JPS6052080B2 - Lift cylinder control device for forklift trucks - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for controlling the lifting and lowering operations of a lift cylinder of a forklift truck. This invention relates to an improvement in a remote control device capable of raising and lowering a vehicle.

In a forklift truck having a hydraulic circuit as shown in FIG. 1, an operator on the fork 1 presses a switch SW.

In the conventional electric circuit shown in Fig. 4, in which the switch is switched to the contact a side,
A rise switch SW or a fall switch SW installed near the fork 1. By operating the switch valve 2, the fork 1 can be raised or lowered by controlling the supply and discharge of pressure oil to the lift cylinder 3, as is clear from Fig. 4. ,
The operation start/stop of the oil pump MP and the opening/closing of the respective positions of the switching valve 2 are performed by operating the up switch SW or the down switch SW2,
The operation timings of the oil pump MP and the switching valve 2 are completely synchronized, and when the ascending operation or the descending operation is stopped, the switching valve 2 is closed at the same time as the power supply to the oil pump 2 is stopped, and therefore the lift cylinder 3 is closed. The oil supply circuit to the lift cylinder 3 or the oil drain circuit from the lift cylinder 3 is instantly cut off, and as a result, due to inertia force, a large impact is applied to the worker and the load on the fork 1, causing a fall accident. It had serious drawbacks such as: In view of the above-mentioned drawbacks, the present invention stops energizing the oil pump when the ascending or descending motion is stopped, but the switching valve maintains the open state at each position for a while, and ideally continues to rotate due to inertia. The purpose of this invention is to eliminate the above-mentioned drawbacks and provide a lift cylinder control device that can be operated smoothly by making the switching valve close only when the oil pump stops naturally. The present invention will be explained in detail below based on the illustrated embodiments. In FIG. 1, a lift cylinder 3 for moving the fork 1 up and down
are connected to pipes 4 and 5 for supplying and discharging pressure oil, and the pipe 5 can be connected to an oil pump MP via a manual switching valve 6 (detailed explanation of this circuit is omitted). The pipe line 4 can be connected to the oil pump MP via the switching valve 2. The switching valve 2 is normally in a closed neutral position, but the solenoid SOL. Due to the excitation of a, the lift cylinder 3 is placed in the open position on the upward movement side.
Also, the solenoid SOL. By the excitation of b, the lowering operation side position of the lift cylinder 3 is brought into an open state. next,
To explain the electric circuit for operating the oil pump Raccoon and the switching valve 2, first, in FIG. 2 showing the first embodiment, the battery 7, the contact b side of the key switch SWKl changeover switch SW3, the lift switch SWL and The oil pump cans are connected in series by wiring,
Switching valve 6 in the driver's seat of a forklift truck
A circuit for manual operation is formed, and a circuit for remote operation is provided in parallel to the manual operation circuit via the contact a side of the changeover switch SW3. In other words, the contact point a side of the changeover switch SW3 is connected to the parallel lift switch SW disposed near the operator's hand (for example, a lift bracket for mooring the fork 1) on the fork 1.
The contact a side of each of the lower switch SWL and lowering switch SW2 is connected to the wiring 8 between the lift switch SWL and the oil pump MP, and the contact b of each is connected to the wiring 9 between the oil pump ■ and the battery 7. The contact c is connected to each solenoid SOL. of the switching valve 2. a, S.O.
L. The delay relays Rel and Re2 are connected to the wiring 9 via the wire 9, and between the respective contacts b and c, delay relays Rel and Re2 are formed which are closed when not energized. Note that the contact a of each of the up switch SWl and the down switch SW2 is normally open, and the contact b of each is normally closed, and these switches SWl and SW2 are set to be in opposite states when operated. has been done. Here, the operation of the first embodiment will be explained. After the key switch SWK is closed, the changeover switch SW3 is moved to the contact a in order to put the lift cylinder 3 into a state where the lift cylinder 3 can be remotely operated.
When switched to the side, the contact b sides of the up switch SWl and down switch SW2 are energized, and the respective solenoids S of the switching valve 2 are energized through the respective contacts C side.
OL. a,SOL. b is energized, and the solenoid SOL
．． a,SOL. b is excited, but since both are excited at the same time, the switching valve 2 maintains a neutral state.

After the set time has elapsed, the delay relays Rel and Re2 open each contact point c, and the solenoid SO
L. a, SOL. The pulse is de-energized. Next, when the operator presses the lift switch SWl to raise the fork 1, the contact b of the switch SWl becomes open, and the contact a
becomes closed. At this time, contact c is closed by the action of delay relay Rel, and solenoid SOL. a is energized and energized, the upward movement side position of the switching valve 2 is opened, and the oil pump MP is activated.
Pressure oil is supplied to the lift cylinder 3 and the fork 1 is raised. When the operator releases the pressure on the lift switch SWl to stop the lifting operation, the switch SWl self-resets so that the contact b becomes closed and the contact a opens. As a result, the power to the oil pump is immediately cut off, but the delay relay Rel keeps the solenoid SOL. After the switching valve 2 maintains the open state in the upward operation side position by continuing to energize the solenoid SOL. Only when the current to a is cut off is the switching valve 2 brought into a neutral state and the upward operation side position into a closed state. Until then, the oil pump MP continues to rotate for a while due to inertia and until it stops naturally, the upward operation side position of the switching valve 2 remains open, so pressure oil continues to be sent to the lift cylinder 3. The amount of pressure oil gradually decreases, and finally the fork 1 comes to a gentle stop. Further, when the lowering switch SW2 is pressed to lower the fork 1, the contact b becomes open and the contact a becomes closed.

At this time, contact c is closed by the action of delay relay Re2, and solenoid SOL. b is energized and energized, the lowering operation side position of the switching valve 2 is brought into an open state, and at the same time, the oil pump (2) is operated. The pressure oil supplied by the operation of the oil pump acts as pilot pressure, and the check valve 10 is opened to open the lift cylinder 3.
The pressure oil inside is discharged and the fork 1 is lowered. When the pressure on the lowering switch SW2 is released to stop the lowering operation, the self-resetting action of the lowering switch SW2 causes the contact b to be closed and the contact a to be opened. As a result, the power to the oil pump is immediately cut off, but the delay relay R
With the action of e2, the solenoid SOL. After the switching valve 2 maintains the open state in the lower operation side position by continuing to energize the solenoid SOL. It is only then that the energization to b is cut off, and the switching valve 2 enters the neutral state and the lowering operation side position becomes the closed state. Until then, the oil pump MP continues to rotate for a while due to inertia and until it stops naturally, the downward operation side position of the switching valve 2 remains open, so that pressure oil is not supplied as the pilot pressure of the check valve 10. The check valve 10 continues to be opened, pressure oil continues to be discharged from the lift cylinder 3, and as the pilot pressure decreases,
The amount of pressure oil discharged gradually decreases, and finally the fork 1 comes to a gentle stop. Next, regarding FIG. 3 showing the second embodiment regarding the above-mentioned electric circuit, as in the first embodiment, the battery 17, the contact b side of the key switch SWKl changeover switch SW3, the lift switch SW and the oil pump MP are connected in series by wiring to form a circuit for manually operating the switching valve 6 from the driver's seat of the forklift truck, and a remote control circuit is connected via the contact a side of the switching switch SW3 to Although it is provided in parallel to the operating circuit, the configuration of the remote operating circuit is different from that of the first embodiment. That is, of the parallel ascending switch SWl and descending switch SW2 connected to the contact a side of the changeover switch SW3, the ascending switch SWl is connected to the wiring 18 between the lift switch SWL and the oil pump MP. Also, the lowering switch SW
2 is connected to delay relays Rel and Re2 whose times are set so that their contacts a are activated sequentially when energized, and these delay relays Rel and Re2 are connected to the solenoid SOL.2 of the switching valve 2 shown in FIG. 1, respectively. b, SOL. It is connected to the wiring 19 between the oil pump MP and the battery 17 via a. The lift switch SWl is normally open, and is closed when the switch SWl is activated. The lowering switch SW2 is set so that the contact a is always closed, the contacts B and c are always open, and the lowering switch SW2 is set to be in the opposite state when the lowering switch SW2 is operated. In addition, delay relay Rel is always closed when not energized, and delay relay Re2 is always open when not energized, and the time constants of these relays when energized are set larger for delay relay Re2 than for delay relay Rel. has been done. Here, the operation of the second embodiment will be explained. After the key switch SWK is closed, when the changeover switch SW3 is switched to the contact a side in order to enable remote control of the lift cylinder 3, the lowering switch S
The delay relays Rel and Re2 are energized from the contact a side of W2, and the solenoid SOL. b is energized and the lowering operation side position of the switching valve 2 is opened, but when the set time elapses, the solenoid SOL.b is activated by the operation of the delay relay Rel. energization to b is cut off, and the switching valve 2
is in the neutral state and the lowering operation side position is in the closed state, and after that, when the next set time (longer than the set time of the delay relay Rel) has elapsed, the delay relay R is turned on.
e2 is activated and becomes closed, solenoid SOL. of switching valve 2 is activated. A is energized and energized, and the upward operation side position of the switching valve 2 is opened and maintained.

In this state, when the lift switch SWl is pressed in order to raise the fork 1, the switch SWl is closed and the oil pump ■ is energized, the oil pump is activated and pressure oil is supplied to the lift cylinder 3, and the fork 1 is pressed. 1 rises. In order to stop the rising operation, the pressure on the rising switch SWl is released, and the switch SWl returns naturally, the power to the oil pump MP is cut off, and the oil pump ■ continues to rotate for a while due to inertia. stop naturally. Even at this time, the upward operation side position of the switching valve 2 remains open, so pressure oil continues to be supplied to the lift cylinder 3, and the supply amount gradually decreases until it slowly reaches the fork 1. stops rising.Also, when the lowering switch SW2 is pressed to lower the fork 1, the contact a of the switch SW2 becomes open, and the contacts B and c become closed; As a result, the delay relay Rel returns to the closed state, the delay relay Re2 returns to the open state, the solenoid SOL.a is de-energized, and the switching valve 2 becomes the neutral state. When the contact b is closed, the no-solenoid SOL.b is excited, and the downward operation side position of the switching valve 2 is opened, and the contact c is closed, which causes the oil pump to open. The oil pump is activated by energizing it.As a result,
Pressure oil supplied from the oil pump MP acts as pilot pressure to open the check valve 10, discharge the pressure oil from the lift cylinder 3, and lower the fork 1.
Then, in order to stop the lowering operation, the lowering switch SW2
When the pressure on switch SW2 is released, the switch SW2 returns to its natural state, contacts B and c become open, and contact a becomes closed. When the contact c becomes open, the power to the oil pump (2) is cut off, and the oil pump (2) continues to rotate for a while due to inertia, and then gradually stops. Also, contact b becomes open and solenoid SOL. Power to b is cut off, but since contact a is closed, delay relay R
Until the set time of el elapses, solenoid SOL. b is energized, and the downward operation side position of the switching valve 2 is maintained in the open state. Then, when the set time of the delay relay Rel has elapsed, the relay Re
1 becomes open, solenoid SOL. b is de-energized, the switching valve 2 is in a neutral state, and the lowering operation side position is in a closed state. At this time, delay relay Rel is in the closed state and solenoid SOL. Only while the switch valve b is excited, the downward operation side position of the switching valve 2 remains open, so the pressure oil sent out from the oil pump MP, which continues to rotate due to inertia, is supplied as pilot pressure to the check valve 10. Since the check valve 10 remains open, the discharge of pressure oil from the lift cylinder 3 continues, and therefore the fork 1 continues to descend, but as the rotation of the oil pump MP decreases, the check valve 10 continues to open. The opening degree of the lift cylinder 3 also decreases, and the amount of pressure oil discharged from the lift cylinder 3 also decreases. It gradually decreases and finally the fork 1 comes to a gentle stop. Then, when the set time of the delay relay Re2 (which is set longer than the delay relay Rel) has elapsed, the relay Re2 is closed and the solenoid SOL. A is energized to open the upward operation side position of the switching valve 2, and this state is maintained to standby for the next operation. As described above, according to the present invention, even if the power supply to the oil pump is cut off, the oil pump continues to rotate for a while due to inertia, and the pressure oil continues to be delivered from the oil pump, and moreover, it gradually decreases. In the meantime, actively take advantage of the fact that it will eventually become nothing.
By keeping the pressure oil supply/discharge circuit to the lift cylinder open, the fork's upward or downward movement can be stopped with a gradual change in speed, thereby reducing the impact on the worker or cargo on the fork. In addition, it is not necessary to incorporate an accumulator or the like, which is known as a shock absorber, into the hydraulic piping, and therefore the control device can be obtained at a relatively low cost, and the space and space for assembling the accumulator can be prevented. It has various remarkable effects such as saving man-hours.

[Brief explanation of the drawing]

Fig. 1 is a hydraulic circuit diagram for supplying and discharging pressure oil to the lift cylinder, Fig. 2 is an electric circuit diagram showing the first embodiment of the remote control device, and Fig. 3 is also a second embodiment. Electric circuit diagram FIG. 4 is an electric circuit diagram also showing a conventional example. 2...Switching valve, 3...Lift cylinder, SWl...Lift switch, SW2...
...Down switch, SW3...Choice switch, MP...Oil pump.

Claims (1)

[Claims] 1. In a device that electrically operates an oil pump installed in a hydraulic circuit for supplying and discharging pressure oil to and from a lift cylinder, and a switching valve that controls the ascending hydraulic circuit and the descending hydraulic circuit, respectively, A delay relay is provided in an electric circuit that simultaneously controls the oil pump and the switching valve using a switch for starting and lowering the switching valve. A lift cylinder control device for a forklift truck characterized by: