JPH0344841Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a throttle circuit for regulating the flow rate of a cylinder return circuit of a hydraulic excavator.

FIG. 1 is a circuit diagram of a conventional hydraulic excavator, in which 1 is a pump, 2 is a control valve, and 3 is a relief valve. 4 is a traveling spool valve, 5 is a turning spool valve, and 6 is an arm spool valve.
7 is a hydraulic oil tank, 8 is an arm cylinder, 9 is a pipe connected to the rod side of the arm cylinder 8, 10
is a conduit connected to the bottom side of the arm cylinder 8, and has a flow rate limiting type check valve 11 which is a combination of a check valve and a fixed throttle.

A flow rate limiting type check valve 11 is provided to regulate the return flow rate in the extension direction of the arm cylinder 8, but depending on the selected area of the constant throttle, the cylinder will drop under its own weight in the extension direction due to an external force, and the engine rotation speed will decrease. If the return flow rate is low, the return flow rate cannot be sufficiently regulated, the pump discharge amount is lower than the cylinder's required supply amount, and the cylinder supply side becomes negative pressure. In addition, when excavating by extending the second cylinder 8, the fixed throttle prevents the flow of pressure oil on the cylinder return side, and the pressure on the cylinder return side increases, making it impossible to effectively convert the cylinder supply side pressure into excavation force, etc. It had the following drawbacks.

The present invention improves these drawbacks, and 1. When the cylinder falls under its own weight due to an external force, the flow rate on the return side of the cylinder is regulated (throttled) so that the required supply amount of the cylinder is always equal to the pump discharge flow rate, which changes depending on the engine speed. to do.

2. During excavation, the flow rate restriction on the cylinder return side is lifted, and the pressure on the cylinder return side is minimized, so that the pressure on the cylinder supply side can be effectively converted into excavation force.

To summarize the configuration for achieving this purpose, a two-position variable throttle spool is provided in the arm spool valve, and the area of the variable throttle spool is controlled by the cylinder return side pressure and the supply side pressure. I'm trying to change it. The higher the pressure on the cylinder return side, the larger the area of the throttle part of the variable throttle spool (increasing the flow rate), and when the pressure on the cylinder supply side reaches a certain value or more, the throttle part of the variable throttle spool The area is maximized.

An embodiment of this invention will be described below with reference to FIGS. 2 and 3. In FIG. 2, the arm spool valve 6' is equipped with a two-position variable throttle spool 6a.

Details of the two-position switching type variable aperture spool 6a are shown in FIGS. 3 to 5. As shown in FIG. 4, the variable aperture spool 6a has a minimum area at the A position, and the aperture area increases as it moves to the A position in FIG. 6b is a spring that always maintains the variable aperture spool 6a at the position A where the aperture area is minimum, that is, the position where the aperture area is the minimum;
6c is the arm spool valve 6' as "A" in Figure 2.
When the arm spool is in the "A" position in FIG.
Passage 10 connected to the bottom side of arm cylinder 8
This passage connects to the parallel passage 2b, and also connects to the parallel passage 2b.

6e is a passage provided so that the pressure generated in the passage 6c switches the variable throttle spool 6a against the spring 6b toward the position B where the throttle area becomes larger;
f is a passage provided so that the pressure generated in the passage 6d switches the variable throttle spool 6a to position B, which increases the throttle area in opposition to the spring 6b; 6g indicates the arm spool 6 in position "A" in FIG. , the passage 6h is connected to the tank passage 2c, and 6h is the chamber on the spring 6b side of the variable throttle spool 6a and the passage 6g.
It is a passageway that connects the

The present invention has the above configuration, and its operation will be explained below. When the arm spool valve 6' is switched to the "A" position in FIG. 2, the neutral passage 2a is blocked and the pump discharge flow to the parallel passage 2b.
It is supplied to the bottom side of the arm cylinder 8 via the passage 6d and the conduit 10. The return flow rate from the rod side of the arm cylinder 8 returns to the hydraulic oil tank 7 through the passage 2c via the pipe 9, the passage 6c, the variable throttle spool 6a, and the passage 6g.

When performing this operation, and (a) when the bucket is off the ground, the arm cylinder 8 receives a force in the direction of extension due to the weight of the bucket arm, etc., resulting in a fall of its own weight. In this case, the flow rate discharged from the rod side of the arm cylinder 8 to the pipe line 9, that is, the return flow rate passes through the variable throttle spool 6a as described above.
Since the variable throttle spool 6a has a properly set area, the return flow rate of the arm cylinder 8 is a regulated flow rate, and a certain pressure is created on the pipe line 9 side.
Pout occurs. Here, the variable throttle spool 6a is set so that the discharge amount of the hydraulic pump 1 always reaches the required supply amount on the bottom side of the arm cylinder 8.
If the area of the constricted portion is determined, the pressure Pin in the bottom side conduit of the arm cylinder 8 will be generated as follows: Pin=Pout×A'/A.

However, A is the bottom side area and A' is the rod side area.

These bottom side pressure Pin and rod side pressure
Pout acts on the variable aperture spool 6a through the passages 6f and 6e, respectively, and moves the variable aperture spool 6a against the spring 6b toward the ``ro'' position, that is, in a direction in which the area of the constricted portion becomes larger. As a result, the return flow rate increases, so the required supply amount on the bottom side of the arm cylinder 8 also increases. However, since the discharge amount of the hydraulic pump 1 is constant, the pressure Pin on the bottom side decreases, and the variable throttle spool 6a is again moved to the A side where the throttle area is smaller by the force of the spring 6b.

By repeating these operations, the variable aperture spool 6a
The opening area is determined at a position where the force of the spring 6b and the pressures Pin and Pout are balanced, and this is maintained to prevent the generation of negative pressure or abnormal pressure on the bottom side of the arm cylinder 8.

(b) Or, in the excavation state, the excavation resistance is large, and a considerable pressure Pin is required on the bottom side of the arm cylinder 8. As in the case where the bucket a is off the ground, the pressure at Pin acts on the variable throttle spool 6a and moves it to the position B against the spring 6b. When a certain Pin is reached, if the force and stroke of the spring 6b are set to maximize the opening area of the variable throttle spool 6a, the pressure Pout on the rod side during excavation will be the minimum, and the pressure Pin will be effective. This acts on the bottom side of the arm cylinder 8, resulting in a large digging force.

As described above, when the arm spool valve 6 is switched to the "A" position so as to extend the arm cylinder 8, and even when the bucket is off the ground, the bottom side of the arm cylinder 8 is under negative pressure or abnormality. Optimum pressure is maintained without overpressure.

Also, during excavation, it depends on the excavation resistance, but generally a high excavation pressure is required, so the area of the constriction part of the variable throttle spool 6a is maximized, the pressure on the return side is minimized, the effective pressure increases, and a large excavation force is required. can get.

Although the above description has been made regarding the spool for an arm, the same effect can be achieved even when used for a spool valve for a bucket.

[Brief explanation of the drawing]

Figure 1 is a hydraulic circuit diagram of a conventional hydraulic excavator. FIG. 2 shows the hydraulic circuit of the present invention. FIG. 3 is an enlarged detailed view of the variable throttle spool in the arm spool valve in FIG. 2; FIG. 4 shows the detailed structure of the variable aperture spool, showing the state where the aperture area is minimum, and FIG. 5 similarly shows the state where the aperture area is maximum. In the figure: 1...hydraulic pump, 2...control valve, 2a...neutral passage (of the control valve), 2b...parallel passage (of the control valve), 2c...tank passage (of the control valve), 3...relief valve, 4... running spool,
5...Swivel spool, 6,6'...Arm spool valve, 7...Hydraulic oil tank, 8...Arm cylinder,
9... Rod side conduit of arm cylinder, 10... Bottom side conduit of arm cylinder, 11... Flow rate limiting type check valve, 6a... Variable throttle spool (2 position switching type), 6b... Spring, 6c... (arm When the spool valve is in the "A" position, the pipe connected to the rod side of the arm cylinder, 6d...
(Connects with the conduit connected to the bottom side of the arm cylinder when in the "A" position) Passage, 6e...Passage 6
A passage for switching the variable throttle spool 6a in the direction B by the pressure generated at c, 6f...A passage (for switching the variable throttle spool in the direction B against the spring), 6
g...passage (connected to the tank passage when in the "A" position), 6i...passage (connecting the spring side chamber of the variable throttle spool and the passage 6f).

Claims (1)

[Scope of utility model registration request] 2 in the spool valve 6' for the arm of the hydraulic excavator.
A position switching type variable throttle spool 6a is provided, and the variable throttle spool 6a is configured to change the throttle area of the variable throttle spool depending on both the cylinder return side pressure and the cylinder supply side pressure, so that the cylinder return side pressure Pout or the cylinder The area of the throttle section increases as the supply side pressure Pin increases, and the area of the throttle section becomes maximum when the cylinder return side pressure Pout or the cylinder supply side pressure Pin reaches a certain pressure or higher. Cylinder throttle circuit for hydraulic excavators.