JP2019094975A - Hydraulic driving device - Google Patents

Abstract

To provide a hydraulic driving device capable of recovering potential energy of a lifting/lowering object while maintaining intended lowering speed of the lifting/lowering object.SOLUTION: A hydraulic driving device 1 includes: a main pump 8 for supplying working fluid to a lift cylinder 2; a variable displacement type sub pump 9; a working fluid regeneration flow passage 42 and a working fluid common flow passage 41 that connect a suction port 26 of the sub pump 9 with the lift cylinder 2; an operation valve 44 disposed in the working fluid common flow passage 41; an accumulator 52 for accumulating pressure of the working fluid discharged from a discharge port 27 of the sub pump 9; a swash plate angle control unit 38 for controlling the capacity of the sub pump 9; and a lowering control section 68 for determining target lowering speed of a fork 4 on the basis of operation amount of a lift operation lever 5, calculating necessary capacity of the sub pump 9 on the basis of the target lowering speed of the fork 4 and speed of an engine 11 and controlling the swash plate angle control unit 38 in accordance with the necessary capacity of the sub pump 9.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hydraulic drive system.

  As a conventional hydraulic drive device, the technique described, for example in patent documents 1 is known. The hydraulic drive device described in Patent Document 1 is disposed between a hydraulic cylinder, a tank, a charge pump for supplying hydraulic fluid to the hydraulic cylinder, a charge pump and a tank and the hydraulic cylinder, and from the charge pump to the hydraulic cylinder. A cylinder control valve assembly having a control valve for controlling the flow rate of supplied hydraulic fluid and a control valve for controlling the flow rate of hydraulic fluid returned to the tank from the hydraulic cylinder, and recovering potential energy when the hydraulic cylinder is under overload condition Energy recovery equipment. The energy recovery device has an accumulator for storing pressurized hydraulic fluid from a hydraulic cylinder, and an accumulator discharge valve for controlling the flow of pressurized hydraulic fluid from the accumulator to the charge pump.

Japanese Patent Application Publication No. 2009-510358

  In the above-mentioned prior art, by storing the pressurized hydraulic oil from the hydraulic cylinder in the accumulator, the potential energy associated with the operation of the tool (lift and lift) is recovered, but there are the following problems. That is, when the elevating object descends with no load on the elevating object, the pressure on the cylinder head side of the hydraulic cylinder is low, and the hydraulic oil does not flow from the hydraulic cylinder to the accumulator, so the desired descending speed can not be obtained. In addition, even when the elevating object descends in a state where there is a load on the elevating object, the pressure on the accumulator side is higher than the pressure on the cylinder head side of the hydraulic cylinder depending on the pressure accumulation state of the accumulator. Because it does not flow, the desired descent speed can not be obtained.

  An object of the present invention is to provide a hydraulic drive capable of recovering potential energy of an elevator while maintaining a desired lowering speed of the elevator.

  The hydraulic drive system according to one aspect of the present invention is driven by an hydraulic cylinder that raises and lowers an elevating object by supplying and discharging hydraulic oil, a tank that stores the hydraulic oil, and an engine that sucks the hydraulic oil from the tank and supplies it to the hydraulic cylinder. A first hydraulic fluid flow path which connects the main pump, the variable displacement sub pump driven by the engine, the suction port of the sub pump and the hydraulic cylinder, and the hydraulic oil from the hydraulic cylinder flows toward the sub pump; 1) An operating valve disposed in the operating oil flow path and controlling the flow of operating oil according to the operation amount of the operating unit for lowering an elevating object, and an accumulator for accumulating the operating oil discharged from the discharge port of the sub pump , A displacement control unit that controls the displacement of the sub pump, a rotation speed detection unit that detects the rotation speed of the engine, and a target descent speed of the elevating object based on the operation amount of the operation unit Descent control unit that determines the required displacement of the sub pump based on the target descent speed of the elevating object and the engine speed detected by the revolution detector, and controls the displacement control unit according to the required displacement of the sub pump And.

  In such a hydraulic drive system, when the lowering and lowering operation of the lifting and lowering object is performed by the operation unit, the hydraulic cylinder operates so that the lifting and lowering object is lowered, and the hydraulic oil from the hydraulic cylinder is the sub-pump Flow toward Then, the hydraulic oil is sucked from the suction port of the sub pump and discharged from the discharge port of the sub pump. The hydraulic oil discharged from the discharge port of the sub pump is accumulated in the accumulator. Thereby, the potential energy of the elevating object is recovered. At this time, the target descent speed of the elevating object is determined based on the operation amount of the operation unit, the required displacement of the sub pump is calculated based on the target descent speed of the elevating object and the rotational speed of the engine, and the required displacement of the sub pump is calculated. Control unit is controlled. Thus, the desired descent speed of the lift is obtained. Thus, the potential energy of the elevating object can be recovered while maintaining the desired lowering speed of the elevating object.

  The hydraulic drive device connects between the suction port of the sub pump and the operation valve in the first hydraulic fluid flow path and the tank, and the second hydraulic fluid flow path in which hydraulic fluid from the hydraulic cylinder flows toward the tank; 2 Between the connection point of the flow control valve disposed in the hydraulic fluid flow path and controlling the flow rate of hydraulic fluid returning to the tank, and the second hydraulic fluid flow path in the first hydraulic fluid flow path and the suction port of the sub pump The flow control valve has a first pilot operating portion acting on the side closing the flow control valve and a second pilot operating portion acting on the side opening the flow control valve. A pilot type flow control valve that adjusts an opening degree according to a pressure difference generated when hydraulic oil from a hydraulic cylinder passes through the operating valve, and between the hydraulic cylinder and the operating valve in the first hydraulic oil flow path The first pilot control unit is the first pilot line It is connected via a between the inlet orifice and the sub-pump in the first operating fluid channel and the second pilot operating unit, may be connected via a second pilot line.

  When the load loaded on the elevator is heavy, hydraulic oil from the hydraulic cylinder tends to flow toward the sub pump because the pressure of the hydraulic cylinder is high. At this time, because a pressure difference occurs between the upstream and downstream sides of the orifice, the pilot pressure of the second pilot line (pressure downstream of the orifice) becomes lower than the pressure upstream of the orifice by the pressure difference of the orifice. . Therefore, the pilot pressure in the first pilot line is higher than the pilot pressure in the second pilot line by the pressure difference of the orifice in addition to the pressure difference generated when passing the control valve, and therefore the flow rate compared to the case without the orifice. The control valve is likely to be driven in the closing direction. Therefore, the hydraulic oil from the hydraulic cylinder preferentially flows to the sub pump side, and the hydraulic oil is accumulated in the accumulator. Thereby, the recovery efficiency of the potential energy of the elevating object is improved. On the other hand, when the load loaded on the elevator is light, the pressure of the hydraulic cylinder is low, so the hydraulic oil from the hydraulic cylinder does not easily flow toward the sub pump. Therefore, since a pressure difference is unlikely to occur between the upstream side and the downstream side of the orifice, a drop in the pilot pressure of the second pilot line is suppressed. For this reason, when the force for driving the flow control valve in the closing direction is weakened, the flow control valve is opened, and the hydraulic oil from the hydraulic cylinder flows to the flow control valve side. Thereby, the desired descent speed of the lifting object can be obtained.

  The hydraulic drive device is disposed between the discharge port of the sub pump and the accumulator, and the first valve portion is switched between an open position for communicating the discharge port and the accumulator and a closed position for closing the discharge port and the accumulator; A second valve portion disposed between the outlet and the tank and switching between an open position communicating the discharge port and the tank and a closed position blocking the discharge port and the tank, and a discharge side detecting the pressure on the discharge side of the sub pump A pressure detection unit, and a valve control unit that determines the pressure accumulation state of hydraulic oil in the accumulator based on the pressure on the discharge side of the sub pump detected by the discharge side pressure detection unit, and controls the first valve unit and the second valve unit; May further be provided.

  When the first valve portion is controlled to be in the open position and the second valve portion is controlled to be in the closed position, the hydraulic oil discharged from the discharge port of the sub pump is accumulated in the accumulator . On the other hand, when the second valve portion is controlled to be in the open position and the first valve portion is controlled to be in the closed position, the hydraulic oil discharged from the discharge port of the sub pump is discharged to the tank. In this case, since the sub pump is unloaded, the fuel consumption can be reduced. Further, since the discharge port of the sub pump and the accumulator are shut off, it is possible to prevent the hydraulic oil accumulated in the accumulator from flowing back to the sub pump.

  The hydraulic drive apparatus is disposed between the accumulator and the suction port of the sub pump, and is a third valve unit that switches between an open position communicating the accumulator and the suction port and a closed position blocking the accumulator and the suction port; The valve control unit further includes a check valve disposed between the orifice in the oil flow passage and the suction port of the sub pump and permitting only the flow of hydraulic fluid from the orifice side to the sub pump side. The first valve portion, the second valve portion, and the third valve portion may be controlled by determining the pressure accumulation state of the hydraulic oil in the accumulator based on the pressure on the discharge side of the sub pump detected by the unit.

  When the hydraulic oil is accumulated in the accumulator, the accumulator and the suction port of the sub pump are shut off by setting the third valve part in the closed position, so the hydraulic oil accumulated in the accumulator is transferred to the suction port of the sub pump It is prevented from flowing in. For example, when raising and lowering the elevator, the accumulator and the suction port of the sub pump are communicated by bringing the third valve portion into the open position, so that the hydraulic oil accumulated in the accumulator flows into the suction port of the sub pump and the hydraulic oil The sub pump is driven by the motor. Therefore, the torque of the engine is assisted by the sub pump. As a result, engine torque can be reduced and fuel consumption can be reduced.

  The hydraulic drive is detected by a suction-side pressure detection unit that detects the pressure on the suction side of the sub pump, a discharge-side pressure detection unit that detects the pressure on the discharge side of the sub pump, and a target torque and suction side pressure detection unit of the sub pump. Based on the pressure on the suction side of the sub pump and the pressure on the discharge side of the sub pump detected by the discharge pressure detection unit, the required capacity of the sub pump is calculated, and torque assist is performed to control the displacement control unit according to the required capacity of the sub pump. And a controller.

  In such a configuration, when assisting the torque of the engine by the sub pump, the torque assist amount by the sub pump is appropriately set. Thereby, the operating point of the engine can be brought closer to the optimum point.

  The hydraulic drive device detects the pressure on the discharge side of the sub pump, and when the pressure on the discharge side of the sub pump detected by the pressure detection portion on the discharge side becomes equal to or higher than a specified value, The system may further include a capacity reduction control unit that controls the capacity control unit to reduce the size.

  In such a configuration, for example, the pressure difference between the pressure of the accumulator and the pressure of the hydraulic cylinder is reduced due to the pressure increase of the accumulator accompanying the accumulation of hydraulic oil to the accumulator, thereby directing the first hydraulic oil flow path to the sub pump When the flow rate of the hydraulic oil flowing is reduced, the displacement control unit is controlled to reduce the displacement of the sub pump. In this case, the flow rate of the hydraulic fluid flowing through the first hydraulic fluid flow path is further reduced, and the differential pressure between the upstream side and the downstream side in the orifice is reduced, so that the reduction of the pilot pressure in the second pilot line is suppressed. , The flow control valve opens. Thereby, the desired descent speed of the lifting object can be obtained.

  The sub pump is a swash plate type variable displacement pump, and the capacity reduction control unit reduces the displacement control unit so as to reduce the inclination angle of the swash plate of the sub pump when the pressure on the discharge side of the sub pump exceeds a specified value. You may control. By thus reducing the inclination angle of the swash plate of the sub pump, the displacement of the sub pump can be easily and reliably reduced.

  According to the present invention, it is possible to recover the potential energy of the elevating object while maintaining the desired lowering speed of the elevating object.

FIG. 1 is a hydraulic circuit diagram showing a hydraulic drive system according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a specific structure of the sub-pump shown in FIG. FIG. 3 is a control system configuration diagram of a hydraulic drive system including functional blocks of the controller shown in FIG. FIG. 4 is a graph showing an example of the relationship between the engine speed and the discharge flow rate of the sub pump. FIG. 5 (a) is a hydraulic circuit diagram showing the flow of hydraulic fluid when hydraulic fluid from the lift cylinder is accumulated in the accumulator when the fork is lowered, and FIG. 5 (b) is an inclination of the swash plate of the sub pump FIG. 8 is a hydraulic circuit diagram showing the flow of hydraulic fluid when hydraulic fluid from the lift cylinder is bypassed due to the smaller angle. FIG. 6 is a timing chart showing the timing relationship when the fork is lowered. FIG. 7 is a hydraulic circuit diagram showing the flow of hydraulic oil when the hydraulic oil from the lift cylinder is bypassed by closing the switching valve. FIG. 8 is a hydraulic circuit diagram showing a modification of the switching valve shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals and redundant description will be omitted.

  FIG. 1 is a hydraulic circuit diagram showing a hydraulic drive system according to an embodiment of the present invention. In the figure, the hydraulic drive 1 of the present embodiment is mounted on, for example, an engine-type forklift.

  The hydraulic drive system 1 includes a lift cylinder 2 and a tilt cylinder 3. The lift cylinder 2 is a hydraulic cylinder that raises and lowers the fork 4 (lifting and lowering object) by supply and discharge of hydraulic oil. The tilt cylinder 3 is a hydraulic cylinder that tilts a mast (not shown) by supply and discharge of hydraulic oil. The lift cylinder 2 is operated by the operation of a lift operation lever 5 (operation portion) for moving the fork 4 up and down (up or down). The tilt cylinder 3 is operated by the operation of the tilt control lever 6 for tilting the mast (forward or backward).

  Further, the hydraulic drive system 1 includes a tank 7 for storing hydraulic oil, a main pump 8, and a sub pump 9 coaxially arranged with the main pump 8. The main pump 8 and the sub pump 9 are directly connected to the engine 11 via the gear 10 and driven by the engine 11. The main pump 8 is a hydraulic pump that can rotate in one direction. The main pump 8 sucks in hydraulic oil from the tank 7 and supplies it to the lift cylinder 2 and the tilt cylinder 3. The sub pump 9 is a variable displacement hydraulic pump. The sub pump 9 will be described in detail later.

  The discharge port 8 a of the main pump 8 and the head chamber 2 a of the lift cylinder 2 are connected via the hydraulic oil supply flow path 12. A control valve 13 for lift lift is disposed in the hydraulic oil supply channel 12. Between the control valve 13 and the lift cylinder 2 in the hydraulic oil supply flow path 12, a check valve 14 is disposed which allows only the flow of hydraulic oil from the control valve 13 side to the lift cylinder 2 side.

  The control valve 13 is configured of a solenoid proportional valve. The operation valve 13 controls the flow of hydraulic fluid in accordance with the amount of operation of the lift operation lever 5 to raise it. A lift operation signal from a controller 65 (described later) is input to the solenoid operation unit 13 a of the operation valve 13. The lift operation signal is a current command value corresponding to the amount of lift operation of the lift control lever 5.

  The control valve 13 is normally in a closed position (shown) for blocking the flow of hydraulic fluid from the main pump 8 to the lift cylinder 2. When a lift operation signal is input to the solenoid operation unit 13a of the control valve 13, the control valve 13 opens at an opening degree corresponding to the lift operation signal. Then, the hydraulic fluid is supplied from the main pump 8 to the head chamber 2 a of the lift cylinder 2 and the lift cylinder 2 is extended, so the fork 4 is lifted.

  A tilt control valve 16 is connected between the main pump 8 and the operation valve 13 in the hydraulic oil supply flow path 12 via the hydraulic oil supply flow path 15. In the hydraulic oil supply flow path 15, a check valve 17 is disposed which allows only the flow of hydraulic oil from the main pump 8 side to the operation valve 16 side. The control valve 16 and the head chamber 3 a and the rod chamber 3 b of the tilt cylinder 3 are connected to one another via hydraulic oil supply channels 18 and 19 respectively.

  The control valve 16 is composed of a solenoid proportional valve. The control valve 16 controls the flow of hydraulic fluid in accordance with the amount of operation of the tilt control lever 6. A forward tilt operation signal from a controller 65 (described later) is input to the solenoid operation unit 16 a of the operation valve 16, and a backward tilt operation signal from the controller 65 is input to the solenoid operation unit 16 b of the operation valve 16. The forward tilt operation signal is a current command value corresponding to the forward tilt operation amount of the tilt control lever 6, and the backward tilt operation signal is a current command value according to the reverse tilt operation amount of the tilt operation lever 6. is there.

  The control valve 16 is normally in a closed position (shown) for blocking the flow of hydraulic fluid from the main pump 8 to the tilt cylinder 3. When a forward lean operation signal is input to the solenoid operation part 16a of the control valve 16, the control valve 16 opens at an opening degree corresponding to the forward lean operation signal. Then, the hydraulic fluid is supplied from the main pump 8 to the head chamber 3a of the tilt cylinder 3 and the tilt cylinder 3 is extended, so that the mast (not shown) is inclined forward. When a rearward tilt operation signal is input to the solenoid operation portion 16 b of the operation valve 16, the operation valve 16 opens at an opening degree corresponding to the rearward tilt operation signal. Then, the hydraulic fluid is supplied from the main pump 8 to the rod chamber 3b of the tilt cylinder 3, and the tilt cylinder 3 contracts, so that the mast (not shown) tilts backward.

  A tank 7 is connected between the main pump 8 and the operation valve 13 in the hydraulic oil supply channel 12 via a hydraulic oil discharge channel 20. An unloading valve 21 is disposed in the hydraulic fluid discharge flow passage 20. The operation valve 16 is connected to the hydraulic fluid discharge channel 20 via the hydraulic fluid discharge channel 22.

  FIG. 2 is a cross-sectional view showing a specific structure of the sub pump 9. In FIG. 2, the sub pump 9 is a swash plate type variable displacement pump. The sub pump 9 has a main casing 23, a rear casing 24 fixed to the main casing 23, and a rotating shaft 25 rotatably supported by the main casing 23 and the rear casing 24. The rotation shaft 25 is rotationally driven by the engine 11. The rear casing 24 is provided with a suction port 26 (see also FIG. 1) for sucking in the hydraulic fluid and a discharge port 27 (see also FIG. 1) for discharging the hydraulic fluid.

  A cylinder block 28 is attached to the rear casing 24. The cylinder block 28 is fixed to the rotation shaft 25 so as to be integrally rotatable. A plurality of cylinder bores 29 are provided around the rotation shaft 25 in the cylinder block 28. In each cylinder bore 29, a plunger 30 is accommodated so as to be capable of reciprocating.

  A valve plate 31 is disposed between the cylinder block 28 and the rear casing 24. The valve plate 31 is provided with a suction hole 31 a for communicating the suction port 26 and the cylinder bore 29, and a discharge hole 31 b for communicating the discharge port 27 and the cylinder bore 29. Thus, the hydraulic oil from the outside of the sub pump 9 is sucked into the cylinder bore 29 through the suction port 26 and the suction hole 31a, and the hydraulic oil in the cylinder bore 29 is pumped through the discharge hole 31b to the discharge port 27. It is discharged.

  In the main casing 23, a swash plate 32 (see also FIG. 1) that defines the stroke of the plunger 30 is disposed. The swash plate 32 is provided with a through hole 32 a through which the rotation shaft 25 passes. A shoe 33 is attached to the tip of each plunger 30. Each shoe 33 is in close contact with the rear surface of the swash plate 32 by a pressure spring (not shown). Each plunger 30 is reciprocated with a stroke corresponding to the inclination angle α of the swash plate 32 as the cylinder block 28 rotates.

  The rear casing 24 is provided with a swash plate angle control pressure port 34 and a piston accommodating portion 35 communicated with the swash plate angle control pressure port 34. The piston accommodating portion 35 accommodates a swash plate angle control piston 36. The tip end portion of the swash plate angle control piston 36 is in close contact with the rear surface of the swash plate 32 by the hydraulic oil supplied to the piston housing portion 35.

  On the other side of the swash plate angle control piston 36 with respect to the swash plate 32 in the main casing 23, a spring 37 is disposed which biases the swash plate 32. One end of the spring 37 is connected to the inner wall surface of the main casing 23, and the other end of the spring 37 is in close contact with the front surface of the swash plate 32 via the pressing member 58. The inclination angle α of the swash plate 32 is determined at a position where the load by the spring 37 and the load by the swash plate angle control piston 36 are balanced.

  Connected to the swash plate angle control pressure port 34 is a swash plate angle control unit 38 (see FIG. 1) that controls the pressure (load) applied to the swash plate angle control piston 36. The swash plate angle control unit 38 is, for example, an electromagnetic proportional pressure control valve. By controlling the pressure applied to the swash plate angle control piston 36 by the swash plate angle control unit 38, the inclination angle α of the swash plate 32 is controlled, and hence the displacement of the sub pump 9 is controlled. The inclination angle α of the swash plate 32 is an angle of the swash plate 32 with respect to a plane perpendicular to the rotation shaft 25. The swash plate angle control unit 38 constitutes a displacement control unit that controls the displacement of the sub pump 9.

  Returning to FIG. 1, the hydraulic drive device 1 includes a hydraulic oil suction passage 39 connecting the suction port 26 of the sub pump 9 and the tank 7. In the hydraulic oil suction flow path 39, a check valve 40 that allows only the flow of hydraulic oil from the tank 7 side to the sub pump 9 side is disposed.

  Also, the hydraulic drive device 1 is connected between the sub-pump 9 and the tank 7 in the hydraulic oil suction flow path 39 and the hydraulic oil common flow path 41 connected in the vicinity of the lift cylinder 2 in the hydraulic oil supply flow path 12. The hydraulic oil regeneration flow path 42 and the hydraulic oil bypass flow path 43 connecting the connection point S of the hydraulic oil common flow path 41 and the hydraulic oil regeneration flow path 42 and the tank 7 are provided. The hydraulic fluid common channel 41 and the hydraulic fluid regeneration channel 42 connect the suction port 26 of the sub pump 9 to the lift cylinder 2, and the first hydraulic fluid channel through which the hydraulic oil from the lift cylinder 2 flows toward the sub pump 9 Are configured. The hydraulic oil bypass channel 43 connects between the suction port 26 of the sub pump 9 and the operation valve 44 (described later) in the first hydraulic oil channel and the tank 7, and the hydraulic oil from the lift cylinder 2 is connected to the tank 7. A second hydraulic fluid flow path is formed to flow toward the same.

  A lift lowering operation valve 44 is disposed in the hydraulic oil common flow path 41. The operation valve 44 controls the flow of hydraulic fluid in accordance with the amount of operation of the lowering operation of the lift operation lever 5. The control valve 44 is configured of a solenoid proportional valve. A down operation signal from a controller 65 (described later) is input to the solenoid operation unit 44 a of the operation valve 44. The descent operation signal is a current command value corresponding to the amount of descent operation of the lift operation lever 5.

  The control valve 44 is normally in a closed position (shown) for blocking the flow of hydraulic fluid from the head chamber 2 a of the lift cylinder 2. When the lowering operation signal is input to the solenoid operation unit 44a of the operation valve 44, the operation valve 44 opens at an opening degree corresponding to the lowering operation signal. Then, since the fork 4 is lowered by the weight of the fork 4, the lift cylinder 2 contracts and the hydraulic fluid flows out from the head chamber 2 a of the lift cylinder 2. Then, the hydraulic oil from the lift cylinder 2 passes through the operation valve 44.

  An orifice 45 is disposed in the hydraulic oil regeneration flow path 42. That is, the orifice 45 is disposed between the connection point S of the first hydraulic fluid channel (described above) with the hydraulic fluid bypass channel 43 and the suction port 26 of the sub pump 9. Between the orifice 45 and the suction port 26 of the sub pump 9 in the hydraulic oil regeneration flow path 42, a check valve 46 is disposed which allows only the flow of hydraulic oil from the orifice 45 side to the sub pump 9 side.

  A bypass flow control valve 47 is disposed in the hydraulic fluid bypass channel 43. The bypass flow control valve 47 controls the flow rate of the hydraulic oil from the head chamber 2 a of the lift cylinder 2 back to the tank 7. The bypass flow control valve 47 is a pilot flow control valve that adjusts the opening degree according to the pressure difference generated when the hydraulic oil from the lift cylinder 2 passes through the operation valve 44. The bypass flow control valve 47 functions as a throttle according to the opening degree, and the opening degree is adjusted between the fully open position (shown) which permits the flow of hydraulic fluid and the fully closed position which blocks the flow of hydraulic fluid. Ru.

  The bypass flow control valve 47 has a pilot operating portion 47a (first pilot operating portion) acting on the side closing the bypass flow control valve 47 and a pilot operating portion 47b operating on the side opening the bypass flow control valve 47 And a second pilot operation unit). Further, the bypass flow control valve 47 has a spring 48 that biases the bypass flow control valve 47 to the open side.

  The bypass flow control valve 47 inputs the pressure on the upstream side and the downstream side of the operation valve 44 as a pilot pressure. Specifically, the pilot operation portion 47a of the bypass flow control valve 47 and the lift cylinder 2 and the operation valve 44 in the hydraulic fluid common flow path 41 are connected via a pilot line 49 (first pilot line) It is done. The pilot operating portion 47 b of the bypass flow control valve 47 and the orifice 45 and the check valve 46 in the hydraulic oil regeneration flow path 42 are connected via a pilot line 50 (second pilot line). That is, the pilot line 49 is connected to the upstream side of the control valve 44. The pilot line 50 is connected to the downstream side of the operation valve 44, more specifically, to the downstream side of the orifice 45.

  The bypass flow control valve 47 controls the flow rate of the hydraulic oil so that the pressure difference (different pressure before and after) generated on the upstream side and the downstream side of the operation valve 44 becomes constant. The differential pressure at this time is referred to as a control differential pressure. When the opening degree of the operation valve 44 is small, the control differential pressure is reached even if the flow rate of the hydraulic oil is small, so that the flow rate control valve 47 for bypass controls the flow rate of the hydraulic oil so as not to increase. When the opening degree of the operation valve 44 is large, the control differential pressure is not reached unless the flow rate of the hydraulic oil is large, so that the flow rate control valve 47 for bypass is controlled to increase the flow rate of the hydraulic oil. As described above, the flow rate of the hydraulic oil flowing through the bypass flow control valve 47 differs according to the operation amount of the lift operation lever 5. The flow rate at this time is called a control flow rate.

  The main function of the bypass flow control valve 47 is to flow the hydraulic oil in the hydraulic oil bypass channel 43 when the hydraulic oil does not easily flow in the hydraulic oil regeneration channel 42 because the load loaded on the fork 4 is light. is there. Thereby, the desired operating speed of lift cylinder 2 can be secured.

  Specifically, when the load loaded on the fork 4 is light and it is difficult for hydraulic fluid to flow through the hydraulic fluid regeneration flow channel 42, the differential pressure generated at the orifice 45 is small. Therefore, the bypass flow rate control valve 47 adjusts the flow rate (bypass flow rate) of the hydraulic fluid flowing through the hydraulic fluid bypass flow path 43 so that the differential pressure across the operation valve 44 becomes constant.

  On the other hand, when the load loaded on the fork 4 is heavy and the working oil easily flows in the working oil regeneration flow path 42, the differential pressure generated at the orifice 45 is large, so it acts on the pilot operation portion 47b via the pilot line 50. The pilot pressure is reduced by the differential pressure of the orifice 45. Therefore, the differential pressure between the pilot pressure acting on the pilot operation portion 47a and the pilot pressure acting on the pilot operation portion 47b is larger than in a state where the hydraulic oil does not flow in the hydraulic oil regeneration flow path 42. Accordingly, the bypass flow control valve 47 is driven in the valve closing direction, and the hydraulic oil flows in the hydraulic oil regeneration flow path 42.

  An accumulator 52 is connected to the discharge port 27 of the sub pump 9 via a hydraulic oil pressure accumulation passage 51. The accumulator 52 accumulates the hydraulic oil discharged from the discharge port 27 of the sub pump 9. The accumulator 52 is filled with gas. As the hydraulic oil is stored in the accumulator 52, the gas is compressed, and the internal pressure of the accumulator 52 increases. The volume of the accumulator 52 is preferably large enough to allow all the hydraulic oil from the lift cylinder 2 to be received by the accumulator 52. However, even if it is difficult to increase the size due to physical constraints, the operation is not accepted by the accumulator 52. Since the oil is discharged to the tank 7 through the hydraulic oil bypass passage 43, there is no problem in operation.

  An electromagnetic switching valve 53 (first valve portion) is disposed in the hydraulic fluid pressure accumulation passage 51. That is, the switching valve 53 is disposed between the discharge port 27 of the sub pump 9 and the accumulator 52. The switching valve 53 is switched between an open position 53a communicating the discharge port 27 and the accumulator 52 and a closed position 53b blocking the discharge port 27 and the accumulator 52 according to a control signal from a controller 65 (described later).

  When hydraulic fluid is accumulated in the accumulator 52, the discharge port 27 of the sub pump 9 and the accumulator 52 are communicated by setting the switching valve 53 to the open position 53a. When the hydraulic oil is not accumulated in the accumulator 52, the discharge port 27 of the sub pump 9 and the accumulator 52 are shut off by setting the switching valve 53 to the closed position 53b (shown). Thereby, the backflow of the hydraulic oil accumulated in the accumulator 52 is prevented.

  The discharge port 27 of the sub pump 9 and the switching valve 53 in the hydraulic fluid pressure accumulation passage 51 are connected to the tank 7 via the hydraulic fluid discharge passage 54. An electromagnetic switching valve 55 (second valve portion) is disposed in the hydraulic oil discharge flow path 54. That is, the switching valve 55 is disposed between the discharge port 27 of the sub pump 9 and the tank 7. The switching valve 55 is switched between an open position 55a for communicating the discharge port 27 and the tank 7 and a closed position 55b for blocking the discharge port 27 and the tank 7 according to a control signal from a controller 65 (described later).

  When hydraulic fluid is accumulated in the accumulator 52, the discharge port 27 of the sub pump 9 and the tank 7 are shut off by setting the switching valve 55 to the closed position 55b (shown). When the hydraulic fluid is not accumulated in the accumulator 52, the discharge port 27 of the sub pump 9 and the tank 7 are communicated by setting the switching valve 55 to the open position 55a. As a result, the sub pump 9 is unloaded, and the fuel consumption is reduced.

  The accumulator 52 is connected to the hydraulic oil regeneration channel 42 via the hydraulic oil assist channel 56. Specifically, the hydraulic fluid assist flow channel 56 is provided between the switching valve 53 and the accumulator 52 in the hydraulic fluid pressure storage flow channel 51, and the check valve 46 and the suction port 26 of the sub pump 9 in the hydraulic fluid regeneration flow channel 42. Connect with each other. An electromagnetic switching valve 57 (third valve portion) is disposed in the hydraulic fluid assist channel 56. That is, the switching valve 57 is disposed between the accumulator 52 and the suction port 26 of the sub pump 9. The switching valve 57 is switched between an open position 57 a communicating the accumulator 52 and the suction port 26 and a closed position 57 b blocking the accumulator 52 and the suction port 26.

  When hydraulic fluid is accumulated in the accumulator 52, the accumulator 52 and the suction port 26 of the sub pump 9 are shut off by setting the switching valve 57 to the closed position 57b (shown). When the hydraulic oil is not accumulated in the accumulator 52, the accumulator 52 and the suction port 26 of the sub pump 9 are communicated by setting the switching valve 57 to the open position 57a.

  At the time of lowering of the fork 4, the hydraulic oil corresponding to the operation amount of the lift control lever 5 flows in the hydraulic oil common flow path 41. Here, when the load loaded on the fork 4 is heavy, the differential pressure is generated at the orifice 45 as described above, so the hydraulic oil flows in the hydraulic oil regeneration flow path 42. Then, the hydraulic oil is supplied to the suction port 26 of the sub pump 9 and discharged from the discharge port 27 of the sub pump 9. At this time, the switching valve 53 is controlled to the open position 53a and the switching valve 55 is controlled to the closed position 55b, whereby the hydraulic oil discharged from the discharge port 27 of the sub pump 9 is accumulated in the accumulator 52. As a result, the potential energy of the load is recovered by the accumulator 52.

  When the fork 4 is lifted or the tilt cylinder 3 is operated, the switching valve 53 is controlled to the closed position 53b and the switching valve 57 is controlled to the open position 57a, whereby the pressurized hydraulic oil accumulated in the accumulator 52 is actuated. The oil is supplied to the suction port 26 of the sub pump 9 through the oil assist passage 56 and the hydraulic oil regeneration passage 42. Then, the sub-pump 9 is rotated and driven by the pressurized hydraulic oil. Thereby, the torque of the engine 11 can be reduced, and the fuel consumption can be reduced. That is, the energy stored in the accumulator 52 is used to assist the torque of the engine 11. At this time, by controlling the inclination angle of the swash plate 32 of the sub pump 9, the assist torque by the sub pump 9 can be adjusted, and the operating point of the engine 11 can be made closer to the optimum point. The timing at which the sub pump 9 is motor-driven by the pressurized hydraulic oil is not particularly limited when the fork 4 is raised or when the tilt cylinder 3 is operated, and may be during travel of the forklift.

  Further, in a state where the engine 11 is operating with a light load, hydraulic fluid is accumulated in the accumulator 52 by pumping the sub pump 9 with the surplus torque of the engine 11. Then, when the engine 11 operates at a high load, the sub-pump 9 is motor-driven by reusing the hydraulic oil accumulated in the accumulator 52 as described above. Thereby, the fuel consumption can be improved.

  Further, as shown in FIG. 3, the hydraulic drive system 1 also includes a lift operation sensor 60, a tilt operation sensor 61, a rotational speed sensor 62 (rotational speed detection unit), and a suction side pressure sensor 63 (suction side pressure). A detection unit), a discharge side pressure sensor 64 (discharge side pressure detection unit), and a controller 65 are provided.

  The lift operation sensor 60 is a sensor that detects the operation direction and the amount of operation of the lift operation lever 5. The tilt operation sensor 61 is a sensor that detects an operation direction and an operation amount of the tilt operation lever 6. The rotation speed sensor 62 is a sensor that detects the rotation speed of the engine 11. The suction side pressure sensor 63 is a sensor that detects the pressure on the suction side of the sub pump 9. The suction side pressure sensor 63 detects, for example, the pressure between the suction port 26 of the sub pump 9 and the check valve 46 in the hydraulic oil regeneration flow path 42. The discharge pressure sensor 64 is a sensor that detects the pressure on the discharge side of the sub pump 9. The discharge side pressure sensor 64 detects the pressure between the discharge port 27 of the sub pump 9 and the switching valve 53 in the hydraulic fluid pressure accumulation passage 51.

  The controller 65 is configured by a CPU, a RAM, a ROM, an input / output interface, and the like. The controller 65 includes an operation valve control unit 66, a switching valve control unit 67 (valve control unit), a lowering control unit 68, a torque assist control unit 69, and a capacity reduction control unit 70.

  The control valve control unit 66 controls the control valve 13 for lift elevation and the control valve 44 for lift reduction based on the detection value of the lift operation sensor 60, and for tilt based on the detection value of the tilt operation sensor 61. The control valve 16 is controlled.

  Specifically, the operation valve control unit 66 outputs, to the solenoid operation unit 13 a of the operation valve 13, an upward operation signal corresponding to the operation amount of the upward operation of the lift operation lever 5 detected by the lift operation sensor 60. Further, the operation valve control unit 66 outputs, to the solenoid operation unit 44 a of the operation valve 44, a descent operation signal corresponding to the operation amount of the descent operation of the lift operation lever 5 detected by the lift operation sensor 60. Further, the operation valve control unit 66 outputs a forward tilt operation signal according to the operation amount of the forward tilt operation of the tilt operation lever 6 detected by the tilt operation sensor 61 to the solenoid operation unit 16 a of the operation valve 16 and tilts. A rearward tilt operation signal corresponding to the operation amount of the rearward tilt operation of the tilt operation lever 6 detected by the operation sensor 61 is output to the solenoid operation portion 16 b of the operation valve 16.

  The switching valve control unit 67 determines the pressure accumulation state of the hydraulic oil in the accumulator 52 based on the pressure on the discharge side of the sub pump 9 detected by the discharge side pressure sensor 64, and controls the switching valve 53, 55, 57.

  Specifically, based on the pressure on the discharge side of the sub pump 9, the switching valve control unit 67 determines whether a predetermined amount (for example, a full state) of hydraulic oil is accumulated in the accumulator 52. Then, when the hydraulic fluid of a predetermined amount is not accumulated in the accumulator 52, the switching valve control unit 67 outputs a control signal to set the switching valve 53 to the open position 53a to the solenoid operation unit 53c of the switching valve 53. The control signal for setting the switching valve 55 to the closed position 55b is output to the solenoid operating portion 55c of the switching valve 55, and the control signal for setting the switching valve 57 to the closed position 57b to the solenoid operating portion 53c of the switching valve 57. It outputs (the state of FIG. 5 (a)). As a result, the hydraulic oil discharged from the discharge port 27 of the sub pump 9 is accumulated in the accumulator 52.

  On the other hand, when the hydraulic fluid of a predetermined amount is accumulated in the accumulator 52, the switching valve control section 67 outputs a control signal to set the switching valve 53 to the closed position 53b to the solenoid operation section 53c of the switching valve 53, A control signal for setting the switching valve 55 to the open position 55a is output to the solenoid operating portion 55c of the switching valve 55, and a control signal for setting the switching valve 57 to the open position 57a is output to the solenoid operating portion 57c of the switching valve 57. Do. As a result, the hydraulic oil discharged from the discharge port 27 of the sub pump 9 is discharged to the tank 7, and the hydraulic oil accumulated in the accumulator 52 is supplied to the suction port 26 of the sub pump 9.

  The descent control unit 68 determines the target descent speed of the fork 4 based on the operation amount of the descent operation of the lift operation lever 5 detected by the lift operation sensor 60 and detects the target descent speed of the fork 4 and the rotation speed sensor 62 The necessary inclination angle of the swash plate 32 of the sub pump 9 when the fork 4 is lowered is calculated based on the rotation speed of the engine 11 and the swash plate angle control unit 38 is controlled according to the necessary inclination angle of the swash plate 32. Do. The required inclination angle of the swash plate 32 of the sub pump 9 corresponds to the required displacement of the sub pump 9.

  The control of the inclination angle of the swash plate 32 by the lowering control unit 68 is specifically performed as follows. Although the effects of pump efficiency and temperature are omitted for simplification of the description, the pump efficiency and temperature are actually corrected to control the inclination angle of the swash plate 32.

The flow rate of the swash plate type variable displacement pump is theoretically expressed by equation (1).
Q = Vp · N (1)

In the equation (1), Vp is displacement [cc / rev], and N is the engine speed. The displacement volume Vp can be obtained from the following equation.

dp: plunger diameter (see FIG. 2) R: distance between cylinder block axis and plunger axis (see FIG. 2) n: number of plungers α: inclination angle of the swash plate (see FIG. 2)

When the equation (2) is substituted into the equation (1) and organized, the relationship between the flow rate of the variable displacement pump and the inclination angle of the swash plate is expressed by the following equation.

  The descent control unit 68 determines the target descent speed of the fork 4 based on the amount of descent operation of the lift operation lever 5, and the discharge flow rate of the sub pump 9 corresponding to the target descent speed of the fork 4 and the rotational speed of the engine 11 The necessary inclination angle of the swash plate 32 of the sub pump 9 is calculated from the equation (3) based on the above, and the swash plate angle control unit 38 is controlled so as to be the required inclination angle. Thereby, the lowering speed of the fork 4 to be aimed can be obtained.

  FIG. 4 is a graph showing an example of the relationship between the rotational speed of the engine 11 and the discharge flow rate of the sub pump 9. In FIG. 4, when the rotational speed of the engine 11 is low, the displacement of the sub pump 9 is increased by increasing the inclination angle of the swash plate 32. Therefore, the discharge flow rate of the sub pump 9 is increased, and the lowering speed of the fork 4 is increased. When the rotational speed of the engine 11 is high, the displacement of the sub pump 9 is reduced by reducing the inclination angle of the swash plate 32. As a result, the discharge flow rate of the sub pump 9 decreases, and the lowering speed of the fork 4 decreases. Thus, the accumulator 52 can accumulate hydraulic fluid while maintaining the desired lowering speed of the fork 4.

  The torque assist control unit 69 is based on the target torque of the sub pump 9, the pressure on the suction side of the sub pump 9 detected by the suction side pressure sensor 63, and the pressure on the discharge side of the sub pump 9 detected by the discharge side pressure sensor 64. The necessary inclination angle of the swash plate 32 of the sub pump 9 at the time of the torque assist by the sub pump 9 is calculated, and the swash plate angle control unit 38 is controlled according to the necessary inclination angle of the swash plate 32. The required inclination angle of the swash plate 32 of the sub pump 9 corresponds to the required displacement of the sub pump 9. The target torque of the sub pump 9 is, for example, a torque that brings the operating point of the engine 11 closer to the optimum point.

  Specifically, the control of the inclination angle of the swash plate 32 by the torque assist control unit 69 is performed as follows. Although the effects of pump efficiency and temperature are omitted for simplification of the description, the pump efficiency and temperature are actually corrected to control the inclination angle of the swash plate 32.

The torque of the swash plate type variable displacement pump is theoretically expressed by equation (4).
T = Dp · ΔP (4)

In the equation (4), Dp is a volume per unit angle [cc / rad], and ΔP is a differential pressure between suction and discharge [MPa]. The volume Dp per unit angle is in the relationship of the displacement volume Vp and the following equation.

The displacement volume Vp of the swash plate type variable displacement pump is expressed by the above equation (2). Therefore, the torque T can be obtained from the following equation as a function of the inclination angle α of the swash plate and the differential pressure ΔP of suction and discharge from the equations (2), (4) and (5).

If this equation is organized, the relationship between the torque T, the suction / discharge differential pressure ΔP, and the inclination angle α of the swash plate is expressed by the following equation.

  The torque assist control unit 69 uses the pressure on the suction side of the sub pump 9 detected by the suction side pressure sensor 63 and the pressure on the discharge side of the sub pump 9 detected by the discharge side pressure sensor 64 to obtain a differential pressure ΔP of suction and discharge. The necessary inclination angle of the swash plate 32 which becomes the target torque is calculated by the equation (7), and the swash plate angle control unit 38 is controlled so as to become the necessary inclination angle. As a result, it is possible to obtain the target sub-pump 9 torque.

  The capacity reduction control unit 70 reduces the inclination angle of the swash plate 32 of the sub pump 9 when the pressure on the discharge side of the sub pump 9 detected by the discharge pressure sensor 64 becomes equal to or higher than a predetermined value. Control the swash plate angle control unit 38; At this time, the capacity reduction control unit 70 controls the swash plate angle control unit 38 so as to make the tilt angle of the swash plate 32 zero when the pressure on the discharge side of the sub pump 9 becomes equal to or higher than the specified value. Good. As the pressure difference between the pressure in the head chamber 2 a of the lift cylinder 2 and the pressure in the accumulator 52 decreases, the flow rate (regeneration flow rate) of the hydraulic oil flowing through the hydraulic oil regeneration flow path 42 decreases. Is a pressure that makes it impossible to obtain the desired descending speed of

  As described above, when the load loaded on the fork 4 is heavy, a pressure loss occurs at the orifice 45, so that the differential pressure between the pilot pressure of the pilot line 49 and the pilot pressure of the pilot line 50 becomes large. The control valve 47 is maintained closed. Therefore, as shown in FIG. 5A, the hydraulic oil from the lift cylinder 2 flows toward the sub pump 9 through the hydraulic oil regeneration flow path 42. Then, the hydraulic oil is supplied to the suction port 26 of the sub pump 9 and is discharged from the discharge port 27 of the sub pump 9. The hydraulic fluid discharged from the discharge port 27 of the sub pump 9 flows through the hydraulic fluid pressure accumulation passage 51 and is accumulated in the accumulator 52.

  As shown in FIG. 6, when the internal pressure of the accumulator 52 (the pressure on the discharge side of the sub pump 9) rises to reach a specified value in accordance with the pressure accumulation of the hydraulic oil to the accumulator 52, the head chamber 2a of the lift cylinder 2 The pressure difference between the pressure (see the broken line P in FIG. 6 (d)) and the internal pressure of the accumulator 52 (see the solid line Q in FIG. 6 (d)) decreases. Then, the capacity reduction control unit 70 controls the swash plate angle control unit 38 so as to reduce the inclination angle of the swash plate 32 of the sub pump 9. As a result, the displacement of the sub pump 9 is reduced, so the regenerative flow rate is reduced. Therefore, since the pressure loss at the orifice 45 is reduced, the differential pressure between the pilot pressure of the pilot line 49 and the pilot pressure of the pilot line 50 is reduced. Therefore, as shown in FIG. 5B, the bypass flow control valve 47 operates in the open state, and the hydraulic oil from the lift cylinder 2 flows in the hydraulic oil bypass flow path 43, and the bypass flow rate Will increase. Thereby, the desired lowering speed of the fork 4 is obtained.

  As described above, in the present embodiment, when the fork 4 is lowered by the lift operation lever 5, the lift cylinder 2 operates so that the fork 4 is lowered, and the hydraulic oil from the lift cylinder 2 is operated. The oil common flow channel 41 and the hydraulic oil regeneration flow channel 42 flow toward the sub pump 9. Then, the hydraulic oil is sucked from the suction port 26 of the sub pump 9 and discharged from the discharge port 27 of the sub pump 9. The hydraulic oil discharged from the discharge port 27 of the sub pump 9 is accumulated in the accumulator 52. As a result, the potential energy of the fork 4 is recovered. At this time, the target descent speed of the fork 4 is determined based on the operation amount of the lift control lever 5, and the required inclination angle of the swash plate 32 of the sub pump 9 is obtained based on the target descent speed of the fork 4 and the rotational speed of the engine 11. The swash plate angle control unit 38 is controlled according to the calculated tilt angle of the swash plate 32 as calculated. Thus, the desired lowering speed of the fork 4 is obtained. Thus, the potential energy of the fork 4 can be recovered while maintaining the desired lowering speed of the fork 4.

  Further, in the present embodiment, when the load loaded on the fork 4 is heavy, the pressure of the lift cylinder 2 is high, so the hydraulic oil from the lift cylinder 2 easily flows toward the sub pump 9. At this time, a pressure difference occurs between the upstream side and the downstream side of the orifice 45, so the pilot pressure of the pilot line 50 (pressure downstream of the orifice 45) is equal to the pressure difference between the orifice 45 and the pressure upstream of the orifice 45 Only lower. Accordingly, the pilot pressure in the pilot line 49 is higher than the pilot pressure in the pilot line 50 by the differential pressure of the orifice 45 in addition to the pressure difference generated when passing through the control valve 44, compared to the case without the orifice 45. The bypass flow control valve 47 is easily driven in the closing direction. Therefore, the hydraulic oil from the lift cylinder 2 preferentially flows to the sub pump 9 side, and the hydraulic oil is accumulated in the accumulator 52. Thereby, the recovery efficiency of the potential energy of the fork 4 is improved. On the other hand, when the load loaded on the fork 4 is light, the pressure of the lift cylinder 2 is low, so the hydraulic oil from the lift cylinder 2 does not easily flow toward the sub pump 9. Therefore, since a pressure difference is unlikely to occur between the upstream side and the downstream side of the orifice 45, a drop in the pilot pressure of the pilot line 50 is suppressed. Therefore, the force for driving the bypass flow control valve 47 in the closing direction is weakened so that the bypass flow control valve 47 is opened, and the hydraulic oil from the lift cylinder 2 flows to the bypass flow control valve 47 side. Become. Thereby, the desired descent speed of the fork 4 can be obtained.

  Further, in the present embodiment, when the switching valve 53 is controlled to be the open position 53a and the switching valve 55 is controlled to be the closed position 55b, the hydraulic oil discharged from the discharge port 27 of the sub pump 9 Is accumulated in the accumulator 52. On the other hand, when the switching valve 55 is controlled to the open position 55a and the switching valve 53 is controlled to the closed position 53b, the hydraulic oil discharged from the discharge port 27 of the sub pump 9 is discharged to the tank 7 Be done. In this case, since the sub pump 9 is unloaded, the fuel consumption can be reduced. In addition, since the discharge port 27 of the sub pump 9 and the accumulator 52 are shut off, the hydraulic oil accumulated in the accumulator 52 is prevented from flowing back to the sub pump 9.

  Further, in the present embodiment, when the hydraulic oil is accumulated in the accumulator 52, the accumulator 52 and the suction port 26 of the sub pump 9 are shut off by setting the switching valve 57 to the closed position 57b. The hydraulic oil accumulated in the lower pump 9 is prevented from flowing into the suction port 26 of the sub pump 9. When the fork 4 is lifted or the tilt cylinder 3 is operated, the accumulator 52 and the suction port 26 of the sub pump 9 communicate with each other by setting the switching valve 57 to the open position 57a, so the hydraulic oil accumulated in the accumulator 52 It flows into the suction port 26 of the sub pump 9, and the sub pump 9 is motor driven by the hydraulic oil. Therefore, the torque of the engine 11 is assisted by the sub pump 9. Thereby, the torque of the engine 11 can be reduced, and the fuel consumption can be reduced.

  Further, in the present embodiment, the necessary inclination angle of the swash plate 32 of the sub pump 9 is calculated based on the target torque of the sub pump 9, the pressure on the suction side of the sub pump 9, and the pressure on the discharge side of the sub pump 9. The swash plate angle control unit 38 is controlled in accordance with the required inclination angle. Therefore, when assisting the torque of the engine 11 by the sub pump 9, the torque assist amount by the sub pump 9 is appropriately set. As a result, the operating point of the engine 11 can be made closer to the optimum point.

  Further, in the present embodiment, the swash plate angle control unit 38 is controlled so as to reduce the inclination angle of the swash plate 32 of the sub pump 9 when the pressure on the discharge side of the sub pump 9 becomes equal to or more than the specified value. For this reason, the pressure difference between the pressure of the accumulator 52 and the pressure of the lift cylinder 2 is reduced by the pressure increase of the accumulator 52 accompanying the accumulation of the hydraulic oil to the accumulator 52, so When the flow rate (regenerative flow rate) of the hydraulic oil flowing toward the lower side, the swash plate angle control unit 38 is controlled so that the inclination angle of the swash plate 32 of the sub pump 9 becomes smaller. In this case, the regenerative flow rate is further reduced, and the differential pressure between the upstream side and the downstream side of the orifice 45 is reduced, so that the drop in pilot pressure of the pilot line 49 is suppressed, and the bypass flow control valve 47 is opened. Do. Thereby, the desired descent speed of the fork 4 can be obtained.

  Also, for example, even if the rotation speed of the engine 11 is lower than a predetermined value and the flow rate of the hydraulic oil discharged from the discharge port 27 of the sub pump 9 can not be ensured, the desired descent speed of the fork 4 can not be ensured. Since the bypass flow control valve 47 is opened by controlling the swash plate angle control unit 38 so that the inclination angle of the swash plate 32 of the sub pump 9 is reduced, a desired descent speed of the fork 4 can be obtained. it can.

  Further, in the present embodiment, when the pressure on the discharge side of the sub pump 9 becomes equal to or higher than the specified value, or when the rotational speed of the engine 11 is lower than the predetermined value, the inclination angle of the swash plate 32 of the sub pump 9 is reduced. Thus, the displacement of the sub pump 9 can be easily and reliably reduced.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the swash plate angle control unit 38 is controlled to reduce the inclination angle of the swash plate 32 of the sub pump 9 when the pressure on the discharge side of the sub pump 9 becomes equal to or higher than the specified value. It is not limited to When the pressure on the discharge side of the sub pump 9 becomes equal to or higher than a specified value, the switching valve 53 may be switched from the open position 53a to the closed position 53b, as shown in FIG. Even in this case, the regenerative flow rate decreases, and the flow control valve for bypass 47 operates in the valve opening state as the pressure loss at the orifice 45 decreases, so that the desired descent speed of the fork 4 can be obtained.

  Moreover, although the hydraulic drive 1 of the said embodiment is provided with switching valve 53,55,57, it is not restricted in particular in the form in particular, As FIG. 8 shows, said switching valve 53,55,57 The functions of the above may be integrated as one switching valve. In this case, the number of parts can be reduced and space can be saved.

  In FIG. 8, the hydraulic drive system 1 includes an electromagnetic switching valve 80. The switching valve 80 is disposed between the discharge port 27 of the sub pump 9 and the accumulator 52, between the discharge port 27 of the sub pump 9 and the tank 7, and between the accumulator 52 and the suction port 26 of the sub pump 9.

  In the switching valve 80, the positions 80a to 80c are switched. The position 80 a communicates the discharge port 27 of the sub pump 9 with the accumulator 52, cuts off the discharge port 27 of the sub pump 9 from the tank 7, and cuts off the accumulator 52 and the suction port 26 of the sub pump 9. The position 80 b is a position where the discharge port 27 of the sub pump 9 and the accumulator 52 are shut off, the discharge port 27 of the sub pump 9 and the tank 7 are communicated, and the accumulator 52 and the suction port 26 of the sub pump 9 are shut off. The position 80 c is a position where the discharge port 27 of the sub pump 9 and the accumulator 52 are shut off, the discharge port 27 of the sub pump 9 and the tank 7 are communicated, and the accumulator 52 and the suction port 26 of the sub pump 9 are communicated.

  The switching valve 80 has a first valve portion in which an open position for communicating the discharge port 27 and the accumulator 52 of the sub pump 9 and a closed position for closing the discharge port 27 and the accumulator 52 for the sub pump 9. And a second valve portion in which the open position communicating the tank 7 and the closed position closing the discharge port 27 of the sub pump 9 and the tank 7 are opened, and the open position communicating the accumulator 52 and the suction port 26 of the sub pump 9 And a closed position at which the suction port 26 of the sub pump 9 is shut off.

  When a control signal is not input to the solenoid operation units 80d and 80e of the switching valve 80, the switching valve 80 is maintained at the position 80b. When a control signal is input to the solenoid operation unit 80d of the switching valve 80, the switching valve 80 is switched to the position 80a. When a control signal is input to the solenoid operation unit 80e of the switching valve 80, the switching valve 80 is switched to the position 80c.

  In the above embodiment, the sub pump 9 is a swash plate type variable displacement pump, but the sub pump 9 is not particularly limited thereto, and may be a vane type variable displacement pump or a gear type variable displacement pump.

  Moreover, in the said embodiment, although the forklift does not have the attachment cylinder which drives an attachment, this invention is applicable also to the forklift provided with the attachment cylinder.

  Furthermore, although the hydraulic drive 1 of the above-described embodiment is mounted on a forklift, the present invention is applicable to hydraulic machines such as a hydraulic lifting device as well as cargo handling vehicles other than forklifts.

  DESCRIPTION OF SYMBOLS 1 ... Hydraulic drive device, 2 ... Lift cylinder (hydraulic cylinder), 4 ... Fork (lifting / lowering object), 5 ... Lift operation lever (operation part), 7 ... Tank, 8 ... Main pump, 9 ... Sub pump, 11 ... Engine, 26: suction port, 27: discharge port, 32: swash plate, 38: swash plate angle control unit (capacity control unit), 41: common hydraulic fluid flow channel (first hydraulic fluid flow channel), 42: hydraulic fluid regenerative flow Path (first hydraulic fluid channel), 43: Hydraulic fluid bypass channel (second hydraulic fluid channel), 44: operation valve, 45: orifice, 46: check valve, 47: flow control valve for bypass (flow rate Control valve) 47a: pilot operation unit (first pilot operation unit) 47b: pilot operation unit (second pilot operation unit) 49: pilot line (first pilot line) 50: pilot line (second pilot line ) 52: Accumulator, 53: Switching valve (first valve portion), 53a: Open position, 53b: Closed position, 55: Switching valve (second valve portion), 55a: Open position, 55b: Closed position, 57: Switching valve (Third valve portion) 57a: open position 57b: closed position 62: rotational speed sensor (rotational speed detection portion) 63: suction side pressure sensor (suction side pressure detection portion) 64: discharge side pressure sensor ( Discharge side pressure detection unit) 67 ... switching valve control unit (valve control unit) 68 ... lowering control unit 69 ... torque assist control unit 70 ... capacity reduction control unit 80 ... switching valve (first valve unit, first 2 valve part, 3rd valve part).

Claims (7)

A hydraulic cylinder that raises and lowers an elevating object by supply and discharge of hydraulic oil;
A tank for storing the hydraulic oil;
A main pump which is driven by an engine and sucks in the hydraulic fluid from the tank and supplies it to the hydraulic cylinder;
A variable displacement sub pump driven by the engine;
A first hydraulic fluid flow path which connects the suction port of the sub pump and the hydraulic cylinder, and in which the hydraulic fluid from the hydraulic cylinder flows toward the sub pump;
A control valve disposed in the first hydraulic fluid flow path and controlling the flow of the hydraulic fluid in accordance with the amount of operation of a control unit for lowering the elevating object;
An accumulator for accumulating the hydraulic oil discharged from the discharge port of the sub pump;
A displacement control unit that controls the displacement of the sub pump;
A rotation number detection unit that detects the rotation number of the engine;
The target descent speed of the elevator is determined based on the operation amount of the operation unit, and the sub pump needs to be determined based on the target descent speed of the elevator and the engine rotational speed detected by the rotational speed detector. And a lowering control unit that calculates a displacement and controls the displacement control unit in accordance with the required displacement of the sub pump. A second hydraulic fluid flow path connecting the tank with the suction port of the sub pump in the first hydraulic fluid flow path and the operation valve, and flowing the hydraulic fluid from the hydraulic cylinder toward the tank When,
A flow control valve disposed in the second hydraulic fluid flow path and controlling a flow rate of the hydraulic fluid returning to the tank;
And an orifice disposed between a connection point of the first hydraulic fluid channel with the second hydraulic fluid channel and the suction port of the sub pump.
The flow control valve has a first pilot operating portion acting on the side closing the flow control valve, and a second pilot operating portion acting on the side opening the flow control valve, and the operation from the hydraulic cylinder A pilot flow control valve that adjusts the opening degree according to the pressure difference that occurs when oil passes through the operation valve,
The first pilot operating portion is connected between the hydraulic cylinder and the operation valve in the first hydraulic fluid flow path via a first pilot line,
The second pilot operation portion is connected between the orifice in the first hydraulic fluid flow path and the suction port of the sub pump via a second pilot line. Hydraulic drive. A first valve portion disposed between the discharge port of the sub pump and the accumulator, and switched between an open position communicating the discharge port and the accumulator and a closed position blocking the discharge port and the accumulator;
A second valve portion disposed between the discharge port of the sub pump and the tank, and switched between an open position for communicating the discharge port and the tank, and a closed position for blocking the discharge port and the tank;
A discharge-side pressure detection unit that detects the pressure on the discharge side of the sub pump;
A valve control unit that determines the pressure accumulation state of the hydraulic fluid in the accumulator based on the pressure on the discharge side of the sub pump detected by the discharge side pressure detection unit, and controls the first valve unit and the second valve unit The hydraulic drive according to claim 2, further comprising: A third valve unit disposed between the accumulator and the suction port of the sub pump, the open position communicating the accumulator and the suction port, and the closed position blocking the accumulator and the suction port;
It further comprises a check valve disposed between the orifice in the first hydraulic fluid flow path and the suction port of the sub pump, and permitting only the flow of the hydraulic fluid from the orifice side to the sub pump side. ,
The valve control unit determines the pressure accumulation state of the hydraulic oil in the accumulator based on the pressure on the discharge side of the sub pump detected by the discharge side pressure detection unit, and the first valve unit and the second valve unit The hydraulic drive system according to claim 3, wherein the third valve portion is controlled. A suction-side pressure detection unit that detects a pressure on the suction side of the sub pump;
Required capacity of the sub pump based on the target torque of the sub pump, the pressure on the suction side of the sub pump detected by the suction side pressure detection unit, and the pressure on the discharge side of the sub pump detected by the discharge pressure detection unit 5. The hydraulic drive system according to claim 4, further comprising: a torque assist control unit that calculates the displacement control unit and controls the displacement control unit according to the required displacement of the sub pump. A discharge-side pressure detection unit that detects the pressure on the discharge side of the sub pump;
And a capacity reduction control unit for controlling the capacity control unit to reduce the capacity of the sub pump when the pressure on the discharge side of the sub pump detected by the discharge pressure detection section exceeds a specified value. The hydraulic drive according to claim 2, comprising: The sub pump is a swash plate type variable displacement pump,
The capacity reduction control unit controls the capacity control unit to reduce the inclination angle of the swash plate of the sub pump when the pressure on the discharge side of the sub pump becomes equal to or more than the predetermined value. The hydraulic drive system according to claim 6.