JP2021003986A - Hydraulic servo device - Google Patents

Abstract

To provide a hydraulic servo device configured so that inconvenience that a servo cylinder operates greatly can be suppressed even if an electromagnetic control valve breaks down.SOLUTION: The hydraulic servo device comprises: a pair of control passages 11 individually communicating with two oil chambers 10s of a servo cylinder 10; a pair of electromagnetic control valves 20 that individually supply the pair of control passages 11 with hydraulic oil from a hydraulic oil pump 12; a pair of on-off valves 30 that individually control flowing of the hydraulic oil through the control passages 11; and drain passages 13 communicating with the pair of control passages 11. The on-off valves 30 close the control passages 11 when pressure of the control passages 11 is less than a set value, and open the control passages 11 when the pressure reaches the set value or more. The on-off valves 30 close the drain passages 13 communicating with the other control passages 11 accompanying the closing, and the on-off valves 30 open the drain passages 13 communicating with the other control passages 11 accompanying the opening.SELECTED DRAWING: Figure 1

Description

The present invention relates to a hydraulic servo device for hydraulically shifting a continuously variable transmission.

As a hydraulic servo device having the above configuration, Patent Document 1 includes a double-acting servo cylinder that controls the angle of the slant plate of the hydrostatic continuously variable transmission, and operates individually for a pair of oil chambers of the servo cylinder. A configuration with a proportional control valve for supplying and discharging oil is described.

In Patent Document 1, the amount of depression of the speed change pedal is detected by a potentiometer, the angle of the swash plate is detected by the slop plate angle sensor, and when the speed change pedal is depressed, the proportional control valve is operated based on the detection signal of the potentiometer. By doing so, the servo cylinder is operated. Further, when the servo cylinder is operated, the swash plate angle sensor feeds back the swash plate angle to control the servo cylinder to be operated by an amount corresponding to the stepping amount.

JP-A-2010-234863

In the configuration of controlling a pair of electromagnetic control valves (proportional control valve in Patent Document 1) as described in Patent Document 1, if the electromagnetic control valve fails, the servo cylinder cannot be properly controlled, and the driver There is a possibility that the running speed will be set against your will.

For this reason, there is a need for a hydraulic servo device that can suppress the inconvenience that the servo cylinder operates significantly even if the electromagnetic control valve that controls the double-acting servo cylinder fails.

The characteristic configuration of the hydraulic servo device according to the present invention is a double-acting servo cylinder that shifts a stepless speed changer, a pair of control flow paths that individually communicate with two oil chambers of the servo cylinder, and a pair. An electromagnetic control valve provided in each of the pair of control flow paths for individually supplying hydraulic oil from the hydraulic oil pump to the control flow path, and the control in response to a pressure change in the pair of control flow paths. A pair of on-off valves arranged in the pair of flow paths of the control flow path and a drain flow path communicating with the pair of the control flow paths are provided to individually control the flow of the hydraulic oil in the flow path. The on-off valve closes one of the control flow paths corresponding to the on-off valve when the pressure of the control flow path is less than the set value, and when the pressure reaches the set value or more, the on-off valve is connected to the on-off valve. When one of the pair of the on-off valves closes one of the control flow paths, the on-off valve is linked to the closing of the control flow path of the other. When the drain flow path communicating with the road is closed and one of the pair of on-off valves opens one of the control flow paths, the opening is linked to the other to communicate with the control flow path. The point is to open the drain flow path.

According to this characteristic configuration, when hydraulic oil is supplied from the hydraulic oil pump to one of the control flow paths by the electromagnetic control valve, the pressure of the hydraulic oil supplied to the control flow path provides the control flow path. The on-off valve is opened, and hydraulic oil is supplied to one of the oil chambers of the servo cylinder. When the servo cylinder operates by supplying the hydraulic oil to one oil chamber in this way, the hydraulic oil discharged from the other oil chamber passes through the drain flow path that communicates with the other control flow path. It is discharged from the on-off valve that is in the open state.
In this configuration, when the hydraulic oil cannot be discharged as in the case where one of the solenoids of the pair of electromagnetic control valves is disconnected, the on-off valve of the control flow path where the hydraulic oil cannot be discharged is maintained in a closed state, resulting in the result. As a result, the hydraulic oil is not discharged from the oil chamber of the servo piston, and there is no inconvenience of causing the servo piston to malfunction.
Therefore, a hydraulic servo device is configured in which the servo cylinder does not operate significantly even if the electromagnetic control valve that controls the double-acting servo cylinder fails.

As a configuration added to the above configuration, the on-off valve is held at a closed position in which one of the control flow paths is blocked by a spring-forced force when the pressure of the control flow path is less than the set value, and the control flow is maintained. An on-off valve body that operates in an open position that opens one of the control flow paths against the spring-forced force when the road pressure reaches the set value or more is provided, and the on-off valve body is in the closed position. It has a drain portion that closes the drain flow path that communicates with the other control flow path in some cases and communicates the drain flow path that communicates with the other control flow path to the discharge side when it is in the open position. You may.

According to this, when hydraulic oil is supplied to the control flow path, the on-off valve body is opened by the pressure of the hydraulic oil, and the hydraulic oil can be supplied from the control oil passage to one oil chamber of the servo cylinder. .. In conjunction with this, the drain portion of the on-off valve body enables the flow of hydraulic oil discharged from the other oil chamber to the drain flow path. This activates the servo cylinder. On the other hand, when neither of the pair of electromagnetic control valves operates, the hydraulic oil does not flow into either of the pair of control flow paths and the pair of drain flow paths, and the servo cylinder is constrained.

As a configuration added to the above configuration, the on-off valve is housed in a pair of on-off valve holes formed in a block-shaped valve housing, and the valve housing has a pair of the control flow path and a pair of the drain flow paths. The on-off valve unit may be formed by forming and, and the pair of on-off valve holes may be arranged at positions symmetrical with respect to a predetermined center point of the valve housing.

According to this, a pair of on-off valve holes are formed in the block-shaped material forming the valve housing, the on-off valves are arranged in each on-off valve hole in the inserted state, and the block-shaped material is paired with a pair of control flow paths. The on-off valve unit can be formed by forming the drain flow path of the above. In particular, when forming an on-off valve hole in a block-shaped material, the block-shaped material is fixed to a table or the like of a machine tool so that it can rotate at a center point, and one on-off valve hole is drilled by drilling or the like. A pair of on-off valve holes can be formed without arranging the tools at different positions by forming the portions, then rotating the table 180 °, and then drilling holes again using the same tool.

In addition to the above configuration, the pair of on-off valve holes are formed in the valve housing in a parallel posture, and the on-off valve has a supply side port capable of delivering hydraulic oil to the oil chamber, and hydraulic oil. A first composite flow path for communicating the supply side port of one on-off valve and the drain-side port of the other on-off valve to the valve housing, and the other A second composite flow path is formed to communicate the supply side port of the on-off valve and the drain side port of one of the on-off valves, and the first composite flow path communicates with one of the oil chambers to communicate with the first oil chamber. The two composite flow paths may communicate with the other oil chamber.

According to this, the pair of composite flow paths has the functions of a control flow path and a drain flow path. For example, when hydraulic oil is supplied from a hydraulic oil pump to one on-off valve, it opens and closes. The valve opens, and along with this opening, hydraulic oil is supplied from one composite flow path (for example, the first composite flow path) to one oil chamber of the servo cylinder from the supply side port. Further, in the state where one on-off valve is opened in this way, the hydraulic oil discharged from the other oil chamber of the servo cylinder flows into the other composite flow path (for example, the second composite flow path), and the open / close state is open. It is discharged from the drain side port of the valve. By forming a pair of composite flow paths in the valve housing in this way, it is not necessary to form a pair of control flow paths and a pair of drain flow paths between the valve housing and the servo cylinder, and the valve housing is compact. Not only can this be achieved, but the number of processing steps for forming the flow path can be reduced.

It is a hydraulic circuit diagram of a continuously variable transmission and a servo device. It is sectional drawing of the electromagnetic proportional pressure reducing valve in the state which shuts off hydraulic oil. It is sectional drawing of the electromagnetic proportional pressure reducing valve in the state of supplying hydraulic oil. It is sectional drawing of the valve housing.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Basic configuration]
FIG. 1 shows a hydrostatic continuously variable transmission A that continuously shifts the driving force of the engine E and transmits the driving force to the traveling mission case 1, and a hydraulic servo device that shifts the continuously variable transmission A by flood control. The hydraulic circuit with B is shown.

The continuously variable transmission A and the hydraulic servo device B indicate those provided in a vehicle such as a tractor, and the hydraulic servo device B indicates a forward direction according to the amount of depression when the accelerator pedal is depressed. The continuously variable transmission A is operated to increase the traveling speed in the reverse direction.

[Continuous variable transmission]
As shown in FIG. 1, the continuously variable transmission A includes a variable displacement hydraulic pump P driven by an engine E and a hydraulic motor M that transmits a driving force to a traveling mission case 1. The continuously variable transmission A includes a pair of drive oil passages 2 for supplying hydraulic oil from the hydraulic pump P to the hydraulic motor M, and the hydraulic motor is adjusted by adjusting the amount of hydraulic oil delivered from the hydraulic pump P. The driving speed of the M is controlled to set the traveling speed of the vehicle.

The continuously variable transmission A includes a charge pump 3 driven by an engine E, and hydraulic oil sent from the charge pump 3 is supplied to a pair of drive oil passages 2 via a charge circuit 4. The charge circuit 4 includes a plurality of relief valves and a pair of check valves, and supplies hydraulic oil to the drive oil passage 2 when the pressure in the drive oil passage 2 drops due to a leak or the like.

The hydraulic pump P is an axial plunger type having a plurality of plungers, and controls the forward speed for rotating the hydraulic motor M in the forward direction by setting the angle (swash plate angle) of the swash plate (not shown), and the hydraulic motor. It is possible to control the reverse speed to reverse the speed.

By setting the swash plate to the preset neutral posture, the hydraulic oil does not flow into the pair of drive oil passages 2, the hydraulic motor M stops, and the running stops. In this continuously variable transmission A, by tilting the swash plate to one side from the neutral posture, hydraulic oil flows to the forward side in the pair of drive oil passages 2, and the vehicle body can move forward. On the other hand, by tilting the swash plate to the other side, hydraulic oil flows to the reverse side in the pair of drive oil passages 2, and the vehicle body can move backward.

[Flood servo servo device]
The hydraulic servo device B is provided with a double-acting servo cylinder 10 so as to set the angle of the inclined plate, and also has a control flow path 11 for supplying and discharging hydraulic oil to a pair of oil chambers 10s of the servo cylinder 10 and a control flow. An electromagnetic proportional pressure reducing valve 20 (an example of an electromagnetic control valve) for supplying hydraulic oil from the hydraulic oil pump 12 to the road 11 is provided.

Further, the hydraulic servo device B includes an on-off valve 30 in the flow path of the control flow path 11 for supplying hydraulic oil from the electromagnetic proportional pressure reducing valve 20 to the oil chamber 10s of the servo cylinder 10. The on-off valve 30 is closed when the pressure of the control flow path 11 is less than the set value, and is opened when the pressure is equal to or higher than the set value, so that the flow of hydraulic oil in the pair of control flow paths 11 can be individually separated. To control. The drain flow path 13 communicating with the pair of control flow paths 11 is connected to the drain side port 8 of the on-off valve 30.

FIG. 1 shows a drain flow path 13 having an on-off valve 30 in each of the pair of control flow paths 11 and branching from the pair of control flow paths 11, which are the control flow path 11 and the drain. A circuit developed to make it easier to understand the function with the flow path 13 is shown. That is, the pair of on-off valves 30 are housed in the valve housing 5 shown in FIG. 4, and the composite flow path F formed in the valve housing 5 has the functions of both the control flow path 11 and the drain flow path 13. doing. The composite flow path F will be described later.

The servo cylinder 10 accommodates the piston 10b so as to be slidable in the cylinder 10a, links the piston rod 10c connected to the piston 10b to the swash plate of the hydraulic pump P, and urges the piston rod 10c to the neutral position. It has.

In the servo cylinder 10, an oil chamber 10s is formed inside the cylinder 10a at a position sandwiching the piston 10b. From such a configuration, when the pressure acting on the pair of oil chambers 10s is reduced, the piston 10b is returned to the neutral position by the urging force of the neutral spring 10d, and the swash plate is operated to the preset neutral posture. ..

[Flood servo servo device: Electromagnetic proportional pressure reducing valve]
As shown in FIGS. 2 and 3, the electromagnetic proportional pressure reducing valve 20 has a sleeve 22 internally fitted in a case 21 and slidably accommodates the spool 23 with respect to the sleeve 22, and the solenoid that operates the spool 23 is operated. The solenoid unit 24 is provided outside the case 21.

The sleeve 22 includes a pump port 22p to which hydraulic oil is supplied from the hydraulic oil pump 12, a supply port 22a to send hydraulic oil to the control flow path 11 (see FIG. 1), and a tank port 22t to discharge hydraulic oil. ing. The spool 23 has a first land portion 23a that controls the flow of hydraulic oil from the pump port 22p to the supply port 22a, and a second land portion 23b that controls the flow of hydraulic oil from the supply port 22a to the tank port 22t. I have.

As shown in FIG. 2 in the OFF state in which the electromagnetic proportional pressure reducing valve 20 does not supply a current to the electromagnetic solenoid unit 24, the hydraulic oil of the supply port 22a is supplied to the tank port 22t in a state where the supply of the hydraulic oil from the pump port 22p is cut off. The spool 23 is held at a position where it is discharged to. As a result, the hydraulic oil in the control flow path 11 is discharged from the tank port 22t.

Further, as shown in FIG. 3, the electromagnetic proportional pressure reducing valve 20 has a pump port 22p in a state of blocking the flow of hydraulic oil from the supply port 22a to the tank port 22t in an ON state in which a current is supplied to the electromagnetic solenoid unit 24. Supply the hydraulic oil from the supply port 22a to the supply port 22a. As a result, the hydraulic oil from the hydraulic oil pump 12 is supplied to the control flow path 11.

The electromagnetic solenoid unit 24 is provided with a spring that holds the spool 23 at the OFF position shown in FIG. 2 in a state where no current is supplied. When the current supplied to the electromagnetic solenoid unit 24 is increased in the above-mentioned ON state, the electromagnetic solenoid unit 24 is provided. Along with this increase, the operating amount of the spool 23 is increased to enable an increase in the flow rate of the hydraulic oil supplied to the control flow path 11.

[Flood servo servo device: on-off valve]
In the hydraulic servo device B, as shown in FIG. 4, a pair of on-off valves 30 are accommodated in the block-shaped valve housing 5, and a pair of composite flow paths F (first composite flow) communicating with the on-off valves 30 are accommodated. A superordinate concept of a road and a second composite flow path) is formed. The valve housing 5, a pair of on-off valves 30, and a pair of composite flow paths F form an on-off valve unit.

That is, the valve housing 5 is rectangular in the directional view shown in FIG. 4, and the on-off valve hole portion 5a is formed on the side surfaces parallel to each other (in FIG. 4, the left and right vertical walls of the valve housing 5). The on-off valve hole portions 5a are in parallel postures with each other and are formed at positions symmetrical with respect to the center point C shown in FIG. As a result, the on-off valve hole portion 5a has a positional relationship in which the valve housing 5 is overlapped with each other in a state of being rotated by 180 °.

The on-off valve 30 seals the on-off valve body 31 that is slidably inserted into the on-off valve hole portion 5a, the spring 32 that urges the on-off valve body 31 to the closing position, and the opening of the on-off valve hole portion 5a. It is provided with a plug 33 to be screwed in the same manner.

A supply opening 6 is formed in which the control flow path 11 for supplying hydraulic oil from the electromagnetic proportional pressure reducing valve 20 communicates with the inner end position of the on-off valve hole 5a, and a drain is formed near the outer end of the on-off valve hole 5a. The opening 7 is formed. On the inner circumference of the on-off valve hole 5a, there is a drain side port 8 capable of discharging the hydraulic oil of the composite flow path F to the drain opening 7, and a supply side port capable of supplying the hydraulic oil from the supply opening 6 to the composite flow path F. 9 and are formed.

As shown in FIG. 4, the on-off valve body 31 is provided with a drain space 31a (an example of a drain portion) that can communicate with the drain opening 7 via a groove-shaped portion formed on the outer periphery.

The pair of composite flow paths F are formed in a parallel posture inward from one end surface (upper wall portion of the valve housing 5 in FIG. 4) orthogonal to the side surface of the valve housing 5. Further, the pair of composite flow paths F individually communicate with the pair of oil chambers 10s.

In this valve housing 5, one (left side in the figure) composite flow path F is an example of the first composite flow path, and the other (right side in the figure) composite flow path F is an example of the second composite flow path. There is. Further, one of the composite flow paths F (first composite flow path) is the supply side port 9 of the on-off valve 30 on one side (upper side in FIG. 4) and the drain side of the on-off valve 30 on the other side (lower side in FIG. 4). It communicates with port 8. Similarly, the other composite flow path F (second composite flow path) supplies the drain side port 8 of the on-off valve 30 on one side (upper side in FIG. 4) and the on-off valve 30 on the other side (lower side in FIG. 4). It communicates with the side port 9.

From this configuration, when hydraulic oil is not supplied to the supply opening 6 of any of the on-off valves 30, the on-off valve body 31 is held in the closed position by the urging force (spring urging force) of the spring 32. In this state where the on-off valve body 31 is in the closed position, hydraulic oil is not supplied to the control flow path 11 communicating with the oil chamber 10s of the servo cylinder 10, and the drain opening 7 and the drain side port 8 are not supplied. Is maintained in a closed state where and is out of communication.

On the other hand, when hydraulic oil is supplied to the supply opening 6 of the on-off valve 30 on one side (upper side of FIG. 4), the on-off valve body 31 opens against the urging force of the spring 32 due to the pressure of the hydraulic oil. As a result of moving to the position, the hydraulic oil is sent from the supply side port 9 to the composite flow path F (first composite flow path) on one side (left side in the figure). When the on-off valve body 31 is moved to the open position in this way, the drain side port 8 communicates (opens) with the drain opening 7 via the drain space 31a, so that the other composite flow path F (second composite flow). Hydraulic oil is discharged from the road).

When the on-off valve 30 is opened in this way, hydraulic oil is supplied to one oil chamber 10s of the servo cylinder 10, and hydraulic oil is discharged from the drain opening 7 of the on-off valve 30 from the other oil chamber 10s. Therefore, the operation of the servo cylinder 10 is realized. Further, when hydraulic oil is supplied to the supply opening 6 of the on-off valve 30 on the other side (lower side of FIG. 4), the other composite flow path F (second composite) is supplied from the supply-side port 9 of the other on-off valve 30. The hydraulic oil is supplied to the flow path), and the hydraulic oil of one of the composite flow paths F is discharged from the drain opening 7 of the on-off valve 30, so that the servo cylinder 10 operates in the opposite direction.

In particular, by providing the pair of on-off valves 30 in this way, for example, when the electromagnetic proportional pressure reducing valve 20 falls into a state where hydraulic oil cannot be supplied due to a failure, the on-off valve 30 is maintained in a closed state. The hydraulic oil cannot be discharged from the oil chamber 10s of the servo cylinder 10, and the phenomenon that the servo cylinder 10 operates improperly is suppressed.

As described above, the composite flow path F has both functions of the control flow path 11 and the drain flow path 13, and as shown in FIG. 4, a pair of composite flow paths F and a pair of on-off valves 30. By providing the valve housing 5 with the above, the number of flow paths is reduced and the configuration is simplified. As in the hydraulic circuit shown in FIG. 1, it is also possible to configure the servo device B so that the pair of drain flow paths 13 branching from the pair of control flow paths 11 are individually connected to the on-off valve 30.

[Action and effect of the embodiment]
This configuration is different from the configuration in which the supply and discharge of hydraulic oil to the oil chamber 10s of the servo cylinder 10 is controlled by a pair of electromagnetic proportional pressure reducing valves 20 (an example of an electromagnetic control valve) as in the conventional technique. By providing the on-off valve 30 in the flow path of the control flow path 11 communicating with the 10s, the inconvenience of improperly discharging the hydraulic oil when the electromagnetic proportional pressure reducing valve 20 fails is solved, and as a result, the vehicle The inconvenience of greatly changing the running speed of the

Further, by providing a pair of on-off valves 30 with respect to the valve housing 5 and forming a pair of composite flow paths F, the number of flow paths formed in the valve housing 5 can be reduced to facilitate the manufacture of a hydraulic circuit. I have to.

Further, although the block-shaped valve housing 5 is provided with a pair of on-off valves 30, the on-off valve hole portion 5a formed at a position symmetrical with respect to a predetermined center point C of the valve housing 5 is provided. It is configured to accommodate the on-off valve 30. Therefore, for example, when forming the on-off valve hole portion 5a, the block-shaped material is fixed to a table or the like of a machine tool so that the block-shaped material can rotate about the center point C, and one hole is drilled with a tool such as a drill. After forming the on-off valve hole, the table can be rotated 180 ° and the same tool can be used for drilling again, eliminating the inconvenience of arranging tools at different positions for machining. It becomes.

[Another Embodiment]
The present invention may be configured as follows in addition to the above-described embodiment (those having the same functions as those in the embodiment are designated by the same number and reference numeral as those in the embodiment).

(A) In order to form the hydraulic servo device B, the control flow path 11 and the drain flow path 13 are formed as independent flow paths as shown in FIG. 1 described in the specification. Even if it is configured in this way, good operation is realized.

(B) The valve housing 5 described in the specification does not necessarily have to be used, and the pair of on-off valves 30 and the pair of electromagnetic proportional pressure reducing valves 20 (electromagnetic control valves) can be supported by a common member. is there. In this configuration, the control flow path 11 and the drain flow path 13 can be configured as independent oil passages, and a pair of composite flow paths F can also be formed.

(C) The target of the hydraulic servo device for shifting operation is not limited to the hydrostatic continuously variable transmission, and may be, for example, a belt continuously variable transmission (belt CVT).

The present invention can be used for a hydraulic servo device that operates a continuously variable transmission by hydraulic pressure.

5 Valve housing 5a On-off valve hole 8 Drain side port 9 Supply side port 10 Servo cylinder 10s Oil chamber 11 Control flow path 12 Hydraulic oil pump 13 Drain flow path 20 Electromagnetic proportional pressure reducing valve (electromagnetic control valve)
30 On-off valve 31 On-off valve body 31a Drain portion A Continuously variable transmission C Center point F Composite flow path (first composite flow path / second composite flow path)

Claims (4)

A double-acting servo cylinder that shifts the continuously variable transmission,
A pair of control flow paths that individually communicate with the two oil chambers of the servo cylinder,
An electromagnetic control valve provided in each of the pair of control flow paths for individually supplying hydraulic oil from the hydraulic oil pump to the pair of control flow paths.
A pair of on-off valves arranged in the pair of control flow paths to individually control the flow of hydraulic oil in the control flow path in response to a pressure change in the pair of control flow paths.
A drain flow path communicating with the pair of control flow paths is provided.
The on-off valve closes one of the control flow paths corresponding to the on-off valve when the pressure in the control flow path is less than the set value, and when the pressure reaches the set value or more, the on-off valve is connected to the on-off valve. Open one of the corresponding control channels and
When one of the pair of on-off valves closes one of the control flow paths, the on-off valve closes the drain flow path that communicates with the other control flow path in cooperation with the blockage. A hydraulic servo device that, when one of the pair of on-off valves opens one of the control flow paths, cooperates with the opening to open the drain flow path communicating with the other control flow path. When the pressure of the control flow path is less than the set value, the on-off valve is held at a closed position that closes one of the control flow paths by a spring-forced force, and the pressure of the control flow path is equal to or higher than the set value. It is provided with an on-off valve body that operates at an open position that opens one of the control flow paths against the spring-forced force when the pressure is reached.
The on-off valve body closes the drain flow path communicating with the other control flow path when it is in the closed position, and discharges the drain flow path communicating with the other control flow path when it is in the open position. The hydraulic servo device according to claim 1, which has a drain portion that communicates with the side. The on-off valve is housed in the pair of on-off valve holes formed in the block-shaped valve housing, and the on-off valve is formed by forming the pair of control flow paths and the pair of drain flow paths in the valve housing. The unit is configured,
The hydraulic servo device according to claim 1 or 2, wherein the pair of on-off valve holes are arranged at positions symmetrical with respect to a predetermined center point of the valve housing. A pair of on-off valve holes are formed in the valve housing in a parallel posture, and the on-off valve has a supply side port capable of delivering hydraulic oil to the oil chamber and a drain side port capable of discharging hydraulic oil. With and
A first composite flow path that communicates the supply-side port of one on-off valve and the drain-side port of the on-off valve with the valve housing, and the supply-side port of the other on-off valve and one of the above. A second composite flow path that communicates with the drain side port of the on-off valve is formed, the first composite flow path communicates with one of the oil chambers, and the second composite flow path communicates with the other oil chamber. The hydraulic servo device according to claim 3.

Images