JP2009138836A - Hydraulic circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic circuit for reducing the size of a generator, having a longer time for continuously rotating a pump motor with inertia even after a change-over valve is operated to establish the condition that pressurized liquid to be returned to a tank during lower load is not supplied to a pump motor, than prior-art one. <P>SOLUTION: Into a bottom chamber 12a of a lift cylinder 12 which drives a fork 11, an operating oil in the operating oil tank 16 in an opened condition is supplied with a hydraulic pump 17 driven by the motor 18. In a return duct 20 for returning the operating oil from the bottom chamber 12a to the operating oil tank 16, the hydraulic motor 21 is provided for driving the generator 22. The bottom chamber 12a is changed over between the condition of being communicated with the hydraulic pump 17 and the condition of being communicated with the return duct 20 by a lift control valve 14. A check valve 24 which is opened to introduce air from the outside of the duct when pressure in the return duct 20 is negative is provided at the upstream side of the return duct 20 beyond the hydraulic motor 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hydraulic circuit, and more particularly to a hydraulic circuit having a regenerative function.

In battery-powered industrial vehicles powered by batteries such as forklifts and construction machinery, hydraulic pressure is used to lift the load against gravity, but a hydraulic pump driven by return oil when the load drops is used. There is one that drives a generator and regenerates the battery. (For example, refer patent document 1 etc.). From the position where the hydraulic oil (pressure oil) is returned to the tank when the load is lowered, that is, from the state where the generator is driven using the hydraulic pump, When the hydraulic oil is switched to a position where it returns to the tank without passing through the hydraulic pump, an impact load is applied to the blades (gears) of the hydraulic pump, and there is a risk that durability may be reduced or damaged. In the hydraulic device of Patent Document 1, as shown in FIG. 6, the check valve 64 is provided with hydraulic oil in the hydraulic oil tank 63 in a state where the return oil of the lift cylinder 61 is switched to a position where it does not pass through the hydraulic pump 62. It is configured to be able to circulate to the hydraulic pump 62 through the pipe 65 formed. Therefore, in a state where the flow path switching valve is suddenly moved to the shut-off position, the hydraulic oil is supplied from the hydraulic oil tank 63 via the conduit 65 by the force with which the hydraulic pump 62 continues to rotate due to inertia. Therefore, an excessive impact load is suppressed from being applied to the blades of the hydraulic pump 62.
JP 2006-117406 A

  However, as in Patent Document 1, in a state where the return oil of the lift cylinder 61 is switched to a position where it does not pass through the hydraulic pump 62, the hydraulic oil of the pressure oil tank 63 is passed through the pipeline 65 provided with the check valve 64. In the configuration that circulates to the hydraulic pump 62, the drive unit of the hydraulic pump 62 rotates in the hydraulic oil having a large viscosity, and thus energy is absorbed by the surrounding hydraulic oil. As a result, a loss occurs in converting the hydraulic oil energy into the rotational energy of the generator, and the time during which the hydraulic pump 62 continues to rotate due to inertia is short.

  The present invention has been made in view of the above-described conventional problems, and the purpose thereof is to operate the switching valve so that pressurized liquid returned to the tank when the load is lowered is not supplied to the pump motor. It is another object of the present invention to provide a hydraulic circuit that can extend the time during which the pump motor continues to rotate due to inertia as compared with the prior art and can reduce the size of the generator.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided a lift cylinder for driving a load, a liquid tank in an open state, and a lift cylinder driven by driving means and pressurizing the liquid in the liquid tank. A hydraulic pump for supplying the bottom chamber, a return line for returning the liquid supplied to the bottom chamber to the liquid tank, a pump motor provided in the middle of the return line, and the pump motor. And a driven generator. Further, it is interposed between the bottom chamber and the hydraulic pump, and can be switched between a state in which the hydraulic pump and the bottom chamber are communicated and a state in which the bottom chamber and the return pipe line are communicated. And a gas intake means provided upstream of the pump motor in the return pipe. Here, the “hydraulic pressure” includes the hydraulic pressure in a general hydraulic circuit, and is a circuit when water or other liquid, which is an incompressible fluid other than oil, is used instead of hydraulic oil used in the hydraulic circuit. It means the pressure generated inside. The “lift cylinder” is not limited to one in which the piston rod is arranged to extend in the vertical direction (vertical direction), but includes one in which there is a moving component in the vertical direction. The “pump motor” means a mechanism that converts the energy of the liquid flowing through the flow path into the rotational force of the rotating shaft.

  In the present invention, the liquid pressurized by the hydraulic pump and supplied to the bottom chamber of the lift cylinder is returned to the open liquid tank from the return line when the load is lowered. Then, the pump motor is rotated by the energy of the pressurized liquid flowing through the return pipe, and the generator is driven by the rotational force to generate power. When the switching valve is operated so that the bottom chamber is not in communication with the return line, the pump motor continues to rotate due to inertia even if no pressurized liquid is supplied from the bottom chamber to the return line. In addition, since gas is supplied from the gas intake means to the return pipe, the viscosity of the fluid that acts to suppress the pump motor from continuing to rotate due to inertia decreases, and the pump motor that continues rotating due to inertia The rotational energy of the rotating part is converted into the kinetic energy of the surrounding gas and the rate of loss is reduced. As a result, the time for which the pump motor continues to rotate due to inertia can be extended as compared with the prior art, and the generator can be downsized.

  According to a second aspect of the present invention, in the first aspect of the present invention, the gas intake means may be configured such that the return pipe has a negative pressure between the switching valve of the return pipe and the pump motor. The valve is opened by a pressure difference between the inside of the passage and the outside of the return pipe, and introduces gas into the return pipe from the outside of the return pipe. Here, “a valve that opens due to a pressure difference between the inside of the return pipe and the outside of the return pipe and introduces gas from outside the pipe” means that a difference of a predetermined pressure or more, such as a check valve or a relief valve, is used. When there is, it means a valve with a configuration in which the valve is opened. In this invention, when the switching valve is operated, the bottom chamber is not in communication with the return line, and in this state, when the pump motor continues to rotate due to inertia and the inside of the return line becomes negative pressure, Thus, the gas is supplied from the gas intake means to the return line. Therefore, for example, the configuration is simplified compared to a configuration in which an electromagnetic valve is provided and gas is taken into the return pipe.

  According to a third aspect of the present invention, in the first aspect of the present invention, the gas intake means is a solenoid valve. In the present invention, when the switching valve is operated and the bottom chamber is not in communication with the return pipe, the electromagnetic valve is opened and gas can be introduced from the outside of the pipe. In the case of a solenoid valve, the opening / closing timing is basically determined by a control means for controlling the solenoid valve, so that the degree of freedom of opening / closing timing is higher than that of a check valve or a relief valve.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein a flywheel is provided in a rotating system of the pump motor and the generator. In this invention, since the inertia of the flywheel is added when the pump motor continues to rotate due to inertia in a state where the pressurized liquid is no longer supplied from the bottom chamber to the return line, the flywheel is not provided. In comparison, it is possible to lengthen the time during which the pump motor continues to rotate due to inertia.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the hydraulic circuit is a hydraulic circuit for cargo handling of a forklift. In the forklift, the lift and lowering of the load are performed by the lift cylinder, so that the potential energy can be effectively used in the invention according to any one of claims 1 to 4.

  According to the present invention, after the switching valve is operated so that the pressurized liquid returned to the tank when the load is lowered is not supplied to the pump motor, the time during which the pump motor continues to rotate due to inertia is reduced. Therefore, it is possible to provide a hydraulic circuit that can be extended as compared with the above and that can reduce the size of the generator.

(First embodiment)
A first embodiment in which the present invention is embodied in a battery-type forklift will be described below with reference to FIGS.

  As shown in FIG. 1, a lift cylinder 12 that raises and lowers a fork 11 as a cargo handling member is connected to a lift control valve 14 as a switching valve via a conduit 13. A direct acting spool valve is used as the lift control valve 14. As the lift control valve 14, a manually operated three-position switching valve is used, and three lifts a, b, and c corresponding to the lift, neutral, and drop operation positions of the lift lever 15 instructing raising and lowering and stopping of the fork 11 are used. The state can be switched.

  A hydraulic pump 17 as a hydraulic pump for supplying hydraulic oil in a hydraulic oil tank 16 as a liquid tank to the bottom chamber 12a of the lift cylinder 12 is a motor 18 as a driving means using a battery (secondary battery) E as a power source. Driven by. The hydraulic oil tank 16 is open to the atmosphere and has the same pressure as the atmospheric pressure.

  The hydraulic pump 17 is connected to the port P of the lift control valve 14 via a hydraulic oil supply pipe 19. The lift control valve 14 is connected to the return line 20 at the port T and to the line 13 at the port A. The pipe line 13 is connected to the bottom chamber 12 a of the lift cylinder 12. The return line 20 serves to return the pressure oil (pressurized hydraulic oil) in the bottom chamber 12 a of the lift cylinder 12 to the hydraulic oil tank 16 when the lift control valve 14 is lowered.

  The lift control valve 14 is arranged at the position a based on the lifting operation of the lift lever 15, and the lift cylinder 12 is extended by communicating the hydraulic oil supply pipe 19 and the pipe 13 at the position a. The lift control valve 14 is disposed at the position c based on the lowering operation of the lift lever 15. The lift line 12 and the return line 20 are communicated with each other at the position c to contract the lift cylinder 12. Further, the lift control valve 14 is disposed at the position b based on the neutral operation of the lift lever 15, shuts off the communication between the conduit 13 and the hydraulic oil supply conduit 19 and the return conduit 20. The hydraulic oil is prevented from moving and is held without being expanded or contracted. That is, the lift control valve 14 is interposed between the lift cylinder 12 and the hydraulic pump 17 and extends and contracts the lift cylinder 12 by position switching.

  A hydraulic motor 21 as a pump motor is disposed in the middle of the return pipe 20, and a generator 22 is connected to the hydraulic motor 21. The generator 22 is driven by a hydraulic motor 21 to perform power regeneration of a battery E as a power storage means. A terminal of the generator 22 is connected to the battery E via the control device 23. For the battery E, for example, a lead storage battery is used.

The control device 23 has a function of converting alternating current generated by the generator 22 into direct current and adjusting the voltage to charge the battery E.
A check valve 24 as a gas intake means is provided upstream of the hydraulic motor 21 in the return line 20. The check valve 24 is provided inside the return line 20 and outside the return line 20 when a negative pressure (pressure lower than atmospheric pressure) is established between the lift control valve 14 in the return line 20 and the hydraulic motor 21. The gas (air) is introduced into the return pipe 20 from outside the return pipe 20.

Next, the operation of the apparatus configured as described above will be described.
When the lift lever 15 is raised, the lift spool is disposed at the position a, and the hydraulic oil discharged from the hydraulic pump 17 is supplied to the bottom chamber 12a of the lift cylinder 12 via the hydraulic oil supply pipe 19 and the pipe 13. The lift cylinder 12 is extended and the fork 11 is raised. When the lift lever 15 is lowered, the lift spool is disposed at the position c, the conduit 13 is communicated with the return conduit 20, and the hydraulic oil in the bottom chamber 12a is returned to the hydraulic oil tank 16. Then, the lift cylinder 12 contracts and the fork 11 descends. Based on the neutral operation of the lift lever 15, the lift spool is disposed at the position b, and the pipe line 13 is disconnected from both the hydraulic oil supply pipe line 19 and the return pipe line 20. As a result, the movement of the hydraulic oil in the lift cylinder 12 is prevented, and the fork 11 is held at a desired position.

  When the fork 11 is lowered, the hydraulic oil discharged from the bottom chamber 12a is guided to the return pipe line 20 through the lift control valve 14 to rotate the hydraulic motor 21. Then, the generator 22 connected to the hydraulic motor 21 is driven to generate power. That is, the hydraulic oil energy is converted into rotational energy (kinetic energy) of the hydraulic motor 21, and the generator 22 generates electric power by converting the kinetic energy of the hydraulic motor 21 into electrical energy.

  When the fork 11 is lowered, in a state where the bottom chamber 12 a is in communication with the return pipe 20, a rotating gear portion (not shown) built in the hydraulic motor 21 is rotated by hydraulic oil flowing through the return pipe 20. When the lift control valve 14 is operated and the lift spool is disposed at the position b, the flow of hydraulic oil from the bottom chamber 12a to the return pipe 20 is interrupted, but the hydraulic motor 21 rotates by inertia. Try to continue. The rotation direction is a direction in which the hydraulic oil in the return pipe 20 is sent to the hydraulic oil tank 16. The viscosity of the hydraulic oil is large and acts to prevent the hydraulic motor 21 from rotating.

  When the hydraulic motor 21 is rotated in the direction in which the hydraulic oil is sent to the hydraulic oil tank 16 in the state where the flow of hydraulic oil from the bottom chamber 12a to the return pipeline 20 is blocked, the lift control valve of the return pipeline 20 The negative pressure is between 14 and the hydraulic motor 21. The check valve 24 is opened by a pressure difference between the inside of the return pipe line 20 and the outside of the return pipe line 20, and air is introduced from the outside of the return pipe line 20 into the return pipe line 20 through the check valve 24. Is done. As a result, the hydraulic oil in the return pipe 20 upstream from the hydraulic motor 21 can easily move in the return pipe 20 toward the hydraulic motor 21.

  The reduction in the rotational energy of the hydraulic motor 21 is largely due to the energy lost by stirring the power generation energy and the hydraulic oil generated by the generator 22. At that time, in the configuration in which the hydraulic oil is circulated as in the prior art, the hydraulic motor 21 agitates the hydraulic oil having a high viscosity, and thus energy loss increases. However, in the configuration in which air is introduced from the check valve 24 without circulating the hydraulic oil, the viscosity is lowered by mixing the air with the hydraulic oil, the rotational energy loss of the hydraulic motor 21 is reduced, and the hydraulic motor 21 is reduced. Will continue to rotate due to inertia.

Comparison was made between the case where the hydraulic motor 21 continued to rotate with inertia by circulating hydraulic oil and the case where air was introduced, using the test apparatus shown in FIG. In the test apparatus, a pipe 34 for pumping up the hydraulic oil in the hydraulic oil tank 33 is connected to the suction port of the pump 32 driven by the motor 31, and the hydraulic oil pumped up in the hydraulic oil tank 33 is connected to the discharge port. A return line 35 is connected. A check valve 36 is provided in the pipe line 34. Further, a branch pipe 37 is provided in the pipe line 34 from an intermediate portion between the suction port of the pump 32 and the check valve 36. The branch pipe 37 is provided with an electromagnetic valve 38 so that air can be introduced from the branch pipe 37.

  In the test, the pump 32 is driven by the motor 31 with the electromagnetic valve 38 closed, the hydraulic oil in the hydraulic oil tank 33 is pumped up from the pipe 34 and returned to the hydraulic oil tank 33 through the pipe 35. The operation was performed, and when the rotation speed of the pump 32 reached a predetermined rotation speed, the operation of the motor 31 was stopped, and the time until the rotation of the pump 32 stopped was measured. Then, after the operation of the motor 31 is stopped, the solenoid valve 38 is kept closed until the rotation of the pump 32 is stopped, and when the operation of the motor 31 is stopped, the solenoid valve 38 is switched to the open state. The comparison was made with the case where air was introduced from the branch pipe 37 into the pipe 34.

  FIG. 3 (a) shows the results when the predetermined rotation speed is 3000 rpm. As shown in FIG. 3 (a), when the hydraulic oil is circulated (solid line), the rate of decrease in the rotational speed in the initial state is larger than when air is introduced (dotted line). The duration was also shortened. When air was introduced, the rotation duration was about 30% longer than when no introduction was performed. Moreover, the result of having calculated the relationship between the fall loss of the pump 32 and the rotation speed is shown in FIG. From FIG. 3 (b), when air was introduced, the loss was reduced by about 30% at maximum compared to the case where air was not introduced.

According to this embodiment, the following effects can be obtained.
(1) The hydraulic circuit is driven by a motor 18 to operate the hydraulic pump 17 that pressurizes the hydraulic oil in the hydraulic oil tank 16 and supplies the hydraulic oil to the bottom chamber 12a of the lift cylinder 12, and the hydraulic oil supplied to the bottom chamber 12a. A return pipe 20 for returning to the oil tank 16, a hydraulic motor 21 provided in the middle of the return pipe 20, and a generator 22 rotated by the hydraulic motor 21 are provided. Further, switching is provided between the bottom chamber 12a and the hydraulic pump 17, and can be switched between a state in which the hydraulic pump 17 and the bottom chamber 12a communicate with each other and a state in which the bottom chamber 12a and the return pipe line 20 communicate with each other. A valve (lift control valve 14) and gas intake means (a check valve 24) provided upstream of the hydraulic pump 17 in the return line 20 are provided. Accordingly, even when the switching valve is operated during the downward movement of the fork 11 and the pressurized hydraulic oil is not supplied from the bottom chamber 12a to the return pipe 20, gas is supplied from the gas intake means to the return pipe 20. In the state, that is, in a state where the viscosity of the fluid acting to suppress the rotation of the hydraulic motor 21 is small, the hydraulic motor 21 continues to rotate due to inertia. As a result, the time during which the hydraulic motor 21 continues to rotate due to inertia can be extended as compared with the prior art, and the generator 22 can be downsized. If the generator 22 can be reduced in size, when the rotational energy of the hydraulic motor 21 becomes smaller, the generator 22 can generate power more effectively than a large generator. Further, if the generator 22 can be reduced in size, it can be easily mounted on a forklift.

  (2) As a gas intake means, when the pressure between the lift control valve 14 of the return pipe 20 and the hydraulic motor 21 becomes negative, it opens due to a pressure difference between the inside of the return pipe 20 and the outside of the return pipe 20. A valve that introduces gas from outside the return pipe 20 into the return pipe 20 is used. Therefore, the lift control valve 14 is operated, and the bottom chamber 12a is not in communication with the return pipe 20. In this state, the hydraulic motor 21 continues to rotate due to inertia, and the inside of the return pipe 20 is negative. When the pressure is reached, the gas is automatically supplied from the gas intake means to the return line 20. Therefore, for example, the configuration is simplified compared to a configuration in which an electromagnetic valve is provided and gas is introduced into the return pipe 20.

  (3) Since the check valve 24 is used as the gas intake means, the configuration is simplified compared to the relief valve. By adjusting the cracking pressure of the check valve 24, the time when the check valve 24 is opened can be set to an appropriate time.

  (4) The hydraulic circuit is applied to a hydraulic circuit for cargo handling of forklifts. In forklifts, the lift cylinder 12 raises and lowers the load. When the fork 11 is lowered even when there is no load, the potential energy is converted into the kinetic energy of hydraulic oil, and the energy is used to generate power. Do. Therefore, the potential energy can be effectively used by providing the hydraulic circuit with the above-described configuration.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG. This embodiment is different from the first embodiment in that the configuration of the pump motor, specifically, the pump motor includes a flywheel. Since other configurations are the same as those of the first embodiment, different portions will be described. In addition, the same code | symbol is attached | subjected about the part similar to 1st Embodiment, and detailed description is abbreviate | omitted.

  As shown in FIG. 4, a flywheel 25 is provided on the rotating shaft 21 a of the hydraulic motor 21 so as to be integrally rotatable. The size and weight of the flywheel 25 are appropriately set in relation to the energy of the hydraulic oil returned from the bottom chamber 12a of the lift cylinder 12 to the hydraulic oil tank 16 via the return pipe line 20.

  In the configuration of this embodiment, when the lift control valve 14 is switched by the operator to the state in which the bottom chamber 12a communicates with the return pipeline 20 in order to lower the fork 11, the hydraulic fluid flowing through the return pipeline 20 As a result, a rotating gear portion (not shown) built in the hydraulic motor 21 is rotated, and the flywheel 25 is also rotated integrally with the rotating shaft 21a. When the lift control valve 14 is operated and the lift spool is disposed at the position b, and the flow of hydraulic oil from the bottom chamber 12a to the return pipe 20 is interrupted, the hydraulic motor 21 rotates due to inertia. Try to continue. In this embodiment, since the flywheel 25 is provided on the rotating shaft 21a, the hydraulic motor 21 continues to rotate not only by its own inertia but also by the inertia of the flywheel 25. By selecting the weight and diameter of the flywheel 25, it becomes easy to adjust the power generation continuation time after the flow of hydraulic oil from the bottom chamber 12a to the return pipeline 20 is interrupted.

Therefore, this embodiment has the following effects in addition to the same effects as the effects (1) to (4) in the first embodiment.
(5) The hydraulic motor 21 includes a flywheel 25. Accordingly, the inertia of the flywheel 25 is added when the hydraulic motor 21 continues to rotate due to inertia in a state where the pressurized hydraulic oil is no longer supplied from the bottom chamber 12a to the return pipeline 20, and the flywheel 25 is provided. Compared to a configuration in which the hydraulic motor 21 does not rotate, the time during which the hydraulic motor 21 continues to rotate due to inertia can be increased. As a result, the power generation time can be lengthened. Further, when the flywheel is provided, when the hydraulic oil 21 and the drive system of the generator 22 have the same energy state when the pressurized hydraulic oil is no longer supplied from the bottom chamber 12a to the return pipeline 20, In the system where the flywheel exists, the power generation time can be lengthened while the fluctuation in the power generation amount is small.

  (6) When the fork 11 is suddenly lowered while the load is heavy, the electric power generated by the generator due to the hydraulic oil flowing through the return pipe 20 only during the lowering time of the fork 11 becomes too large, and the battery When E is charged, the battery may be adversely affected. However, since the inertia is increased by providing the flywheel 25 in the rotating system, the power generation time can be extended by leveling the power generation time, and charging of the battery E with a large current can be suppressed.

The embodiment is not limited to the above, and may be embodied as follows, for example.
As a method of extending the time during which the hydraulic motor 21 continues to rotate in a state where pressurized hydraulic oil is no longer supplied from the bottom chamber 12a to the return pipeline 20, as shown in FIG. An accumulator 26 may be provided between the lift control valve 14 and the hydraulic motor 21. In this configuration, a part of the hydraulic oil is stored in the flywheel 25 while the pressurized hydraulic oil supplied from the bottom chamber 12 a flows through the return pipe 20. When the lift control valve 14 is switched and the pressurized hydraulic oil is no longer supplied from the bottom chamber 12a to the return pipe 20, the pressurized hydraulic oil first stored in the accumulator 26 is returned to the return pipe. It is sent out to the road 20. The hydraulic oil contributes to rotating the hydraulic motor 21. Next, when the pressure between the lift control valve 14 in the return line 20 and the hydraulic motor 21 becomes negative, the check valve 24 is opened and air is introduced into the return line 20. . Therefore, as compared with the configuration of the first embodiment, the time during which the hydraulic motor 21 continues to rotate in the state where the pressurized hydraulic oil is no longer supplied from the bottom chamber 12a to the return pipe line 20 becomes longer.

  The flywheel 25 only needs to be provided in the rotating system of the hydraulic motor 21 and the generator 22, and is integrated with the rotor of the generator 22 instead of the configuration provided on the rotating shaft 21 a that connects the hydraulic motor 21 and the generator 22. You may provide so that rotation is possible.

  The flywheel 25 is provided on the generator 22 side, and the hydraulic motor 21 and the generator 22 are configured to be detachable via an electromagnetic clutch. When the electromagnetic clutch is disconnected, the hydraulic motor 21 is connected to the generator 22 and You may comprise so that it may be in the state isolate | separated from the rotating system of the flywheel. In this case, in a state where the communication between the bottom chamber 12a and the return pipe line 20 is interrupted, a large impact is suppressed from being applied to the hydraulic motor 21, and then the electromagnetic clutch is disengaged. Thereafter, the hydraulic motor 21 The generator 22 may continue to rotate integrally with the flywheel 25 in a state where is disconnected. In the state where hydraulic oil is present in the rotating part (gear part) of the hydraulic motor 21, the rotation is suppressed by the viscous resistance of the hydraulic oil. Therefore, it is preferable to disconnect the hydraulic motor 21 from the rotating system of the generator 22. Can continue power generation for a long time. However, when the inertia of the hydraulic motor 21 is large, the power generation time may be longer when the hydraulic motor 21 remains connected, and therefore either is selected in consideration of the inertia force of the hydraulic motor 21.

  When the flywheel 25 is configured to be rotatable with the rotating system via the electromagnetic clutch, the connection and disconnection of the electromagnetic clutch may be controlled by the lowered state of the fork 11. For example, when the energy applied to the hydraulic oil is small, such as when the load is light or when the load is light, the power may be generated without connecting the electromagnetic clutch. .

In the configuration provided with the flywheel 25, the accumulator 26 may be provided.
○ When the pressure between the lift control valve 14 of the return line 20 and the hydraulic motor 21 becomes negative, it is opened due to the pressure difference between the inside of the return line 20 and the outside of the return line 20. Is not limited to the check valve 24. For example, a relief valve may be provided.

  The gas introduction means is not limited to a valve configured to automatically open when a negative pressure is generated between the lift control valve 14 of the return pipe 20 and the hydraulic motor 21. For example, an electromagnetic valve may be provided. When the solenoid valve is provided, the timing at which the solenoid valve switches to a state where the external gas can be introduced into the return pipe line 20 (open state) is based on, for example, a detection signal of a position sensor that detects the position of the lift lever 15. Do it. Specifically, the control device inputs a detection signal from the position sensor, and controls the electromagnetic valve to be switched to the open state when the lift lever 15 is operated from the lowered position to the neutral position. The electromagnetic valve is not necessarily switched to the open state when the pressure between the lift control valve 14 in the return line 20 and the hydraulic motor 21 becomes negative, but may be opened before the negative pressure is reached. In the case of an electromagnetic valve, the opening / closing timing is basically determined by a control device that controls the electromagnetic valve, so that the degree of freedom of the opening / closing timing is higher than that of a check valve or a relief valve.

The lift cylinder 12 may be configured to operate with a liquid other than hydraulic oil, such as water or a liquid mainly composed of water.
The battery E is not limited to a lead storage battery, and may be another secondary battery such as a nickel hydride storage battery or a lithium ion battery.

  (Circle) the electrical storage means which stores the electric power generated with the generator 22 is not restricted to a battery (secondary battery), For example, you may use a capacitor. Alternatively, the battery E may be recharged after the capacitor is charged. When charging the capacitor, since it may be charged with a large current value in a range not exceeding the capacity of the capacitor, the power generation by the generator 22 is compared with the case where the battery E is directly charged. Increased freedom of conditions.

O Not only a battery type forklift (battery vehicle) but also an engine type forklift (engine vehicle), the hydraulic pump 17 may be rotated by the engine.
○ There are two types of forklifts: counter balance type and reach type. Like the reach type forklift, energy recovery is more effective when applied to a forklift that moves in a narrow area such as in a warehouse and frequently lifts and lowers loads. This is preferable because there are many opportunities.

  The lift cylinder is not limited to being used in a vertically extending state like a cargo handling device equipped on a forklift, but may be used in a state where it is disposed obliquely. For example, a load handling member loaded with a load (including an operator) such as a device for raising and lowering a platform of an aerial work vehicle and a device for raising and lowering a shovel of a shovel loader is moved to a low position and a high position by a lift cylinder. Includes things to move.

○ The gas to be introduced is not limited to air but may be other gases. For example, when an unmanned forklift is operated in a nitrogen atmosphere, the introduced gas is not air but nitrogen gas.
○ The hydraulic circuit may be a closed system instead of an open system. In that case, after the gas and liquid are separated by the gas-liquid separator so that the gas introduced into the return pipe 20 is not sucked into the hydraulic pump 17, only the liquid is returned to the hydraulic oil tank 16.

  The control device 23 converts the alternating current generated by the generator 22 into direct current, detects the electromotive force of the generator 22 with a voltage sensor, and when the electromotive force is larger than the voltage of the battery E, You may comprise so that a terminal may be switched to the state electrically connected to the battery E.

The following technical idea (invention) can be understood from the embodiment.
(1) The hydraulic circuit according to any one of claims 1 to 5 includes power storage means for storing electric power generated by the generator.

  (2) In the invention described in the technical idea (1), the power storage means is a battery.

The block diagram of 1st Embodiment. The schematic diagram of a testing apparatus. (A) is a graph which shows the relationship between elapsed time and rotation speed, (b) is a graph which shows the loss characteristic of a pump fall. The block diagram of 2nd Embodiment. The block diagram of another embodiment. The block diagram of a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Fork as load, 12 ... Lift cylinder, 12a ... Bottom chamber, 14 ... Lift control valve as switching valve, 16 ... Hydraulic oil tank as liquid tank, 17 ... Hydraulic pump as hydraulic pump, 18 ... Motor as drive means, 20 ... return pipe, 21 ... hydraulic motor as pump motor, 22 ... generator, 24 ... check valve as gas intake means, 25 ... flywheel.

Claims (5)

A lift cylinder that drives the load;
An open liquid tank;
A hydraulic pump that is driven by the driving means and pressurizes the liquid in the liquid tank and supplies the liquid to the bottom chamber of the lift cylinder;
A return line for returning the liquid supplied to the bottom chamber to the liquid tank;
A pump motor provided in the middle of the return line;
A generator driven by the pump motor;
Switching between the bottom chamber and the hydraulic pump, which can be switched between a state in which the hydraulic pump and the bottom chamber communicate with each other and a state in which the bottom chamber and the return pipe line communicate with each other. A valve,
A hydraulic circuit comprising gas intake means provided upstream of the pump motor in the return line.   The gas intake means is opened by the pressure difference between the inside of the return pipe and the outside of the return pipe when a negative pressure is generated between the switching valve of the return pipe and the pump motor. The hydraulic circuit according to claim 1, wherein the hydraulic circuit is a valve that introduces gas into the return pipeline from outside the pipeline.   The hydraulic circuit according to claim 1, wherein the gas intake means is an electromagnetic valve.   The hydraulic circuit according to any one of claims 1 to 3, wherein a flywheel is provided in a rotation system of the pump motor and the generator.   The hydraulic circuit according to any one of claims 1 to 4, wherein the hydraulic circuit is a hydraulic circuit for handling a forklift.

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