LINEAR COMPRESSOR

Abstract

A linear compressor is provided. The linear compressor may include a cylinder that forms a compression space for a refrigerant, a piston that reciprocates in an axial direction inside of the cylinder, and a linear motor that supplies power to the piston. The linear motor may include an outer stator including a first stator magnetic pole, a second stator magnetic pole, and an opening defined between the first stator magnetic pole and the second stator magnetic pole; an inner stator disposed apart from the outer stator to form an air gap therebetween; and a permanent magnet movably disposed in the air gap between the outer stator and the inner stator and having three poles. The three poles may include two end magnetic poles, and a central magnetic pole disposed between the two end magnetic poles. The piston may be moveable by a stroke between a top dead center position and a bottom dead center position, and a length of the first stator magnetic pole or the second stator magnetic pole may be greater than a length of the stroke.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority under 35 U.S.C. 119 and 35 U.S.C. 365 to Korean Patent Application No. 10-2013-0075512, filed in Korea on Jun. 28, 2013, which is hereby incorporated by reference in its entirety.

BACKGROUND

1. Field

A linear compressor is disclosed herein.

2. Background

In general, compressors may be mechanisms that receive power from power generation devices, such as electric motors or turbines, to compress air, refrigerants, or other working gases, thereby increasing a pressure of the working gas. Compressors are widely used in home appliances or industrial machineries, such as refrigerators and air-conditioners.

Compressors may be largely classified into reciprocating compressors, in which a compression space, into and from which a working gas, such as a refrigerant, is suctioned and discharged, is defined between a piston and a cylinder to compress the refrigerant while the piston is linearly reciprocated within the cylinder; rotary compressors, in which a compression space, into and from which a working gas, such as a refrigerant, is suctioned and discharged, is defined between a roller, which is eccentrically rotated, and a cylinder to compress the refrigerant while the roller is eccentrically rotated along an inner wall of the cylinder; and scroll compressors in which a compression space, into and from which a working gas, such as a refrigerant, is suctioned and discharged, is defined between an orbiting scroll and a fixed scroll to compress the refrigerant while the orbiting scroll is rotated along the fixed scroll. In recent years, among the reciprocating compressors, linear compressors having a simple structure in which a piston is directly connected to a drive motor, which is linearly reciprocated, to improve compression efficiency without mechanical loss due to switching in moving, are being actively developed. Generally, such a linear compressor is configured to suction and compress a refrigerant while a piston is linearly reciprocated within a cylinder by a linear motor in a sealed shell, thereby discharging the compressed refrigerant.

The linear motor has a structure in which a permanent magnet is disposed between an inner stator and an outer stator. The permanent magnet may be linearly reciprocated by a mutual electromagnetic force between the permanent magnet and the inner (or outer) stator. Also, as the permanent magnet is operated in a state in which the permanent magnet is connected to the piston, the refrigerant may be suctioned and compressed while the piston is linearly reciprocated within the cylinder and then be discharged.

A linear compressor according to the related art is disclosed in Korean Patent Publication No. 10-2010-0010421. The linear compressor according to the related art includes a linear motor, which is provided with an outer stator having a core and a coil-wound body, an inner stator, and a permanent magnet. One end of a piston is connected to the permanent magnet. The permanent magnet may include one magnet having a single polarity, and may be a rare-earth magnet.

When the permanent magnet is linearly reciprocated by mutual electromagnetic force between the inner stator and the outer stator, the piston linearly reciprocates in a cylinder along with the permanent magnet. However, rare earth metals are expensive.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements, and wherein:

FIG. 1 is a cross-sectional view of a linear compressor according to an embodiment;

FIG. 2 is an enlarged view of a portion “A” of the linear compressor of FIG. 1;

FIGS. 3 and 4 are cross-sectional views illustrating a reciprocating motion of a permanent magnet in an axial direction according to operation a linear motor of the linear compressor of FIG. 1;

FIGS. 5 and 6 are cross-sectional views schematically illustrating the linear motor of FIGS. 3-4;

FIG. 7A illustrates magnetic flux in a linear motor having a magnetic pole tip distance of T1, FIG. 7B illustrates magnetic flux in a linear motor having a magnetic pole tip distance of T2, and FIG. 7C illustrates a magnitude of leakage magnetic flux in the linear motors of FIGS. 7A and 7B;

FIG. 8 is a cross-sectional view of a linear motor illustrating a position of a permanent magnet when a piston is positioned at a bottom dead center (BDC) position, according to an embodiment;

FIG. 9 is a cross-sectional view of a linear motor illustrating a position of a permanent magnet when a piston is positioned at a top dead center (TDC) position, according to an embodiment;

FIG. 10 is a graph showing a magnitude of a thrust generated according to lengths of magnetic poles at both ends, in a permanent magnet according to an embodiment;

FIG. 11 is a graph showing variations in a cogging force according to lengths of magnetic poles at both ends, in a permanent magnet according to an embodiment;

FIG. 12 is a graph showing a magnitude of a thrust generated according to a length of a central magnetic pole, in a permanent magnet according to an embodiment; and

FIG. 13 is a graph showing variations in a cogging force according to a length of a central magnetic pole, in a permanent magnet according to an embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments will be described with reference to accompanying drawings. However, the scope is not limited to embodiments disclosed herein, and thus, a person skilled in the art, who understood the scope, would easily suggest other embodiments within the same scope thereof.

FIG. 1 is a cross-sectional view of a linear compressor according to an embodiment. Referring to FIG. 1, the linear compressor 10 may include a cylinder 120 disposed in a shell 100, a piston 130 that linearly reciprocates inside the cylinder 120, and a motor assembly 200, which may be in the form of a linear motor, that exerts a drive force on the piston 130. The shell 100 may include an upper shell and a lower shell.

The shell 100 may further include an inlet 110, through which a refrigerant may flow into the shell 100, and an outlet 105, through which the refrigerant compressed inside the cylinder 120 may be discharged from the shell 100. The refrigerant suctioned in through the inlet 101 may flow into the piston 130 via a suction muffler 140. While the refrigerant is passing through the suction muffler 140, noise may be reduced.

The piston 130 may be made of a nonmagnetic material, such as an aluminum-based material, for example, aluminum or aluminum alloy. As the piston 130 may be made of the aluminum-based material, magnetic flux generated in the motor assembly 200 may be delivered to the piston 130, thereby preventing the magnetic flux from being leaked outside of the piston 130. The piston 130 may be formed by forging, for example.

The cylinder 120 may be made of a nonmagnetic material, such as an aluminum-based material, for example, aluminum or aluminum alloy. The cylinder 120 and the piston 130 may have a same material composition ratio, that is, type and composition ratio.

As the cylinder 120 may be made of the aluminum-based material, magnetic flux generated in the motor assembly 200 may be delivered to the cylinder 120, thereby preventing the magnetic flux from being leaked outside of the cylinder 120. The cylinder 120 may be formed by extruded rod processing, for example.

The piston 130 and the cylinder 120 may be made of the same material, for example, aluminum, and thus, may have a same thermal expansion coefficient. During operation of the linear compressor 10, a high-temperature environment (about 100 ) may be created in the shell 100. At this time, the piston 130 and the cylinder 120 may have the same thermal expansion coefficient, and thus, may have a same amount of thermal deformation. As the piston 130 and the cylinder 120 may be thermally deformed in different amounts or directions, it is possible to prevent interference with the cylinder 120 during movement of the piston 130.

A compression space P to compress the refrigerant by the piston 130 may be defined in the cylinder 120. A suction hole 131a, through which the refrigerant may be introduced into the compression space P, may be defined in the piston 130, and a suction valve 132 to selectively open the suction hole 131a may be disposed at a side of the suction hole 131a.

A discharge valve assembly 170, 172, and 174 to discharge the refrigerant compressed in the compression space P may be disposed at a side of the compression space P. That is, the compression space P may be formed between an end of the piston 130 and the discharge valve assembly 170, 172, and 174.

The discharge valve assembly 170, 172, and 174 may include a discharge cover 172, in which a discharge space of the refrigerant may be defined; a discharge valve 170, which may be opened and introduce the refrigerant into the discharge space when the pressure of the compression space P is not less than a discharge pressure; and a valve spring 174, which may be disposed between the discharge valve 170 and the discharge cover 172 to exert an elastic force in an axial direction. The term “axial direction” used herein may refer to a direction in which the piston linearly reciprocates, that is, a substantially horizontal direction in FIG. 1, while the term “radial direction” may refer to a direction substantially perpendicular to the reciprocating direction of the piston 130, that is, a substantially vertical direction in FIG. 1.

The suction valve 132 may be disposed at a first side of the compression space P, and the discharge valve 170 may be disposed at a second side of the compression space P, that is, at an opposite side to the suction valve 132. While the piston 130 linearly reciprocates inside the cylinder 120, the suction valve 132 may be opened to allow the refrigerant to be introduced into the compression space P when the pressure of the compression space P is lower than the discharge pressure and not greater than a suction pressure. In contrast, when the pressure of the compression space P is not less than the suction pressure, the refrigerant of the compression space P may be compressed in a state in which the suction valve 132 is closed.

If the pressure of the compression space P is the discharge pressure or greater, the valve spring 174 may be deformed to open the discharge valve 170, and the refrigerant may be discharged from the compression space P into a discharge space of the discharge cover 172. The refrigerant of the discharge space may flow into a loop pipe 178 via a discharge muffler 176. The discharge muffler 176 may reduce flow noise of the compressed refrigerant, and the loop pipe 178 may guide the compressed refrigerant to the outlet 105. The loop pipe 178 may be coupled to the discharge muffler 176 and curvedly extend to be coupled to the outlet 105.

The linear compressor 10 may further include a frame 110. The frame 110, which may fix the cylinder 120 within the shell 100, may be integrally formed with the cylinder 120 or may be coupled to the cylinder 120 by means of a separate fastening member, for example. The discharge cover 172 and the discharge muffler 176 may be coupled to the frame 110.

The motor assembly 200 may include an outer stator 210, which may be fixed to the frame 110 and disposed so as to surround the cylinder 120, an inner stator 220 disposed apart from an inside of the outer stator 210, and a permanent magnet 230 disposed in a space between the outer stator 210 and the inner stator 220. The permanent magnet 230 may linearly reciprocate due to a mutual electromagnetic force between the outer stator 210 and the inner stator 220. The permanent magnet 230 may include a single magnet having one pole facing the outer stator 210, or multiple magnets having three poles facing the outer stator 210. In the case of the permanent magnet 230 having three poles, one surface there may have a polar distribution of N-S-N, and the other surface thereof may have a polar distribution of S-N-S

The permanent magnet 230 may be coupled to the piston 130 by a connection member 138. The connection member 138 may extend to the permanent magnet 230 from an end of the piston 130. As the permanent magnet 230 linearly moves, the piston 130 may linearly reciprocate in an axial direction along with the permanent magnet 230.

The outer stator 210 may include a bobbin 213, a coil 215, and a stator core 211. The coil 215 may be wound in a circumferential direction of the bobbin 213. The coil 215 may have a polygonal section, for example, a hexagonal section. The stator core 211 may be formed by stacking a plurality of laminations in a circumferential direction, and may be disposed to surround the bobbin 213 and the coil 215.

A stator cover 240 may be disposed at a side of the outer stator 210. A first end of the outer stator 210 may be supported by the frame 110, and a second end of the outer stator 210 may be supported by the stator cover 240.

The inner stator 220 may be fixed to an outer circumference of the cylinder 120. The inner stator 220 may be formed by stacking a plurality of laminations at an outer side of the cylinder 120 in a circumferential direction.

The linear compressor 10 may further include a supporter 135 that supports the piston 130, and a back cover 115 that extends toward the inlet 101 from the piston 130. The back cover 115 may be disposed to cover at least a portion of the suction muffler 140.

The linear compressor 10 may include a plurality of springs 151 and 155, a natural frequency of each of which may be adjusted so as to allow the piston 130 to perform resonant motion. The plurality of springs 151 and 155 may include a plurality of first springs 151 supported between the supporter 135 and the stator cover 240, and a plurality of second springs 155 supported between the supporter 135 and the back cover 115.

The plurality of first springs 151 may be provided at both sides of the cylinder 120 or the piston 130, and the plurality of second springs 155 may be provided at a front of the cylinder 120 or the piston 130. The term “front” used herein may refer to a direction oriented toward the inlet 101 from the piston 130. The term “rear” may refer to a direction oriented toward the discharge valve assembly 170, 172, and 174 from the inlet 101. These terms may also be equally used in the following description.

A predetermined amount of oil may be stored on an inner bottom surface of the shell 100. An oil supply device 160 to pump oil may be provided in a lower portion of the shell 100. The oil supply device 160 may be operated by vibration generated according to the linear reciprocating motion of the piston 130 to thereby pump the oil upward.

The linear compressor 10 may further include an oil supply pipe 165 that guides flow of the oil from the oil supply device 160. The oil supply pipe 165 may extend from the oil supply device 160 to a space between the cylinder 120 and the piston 130. The oil pumped from the oil supply device 160 may be supplied to the space between the cylinder 120 and the piston 130 via the oil supply pipe 165, and perform cooling and lubricating operations.

FIG. 2 is an enlarged view of a portion “A” of the linear compressor of FIG. 1. FIGS. 3 and 4 are cross-sectional views illustrating a reciprocating motion of the permanent magnet in an axial direction according to operation of a linear motor of the linear compressor of FIG. 1.

Referring to FIGS. 2 to 4, the outer stator 210 according to embodiments may include the stator core 211, in which the plurality of laminations may be stacked in the circumferential direction. The stator core 211 may be configured such that a first core 211a and a second core 211b are coupled at a coupling portion 211c.

An accommodation space, in which the bobbin 213 and the coil 215 may be disposed, may be defined in the stator core 211, and an opening 219 may be provided at a side of the accommodation space. That is, the first core 211a and the second core 211b may be coupled, such that the stator core 211 has the opening 219 at a central portion thereof to thereby have a C-shape.

The first core 211a may include a first stator magnetic pole 217 that acts with the permanent magnet 230. The second core 211b may include a second stator magnetic pole 218 that acts with the permanent magnet 230. The first stator magnetic pole 217 and the second stator magnetic pole 218 may be portions of the first and second cores 211a and 211b, respectively. The opening 219 may be a space between the first stator magnetic pole 217 and the second magnetic pole 218.

The permanent magnet 230 may be formed of a ferrite material, which may be relatively inexpensive. The permanent magnet 230 may include multiple poles 231, 232 and 233, polarities of which may be alternately arranged. The multiple poles 231, 232, and 233 may include a first pole 231, a second pole 232, and a third pole 233, which may be coupled to each other.

When a current is applied to the motor assembly 200, a current may flow through the coil 215, a magnetic flux may be formed around the coil 215 by the current flowing through the coil 215, and the magnetic flux may flow along the outer stator 210 and the inner stator 220 while forming a closed circuit. The first stator magnetic pole 217 may form one of an N-pole or a S-pole, and the second stator magnetic pole 218 may form the other one of the N-pole or the S-pole (see solid line arrow A in FIG. 5).

The multiple poles 231, 232, and 233 (permanent magnet 230) may linearly reciprocate in an axial direction between the outer stator 210 and the inner stator 220 by means of an interaction force of the magnetic flux flowing through the outer stator 210 and the inner stator 220 and the magnetic flux formed by the multiple poles 231, 232, and 233 (permanent magnet 230). The piston 130 may move inside the cylinder 120 by motions of the multiple poles 231, 232, and 233 (permanent magnet 230).

When the current flowing through the coil 215 changes its direction, a direction of the magnetic flux passing through the outer stator 210 and the inner stator 220 may be changed. That is, in the above-described example, polarities of the first and second stators 217 and 218 may be interchanged. Therefore, a movement direction of the multiple poles 231, 232, and 233 (permanent magnet 230) may be reversed, and therefore, a movement direction of the piston 130 may also be changed. In this way, as the direction of the magnetic flux is changed repetitively, the piston 130 may linearly reciprocate.

FIG. 3 illustrates a mode in which first spring 151 is elongated when the multiple poles 231, 232, and 233 (permanent magnet 230) move in a first direction. FIG. 4 illustrates a mode in which the second spring 151 is compressed when the multiple poles 231, 232, and 233 (permanent magnet 230) move in a second direction.

The multiple poles 231, 232, and 233 (permanent magnet 230) and the piston 130 may linearly reciprocate by repeating the modes of FIGS. 3 and 4. For example, when the permanent magnet 230 is at a position shown in FIG. 3, the piston 130 is positioned at a bottom dead center (BDC) position, and when the permanent magnet 230 is at a position shown in FIG. 4, the piston 130 is positioned at a top dead center (TDC) position.

The term BDC may refer to a position when the piston 130 is at a lowest position inside the cylinder 120, that is, a position when the piston 130 is disposed farthest away from the compression space P. The term TDC may refer to a position when the piston 130 is at a highest position inside the cylinder 120, that is, a position when the piston 130 is disposed closest to the compression space P.

Hereinafter, a structure of the motor assembly 200 will be more fully described with reference to the drawings.

FIGS. 5 and 6 are cross-sectional views schematically illustrating the linear motor of FIGS. 3-4. Referring to FIG. 5, according to an embodiment, the first stator magnetic pole 217 of the first core 211a and the second stator magnetic pole 218 of the second core 211b may be disposed apart from each other with respect to the opening 219.

In more detail, a first tip 217a may be provided at an end of the first stator magnetic pole 217, and a second tip 218a may be provided at or on the second stator magnetic pole 218. The opening 219 may be formed by a separation between the first tip 217a and the second tip 218a. An axial direction length of the opening 219 may be defined as “T”, which may be a distance between the first tip 217a and the second tip 218a.

A gap between the outer stator 210 and the inner stator 220 may be an air gap. More specifically, the air gap may be a portion at which the magnetic flux generated in the outer stator 210 and the magnetic flux generated in the permanent magnet 230 meet, and thus, a thrust for the permanent magnet 230 may be formed by interaction of the magnetic fluxes. A height of the air gap may be defined as “G”. As the permanent magnet 230 reciprocates in the air gap, a thickness MT of the permanent magnet 230 may be formed smaller than the height G of the air gap.

As described in FIG. 5, when a current is applied to the coil 215 so as to form the magnetic flux in a clockwise direction, a portion of the magnetic flux may pass through the first stator magnetic pole 217, the second stator magnetic pole 218, the permanent magnet 230, and the inner stator 220. A first portion of the magnetic flux may be referred to as an “air gap magnetic flux”. The air gap magnetic flux may generate a thrust for the permanent magnet 230.

A second portion of the magnetic flux may be formed to pass through the first stator magnetic pole 217 from the second stator magnetic pole 218. The other portion of the magnetic flux is not helpful for generating a thrust to act on the permanent magnet 230, and thus, may be referred to as “leakage magnetic flux (dotted arrow).

A relationship between the height G of the air gap and the axial direction length T of the opening 219 is provided hereinbelow.

As described above, the magnetic flux may include the air gap magnetic flux and the leakage magnetic flux. When one of the air gap magnetic flux or the leakage magnetic flux increases, the other magnetic flux may decrease, relatively.

A ratio between the air gap magnetic flux and the leakage magnetic flux may vary with a ratio between the height G of the air gap and the axial direction length T of the opening 219. In more detail, as the gap between the outer stator 210 and the inner stator 220 increases as the height G of the air gap increases, a magnitude of the magnetic flux flowing into the inner stator 220 from the outer stator 210 decreases. That is, the magnitude of the air gap magnetic flux decreases.

As the gap between the outer stator 210 and the inner stator 220 decreases as the axial direction length T of the opening 219 decreases, a magnitude of the magnetic flux flowing from one of the inner stator 220 or the outer stator 210 into the other stator increases. That is, the magnitude of the air gap magnetic flux increases.

Therefore, to reduce the leakage magnetic flux and increase the air gap magnetic flux relatively, the axial direction length T of the opening 219 may be equal to or greater than the height G of the air gap. That is, T≧G may be established. Related effects may be confirmed in FIGS. 7A to 7C.

FIG. 7A illustrates magnetic flux in a linear motor having a magnetic pole tip distance of T1. FIG. 7B illustrates magnetic flux in a linear motor having a magnetic pole tip distance of T2. FIG. 7C illustrates a magnitude of a leakage magnetic flux in the linear motor of FIGS. 7A and 7B.

FIG. 7A illustrates a flow of the magnetic flux generated in the motor assembly 200 when the axial direction length of the opening 219 is T1, and FIG. 7B illustrates a flow of the magnetic flux generated in the motor assembly 200 when the axial direction length of the opening 219 is T2. T2 is greater than T1. For example, T1 may be approximately 3 mm and T2 may be approximately 9 mm. The air gaps in FIGS. 7A and 7B may have a same height G.

In FIGS. 7A and 7B, when a point where a first line in a radial direction, which penetrates through a center of the opening 219, meets the inner stator 220 is defined as a zero point (O), a point intersecting with a second line that connects the first and second stator magnetic poles 217 and 218 may be defined as a first point (P1). A distance between the zero point O and the first point P1 may correspond to the height of the air gap. Also, when a point on the bobbin 213 at which the first line intersects with the coupling part 211c is defined in as a second point (P2), FIG. 7C illustrates a magnetic flux that leaks from the motor assembly 200.

In more detail, as illustrated in FIG. 7A, in the height G of the air gap, if the opening 219 has a relatively small axial length, a leakage magnetic flux of the magnetic flux generated in the outer stator 210, for example, a leakage magnetic flux of a positive (+) pole may significantly increase from the zero point O to the first point P1 to form a maximum leakage magnetic flux at the point P1. The leakage magnetic flux may gradually decrease from the first point P1 to the second point P2.

Also, the leakage magnetic flux of the positive (+) pole may be switched in direction to a negative (−) pole to significantly increase. Away from the second point P2, the magnitude of the leakage magnetic flux may have an approximately constant value (a constant magnetic flux). Herein, the terms “positive (+) pole” and “negative (−) pole” may denote leakage magnetic flux directions opposite to each other. Also, the constant magnetic flux may be a maximum magnetic flux of the negative (−) pole.

On the other hand, as illustrated in FIG. 7B, in the height G of the air gap, if the opening 219 has a relatively large axial length, a leakage magnetic flux of the magnetic flux generated in the outer stator 210, for example, a leakage magnetic flux of a positive (+) pole may smoothly increase from the zero point O to the first point P1 to form a maximum leakage magnetic flux at the first point P1. The maximum magnetic flux in FIG. 7B may have a value relatively less than that in FIG. 7A. The leakage magnetic flux may gradually decrease from the first point P1 to the second point P2.

The leakage magnetic flux of the positive (+) pole may be switched in direction to the negative (−) pole to significantly increase. Away from the first point P2, the magnitude of the leakage magnetic flux may have an approximately constant value (a constant magnetic flux). However, the constant magnetic flux in FIG. 7B may have a value relatively greater than that in FIG. 7A.

As illustrated in FIG. 7C, with respect to the height G of the predetermined air gap, the more the opening increases in length T, the more the maximum leakage magnetic flux, that is, the maximum magnetic fluxes of the positive (+) and negative (−) poles decrease. Thus, a larger amount of thrust may be provided to the permanent magnet 230 to improve the operation efficiency of the motor assembly 200.

FIG. 8 is a cross-sectional view of a linear motor illustrating a position of a permanent magnet when a piston is positioned at the BDC position, according to an embodiment. FIG. 9 is a cross-sectional view of a linear motor illustrating a position of a permanent magnet when a piston is positioned at the TDC position, according to an embodiment.

Referring to FIGS. 5, 6, 8, and 9, the permanent magnet according to embodiments may include the plurality of poles 231, 232, and 233, which may be alternately arranged in polarity. The plurality of poles 231, 232, and 233 may include the first pole 231, the second pole 232 coupled to the first pole 231, and the third pole 233 coupled to the second pole 232.

The second pole 232 may be referred to as a “central magnetic pole”, and the first and third poles 231 and 233 may be referred to as “both end magnetic poles” in that the second pole 232 is disposed between the first and third poles 231 and 233.

The central magnetic pole 232 may have a length greater than a length of each of the both end magnetic poles 231. 233. A length of the central magnetic pole 232 may be defined as a length “MC”, a length of the first pole 231 may be defined as a length “MF”, and a length of the third pole 233 may be defined as a length “MR”. The lengths MF and MR may have the same value. On the other hand, the lengths MF and MR may have values different from each other so as to increase the thrust according to a design of the compressor.

A first interface surface 235 may be disposed between the first pole 231 and the second pole 232, and a second interface surface 236 may be disposed between the second pole 232 and the third pole 233. The first interface surface 235 may be reciprocated within a range which is not out of a range of the first stator magnetic pole 217 with respect to a center of the first stator magnetic pole 217, and the second interface surface 236 may be reciprocated within a range which is not out of a range of the second stator magnetic pole 218 with respect to a center of the second stator magnetic pole 218.

That is, the first interface surface 235 may be reciprocated in an axial direction between both ends of the first stator magnetic pole 217 with respect to the center of the first stator magnetic pole 217. Also, the second interface surface 236 may be reciprocated in the axial direction between both ends of the second stator magnetic pole 218 with respect to the center of the second stator magnetic pole 218.

A force (thrust) pulled and pushed between polarities (an N pole or an S pole) of the first stator magnetic pole 217 and polarities of the first and second poles 231 and 232 may occur. Also, as the force pulled and pushed between polarities (an N pole or an S pole) of the second stator magnetic pole 217 and polarities of the second and third poles 231 and 232 may occur, the permanent magnet may be reciprocated.

The first and second poles 231 and 233 may have the same polarity. The second pole 232 disposed between the first and third poles 231 and 233 may have a polarity opposite to a polarity of each of the first and second poles 231 and 233. For example, if each of the first and third poles 231 and 233 is a N pole, the second pole 232 may be a S pole. If each of the first and third poles 231 and 233 is a S pole, the second pole 232 may be a N pole.

A structure, in which two poles acting on each other with respect to the first stator magnetic pole 217 are disposed, and the other two poles acting on each other with respect to the second stator magnetic pole 218 are disposed, may be provided to generate a larger amount of thrust on the permanent magnet 230. The two poles acting on each other may have the same length, and also, the other two poles may have the same length. However, when considering the limited inner space of the compressor 10, a permanent magnet having four poles may be limited in arrangement. That is, if the four poles are arranged, the permanent magnet may increase in length, and thus, the linear motor may increase in length.

Thus, the permanent magnet 230 according to embodiments may have two poles positioned at a central portion to serve as one pole and three poles that are alternately arranged. Thus, the pole disposed at the central portion, that is, the central magnetic pole may have a length greater than a length of each of both end magnetic poles. Thus, when compared to a case in which four poles are arranged, a compact structure may be realized. In addition, both end magnetic poles may be reduced by a half or less in length. That is, the following relational expression may be defined.

MF or MR≦MC≦2*MF or 2*MR

Also, the central magnetic pole may have a length MC less than a sum of the length MF of the first pole 231 and the length MR of the second pole 232.

In summary, the greater the length of the central magnetic pole increases, the more the mutual acting force with the first stator magnetic pole 217 or the second stator magnetic pole 218 increases. Thus, the thrust may increase.

However, when considering a whole size of the linear motor, that is, when considering miniaturization or compactification, if the forgoing relational expression is satisfied, the two effects, that is, increase of the thrust and the compactification of the compressor may be achieved.

The length P of the first stator magnetic pole 217 or the second stator magnetic pole 218 in the axial direction may be determined on the basis of stroke S of the piston 130 when a maximum load is applied to the compressor 10. The stroke S of the piston 130 may be a distance between the TDC position and the BDC position.

When the piston 130 is positioned at the BDC position, a first end (a left end in FIG. 8) of the first pole 231 may be disposed outside the first core 211a. The first end of the first pole 231 may be defined as an end opposite the first interface surface 235, which defines a second end of the first pole 231.

Also, outside of the first core 211a may be understood as an area defined as outside of a virtual line in a radius direction, which passes through an outer end of the first core 211s. Also, the terms “outside” or “outward direction” may refer to a direction extending away from the center of the opening 219, and “inside or inward direction” may refer to a direction toward or closer to the center of the opening 219.

Also, when the piston 130 is positioned at the TDC position, the first end of the first pole 231 may be disposed inside the first core 211a. That is, the first end of the first pole 231 may be disposed within a region, in which the first core 211a is disposed, with respect to the axial direction.

However, the first end of the first pole 231 may not move inside of the first stator magnetic pole 217. That is, the first end of the first pole 231 may be disposed at a position corresponding to an end of the first stator magnetic pole 217 or disposed outside of the first stator magnetic pole 217. Herein, the phrase inside of the first stator magnetic pole 217 may be refer to a space between virtual lines in the radial direction, which pass through both ends of the first stator magnetic pole 217.

The first stator magnetic pole 217 may have the same axial length as the second stator magnetic pole 218. In more detail, an axial length P of the first or second stator magnetic pole 217 or 218 may be determined by adding a control error or mechanical error to the stroke S of the piston 130. For example, if the stroke S is about 16 mm, the length P may be set to about 18 mm.

If the length P is less than the stroke S, the first or second interface surface 235 or 236 may move outward from the first or second stator magnetic pole 217 or 218. Thus, the force pushed and pulled between the magnetic poles 217 and 218 and the permanent magnet 230 may be reduced. Thus, the length P may be determined to be greater than the stroke S.

A relational expression between the length P and the length of the first pole 231 or the second pole 233 is defined. When each of the first and second interface surfaces 235 and 236 is reciprocated with respect to the center of each of the first and second stator magnetic poles 217 and 218, if both ends of both end magnetic poles 231 and 233 move into both ends of the first and second stator magnetic poles 217 and 218, the thrust applied to the permanent magnet may be reduced. That is, if at least a portion of both end magnetic poles 231 and 233 is not disposed outside both ends of the first and second stator magnetic poles 217 and 218, the mutual acting force between the magnetic fluxes of the outer stator 210 and the permanent magnet 230 may be weakened.

Thus, when considering the thrust for generating the reciprocating motion of the permanent magnet 230, the length MF of the first pole 231 and the length MR of the third pole 233 may be greater than the length P of each of the first and second stator magnetic poles 217 and 218.

However, the length MF of the first pole 231 and the length MR of the third pole 233 are factors that have an influence on a whole length of the permanent magnet 230. Thus, the lengths MF and MR may be used as a limiting factor to realize miniaturization of the linear compressor 10.

Thus, the current embodiment proposes the following relational expression.

MF or MR≧0.9*P

According to the above-described relational expression, if the length MF of the first pole 231 and the length MR of the third pole 233 are within a range similar to the length P of each of the first and second stator magnetic poles 217 and 218, the thrust may be reduced, and the linear compressor 10 may be compact.

FIG. 10 is a graph showing a magnitude of a thrust generated according to lengths of magnetic poles at both ends, in the permanent magnet according to an embodiment. FIG. 11 is a graph showing a magnitude of a cogging force according to lengths of magnetic poles at both ends, in a permanent magnet according to an embodiment.

Referring to FIG. 10, a change in thrust with respect to a same input current according to a length of each of both end magnetic poles 231 and 233 according to embodiments is illustrated. The horizontal axis in FIG. 10 illustrates a position of the permanent magnet 230. A zero point (O) on the horizontal axis may be defined as a state in which each of the first and second interface surfaces 235 and 236 is disposed at the center of each of the first and second stator magnetic poles 217 and 218. This state may be understood as a state in which the permanent magnet is disposed at the zero point.

Also, a negative (−) position may be defined as a case in which the permanent magnet 230 moves from the zero point in a first direction, and a positive (+) position may be defined as a case in which the permanent magnet 230 moves from the zero point in a second direction. Along the horizontal axis, the more a critical value in position increases, the greater a distance from the zero point.

Referring to FIG. 10, when the permanent magnet 230 is disposed at the zero point, the thrust may be maximally generated. Also, the more each of both end magnetic poles 231 and 233 increases in length, the more the maximum thrust may increase.

For example, under a same condition in which the central magnetic pole 232 has a length of about 24 mm, if each of both end magnetic poles 231 and 233 has a length of about 19 mm, the maximum thrust may be F1 N. Also, if each of both end magnetic poles 231 and 233 has a length of about 17 mm, the maximum thrust may be F2 N. Here, the maximum thrusts may be defined as follow: F1>F2>F3

Also, the more each of both end magnetic poles 231 and 233 increases in length, the more a magnitude of the thrust may significantly increase on the whole. That is, as the more each of both end magnetic poles 231 and 233 increase in length, the more the magnitude of the thrust applied to the permanent magnet 230 increases, operation efficiency of the compressor may be improved.

FIG. 11 illustrates variations or a change in peak value of a force due to magnetic reluctance of the permanent magnet 230, that is, a cogging force according to length of each of both end magnetic poles 231 and 233 according to an embodiment.

The magnetic reluctance or cogging force of the permanent magnet 230 may be understood as electrical resistance with respect to an mutual acting force between the magnetic flux generated in the outer stator 210 and the magnetic flux of the permanent magnet 230. The cogging force may increase to a peak value according to a position (position (+) or negative (−) position) of the permanent magnet or vary in a direction in which the peak value decreases. In more detail, when the permanent magnet 230 is disposed at the positive (+) position, the cogging force may be formed in a positive (+) direction and have a peak value at a predetermined position. On the other hand, when the permanent magnet 230 is disposed at the negative (−) position, the cogging force may be formed in a negative (−) direction and have a peak value at a predetermined position. Here, the positive (+) and negative (−) directions of the cogging force may denote forces acting in directions opposite to each other.

The more the peak value increases, the more the force applied to the springs 151 and 155 may increase. Thus, it may be difficult to control the linear motor 200.

Referring to FIG. 11, the more each of both end magnetic poles 231 and 233 increases in length, the more the positive (+) and negative (−) peak value of the cogging force may decrease. Thus, the linear motor 200 may be easily controlled.

For example, under the same condition in which the central magnetic pole 232 has a length of about 24 mm, if each of both end magnetic poles 231 and 233 has a length of about 19 mm, a peak value of the cogging force may be about 15 N. Also, if each of both end magnetic poles 231 and 233 has a length of about 18 mm, a peak value of the cogging force may be about 20 N. Also, if each of both end magnetic poles 231 and 233 has a length of about 17 mm, a peak value of the cogging force may be about 27 N.

FIG. 12 is a graph showing a magnitude of a thrust generated according to a length of a central magnetic pole, in the permanent magnet according to an embodiment. FIG. 13 is a graph showing variations in a cogging force according to a length of a central magnetic pole, in the permanent magnet according to an embodiment.

Referring to FIGS. 12 and 13, the more each of both end magnetic poles increase in length, the more the thrust may increase, and the peak value of the cogging force may decrease. As described with reference to FIGS. 10 and 11, as the thrust increases, operation efficiency of the linear motor may be improved. Also, as the peak value of the cogging force decreases, the control reliability of the linear motor may be improved.

Referring to FIG. 12, it can be seen that the thrust increases as the central magnetic pole increases in length MC under the condition in which both end magnetic poles have the same length. For example, under the condition in which the lengths MF and MR are about 18 mm, it is seen that the thrust (the maximum thrust: 85 V/m/s) when the length MC is about 26 mm may be greater than that (the maximum thrust: 83 V/m/s) when the length MC is about 24 mm.

Referring to FIG. 13, it is seen that the peak value of the cogging force decreases as the central magnetic pole increases in length MC under the condition in which both end magnetic poles may have the same length. For example, under a condition in which the lengths MF and MR are about 18 mm, it is seen that the peak value (about 13 N) of the cogging force when the length MC is about 26 mm may be less than that (about 20 N) of the cogging force when the length MC is about 24 mm.

According to embodiments, as the permanent magnet may include a magnet having three polarities, an amount of a magnetic flux generated may be increased. Also, the increased magnetic flux of the permanent magnet may interact with a magnetic flux generated from the outer stator, thereby increasing a thrust exerted on the piston.

Further, as a length of the opening between the magnetic poles disposed in the outer stator may be maintained equal to or greater than the air gap between the outer stator and the inner stator, it is possible to reduce a leaked magnetic flux and increase a magnitude of the magnetic flux generated from the outer stator and oriented toward the inner stator. Accordingly, the air gap magnetic flux and the magnetic flux of the permanent magnet may interact with each other, thereby generating higher thrust.

Moreover, in the permanent magnet having three poles, a length of the both-end magnetic pole may be a predetermined proportion of a length of magnetic pole of the outer stator, thus making it possible to increase a generated thrust in comparison with a current applied to the linear motor and also reduce a cogging force (or torque).

Additionally, in the permanent magnet having three poles, a length of the central magnetic pole may be greater than lengths of the both-end magnetic poles, and may be twice or less than the lengths of the both-end magnetic poles. This also enables a generated thrust to be increased and a cogging force (or torque) to be reduced.

Also, the piston and the cylinder may be made of a nonmagnetic material, such as aluminum or aluminum alloy, and thus, magnetic flux may be prevented from being leaked to the outside through the piston or cylinder. In addition, the permanent magnet may be made of an inexpensive ferrite material, thereby reducing a manufacturing cost for the motor assembly.

Embodiments disclosed herein provide a linear compressor provided with a linear motor capable of generating a sufficient force (a thrust).

Embodiments disclosed herein provide a linear compressor that may include a cylinder that forms a compression space for a refrigerant; a piston that reciprocatably moves in an axial direction inside the cylinder; and a linear motor that supplies a power to the piston. The linear motor may include an outer stator including a first stator magnetic pole, a second stator magnetic pole, and an opening defined between the first stator magnetic pole and the second stator magnetic pole; an inner stator disposed apart from the outer stator; and a permanent magnet movably disposed in an air gap between the outer stator and the inner stator, and having three poles. The three poles may include two both-end magnetic poles, and a central magnetic pole disposed between the two both-end magnetic poles. The central magnetic pole may have a length greater than the both-end magnetic poles.

A length of the central magnetic pole may be twice or less than that of any one of the two both-end magnetic poles. A length of the central magnetic pole may be equal to or less than a sum of, lengths of the two both-end magnetic poles. An axial direction length of the opening may be equal to or greater than a radial direction height of the air gap.

The piston may be moveable by a stroke between a top dead center (TDC) and a bottom dead center (BDC), and a length of the first stator magnetic pole or the second stator magnetic pole may be equal to or less than the stroke. A length of any one of the two both-end magnetic poles may be approximately 90% or more of a length of the first stator magnetic pole or second stator magnetic pole.

The two both-end magnetic poles may include a first pole coupled to the central magnetic pole at a first interface, and a second pole coupled to the central magnetic pole at a second interface. The first interface may reciprocate in an axial direction between both ends of the first stator magnetic pole, based on a center of the first stator magnetic pole, and the second interface may reciprocate in an axial direction between both ends of the second stator magnetic pole, based on a center of the second stator magnetic pole.

The first pole may include an end at a position facing the first interface, and the end of the first pole may be positioned outside the outer stator when the piston is positioned at the BDC. The end of the first pole may be positioned at an end of or outside the first stator magnetic pole when the piston is positioned at the TDC.

The two both-end magnetic poles may include a first pole coupled to one side of the central magnetic pole, and at least a portion of the first pole may be positioned in an air gap between the first stator magnetic pole and the inner stator. The two both-end magnetic poles may include a second pole coupled to the other side of the central magnetic pole, and at least a portion of the second pole may be positioned in an air gap between the second stator magnetic pole and the inner stator.

The opening may be defined between a tip of the first stator magnetic pole and a tip of the second stator magnetic pole, at one side of an accommodation space for accommodating a coil.

The permanent magnet may be made of a ferrite material. The piston and the cylinder may be made of aluminum or aluminum alloy.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

Claims

1. A linear compressor, comprising: a cylinder that forms a compression space for a refrigerant;a piston that reciprocates in an axial direction inside of the cylinder; anda linear motor that supplies power to the piston, wherein the linear motor comprises: an outer stator comprising a first stator magnetic pole, a second stator magnetic pole, and an opening defined between the first stator magnetic pole and the second stator magnetic pole;an inner stator disposed apart from the outer stator to form an air gap therebetween; anda permanent magnet movably disposed in the air gap between the outer stator and the inner stator and having three poles, wherein the three poles include: two end magnetic poles; anda central magnetic pole disposed between the two end magnetic poles, wherein the piston is moveable by a stroke between a top dead center position and a bottom dead center position, and wherein a length of the first stator magnetic pole or the second stator magnetic pole is greater than a length of the stroke.

2. The linear compressor according to claim 1, wherein the central magnetic pole has a length greater than a length of any one of the two end magnetic poles.

3. The linear compressor according to claim 2, wherein the length of the central magnetic pole is twice or less than the length of the any one of the two end magnetic poles.

4. The linear compressor according to claim 1, wherein a length of the central magnetic pole is equal to or less than a sum of lengths of the two end magnetic poles.

5. The linear compressor according to claim 1, wherein an axial direction length of the opening is equal to or greater than a radial direction height of the air gap.

6. The linear compressor according to claim 1, wherein a length of any one of the two end magnetic poles is approximately 90% or more of a length of the first stator magnetic pole or the second stator magnetic pole.

7. The linear compressor according to claim 1, wherein the two end magnetic poles comprise: a first pole coupled to the central magnetic pole at a first interface; anda second pole coupled to the central magnetic pole at a second interface.

8. The linear compressor according to claim 7, wherein the first interface reciprocates in an axial direction between both ends of the first stator magnetic pole, based on a center of the first stator magnetic pole, and the second interface reciprocates in an axial direction between both ends of the second stator magnetic pole, based on a center of the second stator magnetic pole.

9. The linear compressor according to claim 7, wherein the first pole comprises an end at a position that faces the first interface, and wherein the end of the first pole is positioned outside of the outer stator when the piston is positioned at the bottom dead center position.

10. The linear compressor according to claim 9, wherein the end of the first pole is positioned at an end of or outside of the first stator magnetic pole when the piston is positioned at the top dead center position.

11. The linear compressor according to claim 1, wherein the two end magnetic poles comprise a first pole coupled to a first side of the central magnetic pole, and wherein at least a portion of the first pole is positioned in the air gap between the first stator magnetic pole and the inner stator.

12. The linear compressor according to claim 11, wherein the two end magnetic poles comprise a second pole coupled to a second side of the central magnetic pole, and wherein at least a portion of the second pole is positioned in the air gap between the second stator magnetic pole and the inner stator.

13. The linear compressor according to claim 1, wherein the opening is defined between a tip of the first stator magnetic pole and a tip of the second stator magnetic pole, at a side of an accommodation space that accommodates a coil.

14. The linear compressor according to claim 1, wherein the piston and the cylinder are made of aluminum or aluminum alloy.

15. A linear compressor, comprising: a cylinder that forms a compression space for a refrigerant;a piston that reciprocates in an axial direction inside of the cylinder; anda linear motor that supplies power to the piston, wherein the linear motor comprises: an outer stator comprising a first stator magnetic pole, a second stator magnetic pole, and an opening defined between the first stator magnetic pole and the second stator magnetic pole;an inner stator disposed apart from the outer stator to form an air gap therebetween; anda permanent magnet movably disposed in the air gap between the outer stator and the inner stator and having three poles, wherein the three poles include: two end magnetic poles; anda central magnetic pole disposed between the two end magnetic poles, wherein the piston is moveable by a stroke between a top dead center position and a bottom dead center position, wherein a length of the first stator magnetic pole or the second stator magnetic pole is greater than a length of the stroke, and wherein the permanent magnet is made of a ferrite material.

16. The linear compressor according to claim 15, wherein the central magnetic pole has a length greater than a length of any one of the two end magnetic poles.

17. The linear compressor according to claim 15, wherein a length of the central magnetic pole is equal to or less than a sum of lengths of the two end magnetic poles.

18. The linear compressor according to claim 15, wherein an axial direction length of the opening is equal to or greater than a radial direction height of the air gap.

19. The linear compressor according to claim 15, wherein a length of any one of the two end magnetic poles is approximately 90% or more of a length of the first stator magnetic pole or the second stator magnetic pole.

20. The linear compressor according to claim 15, wherein the two end magnetic poles comprise: a first pole coupled to the central magnetic pole at a first interface; anda second pole coupled to the central magnetic pole at a second interface.

21. The linear compressor according to claim 20, wherein the first interface reciprocates in an axial direction between both ends of the first stator magnetic pole, based on a center of the first stator magnetic pole, and the second interface reciprocates in an axial direction between both ends of the second stator magnetic pole, based on a center of the second stator magnetic pole.

22. The linear compressor according to claim 20, wherein the first pole comprises an end at a position that faces the first interface, and wherein the end of the first pole is positioned outside of the outer stator when the piston is positioned at the bottom dead center position.

23. The linear compressor according to claim 22, wherein the end of the first pole is positioned at an end of or outside of the first stator magnetic pole when the piston is positioned at the top dead center position.

24. The linear compressor according to claim 15, wherein the two end magnetic poles comprise a first pole coupled to a first side of the central magnetic pole, wherein at least a portion of the first pole is positioned in the air gap between the first stator magnetic pole and the inner stator, and wherein the two end magnetic poles comprise a second pole coupled to a second side of the central magnetic pole, and wherein at least a portion of the second pole is positioned in the air gap between the second stator magnetic pole and the inner stator.

25. The linear compressor according to claim 24, wherein the piston and the cylinder are made of aluminum or aluminum alloy.