JP6879250B2 - 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. By the way, in recent years, it has been required to save space in the hydraulic drive system.

An object of the present invention is to provide a hydraulic drive device capable of recovering the potential energy of an elevating object while saving space.

The hydraulic drive device according to one aspect of the present invention includes a hydraulic cylinder that raises and lowers an object by supplying and discharging hydraulic oil, a tank that stores hydraulic oil, and a hydraulic pump that sucks hydraulic oil from the tank and supplies it to the hydraulic cylinder. , An operation valve that is arranged between the hydraulic pump and tank and the hydraulic cylinder and controls the flow of hydraulic oil according to the amount of operation of the operation unit for raising and lowering the lifting object, and the suction port of the hydraulic pump and the hydraulic cylinder. The first hydraulic oil flow path through which the hydraulic oil from the hydraulic cylinder flows toward the hydraulic pump, the first hydraulic oil flow path and the tank are connected, and the hydraulic oil from the hydraulic cylinder flows toward the tank. An accumulator that is connected between the connection branch point between the second hydraulic oil flow path and the second hydraulic oil flow path in the first hydraulic oil flow path and the hydraulic pump to accumulate hydraulic oil from the hydraulic cylinder, and the first The first flow control valve, which is arranged between the connection branch point in the hydraulic oil flow path and the accumulator and controls the flow rate of the hydraulic oil supplied to the accumulator, and the second hydraulic oil flow path, which is arranged in the tank. A second flow control valve for controlling the flow rate of the discharged hydraulic oil is provided, and the first flow control valve and the second flow control valve have a pressure difference generated when the hydraulic oil from the hydraulic cylinder passes through the operation valve. It is a pilot type flow control valve that controls the opening degree accordingly, and is characterized in that the second flow control valve and the connection branch point are arranged inside the operation valve.

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 flows out from the hydraulic cylinder. Here, 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 flows through the first hydraulic oil flow path and is accumulated in the accumulator. As a result, the potential energy of the lifting object is recovered. Further, the second flow rate control valve arranged in the second hydraulic oil flow path and the connection branch point between the first hydraulic oil flow path and the second hydraulic oil flow path are arranged inside the operation valve. As a result, the space of the hydraulic drive device can be saved.

The hydraulic drive system includes a resistance element arranged between the connection branch point in the first hydraulic oil flow path and the first flow control valve, and a pilot operating unit and a pilot operating unit that act in the valve closing direction in the first flow control valve. 1 The first pilot line connecting the upstream side of the operation valve in the hydraulic oil flow path, the pilot operation unit acting in the valve opening direction in the first flow control valve, and the upstream side of the resistance element in the first hydraulic oil flow path. A second pilot line connecting the two, a third pilot line connecting the pilot operating unit acting in the valve closing direction in the second flow rate control valve, and the upstream side of the operating valve in the first hydraulic oil flow path, and the second flow rate. A fourth pilot line connecting the pilot operating portion acting in the valve opening direction of the control valve and the downstream side of the resistance element in the first hydraulic oil flow rate may be further provided.

When the load loaded on the lifting object is heavy, a differential pressure is generated between the upstream side and the downstream side of the resistance element, so the pressure of the 4th pilot line (pressure on the downstream side of the resistance element) is the pressure of the 2nd pilot line. It is lower than (pressure on the upstream side of the resistance element) by the differential pressure of the resistance element. Therefore, the differential pressure between the pressure of the third pilot line and the pressure of the fourth pilot line in the second flow control valve is the differential pressure between the pressure of the first pilot line and the pressure of the second pilot line in the first flow control valve. Since the pressure difference of the resistance element is larger than that of the first flow control valve, the second flow control valve is more likely to be closed. Therefore, the hydraulic oil from the hydraulic cylinder preferentially flows to the first hydraulic oil flow path side (first flow rate control valve side) and is accumulated in the accumulator. This improves the potential energy recovery efficiency of the lifting object.

The resistance element may be located inside the operating valve. With such a configuration, further space saving of the hydraulic drive device can be achieved.

The hydraulic drive system may further include a control valve which is arranged between the accumulator and the hydraulic pump in the first hydraulic oil flow path and discharges the hydraulic oil accumulated in the accumulator toward the hydraulic pump. In such a configuration, the hydraulic oil accumulated in the accumulator can be supplied to the hydraulic pump at an appropriate timing.

The hydraulic drive system may be further provided with a check valve which is arranged between the connection branch point in the first hydraulic oil flow path and the accumulator and allows only the flow of hydraulic oil from the connection branch point side to the accumulator side. Good. In such a configuration, the hydraulic oil accumulated in the accumulator is prevented from flowing back to the first flow rate control valve side.

According to the present invention, the potential energy of an elevating object can be recovered while saving space.

It is a hydraulic circuit diagram which shows the hydraulic drive system which concerns on one Embodiment of this invention. It is a hydraulic circuit diagram which shows the operation of the hydraulic drive device shown in FIG. It is a hydraulic circuit diagram which shows the hydraulic drive system which concerns on other embodiment of this invention. It is a hydraulic circuit diagram which shows the operation of the hydraulic drive device 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 (operation unit) for raising and lowering the fork 4. The tilt cylinder 3 is operated by operating a tilt operating lever (not shown) for tilting the mast.

Further, the hydraulic drive device 1 includes a hydraulic pump 6 and an engine 8 that drives the hydraulic pump 6 via a gear 7. The hydraulic pump 6 has a suction port 6a for sucking hydraulic oil and a discharge port 6b for discharging hydraulic oil. A tank 9 for storing hydraulic oil is connected to the suction port 6a of the hydraulic pump 6 via a suction flow path 10. The suction flow path 10 is provided with a check valve 11 that allows only the flow of hydraulic oil from the tank 9 side to the hydraulic pump 6 side.

An operation valve 12 for lifting is arranged between the lift cylinder 2, the hydraulic pump 6, and the tank 9. The operating valve 12 is a mechanical directional control valve that controls the flow of hydraulic oil according to the operating state of the lift operating lever 5.

The bottom chamber 2a of the lift cylinder 2 and the operation valve 12 are connected via a common flow path 13. The discharge port 6b of the hydraulic pump 6 and the operation valve 12 are connected via a supply flow path 14. The suction flow path 10 and the operation valve 12 are connected via the regenerative flow path 15. The operation valve 12 and the tank 9 are connected via a bypass flow path 16.

Inside the operation valve 12, an internal flow path 17 that communicates the common flow path 13 and the supply flow path 14, an internal flow path 18 that communicates the common flow path 13 and the regenerative flow path 15, and a common flow path 13 An internal flow path 19 for communicating the bypass flow path 16 with the bypass flow path 16 is arranged. The internal flow path 19 is branched and connected to the internal flow path 18.

The common flow path 13, the internal flow path 18, the regeneration flow path 15, and the suction flow path 10 connect the lift cylinder 2 and the suction port 6a of the hydraulic pump 6, and the hydraulic oil from the lift cylinder 2 is directed toward the hydraulic pump 6. It constitutes a hydraulic oil flow path 20 (first hydraulic oil flow path). The internal flow path 19 and the bypass flow path 16 connect the hydraulic oil flow path 20 and the tank 9, and the hydraulic oil flow path 21 (second hydraulic oil flow path) in which the hydraulic oil from the lift cylinder 2 flows toward the tank 9. ). The connection branch point A of the internal flow paths 18 and 19 corresponds to the connection branch point A between the hydraulic oil flow path 20 and the hydraulic oil flow path 21. Therefore, the connection branch point A between the hydraulic oil flow path 20 and the hydraulic oil flow path 21 is arranged inside the operation valve 12.

The operation valve 12 has a closed position 12a (not shown) that shuts off the common flow path 13, the supply flow path 14, the regenerative flow path 15, and the bypass flow path 16, and an internal flow path between the common flow path 13 and the supply flow path 14. The open position 12b that communicates with the common flow path 13 and blocks the common flow path 13, the regenerative flow path 15 and the bypass flow path 16 and the common flow path 13 and the regenerative flow path 15 and the bypass flow path 16 are internally flown, respectively. The opening degree is controlled according to the operation amount of the lift operation lever 5 between the open position 12c that communicates through the paths 18 and 19 and blocks the common flow path 13 and the supply flow path 14.

When the lift operation lever 5 is lifted, the operation valve 12 is switched from the closed position 12a to the open position 12b side, and opens with an opening degree corresponding to the operation amount of the lift operation lever 5. Then, hydraulic oil is supplied from the hydraulic pump 6 to the bottom chamber 2a of the lift cylinder 2, and the lift cylinder 2 extends, so that the fork 4 rises.

When the lift operation lever 5 is lowered, the operation valve 12 is switched from the closed position 12a to the open position 12c side, and opens with an opening degree corresponding to the operation amount of the lift operation lever 5. Then, since the fork 4 is lowered by its own weight, the lift cylinder 2 contracts, and the hydraulic oil flows out from the bottom chamber 2a of the lift cylinder 2. Then, the hydraulic oil from the lift cylinder 2 passes through the operation valve 12.

A bypass flow rate control valve 22 (second flow rate control valve) is arranged inside the operation valve 12. The bypass flow rate control valve 22 is arranged in the internal flow path 19. The bypass flow control valve 22 will be described in detail later.

An accumulator 23 for accumulating hydraulic oil from the lift cylinder 2 is connected to the regenerative flow path 15. That is, the accumulator 23 is connected between the connection branch point A with the hydraulic oil flow path 21 in the hydraulic oil flow path 20 and the hydraulic pump 6. The inside of the accumulator 23 is filled with nitrogen gas. As the amount of hydraulic oil supplied to the accumulator 23 increases, the nitrogen gas is compressed and the pressure of the accumulator 23 increases.

A flow rate control valve 24 (first flow rate control valve) for accumulating pressure is provided on the upstream side of the accumulator 23 in the regenerative flow path 15. An orifice 25, which is a resistance element that limits the flow rate of hydraulic oil supplied to the accumulator 23, is provided on the upstream side of the pressure accumulator flow rate control valve 24 in the regenerative flow path 15. That is, the pressure accumulator flow rate control valve 24 is arranged between the connection branch point A in the hydraulic oil flow path 20 and the accumulator 23. The orifice 25 is arranged between the connection branch point A in the hydraulic oil flow path 20 and the flow rate control valve 24 for accumulating pressure.

The pressure accumulator flow rate control valve 24 controls the flow rate (accumulation flow rate) of the hydraulic oil supplied from the bottom chamber 2a of the lift cylinder 2 to the accumulator 23. The pressure accumulator flow rate control valve 24 is a pilot type flow rate control valve that controls the opening degree according to the pressure difference generated when the hydraulic oil from the lift cylinder 2 passes through the operation valve 12. The opening degree of the pressure accumulator flow rate control valve 24 is controlled between an open position (not shown) that allows the flow of hydraulic oil and a closed position that blocks the flow of hydraulic oil. Specifically, the pressure accumulator flow rate control valve 24 controls the flow rate of hydraulic oil so that the pressure difference (front-rear differential pressure) generated on the upstream side and the downstream side of the operation valve 12 becomes constant. The pressure accumulator flow rate control valve 24 is provided with a spring 26 for urging in the valve opening direction.

The pressure accumulator flow rate control valve 24 inputs the pressures on the upstream side and the downstream side of the operation valve 12 as pilot pressures. Specifically, the pilot operation unit 24a acting in the valve closing direction of the pressure accumulator flow rate control valve 24 and the common flow path 13 are connected via a pilot line 27 (first pilot line). That is, the pilot line 27 connects the pilot operating portion 24a acting in the valve closing direction of the pressure accumulator flow rate control valve 24 and the upstream side of the operating valve 12 in the hydraulic oil flow path 20. The pilot operating unit 24b acting in the valve opening direction of the pressure accumulating flow control valve 24 and the operating valve 12 and the orifice 25 in the regenerative flow path 15 are connected via a pilot line 28 (second pilot line). There is. That is, the pilot line 28 connects the pilot operating portion 24b acting in the valve opening direction of the pressure accumulator flow rate control valve 24 to the upstream side of the orifice 25 in the hydraulic oil flow path 20.

A pressure release control valve 29 is arranged between the accumulator 23 and the hydraulic pump 6 in the regenerative flow path 15. That is, the pressure release control valve 29 releases the hydraulic oil accumulated in the accumulator 23 toward the hydraulic pump 6. The release pressure control valve 29 is composed of an electromagnetic proportional valve. The opening degree of the release pressure control valve 29 is controlled between a closed position (not shown) that blocks the flow of hydraulic oil and an open position that allows the flow of hydraulic oil. When the lift operating lever 5 is being lowered, the pressure release control valve 29 is in the closed position (not shown), and the hydraulic oil accumulated in the accumulator 23 is not supplied to the hydraulic pump 6.

A check valve 30 is arranged between the pressure accumulating flow rate control valve 24 and the pressure release control valve 29 in the regenerative flow path 15. The check valve 30 allows only the flow of hydraulic oil from the connection branch point A side between the hydraulic oil flow path 20 and the hydraulic oil flow path 21 to the accumulator 23 side, and from the accumulator 23 side to the connection branch point A side. Block the flow of hydraulic oil. The check valve 30 may be arranged between the connection branch point A with the hydraulic oil flow path 21 and the accumulator 23 in the hydraulic oil flow path 20.

The bypass flow rate control valve 22 arranged inside the operation valve 12 controls the flow rate (bypass flow rate) of the hydraulic oil discharged from the bottom chamber 2a of the lift cylinder 2 to the tank 9. Like the pressure accumulator flow rate control valve 24, the bypass flow rate control valve 22 is a pilot type flow rate control valve that controls the opening degree according to the pressure difference generated when the hydraulic oil from the lift cylinder 2 passes through the operation valve 12. Is. The opening degree of the bypass flow rate control valve 22 is controlled between an open position (not shown) that allows the flow of hydraulic oil and a closed position that blocks the flow of hydraulic oil. Specifically, the bypass flow rate control valve 22 controls the flow rate of hydraulic oil so that the pressure difference (front-rear differential pressure) generated on the upstream side and the downstream side of the operation valve 12 becomes constant. The bypass flow rate control valve 22 is provided with a spring 31 that urges the valve in the valve opening direction.

Like the pressure accumulator flow rate control valve 24, the bypass flow rate control valve 22 inputs the pressures on the upstream side and the downstream side of the operation valve 12 as pilot pressures. Specifically, the pilot operation unit 22a acting in the valve closing direction of the bypass flow rate control valve 22 and the common flow path 13 are connected via a pilot line 32 (third pilot line). That is, the pilot line 32 connects the pilot operating portion 22a acting in the valve closing direction of the bypass flow rate control valve 22 and the upstream side of the operating valve 12 in the hydraulic oil flow path 20. The pilot operating unit 22b acting in the valve opening direction of the bypass flow control valve 22 and the orifice 25 in the regenerative flow path 15 and the pressure accumulating flow control valve 24 are connected via a pilot line 33 (fourth pilot line). It is connected. That is, the pilot line 33 connects the pilot operating portion 22b acting in the valve opening direction of the bypass flow rate control valve 22 to the downstream side of the orifice 25 in the hydraulic oil flow path 20.

The bypass flow rate control valve 22 and the pressure accumulator flow rate control valve 24 are set so that the flow rates of the hydraulic oil flowing according to the operation amount of the lift operation lever 5 are equal. Specifically, for example, by adjusting the spring 31 of the bypass flow rate control valve 22 and the spring 26 of the accumulator flow rate control valve 24, the flow rate of hydraulic oil flowing through the bypass flow rate control valve 22 and the accumulator flow rate control valve 24. Are set to be equal. At this time, the bypass flow rate control valve 22 and the accumulator flow rate control valve 24 may be configured as flow rate control valves having the same structure.

The bypass flow rate control valve 22 and the pressure accumulator flow rate control valve 24 automatically change the flow rate of the hydraulic oil from the lift cylinder 2 according to the operation amount of the lift operating lever 5, the load of the fork 4, the oil temperature of the hydraulic oil, and the like. To control. Thereby, it is possible to obtain a desired operating speed of the lift cylinder 2.

An operation valve 34 for tilting is arranged between the tilt cylinder 3, the hydraulic pump 6, and the tank 9. The operating valve 34 is an electromagnetic proportional valve that controls the flow of hydraulic oil according to the operating state of the tilt operating lever (not shown).

The supply flow path 14 and the operation valve 34 are connected via the supply flow path 35. The supply flow path 14 and the tank 9 are connected via a discharge flow path 36. An unload valve 37 is provided in the discharge flow path 36. The tank 9 and the unload valve 37 in the discharge flow path 36 and the operation valve 34 are connected via the discharge flow path 38.

The operation valve 34 and the bottom chamber 3a and the rod chamber 3b of the tilt cylinder 3 are connected to each other via common flow paths 39 and 40, respectively. The operation valve 34 communicates the supply flow path 35 and the closed position 34a (not shown) that shuts off the supply flow path 35 and the discharge flow path 38 and the common flow paths 39 and 40, and the supply flow path 35 and the common flow path 39, and discharge flow. Between the open position 34b that communicates the road 38 and the common flow path 40 and the open position 34c that communicates the supply flow path 35 and the common flow path 40 and also communicates the discharge flow path 38 and the common flow path 39. Then, the opening degree is controlled according to the operation amount of the tilt operation lever (not shown).

When the tilt operation lever is tilted forward, the operation valve 34 is switched from the closed position 34a to the open position 34b side, and opens with an opening degree corresponding to the operation amount of the tilt operation lever. Then, hydraulic oil is supplied from the hydraulic pump 6 to the bottom chamber 3a of the tilt cylinder 3, and the tilt cylinder 3 extends, so that the mast (not shown) tilts forward. When the tilt operation lever is tilted backward, the operation valve 34 is switched from the closed position 34a to the open position 34c side, and opens with an opening degree corresponding to the operation amount of the tilt operation lever. Then, hydraulic oil is supplied from the hydraulic pump 6 to the rod chamber 3b of the tilt cylinder 3, and the tilt cylinder 3 contracts, so that the mast (not shown) tilts backward.

In the above-mentioned hydraulic drive device 1, when the operator performs a lowering operation by the lift operation lever 5, the operation valve 12 switches from the closed position 12a to the open position 12c side as described above, so that the fork 4 has its own weight. The hydraulic oil flows out from the bottom chamber 2a of the lift cylinder 2.

Here, when the load loaded on the fork 4 is heavy, the pressure (cylinder pressure) of the bottom chamber 2a of the lift cylinder 2 becomes high. Therefore, as shown in FIG. 2, the hydraulic oil from the lift cylinder 2 is accumulated in the accumulator 23 through the operation valve 12, the orifice 25, and the flow rate control valve 24 for accumulating pressure. As a result, the potential energy of the fork 4 is recovered. After that, for example, when the fork 4 is raised or the tilt cylinder 3 is operated, the pressure release control valve 29 is opened, so that the hydraulic oil accumulated in the accumulator 23 is supplied to the hydraulic pump 6 through the pressure release control valve 29. , The regenerative operation is performed. As a result, the potential energy of the fork 4 is reused.

In a state where the load loaded on the fork 4 is heavy and the accumulating flow rate is generated in the regenerative flow path 15, the orifice 25 causes a front-rear differential pressure at the orifice 25. That is, the pressure on the downstream side of the orifice 25 is lower than the pressure on the upstream side of the orifice 25 by the differential pressure of the orifice 25. Therefore, the pilot pressure of the pilot line 32 is higher than the sum of the pilot pressure of the pilot line 33 and the urging force of the spring 31. Therefore, as shown in FIG. 2A, since the bypass flow rate control valve 22 is driven in the valve closing direction, the hydraulic oil from the lift cylinder 2 preferentially flows to the regenerative flow path 15 side. , Hydraulic oil does not flow in the bypass flow path 16. That is, the bypass flow rate is zero, and only the accumulator flow rate is used. As a result, the hydraulic oil is quickly accumulated in the accumulator 23.

When the pressure of the accumulator 23 (accumulator pressure) increases with the accumulation of hydraulic oil in the accumulator 23, the difference between the cylinder pressure and the accumulator pressure becomes small, so that the accumulator flow rate decreases. Then, the front-rear differential pressure of the orifice 25 becomes small, and the decrease of the pressure on the downstream side of the orifice 25 (corresponding to the pilot pressure of the pilot line 33) is suppressed. Therefore, the sum of the pilot pressure of the pilot line 33 and the urging force of the spring 31 becomes larger than the pilot pressure of the pilot line 32. Therefore, as shown in FIG. 2B, the bypass flow rate control valve 22 opens, and the bypass flow rate increases. After that, when the accumulator pressure reaches a predetermined pressure, the hydraulic oil cannot be accumulated in the accumulator 23 any more, so that the accumulator flow rate becomes zero and only the bypass flow rate is obtained.

When the load loaded on the fork 4 is light and the accumulated pressure flow rate does not flow, the front-rear differential pressure does not occur at the orifice 25. Therefore, the bypass flow rate control valve 22 controls the bypass flow rate so that the front-rear differential pressure of the operation valve 12 becomes constant.

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 that the fork 4 is lowered, and the hydraulic oil flows out from the lift cylinder 2. Here, 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 flows through the hydraulic oil flow path 20 and is accumulated in the accumulator 23. As a result, the potential energy of the fork 4 is recovered. Further, the bypass flow rate control valve 22 arranged in the hydraulic oil flow path 21, and the connection branch point A between the hydraulic oil flow path 20 and the hydraulic oil flow path 21 are arranged inside the operation valve 12. As a result, the space of the hydraulic drive device 1 can be saved.

Further, in the present embodiment, when the load loaded on the fork 4 is heavy, a differential pressure is generated between the upstream side and the downstream side of the orifice 25, so that the pressure of the pilot line 33 (the pressure on the downstream side of the orifice 25) is increased. It is lower than the pressure of the pilot line 28 (the pressure on the upstream side of the orifice 25) by the differential pressure of the orifice 25. Therefore, the differential pressure between the pressure of the pilot line 32 and the pressure of the pilot line 33 in the bypass flow control valve 22 is larger than the differential pressure between the pressure of the pilot line 27 and the pressure of the pilot line 28 in the accumulating flow control valve 24. Since the pressure is increased by the differential pressure of the orifice 25, the bypass flow rate control valve 22 is more likely to be closed than the pressure accumulator flow rate control valve 24. Therefore, the hydraulic oil from the lift cylinder 2 preferentially flows to the hydraulic oil flow path 20 side (accumulation flow rate control valve 24 side) and is accumulated in the accumulator 23. This improves the potential energy recovery efficiency of the fork 4.

Further, in the present embodiment, the bypass flow rate control valve 22 and the pressure accumulator flow rate control valve 24 are set so that the flow rates of the hydraulic oil flowing according to the operation amount of the lift operation lever 5 are equal. Therefore, when the lift cylinder 2 operates so that the fork 4 loaded with a heavy load descends, the destination where the hydraulic oil flows from the lift cylinder 2 is for accumulating pressure according to the pressure accumulating state of the hydraulic oil in the accumulator 23. Even if the flow rate control valve 24 side is switched to the bypass flow rate control valve 22 side, the flow rates of the hydraulic oil flowing through the accumulator flow rate control valve 24 and the bypass flow rate control valve 22 are the same. As a result, the desired operating speed of the lift cylinder 2 can be maintained.

Further, in the present embodiment, since the discharge control valve 29 for releasing the hydraulic oil accumulated in the accumulator 23 toward the hydraulic pump 6 is provided, the hydraulic oil accumulated in the accumulator 23 is hydraulically charged at an appropriate timing. It can be supplied to the pump 6.

Further, in the present embodiment, since the check valve 30 that allows only the flow of the hydraulic oil from the connection branch point A side between the hydraulic oil flow path 20 and the hydraulic oil flow path 21 to the accumulator 23 side is provided. It is prevented that the hydraulic oil accumulated in the accumulator 23 flows back to the accumulator flow rate control valve 24 side.

Further, in the present embodiment, since the load sensor and the hydraulic pump / motor dedicated to regeneration are not required, the configuration of the hydraulic drive device 1 can be simplified and downsized, and the cost of the hydraulic drive device 1 is low. become.

FIG. 3 is a hydraulic circuit diagram showing a hydraulic drive device according to another embodiment of the present invention. In FIG. 3, the present embodiment includes an orifice 45 (resistance element) instead of the orifice 25 in the above-described embodiment. The orifice 45 is arranged inside the operating valve 12. Specifically, the orifice 45 is arranged in the internal flow path 18 of the operation valve 12.

The connection branch point A between the pilot operating unit 24b acting in the valve opening direction of the pressure accumulator flow control valve 24 and the internal flow path 19 in the internal flow path 18 and the orifice 41 are connected via the pilot line 28. ing. That is, the pilot line 28 connects the pilot operating portion 24b acting in the valve opening direction of the pressure accumulator flow rate control valve 24 to the upstream side of the orifice 45 in the hydraulic oil flow path 20.

The pilot operating unit 22b acting in the valve opening direction of the bypass flow rate control valve 22 and the operation valve 12 in the regenerative flow path 15 and the pressure accumulating flow rate control valve 24 are connected via a pilot line 33. That is, the pilot line 33 connects the pilot operating portion 22b acting in the valve opening direction of the bypass flow rate control valve 22 to the downstream side of the orifice 45 in the hydraulic oil flow path 20.

When the load loaded on the fork 4 is heavy and the accumulating flow rate is generated in the regenerative flow path 15, the pressure on the downstream side of the orifice 45 decreases due to the action of the orifice 45, and is therefore shown in FIG. 4 (a). As described above, the bypass flow rate control valve 22 is driven in the valve closing direction, and the hydraulic oil from the lift cylinder 2 preferentially flows to the regeneration flow path 15 side. When the accumulator pressure rises with the accumulation of hydraulic oil in the accumulator 23, the pressure lowering action of the orifice 45 is suppressed, so that the bypass flow rate control valve 22 opens as shown in FIG. 4 (b). Will be.

In the present embodiment, since the orifice 45 is arranged inside the operation valve 12, the space of the hydraulic drive device 1 can be further saved.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the flow rates of the hydraulic oil flowing through the bypass flow rate control valve 22 and the accumulator flow rate control valve 24 are set to be equal, but the operation is not particularly limited to that mode and is operated from the lift cylinder 2. If the operator hardly feels a change in the operating speed of the lift cylinder 2 when the oil flow destination is switched from the accumulator flow rate control valve 24 side to the bypass flow rate control valve 22 side, the bypass flow rate The flow rates of the hydraulic oil flowing through the control valve 22 and the pressure accumulator flow rate control valve 24 may be different.

Further, although the hydraulic drive device 1 of the above embodiment is mounted on an engine type forklift, the present invention can also be applied to an electric forklift. The present invention is also applicable to a forklift equipped with an attachment.

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), 6 ... Hydraulic pump, 6a ... Suction port, 9 ... Tank, 12 ... Operation Valve, 20 ... Hydraulic oil flow path (first hydraulic oil flow path), 21 ... Hydraulic oil flow path (second hydraulic oil flow path), 22 ... Bypass flow rate control valve (second flow rate control valve), 22a, 22b ... Pilot operation unit, 23 ... Accumulator, 24 ... Accumulation flow control valve (first flow control valve), 24a, 24b ... Pilot operation unit, 25 ... orifice (resistance element), 27 ... Pilot line (first pilot line) , 28 ... Pilot line (2nd pilot line), 29 ... Pressure release control valve (control valve), 30 ... Check valve, 32 ... Pilot line (3rd pilot line), 33 ... Pilot line (4th pilot line) , 45 ... orifice (resistance element), A ... connection branch point.

Claims (5)

A hydraulic cylinder that raises and lowers objects by supplying and discharging hydraulic oil,
A tank for storing the hydraulic oil and
A hydraulic pump that sucks the hydraulic oil from the tank and supplies it to the hydraulic cylinder,
An operation valve, which is arranged between the hydraulic pump and the tank and the hydraulic cylinder, and controls the flow of the hydraulic oil according to the operation state of the operation unit for raising and lowering the elevating object.
A first hydraulic oil flow path that connects the suction port of the hydraulic pump and the hydraulic cylinder and allows the hydraulic oil from the hydraulic cylinder to flow toward the hydraulic pump.
A second hydraulic oil flow path that connects the first hydraulic oil flow path and the tank and allows the hydraulic oil from the hydraulic cylinder to flow toward the tank.
An accumulator that is connected between the connection branch point with the second hydraulic oil flow path in the first hydraulic oil flow path and the hydraulic pump and accumulates the hydraulic oil from the hydraulic cylinder.
A first flow rate control valve arranged between the connection branch point in the first hydraulic oil flow path and the accumulator and controlling the flow rate of the hydraulic oil supplied to the accumulator.
It is provided with a second flow rate control valve which is arranged in the second hydraulic oil flow path and controls the flow rate of the hydraulic oil discharged to the tank.
The first flow rate control valve and the second flow rate control valve are pilot type flow rate control valves that control the opening degree according to the pressure difference generated when the hydraulic oil from the hydraulic cylinder passes through the operation valve. ,
A hydraulic drive system characterized in that the second flow rate control valve and the connection branch point are arranged inside the operation valve. A resistance element disposed between the connection branch point in the first hydraulic oil flow path and the first flow rate control valve,
A first pilot line connecting the pilot operating unit acting in the valve closing direction of the first flow control valve and the upstream side of the operating valve in the first hydraulic oil flow path,
A second pilot line connecting the pilot operating unit acting in the valve opening direction of the first flow control valve and the upstream side of the resistance element in the first hydraulic oil flow path, and
A third pilot line connecting the pilot operating unit acting in the valve closing direction of the second flow rate control valve and the upstream side of the operating valve in the first hydraulic oil flow path,
The claim is characterized in that it further includes a pilot operating unit that acts in the valve opening direction of the second flow control valve and a fourth pilot line that connects the downstream side of the resistance element in the first hydraulic oil flow path. 1. The hydraulic drive device according to 1. The hydraulic drive device according to claim 2, wherein the resistance element is arranged inside the operation valve. It is further provided with a control valve which is arranged between the accumulator and the hydraulic pump in the first hydraulic oil flow path and discharges the hydraulic oil accumulated in the accumulator toward the hydraulic pump. The hydraulic drive device according to any one of claims 1 to 3. A check valve that is disposed between the connection branch point and the accumulator in the first hydraulic oil flow path and allows only the flow of the hydraulic oil from the connection branch point side to the accumulator side is further provided. The hydraulic accumulator according to any one of claims 1 to 4.

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