Patent Description:
In conventional spool valves, a spool is moved according to whether or not a pilot pressure acts thereon. The conventional spool valves are configured such that a pilot pressure acts from a direction different from the direction of action of a load pressure (a direction perpendicular to the direction of action of a load pressure) so as to control movement of the spool (see, for example, Patent Literature <NUM>).

However, for example, a fluid apparatus having the conventional spool valve, in which a pilot pressure is supplied from a direction perpendicular to the direction of action of a load pressure, unfavorably requires a large space and has a large size. In other cases, the direction of action of the pilot pressure needs to be opposite to the direction of action of the load pressure due to requirements related to layout of a fluid apparatus.

It is also possible that the direction of action of the pilot pressure is opposite to the direction of action of the load pressure on the spool, and the ratio between these pressures determines the area of a surface acted on by the pilot pressure and the area of a surface acted on by the load pressure. However, a pilot pressure is typically very small as compared to a load pressure. Therefore, it is impractical to attempt to balance the pilot pressure and the load pressure by adjusting the area of the surface acted on by the load pressure and the area of the surface acted on by the pilot pressure, because such a fluid apparatus has a very large structure.

Patent Literature <NUM>: <CIT> spool valve as described in the preamble of claim <NUM> is already known from <CIT>. <CIT> discloses a similar spool valve as described in the preamble of claim <NUM>.

The present invention addresses the above drawbacks, and one object thereof is to provide a spool valve and a valve system having a small size and configured such that the direction of action of the pilot pressure can be opposite to the direction of action of the load pressure.

The above and other objects of the invention are achieved by the spool valve according to claim <NUM> and the valve system according to claim <NUM>. Preferred embodiments are claimed in the dependent claims.

The present invention is a spool valve comprising: a valve body; and a spool housed in the valve body so as to be movable in an axial direction, the spool having a load pressure acting surface and a pilot pressure acting surface, the load pressure acting surface being formed on one axial end side of the spool and configured to be acted on by a load pressure, the pilot pressure acting surface being formed on another axial end side of the spool and configured to be acted on by a pilot pressure, wherein the spool includes a spool body and a shoulder radially enlarged from the spool body, the shoulder has a first acting surface positioned on the other axial end side and a second acting surface positioned on the one axial end side, and the spool has a first communication hole and a second communication hole formed therein, the first communication hole communicating between the load pressure acting surface and the first acting surface of the shoulder, the second communication hole communicating between the pilot pressure acting surface and the second acting surface of the shoulder.

An area of the load pressure acting surface is equal to an area of the first acting surface of the shoulder.

An area of the pilot pressure acting surface is smaller than an area of the second acting surface of the shoulder.

The present invention is the spool valve, wherein when the pilot pressure acts on the pilot pressure acting surface, the pilot pressure acts on the second acting surface of the shoulder to move the spool toward the other axial end side.

The present invention is the spool valve, further comprising a first biasing member for pressing the spool toward the one axial end side.

The present invention is a valve system comprising: the spool valve; and an electromagnetic proportional valve connected to the other axial end side of the spool valve and configured to cause the pilot pressure to act on the pilot pressure acting surface of the spool valve.

The present invention is the valve system, wherein the electromagnetic proportional valve includes an electromagnetic proportional valve body, an electromagnetic proportional valve spool, and a drive device, the electromagnetic proportional valve spool being housed in the electromagnetic proportional valve body so as to be movable in the axial direction, and the drive device being disposed on the electromagnetic proportional valve body so as to be movable in the axial direction, and the drive device being disposed on the electromagnetic proportional valve body and configured to press the electromagnetic proportional valve spool toward the one axial end side, and the spool of the spool valve and the electromagnetic proportional valve spool of the electromagnetic proportional valve are connected together by a second biasing member.

The present invention provides a spool valve and a valve system having a small size and configured such that the direction of action of the pilot pressure can be opposite to the direction of action of the load pressure.

The first embodiment of the present invention will now be described with reference to <FIG> and <FIG>. <FIG> and <FIG> are sectional views showing a spool valve according to the embodiment. <FIG> shows the case where a spool is in a neutral position, and <FIG> shows the case where the spool is in a supply position.

As shown in <FIG> and <FIG>, the spool valve (spool cartridge valve) <NUM> according to the embodiment includes a valve body <NUM> having a cylindrical shape and a spool <NUM> housed in the valve body <NUM> so as to be movable in the axial direction.

In this specification, "the axial direction" refers to the direction of the central axis of the spool <NUM> (the longitudinal direction of the spool <NUM>, or the direction X), "one axial end side" refers to the side of the spool <NUM> having a load pressure applied thereto (the positive side in the direction X), and "the other axial end side" refers to the side of the spool <NUM> having a pilot pressure applied thereto (the negative side in the direction X).

The valve body <NUM> has a spool receiving hole <NUM> that receives the spool <NUM> and extends in the axial direction. A pressure source port <NUM> is disposed in the one axial end side of the valve body <NUM>. The pressure source port <NUM> receives the flow of a working fluid such as an oil having a load pressure. The pressure source port <NUM> is in communication with the one axial end side of the spool receiving hole <NUM> and is connected to a pressure source such as a pump.

In a side surface of the valve body <NUM>, a control port <NUM> is formed to face the spool receiving hole <NUM>. The control port <NUM> extends perpendicularly to the axial direction. The control port <NUM> is connected to a hydraulic apparatus (not shown) to be supplied with an oil for control. When the spool <NUM> is in a supply position (see <FIG>), the control port <NUM> communicates with the pressure source port <NUM>, and the oil having the load pressure flows out through the control port <NUM>. When the spool <NUM> is in a neutral position (see <FIG>), the control port <NUM> is closed by the spool <NUM> and does not communicate with the pressure source port <NUM>.

A pilot source port <NUM> is disposed in the other axial end side of the valve body <NUM>. The pilot source port <NUM> receives the flow of an oil having a pilot pressure. The pilot pressure is significantly smaller than the load pressure. The pilot source port <NUM> is in communication with the other axial end side of the spool receiving hole <NUM> and is connected to a pilot source such as an electromagnetic valve.

Further, a drain port <NUM> is formed in the side surface of the valve body <NUM>. The drain port <NUM> is in communication with the spool receiving hole <NUM> and is connected to, for example, a tank T for storing the oil.

In the inner side surface of the valve body <NUM>, there are provided an inner circumferential groove 21a, a shoulder movement space 21b, and a drain port communication space 21c. The inner circumferential groove 21a, the shoulder movement space 21b, and the drain port communication space 21c are arranged in this order from the one axial end side toward the other axial end side. Each of the inner circumferential groove 21a, the shoulder movement space 21b, and the drain port communication space 21c constitutes a part of the spoo I receiving hole <NUM>.

The inner circumferential groove 21a extends annularly over the entire circumference of the inner side surface of the valve body <NUM> and communicates with the control port <NUM>. The shoulder movement space 21b allows a shoulder <NUM> (described later) to move therein and communicates with the pressure sou rce port <NUM> via a first communication hole <NUM> (described later). The drain port communication space 21c extends annularly over the entire circumference of the inner side surface of the valve body <NUM> and communicates with the drain port <NUM>. The drain port communication space 21c allows an other-end side step <NUM> of the spool <NUM> to move therein.

Further provided in the inner side surface of the valve body <NUM> are a first step <NUM>, a second step <NUM>, and a third step <NUM>. The first step <NUM> is positioned on the other axial end side of the drain port communication space 21c, and when the spool <NUM> moves most toward the other axial end side, the first step <NUM> contacts with the other-end side step <NUM> of the spool <NUM>. The second step <NUM> is positioned on the other axial end side of the shoulder movement space 21b and is joined to the other end side of a spring <NUM> (described later). The third step <NUM> is positioned on the one axial end side of the shoulder movement space 21b. When the spool <NUM> moves most toward the one axial end side, the third step <NUM> contacts with a second acting surface 34b (described later) of the spool <NUM>.

The valve body <NUM> is not necessarily constituted by a single member, but may be constituted by a plurality of members joined together.

The spool <NUM> moves in the spool receiving hole <NUM> of the valve body <NUM> between the neutral position (<FIG>) and the supply position (<FIG>). As shown in <FIG>, when the pilot pressure is not supplied through the pilot source port <NUM> of the valve body <NUM>, the spool <NUM> enters the neutral position on the one axial end side, and the spool <NUM> closes the control port <NUM>. On the other hand, as shown in <FIG>, when the pilot pressure is supplied through the pilot source port <NUM> of the valve body <NUM>, the spool <NUM> moves toward the other axial end side and enters the supply position, and the control port <NUM> is opened to be in communication with the pressure source port <NUM>.

The spool <NUM> has a load pressure acting surface <NUM> having a circular shape and formed on the one axial end side and a pilot pressure acting surface <NUM> having a circular shape and formed on the other axial end side. That is, the load pressure acting surface <NUM> and the pilot pressure acting surface <NUM> are opposed to each other in the axial direction. The load pressure acting surface <NUM> is in communication with the pressure source port <NUM> of the valve body <NUM> and is acted on by the oil having the load pressure from the pressure source. The pilot pressure acting surface <NUM> is in communication with the pilot source port <NUM> of the valve body <NUM> and is acted on by the oil having the pilot pressure from the pilot source.

The spool <NUM> includes a spool body <NUM> and the shoulder <NUM> joined to a side surface of the spool body <NUM>. The spool body <NUM> extends in the spool receiving hole <NUM> from the one axial end side toward the other axial end side. The spool body <NUM> is constituted by a solid member except for a first communication hole <NUM> and a second communication hole <NUM> (described later).

The shoulder <NUM> constitutes a portion radially enlarged from the spool body <NUM>. The shoulder <NUM> extends annularly over the entire circumference of the spool body <NUM> and is integrated with the spool body <NUM>.

The shoulder <NUM> has a first acting surface 34a positioned on the other axial end side and a second acting surface 34b positioned on the one axial end side. The first acting surface 34a and the second acting surface 34b are opposed to each other in the axial direction.

The spool <NUM> has a first communication hole <NUM> formed therein to communicate between the load pressure acting surface <NUM> and the first acting surface 34a. The first communication hole <NUM> includes an axial portion 35a extending in the axial direction and a peripheral portion 35b connected with the axial portion 35a and extending in the peripheral direction. The axial portion 35a is open to the load pressure acting surface <NUM>. The peripheral portion 35b is open to a side surface of the spool body <NUM> on the other axial end side of the shoulder <NUM>. The peripheral portion 35b is in communication with the other axial end side of the shoulder movement space 21b. In this way, the load pressure acting surface <NUM> and the first acting surface 34a communicate with each other, and therefore, a load pressure acting on the load pressure acting surface <NUM> toward the other axial end side (the negative side in the direction X) also acts on the first acting surface 34a toward the one axial end side (the positive side in the direction X).

Further, the spool <NUM> has a second communication hole <NUM> formed therein to communicate between the pilot pressure acting surface <NUM> and the second acting surface 34b. The second communication hole <NUM> includes an axial portion 36a extending in the axial direction and a peripheral portion 36b connected with the axial portion 36a and extending in the peripheral direction. The axial portion 36a is open to the pilot pressure acting surface <NUM>. The peripheral portion 36b is open to a side surface of the spool body <NUM> in the second acting surface 34b and is in communication with the one axial end side of the shoulder movement space 21b. A part of the peripheral portion 36b is constituted by a peripheral groove formed in the second acting surface 34b. In this way, the pilot pressure acting surface <NUM> and the second acting surface 34b communicate with each other, and therefore, a pilot pressure acting on the pilot pressure acting surface <NUM> toward the one axial end side (the positive side in the direction X) also acts on the second acting surface 34b toward the other axial end side (the negative side in the direction X).

It is also possible that the peripheral portion 35b of the first communication hole <NUM> and the peripheral portion 36b of the second communication hole <NUM> are replaced with oblique portions extending obliquely to the axial direction. That is, as in the variation shown in <FIG>, the axial portion 35a of the first communication hole <NUM> and the axial portion 36a of the second communication hole <NUM> may extend in the same axis (the central axis of the spool <NUM>), and the peripheral portions 35b, 36b may extend obliquely to the axial direction from the axial portions 35a, 36a, respectively. In this way, the axial portions 35a, 36a may be arranged in the same axis thereby to downsize the spool <NUM>. The arrangement in the variation shown in <FIG> may also be applied to second and third embodiments described later.

Referring again to <FIG> and <FIG>, a spring (first biasing member) <NUM> is interposed between the valve body <NUM> and the spool <NUM> so as to press the spool <NUM> toward the one axial side. The spring <NUM> is a compression spring. More specifically, one end of the spring <NUM> is joined to the first acting surface 34a of the shoulder <NUM>, and the other end of the spring <NUM> is joined to the second step <NUM> of the valve body <NUM>. Thus, the spring <NUM> presses the spool <NUM> via the shoulder <NUM> toward the one axial end side.

In the embodiment, the area of the load pressure acting surface <NUM> of the spool <NUM> is equal to the area of the first acting surface 34a of the shoulder <NUM>. The area of the load pressure acting surface <NUM> refers to the entire area of the load pressure acting surface <NUM> having, for example, a circular shape, including the area of the opening of the first communication hole <NUM>. The area of the first acting surface 34a refers to the entire area of the first acting surface 34a having, for example, an annular shape. In this way, the load pressure acting surface <NUM> and the first acting surface 34a have the same area, and therefore, the force applied by the load pressure to the load pressure acting surface <NUM> (the force applied toward the other axial end side (the negative side in the direction X)) is balanced with the force applied by the load pressure to the first acting surface 34a (the force applied toward the one axial end side (the positive side in the direction X)). Therefore, in a neutral state, the spool <NUM> is urged toward the one axial end side only by the pressing force of the spring <NUM>.

The area of the pilot pressure acting surface <NUM> is smaller than the area of the second acting surface 34b of the shoulder <NUM>. The area of the pilot pressure acting surface <NUM> refers to the entire area of the pilot pressure acting surface <NUM> having, for example, a circular shape, including the area of the opening of the second communication hole <NUM>. The area of the second acting surface 34b refers to the entire area of the second acting surface 34b having, for example, an annular shape. In this way, the area of the pilot pressure acting surface <NUM> is smaller than the area of the second acting surface 34b, and therefore, when the pilot pressure is applied to the pilot pressure acting surface <NUM>, the spool <NUM> can be moved from the one axial end side (the positive side in the direction X) toward the other axial end side (the negative side in the direction X) against the biasing force of the spring <NUM>. Therefore, when the pilot pressure is applied to the pilot pressure acting surface <NUM>, the spool <NUM> can be displaced from the neutral state to the supply position. The area of the second acting surface 34b is smaller than the area of the first acting surface 34a described above.

The valve body <NUM> is housed in a block <NUM>. The block <NUM> includes a first block portion <NUM> on the one axial end side and a second block portion <NUM> on the other axial end side. The block <NUM> has formed therein a pressure source channel <NUM>, a control channel <NUM>, a pilot source channel <NUM>, and a first drain channel <NUM>. The pressure source channel <NUM>, the control channel <NUM>, the pilot source channel <NUM>, and the first drain channel <NUM> communicate with the pressure source port, the control port <NUM>, the pilot source port <NUM>, and the drain port <NUM> of the valve body <NUM>, respectively.

Operation in the embodiment configured as above will be hereinafter described.

First, when an oil having the pilot pressure is not supplied through the pilot source port <NUM> of the valve body <NUM>, a tank pressure (a low pressure) acts on the pilot pressure acting surface <NUM> of the spool <NUM> toward the one axial end side. At this time, the tank pressure also acts on the second acting surface 34b of the shoulder <NUM>. Further, since the drain port communication space <NUM> communicates with the drain port <NUM>, the tank pressure also acts on the other-end side step <NUM> of the valve body <NUM>.

An oil having the load pressure is supplied through the pressure source port <NUM> of the valve body <NUM>. Therefore, the load pressure acts on the load pressure acting surface <NUM> of the spool <NUM> toward the other axial end side. The oil having the load pressure also flows from the load pressure acting surface <NUM> into the shoulder movement space 21b through the first communication hole <NUM>. Therefore, the load pressure acts on the first acting surface 34a of the shoulder <NUM> toward the one axial end side.

As described above, the area of the load pressure acting surface <NUM> of the spool <NUM> is equal to the area of the first acting surface 34a of the shoulder <NUM>. Therefore, the pressure acting on the load pressure acting surface <NUM> of the spool <NUM> is balanced with the pressure acting on the first acting surface 34a of the shoulder <NUM>, and thus the spool <NUM> is in the neutral position (see <FIG>). At this time, the control port <NUM> is closed by the spool <NUM> and does not communicate with the pressure source port <NUM>. Accordingly, the oil having the load pressure from the pressure source such as a pump is not supplied to the hydraulic apparatus connected to the control port <NUM>. Meanwhile, since the spring <NUM> presses the spool <NUM> toward the one axial end side, the second acting surface 34b of the shoulder <NUM> contacts with the third step <NUM> of the valve body <NUM>, thereby stopping the spool <NUM>.

In this way, since the area of the load pressure acting surface <NUM> of the spool <NUM> is equal to the area of the first acting surface 34a of the shoulder <NUM>, the spool <NUM> can be retained in the neutral position irrespective of the magnitude of the load pressure.

In this state, when an oil having the pilot pressure is supplied through the pilot source port <NUM> of the valve body <NUM>, the pilot pressure acts on the pilot pressure acting surface <NUM> of the spool <NUM> toward the one axial end side. At this time, the oil having the pilot pressure also flows from the pilot pressure acting surface <NUM> into the shoulder movement space 21b through the second communication hole <NUM>. Therefore, the pilot pressure also acts on the second acting surface 34b of the shoulder <NUM>. As described above, the area of the pilot pressure acting surface <NUM> is smaller than the area of the second acting surface 34b of the shoulder <NUM>. Therefore, the pilot pressure acting on the second acting surface 34b of the shoulder <NUM> causes the spool <NUM> to move from the one axial end side toward the other axial end side against the biasing force of the spring <NUM>.

The spool <NUM> moves toward the other axial end side to reach the supply position (see <FIG>). At this time, the load pressure acting surface <NUM> of the spool <NUM> moves to directly above the control port <NUM>, and thus the control port <NUM> is opened and in communication with the pressure source port <NUM>. Accordingly, the oil is supplied from the pressure source such as a pump connected to the pressure source port <NUM> to the hydraulic apparatus connected to the control port <NUM>. The amount of oil supplied from the pressure source to the hydraulic apparatus when the spool <NUM> is in the supply position can be varied in accordance with the overlapping area of the spool <NUM> and the control port <NUM>. Subsequently, the other-end side step <NUM> of the spool <NUM> contacts with the first step <NUM> of the valve body <NUM>, and the spool <NUM> stops moving.

During this operation, the pressure acting on the load pressure acting surface <NUM> of the spool <NUM> is constantly balanced with the pressure acting on the first acting surface 34a of the shoulder <NUM>, and thus the magnitude of the load pressure acting on the load pressure acting surface <NUM> does not affect the movement of the spool <NUM>.

Subsequently, the supply of the pilot pressure from the pilot source port <NUM> is stopped to cause the tank pressure to act on the pilot pressure acting surface <NUM>. Because of the biasing force of the spring <NUM>, the spool <NUM> moves from the supply position to the neutral position to close the control port <NUM>. Thus, no oil is supplied to or discharged from the hydraulic apparatus connected to the control port <NUM>.

As described above, in the embodiment, the spool <NUM> has the load pressure acting surface <NUM> and the pilot pressure acting surface <NUM>. The load pressure acting surface <NUM> is formed on the one axial end side and acted on by the load pressure, and the pilot pressure acting surface <NUM> is formed on the other axial end side and acted on by the pilot pressure. Further, the direction in which the oil having the load pressure is supplied to the control port <NUM> is aligned with the direction in which the oil having the pilot pressure is supplied to the pilot source port <NUM>. This arrangement makes it possible to downsize the spool valve <NUM> and configure it such that the direction of action of the pilot pressure is opposite to the direction of action of the load pressure. Therefore, a fluid apparatus having the spool valve <NUM> neither requires a large space nor have a large size, unlike a fluid apparatus having the conventional spool valve, in which the pilot pressure is supplied from a direction perpendicular to the axial direction, for example.

In the embodiment, the area of the load pressure acting surface <NUM> is equal to the area of the first acting surface 34a of the shoulder <NUM>. Therefore, the pressure acting on the load pressure acting surface <NUM> of the spool <NUM> can be balanced with the pressure acting on the first acting surface 34a of the shoulder <NUM>, irrespective of the magnitude of the load pressure.

In the embodiment, the area of the pilot pressure acting surface <NUM> is smaller than the area of the second acting surface 34b of the shoulder <NUM>. Therefore, when the pilot pressure is applied to the pilot pressure acting surface <NUM>, the spool <NUM> can be moved from the neutral state to the supply position.

In the embodiment, when the pilot pressure acts on the pilot pressure acting surface <NUM>, the pilot pressure acts on the second acting surface 34b of the shoulder <NUM> to move the spool <NUM> toward the other axial end side. Thus, it is possible to control the movement of the spool <NUM> according to whether or not the pilot pressure acts thereon.

In the embodiment, the spring <NUM> presses the spool <NUM> toward the one axial end side. Therefore, when the pilot pressure does not act on the pilot pressure acting surface <NUM>, the shoulder <NUM> is pressed toward the one axial end side, and the spool <NUM> is retained in the neutral position.

Next, the second embodiment of the invention will be described. <FIG> are sectional views showing a valve system according to the embodiment. The second embodiment shown in <FIG> are distinctive in that an electromagnetic proportional valve is provided on the other axial end side of the spool. In other respects, this embodiment is configured in substantially the same way as the first embodiment described above. In <FIG>, the same elements as in the first embodiment are denoted by the same reference numerals and detailed descriptions thereof will be omitted.

In <FIG>, the spool of the spool valve is in the neutral position and an electromagnetic proportional valve spool of the electromagnetic proportional valve is in the discharge position. In <FIG>, the spool of the spool valve is in the supply position and the electromagnetic proportional valve spool of the electromagnetic proportional valve is in the supply position. In <FIG>, the spool of the spool valve is in the supply position and the electromagnetic proportional valve spool of the electromagnetic proportional valve is in the neutral position.

As shown in <FIG>, the valve system <NUM> according to the embodiment includes the spool valve <NUM> and the electromagnetic proportional valve <NUM> connected to the spool valve <NUM>.

The spool valve <NUM> is substantially the same as the spool valve <NUM> in the first embodiment and thus is not described here.

The electromagnetic proportional valve <NUM> is connected to the other axial end side of the spool valve <NUM> and is configured to cause the pilot pressure to act on the pilot pressure acting surface <NUM> of the spool valve <NUM>. The electromagnetic proportional valve <NUM> is retained in any of a supply position, a discharge position, and a neutral position. In the supply position, the electromagnetic proportional valve <NUM> allow communication between a pilot pressure source as a source for supplying the oil and the pilot source channel <NUM> of the spool valve <NUM>, and the oil is supplied from the pilot pressure source to the spool valve <NUM>. In the discharge position, the electromagnetic proportional valve <NUM> allow communication between the tank T for storing the oil and the pilot source channel <NUM> of the spool valve <NUM>, and the oil is discharged from the pilot source channel <NUM> into the tank T. In the neutral position, the electromagnetic proportional valve <NUM> shuts off the spool valve <NUM> from the pilot pressure source and the tank T.

As shown in <FIG>, the main components of the electromagnetic proportional valve <NUM> include an electromagnetic proportional valve body <NUM>, an electromagnetic proportional valve spool <NUM>, and a drive device <NUM>. The electromagnetic proportional valve spool <NUM> is housed in the electromagnetic proportional valve body <NUM> so as to be movable in the axial direction, and the drive device <NUM> is disposed on the electromagnetic proportional valve body <NUM> and configured to press the electromagnetic proportional valve spool <NUM> toward the one axial end side. The electromagnetic proportional valve <NUM> switches a flow path between the supply position, the discharge position, and the neutral position by moving the electromagnetic proportional valve spool <NUM>.

The drive device <NUM> drives the electromagnetic proportional valve spool <NUM> to control the position of the electromagnetic proportional valve spool <NUM>. The drive device <NUM> includes a drive rod <NUM> and a drive unit <NUM> retaining the drive rod <NUM>. The drive rod <NUM> is retained by the drive unit <NUM> so as to be able to advance and retract along the central axis thereof. The drive unit <NUM> controls driving of the drive rod <NUM> in the axial direction (the direction X). The drive device <NUM> shown is configured as a solenoid actuator.

In the drive device <NUM> configured as described above, when an excitation current flows in a solenoid coil (not shown) of the drive unit <NUM>, the drive rod <NUM> moves toward the one axial end side (the positive side in the direction X) against the biasing force of a spring (a biasing member) <NUM> provided in the electromagnetic proportional valve body <NUM>. The amount of movement of the drive rod <NUM> is proportional to the magnitude of the excitation current in the solenoid coil of the drive unit <NUM>, if no reaction force is applied from the electromagnetic proportional valve spool <NUM>. In the example shown, the drive rod <NUM> projects from the drive unit <NUM> in proportional to the magnitude of the excitation current.

Next, the electromagnetic proportional valve body <NUM> will be described. The electromagnetic proportional valve body <NUM> has a spool receiving hole <NUM>. The electromagnetic proportional valve spool <NUM>, which has a shaft-like shape, is movable in the axial direction in the spool receiving hole <NUM>. The drive rod <NUM> can advance into and retract from the spool receiving hole <NUM>. Further, the spring <NUM> is disposed in the electromagnetic proportional valve body <NUM>. The spring <NUM> biases the electromagnetic proportional valve spool <NUM> toward the drive rod <NUM>. As a result, the distal end portion of the drive rod <NUM> contacts with the electromagnetic proportional valve spool <NUM>. In the example shown, the spring <NUM> is a compression spring. The spring <NUM> retains the contact between the drive rod <NUM> and the electromagnetic proportional valve spool <NUM>. The biasing force of the spring <NUM> is significantly smaller than a thrust applied from the drive rod <NUM> to the electromagnetic proportional valve spool <NUM>.

When the drive rod <NUM> advances from the drive unit <NUM>, the electromagnetic proportional valve spool <NUM> is pressed by the drive rod <NUM> and moves with respect to the electromagnetic proportional valve body <NUM>. When the drive rod <NUM> retracts into the drive unit <NUM>, the electromagnetic proportional valve spool <NUM> is pressed by the spring <NUM> and moves with respect to the electromagnetic proportional valve body <NUM> while contacting with the drive rod <NUM>.

The electromagnetic proportional valve body <NUM> has a pilot pressure source port <NUM>, a drain port <NUM>, and a control port <NUM> formed therein. The electromagnetic proportional valve spool <NUM> has channels <NUM>, <NUM>, <NUM> formed therein. When the electromagnetic proportional valve spool <NUM> is in the discharge position shown in <FIG>, the control port <NUM> communicates with the drain port <NUM>, and the pilot pressure source port <NUM> is shut off from the other ports <NUM>, <NUM>. When the electromagnetic proportional valve spool <NUM> is in the supply position shown in <FIG>, the control port <NUM> communicates with the pilot pressure source port <NUM>, and the drain port <NUM> is shut off from the other ports <NUM>, <NUM>. When the electromagnetic proportional valve spool <NUM> is in the neutral position shown in <FIG>, each of the ports <NUM>, <NUM>, <NUM> is shut off from the other ports.

The control port <NUM> is open to the spool receiving hole <NUM> and outputs the pilot pressure to the pilot source port <NUM> of the spool valve <NUM>. Thus, the control port <NUM> supplies the oil having the pilot pressure to the spool valve <NUM>. The pilot pressure source port <NUM> is open to the spool receiving hole <NUM> and communicates with the pilot pressure source such as a pump. The drain port <NUM> is open to the spool receiving hole <NUM> and communicates with the tank T for storing the oil. Accordingly, in the electromagnetic proportional valve <NUM> in which the electromagnetic proportional valve spool <NUM> is in the supply position, the oil is supplied from the pilot pressure source to the spool valve <NUM>, and in the electromagnetic proportional valve <NUM> in which the electromagnetic proportional valve spool <NUM> is in the discharge position, the oil is discharged from the spool valve <NUM> to the tank T. In the electromagnetic proportional valve <NUM> in which the electromagnetic proportional valve spool <NUM> is in the neutral position, the oil in the spool valve <NUM> is retained.

In the example shown, the electromagnetic proportional valve body <NUM> has a first core <NUM> and a second core <NUM> fixed thereto. The first core <NUM> has a through-hole passed by the drive rod <NUM> of the drive device <NUM> for advancement and retraction. The first core <NUM> has a through-hole penetrated by the drive rod <NUM> of the drive device <NUM> for advancement and retraction. The distal end portion of the drive rod <NUM> is positioned in the spool receiving hole <NUM>.

A spare chamber <NUM> is defined by the first core <NUM>, the second core <NUM>, and the electromagnetic proportional valve body <NUM>. Between the drain po rt <NUM> and the spare chamber <NUM>, there is provided a connecting channel <NUM>. The connecting channel <NUM> is formed in the electromagnetic proportional valve body <NUM>. The connecting channel <NUM> communicates between the spare chamber <NUM> and the drain port <NUM>.

Next, the electromagnetic proportional valve spool <NUM> will be described. The electromagnetic proportional valve spool <NUM> is pressed on the one axial end side thereof by the spring <NUM> and thus is biased toward the drive rod <NUM>. The electromagnetic proportional valve spool <NUM> contacts on the other axial end side thereof with the distal end portion of the drive rod <NUM>.

The electromagnetic proportional valve spool <NUM> has formed therein a main channel <NUM> extending in the axial direction. The main channel <NUM> is open to the control port <NUM>. The electromagnetic proportional valve spool <NUM> also has formed therein a first branch channel <NUM> and a second branch channel <NUM>, each connecting with the main channel <NUM>. When the electromagnetic proportional valve spool <NUM> is in the supply position, the first branch channel <NUM> communicates between the pilot pressure source port <NUM> and the main channel <NUM>. When the electromagnetic proportional valve spool <NUM> is in the discharge position, the second branch channel <NUM> communicates between the drain port <NUM> and the main channel <NUM>.

Further, the electromagnetic proportional valve spool <NUM> has formed therein a third branch channel <NUM> that communicates between the main channel <NUM> and an action space <NUM>. Accordingly, the action space <NUM> is in communication with the control port <NUM> via the third branch channel <NUM> and the main channel <NUM>. The action space <NUM> is retained at the pressure of the oil in the control port <NUM>.

In the embodiment, the block <NUM> further has a pilot pressure supply channel <NUM> and a second drain channel <NUM> formed therein. The pilot pressure supply channel <NUM> and the second drain channel <NUM> communicate with the pilot pressure source port <NUM> and the drain port <NUM> of the electromagnetic proportional valve body <NUM>, respectively.

Next, operation in the embodiment configured as above will be hereinafter described.

First, when the solenoid coil of the drive unit <NUM> of the electromagnetic proportional valve <NUM> is not excited, the drive rod <NUM> is retracted toward the drive unit <NUM> by the biasing force of the spring <NUM>. The electromagnetic proportional valve spool <NUM> is contacted with the drive rod <NUM> by the biasing force of the spring <NUM> at the discharge position shown in <FIG>. At this time, the control port <NUM> is in communication with the drain port <NUM> via the main channel <NUM> and the second branch channel <NUM> of the electromagnetic proportional valve spool <NUM>. Accordingly, the pilot source port <NUM> of the spool valve <NUM> is in communication with the tank T connected to the drain port <NUM>.

In this state, the pilot pressure does not act on the pilot pressure acting surface <NUM> of the spool valve <NUM>. Therefore, the spool <NUM> of the spool valve <NUM> is retained in the neutral position (see the description of the first embodiment for details of the operation of the spool <NUM>). At this time, the control port <NUM> is closed by the spool <NUM>, and therefore, the oil having the load pressure from the pressure source such as a pump is not supplied to the hydraulic apparatus connected to the control port <NUM>.

In this state, when the solenoid coil of the drive unit <NUM> is excited, the drive rod <NUM> advances from the drive unit <NUM> and drives the electromagnetic proportional valve spool <NUM>. The electromagnetic proportional valve spool <NUM> moves from the discharge position to the neutral position. When the electromagnetic proportional valve spool <NUM> is in the neutral position, the communication between the second branch channel <NUM> and the drain port <NUM> is shut off while the communication between the first branch channel <NUM> and the pilot pressure source port <NUM> remains shut off. Therefore, the control port <NUM> is shut off from both the pilot pressure source port <NUM> and the drain port <NUM>. Accordingly, no oil is supplied to or discharged from the spool valve <NUM> connected to the control port <NUM>.

When a larger excitation current flows in the solenoid coil of the drive unit <NUM>, the drive rod <NUM> further advances the electromagnetic proportional valve spool <NUM>, and the first branch channel <NUM> of the electromagnetic proportional valve spool <NUM> moves to directly above the pilot pressure source port <NUM>. In the supply position shown in <FIG>, the control port <NUM> is in communication with the pilot pressure source port <NUM> via the main channel <NUM> and the first branch channel <NUM> of the electromagnetic proportional valve spool <NUM>. Accordingly, the oil having the pilot pressure is supplied from the pilot pressure source such as a pump connected to the pilot pressure source port <NUM> to the pilot source port <NUM> of the spool valve <NUM> connected to the control port <NUM>.

Meanwhile, the control port <NUM> is in communication with the action space <NUM> via the main channel <NUM> and the third branch channel <NUM> of the electromagnetic proportional valve spool <NUM>. Accordingly, the action space <NUM> receives a pressure equal to the pilot pressure output to the control port <NUM>. In the action space <NUM>, the distal end portion of the drive rod <NUM> is exposed in the axial direction. Therefore, the pilot pressure constantly acts on the drive rod <NUM> in a direct manner in a direction opposite to the thrust applied to the electromagnetic proportional valve spool <NUM> by the drive rod <NUM>.

As described above, since the oil having the pilot pressure is supplied from the electromagnetic proportional valve <NUM> to the spool valve <NUM>, the pilot pressure acts on the pilot pressure acting surface <NUM> of the spool valve <NUM>. Therefore, the spool <NUM> of the spool valve <NUM> is displaced from the neutral position to the supply position (see the description of the first embodiment for details of the operation of the spool <NUM>). The movement of the spool <NUM> causes the control port <NUM> to be opened and in communication with the pressure source port <NUM>. Accordingly, the oil is supplied from the pressure source such as a pump connected to the pressure source port <NUM> to the hydraulic apparatus connected to the control port <NUM>.

When the excitation of the solenoid coil of the drive unit <NUM> is reduced, the drive rod <NUM> is moved back toward the drive unit <NUM> to some degree. At this time, the electromagnetic proportional valve spool <NUM> reaches the neutral position shown in <FIG>. When the electromagnetic proportional valve spool <NUM> is in the neutral position, the communication between the first branch channel <NUM> and the pilot pressure source port <NUM> is shut off while the communication between the second branch channel <NUM> and the drain port <NUM> remains shut off. Therefore, the control port <NUM> is shut off from both the pilot pressure source port <NUM> and the drain port <NUM>. Accordingly, the control port <NUM> is retained at the pilot pressure, and the pilot pressure acting surface <NUM> of the spool valve <NUM> remains acted on by the pilot pressure. Accordingly, the spool <NUM> of the spool valve <NUM> is retained in the supply position, and the oil continues to be supplied from the pressure source such as a pump connected to the pressure source port <NUM> to the hydraulic apparatus connected to the control port <NUM>.

In the embodiment, it is possible with a simple arrangement to drive the electromagnetic proportional valve spool <NUM> with a control pressure and thereby control the spool valve <NUM>. In other words, the arrangement to drive the electromagnetic proportional valve spool <NUM> with the pilot pressure can be simplified significantly. Thus, the electromagnetic proportional valve spool <NUM> can be simplified significantly.

Next, the third embodiment of the invention will be described. <FIG> are sectional views showing a valve system according to the embodiment. The third embodiment shown in <FIG> are distinctive in that the spring <NUM> disposed in the electromagnetic proportional valve body <NUM> is replaced with a feedback spring <NUM> connecting between the spool <NUM> of the spool valve <NUM> and the electromagnetic proportional valve spool <NUM> of the electromagnetic proportional valve <NUM>. In other respects, this embodiment is configured in substantially the same way as the second embodiment described above. In <FIG>, the same elements as in the first and second embodiments are denoted by the same reference numerals and detailed descriptions thereof will be omitted.

In <FIG>, the spool of the spool valve is in the neutral position and the electromagnetic proportional valve spool of the electromagnetic proportional valve is in the discharge position. In <FIG>, the spool of the spool valve is in the neutral position and the electromagnetic proportional valve spool of the electromagnetic proportional valve is in the neutral position. In <FIG>, the spool of the spool valve is in the supply position and the electromagnetic proportional valve spool of the electromagnetic proportional valve is in the supply position. In <FIG>, the spool of the spool valve is in the supply position and the electromagnetic proportional valve spool of the electromagnetic proportional valve is in the discharge position.

As shown in <FIG>, the valve system 100A according to the embodiment includes the spool valve <NUM> and the electromagnetic proportional valve <NUM> connected to the spool valve <NUM>. The spool valve <NUM> and the electromagnetic proportional valve <NUM> are substantially the same as those in the first embodiment and the second embodiment and thus are not described here.

In the embodiment, the spool <NUM> of the spool valve <NUM> and the electromagnetic proportional valve spool <NUM> of the electromagnetic proportional valve <NUM> are connected to each other by the feedback spring (a second biasing member) <NUM>. The feedback spring <NUM> is a compression spring. More specifically, the feedback spring <NUM> elastically connects between the pilot pressure acting surface <NUM> of the spool <NUM> and the one axial end side of the electromagnetic proportional valve spool <NUM>. With this arrangement, feedback control of the spool <NUM> of the spool valve <NUM> is possible.

First, when the solenoid coil of the drive unit <NUM> of the electromagnetic proportional valve <NUM> is not excited, the drive rod <NUM> is retracted toward the drive unit <NUM> by the biasing force of the feedback spring <NUM>. At this time, the electromagnetic proportional valve spool <NUM> is in the discharge position shown in <FIG>. The control port <NUM> is in communication with the drain port <NUM> via the main channel <NUM> and the second branch channel <NUM> of the electromagnetic proportional valve spool <NUM>. Accordingly, the pilot source port <NUM> of the spool valve <NUM> is in communication with the tank T connected to the drain port <NUM>.

In this state, the pilot pressure does not act on the pilot pressure acting surface <NUM> of the spool valve <NUM>. Therefore, the spool <NUM> of the spool valve <NUM> is retained in the neutral position (see <FIG>). At this time, the control port <NUM> is closed by the spool <NUM>, and therefore, the oil having the load pressure from the pressure source such as a pump is not supplied to the hydraulic apparatus connected to the control port <NUM>.

In this state, when the solenoid coil of the drive unit <NUM> is excited, the drive rod <NUM> advances from the drive unit <NUM> and drives the electromagnetic proportional valve spool <NUM>. The electromagnetic proportional valve spool <NUM> moves from the discharge position to the neutral position (see <FIG>). When the electromagnetic proportional valve spool <NUM> is in the neutral position, the communication between the second branch channel <NUM> and the drain port <NUM> is shut off while the communication between the first branch channel <NUM> and the pilot pressure source port <NUM> remains shut off. Therefore, the control port <NUM> is shut off from both the pilot pressure source port <NUM> and the drain port <NUM>. Accordingly, no oil is supplied to or discharged from the spool valve <NUM> connected to the control port <NUM>.

In this state, the pilot pressure still does not act on the pilot pressure acting surface <NUM> of the spool valve <NUM>. Therefore, the spool <NUM> of the spool valve <NUM> is retained in the neutral position by the pressing force of the spring <NUM> (see.

When a larger excitation current flows in the solenoid coil of the drive unit <NUM>, the drive rod <NUM> further advances the electromagnetic proportional valve spool <NUM>, and the first branch channel <NUM> of the electromagnetic proportional valve spool <NUM> moves to directly above the pilot pressure source port <NUM>. Therefore, as shown in <FIG>, the electromagnetic proportional valve spool <NUM> reaches the supply position. In the supply position, the control port <NUM> is in communication with the pilot pressure source port <NUM> via the main channel <NUM> and the first branch channel <NUM> of the electromagnetic proportional valve spool <NUM>. Accordingly, the oil having the pilot pressure is supplied from the pilot pressure source such as a pump connected to the pilot pressure source port <NUM> to the pilot source port <NUM> of the spool valve <NUM> connected to the control port <NUM>.

In this state, the pilot pressure acts on the pilot pressure acting surface <NUM> of the spool valve <NUM>. Therefore, the spool <NUM> of the spool valve <NUM> is moved toward the other axial end side and is displaced from the neutral position to the supply position (see <FIG>). This movement of the spool <NUM> of the spool valve <NUM> causes the control port <NUM> to be opened and in communication with the pressure source port <NUM>. Accordingly, the oil is supplied from the pressure source such as a pump connected to the pressure source port <NUM> to the hydraulic apparatus connected to the control port <NUM>.

As the spool <NUM> is moved toward the other axial end side, the feedback spring <NUM> is more compressed. Therefore, the biasing force of the feedback spring <NUM> causes the electromagnetic proportional valve spool <NUM> to move toward the other axial end side against the pressing force of the drive rod <NUM>. The electromagnetic proportional valve spool <NUM> moves via the neutral position to the discharge position (see <FIG>). When the electromagnetic proportional valve spool <NUM> enters the discharge position, the control port <NUM> communicates with the drain port <NUM> and is shut off from the pilot pressure source port <NUM>. Accordingly, the oil from the pilot source port <NUM> of the spool valve <NUM> is collected into the tank T connected to the drain port <NUM>, and the pressure acting on the pilot pressure acting surface <NUM> is reduced.

When the pressure acting on the pilot pressure acting surface <NUM> is reduced, the spool <NUM> returns toward the one axial end side by the biasing force of the spring <NUM>. As the spool <NUM> is moved toward the one axial end side, the feedback spring <NUM> is more stretched. Therefore, the biasing force of the feedback spring <NUM> is reduced, and the electromagnetic proportional valve spool <NUM> is moved toward the one axial end side by the pressing force of the drive rod <NUM>. As a result, the electromagnetic proportional valve spool <NUM> moves via the neutral position and reaches the supply position again (see <FIG>). When the electromagnetic proportional valve spool <NUM> enters the supply position, the control port <NUM> communicates with the pilot pressure source port <NUM> and is shut off from the drain port <NUM>. Accordingly, the oil having the pilot pressure is supplied again from the pilot pressure source to the spool valve <NUM>.

In this way, the electromagnetic proportional valve spool <NUM> moves repeatedly between the supply position (<FIG>) and the discharge position (<FIG>), such that the spool <NUM> is controlled into a position where the biasing force of the feedback spring <NUM> is balanced with the pressing force of the drive rod <NUM> applied by the drive device <NUM>.

Claim 1:
A spool valve, comprising:
a valve body (<NUM>); and
a spool (<NUM>) housed in the valve body (<NUM>) so as to be movable in an axial direction,
the spool (<NUM>) having a load pressure acting surface (<NUM>) and a pilot pressure acting surface (<NUM>), the load pressure acting surface (<NUM>) being formed on one axial end side of the spool (<NUM>) and configured to be acted on by a load pressure, the pilot pressure acting surface (<NUM>) being formed on another axial end side of the spool (<NUM>) and configured to be acted on by a pilot pressure,
wherein the spool (<NUM>) includes a spool body (<NUM>) and a shoulder (<NUM>) radially enlarged from the spool body (<NUM>),
the shoulder (<NUM>) has a first acting surface (34a) positioned on the other axial end side and a second acting surface (34b) positioned on the one axial end side, and
the spool (<NUM>) has a first communication hole (<NUM>) and a second communication hole (<NUM>) formed therein, and
the first communication hole (<NUM>) communicating between the load pressure acting surface (<NUM>) and the first acting surface (34a) of the shoulder (<NUM>), the second communication hole (<NUM>) communicating between the pilot pressure acting surface (<NUM>) and the second acting surface (34b) of the shoulder (<NUM>);
characterized in that
an area of the load pressure acting surface (<NUM>) is equal to an area of the first acting surface (34a) of the shoulder (<NUM>), and
an area of the pilot pressure acting surface (<NUM>) is smaller than an area of the second acting surface (34b) of the shoulder (<NUM>).