SALIENT-POLE TYPE LINEAR MOTOR AND RECIPROCAL DOUBLE PISTON COMPRESSOR WITH SALIENT-POLE TYPE LINEAR MOTOR

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

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

1. Field of the Invention

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.

2. Description of the Related Art

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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:

(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.

(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.

(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.

(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.

(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.

(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

FIG. 1 is an exploded view of a salient-pole type linear motor of the present invention;

FIG. 2 is a front view of a salient-pole type linear motor of the present invention;

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;

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;

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;

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;

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;

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;

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;

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

FIG. 7 is a schematic view of a salient-pole type linear motor with enhanced magnetic forces at the ends.

DETAILED DESCRIPTION

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

With reference to FIGS. 3A, 3B, and 4A to 4C, 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Claims

1. A salient-pole type linear motor, comprising:

a housing;

a stator, installed in the housing, and comprising a middle stator core and two side stator cores coupled along a central axial direction, and the middle stator core and the two side stator cores further having a plurality of magnetic poles paired and protruded inwardly;

a plurality of coil units, wound around the magnetic poles; and

a mover, having a shaft and a plurality of salient-poles, and the shaft movably penetrating along the central axial direction through the stator, such that when 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 to attract the mover to perform a reciprocal linear motion along the central axial direction of the stator.

2. The salient-pole type linear motor of claim 1, wherein 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.

3. The salient-pole type linear motor of claim 1, wherein the mover has a number of salient poles equal to the number of magnetic poles of the middle stator core, and the salient poles are disposed at positions corresponding to the positions of the magnetic poles of the middle stator core respectively, and the middle stator core and the two side stator cores are made of iron, silicon steel or a magnetically permeable material.

4. The salient-pole type linear motor of claim 1, wherein the mover is made of iron, silicon steel, a permanent magnet or a magnetically permeable material.

5. The salient-pole type linear motor of claim 1, wherein the middle stator core and the two side stator cores are integrally formed, or the middle stator core is integrally formed with one of the two side stator cores, and the magnetic poles of the two side stator cores are staggered or arranged opposite to each other along the central axial direction.

6. A reciprocal double piston compressor with a salient-pole type linear motor, comprising:

a housing;

a stator, installed in the housing, and comprising a middle stator core and two side stator cores coupled along a central axial direction of the stator, and the middle stator core and the two side stator cores having a plurality of magnetic poles paired and protruded inwardly;

a plurality of coil units, wound around the magnetic poles;

a mover, having a shaft and a plurality of salient-poles, and the shaft movably penetrating through the stator along the central axial direction, such that when 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 to attract the mover to perform a reciprocal linear motion along the central axial direction of the stator; and

a plurality of compressor cylinders, each having a piston coupled separately to both ends of the shaft of the mover.

7. The reciprocal double piston compressor with a salient-pole type linear motor according to claim 6, wherein 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.

8. The reciprocal double piston compressor with a salient-pole type linear motor according to claim 6, wherein the mover has a number of salient poles equal to the number of magnetic poles of the middle stator core, and the salient poles are disposed at positions corresponding to the positions of the magnetic poles of the middle stator core respectively, and the middle stator core and the two side stator cores are made of iron, silicon steel or a magnetically permeable material.

9. The reciprocal double piston compressor with a salient-pole type linear motor according to claim 6, wherein the compressor cylinders further comprise a plurality of intake check valves and a plurality of outlet check valves.

10. The reciprocal double piston compressor with a salient-pole type linear motor according to claim 6, wherein the middle stator core and the two side stator cores are integrally formed, or the middle stator core is integrally formed with one of the two side stator cores, and the magnetic poles of the two side stator cores are staggered or arranged opposite to each other along the central axial direction.