JPH0212313B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a low pressure selection valve suitable for a flushing valve in a hydraulic closed circuit for driving an actuator.

FIG. 1 shows a conventional hydraulic closed circuit for driving an actuator. A double tilting hydraulic pump 1 and an actuator 2 are connected by main circuits 3 and 4 to form a closed circuit. The low pressure selection valve 5 connects the lower pressure one of the main circuits 3 and 4 to the low pressure circuit 6, and discharges excess oil into the tank 7. Charge circuit 8
It consists of a charge pump 9, check valves 10 and 11, and a relief valve 12, and supplies oil so that the main circuits 3 and 4 do not become under negative pressure. The poppet type switching valves 13 and 14 maintain the stop position when the actuator 2 is stopped, and thus prevent oil from leaking from the high pressure side of the actuator 2 through the main circuits 3 and 4 and the hydraulic pump 1 to the low pressure side.
Although not shown, the poppet type switching valves 13 and 14 have a function of switching to the open position when the actuator 2 is operated.

In FIG. 1, the internal leakage of the actuator 2 is very small, and the internal leakage of the hydraulic pump 1 is prevented by the poppet type switching valves 13 and 14, but there is no internal leakage in the low pressure selection valve 5. Therefore, there was a drawback that the stop position of the actuator 2 could not be accurately maintained.

An example of a conventional low pressure selection valve is shown in FIG. A core part 15 connected to the low voltage circuit 6 is provided in the center, and core parts 16 and 17 connected to the main circuits 3 and 4 are provided on the left and right sides of the core part 15, respectively. Between the land portions 18 and 1
9 is formed. A spool valve body 20 is disposed astride the core portions 16, 15, and 17, and the spool valve body 20 is provided with spool land portions 21, 22 that slide on the land portions 18, 19. Pressure receiving chambers 23 and 24 are formed on the left and right outer sides of the spool valve body 20, and the pressure receiving chambers 23 and 24 are connected to the core portions 16 and 17.
and communicate with each other through communication holes 25 and 26. 27,2
8 is a return spring, 29 is a housing, and 30 and 31 are notches.

When there is no pressure difference between the main circuits 3 and 4, the spool valve body 20 is in the position shown in FIG. 2, and the spool lands 21 and 22 are in contact with the lands 18 and 19. , 19 are closed, and the circuit between the core parts 16, 17 and the core part 15 is closed. For example, when the pressure in the main circuit 3 becomes higher than the pressure in the main circuit 4, the spool valve body 20 moves to the right in FIG.
9, the land portion 19 opens and the circuit between the core portions 17 and 15 is opened. During such switching, since the notches 30 and 31 are cut, the oil flow is gradually cut off, so that the switching is smooth and there is no vibration or pressure trapping. However, between the spool valve body 20 and the housing 29, in order to prevent the spool valve body 20 from sticking, there is normally a diametrical clearance of several tens of microns, and a large amount of internal leakage occurs from this clearance.

Although the above-mentioned drawbacks can be solved by using the known low pressure selection valve shown in FIG. 3, other problems arise. The low pressure selection valve shown in Fig. 3 has a poppet valve body 3.
2 and 33 are arranged with a push rod 34 interposed therebetween,
Place the poppet seat parts 35 and 36 on the seat surface 3.
7 and 38. In this structure, there is no pressure difference between the main circuits 3 and 4, and there is an open circuit between the core parts 16 and 17 and the core part 15, so if the main circuit 3 becomes high pressure from this state, for example, Core part 16 to core part 15
A blow-through occurs and switching becomes impossible. Alternatively, there is a problem in that the actuator 2 suddenly starts to switch when a certain amount or more of pressure oil has blown through.

The object of the present invention is to solve the above-mentioned drawbacks and problems and to provide a low-pressure selection valve that can be switched smoothly and completely eliminate internal leaks.

In order to achieve this object, the present invention provides a first valve body which is arranged to be movable in the direction of the first core part by the pressure of the second core part, and a first valve body which is arranged to be movable in the direction of the first core part by the pressure of the third core part. A second valve body disposed so as to be movable in the direction of the first core part is connected to the pressure of the second core part and the third valve body.
A spool is provided on each of the first and second valve bodies and slides on a land portion formed between the three core portions. A land portion and a poppet seat portion that contacts the seat surface formed outside the land portion are provided, and when the pressure difference between the two main circuits is smaller than a predetermined value, the spool land portion causes the second
and closes the communication between the third core part and the first core part, and when the pressure difference is greater than a predetermined value, the poppet seat part closes the communication between the second and third core parts, which has a higher pressure, and the first core part. It is characterized by the fact that communication between the department and the department is closed.

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

FIG. 4 shows an embodiment of the present invention. Components similar to those in FIGS. 2 and 3 are designated by the same reference numerals.

A first valve body 39 that moves toward the core portion 15 due to the pressure in the pressure receiving chamber 23, and a second valve body 4 that moves toward the core portion 15 due to the pressure in the pressure receiving chamber 24.
0 and the push rod 41 are placed in between so as to be interlocked with each other. Each valve body 39, 40 has a seat surface 37, 38 having a spool land portion 42, 43 that slides on the land portion 18, 19, respectively, and a poppet seat portion 44, 45 that contacts the seat surface 37, 38, respectively. , land portions 18, 19
formed on the outside. Pressure receiving chambers 23, 24
communicate with the core parts 16 and 17 through communication holes 25 and 26, respectively.

When the pressure difference between the two main circuits 3, 4 is smaller than a predetermined value, the valve bodies 39, 40 are in the neutral position shown in FIG. , the spool land portions 42 and 43 are in contact with the land portions 18 and 19. Therefore, the communication between the core parts 16, 17 and the core part 15 is through the spool land parts 42, 4.
Closed by 3.

For example, when the main circuit 3 becomes high pressure and the pressure difference becomes larger than a predetermined value, the core part 16 and the pressure receiving chamber 23
becomes high pressure, and the valve body 39, push rod 41 and valve body 4
0 are inserted as one to the right. As a result, first, the spool land portion 43 of the valve body 40 comes off from the land portion 19, and the core portion 17 and the core portion 15
The main circuit 4 on the low voltage side is connected to the low voltage circuit 6.
connected to. Further, as the valve bodies 39 and 40 move to the right, the poppet seat part 44 of the valve body 39 comes into contact with the seat surface 37, completely cutting off the communication between the core part 16 and the core part 15. .

In the switching process, while the spool land portion 42 of the valve body 39 slides on the land portion 18, the valve body 39
While moving to the right, the notch 30 provided in the spool land portion 42 and the spool land portion 42
through the clearance between and the land portion 18,
Because a small amount of oil flows, switching is smooth without vibration or pressure trapping. Valve body 39
At the stroke end where the poppet seat portion 44 contacts the seat surface 37, the communication is completely cut off, thereby eliminating internal leakage.

Even when the main circuit 4 is on the high pressure side, it operates in the same way, switching is performed smoothly, and complete switching is performed without internal leakage at the end of the stroke.

In addition, in FIG. 4, the push rod 41 is connected to the valve body 3.
It can also be integrated with either one of 9 and 40.

FIG. 5 shows another embodiment of the invention. In this embodiment, two valve bodies 39 and 40 are hydraulically interlocked.

A cylinder hole 4 is provided on the outside of the pressure receiving chambers 23 and 24.
Pistons 48, 49 formed with 6, 47 and slidably disposed within cylinder holes 46, 47 are connected to valve bodies 39, 40 by rods 50, 51, respectively. Two hydraulic chambers 5 are formed inside the cylinder holes 46 and 47 by pistons 48 and 49, respectively.
It is divided into 2a, 52b, 53a, and 53b. The hydraulic chambers 52a and 53b are provided with passages 54a and 54b in the core portion 16, respectively.
55b, and the hydraulic chambers 52b, 53a
are connected to the core portion 17 via passages 54b and 55a. 56a and 56b, 57a and 57b are return springs set to the same mounting spring pressure, and 58 is a relief valve provided in the low pressure circuit 6.

When the pressure difference between the two main circuits 3, 4 is smaller than a predetermined value, the valve bodies 39, 40 are in the neutral position shown in FIG.

For example, when the pressure in the main circuit 3 and the core section 16 becomes higher than the pressure in the main circuit 4 and the core section 17, the pressure difference between the core section 16 and the core section 15 passes through the pressure receiving chamber 23 communicated with the core section 16 to the valve body 39. At the same time, the pressure difference between the core portion 16 and the core portion 17 acts on the piston 48 within the hydraulic chambers 52a and 52b, thereby causing the valve body 39 to move to the right. The effective pressure receiving area of the piston 48 is large enough to move the valve body 39 to the right even if the pressure difference between the pressure receiving chamber 23 and the core portion 15 does not act on the valve body 39. At the same time, the core part 16 and the core part 17
A pressure difference between the piston 4 and the hydraulic chambers 53a and 53b
9, the valve body 40 moves to the right. At this time, since the pressure difference between the core part 15 and the pressure receiving chamber 24 communicating with the main circuit 4 on the low pressure side is a small value that can be almost ignored,
The pressure difference between the core portion 15 and the pressure receiving chamber 24 does not become a hindrance. Therefore, the spool land portion 43 of the valve body 40 comes off from the land portion 19, and communication between the core portions 17 and 15 is opened. Furthermore, the poppet seat portion 44 of the valve body 39 comes into contact with the seat surface 37, and communication between the core portions 16 and 15 is completely cut off.

In other words, the cylinder holes 46, 47, the piston 4
8, 49, rod 50, 51, valve body 39, 40,
Hydraulic chambers 52a, 52b, 53a, 53b, passage 5
4a, 54b, 55a, 55b, return spring 56
a, 56b, 57a, 57b are valve bodies 39, 40
It has a function as an interlocking means for interlocking the core parts 16 and 17 according to the pressure difference between the core parts 16 and 17.

The embodiment of FIG. 5 can also exhibit the same effect as the embodiment of FIG. 3.

As explained above, according to the present invention, the first valve body is arranged to be movable in the direction of the first core part by the pressure of the second core part, and the first valve body is arranged to be movable in the direction of the first core part by the pressure of the third core part. A second valve body disposed so as to be movable in the direction of the first core part is connected to the pressure of the second core part and the third valve body.
A spool is provided on each of the first and second valve bodies and slides on a land portion formed between the three core portions. A land portion and a poppet seat portion that contacts the seat surface formed outside the land portion are provided, and when the pressure difference between the two main circuits is smaller than a predetermined value, the spool land portion causes the second
and closes the communication between the third core part and the first core part, and when the pressure difference is greater than a predetermined value, the poppet seat part closes the communication between the second and third core parts, which has a higher pressure, and the first core part. Since the communication between the two parts is closed, smooth switching is possible, and internal leakage can be completely eliminated.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional hydraulic closed circuit for starting an actuator using a low-pressure selection valve, Figure 2 is a sectional view showing an example of a conventional low-pressure selection valve, and Figure 3 is another example of a conventional low-pressure selection valve. FIG. 4 is a cross-sectional view showing one embodiment of the present invention, and FIG. 5 is a cross-sectional view showing another embodiment of the present invention. 3, 4...Main circuit, 5...Low pressure selection valve, 6...
Low voltage circuit, 15, 16, 17... core part, 18,
19... Land portion, 37, 38... Seat surface, 3
9, 40... Valve body, 41... Push rod, 42, 43
... Spool land part, 44, 45 ... Poppet seat part, 46, 47 ... Cylinder hole, 48, 4
9... Piston, 50, 51... Rod, 52
a, 52b, 53a, 53b...hydraulic chamber, 54
a, 54b, 55a, 55b... passage, 56a,
56b, 57a, 57b...Return spring.

Claims (1)

[Claims] 1 A first core part connected to a low voltage circuit is provided in the center, and second and third core parts each connected to two main circuits that switch between high and low voltages are provided on the left and right sides of the first core part, respectively. By forming a land portion between the three core portions and moving the valve body based on the pressure difference between the second and third core portions, the lower pressure of the second and third core portions is reduced. In the low pressure selection valve, the first valve body is arranged to be movable in the direction of the first core part by the pressure of the second core part, and the third core part is arranged to be movable in the direction of the first core part. A second valve body disposed so as to be movable in the direction of the first core part by the pressure of the second core part is interlocked according to the pressure difference between the pressure of the second core part and the pressure of the third core part. An interlocking means is provided, and each of the first and second valve bodies is provided with a spool land portion that slides on the land portion, and a poppet seat portion that comes into contact with a seat surface formed outside the land portion. A low pressure selection valve characterized by: