JP3175513B2 - Control circuit of hydraulic cylinder in forklift - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a control to that control circuit the operation order of the lift cylinder and the full free cylinder in forklifts as industrial vehicle handling, more particularly, the back pressure in the lift cylinder about control circuit so as not to cause an error dynamic by giving the order of the lift cylinder and the full free cylinder a.

[0002]

2. Description of the Related Art The configuration of a hydraulic circuit for controlling a plurality of hydraulic cylinders provided in a forklift is as shown in FIG.

Referring to FIG. 3, only the structure of the main part will be described. The main circuit 3 connected to the hydraulic pump 1 and a lift cylinder 5 in a forklift (the overall view is omitted)
A lift valve 9 is disposed between the hydraulic circuit 7 and the hydraulic circuit 7 connected to the piston side chamber 5L. A flow regulator valve 11 is disposed in the hydraulic circuit 7, and one lift cylinder 5 is connected via a down safety valve 13. The upper rod side chamber 5U of the lift cylinder 5 is simply connected to the tank T.

[0004] A branch circuit 15 is connected to the hydraulic circuit 7 in a branched manner, and the branch circuit 15 is connected to a piston side chamber 17 on a lower side of a full free cylinder 17 in a forklift.
L, and one full free cylinder 17 is connected via a down safety valve 19. The rod-side chamber 17 on the upper side of the full free cylinder 17
U is simply connected to tank T.

[0005] A tilt valve 23 is arranged in a circuit 22 connecting the tilt cylinder 21 and the hydraulic pump 1 in the forklift. Further, a circuit 27 connecting the power steering cylinder 25 and the hydraulic pump 1 in the forklift includes a steering wheel 29.
A power steering valve 31 operated by the controller is disposed.

In the above configuration, when both the lift valve 9 and the tilt valve 23 are at the neutral position,
The pressure oil from the hydraulic pump 1 is circulated through a drain circuit 33. When the operation lever 23L provided on the tilt valve 23 is operated rightward or leftward, the piston rod of the tilt cylinder 21 is moved leftward or rightward in FIG. When the power steering wheel 29 is operated to rotate, the power steering cylinder 25 operates in the right or left direction corresponding to the rotation direction.

An operation lever 9 provided on the lift valve 9
When L is operated to connect the main circuit 3 and the hydraulic circuit 7, the pressure oil from the hydraulic pump 1 is supplied to the piston side chamber 5L of the lift cylinder 5 and the piston side chamber 17L of the full free cylinder 17.

Here, the operation sequence is such that the piston rod of the lift cylinder 5 receives the pressure of the piston in the lift cylinder 5 so that the piston rod of the lift cylinder 5 starts rising after reaching the stroke end after the piston rod of the full free cylinder 17 has moved upward. The pressure receiving area of the piston in the full free cylinder is configured to be larger than the area.

In other words, the diameter of the full free cylinder 17 is configured to be larger than the diameter of the lift cylinder 5 (see JP-A-2-291399, JP-A-2-18496, etc.).

[0010]

As described above, since the diameter of the full free cylinder 17 is made larger than the diameter of the lift cylinder 5 to increase the pressure receiving area, the piston rod in the full free cylinder 17 moves upward. After raising the fork of the forklift, the piston rod of the lift cylinder 5 starts to rise, and the full free cylinder 17 and the fork are integrally raised.

However, the difference between the pressure receiving area of the piston in the lift cylinder 5 and the pressure receiving area of the piston in the full free cylinder 17 is small, the pipe resistance of the branch circuit 15 is large, or the viscosity of the hydraulic oil is high at low temperature. In some cases, the lift cylinder 5 may operate before the full free cylinder 17 operates.

Therefore, it is conceivable to increase the diameter of the full free cylinder 17 as compared with the lift cylinder 5 to increase the difference in pressure receiving area. However, if the pressure receiving area difference is increased, a large amount of hydraulic oil flowing into the full free cylinder 17 suddenly flows into the small-diameter lift cylinder 5 after the full free cylinder 17 stops.

Accordingly, the speed difference between the ascending speed of the full free cylinder 17 and the ascending speed of the lift cylinder 5 becomes large, and an impact is generated due to the large speed difference, so that the fork collapses easily. There is a problem.

[0014]

The present invention SUMMARY OF] has been made in view of conventional problems such as described above, forklifts
Between the piston side chamber of the lift cylinder and the hydraulic pump
Fully free branch circuit branched from connected hydraulic circuit
In the control circuit connected to the piston side chamber of the cylinder
And the pressure receiving area of the lift cylinder
The pressure receiving area of the rotor
The connection circuit connecting the rod side chamber and the tank in the Linda
On the road, after stopping the raising operation of the full free cylinder,
Set the lift cylinder so that the lift cylinder starts to rise.
Pressure control for applying back pressure to the rod side chamber of the cylinder
This is a configuration in which a control valve is arranged .

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. Since the overall configuration is almost the same as the above-mentioned conventional configuration, components having the same functions are denoted by the same reference numerals. And a duplicate description will be omitted.

In FIG. 1, the point different from the above-described conventional circuit configuration is that the rod side chamber 5U is connected to the upper rod side chamber 5U of the lift cylinder 5 and is connected to the connection circuit 35.
A pressure control valve 37, such as a relief valve, which can apply a back pressure when discharging the pressure oil from U, is disposed, and the check valve 39 for preventing the flow of the pressure oil in the tank T direction is controlled by the pressure control. In this configuration, the valve 37 is connected in parallel. The pressure control valve 37 is a variable pressure control valve capable of adjusting the set pressure so that the pressure in the connection circuit 35 can be adjusted, and is set to a pressure equal to or higher than the pressure capable of canceling the pipe resistance of the branch circuit 15. I have.

In this embodiment, the lift cylinder 5 and the full free cylinder 17 have substantially the same diameter, and the pressure receiving areas of the pistons in both cylinders are provided substantially equal.

In the configuration described above, when the main circuit 3 and the hydraulic circuit 7 are connected by operating the lift valve 9, FIG.
As understood from the hydraulic circuit 1, the hydraulic oil from the hydraulic pump 1 is lifted through the hydraulic circuit 7 and the branch circuit 15.
5 L of piston side chamber of the cylinder 5 and the full free cylinder 17
To the piston side chamber 17L of the lift cylinder 5
Tend to flow into the piston side chamber 5L. However, the pressure in the rod side chamber 5U of the lift cylinder 5 is
Since the hydraulic oil in the rod side chamber 5U is not drained to the tank T unless it rises above the set pressure of 7, the pressure oil in the hydraulic circuit 7 flows into the piston side chamber 17L of the full free cylinder 17 via the branch circuit 15.

Therefore, the piston rod in the full free cylinder 17 is operated to rise, and the fork in the forklift is raised. Then, when the piston rod of the full free cylinder 17 reaches the rising end and stops, the pressure of the piston side chamber 5L in the branch circuit 15, the hydraulic circuit 7, and the lift cylinder 5 gradually increases.

As described above, when the pressure in the piston side chamber 5L of the lift cylinder 5 gradually increases, the pressure in the rod side chamber 5U of the lift cylinder 5 also gradually increases. When the pressure in the rod side chamber 5U exceeds the pressure set by the pressure control valve 37, the pressure oil in the rod side chamber 5U is released from the pressure control valve 3U.
Then, it is discharged to the tank T via 7 and the lifting operation of the lift cylinder 5 is started.

Therefore, even when the pressure receiving area of the lift cylinder 5 and the pressure receiving area of the full free cylinder 17 are substantially equal and the pipe resistance of the branch circuit 15 leading to the full free cylinder 17 is relatively large, the lift cylinder 5 And the order of operation of the full free cylinder 17 can be accurately controlled.

Further, when the lift cylinder 5 immediately starts the raising operation after the lifting operation of the full free cylinder 17 is stopped, since the pressure receiving areas of the two cylinders 17 and 5 are almost equal, the rising speed of the two cylinders 17 and 5 is almost equal. Equally, the speed difference is zero, and the impact caused by the speed difference can be suppressed.

The lowering operation of the full free cylinder 17 and the lift cylinder 5 is performed by its own weight, and hydraulic oil is sucked into the rod side chamber 5U of the lift cylinder 5 via a check valve 39.

In this case, a pressure corresponding to the weight of the mast, the full free cylinder 17 and the fork in the fork lift acts on the piston side chamber 5L of the lift cylinder 5, and the fork weight is applied to the piston side chamber 17L of the full free cylinder 17. Since the corresponding pressure acts, the lift cylinder 5 descends earlier than the full free cylinder 17, and the descending operation of the full free cylinder 17 starts after the lift cylinder 5 reaches the descending end and stops. And the order of operation is accurate.

In the above configuration, the pressure control valve 37
By adjusting the set pressure, the back pressure applied to the rod side chamber 5U of the lift cylinder 5 can be adjusted, and the line resistance due to the difference in the viscosity of the hydraulic oil and the difference in the length of the branch circuit 15 can be adjusted. Even if there is a difference, it can be easily handled.

FIG. 2 shows a second embodiment. In the second embodiment, the pressure control valve 37 is connected to the drain circuit 33.
And a connection circuit 35 on the primary side of the pressure control valve 37.
Are connected.

In the structure of the second embodiment, a back pressure can be applied to the rod-side chamber 5U of the lift cylinder 5, and the same operation and effect as those of the first embodiment can be obtained.

[0037]

As will be understood from the above description of the embodiment, according to the present invention, the back pressure is applied to the rod side chamber of the lift cylinder so that the lift cylinder does not operate prior to the operation of the full free cylinder. Can be granted.

[0038]

Therefore, the order of the operation of the lift cylinder and the operation of the full free cylinder can be accurately controlled.

Further, in the present invention , since the pressure receiving area of the lift cylinder and the pressure receiving area of the full free cylinder are provided substantially equal, the speed difference between the operating speed of the full free cylinder and the operating speed of the lift cylinder is substantially reduced. It can be set to zero, and the impact can be prevented due to the large speed difference.

Further, since the diameter of the full free cylinder can be reduced, the field of view of the operator can be further widened.

[0042]

[0043]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a control circuit of a hydraulic cylinder according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a control circuit of a hydraulic cylinder according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional hydraulic cylinder control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydraulic pump 3 Main circuit 5 Lift cylinder 7 Hydraulic circuit 15 Branch circuit 17 Full free cylinder 35 Connection circuit 37 Pressure control valve

Claims (1)

(57) [Claims] 1. A lift cylinder in a forklift
From the hydraulic circuit connecting the piston side chamber and the hydraulic pump
The branched circuit is divided into a full free cylinder piston side chamber.
A control circuit connected to the lift cylinder;
Pressure receiving area of the full free cylinder
And the rod side of the lift cylinder
The connection circuit connecting the chamber and the tank
After the lifting operation of the cylinder is stopped, the lift cylinder
The rod side chamber of the lift cylinder to be started
A control circuit for a hydraulic cylinder in a forklift, comprising a pressure control valve for applying a back pressure to the forklift.