JPH10273294A - Speed control device for tilt cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a speed control device for a tilt cylinder formed so as to reduce a shock in a stroke end by automatically decelerating a speed of the tilt cylinder when it comes adjacent to the stroke end, when a mast is tilt operated. SOLUTION: Between a tilt cylinder 2 and an oil hydraulic pump 5 for tilting a mast 1 in a forklift, a solenoid flow regulating valve 6 is provided, which adjusts a feed or return amount of pressure oil relating to the tilt cylinder 2 when the mast 1 is tilted. When the tilt cylinder 2 leads to a prescribed deceleration control start point in the halfway of a cylinder stroke, a flow amount of pressure oil relating to the tilt cylinder 2 is reduced to a preset fixed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control device for a tilt cylinder used for tilting a mast of a forklift forward and backward, and more particularly to a speed control device effective for reducing an impact at a stroke end.

[0002]

2. Description of the Related Art Generally, when a mast is tilted back and forth at a certain speed by a tilt cylinder in a forklift, an impact is generated at a stroke end of the cylinder. Since such an impact sometimes causes collapse of the load, when approaching the stroke end, the operator operates the tilt lever so that the speed of the tilt cylinder is gradually reduced, and the pressure oil sent to the tilt cylinder is reduced. The flow rate had to be reduced.

[0003]

However, the operation of the tilt lever for deceleration by the operator actually requires a high degree of skill and is very troublesome.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to automatically reduce the speed of a tilt cylinder when a mast approaches a stroke end.
It is an object of the present invention to provide a tilt cylinder speed control device capable of reducing an impact at a stroke end.

[0005]

Means for Solving the Problems In order to solve the above problems, the present invention is configured as follows. That is, the invention of claim 1 is a tilt cylinder speed control device, wherein a feed amount or return amount of pressure oil to the tilt cylinder during tilting of the mast is provided between the tilt cylinder for tilting the mast and the hydraulic pump in the forklift. A flow control valve for adjusting the pressure, and when the tilt cylinder reaches a predetermined deceleration control start point in the middle of the cylinder stroke, the flow rate of the pressure oil to the tilt cylinder is reduced to a predetermined constant flow rate. And

According to the first aspect of the present invention, when the tilt cylinder moves to the deceleration control start point during tilting of the mast, the flow rate of the pressure oil to the tilt cylinder is kept constant by the flow rate adjusting valve. The flow rate is reduced, and the speed of the tilt cylinder is reduced. Thus, it is possible to reduce or prevent the impact at the stroke end without performing the troublesome tilt lever operation for deceleration by the operator.

In this case, as in the invention described in claim 2,
2. The tilt cylinder speed control device according to claim 1, wherein the flow rate control valve is an electromagnetic flow rate control valve having an intermediate flow rate region capable of flowing a constant flow rate with respect to a predetermined current width in the middle of the flow rate control range. It is desirable to configure. When such a configuration is adopted, a predetermined target flow rate can be obtained even when the flow characteristics of the electromagnetic flow control valve are offset due to a variation in spring force or when the current varies, so that the tilt cylinder is used. The operation is surely performed to the stroke end to enhance the positional accuracy, and a stable impact reduction effect at the stroke end can be obtained.

According to a third aspect of the present invention, in the tilt cylinder speed control apparatus according to the first aspect,
The directional control valve for controlling the flow direction of the pressure oil with respect to the tilt cylinder is constituted by an electromagnetic flow control valve having an intermediate flow rate region capable of flowing a constant flow rate with a predetermined current width in the middle of the flow rate control range. You may. In this case, the same operation and effect as those of the second aspect can be obtained, and the number of valves can be reduced.

According to a fourth aspect of the present invention, in the tilt cylinder speed control device according to the first aspect,
The flow rate control valve may be configured by a plurality of on-off valves provided in parallel, and at least one of the on-off valves may be operated to the closing side when the tilt cylinder reaches a deceleration control start point. When such a configuration is employed, the same operation and effect as those of the second aspect of the invention can be obtained, and the structure becomes simpler than that of the electromagnetic flow control valve.

According to a fifth aspect of the present invention, in the tilt cylinder speed control apparatus according to any one of the first to fourth aspects,
The deceleration control start point is made variable according to the cylinder speed such that the throttle action of the flow rate by the flow rate control valve is started at a position farther from the stroke end as the tilt cylinder speed increases.

Therefore, according to the fifth aspect of the invention, it is possible to obtain an effect of reducing the impact corresponding to the speed of the tilt cylinder, and to prevent the deceleration region for reducing the impact from becoming unnecessarily large. Workability can be prevented.

[0012]

Embodiments of the present invention will be specifically described below with reference to the drawings. First, a first embodiment will be described with reference to FIGS. FIG. 1 is a speed control circuit diagram of a tilt cylinder, in which a tilt cylinder 2 for tilting a mast 1 back and forth includes a control valve 3 for cargo handling.
The tilt spool 4 is connected to a hydraulic pump 5 so as to be expanded and contracted by switching the tilt spool 4.

The tilt spool 4 and the tilt cylinder 2
An electromagnetic flow control valve 6 that adjusts the flow so that the tilt cylinder 2 is decelerated before the stroke end is provided in an oil passage connecting the rod-side oil chamber. However, in the present embodiment, a throttle 4a is provided in the forward tilting oil passage of the tilt spool 4 so that the forward tilting operation of the mast 1 is performed at a lower speed than the backward tilting operation, and safety during unloading work is provided. Is taken into account. For this reason, the electromagnetic flow regulating valve 6
Is mainly used for speed control when the mast is tilted backward. In FIG. 1, reference numeral 21 denotes an oil tank;
Is a flow dividing valve, and 23 is a PS (power steering) valve.

The electromagnetic flow control valve 6 comprises a flow control unit 7 for controlling the flow rate of the pressure oil, and a solenoid unit 8 for generating pilot pressure for controlling the flow control unit 7. When a current is supplied, a pilot pressure having a magnitude proportional to the current value is applied to the flow rate adjusting unit 7 to control the flow rate (opening degree). It is configured to have flow characteristics.

That is, in the maximum flow rate range (a) at the time of full opening and the flow rate adjustment range (full opening / full closing) in which a flow rate proportional to the current can be obtained, a constant flow rate (change) for a predetermined current width (change) is obtained. (Opening degree), for example, a half-open state is provided. Then, in order to obtain such flow characteristics, the electromagnetic flow control valve 6 is configured as shown in FIG.

As shown in the figure, the flow control unit 7 has a valve body 9 and a rod-shaped spool 10 fitted in the valve body 9 so as to be slidable in the axial direction. And a cylinder port 12 communicating with the tilt cylinder 2 side.

The spool 10 is provided with a first passage 13 and a second passage 14 for connecting the pump port 11 and the cylinder port 12, and the first passage 13 is provided through the center of the shaft of the spool 10. 2 passage 14 is spool 1
0 is formed on the outer peripheral surface. The inlets of the first passage 13 and the second passage 14 are always in communication with the pump port 11 irrespective of the displacement of the spool 10.
Are sequentially opened and closed with respect to the cylinder port 12 by the displacement of.

The valve body 9 is provided with a pilot chamber 15 on a side facing one end of the spool 10 and houses a compression coil spring 16 acting on the other end of the spool 10 on the opposite side. Therefore, the spool 10 is displaced to the side where the passages 13 and 14 are opened by the pilot pressure acting on one end in the axial direction, and displaced to the side where the passages 13 and 14 are closed by the compression coil spring 16 acting on the other end. The maximum displacement of the spool 10 is regulated by the stopper bolt 17.

The pressure in the pilot chamber 15 is controlled by the solenoid unit 8. That is, the pilot room 1
A pilot pressure controlled by an electromagnetic force generated when a current is supplied to the coil of the solenoid unit 8 is introduced into the solenoid unit 5. Therefore, the pilot pressure in the pilot chamber 15 is controlled by the solenoid unit 8. Is proportional to the electromagnetic force generated. Therefore, the amount of displacement of the spool 10 is
It is determined by the balance between the pilot pressure acting on one end of the zero and the spring force acting on the other end. In addition,
The pilot pressure is such that pressure oil discharged from the hydraulic pump 5 is introduced through a pilot line 20 with a pressure reducing valve 19.

The electromagnetic flow control valve 6 configured as described above operates as follows. FIG. 3A shows a closed state of the flow rate adjusting unit 7. At this time, no current is supplied to the coil of the solenoid unit 8 and no pilot pressure is generated in the pilot chamber 15. Therefore, the spool 10 is held at the closed position by the compression coil spring 16. That is, the two passages 13 and 14 are held at positions where their outlets close to the cylinder port 12.

FIG. 3B shows a half-open state (intermediate flow rate region) of the flow rate adjusting unit 7. This is the solenoid part 8
Flow control current I for the intermediate flow region
c is energized, and a pilot pressure proportional to the intermediate flow control current Ic is introduced into the pilot chamber 15, so that the spool 10 is pushed leftward in the figure by the pilot pressure, and the spring force of the compression coil spring 16 is increased. Is held in a balanced position.

The outlet of the first passage 13 is opened to the cylinder port 12 with the displacement of the spool 10,
The pressure oil flowing into the pump port 11 flows to the cylinder port 12 side through the first passage 13, but the flow rate from when the outlet starts to open to when the first passage 13 reaches the full opening (half opening of the flow regulating unit 7). Is proportional to the current, and after the first passage 13 is fully opened (half-opening of the flow regulating unit 7), a constant intermediate flow region (b)
This region is held until the outlet of the second passage 14 is opened to the cylinder port 12.

FIG. 3C shows a fully opened state of the flow rate adjusting section 7. This is a case where a constant current for full opening is applied to the coil of the proportional solenoid unit 10, and a pilot pressure proportional to the current is introduced into the pilot chamber 15. Therefore, the spool 10 is pushed leftward in the figure by the pilot pressure, and is held at a position balanced with the spring force of the compression coil spring 16.

The outlet of the second passage 14 is opened to the cylinder port 12 with the displacement of the spool 10, and the state of the outlet of the first passage 13 opened to the cylinder port 12 is maintained. The pressure oil that has flowed into 11 flows through both the first passage 13 and the second passage 14 to the cylinder port 12 side, and the flow rate is increased. In this case, the flow rate from when the outlet of the second passage 14 starts to open until it reaches the fully open state is proportional to the current,
After full opening (when the opening cross-sectional area of the outlet coincides with the minimum cross-sectional area of the second passage 14), it is maintained in the maximum flow rate region (a).

FIG. 4 is a control block diagram of the electromagnetic flow regulating valve 6 constructed and operating as described above. As shown, when the tilt spool 4 is operated to the forward tilt side or the backward tilt side, the operation is detected by a tilt sensor 24F for forward tilt detection or a tilt sensor 24R for backward tilt detection such as a limit switch. The controller 25 is configured to output a drive signal to the solenoid unit 8 of the electromagnetic flow control valve 6 based on the input to the controller 25. As a result, a constant current is supplied to the solenoid unit 8 so that the flow rate adjustment by the flow rate adjustment unit 7 is performed in the maximum flow rate region (a).

When the tilt cylinder 2 approaches the stroke end and reaches a predetermined deceleration control start point, this is detected by a stroke sensor 26 such as a potentiometer or a proximity switch and input to the controller 25. The controller 25 is configured to output a deceleration signal to the solenoid unit 8 based on the detection signal. As a result, the solenoid unit 8 is supplied with the intermediate flow control current Ic for adjusting the flow rate by the flow rate adjusting unit 7 to the intermediate flow rate region (b). That is, as shown in FIG. 5, the deceleration control is set to be started a certain fixed stroke before the stroke end.

By the way, in the above-described circuit, particularly when a load in the forward tilt direction due to a load is acting on the mast 1, the pressure oil in the rod-side oil chamber of the tilt cylinder 2 is supplied to the electromagnetic type flow control valve 6. There is a possibility that the mast 1 naturally leans forward due to leakage from the spool sliding surface of the flow rate adjusting unit 7 or the sliding surface of the tilt spool 4. For this reason, in this embodiment, a pilot check valve 18 for preventing oil from leaking from the tilt cylinder 2 is provided between the flow rate adjusting unit 7 and the tilt cylinder 2, and the pilot check valve 18 is provided with an electromagnetic flow rate adjusting mechanism. It is configured to operate by a pilot pressure controlled by a solenoid section 8 of the valve 6.

The tilt cylinder speed control device according to the present embodiment is configured as described above, and the operation and effect thereof will be described below. According to the present embodiment, when the tilt spool 4 is in the neutral state, the current to the solenoid 8 of the electromagnetic flow control valve 6 is cut off, and the flow control 7 is closed. When the tilt spool 4 is operated, for example, backward, the solenoid portion 8 of the electromagnetic flow control valve 6 is energized based on the backward tilt detecting operation of the tilt sensor 24R, and the flow control portion 7 is opened.

Therefore, the pressure oil sent from the hydraulic pump 5 is sent to the rod-side oil chamber of the tilt cylinder 2 via the flow rate adjusting unit 7 and the pilot check valve 18, and the pressure oil sent from the bottom-side oil chamber is It is returned to the tank 21. At this time, the flow rate of the pressure oil sent to the tilt cylinder 2 is controlled by the flow rate adjusting unit 7. That is, at normal times, the tilt cylinder 2 is tilted backward at a speed corresponding to the flow rate regulated in the maximum flow rate area (a), that is, in the fully opened state.

When the tilt cylinder 2 reaches the deceleration control start point before the stroke end, an intermediate flow control current Ic is supplied to the solenoid 8 based on the detection signal of the stroke sensor 26, and the opening of the flow adjustment unit 7 is controlled. Is controlled to the intermediate flow rate region (b). As a result, the flow rate of the pressure oil is reduced, the speed of the tilt cylinder 2 is reduced, and the impact at the stroke end is reduced. At the same time as the return of the tilt spool 4 to the neutral position, the flow rate adjusting unit 7 loses the input to the controller 25 from the front and rear tilt detection sensors 24F and 24R, and the power to the solenoid unit 8 is cut off. The compression coil spring 16 returns to the fully closed state by the spring force.

As described above, according to the present embodiment, when the tilt cylinder 2 approaches the stroke end, the speed of the tilt cylinder 2 can be automatically reduced to reduce the impact at the stroke end. The troublesome tilt lever operation for deceleration by the operator can be eliminated.

In the first embodiment, an intermediate flow rate region (b) is used as means for reducing the impact at the stroke end.
Instead of using the electromagnetic flow control valve 6 having the above, it is also possible to use a conventionally known proportional electromagnetic flow control valve instead. The proportional electromagnetic flow control valve includes a flow control unit and a solenoid unit, and a displacement amount of the flow control unit spool, that is, a displacement amount of the flow control unit spool by a balance between an electromagnetic force (in proportion to a current flowing through the coil) generated in the solenoid unit and a spring force. , The opening degree is determined, and a flow rate proportional to the current can be obtained. The current-flow rate characteristic is proportional as shown in FIG.

However, in the proportional solenoid type flow control valve, the spring force for pushing the spool and the current (electromagnetic force generated in the solenoid portion) often vary, and for example, the flow characteristic is not improved due to the variation in the spring force. When the tilt cylinder is offset as shown by the broken line, the actual adjustment flow rate when the tilt cylinder approaches the stroke end is different from the target flow rate. As a result, the tilt cylinder stops before reaching the stroke end or a predetermined flow rate at the stroke end. The impact reduction effect may not be obtained.

In the first embodiment, however, the intermediate flow rate control current Ic for obtaining a constant flow rate in the intermediate flow rate range (b) has a width. Fig. 2
A constant flow rate can be obtained even in the case of offset as shown by the broken line or in the case where the intermediate flow rate control current varies. Therefore, a stable predetermined impact reduction effect can be obtained at the stroke end. In addition, since the electromagnetic flow control valve 6 is held at the opening degree in the intermediate flow rate region (b), there is no possibility of stopping before the stroke end, so that the solenoid flow control valve 6 operates reliably until the stroke end, and the stop position accuracy is secured. Is done.

In this embodiment, when the mast 1 is tilted forward, the operation of the tilt cylinder 2 is always restricted by the throttle 4a of the tilt spool 4, and is performed at a lower speed than when the mast 1 is tilted backward. When the point is reached, the speed is further reduced by being subjected to throttle control by the electromagnetic flow control valve 6 in the same manner as in the case of the backward tilt, whereby the effect of reducing the impact at the stroke end is enhanced.

Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment, as shown,
As a flow control valve for controlling the speed of the tilt cylinder 2, the tilt spool 4 itself, which is a direction switching valve for controlling the flow direction of the pressure oil to the tilt cylinder 2, is constituted by an electromagnetic flow control valve 6. The electromagnetic flow control valve 6 in this case is illustrated by an electromagnetic internal pilot system, and is configured to obtain the same current-flow characteristics as in the first embodiment.

Therefore, also according to the second embodiment,
As in the case of the first embodiment, the tilt cylinder 2
The impact at the end of the stroke can be reduced, the tilt cylinder 2 can be reliably operated to the end of the stroke, and the number of valves can be reduced.

Next, a third embodiment of the present invention will be described with reference to FIG. This embodiment, as shown,
Between the rod-side oil chamber of the tilt cylinder 2 and the tilt spool 4, two electromagnetic on-off valves 27 as flow control valves,
28 are provided in parallel. When the tilt cylinder 2 reaches the deceleration control start point, the solenoid-operated on-off valves 27 and 28 are both switched to the open position by energization based on the operation detection signals for the tilt-slope forward and backward tilts of the tilt spool 4. Based on the detection signal, the two solenoid on-off valves 2
Either one of 7, 28 is de-energized and returned to the closed position.

Therefore, according to this embodiment, when the tilt spool 4 is in the neutral position, the two solenoid valves 27, 2
8 are held in the closed position, but when the tilt spool 4 is operated, for example, backward, the two electromagnetic on-off valves 2
When the tilt cylinder 2 reaches the deceleration control position when the tilt cylinder 2 reaches the deceleration control position, pressure is supplied to the tilt cylinder 2 via the two electromagnetic on-off valves 27 and 28. Is closed, the speed of the tilt cylinder 2 is reduced, and the impact at the stroke end can be reduced.

Although not shown, the pilot check valve 18 is also provided in the second and third embodiments, similarly to the first embodiment, and the tilt cylinder 2 It is desirable to prevent oil from leaking from.

In the above embodiments, the start point of the deceleration control for the tilt cylinder 2 is fixed at a fixed position during the cylinder stroke. However,
When the tilt spool 4 is of a manual operation type, the operating speed of the tilt cylinder 2 during the actual cargo handling operation is
The opening degree of the tilt spool 4 corresponding to the operation amount of the tilt lever by the operator and the discharge amount of the hydraulic pump 5 changed by the rotation of the engine or the motor are determined. Therefore, when the deceleration control start point for the tilt cylinder 2 is fixed at a fixed position, the impact reduction effect and workability may be reduced depending on the speed of the tilt cylinder 2.

In view of this, the deceleration control start point is made variable in accordance with the operating speed of the tilt cylinder 2, that is, as shown in FIG. It is preferable to start the deceleration control near the stroke end when the vehicle is late.

In such a deceleration control, for example, a control point is set at an appropriate position during the cylinder stroke of the tilt cylinder 2, and the output timing of a deceleration control signal to the solenoid is set in accordance with the speed at which the control point passes. It is realized by changing it. When such a configuration is adopted, the required impact reduction effect can be obtained by starting the deceleration control after passing the control point early at a high speed, and the deceleration region can be obtained by starting the deceleration at a low speed late. It is possible to shorten the length and avoid a decrease in workability.

Furthermore, the deceleration control start point for the tilt cylinder 2 may be made variable in accordance with the magnitude of the load applied to the tilt cylinder 2 or in accordance with the height of the mast 1. At this time, the load may detect the hydraulic pressure of the tilt cylinder 2 by a pressure sensor, or may detect the value of the hydraulic pressure applied to the lift cylinder by the pressure sensor as the load applied to the tilt cylinder 2. Further, the lift of the mast 1 may be detected by using a contact / non-contact type proximity sensor or a reel-type sensor that detects a winding amount of a reel wound in accordance with the elevation of the mast 1.

[0045]

As described in detail above, according to the present invention,
A stable predetermined impact reduction effect can be obtained while securing the stop position accuracy at the stroke end of the tilt cylinder of the forklift.

[Brief description of the drawings]

FIG. 1 is a speed control circuit diagram of a tilt cylinder according to a first embodiment.

FIG. 2 is a current-flow characteristic diagram of an electromagnetic flow regulating valve.

FIGS. 3A and 3B are cross-sectional views of a flow control unit of the electromagnetic flow control valve according to the embodiment, in which FIG. 3A shows a closed state, FIG. 3B shows a half-open state (intermediate flow area), and FIG. Indicates a fully open state (maximum flow rate region).

FIG. 4 is a control block diagram of an electromagnetic flow regulating valve.

FIG. 5 is a diagram showing a relationship between a cylinder stroke of a tilt cylinder and a current value of a solenoid valve.

FIG. 6 is a speed control circuit diagram of a tilt cylinder according to a second embodiment.

FIG. 7 is a speed control circuit diagram of a tilt cylinder according to a third embodiment.

FIG. 8 is a diagram illustrating a relationship between a cylinder speed and a cylinder stroke when a deceleration control start point of the tilt cylinder is variable.

FIG. 9 is a current-flow characteristic diagram of a general proportional electromagnetic flow control valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Mast 2 ... Tilt cylinder 4 ... Tilt spool 6 ... Electromagnetic flow control valve 7 ... Flow control part 8 ... Solenoid part

Claims (5)

[Claims] A forklift is provided with a flow control valve between a tilt cylinder for tilting a mast in a forklift and a hydraulic pump for adjusting a feed amount or a return amount of pressurized oil to the tilt cylinder when the mast tilts, wherein the tilt cylinder is a cylinder. A tilt cylinder speed control device that reduces the flow rate of pressure oil to the tilt cylinder to a preset constant flow rate when a predetermined deceleration control start point in the middle of a stroke is reached. 2. The tilt according to claim 1, wherein the flow control valve is constituted by an electromagnetic flow control valve having an intermediate flow region capable of flowing a constant flow with a predetermined current width in the middle of the flow control range. Cylinder speed control device. 3. An electromagnetic flow rate control device, comprising: a directional control valve for controlling a flow direction of pressure oil to the tilt cylinder; and an intermediate flow rate region capable of flowing a constant flow rate with respect to a predetermined current width in the middle of a flow rate adjustment range. 2. The tilt cylinder speed control device according to claim 1, wherein the tilt cylinder speed control device is constituted by an adjustment valve. 4. The flow control valve is constituted by a plurality of on-off valves provided in parallel, and at least one of the on-off valves is operated to a closed side when the tilt cylinder reaches a deceleration control start point. 2. The tilt cylinder speed control device according to claim 1, wherein the tilt cylinder speed control device has a configuration. 5. The deceleration control start point is variable according to the cylinder speed so that the flow restricting action by the flow control valve is started at a position farther from the stroke end as the tilt cylinder speed increases. 5. The tilt control device for a tilt cylinder according to any one of claims 1 to 4.