JPH0225069B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a relief valve used in a hydraulic circuit.

[Background of the invention]

Relief valves are provided in many hydraulic circuits, and when the pressure in the hydraulic circuit reaches a certain value,
This is to relieve the pressure oil in the circuit to the low pressure circuit and prevent the pressure in the hydraulic circuit from exceeding the above value, thereby preventing damage to the piping, equipment, etc. that constitute the hydraulic circuit. Such a relief valve will be explained with reference to the drawings.

FIG. 3 is a sectional view of a conventional relief valve. In the figure, 1 is the sleeve of the relief valve, and the end wall 1
a, a cylindrical side wall 1b, an introduction passage 1c into which pressure oil of the hydraulic circuit is introduced, a first relief passage 1d and a second relief passage 1e on the low-pressure circuit side, and a seat part 1f on which a poppet to be described later is seated. have 2
3 is a poppet slidably mounted on the piston 2; 4 is a poppet diaphragm formed through the end face of the poppet 3; 5 is a poppet; A spring 3 urges the spring to the left in the figure, and a spring chamber 6 houses the spring 5. 7 is the end face of piston 2 and poppet 3
It is a differential pressure chamber formed by the inner surface of the tube and communicates with the introduction passage 1c via the poppet throttle 4. The diameter of the differential pressure chamber 7 is smaller than the diameter of the introduction passage 1c.

When this relief valve is connected to a hydraulic circuit, the pressure _P1 of the hydraulic circuit acts as a force F that tends to move the poppet 3 from side to side in the figure. This force F has the diameter of the introduction passage 1c as d ₁ and the diameter of the differential pressure chamber 7 as d ₂
Then, F=(d ₁ ² −d ₂ ² )P ₁ π/4 (1). When the pressure P ₁ in the hydraulic circuit is small, the force F
is also smaller, and the spring force is larger. In this case, the poppet 3 is pressed by the spring 5 and seats on the seat portion 1f, blocking the introduction passage 1c and the first relief passage 1d. However, the pressure P ₁ in the hydraulic circuit increases,
When the force F becomes larger than the spring force of the spring 5, the poppet 3 moves to the right, connects the introduction passage 1c and the first relief passage 1d, relieves the pressure oil in the hydraulic circuit, and prevents the pressure from increasing. do. The pressure at this time becomes the set pressure of the relief valve. As the poppet 3 moves to the right, the oil in the differential pressure chamber 7 passes through the poppet throttle 4 and is discharged to the introduction passage 1c side, and at this time, due to the passage resistance of the oil passing through the poppet throttle 4, it A damping effect is provided. Note that the second relief passage 1e is for letting oil leaking from the poppet 3 escape.

As mentioned above, the poppet throttle 4 provides a damping effect to prevent the relief valve from oscillating due to fluctuations in oil pressure and flow rate when the relief valve is relieved. The existence of 4 causes the following drawbacks. That is, when the pressure in the hydraulic circuit suddenly increases due to a sudden start or stop of the actuator, the opening of the poppet 3 is delayed due to the damping effect of the poppet throttle 4, and surge pressure is generated in the hydraulic circuit. This was the cause of the occurrence.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a relief valve that eliminates the above-mentioned conventional drawbacks and can prevent the generation of surge pressure in a hydraulic circuit.

[Summary of the invention]

In order to achieve the above object, the present invention comprises a passage between the differential pressure chamber of the relief valve and the low pressure side circuit, which communicates the two, and maintains this passage at a certain constant pressure in the hydraulic circuit. When this pressure reaches the pressure, the spool moves to shut off, and the relief valve is once opened between the time the spool starts moving and the passage is shut off to absorb the energy caused by the pressure rise.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a sectional view of a relief valve according to an embodiment of the present invention. In the figure, parts that are the same as those shown in FIG. 3 are given the same reference numerals, and explanations thereof will be omitted. 10 is an oil chamber formed in the portion of the piston 2 on the differential pressure chamber 7 side;
11 is a spool slidably inserted into the oil chamber 10, and 12 is a spring that urges the spool 11 to protrude into the differential pressure chamber 7. 13 is piston 2
This is the piston seat portion formed in the spool 11, and is the portion on which the spool 11 is seated. 14 is spool 11
15 is a small hole that communicates the extension of the oil chamber 10 with the spring chamber 6.

Next, the operation of this embodiment will be explained with reference to the graph shown in FIG. The pressure in the hydraulic circuit is now 0.
Consider the case where the pressure rises from above to the set pressure. First, as the pressure in the hydraulic circuit increases as shown in the straight line section A in FIG.
4. It flows to the low pressure circuit side via the oil chamber 10, the small hole 15, the spring chamber 6, and the second relief passage 1e. This flow of oil creates a pressure difference between the differential pressure chamber 7 and the oil 10, and this pressure difference acts on the spool 11. By the way, when pressure oil is flowing through the above path, a pressure drop occurs in the poppet throttle 4, and the pressure in the pressure chamber 7 and the hydraulic circuit are not the same pressure as in a conventional relief valve, but are different pressures. becomes. For this reason,
The pressure acting on the poppet 3 is also different from that of a conventional relief valve. Here, if the pressure of the hydraulic circuit, the diameter of the introduction passage 1c, and the diameter of the differential pressure chamber 7 are respectively P ₁ , d ₁ , and d ₂ , which are the same as in the conventional relief valve, and the pressure of the differential pressure chamber is P ₂ , then the poppet force acting on 3
F' is F' = (d ₁ ² P ₁ - _{d 2} ² P ₂ ) x π/4 = {d ₁ ² - (P ₂ /P ₁ ) d ₂
² }P ₁ π/4...(2). Comparing equations (1) and (2) above, we find that in equation (2), the area of action of the differential pressure chamber 7 is apparently smaller by P ₂ /P ₁ (P ₁ > P ₂ ). I understand. Therefore, while the pressure oil flow is occurring, the force F' acting on the poppet 3 in this embodiment is greater than the force F acting on the poppet 3 of the conventional relief valve. Therefore, the poppet 3 moves to the right at a pressure P s _' lower than the pressure P _s set by the spring 6, and the introduction passage 1 c and the first relief passage 1 d are brought into conduction, so that the pressure in the hydraulic circuit is reduced. As shown in the straight line section B of FIG. 2, the value P _s ' becomes constant.

On the other hand, as described above, a differential pressure acts on the spool 11, and the pressure in the hydraulic circuit increases as shown in the straight line section A in FIG. Then, the spool 11 moves to the right and seats on the piston seat portion 13. In this case, spring 1
The spring force 2 is selected to be such that it causes the spool 11 to move to the right when the pressure in the hydraulic circuit reaches a pressure slightly lower than the value P _s '. When the spool 11 is seated on the piston seat portion 13, the passage communicating from the differential pressure chamber 7 to the small hole 15 is blocked.

When the passage is blocked by the spool 11, the pressure in the hydraulic circuit becomes equal to the pressure in the differential pressure chamber 7 with a slight delay from when the passage is blocked. Then, the force acting on the poppet 3 changes from force F' to F, and since the force F is small, the poppet 3 begins to move in the closing direction (leftward) due to the spring force of the spring 6, and the pressure in the hydraulic circuit increases. increases as shown in straight line section C in FIG. During this time, the poppet 3 is moved to the seat portion 1f.
and the introduction passage 1c and the first relief passage 1.
d is blocked. Hydraulic circuit pressure is set pressure
When P _s is reached, the poppet 3 moves to the right against the spring force of the spring 6, as in the conventional relief valve, and the introduction passage 1c and the first relief passage 1d are brought into continuity, and from then on, the pressure in the hydraulic circuit is reduced. The pressure is maintained at a constant pressure P _s as shown by straight line section D in FIG.

In this way, in this embodiment, by configuring the passage between the differential pressure chamber and the second relief passage,
Until this passage was blocked by the spool, the force acting on the poppet was increased, and as a result, the poppet was temporarily opened and relieved in the middle of the rise in pressure in the hydraulic circuit. The energy of the pressure increase (proportional to the product of pressure and time) is absorbed, and the energy of the subsequent pressure increase can be reduced. It is possible to prevent the generation of surge pressure even when there is a sudden rise in pressure. Also, when viewed from the actuator's perspective, the apparent pressure rise becomes gentler, so the impact upon starting and stopping can be alleviated.

In addition, in the description of the above embodiment, a conical hole formed in the spool was exemplified as a passage communicating between the differential pressure chamber and the low pressure side circuit, but the conical hole formed in the spool is not limited to such a conical hole, and for example, It is also possible to form a considerable gap between the oil chamber side wall and the spool outer wall and use this gap as a passage; in short, any passage that can be blocked by the spool is sufficient.

〔Effect of the invention〕

As described above, in the present invention, a passage is formed between the differential pressure chamber and the low pressure side circuit, and this passage is blocked by a spool that operates at a certain pressure in the hydraulic circuit, so that the pressure in the hydraulic circuit is Since the relief valve is opened once in the middle of the ascent, it is possible to prevent the generation of surge pressure even when the pressure in the hydraulic circuit suddenly increases, and it is also possible to reduce the impact when starting and stopping the actuator. .

[Brief explanation of drawings]

FIG. 1 is a sectional view of a relief valve according to an embodiment of the present invention, FIG. 2 is a graph showing pressure changes in a hydraulic circuit, and FIG. 3 is a sectional view of a conventional relief valve. 1...Sleeve, 1c...Introduction passage, 1d...
First relief passage, 1e... Second relief passage, 2... Piston, 3... Poppet, 4... Poppet throttle, 5, 12... Spring, 7... Differential pressure chamber,
10...Oil chamber, 11...Spool.

Claims (1)

[Claims] 1. A piston, a poppet that is slidable with respect to the piston, and a spring that biases the poppet.
A relief valve comprising a sleeve having a seat portion on which the poppet is seated, and a differential pressure chamber formed by the piston and the poppet and communicated with a hydraulic circuit through a restriction provided in the poppet,
A relief valve comprising: a passage communicating between the differential pressure chamber and a low pressure circuit side; a spool that blocks the passage according to the pressure of the hydraulic circuit; and a spring that biases the spool. 2. The relief valve according to claim 1, wherein the spool is slidably provided within the piston. 3. The relief valve according to claim 1, wherein the passage is partially formed within the spool.