Abstract:
A salient-pole type linear motor comprises a housing, a stator, a mover and coil units. The stator comprises a middle stator core and two side stator cores which have a plurality of magnetic poles on the inner peripheral surface of the stator. A plurality of coil units is wound around the plurality of magnetic poles. By generating a current that passes through the coil units sequentially, magnetic fields are produced about the magnetic poles and an attractive force is produced to enable a reciprocal motion of the mover by magnetic attraction. The salient-pole type linear motor further connects two compressor cylinders at both ends thereof for compressing gases or draining fluids so as to form a reciprocal double piston compressor with a salient-pole type linear motor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 U.S.C. §119 of Taiwanese Patent Application No. 101128744, filed Aug. 9, 2012, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a salient-pole type linear motor and a reciprocal double piston compressor with the salient-pole type linear motor, in particular to the salient-pole type linear motor that uses magnetic poles of a stator core arranged in front and behind a stator to drive coils on the front and rear magnetic poles to produced a magnetic field in order to attract a mover by the magnetic poles to perform a reciprocal linear motion along a central axial direction of the stator. Two compressor cylinders are further connected to both ends of the salient-pole type linear motor for compressing gases or draining fluids to form a reciprocal double piston compressor with the salient-pole type linear motor. 
         [0004]    2. Description of the Related Art 
         [0005]    In a conventional rotary switched reluctance motor (SRM), two magnetically permeable materials in a magnetic circuit will take a path with the minimum magnetic reluctance when the lines of magnetic forces are sealed, so that the two magnetically permeable materials in the magnetic circuit will move in a direction towards a position with the minimum magnetic reluctance to push the movable magnetically permeable materials to the fixed magnetically permeable materials. To produce magnetic attractions with respect to one another, and the magnetic attraction can serve as a driving torque source of the motor. Due to the principle of torque, the rotor and the stator of the motor are situated in a salient pole status. No wiring with an exciting field or permanent magnet is required on the rotor, and a simple structure of a core with good magnetic permeability is used instead lower the cost of the assembly, and thus the magnetic reluctance motor has the advantages of a simple structure and a small volume that can be used in an application of high rotating speeds. 
         [0006]    Conventional reciprocal compressors generally require a greater pushing force of the motor to achieve the compression cycle of gases or draining of the fluid. However, the conventional reciprocal compressors are limited by the total volume of the compressor, and the general cylindrical linear motor cannot meet the requirement for the high driving forces. Only the conventional reciprocal compressors can meet the requirements of such a high driving force, and the compressors of this kind mainly use a rotary motor to drive a crank, and a link rod mechanism to push a piston, so that the gas in the cylinder can be compressed or the fluid in the cylinder can be drained, so as to obtain the required pressure. 
         [0007]    Although the reciprocal compressor driven by the conventional rotary motor has the advantages of low cost and a broad operation range, yet a lateral force may be produced during the compression process of the piston due to the linear motion of the piston driven by the rotary motor, and thus the wall of the cylinder may be worn out or damaged easily to indirectly causing the problems of noise, vibrations and high mechanical losses, so as to affect the overall system performance adversely. Although the problem can be resolved by applying a lubricant, the lubricant may contaminate the compressed gas or fluid. 
       BRIEF SUMMARY 
       [0008]    In view of the shortcomings of the prior art, it is a primary objective of the present invention to provide a salient-pole type linear motor and a reciprocal double piston compressor with the salient-pole type linear motor, wherein magnetic poles of a stator are arranged at the front and rear of the stator and a coil installed on the magnetic pole is also provided for driving the salient-pole type mover to perform a linear reciprocal motion, so as to drive a piston installed separately at both ends of a compressor. The linear motor of the present invention is provided for driving the compressor, not just creating a high magnetic flux density of the coil on the magnetic poles of the stator and a strong magnetic driving force only, but also featuring a simple structure of the salient-pole mover made of a material with good magnetic permeability or a permanent magnet, so as to simplify the quantity of components and reduce manufacturing costs. In addition, the motion direction of the mover is a linear reciprocal motion, which can reduce the lateral force produced from the motion of the piston and friction and loss to achieve the effects of high mechanical strength, low mechanical loss, low noise levels and high efficiency. 
         [0009]    To achieve the foregoing objective, the present invention provides a salient-pole type linear motor comprising a housing, a stator, a mover and a plurality of coil units. 
         [0010]    Wherein, the stator is installed in the housing. The stator comprises a middle stator core and two side stator cores coupled along a central axial direction. Wherein, the middle stator core and the two side stator cores further have a plurality of magnetic poles paired and protruded inwardly. In addition, the middle stator core has the magnetic poles disposed at positions corresponding to the positions of the magnetic poles of the two side stator cores respectively, so that the magnetic poles of the two side stator cores are staggered or arranged opposite to each other along the central axial direction, so as to wind the plurality of coil units on the front and rear magnetic poles. In addition, the middle stator core is selectively and integrally formed with the two side stator cores or the middle stator core is integrally formed with one of the two side stator cores. 
         [0011]    Further, the mover of the salient-pole type linear motor has a shaft and a plurality of salient-poles. Wherein, the shaft is movably penetrated along the central axial direction through the stator. The number of salient-poles is equal to the number of magnetic poles of the middle stator core, and the position of the salient-pole is corresponsive to the position of the magnetic pole of the middle stator core. When a current is applied sequentially at the coil units, a magnetic field is produced by the coil units wound around the magnetic poles to drive the magnetic poles, in order to attract the mover to perform a reciprocal linear motion along the central axial direction of the stator. 
         [0012]    In the salient-pole type linear motor, the length of the stator can be extended in a unit of the middle stator core and/or two side stator cores, and the length of the salient pole of the mover can be increased to increase the motion stroke of the mover, and the number of salient poles of the mover and the number of salient poles of the stator can be increased to strengthen the magnetic attraction of the magnetic pole to the mover, so as to enhance the driving force of the motor effectively. 
         [0013]    A further objective of the present invention is to provide a reciprocal double piston compressor with a salient-pole type linear motor. The reciprocal double piston compressor with a salient-pole type linear motor comprises a housing, a stator, a mover, a plurality of coil units and a plurality of compressor cylinders. 
         [0014]    The salient-pole type linear motor can be coupled to a plurality of compressor cylinders with a piston. Wherein, the piston of the compressor cylinder is coupled separately to both ends of the shaft of the mover, so that the gas in the compressor cylinder can be compressed, or the fluid in the compressor cylinder can be drained. Electric energy passed into the driving coils at the front and rear magnetic poles of the stator core of the salient-pole type linear motor is converted into mechanical energy of the linear motion through magnetic energy, without requiring any additional conversion and transmission mechanism or component. The mover is driven directly for the reciprocal linear motion, thus not only reducing the lateral force produced from the piston motion, but also reducing friction and loss, so as to further achieve the effects of high mechanical strength, low mechanical loss, low noise and high efficiency. 
         [0015]    In summation, the reciprocal double piston compressor of the salient-pole type linear motor of the present invention has one or more of the following advantages: 
         [0016]    (1) In the salient-pole type linear motor of the present invention, the length of the stator can be extended in the unit of a middle stator core and two side stator cores, and the length of the salient pole of the mover can be increased in order to increase the motion stroke of the mover. 
         [0017]    (2) In the salient-pole type linear motor of the present invention, the number of salient poles of the mover and the number of magnetic poles of the stator core can be increased to strengthen the magnetic attraction of the magnetic pole to the mover, so as to enhance the driving force of the motor effectively. 
         [0018]    (3) In the salient-pole type linear motor of the present invention, a plurality of compressor cylinders with a piston can be coupled, such that the reciprocal linear motion of the mover of the salient-pole type linear motor can be used to reduce the lateral force produced during the piston motion and also reduce friction and loss, so as to further achieve the effects of high mechanical strength, low mechanical loss, low noise and high efficiency. 
         [0019]    (4) In the salient-pole type linear motor of the present invention, a high magnetic flux density of the coil is formed on the stator magnetic pole, and a strong magnetic driving force is produced. In addition, the salient pole mover is made of a material with good magnetic permeability or a permanent magnet to simplify the components and reduces manufacturing costs significantly. 
         [0020]    (5) With the design of the salient-pole type linear motor separated from the two side compressors, the compressed gas or liquid of the two side compressors does not flow through the motor, so that the magnetic force of the motor will not be affected by the high-temperature of the compressed gas or liquid that leads to a loss of driving power. Therefore, the linear motor can be designed to meet different requirements of dimensions and compression forces and can be used for the transmission of special hazardous chemical gases or fluids. 
         [0021]    (6) The salient-pole type linear motor of the present invention comes with simple components, and the stator coil provided for driving the motion of the salient pole mover has a very high linearity of the direct linear reciprocal motion, so that the compressor can be designed as lubricant-free, which is a design with excellent energy-saving effect and high efficiency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is an exploded view of a salient-pole type linear motor of the present invention; 
           [0023]      FIG. 2  is a front view of a salient-pole type linear motor of the present invention; 
           [0024]      FIG. 3A  is a schematic view of a salient-pole type linear motor with a current applied to a first coil unit of the present invention; 
           [0025]      FIG. 3B  is a schematic view of a salient-pole type linear motor with a current applied to a second coil unit of the present invention; 
           [0026]      FIG. 4A  is a schematic view of a salient-pole type linear motor having a stator with an extended length and a current applied to a third coil unit of the present invention; 
           [0027]      FIG. 4B  is a schematic view of a salient-pole type linear motor having a stator with an extended length and a current applied to a first coil unit of the present invention; 
           [0028]      FIG. 4C  is a schematic view of a salient-pole type linear motor having a stator with an extended length and a current applied to a second coil unit of the present invention; 
           [0029]      FIG. 5  is a cross-sectional view of a salient-pole type linear motor with both ends coupled to a compressor cylinder of the present invention; 
           [0030]      FIG. 6A  is a cross-sectional view of a salient-pole type linear motor having two sets of double piston compressors serially connected to a piston of the present invention, showing its motion towards both sides; 
           [0031]      FIG. 6B  is a cross-sectional view of a salient-pole type linear motor having two sets of double piston compressors serially connected to a piston of the present invention, showing its motion towards the middle; and 
           [0032]      FIG. 7  is a schematic view of a salient-pole type linear motor with enhanced magnetic forces at the ends. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    The technical characteristics of the present invention will become apparent with the detailed description of the preferred embodiments accompanied with the illustration of related drawings as follows. It is noteworthy that same numerals are used for representing the same respective elements in the drawings, and the drawings are provided for the purpose of illustrating the invention, but not intended for limiting the scope of the invention. 
         [0034]    In a salient-pole type linear motor of the present invention, magnetic poles of front and rear stator cores are disposed on a stator, and a coil is formed on the magnetic pole, such that a magnetic field produced by the front and rear coils will go through a path with a minimum magnetic reluctance by sealing the magnetic lines of force, such that the mover will be moved in a direction towards the minimum magnetic reluctance, so as to constitute the salient-pole type linear motor of a linear motion. In addition, the salient-pole type linear motor adopts a compressor with the design of driving a fluid or compressing a gas by double pistons through double paths to replace the conventional rotary motor operated together with a link rod mechanism for driving the piston. 
         [0035]    With reference to  FIG. 1  for an exploded view of a salient-pole type linear motor of the present invention, the salient-pole type linear motor comprises a housing  400 , a stator, a mover  300  and a plurality of coil units. 
         [0036]    Wherein, the stator is installed in the housing  400  and further includes a plurality of heat dissipating elements  410  installed thereon, and the heat dissipating elements  410  can be fins or any other components capable of dissipating the heat from the housing  400 . In addition, a plurality of screws  430  and a cover  420  are provided for covering both ends of the housing  400 . The stator is comprised of a middle stator core  100 , a front stator core  110  and a rear stator core  120  and coupled along the central axial direction of the stator. The middle stator core  100 , the front stator core  110  and the rear stator core  120  are made of iron, silicon steel or any other magnetically permeable material. Further, the middle stator core  100  can be selectively and integrally formed with the front stator core  110  and the rear stator core  120 , or the middle stator core  100  is integrally formed with the front stator core  110  or the rear stator core  120 . In other words, the salient-pole type linear motor of the present invention may not include the middle stator core  100 , and magnetic poles of the front stator core  110  and the rear stator core  120  can be staggered or arranged in opposite positions with each other along the central axial direction. 
         [0037]    The middle stator core  100  further includes a first magnetic pole unit  101  and a second magnetic pole unit  102  paired and protruded inwardly, and the quantities of the first magnetic pole units  101  and the second magnetic pole units  102  can be two, three, or four respectively, but the present invention is not limited to such quantities only. The front stator core  110  and the rear stator core  120  have a third magnetic pole unit  111  and a fourth magnetic pole unit  121  paired and protruded inwardly and respectively, wherein the quantities of the third magnetic pole unit  111  and the fourth magnetic pole unit  121  can be two, three, or four respectively, but the present invention is not limited to such quantities only. In addition, the quantity of magnetic poles of the middle stator core  100  can be equal to the total quantity of magnetic poles of the front stator core  110  and the rear stator core  120 . In other words, the total quantity of the first magnetic pole units  101  and the second magnetic pole units  102  is equal to the total quantity of the third magnetic pole units  111  and the fourth magnetic pole units  121 . 
         [0038]    Further, the position of the first magnetic pole unit  101  is corresponsive to the position of the fourth magnetic pole unit  121 , and the position of the second magnetic pole unit  102  is corresponsive to the position of the third magnetic pole unit  111 . Therefore, the third magnetic pole unit  111  and the fourth magnetic pole unit  121  can be staggered along the central axial direction of the stator. In addition, the first coil unit  130  is wound around the second magnetic pole unit  102  and the third magnetic pole unit  111 , and the second coil unit  140  is wound around the first magnetic pole unit  101  and the fourth magnetic pole unit  121 . 
         [0039]    Further, the mover  300  of the salient-pole type linear motor has a shaft  320  and a plurality of salient poles  310 . Wherein, the mover  300  is made of iron, silicon steel, a permanent magnet or any other magnetically permeable material. The number of salient poles  310  is equal to the number of magnetic poles of the middle stator core  100 . In other words, if the total quantity of the first magnetic pole units  101  and the second magnetic pole units  102  is equal to four, then the quantity of salient poles  310  is also equal to four. Wherein, the shaft  320  is movably penetrated through the stator along the central axial direction, and the shaft  320  is protruded from the cover  420 . The position of the salient pole  310  is corresponsive to the positions of the first magnetic pole unit  101  and the second magnetic pole unit  102 . 
         [0040]    Therefore, when a current is applied to the first coil unit  130 , the magnetic field produced by the first coil unit  130  wound around the second magnetic pole unit  102  and the third magnetic pole unit  111  can attract the mover  300  to move along the central axial direction of the stator towards the positions of the second magnetic pole unit  102  and the third magnetic pole unit  111 . On the other hand, when a current is applied to the second coil unit  140 , the magnetic field produced by the second coil unit  140  wound around the first magnetic pole unit  101  and the fourth magnetic pole unit  121  can attract the mover  300  to move along the central axial direction of the stator towards the positions of the first magnetic pole unit  101  and the fourth magnetic pole unit  121 . Therefore, when the current is applied sequentially to the first coil unit  130  and the second coil unit  140 , the magnetic pole is driven to attract the mover  300  to perform a reciprocal linear motion in the central axial direction of the stator. 
         [0041]    In the salient-pole type linear motor, the length of the stator can be extended in a unit of the middle stator core  100 , the front stator core  110  and/or the rear stator core  120 , and the length of the salient pole  310  of the mover  300  is also increased to increase the motion stroke of the mover  300 . In addition, the salient-pole type linear motor can have an increased number of salient poles  310  of the mover  300  and an increased number of magnetic poles of the stator core, so as to enhance the magnetic attraction of the magnetic pole to the mover  300  and improve the driving force of the motor effectively. 
         [0042]    With reference to  FIGS. 1 and 2 ,  FIG. 2  shows the front view of the salient-pole type linear motor of the present invention. For simplicity, the housing  400 , the heat dissipating element  410 , the cover  420  and the screw  430  are not shown in the figure. 
         [0043]    Further, the first coil unit  130  of the salient-pole type linear motor is wound around the second magnetic pole unit  102  and the third magnetic pole unit  111 , and the second coil unit  140  is wound around the first magnetic pole unit  101  and the fourth magnetic pole unit  121 . If current is applied sequentially to the first coil unit  130  and the second coil unit  140 , the magnetic force will drive the magnetic pole to attract the mover  300  to perform a reciprocal linear motion along the central axial direction of the stator. 
         [0044]    With reference to  FIGS. 3A and 3B  for schematic views of a salient-pole type linear motor of the present invention respectively, after the salient-pole type linear motor is assembled, the second magnetic pole unit  102  and the third magnetic pole unit  111  jointly constitute the first magnetic pole  210 , and the first magnetic pole unit  101  and the fourth magnetic pole unit  121  jointly constitute the second magnetic pole  220 . 
         [0045]    In  FIG. 3A , when a current is applied to the first coil unit  130 , the magnetic field produced by the first coil unit  130  wound around the first magnetic pole  210  attracts the mover  300  to move along the central axial direction of the stator towards the position of the first magnetic pole  210 . In  FIG. 3B , when the current is applied to the second coil unit  140 , the magnetic field produced by the second coil unit  140  wound around the second magnetic pole  220  attracts the mover  300  to move along the central axial direction of the stator towards the position of the second magnetic pole  220 . When the current is applied sequentially to the first coil unit  130  and the second coil unit  140 , a magnetic flux is passed through the magnetic pole to attract the mover  300  to perform a reciprocal linear motion along the central axial direction of the stator. 
         [0046]    With reference to  FIGS. 3A ,  3 B, and  4 A to  4 C,  FIGS. 4A to 4C  are schematic views of a salient-pole type linear motor extended with the length of a stator in accordance with the present invention. For simplicity, the housing  400 , the heat dissipating element  410 , the cover  420  and the screw  430  are not shown in the figure. 
         [0047]    Further, before the third magnetic pole  200  of the salient-pole type linear motor is coupled to the first magnetic pole  210 , the third coil unit  150  is wound around the third magnetic pole  200 . In  FIG. 4A , when a current is applied to the third coil unit  150 , the magnetic field produced by the third coil unit  150  wound around the third magnetic pole  200  attracts the mover  300  to move along a central axial direction towards the position of the third magnetic pole  200  of the stator. 
         [0048]    In  FIG. 4C , when a current is applied to the first coil unit  130 , the magnetic field produced by the first coil unit  130  wound around the first magnetic pole  210  attracts the mover  300  to move along the central axial direction of the stator towards the position of the first magnetic pole  210 . 
         [0049]    In  FIG. 4C , when a current is applied to the second coil unit  140 , the magnetic field produced by the second coil unit  140  wound around the second magnetic pole  220  attracts the mover  300  to move along the central axial direction of the stator towards the position of the second magnetic pole  220 . 
         [0050]    Therefore, when the current is applied sequentially to the first coil unit  130 , the second coil unit  140  and the third coil unit  150 , the magnetic pole is driven to attract the mover  300  to perform a reciprocal linear motion along the central axial direction of the stator, so as to enhance the motion stroke of the mover  300 . 
         [0051]    With reference to  FIG. 5  for a cross-sectional view of a salient-pole type linear motor with both ends coupled to a compressor cylinder of the present invention, a mover  300  with eight salient poles  310  is used as an example for illustrating the present invention, the salient-pole type linear motor is further coupled to a compressor cylinder  500  with a piston  510 , and the compressor cylinder  500  further includes a plurality of heat dissipating elements  410  which can be fins or any other component capable of dissipating heat from the housing  400 . The piston  510  of the compressor cylinder  500  is coupled separately to both ends of the shaft  320  of the mover  300  and provided for compressing a gas or draining a fluid in the compressor cylinder  500 . 
         [0052]    The compressor cylinder  500  further comprises four intake check valves  520  and four outlet check valves  530 . When a current is applied to the first coil unit  130 , the first magnetic pole  210  attracts the mover  300  to drive the piston  510  on both sides to compress towards the left side, so as to open the outlet check valve  530  disposed at the lower left of the compressor cylinder  500 , and compress the gas or the fluid and discharge from the outlet check valve  530  disposed at the lower left of the compressor cylinder  500 . In the mean time, the intake check valve  520  disposed on the upper right of the two side compressor cylinders  500  will be opened due to the negative pressure formed inside the compressor cylinder  500 , so that the gas or the fluid can enter from the intake check valve  520  at the upper right of the compressor cylinder  500  into the compressor cylinder  500 . 
         [0053]    When a current is applied to the second coil unit  140 , the second magnetic pole  220  attracts the mover  300  to drive the piston  510  on both sides to compress at the right side, so as to open the outlet check valve  530  disposed at the lower right of the two side compressor cylinders  500  and compress the gas or fluid to discharge out from the outlet check valve  530  at the lower right of the compressor cylinder  500 . In the meantime, the intake check valve  520  at the upper left of the two side compressor cylinders  500  is opened due to the negative pressure formed inside the compressor cylinder  500 , so that the gas or fluid can enter from the intake check valve  520  at the upper left of the compressor cylinder  500  into the compressor cylinder  500 . 
         [0054]    Therefore, the reciprocal linear motion of the mover  300  of the salient-pole type linear motor not only can reduce the lateral force produced from the motion of the piston  510 , but can also reduce friction and loss, so as to achieve the effects of high mechanical strength, low mechanical loss, low noise and a high efficiency. The linear motor of the present invention drives the reciprocal double piston compressor can be designed with a high-low compressor model, and applied to provide a driving source for air conditioners of electric cars, dehumidifiers, cold drink machines, water chillers, refrigerators, home air-conditioners, refrigeration compressors, electric appliances, air-conditioning compressor, air-conditioner compressors, industrial compressors or any system requiring a reciprocal motion compression. 
         [0055]    With reference to  FIGS. 6A and 6B , both ends of two salient-pole type linear motors  500  can be connected in series with the compressor cylinder in order to inhibit vibrations produced by the salient-pole type linear motor with both ends coupled to the compressor cylinder  500 , and two sets of pistons  510  are arranged to have motions with respect to each other to offset the vibrations caused by the reciprocal motion of the pistons, so as to achieve the effect of balancing the force to reduce vibrations. 
         [0056]    With reference to  FIG. 7  for a perspective view of a salient-pole type linear motor with enhanced magnetic forces at the ends, a mover  300  with eight salient poles  310  is used as an example for the illustration of the invention. A fourth magnetic pole  230  is further installed at a front end of the second magnetic pole  220 , and the fourth coil unit  160  is wound around the fourth magnetic pole  230 . In addition, a fifth magnetic pole  240  is installed at an end of the first magnetic pole  210  and the fifth coil unit  170  is wound around the fifth magnetic pole  240 . 
         [0057]    Further, when a current is applied to the first coil unit  130  and the fourth coil unit  160 , the first magnetic pole  210  and the fourth magnetic pole  230  attract the mover  300  to move along the central axial direction of the stator towards the positions of the first magnetic pole  210  and the fourth magnetic pole  230 . On the other hand, when the current is applied to the second coil unit  140  and the fifth coil unit  170 , the second magnetic pole  220  and the fifth magnetic pole  240  attract the mover  300  to move along the central axial direction of the stator towards the positions of the second magnetic pole  220  and the fifth magnetic pole  240 . 
         [0058]    Therefore, the fourth magnetic pole  230  and the fifth magnetic pole  240  are provided and disposed at the front and rear ends of the salient-pole type linear motor respectively to enhance the magnetic forces at the front and rear ends of the magnetic force, so as to improve the driving force at both ends of the motor.