Abstract:
A magnetic armature is attracted and driven by a magnetic force which is intermittently generated between magnetic poles, and a piston reciprocated by being pushed back by a coil spring is not rotated by the coil spring. When the magnetic armature ( 28 ) as attracted between the magnetic pole members ( 10,12 ) by the magnetic force comes to a predetermined rotational angle position about the axis, the armature receives a rotational torque that is derived from the magnetic force and acts in a direction opposite to that of the rotational torque applied by a coil spring ( 30 ), thereby preventing the armature from being rotated in the predetermined direction. More specifically, the armature ( 28 ) has a circular cross-section as a whole and has a chamfered part ( 28 ′) parallel to the axis. When the chamfered part enters between the magnetic pole members, the armature receives a rotational torque that is derived from the magnetic force.

Description:
This application is a continuation of PCT/JP2005/021052, filed Nov. 16, 2005, which claims priority to Japanese Application No. JP2004-342819 filed Nov. 26, 2004. The entire contents of these applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electromagnetic reciprocating fluid devices, e.g. pumps and compressors, including a magnetic circuit having induction coils and a pair of opposed magnetic poles, wherein magnetic force is intermittently generated between the magnetic poles by intermittently exciting the induction coils, and a magnetic armature is attracted and driven by the magnetic force to reciprocate a piston connected to the magnetic armature. 
     2. Description of the Related Arts 
       FIGS. 1 and 2  are schematic views of an electromagnetic reciprocating fluid device used as a pump or a compressor. 
     As illustrated in the figures, the device includes an exciting circuit having induction coils  16  and  18  wound around magnetic pole members  10  and  12 , respectively, and a half-wave rectifier  20 . The device further includes a piston  24  slidably fitted in a cylinder  22 . A magnetic armature  28  is secured to the rod portion of the piston  24 . A coil spring  30  urges the piston  24  leftward as viewed in the figures. 
     When an AC voltage is applied to the exciting circuit, an electric current intermittently flows through the exciting circuit. Thereupon, the induction coils  16  and  18  are intermittently excited, and magnetic force is intermittently generated between the magnetic pole members  10  and  12 . When magnetic force is generated, the magnetic armature  28  is magnetically attracted rightward to drive the piston  24  rightward. When the magnetic force disappears, the piston  24  is driven leftward by the coil spring  30 . In this way, the piston  24  is driven to reciprocate. The cylinder  22  is provided with a pair of check valves  32  and  34 . The reciprocating motion of the piston  24  causes the check valves  32  and  34  to open and close alternately, thereby allowing a fluid to flow in through a fluid inlet  38  formed in a housing  36  and to flow out through a fluid outlet  40  formed in the housing  36 . 
       FIGS. 3 and 4  show an example of a specific arrangement of an electromagnetic reciprocating fluid device. 
     The device includes magnetic pole members  10  and  12 , induction coils  16  and  18 , a cylinder  22 , a piston  24 , a magnetic armature  28 , a coil spring  30 , check valves  32  and  34 , and a housing  36  having a fluid inlet  38  and a fluid outlet  40  in the same way as the device shown in  FIGS. 1 and 2 . This type of electromagnetic reciprocating fluid device is disclosed, for example, in Patent Document 1 noted below. 
       FIG. 4  shows the relationship between the magnetic armature  28  and the magnetic pole members  10  and  12 . More specifically, the magnetic pole members  10  and  12  are constituted by mutually opposing left and right projecting inner side wall portions of a magnetic circuit member  41  made of a substantially quadrangular magnetic material. The induction coils  16  and  18  are respectively wound around the left and right projecting inner side wall portions constituting the magnetic pole members  10  and  12 . Mutually opposing surfaces  10 ′ and  12 ′ of the magnetic pole members  10  and  12  are circular-arc surfaces along a circle with a center axis perpendicularly intersecting the mutual axis of the magnetic pole members  10  and  12  at the center therebetween. The magnetic armature  28  has a circular cross-section with a center axis coincide with the above-mentioned center axis of the circle. 
     As shown in  FIG. 3 , the coil spring  30  is set between a piston rod  26  and a support member  36 - 1  constituting a part of the housing  36 . Specifically, the left end of the coil spring  30  is secured by being press-fit into the rear end portion of the piston rod  26 . The right end of the coil spring  30  is secured by being press-fit into a spring seat  30 - 1  rotatably supported on a hemispherical distal end of the support member  36 - 1 . 
     When the induction coils  16  and  18  are intermittently excited in the device having the above-described structure, the piston  24  is reciprocated right and left as viewed in the figure by magnetic attraction force generated by the induction coils  16  and  18  and the spring force of the coil spring  30 , as has been stated above. During the reciprocation of the piston  24 , every time the coil spring  30  expands and contracts, it applies rotational torque to the piston  24  in a predetermined direction of rotation about the axis thereof. Accordingly, the piston  24  is rotated little by little every time it reciprocates. For the sake of the following description, let us assume that the piston  24  is rotated clockwise.
     PATENT DOCUMENT 1: Japanese Patent Application Publication No. S57-30984   

     Such a piston displacement causes the following problem. The piston  24  has a strip-shaped liner  44  wound and bonded around the periphery thereof to allow the piston  24  to smoothly slide along the inner peripheral surface of the cylinder  22 . The opposite end edges  44 - 1  and  44 - 2  of the liner  44  have L-shaped configurations that are complementary to each other as shown in  FIG. 3 . 
     When the L-shaped joint between the end edges  44 - 1  and  44 - 2  of the liner  44  comes to the position in the cylinder  22  where the check valve  32  is provided as a result of the piston  24  being intermittently rotated as it reciprocates, as stated above, a fluid leakage occurs through the joint, which causes generation of large noise. 
     An object of the present invention is to hold the piston, and hence the armature, in a predetermined angular position so that it will not rotate as in the above-described conventional device, thereby preventing the generation of noise. 
     The present invention provides an electromagnetic reciprocating fluid device including a piston having a piston rod and a magnetic armature secured to the piston rod. The piston is reciprocatable along the longitudinal axis of the piston rod. The device further includes a magnetic circuit having a pair of magnetic pole members spaced from each other in a direction perpendicularly intersecting the axis. The magnetic circuit is intermittently excited to generate magnetic force between the magnetic pole members, thereby magnetically attracting the armature to drive the piston in the direction of the axis. Further, the device includes a coil spring that urges the piston in a direction opposite to the direction in which the piston is magnetically attracted and driven by the magnetic circuit. Every time the piston is reciprocated in the direction of the axis by the magnetic force of the magnetic circuit and the urging force of the coil spring, the piston is driven to rotate in a predetermined direction by rotational torque applied thereto by the coil spring. The electromagnetic reciprocating fluid device is characterized in that the magnetic armature has magnetic properties with which the armature receives a rotational torque that is derived from the magnetic force and acts in a direction opposite to that of the rotational torque applied by the coil spring when the armature as attracted between the magnetic pole members by the magnetic force comes to a predetermined rotational angle position about the axis, thereby preventing the armature from being rotated in the predetermined direction. Specifically, the armature receives rotational torque in a direction opposite to that of the rotational torque applied by the coil spring that is generated by the magnetic force in accordance with the rate of change of permeance between the magnetic pole members caused by the rotation of the armature. 
     The armature has a first angle range portion defining a predetermined angle range about the axis and a second angle range portion defining an angle range that is different from that of the first angle range portion. The armature has magnetic properties with which the armature is driven to rotate in the predetermined direction by the rotational torque applied to the piston by the coil spring when the first angle range portion is present in the magnetic circuit between the magnetic pole members, but when the second angle range portion enters between the magnetic pole members, the magnetic force between the magnetic pole members generates a rotational torque that drives the piston to rotate in a direction opposite to the predetermined direction against the rotational torque applied thereto by the coil spring. 
     More specifically, the arrangement may be as follows. The armature has a circular cross-section as a whole and has a chamfered part parallel to the axis. The chamfered part constitutes the second angle range portion, and the portion of the armature other than the chamfered part constitutes the first angle range portion. 
     In another specific example, the arrangement may be as follows. The armature has a circular cross-section as a whole and has a through-hole extending therethrough at a predetermined angle position about the axis. An angle portion of the armature including the through-hole constitutes the second angle range portion, and the portion of the armature other than the angle portion constitutes the first angle range portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an electromagnetic reciprocating fluid device, showing the way in which a fluid is sucked to flow into the device. 
         FIG. 2  is a schematic view of the electromagnetic reciprocating fluid device, showing the way in which the fluid is discharged from the device. 
         FIG. 3  is a longitudinal sectional side view of a conventional electromagnetic reciprocating fluid device. 
         FIG. 4  is a sectional view taken along the line IV-IV in  FIG. 3 . 
         FIG. 5  is a sectional view similar to  FIG. 4 , showing an electromagnetic reciprocating fluid device according to the present invention. 
         FIG. 6   a  is a diagram showing the relationship between an armature and magnetic pole members to explain the electromagnetic reciprocating fluid device according to the present invention. 
         FIG. 6   b  is a diagram schematically illustrating the relationship between the armature and the magnetic pole members in  FIG. 6   a.    
         FIG. 7  is a chart showing the change of rotational torque generated by magnetic force that acts on the armature in the electromagnetic reciprocating fluid device according to the present invention. 
         FIG. 8  is a sectional view similar to  FIG. 5 , showing a second embodiment of the electromagnetic reciprocating fluid device according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the electromagnetic reciprocating fluid device according to the present invention will be described below with reference to  FIGS. 5 and 8 . 
     The general structure of the electromagnetic reciprocating fluid device according to the present invention is substantially the same as that shown in  FIG. 3 . It should be noted, however, that the magnetic armature  28  of the device according to the present invention has a cross-section that is not completely round, unlike that of the above-described conventional device. 
       FIG. 5  shows a first embodiment of the electromagnetic reciprocating fluid device according to the present invention. In this embodiment, the armature  28  is provided with a chamfered part  28 ′ extending along the direction of the axis thereof. 
     It has been confirmed that the armature  28  formed with a cross-sectional configuration as shown in the figure can be held substantially in the illustrated position in the rotational direction even when the piston is reciprocated. The reason for this may be explained as follows. 
     A. The relationship between rotational torque T and electromagnetic energy W:
         Letting dW represent a change in electromagnetic energy W caused by the rotation of the armature  28 , force F is expressed by:
 
 F=dW/rdθ   (A-1)
   where:
           r is the distance from the point of application of force F to the center about which torque is applied; and   dθ is the angle of displacement.   
           Rotational torque T is, as is commonly known, given by:
 
T=Fr  (A-2)
   From Equations (A-1) and (A-2), rotational torque T is expressed by:
 
 T=dW/dθ   (A-3)
       

     B. Electromagnetic energy W in a magnetic circuit:
         In a circuit including a coil, electromagnetic energy W stored in the coil is, as is commonly known, given by:
 
 W= 1/2 LI   2   (B-1)
   where:
           L is the self-inductance of the coil; and   I is the electric current passed through the circuit.   
           As is generally known, the self-inductance L of an annular coil is given by:
 
L=PN 2   (B-2)
   where P is permeance.   From Equations (B-1) and (B-2), electromagnetic energy W stored in the magnetic circuit is expressed by:
 
 W= 1/2( NI ) 2   P   (B-3)
   From Equations (A-3) and (B-3), rotational torque T is expressed by:
 
 T= 1/2( NI ) 2   dP/dθ   (AB-1)
       

     C. The armature  28  shown in  FIG. 5  is formed with the chamfered part  28 ′. Accordingly, when the armature  28  rotates about its center axis, the air gap between the magnetic pole members  10  and  12  changes. Hence, the permeance P of the air gap also changes. 
     To clarify the relationship between the change of the air gap and the change of the permeance, let us consider a modeled relationship between the magnetic pole members  10  and  12  and the armature  28  as shown in  FIG. 6   a . Let us assume that the armature  28  has a portion with a radius r 1  and a recessed portion with a radius r 2 . To simplify the mathematical expression, it is assumed that when the portion of radius r 1  is in sliding contact with the magnetic pole member  10 , as shown in  FIG. 6   b , air gaps δ 1  and δ 2  are formed between the magnetic pole member  12  and the portion of radius r 1  and the portion of radius r 2 , respectively, and an angle γ is formed between imaginary lines connecting the center axis of the armature  28  and the upper and lower end edges, respectively, of the magnetic pole member  12  (as viewed in  FIGS. 6   a  and  6   b ). In this model, let us assume that the armature  28  rotates clockwise so that the recessed portion thereof enters the magnetic circuit between the magnetic pole members  10  and  12  from one end thereof, and the angle made between the one end of the recessed portion of the armature  28  and the upper end edge of the magnetic pole member  12  (as viewed in  FIGS. 6   a  and  6   b ) is represented by θ. The permeance P of the air gap between the magnetic pole members  10  and  12  at this time is expressed by the following equation on the condition that δ 1  and δ 2 &lt;&lt;r 1  and r 1 ≈r 2 ≈r:
 
 P=μr (γ−θ) t/δ   1   +μrθt/δ   2   (C-1)
         where:
           μ is the permeability in a vacuum; and   t is the thickness of the armature and the magnetic pole members.   
           The amount of change in P with the change of θ is given by:       

     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
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             From Equations (AB-1) and (C-2), torque T acting on the armature is given by: 
           
         
       
    
     
       
         
           
             
               
                 
                   
                     
                       
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     In Equation (C-3), N, μ, r, t, δ 1  and δ 2  are all constants, and I=I max  sin ωt=I rms . Under certain conditions, I is constant, and hence torque T is constant. 
     When the recessed portion of the armature  28  is not present between the magnetic pole members  10  and  12 , the permeance P of the air gap between the magnetic pole members  10  and  12  is given by:
 
 P=μrγt/δ   1  
         P, in this case, is constant independently of the displacement angle of the armature  28  and not a function of θ.   Accordingly, torque, which is expressed by T=1/2·(NI) 2 dP/dθ, is:
 
T=0
       

     Accordingly, torque T before and after the angle θ becomes zero (θ=0) is as shown in  FIG. 7 . 
     It will be understood from the above that even if the portion of the armature that is involved in the magnetic circuit is displaced around the axis of the armature, no torque is applied from the magnetic circuit to the armature when there is no change in permeance P between the magnetic pole members  10  and  12  (i.e. when the permeance P is not a function of the rotational angle of the armature). Accordingly, in this case, the armature is rotated according to the rotational torque applied thereto by the coil spring. It may be considered that the rotation of the armature in the conventional device in  FIG. 4  is caused as stated above. 
     In contrast, if the portion of the armature that is involved in the magnetic circuit causes a change in permeance of the magnetic circuit as the armature is angularly displaced around the axis thereof (i.e. if the permeance is a function of the rotational angle of the armature), rotational torque is applied to the armature. The rotational torque in this case acts on the armature in either a clockwise or counterclockwise direction depending on the term (δ 1 -δ 2 ) in the above-described Equation of T=1/2·(NI) 2 ·μrt(δ 1 -δ 2 )/δ 1 δ 2 . A detailed description of this action is omitted, but specifically, the rotational torque acts in a direction in which the permeance between the magnetic pole members increases with the rotational displacement of the armature. In the example shown in  FIG. 5 , when the armature  28  is rotationarily moved clockwise and the chamfered part  28 ′ enters between the magnetic pole members  10  and  12 , the permeance decreases. Accordingly, the rotational torque generated by magnetic force acts in a direction counter to the rotational motion of the armature  28 . Therefore, if the rotational torque generated by magnetic force is designed to be larger than the rotational torque applied to the armature  28  by the coil spring  30 , the armature  28  is pushed back when the chamfered part  28 ′ enters between the magnetic pole members  10  and  12 . When the chamfered part  28 ′ has come out from between the magnetic pole members  10  and  12 , the rotational torque generated by magnetic force becomes zero, so that the armature  28  is rotationarily moved clockwise again. The reason why the chamfered part  28 ′ is held at the illustrated position in the example shown in  FIG. 5  is due to equilibrium brought about by the rotational torque from the coil spring  30  and the rotational torque from the magnetic force between the magnetic pole members  10  and  12 . 
       FIG. 8  shows another embodiment of the magnetic armature  28  in the device according to the present invention. The armature  28  in this embodiment is provided with a through-hole  28 ″ extending in the direction of the axis thereof in place of the above-described chamfered part. In this case also, when the through-hole  28 ″ enters between the magnetic pole members  10  and  12  as the armature  28  is rotationarily moved clockwise by the action of the coil spring  30 , the permeance P changes with the angular position of the through-hole  28 ″. Consequently, the armature  28  receives rotational torque generated by magnetic force. Specifically, when the through-hole  28 ″ enters between the magnetic pole members  10  and  12 , the permeance becomes lower than before. Therefore, the rotational torque generated by magnetic force acts in a direction in which the permeance increases, i.e. in a direction in which the armature  28  is urged to rotate counterclockwise. Accordingly, the magnetic armature  28  is held substantially in the angle position illustrated in the figure. 
     Although the embodiments of the electromagnetic reciprocating fluid device according to the present invention have been shown above, the armature is not necessarily limited to those in these embodiments. The above-described chamfer or through-hole  28 ′ is not necessarily limited to the illustrated configuration but may have any configuration that is not symmetric in terms of magnetic reluctance with respect to the axis of the magnetic armature  28 . The armature in each of the foregoing embodiments has a completely round cross-section as a whole and is arranged such that when the portion thereof that is not provided with either a chamfer or through-hole  28 ′ is present between the magnetic pole members, no rotational driving force is generated by magnetic force, thus allowing the armature and the piston to be rotationarily moved in a predetermined direction by rotational driving force from the coil spring. The portion that is not provided with either a chamfer or through-hole  28 ′, however, need not necessarily be completely round. Even if this portion of the armature is configured so that the magnetic force generates a rotational torque when it is present between the magnetic pole members, the coil spring occurs will rotationarily move the armature, provided that the rotational torque generated by magnetic force is smaller than the rotational torque applied by the coil spring. It is essential only that a rotational torque that is larger than and counter to the rotational torque applied by the coil spring be generated by magnetic force when the armature comes to a predetermined angular position so that a portion thereof that is appropriately configured, such as being provided with the above-described chamfer or through-hole  28 ′, enters between the magnetic pole members.