JP5825160B2 - lift device - Google Patents

Description

  The present invention relates to a lifting device that lifts and lowers a lift by hydraulic drive of a hydraulic cylinder.

  For example, in a lifting device for a forklift, when a fork (lifting object) is moved down, a cargo handling regeneration that generates power by returning hydraulic oil from a hydraulic cylinder for lifting the fork to a hydraulic pump using the weight of the load is known. is there. In such cargo handling regeneration, when the switching valve is opened when the fork starts to descend, a shock (vibration) is generated in the fork due to the pressure difference between the hydraulic oil upstream and downstream of the switching valve.

  As a measure to prevent such problems, there is a method of using a proportional valve and gradually opening the proportional valve when the fork starts to descend, but the cost and physique of the valve increase, or due to pressure loss Decrease in descent speed occurs. In addition, when the fork starts to descend, the pressure difference between the upstream side and the downstream side of the switching valve is eliminated by rotating the hydraulic pump once in the fork ascending direction before opening the switching valve, and then the switching valve is opened. There is also a method. However, in this case, the fork may rise momentarily, resulting in a delay in operation from the lowering operation.

  Moreover, as a prior art of the lifting device, for example, those described in Patent Documents 1 and 2 are known. In the lifting device described in Patent Document 1, when the fork descending is instructed, the hydraulic pump is rotated in the fork ascending direction with the torque command value stored in the storage unit, and then the switching valve is moved from the ascending position to the descending position. At the same time, the hydraulic pump is rotated in the fork descending direction with a torque command value calculated from the target rotational speed and the actual rotational speed of the motor.

  In the lifting device described in Patent Document 2, when the lowering of the fork is instructed, the hydraulic pump is rotated in the upward direction of the fork at the commanded rotational speed for the commanded rotation time, and then the switching valve is switched from the raised position to the lowered position. The hydraulic pump is rotated in the fork lowering direction at a predetermined rotational speed.

JP 2008-63072 A JP 2008-7258 A

  In Patent Document 1, the output torque of the motor at the time when the actual rotational speed of the hydraulic pump becomes 0 rpm when the fork is stopped is stored. At this time, the switching valve is closed, so that the motor The output torque is 0 Nm. For this reason, the pressure difference between the upstream side and the downstream side of the switching valve cannot be eliminated at the next start of lowering of the fork, and it is inevitable that a shock occurs in the fork.

  In Patent Document 2, the command rotation speed and the command rotation time are determined based on the elapsed time from the end of the previous lowering operation and the cylinder pressure of the hydraulic cylinder. However, the cylinder pressure when the hydraulic cylinder is pulsating is determined. The value may be detected by a pressure sensor. In this case, if the hydraulic pump is rotated in the fork ascending direction when the fork starts to descend, the fork rises momentarily, or the pressure difference between the upstream side and the downstream side of the switching valve is hardly eliminated, and the switching valve is opened. Shock may occur on the fork.

  The objective of this invention is providing the raising / lowering apparatus which can reduce the shock which generate | occur | produces in a raising / lowering object, without generating the raising of a raising / lowering object temporarily at the time of the fall start of a raising / lowering object.

The present invention relates to a lifting device that lifts and lowers an object by hydraulic drive of a hydraulic cylinder, and is connected to a hydraulic pump motor that supplies hydraulic oil to the hydraulic cylinder and the hydraulic pump motor, and the hydraulic pump motor operates as a hydraulic pump. An electric motor that functions as an electric motor in the case, and functions as a generator when the hydraulic pump motor operates as a hydraulic motor , and valve means that allows or blocks the flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump motor , An oil passage connecting the valve means and the hydraulic cylinder, a lift operation lever for instructing the lifting operation of the lifting object, and a control unit that performs the cargo handling regeneration operation by causing the electric motor to function as a generator, oil passage when the flow of hydraulic fluid from the hydraulic cylinder to the hydraulic pump motor is in a state allowed by the valve means Comprise buffering volumetric forming section the hydraulic oil flows from the hydraulic cylinder during the downward movement of the lifting thereof, the total volume of the oil path including a buffer for volume forming unit, the maximum acceleration of the lift object in descending starting elevation thereof The control unit controls the valve means so as to allow the flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump motor during the lowering operation of the lifting object, and the predetermined time has elapsed. Later, by controlling the electric motor to rotate the hydraulic pump motor in the descending direction of the lift with the number of rotations according to the amount of operation of the lift operation lever, the hydraulic pump motor drives the hydraulic oil discharged from the hydraulic cylinder. It is characterized by operating as a hydraulic motor .

In such a lifting device of the present invention, the valve means is controlled so as to allow the flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump motor during the lowering operation of the lifting object, and the amount of operation of the lift operating lever after a predetermined time has elapsed. By controlling the electric motor so that the hydraulic pump motor is rotated in the descending direction of the lifted object at a rotation speed corresponding to the hydraulic pump motor , the hydraulic pump motor is operated as a hydraulic motor using the hydraulic oil discharged from the hydraulic cylinder as a driving force. . As a result, the hydraulic oil from the hydraulic cylinder returns to the hydraulic pump motor through the valve means. At this time, a buffer volume is formed in which the hydraulic fluid flows from the hydraulic cylinder during the descending operation of the lift when the hydraulic passage is allowed to flow from the hydraulic cylinder to the hydraulic pump motor by the valve means. Part. Thereby, since the total volume of the oil path between the valve means and the hydraulic cylinder increases, it is possible to reduce the shock generated in the lift. Further, since it is not necessary to rotate the hydraulic pump motor in the ascending direction of the lift to eliminate the pressure difference between the upstream side and the downstream side of the valve means, the pressure between the hydraulic pump motor and the valve means is the hydraulic cylinder. The cylinder pressure does not become higher. Thereby, the temporary raising of the raising / lowering object by the action | operation of the reverse direction (ascending direction) of a hydraulic cylinder can be prevented. In addition, the total volume of the oil passage including the buffer volume forming portion is set to an amount such that the maximum acceleration value of the lifted object at the start of the descending of the lifted object becomes a certain value or less. The shock generated in the lifting object is expressed as the maximum acceleration value of the lifting object when the lifting object starts to descend. Therefore, by setting the total volume of the oil passage including the buffer volume forming portion to such an amount that the acceleration maximum value of the lifted object at the start of the descending of the lifted object is below a certain value, It is possible to reliably reduce the shock generated in the lifted object.

Also, preferably, the valve means is disposed in the oil path between the hydraulic pump motor and the hydraulic cylinder, the hydraulic pump motor from the open position and the hydraulic cylinder to allow flow of hydraulic fluid to the hydraulic pump motor from the hydraulic cylinder This is an electromagnetic switching valve that is switched between a closed position that blocks the flow of hydraulic oil to the valve. In this case, the valve means can be configured with the minimum necessary number of parts.

The valve means includes an orifice for supplying the pilot flow path which is connected to the hydraulic pump motor hydraulic oil from the hydraulic cylinder, the logic valve for opening and closing the oil passage between the hydraulic pump motor and the hydraulic cylinder When switching between the disposed pilot flow path, a closed position for blocking the flow of hydraulic fluid from the open position and the logic valve that allows the flow of hydraulic fluid to the hydraulic pump motor from the logic valve to the hydraulic pump motor And a pilot electromagnetic switching valve. In this case, the electromagnetic switching valve to be used is a small size because it is for pilot use. Therefore, the physique and cost of the valve means and the power consumption for driving the electromagnetic switching valve can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the shock which generate | occur | produces in a raising / lowering object can be reduced, without generating the temporary raise of a raising / lowering object at the time of the fall start of a raising / lowering object. Thereby, it is possible to smoothly move the elevating object downward.

1 is a system configuration diagram showing a first embodiment of a lifting device according to the present invention. It is a flowchart which shows the raising / lowering object descent | fall process procedure performed by the main control part shown in FIG. It is a graph which shows an example of the shock which generate | occur | produces in a raising / lowering object at the time of a raising / lowering object fall start. It is a graph which shows an example of the difference in the pressure reduction amount between a lift cylinder and an electromagnetic switching valve by the presence or absence of the buffer volume formation part shown in FIG. It is a system block diagram which shows 2nd Embodiment of the raising / lowering apparatus which concerns on this invention. It is a figure which shows schematically the structure of the logic valve shown in FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a lifting device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system configuration diagram showing a first embodiment of a lifting apparatus according to the present invention. In the figure, a lifting device 1 of this embodiment is a device that is mounted on, for example, a picking lift that is one of forklifts, and lifts and lowers a lift 2. The lift 2 is composed of a fork for loading luggage and a cab provided on the fork. The lifting / lowering device 1 lifts / lowers the fork and the cab as the lifting / lowering object 2 at the same time.

  The lifting device 1 includes a lift cylinder 3, a hydraulic pump motor 4 and a tank 5, and an electromagnetic switching valve 7 disposed on an oil path 6 between the hydraulic pump motor 4 and the lift cylinder 3. One flow port 4 a of the hydraulic pump motor 4 and the electromagnetic switching valve 7 are connected via a hydraulic pipe 8 constituting a part of the oil passage 6. The other circulation port 4 b of the hydraulic pump motor 4 and the tank 5 are connected via a hydraulic pipe 9. The electromagnetic switching valve 7 and the bottom chamber 3 a of the lift cylinder 3 are connected via a hydraulic pipe 10 that constitutes a part of the oil passage 6.

  The lift cylinder 3 is a hydraulic cylinder that moves the lift 2 up and down by hydraulic drive. The hydraulic pump motor 4 sucks the hydraulic oil from the tank 5 and supplies the hydraulic oil to the bottom chamber 3 a of the lift cylinder 3. The hydraulic pump motor 4 can rotate in both directions. The flow ports 4a and 4b of the hydraulic pump motor 4 become suction ports or discharge ports depending on the flow direction of the hydraulic oil.

  An electric motor 11 that functions as an electric motor or a generator is connected to the hydraulic pump motor 4. The electric motor 11 functions as an electric motor when the hydraulic pump motor 4 operates as a hydraulic pump, and functions as a generator when the hydraulic pump motor 4 operates as a hydraulic motor.

  The electromagnetic switching valve 7 is a valve that is switched between an open position 7a having an orifice and a closed position 7b having a spring check valve. The open position 7 a is a position where the flow of hydraulic oil from the hydraulic pump motor 4 to the lift cylinder 3 and the flow of hydraulic oil from the lift cylinder 3 to the hydraulic pump motor 4 are both allowed. The closed position 7b permits the flow of hydraulic oil from the hydraulic pump motor 4 to the lift cylinder 3 only when the pressure in the hydraulic pipe 8 is equal to or greater than the spring force, and allows the hydraulic oil to flow from the lift cylinder 3 to the hydraulic pump motor 4. This is the position where the flow is interrupted. The electromagnetic switching valve 7 is normally in the closed position 7b (illustrated) by the force of the spring 7c, and is switched from the closed position 7b to the open position 7a when an electric signal is input to the solenoid operating portion 7d.

  In the middle of the hydraulic pipe 10, there is provided a buffer volume forming portion 12 for buffering a shock generated in the lift 2 when the electromagnetic switching valve 7 is switched from the closed position 7b to the open position 7a. The buffer volume forming portion 12 also constitutes a part of the oil passage 6. The buffer volume forming unit 12 is configured as a container for storing hydraulic oil, for example. Further, the buffer volume forming section 12 may be configured such that a plurality of pipes connected to the hydraulic pipe 10 are arranged in parallel, or a part of the hydraulic pipe 10 may be formed in a spiral shape. The volumes of the buffer volume forming unit 12 and the hydraulic pipe 10 will be described in detail later.

  In addition, the lifting device 1 includes a lift operation lever 13 for instructing the lifting operation of the lift 2, a main control unit 14, a solenoid valve drive circuit 15, and a motor driver 16. The main control unit 14 inputs an operation signal for the lift operation lever 13, performs a predetermined process, and outputs a command signal to the electromagnetic valve drive circuit 15 and the motor driver 16. The electromagnetic valve drive circuit 15 drives the electromagnetic switching valve 7 by outputting an electric signal to the solenoid operation unit 7d of the electromagnetic switching valve 7 in accordance with a command signal from the main control unit 14. The motor driver 16 drives the electric motor 11 by outputting an electric signal to the electric motor 11 in accordance with a command signal from the main control unit 14.

  When the main controller 14 raises the lifting / lowering object 2, the motor driver 16 sends a command signal for rotating the hydraulic pump motor 4 in the lifting / lowering object raising direction while maintaining the electromagnetic switching valve 7 at the closed position 7b. And the electric motor 11 is controlled. As a result, the hydraulic pump motor 4 rotates in the lifted object ascending direction, and the hydraulic oil discharged from the communication port 4a of the hydraulic pump motor 4 is supplied to the bottom chamber 3a of the lift cylinder 3 through the oil passage 6. The Then, the lift 2 is lifted by the extension of the lift cylinder 3. At this time, the hydraulic pump motor 4 operates as a hydraulic pump.

  On the other hand, the main control unit 14 executes processing according to the flowchart shown in FIG. Note that the rotational speed of the hydraulic pump motor 4 is 0 rpm before the elevator 2 is lowered.

  In FIG. 2, it is first determined whether or not an instruction operation for the lifting / lowering object lowering operation has been performed by the lift operation lever 13 (step S101), and when the instruction operation for the lifting / lowering object lowering operation is performed, the electromagnetic switching valve 7 is opened. Such a command signal is output to the electromagnetic valve drive circuit 15, and the electromagnetic switching valve 7 is switched from the closed position 7b to the open position 7a (step S102). Thereby, the descent | fall operation | movement of the raising / lowering object 2 by dead weight is started, and the lift cylinder 3 shrink | contracts.

  Then, it is determined whether or not a predetermined time (for example, about 0.1 sec) has elapsed (step S103), and when the predetermined time has elapsed, the rotational speed of the hydraulic pump motor 4 according to the operation amount of the lift operation lever 13 is determined. Then, a command signal for rotating in the descending direction is output to the motor driver 16 to control the electric motor 11 (step S104). As a result, the hydraulic pump motor 4 rotates in the descending / lowering direction.

  Then, the hydraulic oil discharged from the bottom chamber 3 a of the lift cylinder 3 is sucked into the hydraulic pump motor 4 through the oil passage 6. At this time, the hydraulic pump motor 4 operates as a hydraulic motor using the hydraulic oil discharged from the bottom chamber 3a as a driving force. As a result, the electric motor 11 functions as a generator, and the electric power generated by the electric motor 11 is stored in a battery (not shown). That is, when the lifting / lowering object 2 is lowered, the cargo handling regeneration operation is performed.

  Thereafter, it is determined whether or not the instruction operation for the lifting / lowering object lowering operation by the lift operation lever 13 has been released (step S105), and when the instruction operation for the lifting / lowering object lowering operation is released, the rotation of the hydraulic pump motor 4 is set in advance. A command signal for decelerating at the decelerated speed is output to the motor driver 16 to control the electric motor 11 (step S106). As a result, the rotational speed of the hydraulic pump motor 4 decreases.

  And it is judged whether the rotation speed of the hydraulic pump motor 4 became 0 rpm (step S107). This determination is made, for example, by detecting the rotation speed and rotation speed of the hydraulic pump motor 4. When the rotation speed of the hydraulic pump motor 4 becomes 0 rpm, a command signal for closing the electromagnetic switching valve 7 is output to the electromagnetic valve driving circuit 15 and the electromagnetic switching valve 7 is switched from the open position 7a to the closed position 7b ( Procedure S108). Thereby, the descent | fall operation | movement of the raising / lowering object 2 is complete | finished.

  Here, when the descending operation of the elevator 2 starts, a shock is generated in the elevator 2 at the timing when the electromagnetic switching valve 7 is switched from the closed position 7b to the open position 7a in step S102. As shown in FIG. 3, the shock is detected as the maximum value of acceleration applied to the load (including the lift 2). In other words, the greater the maximum value of acceleration applied to the load, the greater the shock generated in the lift 2. At this time, acceleration can be detected by attaching an acceleration sensor to the load or the lift 2.

ａ：ショック（積荷加速度の最大値）
Ｍ：リフトを含む積荷の重量
ｍ：シリンダ重量
Ｓ：シリンダ受圧面積
ｋ：シリンダ摩擦係数
Δν：シリンダの作動速度（初期値からの変化量）
ΔＰ_１：シリンダと電磁切換弁との間の圧力減少量
Ｅ：作動油体積弾性率
Ｖ_ｃ１：シリンダと電磁切換弁との間の油路の幾何容積
ΔＶ_１：シリンダと電磁切換弁との間の作動油減少量 Then, as described below, the shock is expressed by an oil passage (hydraulic pipe 10 and buffer volume forming unit 12) between the lift cylinder 3 and the electromagnetic switching valve 7 according to an equation such as a cylinder equation of motion and a fluid volume expansion coefficient. The volume of the oil passage between the lift cylinder 3 and the electromagnetic switching valve 7 increases as the volume of the oil passage increases.

a: Shock (maximum load acceleration)
M: Weight of load including lift
m: cylinder weight
S: Cylinder pressure receiving area
k: Cylinder friction coefficient
Δν: Cylinder operating speed (change from the initial value)
ΔP ₁ : Pressure reduction amount between the cylinder and the electromagnetic switching valve
E: Hydraulic oil bulk modulus
V _c1 : geometric volume of the oil passage between the cylinder and the electromagnetic switching valve
ΔV ₁ : Reduced amount of hydraulic oil between the cylinder and the electromagnetic switching valve

Therefore, by providing the buffer volume forming portion 12 in the middle of the hydraulic pipe 10 as described above, the geometric volume V _c1 of the oil passage between the lift cylinder 3 and the electromagnetic switching valve 7 is increased. For this reason, as shown in FIG. 4, when the buffer volume forming portion 12 is provided, the cylinder pressure P ₁ (see the solid line R) of the lift cylinder 3 immediately after opening the electromagnetic switching valve 7 is the buffer volume forming portion. When 12 is not provided, the pressure becomes higher than the cylinder pressure P ₁ (see the solid line S) of the lift cylinder 3 immediately after opening the electromagnetic switching valve 7. The cylinder pressure of the lift cylinder 3 is a pressure between the lift cylinder 3 and the electromagnetic switching valve 7. Therefore, by providing the buffer volume forming portion 12, the cylinder pressure (initial pressure) P _{1 (0)} of the lift cylinder 3 before opening the electromagnetic switching valve 7 and the lift cylinder 3 after opening the electromagnetic switching valve 7 are set. The difference from the cylinder pressure P ₁ , that is, the pressure decrease amount ΔP ₁ between the lift cylinder 3 and the electromagnetic switching valve 7 is reduced, and as a result, the shock a is reduced.

At this time, the geometric volume V _c1 of the oil passage between the lift cylinder 3 and the electromagnetic switching valve 7 is such that the shock (maximum value of the load acceleration) a generated in the lift 2 when the lift 2 starts to descend is a constant value ( For example, it is set to be 0.2 G) or less.

As described above, according to the present embodiment, the buffer volume forming portion 12 for buffering the shock generated in the elevator 2 when the electromagnetic switching valve 7 is opened when the elevator 2 starts to descend is provided on the hydraulic pipe 10. Since it was provided in the middle, the total volume of the oil passage between the lift cylinder 3 and the electromagnetic switching valve 7 is increased. For this reason, as described above, the pressure decrease amount ΔP ₁ between the lift cylinder 3 and the electromagnetic switching valve 7 becomes low. Thereby, the shock which generate | occur | produces in the raising / lowering object 2 at the time of the fall start of the raising / lowering object 2 can be suppressed. As a result, since the lifting / lowering object 2 can be smoothly lowered, it is possible to reduce the influence on the driving operation of the operator who is on the cab of the lifting / lowering object 2.

  Further, since the total volume of the hydraulic pipe 10 including the buffer volume forming unit 12 is determined so that the shock generated in the lift 2 at the start of lowering of the lift 2 becomes a certain value or less, the total volume of the hydraulic pipe 10 is While being set appropriately, the shock which generate | occur | produces in the raising / lowering object 2 can be suppressed reliably.

  Furthermore, since it is not necessary to rotate the hydraulic pump motor 4 in the lifting / lowering object lifting direction in order to eliminate the pressure difference generated between the upstream side and the downstream side of the electromagnetic switching valve 7 when the lifting / lowering object 2 starts to descend, The pressure between the pump motor 4 and the electromagnetic switching valve 7 does not become higher than the cylinder pressure of the lift cylinder 3. Thereby, the temporary raising of the raising / lowering object 2 by extension of the lift cylinder 3 can be prevented.

  FIG. 5 is a system configuration diagram showing a second embodiment of the lifting device according to the present invention. In the figure, the same or equivalent elements as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the figure, the lifting device 1 of this embodiment includes a logic valve 20 and a pilot electromagnetic switching valve 21 instead of the electromagnetic switching valve 7 described above. The logic valve 20 is disposed on the oil passage 6 between the hydraulic pump motor 4 and the lift cylinder 3. The hydraulic pump motor 4 and the logic valve 20 are connected via a hydraulic pipe 8, and the logic valve 20 and the lift cylinder 3 are connected via a hydraulic pipe 10. The pilot electromagnetic switching valve 21 is disposed on a pilot flow path 22 connected between the logic valve 20 and the flow port 4 a of the hydraulic pump motor 4.

  As shown in FIG. 6, the logic valve 20 has a plunger 23 that opens and closes the flow path 6 between the hydraulic pump motor 4 and the lift cylinder 3. The plunger 23 is formed with an orifice 24 for supplying hydraulic oil from the lift cylinder 3 to the pilot flow path 22. In addition, the logic valve 20 has a spring 25 that biases the plunger 23 in a direction to close the flow path 6 between the hydraulic pump motor 4 and the lift cylinder 3.

  The pilot electromagnetic switching valve 21 is a valve that is switched between an open position 21a having an orifice and a closed position 21b having a spring check valve. The open position 21 a is a position that allows the flow of hydraulic oil from the logic valve 20 to the hydraulic pump motor 4. The closed position 21b is a position that allows the flow of hydraulic oil from the logic valve 20 to the hydraulic pump motor 4 only when the pressure between the logic valve 20 and the pilot electromagnetic switching valve 21 is equal to or greater than the spring force. Since the pressure between the logic valve 20 and the pilot electromagnetic switching valve 21 does not exceed the spring force by the orifice 24, the flow of hydraulic oil from the logic valve 20 to the hydraulic pump motor 4 is substantially cut off. Position. The pilot electromagnetic switching valve 21 is normally in the closed position 21b (illustrated) by the force of the spring 21c, and is switched from the closed position 21b to the open position 21a when an electric signal is input to the solenoid operating portion 21d.

  The electromagnetic valve drive circuit 15 drives the pilot electromagnetic switching valve 21 by outputting an electrical signal to the solenoid operation unit 21d of the pilot electromagnetic switching valve 21 in response to a command signal from the main control unit 14. Note that the drive control processing procedure of the solenoid valve drive circuit 15 and the motor driver 16 by the main control unit 14 is the same as that in the first embodiment.

  Further, in the middle of the hydraulic pipe 10, there is provided a buffer volume forming portion 12 for buffering a shock generated in the lift 2 when the pilot electromagnetic switching valve 21 is switched from the closed position 21b to the open position 21a. It has been.

  In the above, when raising / lowering the raising / lowering object 2, the hydraulic pump motor 4 is rotated in the raising / lowering object raising direction in the state which maintained the pilot electromagnetic switching valve 21 in the closed position 21b. Then, the hydraulic oil discharged from the communication port 4 a of the hydraulic pump motor 4 pushes up the plunger 23 against the biasing force of the spring 25, so that the flow between the hydraulic pump motor 4 and the lift cylinder 3 in the logic valve 20. The road opens. For this reason, hydraulic fluid is supplied to the bottom chamber 3 a of the lift cylinder 3, and the lift 2 is raised by the extension of the lift cylinder 3.

  On the other hand, when the descending operation of the elevator 2 is started, the pilot electromagnetic switching valve 21 is switched from the closed position 21b to the open position 21a, and the hydraulic pump motor 4 is rotated in the elevator descending direction. Then, the descent | fall operation | movement of the raising / lowering object 2 by a dead weight is started, and the lift cylinder 3 shrink | contracts. At this time, immediately after the pilot electromagnetic switching valve 21 is opened, the hydraulic oil from the lift cylinder 3 returns to the flow port 4a of the hydraulic pump motor 4 through the orifice 24 and the pilot flow path 22 of the logic valve 20 (FIG. 5). (See arrow A in the middle).

  Thereafter, the hydraulic oil leaks inside the hydraulic pump motor 4 or the hydraulic pump motor 4 is gradually rotated in the ascending / descending object lowering direction, whereby the flow rate of the hydraulic oil passing through the orifice 24 is gradually increased. When the flow rate of the hydraulic oil exceeds a certain level, the plunger 23 is pushed up against the biasing force of the spring 25 due to the pressure difference between the upstream side and the downstream side of the orifice 24, so that the hydraulic pump motor 4 in the logic valve 20. And the flow path between the lift cylinder 3 is opened. As a result, the hydraulic oil from the lift cylinder 3 returns to the flow port 4a of the hydraulic pump motor 4 through the hydraulic pipe 8 (see arrow B in FIG. 5).

  Further, when stopping the descending operation of the lift 2, the rotation of the hydraulic pump motor 4 is stopped and the pilot electromagnetic switching valve 21 is switched from the open position 21 a to the closed position 21 b. At this time, since the pressure between the logic valve 20 and the pilot electromagnetic switching valve 21 is lower than the spring force, the hydraulic oil does not flow from the logic valve 20 through the pilot flow path 22 to the hydraulic pump motor 4. Accordingly, since the plunger 23 is pushed downward by the cylinder pressure of the lift cylinder 3, the flow path between the hydraulic pump motor 4 and the lift cylinder 3 is closed in the logic valve 20, and the descending operation of the lift 2 is stopped.

  Also in the present embodiment as described above, since the buffer volume forming portion 12 is provided, as in the first embodiment, the lift 2 is temporarily raised when the lift 2 starts to descend. The shock which generate | occur | produces in the raising / lowering object 2 can be suppressed, preventing.

  Further, since the valve means used between the hydraulic pump motor 4 and the lift cylinder 3 is the logic valve 20 and the pilot electromagnetic switching valve 21, the power consumption for driving the electromagnetic valve while suppressing the size and cost of the valve. Can be reduced.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the buffer volume forming portion 12 is provided in the middle of the hydraulic pipe 10. However, in addition to such a configuration, for example, the hydraulic pipe 10 can be made longer or thicker than the hydraulic pipe 8. The capacity of the hydraulic pipe 10 itself may be configured as a buffer volume forming section. In this case, the cost for manufacturing the buffer volume forming portion can be reduced.

  Moreover, in the said embodiment, although the electromagnetic switching valve 7 and the pilot electromagnetic switching valve 21 have a check valve with a spring, especially as an electromagnetic switching valve and a pilot electromagnetic switching valve to be used, it is not restricted to it, An ON / OFF valve or the like that always cuts off the flow of bidirectional hydraulic fluid in the closed position may be used.

  In the above embodiment, the lifting device 1 is mounted on a picking lift. However, the lifting device of the present invention is not limited to such a picking lift, and may be applied to a counter-type forklift. At this time, as a hydraulic cylinder in the forklift, in addition to the configuration for raising and lowering the fork as in the above-described embodiment, a configuration in which an attachment such as a roll clamp is attached may be raised and lowered.

  Furthermore, the lifting device of the present invention is not limited to a forklift, and can be applied as long as the lowering operation is performed by its own weight, such as a hydraulic elevator.

  DESCRIPTION OF SYMBOLS 1 ... Elevating device, 2 ... Elevated object, 3 ... Lift cylinder (hydraulic cylinder), 4 ... Hydraulic pump motor (hydraulic pump), 6 ... Oil path, 7 ... Electromagnetic switching valve (valve means), 7a ... Open position, 7b ... Closed position, 10 ... Hydraulic piping (oil path), 12 ... Buffer volume forming part (oil path), 20 ... Logic valve (valve means), 21 ... Pilot electromagnetic switching valve (valve means), 21a ... Open position , 21b ... closed position, 22 ... pilot flow path, 24 ... orifice.

Claims (3)

In the lifting device that lifts and lowers the lifting object by the hydraulic drive of the hydraulic cylinder,
A hydraulic pump motor for supplying hydraulic oil to the hydraulic cylinder;
An electric motor that is connected to the hydraulic pump motor and functions as an electric motor when the hydraulic pump motor operates as a hydraulic pump, and functions as a generator when the hydraulic pump motor operates as a hydraulic motor;
Valve means for allowing or blocking the flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump motor ;
An oil passage connecting the valve means and the hydraulic cylinder ;
A lift operation lever for instructing a lifting operation of the lifting object;
A control unit for causing the electric motor to function as a generator and performing a cargo handling regeneration operation,
The oil passage is a buffer through which hydraulic oil from the hydraulic cylinder flows when the lifting / lowering object is lowered when the valve means allows the hydraulic oil to flow from the hydraulic cylinder to the hydraulic pump motor . Including a volume forming part ,
The total volume of the oil passage including the buffer volume forming portion is set to an amount such that the maximum acceleration value of the lifting object at the start of lowering of the lifting object is equal to or less than a certain value.
The control unit controls the valve means so as to allow the flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump motor during the lowering operation of the lift, and sets the operation amount of the lift operation lever after a predetermined time has elapsed. By controlling the electric motor so as to rotate the hydraulic pump motor in the descending direction of the lifted object at a corresponding rotational speed, the hydraulic pump motor uses hydraulic oil discharged from the hydraulic cylinder as a driving force. A lifting device characterized by operating as a motor . The valve means is disposed on an oil passage between the hydraulic pump motor and the hydraulic cylinder, and has an open position that allows a flow of hydraulic oil from the hydraulic cylinder to the hydraulic pump motor , and the hydraulic pressure from the hydraulic cylinder. claim 1 Symbol placement of the elevator device, characterized in that an electromagnetic switching valve that is switched between a closed position for blocking the flow of hydraulic fluid to the pump motor. It said valve means includes an orifice for supplying the pilot flow path of hydraulic oil is connected to the hydraulic pump motor from the hydraulic cylinder, open and close the oil path between the hydraulic pump motor and the hydraulic cylinder blocking logic valve is disposed in the pilot flow path, a flow of hydraulic fluid from the open position and the logic valve that allows the flow of hydraulic fluid to the hydraulic pump motor from the logic valve to the hydraulic pump motor claim 1 Symbol placement of the elevator device and having a pilot selector valve is switched between a closed position to.

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