Patent Publication Number: US-2013243626-A1

Title: Motor for compressor and compressor having the same

Description:
TECHNICAL FIELD 
     The present disclosure relates to a motor for a compressor employing an aluminum coil. 
     BACKGROUND ART 
     In general, small home alliances, such as a refrigerator, an air conditioner and the like, employ a compressor for compression of a refrigerant. An induction motor is widely known as a motor for the compressor, namely, a driving source of the compressor. The induction motor includes a stator on which a coil is wound, a rotor having a conductor in form of a squirrel case and rotatably inserted into the stator, and a rotation shaft pressed into the center of the rotor to transfer, to a compression unit of the compressor, a rotational force, which is generated by interaction between a rotating magnetic field by an alternating current (AC) flowing on the coil of the stator and an induced current generated in the rotor. 
     Each of the stator and the rotor may be formed by laminating several sheets of cores and welding them. The core includes a yoke portion formed in an approximately annular shape to define a flow path of a magnetic flux, a plurality of tooth portions protruding from an inner circumferential surface of the yoke portion by predetermined intervals from one another and having the coil wound thereon, and slot portions recessed between the adjacent tooth portions in a cutting manner. 
     For the coil, copper (Cu) with high conductivity and relatively low price is widely used. For reference, Argentums (Ag) is a metal exhibiting the highest conductivity but is expensive, so it is not used for the coil for the compressor motor, which is applied to the home electric devices. However, since the copper is not largely cheap, an aluminum exhibiting high conductivity as compared to its price is being used in recent time. Here, the aluminum is used for both main coil and sub coil forming a winding coil or for one of the main coil and the sub coil. 
     Here, a coil (magnetic wire) drawn out of each of the main coil and the sub coil is coated with an insulation layer. Hence, to make a current flow, the insulation layer should be removed or a connector terminal should penetrate into the insulation layer to directly contact the copper. However, the removing method for the insulation layer requires complicated processes and high investment, and is uneasy to ensure quality. Therefore, a pressing method, in which a serration shape is formed at a connector terminal, such that the serration penetrates into the insulation layer upon pressing the connector terminal, so as to directly contact the copper to allow for a current flow, has been widely used. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The pressing method using the serration may be useful for a material, such as copper, having a high tensile strength. However, when a material, such as aluminum, having a low tensile strength is pressed onto the terminal, a cut-off defect has been caused due to a low tensile strength at the pressed portion. That is, a tensile force of the copper coil is 24.2 kgf·cm whereas a tensile force of the aluminum coil is merely 11.42 kgf·cm. Accordingly, upon use of the terminal having the serration, the cut-off defect may be frequently caused. 
     Solution to Problem 
     Therefore, to obviate those problems, an aspect of the detailed description is to provide a motor for a compressor capable of preventing an aluminum coil from being cut off even if the aluminum coil is connected to a terminal by a pressing method, and a compressor having the same. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a motor for a compressor including a stator, a winding coil wound on the stator, the winding coil formed by coating an insulation layer made of an insulating material on an outer circumferential surface of a conductor having at least a part made of aluminum, and terminals each pressed onto the winding coil such that at least a part penetrates into the insulating layer to be connected to the conductor, wherein a part of the winding coil is connected to the terminal together with reinforcing wire. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a reciprocal compressor including a hermetic container, a driving motor installed within the hermetic container to generate a rotational force, a cylinder block installed within the hermetic container to form a compression space, a connecting rod having one end coupled to a rotational shaft of the driving motor to convert a rotating motion into a linear motion, a piston coupled to the other end of the connecting rod to compress a refrigerant while linearly reciprocating within the compression space of the cylinder block, and a valve assembly coupled to the cylinder block to restrict suction and discharge of the refrigerant, wherein a part of a winding coil of the driving motor is pressed onto terminals together with reinforcing wires made of a material having a higher tensile strength than aluminum. 
     Advantageous Effects of Invention 
     As the driving motor having the aluminum coil is employed, a fabricating cost of the driving motor can be reduced that much, accordingly, a production cost of the reciprocal compressor can be remarkably reduced without great change in the efficiency thereof, as compared with the copper coil wound. The efficiency of the reciprocal compressor as compared with the price of the compressor can be enhanced by virtue of an appropriate design of the individual cross section, the entire cross section or the number of the main slot portions and the sub slot portions. 
     When the main coil or the sub coil of the winding coil of the driving motor is formed of aluminum with a low tensile strength and the winding coil is pressed onto terminals having serrations for connection, the reinforcing wires with a relatively great tensile strength, such as copper, can be pressed onto the terminals together with the aluminum, thereby preventing in advance the aluminum coil from being cut off, resulting in enhancement of assembly reliability of the reciprocal compressor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a disassembled perspective view of a motor for a compressor in accordance with this specification; 
         FIG. 2  is a planar view of the motor for the compressor shown in  FIG. 1 ; 
         FIG. 3  is a perspective view showing a stator of the motor for the compressor shown in  FIG. 1 ; 
         FIG. 4  is a planar view showing the stator of the motor for the compressor shown in  FIG. 1 ; 
         FIG. 5  is a planar view showing a connected state between an aluminum coil and a lead wire in the motor for the compressor shown in  FIG. 1 ; 
         FIGS. 6 and 7  are a planar view and a front view schematically showing one exemplary embodiment for connecting a terminal to a sub coil made of aluminum according to  FIGS. 5 ; and 
         FIG. 8  is a longitudinal sectional view showing a reciprocal compressor having the motor for the compressor shown in  FIG. 1 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described below in detail with reference to the accompanying drawings where those components are rendered the same reference number that are the same or are in correspondence, regardless of the figure number, and redundant explanations are omitted. In describing the present invention, if a detailed explanation for a related known function or construction is considered to unnecessarily divert the gist of the present invention, such explanation has been omitted but would be understood by those skilled in the art. The accompanying drawings are used to help easily understood the technical idea of the present invention and it should be understood that the idea of the present invention is not limited by the accompanying drawings. The idea of the present invention should be construed to extend to any alterations, equivalents and substitutes besides the accompanying drawings. 
     A motor  200  for a compressor according to the present disclosure, as shown in  FIGS. 1 and 2 , may include a stator  210  secured with a hermetic container of the compressor and having a coil  240  wound thereon, a rotor  220  rotatably inserted into the stator  210  and having conductors  250  therein, and a rotation shaft  230  press-fitted into the center of the rotor  220  to transfer a rotational force to a compression unit of the compressor. 
     The stator  210  may be implemented by laminating several sheets of cores by a predetermined height in an axial direction and welding them. The core may be provided with a rotor insertion hole  210   a  having an outer circumferential surface in an approximately rectangular shape (in some cases, similar to a circular shape) and an inner circumferential surface in form of an approximately circular shape. 
     The core may be provided with a yoke portion  211  connected to an outer periphery thereof in an approximately circumferential direction so as to define a flow path of a magnetic flux. The yoke portion  211  may be integrally formed, but formed in an arcuate shape according to a sheet metal work of the core, so as to be coupled together by an uneven coupling or welding. The yoke portion  211  may greatly affect efficiency of the motor. An entire available area of the yoke portion  211  may be appropriately decided depending on an inner diameter of the stator  210  and an entire area of a slot portion  213  to be explained later. 
     The core, as shown in  FIGS. 3 and 4 , may be provided with a plurality of tooth portions  212  located at a central portion thereof and protruding from an inner circumferential surface of the yoke portion  211  in a radial direction by predetermined intervals and having the coil wound thereon. The tooth portions  212  may be formed in a circumferential direction by approximately uniform intervals with interposing slot portions  213  therebetween, which will be explained later. The tooth portions  212  may have approximately the same width length B in a lengthwise direction, and the width length B of each of the tooth portions  212 , although depending on a capacity of the motor, may not be longer than approximately a length L of each tooth portion  212  in an radial direction. Outer sides of the tooth portions  212  may be connected to the neighboring tooth portions  212  to be curved with each other by a predetermined curvature R. 
     A ratio of the width length B of each of the tooth portions  212  to the curvature R between the tooth portions  212 , namely, a curvature R of a slot portion  213 , which will be explained later, may be involved to the efficiency of the motor for the compressor. That is, the motor  200  for the compressor may have an increased efficiency when the ratio (B/R) of the width length B of the tooth portion  212  to the curvature R of the slot portion  213  is lower. The range of the ratio (B/R) may preferably approximately higher than 1.05 and lower than 1.15. 
     A ratio (D/B) of an inner diameter D of the stator  210  to the width length B of the tooth portion  212  may also be involved to the efficiency of the motor for the compressor. That is, the motor  200  for the compressor may obtain an increased efficiency when the ratio (D/B) of the inner diameter D of the stator  210  to the width length B of the tooth portion  212  is higher, and the range of the ratio (D/B) may preferably approximately be higher than 13.9 and lower than 15.0. 
     A pole portion  212   a  may extend from an end of each tooth portion  212  at the side of the center thereof to have predetermined intervals from neighboring tooth portions  212 . The interval A between the pole portions  212   a  (or the interval between the tooth portions) should not be narrower than a diameter d of the coil  240  for facilitation of a winding work of the coil  240 . The interval A between the pole portions  212   a  may greatly affect the efficiency of the motor, and accordingly depend on the material of the coil  240 , the diameter d of the coil  240  and the number of slots of the stator  210 . For example, when the diameter of the coil is 0.5 mm, the interval A between the pole portions may preferably be less than about 1.73 mm for a 20-slot stator, about 2.10 mm for a 24-slot stator, and about 2.00 mm for a 28-slot stator. 
     The core may be provided with slot portions  213  each recessed in a cutting manner to define a space for insertion of the coil  240  therein and disposed at about a uniform interval. The slot portions  213  may be formed long in a radial direction upon a planar projection. Both side surfaces thereof may more extend from a central side toward an outer side, and an outer surface thereof may be curved outwardly. 
     The slot portion  213 , as shown in  FIGS. 3 and 4 , may include a plurality of main slot portions  213   a  on which a main coil is wounded, and a plurality of sub slot portions  213   b  on which a sub coil is wound. The main slot portions  213   a  and the sub slot portions  213   b  may be alternately formed in a circumferential direction with predetermined intervals. For example, as shown in  FIG. 4 , the plurality of main slot portions  213   a  may be formed in the circumferential direction, and the plurality of sub slot portions  213   b  may then be formed by a 90-degree phase difference. Afterwards, the plurality of main slot portions  213   a  may be formed again by a 90-degree phase difference, and in turn the plurality of sub slot portions  213   n  may be formed by a 90-degree phase difference. 
     A cross section of the main slot portions  213   a  may be greater than a cross section of the sub slot portions  213   b.  The cross sections of the main slot portions  213   a  and the sub slot portions  213   b  may be appropriately decided according to the number of turns of the coil in consideration of productivity of the motor. That is, for the main slot portion  213   a,  a ratio (S 1 /N) of the cross section S 1  of the main slot  213   a  to the number of turns N may be in the range of 2.18 to 2.22. Also, for the sub slot portion  213   b,  the ratio N/S 2  may be in the range of 1.85 to 1.89. Here, the cross section of the main slot portion  213   a  and the cross section of the sub slot portion  213   b  may be equally applied to a case where a copper coil is wound on the main slot portion  213   a  and an aluminum coil is wound on the sub slot portion  213   b  as well as a case where an aluminum coil is wound on both the main slot portion  213   a  and the sub slot portion  213   b.    
     The main slot portions  213   a  and the sub slot portions  213   b  may be formed to be the same as or different from each other in view of an individual cross section, an entire cross section and the number. These may be designed in consideration of an efficiency against the price of the coil wound on the motor. For example, when the coil  240  is the aluminum coil, the individual cross section or entire cross section and the number of the main slot portions  213   a  and the sub slot portion  213   b  may be increased as compared to those of the copper coil, but a relative ratio thereof may not be greatly different from the shape of a slot portion of a general motor. However, when the aluminum coil is wound on the main slot portions  213   a  and the copper coil is wound on the sub slot portions  213   b,  a diameter of the aluminum coil is increased more than a diameter of the copper coil, accordingly, the individual cross section or entire cross section and the number of the main slot portions  213   a  may be relatively increased as compared to the sub slot portions  213   b.  On the contrary, when the copper coil is wound on the main slot portions  213   a  and the aluminum coil is wound on the sub slot portions  213   b,  the individual cross section or entire cross section and the number of the sub slot portions  213   b  may be relatively increased as compared to the main slot portions  213   a.    
     The coil  240  wound on the stator  210  may be implemented by the aluminum (exhibiting 62.7% of conductivity) whose conductivity is not greatly lower than that of the copper (exhibiting 99.9% of conductivity), although it is actually lower than the conductivity of the copper, and especially, price of the aluminum is much cheaper than the copper. 
     The aluminum coil exhibits the lower conductivity than the copper coil and accordingly may lower the efficiency of the motor  200  for the compressor. Thus, to compensate for this, the diameter of the aluminum coil may preferably be approximately 25% thicker than that of the copper coil. 
     The aluminum coil has rigidity lower than the copper in view of its material characteristic. Hence, in order to maintain the rigidity of the coil, it may be preferable to prevent a thickness of an enamel layer coated as an insulation layer on an outer circumferential surface of the aluminum coil from being thinner than a thickness of at least an enamel layer coated on an outer circumferential surface of the copper coil. 
     The rigidity of the aluminum coil, which is lower than the copper in view of its material characteristic, may deteriorate a damping effect. Accordingly, noise may increase specifically at a low frequency band, but it can be addressed by optimizing an inner diameter D of the stator  210  and an area S of the slot portion  213 , or optimizing the inner diameter D of the stator  210  and a height of a lower end coil  244 . 
     The motor for the compressor may operate in response to power applied from the exterior. To this end, as shown in  FIG. 5 , terminals  260  which are electrically connected to an external power source may be provided. The terminals  260  may have a one-to-one coupling with respective coils (for example, a single-phase motor has two main coils and one sub coil), and tied up by a bundle of wires typically known as a harness  270 , thereby being connected to the external power source. 
     As a method for connecting the terminals and the coils by one by one, serrations are provided at each terminal and protrude into the insulation layer of the coil to be connected to a conductor. However, when the conductor is made of aluminum having a low tensile strength, the coil may be cut off. In consideration of this, an intermediate wire connecting method is used in which the terminals are coupled to lead wires, respectively, and ends of the lead wires are connected to the coil. 
     Examples of the intermediate wire connecting method may include welding, soldering and the like. The welding method is able to reduce a cost by virtue of direct welding without peeling the insulation layer. However, it requires many components for welding, exhibits low working efficiency, causes deviations according to an operator s skill, and is unable to be automated. Especially, the coil may be melted due to welding heat. The soldering method may have a disadvantage in view of an addition of a peeling process as compared to the welding method. Especially, upon applying the aluminum coil, a defect may be caused due to the lack of affinity. Therefore, the present disclosure proposes a method for reducing a cut-off detect even with employing an aluminum coil having a low tensile strength when directly connecting terminals each having serrations to the coil in a clamping manner. 
     To this end, according to this exemplary embodiment, as shown in  FIG. 6 , for a single-phase motor having two main coils  241  made of copper and one sub coil  242  made of aluminum, a reinforcing wire  245  having a predetermined tensile strength (approximately similar to the copper coil) may be pressed onto the serrations  263  together with the aluminum sub coil  242  prior to, as shown in  FIG. 7 , connecting the terminal  260  to the sub coil  242 , thereby preventing in advance the sub coil  242  from being cut off. 
     The reinforcing wire  245  may be formed by coating an insulation layer such as enamel on a conductor, which is made of a material having a higher tensile strength than the aluminum. When the conductor is exposed as both ends of the reinforcing wire  245  is cut off, in order to prevent a current from being applied via the exposed conductor, a middle portion of the reinforcing wire  245  may be folded and the folded portion may be wound on the sub coil  242  or fixed onto an end coil by a coil fixing thread  246 . On the other hand, the both ends where the conductor is exposed may be pressed by a fixing piece  262  together with an end portion of the sub coil  242  at a body part  261  of each terminal  260 , thereby being fixedly pressed onto the serrations  263 . Alternatively, an insulation processing may be performed for the both cut-off ends by coating the insulation layer thereon so as to prevent external power from being supplied to the reinforcing wire. 
     As such, upon use of the aluminum coil having a low tensile strength as the winding coil of the motor for the compressor, when terminals having serrations are connected to the aluminum coil, a reinforcing wire having a relatively high tensile strength may be pressed onto the serrations together with the aluminum coil, which may result in preventing in advance the aluminum coil from being cut off due to a pressing force and accordingly preventing a cut-off defect of the motor for the compressor having the aluminum coil, thereby improving reliability and simultaneously reducing a fabricating cost of the motor. 
     Hereinafter, description will be given of a reciprocal compressor having a reciprocal motor according to this specification, with reference to  FIG. 8 . 
     That is, a reciprocal compressor according to this specification may include a hermetic container  100 , a driving motor  200  as a driving source installed within the hermetic container  100 , a compression unit  300 , in which a piston  320  is connected to a rotational shaft  230  of the driving motor  200  via a connecting rod  330  and linearly reciprocates within a compression space of a cylinder block  310  having a valve assembly  340  so as to compress a refrigerant, and a support unit  400  located between a bottom surface of the hermetic container  100  and a lower surface of the driving motor  200  to elastically support the driving motor  200  and the compression unit  300 . 
     The driving motor  300  may be implemented as the aforementioned motor for the compressor, namely, an induction motor, in which the aluminum coil is inserted into both the main slot portions  213   a  and the sub slot portions  213   b  of the stator  210  to be wound on the tooth portions  212 , or the copper coil is inserted in the main slot portions  213   a  and the aluminum coil is inserted into the sub slot portions  213   b  so as to be wound on each of the tooth portions  212 . The structure of the stator  210  of the driving motor  200  is the same as the aforementioned in the reciprocal motor, so detailed description thereof will be omitted. 
     Here, as the diameter of the aluminum coil is greater than the typical copper coil in order to maintain the efficiency of the motor, a weight of the stator  210  of the driving motor  200  may increase. Additionally, as heights of an upper end coil  243  and a lower end coil  244  of the stator  210  increase, it is necessary to make an installation position of the compression unit  300  high and make the height of the hermetic container  100  high in consideration of interference with the compression unit  300 . Also, as the weight of the stator  210  increases, it is required to increase an elastic force of the support unit  400  in a longitudinal direction. To this end, a height of a compression coil spring implementing the support unit  400  may be lowered, but in this case, it should be considered that an oil feeder  231  installed at a lower end of the rotational shaft  230  of the driving motor  200  be not bumped against the hermetic container  100 . Considering that the weight of the stator  210  and the height of the compression unit  300  increase, a weight of an eccentric mass installed at the rotor  220  or the rotational shaft  230  should be appropriately adjusted, in order to prevent friction and thusly-caused noise between the stator  210  and the rotor  220  of the driving motor  200 . 
     With the configuration of the reciprocal compressor, when power is supplied to the driving motor  200 , the rotational shaft  230  rotates and the rotational force is converted into a linear reciprocating motion of the compression unit  300  by the connecting rotor  330 . The compression unit  300  sucks and compresses a refrigerant via a valve assembly  340  and discharges the compressed refrigerant into a refrigerating system, while the piston  320  linearly reciprocates within the compression space of the cylinder block  310 . The series of operations are repeated. 
     Here, when alternating current (AC) power is applied from the outside to the main coil and the sub coil wound on the stator  210  of the driving motor  200 , a force of preferentially rotating the sub coil, whose polar axis goes  90  ahead as compared with that of the main coil, is applied in response to formation of a rotating magnetic field by the current. Also, since a current phase of the sub coil  242  is prior to a current phase of the main coil  241  by the capacitor which is connected to the sub coil  242  in series, the sub coil  242  performs a high-speed rotation. With the high-speed rotation of the driving motor  200 , the rotating force is converted into a linear motion via the connecting rod  330  to be transferred to the piston  320 . 
     As the driving motor having the aluminum coil is employed, a fabricating cost of the driving motor can be reduced that much, accordingly, a production cost of the reciprocal compressor can be remarkably reduced without great change in the efficiency thereof, as compared with the copper coil wound. The efficiency of the reciprocal compressor as compared with the price of the compressor can be enhanced by virtue of an appropriate design of the individual cross section, the entire cross section or the number of the main slot portions and the sub slot portions. 
     When the main coil or the sub coil of the winding coil of the driving motor is formed of aluminum with a low tensile strength and the winding coil is pressed onto terminals having serrations for connection, the reinforcing wires with a relatively great tensile strength, such as copper, can be pressed onto the terminals together with the aluminum, thereby preventing in advance the aluminum coil from being cut off, resulting in enhancement of assembly reliability of the reciprocal compressor.