is connected to the adjustment flow path 37.

  The first check valve 44 is disposed between the main pump 10 and the hydraulic actuator 14 in the hydraulic oil passage 15. The first check valve 44 allows the flow of hydraulic oil from the main pump 10 to the hydraulic actuator 14. The first check valve 44 prohibits the flow of hydraulic oil from the hydraulic actuator 14 to the main pump 10. Specifically, the first check valve 44 is connected to the first pump passage 33 from the first pump passage 33 when hydraulic fluid is supplied from the first pump passage 33 to the first actuator passage 31 by the passage switching valve 16. The flow of hydraulic oil to the actuator flow path 31 is allowed, and the flow of hydraulic oil from the first actuator flow path 31 to the first pump flow path 33 is prohibited.

  The flow path switching valve 16 further includes a second pump port 16e, a second cylinder port 16f, a second adjustment port 16g, and a second bypass port 16h. The second pump port 16 e is connected to the second pump flow path 34 via the second check valve 45. The second check valve 45 is a check valve that regulates the flow of hydraulic oil in one direction. The second cylinder port 16 f is connected to the second actuator flow path 32. The second adjustment port 16g is connected to the adjustment flow path 37.

  The second check valve 45 is disposed between the main pump 10 and the hydraulic actuator 14 in the hydraulic oil passage 15. The second check valve 45 allows the flow of hydraulic oil from the main pump 10 to the hydraulic actuator 14. The second check valve 45 prohibits the flow of hydraulic oil from the hydraulic actuator 14 to the main pump 10. Specifically, the second check valve 45 is connected to the second pump passage 34 from the second pump passage 34 when hydraulic fluid is supplied from the second pump passage 34 to the second actuator passage 32 by the passage switching valve 16. The flow of hydraulic oil to the actuator flow path 32 is allowed, and the flow of hydraulic oil from the second actuator flow path 32 to the second pump flow path 34 is prohibited.

  The flow path switching valve 16 can be switched between the first position state P1, the second position state P2, and the neutral position state Pn. In the first position state P1, the flow path switching valve 16 communicates the first pump port 16a and the first cylinder port 16b and communicates the second cylinder port 16f and the second bypass port 16h. . Accordingly, the flow path switching valve 16 connects the first pump flow path 33 to the first actuator flow path 31 via the first check valve 44 and the second actuator flow path 32 in the first position state P1. Is connected to the second pump flow path 34 without passing through the second check valve 45. When the flow path switching valve 16 is in the first position state P1, any of the first bypass port 16d, the first adjustment port 16c, the second pump port 16e, and the second adjustment port 16g It is also blocked.

  When the hydraulic actuator 14 is extended, the first hydraulic pump 12 and the second hydraulic pump 13 are driven in the first discharge state, and the flow path switching valve 16 is set to the first position state P1. As a result, the hydraulic oil discharged from the first pump port 12a of the first hydraulic pump 12 and the first pump port 13a of the second hydraulic pump 13 flows into the first pump flow path 33, the first check valve 44, the first The first actuator flow path 31 is supplied to the first chamber 14 c of the hydraulic actuator 14. Further, the hydraulic oil in the second chamber 14 d of the hydraulic actuator 14 passes through the second actuator flow path 32 and the second pump flow path 34 and is collected in the second pump port 12 b of the first hydraulic pump 12. As a result, the hydraulic actuator 14 extends.

  In the second position state P2, the flow path switching valve 16 communicates the second pump port 16e and the second cylinder port 16f, and communicates the first cylinder port 16b and the first bypass port 16d. . Therefore, in the second position state P2, the flow path switching valve 16 connects the first actuator flow path 31 to the first pump flow path 33 without passing through the first check valve 44, and the second pump flow path 34 is connected to the second actuator flow path 32 via the second check valve 45. When the flow path switching valve 16 is in the second position state P2, any of the first pump port 16a, the first adjustment port 16c, the second bypass port 16h, and the second adjustment port 16g It is also blocked.

  When the hydraulic actuator 14 is contracted, the first hydraulic pump 12 and the second hydraulic pump 13 are driven in the second discharge state, and the flow path switching valve 16 is set to the second position state P2. As a result, the hydraulic oil discharged from the second pump port 12 b of the first hydraulic pump 12 passes through the second pump flow path 34, the second check valve 45, and the second actuator flow path 32, and the hydraulic actuator 14 It is supplied to the two chambers 14d. Further, the hydraulic oil in the first chamber 14 c of the hydraulic actuator 14 passes through the first actuator flow path 31 and the first pump flow path 33 and passes through the first pump port 12 a of the first hydraulic pump 12 and the second hydraulic pump 13. It is recovered in the first pump port 13a. As a result, the hydraulic actuator 14 contracts.

  In the neutral position state Pn, the flow path switching valve 16 communicates the first bypass port 16d and the first adjustment port 16c, and communicates the second bypass port 16h and the second adjustment port 16g. Therefore, in the neutral position state Pn, the flow path switching valve 16 connects the first pump flow path 33 to the adjustment flow path 37 without passing through the first check valve 44, and the second pump flow path 34 The second check valve 45 is not connected to the adjustment flow path 37. When the flow path switching valve 16 is in the neutral position state Pn, the first pump port 16a, the first cylinder port 16b, the second pump port 16e, and the second cylinder port 16f are in any port. It is also blocked.

  The hydraulic drive system 1 further includes an operation device 46. The operation device 46 includes an operation member 46a and an operation detection unit 46b. The operation member 46a is operated by an operator to command various operations of the work machine. For example, when the hydraulic actuator 14 is a boom cylinder that drives a boom, the operation member 46a is a boom operation lever for operating the boom. The operation member 46a can be operated in two directions: a direction in which the hydraulic actuator 14 is extended from the neutral position, and a direction in which the hydraulic actuator 14 is contracted. The operation detection unit 46b detects an operation amount and an operation direction of the operation member 46a. The operation detection unit 46b is a sensor that detects the position of the operation member 46a, for example. When the operation member 46a is located at the neutral position, the operation amount of the operation member 46a is zero. A detection signal indicating the operation amount and operation direction of the operation member 46a is input from the operation detection unit 46b to the pump controller 24. The pump controller 24 calculates a target flow rate of the hydraulic oil supplied to the hydraulic actuator 14 in accordance with the operation amount of the operation member 46a.

  The engine controller 22 controls the output of the engine 11 by controlling the fuel injection device 21. The engine controller 22 maps and stores engine output torque characteristics set based on the set target engine speed and work mode. The engine output torque characteristic indicates the relationship between the output torque of the engine 11 and the rotation speed. The engine controller 22 controls the output of the engine 11 based on the engine output torque characteristics.

  The pump controller 24 controls the flow rate of hydraulic oil supplied to the hydraulic actuator 14 in accordance with the target flow rate set by the operation member 46a. When the hydraulic actuator 14 is extended, the pump controller 24 The flow rate of hydraulic fluid supplied to the hydraulic actuator 14 is controlled by the pump flow rate control unit 25 and the second pump flow rate control unit 26. When contracting the hydraulic actuator 14, the pump controller 24 controls the flow rate of hydraulic oil supplied to the hydraulic actuator 14 by the first pump flow rate control unit 25.

  The pump controller 24 controls the flow path switching valve 16 according to the operation direction of the operation member 46a. When the operation member 46a is operated in the direction of extending the hydraulic actuator 14 from the neutral position, the pump controller 24 sets the flow path switching valve 16 to the first position state P1. Thereby, the first pump flow path 33 and the first actuator flow path 31 are connected via the first check valve 44. Further, the second pump flow path 34 and the second actuator flow path 32 are connected without passing through the second check valve 45. Then, hydraulic oil is discharged from the first pump port 12 a of the first hydraulic pump 12 and the first pump port 13 a of the second hydraulic pump 13 to the first pump flow path 33. However, the first check valve 44 is not opened and the hydraulic actuator 14 does not operate until the hydraulic pressure in the first pump flow path 33 exceeds the holding pressure in the first actuator flow path 31. On the other hand, the hydraulic oil in the second pump flow path 34 is sucked into the second pump port 12 b of the first hydraulic pump 12. For this reason, the hydraulic pressure of the second pump flow path 34 decreases. When the hydraulic pressure of the second pump flow path 34 becomes equal to or lower than the hydraulic pressure of the charge flow path 35, the check valve 41b is opened, and the charge flow path 35 and the second pump flow path 34 communicate with each other. As a result, hydraulic oil is replenished from the charge flow path 35 to the second pump flow path 34. At this time, together with the hydraulic oil from the charge pump 28, the hydraulic oil from the accumulator 38 that has been pre-stressed by the charge pump 28 is replenished to the second pump flow path 34 via the charge flow path 35. When the hydraulic pressure of the first pump flow path 33 exceeds the holding pressure of the first actuator flow path 31, the first check valve 44 is opened and the first pump flow path 33 and the first actuator flow path 31 communicate with each other. To do. As a result, hydraulic oil is supplied to the first chamber 14c of the hydraulic actuator 14, and the hydraulic actuator 14 extends. Further, during the extension operation of the hydraulic actuator 14, the hydraulic oil is discharged from the second chamber 14 d of the hydraulic actuator 14, passes through the second actuator flow path 32 and the second pump flow path 34, and the first hydraulic pump 12. Return to the second pump port 12b. At this time, the hydraulic oil having a flow rate necessary for compressing the hydraulic oil in the first hydraulic pump 12 and the hydraulic oil having a flow rate sufficient to replenish the leakage amount of the hydraulic oil in the first hydraulic pump 12 are charged. The second pump channel 34 is replenished from the channel 35.

  When the operation member 46a is operated in a direction to contract the hydraulic actuator 14 from the neutral position, the pump controller 24 sets the flow path switching valve 16 to the second position state P2. Thereby, the second pump flow path 34 and the second actuator flow path 32 are connected via the second check valve 45. Further, the first pump flow path 33 and the first actuator flow path 31 are connected without passing through the first check valve 44. Then, the hydraulic oil is discharged from the second pump port 12 b of the first hydraulic pump 12 to the second pump flow path 34. However, the second check valve 45 is not opened and the hydraulic actuator 14 does not operate until the hydraulic pressure of the second pump flow path 34 exceeds the holding pressure of the second actuator flow path 32. On the other hand, the hydraulic oil in the first pump flow path 33 is sucked into the first pump port 12 a of the first hydraulic pump 12 and the first pump port 13 a of the second hydraulic pump 13. For this reason, the hydraulic pressure of the first pump flow path 33 decreases. When the hydraulic pressure of the first pump flow path 33 becomes equal to or lower than the hydraulic pressure of the charge flow path 35, the check valve 41a is opened, and the charge flow path 35 and the first pump flow path 33 communicate with each other. As a result, hydraulic oil is replenished from the charge flow path 35 to the first pump flow path 33. At this time, together with the hydraulic oil from the charge pump 28, the hydraulic oil from the accumulator 38 that has been preloaded by the charge pump 28 is replenished to the first pump flow path 33 via the charge flow path 35. When the hydraulic pressure of the second pump flow path 34 exceeds the holding pressure of the second actuator flow path 32, the second check valve 45 opens, and the second pump flow path 34 and the second actuator flow path 32 communicate with each other. To do. As a result, hydraulic oil is supplied to the second chamber 14d of the hydraulic actuator 14, and the hydraulic actuator 14 contracts. Further, during the contraction operation of the hydraulic actuator 14, the hydraulic oil is discharged from the first chamber 14 c of the hydraulic actuator 14, passes through the first actuator flow path 31 and the first pump flow path 33, and the first hydraulic pump 12. Return to the first pump port 12a and the first pump port 13a of the second hydraulic pump 13. At this time, the hydraulic oil having a flow rate necessary for compressing the hydraulic oil in the first hydraulic pump 12 and the hydraulic oil having a flow rate sufficient to replenish the leakage amount of the hydraulic oil in the first hydraulic pump 12 are charged. Replenishment from the flow path 35 to the first pump flow path 33 is performed.

  The hydraulic drive system 1 according to the present embodiment has the following features.

  During the operation of the hydraulic actuator 14, the hydraulic oil discharged from the charge pump 28 can sufficiently supplement the first pump flow path 33 or the second pump flow path 34 with the hydraulic oil. In addition, when the pressure of the hydraulic oil passage 15 between the main pump 10 and the check valves 44 and 45 is increased to the holding pressure, the hydraulic oil stored in the accumulator 38 is discharged together with the hydraulic oil discharged from the charge pump 28. The first pump channel 33 or the second pump channel 34 is replenished via the charge channel 35. For this reason, the charge pump 28 can be reduced in size compared with the case where the hydraulic oil is replenished only by the charge pump 28. Thereby, the energy loss in the charge pump 28 can be reduced.

2. Second Embodiment The switching of the flow direction of hydraulic oil to the hydraulic actuator 14 is not limited to the flow path switching valve 16 of the first embodiment, and may be performed by other configurations. FIG. 2 is a block diagram showing the configuration of the hydraulic drive system 2 according to the second embodiment of the present invention. In the hydraulic drive system 2, a first pilot check valve 51 and a second pilot check valve 52 are used in place of the flow path switching valve 16 of the first embodiment. The first pilot check valve 51 is switched between a restricted state and an open state by a command signal from the pump controller 24. In the restricted state, the first pilot check valve 51 allows the flow of hydraulic oil from the first pump flow path 33 to the first actuator flow path 31 and allows the first pilot check valve 51 to flow from the first actuator flow path 31 to the first pump flow path 33. Prohibit hydraulic fluid flow. The first pilot check valve 51 permits the flow of hydraulic oil from the first actuator flow path 31 to the first pump flow path 33 in the open state. The second pilot check valve 52 is switched between a restricted state and an open state by a command signal from the pump controller 24. The second pilot check valve 52 permits the flow of hydraulic oil from the second pump flow path 34 to the second actuator flow path 32 in the restricted state, and allows the second actuator check flow path 32 to flow to the second pump flow path 34. Prohibit hydraulic fluid flow. The second pilot check valve 52 allows the flow of hydraulic oil from the second actuator flow path 32 to the second pump flow path 34 in the open state.

  When the operation member 46a is operated in the direction in which the hydraulic actuator 14 is extended from the neutral position, the pump controller 24 sets the first pilot check valve 51 to the restricted state and sets the second pilot check valve 52 to the open state. To do. Therefore, when the hydraulic pressure of the first pump flow path 33 exceeds the holding pressure of the first actuator flow path 31, the first pilot check valve 51 is opened and the operation discharged from the first hydraulic pump 12 and the second hydraulic pump 13 is performed. Oil is supplied to the first chamber 14 c of the hydraulic actuator 14 through the first pump flow path 33 and the first actuator flow path 31. Further, the hydraulic oil is discharged from the second chamber 14 d of the hydraulic actuator 14, returns to the first hydraulic pump 12 through the second actuator flow path 32 and the second pump flow path 34.

  When the operation member 46a is operated in a direction to contract the hydraulic actuator 14 from the neutral position, the pump controller 24 sets the first pilot check valve 51 to the open state and sets the second pilot check valve 52 to the restricted state. To do. Therefore, when the hydraulic pressure of the second pump flow path 34 exceeds the holding pressure of the second actuator flow path 32, the hydraulic oil discharged from the first hydraulic pump 12 becomes the second pump flow path 34 and the second actuator flow path. 32 is supplied to the second chamber 14 d of the hydraulic actuator 14. Further, the hydraulic oil is discharged from the first chamber 14 c of the hydraulic actuator 14, returns to the first hydraulic pump 12 and the second hydraulic pump 13 through the first actuator flow path 31 and the first pump flow path 33. .

  Other configurations of the hydraulic drive system 2 are the same as those of the hydraulic drive system 1 of the first embodiment. Also, the hydraulic drive system 2 of the second embodiment has the same features as the hydraulic drive system 1 of the first embodiment.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of invention.

  In said 1st Embodiment and 2nd Embodiment, the pump flow control parts 25 and 26 control the discharge flow volume of the hydraulic pumps 12 and 13 by controlling the tilt angle of the hydraulic pumps 12 and 13. FIG. . However, the discharge flow rates of the hydraulic pumps 12 and 13 may be controlled by controlling the rotational speeds of the hydraulic pumps 12 and 13. For example, as shown in FIG. 3, an electric motor 57 may be used as a drive source. In FIG. 3, in the hydraulic drive system 1 of the first embodiment, an electric motor 57 is used instead of the engine 11. The hydraulic pumps 12 and 13 are fixed displacement hydraulic pumps. In this case, the pump controller 24 controls the rotational speed of the electric motor 57 so that the discharge flow rate of the hydraulic pumps 12 and 13 becomes a target flow rate corresponding to the operation amount of the operation member 46a. To control the rotation speed. Alternatively, as shown in FIG. 4, in the hydraulic drive system 2 of the second embodiment, an electric motor 57 may be used as a drive source instead of the engine 11.

  In the above embodiment, the present invention is applied to a two-pump hydraulic drive system in which two hydraulic pumps 12 and 13 are connected to the hydraulic actuator 14, but one hydraulic pump is connected to the hydraulic actuator. The present invention may be applied to a one-pump hydraulic drive system. In the above embodiment, the hydraulic actuator 14 is a hydraulic cylinder, but other types of hydraulic actuators may be used. For example, a hydraulic motor may be used as a hydraulic actuator. The hydraulic motor is, for example, a traveling hydraulic motor constituting an HST (Hydro Static Transmission). Alternatively, the hydraulic motor may be a hydraulic motor that rotates the upper swing body.

  In the above embodiment, the relief valve 43 is used as the first hydraulic pressure adjusting unit of the present invention, but other configurations may be used. In the above embodiment, the charge relief valve 42 is used as the second hydraulic pressure adjusting unit of the present invention, but other configurations may be used. In the above embodiment, the check valves 41a and 41b are used as the flow path opening / closing portion of the present invention, but other configurations may be used.

  ADVANTAGE OF THE INVENTION According to this invention, the hydraulic drive system which can reduce the energy loss in a charge pump can be provided.

DESCRIPTION OF SYMBOLS 1, 2 Hydraulic drive system 10 Main pump 14 Hydraulic actuator 15 Hydraulic fluid flow path 17 First flow path 18 Second flow path 28 Charge pump 35 Charge flow path 38 Accumulator 41a, 41b Check valve (flow path opening / closing part)
42 Charge relief valve (second hydraulic pressure regulator)
43 Relief valve (first hydraulic pressure adjustment part)
44 First check valve 45 Second check valve

Claims (2)

A main pump that discharges hydraulic oil;
A hydraulic actuator driven by hydraulic oil discharged from the main pump;
A hydraulic fluid passage connecting the main pump and the hydraulic actuator, and forming a closed circuit between the main pump and the hydraulic actuator;
The hydraulic oil passage is disposed between the main pump and the hydraulic actuator in the hydraulic oil passage, allows the hydraulic oil to flow from the main pump to the hydraulic actuator, and flows from the hydraulic actuator to the main pump. A check valve that prohibits,
A first hydraulic pressure adjustment unit that adjusts the hydraulic pressure of the hydraulic fluid passage so that the hydraulic pressure of the hydraulic fluid passage does not exceed a predetermined first set pressure;
A charge flow path connected between the main pump and the check valve in the hydraulic oil flow path;
A charge pump for discharging hydraulic oil into the charge flow path;
A second hydraulic pressure adjustment unit that is connected to the charge flow path and adjusts the hydraulic pressure of the charge flow path so that the hydraulic pressure of the charge flow path does not exceed a second set pressure that is smaller than the first set pressure;
A flow path opening / closing section that allows the flow of hydraulic oil from the charge flow path to the hydraulic oil flow path and prohibits the flow of hydraulic oil from the hydraulic oil flow path to the charge flow path;
An accumulator connected to the charge flow path;
Hydraulic drive system with The main pump has a first pump port and a second pump port, a state in which hydraulic oil is supplied to the second pump port and hydraulic oil is discharged from the first pump port, and the first pump port Is switched to a state in which hydraulic oil is supplied to and discharged from the second pump port,
The hydraulic actuator has a first actuator port and a second actuator port, a state in which hydraulic oil is supplied to the second actuator port and discharged from the first actuator port, and the first actuator port Is switched to a state in which hydraulic oil is supplied to and discharged from the second actuator port,
The hydraulic oil flow path includes a first flow path that connects the first pump port and the first actuator port, and a second flow path that connects the second pump port and the second actuator port. Have
The charge channel is connected to the first channel and the second channel.
The hydraulic drive system according to claim 1.

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