JPH04256698A - Fork lift control device - Google Patents

Abstract

PURPOSE:To prevent tumble of a fork lift, drop of object, and application of an excessive stress to the mast at the time of forward tilting even in the case with heavy load, 5y changing the forward tilting speed in accordance with the load. CONSTITUTION:An operating amount/control amount corresponding table by loads 24 is prepared, and the load is judged from an oil pressure signal S3 given by an oil pressure sensor 17. The control amount corresponding to the operating amount of a working machine lever for tilting 9b is determined from the table which is applicable for the current load, and a solenoid-operated proportional control valve 11A is controlled with this control amount determined so as to control the rate of flow of the pressure oil flowing to a tilting cylinder 8. Thus the tilting speed is varied in accordance with the load.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for a forklift, and more particularly to control of the forward tilting speed of a mast.

0002

2. Description of the Related Art A forklift is an industrial vehicle for cargo handling that is equipped with a mast for raising and lowering loaded cargo, and is capable of moving between locations. In order to facilitate cargo handling work and to improve the stability of cargo while traveling, a hydraulic cylinder called a tilt cylinder is used to tilt the mast back and forth by expanding and contracting its piston rod. . Furthermore, the mast tilt speed is determined by the flow rate of pressure oil to the tilt cylinder, and this flow rate is adjusted by operating the work equipment lever. In other words,
The operator operates the work equipment lever to adjust the tilt speed.

[0003] However, in the past, the forward tilting speed of the mast,
The relationship between the tilt backward speed and the amount of operation of the work equipment lever was constant regardless of the magnitude of the load.

0004

As described above, if the tilt forward speed characteristic is constant regardless of the load, the heavier the load, the larger the gravitational moment becomes, and the inching characteristic becomes unstable, making control difficult. Therefore, when the load is heavy, it is necessary to operate the lever of the work equipment in order to prevent it from tipping over, to avoid shock or lifting of the butt when stopping, to prevent the load from falling, and to prevent excessive stress from being applied to the mast. Need to pay attention.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, it is an object of the present invention to provide a device that controls the tilt forward speed characteristics to vary depending on the load.

[0006]

[Means for Solving the Problems] A forklift control device according to the present invention that achieves the above object has a structure in which the relationship between the operation amount of the forklift's tilt working machine lever and the control amount of the tilt solenoid valve is determined in advance for each load. Table by load,
A means for detecting a load, and a control amount corresponding to the detected load and the operating amount of the tilting work equipment lever are determined from the table, and the determined control amount is used to control the tilting position arranged in the pressure oil pipe line of the tilting hydraulic cylinder. The invention is characterized by comprising means for controlling a solenoid valve for use.

[0007]

[Operation] The forklift control device of the present invention detects the load, determines the control amount corresponding to the operation amount from a table suitable for the load, and controls the solenoid valve. As a result, it is possible to adjust not only the amount of operation of the tilting work equipment lever but also the load.
The flow rate of the pressure oil flowing into the tilting hydraulic cylinder changes, and therefore the tilting speed changes.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but first, an example of a forklift to which the present invention is applied will be explained with reference to FIGS. 4 and 5.

FIG. 4 is a perspective view showing an example of a forklift. As shown in the figure, a lift cylinder 1 is fixed to a pair of left and right outer masts 2, and a piston rod 1
With the expansion and contraction of a, a pair of left and right inner masts 3 are raised and lowered using the outer mast 2 as a guide. At this time, the outer mast 2 is fixed to the vehicle body 7 at the front of the vehicle body 7. As a result, as the inner mast 3 moves up and down, an elevating section consisting of a bracket 5 suspended from a chain (not shown) and a fork 4 for directly loading cargo moves up and down. That is, the chain is suspended from a chain wheel (not shown) rotatably supported by the inner mast 3, and is fixed to the bracket 5 at one end and to the outer mast 2 at the other end.

[0010] Thus, the fork 4 and bracket 5, which are elevating parts, not only rise as the inner mast 3 rises, but also rise in relative position with respect to the inner mast 3 as the chain wheel rises with respect to the outer mast 2. do. That is, the amount of rise of the elevating section relative to the ground surface is the sum of the relative rise of the elevating section with respect to the inner mast 3 defined by the length of the chain to the amount of rise of the inner mast 3. Regarding the lowering of the elevating section, the same relationship as when ascending is established, only that the direction of movement is reversed.

The tilt cylinder 8 is used to tilt the elevating section together with the outer mast 2 and the inner mast 3 forward (toward the vehicle body 7 side) and rearward (toward the vehicle body 7 side). That is, it tilts forward when unloading, and tilts backward when loading and transporting cargo, thereby maintaining good workability and ensuring safety.

The work machine levers 9a and 9b are operated by an operator to control the lift cylinder 1 via a work machine control controller 10 and an electromagnetic proportional control valve 11.
It controls the operation of the tilt cylinder 8 and is housed in a joystick box 13 together with a safety switch 12 for making an emergency stop. Work equipment lever 9
Reference characters c, 9d, and 9e are used to accommodate various attachments such as roll clamps, bail clamps, etc. The seat switch 14 is a switch that operates when an operator sits on the driver's seat 15, and its output signal is sent to the controller 10.

FIG. 5 is a block diagram showing an example of the entire control device for the forklift. In the figure, parts that are the same as those in FIG. 4 are given the same numbers and redundant explanations will be omitted.

As shown in FIG. 5, the work machine levers 9a, 9
b is formed by a potentiometer, and sends a lever operation signal S1 whose current value is proportional to the amount of operation to the controller 10.
Send to. The controller 10 is a microprocessor (
CPU), and lever operation signal S1
Based on this, a flow rate control signal S2 is sent out to adjust the opening degree of the spool of the electromagnetic proportional control valve 11. Solenoid proportional control valve 1
1 controls the flow rate of pressure oil flowing through the hydraulic pipe 16 by moving its spool in proportion to the magnitude of the flow rate control signal S2, thereby controlling the lift cylinder 1 and the tilt cylinder 8.
The operating speed of the working machine levers 9a and 9b is controlled to correspond to the amount of operation of the working machine levers 9a and 9b.

The hydraulic pressure sensor 17 is disposed in the hydraulic line 16 and sends out a hydraulic signal S3 representing the pressure of the pressure oil in the hydraulic line 16. Controller 10 receives oil pressure signal S3
is processed to calculate the load acting on the lift cylinder 1 or the tilt cylinder 8.

Furthermore, the controller 10 has a warning light 18.
When the starter switch 20 housed in the console box 19 is turned on, power is supplied from the battery 21 to operate, and when the safety switch 12 is operated or the seat switch 14 is not operated, the current value of the flow rate control signal S2 is zero. As electromagnetic proportional control valve 11
The opening degree of the opening is controlled to be zero.

In the figure, 22 is a hydraulic pump, and 23 is a hydraulic oil source. In addition, an electromagnetic proportional control valve 11, a hydraulic pipe line 16
, hydraulic system parts such as the oil pressure sensor 17 are connected to the work machine lever 9a.
The number corresponding to the number of through 9e is provided. In this example,
Since it has two working machine levers 9a and 9b for lifting and tilting, it is possible to perform lifting and tilting operations.
A hydraulic system is installed.

Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 shows a block configuration of a control device including a tilt control system. In FIG. 1, the same functional parts as those in FIGS. 4 and 5 are given the same numbers and redundant explanation will be omitted.

As shown in FIG. 1, the controller 10 includes a tilt load table 24 and a control amount extraction means 25.
, a control amount output means 26 , and a load determination means 27 .

The load-specific table 24 of this embodiment shows the amount of operation of the tilting work machine lever 9b in the forward tilting direction (lever opening degree) and the amount of control (table output value) for the tilting electromagnetic proportional control valve 11A. As shown in Figure 3, there are three types of correspondence: small load, medium load, and large load 24A and 24B.
, 24C. As can be seen from FIG. 3, if the lever opening degree is the same, the larger the load, the smaller the table output value (control amount). Note that although the lever opening degree in the backward tilting direction is omitted in FIG. 3, the control amount is made to correspond to it regardless of the load.

The load determining means 27 determines whether the load is in a small load, medium load, or large load range based on a hydraulic pressure signal S3 sent from a hydraulic pressure sensor 17 disposed in the hydraulic pipe line 16A of the lift cylinder 1. is determined, and a signal S4 representing the determination result is sent to the control amount extraction means 25. As a specific example of the determination method, the first setting value is the oil pressure corresponding to the boundary between the small load and the medium load, the second setting value is the oil pressure corresponding to the boundary between the medium load and the large load, and the oil pressure signal S3 is set as the second setting value. is less than the first set value, it is determined that the load is small, and the oil pressure signal S3 is lower than the first set value.
If it is more than the set value and less than the second set value, it is determined that the load is being applied,
If the oil pressure signal S3 is greater than or equal to the second set value, it is determined that the load is large.

When the control amount extracting means 25 receives the lever operation signal S1 in the forward tilting direction from the tilt work machine lever 9b, the control amount extracting means 25 extracts the information from the load classification table 24 according to the small, medium, or large load determined by the load determining means 27. A control amount corresponding to the lever operation signal S1 is extracted with reference to the corresponding table 24A, 24B, or 24C, and a flow rate control signal S2 representing this control amount is sent out. Therefore, this flow rate control signal S2
takes a smaller value as the load increases from small to medium to large, and is supplied to the tilt electromagnetic proportional control valve 11A via the control amount output means 26.

Thus, the spool of the electromagnetic proportional control valve 11A moves in proportion to the magnitude of the flow rate control signal S2, which corresponds not only to the amount of operation of the work implement lever 9b but also to the small, medium, or large load. By controlling the flow rate of the pressure oil flowing through the hydraulic pipe 16B, the forward tilt speed of the tilt cylinder 8 is made smaller as the load increases from small to medium to large.

[0025] As described above, since the tilt forward speed characteristic changes depending on the load, the inching characteristic remains constant, and there is no risk of overturning even when the load becomes heavy. In addition, even if you suddenly stop, it is difficult to cause a shock and it is difficult to raise your butt. It also prevents cargo from falling and eliminates excessive stress on the mast.

Here, when the work implement lever 9b is in the neutral position, the controlled amount is zero, that is, the current value of the flow rate control signal S2 is zero.

The series of control operations described above is shown in a flowchart as shown in FIG.

Note that in the above-mentioned embodiment, the working machine lever 9b
When the is operated in the backward tilting direction, the control amount is set in accordance with the operation amount regardless of the load, but it is also possible to change the backward tilting speed according to the load.

[0029]

As explained above in conjunction with the embodiments, according to the present invention, the tilting speed characteristics change depending on the load, so the inching characteristics can be kept constant. Also,
It becomes easier to control the speed safely, and prevents overturning of the forklift, dropping of cargo, shock and tail lifting during sudden stops, and excessive stress on the mast.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing extracted main parts of a control device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of the embodiment shown in FIG. 1;

FIG. 3 is a diagram showing a load-based correspondence table of manipulated variables and corresponding controlled variables;

FIG. 4 is a perspective view showing a forklift to which an embodiment of the present invention is applied.

FIG. 5 is a block diagram showing the entire control device according to the embodiment of the present invention.

[Explanation of symbols]

1 Lift cylinder 8 Tilt cylinder 9b Tilt work equipment lever 10 Controller 11A Solenoid proportional control valve for tilt 16A, 16B Hydraulic pipe line 17 Oil pressure sensor 24 Load-specific table 25 Controlled amount extraction means 26 Controlled amount output means 27 Load determination means

Claims (1)

[Claims] [Claim 1] A load-specific table that predetermines the relationship between the operation amount of a tilt work equipment lever of a forklift and the control amount of a tilt solenoid valve for each load, a means for detecting the load, and a means for detecting the load and a tilt control amount. and means for determining a control amount corresponding to the operation amount of the work equipment lever from the table, and controlling a tilting solenoid valve disposed in a pressure oil pipe of a tilting hydraulic cylinder with the determined control amount. Features: Forklift control device.