JP2022024841A - Impact suppression device for industrial vehicle - Google Patents

Abstract

To provide an impact suppression device for an industrial vehicle capable of suppressing increase in upward and downward movement of a loading part when operation is stopped.SOLUTION: In an impact suppression device of a forklift, a control device 60 switches a switching valve 51 to an open position K1 when a lift operation lever 17 is in a neutral position. The control device 60 switches the switching valve 51 to a close position K2 while operation is performed from the start of operation of the lift operation lever 17 in the neutral position and switches the switching valve 51 to the open position K1 at a convergence time when variation of hydraulic oil pressure of a bottom chamber 14b caused accompanying the stop of vertical movement of a fork 15a is converged after stopping the operation of the lift operation lever 17.SELECTED DRAWING: Figure 4

Description

The present invention relates to an impact suppression device for an industrial vehicle including an accumulator.

For example, in a forklift, when the load loaded on the fork as a loading portion sinks when traveling on an uneven surface or the like, the hydraulic oil is rapidly compressed by the piston in the bottom chamber of the lift cylinder. Then, the hydraulic pressure may rise sharply, causing a large impact on the load. In order to suppress the occurrence of such a large impact, it has been proposed to connect an accumulator to the bottom chamber of the lift cylinder.

The accumulator includes an accumulator hydraulic chamber into which hydraulic oil is introduced from a lift cylinder, and an accumulator gas chamber partitioned from the accumulator hydraulic chamber. Then, when the load loaded on the fork sinks, the hydraulic oil is pushed out from the bottom chamber of the lift cylinder, and the pushed out hydraulic oil is introduced into the accumulator hydraulic chamber. At this time, in the accumulator, the gas in the accumulator gas chamber is compressed, so that the hydraulic pressure is gradually increased, and it is suppressed that a large impact is generated on the load.

Further, the bottom chamber of the lift cylinder and the accumulator hydraulic chamber are connected by a connecting oil passage branching from an oil supply / drainage passage for supplying hydraulic oil to the bottom chamber. A flow control valve is provided in the connecting oil passage (see, for example, Patent Document 1). The flow control valve is equipped with a variable orifice. The variable orifice allows the hydraulic oil to flow from the bottom chamber to the accumulator hydraulic chamber without resistance, and the flow from the accumulator hydraulic chamber to the bottom chamber provides resistance by the variable orifice, reducing pressure fluctuations in the bottom chamber.

Therefore, in Patent Document 1, the speed of pressure drop when the pressure in the bottom chamber suddenly drops due to the variable orifice, such as when lowering the load held in the ascending position or when stopping while ascending, is the speed of pressure drop. It will be relaxed.

Japanese Patent Application Laid-Open No. 2003-201098

However, during a sudden stop while the fork is rising and a sudden stop while the fork is descending, the hydraulic oil is repeatedly exchanged between the bottom chamber and the accumulator hydraulic chamber due to the inertial force acting on the load. The ups and downs of the fork increase due to the provision of the accumulator.

An object of the present invention is to provide an impact suppressing device for an industrial vehicle capable of suppressing an increase in ups and downs of a loading portion when an operation is stopped.

The impact suppression device for an industrial vehicle for solving the above problems has a vehicle body provided with a loading portion for loading a load and a bottom chamber, and the loading portion is provided according to the hydraulic pressure introduced into the bottom chamber. An accumulator including an elevating lift cylinder, an oil tank connected to the bottom chamber via an oil supply / drainage passage, an accumulator hydraulic chamber whose volume changes according to the introduction of hydraulic oil, and the supply. The connecting oil passage that branches from the oil drainage channel and is connected to the accumulator hydraulic chamber, the open position that opens the connecting oil passage to communicate the bottom chamber and the accumulator hydraulic chamber, and the connecting oil passage are cut off. To operate the lift cylinder by connecting a signal to a switching valve that can take a closed position that does not communicate between the bottom chamber and the accumulator hydraulic chamber, a control device that controls switching of the switching valve, and the control device. The control device is switched from the switching valve to the open position at the neutral position of the operation member, and the control device is said to start operating the operation member at the neutral position. While the operation is being performed, the switching valve is switched to the closed position, and the control device is at a time point after the operation of the operating member is stopped, and the bottom is generated when the loading portion is stopped up and down. The gist is to switch the switching valve to the open position at the time of convergence when the fluctuation of the hydraulic pressure in the chamber converges.

According to this, when the ascending / descending of the loading portion is stopped due to the stopping of the operation of the operating member, an inertial force acts on the load. The amplitude of the hydraulic pressure caused by this inertial force is generated in the hydraulic oil in the bottom chamber. However, the switching valve is in the closed position until the convergence point when the amplitude of the hydraulic pressure converges, and the bottom chamber and the accumulator hydraulic pressure chamber are cut off. For this reason, the flow of hydraulic oil between the bottom chamber and the accumulator hydraulic chamber is blocked from the time when the loading portion is stopped ascending and descending to the time when it converges. Then, when the amplitude of the hydraulic pressure converges, the control device switches the switching valve to the open position. Therefore, it is possible to suppress an increase in the ups and downs of the loading portion when the operation of the operating member is stopped.

Regarding the impact suppression device of an industrial vehicle, the convergence time is when the waiting time required from the operation stop time of the operation member to the convergence of the amplitude of the hydraulic pressure generated by the ascending / descending stop of the loading portion has elapsed. There may be.

According to this, since the time point at which the amplitude of the hydraulic pressure converges can be grasped by the passage of time, the control load of the control device can be suppressed.
The impact suppression device for an industrial vehicle includes a lift cylinder pressure sensor that measures the hydraulic pressure in the bottom chamber, and the control device acquires the hydraulic pressure measured by the lift cylinder pressure sensor and obtains the hydraulic pressure at the time of convergence. May be the time when the hydraulic pressure obtained from the lift cylinder pressure sensor becomes less than the threshold value.

According to this, since the hydraulic pressure of the bottom chamber can be actually measured by the pressure sensor for the lift cylinder, it is possible to accurately determine whether or not the amplitude of the hydraulic pressure has converged.
The impact suppression device for an industrial vehicle is provided with an acceleration sensor that detects the acceleration of the loading portion, the control device acquires the acceleration measured by the acceleration sensor, and the convergence time point is the acceleration acquired from the acceleration sensor. May be less than the threshold.

According to this, since the hydraulic pressure of the bottom chamber can be indirectly measured by the acceleration sensor, it is possible to determine whether or not the amplitude of the hydraulic pressure has converged.
For the impact suppression device of an industrial vehicle, when the loading portion is raised, the control device is set after the operation start time of the operation member from the neutral position and before the operation stop time. The switching valve is switched to the closed position at the time when the preparation is completed, and the time when the preparation is completed is the time when the hydraulic pressure in the bottom chamber and the hydraulic pressure in the accumulator hydraulic chamber are in equilibrium after the operation start time. good.

According to this, the hydraulic pressure of the bottom chamber and the hydraulic pressure of the accumulator hydraulic chamber can be balanced by the time when the preparation is completed. Therefore, when the switching valve is switched to the open position at the time of convergence after the operation is stopped, for example, it is possible to prevent the hydraulic oil in the bottom chamber from suddenly flowing into the accumulator hydraulic chamber.

According to the present invention, it is possible to suppress an increase in ups and downs of the loading portion when the operation is stopped.

The side view which shows the forklift of an embodiment. The figure which shows the impact suppression device in the state which exerts an impact suppression function. The figure which shows the impact suppression device which the switching valve is open position when the fork rises. The figure which shows the impact suppression device at the time of preparation completion. The figure which shows the impact suppression device at the time of stopping the ascending operation. (A) is a graph showing the relationship between the lift operating lever and the valve position when ascending, and (b) is a graph showing the relationship between the fork height and the hydraulic pressure. The figure which shows the impact suppression device at the time of convergence for ascending. (A) is a graph showing the relationship between the lift operating lever and the valve position during descent, and (b) is a graph showing the relationship between the fork height and the hydraulic pressure. The figure which shows the impact suppression device at the time of starting a descent operation. The figure which shows the impact suppression device at the time of stopping a descent operation. The schematic diagram which shows another example of the impact suppression device.

Hereinafter, an embodiment in which an impact suppression device for an industrial vehicle is embodied as an impact suppression device for a forklift will be described with reference to FIGS. 1 to 10.
As shown in FIG. 1, a mast 13 is erected in front of the vehicle body 12 of a battery-powered forklift 11 as an industrial vehicle. The mast 13 is composed of a pair of left and right outer masts 13a that are supported so as to be tiltable back and forth with respect to the vehicle body 12, and an inner mast 13b that slides up and down on these outer masts 13a. A lift cylinder 14 is disposed at the rear of each outer mast 13a, and the tip of the piston rod 14a of the lift cylinder 14 is connected to the upper part of the inner mast 13b. A lift bracket 15 is attached to the inside of the inner mast 13b. The lift bracket 15 includes a fork 15a.

As shown in FIG. 2, since the load W is loaded on the fork 15a, the fork 15a constitutes a loading portion. When the piston rod 14a of the lift cylinder 14 is retracted and retracted with respect to the cylinder tube 14c, the lift bracket 15 moves up and down via the chain 18, and the fork 15a moves up and down.

As shown in FIG. 1, a driver's cab 16 is provided on the upper part of the vehicle body 12. A lift operating lever 17 as an operating member for operating the lift cylinder 14 to raise and lower the lift bracket 15 is provided in the front portion of the driver's cab 16. The forklift 11 includes a hydraulic device 20 that operates the lift cylinder 14.

As shown in FIG. 2, in the hydraulic device 20, an oil tank 24 is connected to the bottom chamber 14b of the lift cylinder 14 via an oil supply / drainage passage 21. A control valve 22 and a hydraulic pump 23 are provided in the oil supply / drainage passage 21. The lift cylinder 14 raises and lowers the fork 15a according to the hydraulic pressure introduced into the bottom chamber 14b.

The control valve 22 is a 3-position 2-port valve. The control valve 22 is switched to any one of the first position 22a, the second position 22b, and the third position 22c. By switching the control valve 22, the connection state between the bottom chamber 14b and the oil tank 24 via the oil supply / drainage passage 21 is switched.

When the control valve 22 is switched to the first position 22a, the hydraulic pump 23 and the bottom chamber 14b communicate with each other at one port. When the control valve 22 is switched to the first position 22a, the hydraulic oil 55 can be supplied from the oil tank 24 to the bottom chamber 14b by pumping the hydraulic oil 55 by the hydraulic pump 23. In the other port, the bottom chamber 14b and the oil tank 24 are cut off.

When the control valve 22 is switched to the second position 22b, the bottom chamber 14b and the oil tank 24 are shut off at both ports.
When the control valve 22 is switched to the third position 22c, the bottom chamber 14b and the oil tank 24 communicate with each other at one port, bypassing the hydraulic pump 23. When the control valve 22 is switched to the third position 22c, the hydraulic oil 55 can be discharged from the bottom chamber 14b to the oil tank 24. In the other port, the bottom chamber 14b and the oil tank 24 are cut off.

The control valve 22 is signal-connected to the control device 60. Further, the lift operation lever 17 is signal-connected to the control device 60. The control device 60 switches the position of the control valve 22 according to the operation of the lift operation lever 17.

In order to raise the fork 15a, the lift operating lever 17 is lifted, and when the control device 60 detects the lifting operation of the lift operating lever 17, the control device 60 switches the control valve 22 to the first position 22a. In order to lower the fork 15a, the lift operation lever 17 is lowered, and when the control device 60 detects the lowering operation of the lift operation lever 17, the control device 60 switches the control valve 22 to the third position 22c. In order to stop the raising and lowering of the fork 15a, the lift operating lever 17 is positioned in the neutral position when the operation of the lift operating lever 17 is stopped. The neutral position is a position in which neither the raising operation nor the lowering operation of the lift operation lever 17 is performed. When the control device 60 detects the neutral position of the lift operation lever 17, the control valve 22 switches the control valve 22 to the second position 22b.

Next, the impact suppression device of the forklift 11 will be described.
The impact suppression device includes an accumulator 26, a switching valve 51, and a control device 60 for controlling the switching valve 51. Further, the impact suppression device includes a connecting oil passage 25 that branches from the oil supply / drainage passage 21 and is connected to the accumulator 26.

An accumulator 26 is connected to the oil supply / drainage passage 21 via a connecting oil passage 25. A piston 27 is slidably housed inside the accumulator 26. The piston 27 divides the inside of the accumulator 26 into an accumulator hydraulic chamber 28 and an accumulator gas chamber 29. A connecting oil passage 25 is connected to the accumulator hydraulic chamber 28. When the hydraulic oil 55 is introduced into the accumulator hydraulic chamber 28, the gas in the accumulator gas chamber 29 is compressed, and the hydraulic pressure is accumulated in the accumulator hydraulic chamber 28.

A switching valve 51 is connected to the connecting oil passage 25. The switching valve 51 is signal-connected to the control device 60. The switching of the switching valve 51 is controlled by the control device 60. The switching valve 51 is a normally open type that is opened in a state where a control signal from the control device 60 is not input. The switching valve 51 closes when a control signal from the control device 60 is input.

When the switching valve 51 is open, the bottom chamber 14b and the accumulator hydraulic chamber 28 communicate with each other via the oil supply / drainage passage 21 and the connecting oil passage 25. In the following description, the position where the switching valve 51 is open is defined as the open position K1. When the switching valve 51 is switched to the open position K1, the hydraulic oil 55 can flow between the bottom chamber 14b and the accumulator hydraulic chamber 28.

On the other hand, when the control signal is input from the control device 60 and the switching valve 51 is closed, the bottom chamber 14b and the accumulator hydraulic chamber 28 are cut off, and the communication is not communicated. In the following description, the position where the switching valve 51 is in the closed state is referred to as the closed position K2. When the switching valve 51 is switched to the closed position K2, the hydraulic oil 55 cannot move between the bottom chamber 14b and the accumulator hydraulic chamber 28. Therefore, the switching valve 51 can be switched between the open position K1 and the closed position K2 by the control of the control device 60. When the control device 60 detects the neutral position of the lift operation lever 17, the control device 60 switches the switching valve 51 to the open position K1.

The control device 60 is an electronic control unit including a storage unit 60b including a RAM, a ROM, and the like, and a timer 60c. The storage unit 60b stores a program or the like for switching the switching valve 51. The control device 60 may include dedicated hardware that executes at least a part of various processes, for example, an integrated circuit for a specific application: ASIC. The control device 60 may be configured as one or more processors operating according to a computer program, one or more dedicated hardware circuits such as an ASIC, or a circuit including a combination thereof. The processor includes a CPU and a memory such as RAM and ROM. The storage unit 60b stores a program code or a command configured to cause the CPU to execute the process.

The storage unit 60b, i.e., a computer-readable medium, includes anything accessible by a general purpose or dedicated computer. The storage unit 60b stores the preparation time UT1, the ascending waiting time UT2, and the descending waiting time DT. The preparation time UT1, the ascending standby time UT2, and the descending standby time DT will be described later.

Next, a configuration for suppressing an increase in ups and downs of the load W that occurs when the fork 15a on which the load W is placed is suddenly stopped to rise will be described.
First, the operation of scooping the load W with the fork 15a will be described. The bottom chamber 14b and the accumulator hydraulic chamber 28 have the minimum volume in a state where the lift bracket 15 is lowered and the fork 15a is in a position where it can slip under the load W.

As shown in FIG. 2, when the lift operation lever 17 is not operated and is in the neutral position, the control valve 22 is in the second position 22b and is in the closed state, and the switching valve 51 is in the open position K1. The valve is open.

In order to raise the load W with the fork 15a, the fork 15a is inserted under the load W. The lift operation lever 17 is lifted by the operator, and the lift bracket 15 is lifted.

As shown in FIGS. 3 and 6A, when the control device 60 detects the start of the ascending operation of the lift operation lever 17, the control valve 22 is switched to the first position 22a and opened at Ut0 at the start of the ascending operation. The valve state is set and the hydraulic pump 23 is driven. The switching valve 51 remains at the open position K1.

Then, as shown in FIG. 6B, the hydraulic pressure of the bottom chamber 14b rises. As the hydraulic pressure rises, the lift bracket 15 starts to rise, and the height of the fork 15a gradually increases.

As the fork 15a comes into contact with the lower surface of the load W, receives the load of the load W, and the hydraulic pressure rises, the hydraulic oil 55 sent from the oil tank 24 passes through the accumulator hydraulic chamber 25 via the connecting oil passage 25. As it is introduced into 28, the gas in the accumulator gas chamber 29 is also compressed, and the gas pressure in the accumulator gas chamber 29 rises. Then, the gas pressure in the accumulator gas chamber 29 is compressed to a predetermined value and stored in the accumulator 26. At this time, the hydraulic pressure of the bottom chamber 14b and the hydraulic pressure of the accumulator hydraulic chamber 28 are in equilibrium. The time when the hydraulic pressure of the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 are in equilibrium is defined as the time when the preparation is completed Ut1.

When the fork 15a is raised, the preparation completion time point Ut1 is set after the raising operation start time point Ut0 of the lift operation lever 17 from the neutral position and before the raising operation stop time point Ut2 described later. Further, the preparation completion time point Ut1 is a time point at which the working hydraulic pressures of the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 are in equilibrium after the ascending operation start time point Ut0.

In the present embodiment, the time required from Ut0 at the start of the ascending operation to Ut1 at the completion of preparation is obtained in advance by an experiment or the like. The time required from Ut0 at the start of the ascending operation to Ut1 at the completion of preparation is defined as the preparation time UT1. Therefore, when the preparation time UT1 elapses from the start time Ut0 of the ascending operation, the hydraulic pressure of the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 is in equilibrium. Hereinafter, the hydraulic pressure when the hydraulic pressure of the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 are in equilibrium is referred to as the equilibrium hydraulic pressure.

The preparation time UT1 is stored in the storage unit 60b of the control device 60. The timer 60c of the control device 60 starts the time measurement from Ut0 at the start of the ascending operation of the lift operation lever 17. When the time measured by the timer 60c reaches the preparation time UT1, the control device 60 switches the switching valve 51 to the closed position K2 as shown in FIGS. 4 and 6A. That is, the control device 60 switches the switching valve 51 to the closed position K2 when the preparation time UT1 has elapsed from Ut0 at the start of the ascending operation. In other words, the control device 60 switches the switching valve 51 from the open position K1 to the closed position K2 while the lift operation lever 17 is being lifted after Ut0 at the start of the ascending operation. The control valve 22 remains at the first position 22a.

Then, in a state where the hydraulic pressure of the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 is in equilibrium, the communication between the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 is cut off. Therefore, the hydraulic oil 55 cannot flow between the bottom chamber 14b and the accumulator hydraulic pressure chamber 28, and is maintained at the equilibrium hydraulic pressure.

Even after the preparation time UT1 has elapsed from the start point Ut0 of the lift operation lever 17, the lift operation lever 17 continues to be raised, and the switching valve 51 is maintained at the closed position K2 while the fork 15a is raised. Will be done. Therefore, the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 are maintained in a disconnected state, and the hydraulic pressure of the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 is maintained at the equilibrium hydraulic pressure. Further, the control valve 22 is maintained at the first position 22a and is maintained in the valve open state. Therefore, the hydraulic oil 55 is pumped to the bottom chamber 14b by the hydraulic pump 23.

Then, the raising operation of the lift operation lever 17 is stopped.
As shown in FIGS. 5 and 6A, when the control device 60 detects that the lift operation lever 17 has stopped ascending operation, the control valve 22 is placed at the first position 22a to the second position at Ut2 when the ascending operation is stopped. Switch to 22b and close the control valve 22. Then, the pressure feeding of the hydraulic oil 55 from the hydraulic pump 23 to the bottom chamber 14b is stopped, and the raising and lowering of the lift bracket 15 is stopped.

When the ascent of the lift bracket 15 is stopped, an upward force acts on the load W due to the inertial force, and the upward force acts to reduce the hydraulic pressure of the bottom chamber 14b. After that, when the load W falls due to gravity, the lift bracket 15 is pressed downward and the hydraulic oil 55 in the bottom chamber 14b is compressed. Then, the hydraulic pressure of the bottom chamber 14b rises. The hydraulic pressure of the bottom chamber 14b is repeatedly lowered and raised until the vertical movement of the load W converges.

The vertical movement of the load W is the largest immediately after the fork 15a stops ascending, and the vertical movement of the load W gradually decreases with the passage of time and finally converges. As shown in FIG. 6B, similar to the vertical movement of the load W, the amplitude of the hydraulic pressure is the largest immediately after the fork 15a stops rising, gradually decreases with the passage of time, and converges. do. The larger the amplitude of the hydraulic pressure, the larger the fluctuation of the hydraulic pressure, and the larger the vertical displacement of the load W.

When the vertical movement of the load W converges, the amplitude of the hydraulic pressure of the bottom chamber 14b also converges, which is close to the equilibrium hydraulic pressure. In the present embodiment, the time point at which the amplitude of the hydraulic pressure converges is defined as the rising convergence time point Ut3. The ascending convergence time point Ut3 is a time when the amplitude of the hydraulic pressure becomes smaller in the range of 5 to 15% of the maximum amplitude. After that, the hydraulic pressure becomes the equilibrium hydraulic pressure, and the fluctuation is settled.

In the present embodiment, the time required from the ascending operation stop time Ut2 to the ascending convergence time Ut3 is obtained in advance by an experiment or the like. The time required from the ascending operation stop time Ut2 to the ascending convergence time Ut3 is defined as the ascending standby time UT2. Therefore, when the ascending standby time UT2 elapses from the ascending operation stop time Ut2, the fluctuation of the working hydraulic pressure converges.

The ascending standby time UT2 is stored in the storage unit 60b of the control device 60. The timer 60c of the control device 60 measures the elapsed time from Ut2 at the time when the lift operation lever 17 stops the ascending operation. When the elapsed time measured by the timer 60c reaches the rising standby time UT2, the control device 60 switches the switching valve 51 to the open position K1.

That is, the control device 60 switches the switching valve 51 to the open position K1 when the ascending standby time UT2 elapses from the ascending operation stop time Ut2. Then, the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 are communicated with each other in a state where the fluctuations in the operating hydraulic pressure of the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 are converged.

Next, a configuration for suppressing an increase in ups and downs of the load W that occurs when the fork 15a on which the load W is placed is suddenly stopped to descend will be described.
As shown in FIGS. 7 and 8A, when the lift operating lever 17 is in the neutral position and the fork 15a is held in the raised position, the hydraulic pressures of the bottom chamber 14b and the accumulator hydraulic chamber 28 are in equilibrium. , Held in equilibrium hydraulic pressure. Further, the control valve 22 is located at the second position 22b and is in a closed state. Further, the switching valve 51 is located at the open position K1.

In order to lower the load W, the lift operation lever 17 is lowered by the operator, and the lift bracket 15 is lowered.
As shown in FIGS. 8A and 9, when the control device 60 detects the start of the lowering operation of the lift operation lever 17, the control valve 22 is switched to the third position 22c and opened at Dt0 at the start of the lowering operation. The valve state is set and the switching valve 51 is switched to the closed position K2. Then, the hydraulic oil is discharged from the bottom chamber 14b to the oil supply / drainage passage 21. The hydraulic oil discharged from the bottom chamber 14b is discharged to the oil tank 24.

When the hydraulic oil is discharged from the bottom chamber 14b, the lift bracket 15 starts to descend, and the height of the fork 15a gradually decreases. After Dt0 at the start of the lowering operation of the lift operating lever 17, the lifting operating lever 17 is lowered and the switching valve 51 is maintained at the closed position K2 while the lift bracket 15 is lowered. That is, the communication between the bottom chamber 14b and the accumulator hydraulic chamber 28 is cut off. Therefore, the state in which the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 are cut off is maintained, and it becomes impossible for the hydraulic pressure to flow between the bottom chamber 14b and the accumulator hydraulic pressure chamber 28. Further, the control valve 22 is maintained at the third position 22c and is maintained in the valve open state. Therefore, the hydraulic oil 55 is discharged from the bottom chamber 14b to the oil tank 24.

Then, the lowering operation of the lift operation lever 17 is stopped.
As shown in FIGS. 8A and 10, when the control device 60 detects the lowering operation stop of the lift operation lever 17, the control valve 22 is placed in the second position from the third position 22c at the lowering operation stop time Dt1. Switch to 22b and close the control valve 22. Then, the discharge of the hydraulic oil 55 from the bottom chamber 14b to the oil tank 24 is stopped, and the lowering of the lift bracket 15 is stopped.

When the lowering of the lift bracket 15 is stopped, a downward force acts on the load W due to the inertial force, and the downward force acts to compress the hydraulic pressure of the bottom chamber 14b and raise it. After that, the compressed hydraulic pressure expands. Then, the hydraulic pressure of the bottom chamber 14b decreases. The hydraulic pressure of the bottom chamber 14b is repeatedly lowered and raised until the vertical movement of the load W converges. The vertical movement of the load W is the largest immediately after the lift bracket 15 stops descending, and the vertical movement of the load W gradually decreases with the passage of time and finally converges.

As shown in FIG. 8B, the amplitude of the working hydraulic pressure of the bottom chamber 14b is the largest immediately after the lift bracket 15 has stopped descending, and the working hydraulic pressure of the bottom chamber 14b becomes larger with the passage of time, similar to the vertical movement of the load W. The amplitude gradually decreases and converges. The larger the amplitude of the hydraulic pressure, the larger the displacement of the load W in the vertical direction.

When the vertical movement of the load W converges, the amplitude of the hydraulic pressure of the bottom chamber 14b also converges, which is close to the equilibrium hydraulic pressure. In the present embodiment, the time point at which the amplitude of the hydraulic pressure converges is defined as the downward convergence time point Dt2. The descent convergence time point Dt2 is the time when the amplitude of the hydraulic pressure becomes smaller in the range of 5 to 15% of the maximum amplitude. After that, the hydraulic pressure becomes the equilibrium hydraulic pressure, and the amplitude is settled.

In the present embodiment, the time required from the descent operation stop time Dt1 to the descent convergence time Dt2 is obtained in advance by an experiment or the like. The time required from the descent operation stop time Dt1 to the descent convergence time Dt2 is defined as the descent standby time DT. Therefore, when the lowering standby time DT elapses from the lowering operation stop time Dt1, the amplitude of the working hydraulic pressure converges.

The lowering standby time DT is stored in the storage unit 60b of the control device 60. The timer 60c of the control device 60 measures the elapsed time from the lowering operation stop time Dt1 of the lift operation lever 17. When the elapsed time measured by the timer 60c reaches the lowering standby time DT, the control device 60 switches the switching valve 51 to the open position K1.

That is, the control device 60 switches the switching valve 51 to the open position K1 when the lowering standby time DT has elapsed from the lowering operation stop time Dt1. Then, the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 are communicated with each other in a state where the fluctuations in the operating hydraulic pressure of the bottom chamber 14b and the accumulator hydraulic pressure chamber 28 are converged.

Next, the operation of the impact suppression device will be described.
As shown in FIG. 7, when the forklift 11 travels with the lift bracket 15 held in the raised position, the control valve 22 is in the second position 22b. Further, the switching valve 51 is in the open position K1.

When the forklift 11 runs on an uneven surface, the load W of the fork 15a sinks. Then, the hydraulic oil 55 in the bottom chamber 14b of the lift cylinder 14 is extruded, and the extruded hydraulic oil 55 flows into the connecting oil passage 25. At this time, since the switching valve 51 is in the open position K1, the hydraulic oil 55 extruded from the bottom chamber 14b is introduced into the accumulator hydraulic chamber 28 via the switching valve 51. As the hydraulic oil 55 is introduced into the accumulator hydraulic pressure chamber 28, the gas in the accumulator gas chamber 29 is compressed, and the hydraulic pressure gradually rises. As a result, an impact is generated on the load W, which is suppressed.

When the forklift 11 is stopped and the load W is placed on the fork 15a, the switching valve 51 is opened until the preparation time UT1 elapses from the start time Ut0 of the ascending operation when the fork 15a is raised. It is located at position K1 and the bottom chamber 14b and the accumulator hydraulic chamber 28 are in equilibrium when the preparation time UT1 elapses.

Then, after the preparation time UT1 has elapsed, the control device 60 switches the switching valve 51 to the closed position K2, so that the communication between the bottom chamber 14b and the accumulator hydraulic chamber 28 is cut off during the raising operation of the lift operating lever 17. After that, when the ascending of the fork 15a is suddenly stopped, the inflow of the hydraulic oil 55 from the bottom chamber 14b to the accumulator hydraulic chamber 28 is suppressed by the switching valve 51 located at the closed position K2. When the ascending standby time UT2 elapses from the ascending operation stop time Ut2, the control device 60 switches the switching valve 51 to the open position K1. That is, when the ups and downs of the load W due to the sudden stop converge and the fluctuation of the hydraulic oil 55 converges, the switching valve 51 is switched to the open position K1.

Further, when the forklift 11 is stopped and the load W is placed on the fork 15a and the fork 15a is lowered, the control device 60 switches the switching valve 51 to the closed position K2, so that the lift operation lever 17 is used. During the lowering operation, the communication between the bottom chamber 14b and the accumulator hydraulic chamber 28 is cut off. After that, when the lowering of the fork 15a is suddenly stopped, the switching valve 51 is located at the closed position K2, and when the lowering standby time DT elapses from the lowering operation stop time Dt1, the control device 60 opens the switching valve 51. Switch to K1. That is, when the ups and downs of the load W due to the sudden stop converge and the fluctuation of the hydraulic oil 55 converges, the switching valve 51 is switched to the open position K1.

According to the above embodiment, the following effects can be obtained.
(1) When the ascending / descending of the fork 15a is suddenly stopped, the control device 60 positions the switching valve 51 at the closed position K2 from the time when the operation is stopped until the waiting times UT2 and DT elapse. The switching valve 51 at the closed position K2 cuts off the space between the bottom chamber 14b and the accumulator hydraulic chamber 28, and prevents the hydraulic oil 55 from coming and going. The control device 60 switches the switching valve 51 to the open position K1 at the time of convergence Ut3 and Dt2 when the amplitude of the hydraulic pressure has converged. Therefore, when the ascending / descending of the fork 15a is suddenly stopped, the increase in the ups and downs of the fork 15a caused by the traffic of the hydraulic oil 55 between the bottom chamber 14b and the accumulator hydraulic chamber 28 is suppressed.

(2) When the preparation time UT1 elapses from Ut0 at the start of the ascending operation, the control device 60 switches the switching valve 51 to the closed position K2. Therefore, during the preparation time UT1, the switching valve 51 is maintained at the open position K1 and communicates the bottom chamber 14b and the accumulator hydraulic chamber 28 to balance the hydraulic pressure of the bottom chamber 14b with the hydraulic pressure of the accumulator hydraulic chamber 28. be able to. After that, when the operation of the lift operation lever 17 is stopped and the switching valve 51 is switched to the open position K1, the hydraulic oil 55 suddenly flows into the low pressure side due to the differential pressure between the bottom chamber 14b and the accumulator hydraulic chamber 28. Can be suppressed.

(3) When the fork 15a is ascended, the ascending convergence time point Ut3 is set as the time when the ascending standby time UT2 has elapsed from the ascending operation stop time Ut2. Further, when the fork 15a is descending, the descent convergence time point Dt2 is set to the time point when the descent standby time DT has elapsed from the descent operation stop time point Dt1. Therefore, since the time point at which the amplitude of the hydraulic pressure converges can be grasped by the passage of time, the control load of the control device 60 can be suppressed.

This embodiment can be modified and implemented as follows. The present embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
○ The switching valve 51 may be a normally closed type. In this case, the control signal output from the control device 60 to the switching valve 51 is the opposite of that in the case of the normal open type.

○ As shown in FIG. 11, a pressure sensor 31 for a lift cylinder that detects the hydraulic pressure of the bottom chamber 14b is arranged in the oil supply / drainage passage 21, and an accumulator that detects the hydraulic pressure of the accumulator hydraulic chamber 28 in the connecting oil passage 25. A pressure sensor 32 is arranged. The lift cylinder pressure sensor 31 and the accumulator pressure sensor 32 are signal-connected to the control device 60. The control device 60 acquires the hydraulic pressure of the bottom chamber 14b detected by the lift cylinder pressure sensor 31. Further, the control device 60 acquires the operating hydraulic pressure of the accumulator hydraulic pressure chamber 28 detected by the accumulator pressure sensor 32.

The time of convergence at which the amplitude of the hydraulic pressure converges may be the time when the hydraulic pressure acquired from the lift cylinder pressure sensor 31 becomes less than a predetermined threshold value.
According to this, since the hydraulic pressure of the bottom chamber 14b can be actually measured by the lift cylinder pressure sensor 31, it is possible to accurately determine whether or not the amplitude of the hydraulic pressure has converged.

○ In the embodiment shown in FIG. 11, when the fork 15a is raised, the control device 60 sets the time when the fluctuation range of the amplitude of the hydraulic pressure acquired from the lift cylinder pressure sensor 31 becomes almost constant as the preparation completion time Ut1. May be good.

○ In the embodiment shown in FIG. 11, during the ascending operation of the fork 15a, the control device 60 until the difference between the hydraulic pressure acquired from the lift cylinder pressure sensor 31 and the hydraulic pressure acquired from the accumulator pressure sensor 32 becomes less than the threshold value. The approximate time point may be set as the preparation completion time point Ut1.

○ As shown in FIG. 11, an acceleration sensor 33 is provided on the lift bracket 15, and the control device 60 acquires the acceleration detected by the acceleration sensor 33. Then, the time point at which the amplitude of the hydraulic pressure converges may be set as the time point when the acceleration acquired from the acceleration sensor 33 becomes less than the threshold value.

When the ascending / descending of the fork 15a is stopped, the acceleration is large at the time when the fork 15a is stopped ascending / descending, and the acceleration gradually decreases as time elapses. Then, as the acceleration becomes smaller, the amplitude of the hydraulic pressure of the bottom chamber 14b also becomes smaller. Therefore, since the hydraulic pressure of the bottom chamber 14b can be indirectly measured by the acceleration sensor 33, it can be determined whether or not the amplitude of the hydraulic pressure has converged.

○ The accumulator 26 may be of a bladder type, a diaphragm type, or a metal bellows type in which the accumulator hydraulic chamber 28 and the accumulator gas chamber 29 are separated by a rubber partition wall.
○ The loading portion may be a fork other than the fork 15a, and may be, for example, a shovel of a construction machine.

○ The operation member may be an operation switch other than the lift operation lever 17.
○ The industrial vehicle may be an engine-powered forklift.

Dt0 ... descent operation start time, Dt1 ... descent operation stop time, Dt2 ... descent convergence time, DT ... descent standby time, K1 ... open position, K2 ... closed position, Ut0 ... ascending operation start time, Ut1 ... preparation completion time , Ut2 ... Ascending operation stop time, Ut3 ... Ascending convergence time, UT2 ... Ascending standby time, W ... Load, 11 ... Forklift as an industrial vehicle, 12 ... Body, 14 ... Lift cylinder, 14b ... Bottom chamber, 15a ... fork as a loading part, 17 ... lift operation lever as an operating member, 21 ... oil supply / drainage passage, 24 ... oil tank, 25 ... connecting oil passage, 26 ... accumulator, 28 ... accumulator hydraulic chamber, 31 ... for lift cylinder Pressure sensor, 33 ... Acceleration sensor, 51 ... Switching valve, 55 ... Hydraulic oil, 60 ... Control device.

Claims (5)

A car body with a loading section for loading loads,
A lift cylinder that has a bottom chamber and raises and lowers the loading unit according to the hydraulic pressure introduced into the bottom chamber.
An oil tank connected to the bottom chamber via an oil supply / drainage channel,
An accumulator with an accumulator hydraulic chamber whose volume changes according to the introduction of hydraulic oil, and an accumulator.
A connecting oil passage that branches from the oil supply / drainage passage and is connected to the accumulator hydraulic chamber,
Switching between an open position where the bottom chamber and the accumulator hydraulic chamber are communicated by opening the connecting oil passage and a closed position where the bottom chamber and the accumulator hydraulic chamber are not communicated by blocking the connecting oil passage. With a valve,
A control device that controls the switching of the switching valve and
It is provided with an operating member that is signal-connected to the control device and for operating the lift cylinder.
The control device switches the switching valve to the open position at the neutral position of the operating member.
The control device switches the switching valve to the closed position while the operation is being performed from the start of the operation of the operating member in the neutral position, and at the same time, the control device switches the switching valve to the closed position.
The control device opens the switching valve at a time point after the operation stop of the operation member and at a time point at which the fluctuation of the hydraulic pressure in the bottom chamber caused by the stoppage of the ascending / descending of the loading portion converges. Impact suppression device for industrial vehicles characterized by switching to a position. The industry according to claim 1, wherein the convergence time point is a time point at which the waiting time required for the amplitude of the hydraulic pressure generated by the ascending / descending stop of the loading portion to converge has elapsed from the operation stop time of the operation member. Vehicle impact suppression device. The lift cylinder pressure sensor for measuring the hydraulic pressure in the bottom chamber is provided, the control device acquires the hydraulic pressure measured by the lift cylinder pressure sensor, and the lift cylinder pressure sensor is at the time of convergence. The impact suppression device for an industrial vehicle according to claim 1, which is the time when the hydraulic pressure obtained from the above is less than the threshold value. The control device includes an acceleration sensor that detects the acceleration of the loading portion, the control device acquires the acceleration measured by the acceleration sensor, and the convergence time point is when the acceleration acquired from the acceleration sensor becomes less than the threshold value. The impact suppression device for an industrial vehicle according to claim 1. When raising the loading portion, the control device sets the switching valve at a preparation completion time set after the operation start time of the operation member from the neutral position and before the operation stop time. Switch to the closed position,
The time according to any one of claims 1 to 4, wherein the preparation completion time point is a time point at which the working hydraulic pressure of the bottom chamber and the working hydraulic pressure of the accumulator hydraulic pressure chamber are in equilibrium after the operation start time point. Impact suppression device for industrial vehicles.

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