JP2744140B2 - Work vehicle hydraulic circuit structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention mainly relates to a backhoe,
Regarding the hydraulic circuit structure of construction equipment such as wheel loaders, in particular, equipped with a hydraulically driven working device by a hydraulic cylinder,
The present invention relates to a hydraulic circuit structure of a working vehicle that constitutes a hydraulic circuit of a pilot operation type in which a control valve of the hydraulic cylinder is switched by a pilot hydraulic pressure generated by a movement operation of an operation lever.

[0002] The present invention can also be applied to tractors and lawnmowers.

[0003]

2. Description of the Related Art A hydraulic circuit of this type is provided in a hydraulic passage 14 for supplying and discharging hydraulic oil to and from a control valve 4 of a hydraulic cylinder 3 like a backhoe shown in FIG. The throttle valve 4A of the control valve 4 is moved slowly by interposing a check valve 6 with a throttle that acts only in the hydraulic oil discharge direction to smoothly change the driving state of the working device (for example, turning). For example, the turning and stopping behavior of the table is made gentle to improve the ride comfort.

[0004]

[Problems to be solved by the invention]

However, the following new problems have arisen.

That is, if the hydraulic circuit is started immediately after the start of work in the cold season, the above-mentioned spool moves because the viscosity increases until the hydraulic oil warms, that is, when the hydraulic oil is in a low temperature state. In such a case, the passing speed of the check valve with a throttle becomes too lower than the set speed, and the moving speed thereof becomes extremely poor, so that the driving and stopping behavior of the working device becomes too slow.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a smooth operating behavior of a set check valve with a throttle even when the operating oil is in a low temperature state.

[0008]

According to the present invention, there is provided a working device which is hydraulically driven by a hydraulic cylinder,
The control circuit of the hydraulic cylinder is configured as a pilot-operated hydraulic circuit that switches by a pilot oil pressure generated by a movement operation of an operation lever, and the control valve is provided in the middle of an oil passage for supplying and discharging hydraulic oil to the control valve. In a hydraulic circuit structure of a work vehicle in which a check valve with a throttle that acts only in the direction of discharge of hydraulic oil to the valve is provided, the check valve with a throttle is used as a return valve of the main circuit in the hydraulic circuit. Hydraulic pilot type that is opened with hydraulic pressure higher than the set value of the circuit.The return circuit set value is set to the upper limit of the allowable range as the oil pressure in the oil passage caused by the viscosity of oil in the normal operating temperature range. It is set as a characteristic configuration that has been set.

[0009]

In the above-mentioned hydraulic circuit, the return circuit of the main circuit portion, which is the operation circuit of the control valve of the working device driving hydraulic cylinder, is always provided with a back pressure for continuously filling the working oil into the circuit. When the operating oil is in a low temperature state, the back pressure increases due to an increase in flow path resistance due to an increase in viscosity of the operating oil. When the operating oil rises to a temperature in a normal use state, the back pressure decreases.

Therefore, the set value of the return circuit is set to approximately the upper limit of the range permitted as the oil passage internal pressure caused by the viscosity of the oil in the normal operating temperature range, and the check valve portion of the check valve with a throttle is set. If it is configured as a pilot type that opens and closes with pilot pressure, and the opening operation is performed with hydraulic pressure equal to or higher than the set value of the return circuit, the check valve part of the check valve with throttle is opened when the operating oil is low temperature, The return oil having a high viscosity can be passed through the open check valve portion, and its passing speed is the same as when the hydraulic oil is at a temperature in a normal use state, and so on. It can be made quicker than before.

When the temperature of the hydraulic oil rises after a certain period of time, the temperature of the hydraulic oil in the return circuit also rises, and the oil pressure in the oil passage falls below the above-mentioned set value. As a result, the check valve section is closed and the warm return oil from the control valve passes through the throttle section, and the operation section of the control valve returns and moves at the set slow speed.

[0012]

As a result, poor return of the control valve due to an increase in the viscosity of the hydraulic oil at a low temperature can be avoided without impairing the function of the check valve with a throttle in a normal use condition in which the temperature of the hydraulic oil rises. Therefore, a smooth change in the driving state of the working device can be obtained regardless of the operating oil temperature, and a hydraulic circuit structure of a working vehicle with improved operability can be provided.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a part of a hydraulic circuit 1 in a backhoe. That is, the excavating work device 2 shown in FIG.
The hydraulic circuit part for operating the three-position switching control valve 4 of the boom cylinder 3 is shown. The control valve 4 and a bucket cylinder control valve (not shown) are operated by a cross operating lever 5. The hydraulic circuit 1 is composed of a pilot circuit section 9 for switching operation by the pilot valves 7, 7 and a main circuit section 10 for supplying and discharging pressure oil to and from the control valve 4.

The return circuit 12 of the main circuit section 10 is provided with a relief valve 11 for maintaining the back pressure of the main circuit 10, and the pilot circuit section 9 is provided with a pilot valve 7, 7. An unload valve 13 is provided which can switch the supply of the hydraulic oil on and off.

In the operation oil passages 14, 14 of the spool 4A of the control valve 4 of the pilot valves 7, 7, only in the direction of hydraulic oil discharge to the control valve 4, that is, the spool 4
Check valves with throttles 6 and 6 are provided, which throttle only in the direction in which A returns to the neutral position. The check valves 6 and 6 with the throttle are connected to the check valve unit 15 so that the return circuit 1
The control oil passage 16 is communicatively connected to a hydraulic pilot type so as to be opened at an oil pressure equal to or higher than the set value of 2.

That is, at a low temperature when the viscosity of the hydraulic oil increases, the back pressure of the return circuit 12 exceeds the set pressure, and the control oil passage 16
The spool 4A is easily moved by opening the check valve unit 15 through the valve. When the temperature of the hydraulic oil rises to reach a normal operating temperature range, the viscosity decreases and the check valve unit 15 is opened.
Is closed, and the return oil of the spool 4A passes only through the throttle valve portion 17.

That is, the set value of the oil pressure of the return circuit 12 is set to about the upper limit of a range allowable as an oil passage internal pressure generated by the viscosity of oil in a normal operating temperature range. Although not shown, the check valve 6 with a throttle that produces the above-described operation is provided for each control valve circuit of each arm, bucket, and turning cylinder.

If the opening amount of the check valve portion 15 of the check valve 6 with a throttle is configured to correspond to a temperature change so as to gradually decrease as the temperature of the hydraulic oil rises, higher quality control can be obtained.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the structure shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing the structure of a boom.

FIG. 2 is a side view of a backhoe.

FIG. 3 is a conventional hydraulic circuit diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydraulic circuit 2 Working device 3 Hydraulic cylinder 4 Control valve 5 Operating lever 6 Check valve with throttle 12 Return circuit

Claims (1)

(57) [Claims] An operating device (2) which is hydraulically driven by a hydraulic cylinder (3) is provided, and a control valve (4) of the hydraulic cylinder (3) is operated by a pilot hydraulic pressure generated by a moving operation of an operating lever (5). A hydraulic circuit (1) of a pilot operation type for switching operation is constituted, and the control valve (4) is provided in the middle of an oil passage for supplying and discharging hydraulic oil to the control valve (4).
A hydraulic circuit structure of a work vehicle having a check valve with a throttle (6) that acts only in the direction in which hydraulic fluid is discharged to the work vehicle, wherein the check valve with a throttle (6) has a check valve portion Return circuit (1) of the main circuit section in the hydraulic circuit (1)
2) A hydraulic pilot type that is opened and operated with a hydraulic pressure equal to or higher than the set value of the return circuit (12)
With the oil pressure in the oil passage caused by the viscosity of the oil in the normal operating temperature range.
Hydraulic circuit structure of the work vehicle set to the upper limit of the allowable range .