JPH04302701A - Load-sensing control circuit - Google Patents

Abstract

PURPOSE:To allow a load-sensing control circuit which drives plural actuators using a single variable pump to prevent oil supply to an actuator in other system from being disabled due to the reduced discharge of a variable pump in response to the increased pressure of an operating system, for example, when a cylinder, which is an actuator in the operating system, reaches the end of a stroke. CONSTITUTION:A relief valve 19 which changes relief pressure in response to the pilot rooms 4, 5 of a directional control valve V is provided. This allows the relief valve 19 to be opened before the pressure of the operating system reaches the upper limit for example when a minor operation of a directional control valve V is performed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load sensing control circuit equipped with a variable pump whose discharge amount is variable in accordance with the load pressure of an actuator.

The conventional control circuit shown in FIG. 5 is of a type that supplies pressure oil to a plurality of actuators using one variable pump (not shown), and the illustrated supply passage 1 is connected to the variable pump and the directional control valve V. It is connected to the inflow port 2 of. This variable pump maintains a constant horsepower control function.

The directional control valve V has pilot chambers 4 and 5 on both sides of the spool 3, and the pilot chambers 4 and 5 are connected to a pilot pressure control mechanism (not shown). Further, this directional switching valve V is formed with a first relay port 6, a second relay port 7, and a drain port 8, as well as actuator ports 9, 10 and a load detection port 11. The load detection port 11 is connected to a maximum load pressure selection mechanism (not shown) that selects the maximum load pressure of each actuator. The maximum pressure selected by this maximum load pressure selection mechanism is transmitted to a regulator of a variable pump (not shown). This regulator controls the discharge pressure of the variable pump to be higher than this maximum load pressure by a certain value.

[0004] The first relay port 6 and the second relay port 7
A pressure compensation valve 12 is connected between the two. This pressure compensation valve 12 has one pilot chamber 12a connected between the first relay port 6 and the pressure compensation valve 12, and the other pilot chamber 12b connected to the maximum load pressure selection mechanism. Note that a spring 1 is installed in the other pilot chamber 12b.
3 is provided, and normally the pressure compensating valve 12 is maintained in the closed position shown in the figure by the action of this spring 13. In addition, in the figure, reference numeral 14 is a passage connecting the first relay port 6 and the pressure compensation valve 12, and 15 is a passage connecting the pressure compensation valve 12 and the second relay port 7.
16 is a drain passage that leads the drain port 8 to the tank, and 17 is a load check valve provided in the passage 14.

When the directional control valve V is in the neutral position shown in the figure, only the drain port 8 and the load detection port 11 communicate with each other, and all other ports remain closed. Therefore, the load pressure of the actuator controlled by this directional switching valve becomes the drain pressure, and this fact is transmitted to the maximum load pressure selection mechanism. In the above state, for example, by applying pilot pressure to one of the pilot chambers 4 and switching the directional control valve V to the left position L in the figure, the inflow port 2 and the first relay port 6 communicate with each other. The degree of opening of the communication passage at this time is determined by the switching amount of the directional control valve V, that is, the pressure acting on the pilot chamber 4.
This will make up 8. When the directional switching valve V is switched to the left position L as described above, the second relay port 7 and one actuator port 9 communicate with each other, and the load detection port 11 also communicates with the actuator port 9. Further, the other actuator port 10 communicates with the drain port 8.

Therefore, the pressure oil from the variable pump supplied to the inflow port 2 via the supply passage 1 flows through the variable throttle 18 → first relay port 6 → pressure compensation valve 12 → second relay port 7 → actuator port. 9 to the actuator. The return oil from this actuator is then returned to the tank from the other actuator port 10 via the drain port 8. Then, the load pressure on the actuator side at this time is transmitted to the maximum load pressure selection mechanism via the load detection port 11.

Further, in the pressure compensating valve 12, the pressure on the downstream side of the variable throttle 18 acts on one pilot chamber 12a, and the pressure selected by the maximum load pressure selection mechanism acts on the other pilot chamber 12b. Therefore, this pressure compensation valve 12 is controlled so that the pressure on its upstream side is a certain value higher than the maximum load pressure acting on the pilot chamber 12b. The pressure on the supply passage 1 side is also controlled to a higher pressure than on the upstream side of the pressure compensation valve 12 by the control function of the variable pump. As a result, the differential pressure before and after the variable throttle 18 is always kept constant, and the variable throttle 18
The flow rate through is also kept constant.

Note that when the directional control valve V is switched to the right position R, which is the opposite direction to the above, the second relay port 7
and the actuator port 10 communicate with each other, and the actuator port 9 and the drain port 8 communicate with each other, and the rest is substantially the same as the above case.

[Problems to be Solved by the Invention] In the conventional control circuit as described above, for example, if the directional control valve V is switched even slightly while the cylinder, which is the actuator, is at the end of its stroke, the circuit pressure immediately reaches its maximum. The pressure will rise to high. Therefore, there is a problem in that the discharge amount of the variable pump that maintains a constant horsepower control function decreases, resulting in a shortage of supply flow to other actuators. An object of the present invention is to provide a control circuit that prevents the circuit pressure from rising to the maximum pressure even if a directional control valve connected to a cylinder at the stroke end is switched, thereby ensuring the flow rate supplied to other actuators. It is to be.

[0009]

[Means for Solving the Problems] The present invention includes a plurality of actuators, a directional switching valve that controls these actuators and whose switching direction and switching amount are controlled by the action of pilot pressure, and The system is based on a load sensing control circuit that includes a pressure compensation valve that maintains a constant differential pressure, and a variable pump that is controlled according to the highest load pressure among a plurality of actuators. Based on the above device, the present invention is characterized in that a relief valve whose set pressure is varied according to the pilot pressure acting on the directional control valve is connected to the downstream side of the directional control valve.

0010

[Operation] Since the present invention is constructed as described above, when the directional switching valve is switched, the set pressure of the relief valve changes in accordance with the pilot pressure. That is, if the directional control valve is switched with a low pilot pressure, the set pressure of the relief valve at that time also becomes low. Therefore, when the pilot pressure is low and the directional control valve is only slightly switched, the set pressure of this relief valve is also low. On the other hand, when a high pilot pressure is applied to either the pilot chamber 12a or 12b to greatly switch the directional control valve V, the set pressure of the relief valve also becomes high.

[0011]

[Effects of the Invention] According to the load sensing control circuit of the present invention,
At the minute switching position, where the directional control valve is only slightly switched, the set pressure of the circuit is kept low, so even if the actuator cylinder is at the end of its stroke, the circuit pressure will not rise to the maximum pressure. . Therefore, the discharge amount of the variable pump does not decrease excessively, and there is no problem that the flow rate supplied to other actuators becomes insufficient and the actuators become unable to operate.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment shown in FIGS. 1 to 3 is characterized in that a relief valve 19 is provided, and the rest of the structure is the same as the conventional one. Therefore, the following description will focus on these feature points, and the same components will be described with the same reference numerals.

The relief valve 19 is provided in a passage 20 that leads the passage 14 to the drain passage 16.
When the pressure exceeds the set pressure of the relief valve 19, the relief valve 19 opens and guides the pressure oil in the passage 14 from the passage 20 to the drain passage 16. The set pressure of the relief valve 19 is determined by the spring force of the spring 21 and the pressure action of the pilot pressure chamber 22 in which the spring 21 is provided. The pilot pressure chamber 22 communicates with both pilot chambers 4 and 5 of the directional control valve V via a shuttle valve 23. Therefore, the higher pressure of the pilot chambers 4 and 5 of the directional control valve V acts on this pilot pressure chamber 22.

FIG. 2 specifically shows the circuit configuration of FIG. 1. When the spool 3 provided on the valve body B in FIG. 2 is moved from the neutral position shown in the figure to the right, the notch 24 overlaps with the first relay port 6, and the variable throttle 18 opens in accordance with the amount of overlap. The degree is determined. Therefore, the pressure oil supplied to the supply port 2a flows to the first relay port 6 via the variable throttle 18, opens the load check valve 17, and the pressure at that time is transferred to one pilot chamber 12a of the pressure compensation valve 12. It acts on

One pilot chamber 12 of the pressure compensation valve 12
When pressure is applied to a, the cylindrical spool 25 rises to a position where the pressure action of one pilot chamber 12a, the pressure action of the other pilot chamber 12b, and the spring force of the spring 13 are balanced. This determines the amount of overlap between the outflow port 26 of the pressure compensation valve 12 and the second relay port 7.

Therefore, the pressure oil flowing into the first relay port 6 is supplied to the actuator port 9 via the second relay port 7 and the first annular groove 27 formed in the spool 3. At this time, the return oil from the actuator is returned to the drain passage 16 via the actuator port 10 and the second annular groove 28. Further, the pilot pressure selected by the maximum load pressure selection mechanism acts on the other pilot chamber 12b of the pressure compensation valve 12. Therefore, as described above, the differential pressure before and after the variable throttle 18 is kept constant, and a constant flow rate corresponding to the throttle opening is supplied.

Further, the valve body B is provided with a relief valve 19. This relief valve 19 is connected to the first relay port 6
It consists of a seat part 29 that opens to the front, a poppet 30 that opens and closes the seat part 29, and a spring 21 that brings the poppet 30 into pressure contact with the seat part 29. A pilot pressure chamber 22 is formed on the spring 21 side, and this pilot pressure chamber 22 is communicated with pilot chambers 4 and 5 at both ends of the spool 3 via a shuttle valve 23.

Next, the operation of this embodiment will be explained. However, the opening degree of the variable throttle 18 is determined according to the switching amount of the directional switching valve, and the flow rate corresponding to the opening degree is supplied to the actuator, as in the conventional case. Therefore, the explanation of the parts similar to the conventional one will be omitted, and the operation of the relief valve 19 will be mainly explained.

Now, when pilot pressure is applied to one pilot chamber 4 of the directional control valve V, this directional control valve V is switched as described above, and the pilot pressure at that time is applied to the pilot pressure chamber of the relief valve 19. 22. Therefore, if a high pilot pressure is applied to the pilot chamber 4 to greatly switch the directional control valve V, the pressure applied to the pilot pressure chamber 22 of the relief valve 19 will also become higher. In other words, the greater the switching amount of the directional switching valve V, the higher the set pressure of the relief valve 19. Conversely, the smaller the switching amount of the directional switching valve V, the lower the set pressure of the relief valve 19. FIG. 3 shows this relationship. FIG. 3 shows the relationship between the pressure Pi acting on the pilot pressure chamber 22 of the relief valve 19 and the set pressure of the relief valve 19.

Therefore, for example, when the cylinder serving as the actuator is near the end of its stroke and the directional control valve V is slightly switched, the set pressure of the relief valve 19 is maintained at a low state. Since the set pressure of the relief valve 19 is thus low, even if the cylinder reaches its stroke end, its circuit pressure does not rise to the maximum pressure. Therefore, the discharge amount of the variable pump does not decrease. In other words, it is possible to eliminate the inconvenience of not being able to supply pressure oil to other actuators due to the pressure increase in the cylinder that has reached the stroke end.

FIG. 4 shows the second embodiment.
The difference between this second embodiment and the first embodiment is that the pressure on the downstream side of the pressure compensation valve 12 and the pressure in the pilot pressure chamber 22 are opposed to each other, and the relief valve 19 is opened according to the pressure difference between them. This is what I did to make it clear. The reason why the relief valve 19 is opened by the pressure action on the downstream side of the pressure compensation valve 12 is as follows.

In the case of the first embodiment, the pressure compensating valve 12
If the maximum load pressure acting on the pilot chamber 12b of the actuator is determined by the pressure of other operating systems, that pressure will naturally be applied to the load detection port 1 that detects the load of the actuator.
It becomes higher than the pressure of 1. Therefore, the pressure in the passage 20 of the first embodiment may become high regardless of the load pressure of the load detection port 11. If the pressure in the passage 20 increases regardless of the load pressure of the operating system, the relief valve 19 may function regardless of the operating status of the actuator of the operating system. For example, if a load operation is performed at low pressure in one operating system, and high pressure is generated in another system, the relief valve 19 will function due to the action of the high pressure, and the actuator of the low pressure load operating system will This may slow down the operating speed.

Therefore, in this second embodiment, the relief valve 19 is provided with a passage 31 on the downstream side of the pressure compensating valve 12, and by connecting the relief valve 19 to this passage 31, the relief pressure can be controlled by its operation system. This is determined by the load pressure of a certain actuator, so that it is not influenced by the maximum load pressure of other systems.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of main parts of a first embodiment.

FIG. 2 is a sectional view of essential parts of the first embodiment.

[Figure 3] Pressure P acting on the pilot pressure chamber of the relief valve
It is a graph showing the relationship between i and the set pressure of the relief valve.

FIG. 4 is a circuit diagram of main parts of a second embodiment.

FIG. 5 is a circuit diagram of a conventional main part.

[Explanation of symbols]

V Directional switching valve 19 Relief valve

Claims (1)

[Claims] Claim 1: A plurality of actuators, a directional valve that controls these actuators and whose switching direction and amount are controlled by the action of pilot pressure, and a pressure that maintains a constant differential pressure across the directional valve. In a load sensing control circuit comprising a compensation valve and a variable pump that maintains a constant horsepower control function according to the highest load pressure of a plurality of actuators, the control circuit is set according to the pilot pressure acting on the directional control valve. A load sensing control circuit characterized in that a relief valve with variable pressure is connected to the downstream side of the directional switching valve.