JP3147026B2 - Forklift tilt control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tilt control device for a forklift, and more particularly to a tilt control device when a mast is stopped in the middle of a tilt range.

[0002]

2. Description of the Related Art A system for automatically stopping a mast at a position where a fork is horizontal when a mast is tilted (tilted) has been developed in order to improve workability when carrying out cargo handling work using a forklift. . This is achieved by detecting the tilt angle of the mast by a tilt angle sensor and operating an electromagnetic switching valve (electromagnetic tilt spool) for operating a tilt cylinder for tilting the mast when the fork level is detected, to the closing side. The cylinder is automatically stopped.

When the tilt cylinder is stopped, the pressure of the tilt cylinder acts on the tilt spool that operates the tilt cylinder. Generally, the tilt spool is of a type in which a sliding surface with the valve body is used as a sealing surface. In order to ensure good operability, the tilt spool is disposed between the sliding surface and the sliding surface so as not to increase the sliding resistance to the valve body. Has a slight gap. Therefore, when the tilt cylinder is stopped and held, there is a problem that the pressure oil of the tilt cylinder leaks from the sliding surface of the tilt spool and the mast naturally leans forward, particularly when the fork is loaded with luggage. Appears noticeably.
For this reason, there is a desire to prevent a leak of pressure oil by providing a pilot check valve of a type in which a ball or a poppet is pressed against a sheet and sealed in an oil passage on the rod side of the tilt cylinder.

[0004]

However, if a pilot check valve is provided in the hydraulic circuit of the system for automatically stopping the mast at a position where the fork is horizontal to prevent leakage, for example, the pilot check valve is provided in front of the mast. When the tilt cylinder is automatically stopped during operation to the tilt side, the rod side of the tilt cylinder is subjected to the pressing force from the bottom side and the pulling force of the rod by the mast load, so the pressure on the rod side of the tilt cylinder instantaneously increases. The pressure rises abnormally, and the abnormally high pressure is sealed by a check valve with almost no leakage. As a result, the high pressure is retained on the rod side. Therefore, when tilting is performed immediately after the mast is automatically stopped, the check valve opens, and at the same time, the high pressure sealed up to that point is suddenly released. There is a problem that occurs.

[0005] The problem of such a starting shock is as follows.
This is not necessarily a unique problem of the automatic stop system.If a pilot check valve is installed to prevent leakage even in a general hydraulic circuit, the tilt operation is interrupted halfway and restarted. This also occurs in the same case.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to prevent the mast from naturally leaning forward and to prevent a starting shock that may occur when the tilt operation is restarted immediately after the mast is stopped. An object of the present invention is to provide a tilt control device for a forklift.

[0007]

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 control device of a forklift, wherein a pilot control is provided between a rod-side oil chamber of a tilt cylinder for mast tilting and a direction switching valve for switching a flow direction of pressure oil to the tilt cylinder. A check valve is provided, and the pilot check valve is configured to be opened for a moment after the mast is stopped halfway within the tilt range.

According to the first aspect of the present invention, when the pilot check valve is momentarily opened after the mast is stopped, the pressure sealed between the rod side of the tilt cylinder and the pilot check valve is reduced. It is transmitted to the directional control valve. The directional control valve with the sliding surface as the sealing surface has a much larger leak amount than the pilot check valve that seals by pressing a ball or the like against the seat, so abnormal high pressure generated on the rod side of the tilt cylinder when the mast is stopped. Alleviated by leakage from the directional control valve. This reduces or prevents the starting shock when the tilt operation is restarted immediately after the stop. In addition, in the state where the mast is stopped and held, even if a forward leaning direction load acting on the mast acts on the rod side of the tilt cylinder, leakage of pressure oil is prevented by the pilot check valve, and natural forward leaning of the mast is prevented. .

According to a second aspect of the present invention, the mast is tilted within a tilting range between a rod-side oil chamber of a tilt cylinder for tilting the mast back and forth and a direction switching valve for switching a flow direction of pressure oil to the tilt cylinder. A tilt control device for a forklift equipped with a control valve for automatically stopping at a position, wherein a pilot check valve is provided between the control valve and a tilt cylinder, and the pilot check valve is automatically stopped at a mast. , So that it is opened only for a moment.

According to the second aspect of the present invention, when the pilot check valve is opened for a moment after the mast is automatically stopped, the pressure sealed between the rod side of the tilt cylinder and the pilot check valve is reduced. Is transmitted to the control valve and the direction switching valve. Since the control valve and the directional control valve have a considerably larger leak amount than the pilot check valve, abnormal high pressure generated on the rod side of the tilt cylinder when the mast is stopped is reduced by the leak from the control valve and the directional control valve. As a result, the start shock when the tilt operation is restarted immediately after the automatic stop of the mast is reduced or prevented. Further, similarly to the first aspect of the invention, it is possible to prevent the mast from naturally leaning forward in the stopped grip state.

In this case, as in the third aspect of the present invention, in the tilt control device for a forklift according to the second aspect, the control valve and the pilot check valve are simultaneously opened for a moment after the mast is automatically stopped. May be configured. When such a configuration is adopted, when the control valve opens, the abnormal high pressure generated on the rod side of the tilt cylinder during automatic stop of the mast is directly transmitted to the directional control valve, and the abnormal high pressure is relieved by the leak therefrom. You.

According to a fourth aspect of the present invention, in the tilt control device for a forklift according to the third aspect, a pilot line for introducing a discharge pressure of a hydraulic pump as a pilot pressure for operating the control valve and the pilot check valve to open sides. And a solenoid valve for controlling the opening and closing of the pilot line when the mast is automatically stopped is provided on the pilot line.

According to the fourth aspect of the present invention, since the opening and closing of the control valve and the pilot check valve are operated by the common solenoid valve, it is possible to avoid a variation in the operation timing of both valves. The structure is simplified.

According to a fifth aspect of the present invention, in the tilt control device for a forklift according to the first or second aspect, the opening operation of the pilot check valve is performed under the condition of a high load in which a load is loaded. It is characterized by the following. According to such a configuration, it is possible to effectively act in a cargo handling operation under a situation where a startup shock is likely to occur.

[0015]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a hydraulic circuit diagram of a tilt cylinder in a forklift. As shown, a mast 1 for guiding the fork (not shown) up and down
The tilt cylinder 2 for tilting the hydraulic pump 5 back and forth is provided with a hydraulic pump 5 through a manual tilt spool 4 as a directional switching valve provided in the cargo control valve 3.
The tilt spool 4 is operated to extend and contract.

The tilt spool 4 and the tilt cylinder 2
The oil passage 6 connecting the rod-side oil chamber is provided with a proportional electromagnetic flow control valve 7 (hereinafter, referred to as an electromagnetic valve) as a control valve for stopping the mast 1 at a predetermined position within the tilting range. . The solenoid valve 7 includes a flow control unit 8 and a solenoid unit 9 for generating pilot, and controls the pilot pressure acting on the flow control unit 8 by the electromagnetic force (proportional to the current flowing through the coil) generated in the solenoid unit 9. The amount of displacement (opening) of the spool of the flow rate adjusting section 8 is determined by the balance between the pilot pressure and the spring force, so that a flow rate proportional to the current can be obtained.

The value of the current supplied to the solenoid 9 is proportional to the amount of operation of the tilt lever 4a for operating the tilt spool 4. Also, the pilot pressure is
A pressure reducing valve 11 is provided in the pilot line 10 to regulate the maximum pilot pressure acting on the flow rate adjusting unit 8.

A pilot check valve 12 for preventing leakage is provided in the oil passage 6 on the downstream side (tilt cylinder 2 side) of the solenoid valve 7, and the pilot check valve 12 is a solenoid portion of the solenoid valve 7. The opening operation is performed by the pilot pressure controlled by the control unit 9. In FIG. 1, 13 is an oil tank, 14 is a flow dividing valve, and 15 is a PS (power steering) valve.

FIG. 2 is a control block diagram of the tilt cylinder. When the tilt operation of the mast 1, that is, the switching operation of the tilt spool 4 to the forward tilt side or the backward tilt side by the tilt lever 4a is performed, the operation is performed by a forward tilt operation sensor 16 or a rear tilt operation sensor 17 such as a micro switch. Detected and input to the controller 22, based on which the controller 22 outputs a drive signal for energizing the solenoid unit 9 of the solenoid valve 7 with a set drive current. As a result, the pilot line 10 is opened, and the pilot pressure acts on the flow control unit 8 and the pilot check valve 12, respectively. Therefore, the oil passage 6 is communicated, the tilt cylinder 2 is operated, and the mast 1 is tilted forward or backward. You.

The tilt lever 4a is provided with an automatic level switch 18 for automatically stopping the mast 1 at the horizontal position of the fork when the tilt is operated.
2 is input. On the other hand, the mast 1 is provided with a tilt angle sensor 19 such as a rotary potentiometer or a limit switch for detecting the tilt angle, and a detection signal is input to the controller 22.

When the operation signal of the automatic horizontal switch 18 is input, the controller 22
When the tilt angle reaches the fork horizontal position, a signal for cutting off the power supply to the solenoid portion 9 of the solenoid valve 7 is output. This allows
Since the pilot pressure of the flow control unit 8 and the pilot check valve 12 is released to the oil tank 13, the flow control unit 8
Then, the pilot check valve 12 is closed and the tilt cylinder 3 is automatically stopped.

Further, a lift cylinder (not shown) for raising and lowering the fork is provided with a load sensor 20 (for example, a pressure switch) for detecting a load (whether or not there is a load). And a lift sensor 21 (for example, a proximity switch) for detecting the height of the shock is provided, and their detection signals are input to the controller 22.

When both the load and the lifting height exceed the set values, the controller 22 adjusts the mast forward tilt angle based on the detection signal from the tilt angle sensor 19 during the forward tilt operation of the mast 1. When reaching a regulation angle within the tilt range, a signal for shutting off the current is output to the solenoid 9 of the solenoid valve 7. As a result, the flow rate adjusting unit 8 and the pilot check valve 12 are closed as described above, and the tilt cylinder 3 is automatically stopped. Such forward leaning angle regulation is significant in that safety is improved by avoiding the possibility of overturning when the mast 1 is tilted forward to the maximum angle while a heavy object is loaded.

According to the tilt control device provided with the mast automatic stop system having the above structure, when the mast 1 is stopped at a predetermined position (horizontal fork position or forward leaning restriction position),
The pressure on the rod side of the tilt cylinder 2 rises abnormally,
Pilot check valve 12 whose pressure is almost leak-free
Therefore, it is sealed in an abnormally high pressure state. This is because when the mast 1 is automatically stopped, a pressing force on the bottom side and a pulling force of the rod by the mast load act on the rod side of the tilt cylinder 2. That is, when the flow rate adjusting unit 8 is switched to the closing side, the pump pressure is acting on the bottom side, and when the tilt spool is returned to the neutral state, the pump pressure is shut off, but the pump pressure is shut off at the bottom side. , A pressure close to the pump pressure is held on the bottom side. Since the tilt spool is inferior in airtightness, the pressure on the bottom side decreases and the pressure on the rod side decreases in accordance with leakage at the tilt spool portion. However, since this leakage phenomenon takes time, the high pressure on the rod side is maintained for a while.

Therefore, in the present embodiment, in order to alleviate abnormal high pressure generated on the rod side of the tilt cylinder 2 at the time of automatic stop, the solenoid portion 9 of the solenoid valve 7 is provided after automatic stop.
Is driven for a moment. That is, in order to re-tilt the mast 1 after the automatic stop, it is necessary to return the tilt lever 4a to the neutral position once. Therefore, the returning operation of the tilt lever 4a is performed by the forward tilt operating switch 16 or the backward tilt operating switch 17. Upon detection, the detection signal is input to the controller 22 as an automatic stop signal of the mast 1, and the controller 22 outputs a drive signal to the solenoid unit 9 for a moment based on the detection signal.

Therefore, after the mast 1 is automatically stopped, when the tilt lever 4a is returned to the neutral position, the pilot check valve 12 and the flow rate adjusting unit 8 are opened, and the abnormally high pressure sealed in the rod side of the tilt cylinder 2 is reduced. It is transmitted to the flow rate adjusting section 8 and the tilt spool 4. At this time, since the tilt spool 4 is in the neutral position and closes the oil passage 6, there is no possibility that the tilt cylinder 2 moves. The flow rate adjusting portion 8 and the tilt spool 4 of the type that seals on the sliding surface with the valve body have a considerably larger leak amount of pressure oil than the pilot check valve 12 that seals by pressing a ball or a poppet against a seat. From
The extraordinary high pressure that has been enclosed is alleviated. As a result, when the tilt operation is restarted, the starting shock generated at the beginning of the movement of the tilt cylinder 2 is reduced or prevented.

That is, conventionally, if the tilt operation is performed immediately after the automatic stop of the mast, the pilot check valve 12
The opening of the valve causes a sudden release of the abnormally high pressure enclosed therein, causing a start-up shock such as a crack at the beginning of movement. However, according to the present embodiment, such a problem is solved. As a result, the tilting operation of the mast 1 when the tilt operation is performed immediately after the mast is stopped is smoothly performed.

When the mast 1 is stopped, the mast 1
, A load in the forward leaning direction is always applied, and a particularly large load is applied when the load is loaded. This load acts on the rod side of the tilt cylinder 2, but since the pilot check valve 12 is provided in the oil path 6 on the rod side, the leakage of the pressure oil from the tilt cylinder 2 is prevented, and It is possible to prevent the mast 1 from leaning forward naturally when the mast 1 is held in the stopped state.

Further, in this embodiment, since the discharge pressure of the hydraulic pump 5 is introduced as pilot pressure,
For example, unlike the case where the pilot pressure is extracted from the downstream side of the tilt spool 4, the pilot check valve 12 and the flow control unit 8 are opened using the returning operation of the tilt spool 4 to the neutral position after the mast 1 is automatically stopped. And pilot check valve 1
2 and the flow rate adjusting unit 8 of the solenoid valve 7 are controlled by a common pilot pressure.
This is effective in preventing a variation in the operation timing of the flow control unit 2 and the flow rate adjusting unit 8 and simplifying the structure.

In this embodiment, the solenoid 9
Although the proportional solenoid valve 7 capable of obtaining a flow rate proportional to the value of the current supplied to the solenoid valve is provided, a similar effect can be obtained by providing an electromagnetic on / off valve instead.
In addition, the action of alleviating abnormally high pressure after the mast is stopped may be changed to a configuration in which only the pilot check valve 12 is opened. Controller 2
2 can be realized. Further, the present invention can be applied to a system in which the tilt spool 4 itself for operating the tilt cylinder 2 is of an electromagnetic type and can automatically stop the mast.

When the tilt operation is restarted immediately after the mast 1 is stopped, the start-up shock problem is caused by a situation where there is a load (at a high load) or a situation where the load is present and the fork is in a high elevation region where the fork is raised. It is easy to occur underneath and may cause load collapse. In other words, when the mast 1 is automatically stopped at the fork horizontal position by operating the automatic level switch 18 in an unloaded state (at a low load), for example, or when the operator operates the tilt lever 4a, the mast 1 is not operated. Is stopped at an arbitrary position, the startup shock is unlikely to occur even if the tilt operation is resumed immediately after the stop, and the shock is small.

In view of this, when the mast 1 is stopped under the condition of high load or high load and high lift, only the pilot check valve 12 or the pilot check valve 12 The adjustment unit 8 may be configured to be opened. That is, the controller 22
However, when it is determined that there is a load based on the signals input from the load sensor 20 and the lift sensor 21, or when it is determined that there is a load and the region is in the high-lift region, the mast 1 is moved halfway within the tilt range. A drive signal for opening is output to an electromagnetic valve dedicated to the pilot check valve 12 or a common solenoid unit 9 of the pilot check valve 12 and the flow rate adjusting unit 8 based on an input signal indicating that the operation has stopped. I do. According to such a configuration, it is possible to effectively work particularly in a cargo handling operation under a situation where a starting shock is likely to occur.

[0033]

As described in detail above, according to the present invention,
After solving the problem of the natural forward lean of the mast, it is possible to prevent a startup shock that may occur when the tilt operation is restarted immediately after the mast is stopped.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram of a tilt cylinder.

FIG. 2 is a control block diagram of an electromagnetic flow control valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Mast 2 ... Tilt cylinder 4 ... Tilt spool 5 ... Hydraulic pump 7 ... Solenoid flow control valve 10 ... Pilot line 12 ... Pilot check valve

Claims (5)

(57) [Claims] 1. A pilot check valve is provided between a rod-side oil chamber of a tilt cylinder for tilting a mast and a direction switching valve for switching a flow direction of pressurized oil to the tilt cylinder, and the mast tilts the pilot check valve. A tilt control device of a forklift configured to be released for a moment after being stopped halfway within the range. 2. A method for automatically stopping a mast at a predetermined position within a tilting range between a rod-side oil chamber of a tilt cylinder for tilting a mast and a direction switching valve for switching a flow direction of pressure oil to the tilt cylinder. A tilt control device for a forklift equipped with a control valve according to (1), wherein a pilot check valve is provided between the control valve and the tilt cylinder, and the pilot check valve is opened only momentarily after the mast is automatically stopped. Forklift tilt control device. 3. The forklift tilt control device according to claim 2, wherein the control valve and the pilot check valve are simultaneously opened for a moment after the mast is automatically stopped. 4. A pilot line for introducing a discharge pressure of a hydraulic pump as a pilot pressure for operating the control valve and the pilot check valve to open the pilot line, and the pilot line controls opening and closing of the pilot line when the mast is automatically stopped. The tilt control device for a forklift according to claim 3, further comprising an electromagnetic valve. 5. The tilt control device for a forklift according to claim 1, wherein the opening operation of the pilot check valve is performed under a condition of a high load in which a load is loaded.