JPH0466500A - Oil pressure device in battery type industrial vehicle - Google Patents

Abstract

PURPOSE:To prevent wasteful electric power consumption of a battery and to prevent a fork from lowering in inching operation of lifting by providing a selector valve driving means and a spare switching means for supplying an operating pilot pipeline without passing through a lift control valve. CONSTITUTION:A selector valve driving means is constituted of an operating pilot pipeline 25 and the like. Also, a spare switching means to switch a connec tion state of a selector valve 11 in advance according to return oil pressure is constituted of a blocking check valve 21 and a second blocking check valve 23, and the like. The selector valve 11 is controlled by the pressure in response to the load of a fork, and is switched to (a) position in the case of heavy load and to (b) position in the case of load. Wasteful electric power consumption can be prevented because an oil pressure pump 1 is not rotated by the return oil of low pressure. Since the operating pilot pipeline 25 is connected to a driv ing check valve 17 without passing through a lift control valve 5, in the case of carrying out the inching operation of lifting, the fork is hindered to be lowered due to lack of a supply amount of the operating oil supplied to a lift cylinder 7 through the lift control valve 5 from a main pipeline 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a regeneration hydraulic system for a battery-powered industrial vehicle.

[Prior Art] A battery-powered industrial vehicle, such as a battery forklift truck, which is equipped with an electric motor that drives a pump in a hydraulic system for cargo handling, uses a hydraulic pump that functions as a motor using return oil from a lift cylinder to generate electricity for the electric motor. There are some that act as a machine to regenerate the battery.

This type of regenerative hydraulic system wastes battery power,
In particular, when a cargo handling member is lowered under a light load after being held at the highest position, the pump is rotated by low-pressure return oil, and this hydraulic system can prevent wasteful battery power consumption. , the applicant filed the patent application No. 2-14 Hei 2-14.
No. 5191 proposes what is shown in Figures 8 and 9. In this hydraulic system, the controller 53 controls the induction motor based on signals from limit switches LSI and LS2 that detect the operating directions of the lift lever 51 and tilt lever 52, and potentiometers SL and S2 that detect the operating amounts of both levers 51 and 52. 54 is rotated, the hydraulic pump 55 is driven, and hydraulic oil is sucked up from the oil tank T via the regeneration check valve 56.

Then, the tilt control valve 57 is switched and controlled based on the operation of the tilt lever 52, and hydraulic oil is supplied to the tilt cylinder 58, which is expanded and contracted, thereby performing a tilt operation of the fork.

Further, the hydraulic pump 55 and the lift pipe 60 are communicated with each other via the lift control valve 59 which is held at the a position shown in FIG. 9 based on the lifting operation of the lift lever 5I. Hydraulic oil is supplied from the lift cylinder 61 to lift the fork. At the same time, the pilot fluid P flowing from the communication line G in the lift control valve 59 into the detour pilot line 63 via the actuating pilot line 62 opens the drive check valve 64 and closes the closing pilot line. The pilot fluid P2 flows from the connection point X to the port pressurizing pilot conduit 66 via the port 65. As a result, the pilot port of the switching valve 67 in position b is pressurized, and the switching valve 67 is pressurized.
7 is switched to position a. This pilot fluid stays in the port pressurizing pilot pipe line 66 from where the exit passage is blocked by the blocking check valve 68, and the switching valve 67 is
It is designed to remain in place.

Then, when the fork is under a heavy load or a similar medium load, when the lift lever 51 in the neutral position is operated downward and the lift control valve 59 is switched to the C position, the high pressure return oil is placed in the a position in advance. The flow to the drain line 69 is cut off by the held switching valve 67, and the flow flows from the return line 70 to the main line 71.

Since the communication to the tank T side is blocked by the regeneration check valve 56, this high pressure return oil is transferred to the hydraulic pump 55.
The induction motor 54 that rotates in response to this rotation functions as a generator, and the battery 72 is charged via the controller 53.

Also, when the lift lever 51 is operated from the neutral position to the lower position when the fork is under no load, light load, or medium load similar to light load, and the return hydraulic pressure cannot cause the induction motor 54 to function as a generator. In this case, the switching valve 67 is switched to the b position in advance. In this case, the connection point Z of the detour pipeline
There is no pressure buildup in the valve, and the opening check valve 73 is never opened. Therefore, the pilot fluid in the operating pilot pipe 74 opens the sealing check valve 68, and the pilot fluid remaining in the pressurizing pilot pipe 66 gradually flows into the drain pipe 69 through the orifice O. to flow out. Therefore, the state of the switching valve 67 that has already been switched to the b position does not change, and vibrations and the like caused by the switching operation are avoided. The low-pressure return oil then flows into the drain pipe 69 via the switching valve 67. Therefore, the low-pressure return oil does not rotate the hydraulic pump 55, that is, the induction motor 54, and wasteful power consumption of the battery 72 is avoided.

[Problems to be Solved by the Invention] However, in the conventional device described above, there is a risk that the fork may descend during a rising operation (so-called upward inching operation) in which the lift lever 51 is slowly moved. That is, during the upward inching operation, the lift lever 51 is slowly operated so as to change from the state shown in FIG. 8 to the state shown in FIG. 62. Therefore, the hydraulic oil supplied from the main pipe 71 to the operating pilot pipe 62 passes through the orifice 75 provided in the detour pilot pipe 63 and flows into the drain pipe 69. There are cases where the amount of hydraulic fluid (pressure) supplied to the lift cylinder 61 is insufficient and the fork moves downward.

The present invention has been made in view of the above problems, and includes:
The purpose of this is to avoid unnecessary consumption of battery power, especially when the cargo handling member is lowered with a light load after being held at the highest position, the pump is rotated by low pressure return oil, resulting in wasted battery power consumption. To provide a hydraulic system for a battery-powered industrial vehicle that can prevent the fork from descending when a lift lever is inched upward.

[Means for Solving the Problems] To achieve the above object, the present invention includes a lift cylinder that raises and lowers a cargo handling member, a hydraulic oil is supplied to the lift cylinder, and when the lift cylinder is contracted, the cargo handling member is When the return hydraulic pressure returned from the lift cylinder based on the load on the member exceeds a predetermined value, a hydraulic pump is rotated by the return oil and functions as a hydraulic motor, and an intervening device is installed between the lift cylinder and the hydraulic pump. a lift control valve that is equipped with a lift cylinder and holds the lift cylinder in an expandable and non-expandable manner by changing its position; and a lift control valve that is operatively connected to the hydraulic pump and is driven by electric power supplied from a battery to rotate the hydraulic pump; In a hydraulic system for a battery-powered industrial vehicle equipped with an electric motor rotated by a hydraulic pump to regenerate battery power, the return oil return path is arranged in the return oil return path, and is arranged in the return oil return path according to the magnitude of the pressure of the return oil. a return path switching valve that selectively connects the switch to the hydraulic pump side and the drain side; and when the lift cylinder is extended, the return path switching valve is driven based on a hydraulic pressure value between the lift control valve and the lift cylinder. and a switching valve driving means for connecting the return path to the hydraulic pump side and for supplying oil discharged from the hydraulic pump as pilot pressure without going through a lift control valve, and a switching valve driving means for causing the lift cylinder to reach a maximum extension position. Preliminary switching means is provided for switching the connection state of the return path switching valve in advance to the connection state based on the return hydraulic pressure when the cylinder is contracted, depending on the magnitude of the pressure in the lift cylinder when the lift cylinder is held.

[Operation] When the lift cylinder is extended, the return path switching valve is driven based on the oil pressure value between the lift control valve and the lift cylinder, and connects the return path to the pump side. The preliminary switching means previously switches the connection state of the return path switching valve to the connection state after the cylinder is retracted, depending on the magnitude of the pressure within the lift cylinder when the lift cylinder is held at the maximum extension position. The oil discharged from the hydraulic pump is directly supplied as pilot pressure to a pilot operating valve provided in a conduit for driving and operating a return path switching valve, without going through a lift control valve.

[Embodiment 1] Hereinafter, a first embodiment in which the present invention is embodied in a battery-powered forklift will be described with reference to FIGS. 1 to 5.

In FIG. 1, a hydraulic pump 1 sucks up hydraulic oil stored in an oil tank T through a regeneration check valve 3 in a supply pipe line 2, and then transfers it to a main pipe line 4 of a fork drive hydraulic circuit. Exhale. A lift control valve 5 is disposed in the main pipe 4, and the lift control valve 5 corresponds to the raising, neutral, and lowering operation positions of a lift lever 6 that instructs to raise, lower, and stop a fork (not shown). It can be switched to three positions: a, b, and c.

The lift control valve 5 controls the amount of hydraulic oil in the bottom chamber 7a of the lift cylinder 7 by changing its position to expand and contract the cylinder 7. In the figure), the main pipe line 4 and the lift pipe line 8 are communicated with each other, and hydraulic oil is supplied from the hydraulic pump l to the bottom chamber 7a of the lift lever 7, thereby extending the same foot cylinder 7.

When the lift control valve 5 is in position b (FIGS. 1 and 4) based on the neutral operation of the lift lever 6, the lift control valve 5 shuts off the lift pipe 8 from the main pipe 4 and the return pipe 9, and prevents the lift cylinder 7 from leaking. The main pipe 4 is opened to the downstream side while preventing fluctuations in the flow rate of the hydraulic oil and keeping it from contracting.

Further, the lift control valve 5 communicates the lift conduit 8 and the return conduit 9 in the C position (FIG. 5) based on the lowering operation of the lift lever 6. A flow control valve IO is disposed in the return pipe 9 to limit the flow rate of return oil returning from the lift cylinder 7 via the lift control valve 5. The flow rate control valve 10 adjusts the flow rate of return oil when the fork is under a light load, and causes the cylinder 7 to contract at an appropriate speed.

A detour line is branched into the return line 9 downstream of the flow rate control valve IO, and this detour line is equipped with a pilot-controlled switching valve 11 that can be switched to positions a and b to switch the return line. It is provided as a valve.

This switching valve 11 is normally held at the home position b by spring pressure, and the detour line is always open to allow the return line 9 to communicate from the drain line 12 to the tank T. Then, the pressure of the return oil (hydraulic pressure in the lift cylinder 7) is set to the preset pump driving pressure (hereinafter referred to as
When the value exceeds the set value, the switching valve 11 is switched to the a position, and the return oil flows into the pump 1 from the return pipe 9 to rotate it.

A port pressurizing pilot conduit I3 is connected to the pilot port of the switching valve 11, and the port pressurizing pilot conduit I3 extends from the lift control valve 5 and is provided with a check valve 14 and an orifice 15. A pressure relief pilot line 16 is connected at the connection point X. When the lift control valve 5 is in the a position (FIG. 2), the pressure relief pilot pipe 16 is connected to the main pipe 4 via the communication passage Ja in the control valve 5, and when the lift control valve 5 is in the b position. When (1st,
4), the control valve 5 is connected to the lift pipe 8 through the communication path Jb, and when the control valve 5 is in the C position (Fig. 5), the main pipe 4 and It is cut off from any of the lift pipes 8. Moreover, the lift pipe line 8
A closing pilot pipe 19 is provided between the pressure release pilot pipe 16 and a pilot-operated drive check valve 17 and a check valve 18 that allows fluid to flow in the opposite direction. is connected.

The port depressurization pipe 20, which communicates with the switching valve 11 at the connection point X, is connected to the drain pipe 12 at the connection point Y1 via a pilot-operated blocking check valve 2I, and The stop valve 21 is normally closed and the switching valve 1
This prevents the pilot pressure applied to the drain pipe 12 from being absorbed into the drain pipe line 12. Further, an orifice 2 is provided between the pressure relief pilot line 16 and the drain line 12.
2 and a conduit 24 provided with a second blocking check valve 23 are connected.

An operating pilot line 25 is connected between the pilot port of the driving check valve 17 and the main line 4, and an orifice 26 is provided in the middle of the pilot line 25. The operating pilot pipe 25 has one end upstream of the orifice 26 and the other end connected to the driving check valve 1.
A detour pilot conduit 27 is branched and connected near the pilot port 7, and the detour pilot conduit 27 has a relief valve R closer to the drive check valve 17 and a relief valve R upstream from the orifice 26. Check valves 28 are provided at positions close to the operating pilot pipes 25, respectively. The pilot port of the second blocking check valve 23 is connected to the check valve 28 and the relief valve R via the pipe 27a.
It is connected to a detour pilot pipe line 27 between the two. The port pressurizing pilot conduit I3, the drive check valve 17, the operating pilot conduit 25, and the like constitute a switching valve driving means. Further, the blocking check valve 21,
The second blocking check valve 23, the relief valve R, the orifice 22, etc. constitute a preliminary switching means that previously switches the connection state of the switching valve 11 to a connection state based on the return hydraulic pressure when the cylinder contracts.

Further, as shown in FIG. 5, when the lift control valve 5 is switched to the C position based on the lowering operation of the lift lever 6, the return pipe is opened via the communication path K of the lift control valve 5. One end of the communication pilot conduit 29 that communicates with the operating pilot conduit 30 is connected to the operating pilot conduit 30 . The operating pilot line 30 is branched into two directions at the connection point W, one side is connected to the pilot operated check valve 31, and the other side is connected to the pilot port of the blocking check valve 2I via the pilot line 30a. connected. The pilot port of the check valve 31 is connected to the detour line at a connection point Z via a switching pilot line 32.

Further, as shown in FIG. 1, a tilt control valve 33 is disposed in the main pipe 4 on the downstream side of the lift control valve 5, and a tilt lever 34 which instructs forward and backward tilting operations of the fork is provided. The tilt control valve 33 is driven to be switched to three positions a, b, and c corresponding to the forward tilting, neutral, and backward tilting operating positions. The tilt control valve 33 is connected to the main pipeline 4 and a backward tilting conduit 36 and a forward tilting conduit 37 communicating with the front chamber 35a and rear chamber 35b of the tilt cylinder 35 by switching between the 3rd position and the C position. The tilt pipe 38 and the drain pipe 39 connected to the tank T are selectively communicated via the drain pipe 12, and the tilt cylinder 35 is expanded and contracted to tilt the fork back and forth.

Next, the electrical configuration for driving the above-mentioned hydraulic circuit will be explained.

The operating positions of the lift lever 6, such as up, neutral, and down, are detected by a lift operating position sensor 40 made up of a limit switch, and the operating amounts at the up and down positions of the lift lever 6 are detected by a lift operating amount made of a potentiometer. It is detected by the sensor 41, and the detection signal is output to the controller 42.

Further, the forward, neutral, and backward tilting positions of the tilt lever 34 are determined by a tilt operation position sensor 4 consisting of a limit switch.
At the same time, the amount of operation of the lever 34 at the forward tilted position and the backward tilted position is detected by a tilt operation amount sensor 44 consisting of a potentiometer, and each detection signal is output to the controller 42.

The controller 42 controls the drive power of the battery 45 to supply power to the induction motor 46.

Further, the electric motor 46 is operatively connected to the hydraulic pump 1, and when the hydraulic pump 1 is rotated with a return oil pressure that is higher than a set value, the electric motor 46 that rotates accordingly connects the battery 45 via the controller 42. Regeneration.

When the controller 42 determines that the lift lever 6 is being operated upward based on the detection result of the lift operation position sensor 40, it calculates the rotational speed of the electric motor 42 with respect to the detected value of the lift operation amount sensor 41. Similarly, the controller 42 calculates the rotational speed of the electric motor 46 with respect to the detected value of the tilt operation amount sensor 44. That is, lift lever 6
When only the tilt lever 34 is operated, the rotation speed command value for the operation amount of the lift lever 6 is set based on predetermined program data. is calculated. Furthermore, when the lifting operation of the lift lever 6 and the operation of the tilt lever 34 are performed at the same time,
The controller 42 calculates a rotational speed command value corresponding to each manipulated variable, and sets the larger rotational speed command value of these two rotational speed command values as the rotational speed of the electric motor 46.

Then, the controller 42 controls the electric power supplied from the battery 45 to the electric motor 46 based on the calculated rotational speed command value, drives the electric motor 46 at a rotational speed according to the rotational speed command value, and discharges the hydraulic pump l. Adjust amount. That is, the lifting speed of the fork and the tilting speed of the mast are controlled according to the amount of operation of the lift lever 6 in the upward direction and the amount of operation of the tilt lever 34.

Next, the operation of the hydraulic system configured as described above will be explained.

Now, as shown in Figure 2, in order to raise the fork,
When the lift lever 6 is operated upward, the lift control valve 5 is held at position 3, and the pump 1 is driven via the electric motor 46 which is rotated at a rotational speed command value according to the amount of operation of the lift lever 6. The hydraulic oil discharged from the pump 1 is supplied to the lift cylinder 7 via the lift control valve 5 and the lift conduit 8, and is extended to raise the fork.

At the same time, the pilot fluid P+ flowing from the main pipe 4 through the operating pilot pipe 25 applies opening pressure to the pilot port of the driving check valve I7.

As a result, the driving check valve 17 is opened, and the pilot fluid P2 flows from the connection point X to the port pressurizing pilot pipe I3 via the closing pilot pipe 19. And b
The pilot port of the switching valve 11 in the position is pressurized,
The switching valve 11 is switched to position a, resulting in the state shown in FIG. This pilot fluid P2 is transferred from the pressurizing pilot pipe 1 to the point where the exit passage is blocked by the blocking check valve 21.
3 and continues to hold the switching valve 11 at position a.

Then, when the lift lever 6 is still operated to the upward side, the rotation speed of the electric motor 46 is increased, and the lift cylinder 7 is extended to the stroke end by the pressure oil sent from the pump 1 through the lift control valve 5, and the fork is Reach the highest position. Accordingly, the pressure inside the cylinder 7 is increased, the discharge pressure of the hydraulic pump 1 becomes the relief pressure of the check valve 47, and the pressure of the pilot fluid in the operating pilot pipe 25 and detour pilot pipe 27 is also increased, and the driving non-return check The relief valve R is opened while the valve 17 is kept open. As a result, the pilot port of the second blocking check valve 23 is pressurized by the pilot fluid flowing through the relief valve R, and the check valve 23 is opened. and,
The pilot fluid of the switching valve 11 supplied from the driving check valve 17 flows through the orifice 22 and the second
The water flows out into the drain pipe 12 through the blocking check valve 23 .

In this state, the pressure of the pilot fluid is sufficiently greater than the pressure required to hold the switching valve 11 in the a position, and the pilot fluid flows through the orifice 22 to the drain pipe 12.
The pressurizing pilot line 13 of the switching valve 11
Sufficient pressure remains within the valve to maintain the switching valve 11 in position a.

When the lift lever 6 is switched to the neutral position from the above state, the lift control valve 5 is switched to the b position as shown in FIG. The discharge pressure suddenly drops to 0. As a result, the pilot fluid of the second blocking check valve 23 is transferred to the check valve 28.
The air flows through the operating pilot pipe 25, and the pilot pressure suddenly becomes 0, causing the check valve 23 to close. on the other hand,
The pilot pressure of the drive check valve 17 is maintained by the orifice 26 at a pressure sufficient to keep the check valve 17 open. At the same time, the communication path J in the lift control valve 5
A lift pipe 8 and a pressure relief pilot pipe 1 are connected via b.
6 are in communication with each other, and a pressure corresponding to the load of the fork is applied from the lift pipe 8 to the depressurizing pilot pipe 16, and this force is applied to the closing side of the check valve 14. Therefore, the pressure within the pressurizing pilot pipe line 13 cannot be evacuated.

Therefore, in this state, pressure oil flows from the lift pipe 8 to the pilot port of the switching valve 11 through the drive check valve 17, the check valve 18, and the connection point X, and the pressure at the connection point X is the load on the fork. The value corresponds to . As a result, the switching valve II is controlled by the pressure corresponding to the load on the fork, and when the fork is under a heavy load or an equivalent medium load, it is in position a (Fig. 4), and when the fork is under no load, under a light load, or under a medium load. At the time of medium load according to this, it is switched to position b (FIG. 1).

Then, when the fork is under a heavy load or a similar medium load, the lift lever 6 in the neutral position is operated downward,
When the lift control valve 5 is switched to the C position as shown in FIG. 5, the return hydraulic pressure flowing from the lift cylinder 7 into the lift pipe 8 exceeds the set value. This return oil increases the pressure at the connection point Z of the bypass line from the lift control valve 5 and the return line 9, and the pilot fluid P3 based thereon opens the opening check valve 3I. Therefore, the pilot fluid flowing from the communication line K of the lift control valve 5 to the operation pilot line 30 via the communication pilot line 29 is transferred to the drain line I.
2. Therefore, no opening pressure acts on the blocking check valve 21, and no change in the pressure of the pilot fluid in the pressurizing pilot pipe line 13 occurs. Therefore,
The switching valve 11 is held at position a.

Therefore, the flow of the high-pressure return oil to the drain pipe line 12 is cut off by the switching valve 11 held in the a position in advance, and flows from the return pipe line 9 to the main pipe line 4. Since the communication to the tank T side is blocked by the regeneration check valve 3, this high pressure return oil is forced into the hydraulic pump 1 and the hydraulic pump l
The electric motor 46 that rotates following this rotation functions as a generator, and the battery 4 is supplied via the controller 42.
5 is charged.

On the other hand, when the lift lever 6 is operated from the neutral position to the lower position when the fork is under no load, light load, or medium load equivalent to light load, and the return hydraulic pressure cannot cause the motor 46 to function as a generator, , the switching valve 11 is previously switched to position b. Therefore, pressure does not build up at the connection point Z of the bypass pipeline, and the opening check valve 31 is never opened. Therefore, the pilot fluid in the operating pilot pipe 30 opens the sealing check valve 21, and the pilot fluid remaining in the pressurizing pilot pipe 13 is transferred to the drain pipe 1.
It flows out into 2. Therefore, the state of the switching valve 11 that has already been switched to the b position does not change, and vibrations and the like caused by the switching operation are avoided. Then, the return oil having a pressure lower than the set value that returns from the lift cylinder 7 flows into the drain pipe 12, avoiding the return pipe 9 having a large internal resistance of the pump 1, and is collected in the tank T. Therefore, the low-pressure return oil does not rotate the hydraulic pump l, that is, the electric motor 46, and wasteful power consumption of the battery 45 is avoided.

In the conventional device, the lift control valve 5 changes from the state shown in Fig. 8 to the state shown in Fig. 9.
Slowly operate the lift lever 51 so as to achieve the state shown in the figure, and perform a so-called upward inching operation to control the hydraulic oil to flow little by little from the main pipe 71 to the lift pipe 60 and the operating pilot pipe 62. In this case, main pipe 7
Hydraulic oil supplied from 1 to the operating pilot line 62 passes through an orifice 75 provided in the detour pilot line 63 and flows out to the drain line 69,
The fork may descend due to insufficient supply of hydraulic oil (pressure) to the fork. However, in the device of the present invention, since the operating pilot pipe 25 is connected to the drive check valve 17 without going through the lift control valve 5, when performing the upward inching operation, the lift control valve is connected to the main pipe 4. A situation in which the fork descends due to insufficient supply amount (pressure) of the hydraulic oil supplied to the lift cylinder 7 via the lift cylinder 7 is reliably prevented.

Further, in the conventional device, when the lift cylinder 6I is extended to the end of the upward stroke, the lift lever 51 is
There is also the problem that the fork descends when the fork is returned to the neutral position (the state shown in Figure 8).

This is because the pressure drop in the opening pilot line 76 that supplies opening pilot pressure to the blocking check valve 68 is slow due to the presence of the orifice 77, and when the lift lever 51 is switched to the neutral position, the driving The check valve 64 and the blocking check valve 68 are held open for a while, and the hydraulic oil in the lift cylinder 61 closes the driving check valve 64, the closing pilot pipe 65, and the blocking check valve 68. This is because the water flows out into the drain pipe 69 through the process. However, in the device of this embodiment, when the lift cylinder 7 is extended to the end of its upward stroke, the lift lever 6 is moved to the neutral position (
1), the pilot fluid supplied to the pilot port of the second blocking check valve 23 immediately flows out through the check valve 28 as described above, and 23 will be closed immediately. Therefore, the hydraulic oil in the lift cylinder 7 passes through the same check valve 23 to the train pipe 12.
This prevents the fork from flowing down, thereby reliably preventing the fork from descending.

Further, when the fork is raised from the lowered position under a light load, the pressure oil in the cylinder 7 may oscillate. In this case, pulsation of the pressure oil occurs in the lift pipe 8, and irregular pilot pressure based on this is transmitted to the pressurizing pilot pipe 13 via the closing pilot pipe 19. When the pressure of this pilot fluid increases extremely, it is transmitted to the pressure relief pilot pipe line 16. and,
Although the pulsation of the pressure oil in the lift pipe 8 is also transmitted to the pressure relief pilot pipe 16, the pressurization pilot pipe 13 and the pressure release pilot are transmitted through several pilot pipes. The transmission speed from the lift pipe 8 is different from that of the pipe 16. Therefore, the pressurizing pilot pipe 13
When the pressure is increased, the pressure in the pressure relief pilot line 16 has been reduced, and the irregularly increased pressure of the pilot fluid in the pressurization pilot line 13 is transferred to the pressure relief pilot line 16. Absorbed. Therefore, even if the pressure oil in the lift cylinder 7 fluctuates when the fork is raised from the lowered position under a light load, vibration of the switching valve II is reliably prevented.

[Example 2] Next, a second embodiment will be explained according to FIGS. 6 and 7.

In this embodiment, the second blocking check valve 23 for controlling the outflow of the pressure oil supplied through the driving check valve 17 to the drain pipe line 12 is not provided, and the detour pilot line 27 is not provided.
A pilot check valve 48 is provided at , and the pilot port of the blocking check valve 21 and the detour pilot pipe line 27 are communicated through a pipe line 27b. In addition, port depressurization pipe line 2
0 is provided with an orifice O, and the communication pilot line 29 and the operating pilot line 30 are integrated into one. The rest of the configuration is the same as the device of the first embodiment.

When the lift lever 6 is operated to raise, hydraulic oil is supplied to the lift cylinder 7 via the lift control valve 5 and the lift pipe 8, as in the previous embodiment, and is extended to raise the fork.

At the same time, the pilot fluid flowing from the main line 4 through the operating pilot line 25 applies opening pressure to the pilot port of the driving check valve 17 . As a result, the driving check valve 17 is opened, and the pilot fluid flows from the connection point X to the port pressurizing pilot pipe 13 via the closing pilot pipe 19. Then, the pilot port of the switching valve 11 at position b is pressurized, and the switching valve 11 is switched to position a, resulting in the state shown in FIG. 7. At this point, since the relief valve R is closed, the blockade check valve 21 is also closed, and the pilot fluid remains in the pressurizing pilot pipe line 13 from where the retreat path is blocked by the blockade check valve 21. , continues to hold the switching valve 11 at position a.

Then, when the lift lever 6 is still operated to the upward side, the rotation speed of the electric motor 46 is increased, and the lift cylinder 7 is extended to the stroke end by the pressure oil sent from the pump 1 through the lift control valve 5, and the fork is Reach the highest position. Accordingly, the pressure inside the cylinder 7 is increased, the discharge pressure of the hydraulic pump 1 becomes the relief pressure of the check valve 47, the pressure of the pilot fluid in the operating pilot pipe 25 is also increased, and the driving check valve 17 is opened. While being held, the relief valve R is opened as shown in FIG.

As a result, the pilot fluid flowing through the relief valve R pressurizes the pilot port of the sealing check valve 21 via the conduit 27b, and the check valve 21 is opened. and,
The pilot fluid of the switching valve 11 supplied from the driving check valve 17 flows out into the drain pipe 12 via the orifice O and the blocking check valve 21.

In this state, the pressure of the pilot fluid is sufficiently higher than the pressure required to hold the switching valve 11 in position a, and since the pilot fluid gradually flows into the drain pipe 12 through the orifice O, the switching valve 11 is Sufficient pressure remains in the pressure pilot line 13 to maintain the switching valve 11 at position a.

When the lift lever 6 is switched to the neutral position from the above state, the lift control valve 5 is switched to the b position, the main line 4 is communicated with the drain line 12, and the discharge pressure of the hydraulic pump 1 suddenly becomes 0. . As a result, the relief valve R is closed, and the pressure oil in the pipe line 27b flows out into the operating pilot pipe line through the pilot check valve 48 and the check valve 28, and the sealing check valve 21 is closed. On the other hand, the pilot pressure of the driving check valve 17 is increased by the action of the orifice 26.
is held under sufficient pressure to hold it open.

At the same time, the lift conduit 8 and the pressure relief pilot conduit 16 are communicated via the communication path Jb in the lift control valve 5, and the fork from the lift conduit 8 is connected to the pressure relief pilot conduit 16. A pressure corresponding to the load is applied, and this force is applied to the closing side of the check valve 14. Therefore, the pressure within the pressurizing pilot pipe line 13 cannot be evacuated. Therefore, in this state, pressure oil flows from the lift pipe 8 to the pilot port of the check valve 11 through the drive check valve 17, the check valve 18, and the connection point X, and the pressure at the connection point X is applied to the fork. The value corresponds to the load. As a result, the switching valve 11 is controlled by the pressure according to the load on the fork, and when the fork is under a heavy load or a similar medium load, it is in the a position (fourth position).
(Fig. 1), when the fork is under no load, light load, or similar medium load, it is switched to position b (Fig. 1).

Therefore, in this embodiment as well, the switching valve 11 is switched in accordance with the load condition of the fork as in the previous embodiment, and the low-pressure return oil is reliably prevented from rotating the hydraulic pump l, that is, the electric motor 46. Wasteful power consumption of the battery 45 is avoided. In addition, since the operating pilot pipe 25 is connected to the pilot port of the drive check valve 17 without going through the lift control valve 5, the main pipe 4 is The amount of hydraulic oil supplied to the lift cylinder 7 via the lift control valve 5 from
This reliably prevents the fork from falling due to lack of pressure.

Note that the present invention is not limited to the above embodiments,
For example, a direct current motor may be used instead of the induction motor 46, or it may be applied to industrial vehicles other than forklifts.

[Effects of the Invention] As detailed above, according to the present invention, when the fork is lowered, the position where the return passage switching valve communicates the return passage with the drain pipe line in response to the load of the fork, and the position where the return passage switching valve communicates with the drain pipe line, The electric motor is rotated by the low-pressure return oil via the hydraulic pump, and wasteful consumption of battery power is reliably avoided. In addition, since the discharge oil of the hydraulic pump is directly supplied as pilot pressure to the pilot operation valve installed in the pipeline for driving and operating the return path switching valve, without going through the lift control valve, the upward inching of the lift lever is prevented. It has the excellent effect of reliably preventing the fork from descending during operation.

[Brief explanation of the drawing]

1 to 5 show a first embodiment embodying the present invention. FIG. 1 is a circuit diagram showing the hydraulic and electrical configuration, and FIG. 2 is a circuit diagram showing the hydraulic and electrical configuration when the fork is raised. Fig. 3 is a hydraulic circuit diagram illustrating the state of the return path switching valve when the fork is in the highest position;
The figure is a circuit diagram showing the hydraulic and electrical configuration when the fork is held without moving up and down, Figure 5 is a circuit diagram showing the hydraulic and electrical configuration when the fork is lowered under a heavy load, and Figures 6 and 7 are The figures show the second embodiment, in which Fig. 6 corresponds to Fig. 1, Fig. 7 corresponds to Fig. 2, and Fig. 8 shows the hydraulic and electrical configuration of the conventional device. The circuit diagram shown in FIG. 9 is a hydraulic circuit diagram showing a state when the fork is raised in a conventional device. Hydraulic pump 1, lift control valve 5, lift cylinder 7,
A switching valve 11 as a return path switching valve, a drain pipe 12,
A pilot pipe line 13 for pressurizing the port, which constitutes the return path check valve driving means. A driving check valve 17, an operating pilot pipe 25, and a blocking check valve 21 constituting a preliminary switching means. Second blocking check valve 23. Relief valve R1 detour pilot pipe 27, battery 45, induction motor 46° Patent applicant Toyota Industries Corporation Nishina Kogyo
Co., Ltd.

Claims (1)

[Claims] 1. A lift cylinder that raises and lowers a cargo handling member, and a return hydraulic pressure that supplies hydraulic oil to the lift cylinder and returns from the lift cylinder based on the load of the cargo handling member when the lift cylinder is contracted. When exceeds a predetermined value, a hydraulic pump is rotatably driven by the return oil and functions as a hydraulic motor, and the lift cylinder is interposed between the lift cylinder and the hydraulic pump, and the lift cylinder can be extended or contracted by changing its position. a lift control valve held in the hydraulic pump; and an electric motor that is operatively connected to the hydraulic pump and is driven by electric power supplied from a battery to rotate the hydraulic pump and is rotated by the hydraulic pump to regenerate electric power from the battery. In a hydraulic system for a battery-powered industrial vehicle, the hydraulic system is disposed in the return oil return path, and the return oil return path is selectively connected to the hydraulic pump side and the drain side according to the magnitude of the pressure of the return oil. a return path switching valve that connects the return path to the hydraulic pump side by driving the return path switching valve based on a hydraulic pressure value between the lift control valve and the lift cylinder when the lift cylinder is extended; , a switching valve driving means to which oil discharged from the hydraulic pump is supplied as pilot pressure without going through a lift control valve; A hydraulic system for a battery-powered industrial vehicle, which is provided with a preliminary switching means for preliminarily switching the connection state of a return path switching valve to a connection state based on the return hydraulic pressure when the cylinder is contracted.