JP2000330646A - Pressure reducing valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple valve structure equipped with a high pressure side oil pressure selecting function and a function as a pressure reducing valve by adopting a pressure reducing valve and a shuttle valve. SOLUTION: This pressure reducing valve is provided with a high pressure selecting function to be used as the signal pressure and/or driving pressure of an oil pressure control circuit and a pressure reducing function. Either an oil pressure introduced to a first input port 12a or an oil pressure introduced to a second input port 13a, which is higher, allows a center spool 16 to move to one side, and an oil pressure is generated in an output port 15a, and first and second pistons 19 and 20 are moved to the center. At that time, the oil pressure of the output port 15a is allowed to act on the piston in the pressure chamber whose input pressure is lower of first and second pressure chambers, and the piston is closely brought into contact with the end face of the center spool 16, and returned to the initial neutral position together with the center spool 16 according to a differential pressure based on a difference between the cross-sections of the piston and the center spool 16. Then, the reduced output pressure is generated in the output port 15a according to the pressure balance at that time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pressure reducing valve. In particular, the present invention relates to a pressure reducing valve that selects a higher one from two different input pressures, reduces the selected pressure, and outputs a pressure between the two input pressures.

[0002]

2. Description of the Related Art As a means for comparing two different pressures and outputting a pressure between the two pressures, for example, a technique disclosed in Japanese Patent Application Laid-Open No. 6-307330 is known.

That is, in a two-flowway type piston pump in which two independent discharge flow rates can be obtained from one cylinder barrel built in one pump body, a technique for outputting an average pressure of two discharge pressures is used. is there. More specifically, the following technology is used.

According to the two-flow-way type piston pump disclosed in the above publication, the maximum discharge amount is obtained when the discharge pressure is low, and high-speed operation is possible. On the other hand, when the resistance is high, that is, when the discharge pressure is high, the discharge amount is low. The speed is reduced and the low-speed operation is performed.

In this two-flowway type piston pump, the arc-shaped outer groove and the arc-shaped inner groove in the discharge stroke region of the valve plate which can communicate alternately with the outer opening hole and the inner opening hole of the cylinder barrel. A pressure communication passage is formed on the circumference passing through the pressure communication passage, and an intermediate pressure between the two discharge pressures is applied to the back surface of the swash plate angle control piston for controlling the discharge amount of the pump through the pressure communication passage. I have to.

That is, in the pressure communication passage, the piston alternately communicates with the outer opening hole and the inner opening hole of the cylinder barrel in the discharge stroke region in accordance with the rotation of the cylinder barrel, and connects the outer opening hole or the inner opening hole of the cylinder barrel. And alternately and instantaneously communicate with the discharge port. At this time, an intermediate pressure of the pressure of each discharge port is generated in the pressure communication passage. At this time, since the capacity on the pressure communication passage side is smaller than the capacity on the discharge port side, it hardly affects the discharge port side. Further, if an accumulator portion is provided in the pressure communication passage, pulsation caused by a difference between two discharge port pressures is smoothed, and if a throttle is provided between the pressure communication passages, an opening of a seal plate of the pressure communication passage is formed. size,
It is stated that deviation and pulsation of the value of the intermediate pressure due to conditions such as the position, the pressure of the pump and the system, the discharge amount, the number of rotations, and the response can be reduced.

[0007] However, in the two-flow-way type piston pump, pulsation cannot be suppressed unless the accumulator portion and the throttle are separately provided in the pressure communication path as described above, and the structure becomes complicated, and the number of processing steps is increased. , The number of parts also increases. In addition, in the technology disclosed in the above publication, it is difficult to maintain accuracy because a fine hole is required. Further, since the holes are minute, clogging of dust easily occurs. Furthermore, it can be integrated into the casing of the pump, but it is difficult to compare two different pressures and output a pressure between the two pressures as an independent valve body.

As means for comparing two different pressures and outputting a pressure between the two pressures, for example, the means shown in FIG. 4 or the means disclosed in Japanese Patent Application Laid-Open No. 9-242707 can be considered. That is, the higher pressure is selected by comparison with the shuttle valve, and the reduced pressure is output. This will be specifically described with reference to FIG. The figure shows the LS mounted on a conventional two-flow-way type piston pump.
2 shows an example of a control circuit of a control unit and a PC control unit.

According to this embodiment, the two discharge lines L1 and L2 of the two-flow-way type piston pump 1 are connected to different actuators (not shown) which are independently driven via operation valves (not shown). Is done. Further, a shuttle valve 2 is connected to the discharge lines L1 and L2, so that the hydraulic pressure on the high pressure side of either the discharge lines L1 or L2 is selected and introduced to the pressure reducing valve 3.
Further, the hydraulic pressure of each of the discharge lines L1 and L2 is connected to a signal pressure introduction port of the pressure reducing valve 3.

The hydraulic pressure on the high pressure side selected by the shuttle valve 2 is reduced to a predetermined pressure through a pressure reducing valve 3, and is introduced into a small diameter port of a control cylinder 4 for controlling the displacement of the pump 1. , LS valve 5 and PC valve 6 are connected to respective hydraulic pressure introduction ports 5b, 6b.
Signal pressure. On the other hand, the load pressure introduction port of the LS valve 5 and the introduction port of the pump discharge pressure are respectively provided with the load pressure from the hydraulic circuit of the actuator and the hydraulic pump 1.
The discharge pressure of the discharge lines L1 and L2 is introduced. The large-diameter port of the control cylinder 4 has the L
The discharge / discharge port of the S valve 5 is connected and the LS
The discharge / discharge port of the PC valve 6 is connected to the valve 5.

FIG. 4 shows a case where the actual LS differential pressure exceeds the set differential pressure of the LS valve 5 and the PC valve 6 is in a non-operating state, and the control cylinder 4 is pushed to the largest diameter side and inclined. Board 1a
Is maximized, the discharge flow rate of the two-flow-way type piston pump 1 is maximized, and the actuator is operated at high speed. At this time, when the discharge pressure of the two-way piston pump 1 increases and the actual LS differential pressure falls below the set differential pressure of the LS valve 5, the LS valve 5 is switched, and the pressure reducing valve 3 is also switched. The hydraulic pressure reduced to a predetermined pressure in 3 is introduced into the large-diameter-side oil chamber of the control cylinder 4 through the hydraulic pressure introduction port of the LS valve 5, and the tilt angle of the swash plate 1a is reduced to reduce the two-way type piston. The actuator is operated at a low speed with the discharge flow rate of the pump 1 minimized.

On the other hand, in the state shown in FIG. 4, when the load pressure during the operation increases and the discharge pressure of the two-flow-way type piston pump 1 increases, the pressure reducing valve 3 is switched as described above to a predetermined value. The pressure oil reduced to the pressure is introduced into the signal pressure introduction port of the PC valve 6, and the PC valve 6 is switched to supply the oil pressure to the large-diameter-side oil chamber of the control cylinder 4.
The discharge amount of the flowway type piston pump 1 is reduced. Conversely, when the load pressure decreases and the discharge pressure of the two-flow-way piston pump 1 decreases, the discharge amount of the two-flow-way piston pump 1 increases. As described above, the PC control and the LS control are performed at the same time, but when the actuator requests a high pressure and a large flow rate, the PC control is performed with priority over the LS control.

According to this example, even when controlling the swash plate angle by using the discharge pressure of the pump itself as the control drive pressure signal of the two-flow-way type piston pump 1, the pulsation is effectively performed because the pressure reducing valve is interposed. It is preferable because it is suppressed. However, in any case, a signal pressure necessary and sufficient to operate the control circuit of the two-flow-way type piston pump 1 must be ensured. To achieve this, a two-way pump 1
Shuttle valve 2 with the higher discharge pressure as the driving source for signal pressure
It is preferable to select and use them. Moreover, when performing the above-described total horsepower control for simultaneously controlling the horsepower of two or more pumps, it is preferable that the selected hydraulic pressure be reduced and introduced into the control device of each pump.

[0014]

As described above, a circuit that compares the pressures with the shuttle valve, selects the pressure on the high pressure side, reduces the pressure, and outputs the reduced pressure can be constituted by generally well-known equipment. However, the pressure selecting means and the pressure reducing means are completely different functions. For this reason, as in the control circuit shown in FIG. 4, the shuttle valve 2 and the pressure reducing valve 3 must be provided separately, which causes a problem that the number of parts increases and the number of pipes increases. On the other hand, it is conceivable to incorporate the pressure selecting means and the pressure reducing means into a single valve body. However, the two functions of the selecting means and the pressure reducing means have to be independent, so that the field area must be increased. There was no problem.

An object of the present invention is to provide a pressure reducing valve in which means for simultaneously realizing a pressure selecting function and a pressure reducing function are incorporated in a single valve body.

[0016]

According to the first aspect of the present invention, a first input port communicating with a first pressure chamber, a second input port communicating with a second pressure chamber, and the first pressure chamber are provided. A center spool that communicates the first pressure chamber or the second pressure chamber with the output port according to a pressure difference between the second pressure chamber and a pipe that introduces pressure of the output port into the third pressure chamber and the fourth pressure chamber; A first piston that moves according to the pressure difference between the first pressure chamber and the third pressure chamber, and a second piston that moves according to the pressure difference between the second pressure chamber and the fourth pressure chamber, The pressure receiving area of the center spool on the first pressure chamber side is the fourth piston of the second piston.
The pressure reducing valve is characterized in that it is smaller than the pressure receiving area on the pressure chamber side, and the pressure receiving area on the second pressure chamber side of the center spool is smaller than the pressure receiving area on the third pressure chamber side of the first piston.

According to the first aspect, the function of selecting the larger input pressure among the two input pressures despite the fact that it is constituted by a single valve body, and the function of selecting the selected input pressure by a predetermined ratio It has a function to reduce the pressure. Therefore, the number of parts is reduced. Further, it is not necessary to individually change various control valves of the conventional two-flow-way type piston pump. If incorporated in the pump body, the size of the device can be reduced. It can also be commonly used as a signal or control thickness source in hydraulic circuits.

The invention according to a second aspect is the invention according to the first aspect, wherein all the pressure receiving areas of the first piston and the second piston are the same, and all pressure receiving areas of the center spool are the same. The pressure receiving area of the center spool is half of the pressure receiving area of each piston.

The center spool is, for example, a first high pressure side.
An attempt is made to move to the second pressure chamber due to the pressure difference between the pressure chamber and the second pressure chamber on the low pressure side. Here, the second piston on the low pressure side tries to move toward the center spool due to the pressure difference between the second pressure chamber and the fourth pressure chamber, and the center spool and the second piston abut.

The force by which the center spool attempts to move toward the second pressure chamber is determined by the pressure acting on both end faces of the center spool and the pressure receiving area of each end face. Since the pressure receiving area of each end face is the same, the force to move to the right direction is the pressure of the first pressure chamber × the pressure receiving area.

The pressure acting on the end face of the second piston on the side of the fourth pressure chamber is a reduced output pressure. The left and right pressure receiving areas of the second piston are twice the pressure receiving area of the center spool. Accordingly, the force at which the second piston attempts to move to the high pressure side is 2 × the pressure of the first pressure chamber × the output pressure.

On the other hand, the value of the output pressure is determined by the movement amount of the center spool. The center spool and the second piston push each other to move in opposite directions. That is,
The balance is achieved at a position where the force of the center spool moving to the low pressure side and the force of the second piston moving to the high pressure side are equal. In the present invention, the output pressure to be reduced is １ ／ of the pressure in the first pressure chamber on the high pressure side.

According to a third aspect of the present invention, the third pressure chamber and the fourth pressure chamber
In one or both of the pressure chambers, a spring for moving the first piston or the second piston having a pressure receiving portion in each pressure chamber toward the center spool is provided so that the spring force can be adjusted. .

By interposing a spring in one or both of the third pressure chamber and the fourth pressure chamber so that the spring force can be adjusted, the pressure reduced by the pressure reducing valve is reduced by the value obtained by subtracting the spring force. The pressure can be further reduced, and the reduced pressure can be arbitrarily changed by adjusting the spring force.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG.
1 schematically shows the structure of a pressure reducing valve having a high pressure selecting function of the present invention.

In this embodiment, the pressure reducing valve 10 comprises a single valve body 11. In the valve body 11, a first pressure chamber 12 and a second pressure chamber 13 are formed on the left and right of a central portion.
The first input port 12a leading to the first pressure chamber 12 is
For example, one first discharge port 1 of a two-flow-way type piston pump 14 in which two independent discharge flow rates can be obtained from one cylinder barrel built in one pump body.
The second input port 13a connected to the second pressure chamber 13 is connected to the other second discharge port 1 of the pump 14.
4b.

The first and second pressure chambers 12, 13
The first and second pressure chambers 1 and 2 are provided in a spool sliding hole 15 connecting the first pressure chamber and the second pressure chamber 1 based on a pressure difference between two discharge pressures introduced into the first and second input ports 12a and 13a.
A center spool 16 reciprocating between 2 and 13 is interposed. On the peripheral surface of the center spool 16, a ring-shaped land portion 16a is left at the center, and 90 ° in the circumferential direction.
Notches 16 parallel to the eight axes for convenience with a phase difference of
b is formed. A ring-shaped oil passage 15a having substantially the same width as the land 16a is formed on the inner surface of the center of the spool sliding hole 15, and an output port 15b for pressure oil is formed in the oil passage 15a.

On the other hand, at the left and right ends of the valve body 11, a third pressure chamber 17 and a fourth pressure chamber 18 are formed on the same axis as the first pressure chamber 12 and the second pressure chamber 13. Third
A first piston 19 is interposed between the pressure chamber 17 and the first pressure chamber 12, and a second piston 20 is interposed between the fourth pressure chamber 18 and the second pressure chamber 13. Is equipped. Further, the third pressure oil introduction port 17a and the fourth pressure oil introduction port 18a formed in the third and fourth pressure chambers 17 and 18 and the output port 15a are connected to the oil passage 21 respectively.
a and 21b.

According to the present embodiment, the cross-sectional area of the center spool 16 is の of each of the cross-sectional areas of the first piston 19 and the second piston 20. Of course, the sectional area of the center spool 16 and the first piston 19 and the second
The ratio of the piston 20 to each cross-sectional area does not need to be 1: 2, and can be arbitrarily changed.

Next, the operation of the pressure reducing valve 10 will be described. Using the two-flow-way type piston pump 14,
The discharge pressure of the first discharge port 14a is 100 kg / cm ² , and the discharge pressure of the second discharge port 14b is 0 kg / cm ²
It is assumed that 100 of the first discharge port 14a
The discharge pressure oil of kg / cm ² is introduced into the first pressure chamber 12, and the discharge pressure oil of 0 kg / cm ² at the second discharge port 14 b is introduced into the second pressure chamber 13.

100 kg / c acting on the first pressure chamber 12
The pressure of m ² acts on the left end face of the center spool 16 and the right end face of the first piston 19. Also, the second pressure chamber 13
0kg / cm ² pressure acting on the center spool 1
6 and the left end surface of the second piston 20.
At this time, the pressure in the first pressure chamber 12 is higher than the pressure in the second pressure chamber 13. Therefore, the center spool 16 moves toward the second pressure chamber 13 (to the right in FIG. 1).

When the center spool 16 moves, the first pressure chamber 12 and the output port 15a communicate with each other via the notch 16b of the center spool 16. The opening area of the notch 16b with respect to the output port 15a is formed so as to increase continuously from zero. Therefore, the notch 16 b acts as a throttle by the movement of the center spool 16. The pressure at the output port 15a is reduced to a pressure lower than the pressure in the first pressure chamber 12.

The reduced pressure acts on the third and fourth pressure chambers 17 and 18 from the output port 15a. Output port 1
The pressure 5a is determined by both the openings of the notch 16b of the center spool 16, that is, the amount of movement of the center spool 16.

Here, the reduced pressure acts on the left end face of the first piston 19 and 100 kg / cm ² on the right end face.
Pressure acts. A pressure of 100 kg / cm ² is applied to the left end face of the center spool 16 and 0 kg is applied to the right end face.
/ Cm ² pressure acts. A pressure of 0 kg / cm ² acts on the left end face of the second piston 20, and a reduced pressure acts on the right end face.

As a result, the first piston 19 is moved by the pressure difference between the first pressure chamber 12 and the third pressure chamber 17.
Move to the left end of 7.

Next, the relationship between the center spool 16 and the second piston 20 will be described. The center spool 16 is the first
An attempt is made to move rightward in the figure due to the pressure difference between the pressure chamber 12 and the second pressure chamber 13. Here, the second piston 20 tends to move leftward due to the pressure difference between the second pressure chamber 13 and the fourth pressure chamber 18. That is, the center spool 1
6 and the second piston 20 abut.

The force by which the center spool 16 moves to the right in the figure is determined by the pressure acting on the left and right end faces and the pressure receiving area of the center spool both end faces. Here, since the pressure receiving area of the left and right end faces is S2 cm ² , the force to move rightward is 100 × S1 kg.

Since the left and right pressure receiving area S1 of the second piston 20 is twice the cross-sectional area S2 of the center spool 16,
2 × S2 cm ² . The pressure acting on the right end face is assumed to be a reduced pressure Ckg / cm ² . At this time, the second
The force by which the piston 20 moves to the left in the figure is 2 × S2 ×
(C-0) kg.

The value of C is determined by the amount of movement of the center spool 16 as described above. The center spool 16 and the second piston 20 push each other to move in opposite directions. In other words, the balance is achieved at a position where the force 100 × S2 of the center spool 16 moving rightward and the force 2 × S2 × (C-0) of the second piston 20 moving leftward are equal. Here, 100 × S2
= 2S2 × (C-0), C = 50 kg / cm ² .

Although the pressure reducing valve 10 according to the present embodiment is constituted by a single valve main body 11, it selects the higher one of the two hydraulic pressures having different pressures, and the pistons 19, 20. The pressure can be reduced and output based on the difference in the cross-sectional area between the center spool 16 and the center spool 16. In the present embodiment, a case will be described in which the control of two or more hydraulic pumps is applied to a self-pressure hydraulic assist control device that employs the discharge pressure of each pump as a signal pressure or a driving pressure. After selecting the maximum value of the discharge pressures of two or more hydraulic pumps, the selected pressure oil is depressurized, and is constituted by a single valve body that acts as a signal pressure or a drive pressure of two or more hydraulic pump control devices. Pressure reducing valve.

This pressure reducing valve is connected to, for example, L as shown in FIG.
The present invention can be applied to the control circuit of the two-flowway type piston pump 14 equipped with the S valve 5 and the PC valve 6. In this specific example, substantially the same members as those in the conventional example shown in FIG. 4 are denoted by the same reference numerals. As can be understood from FIG. 2, the output port 15a formed in the pressure reducing valve 10 is connected to the small-diameter-side hydraulic pressure introduction port 4a of the control cylinder 4 for controlling the swash plate angle of the two-flow-way type piston pump 14, and the LS valve 5 Hydraulic introduction port 5b, PC
It is connected to a signal pressure / drive pressure input port 6 a of the valve 6 and a hydraulic pressure introduction port 6 b of the PC valve 6.

In the embodiment shown in FIG. 2, the pump 14 reaches the maximum discharge amount when the control cylinder 4 is pushed to the largest diameter chamber side. The LS valve 5 controls the discharge amount of the pump 14 so as to keep the differential pressure between the discharge pressure of the pump 14 and the load pressure of the actuator constant. LS valve 5 is LS
The differential pressure between the pressure acting on the pressure introduction port 5c and the pressure acting on the pump pressure introduction port 5a is balanced at a position where the differential pressure balances the spring force of the spring 5d. The differential pressure is determined by the spring 5d.

To the pump pressure introducing port 5a, the higher one of the two discharge ports or the more important one of the discharge pressure oils as a hydraulic circuit is appropriately introduced.
A pressure corresponding to the maximum load pressure acting on the actuator in the circuit is introduced into the LS valve 5.

If the differential pressure acting on the LS valve 5 is small, the large-diameter chamber of the control cylinder 4 communicates with the tank, and the pump 14 increases the discharge amount. Conversely, if the differential pressure is large, the output pressure of the pressure reducing valve 10 is guided to the large-diameter chamber of the control cylinder 4, and the discharge amount of the pump 14 decreases.

The PC valve 6 determines the upper limit of the absorption horsepower of the pump 14. The absorption horsepower is generally represented by a product of a discharge amount and a discharge pressure. The set value of the PC valve 6 is determined by the output of an engine (not shown) that drives the pump 14.

According to the embodiment shown in FIG.
The discharge amount of the pump 14 is configured to decrease as the average value of the two discharge pressures of the pump 14 having the output pressure of 0 increases. When the output pressure of the pressure reducing valve 10 decreases, the large-diameter chamber of the control cylinder 4 communicates with the tank, and the pump 14 increases the discharge amount. Conversely, when the output pressure of the pressure reducing valve increases, the output pressure of the pressure reducing valve 10 is guided to the large-diameter chamber of the control cylinder 4, and the discharge amount of the pump 14 decreases.

FIG. 3 shows a partial structure of a pressure reducing valve 100 according to another embodiment of the present invention having a high pressure selecting function.
According to this embodiment, the force acting on the left end face of the first piston 19 on the third pressure chamber 17 side can be changed. A plug 120 is attached to an end of the third pressure chamber 107 of the valve body 101. The plug 120 has a set pressure changing member 121 and a spring force between the set pressure changing member 121 and the first piston 19 is Fk.
g compression spring 122 is provided. Therefore,
By changing the screwing amount of the set pressure changing member 121, the value of the spring force Fkg changes, and the force acting on the left end face of the first piston 19 changes.

For example, using the two-flow-way type piston pump 14, the discharge pressure of the first discharge port 14a is set to Ak.
g / cm ² and the discharge pressure of the second discharge port 14b is B
It is assumed that the pressure is kg / cm ² . First discharge port 1
4a of Akg / cm ² discharge pressure oil is supplied to the first pressure chamber 12
At the second discharge port 14b.
cm ² of discharge pressure oil is introduced into the second pressure chamber 13. Here, B> (A + F / pressure receiving area S1 of first piston 19)
And

Akg / cm ² acting on first pressure chamber 12
Pressure acts on the left end face of the center spool 16 and the right end face of the first piston 19. Further, the pressure of Bkg / cm ² acting on the second pressure chamber 13 acts on the right end face of the center spool 16 and the left end face of the second piston 20. At this time, since B> (A + F / S1), the center spool 16 moves toward the first pressure chamber 12 (to the left in FIG. 1).

When the center spool 16 moves, the second pressure chamber 12 and the output port 15a communicate with each other via the notch 16b of the center spool 16. The pressure Ckg / cm ^{2 at} the output port 15a is reduced to a pressure lower than the pressure Bkg / cm ² in the second pressure chamber 13.

The reduced pressure Ckg / cm ² acts on the third and fourth pressure chambers 107 (see FIG. 3) and 18 from the output port 15a. Output port 15a pressure Ckg / c
m ² is determined by the opening amount of the notch 16 b of the center spool 16, that is, the moving amount of the center spool 16.

Here, the left end face of the first piston 19 (the reduced pressure Ckg / cm ² × S1 + spring 1
22 spring force F / S 1 kg / cm ² )
A pressure of Akg / cm ² acts on the right end face. A pressure of Akg / cm ² acts on the left end face of the center spool 16, and a pressure of Bkg / cm ² acts on the right end face. Second
A pressure of Bkg / cm ² acts on the left end face of the piston 20, and a reduced pressure Ckg / cm ² acts on the right end face.

As a result, the first piston 19 exerts a difference (AC) between the pressure Akg / cm ² of the first pressure chamber 12 and the pressure (C × S1 + F / S1) acting on the left end face of the first piston 19.
× S1-F / S1) 3rd pressure chamber 1 by kg / cm ²
Attempt to move towards the left end of 7. The second piston 20 has a difference (B) between the pressure Bkg / cm ^{2 in} the second pressure chamber 13 and the pressure C × S1 acting on the right end face of the second piston 20.
−C × S1) Move toward the right end of the fourth pressure chamber 18 by kg / cm ² .

On the other hand, the center spool 16 has a pressure difference between the first pressure chamber 12 and the second pressure chamber 13 (BA) kg / cm.
^It tries to move to the left in the figure by ² . Here the first
The piston 19 tends to move leftward due to the pressure difference (C-A-F / S1) kg / cm ² between the first pressure chamber 12 and the third pressure chamber 107. That is, the center spool 1
6 and the second piston 20 abut.

The force by which the center spool 16 attempts to move to the left in the figure is determined by the pressure acting on the left and right end faces and the pressure receiving area on both end faces of the center spool. Here, the pressure receiving areas of the left and right end surfaces of the center spool 16 are represented by S
Assuming 2cm ² , the force to move to the left is B ×
S2kg.

The first piston 19 has a left and right pressure receiving area S1 that is twice as large as the cross-sectional area S2 of the center spool 16.
2 × S2 cm ² . The pressure acting on the left end face of the first piston 19 is (A + F / S1) kg / cm ² . At this time, the force by which the first piston 19 moves rightward in the drawing is B × 2 × S2 kg.

The value of C is determined by the amount of movement of the center spool 16 as described above. The center spool 16 and the first piston 19 press against each other to move in opposite directions. In other words, the position is balanced at a position where the force B × S2 of the center spool 16 moving leftward and the force C × 2 × S2 + F of the first piston 19 moving rightward are equal. Here, B × S2 = C × 2 × S2 +
By F, C = B / 2−Fkg / cm ² .

That is, as described above, the compression spring 1
By interposing 22 in the third pressure chamber 107, the pressure reduced by the pressure reducing valve can be further reduced by the spring force of the spring 122, and the reduced pressure can be adjusted by adjusting the spring force of the compression spring 122. Can be changed arbitrarily.

The force acting on the piston by the spring 122 may be changed not only in the third pressure chamber 17 but also in the fourth pressure chamber 18. In this case, the set pressure changing member 121 and the compression spring 122 described above may be attached to the fourth pressure chamber 17.
When the set pressure of both the third pressure chamber 17 and the fourth pressure chamber 18 is changed, a difference may be made between the spring forces of the compression springs arranged respectively.

As can be understood from the above description, the pressure reducing valve having the high pressure selecting function of the present invention can be selected as the highest input pressure among a plurality of introduction pressures by a simple processing into a single valve body. The input pressure can be reduced and output at a predetermined ratio, and can be easily incorporated into the conventional variable displacement hydraulic pump without greatly changing the structure of the conventional variable displacement hydraulic pump. Since the self-pressure type hydraulic assist control device of the two-flowway type displacement pump having two or more discharge ports can be used as it is, there is no need to particularly change the configuration of the hydraulic pump.

The present invention is not applied only to a pump. For example, a case in which the present invention is applied to a traveling device of a construction machine having two motors may be considered. At this time, the load pressure of the two motors can be detected as the input pressure, and the average value as the output pressure can be detected as the signal pressure.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a configuration example of a pressure reducing valve having a high pressure selecting function according to the present invention.

FIG. 2 shows an example of a control circuit diagram when the pressure reducing valve is applied to a two-flow-way displacement hydraulic pump.

FIG. 3 is a sectional view partially showing another configuration example of the pressure reducing valve having the high pressure selecting function of the present invention.

FIG. 4 shows an example of a control circuit diagram applied to a conventional two-flowway displacement hydraulic pump.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 2 Flowway type piston pump 2 Shuttle valve 3 Pressure reducing valve 4 Control cylinder 5 LS valve 5a Hydraulic pressure introduction port 6 PC valve 6a Signal pressure / drive pressure input port 6b Hydraulic pressure introduction port 10, 100 Pressure reducing valve provided with high pressure selection function 11 , 101 Valve body 12 First pressure chamber 12a First input port 13 Second pressure chamber 13a Second input port 14 2 Flowway type hydraulic pump 14a First discharge port 14b Second discharge port 14c Swash plate 15 Spool sliding hole 15a Ring-shaped oil passage 15b Output port 16 Center spool 16a Ring-shaped land 16b Oil passage 17,107 Third pressure chamber 17a Third pressure oil introduction port 18 Fourth pressure chamber 18a Fourth pressure oil introduction port 19 First piston 20 First 2 piston 21a, 21b Oil passage 120 Plug 121 Set pressure change Member 122 compression spring

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3H056 AA09 BB32 CA02 CA03 CB02 CB07 CD02 DD03 EE06 GG12 3H089 DA03 DB05 EE17 GG02 5H316 AA18 AA20 BB09 CC02 DD12 EE10 EE17 EE22 EE26 ES02 FF02 GG15 HH11 JJ15 GG15 HJ11

Claims (3)

[Claims] A first input port (1) leading to a first pressure chamber (12).
2a), a second input port (13a) communicating with the second pressure chamber (13), and a first pressure chamber according to a pressure difference between the first pressure chamber (12) and the second pressure chamber (13). (12) or the second pressure chamber (13) to the output port (1
The center spool (16) communicating with 5a) and the pressure of the output port (15a) are supplied to the third pressure chamber (17) and the fourth pressure chamber.
(18) a pipe, a first piston (19) that moves according to a pressure difference between the first pressure chamber (12) and the third pressure chamber (17), and a second pressure chamber (13). A second piston (20) that moves in accordance with a pressure difference from the fourth pressure chamber (18). The pressure receiving area of the center spool (16) on the first pressure chamber (12) side is equal to the second piston (20). ) Is smaller than the pressure receiving area on the fourth pressure chamber (18) side, and the pressure receiving area on the second pressure chamber (13) side of the center spool (16) is on the third pressure chamber (17) side of the first piston (19). A pressure reducing area smaller than the pressure receiving area of the pressure reducing valve. 2. The pressure receiving areas of the first piston (19) and the second piston (20) are all the same, and the pressure receiving areas of the center spool (16) are the same. The pressure receiving area of each piston (19,2
2. The pressure reducing valve according to claim 1, wherein the pressure receiving area is 1/2 of the pressure receiving area. 3. A first piston (19) or a second piston (19) having a pressure receiving portion in each of the pressure chambers (17, 18) in one or both of the third pressure chamber (17) and the fourth pressure chamber (18). The pressure reducing valve according to claim 1 or 2, wherein springs for moving the pistons (20) toward the center spool (16) are provided so that their spring forces can be adjusted.