Reciprocating compressor with gas bearing

A reciprocating compressor with a gas bearing is configured to support a portion between a cylinder and a piston by the gas bearing and induce a resonating motion of the piston by the use of compression coil springs. Therefore, a proper resonating motion of a vibrating body can be induced by the use of the gas bearing, without using plate springs, and accordingly manufacturing costs and the number of assembly processes can be reduced and the installation direction of the compressor can be freely designed.

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure relates to subject matter contained in priority Korean Application No. 10-2011-0090324, filed on Sep. 6, 2011, which is herein expressly incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a reciprocating compressor, and more particularly, to a reciprocating compressor with a gas bearing.

2. Background of the Invention

Generally, a reciprocating compressor serves to intake, compress, and discharge a refrigerant as a piston linearly reciprocates within a cylinder. The reciprocating compressor may be classified into a connection type reciprocating compressor or a vibration type reciprocating compressor according to the method employed to drive the piston.

In the connection type reciprocating compressor, the piston is connected to a rotating shaft associated with a rotation motor by a connection rod, which causes the piston to reciprocate within the cylinder, thereby compressing the refrigerant. On the other hand, in the vibration type reciprocating compressor, the piston is connected to a mover associated with a reciprocating motor, which vibrates the piston while the piston reciprocates within the cylinder, thereby compressing the refrigerant. The present invention relates to the vibration type reciprocating compressor, and the term “reciprocating compressor” will hereinafter refer to the vibration type reciprocating compressor.

To enhance the performance of a reciprocating compressor, a portion between the cylinder and the piston, being hermetically sealed, has to be properly lubricated. To this end, there has been conventionally known a reciprocating compressor which seals and lubricates a portion between the cylinder and the piston by supplying a lubricant such as oil between the cylinder and the piston and forming an oil film.

However, the supplying of the lubricant requires an oil supply apparatus, and an oil shortage may occur depending on operation conditions, thereby degrading compressor performance. Also, the compressor size needs to be increased because a space for receiving a certain amount of oil is required, and the installation direction of the compressor is limited because the entrance of the oil supply apparatus should always be kept immersed in oil.

Taking into consideration the disadvantages of the oil-lubricated type reciprocating compressor, as shown inFIG. 1, there has been conventionally known a technique of forming a gas bearing between the piston1and the cylinder2by bypassing a part of compressed gas between the piston1and the cylinder2. In this technique, a plurality of gas flow paths2awith a small diameter are formed in the cylinder2, or a sintered porous material member (not shown) is provided on an inner circumferential surface of the cylinder2. This technique can simplify a lubrication structure of the compressor because it requires no oil supply apparatus, unlike the oil-lubricated type for supplying oil between the piston1and the cylinder2, and can maintain constant compressor performance by preventing an oil shortage depending on operating conditions. Also, this technique has the advantage that the compressor can be smaller in size and the installation direction of the compressor can be freely designed because no space for receiving oil is required in the casing of the compressor.

In the case the gas bearing is applied to the reciprocating compressor, a plate spring3is used for a resonating motion of the piston, as shownFIG. 2.

In the case the plate spring3is used, the piston (shown inFIG. 1)1constituting a compression portion4and the plate spring (shown inFIG. 2)3are connected by a flexible connecting bar (not shown) so that the piston1has forward movability within the cylinder (shown inFIG. 1)2, or the connecting bar is divided into a plurality of parts5ato5cand connected by at least one (preferably two or more) links6aand6b. In the drawings, unexplained reference numeral7denotes a reciprocating motor.

In the case that the reciprocating compressor with a gas bearing uses the plate spring for a resonating motion as described above, the aforementioned flexible connecting bar has to be used to connect between members, or a plurality of connecting bars have to be connected by links, which may increase material costs and the number of assembly processes.

Moreover, displacement in the movement direction of the piston (hereinafter, ‘longitudinal displacement’) occurs a lot because of the characteristics of the plate spring, whereas displacement in a direction orthogonal to the motion direction of the piston (hereinafter, lateral displacement) rarely occurs. Thus, if the piston is arranged to move in a vertical direction, the piston may hang vertically downward when stopped, thus distorting the initial position of the piston. Taking this into account, the piston needs to be arranged so as to move in a horizontal direction, which is a limitation to the installation of a compression portion and a driving portion.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a reciprocating compressor with a gas bearing which induces a proper resonating motion of a vibrating body by using the gas bearing, without the use of a plate spring, and therefore decreases material costs and the number of assembly processes and freely design the installation direction of the compressor.

To achieve these and other advantages and in accordance with the purpose of this specification, as embodied and broadly described herein, there is provided a reciprocating compressor with a gas bearing, the reciprocating compressor comprising: a cylinder having a compression space; a piston inserted into the compression space and reciprocating relative to the cylinder; a gas bearing for lubricating a bearing surface of the cylinder and the piston by gas; and resonant springs supporting both sides of a reciprocating member, which is either the cylinder or the piston, in the motion direction, wherein the resonant springs comprise a first resonant spring and a second resonant spring that are formed as compression coil springs and respectively provided on both sides of the reciprocating member, at least either the first resonant spring or the second resonant spring being provided in plural.

Furthermore, there is provided a reciprocating compressor with a gas bearing, the reciprocating compressor comprising: a cylinder having a compression space; a piston inserted into the compression space and reciprocating relative to the cylinder; a gas bearing for lubricating a bearing surface of the cylinder and the piston by gas; and resonant springs supporting both sides of a reciprocating member, which is either the cylinder or the piston, in the motion direction, wherein the resonant springs comprise a first resonant spring and a second resonant spring that are formed as compression coil springs and respectively provided on both sides of the reciprocating member, at least either the first resonant spring or the second resonant spring being provided in plural, the plurality of resonant springs being arranged such that lines orthogonal to the front end surfaces of at least two resonant springs in the winding direction meet at one point.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a reciprocating compressor with a gas bearing according to the present invention will be described in detail with reference to an embodiment illustrated in the accompanying drawings.

As shown inFIG. 3, in the reciprocating compressor according to this embodiment, a frame20is installed within a sealed casing10, a reciprocating motor30and a cylinder41are fixed to the frame20, a piston42coupled to a mover32of the reciprocating motor30is inserted into the cylinder41to reciprocate, and resonant springs51and52for inducing a resonating motion of the piston42are installed at both sides of the piston42in the motion direction of the piston42.

In the aforementioned reciprocating compressor according this embodiment, when power is applied to a coil35of the reciprocating motor30, the mover32of the reciprocating motor30reciprocates. Then, the piston42coupled to the mover32sucks and compresses a refrigerant gas while linearly reciprocating within the cylinder41, and discharges it.

More specifically, when the piston42moves backwards, the refrigerant gas in the sealed casing10is sucked into the compression space S1through the suction path F of the piston42, and when the piston42moves forwards, the suction path F is closed and the refrigerant gas in the compression space S1is compressed. Also, when the piston42further moves forwards, the discharge valve44is opened to discharge the refrigerant gas compressed in the compression space S1and move it to the outside refrigeration cycle.

As shown inFIGS. 4 and 5, the reciprocating motor30comprises a stator31having a coil35and an air gap formed at only one side of the coil35and a mover32inserted into the air gap of the stator31and having a magnet325that linearly moves in the motion direction.

The stator31includes a plurality of stator blocks311and a plurality of pole blocks315respectively coupled to sides of the stator blocks311and forming an air gap portion31aalong with the stator blocks311.

The stator blocks311and the pole blocks315include a plurality of thin stator cores laminated sheet by sheet in a circular arc shape when axially projected.

The stator blocks311are formed in the shape of recesses when axially projected, and the pole blocks315are formed in a rectangular shape when axially projected.

The stator block (or each of the stator core sheets constituting the stator blocks)311may include a first magnetic path312positioned inside the mover32to form the inner stator and a second magnetic path313extending integrally from an axial side of the first magnetic path312, i.e., the opposite end of the air portion31a, and positioned outside the mover32to form the outer stator.

While the first magnetic path312is formed in a rectangular shape, the second magnetic path313is formed in a stepwise manner and extends from the first magnetic path312.

A coil receiving slot31bopened in an axial direction, i.e., the direction of the air gap portion, is formed on inner wall surfaces of the first and second magnetic paths312and313, and the pole block315is coupled to an axial cross-section of the second magnetic path313which constitutes the coil receiving slot31bso as to open an axial open surface of the coil receiving slot31b.

Also, a coupling groove311band a coupling protrusion315bmay be formed on a coupling surface of the stator block311and a coupling surface of the pole block315, which connect the stator block311and the pole block315to form a magnetic path connecting portion (not shown), to firmly couple the stator block311and the pole block315and maintain a given curvature. Although not shown, the stator block311and the pole block315may be coupled in a stepwise manner.

The coupling surface311aof the stator block311and the coupling surface315aof the pole block315, except the coupling groove311band the coupling protrusion315b, are formed to be flat, thereby preventing an air gap between the stator block311and the pole block315. This prevents magnetic leakage between the stator block311and the pole block315, thereby leading to an increase in motor performance.

A first pole portion311chaving an increasing cross-sectional area is formed at a distal end of the second magnetic path313of the stator block311, i.e., a distal end of the air gap portion31a, and a second pole portion315chaving an increasing cross-sectional area is formed at a distal end of the pole block315, corresponding to the first pole portion311cof the stator block311.

The mover32may include a magnet holder321having a cylindrical shape and a plurality of magnets325attached onto an outer circumferential surface of the magnet holder321in a circumferential direction to form a magnetic flux together with the coil35.

The magnetic holder321may be formed of a non-magnetic substance in order to prevent flux leakage; however, it is not limited thereto. The outer circumferential surface of the magnetic holder321may be formed in a circular shape so that the magnets325are in line contact therewith and adhered thereto. Also, a magnet mounting groove (not shown) may be formed in a strip shape on the outer circumferential surface of the magnet holder321so as to insert the magnets325therein and support them in the motion direction.

The magnets325may be formed in a hexahedral shape and adhered one by one to the outer circumferential surface of the magnet holder321. In the case of attaching the magnets325one by one, supporting members (not shown), such as fixing rings or a tape made up of a composite material.

Although the magnets325may be serially adhered in a circumferential direction to the outer circumferential surface of the magnet holder321, it is preferable that the magnets325are adhered at predetermined intervals, i.e., between the stator blocks in a circumferential direction to the outer circumferential surface of the magnet holder321to minimize the use of the magnets, because the stator31comprises a plurality of stator blocks311and the plurality of stator blocks311are arranged at predetermined intervals in the circumferential direction. In this case, the magnets325are preferably formed to have a length corresponding to the air gap length of the magnetic holder321, i.e., the circumferential length of the air gap.

Preferably, the magnet325may be configured such that its length in a motion direction is not shorter than a length of the air gap portion31ain the motion direction, more particularly, longer than the length of the air gap portion31ain the motion direction. At its initial position or during its operation, the magnet325may be disposed such that at least one end thereof is located inside the air gap portion31a, in order to ensure a stable reciprocating motion.

Moreover, though only one magnet325may be disposed in the motion direction, a plurality of magnets325may be disposed in the motion direction in some cases. In addition, the magnets may be disposed in the motion direction so that an N pole and an S pole correspond to each other.

Although the above-described reciprocating motor may be configured such that the stator has one air gap portion314as shown inFIG. 5, it may be configured such that in some cases the stator has air gap portions31aand31con both sides of the coil in the reciprocating direction as shown inFIG. 6. In this case, too, the mover32may be formed in the same manner as the foregoing embodiment.

In the above-stated reciprocating compressor, it is required to reduce a frictional loss between the cylinder and the piston to improve the performance of the compressor. To this end, there has been conventionally known a gas bearing which lubricates between the cylinder and the piston by gas force by bypassing a part of compressed gas between an inner circumferential surface of the cylinder and an outer circumferential surface of the piston. In this case, gas flow paths with a small diameter may be formed in the cylinder, or a sintered porous material member may be provided on the inner circumferential surface of the cylinder.

In the case of forming the gas flow paths as fine pores, however, it is difficult to form the gas flow paths as fine pores, and impurities such as iron powder produced during the operation of the compressor may block the fine gas flow paths. Then, some of the gas flow paths are blocked and a gas force cannot be uniformly applied in a circumferential direction of the piston, and hence a partial friction may occur between the cylinder and the piston. Due to this, the performance and the reliability of the compressor may be degraded, thus requiring very high cleanness.

On the other hand, in the case that a sintered porous material member is inserted into the inner circumferential surface of the cylinder, the porous material member may be abraded upon initial startup before the formation of the gas bearing because of high manufacturing cost of the porous material member and low abrasion resistance thereof, and therefore the lifespan of the porous material member may be degraded. Also, it is difficult to properly regulate the distribution of pores because of the characteristics of the porous material member, which can make it difficult to design the gas bearing so as to properly seal and lubricate a portion between the cylinder and the piston.

Moreover, in the case that the exits of the gas flow paths are formed in the cylinder, suction loss occurs as the outlets of the gas flow paths are exposed to the compression space during a suction stroke to thus cause a high-pressure refrigerant to enter the compression space. On the other hand, in the case that the inlets of the gas flow paths are formed in the piston, gas from the gas bearing flows backward to the compression space as the inlets of the gas flow paths are exposed to the compression space during a suction stroke.

Taking this into consideration, the gas bearing according to these embodiments allows a high-pressure compressed gas to be uniformly distributed between the cylinder and the piston by forming an oxide film layer having a plurality of fine through holes on the inner circumferential surface of the cylinder or the outer circumferential surface of the piston to make it easy to regulate the distribution of the fine through holes, or by forming gas flow paths in the cylinder and coupling a porous material member to the outer circumferential surface of the piston to uniformly distribute and supply a high-pressure compressed gas guided through the gas flow paths between the cylinder and the piston, or by forming gas flow paths in the cylinder and coupling a gas guide member having gas through holes to the outer circumferential surface of the piston to uniformly distribute and supply a high-pressure compressed gas guided through the gas flow paths between the cylinder and the piston, or by forming gas flow paths in the cylinder.

As shown inFIG. 7, the oxide film layer412may be formed on an inner circumferential surface of a cylinder body411(or on an outer circumferential surface of a piston body) to have a plurality of fine through holes412a. In this case, compressed gas guided to the fine through holes through gas flow paths401is uniformly supplied between the cylinder41and the piston42through the fine through holes412ato form a gas bearing.

The oxide film layer412may be formed by anodizing or micro arc oxidation (MAO).

The gas flow paths401may be formed in the cylinder body411as shown inFIG. 7. The gas flow paths401may comprise at least one first flow path401aformed in a reciprocating direction of the piston42on a front end surface411aof the discharge side of the cylinder body411and a plurality of second flow paths401bpenetrating toward an inner circumferential surface of the cylinder body411on the midway of the first flow path401a.

The front end surface411aof the cylinder body411protrudes to a predetermined height to form a protruding portion411b, and a discharge cover46is inserted and coupled to an outer circumferential surface of the protrusion411b.

A starting end of the first flow path401a, i.e., the inlet end of the first flow path401acontacting a discharge space S2, is preferably formed at a greater distance than the radius Ds of the discharge valve45relative to the center of the discharge valve45so that it is positioned out of the attachment/detachment range of the discharge valve45which is selectively attached to and detached from the front end surface411aof the cylinder body411.

Although the diameter of the second flow paths401brelative to the diameter of the first flow path401amay fall within the range of 1/10 to 1, the diameter of the second flow paths401bmay be equal to or slightly greater than the diameter of the first flow path401abecause distal ends of the second flow paths401bare in contact with the oxide film layer412.

An annular filter47may be installed on the front end of the first gas flow path401a, i.e., the front end surface411aof the cylinder body411so as to prevent impurities from entering the gas flow paths401.

Although at least one gas diffusion groove (not shown) may be further formed on the outer circumferential surface of the piston42, a high-pressure compressed gas may be uniformly distributed over a bearing area between the cylinder41and the piston42, as shown inFIG. 8, without forming a gas diffusion groove on the outer circumferential surface of the piston42, because the oxide film layer412has a porous structure.

In the case that the a porous layer is formed of the oxide film layer, the porous layer is easily formed on the inner circumferential surface of the cylinder body, and the reliability of the compressor is improved because of high abrasion resistance and high rub resistance resulting from an increase in the strength of a bearing surface formed of an oxide film layer.

As shown inFIGS. 9 and 10, a porous material member422may be inserted and coupled to an inner circumferential surface of the piston body421(or on an outer circumferential surface of the cylinder body). In this case, compressed gas guided to fine through holes422aof the porous material member422through the gas flow paths401is uniformly supplied between the cylinder41and the piston42through the fine through holes422ato form a gas bearing.

The gas flow paths401may comprise a cylinder side gas flow path402formed at the cylinder41and a piston side gas flow path403communicating with the cylinder side gas flow path402and formed at the piston42.

The cylinder side gas flow path402may comprises at least one gas inlet opening411cformed in a reciprocating direction of the piston42on a front end surface of the discharge side of the cylinder41and a gas pocket411dformed on the inner circumferential surface of the cylinder41, with its side wall surface communicating with the gas inlet opening411c. The cross-sectional area of the gas pocket411dmay be much greater than the cross-sectional area of the gas inlet opening411c.

The piston side gas flow path403may comprises a gas communication opening422bformed at a center portion of the porous material member422and communicating with the gas pocket411dof the cylinder41and a gas guide groove421aformed on the outer circumferential surface of the piston body421and communicating with the gas communication opening422b.

The gas guide groove421ahas an annular shape. Preferably, the gas guide groove421ahas a width in the reciprocating direction much larger than the width of the gas communication opening422bin the reciprocating direction so that gas introduced into the gas guide groove421ais uniformly distributed over the entire bearing surface, that is, the length of the gas guide groove421ais as similar to the width of the porous material member422in the reciprocating direction as possible to increase the baring surface area as much as possible.

Although at least one gas diffusion groove (not shown) may be further formed on an outer circumferential surface of the porous material member422, gas may be uniformly distributed over the bearing area between the cylinder41and the piston42, without forming a gas diffusion groove on the outer circumferential surface of the porous material member422, because gas is uniformly distributed due to the porous structure of the porous material member422.

As in this embodiment, in the case that the porous material member422is inserted and coupled to the piston body421, a part of compressed gas discharged to the discharge space S2enters the gas pocket411dthrough the gas inlet opening411c, and this compressed gas enters the gas guide groove421athrough the gas communication opening422bof the porous material member422and diffused in the gas guide groove421a, thereby supplying the compressed gas between the cylinder41and the piston42through the fine through holes422aof the porous material member422.

Accordingly, a high-pressure compressed gas supplied between the cylinder41and the piston42is prevented from entering the compression space S1, thereby preventing a suction loss. Also, in the case that a gas inlet opening is formed in the piston42, the gas inlet opening has to communicate with the compression space. Thus, it is necessary to install a check valve to prevent a refrigerant sucked into the compression space from leaking into the gas inlet opening when the piston performs a suction stroke, and this may increase manufacturing costs. Nevertheless, this embodiment allows a reduction in manufacturing costs because the gas inlet opening is formed at the cylinder side and makes the process easier.

As shown inFIGS. 11 and 12, in the case that gas flow paths are formed in the piston42, the gas flow paths are not exposed to the suction space even when the piston performs a suction stroke, thereby preventing a suction loss.

For example, at least one gas inlet opening411cconstituting the cylinder side gas flow path402is formed in a reciprocating direction of the piston body421on the front end surface411aof the discharge side of the cylinder body411, and a gas pocket411d, whose side wall surface communicates with the gas inlet opening411cand constitutes the gas flow path402along with the gas inlet opening411c, is formed on the inner circumferential surface of the cylinder body411.

A cylindrical gas guide member423is inserted and coupled to the outer circumferential surface of the piston body421. A gas communication opening423acommunicating with the gas pocket411dand constituting the piston side gas flow path403is formed at a center portion of the gas guide member423, a gas guide groove421communicating with the gas communication opening423aand constituting the piston side gas flow path403is formed on the outer circumferential surface of the piston body421, and a plurality of bearing holes423bare formed on both end portions of the gas guide member423so that gas guided through the gas guide groove421ais supplied between the cylinder41and the piston42.

Preferably, the bearing holes423bhave a significantly smaller size than the gas communication opening423ato prevent excessive exposure of compressed gas.

Preferably, one or more gas diffusion groove (not shown) may be further formed on an outer circumferential surface of the gas guide member423because the compressed refrigerant gas is uniformly distributed over the bearing area between the cylinder41and the piston42.

Preferably, the gas diffusion groove is formed to communicate with the gas communication opening423aor the bearing holes423bso that the compressed gas entering or introduced into the gas guide groove421aquickly enters the gas diffusion groove.

In the above-described embodiment, because the gas flow paths are formed in the piston42, the gas flow paths are not exposed to the compression space S1during a suction stroke of the piston thereby preventing a degradation in the performance of the compressor caused by a suction loss.

Moreover, the gas guide member423has a simple cylindrical shape, and hence the manufacturing costs can be reduced, compared to the porous material member.

As shown inFIGS. 13 and 14, a gas diffusion groove424may be formed on the outer circumferential surface of the piston without providing a porous member or gas guide member in the piston42.

The gas diffusion groove424may comprise a linear groove424acommunicating with the gas pocket411dof the cylinder side gas flow path402and an annular groove424bcommunicating with the linear groove424aand having an annular shape.

A piston side gas pocket421bmay be formed on the outer circumferential surface of the piston to communicate with the gas pocket411dof the gas flow path402, and the linear groove424aof the gas diffusion groove424may be formed to communicate with the piston side gas pocket421b.

In the above-described embodiment, it is preferable that the linear groove424aof the gas diffusion groove424is formed to communicate with the piston side gas pocket421bbecause a refrigerant entering the piston side gas pocket421bis diffused fast over the bearing surface between the cylinder41and the piston42while quickly moving to the gas diffusion groove424.

In the above-described reciprocating compressor with the gas bearing, the resonant springs may be plate springs, which have a small lateral displacement, because the piston42has to maintain forward movement.

However, the plate springs have a small lateral displacement but a large longitudinal displacement. Therefore, if the compressor is installed stood in the motion direction of the piston, a compression stroke may not be properly performed because the piston hangs vertically downward. Moreover, when the plate springs are used, the plate springs and the piston have to be connected by a connecting bar made of soft material or by at least one link (preferably two links) on the midway of the connecting bar, in order to maintain the forward movement of the piston, which may increase material costs and the number of assembly processes.

The above-described reciprocating compressor with the gas bearing according to this embodiment is devised to reduce material costs and the number of assembly processes by varying the configuration of the compressor by using not plate springs but coil springs as the resonant springs, and avoiding the use of a connecting bar or link.

As shown inFIG. 15, the resonant springs may comprise a first resonant spring and a second resonant spring52which are respectively provided on both front and back sides of a spring supporter53coupled to the mover32and the piston42.

The first resonant spring51and the second resonant spring52each are provided in plural and arranged in a circumferential direction. However, either the first resonant spring51or the second resonant spring52may be provided in plural, and the other resonant spring may be provided in singular.

If the first resonant spring51and the second resonant spring52are compressed coil springs as described above, a side force may be produced when the resonant springs51and52are expanded. Accordingly, the resonant springs51and52may be arranged so as to offset a side force or torsion moment of the resonant springs51and52.

For example, as shown inFIG. 16, in the case that the first resonant spring51and the second resonant spring52are arranged alternately by twos in a circumferential direction, distal ends of the first and second resonant springs51and52are wound at the same position in opposite directions (counterclock wise) relative to the center of the piston42, and the resonant springs on the same side positioned in their respective diagonal directions are arranged to symmetrically engage each other so that a side force and a torsion moment are produced in opposite directions.

Also, the first resonant spring51and the second resonant spring52may be arranged to symmetrically engage the distal ends of the resonant springs with each other so that a side force and a torsion moment are produced in opposite directions along the circumferential direction.

Although not shown, if the number of first resonant springs51is odd, they are arranged so that lines orthogonal to the front end surfaces of the springs meet at one point to thus offset a side force and a torsion moment.

Preferably, spring fixing protrusions531and532are respectively formed on a frame or spring supporter53to which the ends of the first and second resonant springs51and52are fixed, in order for the resonant springs51and52to be forcibly fit and fixed to the spring fixing protrusions53, because the engaging resonant springs are prevented from turning.

The number of first resonant springs51may be equal to or different from the number of second resonant springs52as long as the first resonant spring51and the second resonant spring52have the same elasticity.

The above-described reciprocating compressor with the gas bearing according to this embodiment has the following operational effects.

That is, when power is applied to the coil35, a magnetic flux is formed around the coil35. The magnetic flux may then create a closed loop along the first magnetic path311, second magnetic path312, and magnetic path connecting portion313of the stator31. In cooperation with an interaction between the magnetic flux formed between the first magnetic path311and the second magnetic path312and a magnetic flux generated by the magnet325, the magnet325linearly moves together with the magnet holder321in the motion direction. When a flow direction of current applied to the coil35alternately changes, the direction of the magnetic flux of the coil35may also change, to make the magnet325linearly reciprocate.

Then, the piston42coupled to the magnet holder321, being inserted in the compression space S1of the cylinder41, reciprocates together with the magnetic holder321. By the reciprocation of the piston42, the first resonant spring51and the second resonant spring52respectively provided on both sides of the piston42in the motion direction are alternately expanded to induce a resonating motion of the piston42.

Hereupon, the resonant springs51and52may produce a side force and a torsion moment when expanded because of the characteristics of compression coil springs, and therefore the forward movement of the piston42may be distorted. In this embodiment, however, the plurality of first resonant springs51and second resonant springs52are arranged to be wound in opposite directions, and therefore the side force and torsion moment produced from the resonant springs51and52are offset by the diagonally corresponding resonant springs. Accordingly, the forward movement of the piston42can be maintained, and abrasion of surfaces contacting the resonant springs51and52can be prevented.

Moreover, the compressor can be installed in a standing type, as well as in a lateral type because compression coil springs, which have a small longitudinal placement, are used as the resonant springs51and52. The manufacturing costs and the number of assembly processes can be reduced because no connecting bar or link is required.

Although the foregoing embodiments have been described with respect to the case where the cylinder is inserted into the stator of the reciprocating motor, the resonant springs may be used in the same manner as above even when the reciprocating motor is mechanically coupled to a compression unit comprising the cylinder with a predetermined interval therefrom. A detailed description of which will be omitted.

Further, in the foregoing embodiments, the piston is configured to reciprocate and the resonant springs are respectively provided on both sides of the piston in the motion direction. In some cases, however, the cylinder may be configured to reciprocate and the resonant springs may be provided on both sides of the cylinder. In this case, too, the resonant springs may be formed as a plurality of compression coil springs, as in the foregoing embodiments, and the plurality of compression coil springs may be arranged in the same manner as the foregoing embodiments. A detailed description of which will be omitted.