JPH0439441Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial field of application> This invention relates to a hydraulic circuit for traveling of construction vehicles such as hydraulic excavators, and in particular, an overload relief system that prevents surge pressure during traveling braking and regulates brake pressure. Regarding those equipped with a valve.

<Prior Art> As a conventional fluid pressure regulating valve for alleviating surge pressure, there is one shown in FIG. This is disclosed in Japanese Patent Publication No. 49-15571, in which a piston 13 is slidably fitted into a valve 6 that opens and closes between the passages 2 and 4 of the main body 1.
The structure is such that the spring 15 is used to press the spring 15. This is valve 6
The difference between the effective pressure receiving area when seated and the effective pressure receiving area of the piston 13 counteracts the spring 8 to determine the pressure regulation value, and the pressure rise buffer time is determined by the throttle 12 of the valve 6 and the effective stroke volume of the piston 13. There is. The spring 15 is provided to make the return of the piston 13 quick and reliable.

<Problems to be Solved by the Invention> The pressure regulating valve shown in FIG. 2 described above has a problem in that it is too large to be used as a crossover relief valve for a hydraulic traveling device. That is, since the spring 8 that presses the valve 6 and the spring 15 that presses the piston 13 inside the valve 6 have a double structure, there are significant restrictions on miniaturization.

This invention differs from the above-mentioned conventional technology in that the spring 1
5 is replaced with hydraulic pressure to achieve miniaturization.

<Means for solving the problem> The means according to this invention provides overload relief valves in both supply and discharge circuits for the hydraulic motor for driving the traveling device, and the overload relief valves are connected to the first port and the first port. A valve seat provided between the two ports is pressed by a spring to close the valve hole, and as pressure increases on the second port side, the valve opens against the spring to communicate the first port and the second port. The main valve has a main valve configured as a second valve through a throttle.
It has an internal chamber that communicates with the port and has a smaller diameter than the valve seat, and a piston is housed in the internal chamber so that it can move forward and backward,
A stopper is placed opposite to the rear surface of the piston, and a passage is provided that communicates the main valve and the back of the piston with a first port, the first port being connected to one side of the supply/discharge circuit, and the second port being connected to the other side It is characterized by being connected to the supply/discharge circuit.

<Function> If the supply and discharge of pressure oil to the hydraulic supply and discharge circuit is cut off while the traveling device is operating with a hydraulic motor, that is, while traveling, the hydraulic motor acts as a pump due to the inertia acting on the hydraulic motor, and the hydraulic The circuit that was supplying pressure oil to the motor becomes low pressure, and the circuit that discharges it becomes high pressure. Therefore, in an overload relief valve whose first port is connected to a circuit that was supplying pressure oil, the piston is in the forward position where the volume of the internal chamber is reduced, and high pressure oil acting on the second port is removed. When the fluid flows into the internal chamber through the throttle, the piston moves backward. During this retraction movement of the piston, the hydraulic pressure in the internal chamber formed between the main valve and the piston is
Since the hydraulic pressure is the same as that of the spring chamber, the main valve receives a pressing force from the hydraulic pressure of the second port acting on the valve seat area. When the piston hits the stopper, the oil pressure in the internal chamber formed between the main valve and the piston becomes equal to the oil pressure in the second port, so the main valve acts on an area obtained by subtracting the cross-sectional area of the piston from the valve seat area. Second
Receives pressing force from port hydraulic pressure. In this way, the pressing force that acts on the main valve when the piston is moving is greater than the pressing force when the piston contacts the stopper, and is equal to the second pressure that acts on the area of the piston.
It increases by the pressing force due to the port's hydraulic pressure. When the pressing force acting on the main valve exceeds the pressing force of the spring, the valve opens and communicates the first and second ports. Therefore, the oil pressure at the second port is set to a low pressure when the piston is moving, and becomes a high pressure setting when the piston contacts the stopper. And the second
The port is connected to the circuit on the side where the brake oil pressure of the hydraulic motor is applied, so the main valve opens slightly to temporarily release the high pressure immediately after stopping the supply and discharge of oil pressure to the hydraulic motor, thereby preventing the generation of surge pressure. To prevent. The function of preventing the generation of this surge pressure is almost the same as that of the conventional one shown in FIG.
Since the piston does not exist, the spring does not return the piston from the retracted state in which it is in contact with the stopper to the initial forward state. Next, when the oil pressure at the first port increases due to restart, the piston moves forward and returns to a state in which it can absorb surge pressure. The other overload relief valve operates in the same manner as described above when the pressure oil supply and discharge circuit is cut off while the hydraulic motor is rotating in the opposite direction.

<Example> An example is shown in FIG. In the same figure, 20,
21 is an overload relief valve, 22 is a hydraulic motor for driving the traveling device of the vehicle, and 23 and 24 are pressure oil supply and discharge circuits.

Since the overload relief valves 20 and 21 have the same structure, only one valve 20 will be described. The overload relief valve 20 includes a valve body 30, a main valve 31, a spring 32, a piston 33, a stopper 34, and the like. The valve body 30 has a first port 35, a second port 36, and an inner hole 37 into which the main valve 31 is slidably inserted. The main valve 31 has a valve seat 38 provided on the second port 35 side within the inner hole 37.
The spring 32 is pressed toward the
The other end of 2 is in contact with an indigo body 39 that closes the inner hole 37. The main valve 31 also houses a piston 33 having a smaller diameter than the valve seat 8 so as to be able to slide coaxially with the main valve 31, and has an internal section on the front surface of the piston 33 that communicates with the second port 36 via a throttle 40. A chamber 41 is formed. A stopper 34 that limits the retracted position of the piston 33 is provided to protrude from the indigo body 39. A spring chamber 42 on the back side of the main valve 31 communicates with the first port 35 through a passage 43 .

The overload relief valve 20 has a first port 35 connected to the supply/discharge circuit 23 and a second port 36 connected to the supply/discharge circuit 24 . Another overload relief valve 21 has a first port 35 connected to the supply/discharge circuit 24 and a second port 36 connected to the supply/discharge circuit 23 .

When pressure oil is supplied to the supply/discharge circuit 23 and the supply/discharge circuit 24 is connected to the tank, the hydraulic motor 22 rotates.
The vehicle is running. The oil pressure of the supply/discharge circuit 23 increases according to the load of the hydraulic motor 22, and the oil pressure of the supply/discharge circuit 24 is low pressure. Therefore, in the overload relief valve 20, the main valve 31 is seated on the valve seat 38 to close the space between the first port 35 and the second port 36, and the piston 33 is moving forward. In the other overload relief valve 21, the main valve 31
is seated, but the piston 33 is in the retracted position.

Now, if the pressure oil supply and discharge side ends of the supply and discharge circuits 23 and 24 are cut off to enter the brake state, the hydraulic motor 22 performs a pumping action due to the inertia acting on the hydraulic motor 22, so the supply and discharge circuit 24 High pressure acts and the supply/discharge circuit 23 becomes low pressure. As a result, the first port 35 of the overload relief valve 20 is under low pressure, and the second port 35 is under low pressure.
Port 36 is subjected to high pressure. The hydraulic pressure in the second port 36 acts on the pressure chamber 41 through the throttle 40, causing the piston 33 to retreat. While pressure oil is being supplied into the internal chamber 41, the pressing force acting on the main valve 31 is applied to the second port 36 acting on the cross-sectional area of the valve seat 38.
This is the pressing force due to the hydraulic pressure. That is, until the piston 33 contacts the stopper 34, the effective pressure-receiving area is larger than when the piston 33 contacts the stopper 34, and a larger pressing force is applied, which is the same as the spring 32 effectively being at a lower set pressure. Therefore, while the piston 33 is moving, the oil pressure in the second port 36 is maintained at a low pressure, so generation of surge pressure in the second port 36 can be prevented. When the piston 43 comes into contact with the stopper 34, the hydraulic pressure in the internal chamber 41 becomes the same as the hydraulic pressure in the second port 36. Therefore, the pressing force acting on the main valve 31 is calculated from the cross-sectional area of the valve seat 38 on the piston 3.
It becomes a small value corresponding to the small effective pressure receiving area obtained by subtracting the cross-sectional area of 3. In other words, it is the same as having a higher set pressure than when the spring 32 is moving against the piston 33. Therefore, the oil pressure in the second port 36 is maintained at a high value.

Then, when the main valve 31 is retracted by the hydraulic pressure acting on the second port 36, both the supply/discharge circuits 23 and 24 are connected, and the hydraulic motor 22 is connected to the main valve 31 by the spring 32.
The main valve 31 rotates while receiving the braking force regulated by the valve closing force of 1, and eventually stops, and the main valve 31 is also seated.

Thus, according to this circuit, the hydraulic motor 2
2, when the supply and discharge of hydraulic pressure is stopped, the hydraulic pressure acting on the second port 36 is initially maintained at a low pressure to prevent the generation of surge pressure, and then the second port 36 is stopped.
Since the brake force is applied by maintaining the hydraulic pressure at a high pressure, the hydraulic motor can be stopped smoothly.

Note that when pressure is supplied to the supply/discharge circuit 23 and the hydraulic motor 22 rotates in the opposite direction, the overload relief valve 21 operates in the same manner as the overload relief valve 20 described above during braking to prevent surges. Avoid pressure.

<Effects of the invention> In this invention, two overload relief valves with a surge pressure absorption function are provided in the travel hydraulic circuit to correspond to the switching of the supply and discharge of the overload relief valves. Since the piston forward state, which is a state in which pressure can be absorbed, is obtained by the traveling hydraulic pressure, the conventional piston forward spring can be omitted, and the overload relief valve can be made smaller accordingly. has.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of this invention and a longitudinal sectional view of an overload relief valve used in the circuit, and FIG. 2 is a longitudinal sectional view showing an example of a conventional pressure regulating valve. 20, 21...Overload relief valve, 22
... Hydraulic motor, 23, 24 ... Supply/discharge circuit, 30
... Valve body, 31 ... Main valve, 32 ... Spring, 33
...Piston, 34...Stopper, 35...1st
Port, 36...Second port, 38...Valve seat, 4
0...Aperture, 41...Inner chamber.

Claims (1)

[Scope of utility model registration request] Overload relief valves are provided in both supply and discharge circuits for the hydraulic motor for driving the traveling device, and the overload relief valves are connected to the first port and the second port.
A valve seat provided between the ports is pressed by a spring to close the valve hole, and as pressure increases on the second port side, the valve opens against the spring to communicate the first port and the second port. The main valve has an internal chamber that communicates with the second port through a throttle and has a smaller diameter than the valve seat, and a piston is accommodated in the internal chamber so as to be able to move forward and backward. A stopper is placed opposite to the rear surface, and a passage is provided that communicates the main valve and the back of the piston with a first port, the first port is connected to one of the supply/discharge circuits, and the second port is connected to the other supply/discharge circuit. A traveling hydraulic circuit characterized by being connected to.