JPH0759161B2 - Hydraulic lifting control device for tractor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic lifting / lowering control device for a tractor, which can lower a working machine connected to a lift arm at a proper lowering speed even if the working machine is lightweight. It is intended to provide a hydraulic lifting control device.

[0002]

2. Description of the Related Art In a conventional electrically controlled hydraulic lift control device, a check solenoid is used to control the discharge of pressure oil in a lift cylinder by a descending solenoid valve to prevent the pressure oil in the lift cylinder from returning. The valve has a structure in which the valve is pushed open by the pressure oil as the lowering solenoid valve opens.

[0003]

In the case of such a conventional apparatus, there is provided a lightweight working machine which does not apply a light load to the lift cylinder when the ground working machine is not connected to the lift arm or when the lift arm is connected. When connected, the hydraulic pressure in the lift cylinder decreases, and even if pressure oil in the lift cylinder is not discharged to lower the lift arm in the raised position, the hydraulic pressure is too low and pushes open the check valve. However, there is a problem that it is difficult to discharge the pressure oil.

[0004]

SUMMARY OF THE INVENTION The present invention is proposed in view of the above problems, and the ground work machine can be lowered at a safe and appropriate speed even when the load on the ground work machine is light. The construction is such that the ground work implement 2 is connected to the tractor 1 via the work implement connection link mechanism 7 to supply pressure oil to the lift cylinder 8 constituting the hydraulic lift mechanism 9 or Ground work machine 2 by discharge control
In the hydraulic circuit of the hydraulic lifting mechanism 9 is provided with an ascending solenoid valve 13 for supplying pressure oil to the lift cylinder 8 and a descending solenoid valve 14 for discharging the pressure oil in the lift cylinder 8. , Further this descending solenoid valve 14
Separately from the lift cylinder 25, when the pressure in the lift cylinder is in a light load state, the descent valve 25 for rapidly discharging the oil in the lift cylinder 8
Is a hydraulic lifting control device for a tractor.

[0005]

When the load applied to the hydraulic lifting mechanism 9 is small, when the hydraulic lifting mechanism 9 is operated to the descending side, the descending valve 25 acts so that the pressure oil in the lift cylinder 8 can be rapidly discharged. Even when the ground work implement 2 is not connected to the lift arm 3, the lift arm 3 can descend at a normal speed.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. First, the structure will be described. As shown in FIG. 2, a rotary tiller as a ground working machine 2 is provided at the rear of the tractor 1 to a pair of left and right lift arms 3 and 3, and left and right lift rods 4 and 4 are provided. Left and right lowers that swing up and down through
The working machine connecting link mechanism 7 is composed of the links 5 and 5 and the top link 6 in the upper center, and the working machine connecting link mechanism 7 has its lift arms 3 and 3 in a single-acting hydraulic mode using hydraulic pressure. The lifting mechanism 9 is configured to perform a lifting operation.

In controlling the supply and discharge of pressure oil to and from the lift cylinder 8, a command from the control unit 10 which is composed of a microcomputer or the like is amplified by the ascending drive unit 11 or the descending drive unit 12. Then, the ascending solenoid valve 13 or the descending solenoid valve 14 is opened / closed so that the pressure oil of the pump 15 is supplied to the lift cylinder 8 to cause the lift arm 3 to move.
Is lifted, or the pressure oil of the lift cylinder 8 is discharged to lower the lift arm 3.

A height sensor S1 formed by connecting a height setting device I constituted by a volume and a detection shaft of a potentiometer to a lift arm 3 is provided in each control unit 10. Connected to the control unit 10 and the ascending / descending command is driven so that the height detection value detected by the height sensor S1 matches the height setting value set by operating the height setting device I. Output to the section 11 or the lowering drive section 12,
As a result, the raising / lowering control is performed. When the raising / lowering switch 16 is operated to the raising position 17, a raising command is issued again.
When the down position 18 is set, the down commands are output from the control unit 10, respectively.

As shown in FIG. 3, the rising solenoid valve 13 is a first solenoid valve for changing the pilot pressure according to the magnitude of the current.
It comprises a pilot pressure control valve 19 and a first opening / closing valve 20 whose flow rate is controlled by receiving the pilot pressure. By energizing the solenoid 19a of the pilot pressure control valve 19, the supply unit 20a of the first opening / closing valve 20 is changed. Open pump 1
5 is supplied to the lift cylinder 8, and when the solenoid 19a is de-energized, the blocking portion 20b holds the pressure oil in the lift cylinder 8 as shown in FIG. The valve 13 is configured so that the flow rate of the pressure oil flowing into the lift cylinder 8 changes according to the value of the current flowing through the solenoid 19a. The descending solenoid valve 14 includes a check valve 22 that blocks the flow of pressure oil discharged from the lift cylinder 8 and a back chamber 22 of the check valve 22.
The control valve 21 controls the amount of hydraulic oil discharged from b to the tank to control the flow rate on the descending side from the check valve 22. By changing the current value flowing to the solenoid 21a of the control valve 21, The amount of pressure oil discharged from the lift cylinder 8 to the tank is adjusted.

When the solenoid 21a of the control valve 21 is not energized, the pressure oil discharge from the back chamber 22b of the check valve 22 is blocked by the blocking portion 21b as shown in FIG.
The valve 22 closes the oil passage 24 communicating with the lift cylinder 8 by the action of the return spring 23, and the pressure oil in the lift cylinder 8 is retained, and the solenoid 21a of the control valve 21 is energized to check the check valve 22. The pressure oil in the back chamber 22a is discharged, the valve 22b is opened, and the pressure oil in the lift cylinder 8 is discharged through the check valve 22. The currents passed through these solenoids 19a and 21a are pulse signals, and the on-time of the pulse signals is changed according to a command from the control unit 10. When the on-time is lengthened (that is, off is narrowed), Solenoid valve for raising 1
3 and the solenoid valve 14 for lowering are controlled so that the flow rate increases.

Then, from the pump 15 to the lift cylinder 8
Is connected to the oil passage 24 in the middle of the hydraulic circuit, which is connected to a rapid lowering valve 25 which acts so that the pressure oil can be rapidly discharged to the tank. When the road is closed by the blocking unit 25b and a difference, that is, a deviation between the height detection value and the height setting value by the height setting device I is observed, or when the elevating switch 16 is operated to the lower position, the hydraulic pressure is increased. When the lifting mechanism 9 should be lowered, the energization command is sent to the solenoid 25a only when the hydraulic lifting mechanism 9 is in a light load state.
The output from 0 is output to the rapid descent driving unit 27. Therefore, except for the light load condition, the descending solenoid valve 14 operates as usual to gently discharge the pressure oil in the lift cylinder 8.

As a light load detecting means 28 for detecting the above-mentioned light load state, as shown in FIG. 2, a cylinder constituted by a load cell such as a load acting on a rear wheel 29 of the tractor 1. It may be detected by the pressure sensor S2, and thereby the oil pressure in the lift cylinder 8 may be estimated and detected (when the load is below the set value, it is determined that the load is light), or the height is The descent angle of the lift arm 3 within a fixed time after the output of the descent command by the setting device I is calculated from the change in the height detection value by the height detector S1, and this descent angle is below a predetermined value. When it is present, it may be configured to judge that the above-mentioned light load state is present, and in addition to that, various things can be used.

The height detector S1 may be, for example, a lower unit.
You may use what detects the vertical rotation angle of the link 5.

[0014]

As described above, according to the present invention,
Even when the pressure in the lift cylinder is in a light load state such as when the work machine is not attached, the hydraulic lifting mechanism can be reliably lowered, and the hydraulic pressure in the lift cylinder is insufficient as in the past. It is now possible to prevent problems such as the inability to lower the working machine.

[Brief description of drawings]

FIG. 1 is a control circuit diagram.

FIG. 2 is a side view of a tractor.

FIG. 3 is a hydraulic circuit diagram illustrating details of a main part.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 tractor 2 ground work machine 8 lift cylinder 9 hydraulic lifting mechanism 13 solenoid valve for raising 14 solenoid valve for lowering 22 check valve 25 lowering valve

Claims (1)

[Claims] Claim: What is claimed is: 1. A ground work machine is connected to a tractor through a work machine connection link mechanism, and the ground work machine is moved up and down by controlling the supply or discharge of pressure oil to a lift cylinder constituting a hydraulic lifting mechanism. A lift solenoid valve for supplying pressure oil to the lift cylinder and a drop solenoid valve for discharging the pressure oil in the lift cylinder are provided in the hydraulic circuit of the lifting mechanism, and the lift cylinder is provided separately from the drop solenoid valve. A hydraulic lift control device for a tractor, wherein a descent valve for rapidly discharging the oil in the lift cylinder is provided when the internal pressure is in a light load state.