JP2813651B2 - Backhoe hydraulic circuit structure - 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 circuit structure of a backhoe load control type, and more particularly to a technique for suppressing a decrease in running speed due to a dozer rising end.

[0002]

2. Description of the Related Art As an example of a load control type hydraulic circuit, there is a closed center system as shown in FIG. In this circuit, the load on the traveling hydraulic motors 6c and 9c becomes large, for example, when the vehicle travels up a hill or when the vehicle travels on a soil.
When the pressure exceeds a predetermined circuit pressure, the on-off valve 3 is switched to the open position, and the adjusting cylinder 2 decreases the discharge amount of the hydraulic pump 1. In other words, the pressure increase is operated so that the pressure oil corresponding to the load is discharged. Then, the operation of closing the on-off valve 3 is performed. In other words, this is an energy saving means capable of eliminating the excessive pump output state and reducing the power loss by automatically adjusting the pump discharge pressure according to the load. Other forms of the load control circuit include a negative control system and a load sensing system.

[0003]

The backhoe mainly performs excavation work, but also performs dozer work for moving and leveling earth and sand by using a dozer while traveling. During the dozer work, the dozer is often moved up and down by the dozer cylinder 4c. However, when the dozer is moving forward while pushing the earth and sand, the dozer ascends to the escape displacement state with respect to the earth and sand.
Since it can be performed with a lighter driving force as compared with the descending movement which is in a state of being displaced into the earth and sand, and because the dozer is located at a position where it is difficult to see the dozer, the dozer tends to be easily operated to the upper limit. Then, the circuit pressure rises to a predetermined pressure set by the main relief valve 26. When this state occurs in the load control circuit shown in FIG.
The rapid increase in the circuit pressure is the same as the sudden increase in the load, and the on-off valve 3 is switched to the open position, so that the discharge oil amount decreases rapidly to increase the discharge pressure of the hydraulic pump 1 rapidly. As a result, the traveling speed is suddenly reduced during the forward dozer work, and the cause is such that the operator cannot immediately understand the cause, resulting in a reduction in work efficiency. SUMMARY OF THE INVENTION An object of the present invention is to provide a backhoe employing a load control type hydraulic circuit so as to prevent a sudden decrease in traveling speed even when the dozer reaches the upper limit during dozer work, thereby suppressing a decrease in work efficiency. .

[0004]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a plurality of hydraulically driven actuators, a variable displacement type hydraulic pump for supplying pressure oil to these actuators, and a discharge pump from the hydraulic pump. A control valve for controlling a supply direction of pressure oil to be supplied to an actuator, an adjustment actuator for variably setting a discharge oil amount per unit time of the hydraulic pump, and a pressure oil supply lower side of the hydraulic pump; and Pressure detection means for detecting the circuit pressure of the oil passage located on the upstream side of the pressure oil supply of the actuator, and the detection pressure of the pressure detection means is increased. In a backhoe hydraulic circuit structure in which a pressure detecting means and an adjusting actuator are linked to each other in a load control state in which a discharge pressure of a hydraulic pump is reduced, a dozer lifting / lowering cylinder is provided. The rising oil passage of the dozer increase the drive side of the pair of supply and discharge oil passage for connecting the dozer control valve,
A dozer relief valve that acts as a relief on the ascending oil passage is connected, and the relief pressure of the dozer relief valve is set to a value lower than the relief pressure of the main relief valve that sets the maximum circuit pressure. It is characterized by.

[0005]

In other words, according to the above feature, even if the dozer rises to the upper limit, if the raising operation is continued, the dozer relief valve having a lower set relief pressure is activated before the main relief valve. The relief valve does not work. Therefore, the circuit pressure when the dozer reaches the rising end can be reduced as compared with the related art, and the decrease rate of the traveling speed can be suppressed. And since the dozer relief valve operates only at the time of the dozer raising operation, the maximum circuit pressure at the time of dozer lowering and other operation forms such as the boom raising and lowering is determined by the main relief valve. There is no inconvenience that adversely affects operations other than the dozer raising operation, such as being reduced by the low relief pressure of the dozer relief valve.

[0006]

Therefore, by a relatively simple modification in which only one relief valve is additionally set, an unexpected decrease in running speed due to the dozer raising operation can be suppressed while maintaining a good backhoe operation, and the dozer work efficiency can be reduced. Could be improved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings for a backhoe hydraulic circuit employing a load sensing system. FIG. 5 is a side view of the backhoe,
1 to 3 show a hydraulic circuit for load control composed of a hydraulic drive unit A, a valve block B, and a plurality of hydraulic actuators. The hydraulic drive unit A is
Two variable displacement hydraulic pumps 1, a control cylinder 2 for changing the angle of the swash plate of the hydraulic pump 1 to adjust the discharge amount per unit time, a pressure compensating pressure control valve for the control cylinder 2 (pilot pressure reducing valve) ) 3 and the like.
The valve block B includes a dozer control valve 4, a bucket control valve 5, a left traveling control valve 6, a boom control valve 7, an arm control valve 8, a right traveling control valve 9, a turning control valve 10, a swing control valve. Control valve 11 and service port control valve 12, and compensators (pressure compensating valves) 4a, 5a, 6a, 7a, 8a, 9a,
10a, 11a, 12a, a dozer elevating cylinder 4c, a bucket cylinder 5c, left and right traveling hydraulic motors 6c, 9c, a boom cylinder 7c,
The actuator is connected to each of an arm cylinder 8c, a turning hydraulic motor 10c, a swing cylinder 11c, and a service actuator (for example, a hydraulic hammer) 12c. Each control valve has a throttle valve 4s,
5s, 6s, 7s, 8s, 9s, 10s, 11s, 12
s is equipped. Each control valve has a pair of switching cylinders 5b, 7b, 8b, 10b, which are operated by a pilot pressure, which will be described later, for switching these spools.
11b is equipped.

Each of the compensators 4a to 12a is on the lower side of the pressure oil supply to each of the throttle valves 4s to 12s, and
It is arranged on the upstream side of the pressure oil supply to each of the actuators 4c to 12c. And each compensator 4a-1
2a spring-side oil chambers 4x to 12x and each actuator 4c
Low-pressure-side oil passages 4t to 12t that communicate the pressure oil supply lower-side portion with respect to -12c, and compensators 4a to 12c
a spring-side oil chamber 4 opposing the spring-side oil chambers 4x to 12x of FIG.
The high-pressure side oil passages 4k-1 which communicate with the hydraulic oil supply side for each of the compensators 4a-12a and the hydraulic oil supply side for each of the throttle valves 4s-12s.
2k are provided respectively. This constitutes an after-orifice type load sensing circuit.

A low-pressure side oil passage 3t is provided for communicating the spring-side oil chamber 3x of the pressure control valve 3 with the lower side of the pressure oil supply to each of the throttle valves 4s to 12s, and the pressure oil of each of the control valves 4 to 12 is provided. An input port 15 to the valve block B in a communication oil passage 13 between the valve block B and the hydraulic drive unit A connected to the supply ports 4p to 12p, and a spring-side oil chamber 3 of the pressure control valve 3.
x is connected to a non-spring side oil chamber 3y opposed to x.
Are in communication. The connection oil passage 14 makes it possible to make the pressure loss value in the external piping constant even if the hydraulic drive unit A and the valve block B have different pipe lengths for each model. This is convenient because there is no need to fine-tune the force.

As shown in FIG. 4, the bucket control valve 5,
Boom control valve 7, arm control valve 8, turning control valve 1
For the control valve 11 for swing and swing, a hydraulic pilot operation structure operated by the pilot pressure of the auxiliary pump 16 is adopted, a first lever 17 for a bucket / boom that can be freely operated in cross direction, their pilot valve 18, arm / rotation. A second lever 19 and a pilot valve 20 thereof are provided, and a third lever 21 for a swing and a pilot valve 22 thereof are provided.

As shown in FIGS. 1 and 2, a pair of oil supply / discharge passages 2 connecting the dozer cylinder 4c and the dozer control valve 4 is provided.
8, 29, the lifting oil passage 28 on the dozer raising drive side
Is connected to a dozer relief valve 27 which acts as a relief on the ascending oil passage 28, and the relief pressure of the dozer relief valve 27 (150 kg / cm 2) is reduced by the relief of the main relief valve 26 for setting the maximum circuit pressure. Pressure (240kg / c
m) is set to a lower value. That is, if the dozer cylinder 4c is continuously raised during the dozer operation,
The dozer relief valve 27 is operated, and load sensing is performed in accordance with the relief pressure at that time. This makes it possible to lower the discharge pressure of the hydraulic pump 1 (increase the discharge amount) as compared with the case where load sensing according to the relief pressure by the main relief valve 26 is performed. To prevent it from occurring.

In the present application, the pressure regulating valve 3 switched by the differential pressure corresponds to the pressure detecting means. In the claims, the boom cylinder 7c and the swing motor 10c are used.
c and the like are collectively expressed as a hydraulically driven actuator D, the bucket control valve 5 and the arm control valve 8 and the like as a control valve E.

[Other Embodiments] The present invention may be applied to a closed center system (dozer relief valve 27 shown by a phantom line in FIG. 6) or to another load control circuit. FIG. 7 shows a principle diagram of a main part of the negative control type load control, in which a negative control throttle 3a disposed after passing through the control valve 4, a pressure oil supply upper side portion thereof and a piston chamber of the adjusting cylinder 2 are illustrated. The pressure detecting means 3 is constituted by the communicating oil passage 3b.

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

[Brief description of the drawings]

FIG. 1 is a system diagram showing a hydraulic circuit, part 1

FIG. 2 is a system diagram showing a hydraulic circuit, part 2

FIG. 3 is a system diagram showing a hydraulic circuit, part 3

FIG. 4 is a system diagram showing a pilot circuit.

FIG. 5 is a side view of the backhoe.

FIG. 6 is a circuit diagram of a closed center type load control.

FIG. 7 is a main part circuit diagram of a negative control type load control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Variable displacement hydraulic pump 2 Adjustment actuator 3 Pressure detecting means 4 Dozer control valve 4c Dozer elevating cylinder 26 Main relief valve 27 Dozer relief valve 28 Elevating oil passage 29 Supply / discharge oil passage D Actuator E Control valve

Claims (1)

(57) [Claims] 1. A plurality of hydraulically driven actuators (D), a variable displacement hydraulic pump (1) for supplying pressure oil thereto, and a supply direction of pressure oil discharged from the hydraulic pump (1). A control valve (E) that controls the hydraulic pump (1) to control the oil supply to the actuator (D), an adjusting actuator (2) that variably sets a discharge oil amount per unit time of the hydraulic pump (1), and the hydraulic pump (1). Pressure detection means (3) for detecting a circuit pressure of an oil passage located on the lower side of the pressure oil supply of the actuator and on the upper side of the pressure oil supply of the actuator (D), wherein the pressure detection means (3) When the detected pressure increases, the discharge pressure of the hydraulic pump (1) increases, and when the detected pressure decreases, the discharge pressure of the hydraulic pump (1) decreases. The adjustment actuator (2 ) Is a hydraulic circuit structure of the backhoe, wherein the dozer lift cylinder (4c) and the dozer control valve (4)
Dozer relief which acts on the lifting oil passage (28) on the dozer raising drive side of the pair of supply / drain oil passages (28) and (29) connecting A backhoe hydraulic circuit structure in which the valve (27) is connected and the relief pressure of the dozer relief valve (27) is set to a value lower than the relief pressure of the main relief valve (26) for setting the maximum circuit pressure. .