JPH0316524B2 - - Google Patents

Description

Detailed Description of the Invention The present invention always maintains the differential pressure across the variable throttle constant even if the primary pressure or secondary pressure to the variable throttle for flow rate adjustment fluctuates, and loads a constant flow rate set by the throttle opening. The present invention relates to a flow rate control circuit configured to supply water to a flow rate.

Conventionally, variable throttles for flow rate adjustment have had the disadvantage that the passing flow rate changes if there is a change in the differential pressure ΔP across the throttle.

That is, if the flow rate through the throttle is Q, the flow coefficient of the throttle part is c, the opening area of the throttle is A, and the density of the fluid is ρ, then the flow rate Q is given by the following formula, Q=cA√2 (1) Throttle The flow rate Q changes depending on the differential pressure ΔP before and after.

Therefore, in conventional flow control valves, based on the principle that if the differential pressure ΔP before and after the throttle is kept constant according to equation (1) above, the flow rate will not change, a throttle valve and a constant differential pressure reducing valve are combined, and Even if pressure fluctuates, the differential pressure across the throttle remains constant to maintain the passing flow rate at the set flow rate.

FIG. 1 shows a conventional flow control circuit combining a constant difference pressure reducing valve, which is realized with the valve structure shown in FIG.

In Fig. 1, reference numeral 1 denotes a variable throttle for flow rate adjustment, and a constant difference pressure reducing valve 2 is arranged in series in the oil passage on the inlet side of the variable throttle 1, and a variable pressure reducing valve 2 is arranged in the primary side pilot chamber of the constant difference pressure reducing valve 2. An inlet pressure P1 of the throttle 1 is introduced, and an outlet pressure P2 of the variable throttle 1 is introduced into a secondary pilot chamber provided with a differential pressure setting spring 3.

Further, to explain in detail with reference to the valve structure shown in FIG. A pressure compensating orifice 5 is formed between the right land and the inflow passage, a primary pilot chamber 7 into which the inlet pressure P1 of the variable throttle 1 is introduced is formed on the right side of the spool 4, and a large diameter piston 8 is formed on the left side. are integrally formed, the inlet pressure P1 is introduced to the right side of the large diameter piston 8, a differential pressure setting spring 10 is provided to the left secondary side pilot chamber 9, and the outlet pressure P2 of the variable throttle 1 is introduced. There is.

The operation of the flow rate control circuit shown in Figs. 1 and 2 is as follows:
The fluid flow enters from the inlet, passes through the pressure compensating orifice 5 and the variable throttle 1, and reaches the outlet. The outlet pressure P2 is acting on the A1 area. Therefore, considering the balance of forces acting on the pressure compensating spool 4 in a steady state where fluid is flowing, F + A1 x P2 = (A2 + A3) x P1 (where F is the compression force of the differential pressure setting spring 10). Since A1+A2=A3, P1-P2=F/A1 (2), and the differential pressure across the variable throttle 1 (P1-P2) becomes constant.

Specifically, when the inlet pressure Po changes, the amount of inflow from the pressure compensation orifice 5 changes according to the pressure Po, the differential pressure across the variable throttle 1 changes, and the balance of the force acting on the pressure compensation spool 4 changes. My body collapses. That is, when the inlet pressure Po increases, the pressure compensating spool 4 moves to the left, and when the inlet pressure Po decreases, the pressure compensating spool 4 moves to the right to a balanced position.

On the other hand, when the outlet pressure P2 changes, the balance of the pressure compensating spool 4 is lost, and the outlet pressure P2
When P2 becomes low, the spool 4 moves to the left, and the outlet pressure P2
When becomes higher, it moves to the right until it reaches a balanced position.

As a result, the operation of the pressure compensating spool 4 causes the
The constant difference pressure reducing valve works so that F/A1 in equation (2) is constant, and the flow rate passing through the variable throttle 1 is kept constant.

However, in such a conventional flow control circuit, the opening degree of the pressure compensating orifice 5 of the constant difference pressure reducing valve 2 is automatically adjusted according to the pressure and flow rate of the fluid flowing through the variable restrictor 1; The fluid force (flow hose) acting on the spool 4 becomes larger as the differential pressure and flow rate increases, and cannot be ignored compared to the spring force. That is, in this example, the spring force acts in the direction of reducing the fluid force. As a result, the differential pressure before and after the variable throttle 1 decreases.

To solve this problem, it is possible to increase the hydraulic action areas A1, A2, A3 of the pressure compensating spool 4 and increase the strength of the differential pressure setting spring 10, but even if the flow rate used is the same, the control valve is large. In addition, as the spool becomes larger, the responsiveness decreases, and if the differential pressure setting spring is strengthened, there is a problem that the minimum pressure for operating the constant differential pressure reducing valve increases.

On the other hand, the decrease in responsiveness can be solved by increasing the flow area of the pilot flow path, but this naturally causes the problem of increasing the size of the valve.

The present invention was made in view of such conventional problems, and it is possible to keep the differential pressure across the variable throttle within the range of the rated flow rate without increasing the size of the pressure compensating spool and differential pressure setting spring of the constant differential pressure reducing valve. It is an object of the present invention to provide a flow rate control circuit which can always maintain a constant flow rate and can appropriately determine a rated flow rate regardless of the strength of a differential pressure setting spring of a constant differential pressure reducing valve.

In order to achieve this object, the present invention arranges constant difference pressure reducing valves in series on the inflow side of a variable throttle for flow rate adjustment,
A variable throttle inlet pressure is introduced into the primary side pilot chamber of the constant difference pressure reducing valve, and a constant flow rate is applied to the oil path connecting the inlet side oil path of the constant difference pressure reducing valve and the secondary side pilot chamber equipped with a differential pressure setting spring. Install a constant flow control valve to
On the other hand, a sequence valve is installed in the oil passage connecting the secondary pilot chamber of the constant difference pressure reducing valve and the outlet of the variable throttle, and the inlet pressure of the variable throttle is introduced into the primary pilot chamber of the sequence valve, and a sequence pressure setting spring is installed. A variable throttle outlet pressure is introduced into the secondary pilot chamber provided, and a fixed orifice is connected in parallel to a sequence valve in a circuit configuration.

Furthermore, an oil passage on the outflow side of the constant flow control valve in the circuit is connected to a tank, and a relief valve that opens at peak pressure when the load is stopped is provided in this oil passage.

According to a flow control circuit having such a circuit configuration, the differential pressure across the variable restrictor is applied as pilot pressure to operate the sequence valve, and when the differential pressure across the throttle decreases, the sequence valve is closed and constant flow control is performed. The fluid flowing through the valve and fixed orifice increases the pilot pressure on the secondary side of the constant differential pressure reducing valve, increases the spool opening of the constant differential pressure reducing valve, and restores the flow rate passing through the throttle to the set flow rate. When the differential pressure increases, the sequence valve is opened to lower the secondary pilot pressure of the constant differential pressure reducing valve, thereby reducing the spool opening and suppressing the flow rate passing through the variable throttle to the set flow rate. Furthermore, by providing a relief valve in the pilot system, the increase in circuit pressure when the load is stopped is suppressed to the relief set pressure.

With such a configuration and operation, the following effects can be obtained according to the present invention.

First, there is no need to increase the size of the spool or strengthen the differential pressure setting spring in order to eliminate balance fluctuations in the constant differential pressure reducing valve, and the newly installed body flow control valve, sequence valve, and fixed orifice Since it is provided in the oil passage of the pilot system, it can be made small and the valve structure that implements the flow control circuit can be significantly downsized.

In addition, increasing the spring load to increase the rated flow rate can be achieved by changing the spring load of the sequence valve, so even if the rated flow rate is increased, the valve structure does not become larger, and the constant differential pressure reducing valve can be used. Rated flow rate can be easily increased without modification.

Furthermore, the circuit can be protected by suppressing the peak pressure when the load is stopped to a set relief pressure, and the stability of the circuit can be improved by operating the relief valve to allow a small flow rate to flow through the pilot system even when the load is stopped.

Embodiments of the present invention will be described below based on the drawings.

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

First, to explain the configuration, a main oil passage 11 connected from a hydraulic pressure source to a load such as a cylinder is provided with a variable throttle 1 for flow rate adjustment, and a constant difference pressure reducing valve 2 is connected in series on the inflow side of the variable throttle 1. The inlet pressure P1 of the variable throttle 1 is introduced into the primary pilot chamber of the constant difference pressure reducing valve 2 via the pilot oil passage 12.
A differential pressure setting spring 10 is installed in the secondary pilot chamber.
is provided. The circuit section consisting of the variable throttle 1 and the constant difference pressure reducing valve 2 has the same configuration as the conventional flow rate control circuit shown in FIGS.

In addition to this configuration, the present invention first includes an oil passage 13 connecting the inflow side of the constant difference pressure reducing valve 2 and the secondary side pilot chamber.
A constant flow control valve 14 is provided to allow a constant small pilot flow to flow, and the constant flow control valve 14 has a structure in which a fixed throttle 15 that determines the flow rate and a constant differential pressure reducing valve 16 are arranged in series. The constant differential pressure reducing valve 16 is configured to operate the fixed throttle 1 so as to keep the differential pressure across the fixed throttle 15 constant.
5 and the differential pressure setting spring 17. Control to keep the differential pressure across the throttle constant by the fixed throttle 15 and constant differential pressure reducing valve 16 that constitute the constant flow control valve 14 is performed by the same operation as the conventional flow control circuit shown in FIGS.

On the other hand, an oil passage 17 connects the secondary side pilot chamber of the constant difference pressure reducing valve 2 and the main oil passage 11 on the outflow side of the variable throttle 1.
is provided with a sequence valve 18, and the inlet pressure P1 of the variable throttle 1 is introduced into the primary pilot chamber of the sequence valve 18 via a pilot oil passage 19, and a secondary pilot chamber equipped with a differential pressure setting spring 20 is provided. The outlet pressure P2 of the variable throttle 1 is introduced into the chamber. Further, a fixed throttle 22 is connected in parallel to the sequence valve 18 with a bypass oil passage 21 .

Here, the spring load Fo of the differential pressure setting spring 10 in the constant differential pressure reducing valve 2 is equal to or smaller than that of the conventional device, and therefore the pressure compensating spool used in the constant differential pressure reducing valve 2 is also equal to or smaller than that of the conventional device. A smaller spool is used. On the other hand, the differential pressure setting spring 20 of the sequence valve 18
The differential pressure setting spring 20 is determined according to the rated flow rate of the variable throttle 1, and has a sufficiently large spring load F1 when increasing the rated flow rate.

Then, the set differential pressure of the constant differential pressure reducing valve 2 is set to 2, for example.
Kgf/cm ² , and the set differential pressure of the sequence valve 18 is set to, for example, 4 Kgf/cm ² , and the pressure reducing valve spool is controlled by the differential pressure of 4 Kgf/cm ² .

Next, the operation of the embodiment shown in FIG. 3 will be explained.

When fluid is flowing through the main oil passage 11 with the opening degree of the variable throttle 1 opened to the degree that allows the set flow rate to be obtained, for example, the differential pressure across the variable throttle 1 may change due to fluctuations in the inlet pressure Po or the outlet pressure P2. ΔP (=P1−P2)
If ΔP decreases, the force applied to the sequence valve 18 due to the differential pressure ΔP across the
When the spring force becomes less than F1, the sequence valve 18 closes as shown in the figure, and the bypass oil passage 21
Constant flow control valve 14 via fixed throttle 22 provided in
A constant flow rate q1 flows, and due to the differential pressure generated at the fixed throttle 22 due to this constant flow rate q1, the pressure against the secondary side pilot chamber of the constant differential pressure reducing valve 2 increases, and the pressure compensation spool of the constant differential pressure reducing valve 2 is connected to the pressure compensating orifice. It moves in the opening direction to achieve balance, and as a result, the flow rate flowing into the variable orifice 1 is increased to restore the front and rear differential pressure ΔP to a constant value corresponding to the set flow rate.

Next, increase the inlet pressure Po or the outlet pressure P
2 decreases, the differential pressure ΔP (= P1
-P2) increases, when the force acting on the sequence valve 18 according to the differential pressure ΔP exceeds the spring force F1 of the differential pressure setting spring 20, the sequence valve 18 switches to open the oil passage. , a constant flow rate q1 from the constant flow rate control valve 14 is caused to flow through the sequence valve 18. As a result, the pressure in the secondary pilot chamber of the constant difference pressure reducing valve 2 decreases, and the pressure compensation spool in the constant difference pressure reducing valve 2 is moved in the direction of closing the pressure compensation orifice to achieve balance, and as a result, the flow rate flowing through the variable throttle 1 is reduced. This restricts the front and rear differential pressure ΔP to a constant value that corresponds to the set flow rate.

By controlling the secondary side pilot pressure of the constant difference pressure reducing valve 2 by operating the sequence valve 18 according to the differential pressure ΔP across the variable throttle 1, the variable throttle 1
The differential pressure ΔP between the front and rear of the
0 or even if the outlet pressure P2 fluctuates, a constant flow rate set by the variable throttle 1 can be supplied to the cylinder load, etc.

To further explain, in FIG. 3, P1 is automatically adjusted to be higher than the pressure P2 on the downstream side of the variable throttle 1 by 4 kgf/cm ² set at the sequence valve 18. This is because the sequence valve 18 is set to 4Kgf/cm ² by the spring 20.
When P1-P2>4, it opens, reduces the resistance to the flow from the oil passage 13, lowers the pressure in the spring chamber of the constant difference pressure reducing valve 2, strengthens the throttling state of the constant difference pressure reducing valve 2, and increases P1. When P1-P2>4, the resistance to the flow from the oil passage 13 is increased, the pressure in the spring chamber of the constant differential pressure reducing valve 2 is increased, the constant differential pressure reducing valve 2 is moved in the direction of opening, and P1
The pressure of is increased, resulting in P1-P2=4.

Although the differential pressure between the oil passages 12 and 13 is set to 2 Kgf/cm ² by the spring 10 as described above, the flow rate flowing through the constant differential pressure reducing valve 2 is large.
Further, when the pressure effect is large, fluid force acts, for example, in a direction that weakens the force of the spring 10. For example, if the force is 1Kgf/cm ² in differential pressure, the pressure in the oil passage 13 is 1Kg lower than the pressure in the oil passage 12, that is, P1.
The pressure is controlled to be as low as f/cm ² .

As described above, in the conventional case, a constant differential pressure is created only by the constant differential pressure reducing valve 2, and therefore it is affected by fluid force. Using the above values, 2Kgf/cm ² →
Since it is 1Kgf/cm ² , the flow rate of variable restrictor 1 is Q∝√
It becomes 70%.

If the constant differential pressure is 4 kgf/cm ² , it becomes 3 kgf/cm ² due to fluid force, so √34=87%.

However, in the present invention, the sequence valve 18 detects the pressure difference and functions under a constant flow rate from the constant flow rate control valve, so the set differential pressure of 4 kgf/cm ² does not change at all.

Further, the secondary side pilot pressure of the constant difference pressure reducing valve 2 is controlled by a sequence valve 18 provided independently from the main oil passage 11.
Since the pressure compensation orifice of the constant differential pressure reducing valve 2 is controlled by There is no need to increase the constant differential pressure reducing valve 2, and it is possible to use a constant differential pressure reducing valve 2 that is equivalent to or even smaller than the conventional one.

Furthermore, the setting of the rated flow rate corresponding to the maximum flow rate that can control the differential pressure ΔP between the front and rear of the variable throttle 1 at a constant level is independent of the differential pressure setting spring 10 of the constant differential pressure reducing valve 2.
Differential pressure setting spring 2 in sequence valve 18
This can be achieved by increasing the spring load F1 of 0, and since only a small flow rate q1 from the constant flow control valve 14 flows through the oil passage 17 provided with the sequence valve 18, the sequence valve 18 itself can also be made smaller. Therefore, even if the spring load F1 of the differential pressure setting spring 20 is increased, there is no need to increase the size of the valve structure, and even if the rated flow rate is increased, the control circuit can be made smaller.

This point also applies to the constant flow control valve provided in the oil passage 13 and the fixed throttle 22 connected in parallel to the sequence valve 18, and since only a small flow rate q1 flows through the constant flow control valve 14, constant flow control is possible. Small valves 14 and fixed throttles 22 can also be used, so that the constant flow control valve 1
4. Even if the sequence valve 18 and fixed throttle 22 are newly provided, the control circuit can be sufficiently miniaturized.

Furthermore, the differential pressure setting spring 10 of the constant differential pressure reducing valve 2
Since a spring with a small spring load Fo can be used, even if a small flow rate is set by the variable throttle 1, control can be performed with high precision to always keep the front and rear differential pressure ΔP constant.

FIG. 4 is a circuit diagram showing another embodiment of the present invention. In this embodiment, a relief valve 24 is provided in the oil passage 13 on the outflow side of the constant flow control valve 14 in FIG. Since the other circuit configurations are the same as the embodiment shown in FIG. 3, the same reference numerals are given and the explanation thereof will be omitted.

Relief valve 24 provided in the embodiment shown in FIG.
This means that when the cylinder load moves to the full stroke, that is, to the end of the cylinder, the outlet pressure P2 of the variable throttle 1 increases and is directly applied to the secondary pilot chamber of the constant differential pressure reducing valve 2 via the fixed orifice 22. This feature is characterized in that the constant difference pressure reducing valve 2 is protected from peak pressure when the load is stopped.

That is, in the embodiment shown in FIG.
A set constant flow rate is supplied to the loaded cylinder via the variable throttle 1, and when the cylinder end is reached, the flow rate becomes zero and the pressure in the circuit increases toward the discharge pressure of the hydraulic pressure source. When this pressure rise reaches the relief setting pressure determined by the relief pressure setting spring 26, the relief valve 24 opens and communicates with the tank 25 to suppress the pressure in the circuit to the relief setting pressure. At this time, relief valve 2
4, a constant small flow rate q1 caused by the constant flow rate control valve 14 and a small flow rate q2 caused by leakage from the constant difference pressure reducing valve 2 and the variable throttle 1 flow through the fixed orifice 22.
In this case, the differential pressure between the primary pilot pressure and the secondary pilot pressure in the constant differential pressure reducing valve 2 is a relatively low differential pressure determined by the pressure setting spring 10, and the differential pressure setting spring 20 of the sequence valve 18
The constant difference pressure reducing valve 2 can be protected from the peak pressure that occurs when the load is stopped.

Of course, since the relief valve 24 only needs to flow the small flow rate q1 from the constant flow control valve 14 and the leak flow rate q2 from the constant difference pressure reducing valve 2 and the variable throttle 1, it can be sufficiently miniaturized, and the relief valve 24 can be replaced with a new one. The valve device can be sufficiently miniaturized even if it is provided in the valve.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional circuit, Fig. 2 is a sectional view showing an example of a conventional valve structure, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 is a circuit diagram showing an example of the conventional valve structure. FIG. 3 is a circuit diagram showing another embodiment of the present invention. 1... Variable throttle for flow rate adjustment, 2, 16... Constant differential pressure reducing valve, 10, 17, 20... Differential pressure setting spring, 11... Main oil path, 12, 19... Pilot oil path, 13, 17... Oil path, 15, 22... Fixed throttle, 18... Sequence valve, 21... Bypass oil path, 24... Relief valve, 25... Tank,
26...Relief setting pressure spring.

Claims (1)

[Scope of Claims] 1. A variable throttle for flow rate adjustment, and a primary side pilot chamber arranged in series on the inflow side of the variable throttle for flow rate adjustment, into which the inlet pressure of the variable throttle is introduced, and a differential pressure setting spring. a constant difference pressure reducing valve having a downstream pilot chamber; a constant flow rate control valve that is provided in an oil passage connecting an inflow side oil passage of the constant difference pressure reducing valve and a secondary side pilot chamber and that allows a constant flow to flow; and the constant difference pressure reducing valve. It is provided in the oil passage connecting the secondary pilot chamber of the valve and the outlet oil passage of the variable throttle, and the inlet pressure of the variable throttle is set in the primary pilot chamber, and the outlet pressure is set in the secondary pilot chamber equipped with a setting spring. A flow control circuit comprising: a sequence valve; and a fixed throttle connected in parallel to the sequence valve. 2. A constant difference pressure reducing valve having a variable throttle for flow rate adjustment, a primary pilot chamber into which the inlet pressure of the variable throttle is introduced, and a secondary pilot chamber equipped with a differential pressure setting spring, and an inflow side of the constant difference pressure reducing valve. a constant flow control valve that is installed in an oil passage that connects an oil passage and a secondary pilot chamber and allows a constant flow to flow; and an oil that connects the secondary pilot chamber of the constant difference pressure reducing valve and the outlet oil passage of the variable throttle. The inlet pressure of the variable throttle is applied to the primary pilot chamber.
A sequence valve that introduces outlet pressure into a secondary pilot chamber equipped with a differential pressure setting spring, a fixed throttle connected in parallel to the sequence valve, and an oil path provided in an oil path from the outlet side of the constant flow control valve to the tank. 1. A flow control circuit comprising a relief valve.