Patent Description:
A servo-valve is used in airplanes or other industrial fields. <CIT> discloses a technique of displacing a nozzle toward left and right sides of a rotation axis based on an electromagnetic principle to adjust the amount of hydraulic oil flowing into two inflow ports formed in a receiver. A combination of a displaceable nozzle and a receiver with two inflow ports is further shown in documents <CIT> and <CIT>. <CIT> further discloses a servo-valve according to the preamble of claim <NUM>. <CIT> discloses a servo-valve according to the preamble of claim <NUM>.

A high response speed of the servo-valve results in a high accuracy of a control using the servo-valve. Thus, there have been various attempts for improving a mechanical mechanism and/or an electrical mechanism for driving the nozzle from the past. However, many of these improvements face various problems involving with a selection of a material, a mechanical strength, a complex control, and a manufacturing cost of the servo-valve.

An object of the invention is to provide a simple technique of giving a high response speed to a servo-valve.

Said object is achieved by a servo-valve according to claims <NUM> and <NUM> respectively.

A fluidic device is also defined in dependent claim <NUM>.

According to the above-described configuration, the fluidic device including the servo-valve can be operated at a high response speed.

The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention, but to exemplify the invention.

In a known servo-valve, a nozzle is designed so that a front end thereof turns (swings) (hereinafter, referred to as "oscillation movement" or "oscillation") in both directions with a predetermined angle range about a rotation axis. The inventors have found a problem in which a hydraulic fluid discharged from a nozzle acts as a drag given to an inner wall surface of the nozzle on the horizontal oscillation movement. Since a large drag on the oscillation movement inhibits a movement switching the flow of the hydraulic fluid, the response performance of a servo-valve and an actuator coupled to the servo-valve are degraded. In the first embodiment, an illustrative servo-valve capable of reducing a drag on the oscillation movement of the nozzle will be described.

<FIG> is a conceptual diagram showing a servo-valve <NUM> of a first embodiment. The servo-valve <NUM> will be described with reference to <FIG>. Terms like "upward", "downward", "leftward", "rightward", "clockwise", "counterclockwise", "vertical", and "horizontal" indicating directions are used merely for the purpose of making the explanation unambiguous. The principle of the embodiments is not by any means limited by these terms denoting the directions.

The servo-valve <NUM> includes a nozzle <NUM> and a receiver <NUM>. The nozzle <NUM> can be oscillated clockwise and counterclockwise about a rotation axis RAX defined on an upper portion of the nozzle <NUM>. The nozzle <NUM> shown in <FIG> is positioned at a "neutral position". At the neutral position, a center line of the nozzle <NUM> matches a vertical line VL.

The nozzle <NUM> includes an upper surface <NUM> and a lower surface <NUM>. The lower surface <NUM> faces the receiver <NUM>. The upper surface <NUM> is located above the lower surface <NUM>. The upper surface <NUM> is provided with an inflow port <NUM>. The inflow port <NUM> is connected to a pump or other fluid supply sources supplying a hydraulic fluid. The hydraulic fluid (which will be referred to as, for example, hydraulic oil, but may be simply referred to as a "fluid" on the condition that the invention is not limited thereto) flows into the nozzle <NUM> through the inflow port <NUM>.

The lower surface <NUM> (the front end surface) is provided with a discharge port <NUM> from which the hydraulic fluid flowing from the inflow port <NUM> is discharged. The center line of the nozzle <NUM> may be defined as a line which passes through the center of the inflow port <NUM> and the center of the discharge port <NUM>.

The lower surface <NUM> includes a discharge edge <NUM> which forms the outline of the discharge port <NUM>. The discharge edge <NUM> may draw a circular outline or a non-circular outline. The principle of the embodiment is not limited to a specific outline form drawn by the discharge edge <NUM>.

The nozzle <NUM> is provided with a nozzle flow path <NUM> which extends downward from the inflow port <NUM> and is coupled to the discharge port <NUM>. The nozzle flow path <NUM> includes a straight run of pipe <NUM> and a tapered pipe portion <NUM> which extends downward from the straight run of pipe <NUM>. The straight run of pipe <NUM> extends along the center line of the nozzle <NUM> at the substantially uniform cross-sectional area. The tapered pipe portion <NUM> grows narrower toward the discharge edge <NUM>. The hydraulic fluid discharge pressure can be increased by the tapered pipe portion <NUM>. The high-pressure hydraulic fluid is discharged from the discharge port <NUM>. When the nozzle <NUM> is at the neutral position, the hydraulic fluid discharge direction from the discharge port <NUM> substantially matches the extension direction of the vertical line VL. When the nozzle <NUM> is oscillated clockwise, the hydraulic fluid is discharged toward lower left from the discharge port <NUM>. When the nozzle <NUM> is oscillated counterclockwise, the hydraulic fluid is discharged toward lower right from the discharge port <NUM>. In the embodiment, the first direction is exemplified by the hydraulic fluid is discharged toward the neutral position from the discharge port <NUM>.

The nozzle <NUM> includes a tapered inner wall <NUM> which forms the outline of the tapered pipe portion <NUM>. The discharge edge <NUM> is positioned at a boundary between the tapered inner wall <NUM> and the lower surface <NUM>.

The receiver <NUM> includes an upper surface <NUM> which faces the lower surface <NUM> of the nozzle <NUM>. The upper surface <NUM> is provided with a left inflow port <NUM> and a right inflow port <NUM>. A left inflow port <NUM> is positioned to the left of the right inflow port <NUM>. The direction of alignment of the left inflow port <NUM> and the right inflow port <NUM> is substantially orthogonal to a direction in which the hydraulic fluid is discharged from the discharge port <NUM> of the nozzle <NUM> at the neutral position. The direction of alignment of the left inflow port <NUM> and the right inflow port <NUM> matches the movement direction of the discharge port <NUM> in accordance with the rotation of the nozzle <NUM> about the rotation axis RAX. In the embodiment, the second direction is exemplified by the direction of alignment of the left inflow port <NUM> and the right inflow port <NUM> and/or the movement direction of the discharge port <NUM> in accordance with the rotation of the nozzle <NUM> about the rotation axis RAX.

The receiver <NUM> is provided with a left flow path <NUM> and a right flow path <NUM>. The left flow path <NUM> extends leftward and downward from the left inflow port <NUM> and is terminated at the left outflow port <NUM>. The right flow path <NUM> extends rightward and downward from the right inflow port <NUM> and is terminated at the right outflow port <NUM>. The left outflow port <NUM> and the right outflow port <NUM> are formed in an outer surface of the receiver <NUM> and are coupled to a spool valve (not shown) or an actuator (not shown).

When the nozzle <NUM> is positioned at the neutral position, the hydraulic fluid discharged from the discharge port <NUM> flow in substantially in the same quantity into the left inflow port <NUM> and the right inflow port <NUM>. In the embodiment, the first flow path is exemplified by one of the left flow path <NUM> and the right flow path <NUM>. The second flow path is exemplified by the other of the left flow path <NUM> and the right flow path <NUM>. The first inflow port is exemplified by one of the left inflow port <NUM> and the right inflow port <NUM>. The second inflow port is exemplified by the other of the left inflow port <NUM> and the right inflow port <NUM>. The inflow surface is exemplified by the upper surface of the receiver <NUM>.

<FIG> shows the center line CL of the left flow path <NUM>. The extension direction of the center line CL matches the extension direction of the left flow path <NUM>. Further, <FIG> shows the inclination angle α (< <NUM>°) of the center line CL from the vertical line VL. As described above, since the right flow path <NUM> has a point-symmetrical relation with respect to the left flow path <NUM>, the inclination angle of the center line (not shown) of the right flow path <NUM> from the vertical line VL matches the inclination angle α of the left flow path <NUM>. In the embodiment, the extended line is exemplified by the vertical line VL.

<FIG> shows a center point LCP of the left inflow port <NUM> and a center point RCP of the right inflow port <NUM>. A relative positional relation between the nozzle <NUM> and the receiver <NUM> is set so that the vertical line VL and the center points LCP and RCP are positioned on the common virtual plane. <FIG> conceptually shows the cross-sections of the nozzle <NUM> and the receiver <NUM> on the common virtual plane. In the embodiment, the alignment line is exemplified by the line passing through the center points LCP and RCP.

<FIG> shows two lines of intersection LIS and RIS formed by the virtual plane and the tapered inner wall <NUM>. The line of intersection LIS is formed at the left of the vertical line VL. The line of intersection RIS is formed at the right of the vertical line VL. Two lines of intersection LIS and RIS are straight lines which have a point-symmetrical relation about the vertical line VL. Further, <FIG> shows the taper angle β of the tapered pipe portion <NUM>. The taper angle β may be defined as a narrow angle (the angle of intersection determined by the lines of intersection LIS and RIS) between the extended lines of two lines of intersection LIS and RIS. The taper angle β is determined so that a relation shown in the following expression (<NUM>) holds. In the following expression (<NUM>), "2α" corresponds to a narrow angle between the left flow path <NUM> and the right flow path <NUM>. In the embodiment, the first line of intersection is exemplified by one of the lines of intersection LIS and RIS. The second line of intersection is exemplified by the other of the lines of intersection LIS and RIS. [Expression <NUM>] <MAT>.

An angle relation explained in the first embodiment contributes to the reduction of the drag in the direction of movement of the nozzle. In a second embodiment, the drag reduction principle will be described.

<FIG> shows flow line data in a known servo-valve. Referring to <FIG>, a flow line generated inside the known servo-valve will be described.

<FIG> shows a receiver RCV disposed below the nozzle NZL and the nozzle NZL. In <FIG>, the left flow path LFP and the right flow path RFP formed in the receiver RCV are drawn. In <FIG>, the tapered inner wall TIW of the nozzle NZL and the tapered flow path TFP surrounded by the tapered inner wall TIW are further drawn. A plurality of curves which are drawn in the left flow path LFP, the right flow path RFP, the tapered flow path TFP, and the gap formed between the nozzle NZL and the receiver RCV and extended in the horizontal direction indicate the flow lines of the hydraulic fluid.

<FIG> shows the vertical line VL passing through the branching point from which the left flow path LFP and the right flow path RFP branch. The nozzle NZL shown in <FIG> moves leftward from the neutral position and the hydraulic fluid discharged from the nozzle NZL through the tapered flow path TFP mainly flows into the left flow path LFP. At this time, the flow line of the hydraulic fluid directed from the tapered flow path TFP toward the left flow path LFP is curved left. The left curving of the flow line means the generation of the centrifugal force exerted on the right of the tapered inner wall TIW. The following expression (<NUM>) shows a relation between a pressure (a left side) generated by a centrifugal force and a radius of a curved flow line. [Expression <NUM>] <MAT>.

<FIG> shows a centrifugal force CF1 acting on the line of intersection RIS. <FIG> shows a centrifugal force CF2 acting on a line SGL having a gradient larger than that of the line of intersection RIS. Referring to <FIG>, <FIG>, a relation between the taper angle and the centrifugal force will be described.

As described above, the centrifugal force CF1 is exerted on the line of intersection RIS on the tapered inner wall <NUM> by the curving of the flow line when the nozzle <NUM> moves leftward. The scalar of the centrifugal force CF1 shown in <FIG> is the same as the scalar of the centrifugal force CF2 shown in <FIG>. The centrifugal force CF1 is orthogonal to the line of intersection RIS. The centrifugal force CF2 is orthogonal to the line SGL.

<FIG> shows a horizontal component HF1 of the centrifugal force CF1 and a vertical component VF1 of the centrifugal force CF1. The horizontal component HF1 is exerted in a direction opposite to the movement direction (the left side) of the nozzle <NUM>. Thus, the horizontal component HF1 acts as a drag against the leftward movement of the nozzle <NUM>.

<FIG> shows a horizontal component HF2 of the centrifugal force CF2 and a vertical component VF2 of the centrifugal force CF2. The horizontal component HF2 is larger than the horizontal component HF1. This means that the drag of the movement direction of the nozzle <NUM> decreases when the taper angle β is a large value. According to the inventors, when the taper angle β is set so that the inequality described in the first embodiment holds, the servo-valve <NUM> can have a response performance higher than that of the known servo-valve. For example, the taper angle β may be set to <NUM>° or more.

The taper angle of the nozzle may be determined based on the pair of inflow ports formed in the receiver. In a third embodiment, a method of determining the taper angle based on the pair of inflow ports formed in the receiver will be described.

<FIG> is a conceptual diagram of a servo-valve 100A embodiment covered by the claims. Referring to <FIG>, the servo-valve 100A will be described. The explanation of the first embodiment is incorporated in the description of the elements denoted by the same reference numerals as those of the first embodiment. In the embodiment, terms like "upward", "downward", "leftward", "rightward", "clockwise", "counterclockwise", "vertical", and "horizontal" indicating directions are used merely for the purpose of making the explanation unambiguous. The principle of the embodiments is not by any means limited by these terms denoting the directions.

Like the first embodiment, the servo-valve 100A includes the nozzle <NUM> and the receiver <NUM>. The explanation in the first embodiment is incorporated in the description of these elements.

The servo-valve 100A further includes a driving unit <NUM>. The driving unit <NUM> oscillates the nozzle <NUM> about the rotation axis RAX. The driving unit <NUM> may be a general torque motor which gives a rotational force to the nozzle <NUM> by using an electromagnetic force or other driving devices. The principle of the embodiment is not limited to a specific device used as the driving unit <NUM>.

The nozzle <NUM> shown in <FIG> is positioned at the neutral position. <FIG> shows a point ISP of intersection between the upper surface <NUM> of the receiver <NUM> and the center line of the nozzle <NUM> at the neutral position. The point ISP of intersection is positioned on the line passing through the center point LCP of the left inflow port <NUM> and the center point RCP of the right inflow port <NUM>.

When the nozzle <NUM> is oscillated clockwise from the neutral position by the driving unit <NUM>, the discharge port <NUM> moves leftward. All this while, the point ISP of intersection moves along the line passing through the center point LCP of the left inflow port <NUM> and the center point RCP of the right inflow port <NUM> and approaches the center point LCP of the left inflow port <NUM>. As a result, the hydraulic fluid mainly flows into the left inflow port <NUM>. As described in the second embodiment, the horizontal component of the centrifugal force of the hydraulic fluid acting on the line of intersection RIS becomes larger than the horizontal component of the centrifugal force of the hydraulic fluid acting on the line of intersection LIS while the hydraulic fluid mainly flows into the left inflow port <NUM>.

When the nozzle <NUM> is oscillated counterclockwise from the neutral position by the driving unit <NUM>, the discharge port <NUM> moves rightward. All this while, the point ISP of intersection moves along the line passing through the center point LCP of the left inflow port <NUM> and the center point RCP of the right inflow port <NUM> and approaches the center point RCP of the right inflow port <NUM>. As a result, the hydraulic fluid mainly flows into the right inflow port <NUM>. As described in the second embodiment, the horizontal component of the centrifugal force of the hydraulic fluid acting on the line of intersection LIS becomes larger than the horizontal component of the centrifugal force of the hydraulic fluid acting on the line of intersection RIS while the hydraulic fluid mainly flows into the right inflow port <NUM>. In the embodiment, the flow force is exemplified by the horizontal component of the centrifugal force of the hydraulic fluid.

<FIG> shows extended lines LEX and REX which extend from the lower ends of the lines of intersection LIS and RIS toward the receiver <NUM>. The taper angle β may be determined so that the extended line LEX extends inside the right inflow port <NUM> and the extended line REX extends inside the left inflow port <NUM>. Since the taper angle β becomes larger than the taper angle of the known nozzle, the horizontal components acting on the lines of intersection LIS and RIS become smaller than those of the known nozzle.

In the above-described embodiments, the form of the tapered pipe portion is a truncated cone with a straight generation line. Alternatively, the form of the tapered pipe portion may be spherical or ellipsoidal. In this case, the tapered inner wall draws an outline curved on a virtual plane enclosing the center of the left inflow port, the center of the right inflow port, and the center of the discharge port. The design principle described in the third embodiment can be also applied to a nozzle including a tapered inner wall drawing an outline curved on a virtual plane. In a fourth embodiment, an illustrative servo-valve including a nozzle with a tapered inner wall drawing an outline curved on a virtual plane will be described.

<FIG> is a conceptual diagram showing a servo-valve 100B of the fourth embodiment covered by the claims. Referring to <FIG>, the servo-valve 100B will be described. The explanation of the third embodiment is incorporated in the description of the elements denoted by the same reference numerals as those of the third embodiment. In the embodiment, terms like "upward", "downward", "leftward", "rightward", "clockwise", "counterclockwise", "vertical", and "horizontal" indicating directions are used merely for the purpose of making the explanation unambiguous. The principle of the embodiments is not by any means limited by these terms denoting the directions.

Like the third embodiment, the servo-valve 100B includes the receiver <NUM> and the driving unit <NUM>. The explanation of the third embodiment is incorporated in the description of these elements.

The servo-valve 100B further includes a nozzle 200B. Like the third embodiment, the nozzle 200B includes the upper surface <NUM> and the lower surface <NUM>. The explanation of the third embodiment is incorporated in the description of these elements.

A nozzle flow path 230B is formed inside the nozzle 200B. The nozzle flow path 230B extends downward from the inflow port <NUM> formed in the upper surface <NUM> and is coupled to the discharge port <NUM> formed in the lower surface <NUM>. Like the third embodiment, the nozzle flow path 230B includes the straight run of pipe <NUM>. The explanation of the third embodiment is incorporated in the description of the straight run of pipe <NUM>.

The nozzle flow path 230B further includes a tapered pipe portion 232B. The tapered pipe portion 232B extends downward from the straight run of pipe <NUM> and is opened at the discharge port <NUM>. The tapered pipe portion 232B has a semi-elliptical spherical form which grows narrower toward the discharge port <NUM>. The discharge pressure of the hydraulic fluid can be increased by the tapered pipe portion 232B. The high-pressure hydraulic fluid is discharged from the discharge port <NUM>. When the nozzle 200B is positioned at the neutral position, the hydraulic fluid discharge direction from the discharge port <NUM> substantially matches the vertical line VL. When the nozzle 200B is oscillated clockwise, the hydraulic fluid is discharged toward lower left from the discharge port <NUM>. When the nozzle 200B is oscillated counterclockwise, the hydraulic fluid is discharged toward lower right from the discharge port <NUM>.

The nozzle 200B includes a tapered inner wall 240B which forms the outline of the tapered pipe portion 232B. The discharge edge <NUM> is positioned at a boundary between the tapered inner wall 240B and the lower surface <NUM>.

<FIG> shows the center point LCP of the left inflow port <NUM> and the center point RCP of the right inflow port <NUM>. A relative positional relation between the nozzle 200B and the receiver <NUM> is set so that the vertical line VL and the center points LCP and RCP are positioned on the common virtual plane. <FIG> conceptually shows the cross-sections of the nozzle 200B and the receiver <NUM> on the common virtual plane.

<FIG> shows two lines of intersection LIC and RIC which are formed by the virtual plane and the tapered inner wall 240B. The line of intersection LIC is formed at the left side of the vertical line VL. The line of intersection RIC is formed at the right side of the vertical line VL. Two lines of intersection LIC and RIC are curves which have a point-symmetrical relation with respect to the vertical line VL. In the embodiment, the first line of intersection is exemplified by one of the lines of intersection LIC and RIC. The second line of intersection is exemplified by the other of the lines of intersection LIC and RIC.

<FIG> shows tangential lines LTG and RTG for the lines of intersection LIC and RIC. The tangential line LTG contacts the line of intersection LIC at the midpoint between the upper end of the line of intersection LIC (that is, the end positioned at the boundary between the tapered pipe portion <NUM> and the straight run of pipe <NUM>) and the discharge edge <NUM> corresponding to the lower end of the line of intersection LIC. The tangential line RTG contacts the line of intersection RIC at the midpoint between the upper end of the line of intersection RIC (that is, the end positioned at the boundary between the tapered pipe portion <NUM> and the straight run of pipe <NUM>) and the discharge edge <NUM> corresponding to the lower end of the line of intersection RIC. The taper angle β may be defined as the angle of intersection of the tangential lines LTG and RTG.

When the nozzle 200B is positioned at the neutral position, the taper angle β may be determined so that the tangential line LTG extends inside the right inflow port <NUM> and the tangential line RTG extends inside the left inflow port <NUM>. Since the taper angle β becomes larger than the taper angle of the known nozzle, a horizontal component exerted on the lines of intersection LIC and RIC becomes smaller than that of the known nozzle.

In the above-described embodiments, the tapered pipe portion is formed at the lower end of the nozzle. In a fifth example not covered by the claims, an illustrative servo-valve including a nozzle provided with a straight run of pipe below a tapered pipe portion will be described.

<FIG> is a conceptual diagram showing a servo-valve 100C of the fifth example not covered by the claims. Referring to <FIG>, the servo-valve 100C will be described. The explanation of the above-described embodiments is incorporated in the description of the elements denoted by the same reference numerals as those of the above-described embodiments. In the embodiment, terms like "upward", "downward", "leftward", "rightward", "clockwise", "counterclockwise", "vertical", and "horizontal" indicating directions are used merely for the purpose of making the explanation unambiguous. The principle of the embodiments is not by any means limited by these terms denoting the directions.

Like the fourth embodiment, the servo-valve 100C includes the receiver <NUM> and the driving unit <NUM>. The explanation of the fourth embodiment is incorporated in the description of these elements.

The servo-valve 100C further includes a nozzle 200C. Like the fourth embodiment, the nozzle 200C includes the upper surface <NUM> and the lower surface <NUM>. The explanation of the fourth embodiment is incorporated in the description of these elements.

A nozzle flow path 230C is formed inside the nozzle 200C. The nozzle flow path 230C extends downward from the inflow port <NUM> formed in the upper surface <NUM> and is coupled to the discharge port <NUM> formed in the lower surface <NUM>. Like the fourth embodiment, the nozzle flow path 230C includes the straight run of pipe <NUM>. The explanation of the fourth embodiment is incorporated in the description of the straight run of pipe <NUM>.

The nozzle flow path 230C further includes a tapered pipe portion 232C and a lower pipe portion <NUM>. The tapered pipe portion 232C becomes narrower downward from the straight run of pipe <NUM> and is coupled to the lower pipe portion <NUM>. The lower pipe portion <NUM> extends downward from the tapered pipe portion 232C and is opened at the discharge port <NUM>. Differently from the tapered pipe portion 232C, the lower pipe portion <NUM> is a straight pipe. The discharge pressure of the hydraulic fluid can be increased by the tapered pipe portion 232C. Subsequently, the hydraulic fluid is slightly straightened by the lower pipe portion <NUM> and is discharged from the discharge port <NUM>. When the nozzle 200C is positioned at the neutral position, the hydraulic fluid discharge direction from the discharge port <NUM> substantially matches the vertical line VL. When the nozzle 200C is oscillated clockwise, the hydraulic fluid is discharged toward lower left from the discharge port <NUM>. When the nozzle 200C is oscillated counterclockwise, the hydraulic fluid is discharged toward lower right from the discharge port <NUM>.

The nozzle 200C includes a tapered inner wall 240C and a lower pipe wall <NUM>. The tapered inner wall 240C forms the outline of the tapered pipe portion 232C. The lower pipe wall <NUM> extends downward from the tapered inner wall 240C and is terminated at the discharge edge <NUM>. The lower pipe wall <NUM> forms the outline of the lower pipe portion <NUM>.

<FIG> shows the center point LCP of the left inflow port <NUM> and the center point RCP of the right inflow port <NUM>. A relative positional relation between the nozzle 200C and the receiver <NUM> is set so that the vertical line VL and the center points LCP and RCP are positioned on the common virtual plane. <FIG> conceptual shows the cross-sections of the nozzle 200C and the receiver <NUM> on the common virtual plane.

<FIG> shows two lines of intersection LIS and RIS which are formed by the virtual plane and the tapered inner wall 240C. The line of intersection LIS is formed at the left side of the vertical line VL. The line of intersection RIS is formed at the right side of the vertical line VL. Two lines of intersection LIS and RIS are curves which have a point-symmetrical relation with respect to the vertical line VL.

<FIG> shows the extended lines LEX and REX which extend from the lower ends of the lines of intersection LIS and RIS toward the receiver <NUM>. The taper angle β may be determined so that the extended line LEX extends inside the right inflow port <NUM> and the extended line REX extends inside the left inflow port <NUM>. Since the taper angle β becomes larger than the taper angle of the known nozzle, a horizontal component exerted on the lines of intersection LIS and RIS becomes smaller than that of the known nozzle.

A force in a direction opposite to the movement direction of the nozzle 200C acts on the lower pipe wall <NUM>. Thus, the axial dimension of the lower pipe portion <NUM> is determined so that a force in a direction opposite to the movement direction of the nozzle 200C does not excessively increase. The axial dimension of the lower pipe portion <NUM> may be smaller than that of the tapered pipe portion 232C.

In the design principle of the above-described embodiments, there is a case in which an excessively large resistance is exerted on the hydraulic fluid around the discharge port. In a sixth embodiment, an illustrative servo-valve including a nozzle with a pipe structure reducing a resistance around a discharge port will be described.

<FIG> is a conceptual diagram showing a servo-valve 100D of the sixth embodiment not covered by the claims. Referring to <FIG>, the servo-valve 100D will be described. The explanation of the above-described embodiments is incorporated in the description of the elements denoted by the same reference numerals as those of the above-described embodiments. In the embodiment, terms like "upward", "downward", "leftward", "rightward", "clockwise", "counterclockwise", "vertical", and "horizontal" indicating directions are used merely for the purpose of making the explanation unambiguous. The principle of the embodiments is not by any means limited by these terms denoting the directions.

Like the fifth example not according to the invention, the servo-valve 100D includes the receiver <NUM> and the driving unit <NUM>. The explanation of the fifth example not according to the invention is incorporated in the description of these elements.

The servo-valve 100D further includes a nozzle 200D. Like the fifth embodiment, the nozzle 200D includes the upper surface <NUM> and the lower surface <NUM>. The explanation of the fifth example not according to the inventionis incorporated in the description of these elements.

A nozzle flow path 230D is formed inside the nozzle 200D. The nozzle flow path 230D extends downward from the inflow port <NUM> formed in the upper surface <NUM> and is coupled to the discharge port <NUM> formed in the lower surface <NUM>. Like the fifth example not according to the invention, the nozzle flow path 230D includes the straight run of pipe <NUM> and the tapered pipe portion 232C. The explanation of the fifth example not according to the invention is incorporated in the description of these elements.

The nozzle flow path 230D further includes a lower pipe portion 233D. The lower pipe portion 233D becomes narrower upward from the discharge port <NUM> and is coupled to the lower end of the tapered pipe portion 232C. Differently from the fifth example not covered by the claims, the cross-section of the lower pipe portion 233D increases downward. Thus, a resistance acting on the hydraulic fluid does not excessively increases around the discharge port <NUM>.

The nozzle 200D includes a lower pipe wall 250D. The tapered inner wall 240C forms the outline of the tapered pipe portion 232C. The lower pipe wall 250D extends downward from the tapered inner wall 240C and is terminated at the discharge edge <NUM>. The lower pipe wall 250D forms the outline of the lower pipe portion 233D.

A force in a direction opposite to the movement direction of the nozzle 200D acts on the lower pipe wall 250D. Thus, the axial dimension of the lower pipe portion 233D is set so that a force in a direction opposite to the movement direction of the nozzle 200D does not excessively increase. The axial dimension of the lower pipe portion 233D may be smaller than that of the tapered pipe portion 232C.

The servo-valve according to the above-described embodiment can be assembled to various fluidic devices driven by the hydraulic fluid. In a seventh embodiment, an illustrative fluidic device will be described.

<FIG> is a schematic diagram showing a fluidic device <NUM> of the seventh embodiment. Referring to <FIG> and <FIG>, the fluidic device <NUM> will be described. The explanation of the third embodiment is incorporated in the description of the elements indicated by the same reference numerals as in the third embodiment.

The fluidic device <NUM> includes a servo-valve 100E, an actuator <NUM>, two pumps <NUM> and <NUM>, and a tank <NUM>. Like the third embodiment, the servo-valve 100E includes a receiver <NUM>. The explanation of the third embodiment is incorporated in the description of the receiver <NUM>. The inclination angles of the left flow path <NUM> and the right flow path <NUM> formed in the receiver <NUM> are determined based on the design principle described in the above-described embodiments.

The servo-valve 100E includes a torque motor 400E. The torque motor 400E corresponds to the driving unit <NUM> described with reference to <FIG>. The explanation of the driving unit <NUM> is incorporated in the description of the torque motor 400E.

The torque motor 400E includes a lower coil <NUM>, an upper coil <NUM>, a lower magnetic piece <NUM>, an upper magnetic piece <NUM>, and a magnetic rod <NUM>. The upper coil <NUM> is disposed above the lower coil <NUM>. The lower magnetic piece <NUM> may be formed in a substantially cylindrical form. The lower coil <NUM> is accommodated inside the lower magnetic piece <NUM>. Like the lower magnetic piece <NUM>, the upper magnetic piece <NUM> may be formed in a substantially cylindrical form. The upper coil <NUM> is disposed inside the upper magnetic piece <NUM>. The lower edge of the upper magnetic piece <NUM> faces the upper edge of the lower magnetic piece <NUM>. The magnetic rod <NUM> extends substantially horizontally. The left and right ends of the magnetic rod <NUM> are located in a gap between the upper edge of the lower magnetic piece <NUM> and the lower edge of the upper magnetic piece <NUM>.

A current is supplied to the lower coil <NUM> and the upper coil <NUM>. As a result, the lower magnetic piece <NUM> and the upper magnetic piece <NUM> serve as magnets. When a current is supplied to the lower coil <NUM> and the upper coil <NUM> so that the right end of the magnetic rod <NUM> is pulled to the lower magnetic piece <NUM> and the left end of the magnetic rod <NUM> is pulled to the upper magnetic piece <NUM>, the magnetic rod <NUM> rotates clockwise. When a current is supplied to the lower coil <NUM> and the upper coil <NUM> so that the left end of the magnetic rod <NUM> is pulled to the lower magnetic piece <NUM> and the right end of the magnetic rod <NUM> is pulled to the upper magnetic piece <NUM>, the magnetic rod <NUM> rotates counterclockwise.

The servo-valve 100E includes a nozzle portion 200E. The nozzle portion 200E corresponds to the nozzle <NUM> described with reference to <FIG>. The explanation of the nozzle <NUM> is incorporated in the description of the nozzle portion 200E.

The nozzle portion 200E includes a nozzle piece <NUM>, a flexible tube <NUM>, and a coupling shaft <NUM>. The flexible tube <NUM> extends vertically to penetrate the torque motor 400E. The nozzle piece <NUM> is attached to the lower end of the flexible tube <NUM>. The high-pressure hydraulic fluid is supplied to the flexible tube <NUM>. The hydraulic fluid is guided by the flexible tube <NUM> to reach the nozzle piece <NUM>.

The nozzle piece <NUM> includes a lower surface <NUM> which faces the upper surface <NUM> of the receiver <NUM>. The lower surface <NUM> is provided with a discharge port <NUM>. The taper angle of the tapered pipe portion extended toward the discharge port <NUM> is determined based on the design principle described in the third embodiment. The high-pressure hydraulic fluid which is supplied to the nozzle piece <NUM> is discharged from the discharge port <NUM>. Subsequently, the hydraulic fluid flows into the receiver <NUM>.

The coupling shaft <NUM> is used so that the flexible tube <NUM> is coupled to an intermediate portion of the magnetic rod <NUM>. The flexible tube <NUM> and the nozzle piece <NUM> move left and right in a reciprocating manner in response to the clockwise and counterclockwise rotations of the magnetic rod <NUM>.

When the magnetic rod <NUM> rotates about the coupling shaft <NUM> clockwise, the discharge port <NUM> of the nozzle piece <NUM> moves leftward along the line connecting the center point LCP of the left inflow port <NUM> and the center point RCP of the right inflow port <NUM>. Since the taper angle of the inner wall portion of the nozzle piece <NUM> is determined based on the design principle described in the third embodiment, a rightward force exerted from the hydraulic fluid to the inner wall of the nozzle piece <NUM> is small. Thus, the nozzle piece <NUM> can quickly move left. When the nozzle piece <NUM> moves leftward, the area of overlapping between the discharge port <NUM> and the left inflow port <NUM> increases and the area of overlapping between the discharge port <NUM> and the right inflow port <NUM> decreases. In this case, the amount of the hydraulic fluid flowing into the left flow path <NUM> formed inside the receiver <NUM> exceeds the flow rate of the hydraulic fluid flowing into the right flow path <NUM>.

When the magnetic rod <NUM> rotates about the coupling shaft <NUM> counterclockwise, the discharge port <NUM> of the nozzle piece <NUM> moves rightward along the line connecting the center point LCP of the left inflow port <NUM> and the center point RCP of the right inflow port <NUM>. Since the taper angle of the inner wall portion of the nozzle piece <NUM> is determined based on the design principle described in the third embodiment, a leftward force exerted from the hydraulic fluid to the inner wall of the nozzle piece <NUM> is small. Thus, the nozzle piece <NUM> can quickly move right. When the nozzle piece <NUM> moves rightward, the area of overlapping between the discharge port <NUM> and the right inflow port <NUM> increases and the area of overlapping between the discharge port <NUM> and the left inflow port <NUM> decreases. In this case, the amount of the hydraulic fluid flowing into the right flow path <NUM> formed inside the receiver <NUM> exceeds the flow rate of the hydraulic fluid flowing into the left flow path <NUM>.

The servo-valve 100E includes a spool valve <NUM>. The spool valve <NUM> includes a casing <NUM>, a spool <NUM>, and a cantilever spring <NUM>. The spool <NUM> is disposed inside the casing <NUM>. As a result, a flow path through which the hydraulic fluid flows is formed inside the casing <NUM>. The cantilever spring <NUM> is used so that the casing <NUM> and the spool <NUM> are coupled to each other. The cantilever spring <NUM> applies a force of keeping the spool <NUM> at the closed position to the spool <NUM>. When the spool <NUM> is located at the closed position, the spool valve <NUM> interrupts the hydraulic fluid supply path from the pumps <NUM> and <NUM> to the actuator <NUM>. When the spool <NUM> moves leftward or rightward from the closed position, the spool valve <NUM> opens the hydraulic fluid supply path from the pumps <NUM> and <NUM> to the actuator <NUM>.

The casing <NUM> is provided with seven ports <NUM> to <NUM>. The port <NUM> is connected in fluid communication with the left outflow port <NUM> of the receiver <NUM>. The port <NUM> is connected in fluid communication with the right outflow port <NUM> of the receiver <NUM>. The pumps <NUM> and <NUM> are respectively attached to the ports <NUM> and <NUM>. The ports <NUM> and <NUM> are connected in fluid communication with the actuator <NUM>. The tank <NUM> is attached to the port <NUM>.

The spool <NUM> includes four partition walls <NUM>, <NUM>, <NUM>, and <NUM> and a coupling shaft <NUM> used so that the partition walls <NUM>, <NUM>, <NUM>, and <NUM> are coupled to one another. The coupling shaft <NUM> extends substantially horizontally. The partition wall <NUM> is formed at the left end of the coupling shaft <NUM>. The partition wall <NUM> is formed at the right end of the coupling shaft <NUM>. The partition wall <NUM> is located between the partition walls <NUM> and <NUM>. The partition wall <NUM> is located between the partition walls <NUM> and <NUM>.

The partition walls <NUM>, <NUM>, <NUM>, and <NUM> divide the inner space of the casing <NUM> into five chambers <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. The chamber <NUM> moves to the leftmost side. The chamber <NUM> moves to the rightmost side. The chamber <NUM> is formed between the partition walls <NUM> and <NUM>. The chamber <NUM> is formed between the partition walls <NUM> and <NUM>. The chamber <NUM> is formed between the partition walls <NUM> and <NUM>.

When the nozzle piece <NUM> moves leftward, the hydraulic fluid mainly flows from the discharge port <NUM> of the nozzle piece <NUM> to the left inflow port <NUM> of the receiver <NUM>. Subsequently, the hydraulic fluid which flows into the left inflow port <NUM> flows into the chamber <NUM> through the left flow path <NUM> of the receiver <NUM>, the left outflow port <NUM> of the receiver <NUM>, and the port <NUM> of the spool valve <NUM>. As a result, the inner pressure of the chamber <NUM> increases and the spool <NUM> moves rightward from the closed position. All this while, the hydraulic fluid which exists inside the chamber <NUM> is blown out from the right inflow port <NUM> through the port <NUM> of the spool valve <NUM>, the right outflow port <NUM> of the receiver <NUM>, and the right flow path <NUM> of the receiver <NUM>. Subsequently, when the nozzle piece <NUM> returns to the neutral position, the hydraulic fluid ejected from the discharge port <NUM> of the nozzle piece <NUM> flows in substantially in the same quantity into the left inflow port <NUM> and the right inflow port <NUM> of the receiver <NUM>. All this while, a force exerted on the left side of the spool <NUM> is larger than a force exerted on the right side of the spool <NUM> by a magnitude commensurate with the resilience of the cantilever spring <NUM>. Thus, the spool <NUM> moves leftward and returns to the closed position.

When the nozzle piece <NUM> moves rightward, the hydraulic fluid mainly flows from the discharge port <NUM> of the nozzle piece <NUM> to the right inflow port <NUM> of the receiver <NUM>. Subsequently, the hydraulic fluid which flows into the right inflow port <NUM> flows into the chamber <NUM> through the right flow path <NUM> of the receiver <NUM>, the right outflow port <NUM> of the receiver <NUM>, and the port <NUM> of the spool valve <NUM>. As a result, the inner pressure of the chamber <NUM> increases and the spool <NUM> moves leftward from the closed position. All this while, the hydraulic fluid which exists inside the chamber <NUM> is blown out from the left inflow port <NUM> through the port <NUM> of the spool valve <NUM>, the left outflow port <NUM> of the receiver <NUM>, and the left flow path <NUM> of the receiver <NUM>. Subsequently, when the nozzle piece <NUM> returns to the neutral position, the hydraulic fluid which is ejected from the discharge port <NUM> of the nozzle piece <NUM> flows in substantially in the same quantity into the left inflow port <NUM> and the right inflow port <NUM> of the receiver <NUM>. All this while, a force exerted on the right side of the spool <NUM> is larger than a force exerted on the left side of the spool <NUM> by a magnitude commensurate with the resilience of the cantilever spring <NUM>. Thus, the spool <NUM> moves rightward and returns to the closed position.

When the spool <NUM> is located at the closed position, the partition wall <NUM> closes the port <NUM>. At this time, the partition wall <NUM> closes the port <NUM>. The pump <NUM> supplies the high-pressure hydraulic fluid to the chamber <NUM> through the port <NUM>. The pump <NUM> supplies the high-pressure hydraulic fluid to the chamber <NUM> through the port <NUM>. When the spool <NUM> moves rightward from the closed position, the hydraulic fluid supply path from the chamber <NUM> to the actuator <NUM> and the hydraulic fluid discharge path from the actuator <NUM> to the chamber <NUM> are opened. When the spool <NUM> moves leftward from the closed position, the hydraulic fluid supply path from the chamber <NUM> to the actuator <NUM> and the hydraulic fluid discharge path from the actuator <NUM> to the chamber <NUM> are opened. Thus, the amount of the hydraulic fluid flowing from the ports <NUM> and <NUM> to the actuator <NUM> is adjusted by the left and right movement of the nozzle piece <NUM>. In the embodiment, the first outflow port is exemplified by one of the ports <NUM> and <NUM>. The second outflow port is exemplified by the other of the ports <NUM> and <NUM>.

The actuator <NUM> includes a casing <NUM> and a movable piece <NUM>. The casing <NUM> is provided with two ports <NUM> and <NUM>. The port <NUM> of the actuator <NUM> is connected in fluid communication with to the port <NUM> of the spool valve <NUM>. The port <NUM> of the actuator <NUM> is connected in fluid communication with to the port <NUM> of the spool valve <NUM>.

The movable piece <NUM> includes a partition wall <NUM> and a rod <NUM>. The partition wall <NUM> divides the inner space of the casing <NUM> into a left chamber <NUM> and a right chamber <NUM>. The port <NUM> is coupled to the left chamber <NUM>. The port <NUM> is coupled to the right chamber <NUM>. The rod <NUM> extends right from the partition wall <NUM> and protrudes to the outside of the casing <NUM>. The rod <NUM> is connected to other external devices (not show) disposed outside the casing <NUM>. In the embodiment, the hollow portion is exemplified by the inner space of the casing <NUM>.

When the spool <NUM> moves rightward from the closed position, the hydraulic fluid which is supplied from the pump <NUM> to the chamber <NUM> through the port <NUM> flows into the left chamber <NUM> through the ports <NUM> and <NUM>. Since the inner pressure of the left chamber <NUM> increases, the movable piece <NUM> moves rightward. All this while, the right chamber <NUM> communicates with the chamber <NUM> through the ports <NUM> and <NUM>. The hydraulic fluid which exists inside the right chamber <NUM> is extruded from the right chamber <NUM> by the movable piece <NUM> moving right so that the hydraulic fluid flows to the chamber <NUM>. Subsequently, the hydraulic fluid which flows into the chamber <NUM> is stored in the tank <NUM>.

When the spool <NUM> moves leftward from the closed position, the hydraulic fluid which is supplied from the pump <NUM> to the chamber <NUM> through the port <NUM> flows into the right chamber <NUM> through the ports <NUM> and <NUM>. Since the inner pressure of the right chamber <NUM> increases, the movable piece <NUM> moves leftward. All this while, the left chamber <NUM> communicates with the chamber <NUM> through the ports <NUM> and <NUM>. The hydraulic fluid which exists inside the left chamber <NUM> is extruded from the left chamber <NUM> by the movable piece <NUM> moving left so that the hydraulic fluid flows into the chamber <NUM>. Subsequently, the hydraulic fluid which flows into the chamber <NUM> is stored in the tank <NUM>.

In <FIG>, the receiver <NUM> is drawn separately from the casing <NUM> of the spool valve <NUM>. However, the receiver <NUM> may be integrated with the casing <NUM> of the spool valve <NUM>.

In the embodiment, the cantilever spring <NUM> is coupled to the spool <NUM> and the casing <NUM>. Instead of the cantilever spring <NUM>, an elastic member coupling the spool <NUM> and the nozzle portion 200E to each other may be used.

In the embodiment, the actuator <NUM> is coupled to the spool valve <NUM>. However, the actuator <NUM> may be directly coupled to the receiver <NUM>.

The inventors analyzed a relation between the taper angle and the pressure distribution inside the nozzle by using a plurality of different models of the taper angle. In an eighth embodiment, an analysis result will be described.

<FIG> are outline maps showing the pressure distribution of the hydraulic fluid around the discharge port. Referring to <FIG>, a relation between the taper angle and the pressure distribution inside the nozzle will be described.

<FIG> shows a nozzle <NUM> and a receiver <NUM>. The nozzle <NUM> is provided with a nozzle flow path <NUM>. The receiver <NUM> is provided with a left flow path <NUM> and a right flow path <NUM>. A gap <NUM> is formed between the lower surface of the nozzle <NUM> and the upper surface of the receiver <NUM>. The taper angle β of the nozzle <NUM> is "<NUM>°". The nozzle <NUM> moves rightward from the neutral position.

<FIG> shows a plurality of outlines showing the pressure distributions inside the nozzle flow path <NUM>, the gap <NUM>, the left flow path <NUM>, and the right flow path <NUM>. As shown in <FIG>, an area representing a highest pressure Pmax in the pressure distribution is shown above the nozzle flow path <NUM>. An area representing a lowest pressure Pmin in the pressure distribution is shown at the left portion of the gap <NUM>.

One outline extends in the area of the nozzle flow path <NUM> in the vicinity of the discharge port in the vertical direction. The left area of the outline is an area of the pressure P1. The right area of the outline is an area of the pressure P2 smaller than the pressure P1. An area above the area of the pressure P1 is an area of the pressure P3 larger than the pressure P1. The area of the pressure P3 is divided from the area of the pressure P1 by the horizontally extended outline. As shown in <FIG>, a left portion of the inner wall forming the nozzle flow path <NUM> is exposed to the high pressure P1 and a right portion of the inner wall forming the nozzle flow path <NUM> is exposed to the low pressure P2. Thus, a force exerted on the left side of the nozzle <NUM> is transmitted from the hydraulic fluid. Since a force exerted from the hydraulic fluid to the nozzle <NUM> is exerted in a direction opposite to the movement direction (that is, the right direction) of the nozzle <NUM>, the response of the nozzle <NUM> is poor.

Like <FIG> shows the receiver <NUM>. Further, <FIG> shows a nozzle <NUM>. The nozzle <NUM> is provided with a nozzle flow path <NUM>. A gap <NUM> is formed between the lower surface of the nozzle <NUM> and the upper surface of the receiver <NUM>. The taper angle β of the nozzle <NUM> is "β1(> <NUM>°)". A relative position of the nozzle <NUM> with respect to the receiver <NUM> is the same as that of the nozzle <NUM>.

The pressures Pmax and Pmin are shown at the substantially same position as that of <FIG>. A substantially horizontal outline representing the boundary between the pressures P1 and P3 approaches the discharge port. This means that a difference between the pressure of the left portion of the nozzle flow path <NUM> and the pressure of the right portion of the nozzle flow path <NUM> is smaller than a horizontal balance of the pressure inside the nozzle flow path <NUM>. Thus, the nozzle <NUM> has a response higher than that of the nozzle <NUM>. However, since the left portion of the inner wall forming the nozzle flow path <NUM> is exposed to a high pressure compared to the right portion of the inner wall forming the nozzle flow path <NUM>, the right displacement of the nozzle <NUM> is slightly inhibited by the pressure of the hydraulic fluid.

Like <FIG>, <FIG> shows the receiver <NUM>. Further, <FIG> shows a nozzle <NUM>. The nozzle <NUM> is provided with a nozzle flow path <NUM>. A gap <NUM> is formed between the lower surface of the nozzle <NUM> and the upper surface of the receiver <NUM>. The taper angle β of the nozzle <NUM> is "β2(> β1)". A relative position of the nozzle <NUM> with respect to the receiver <NUM> is the same as that of the nozzle <NUM>.

The pressures Pmax and Pmin are shown at the substantially same position as that of <FIG>. The outline showing the boundary between the pressures P1 and P3 becomes horizontal compared to the outline of <FIG>. Thus, the nozzle <NUM> has a response higher than that of the nozzle <NUM>. Since the pressure to which the left portion of the inner wall forming the nozzle flow path <NUM> is exposed is substantially the same as the pressure to which the right portion of the inner wall forming the nozzle flow path <NUM> is exposed, the pressure of the hydraulic fluid substantially does not inhibit the right displacement of the nozzle <NUM>.

<FIG> is a graph showing a relation among the relative position of the nozzle <NUM> of <FIG> with respect to the receiver <NUM>, the flow rate of the hydraulic fluid discharged from the nozzle <NUM>, and the force exerted from the hydraulic fluid to the nozzle <NUM>. <FIG> is a graph showing a relation among the relative position of the nozzle <NUM> of <FIG> with respect to the receiver <NUM>, the flow rate of the hydraulic fluid discharged from the nozzle <NUM>, and the force exerted from the hydraulic fluid to the nozzle <NUM>. <FIG> is a graph showing a relation among the relative position of the nozzle <NUM> of <FIG> with respect to the receiver <NUM>, the flow rate of the hydraulic fluid discharged from the nozzle <NUM>, and the force exerted from the hydraulic fluid to the nozzle <NUM>. Referring to <FIG> and <FIG> A to 10C, a relation between the taper angle β and the pressure inside the nozzles <NUM>, <NUM>, and <NUM> will be described.

The horizontal axes of the graphs of <FIG>, <FIG>, and <FIG> respectively indicate the relative positions of the nozzles <NUM>, <NUM>, and <NUM> with respect to the receiver <NUM>. The original points of the graphs of <FIG>, <FIG>, and <FIG> indicate the neutral positions. The vertical axes of the graphs of <FIG>, <FIG>, and <FIG> indicate the hydraulic fluid discharge amount, the force exerted from the hydraulic fluid to the inner walls of the nozzles <NUM>, <NUM>, and <NUM>, the force exerted from the hydraulic fluid to the lower surfaces of the nozzles <NUM>, <NUM>, and <NUM> (that is, the surface facing the receiver <NUM>), the force exerted from the hydraulic fluid to the outer circumferential surfaces of the nozzles <NUM>, <NUM>, and <NUM>, and the sum of these forces.

From the graphs of <FIG>, <FIG>, and <FIG>, when the taper angle β approaches <NUM>°, it is understood that the force exerted from the hydraulic fluid to the inner wall of the nozzle occupies a large part of the entire force exerted from the hydraulic fluid to the nozzle. As the taper angle β becomes larger than <NUM>°, the influence on the inner wall of the nozzle due to the hydraulic fluid decreases. The analysis result shown in <FIG> matches the dynamic model (see <FIG>) described in the second embodiment and verifies the efficiency of the taper angle β with respect to the response performance of the nozzle. The designer who designs the nozzle may determine the taper angle β in consideration of the resistance of the discharge port of the nozzle and the pressure in the horizontal direction exerted from the hydraulic fluid to the inner wall of the nozzle. Thus, the principle of the above-described embodiments is not limited to a specific value of the taper angle β.

The embodiments have been described above. In the embodiment, the taper angle β determined by the tapered inner wall coupled to the discharge port of the nozzle is larger than twice the angle α formed by the flow path extension direction and a direction orthogonal to the inflow surface. Accordingly, since a component of the flow force exerted from the fluid to the tapered inner wall (a force of inhibiting the displacement of the nozzle) decreases so that the nozzle can be quickly displaced, the response speed of the actuator is improved.

The flow force exerted on the nozzle increases in proportional to the pressure gradient expressed by the above-described expression (<NUM>). As shown in <FIG>, a case in which the nozzle NZL moves in a direction indicated by an arrow D toward the left flow path LFP will be supposed. A graph of the pressure gradient of the hydraulic fluid in the vicinity of the discharge port is illustrated at the bottom of <FIG>. As indicated by the one-dotted chain line of the graph of <FIG>, the pressure of the hydraulic fluid increases from the left flow path LFP toward the right flow path RFP in the vicinity of the discharge port and in the case of the pressure gradient on the upside, the flow force is generated in a direction different from the arrow D. Accordingly, the movement of the nozzle NZL is inhibited. Meanwhile, as indicated by the solid line of the graph of <FIG>, the pressure of the hydraulic fluid becomes uniform or in the case of the pressure gradient on the downside, the flow force of inhibiting the movement of the nozzle NZL can be controlled.

Here, it is assumed that the flow force FF exerted in a direction opposite to the movement direction of the nozzle NZL is proportional to the pressure gradient shown in the above-described expression (<NUM>) as indicated by the following expression (<NUM>). [Expression <NUM>] <MAT>.

The radius r of the flow line of the hydraulic fluid is expressed by the following expression (<NUM>) using a gap Lng between the surface facing the nozzle NZL and the inflow surface of the receiver RCV. [Expression <NUM>] <MAT>.

As shown in the following expression (<NUM>), since the flow force FF is inversely proportional to the radius r of the flow line of the hydraulic fluid, the following expression (<NUM>) holds. Further, the expression (<NUM>) is derived from the expression (<NUM>). [Expression <NUM>] <MAT>
[Expression <NUM>] <MAT>
[Expression <NUM>] <MAT>.

<FIG> is a diagram illustrating a relation between an angle ratio β/α and a pressure gradient obtained from the above-described relational expression. <FIG> shows a pressure gradient of a hydraulic fluid directed from the left flow path LFP side to the right flow path RFP side when the nozzle NZL is moved toward the left flow path LFP, wherein the angles of inclination α of the flow path is <NUM>°, <NUM>°, <NUM>°, and <NUM>°. When the pressure gradient is larger than <NUM>, the flow force FF increases. Further, the flow force FF decreases when the pressure gradient is zero or less. From the relation shown in <FIG>, since the pressure gradient becomes zero or less when the angle ratio β/α is larger than <NUM>, that is, the taper angle β of the nozzle is larger than twice the inclination angle α of the flow path, the flow force FF can be controlled. In such a configuration, since the flow force can be controlled, the nozzle easily moves and thus the response speed of the actuator is improved.

Claim 1:
A servo-valve (<NUM>) for driving an actuator by using a fluid, the servo-valve (<NUM>) comprising:
a nozzle (<NUM>) that includes a lower surface (<NUM>) provided with a discharge edge (<NUM>) forming an outline of a discharge port (<NUM>) from which the fluid is discharged and a tapered inner wall (<NUM>) growing narrower toward the discharge edge (<NUM>); and
a receiver (<NUM>) that is provided with a flow path (<NUM>, <NUM>) into which the fluid discharged from the discharge port (<NUM>) flows,
wherein the nozzle (<NUM>) is displaced in a direction different from the fluid discharge direction,
wherein the flow path (<NUM>, <NUM>) extension direction is inclined with respect to a direction orthogonal to an inflow surface of the receiver which faces the lower surface (<NUM>) of the nozzle (<NUM>) by an angle α, and
wherein a taper angle (β) determined by the tapered inner wall (<NUM>) is larger than twice the angle α characterized in that
the tapered inner wall (<NUM>) is formed at the lower end of the nozzle (<NUM>) such that the discharge edge (<NUM>) is positioned at a boundary between the tapered inner wall (<NUM>) and the lower surface (<NUM>) of the nozzle (<NUM>).