Servo valve

A first flow path area at a position where one of multiple openings of a sleeve and one of multiple grooves of a spool overlap with each other is different in size from a second flow path area at a position where another one of the openings of the sleeve and another one of the grooves of the spool overlap with each other. The one opening and the one groove form a flow path for connecting one of one pressure chamber and the other pressure chamber to a fluid supply source, due to displacement of the spool. The other opening and the other groove form a flow path for connecting another one of the other pressure chamber and the one pressure chamber to a fluid discharge port, due to the displacement of the spool.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-163580 filed on Sep. 9, 2019, the contents all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a servo valve that controls the flow rate of a fluid supplied to or discharged from two pressure chambers of a fluid pressure cylinder.

Description of the Related Art

For example, a servo valve that controls an operational position of a spool using a moving-magnet-type electromagnetic actuator as a driving source so as to control the flow rate of air supplied to an air cylinder has conventionally been known (for example, Japanese Laid-Open Patent Publication No. 2003-206908).

On the other hand, there has been known a technique in which meter-out control or meter-in control is performed with a speed controller (variable throttle valve) being provided to the air cylinder or a pipe (or tube) connected to the air cylinder. The meter-out control is control in which the flow rate of the air discharged from a pressure chamber of the air cylinder is reduced. The meter-in control is control in which the flow rate of the air supplied to the pressure chamber of the air cylinder is reduced. The meter-out control is performed in a case that operation needs to be stabilized against external disturbance or in a case that thrust force needs to rise quickly after a stroke end has been reached. The meter-in control is performed in a case that “jumping-out phenomenon” in which the cylinder starts to move swiftly needs to be suppressed or in a case that thrust force needs to rise gradually after the stroke end has been reached.

SUMMARY OF THE INVENTION

In the air cylinder controlled by the servo valve, if the meter-out control or the meter-in control is performed, it is necessary to provide the speed controller to the air cylinder or the pipe (or tube) additionally.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a servo valve including a unique structure that achieves meter-out control or meter-in control.

According to an aspect of the present invention, there is provided a servo valve configured to control a flow rate of a fluid supplied to and discharged from one pressure chamber and the other pressure chamber of a fluid pressure cylinder, and the servo valve includes a sleeve including a plurality of openings and a spool that is provided inside the sleeve, wherein the spool includes a plurality of lands and a plurality of grooves. In addition, a first flow path area at a position where one opening of the openings and one groove of the grooves overlap with each other is different in size from a second flow path area at a position where another opening of the openings and another groove of the grooves overlap with each other. The one opening and the one groove form a flow path for connecting one of the one pressure chamber and the other pressure chamber to a fluid supply source, due to displacement of the spool. The other opening and the other groove form a flow path for connecting another one of the other pressure chamber and the one pressure chamber to a fluid discharge port, due to the displacement of the spool.

According to the servo valve described above, meter-out control or meter-in control can be achieved by the structure of the servo valve itself without a speed controller attached to the fluid pressure cylinder.

In the servo valve according to the present invention, when the spool is displaced, the first flow path area at the place where a predetermined opening of the sleeve and a predetermined groove of the spool overlap with each other is different in size from the second flow path area at the place where another predetermined opening of the sleeve and another predetermined groove of the spool overlap with each other. Thus, the meter-out control or the meter-in control can be achieved by the structure of the servo valve itself.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a servo valve according to the present invention are hereinafter described with reference to the attached drawings.

First Embodiment

A servo valve10according to a first embodiment of the present invention is described with reference toFIG. 1toFIG. 9.

FIG. 1is a schematic diagram illustrating an entire system that controls a fluid pressure cylinder36by the servo valve10. The servo valve10is a valve that controls the flow rate of a fluid supplied to or discharged from one pressure chamber36aand the other pressure chamber36bof the fluid pressure cylinder36. The operation of the servo valve10is controlled by a valve controller68. Here, the term “fluid” means a compressible fluid including air. For the convenience of description, inFIG. 1, the servo valve10is expressed using general circuit symbols.

As illustrated inFIG. 2, the servo valve10includes a flow path switching mechanism unit12and an actuator unit14. The flow path switching mechanism unit12includes a tubular-shaped valve body16and a spool28that is disposed in the valve body16. The actuator unit14includes a stator part38that is disposed on an end of the valve body16, and a magnet part52that is connected to an end of the spool28through a connection shaft54. In the description below, a direction that is parallel to an axis direction of the spool28, that is, a direction in which the spool28moves is referred to as an X direction. Moreover, a direction in which the spool28is separated from the actuator unit14along the X direction is referred to as an X1direction, and a direction in which the spool28comes close to the actuator unit14along the X direction is referred to as an X2direction.

The valve body16includes a hole that penetrates the valve body16in a longitudinal direction thereof. This hole is made up of a first large-diameter hole18athat is formed at an end of the valve body16in the X1direction, a second large-diameter hole18bthat is formed at an end of the valve body16in the X2direction, and a small-diameter hole18cthat is formed between the first large-diameter hole18aand the second large-diameter hole18b.

The valve body16is provided with a first port20ato a fifth port20ethat communicate with the small-diameter hole18cand are open at an outer peripheral surface of the valve body16. The first to fifth ports20ato20eare arranged in the X direction. The first port20aand the fifth port20eare connected to a fluid supply source (not shown), and the third port20cis connected to a fluid discharge port (not shown). In addition, the second port20band the fourth port20dare connected to the one pressure chamber36aand the other pressure chamber36bof the fluid pressure cylinder36, respectively (seeFIG. 1).

A sleeve22with a cylindrical shape is inserted into the small-diameter hole18cof the valve body16. The sleeve22is positioned and fixed in the valve body16in the axis direction using a tubular-shaped sleeve stopper25that is fixed to the first large-diameter hole18aof the valve body16and a snap ring26that is fixed to an end of the second large-diameter hole18bof the valve body16in the X1direction.

As illustrated inFIG. 3, the sleeve22includes a first opening24a, a second opening24b, a third opening24c, a fourth opening24d, and a fifth opening24e. Each of the first opening24ato the fifth opening24eincludes a pair of openings that penetrates a wall surface of the sleeve22on both sides in a diameter direction. The first opening24ato the fifth opening24ecommunicate with the first port20ato the fifth port20eof the valve body16, respectively. The shape of the first opening24ato the fifth opening24ewhen viewed in a radial direction is the same rectangular shape, and the width thereof (length that is orthogonal to the X direction) is constant in the X direction. In the present embodiment, the shape of the first opening24ato the fifth opening24eis the rectangular shape; however, the shape thereof may be a circular shape including an oval or elliptical shape.

The cylindrical spool28is inserted into the sleeve22so as to be movable in the X direction. The spool28is provided with a first land30a, a second land30b, a third land30c, and a fourth land30dthat are in close contact with an inner peripheral surface of the sleeve22. The first land30ato the fourth land30dare arranged in the X direction. A first groove32ais formed between the first land30aand the second land30bso as to surround an outer peripheral surface of the spool. Similarly, between the second land30band the third land30c, a second groove32bis formed so as to surround the outer peripheral surface, and between the third land30cand the fourth land30d, a third groove32cis formed so as to surround the outer peripheral surface.

As illustrated inFIG. 3, when the actuator unit14is not energized and the spool28is at a neutral position, the second opening24bof the sleeve22is closed by the second land30bof the spool28, and the fourth opening24dof the sleeve22is closed by the third land30cof the spool28. Thus, the second opening24bconnected to the one pressure chamber36aof the fluid pressure cylinder36is blocked from the first opening24aconnected to the fluid supply source and is also blocked from the third opening24cconnected to the fluid discharge port. In addition, the fourth opening24dconnected to the other pressure chamber36bof the fluid pressure cylinder36is blocked from the fifth opening24econnected to the fluid supply source and is also blocked from the third opening24cconnected to the fluid discharge port.

When the spool28is at the neutral position, an X-direction length (lap length) a1is less than an X-direction length (lap length) b1. The X-direction length a1is a length, in the X direction, of a portion where the second land30bis in contact with an inner wall surface of the sleeve22between the first opening24aand the second opening24b. The X-direction length b1is a length, in the X direction, of a portion where the third land30cis in contact with an inner wall surface of the sleeve22between the third opening24cand the fourth opening24d. In addition, when the spool28is at the neutral position, an X-direction length (lap length) a2is less than an X-direction length (lap length) b2. The X-direction length a2is a length, in the X direction, of a portion where the third land30cis in contact with an inner wall surface of the sleeve22between the fourth opening24dand the fifth opening24e. The X-direction length b2is a length, in the X direction, of a portion where the second land30bis in contact with an inner wall surface of the sleeve22between the second opening24band the third opening24c. In the present embodiment, the length a2is equal to the length a1, and the length b2is equal to the length b1.

The stator part38is housed in a stator housing40that is fixed to the end of the valve body16in the X2direction. The stator part38includes a fixed yoke42that is made from a ferromagnetic body and an exciting coil50that is disposed inside the fixed yoke42. The fixed yoke42includes a thick-walled-tubular-shaped first end yoke44that is disposed on the side of the X1direction, a thick-walled-tubular-shaped second end yoke46that is disposed on the side of the X2direction, and a thin-walled-tubular-shaped outer yoke48that is disposed between the first end yoke44and the second end yoke46so as to be flush with outer peripheral surfaces of the first end yoke44and the second end yoke46.

The first end yoke44has, on an inner peripheral side thereof, a first pole tooth44athat is formed protruding so as to extend toward the second end yoke46. The second end yoke46has, on an inner peripheral side thereof, a second pole tooth46athat is formed protruding so as to extend toward the first end yoke44. When electric current is applied to the exciting coil50in a predetermined direction, the first pole tooth44abecomes the north pole (N-pole) and the second pole tooth46abecomes the south pole (S-pole). When electric current is applied to the exciting coil50in the opposite direction, the first pole tooth44abecomes S-pole and the second pole tooth46abecomes N-pole.

A magnet part52includes a first magnet52a, a second magnet52b, and a tubular inner yoke52cmade of a ferromagnetic body. The first magnet52aand the second magnet52bare permanent magnets with a tubular shape. The inner yoke52cis disposed between the first magnet52aand the second magnet52b. An outer peripheral surface of the first magnet52afaces an inner peripheral surface of the first pole tooth44aof the first end yoke44, and an outer peripheral surface of the second magnet52bfaces an inner peripheral surface of the second pole tooth46aof the second end yoke46. The first magnet52ais magnetized so that the X1direction side thereof becomes N-pole and the X2direction side becomes S-pole. The second magnet52bis magnetized so that the X1direction side becomes S-pole and the X2direction side becomes N-pole.

One end of the connection shaft54is fixed to the spool28, and the magnet part52is fixed to the other end of the connection shaft54. Specifically, a small-diameter shaft portion54ais formed at the other end of the connection shaft54through a step portion. This small-diameter shaft portion54ais inserted into the magnet part52and is further inserted into a magnet stopper55, and then an end of the small-diameter shaft portion54ais screw-engaged with a nut56, whereby the magnet part is fixed. Thus, the spool28can be displaced in the X direction together with the magnet part52.

In the second large-diameter hole18bof the valve body16on the outer peripheral side of the connection shaft54, a first coil spring58and a second coil spring60are disposed. The first coil spring58is placed between a common spring receiver62and a first spring receiver64. The common spring receiver62is in contact with the end of the spool28in the X2direction and can move with the spool28. The first spring receiver64is in contact with an end of the first end yoke44in the X1direction. The second coil spring60is disposed inside the first coil spring58and placed between the common spring receiver62and a second spring receiver66. The second spring receiver66is fixed on the outer periphery of the connection shaft54.

When the spool28is displaced in the X2direction from the neutral position, the first coil spring58is compressed in the X direction and applies biasing force in the X1direction to the spool28. When the spool28is displaced in the X1direction from the neutral position, the second coil spring60is compressed in the X direction and applies biasing force in the X2direction to the spool28. That is to say, when energization to the exciting coil50is stopped, the first coil spring58and the second coil spring60return the spool28to the neutral position, and when the exciting coil50is not energized, the first coil spring58and the second coil spring60keep the spool28at the neutral position stably.

The stator housing40is provided with a magnetic sensor53capable of detecting magnetic flux that changes in accordance with the displacement of the magnet part52in the X direction. This magnetic sensor53can detect the position of the spool28that is displaced together with the magnet part52.

The servo valve10according to the present embodiment is basically structured as described above, and the operation thereof is hereinafter described. Note that in an initial state, the spool28is at a neutral position as illustrated inFIG. 3.

In the initial state, the second opening24bof the sleeve22is closed by the second land30bof the spool28, and the fourth opening24dof the sleeve22is closed by the third land30cof the spool28. Thus, the fluid is not supplied to or discharged from the one pressure chamber36aand the other pressure chamber36bof the fluid pressure cylinder36.

In the initial state, when the exciting coil50is energized so that the current flows into the exciting coil50in the predetermined direction, the first pole tooth44aof the first end yoke44becomes N-pole and the second pole tooth46aof the second end yoke46becomes S-pole. Then, the spool28that is integral with the magnet part52is displaced in the X1direction due to an interaction between the magnetic flux that occurs in the first end yoke44and the magnetic flux of the first magnet52aand an interaction between the magnetic flux that occurs in the second end yoke46and the magnetic flux of the second magnet52b.

As the spool28is displaced in the X1direction, the following occurs. First, when the displaced amount of the spool28reaches a2, the closed state of the fourth opening24dof the sleeve22by the third land30cof the spool28is canceled and the fourth opening24dof the sleeve22starts to overlap with the third groove32cof the spool28. Next, when the displaced amount of the spool28reaches b2, the closed state of the second opening24bof the sleeve22by the second land30bof the spool28is canceled and the second opening24bof the sleeve22starts to overlap with the second groove32bof the spool28.

When the fourth opening24dof the sleeve22overlaps with the third groove32cof the spool28, the fourth port20dconnected to the other pressure chamber36bof the fluid pressure cylinder36communicates with the fifth port20econnected to the fluid supply source. In addition, when the second opening24bof the sleeve22overlaps with the second groove32bof the spool28, the second port20bconnected to the one pressure chamber36aof the fluid pressure cylinder36communicates with the third port20cconnected to the fluid discharge port.

As illustrated inFIG. 4, when the spool28has been displaced in the X1direction by a predetermined amount, the fourth opening24doverlaps with the third groove32cby a length L1in the X direction, and the second opening24boverlaps with the second groove32bby a length L2in the X direction.

At the neutral position, the lap length a2is less than the lap length b2, wherein the lap length a2is a length, in the X direction, of a portion where the third land30cis in contact with an inner wall surface of the sleeve22between the fourth opening24dand the fifth opening24e, and the lap length b2is a length, in the X direction, of a portion where the second land30bis in contact with an inner wall surface of the sleeve22between the second opening24band the third opening24c. Thus, the length L2is less than the length L1by (b2−a2). Therefore, the effective area of a flow path from the one pressure chamber36ato the fluid discharge port is smaller than the effective area of a flow path from the fluid supply source to the other pressure chamber36b. As a result, when the fluid is supplied to the other pressure chamber36band the fluid is discharged from the one pressure chamber36a, meter-out control that reduces the flow rate of the discharged fluid is performed. Note that the term “effective area of flow path” is a cross-section area at the smallest portion in the flow path.

As illustrated inFIG. 5, when the spool28has been further displaced in the X1direction by the predetermined amount, the fourth opening24doverlaps with the third groove32cin the X direction by a length L3that is greater than the length L1, and the second opening24boverlaps with the second groove32bin the X direction by a length L4that is greater than the length L2. Since the length L4is less than the length L3, the meter-out control is performed.

Since the length L3is greater than the length L1, the flow rate of the fluid supplied to the other pressure chamber36bis large compared with the case inFIG. 4. Moreover, since the length L4is greater than the length L2, the flow rate of the fluid discharged from the one pressure chamber36ais also large compared with the case inFIG. 4. Thus, the operation speed of the fluid pressure cylinder36is high.

Next, after the energization to the exciting coil50is stopped so that the spool28is returned to the neutral position, when the exciting coil50is energized again so that the current flows into the exciting coil50in an opposite direction of the predetermined direction, the first pole tooth44aof the first end yoke44becomes S-pole and the second pole tooth46aof the second end yoke46becomes N-pole. Then, the spool28that is integral with the magnet part52is displaced in the X2direction due to the interaction between the magnetic flux that occurs in the first end yoke44and the magnetic flux of the first magnet52aand the interaction between the magnetic flux that occurs in the second end yoke46and the magnetic flux of the second magnet52b.

As the spool28is displaced in the X2direction, the following occurs. First, when the displaced amount of the spool28reaches a1, the closed state of the second opening24bof the sleeve22by the second land30bof the spool28is canceled and the second opening24bof the sleeve22starts to overlap with the first groove32aof the spool28. Next, when the displaced amount of the spool28reaches b1, the closed state of the fourth opening24dof the sleeve22by the third land30cof the spool28is canceled and the fourth opening24dof the sleeve22starts to overlap with the second groove32bof the spool28.

When the second opening24bof the sleeve22overlaps with the first groove32aof the spool28, the second port20bconnected to the one pressure chamber36aof the fluid pressure cylinder36communicates with the first port20aconnected to the fluid supply source. In addition, when the fourth opening24dof the sleeve22overlaps with the second groove32bof the spool28, the fourth port20dconnected to the other pressure chamber36bof the fluid pressure cylinder36communicates with the third port20cconnected to the fluid discharge port.

As illustrated inFIG. 6, when the spool28has been displaced in the X2direction by the predetermined amount, the second opening24boverlaps with the first groove32aby a length L5in the X direction and the fourth opening24doverlaps with the second groove32bby a length L6in the X direction.

At the neutral position, the lap length a1is less than the lap length b1. The lap length a1is a length, in the X direction, of a portion where the second land30bis in contact with an inner wall surface of the sleeve22between the first opening24aand the second opening24b. The lap length b1is a length, in the X direction, of a portion where the third land30cis in contact with an inner wall surface of the sleeve22between the third opening24cand the fourth opening24d. Thus, the length L6is less than the length L5by (b1−a1). Therefore, the effective area of the flow path from the other pressure chamber36bto the fluid discharge port is smaller than the effective area of the flow path from the fluid supply source to the one pressure chamber36a. As a result, when the fluid is supplied to the one pressure chamber36aand the fluid is discharged from the other pressure chamber36b, the meter-out control that reduces the flow rate of the discharged fluid is performed.

As illustrated inFIG. 7, when the spool28has been further displaced in the X2direction by the predetermined amount, the second opening24boverlaps with the first groove32ain the X direction by a length L7that is greater than the length L5and the fourth opening24doverlaps with the second groove32bin the X direction by a length L8that is greater than the length L6. Since the length L8is less than the length L7, the meter-out control is performed.

Since the length L7is greater than the length L5, the flow rate of the fluid supplied to the one pressure chamber36ais large compared with the case inFIG. 6. Moreover, since the length L8is greater than the length L6, the flow rate of the fluid discharged from the other pressure chamber36bis also large compared with the case inFIG. 6. Thus, the operation speed of the fluid pressure cylinder36is high.

FIG. 8shows a relation between the position of the spool28and the effective area of the flow path including the second port20band a relation between the position of the spool28and the effective area of the flow path including the fourth port20din the case where the above meter-out control is performed. A horizontal axis represents the position of the spool28, and the origin is the point when the spool28is at the neutral position. The displaced amount of the spool28in the X1direction is expressed by a negative value, and the displaced amount of the spool28in the X2direction is expressed by a positive value. A vertical axis shows the effective area of the flow path. The effective area of the flow path when the fluid is supplied to the one pressure chamber36aor the other pressure chamber36bis expressed by a positive value, and the effective area of the flow path when the fluid is discharged from the other pressure chamber36bor the one pressure chamber36ais expressed by a negative value.

The relation between the position of the spool28and the effective area of the flow path including the second port20bis shown by a solid line, and the relation between the position of the spool28and the effective area of the flow path including the fourth port20dis shown by a dashed line. As can be understood fromFIG. 8, when the spool28has been displaced from the neutral position in the X1direction by the predetermined amount or more, the effective area of the flow path where the fluid in the other pressure chamber36bis discharged through the fourth port20dis smaller than the effective area of the flow path where the fluid is supplied to the one pressure chamber36athrough the second port20b. Moreover, when the spool28has been displaced from the neutral position in the X2direction by the predetermined amount or more, the effective area of the flow path where the fluid in the one pressure chamber36ais discharged through the second port20bis smaller than the effective area of the flow path where the fluid is supplied to the other pressure chamber36bthrough the fourth port20d.

Here, the maximum displaced amount of the spool28in the X1direction is set within a range in which a flow path area where the fourth opening24doverlaps with the third groove32cdoes not exceed the flow path area where the fifth opening24eoverlaps with the third groove32c, for example. Similarly, the maximum displaced amount of the spool28in the X2direction is set within a range in which the flow path area where the second opening24boverlaps with the first groove32adoes not exceed the flow path area where the first opening24aoverlaps with the first groove32a, for example.

In the present embodiment, when the spool28is at the neutral position, a magnitude relation is set so that the lap length a1is less than the lap length b1and the lap length a2is less than the lap length b2. On the other hand, when meter-in control is to be performed, it is only necessary to set this magnitude relation in reverse. That is to say, when the spool28is at the neutral position, if the magnitude relation is set so that the lap length a1is greater than the lap length b1and the lap length a2is greater than the lap length b2, the meter-in control can be performed.

Moreover, in the present embodiment, the fluid supply source is connected to the first port20aand the fifth port20eand the fluid discharge port is connected to the third port20c. However, if the fluid supply source is connected to the third port20cand the fluid discharge port is connected to the first port20aand the fifth port20e, the meter-in control can be performed.

FIG. 9shows the relation between the position of the spool28and the effective area of the flow path including the second port20band the relation between the position of the spool28and the effective area of the flow path including the fourth port20din the case where the meter-in control is performed. The former is shown by a solid line, and the latter is shown by a dashed line.

As can be understood fromFIG. 9, when the spool28has been displaced from the neutral position in the X1direction by the predetermined amount or more, the effective area of the flow path where the fluid is supplied to the other pressure chamber36bthrough the fourth port20dis smaller than the effective area of the flow path where the fluid in the one pressure chamber36ais discharged through the second port20b. Moreover, when the spool28has been displaced from the neutral position in the X2direction by the predetermined amount or more, the effective area of the flow path where the fluid is supplied to the one pressure chamber36athrough the second port20bis smaller than the effective area of the flow path where the fluid in the other pressure chamber36bis discharged through the fourth port20d.

The position of the spool28is controlled by the valve controller68. To the valve controller68, a command signal regarding a target position of the spool28is input from an upper-level controller (PLC or the like) that is not shown, and a detection signal regarding the current position of the spool28is also input from the magnetic sensor53. On the basis of these signals, the valve controller68outputs a required electric power supply signal to the exciting coil50so as to displace the spool28to the target position.

The target position of the spool28can be set to any position (steplessly), and can be set to a plurality of predetermined positions other than the neutral position. Examples of the predetermined positions include two predetermined positions respectively in the X1direction and the X2direction, and four positions including two predetermined positions in the X1direction and two predetermined positions in the X2direction. If the target positions include a plurality of positions in the X1direction and a plurality of positions in the X2direction, the operation speed of the fluid pressure cylinder36in both ways of the reciprocal motion can be adjusted step by step. These target positions can be set in the valve controller68in advance. If the number of settings of the target position is small, the command signal from the upper-level controller can be simplified, for example, combination of binary signals (ON/OFF signals).

In the servo valve10according to the present embodiment, each lap length between the land and the inner wall surface of the sleeve22that lies between the two adjacent openings when the spool28is at the neutral position is set ingeniously. Thus, the meter-out control or the meter-in control can be performed by the servo valve10alone.

Second Embodiment

Next, a servo valve according to a second embodiment of the present invention is described with reference toFIG. 10. In the second embodiment, the shape of the spool is different from that in the first embodiment. Note that the constituent elements other than the sleeve and the spool are described using the constituent elements of the servo valve10according to the first embodiment and the reference symbols thereof as appropriate.

A cylindrical spool74is provided with a first land76a, a second land76b, and a third land76cthat are in close contact with the inside of a sleeve70. The first to third lands76ato76care arranged in the X direction. Between the first land76aand the second land76b, a first groove78ais formed so as to surround the outer peripheral surface. Similarly, between the second land76band the third land76c, a second groove78bis formed so as to surround the outer peripheral surface.

A first opening72a, a second opening72b, a third opening72c, a fourth opening72d, and a fifth opening72eof the sleeve70communicate with the first port20ato the fifth port20eof the valve body16, respectively. The shape of the first opening72ato the fifth opening72ewhen viewed in the radial direction is the same rectangular shape, and the width thereof is constant in the X direction.

As illustrated inFIG. 10, when the actuator unit14is not energized and the spool74is at the neutral position, the first opening72aof the sleeve70is closed by the first land76aof the spool74. Similarly, the third opening72cof the sleeve70is closed by the second land76bof the spool74, and the fifth opening72eof the sleeve70is closed by the third land76cof the spool74. Thus, the second opening72bconnected to the one pressure chamber36aof the fluid pressure cylinder36is blocked from the first opening72aconnected to the fluid supply source and is also blocked from the third opening72cconnected to the fluid discharge port. In addition, the fourth opening72dconnected to the other pressure chamber36bof the fluid pressure cylinder36is blocked from the fifth opening72econnected to the fluid supply source and is also blocked from the third opening72cconnected to the fluid discharge port.

When the spool74is at the neutral position, a lap length d1is less than a lap length c1. The lap length d1is a length, in the X direction, of a portion where the second land76bis in contact with an inner wall surface of the sleeve70that lies between the third opening72cand the fourth opening72d. The lap length c1is a length, in the X direction, of a portion where the first land76ais in contact with an inner wall surface of the sleeve70that lies between the first opening72aand the second opening72b. In addition, when the spool74is at the neutral position, a lap length d2is less than a lap length c2. The lap length d2is a length, in the X direction, of a portion where the second land76bis in contact with an inner wall surface of the sleeve70that lies between the second opening72band the third opening72c. The lap length c2is a length, in the X direction, of a portion where the third land76cis in contact with an inner wall surface of the sleeve70that lies between the fourth opening72dand the fifth opening72e. In the present embodiment, the lap length c2is equal to the lap length c1, and the lap length d2is equal to the lap length d1.

As the spool74is displaced in the X1direction from the neutral position, the following occurs. First, when the displaced amount of the spool74reaches d1, the closed state of the third opening72cof the sleeve70by the second land76bof the spool74is canceled, and the third opening72cof the sleeve70starts to overlap with the second groove78bof the spool74. Next, when the displaced amount of the spool74reaches c1, the closed state of the first opening72aof the sleeve70by the first land76aof the spool74is canceled, and the first opening72aof the sleeve70starts to overlap with the first groove78aof the spool74.

When the third opening72cof the sleeve70overlaps with the second groove78bof the spool74, the fourth port20dconnected to the other pressure chamber36bof the fluid pressure cylinder36communicates with the third port20cconnected to the fluid discharge port. In addition, when the first opening72aof the sleeve70overlaps with the first groove78aof the spool74, the second port20bconnected to the one pressure chamber36aof the fluid pressure cylinder36communicates with the first port20aconnected to the fluid supply source.

In this case, the length, in the X direction, of an overlapped portion where the first opening72aoverlaps with the first groove78ais less than the length, in the X direction, of an overlapped portion where the third opening72coverlaps with the second groove78b(not shown). Therefore, the effective area of the flow path from the fluid supply source to the one pressure chamber36ais smaller than the effective area of the flow path from the other pressure chamber36bto the fluid discharge port. Thus, when the fluid is supplied to the one pressure chamber36aand the fluid is discharged from the other pressure chamber36b, the meter-in control that reduces the flow rate of the fluid to be supplied is performed.

As the spool74is displaced in the X2direction from the neutral position, the following occurs. First, when the displaced amount of the spool74reaches d2, the closed state of the third opening72cof the sleeve70by the second land76bof the spool74is canceled and the third opening72cof the sleeve70starts to overlap with the first groove78aof the spool74. Next, when the displaced amount of the spool74reaches c2, the closed state of the fifth opening72eof the sleeve70by the third land76cof the spool74is canceled and the fifth opening72eof the sleeve70starts to overlap with the second groove78bof the spool74.

When the third opening72cof the sleeve70overlaps with the first groove78aof the spool74, the second port20bconnected to the one pressure chamber36aof the fluid pressure cylinder36communicates with the third port20cconnected to the fluid discharge port. In addition, when the fifth opening72eof the sleeve70overlaps with the second groove78bof the spool74, the fourth port20dconnected to the other pressure chamber36bof the fluid pressure cylinder36communicates with the fifth port20econnected to the fluid supply source.

In this case, the length, in the X direction, of an overlapped portion where the fifth opening72eoverlaps with the second groove78bis less than the length, in the X direction, of an overlapped portion where the third opening72coverlaps with the first groove78a(not shown). Therefore, the effective area of the flow path from the fluid supply source to the other pressure chamber36bis smaller than the effective area of the flow path from the one pressure chamber36ato the fluid discharge port. Thus, when the fluid is supplied to the other pressure chamber36band the fluid is discharged from the one pressure chamber36a, the meter-in control that reduces the flow rate of the fluid to be supplied is performed.

In the present embodiment, when the spool74is at the neutral position, the magnitude relationship is set such that the lap length d1is less than the lap length c1and the lap length d2is less than the lap length c2. On the other hand, when the meter-out control is to be performed, it is only necessary to set this magnitude relationship in reverse. Moreover, in the present embodiment, the fluid supply source is connected to the first port20aand the fifth port20eand the fluid discharge port is connected to the third port20c. However, if the fluid supply source is connected to the third port20cand the fluid discharge port is connected to the first port20aand the fifth port20e, the meter-out control can be performed.

In the servo valve according to the present embodiment, the lap length of a portion where the land is in contact with an inner wall surface of the sleeve70that lies between the two adjacent openings when the spool74is at the neutral position is set ingeniously. Thus, the meter-out control or the meter-in control can be performed by the servo valve alone.

Third Embodiment

Next, a servo valve according to a third embodiment of the present invention is described with reference toFIG. 11toFIG. 13. In the third embodiment, the relation of the lap lengths at the neutral position and the shapes of the openings of the sleeve are different from those in the first embodiment. Note that the constituent elements other than the sleeve and the spool are described using the constituent elements of the servo valve10according to the first embodiment and the reference symbols thereof as appropriate.

As illustrated inFIG. 11, when a spool84is at the neutral position, a second opening82bof a sleeve80is closed by a second land86bof the spool84, and a fourth opening82dof the sleeve80is closed by a third land86cof the spool84.

When the spool84is at the neutral position, the lap length of a portion where the second land86bis in contact with an inner wall surface of the sleeve80that lies between a first opening82aand the second opening82bis equal to the lap length of a portion where the third land86cis in contact with an inner wall surface of the sleeve80that lies between the third opening82cand the fourth opening82d. In addition, when the spool84is at the neutral position, the lap length of a portion where the third land86cis in contact with an inner wall surface of the sleeve80that lies between the fourth opening82dand a fifth opening82eis equal to the lap length of a portion where the second land86bis in contact with an inner wall surface of the sleeve80that lies between the second opening82band the third opening82c.

The shape of the second opening82bwhen viewed in the radial direction is a triangular shape having a base positioned on the side of an end in the X1direction and a vertex opposed to the base being positioned on the side of an end in the X2direction. The shape of the fourth opening82dwhen viewed in the radial direction is a triangular shape having a base positioned on the side of the end in the X2direction and a vertex opposed to the base being positioned on the side of the end in the X1direction. The shape of the fourth opening82dis obtained by inversing the shape of the second opening82bin the X direction.

On the other hand, the shape of the first opening82a, the third opening82c, and the fifth opening82ewhen viewed in the radial direction is the same rectangular shape, and the width thereof is constant in the X direction and is substantially the same as the length of the base of the above triangle corresponding to the maximum width of the second opening82band the fourth opening82d. In the present embodiment, the second opening82band the fourth opening82dhave a triangular shape. However, it is only necessary that the shape of each of the second opening82band the fourth opening82dis asymmetric in the X1direction and the X2direction and the shape of the second opening82bis obtained by inversing the shape of the fourth opening82din the X direction. Moreover, it is preferable that the shape with the width gradually increasing in the X1direction and the shape with the width gradually increasing in the X2direction are paired.

The operation of the servo valve according to the third embodiment is hereinafter described on the premise that the first opening82ais connected to the fluid supply source, the second opening82bis connected to the one pressure chamber36aof the fluid pressure cylinder36, the third opening82cis connected to the fluid discharge port, the fourth opening82dis connected to the other pressure chamber36bof the fluid pressure cylinder36, and the fifth opening82eis connected to the fluid supply source.

As illustrated inFIG. 12, when the spool84has been displaced in the X1direction by the predetermined amount or more, an X-direction length e1is equal to an X-direction length e2. The X-direction length e1is a length, in the X direction, of a portion where the second opening82bof the sleeve80overlaps with a second groove88bof the spool84. The X-direction length e2is a length, in the X direction, of a portion where the fourth opening82dof the sleeve80overlaps with a third groove88cof the spool84. However, an area S1of a portion where the second opening82boverlaps with the second groove88bon the vertex side of the triangle is smaller than an area S2of a portion where the fourth opening82doverlaps with the third groove88con the base side of the triangle. Therefore, the effective area of the flow path from the one pressure chamber36ato the fluid discharge port is smaller than the effective area of the flow path from the fluid supply source to the other pressure chamber36b, so that the meter-out control is performed.

As illustrated inFIG. 13, when the spool84has been displaced in the X2direction by the predetermined amount or more, an X-direction length e3is equal to an X-direction length e4. The X-direction length e3is a length, in the X direction, of a portion where the fourth opening82dof the sleeve80overlaps with the second groove88bof the spool84. The X-direction length e4is a length, in the X direction, of a portion where the second opening82bof the sleeve80overlaps with a first groove88aof the spool84. However, an area S3of a portion where the fourth opening82doverlaps with the second groove88bon the vertex side of the triangle is smaller than an area S4of a portion where the second opening82boverlaps with the first groove88aon the base side of the triangle. Therefore, the effective area of the flow path from the other pressure chamber36bto the fluid discharge port is smaller than the effective area of the flow path from the fluid supply source to the one pressure chamber36a, so that the meter-out control is performed. Note that inFIG. 12andFIG. 13, hatched areas of the second opening82band the fourth opening82dindicate a state where these areas are closed by the spool84.

Here, the maximum displaced amount of the spool84in the X1direction is set within a range in which the entire second opening82boverlaps with the second groove88band the entire fourth opening82ddoes not overlap with the third groove88c. This is because the effective area of the flow path from the one pressure chamber36ato the fluid discharge port is equal to the effective area of the flow path from the fluid supply source to the other pressure chamber36bin the case that the entire fourth opening also overlaps with the third groove. Similarly, the maximum displaced amount of the spool84in the X2direction is set within a range in which the entire second opening82boverlaps with the first groove88aand the entire fourth opening82ddoes not overlap with the second groove88b.

In the present embodiment, the second opening82bhas a triangular shape having the base positioned on the side of the end in the X1direction and the fourth opening82dhas a triangular shape having the base positioned on the side of the end in the X2direction. However, if the second opening82bhas a triangular shape having the base positioned on the side of the end in the X2direction and the fourth opening82dhas a triangular shape having the base positioned on the side of the end in the X1direction, the meter-in control can be performed.

In addition, in the present embodiment, the fluid supply source is connected to the first port20aand the fifth port20eand the fluid discharge port is connected to the third port20c. However, if the fluid supply source is connected to the third port20cand the fluid discharge port is connected to the first port20aand the fifth port20e, the meter-in control can be performed.

In the servo valve according to the present embodiment, the shapes of the openings of the sleeve80are formed ingeniously. Thus, the meter-out control or the meter-in control can be performed by the servo valve alone.

Fourth Embodiment

Next, a servo valve according to a fourth embodiment of the present invention is described with reference toFIG. 14toFIG. 16. In the fourth embodiment, the relationship of the lap lengths at the neutral position and the shapes of the openings of the sleeve are different from those in the second embodiment. Note that the constituent elements other than the sleeve and the spool are described using the constituent elements of the servo valve10according to the first embodiment and the reference symbols thereof as appropriate.

As illustrated inFIG. 14, when a spool94is at the neutral position, a first opening92a, a third opening92c, and a fifth opening92eof a sleeve90are closed by a first land96a, a second land96b, and a third land96cof the spool94, respectively.

When the spool94is at the neutral position, the lap length of a portion where the second land96bis in contact with an inner wall surface of the sleeve90that lies between the third opening92cand a fourth opening92dis equal to the lap length of a portion where the first land96ais in contact with an inner wall surface of the sleeve90that lies between the first opening92aand a second opening92b. In addition, when the spool94is at the neutral position, the lap length of a portion where the second land96bis in contact with an inner wall surface of the sleeve90that lies between the second opening92band the third opening92cis equal to the lap length of a portion where the third land96cis in contact with an inner wall surface of the sleeve90that lies between the fourth opening92dand the fifth opening92e.

The shape of the first opening92awhen viewed in the radial direction is a triangular shape having a base positioned on the side of an end in the X1direction and a vertex opposed to the base being positioned on the side of an end in the X2direction. The shape of the fifth opening92ewhen viewed in the radial direction is a triangular shape having a base positioned on the side of the end in the X2direction and a vertex opposed to the base being positioned on the side of the end in the X1direction. The shape of the fifth opening92eis obtained by inversing the shape of the first opening92ain the X direction.

On the other hand, the shape of the second opening92b, the third opening92c, and the fourth opening92dwhen viewed in the radial direction is the same rectangular shape, and the width thereof is constant in the X direction and is substantially the same as the length of the base of the above triangle corresponding to the maximum width of the first opening92aand the fifth opening92e. In the present embodiment, the first opening92aand the fifth opening92ehave a triangular shape. However, it is only necessary that the shape of each of the first opening92aand the fifth opening92eis asymmetric in the X1direction and the X2direction and the shape of the first opening92ais obtained by inversing the shape of the fifth opening92ein the X direction. Alternatively, it is only necessary that the shape of each of the first opening92aand the fifth opening92eis the same shape that is symmetric in the X1direction and the X2direction. Note that it is necessary that the width of the first opening92aand the width of the fifth opening92eare within the range of the width of the third opening92c.

The operation of the servo valve according to the fourth embodiment is hereinafter described on the premise that the first opening92ais connected to the fluid discharge port, the second opening92bis connected to the one pressure chamber36aof the fluid pressure cylinder36, the third opening92cis connected to the fluid supply source, the fourth opening92dis connected to the other pressure chamber36bof the fluid pressure cylinder36, and the fifth opening92eis connected to the fluid discharge port.

As illustrated inFIG. 15, when the spool94has been displaced in the X1direction by the predetermined amount or more, an X-direction length e5is equal to an X-direction length e6. The X-direction length e5is a length, in the X direction, of a portion where the first opening92aof the sleeve90overlaps with a first groove98aof the spool94. The X-direction length e6is a length, in the X direction, of a portion where the third opening92cof the sleeve90overlaps with a second groove98bof the spool94. However, an area S5of a portion where the first opening92aoverlaps with the first groove98aon the vertex side of the triangle is smaller than an area S6of a portion where the third opening92chaving the constant width overlaps with the second groove98b. Therefore, the effective area of the flow path from the one pressure chamber36ato the fluid discharge port is smaller than the effective area of the flow path from the fluid supply source to the other pressure chamber36b, so that the meter-out control is performed.

As illustrated inFIG. 16, when the spool94has been displaced in the X2direction by the predetermined amount or more, an X-direction length e7is equal to an X-direction length e8. The X-direction length e7is a length, in the X direction, of a portion where the fifth opening92eof the sleeve90overlaps with the second groove98bof the spool94. The X-direction length e8is a length, in the X direction, of a portion where the third opening92cof the sleeve90overlaps with the first groove98aof the spool94. However, an area S7of a portion where the fifth opening92eoverlaps with the second groove98bon the vertex side of the triangle is smaller than an area S8where the third opening92chaving the constant width overlaps with the first groove98a. Therefore, the effective area of the flow path from the other pressure chamber36bto the fluid discharge port is smaller than the effective area of the flow path from the fluid supply source to the one pressure chamber36a, so that the meter-out control is performed. Note that inFIG. 15andFIG. 16, hatched areas of the first opening92a, the third opening92c, and the fifth opening92eindicate a state where these areas are closed by the spool94.

In the present embodiment, the first opening92ahas a triangular shape in which the base is positioned on the side of the end in the X1direction, and the fifth opening92ehas a triangular shape in which the base is positioned on the side of the end in the X2direction. However, if the first opening92ahas a triangular shape in which the base is positioned on the side of the end in the X2direction and the fifth opening92ehas a triangular shape in which the base is positioned on the side of the end in the X1direction, the meter-in control can be performed.

In addition, in the present embodiment, the fluid supply source is connected to the third port20cand the fluid discharge port is connected to the first port20aand the fifth port20e. However, if the fluid supply source is connected to the first port20aand the fifth port20eand the fluid discharge port is connected to the third port20c, the meter-in control can be performed.

In the servo valve according to the present embodiment, the shapes of the openings of the sleeve90are formed ingeniously. Thus, the meter-out control or the meter-in control can be performed by the servo valve alone.

Fifth Embodiment

Next, a servo valve according to a fifth embodiment of the present invention is described with reference toFIG. 17toFIG. 19. In the fifth embodiment, the relation of the lap lengths at the neutral position and the shapes of the openings of the sleeve are different from those in the second embodiment. Note that the constituent elements other than the sleeve and the spool are described using the constituent elements of the servo valve10according to the first embodiment and the reference symbols thereof as appropriate.

As illustrated inFIG. 17, when a spool104is at the neutral position, a first opening102a, a third opening102c, and a fifth opening102eof a sleeve100are closed by a first land106a, a second land106b, and a third land106cof the spool104, respectively.

When the spool104is at the neutral position, the lap length of a portion where the second land106bis in contact with an inner wall surface of the sleeve100that lies between the third opening102cand a fourth opening102dis equal to the lap length of a portion where the first land106ais in contact with an inner wall surface of the sleeve100that lies between the first opening102aand a second opening102b. In addition, when the spool104is at the neutral position, the lap length of a portion where the second land106bis in contact with an inner wall surface of the sleeve100that lies between the second opening102band the third opening102cis equal to the lap length of a portion where the third land106cis in contact with an inner wall surface of the sleeve100that lies between the fourth opening102dand the fifth opening102e.

The shape of the third opening102cwhen viewed in the radial direction is a rhombic shape that is symmetric in the X1direction and the X2direction, that is, a rhombic shape with one of the diagonal lines being oriented in the X direction. On the other hand, the shape of the first opening102a, the second opening102b, the fourth opening102d, and the fifth opening102ewhen viewed in the radial direction is the same rectangular shape, and the width thereof is constant in the X direction and is substantially the same as the length of the other diagonal line of the rhombic shape corresponding to the maximum width of the third opening102c. In the present embodiment, the third opening102chas a rhombic shape. However, as long as the shape thereof is symmetric in the X1direction and the X2direction and the width thereof is within the range of the width of the first opening102aand the fifth opening102ewith a rectangular shape, any shape may be employed.

The operation of the servo valve according to the fifth embodiment is hereinafter described on the premise that the first opening102ais connected to the fluid supply source, the second opening102bis connected to the one pressure chamber36aof the fluid pressure cylinder36, the third opening102cis connected to the fluid discharge port, the fourth opening102dis connected to the other pressure chamber36bof the fluid pressure cylinder36, and the fifth opening102eis connected to the fluid supply source.

As illustrated inFIG. 18, when the spool104has been displaced in the X1direction by the predetermined amount or more, an X-direction length e9is equal to an X-direction length e10. The X-direction length e9is a length, in the X direction, of a portion where the third opening102cof the sleeve100overlaps with a second groove108bof the spool104. The X-direction length e10is a length, in the X direction, of a portion where the first opening102aof the sleeve100overlaps with a first groove108aof the spool104. However, an area S9of a portion where the third opening102coverlaps with the second groove108bon a vertex side of the rhombus in the X2direction is smaller than an area S10of a portion where the first opening102ahaving the constant width overlaps with the first groove108a. Therefore, the effective area of the flow path from the other pressure chamber36bto the fluid discharge port is smaller than the effective area of the flow path from the fluid supply source to the one pressure chamber36a, so that the meter-out control is performed.

As illustrated inFIG. 19, when the spool104has been displaced in the X2direction by the predetermined amount or more, an X-direction length e11is equal to an X-direction length e12. The X-direction length e11is a length, in the X direction, of a portion where the third opening102cof the sleeve100overlaps with the first groove108aof the spool104. The X-direction length e12is a length, in the X direction, of a portion where the fifth opening102eof the sleeve100overlaps with the second groove108bof the spool104. However, an area S11of a portion where the third opening102coverlaps with the first groove108aon the vertex side in the X1direction of the rhombus is smaller than an area S12of a portion where the fifth opening102ewith the constant width overlaps with the second groove108b. Therefore, the effective area of the flow path from the one pressure chamber36ato the fluid discharge port is smaller than the effective area of the flow path from the fluid supply source to the other pressure chamber36b, so that the meter-out control is performed. Note that inFIG. 18andFIG. 19, hatched areas of the first opening102a, the third opening102c, and the fifth opening102eindicate a state where these areas are closed by the spool104.

In the present embodiment, the fluid supply source is connected to the first port20aand the fifth port20eand the fluid discharge port is connected to the third port20c. However, if the fluid supply source is connected to the third port20cand the fluid discharge port is connected to the first port20aand the fifth port20e, the meter-in control can be performed.

In the servo valve according to the present embodiment, the shapes of the openings of the sleeve100are formed ingeniously. Thus, the meter-out control or the meter-in control can be performed by the servo valve alone.

The servo valve according to the present invention is not limited to the above embodiments, and can employ various structures without departing from the gist and essence of the present invention.