JP5212035B2 - Valve device and servo valve - Google Patents

Description

  The present invention relates to a valve device comprising a spool that is movable in a longitudinal direction within a sleeve having a port and that defines an opening ratio of the port according to a moving position, and a position control means for controlling the position of the spool. And the servo valve.

As is well known, when it is necessary to adjust the flow rate of the fluid, a so-called spool valve (valve device) is used.
The spool valve includes a sleeve having a port which is an inflow / outlet of a fluid, and a spool which is movable in the longitudinal direction within the sleeve. The opening ratio of the port changes depending on the position of movement of the spool, and a flow rate corresponding to the opening ratio is discharged from the port.

For example, Patent Document 1 discloses, as an example of the spool valve as described above, a servo valve that adjusts the flow rate of fluid by adjusting the amount of current supplied to a position control unit that controls the movement position of the spool valve. Has been.
JP 2001-12409 A

By the way, the spool has a portion (regulating member) having a surface wider than the opening area of the port formed in the sleeve, and the coverage of the port by the defining member is changed by movement in the longitudinal direction. The aperture ratio is changed.
Further, since the distance from the reference position of the spool that is used as a reference when moving is fixed, the opening ratio of the port can be accurately specified by controlling the position of the reference position. ing.

On the other hand, the opening start timing or the closing start timing of the port differs depending on where the end of the defining member is located with respect to the end of the port when the reference position is the reference position.
Specifically, when the end of the defining member is spaced apart from the end of the port with the port completely closed, the end of the defining member is moved to the port end after the spool is moved. Since it takes time to move to the port, the opening timing of the port is delayed.
When the end of the defining member is close to the end of the port with the port completely closed, the end of the defining member reaches the port end immediately after the spool is moved. The start timing is earlier.
Further, the closing timing of the port is determined by the positional relationship between the end of the defining member and the end of the port when the port is fully opened.

The difference between the opening start timing or the closing start timing of the port is a characteristic of the spool valve, and if the positional relationship between the reference position and the port is determined, it is determined by the distance from the end of the defining member to the reference position. Will be.
Therefore, the characteristics of such a spool valve are determined at the stage of manufacturing the spool valve and cannot be adjusted.

  However, in a device that actually incorporates a spool valve, it may be preferable to adjust the characteristics of the spool valve. In such a case, in the conventional apparatus, it is necessary to replace the spool valve with a different characteristic.

  The present invention has been made in view of the above-described problems. In the valve device that changes the opening ratio of the port by allowing the spool to move in the longitudinal direction in the sleeve having the port, the valve device itself is replaced. It aims at making it possible to change the characteristics of the valve device.

  The present invention adopts the following configuration as means for solving the above-described problems.

  A first invention includes a spool that is movable in a longitudinal direction in a sleeve having a port and that defines an opening ratio of the port according to a moving position, and a position control unit that controls the position of the spool. A valve device comprising a distance adjusting means capable of adjusting a distance in the longitudinal direction from a defining member that defines an opening ratio of the port of the spool to a reference position that is a control reference of the position control means. Is adopted.

  According to a second invention, in the first invention, the sleeve includes a plurality of ports, the spool includes the defining member with respect to two or more ports, and the distance adjusting means includes the defining member. A configuration is adopted in which the distance to the reference position can be adjusted independently.

  According to a third invention, in the first or second invention, the distance adjusting means includes an actuator disposed between the defining member and the reference position, and a control means for controlling the actuator. Adopt the configuration.

  According to a fourth invention, in the third invention, the actuator is an electrostrictive element.

  According to a fifth aspect of the invention, there is provided a sleeve having a first inflow port, a second inflow port, a first outflow port, a second outflow port, a first outflow / inflow port, and a second outflow / inflow port, and an opening ratio of the first inflow port. A first defining member that defines the opening ratio of the first outflow port according to the moving position, a second defining member that defines the opening ratio of the first outflow port according to the moving position, and an opening ratio of the second outflow port according to the moving position. A spool that has a third defining member, a fourth defining member that defines the opening ratio of the second inflow port according to the movement position, and that is moved in the longitudinal direction within the sleeve, and a position that controls the position of the spool A servo valve comprising: a control means; a distance from the first prescribed member of the spool to a reference position which is a control reference of the position control means; and a position from the second prescribed member of the spool to the position. A distance from a reference position to be a control reference of the control means, a distance from the third defining member of the spool to a reference position to be a control reference of the position control means, and a distance from the fourth defining member of the spool. A configuration is adopted in which distance adjusting means is provided that can independently adjust the distance to the reference position that is the control reference of the position control means.

According to the present invention, the distance adjusting means can adjust the distance from the spool defining member (part defining the aperture ratio) to the reference position serving as the control reference. That is, the distance from the defining member to the reference position is variable.
For this reason, when the reference position is moved, the opening start timing or the closing start timing of the port can be changed, and the characteristics of the valve device can be changed.
Therefore, according to the present invention, in the valve device that changes the opening ratio of the port by allowing the spool to move in the longitudinal direction in the sleeve having the port, the characteristics of the valve device are changed without replacing the valve device itself. It becomes possible.

  Hereinafter, an embodiment of a valve device according to the present invention will be described with reference to the drawings. In the following drawings, the scale of each member is appropriately changed in order to make each member a recognizable size. In the following description, a nozzle flapper type servo valve will be described as an example of the valve device of the present invention.

FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a servo valve 1 of the present embodiment. FIG. 2 is an enlarged cross-sectional view of the sleeve 3 and the spool 4 included in the servo valve 1.
As shown in FIG. 1, the servo valve 1 according to the present embodiment includes a housing 2, a sleeve 3, a spool 4, a telescopic device 5 (distance adjusting means), a nozzle 6, a nozzle flapper 7, and a torque motor 8. (Position control means).

The casing 2 forms the outer shape of the servo valve 1 and includes a plurality of flow paths inside and accommodates the sleeve 3, the spool 4, the nozzle 6, the nozzle flapper 7, and the like.
A flow path formed inside the housing 2 will be described later.

The sleeve 3 has a thin cylindrical shape whose both ends are open ends, and accommodates the spool 4 in a slidable manner. The sleeve 3 is horizontally placed inside the housing 2 by the wall surface of the housing 2. It is supported.
The sleeve 3 includes a plurality of ports that allow communication between the inside and the outside. More specifically, the sleeve 3 has three ports symmetrically, and an inlet port 3a for introducing a fluid into the sleeve 3 on each side, and a fluid for the sleeve 3 An outflow port 3b for leading out to the outside, and an outflow / inlet port 3c for conducting and introducing the fluid between the sleeve 3 and the fluid supply destination by the servo valve 1 are provided.
In the following description, for convenience of description, as shown in FIG. 2, one side (left side in FIG. 1) of the sleeve 3 is described as the left side, and the other side (right side in FIG. 1) of the sleeve 3 is described as the right side. . The inflow port 3a located on the left side is the first inflow port 3a1, the inflow port 3a located on the right side is the second inflow port 3a2, the outflow port 3b located on the left side is the first outflow port 3b1, and the outflow port is located on the right side. 3b may be described as the second outflow port 3b2, the outflow / inflow port 3c located on the right side as the first outflow / inflow port 3c1, and the outflow / inflow port 3c located on the left side may be described as the second outflow / inflow port 3c2.

The spool 4 is a shaft member that is accommodated in the sleeve 3 and is slidable in the longitudinal direction. The spool 4 includes a defining member 4a that defines the opening ratio of the inflow port 3a and the outflow port 3b of the sleeve 3 depending on the position of the spool 4 in the moving direction. That is, in the present embodiment, the spool 4 includes four defining members 4a. In the following description, for convenience of explanation, as shown in FIG. 2, the defining member 4a for defining the opening ratio of the first inflow port 3a1 is used as the opening ratio of the first defining member 4a1 and the first outflow port 3b1. The defining member 4a for defining the second defining member 4a2 and the defining member 4a for defining the opening ratio of the second outflow port 3b2 to define the opening ratio of the third defining member 4a3 and the second inflow port 3a2 The defining member 4a may be described as a fourth defining member 4a4.
The defining member 4a is a cylindrical member having a diameter substantially the same as the inner diameter of the sleeve 3, and has a width wider than the opening areas of the inflow port 3a and the outflow port 3b.

The spool 4 is extended in one direction by connecting the above-mentioned defining member 4a by a connecting portion 4b which is a cylindrical member having a diameter smaller than that of the defining member 4a.
The spool 4 moves from the position where the inflow port 3a and the outflow port 3b are covered and closed by the respective defining members 4a to the position where the inflow port 3a and the outflow port 3b are opened without being covered by the defining member 4a. It is possible.

The telescopic device 5 is for adjusting the length (distance) of the spool 4 in the longitudinal direction, and includes an electrostrictive element 5a (actuator) and a control unit 5b (control means).
The electrostrictive element 5a is incorporated in each connecting portion 4b and disposed between the defining members 4a, and expands and contracts under the control of the control portion 5b.
The control unit 5b is electrically connected to each electrostrictive element 5a via wiring (not shown) that passes through the inside of the spool 4.
Then, the length of the spool 4 is adjusted by the expansion / contraction device 5 by causing the electrostrictive element 5a to expand and contract under the control of the control unit 5b.

In the present embodiment, the first defining member 4a1 to the second defining member are formed by the first electrostrictive element 5a1 which is the electrostrictive element 5a disposed between the first defining member 4a1 and the second defining member 4a2. The distance to 4a2 is adjusted.
Further, the distance from the second defining member 4a2 to the third defining member 4a3 is adjusted by the second electrostrictive element 5a2 which is the electrostrictive element 5a disposed between the second defining member 4a2 and the third defining member 4a3. Is done.
Further, the distance from the third defining member 4a3 to the fourth defining member 4a4 is adjusted by the third electrostrictive element 5a3 which is the electrostrictive element 5a disposed between the third defining member 4a3 and the fourth defining member 4a4. Is done.
That is, the electrostrictive element 5a is disposed between the defining members 4a, and the position of each defining member 4a can be adjusted independently.

The nozzles 6 inject the fluid supplied from the outside toward the nozzle flapper 7, and two nozzles 6 are arranged symmetrically across the nozzle flapper 7 above the sleeve 3.
In the following description, the nozzle 6 positioned above the left side of the sleeve 3 may be described as a first nozzle 6a, and the nozzle 6 positioned above the right side of the sleeve 3 may be described as a second nozzle 6b.

The nozzle flapper 7 is a plate-like member connected to the torque motor 8, and is disposed between the first nozzle 6a and the second nozzle 6b.
The nozzle flapper 7 is connected to the spool 4 via a feedback spring 9. The nozzle flapper 7 is fixed to the right side surface of the second defining member 4a2 of the spool 4. In the present embodiment, the right side surface of the second defining member 4a2 is the reference position 4c when the spool 4 is moved.

The torque motor 8 generates torque based on an instruction from the outside, and tilts the nozzle flapper 7 by the torque. The armature 8a is fixed to the nozzle flapper 7 and applies torque to the nozzle flapper 7, and the armature 8a is tilted. The coil 8b etc. which generate | occur | produce the magnetic force to be provided are provided.
The torque motor 8 is fixed to the upper part of the housing 2.

Returning to the description of the casing 2, the casing 2 has a flow path 2 a that distributes the fluid supplied from a supply source outside the casing 2 to the first nozzle 6 a and the second nozzle 6 b evenly. , A flow path 2b for guiding the fluid ejected from the nozzle 6 to the inflow port 3a of the sleeve 3, a flow path 2c for guiding the fluid derived from the outflow port 3b of the sleeve 3 to the discharge port 2A, and an outflow / inflow port of the sleeve 3 3c and the flow path 2c which connects a supply destination are provided.
The flow path 2a includes a flow path 2a1 for supplying fluid to the first nozzle 6a and a flow path 2a2 for supplying fluid to the second nozzle 6b. The flow path 2a1 is connected to the open end on the left side of the sleeve 3, the flow path 2a2 is connected to the open end on the right side of the sleeve 3, and the left end face of the spool 4 receives the pressure of the fluid flowing through the flow path 2a1, The right end face of 4 is configured to receive the pressure of the fluid flowing through the flow path 2a2.

  Next, the operation of the servo valve 1 of the present embodiment configured as described above will be described.

When the nozzle flapper 7 is not inclined by the torque motor 8, when the fluid is supplied from an external supply source to the flow path 2a formed inside the housing 2, the fluid supplied to the flow path 2a is The first nozzle 6a and the second nozzle 6b are ejected equally. At this time, the pressure of the fluid in the channel 2a1 is equal to the pressure of the fluid in the channel 2a2. Therefore, the spool 4 does not move.
In the following description, a position in a state where the spool 4 is not moved is set as a reference position.

Further, when the nozzle flapper 7 is tilted to the right side by the torque motor 8, the nozzle flapper 7 approaches the first nozzle 6a and moves away from the second nozzle 6b. As a result, the ejection of fluid from the first nozzle 6a is hindered by the nozzle flapper 7, the pressure in the flow path 2a1 communicating with the first nozzle 6a rises, and the force received by the left end surface of the spool 4 is relative to the right end surface. The spool 4 moves to the right.
Note that as the inclination angle of the nozzle flapper 7 to the right increases, the pressure in the flow path 2a1 increases and the amount of movement of the spool 4 to the right increases.
Since the inclination angle of the nozzle flapper 7 is proportional to the magnitude of the torque that the torque motor 8 acts on the nozzle flapper 7, the movement amount of the spool 4 can be controlled by controlling the output of the torque motor 8.

Further, when the nozzle flapper 7 is tilted to the left by the torque motor 8, the nozzle flapper 7 approaches the second nozzle 6b and moves away from the first nozzle 6a. As a result, the ejection of the fluid from the second nozzle 6a is hindered by the nozzle flapper 7, the pressure in the flow path 2a2 communicating with the second nozzle 6a rises, and the force received by the right end surface of the spool 4 is relative to the left end surface. The spool 4 moves to the left side.
Note that as the inclination angle of the nozzle flapper 7 to the left increases, the pressure in the flow path 2a2 increases and the amount of movement of the spool 4 to the left increases.

And the servo valve 1 of this embodiment can adjust the length of the spool 4 with the expansion-contraction apparatus 5, and can change an own characteristic.
For example, the servo valve 1 is characterized by a critical center in which fluid flows into the inflow / outflow port 3c when the spool 4 is slightly displaced from the reference position, and a fluid in the inflow / outflow port 3c when the spool 4 changes greatly from the reference position. And an underlap in which fluid flows into the inflow / outflow port 3c even when the spool 4 is at the reference position.
Below, the method for achieving the said characteristic with the servo valve 1 of this embodiment is demonstrated.

(Critical Center)
When the characteristic of the servo valve 1 is a critical center, as shown in FIG. 2, when the spool 4 is at the reference position, the right end of the first defining member 4a1 is the right end of the first inflow port 3a1. And the left end of the second defining member 4a2 is aligned with the left end of the first outflow port 3b1, the right end of the third defining member 4a3 is aligned with the right end of the second outflow port 3b2, and the fourth defining The distance from the reference position 4c to each regulating member 4a is adjusted by the telescopic device 5 so that the left end of the member 4a4 is aligned with the left end of the second inflow port 3a2.

When the spool 4 is moved to the left side by the arrangement of the defining member 4a, the first inflow port 3a1 and the second outflow port 3b2 are opened immediately after the spool 4 starts moving.
When the first inflow port 3a1 and the second outflow port 3b2 are opened, fluid flows from the first inflow port 3a1 into the sleeve 3 and is supplied to the supply destination through the first inflow / outflow port 3c1. The fluid returned from the supply destination flows again into the sleeve 3 through the second inflow / outflow port 3c2, and then is discharged to the outside of the sleeve 3 through the second outflow port 3b2. Is discharged to the outside of the servo valve 1 through the discharge port 2A.

On the other hand, when the spool 4 is moved to the right side, the second inflow port 3a2 and the first outflow port 3b1 are opened immediately after the start of the movement of the spool 4.
When the second inflow port 3a2 and the first outflow port 3b2 are opened, fluid flows from the second inflow port 3a2 into the sleeve 3 and is supplied to the supply destination through the second inflow / outflow port 3c2. The fluid returned from the supply destination flows again into the sleeve 3 through the first inflow / outflow port 3c1, and then is discharged to the outside of the sleeve 3 through the first outflow port 3b1. Is discharged to the outside of the servo valve 1 through the discharge port 2A.

  In other words, the fluid is immediately supplied to the supply destination when the sleeve 3 is moved by the arrangement of the defining member 4a. For this reason, the characteristic of the servo valve 1 can be a critical center in which the fluid flows to the inflow / outflow port 3c when the spool 4 is slightly displaced from the reference position.

(Overlap)
When the characteristics of the servo valve 1 are overlapped, as shown in FIG. 3, when the spool 4 is at the reference position, the right end of the first defining member 4a1 is the right end of the first inflow port 3a1. The left end of the second defining member 4a2 is located on the left side of the left end of the first outflow port 3b1, and the right end of the third defining member 4a3 is on the right side of the second outflow port 3b2. The distance from the reference position 4c to each regulating member 4a is set so that the left end of the fourth defining member 4a4 is located on the left side of the left end of the second inflow port 3a2. Adjustment is performed by the telescopic device 5.

  When the spool 4 is moved to the left side due to the arrangement of the defining member 4a, the first inflow port 3a1 and the second outflow port 3b2 are not opened immediately after the start of the movement of the spool 4, and the first The right end of the defining member 4a1 reaches the right end of the first inflow port 3a1, and the right end of the third defining member 4a3 reaches the right end of the second outflow port 3b2, and then the first inflow port 3a1 and the first inflow port 3a1. 2 outflow port 3b2.

  On the other hand, when the spool 4 is moved to the right, the second inflow port 3a2 and the first outflow port 3b1 are not opened immediately after the start of the movement of the spool 4, and the left end portion of the second defining member 4a2 is The second inflow port 3a2 and the first outflow port 3b1 are opened after reaching the left end of the first outflow port 3b1 and the left end of the fourth regulating member 4a4 reaching the right end of the second inflow port 3a2. The

  That is, the fluid is not supplied to the supply destination immediately after the sleeve 3 is moved due to the arrangement of the defining member 4a. For this reason, the characteristic of the servo valve 1 can be an overlap in which fluid flows to the inflow / outflow port 3c when the spool 4 is largely changed from the reference position.

(Underlap)
When the servo valve 1 has an underlap characteristic, as shown in FIG. 4, when the spool 4 is at the reference position, the right end of the first defining member 4a1 is the right end of the first inflow port 3a1. The left end of the second defining member 4a2 is located on the right side of the left end of the first outflow port 3b1, and the right end of the third defining member 4a3 is on the right side of the second outflow port 3b2. The distance from the reference position 4c to each regulating member 4a is set so that it is located on the left side of the end and the left side of the fourth regulating member 4a4 is located on the right side of the left side of the second inflow port 3a2. Adjustment is performed by the telescopic device 5.

Due to the arrangement of the regulating member 4a, the first inflow port 3a1, the second inflow port 3a2, the first outflow port 3b1, and the second outflow port 3b2 are connected even when the spool 4 is disposed at the reference position. It is open.
In other words, due to the arrangement of the defining member 4a, the fluid is supplied to the supply destination even when the spool 4 is in the reference position. For this reason, the characteristic of the servo valve 1 can be an underlap in which fluid flows into the inflow / outflow port 3c even when the spool 4 is at the reference position.

  Thus, according to the servo valve 1 of the present embodiment, the characteristics of the servo valve 1 can be arbitrarily changed by adjusting the position from the reference position of the spool 4 to each regulating member 4a by the expansion / contraction device 5. it can.

When the above three characteristics are realized, the opening timing of the first inflow port 3a1 and the second outflow port 3b2 when the spool 4 moves to the left side is the same, and the spool 4 moves to the right side. The opening timings of the second inflow port 3a2 and the first outflow port 3b1 are the same.
However, the opening timing of the first inflow port 3a1 and the second outflow port 3b2 and the opening timing of the second inflow port 3a2 and the first outflow port 3b1 do not necessarily have to be the same.
For example, when the spool 4 is at the reference position, the position of the first defining member 4a1 may be adjusted by the telescopic device 5 so that only the first inflow port 3a1 is slightly opened. Thereby, the pressure on the first inflow / outflow port 3c1 side at the supply destination can be increased.
Further, when the spool 4 is at the reference position, the position of the fourth defining member 4a4 may be adjusted by the telescopic device 5 so that only the second inflow port 3a2 is slightly opened. Thereby, the pressure on the second inflow / outflow port 3c2 side at the supply destination can be increased.
That is, according to the servo valve 1 of the present embodiment, the fluid pressure at the supply destination can be adjusted.

According to the servo valve 1 of this embodiment as described above, the distance from the defining member 4a of the spool 4 to the reference position 4c can be adjusted by the expansion / contraction device 5. That is, the distance from the defining member 4a to the reference position 4c is variable.
Therefore, the opening start timing or closing start timing of the first inflow port 3a1, the second inflow port 3a2, the first outflow port 3b1, and the second outflow port 3b2 when the reference position 4c is moved can be changed. The characteristics of the valve device can be changed.
Therefore, according to the servo valve 1 of the present embodiment, in the servo valve that changes the opening ratio of the port by allowing the spool to move in the longitudinal direction in the sleeve having the port, the servo valve itself is not replaced. It is possible to change the characteristics of the.

  As mentioned above, although preferred embodiment of the valve apparatus and servo valve which concern on this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the said embodiment. Various shapes, combinations, and the like of the constituent members shown in the above-described embodiments are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

For example, in the above embodiment, a servo valve has been described as an example of the valve device of this embodiment.
However, the present invention is not limited to this, and can be applied to all spool valves including a sleeve and a spool.

Moreover, in the said embodiment, the expansion / contraction apparatus 5 (distance adjustment means) demonstrated the structure provided with an electrostrictive element as an actuator.
However, the present invention is not limited to this, and any mechanism capable of displacing the defining member 4a of the spool 4 with respect to the reference position 4c can be used as an actuator of the telescopic device 5.

It is sectional drawing which showed typically the schematic structure of the servo valve in one Embodiment of this invention. It is drawing which expanded the sleeve and spool in case the characteristic of the servo valve in one Embodiment of this invention is a critical center. It is drawing which expanded the sleeve and spool in case the characteristic of the servo valve in one Embodiment of this invention is an overlap. 4 is an enlarged view of a sleeve and a spool when the servo valve according to an embodiment of the present invention has an underlap characteristic.

Explanation of symbols

  1 ... Servo valve (valve device), 2 ... Housing, 3 ... Sleeve, 3a ... Inflow port (port), 3a1 ... First inflow port (port), 3a2 ... Second inflow port (port) ), 3b .. Outflow port (port), 3b1... First outflow port (port), 3b2... Second outflow port (port), 3c... Outflow / inflow port, 3c1. …… Second inflow / outflow port, 4 …… Spool, 4a …… Regulating member, 4a1 …… First defining member (regulating member), 4a2 …… Second defining member (regulating member), 4a3 …… 3rd defining member (Regulating member), 4a4... 4th defining member (regulating member), 4b... Connecting portion, 4c... Reference position, 5 .. telescopic device (distance adjusting means), 5a. 5a1... First electrostrictive element (actuator), 5a2. 2nd electrostrictive element (actuator), 5a3... 3rd electrostrictive element (actuator), 5b... Control unit (control means), 6... Nozzle, 7. 9) Feedback spring

Claims (4)

A valve device comprising: a spool that is movable in a longitudinal direction in a sleeve having a port and that defines an opening ratio of the port according to a moving position; and a position control unit that controls the position of the spool,
A distance adjusting means capable of adjusting a distance in the longitudinal direction from a defining member that defines an aperture ratio of the port of the spool to a reference position that is a control reference of the position control means ;
The sleeve includes a plurality of ports, and the spool includes the defining member for two or more ports;
The distance adjusting means is capable of independently adjusting the distance of each defining member to the reference position . Said distance adjusting means, said regulating member and an actuator disposed between the reference position, the valve device according to claim 1, characterized in that it comprises a control means for controlling the actuator. The valve device according to claim 2 , wherein the actuator is an electrostrictive element. A sleeve having a first inflow port, a second inflow port, a first outflow port, a second outflow port, a first outflow port, and a second outflow port;
A first defining member that defines the opening ratio of the first inflow port according to the movement position, a second defining member that defines the opening ratio of the first outflow port according to the movement position, and the opening ratio of the second outflow port A spool that has a third defining member that defines the opening ratio of the second inflow port according to the moving position, and a fourth defining member that defines the opening ratio of the second inflow port according to the moving position, and is moved in the longitudinal direction within the sleeve;
Position control means for controlling the position of the spool;
A servo valve comprising:
A distance from the first defining member of the spool to a reference position as a control reference of the position control means;
A distance from the second defining member of the spool to a reference position as a control reference of the position control means;
A distance from the third defining member of the spool to a reference position as a control reference of the position control means;
A distance from the fourth defining member of the spool to a reference position as a control reference of the position control means;
A servo valve comprising a distance adjusting means that can be independently adjusted.

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