JPH0218471B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a relief valve with a backflow check valve that can effectively prevent cavitation.

In a hydraulic circuit with a balanced piston type relief valve, cavitation occurs on the cylinder port side when the pressure at the cylinder port becomes lower than the pressure at the tank port.To prevent this, oil from the tank port must flow back to the cylinder port. Must be.

Fig. 1 shows an example of a conventional relief valve with a backflow check valve having such a function.
A pilot valve consisting of a spring 3 that presses the valve against the valve seat 2a and a pressure adjustment screw S that adjusts its pressing force, a hollow balance piston 4, and a spring 5 that presses the balance piston 4 against the valve seat 1a.
A balance piston type relief valve which opens and closes a flow path communicating between the cylinder port 6 and the tank port 7 by means of the balance piston 4,
An oil passage 8 communicating with the tank port 7 is provided on the circumferential side of the balance piston 4, and a check valve 9 having an oil passage 9a formed through the center thereof is attached to the end on the cylinder port 6 side so as to be displaceable in the axial direction. The spring 10 presses the valve seat of the balance piston 4 to close the valve.

When the pressure in the cylinder port 6 becomes higher than the value set by the pilot valve, the poppet valve 2 opens and the oil in the piston chamber 1b drains into the drain oil passage 1c.
In order to flow out through the tank port 7, the balance piston 4 moves to the right in the figure against the spring 5, opens a flow path that communicates the cylinder port 6 and the tank port 7, and acts as a relief valve.

Conversely, when the pressure at the cylinder port 6 becomes lower than the pressure at the tank port 7, the check valve 9 resists the spring 10 and moves to the left from the position shown by the solid line in the figure to the position shown by the imaginary line. The oil inside passes through the path shown by arrow A to cylinder port 6.
This prevents cavitation from occurring on the cylinder port 6 side.

However, in such a conventional relief valve with a backflow check valve, backflow oil from the tank port 7 to the cylinder port 6 flows through the oil passage 8 of the balance piston 4 and the narrow space between the balance piston 4 and the check valve 9. Since the oil flows through a gap, there is a large flow resistance against backflow oil, and it is not possible to instantly flow a large amount of oil.

However, in order to prevent cavitation in, for example, hydraulic circuits for construction machinery, it is necessary to instantly flow a large flow from the tank port to the cylinder port with a low differential pressure during backflow, and in this respect, the Conventional relief valves with backflow check valves have the drawback of not being able to exhibit sufficient performance.

This invention was made in view of the above points,
It is an object of the present invention to provide a relief valve with a backflow check valve that allows a large flow rate to flow instantaneously when backflow occurs from a tank port to a cylinder port.

Therefore, in the relief valve with a backflow check valve according to the present invention, a cylinder chamber communicating with the tank port is formed in the balance piston that opens and closes a flow path communicating between the cylinder port and the tank port of the balance piston type relief valve, and a cylinder chamber communicating with the tank port is formed. A stopper piston is slidably mounted, one side of which faces the cylinder chamber, the other side faces the cylinder port, and has an oil passage communicating between the cylinder port and the piston chamber into which the balance piston is fitted;
By providing a stopper member that regulates the movement of the stopper piston toward the cylinder port, when the pressure in the cylinder port becomes lower than the pressure in the tank port and there is a backflow, the stopper piston and the balance slide relative to each other. The balance piston itself widens the flow path that communicates the cylinder port and tank port, allowing a large amount of flow to flow instantaneously.

Embodiments of the present invention will be described below with reference to FIGS. 2 to 4 of the accompanying drawings, in which the same parts as in FIG. 1 are denoted by the same reference numerals.

The balanced piston type relief valve according to this embodiment has a balanced piston 13 slidably fitted into a piston chamber 12 provided in a body 11, and when the pressure in the cylinder port 6 exceeds a set pressure, the poppet valve 2 is activated. The balance piston 13 slides to the right in the figure and opens the flow path that communicates the cylinder port 6 and tank port 7. This is the same as before.

A cylinder chamber 13a is formed on the cylinder port 6 side of this balance piston 13, and a guide hole 13b having a smaller diameter than the cylinder chamber 13a is formed on the piston chamber 12 side. Communicating oil passage 13c
will be established.

Further, a stopper piston 14 is slidably inserted into the cylinder chamber 13a and guide hole 13b of the balance piston 13.

This stopper piston 14 includes a piston part 14a that fits into the large diameter part of the cylinder chamber 13a of the balance piston 13, a rod part 14b that fits into the guide hole 13b, and a projection part 14c that projects from the piston part 14a toward the cylinder port 6 side. It passes through the piston part 14a and the rod part 14b,
An oil passage 14d is formed that communicates the cylinder port 6 side and the piston chamber 12 side.

Note that one pressure receiving surface (the right side in the figure) of the piston portion 14a faces the cylinder chamber 13a, and the other pressure receiving surface (the left side in the figure) faces the cylinder port 6.

Further, a stopper pin 15 that engages with a protrusion 14c of the stopper piston 14 is fixed in an opening 11b that communicates the seat portion 11a of the body 11 with the cylinder port 6.

According to this embodiment configured in this way, when the pressure in the cylinder port 6 is higher than that in the tank port 7, the pressure on the cylinder port 6 side of the piston portion 14a of the stopper piston 14 is reduced to the pressure on the cylinder chamber 13a side. Since it is higher than the pressure, the stopper piston 14 is pushed into the balance piston 13, as shown in FIG. 2, and the two work together as a proper relief valve.

When the balance piston 13 is seated on the seat portion 11a of the body 11, the protrusion 14c of the stopper piston 14 is attached to the stopper pin 15.
Their positional relationship is determined so that they are in contact with or have a slight gap between them.

Next, when the pressure in the cylinder port 6 becomes lower than the pressure in the tank port 7, the pressure in the cylinder port 6 and the piston chamber 12 becomes lower than the pressure in the cylinder chamber 13a communicating with the tank port 7.
The stopper piston 14 is the balance piston 13
It is pushed out slightly toward the cylinder port 6 side, and its protrusion 14c comes into contact with the stopper pin 15, and in this state, movement to the left in the figure is prevented.

After the stopper piston 14 is prevented from moving to the left, the balance piston 13 moves to the right against the spring 5 due to the oil pressure in the cylinder chamber 13a and becomes the state shown in FIG. The tank port 7 communicates with the cylinder port 7 at a large opening, and a sufficient amount of backflow oil flows from the tank port 7 into the cylinder port 6 as shown by arrow B, thereby completely preventing cavitation.

As described above, according to the present invention, a cylinder chamber communicating with a tank port is formed in the balance piston of a balance piston type relief valve, a stopper piston is slidably inserted therein, and the stopper piston is slidably inserted therein. Since a stopper member is provided to prevent the movement of the balance piston toward the cylinder port side at a predetermined position, the stopper piston is normally pressed by the pressure of the cylinder port and operates together with the balance piston, and the cylinder When the port pressure becomes lower than the tank port pressure, even if the differential pressure between the two is small, the stopper piston and balance piston slide relative to each other, causing the balance piston itself to function as a check valve. Since a large annular gap is formed between the tank and the seat, the flow resistance of the reverse oil flow from the tank port to the cylinder port is small, and a large amount of reverse oil flows instantly, completely eliminating cavitation. It can be prevented.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view illustrating a conventional relief valve with a backflow check valve, FIG. 2 is a longitudinal sectional view similar to FIG. 1 illustrating an embodiment of the present invention, and FIG.
Similarly, FIG. 4 is a front view showing the stopper pin mounting portion of the body, and a longitudinal sectional view showing the reverse flow operation state of the embodiment of FIG. 2. 6...Cylinder port, 7...Tank port, 11
...Body, 12...Piston chamber, 13...Balance piston, 13a...Cylinder chamber, 14...Stopper piston, 14a...Piston part, 14d...Oil passage,
15...Stupapin.

Claims (1)

[Claims] 1 A cylinder chamber communicating with the tank port is formed in the balance piston of a balance piston type relief valve equipped with a balance piston that opens and closes a flow path communicating between the cylinder port and the tank port, and one side is provided in the cylinder chamber. A stopper piston having a pressure receiving surface facing the cylinder chamber, the other pressure receiving surface facing the cylinder port, and an oil passage communicating between the cylinder port and the piston chamber into which the balance piston is fitted is slidable. 1. A relief valve with a backflow check valve, comprising a stopper member which is inserted and which prevents the stopper piston from moving toward the cylinder port at a predetermined position.