JP6907899B2 - Hydraulic drive - Google Patents

Description

The present invention relates to a hydraulic drive device.

As a conventional hydraulic drive device, for example, the technique described in Patent Document 1 is known. The hydraulic drive device described in Patent Document 1 is arranged between a hydraulic cylinder, a tank, a charge pump that supplies hydraulic oil to the hydraulic cylinder, and the charge pump and the tank and the hydraulic cylinder, and from the charge pump to the hydraulic cylinder. A cylinder control valve assembly with a control valve that controls the flow rate of the hydraulic oil supplied and a control valve that controls the flow rate of the hydraulic oil returned from the hydraulic cylinder to the tank, and recovers position energy when the hydraulic cylinder is under overload conditions. It is equipped with an energy recovery device. The energy recovery device includes an accumulator that stores the pressurized hydraulic oil from the hydraulic cylinder and an accumulator discharge valve that controls the flow of the pressurized hydraulic oil from the accumulator to the charge pump.

Special Table 2009-510358 Gazette

In the above-mentioned prior art, the potential energy related to the operation of the appliance (elevating object) is recovered by storing the pressurized hydraulic oil from the hydraulic cylinder in the accumulator, but there are the following problems. That is, when the lifting object is lowered with no load on the lifting 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 that the desired lowering speed cannot be obtained. In addition, even when the lifting object is lowered with a load on the lifting object, the pressure on the accumulator side is higher than the pressure on the cylinder head side of the hydraulic cylinder depending on the accumulator pressure accumulation state, and the hydraulic oil flows from the hydraulic cylinder to the accumulator. Since it does not flow, the desired descent speed cannot be obtained.

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

The hydraulic drive device of one aspect of the present invention is driven by a hydraulic cylinder that raises and lowers an elevating object by supplying and discharging hydraulic oil, a tank that stores hydraulic oil, and an engine, and sucks hydraulic oil from the tank and supplies it to the hydraulic cylinder. The first hydraulic oil flow path, which connects the main pump, the variable capacity type 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, and the first 1 An operating valve that is arranged in the hydraulic oil flow path and controls the flow of hydraulic oil according to the amount of operation of the operation unit for lowering the lifting object, and an accumulator that accumulates the hydraulic oil discharged from the discharge port of the sub pump. The target descent speed of the lifting object is determined based on the capacity control unit that controls the capacity of the sub-pump, the rotation speed detecting unit that detects the rotation speed of the engine, and the operation amount of the operating unit. It is characterized by including a lowering control unit that calculates the required capacity of the sub-pump based on the required capacity of the sub-pump based on the required capacity of the sub-pump and controls the capacity control unit according to the required capacity of the sub-pump.

In such a hydraulic drive device, when the moving object is lowered by the operation unit, the hydraulic cylinder operates so that the lifting object is lowered, and the hydraulic oil from the hydraulic cylinder sub-pumps the first hydraulic oil flow path. 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. As a result, the potential energy of the lifting object is recovered. At this time, the target descending speed of the elevating object is determined based on the operation amount of the operation unit, and the required capacity of the sub-pump is calculated based on the target descending speed of the elevating object and the engine speed, according to the required capacity of the sub-pump. The capacity control unit is controlled. Therefore, the desired descending speed of the elevating object can be obtained. As described above, the potential energy of the elevating object can be recovered while maintaining the desired descending speed of the elevating object.

The hydraulic drive device connects the suction port of the sub pump and the operation valve in the first hydraulic oil flow rate to the tank, and the hydraulic oil from the hydraulic cylinder flows toward the tank, and the second hydraulic oil flow rate and the second. 2 Between the flow control valve arranged in the hydraulic oil flow path and controlling the flow rate of the hydraulic oil returning to the tank, the connection point between the second hydraulic oil flow path in the first hydraulic oil flow path, and the suction port of the sub pump. The flow rate control valve further includes a first pilot operating unit that acts on the side that closes the flow rate control valve, and a second pilot operating unit that acts on the side that opens the flow rate control valve. , A pilot type flow control valve that adjusts the opening degree according to the pressure difference generated when the hydraulic oil from the hydraulic cylinder passes through the operation valve, and is between the hydraulic cylinder and the operation valve in the first hydraulic oil flow path. The first pilot operation unit is connected via the first pilot line, and the second pilot operation unit is connected to the second pilot operation unit between the orifice and the suction port of the sub pump in the first hydraulic oil flow rate. It may be connected via.

When the load loaded on the lifting object is heavy, the pressure of the hydraulic cylinder is high, so that the hydraulic oil from the hydraulic cylinder easily flows toward the sub-pump. At this time, since a differential pressure is generated between the upstream side and the downstream side of the orifice, the pilot pressure of the second pilot line (the pressure on the downstream side of the orifice) is lower than the pressure on the upstream side of the orifice by the differential pressure of the orifice. .. Therefore, in addition to the pressure difference generated when passing through the operating valve, the pilot pressure of the first pilot line becomes higher than the pilot pressure of the second pilot line by the differential pressure of the orifice, so that the flow rate is higher than that without the orifice. The control valve is easily driven in the closing direction. Therefore, the hydraulic oil from the hydraulic cylinder flows preferentially to the sub-pump side, and the hydraulic oil is accumulated in the accumulator. As a result, the efficiency of recovering the potential energy of the lifting object is improved. On the other hand, when the load loaded on the lifting object is light, the pressure of the hydraulic cylinder is low, so that the hydraulic oil from the hydraulic cylinder does not easily flow toward the sub pump. Therefore, since a differential pressure is unlikely to occur between the upstream side and the downstream side of the orifice, a decrease in the pilot pressure of the second pilot line is suppressed. Therefore, the force for driving the flow control valve in the closing direction weakens, so that the flow control valve opens and the hydraulic oil from the hydraulic cylinder flows to the flow control valve side. Thereby, the desired descending speed of the elevating object can be obtained.

The hydraulic drive device is arranged between the discharge port of the sub-pump and the accumulator, and has a first valve portion that switches between an open position for communicating the discharge port and the accumulator and a closed position for shutting off the discharge port and the accumulator, and the discharge of the sub-pump. The second valve, which is located between the outlet and the tank and switches between the open position for communicating the discharge port and the tank and the closed position for shutting off the discharge port and the tank, and the discharge side for detecting the pressure on the discharge side of the sub pump. A pressure detection unit and a valve control unit that determines the accumulator's hydraulic oil accumulation state based on the pressure on the discharge side of the subpump detected by the discharge side pressure detection unit and controls the first valve unit and the second valve unit. May be further 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 cut off, the hydraulic oil accumulated in the accumulator is prevented from flowing back to the sub pump.

The hydraulic drive system is arranged between the accumulator and the suction port of the sub-pump, and has a third valve portion that switches between an open position for communicating the accumulator and the suction port and a closed position for shutting off the accumulator and the suction port, and the first operation. A check valve, which is arranged between the orifice in the oil flow path and the suction port of the sub pump and allows only the flow of hydraulic oil from the orifice side to the sub pump side, is further provided, and the valve control unit detects the pressure on the discharge side. The pressure accumulator state of the hydraulic oil in the accumulator may be determined based on the pressure on the discharge side of the sub-pump detected by the unit, and the first valve portion, the second valve portion, and the third valve portion may be controlled.

When accumulating hydraulic oil in the accumulator, by closing the third valve, the accumulator and the suction port of the sub pump are shut off, so the hydraulic oil accumulated in the accumulator becomes the suction port of the sub pump. It is prevented from flowing in. For example, when the lifting object is raised, the accumulator and the suction port of the sub pump are communicated with each other by opening the third valve portion, so that the hydraulic oil accumulated in the accumulator flows into the suction port of the sub pump, and the hydraulic oil thereof. Drives the sub-pump to the motor. Therefore, the engine torque is assisted by the sub pump. As a result, the torque of the engine can be reduced and the fuel consumption can be reduced.

The hydraulic drive device 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. Torque assist that calculates the required capacity 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-side pressure detector, and controls the capacity control unit according to the required capacity of the sub-pump. A control unit may be further provided.

In such a configuration, when the sub-pump assists the torque of the engine, the torque assist amount by the sub-pump is appropriately set. As a result, the operating point of the engine can be brought close to the optimum point.

The hydraulic drive system measures the capacity of the sub-pump when the pressure on the discharge side of the sub-pump is detected by the pressure detection unit on the discharge side and the pressure on the discharge side of the sub-pump detected by the pressure detection unit on the discharge side exceeds the specified value. A capacity reduction control unit that controls the capacity control unit so as to make it smaller may be further provided.

In such a configuration, for example, the pressure difference between the accumulator pressure and the hydraulic cylinder pressure becomes smaller due to the pressure increase of the accumulator due to the accumulation of hydraulic oil in the accumulator, so that the first hydraulic oil flow path is directed to the sub pump. When the flow rate of the hydraulic oil flowing is reduced, the capacity control unit is controlled so that the capacity of the sub pump is reduced. In this case, the flow rate of the hydraulic oil flowing through the first hydraulic oil flow path is further reduced, and the differential pressure between the upstream side and the downstream side at the orifice is reduced, so that the decrease in the pilot pressure of the second pilot line is suppressed. , The flow control valve opens. Thereby, the desired descending speed of the elevating object can be obtained.

The sub-pump is a swash plate type variable capacity pump, and the capacity reduction control unit sets the capacity control unit so that the tilt angle of the swash plate of the sub pump is reduced when the pressure on the discharge side of the sub pump exceeds the specified value. You may control it. By reducing the inclination angle of the swash plate of the sub pump in this way, the capacity of the sub pump can be easily and surely reduced.

According to the present invention, the potential energy of the elevating object can be recovered while maintaining the desired descending speed of the elevating object.

FIG. 1 is a hydraulic circuit diagram showing a hydraulic drive device 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 the hydraulic drive device including the functional block 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. 5A is a hydraulic circuit diagram showing the flow of hydraulic oil when the hydraulic oil from the lift cylinder is accumulated in the accumulator when the fork is lowered, and FIG. 5B is an inclination of the sloping plate of the subpump. It is a hydraulic circuit diagram which shows the flow of the hydraulic oil when the hydraulic oil from a lift cylinder is bypassed by reducing an angle. FIG. 6 is a timing diagram 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 modified example 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 figure, the same or equivalent elements are designated by the same reference numerals, and duplicate description will be omitted.

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

The hydraulic drive device 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 (elevating object) by supplying and discharging hydraulic oil. The tilt cylinder 3 is a hydraulic cylinder that tilts a mast (not shown) by supplying and discharging hydraulic oil. The lift cylinder 2 operates by operating the lift operating lever 5 (operating unit) for raising and lowering (raising or lowering) the fork 4. The tilt cylinder 3 is operated by operating the tilt operating lever 6 for tilting (forward tilting or backward tilting) the mast.

Further, the hydraulic drive device 1 includes a tank 7 for storing hydraulic oil, a main pump 8, and a sub-pump 9 arranged coaxially with the main pump 8. The main pump 8 and the sub pump 9 are directly connected to the engine 11 via a gear 10 and are driven by the engine 11. The main pump 8 is a hydraulic pump that can rotate in one direction. The main pump 8 sucks 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 8a of the main pump 8 and the head chamber 2a of the lift cylinder 2 are connected via a hydraulic oil supply flow path 12. An operation valve 13 for raising the lift is provided in the hydraulic oil supply flow path 12. A check valve 14 that allows only the flow of hydraulic oil from the operating valve 13 side to the lift cylinder 2 side is provided between the operating valve 13 and the lift cylinder 2 in the hydraulic oil supply flow path 12.

The operation valve 13 is composed of an electromagnetic proportional valve. The operation valve 13 controls the flow of hydraulic oil according to the operation amount of the lift operation lever 5. An ascending operation signal from the controller 65 (described later) is input to the solenoid operating unit 13a of the operating valve 13. The ascending operation signal is a current command value corresponding to the operating amount of the ascending operation of the lift operating lever 5.

The operating valve 13 is normally in a closed position (not shown) that blocks the flow of hydraulic oil from the main pump 8 to the lift cylinder 2. When an ascending operation signal is input to the solenoid operating unit 13a of the operating valve 13, the operating valve 13 opens at an opening degree corresponding to the ascending operation signal. Then, hydraulic oil is supplied from the main pump 8 to the head chamber 2a of the lift cylinder 2, and the lift cylinder 2 extends, so that the fork 4 rises.

A tilt operating valve 16 is connected between the main pump 8 and the operating valve 13 in the hydraulic oil supply flow path 12 via the hydraulic oil supply flow path 15. The hydraulic oil supply flow path 15 is provided with a check valve 17 that allows only the flow of hydraulic oil from the main pump 8 side to the operation valve 16 side. The operation valve 16 and the head chamber 3a and the rod chamber 3b of the tilt cylinder 3 are connected to each other via the hydraulic oil supply flow paths 18 and 19, respectively.

The operation valve 16 is composed of an electromagnetic proportional valve. The operation valve 16 controls the flow of hydraulic oil according to the operation amount of the tilt operation lever 6. A forward tilt operation signal from the controller 65 (described later) is input to the solenoid operation unit 16a of the operation valve 16, and a backward tilt operation signal from the controller 65 is input to the solenoid operation unit 16b of the operation valve 16. The forward tilt operation signal is a current command value according to the operation amount of the forward tilt operation of the tilt operation lever 6, and the backward tilt operation signal is a current command value according to the operation amount of the backward tilt operation of the tilt operation lever 6. be.

The operating valve 16 is normally in a closed position (not shown) that blocks the flow of hydraulic oil from the main pump 8 to the tilt cylinder 3. When a forward tilt operation signal is input to the solenoid operation unit 16a of the operation valve 16, the operation valve 16 opens at an opening degree corresponding to the forward tilt operation signal. Then, hydraulic oil is supplied from the main pump 8 to the head chamber 3a of the tilt cylinder 3, and the tilt cylinder 3 extends, so that the mast (not shown) tilts forward. When a backward tilt operation signal is input to the solenoid operation unit 16b of the operation valve 16, the operation valve 16 opens at an opening degree corresponding to the backward tilt operation signal. Then, hydraulic oil 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 flow path 12 via the hydraulic oil discharge flow path 20. An unload valve 21 is provided in the hydraulic oil discharge flow path 20. The operation valve 16 is connected to the hydraulic oil discharge flow path 20 via the hydraulic oil discharge flow path 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 rotary shaft 25 is rotationally driven by the engine 11. The rear casing 24 is provided with a suction port 26 for sucking the hydraulic oil (see also FIG. 1) and a discharge port 27 for discharging the hydraulic oil (see also FIG. 1).

A cylinder block 28 is attached to the rear casing 24. The cylinder block 28 is integrally rotatably fixed to the rotating shaft 25. A plurality of cylinder bores 29 are provided around the rotating shaft 25 in the cylinder block 28. A plunger 30 is housed in each cylinder bore 29 so as to be reciprocating.

A valve plate 31 is arranged between the cylinder block 28 and the rear casing 24. The valve plate 31 is provided with a suction hole 31a for communicating the suction port 26 and the cylinder bore 29, and a discharge hole 31b for communicating the discharge port 27 and the cylinder bore 29. As a result, 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 passes through the discharge hole 31b by the pumping action and is sent from the discharge port 27. It is discharged.

A swash plate 32 (see also FIG. 1) that defines the stroke of the plunger 30 is arranged in the main casing 23. The swash plate 32 is provided with a through hole 32a through which the rotating shaft 25 penetrates. 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 pressing 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.

Further, 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 swash plate angle control piston 36 is housed in the piston accommodating portion 35. The tip 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 accommodating portion 35.

A spring 37 urging the swash plate 32 side is arranged on the opposite side of the swash plate angle control piston 36 with respect to the swash plate 32 in the main casing 23. 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 of the spring 37 and the load of the swash plate angle control piston 36 are balanced.

A swash plate angle control unit 38 (see FIG. 1) that controls the pressure (load) applied to the swash plate angle control piston 36 is connected to the swash plate angle control pressure port 34. 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 the capacity of the sub pump 9 is controlled. The inclination angle α of the swash plate 32 is the angle of the swash plate 32 with respect to the surface perpendicular to the rotation axis 25. The swash plate angle control unit 38 constitutes a capacity control unit that controls the capacity of the sub pump 9.

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

Further, the hydraulic drive device 1 is connected between the hydraulic oil common flow path 41 connected in the vicinity of the lift cylinder 2 in the hydraulic oil supply flow path 12 and the sub pump 9 and the tank 7 in the hydraulic oil suction flow path 39. The hydraulic oil regeneration flow path 42 and the hydraulic oil bypass flow path 43 connecting the connection point S between the hydraulic oil common flow path 41 and the hydraulic oil regeneration flow path 42 and the tank 7 are provided. The hydraulic oil common flow path 41 and the hydraulic oil regenerative flow path 42 connect the suction port 26 of the sub pump 9 and the lift cylinder 2, and the hydraulic oil from the lift cylinder 2 flows toward the sub pump 9. Consists of. The hydraulic oil bypass flow path 43 connects the suction port 26 of the sub pump 9 in the first hydraulic oil flow path, the operation valve 44 (described later), and the tank 7, and the hydraulic oil from the lift cylinder 2 is transferred to the tank 7. It constitutes a second hydraulic oil flow path that flows toward.

An operation valve 44 for lowering the lift is provided in the hydraulic oil common flow path 41. The operation valve 44 controls the flow of hydraulic oil according to the operation amount of the lowering operation of the lift operation lever 5. The operation valve 44 is composed of an electromagnetic proportional valve. A lowering operation signal from the controller 65 (described later) is input to the solenoid operation unit 44a of the operation valve 44. The lowering operation signal is a current command value corresponding to the operating amount of the lowering operation of the lift operation lever 5.

The operation valve 44 is normally in a closed position (not shown) that blocks the flow of hydraulic oil from the head chamber 2a of the lift cylinder 2. When a lowering operation signal is input to the solenoid operating unit 44a of the operating valve 44, the operating 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 oil flows out from the head chamber 2a of the lift cylinder 2. Then, the hydraulic oil from the lift cylinder 2 passes through the operation valve 44.

An orifice 45 is provided in the hydraulic oil regeneration flow path 42. That is, the orifice 45 is arranged between the connection point S with the hydraulic oil bypass flow path 43 in the first hydraulic oil flow path (described above) and the suction port 26 of the sub pump 9. A check valve 46 is provided between the orifice 45 in the hydraulic oil regenerative flow path 42 and the suction port 26 of the sub pump 9 to allow only the flow of hydraulic oil from the orifice 45 side to the sub pump 9 side.

A bypass flow rate control valve 47 is provided in the hydraulic oil bypass flow path 43. The bypass flow rate control valve 47 controls the flow rate of the hydraulic oil returning from the head chamber 2a of the lift cylinder 2 to the tank 7. The bypass flow rate control valve 47 is a pilot type flow rate 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 rate control valve 47 functions as a throttle according to the opening degree, and the opening degree is adjusted between the fully open position (not shown) that allows the flow of hydraulic oil and the fully closed position that blocks the flow of hydraulic oil. NS.

The bypass flow rate control valve 47 includes a pilot operation unit 47a (first pilot operation unit) acting on the side that closes the bypass flow control valve 47 and a pilot operation unit 47b (acting on the side that opens the bypass flow control valve 47). It has a second pilot operation unit). Further, the bypass flow rate control valve 47 has a spring 48 that urges the bypass flow rate control valve 47 to open.

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

The bypass flow rate control valve 47 controls the flow rate of the hydraulic oil so that the pressure difference (front-rear differential pressure) generated on the upstream side and the downstream side of the operation valve 44 becomes constant. The differential pressure at this time is called 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 the flow rate control valve 47 for bypass controls the flow rate of the hydraulic oil to increase. In this way, the flow rate of the hydraulic oil flowing through the bypass flow rate control valve 47 differs depending on the amount of operation 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 through the hydraulic oil bypass flow path 43 when the hydraulic oil is difficult to flow into the hydraulic oil regenerative flow path 42 because the load loaded on the fork 4 is light. be. As a result, the desired operating speed of the lift cylinder 2 can be secured.

Specifically, when the hydraulic oil does not easily flow into the hydraulic oil regenerative flow path 42 because the load loaded on the fork 4 is light, 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 oil flowing through the hydraulic oil bypass flow path 43 so that the front-rear differential pressure of the operation valve 44 becomes constant.

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

An accumulator 52 is connected to the discharge port 27 of the sub pump 9 via a hydraulic oil accumulator flow path 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. It is preferable that the volume of the accumulator 52 is sufficiently large so that all the hydraulic oil from the lift cylinder 2 can be received by the accumulator 52. Since the oil is discharged to the tank 7 through the hydraulic oil bypass flow path 43, there is no operational problem.

An electromagnetic switching valve 53 (first valve portion) is provided in the hydraulic oil accumulating flow path 51. That is, the switching valve 53 is arranged 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 for communicating the discharge port 27 and the accumulator 52 and a closed position 53b for shutting off the discharge port 27 and the accumulator 52 by a control signal from the controller 65 (described later).

When accumulating hydraulic oil in the accumulator 52, the switching valve 53 is set to the open position 53a so that the discharge port 27 of the sub pump 9 and the accumulator 52 communicate with each other. When the hydraulic oil is not accumulated in the accumulator 52, the switching valve 53 is set to the closed position 53b (not shown) to shut off the discharge port 27 of the sub pump 9 and the accumulator 52. As a result, 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 oil accumulator flow path 51 are connected to the tank 7 via the hydraulic oil discharge flow path 54. An electromagnetic switching valve 55 (second valve portion) is provided in the hydraulic oil discharge flow path 54. That is, the switching valve 55 is arranged 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 shutting off the discharge port 27 and the tank 7 by a control signal from the controller 65 (described later).

When accumulating hydraulic oil in the accumulator 52, the switching valve 55 is set to the closed position 55b (not shown) to shut off the discharge port 27 of the sub pump 9 and the tank 7. When the hydraulic oil is not accumulated in the accumulator 52, the switching valve 55 is set to the open position 55a so that the discharge port 27 of the sub pump 9 and the tank 7 communicate with each other. As a result, the sub pump 9 is unloaded, so that the fuel consumption is reduced.

The accumulator 52 is connected to the hydraulic oil regeneration flow path 42 via the hydraulic oil assist flow path 56. Specifically, the hydraulic oil assist flow path 56 includes the switching valve 53 and the accumulator 52 in the hydraulic oil accumulator flow path 51, the check valve 46 in the hydraulic oil regenerative flow path 42, and the suction port 26 of the sub pump 9. Connect between. An electromagnetic switching valve 57 (third valve portion) is provided in the hydraulic oil assist flow path 56. That is, the switching valve 57 is arranged between the accumulator 52 and the suction port 26 of the sub pump 9. The switching valve 57 switches between an open position 57a that communicates the accumulator 52 and the suction port 26 and a closed position 57b that shuts off the accumulator 52 and the suction port 26.

When accumulating hydraulic oil in the accumulator 52, the switching valve 57 is set to the closed position 57b (not shown) to shut off the accumulator 52 and the suction port 26 of the sub pump 9. When the hydraulic oil is not accumulated in the accumulator 52, the switching valve 57 is set to the open position 57a so that the accumulator 52 and the suction port 26 of the sub pump 9 communicate with each other.

When the fork 4 is lowered, the hydraulic oil corresponding to the operation amount of the lift operation lever 5 flows through the hydraulic oil common flow path 41. Here, when the load loaded on the fork 4 is heavy, a differential pressure is generated at the orifice 45 as described above, so that the hydraulic oil flows 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 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, so that 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 cargo is recovered by the accumulator 52.

When the fork 4 is raised 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, so that the pressurized hydraulic oil accumulated in the accumulator 52 operates. It is supplied to the suction port 26 of the sub pump 9 through the oil assist flow path 56 and the hydraulic oil regeneration flow path 42. Then, the sub-pump 9 is rotated by the pressurized hydraulic oil to drive the motor. As a result, 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 brought close to the optimum point. The timing of driving the sub-pump 9 by the pressurized hydraulic oil is not limited to the time when the fork 4 is raised or the tilt cylinder 3 is operated, and the forklift may be running.

Further, in a state where the engine 11 is operating with a light load, hydraulic oil is accumulated in the accumulator 52 by driving the sub-pump 9 with the surplus torque of the engine 11. Then, when the engine 11 operates at a high load, the hydraulic oil accumulated in the accumulator 52 is reused as described above to drive the sub pump 9 as a motor. As a result, fuel consumption can be improved.

Further, as shown in FIG. 3, the hydraulic drive device 1 includes a lift operation sensor 60, a tilt operation sensor 61, a rotation speed sensor 62 (rotation 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 operation amount of the lift operation lever 5. The tilt operation sensor 61 is a sensor that detects the operation direction and the 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 side 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 oil accumulator flow path 51.

The controller 65 includes a CPU, RAM, 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 operation valve control unit 66 controls the operation valve 13 for raising the lift and the operation valve 44 for lowering the lift based on the detection value of the lift operation sensor 60, and also controls the operation valve 44 for tilting based on the detection value of the tilt operation sensor 61. Controls the operating valve 16.

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

The switching valve control unit 67 determines the accumulated pressure 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 valves 53, 55, 57.

Specifically, the switching valve control unit 67 determines whether or not a predetermined amount (for example, a full state) of hydraulic oil has been accumulated in the accumulator 52 based on the pressure on the discharge side of the sub pump 9. Then, when a predetermined amount of hydraulic oil is not accumulated in the accumulator 52, the switching valve control unit 67 outputs a control signal for setting the switching valve 53 to the open position 53a to the solenoid operating unit 53c of the switching valve 53. , A control signal for setting the switching valve 55 to the closed position 55b is output to the solenoid operating section 55c of the switching valve 55, and a control signal for setting the switching valve 57 to the closed position 57b is sent to the solenoid operating section 53c of the switching valve 57. Output (state in FIG. 5A). 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 a predetermined amount of hydraulic oil is accumulated in the accumulator 52, the switching valve control unit 67 outputs a control signal for setting the switching valve 53 to the closed position 53b to the solenoid operating unit 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 section 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 section 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 lowering control unit 68 determines the target lowering speed of the fork 4 based on the operation amount of the lowering operation of the lift operation lever 5 detected by the lift operation sensor 60, and detects it by the target lowering speed of the fork 4 and the rotation speed sensor 62. The required tilt angle of the swash plate 32 of the sub pump 9 when the fork 4 is lowered is calculated based on the required rotation speed of the engine 11, and the slop plate angle control unit 38 is controlled according to the required tilt angle of the swash plate 32. do. The required tilt angle of the swash plate 32 of the sub pump 9 corresponds to the required capacity of the sub pump 9.

Specifically, the lowering control unit 68 controls the inclination angle of the swash plate 32 as follows. Although the effects of pump efficiency and temperature are omitted for the sake of simplification of the description, the inclination angle of the swash plate 32 is actually controlled by correcting the pump efficiency and temperature.

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

ｄｐ：プランジャ径（図２参照）、Ｒ：シリンダブロック軸心とプランジャ軸心との間の距離（図２参照）、ｎ：プランジャの本数、α：斜板の傾斜角度（図２参照） In equation (1), Vp is the push-out volume [cc / rev], and N is the engine speed. The push-out 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: Inclined angle of sloping plate (see FIG. 2)

Substituting Eq. (2) into Eq. (1), the relationship between the flow rate of the variable displacement pump and the tilt angle of the swash plate is expressed by the following equation.

The lowering control unit 68 determines the target lowering speed of the fork 4 based on the operation amount of the lowering operation of the lift operation lever 5, and determines the discharge flow rate of the sub pump 9 and the rotation speed of the engine 11 corresponding to the target lowering speed of the fork 4. The required tilt angle of the swash plate 32 of the sub pump 9 is calculated from the equation (3), and the swash plate angle control unit 38 is controlled so as to have the required tilt angle. As a result, the target descending speed of the fork 4 can be obtained.

FIG. 4 is a graph showing an example of the relationship between the rotation speed of the engine 11 and the discharge flow rate of the sub pump 9. In FIG. 4, when the rotation speed of the engine 11 is low, the capacity 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 increases, and the descending speed of the fork 4 increases. When the rotation speed of the engine 11 is high, the capacity of the sub pump 9 is reduced by reducing the inclination angle of the swash plate 32. Therefore, the discharge flow rate of the sub pump 9 is reduced, and the descending speed of the fork 4 is slowed down. In this way, hydraulic oil can be accumulated in the accumulator 52 while maintaining the desired descending 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 required tilt angle of the swash plate 32 of the sub pump 9 at the time of torque assist by the sub pump 9 is calculated, and the slop plate angle control unit 38 is controlled according to the required tilt angle of the swash plate 32. The required tilt angle of the swash plate 32 of the sub pump 9 corresponds to the required capacity 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 torque assist control unit 69 controls the inclination angle of the swash plate 32 as follows. Although the effects of pump efficiency and temperature are omitted for the sake of simplification of the description, the inclination angle of the swash plate 32 is actually controlled by correcting the pump efficiency and temperature.

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

Dp in Eq. (4) is the volume [cc / rad] per unit angle, and ΔP is the differential pressure [MPa] between suction and discharge. The volume Dp per unit angle has the following relationship with the push-out volume Vp.

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

To summarize this equation, 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 calculates the suction / discharge differential pressure ΔP from the suction side pressure of the sub pump 9 detected by the suction side pressure sensor 63 and the discharge side pressure of the sub pump 9 detected by the discharge side pressure sensor 64. The required tilt angle of the swash plate 32, which is the target torque, is calculated by the calculation formula (7), and the slop plate angle control unit 38 is controlled so as to have the required tilt angle. As a result, the target torque of the sub-pump 9 can be obtained.

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 side pressure sensor 64 becomes equal to or higher than a predetermined value. Controls the swash plate angle control unit 38. At this time, even if the capacity reduction control unit 70 controls the swash plate angle control unit 38 so that the inclination angle of the swash plate 32 becomes zero when the pressure on the discharge side of the sub pump 9 becomes equal to or higher than the specified value. good. The specified value is that the pressure difference between the pressure in the head chamber 2a of the lift cylinder 2 and the pressure in the accumulator 52 becomes smaller, so that the flow rate (regenerative flow rate) of the hydraulic oil flowing through the hydraulic oil regenerative flow path 42 decreases, and the fork 4 The pressure is such that the desired descending speed of the above cannot be obtained.

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, and the flow rate for bypassing becomes large. The control valve 47 is maintained in the closed state. Therefore, as shown in FIG. 5A, the hydraulic oil from the lift cylinder 2 flows in the hydraulic oil regeneration flow path 42 toward the sub pump 9. 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. The hydraulic oil discharged from the discharge port 27 of the sub pump 9 flows through the hydraulic oil accumulator flow path 51 and is accumulated in the accumulator 52.

As shown in FIG. 6, when the internal pressure of the accumulator 52 (pressure on the discharge side of the sub pump 9) rises with the accumulation of hydraulic oil in the accumulator 52 and reaches a specified value, the head chamber 2a of the lift cylinder 2 The pressure difference between the pressure (see the broken line P in FIG. 6D) and the internal pressure of the accumulator 52 (see the solid line Q in FIG. 6D) becomes small. 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 push-out volume of the sub-pump 9 is reduced, so that 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 rate control valve 47 operates in the valve open state, and the hydraulic oil from the lift cylinder 2 flows through the hydraulic oil bypass flow path 43, so that the bypass flow rate Will increase. As a result, the desired descending speed of the fork 4 can be obtained.

As described above, in the present embodiment, when the fork 4 is lowered by the lift operating lever 5, the lift cylinder 2 operates so as to lower the fork 4, and the hydraulic oil from the lift cylinder 2 operates. It flows through the oil common flow path 41 and the hydraulic oil regeneration flow path 42 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 lowering speed of the fork 4 is determined based on the operation amount of the lift operating lever 5, and the required tilt angle of the swash plate 32 of the sub pump 9 is determined based on the target lowering speed of the fork 4 and the rotation speed of the engine 11. The calculated swash plate angle control unit 38 is controlled according to the required tilt angle of the swash plate 32. Therefore, the desired descending speed of the fork 4 can be obtained. As described above, the potential energy of the fork 4 can be recovered while maintaining the desired descending 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 that the hydraulic oil from the lift cylinder 2 tends to flow toward the sub pump 9. At this time, since a differential pressure is generated between the upstream side and the downstream side of the orifice 45, the pilot pressure of the pilot line 50 (the pressure on the downstream side of the orifice 45) is the differential pressure of the orifice 45 rather than the pressure on the upstream side of the orifice 45. Only lower. Therefore, in addition to the pressure difference generated when passing through the operating valve 44, the pilot pressure of the pilot line 49 is higher than the pilot pressure of the pilot line 50 by the differential pressure of the orifice 45, so that the pressure difference is higher than the pilot pressure of the pilot line 50, as compared with the case where the orifice 45 is not provided. The bypass flow control valve 47 is likely to be driven in the closing direction. Therefore, the hydraulic oil from the lift cylinder 2 flows preferentially to the sub pump 9 side, and the hydraulic oil is accumulated in the accumulator 52. As a result, the efficiency of recovering 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 that the hydraulic oil from the lift cylinder 2 does not easily flow toward the sub pump 9. Therefore, since a differential pressure is unlikely to occur between the upstream side and the downstream side of the orifice 45, a decrease in the pilot pressure of the pilot line 50 is suppressed. Therefore, the force for driving the bypass flow rate control valve 47 in the closing direction weakens, so that the bypass flow rate control valve 47 opens and the hydraulic oil from the lift cylinder 2 flows to the bypass flow rate control valve 47 side. Become. As a result, the desired descending speed of the fork 4 can be obtained.

Further, in the present embodiment, when the switching valve 53 is controlled to be in the open position 53a and the switching valve 55 is controlled to be in the closed position 55b, the hydraulic oil discharged from the discharge port 27 of the sub pump 9 is controlled. Will be accumulated in the accumulator 52. On the other hand, when the switching valve 55 is controlled to be in the open position 55a and the switching valve 53 is controlled to be in the closed position 53b, the hydraulic oil discharged from the discharge port 27 of the sub pump 9 is discharged to the tank 7. Will be done. In this case, since the sub pump 9 is unloaded, the fuel consumption can be reduced. Further, since the discharge port 27 of the sub pump 9 and the accumulator 52 are cut 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 accumulating hydraulic oil 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, so that the accumulator 52 The hydraulic oil accumulated in the pump 9 is prevented from flowing into the suction port 26 of the sub pump 9. When the fork 4 is raised or the tilt cylinder 3 is operated, the accumulator 52 and the suction port 26 of the sub pump 9 are communicated with each other by setting the switching valve 57 to the open position 57a, so that the hydraulic oil accumulated in the accumulator 52 is collected. The sub-pump 9 flows into the suction port 26 of the sub-pump 9, and the sub-pump 9 is driven by the hydraulic oil thereof. Therefore, the torque of the engine 11 is assisted by the sub pump 9. As a result, the torque of the engine 11 can be reduced and the fuel consumption can be reduced.

Further, in the present embodiment, the required 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, and the swash plate 32 is calculated. The swash plate angle control unit 38 is controlled according to the required inclination angle. Therefore, when the sub-pump 9 assists the torque of the engine 11, the torque assist amount by the sub-pump 9 is appropriately set. As a result, the operating point of the engine 11 can be brought close to the optimum point.

Further, in the present embodiment, when the pressure on the discharge side of the sub pump 9 becomes equal to or higher than a specified value, 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. Therefore, the pressure difference between the pressure of the accumulator 52 and the pressure of the lift cylinder 2 becomes smaller due to the pressure increase of the accumulator 52 accompanying the accumulation of hydraulic oil in the accumulator 52, so that the hydraulic oil regeneration flow path 42 becomes the sub pump 9. When the flow rate (regenerative flow rate) of the hydraulic oil flowing toward the subpump 9 becomes small, the sloping plate angle control unit 38 is controlled so that the inclination angle of the swash plate 32 of the sub pump 9 becomes small. 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 decrease in the pilot pressure of the pilot line 49 is suppressed, and the bypass flow rate control valve 47 is opened. do. As a result, the desired descending speed of the fork 4 can be obtained.

Further, for example, even when 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 is maximized, the desired lowering speed of the fork 4 cannot be secured. By controlling the swash plate angle control unit 38 so that the inclination angle of the swash plate 32 of the sub pump 9 becomes small, the bypass flow rate control valve 47 opens, so that a desired lowering speed of the fork 4 can be obtained. 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 rotation 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. Thereby, the capacity of the sub-pump 9 can be easily and surely 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 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 higher than a specified value. Not limited to. When the pressure on the discharge side of the sub pump 9 becomes equal to or higher than the 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 is reduced, and the bypass flow rate control valve 47 operates in the valve open state as the pressure loss at the orifice 45 decreases, so that a desired lowering speed of the fork 4 can be obtained.

Further, although the hydraulic drive device 1 of the above embodiment includes switching valves 53, 55, 57, the present invention is not particularly limited to that form, and as shown in FIG. 8, the above switching valves 53, 55, 57 Functions may be integrated as one switching valve. In this case, the number of parts can be reduced and the space can be saved.

In FIG. 8, the hydraulic drive device 1 includes an electromagnetic switching valve 80. The switching valve 80 is arranged 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.

The position 80a to 80c of the switching valve 80 can be switched. The position 80a is a position where the discharge port 27 of the sub pump 9 and the accumulator 52 are communicated with each other, the discharge port 27 of the sub pump 9 and the tank 7 are shut off, and the accumulator 52 and the suction port 26 of the sub pump 9 are cut off. The position 80b is a position where the discharge port 27 of the sub pump 9 and the accumulator 52 are cut off, the discharge port 27 of the sub pump 9 and the tank 7 are communicated with each other, and the accumulator 52 and the suction port 26 of the sub pump 9 are cut off. The position 80c is a position where the discharge port 27 of the sub pump 9 and the accumulator 52 are cut off, the discharge port 27 of the sub pump 9 and the tank 7 are communicated with each other, and the accumulator 52 and the suction port 26 of the sub pump 9 are communicated with each other.

The switching valve 80 has a first valve portion that switches between an open position for communicating the discharge port 27 of the sub pump 9 and the accumulator 52 and a closed position for shutting off the discharge port 27 and the accumulator 52 of the sub pump 9, and the discharge port 27 of the sub pump 9. The second valve portion that switches between the open position for communicating the tank 7 and the discharge port 27 of the sub pump 9 and the closed position for shutting off the tank 7, and the open position and the accumulator 52 for communicating the accumulator 52 and the suction port 26 of the sub pump 9. It also constitutes a third valve portion that can be switched between a closed position that shuts off the suction port 26 of the sub pump 9.

When no control signal is input to the solenoid operating 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 operating 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 operating unit 80e of the switching valve 80, the switching valve 80 is switched to the position 80c.

Further, in the above embodiment, the sub-pump 9 is a swash plate type variable-capacity pump, but the sub-pump 9 is not particularly limited to that, and may be a vane-type variable-capacity pump, a gear-type variable-capacity pump, or the like.

Further, in the above embodiment, the forklift does not include an attachment cylinder for driving the attachment, but the present invention is also applicable to a forklift provided with an attachment cylinder.

Further, although the hydraulic drive device 1 of the above embodiment is mounted on a forklift, the present invention can be applied to a hydraulic machine such as a hydraulic lifting device as well as a cargo handling vehicle other than the forklift.

1 ... Hydraulic drive device, 2 ... Lift cylinder (hydraulic cylinder), 4 ... Fork (elevating object), 5 ... Lift operation lever (operation unit), 7 ... Tank, 8 ... Main pump, 9 ... Sub pump, 11 ... Engine, 26 ... Suction port, 27 ... Discharge port, 32 ... Slanted plate, 38 ... Slanted plate angle control unit (capacity control unit), 41 ... Hydraulic oil common flow path (first hydraulic oil flow path), 42 ... Hydraulic oil regeneration flow Road (first hydraulic oil flow path), 43 ... hydraulic oil bypass flow path (second hydraulic oil flow path), 44 ... operation valve, 45 ... orifice, 46 ... check valve, 47 ... bypass flow control valve (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 part), 53a ... Open position, 53b ... Closed position, 55 ... Switching valve (second valve part), 55a ... Open position, 55b ... Closed position, 57 ... Switching valve (third valve portion), 57a ... open position, 57b ... closed position, 62 ... rotation rate sensor (rotation speed detection unit), 63 ... suction side pressure sensor (suction side pressure detection unit), 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) , 2nd valve, 3rd valve).

Claims (6)

A hydraulic cylinder that raises and lowers objects by supplying and discharging hydraulic oil,
A tank for storing the hydraulic oil and
A main pump driven by an engine that sucks the hydraulic oil from the tank and supplies it to the hydraulic cylinder.
A variable displacement sub-pump driven by the engine,
A first hydraulic oil flow path that connects the suction port of the sub-pump and the hydraulic cylinder and allows the hydraulic oil from the hydraulic cylinder to flow toward the sub-pump.
An operation valve disposed in the first hydraulic oil flow path and controlling the flow of the hydraulic oil according to the amount of operation of the operation unit for lowering the elevating object.
A second hydraulic oil flow path in which the tank is connected between the suction port of the sub pump and the operation valve in the first hydraulic oil flow path, and the hydraulic oil from the hydraulic cylinder flows toward the tank. When,
A flow rate control valve arranged in the second hydraulic oil flow path and controlling the flow rate of the hydraulic oil returning to the tank,
An orifice disposed between a connection point with the second hydraulic oil flow path in the first hydraulic oil flow path and the suction port of the sub pump.
An accumulator that accumulates the hydraulic oil discharged from the discharge port of the sub pump, and
A capacity control unit that controls the capacity of the sub pump and
A rotation speed detection unit that detects the rotation speed of the engine, and
The target descent speed of the elevating object is determined based on the operation amount of the operation unit, and the sub-pump is required based on the target descent speed of the elevating object and the rotation speed of the engine detected by the rotation speed detection unit. It is provided with a lowering control unit that calculates the capacity and controls the capacity control unit according to the required capacity of the sub pump .
The flow control valve has a first pilot operating unit that acts on the side that closes the flow control valve and a second pilot operating unit that acts on the side that opens the flow control valve, and the operation from the hydraulic cylinder. It is a pilot type flow rate control valve that adjusts the opening degree according to the pressure difference generated when oil passes through the operation valve.
The hydraulic cylinder and the operation valve in the first hydraulic oil flow path and the first pilot operation unit are connected via a first pilot line.
A hydraulic drive system characterized in that the orifice in the first hydraulic oil flow path, the suction port of the sub pump, and the second pilot operating unit are connected via a second pilot line. A first valve portion that is arranged between the discharge port of the sub-pump and the accumulator and can switch between an open position for communicating the discharge port and the accumulator and a closed position for shutting off the discharge port and the accumulator.
A second valve portion which is arranged between the discharge port and the tank of the sub pump and can switch between an open position where the discharge port and the tank communicate with each other and a closed position where the discharge port and the tank are shut off.
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 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 portion and the second valve portion. hydraulic drive system according to claim 1, further comprising and. A third valve portion which is arranged between the accumulator and the suction port of the sub-pump and can switch between an open position for communicating the accumulator and the suction port and a closed position for blocking the accumulator and the suction port.
Further provided is a check valve that is disposed between the orifice in the first hydraulic oil flow path and the suction port of the sub pump and allows only the flow of the hydraulic oil 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 determines the pressure accumulation state of the hydraulic oil in the accumulator, and the first valve unit and the second valve unit. The hydraulic drive device according to claim 2, wherein the third valve portion is controlled. A suction side pressure detection unit that detects the pressure on the suction side of the sub pump,
The required capacity of the sub-pump is 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-side pressure detection unit. The hydraulic drive system according to claim 3 , further comprising a torque assist control unit that calculates the above-mentioned capacity and controls the capacity control unit according to the required capacity of the sub-pump. A discharge side pressure detection unit that detects the pressure on the discharge side of the sub pump,
When the pressure on the discharge side of the sub-pump detected by the discharge-side pressure detection unit becomes equal to or higher than a specified value, a capacity reduction control unit that controls the capacity control unit so as to reduce the capacity of the sub-pump is further added. The hydraulic drive device according to claim 1, further comprising. The sub-pump is a swash plate type variable displacement pump.
The capacity reduction control unit is characterized in that when the pressure on the discharge side of the sub pump becomes equal to or higher than the specified value, the capacity control unit is controlled so as to reduce the inclination angle of the swash plate of the sub pump. The hydraulic drive device according to claim 5.

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