JPS5947099B2 - Hydraulic excavator hydraulic control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic control device for a hydraulic excavator that uses a variable discharge amount hydraulic pump as a pressure oil source and controls the speed of an actuator by operating a spool of a switching valve.

Speed control of actuators such as hydraulic cylinders and hydraulic motors in hydraulic excavators is generally performed by using a lever, a lever,
This is done by adjusting the opening of the throttle, either directly using a link mechanism or indirectly using pilot oil pressure.

A switching valve used in such a control device and -ψ1 of a hydraulic system incorporating the switching valve will be explained with reference to FIG.

A spool 3 having a constricted portion 3a is inserted into the valve body 2 of the switching valve 1 so as to be slidable in the axial direction.

The valve body 2 has ports P, A, and B. R is provided,
Port P is connected to the delivery side of the variable discharge amount hydraulic pump 4, ports A and B are connected to the chamber on the opposite side of the hydraulic cylinder 50 and the chamber on the rod side, and port R is connected to the oil tank 6. .

A relief valve 7 is installed in the circuit on the output side of the hydraulic pump 4q.

The driving speed of the hydraulic cylinder 5 is controlled by operating the stroke of the spool 30 of the switching valve 1 to change the opening degree of the throttle portion 3a and controlling the flow rate that escapes to the oil tank 6.

The opening area of the throttle portion 3a relative to the stroke of the spool 3 usually changes as shown by the diagonal line in FIG.

In other words, the neutral position (zero stroke position) of the switching valve
Therefore, the oil discharged from the hydraulic pump 4 escapes to the oil tank 6 with almost no resistance.

As the stroke progresses, the opening area of the throttle portion 3a becomes smaller, reducing the flow rate escaping to the oil tank and increasing the flow rate flowing to the hydraulic cylinder 5.

Eventually, the opening area becomes zero, and the entire discharge amount of the hydraulic pump is sent to the hydraulic cylinder 5.

By the way, when using a variable specific output hydraulic pump, in order to reduce wasteful power consumption, the pump discharge rate should be reduced when driving a load at a small speed, and when a large speed is required, the pump discharge amount should be reduced. In this case, it is advantageous to control the discharge amount by increasing the discharge amount in conjunction with the stroke of the spool of the switching valve.

An example is shown in FIG. In this case, if the opening degree of the throttle portion of the switching valve changes as shown in FIG. 2, the following problems will occur.

(A) The flow rate that drives the load is determined by the pump discharge amount and the opening degree of the throttle section of the switching valve, but since errors from both are accumulated, errors in the control flow rate tend to become large.

(B) While the pump discharge amount increases in accordance with the stroke of the spool of the switching valve, the opening degree of the throttle portion decreases, so the flow rate to the load tends to increase rapidly due to both effects.

(When the spool of the C switching valve is operated indirectly by pilot oil pressure, etc., the spool shifts from a given position due to flow force (a force that responds to changes in the momentum of the flow, or is called Bernoulli's force), causing the spool to become throttled. Since the opening degree changes, the flow control characteristics are greatly affected.

That is, the flow that enters the opening of a stool valve or the like is generally treated as a jet flow, and a force acts on the valve due to a change in the momentum of the flow.

This invention is intended to eliminate the above-mentioned drawbacks, and is aimed at a variable output pump that increases the output amount in conjunction with the stroke of the spool of the switching valve. A switching valve is connected that has a portion whose area remains constant as the stroke of the spool increases.

The hydraulic control device of the present invention includes a variable output pump 10, a loaf output variable device, and a switching valve that are interlocked by operating a lever, and supplies pressure oil from the variable output hydraulic pump to an actuator by switching the switching valve. In the hydraulic system of a hydraulic excavator, the spool of the switching valve has an opening area that decreases in accordance with the stroke amount in a predetermined small stroke range in order to release pressure oil to the oil tank. In the range of a defined stroke that is larger than the defined stroke, the opening area is constant or varies very little, and in the range of a defined stroke that is thicker than the respective defined stroke, the opening area is zero. It is characterized by forming a passage that becomes smaller until it becomes smaller.

FIG. 4 shows the opening area of the throttle section according to the present invention, the pump discharge amount, and the flow rate to the load with respect to the stroke of the spool of the switching valve, respectively, by lines S, D, and F.

In the figure, b is a portion where the aperture area of the diaphragm remains constant as the stroke of the spool increases.

That is, this invention makes the opening degree of the throttle of the switching valve constant as shown in b, and increases the discharge amount in conjunction with the stroke of the spool of the switching valve by taking advantage of the characteristics of the variable discharge amount pump.
The speed of the actuator is controlled by increasing the flow rate flowing to the load as indicated by the diagonal line F.

Instead of being constant like b, it may be possible to have a very gentle diagonal line characteristic.

FIG. 5 shows an example of the switching valve 8 according to the present invention.
The spool 10 inserted into the valve body 9 has a notch 10a,
An annular protrusion 10b protrudes toward the notch 10a, and a constriction part with a hole 10c drilled in the radial direction is formed in the annular protrusion 10b, and this constriction part is connected to the discharge side of the variable discharge amount hydraulic pump. It faces Port R, which is connected to Port P and the oil tank.

In the figure, parts a, b, and c are respectively a, b, and c in Figure 4.
It represents the part corresponding to the range of c.

Port A connects to the hydraulic cylinder. B is not shown.

At part a of the spool 10, the opening of the iris gradually decreases as the spool moves, at part b of the spool 10, the opening of the iris remains constant, and at part C of the spool 10, the opening of the iris decreases. and reaches zero.

Hereinafter, one embodiment of the hydraulic control device according to the present invention will be described in the sixth embodiment.
This will be explained using figures.

Variable discharge amount hydraulic pump 11 and auxiliary circuit hydraulic pump 12
is driven by a prime mover 13.

On the discharge side of the hydraulic pump 11, the switching valve 8 according to the present invention described earlier and a relief valve 14 for setting the maximum discharge pressure of the hydraulic pump 11 are connected, and the ports A and B of the switching valve 8 are Hydraulic cylinder 150 anti-rod side chamber, respectively;
The rod is connected to the side chamber.

On the discharge side of the hydraulic pump 12, there is a remote control valve 1 (a valve that controls secondary pressure according to the amount of operation) operated by a lever 16.
7.18 and IJ to set the maximum pressure of the hydraulic pump 12
IJ-F valve 19 is connected.

The secondary sides of the remote control valves 17 and 18 are connected to the operation chamber of the switching valve 8 through a circuit shown by a broken line, and are also connected to a cylinder (discharge (amount variable device) 21.

When the remote valve 17 or 18 is operated by the lever 16, the primary pressure from the hydraulic pump 12 is controlled to the secondary pressure according to the operation, and the secondary pressure oil is guided to the switching valve 8, and the shuttle valve 20 It is guided to the hydraulic cylinder 21 through the.

As a result, the spool 100 stroke of the switching valve B and the delivery amount of the hydraulic pump 11 are controlled as described above.

According to the invention described above, the following effects can be obtained.

(1) In the range where the flow rate to the load is controlled, the opening degree of the switching valve's throttle is almost constant with respect to the stroke of the spool, and therefore the flow rate flowing to the load is determined by the discharge rate of the variable displacement hydraulic pump. , the control error is smaller than when the opening degree of the throttle of the switching valve changes.

(2) Since it is determined by the rate of increase in flow rate for the load relative to the manipulated variable, or the rate of increase in the pump discharge amount, the flow rate will increase compared to when the switching valve q opening degree is decreased at the same time. The ratio becomes smaller.

Therefore, smoother speed control can be performed.

(3) Even if the spool of the switching valve deviates from its normal position due to the action of flow force, the opening area of the throttle does not change, so the speed control performance does not change.

This is effective when the spool of the switching valve is indirectly operated using pilot oil pressure or the like.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing an example of a switching valve and a hydraulic circuit incorporating the switching valve, which are conventionally used in the control device of a hydraulic excavator. Figure 3 is a diagram showing the relationship between the opening of the throttle that releases water to the tank and the stroke of the spool, Figure 3 is a diagram showing the discharge amount relative to the command amount of a variable discharge hydraulic pump used in a hydraulic excavator, and Figure 4 is this diagram. Figure 5 is a diagram showing the relationship between the throttle opening for releasing pressure oil to the oil tank in the switching valve according to the invention, the pump discharge amount, the flow rate to the load, and the stroke of the spool. 5. FIG. 6 is a cross-sectional view showing a portion of the relief throttle, and FIG. 6 is a system diagram showing an embodiment of the hydraulic control device for a hydraulic excavator according to the present invention. 8...Switching valve, 10...Spool, 10a...Notch,
10b... Annular protrusion, 10c... Hole, 11... Variable discharge amount hydraulic pump, 12... Hydraulic pump for auxiliary circuit, 14
．． 19.Relief valve, 15.Hydraulic cylinder, 16.
- Lever, 17.18...Remote control valve, 20...Shuttle valve, 21...Hydraulic cylinder.

Claims (1)

[Claims] 1. It is equipped with a discharge amount variable device and a switching valve for a variable ratio output pump that are linked by operating a lever, and is equipped with a circuit that supplies pressure oil from the variable ratio output hydraulic pump to an actuator by switching the switching valve. In the hydraulic system of a hydraulic excavator, in order to release pressure oil to the oil tank, the spool of the switching valve has an opening area force that is reduced by 1 in accordance with the stroke amount in a predetermined small stroke range. In the range of a prescribed stroke larger than the stroke, the opening area is constant or changes very little, and in the range of a prescribed stroke larger than the respective prescribed stroke, the opening area decreases by lJX until it becomes zero. Hydraulic control system characterized by forming a passage