Patent Publication Number: US-2010123092-A1

Title: Fluid control valve

Description:
The present application claims priority based on Japan Patent Application No. 2008-293867 filed on Nov. 17, 2008, and the entire contents of that application is incorporated by reference in this specification. 
     FIELD OF THE INVENTION 
     The present invention relates to a fluid control valve that controls the flow of a fluid. 
     BACKGROUND OF THE INVENTION 
     This type of fluid control valve will adjust the path dimensions of a fluid pathway by causing a spool housed inside a sleeve to slide (see, for example, Patent Document 1). As shown in  FIG. 14 , a fluid control valve  900  described in Patent Reference 1 slidably houses a spool  932  having different diameters in accordance with the positions in the axial direction, inside a cylindrical sleeve  931  in which a plurality of fluid pathways are formed that communicate with the exterior. A linear solenoid mechanism  911  that drives the spool  932  is arranged on one end of the spool  932  in the axial direction, and a spring housing chamber  943  is arranged on the other end of the spool  932  in the axial direction and a return spring  944  is housed in the fluid control valve  900 . The return spring  944  urges the spool  932  toward the linear solenoid mechanism  911 . The fluid control valve  900  controls the flow of fluid by causing the spool  932  to move against the urging force of the return spring  944  by means of the linear solenoid mechanism  911 , and adjusting the position of the spool  932 . 
     [Patent Document 1] Japan Published Patent Application No. 10-122412 
     SUMMARY OF THE INVENTION 
     With the fluid control valve  900  disclosed in Patent Reference 1, lengthening of the fluid control valve  900  in the axial direction of the spool  932  cannot be avoided because the linear solenoid mechanism  911  is arranged on the spool  932  in the axial direction. 
     In addition, even with a fluid control valve comprising another drive mechanism such as an air cylinder, an electromotive cylinder, etc., lengthening of the fluid control valve in the axial direction of the spool cannot be avoided because these drive mechanisms are arranged in the axial direction of the spool. 
     In view of the aforementioned situation, a primary object of the present invention is to provide a fluid control valve that can shorten the length of the fluid control valve in the axial direction of the spool. 
     In order to solve the aforementioned problem, a first aspect of the invention comprises a fluid control valve comprising a sleeve member in which a plurality of fluid pathways that communicate with an exterior are formed, a column shaped spool which is slidably housed inside the sleeve member, and an urging means that urges the spool in the sliding direction, the fluid control valve adjusting the path dimensions of each of the fluid pathways by causing the spool to move in the axial direction thereof against the urging force of the urging means. The fluid control valve comprises a ferromagnetic portion that is formed on the spool so as to extend in the axial direction of the spool, permanent magnets arranged opposite each other having the ferromagnetic portion therebetween in a direction that is orthogonal to the axial direction of the spool, form an oppositely oriented magnetic field between the two that is aligned with the axial direction, and are formed to be longer in the axial direction of the spool than the ferromagnetic portion, and a coil that is arranged in a direction orthogonal to the axial direction of the spool with respect to the permanent magnets, and which generates a magnetic field that penetrates the opposing permanent magnets due to the conduction of electricity. 
     According to the first aspect of the invention, because a ferromagnetic portion that is formed on the spool so as to extend in the axial direction of the spool, and permanent magnets arranged opposite each other having the ferromagnetic portion therebetween in a direction that is orthogonal to the axial direction of the spool, form an oppositely oriented magnetic field between the two that is aligned with the axial direction, the ferromagnetic portion that extends in the axial direction will receive the magnetic force from the permanent magnets. In addition, because the permanent magnets are formed to be longer than the ferromagnetic material portion in the axial direction of the spool, the ferromagnetic material portion will be located within the range of the permanent magnets in the axial direction of the spool. 
     Here, because a coil is provided that is located in a direction orthogonal to the axial direction of the spool with respect to the permanent magnets, and generates a magnetic field that penetrates the opposing permanent magnets due to the conduction of electricity, one of the oppositely oriented magnetic fields aligned in the axial direction will be weakened and the other will be strengthened by causing a magnetic field to be generated that penetrates the opposing permanent magnets due to the conduction of electricity through the coil. Because of this, a magnetic force can be applied in the axial direction of the spool so as to move the ferromagnetic portion from the side in which the magnetic field was weakened to the side in which it was strengthened, and thus the spool can be moved against the urging force of the urging means. As a result, because the spool on which the ferromagnetic portion is formed is moved by conducting electricity through a coil that is arranged in a direction orthogonal to the axial direction thereof, there is no need to arrange a drive mechanism such as a coil or cylinder in the axial direction of the spool, and thus the length of the fluid control valve can be shortened in the axial direction of the spool. Note that adjusting the path dimensions of the fluid pathways includes continually enlarging or reducing the path dimensions of the fluid pathways, switching the state of the fluid pathways between fully open and fully closed, or others. 
     Because the permanent magnets are formed to be longer than the ferromagnetic portion in the axial direction of the spool, the ferromagnetic portion will be located within the range of the permanent magnets in the axial direction of the spool. Then, by conducing electricity through the coil, the ferromagnetic material portion will move along the length of the permanent magnets in the axial direction of the spool. 
     A second aspect of the invention is a fluid control valve according to the first aspect, in which, in a state in which electricity is not being conducted through the coil, the length from an end surface of the ferromagnetic portion to an end surface of the permanent magnets in one axial direction is set to be equal to the length that the spool will be slid in order to fully open or fully close at least one fluid pathway. Thus, by causing the ferromagnetic material portion to move in a range that is the length of the permanent magnets in the axial direction of the spool by conducing electricity through the coil, at least one of the fluid pathways can be easily adjusted to be fully open or fully closed. 
     A third aspect of the invention is a fluid control valve according to the first or second aspect, further comprises a magnetic path formation portion that comprises opposing portions that sandwich the opposing permanent magnets and the coil, and a connecting portion that connects the opposing portions on one side thereof along a surface that is orthogonal to the axial direction of the spool, and which guides the magnetic field generated due to the conduction of electricity through the coil to the permanent magnets, and the plurality of fluid pathways of the sleeve member have fluid pathways that pass between the spool and the connecting portion and communicate with the spool, and fluid pathways that communicate with the spool on the other side of the spool from the side toward the connecting portion side and communicate with the exterior on the side opposite to the connecting portion side behind the spool. 
     According to the third aspect of the invention, because a magnetic path formation portion is provided that comprises opposing portions that sandwich the opposing permanent magnets and the coil, and a connecting portion that connects the opposing portions on one side thereof along a surface that is orthogonal to the axial direction of the spool, and which guides the magnetic field generated due to the conduction of electricity through the coil to the permanent magnets, the force that causes the spool to move can be increased without extending the length of the fluid control valve in the axial direction of the spool. 
     Here, a magnetic path formation portion is not formed on the side opposite to the connecting portion side behind the spool. Because the plurality of fluid pathways of the sleeve member have fluid pathways that pass between the spool and the connecting portion and communicate with the spool, and fluid pathways that communicate with the spool on the other side of the spool from the side toward the connecting portion and communicate with the exterior on the side opposite to the connecting portion behind the spool, fluid pathways can be formed in the portion between the spool and the connecting portion, and the portion in which a magnetic path is not formed on the side opposite to the connecting portion side. As a result, the force that causes the spool to move can be increased by means of the magnetic path formation portion while efficiently arranging the fluid pathways. 
     A fourth aspect of the invention is a fluid control valve according to the first or second aspect, further comprises a magnetic path formation portion is provided that comprises opposing portions that sandwich the opposing permanent magnets and the coil, and connecting portions that connect the opposing portions via the end portion sides of the spool in the axial direction, and which guides the magnetic field generated due to the conduction of electricity through the coil to the permanent magnets, the plurality of fluid pathways of the sleeve member have fluid pathways that each communicate with both mutually opposing side surfaces of the spool in between the opposing permanent magnets, and each communicate with the exterior in a direction that is orthogonal to the axial direction of the spool. 
     According to the fourth aspect of the invention, because a magnetic path formation portion is provided that comprises opposing portions that sandwich the opposing permanent magnets and the coil, and connecting portions that connect the opposing portions via the end portion sides of the spool in the axial direction, and which guides the magnetic field generated due to the conduction of electricity through the coil to the permanent magnets, the length of the magnetic path can be shortened compared to when a drive mechanism for the spool is provided, even though the magnetic path formation portion is formed in the axial direction of the spool. Because the plurality of fluid pathways of the sleeve member have fluid pathways that each communicate with both mutually opposing side surfaces of the spool in between the opposing permanent magnets, and each communicate with the exterior in a direction that is orthogonal to the axial direction of the spool, fluid pathways can be formed that each communicate with the exterior in a orthogonal direction to the axial direction of the spool (a direction in which a magnetic path is not formed). As a result, the force that causes the spool to move can be increased by means of the magnetic path, and the flow resistance of the fluid can be reduced. 
     A fifth aspect of the invention is a fluid control valve according to any of the first to fourth aspects, in which the opposing permanent magnets are comprised of a pair of permanent magnets in which the magnetic poles thereof are oppositely oriented along the axial direction of the spool, and thus magnetic fields can be formed only by means of the pair of permanent magnets. As a result, the number of permanent magnets can be reduced, and the manufacturing cost of the fluid control valve can be lowered. 
     When the ferromagnetic portion is formed from a material that is different than other portions of the spool, those portions must be joined, and the strength of those joined portions may be reduced. 
     A sixth aspect of the invention is a fluid control valve according to any of the first to fifth aspects, in which a portion of the spool excluding the ferromagnetic portion is formed with an iron material that is not a ferromagnetic material, and the ferromagnetic portion is formed with a ferromagnetic material that is produced by annealing the iron material. Thus, by unitarily forming the spool with an iron material that is not a ferromagnetic material, and annealing only the portion to be made a ferromagnetic material, a ferromagnetic portion and another portion that is not a ferromagnetic material can be formed. As a result, the strength of the spool can be improved and the joining process can be omitted. 
     Because the spool is housed inside the sleeve member, the magnetic field must penetrate the sleeve member and be applied to the ferromagnetic portion of the spool. Because of this, when the sleeve member is formed with a ferromagnetic material, it will be difficult for a magnetic field to be applied to the ferromagnetic portion of the spool. 
     A seventh aspect of the invention is a fluid control valve according to any of the first to sixth aspects, in which the sleeve member is formed from a synthetic resin that is not a ferromagnetic material, and thus the magnetic field can penetrate the sleeve member and be applied to the ferromagnetic portion of the spool. 
     The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view showing the construction of a fluid control valve according to a first embodiment. 
         FIG. 2  is a front view showing the construction of the fluid control valve of  FIG. 1 . 
         FIG. 3  is a side view showing the construction of the fluid control valve of  FIG. 1 . 
         FIG. 4  is a cross-sectional view along line  4 - 4  of  FIG. 1 . 
         FIG. 5  is a cross-sectional view along line  5 - 5  of  FIG. 2 . 
         FIG. 6  is a front view showing the operation of the fluid control valve of  FIG. 4 . 
         FIG. 7  is a cross-sectional view showing the operation of the fluid control valve of  FIG. 1 . 
         FIG. 8  is a cross-sectional view showing the construction of a fluid control valve according to a second embodiment. 
         FIG. 9  is a cross-sectional view along line  9 - 9  of  FIG. 8 . 
         FIG. 10  is a cross-sectional view showing the construction of a fluid control valve according to a third embodiment. 
         FIG. 11  is a cross-sectional view along line  11 - 11  of  FIG. 10 . 
         FIG. 12  is a cross-sectional view showing the construction of a fluid control valve according to a fourth embodiment. 
         FIG. 13  is a cross-sectional view along line  13 - 13  of  FIG. 12 . 
         FIG. 14  is a cross-sectional view showing the construction of a conventional fluid control valve. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment in which a fluid control valve according to the present invention is realized will be explained below with reference to the drawings. Note that  FIG. 1  is a cross-sectional view that has been cut along a plane that includes the fluid pathways of the fluid control valve. 
     As shown in  FIG. 1 , the fluid control valve comprises a sleeve member  10  in which a cross section thereof forms a rectangular shape. A cylinder  16  that extends in the longer direction is formed near the central portion in the shorter direction of the sleeve member  10 . The cylinder  16  passes through the sleeve member  10 , and the openings thereof are sealed by O rings  25   a  and  25   b  and caps  26   a  and  26   b . The sleeve member  10  is formed from a material other than a ferromagnetic material, e.g., formed from a synthetic resin that is not a ferromagnetic material. 
     A cylindrical spool  20  is slidably housed in the cylinder  16  along the axial line of the cylinder  16 . The axial line of the cylinder  16  and the axial line of the spool  20  are the same. In the axial direction of the cylinder  16 , the spool  20  is formed to be shorter than the cylinder  16 , and the portions of the cylinder  16  that extend beyond both ends of the spool  20  are housing chambers  16   a  and  16   b  for springs  23   a  and  23   b . Concave portions  22   a  and  22   b  are respectively formed in each end surface of the spool  20  in the axial direction. The end portions of the springs  23   a  and  23   b  that contact with the spool  20  are respectively fitted with the concave portions  22   a  and  22   b . The spool  20  is urged with equal force in the axial direction by means of these springs  23   a  and  23   b  in opposite directions, and the position in which these urging forces are balanced is the neutral position of the spool  20 . Note that the springs  23   a  and  23   b  comprise urging means that urge the spool in the sliding direction. 
     Slide bearings  24   a  and  24   b  are respectively arranged near both ends of the cylinder  16  in the axial direction, and slidably support the spool  20 . In addition, a through hole  21  that passes through the central axis of the spool  20  is formed in the spool  20 . When the spool  20  slides, fluid inside the housing chambers  16   a  and  16   b  will move from the high pressure area amongst housing chambers  16   a  and  16   b  to the low pressure area thereof. In this way, when the spool  20  slides, an increase in resistance due to the fluid inside the housing chambers  16   a  and  16   b  coming under pressure can be inhibited. 
     In addition, a supply pathway  11 , a first discharge pathway  13 , and a second discharge pathway  15  that respectively communicate with the exterior are formed in the sleeve member  10 . The supply pathway  11  opens on a side surface of the sleeve member  10  perpendicular to the axial direction of the spool  20 , and extends in a straight line between the spool  20  and a perpendicular portion  30   c  of a yoke described below. A first supply pathway  12  and a second supply pathway  14  that each perpendicularly communicate with the supply pathway  11  and the cylinder  16  are formed in sequence and in a straight line from the upstream side of the supply pathway  11 . The first discharge pathway  13  and the second discharge pathway  15  are respectively formed in a straight line along lines that each extends from the first supply pathway  12  and the second supply pathway  14 . The first discharge pathway  13  and the second discharge pathway  15  respectively communicate perpendicularly with the cylinder  16 . In other words, the discharge pathways  13  and  15  both communicate with the spool  20  on the other side of the spool from the side toward the perpendicular portion  30   c  of the yoke and communicate with the exterior on the side opposite to the perpendicular portion  30   c  side behind the spool. The supply pathways  12  and  14  and the discharge pathways  13  and  15  are formed to be perpendicular to the perpendicular portion  30   c  of the yoke. The first supply pathway  12  and the second supply pathway  14  are formed to be parallel along the axial direction of the spool  20 , and the first discharge pathway  13  and the second discharge pathway  15  are formed to be parallel along the axial direction of the spool  20 . Thus, the supply pathway  11 , the first supply pathway  12 , the second supply pathway  14 , the first discharge pathway  13 , and the second discharge pathway  15  are formed along a plane that includes the central axis of the spool  20  and is perpendicular to the perpendicular portion  30   c  of the yoke. These pathways are formed to be circular and have the same diameters in any cross-section. 
     The spool  20  is comprised of end portions  20   a  and  20   b  arranged on the ends in the axial direction, and a middle portion  20   c  that lies between the end portions  20   a  and  20   b  and is arranged in the middle in the axial direction. The end portions  20   a  and  20   b  are formed from a material that is not a ferromagnetic material, and more specifically is formed from aluminum. The middle portion  20   c  is formed from a ferromagnetic material, and more specifically is formed from steel. Grooves  27  and  28  each having a width in the axial direction of the spool  20  that is approximately equal to the diameter of the supply pathways  12  and  14  are respectively formed in the outer circumferential surface of the end portions  20   a  and  20   b  of the spool  20 . When the spool  20  is in the neutral position (the position of  FIG. 1 ), half of the width of each of the grooves  27  and  28  is formed in a position that overlaps with the first supply pathway  12  and the second supply pathway  14 . In the axial direction of the spool  20 , the path dimensions of the grooves  27  and  28  will increase as the width that overlaps with each of the first supply pathway  12  and the second supply pathway  14  increases, and the volume of fluid that passes through the spool  20  and flows through the first discharge pathway  13  and the second discharge pathway  15  will increase. Thus, by adjusting the position of the spool  20  in the sliding direction (the axial direction), the volume of fluid that flows from the first supply pathway  12  to the first discharge pathway  13 , and the volume of fluid that flows from the second supply pathway  14  to the second discharge pathway  15 , can be controlled. Note that when one of the supply pathways  12  or  14  are fully open, the other will be fully closed, and when one of the supply pathways  12  or  14  are half open, the other will also be half open. 
       FIG. 2  is a front view which shows the fluid control valve as seen from the openings of the discharge pathways  13  and  15 , and  FIG. 3  is a side view which shows the fluid control valve as seen from the openings of the supply pathway  11 . 
     As shown in  FIGS. 2 and 3 , on the sleeve member  10 , rectangular plate shaped side wall portions  10   a  and  10   b  are arranged on both ends in the axial direction of the spool  20  so as to be perpendicular to that axial direction. In addition, opposing portions  30   d  and  30   e  are arranged on the yoke  30  so as to perpendicularly extend outward from the perpendicular portion  30   c  as a base end. Thus, between the side wall portion  10   a  and the side wall portion  10   b , the opposing portion  30   d  and the opposing portion  30   e  are connected by the perpendicular portion  30   c , and a magnetic path is formed by the yoke  30  comprised of these opposing portions  30   d  and  30   e , and the perpendicular portion  30   c . The opposing portions  30   d  and  30   e  and the perpendicular portion  30   c  are unitarily formed by steel plates that are layered in the axial direction of the spool  20 . 
     A coil  40   a  is arranged between the opposing portion  30   d  and the cylinder  16  (spool  20 ) so that the axial direction is perpendicular to the opposing portion  30   d , and a coil  40   b  is arranged between the opposing portion  30   e  and the cylinder  16  (spool  20 ) so that the axial direction is perpendicular to the opposing portion  30   e . Thus, the coil  40   a , the spool  20 , and the coil  40   b  are sandwiched by the opposing portion  30   d  and the opposing portion  30   e . The opposing portion  30   d  and the opposing portion  30   e  are arranged to be mutually parallel, and are parallel with respect to a plane that includes both central axes of the discharge pathways  13  and  15 . In addition, the opposing portions  30   d  and  30   e , the coils  40   a  and  40   b , and the discharge pathways  13  and  15  are formed to be symmetrical along the axial direction of the coils  40   a  and  40   b.    
       FIG. 4  shows a cross-section along line  4 - 4  of  FIG. 1 , and  FIG. 5  shows a cross-section along line  5 - 5  of  FIG. 2 . 
     As shown in  FIGS. 4 and 5 , cylindrically shaped convex portions  30   a  and  30   b  are respectively formed near the center of opposing portions  30   d  and  30   e  of the yoke  30 . The convex portions  30   a  and  30   b  extend to the vicinity of the cylinder  16 , and the end surfaces thereof form an arc shape along the circumferential surface of the cylinder  16 . The convex portions  30   a  and  30   b  are each formed to be integral and perpendicular with the opposing portions  30   d  and  30   e . The convex portions  30   a  and  30   b  also extend perpendicularly with respect to the cylinder  16 . 
     A permanent magnet  50   a  is arranged between the cylinder  16  and the convex portion  30   a , and a permanent magnet  50   b  is arranged between the cylinder  16  and the convex portion  30   b . The permanent magnets  50   a  and  50   b  are formed so as to extend in the axial direction of the spool  20  with an arc shaped cross-section along the circumferential surface of the cylinder  16  and respectively fixed to the end surfaces of the convex portion  30   a  and  30   b . The permanent magnet  50   a  and the permanent magnet  50   b  are arranged on opposing sides of the middle portion  20   c  of the spool  20  in a direction that is orthogonal to the axial direction of the spool  20 . The opposing pair of permanent magnets  50   a  and  50   b  is aligned so that the magnetic poles thereof are oppositely oriented along the axial direction of the spool  20 . More specifically, the permanent magnet  50   a  is aligned along the axial direction of the spool  20  so that the end portion  20   a  side is the S pole and the end portion  20   b  side is the N pole, and the permanent magnet  50   b  is aligned along the axial direction of the spool  20  so that the end portion  20   a  side is the N pole and the end portion  20   b  side is the S pole. The permanent magnets  50   a  and  50   b  are both formed to have N pole portions and S pole portions that are of equal length in the axial direction of the spool  20 . Thus, as shown by arrow A and arrow B, oppositely oriented magnetic fields are aligned in the axial direction of the spool  20  between the permanent magnet  50   a  and the permanent magnet  50   b.    
     The convex portions  30   a  and  30   b  of the yoke  30  are each iron cores of the coils  40   a  and  40   b , and the coils  40   a  and  40   b  are formed by wrapping conductive wire around the convex portions  30   a ,  30   b . These coils  40   a  and  40   b  are arranged in a direction that is orthogonal to the axial direction of the spool  20  with respect to the permanent magnets  50   a  and  50   b , and as shown by arrow C, a magnetic field that penetrates the oppositely oriented permanent magnets  50   a  and  50   b  and the middle portion  20   c  of the spool  20  will be generated by conducting electricity. In addition, by conducting electricity in a direction opposite this, the coils  40   a  and  40   b  will generate a magnetic field in a direction opposite the arrow C. 
     The yoke  30  comprises opposing portion  30   d  and opposing portion  30   e  that sandwich the opposing permanent magnets  50   a  and  50   b  and the coils  40   a  and  40   b . The perpendicular portion  30   c  connects these opposing portions  30   d  and  30   e  along a surface T that is orthogonal to the axial direction of the spool  20  on one side (the side opposite to the cylinder  16  side across the supply pathway  11 ). In other words, a perpendicular portion that connects the opposing portions  30   d  and  30   e  is not arranged on the other side of these opposing portions  30   d  and  30   e  (the side opposite to the supply pathway  11  side behind the cylinder  16 ) along a surface T that is orthogonal to the axial direction of the spool  20 . Because the yoke  30  is formed in this way, the magnetic field generated by the conduction of electricity through the coils  40   a  and  40   b  will be guided to the permanent magnets  50   a  and  50   b  as shown by arrow C. Note that the perpendicular portion  30   c  of the yoke  30  forms a connecting portion that connects the opposing portions  30   d ,  30   e  on one side thereof along a surface T that is orthogonal in the axial direction of the spool  20 , and the yoke  30  forms a magnetic path formation portion that guides the magnetic field generated by conducting electricity through the coils  40   a  and  40   b  to the permanent magnets  50   a  and  50   b.    
     In the axial direction of spool  20 , the permanent magnets  50   a  and  50   b  are formed to be longer than the middle portion  20   c  of the spool  20  (the ferromagnetic portion). More specifically, the permanent magnets  50   a  and  50   b  are formed to be twice as long as the middle portion  20   c . Thus, in the neutral state in which the middle portion  20   c  is positioned in the central portion of the permanent magnets  50   a  and  50   b , one half of the middle portion  20   c  overlaps with the N pole and the other half overlaps with the S pole of the permanent magnets  50   a  and  50   b  in the axial direction of the spool  20 . In a state in which the coils  40   a  and  40   b  are not conducting electricity, the length from the end surface of the middle portion  20   c  to the end surface of the permanent magnets  50   a  and  50   b  on the spring  23   a  side in the axial direction of spool  20  is set to be equal to the length in which the spool  20  will be slid in order for the first supply pathway  12  to be fully open and the second supply pathway to be fully closed. Thus, the area in which the middle portion  20   c  does not overlap with the permanent magnets  50   a  and  50   b  will become the area in which the middle portion  20   c  will move in the axial direction of the spool  20 . In other words, the middle portion  20   c  will move in the axial direction of the spool  20  along the length of the permanent magnets  50   a  and  50   b.    
     The synthetic resin of the sleeve material  10  that forms the inner wall of the cylinder  16  is between the permanent magnets  50   a  and  50   b , and the middle portion  20   c  of the spool  20 . In other words, the magnetic fields that are generated from the permanent magnets  50   a  and  50   b  and the coils  40   a  and  40   b  will penetrate the sleeve material  10  and be applied to the middle portion  20   c  of the spool  20 . Because of this, the portion of the sleeve material  10  that is interposed between the permanent magnets  50   a  and  50   b , and the middle portion  20   c  of the spool  20  is formed with the minimum thickness that allows the cylinder  16  to maintain rigidity in order for the magnetic field to efficiently penetrate. 
     In a state in which the coils  40   a  and  40   b  are not conducting electricity, a magnetic field shown with arrow C will not be generated, but the magnetic fields shown with arrow A and arrow B will be generated by the permanent magnets  50   a  and  50   b . In this state, the end portions  20   a  and  20   b  that are formed from aluminum will not be affected by magnetic force. The middle portion  20   c  that is formed from steel will be affected by magnetic force, but that magnetic force will be balanced along the axial direction of the spool  20 . In addition, due to the affects of the urging force of the springs  23   a  and  23   b  that urge the spool  20  in the sliding direction, the middle portion  20   c  will be positioned in the center of the permanent magnets  50   a  and  50   b  in the axial direction of the spool  20  when in the neutral state in which the coils  40   a  and  40   b  are not conducting electricity. 
     Next, the operation of the fluid control valve constructed as noted above will be explained. 
     When the spool  20  is to be moved in the axial direction, the direction of conducting electricity to the coils  40   a  and  40   b  and the size of the current thereof will be controlled. For example, when electricity is conducted through the coils  40   a  and  40   b , and a magnetic field that passes in the direction from the permanent magnet  50   b  to the permanent magnet  50   a  is generated as shown with the arrow C, the magnetic field as shown with the arrow A from the N pole of the permanent magnet  50   a  toward the S pole of the permanent magnet  50   b  will be weakened, and the magnetic field as shown with the arrow B from the N pole of the permanent magnet  50   b  toward the S pole of the permanent magnet  50   a  will be strengthened. 
     Then, for example, as shown in  FIG. 6 , between the permanent magnet  50   a  and the permanent magnet  50   b , the magnetic field from the N pole of the permanent magnet  50   a  toward the S pole of the permanent magnet  50   b  will be extinguished, and a strong magnetic field shown with the arrow D will be formed from the N pole of the permanent magnet  50   b  toward the S pole of the permanent magnet  50   a . This magnetic field will be applied to the middle portion  20   c  of the spool  20 , which will apply a force to the spool  20  that will cause it to move toward the spring  23   a  in the axial direction. 
     As a result, as shown in  FIG. 7 , the spool  20  will move against the urging force of the spring  23   a  in a direction in which the supply pathway  11  is open, the path dimensions of the first supply pathway  12  and the first discharge pathway  13  will become larger, and the path dimensions of the second supply pathway  14  and the second discharge pathway  15  will become smaller. Here, because the magnetic field generated will become stronger as the amount of electricity conducted through the coils  40   a  and  40   b  increases, the magnetic field from the N pole of the permanent magnet  50   a  toward the S pole of the permanent magnet  50   b  will become weaker, and the magnetic field from the N pole of the permanent magnet  50   b  toward the S pole of the permanent magnet  50   a  will become stronger. Thus, by controlling the amount of electricity conducted through the coils  40   a  and  40   b , not only can the size of the magnetic force that causes the spool to move be controlled, but the amount of movement of the spool  20  can also be controlled. 
     In addition, when the spool  20  is to be moved toward the opposite side in the axial direction, the direction in which electricity is conducted through the coils  40   a  and  40   b  will be reversed, and by controlling the amount of electricity conducted, the amount of movement of the spool  20  can be controlled. In this way, the path dimensions of the supply pathways  12  and  14  can be adjusted and the amount of fluid controlled. 
     According to the construction of the present embodiment described in detail above, the following effects will be obtained. 
     A middle portion  20   c  (ferromagnetic portion) is provided that is formed on the spool  20  so as to extend in the axial direction of the spool  20 , and permanent magnets  50   a  and  50   b  are provided opposite each other having the middle portion  20   c  of the spool  20  therebetween in a direction that is orthogonal to the axial direction of the spool  20  and form magnetic fields that are both aligned opposite each other in the axial direction (the magnetic fields shown with arrow A and arrow B in  FIG. 4 ). Because of this, the middle portion  20   c  that extends in the axial direction of the spool  20  will receive the magnetic forces from the permanent magnets  50   a  and  50   b . In addition, because the permanent magnets  50   a  and  50   b  are formed to be longer than the middle portion  20  in the axial direction of the spool  20 , the middle portion  20   c  will be positioned within the range of the permanent magnets  50   a  and  50   b  in the axial direction of the spool  20 . 
     Here, because coils  40   a ,  40   b  are provided in a direction orthogonal to the axial direction of the spool  20  with respect to the permanent magnets  50   a  and  50   b  and generate a magnetic field (the magnetic field shown with arrow C in  FIG. 4 ) that passes through the opposing permanent magnets  50   a  and  50   b , one of the oppositely oriented magnetic fields aligned in the axial direction will be weakened and the other will be strengthened by causing a magnetic field to be generated that passes through the opposing permanent magnets  50   a  and  50   b  due to the conduction electricity through the coils  40   a  and  40   b . Because of this, a magnetic force can be applied so as to move the middle portion  20   c  from the side in which the magnetic field is weakened to the side in which it is strengthened in the axial direction of the spool  20 , and the spool  20  can be moved against the urging force of the springs  23   a  and  23   b . As a result, because the spool  20  on which the middle portion  20   c  is formed is moved by conducting electricity through coils  40   a  and  40   b  positioned in a direction orthogonal to the axial direction thereof, there is no need to arrange a drive mechanism such as a coil or cylinder in the axial direction of the spool  20 , and thus the length of the fluid control valve in the axial direction of the spool  20  can be shortened. 
     Because the permanent magnets  50   a  and  50   b  are formed to be longer than the middle portion  20  in the axial direction of the spool  20 , the middle portion  20   c  will be positioned within the range of the permanent magnets  50   a  and  50   b  in the axial direction of the spool  20 . Thus, by conducting electricity through the coils  40   a  and  40   b , the middle portion  20   c  will move in the axial direction of the spool  20  along the length of the permanent magnets  50   a  and  50   b.    
     Here, in a state in which electricity is not being conducted through the coils  40   a  and  40   b , the length from the end surface of the middle portion  20   c  to the end surfaces of the permanent magnets  50   a  and  50   b  in one axial direction of the spool  20  is set to be equal to the length in which the spool  20  will be slid in order to fully open or fully close at least one of the fluid pathways. Thus, by causing the middle portion  20   c  to be moved along the length of the permanent magnets  50   a  and  50   b  in the axial direction of the spool  20  by conducting electricity through the coils  40   a  and  40   b , at least one of the fluid pathways can be easily adjusted to be fully open or fully closed. 
     Because the yoke  30  (magnetic path formation portion) comprises opposing portions  30   d ,  30   e  that sandwich the opposing permanent magnets  50   a  and  50   b  and the coils  40   a  and  40   b , and a perpendicular portion  30   c  that links these opposing portions  30   d  and  30   e  on one side along a surface T that is orthogonal to the axial direction of the spool  20 , and guides the magnetic field generated by conducting electricity through the coils  40   a  and  40   b  to the permanent magnets  50   a  and  50   b , the force that causes the spool  20  to move can be increased without extending the length of the fluid control valve in the axial direction of the spool  20 . 
     Here, a magnetic path is not formed on the side opposite to the perpendicular portion  30   c  side behind the spool  20 . Thus, because a plurality of fluid pathways formed in the sleeve member  10  have supply pathways  11 ,  12  and  14  that pass between the spool  20  and the perpendicular member  30   c  and communicate with the spool  20 , and discharge pathways  13  and  15  that both communicate with respect to the spool  20  on the other side from the side toward the perpendicular portion  30   c  and communicate with the exterior on the side opposite to the perpendicular portion  30   c  side behind the spool  20 , fluid pathways can be formed in the portion between the spool  20  and the perpendicular portion  30   c  and the portion on the side opposite to the perpendicular portion  30   c  side in which a magnetic path is not formed. As a result, the force that causes the spool  20  to move can be increased by means of the yoke  30 , and the fluid pathways can be efficiently located. 
     Because the permanent magnets arranged opposite each other are comprised of a pair of permanent magnets  50   a  and  50   b  in which their magnetic poles are arranged to be oppositely oriented along the axial direction of the spool  20 , magnetic fields can be formed with only the pair of permanent magnets  50   a  and  50   b . As a result, the number of permanent magnets can be reduced, and the manufacturing cost of the fluid control valve can be lowered. 
     Because the spool  20  is housed inside the sleeve member  10 , the magnetic fields must penetrate the sleeve member  10  and be applied to the middle portion  20   c  (ferromagnetic portion) of the spool  20 . Because of this, when the sleeve member  10  is formed with ferromagnetic material, it will be difficult for magnetic fields to be applied to the middle portion  20   c  of the spool  20 . 
     According to the present embodiment, because the sleeve member  10  is formed from a synthetic resin which is not a ferromagnetic material, magnetic fields can penetrate the sleeve member  10  and be applied to the middle portion  20   c  of the spool  20 . In addition, the portion of the sleeve material  10  that is interposed between the permanent magnets  50   a  and  50   b  and the middle portion  20   c  of the spool  20  is formed with the minimum thickness that allows the cylinder  16  to maintain rigidity in order for the magnetic fields to efficiently penetrate. Because of this, the magnetic fields applied to the middle portion  20   c  of the spool  20  can be increased, and it will not be necessary to provide permanent magnets having a large magnetic force or to increase the amount of electricity conducted through the coils. 
     Second Embodiment 
     A second embodiment in which the fluid control valve according to the present invention is realized will be explained below with reference to the drawings. The second embodiment will be explained with focus on the points that differ with the first embodiment, and an explanation of the members that are identical with the first embodiment will be omitted by assigning the same reference number thereto. 
     In the present embodiment, the construction of the yoke that forms the magnetic path and the construction of the fluid pathways that are formed in the sleeve member will be changed from the first embodiment. Note that  FIG. 8  is a cross-sectional view that has been cut along a plane that includes the fluid pathways of the fluid control valve, and  FIG. 9  is a cross-sectional view of line  9 - 9  of  FIG. 8 . 
     As shown in  FIGS. 8 and 9 , a supply pathway  111 , a first supply pathway  112 , a second supply pathway  114 , a first discharge pathway  13 , and a second discharge pathway  15  are formed in the sleeve member  110  so as to extend along the same plane between opposing permanent magnets  50   a  and  50   b . The supply pathway  111  communicates with the exterior in a direction that is orthogonal to the axial direction of spool  20 . The supply pathways  112  and  114  each communicate with the supply pathway  111 , and each communicate perpendicularly to the cylinder  16  (the spool  20 ). The supply pathway  112  and the discharge pathway  13  communicate with both opposing side surfaces of the spool  20 , and the supply pathway  114  and the discharge pathway  15  communicate with both opposing side surfaces of the spool  20 . In other words, the supply pathway  112  and the discharge pathway  13  communicate with the spool  20  on mutually opposing sides thereof, and the supply pathway  114  and the discharge pathway  15  communicate with the spool  20  on mutually opposing sides thereof. The first discharge pathway  13  and the second discharge pathway  15  are formed in a straight line along lines that respectively extend from the first supply pathway  112  and the second supply pathway  114 . The supply pathways  13  and  15  each communicate with the exterior in a direction that is orthogonal to the axial direction of spool  20 . Note that these pathways are formed to be circular and have the same diameters in any cross-section. 
     The yoke  130  is formed so as to connect opposing portions  130   d  and  130   e  via the end portion sides of the spool  20  in the axial direction. More specifically, the yoke  130  comprises opposing portion  130   d  and opposing portion  130   e  that sandwich the permanent magnets  50   a  and  50   b  and the coils  40   a  and  40   b . The opposing portions  130   d  and  130   e  are each formed into a rectangular plate shape that is perpendicular to the axial direction of the coils  40   a  and  40   b . The perpendicular portions  130   c  (connecting portions) connect these opposing portion  130   d  and  130   e  via both end portion sides of the spool  20  in the axial direction. A magnetic path is formed by the yoke  130  comprised of these opposing portions  130   d  and  130   e  and the perpendicular portion  130   c . These opposing portions  130   d  and  130   e  and the perpendicular portion  130   c  are unitarily formed by steel plates that are layered in the direction in which the discharge pathways  13  and  15  extend. Because the yoke  130  is formed in this way, a magnetic field generated by the conduction of electricity through the coils  40   a  and  40   b  will flow through the permanent magnets  50   a  and  50   b  as shown by arrow C. 
     According to the construction of the present embodiment noted in detail above, in addition to the effects according to the first embodiment, the following unique effects will be obtained. 
     Because the yoke  130  comprises opposing portions  130   d  and  130   e  that sandwich the opposing permanent magnets  50   a  and  50   b  and the coils  40   a  and  40   b , and perpendicular portions  130   c  that connect these opposing portions  130   d  and  130   e  via the end portion sides of the spool  20  in the axial direction, and guides the magnetic field generated by conducting electricity through the coils  40   a  and  40   b  to the permanent magnets  50   a  and  50   b , the length of the yoke  130  can be shorter than when a drive mechanism of the spool  20  is provided, even though the perpendicular portions  130   c  of the yoke  130  are provided in the axial direction of the spool  20 . Thus, because the plurality of fluid pathways of the sleeve member  110  each communicate with both opposing side surfaces of the spool  20  between the opposing permanent magnets  50   a  and  50   b , and have the supply pathway  111  and the discharge pathways  13  and  15  that each communicate with the exterior in the direction orthogonal to the axial direction of the spool  20 , fluid pathways can be formed that each communicate with the exterior in a orthogonal direction to the axial direction of the spool  20  in which a magnetic path is not formed. As a result, the force that causes the spool  20  to move can be increased by means of the yoke  130 , and the flow resistance of the fluid can be reduced. 
     Because the perpendicular portions  130   c  of the yoke  130  are formed on both end portion sides of the spool  20  in the axial direction, the magnetic field can be efficiently guided compared to when the perpendicular portion  130   c  was formed on only one end portion side. As a result, the force that causes the spool  20  to move can be increased even more. 
     Third Embodiment 
     A third embodiment in which the fluid control valve according to the present invention is realized will be explained below with reference to the drawings. The third embodiment will be explained with focus on the points that differ with the first embodiment, the same reference numbers will be applied to the same members in the first embodiment, and an explanation of the members that are identical with the first embodiment will be omitted by assigning reference numbers that have 200 added thereto. 
     In the present embodiment, the construction of the fluid pathways that are formed in the sleeve member and the construction of the spool that adjusts the path dimensions thereof will be changed from the first embodiment. Note that  FIG. 10  is a cross-sectional view that has been cut along a plane that includes the fluid pathways of the fluid control valve, and  FIG. 11  is a cross-sectional view of line  11 - 11  of  FIG. 10 . 
     As shown in  FIGS. 10 and 11 , a supply pathway  211 , a first discharge pathway  213 , a second discharge pathway  215  and a third discharge pathway  218  that respectively communicate with the exterior are formed in a sleeve member  210 . The supply pathway  211  opens on a side surface of the sleeve member  210  perpendicular to the axial direction of the spool  220 , and extends in a straight line between the spool  220  and a perpendicular portion  230   c  of a yoke  230 . A first supply pathway  212 , a second supply pathway  214 , and a third supply pathway  217  that each perpendicularly communicate with the supply pathway  211  and the cylinder  216  are formed in sequence and in a straight line from the upstream side of the supply pathway  211 . The first discharge pathway  213 , the second discharge pathway  215 , and the third discharge pathway  218  are formed in a straight line along respective lines that extend from the first supply pathway  212 , the second supply pathway  214  and the third supply pathway  217 . The first discharge pathway  213 , the second discharge pathway  215 , and the third discharge pathway  216  perpendicularly communicate with the cylinder  216 , respectively. In other words, the discharge pathways  213 ,  215  and  218  communicate with the spool  220  on the other side of the spool from the side toward the perpendicular portion  230   c  of the yoke  230 , and communicate with the exterior on the side opposite to the perpendicular portion  230   c  side behind the spool  220 . 
     The supply pathways  212 ,  214  and  217  and the discharge pathways  213 ,  215  and  218  are formed to be perpendicular with respect to the perpendicular portion  230   c  of the yoke  230 . The first supply pathway  212 , the second supply pathway  214 , and the third supply pathway  217  are formed side by side and aligned in the axial direction of the spool  220 , and the first discharge pathway  213 , the second discharge pathway  215 , and the third discharge pathway  218  are formed side by side and aligned in the axial direction of the spool  220 . Thus, the supply pathway  211 , the first supply pathway  212 , the second supply pathway  214 , the third supply pathway  217 , the first discharge pathway  213 , the second discharge pathway  215  and the third discharge pathway  218  are formed along a plane that includes the central axis of the spool  220  and that is perpendicular to the perpendicular portion  230   c  of the yoke  230 . These pathways are formed to be circular and have the same diameters in any cross-section. 
     The spool  220  is comprised of end portions  220   a  and  220   b  arranged on the ends in the axial direction, and a middle portion  220   c  that lies between the end portions  220   a  and  220   b  and is arranged in the middle in the axial direction. The end portions  220   a  and  220   b  are formed from a material that is not a ferromagnetic material, and more specifically are formed from aluminum. The middle portion  220   c  is formed from a ferromagnetic material, and more specifically is formed from steel. A groove  227  is formed in the outer circumferential surface of the end portion  220   a  of the spool  220  and the width thereof in the axial direction of the spool  220  is approximately equivalent to the diameter of the supply pathway  212 . Grooves  228 ,  229  are respectively formed in the outer circumferential surface of the end portion  220   b  and their widths in the axial direction of the spool  220  thereof are approximately equivalent to the diameters of the supply pathways  214  and  217 . In order to close the second supply pathway  214 , the middle portion  220   c  in the axial direction of the spool portion  220  must have a width that is equivalent to the diameter of the supply pathway  214 . Here, the width of the middle portion  220   c  in the axial direction of the spool  220  is formed to be larger than the diameter of the supply pathway  214 , and more specifically, formed to be approximately two times the diameter of the supply pathway  214 . When the spool  220  is in the neutral position (the positions shown in  FIGS. 10 and 11 ), the first supply pathway  212  and the third supply pathway  217  will be fully closed, and the second supply pathway  214  will be fully open. Thus, path dimensions will increase in the axial direction of the spool  220  as the widths of the grooves  227 - 229  that overlap with each supply pathway increase, and the quantity of fluid that passes through the spool  220  and flows into each discharge pathway will increase. Thus, by adjusting the position in the sliding direction (axial direction) of the spool  220 , the quantity of fluid that flows through each pathway can be controlled. 
     In the axial direction of spool  220 , the permanent magnets  250   a  and  250   b  are formed to be longer than the middle portion  220   c  of the spool  220  (the ferromagnetic portion). More specifically, the permanent magnets  250   a  and  250   b  are formed to be twice as long as the middle portion  220   c . Thus, in the neutral state in which the middle portion  220   c  is positioned in the central portion of the permanent magnets  250   a  and  250   b , one half of the middle portion  220   c  overlaps with the N pole and the other half overlaps with the S pole of the permanent magnets  250   a  and  250   b  in the axial direction of the spool  220 . Furthermore, half of the S pole of the permanent magnet  250   a  will overlap in the axial direction of the spool  220  so as to match the groove  227  of the spool  220  and half of the N pole thereof will overlap so as to match the groove  228  of the spool  220 . In addition, half of the N pole of the permanent magnet  250   b  will overlap in the axial direction of the spool  220  so as to match the groove  227  of the spool  220  and half of the S pole thereof will overlap so as to match the groove  228  of the spool  220 . In a state in which electricity is not being conducted to coils  240   a  and  240   b , the length from the end surface of the middle portion  220   c  to the end surface of the permanent magnets  250   a  and  250   b  on the spring  223   a  side in the axial direction of spool  220  is set to be equal to the length in which the spool  220  will be slid in order for the first supply pathway  212  to be fully open and the second supply pathway to be fully closed. In a state in which electricity is not being conducted to the coils  240   a  and  240   b , the length from the end surface of the middle portion  220   c  to the end surface of the permanent magnets  250   a  and  250   b  on the spring  223   b  side in the axial direction of spool  220  is set to be equal to the length in which the spool  220  will be slid in order for the second supply pathway  214  to be fully closed and the third supply pathway  217  to be fully open. 
     Then, the area in which the middle portion  220   c  does not overlap with the permanent magnets  250   a  and  250   b  will become the area in which the middle portion  220   c  will move in the axial direction of the spool  220 . In other words, the middle portion  220   c  will move in the axial direction of the spool  220  along the length of the permanent magnets  250   a  and  250   b . Due to the effects of the urging force of the springs  223   a  and  223   b  that urge the spool  220  in the sliding direction, the middle portion  220   c  will be positioned in the center of the permanent magnets  250   a  and  250   b  in the axial direction of the spool  220  in a neutral state in which electricity is not being conducted to the coils  240   a  and  240   b.    
     According to the construction of the present embodiment noted in detail above, in addition to the effects according to the first embodiment, the following unique effects will be obtained. 
     Half of the S pole of the permanent magnet  250   a  will overlap in the axial direction of the spool  220  so as to match the groove  227  of the spool  220  and half of the N pole thereof will overlap so as to match the groove  228  of the spool  220 . In addition, half of the N pole of the permanent magnet  250   b  will overlap in the axial direction of the spool  220  so as to match the groove  227  of the spool  220  and half of the S pole thereof will overlap so as to match the groove  228  of the spool  220 . Thus, because the middle portion  220   c  will move in the axial direction of the spool  22  along the length of the permanent magnets  250   a  and  250   b , the spool  220  can be moved the width of the grooves  227  and  228  by conducting electricity through the coils  240   a  and  240   b , and the supply pathways  212 ,  214  and  217  can each be adjusted from fully closed to fully open. 
     In order to close the second supply pathway  214 , the middle portion  220   c  in the axial direction of the spool portion  220  must have a width that is equivalent to the diameter of the supply pathway  214 . In the present embodiment, the width of the middle portion  220   c  in the axial direction of the spool  220  is formed to be larger than the diameter of the supply pathway  214 , and more specifically, formed to be approximately two times the diameter of the supply pathway  214 , and thus a magnetic field that penetrates the middle portion  220   c  can be received in a wider range. As a result, the force that causes the spool  220  to move can be increased even more. 
     Fourth Embodiment 
     A fourth embodiment in which the fluid control valve according to the present invention is realized will be explained below with reference to the drawings. The second embodiment will be explained with focus on the points that differ with the first embodiment, and an explanation of the members that are identical with the first embodiment will be omitted by assigning the same reference number thereto. 
     In the present embodiment, the construction of the permanent magnets will be changed from the first embodiment. Note that  FIG. 12  is a cross-sectional view that has been cut along a perpendicular plane that includes the fluid pathways of the fluid control valve, and  FIG. 13  is a cross-sectional view of line  13 - 13  of  FIG. 12 . 
     As shown in  FIGS. 12 and 13 , permanent magnets  351   a  and  352   a  are arranged between the cylinder  16  and the convex portion  30   a , and permanent magnets  351   b  and  352   b  are arranged between the cylinder  16  and the convex portion  30   b . These permanent magnets are formed so as to be arc shaped in cross-section along the circumferential surface of the cylinder  16  and to extend in the axial direction of the spool  20 , and are respectively fixed to the end surfaces of convex portions  30   a  and  30   b  that are formed so as to extend in the axial direction with the same arc shape. The permanent magnet  351   a  and the permanent magnet  351   b  are located opposite each other having the middle portion  20   c  of the spool  20  therebetween in a direction orthogonal to the axial direction of the spool  20 , and the permanent magnet  352   a  and the permanent magnet  352   b  are located opposite each other having the middle portion  20   c  of the spool  20  therebetween in a direction orthogonal to the axial direction of the spool  20 . The permanent magnet  351   a  and the permanent magnet  352   a  are aligned with each other in the axial direction of the spool  20 , and the permanent magnet  351   b  and the permanent magnet  352   b  are aligned with each other in the axial direction of the spool  20 . 
     These permanent magnets are all radial anisotropic permanent magnets in which the magnetic poles have been arranged in a orthogonal direction to the axial direction of the spool  20 . The permanent magnet  351   a  and the permanent magnet  352   a  are aligned such that the magnetic poles thereof oppose each other, and more specifically, the spool  20  side of the permanent magnet  351   a  is the S pole, and the spool  20  side of the permanent magnet  352   a  is the N pole. The permanent magnet  351   b  and the permanent magnet  352   b  are aligned such that the magnetic poles thereof oppose each other, and more specifically, the spool  20  side of the permanent magnet  351   b  is the N pole, and the spool  20  side of the permanent magnet  352   b  is the S pole. The permanent magnets  351   a  and  352   a  are formed such that the lengths thereof are equal in the axial direction of the spool  20 , and the permanent magnets  351   b  and  352   b  are formed such that the lengths thereof are equal in the axial direction of the spool  20 . Thus, a magnetic field is formed from the N pole of the permanent magnet  352   a  to the S pole of the permanent magnet  352   b  as shown with the arrow A, and a magnetic field is formed from the N pole of the permanent magnet  351   b  to the S pole of the permanent magnet  351   a  as shown with the arrow B. In other words, magnetic fields that are aligned in the axial direction of the spool  20  and are oppositely oriented are formed by these permanent magnets. 
     In the axial direction of the spool  20 , the total length of the permanent magnets  351   a ,  352   a , and the total length of the permanent magnets  351   b ,  352   b , are each formed to be longer than the middle portion  20   c  (the ferromagnetic portion). More specifically, the permanent magnets  351   a ,  352   a ,  351   b  and  352   b  are together formed to be equal in length to the middle portion  20 . Thus, in the axial direction of the spool  20 , the middle portion  20   c  overlaps with half of each permanent magnet  351   a ,  352   a ,  351   b  and  352   b  when in the neutral state, in which the middle portion  20   c  is positioned on the boundary between the permanent magnet  351   a  and the permanent magnet  352   a  (the permanent magnet  351   b  and the permanent magnet  352   b ). Thus, the area in which the middle portion  20   c  does not overlap with the permanent magnets  351   a  and  351   b  and the area in which the middle portion  20   c  does not overlap with the permanent magnets  352   a  and  352   b  are the areas in which the middle portion  20   c  will move in the axial direction of the spool  20 . In other words, the middle portion  20   c  will slide in an area the length of the permanent magnet  351   a  and the permanent magnet  352   a  (the permanent magnet  351   b  and the permanent magnet  352   b ) in the axial direction of the spool  20 . 
     According to the construction of the present embodiment described in detail above, effects in accordance with the first embodiment will be obtained. 
     The present invention is not limited to the aforementioned embodiment, and may for example be implemented as follows. 
     In each of the aforementioned embodiments, a cylindrical spool was adopted, but a square pole shaped spool and the like, or a column shaped spool having another shape in cross-section can also be adopted. 
     In each of the aforementioned embodiments, slide bearings were respectively arranged near both end portions of the cylinder in the axial direction, but instead of these slide bearings, a member having little slide resistance can be unitarily arranged on the outer circumference of both end portions of the spool, or the slide bearing can be omitted. 
     In each of the aforementioned embodiments, the path dimensions of the fluid pathways were designed to be continually enlarged or reduced as one mode of adjustment. However, the fluid pathway state may instead be switched between fully open and fully closed. 
     In each of the aforementioned embodiments, the end portions  20   a  and  20   b  of the spool  20  and the end portions  220   a  and  220   b  of the spool  220  were formed from aluminum, which is not a ferromagnetic material. However, if these are located in positions in which the effects of the magnetic fields generated by the permanent magnets and coils can be ignored, ferromagnetic portions may be included on the end portions of the spool. 
     In the aforementioned second embodiment, the perpendicular portions  130   c  of the yoke  130  was formed on both end portion sides of the spool  20  in the axial direction. However, a perpendicular portion  130   c  of the yoke  130  can also be formed on only one end portion side of the spool  20  in the axial direction. In addition, the perpendicular portion  130   c  of the yoke  130  can also be omitted. According to this construction, although the force that causes the spool  20  to move will be reduced, the length of the fluid control valve in the axial direction of the spool  20  can be shortened. 
     In each of the aforementioned embodiments, the coils were located opposite each other having the spool and the permanent magnets therebetween. However, the coils can also be arranged in only one of the directions orthogonal to the axial direction of the spool with respect to the permanent magnets. Even in this case, a force that causes the spool to move can be ensured by means of a construction comprising a magnetic path formation portion that guides a magnetic field generated by conducing electricity through the coils to the permanent magnets. 
     In each of the aforementioned embodiments, the supply pathways and the discharge pathways were formed along a plane that includes the central axis of the spool and that is perpendicular to the yoke, i.e., a plane that is parallel to the opposing portions of the yoke. However, the supply pathways and the discharge pathways may be formed along a plane that is diagonal with respect to this plane if between the opposing permanent magnets. In addition, the supply pathways and the discharge pathways need not necessarily be formed along a specific plane. 
     In each of the aforementioned embodiments, a fluid pathway that branches into a plurality of supply pathways from one supply pathway was adopted, but a fluid pathway comprised of a plurality of independent supply pathways can also be adopted. In this case, as with the second embodiment, by providing opposing portions that sandwich the opposing permanent magnets and the coils, and a magnetic path formation portion that comprises a connecting portion that connects these opposing portions via the end portion sides of the spool in the axial direction, each of the supply pathways can be formed in a straight line between the opposing permanent magnets and can each communicate with the exterior in a orthogonal direction to the axial direction of the spool (a direction in which a magnetic path is not formed). As a result, the force that causes the spool to move can be increased by means of the magnetic path formation portion, and the flow resistance of the fluid can be reduced. 
     In each of the aforementioned embodiments, the present invention was realized as a fluid control valve that causes fluid to pass through the spool  20  from the supply pathway  11  side and flow toward the discharge pathways  13  and  15 , or a fluid control valve that causes fluid to pass through the spool  20  from the supply pathway  111  side and flow toward the discharge pathways  13  and  15 . However, with the same construction, the present invention can be realized as a fluid control valve that causes fluid to pass through the spool  20  from the discharge pathway  13  and  15  side and flow toward the supply pathway  11  side, or a fluid control valve that causes fluid to pass through the spool  20  from the discharge pathway  13  and  15  side and flow toward the supply pathway  111  side. 
     In each of the aforementioned embodiments, the sleeve members  10 ,  110  and  210  were formed from a synthetic resin that is not a ferromagnetic material, but can also be formed from a metal such as aluminum or the like that is not a ferromagnetic material. 
     In each of the aforementioned embodiments, because the middle portion  20   c  of the spool  20  is formed with a ferromagnetic material and the end portions  20   a  and  20   b  are formed with aluminum, or the middle portion  220   c  of the spool  220  is formed with a ferromagnetic material and the end portions  220   a  and  220   b  are formed with aluminum, a middle portion and end portions comprising different materials must be joined together. In contrast to this, by forming the middle portion and the end portions from an iron material that is not a ferromagnetic material, and annealing only the middle portion, the middle portion can be made into a ferromagnetic material and the end portions can be a material that is not a ferromagnetic material. According to this construction, because the middle portion and the end portions are unitarily formed, strength can be improved and the joining process can be omitted.