Patent Description:
Spool valves have been known as one type of flow control valves for use in hydraulic circuits. In such a spool valve, a spool is slidably located in a slide hole of a housing, and the flow rate of a fluid flowing between passages formed in the housing is controlled by the position of the spool.

In one type of spool valve, the spool is shifted by pilot pressure, and in another type of spool valve, the spool is shifted by an electric motor. For example, Patent Literature <NUM> discloses a spool valve that includes a linear motion mechanism between an electric motor and a spool. The linear motion mechanism converts rotational motion into linear motion. Specifically, in the spool valve, the spool is coupled to a piston; a nut is fixed to the piston; and a screw shaft screwed with the nut is rotated by the electric motor.

<CIT> discloses a hydraulic distribution device that is designed to avoid sticking and provide better balance of a drawer. The distribution device is characterised in that the distribution device comprises means for ensuring a translation of the drawer of amplitude proportional to the angular value of rotation of the shaft of a digital motor assembly.

In the spool valve disclosed by Patent Literature <NUM>, in a case where the diameter of the spool is large, a force that the spool receives from the fluid flowing between the passages is great (this force is often called "flow force"). Therefore, in this case, a high-power electric motor is necessary for precise control of the position of the spool. This causes an increase in cost as well as an increase in the size of the spool valve.

In view of the above, an object of the present disclosure is to provide a spool valve that makes it possible to precisely control the position of the spool even in a case where the electric motor is a low-power motor.

In order to solve the above-described problems, a spool valve according to the present disclosure includes: a first housing including passages and a slide hole; a spool slidably located in the slide hole; a second housing that forms a servo chamber that is coaxial with the slide hole; a sleeve slidably located in the servo chamber, the sleeve dividing the servo chamber into a first pressure chamber and a second pressure chamber, the first pressure chamber being adjacent to the first housing, the second pressure chamber being away from the first housing, the sleeve being coupled to the spool in the first pressure chamber; a piston slidably fitted in the sleeve and extending from inside the sleeve beyond the second pressure chamber; a nut fixed to the piston; a screw shaft screwed with the nut; and an electric motor that rotates the screw shaft. The second housing includes a drain port and an input port that is to be connected to a pressure source of a hydraulic fluid. The first pressure chamber communicates with the input port. In a balanced state where a force that is applied to the sleeve by the hydraulic fluid in the first pressure chamber, and a force that is applied to the sleeve by the hydraulic fluid in the second pressure chamber, are balanced, the second pressure chamber is blocked from the input port and the drain port by the piston. From the balanced state, when the piston shifts in a direction toward the spool, the second pressure chamber comes into communication with the input port. From the balanced state, when the piston shifts in a direction away from the spool, the second pressure chamber comes into communication with the drain port.

According to the above configuration, from the balanced state, when the piston is shifted by the electric motor in the direction toward the spool, the second pressure chamber comes into communication with the input port. Consequently, the pressure in the second pressure chamber increases, and the sleeve also shifts in the direction toward the spool. However, when the sleeve shifts beyond the position where the balanced state is achieved, the second pressure chamber comes into communication with the drain port, and consequently, the pressure in the second pressure chamber decreases. Due to this function, the sleeve comes to a stop again at the position where the balanced state is achieved. That is, the sleeve shifts in a manner to follow the shifting of the piston. The same applies to a case where, from the balanced state, the piston is shifted by the electric motor in the direction away from the spool.

Meanwhile, in a case where the piston does not shift, the balanced state is maintained. That is, the second pressure chamber is blocked from the input port and the drain port by the piston. Therefore, even when the spool receives a force from the fluid flowing between the passages of the first housing, due to the incompressibility of the hydraulic fluid in the second pressure chamber, the sleeve does not shift.

As described above, in the present disclosure, since the force that the spool receives from the fluid flowing between the passages does not affect the electric motor, even in a case where the electric motor is a low-power motor, the position of the spool can be controlled precisely.

The present disclosure makes it possible to precisely control the position of the spool even in a case where the electric motor is a low-power motor.

<FIG> shows a spool valve <NUM> according to one embodiment of the present disclosure. In the present embodiment, the spool valve <NUM> is a three-position valve including three ports 2a to 2c. Alternatively, the spool valve <NUM> may be a two-position valve. The number of ports of the spool valve <NUM> may be changed as necessary.

Specifically, the spool valve <NUM> includes a first housing <NUM> and a spool <NUM>. The first housing <NUM> includes the ports 2a to 2c on its outer surface. The spool <NUM> is held by the first housing <NUM>. The spool valve <NUM> further includes a second housing <NUM>, a casing <NUM>, and an electric motor <NUM>, which are coaxial with the spool <NUM>. The second housing <NUM> is mounted to the first housing <NUM>, and the electric motor <NUM> is mounted to the second housing <NUM> via the casing <NUM>.

The first housing <NUM> includes a slide hole <NUM> therein. The spool <NUM> is slidably located in the slide hole <NUM>. The first housing <NUM> further includes three passages <NUM> to <NUM>, which extend from the slide hole <NUM> to the ports 2a to 2c, respectively. The number of passages in the first housing <NUM> may be changed as necessary in accordance with the number of ports.

The spool <NUM> includes two annular grooves <NUM> and <NUM>. Hereinafter, for the sake of convenience of the description, one side in the axial direction of the spool <NUM> (the right side in <FIG>) is referred to as the right side, and the other side in the axial direction of the spool <NUM> (the left side in <FIG>) is referred to as the left side. When the spool <NUM> is at a neutral position thereof, the spool <NUM> blocks the passage <NUM> from both of the passages <NUM> and <NUM>. When the spool <NUM> shifts from the neutral position toward the right side, the passage <NUM> comes into communication with the passage <NUM> via the annular groove <NUM>. When the spool <NUM> shifts from the neutral position toward the left side, the passage <NUM> comes into communication with the passage <NUM> via the annular groove <NUM>.

In the present embodiment, when the spool <NUM> is at the neutral position, the left end of the spool <NUM> protrudes from the first housing <NUM>. However, the length of the spool <NUM> may be changed as necessary. When the spool <NUM> is at the neutral position, the left end of the spool <NUM> may be accommodated within the first housing <NUM>. In the present embodiment, the diameter of the left end of the spool <NUM> is less than the diameter of the slide hole <NUM>. Alternatively, the diameter of the left end of the spool <NUM> may be the same as the diameter of the slide hole <NUM>. Further alternatively, the diameter of the left end of the spool <NUM> may be larger than the diameter of the slide hole <NUM>, so long as within the movable range of the spool <NUM>, the left end of the spool <NUM> does not interfere with the first housing <NUM>.

As shown in <FIG>, the second housing <NUM> forms a servo chamber <NUM>, which is coaxial with the slide hole <NUM> of the first housing <NUM>. Specifically, the second housing <NUM> includes a deep bottomed hole whose center line coincides with the center line of the slide hole <NUM>. The bottomed hole, by being covered by the first housing <NUM> and the spool <NUM>, forms the servo chamber <NUM>.

A sleeve <NUM> is slidably located in the servo chamber <NUM>. Specifically, the sleeve <NUM> divides the servo chamber <NUM> into a first pressure chamber <NUM> and a second pressure chamber <NUM>. The first pressure chamber <NUM> is adjacent to the first housing <NUM>. The second pressure chamber <NUM> is away from the first housing <NUM>. The sleeve <NUM> includes a tubular portion and a sealing portion. The tubular portion surrounds an internal space of the sleeve <NUM>. The sealing portion seals the internal space of the sleeve <NUM> from the right side. That is, the internal space of the sleeve <NUM> is open only toward the left side.

In the first pressure chamber <NUM>, the sleeve <NUM> is coupled to the spool <NUM>. In the present embodiment, the right end of the sleeve <NUM> and the left end of the spool <NUM> are coupled to each other by a universal joint. Specifically, the spool <NUM> includes a groove <NUM> at its left end. A ball <NUM> is held in the groove <NUM>. The sleeve <NUM> includes a plate-shaped protrusion <NUM> at its right end. The plate-shaped protrusion <NUM> is located in the groove <NUM>. The protrusion <NUM> includes a hole that is fitted to the ball <NUM>.

Conversely to the present embodiment, the sleeve <NUM> may include, at its right end, the groove <NUM> in which the ball <NUM> is held, and the spool <NUM> may include, at its left end, the protrusion <NUM> located in the groove <NUM>. Alternatively, the right end of the sleeve <NUM> and the left end of the spool <NUM> may be coupled to each other by a joint different from a universal joint (e.g., a ball joint or spherical joint).

A piston <NUM> extends from inside the sleeve <NUM> toward the left side beyond the second pressure chamber <NUM>. The piston <NUM> is slidably fitted in the sleeve <NUM>. The piston <NUM> penetrates a part of the second housing <NUM>, the part being positioned on the left side of the second pressure chamber <NUM>. A left side portion of the piston <NUM>, the left side portion being positioned outside the second housing <NUM>, is accommodated in the casing <NUM>.

A nut <NUM> is fixed to the left side portion of the piston <NUM>. To be more specific, the piston <NUM> includes a holding hole <NUM> in its left side portion. The holding hole <NUM> is positioned on the center line of the piston <NUM>, and is open toward the left side. The nut <NUM> is located in the holding hole <NUM>. An unshown guide mechanism guides the piston <NUM> such that the piston <NUM> is shiftable only in the left-right direction (i.e., the piston <NUM> is prevented from rotating).

A screw shaft <NUM> is screwed with the nut <NUM>. The screw shaft <NUM> is rotated by the aforementioned electric motor <NUM>. Specifically, when the electric motor <NUM> rotates the screw shaft <NUM> in one direction, the piston <NUM> to which the nut <NUM> is fixed shifts toward the right side, whereas when the electric motor <NUM> rotates the screw shaft <NUM> in the opposite direction, the piston <NUM> to which the nut <NUM> is fixed shifts toward the left side. Since the sleeve <NUM> shifts in a manner to follow the shifting of the piston <NUM>, the spool <NUM> coupled to the sleeve <NUM> also shifts in the same direction and by the same amount as the piston <NUM>. This will be described below in detail.

As shown in <FIG>, the present embodiment includes a mechanism between the casing <NUM> and the left side portion of the piston <NUM>. The mechanism serves to keep the spool <NUM> at the neutral position when the electric motor <NUM> is not supplied with electric power. The mechanism includes: a coil spring <NUM>, within which the nut <NUM> is positioned; and a first spring receiver <NUM> and a second spring receiver <NUM>, which support both ends of the coil spring <NUM>, respectively.

The coil spring <NUM> applies an urging force to the piston <NUM> to keep the spool <NUM> at the neutral position. Each of the first spring receiver <NUM> and the second spring receiver <NUM> is ringshaped and slidably fitted to the left side portion of the piston <NUM>.

The piston <NUM> includes a flange <NUM> at its left end. The flange <NUM> contacts the first spring receiver <NUM>. At a position that is away from the flange <NUM> toward the right side, a stopper <NUM>, which contacts the second spring receiver <NUM>, is mounted to the piston <NUM>.

On the inner side surface of the tubular casing <NUM>, a first stepped portion <NUM> is located at a position corresponding to the flange <NUM>, and a second stepped portion <NUM> is located at a position corresponding to the stopper <NUM>.

With the above-described structure, when the electric motor <NUM> is not supplied with electric power, the urging force of the coil spring <NUM> causes the first spring receiver <NUM> to contact both the flange <NUM> and the first stepped portion <NUM>, and causes the second spring receiver <NUM> to contact both the stopper <NUM> and the second stepped portion <NUM>. Consequently, the spool <NUM> is kept at the neutral position.

From a state where the spool <NUM> is at the neutral position, when the piston <NUM> shifts toward the right side, the first spring receiver <NUM> is pushed by the flange <NUM> to become spaced apart from the first stepped portion <NUM>, and also, the stopper <NUM> becomes spaced apart from the second spring receiver <NUM>. On the other hand, from the state where the spool <NUM> is at the neutral position, when the piston <NUM> shifts toward the left side, the flange <NUM> becomes spaced apart from the first spring receiver <NUM>, and also, the second spring receiver <NUM> is pushed by the stopper <NUM> to become spaced apart from the second stepped portion <NUM>.

Next, the second housing <NUM> and the internal structure thereof are described in more detail with reference to <FIG>.

The second housing <NUM> includes an input port 4a and a drain port 4b on its outer surface. The input port 4a is to be connected to a pressure source <NUM> of a hydraulic fluid (e.g., a hydraulic pump). The drain port 4b is connected to, for example, a tank <NUM>, which stores the hydraulic fluid. For example, in a case where a fluid flowing between the passages <NUM> to <NUM> of the first housing <NUM> is oil, the hydraulic fluid supplied from the pressure source <NUM> to the input port 4a may be the same oil as the oil flowing between the passages <NUM> to <NUM>.

The second housing <NUM> includes a first passage <NUM>, which extends from the input port 4a to the first pressure chamber <NUM>. That is, the first pressure chamber <NUM> communicates with the input port 4a via the first passage <NUM>.

At the bottom (the right side) of the internal space of the sleeve <NUM>, there is a drain chamber <NUM>, which faces the right end surface of the piston <NUM>. The sleeve <NUM> includes side holes <NUM> and <NUM>, which extend radially outward from the drain chamber <NUM>.

The second housing <NUM> includes an annular groove <NUM> on the inner peripheral surface of the servo chamber <NUM>. The annular groove <NUM> is located at a position corresponding to the side holes <NUM> and <NUM>. The second housing <NUM> further includes a second passage <NUM>, which extends from the bottom of the annular groove <NUM> to the drain port 4b.

The piston <NUM> includes a longitudinal hole <NUM>, which extends along the center line of the piston <NUM>. The longitudinal hole <NUM> allows the drain chamber <NUM> and the above-described holding hole <NUM> to communicate with each other.

The piston <NUM> further includes, on its outer peripheral surface, a first annular groove <NUM> and a second annular groove <NUM>. The second annular groove <NUM> is positioned on the right side relative to the first annular groove <NUM>. Accordingly, there is a land <NUM> between the first annular groove <NUM> and the second annular groove <NUM>.

The sleeve <NUM> includes a first passage <NUM> and a second passage <NUM>. The first passage <NUM> allows the first pressure chamber <NUM> and the first annular groove <NUM> to communicate with each other. The second passage <NUM> allows the second pressure chamber <NUM> to communicate with the first annular groove <NUM> or the second annular groove <NUM>. The second passage <NUM> includes, on the inner peripheral surface of the sleeve <NUM>, a first opening 52a for the first annular groove <NUM> and a second opening 52b for the second annular groove <NUM>.

The distance from the left end of the first opening 52a to the right end of the second opening 52b is set to be equal to the width of the land <NUM> (i.e., the distance from the first annular groove <NUM> to the second annular groove <NUM>). The piston <NUM> further includes side holes <NUM>, which extend from the bottom of the second annular groove <NUM> to the longitudinal hole <NUM>.

The external diameter of the sleeve <NUM> is set to be larger than the maximum diameter of the spool <NUM> in the slide hole <NUM>. Accordingly, a leftward force F1 of the hydraulic fluid in the first pressure chamber <NUM> is applied to the sleeve <NUM>. In a case where the pressure in the first pressure chamber <NUM> is P1, the maximum diameter of the spool <NUM> in the slide hole <NUM> is Da, and the external diameter of the sleeve <NUM> is Db, the following equation holds true.

Meanwhile, a rightward force F2 of the hydraulic fluid in the second pressure chamber <NUM> is also applied to the sleeve <NUM>. In a case where the pressure in the second pressure chamber <NUM> is P2, the external diameter of the sleeve <NUM> is Db, and the diameter of the piston <NUM> is Dc, the following equation holds true.

In the configuration as described above, the pressure P2 in the second pressure chamber <NUM> is adjusted such that the leftward force F1 and the rightward force F2, which are applied to the sleeve <NUM>, are balanced (F1 = F2). In the balanced state, the sleeve <NUM> is at such a position that the first opening 52a and the second opening 52b of the second passage <NUM> are sealed by the land <NUM> of the piston <NUM>. Therefore, the second pressure chamber <NUM> is blocked from the input port 4a and the drain port 4b by the piston <NUM>.

From the balanced state, when the piston <NUM> is shifted by the electric motor <NUM> toward the right side (in a direction toward the spool <NUM>), the second pressure chamber <NUM> comes into communication with the input port 4a via the second passage <NUM>, the first annular groove <NUM>, the first passage <NUM>, the first pressure chamber <NUM>, and the first passage <NUM>. Consequently, the pressure in the second pressure chamber <NUM> increases, and the sleeve <NUM> also shifts toward the right side. However, when the sleeve <NUM> shifts toward the right side beyond the position where the balanced state is achieved, the second pressure chamber <NUM> comes into communication with the drain port 4b via the second passage <NUM>, the second annular groove <NUM>, the side holes <NUM>, the longitudinal hole <NUM>, the drain chamber <NUM>, the side holes <NUM> and <NUM>, the annular groove <NUM>, and the second passage <NUM>. Consequently, the pressure in the second pressure chamber <NUM> decreases. Due to this function, the sleeve <NUM> comes to a stop again at the position where the balanced state is achieved. That is, the sleeve <NUM> shifts toward the right side in a manner to follow the rightward shifting of the piston <NUM>.

On the other hand, from the balanced state, when the piston <NUM> is shifted by the electric motor <NUM> toward the left side (in a direction away from the spool <NUM>), the second pressure chamber <NUM> comes into communication with the drain port 4b via the second passage <NUM>, the second annular groove <NUM>, the side holes <NUM>, the longitudinal hole <NUM>, the drain chamber <NUM>, the side holes <NUM> and <NUM>, the annular groove <NUM>, and the second passage <NUM>. Consequently, the pressure in the second pressure chamber <NUM> decreases, and the sleeve <NUM> also shifts toward the left side. However, when the sleeve <NUM> shifts toward the left side beyond the position where the balanced state is achieved, the second pressure chamber <NUM> comes into communication with the input port 4a via the second passage <NUM>, the first annular groove <NUM>, the first passage <NUM>, the first pressure chamber <NUM>, and the first passage <NUM>. Consequently, the pressure in the second pressure chamber <NUM> increases. Due to this function, the sleeve <NUM> comes to a stop again at the position where the balanced state is achieved. That is, the sleeve <NUM> shifts toward the left side in a manner to follow the leftward shifting of the piston <NUM>.

Meanwhile, in a case where the piston <NUM> does not shift, the balanced state is maintained. That is, the second pressure chamber <NUM> is blocked from the input port 4a and the drain port 4b by the piston <NUM>. Therefore, even when the spool <NUM> receives a force from the fluid flowing between the passages <NUM> to <NUM> of the first housing <NUM>, due to the incompressibility of the hydraulic fluid in the second pressure chamber <NUM>, the sleeve <NUM> does not shift.

As described above, in the present disclosure, since the force that the spool <NUM> receives from the fluid flowing between the passages <NUM> to <NUM> does not affect the electric motor <NUM>, even in a case where the electric motor <NUM> is a low-power motor, the position of the spool <NUM> can be controlled precisely.

The present disclosure is not limited to the above-described embodiment. Various modifications can be made without departing from the scope of the present disclosure.

For example, the coil spring <NUM> for keeping the spool <NUM> at the neutral position may be eliminated. However, in the case of including the coil spring <NUM> as in the above-described embodiment, regardless of whether or not the electric motor <NUM> is being supplied with electric power, the spool <NUM> can be kept at a constant position even when the force that the spool <NUM> receives from the fluid flowing between the passages <NUM> to <NUM> is great. In addition, in the case of including the coil spring <NUM>, the nut <NUM> is positioned within the coil spring <NUM>. Therefore, it is not necessary to increase the length of the entire spool valve <NUM> due to the inclusion of the coil spring <NUM>.

A spool valve according to the present disclosure includes: a first housing including passages and a slide hole; a spool slidably located in the slide hole; a second housing that forms a servo chamber that is coaxial with the slide hole; a sleeve slidably located in the servo chamber, the sleeve dividing the servo chamber into a first pressure chamber and a second pressure chamber, the first pressure chamber being adjacent to the first housing, the second pressure chamber being away from the first housing, the sleeve being coupled to the spool in the first pressure chamber; a piston slidably fitted in the sleeve and extending from inside the sleeve beyond the second pressure chamber; a nut fixed to the piston; a screw shaft screwed with the nut; and an electric motor that rotates the screw shaft. The second housing includes a drain port and an input port that is to be connected to a pressure source of a hydraulic fluid. The first pressure chamber communicates with the input port. In a balanced state where a force that is applied to the sleeve by the hydraulic fluid in the first pressure chamber, and a force that is applied to the sleeve by the hydraulic fluid in the second pressure chamber, are balanced, the second pressure chamber is blocked from the input port and the drain port by the piston. From the balanced state, when the piston shifts in a direction toward the spool, the second pressure chamber comes into communication with the input port. From the balanced state, when the piston shifts in a direction away from the spool, the second pressure chamber comes into communication with the drain port.

Claim 1:
A spool valve (<NUM>) comprising:
a first housing (<NUM>) including passages (<NUM>, <NUM>, <NUM>) and a slide hole (<NUM>);
a spool (<NUM>) slidably located in the slide hole (<NUM>);
a second housing (<NUM>) that forms a servo chamber (<NUM>) that is coaxial with the slide hole (<NUM>);
a sleeve (<NUM>) slidably located in the servo chamber (<NUM>), the sleeve (<NUM>) dividing the servo chamber (<NUM>) into a first pressure chamber (<NUM>) and a second pressure chamber (<NUM>), the first pressure chamber (<NUM>) being adjacent to the first housing (<NUM>), the second pressure chamber (<NUM>) being away from the first housing (<NUM>);
a piston (<NUM>) slidably fitted in the sleeve (<NUM>) and extending from inside the sleeve (<NUM>) beyond the second pressure chamber (<NUM>);
a nut (<NUM>);
a screw shaft (<NUM>) screwed with the nut (<NUM>); and
an electric motor (<NUM>) that rotates the screw shaft (<NUM>), wherein
the second housing (<NUM>) includes a drain port (4b) and an input port (4a) that is to be connected to a pressure source (<NUM>) of a hydraulic fluid,
the first pressure chamber (<NUM>) communicates with the input port (4a),
in a balanced state where a force that is applied to the sleeve (<NUM>) by the hydraulic fluid in the first pressure chamber (<NUM>), and a force that is applied to the sleeve (<NUM>) by the hydraulic fluid in the second pressure chamber (<NUM>), are balanced, the second pressure chamber (<NUM>) is blocked from the input port (4a) and the drain port (4b) by the piston (<NUM>),
from the balanced state, when the piston (<NUM>) shifts in a direction toward the spool (<NUM>), the second pressure chamber (<NUM>) comes into communication with the input port (4a), and
from the balanced state, when the piston (<NUM>) shifts in a direction away from the spool (<NUM>), the second pressure chamber (<NUM>) comes into communication with the drain port (4b);
characterised by the sleeve (<NUM>) being coupled to the spool (<NUM>) in the first pressure chamber (<NUM>), and
the nut (<NUM>) being fixed to the piston (<NUM>).