Patent Publication Number: US-2007114874-A1

Title: Motor having a stator and a rotor made of soft magnetic powder material

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to a motor having a stator and a rotor made of soft magnetic powder, and, more particularly, to a motor having a stator and rotor, which are made of soft magnetic powder so that the stator and the rotor can be smoothly and force-fitted into a shell of the motor without being physically damaged during a motor assembly process.  
     BACKGROUND OF THE INVENTION  
      As well known to those skilled in the art, motors are devices which convert electric energy into mechanical energy to provide rotating force. The motors are widely used in industrial apparatuses as well as in domestic electronic products. As examples of domestic electronic products in which the motors are used, there are washing machines, cleaners, optical disk players, hard disk-drives of computers, and compressors, which are provided in air cooling devices, such as air-conditioners and refrigerators, to condense refrigerants into liquid states.  
      A conventional representative motor will be explained herein below with reference to the attached drawing.  
       FIG. 1  is a sectional view showing a motor according to a conventional technique. As shown in the drawing, the conventional motor  10  is provided at a predetermined position in a compressor  1  of a refrigerator and includes a shell  11 , a stator  12  fixed to the inner surface of the shell  11 , a rotor  13 , which is rotatably provided in the stator  12 , and a rotating shaft  14 , which is firmly fitted into the rotor  13 .  
      The shell  11  is closed at opposite ends thereof by an upper cover  11   a  and a lower cover  11   b , thus defining a space for installation of the stator  12  and the rotor  13  therein.  
      The stator  12  is manufactured from layered silicon steel plates. A coil  12   a  is wound around the stator  12 .  
      The rotor  13  is manufactured by layering thin silicon steel plates, each of which has a ring shape, thus forming a cylindrical shape. Furthermore, an upper ring  13   a  and a lower ring  13   b  are respectively provided on the upper end and under the lower end of the rotor  13 . A balance weight  13   c , which prevents vibration due to weight imbalance during the rotation of the rotor  13 , is coupled at a predetermined position to the lower ring  13   b.    
      The rotating shaft  14  is firmly fitted into the rotor  13  along the rotating center axis of the rotor  13 .  
      In the conventional motor  10  having the above-mentioned construction, when the motor  10  is operated, the rotating shaft  14 , which is rotated along with the rotor  13 , provides rotating force to a compressing unit  20  of the compressor  1 , which compresses refrigerant, which is drawn thereinto from the outside through an inlet  31  after passing through an accumulator  30 , and which discharges it through an outlet (not shown). As such, to condense refrigerant in the refrigerator into a liquid state, the motor  10  generates a relatively large torque, sufficient to ensure superior compressing ability, and is rotated at a relatively high speed.  
      However, in the conventional motor  10 , because the stator  12  is made of layered silicon steel plates, when the stator  12  is force-fitted into the shell  11 , a portion of the stator  12  at which stress is concentrated may be physically damaged by torsion, for example, the layered silicon steel plates may be separated from each other or may be bent. Consequently, this makes insertion of the stator  12  into the shell  11  difficult. In the same manner, because the rotor  13  is also made of layered silicon steel plates, when the rotating shaft  14  is force-fitted into the rotor  13 , the portion of the rotor  13  at which stress is concentrated may be physically damaged by torsion, for example, the layered silicon steel plates may be separated from each other or bent. In addition, this makes insertion of the rotating shaft  14  into the rotor  13  difficult.  
      Therefore, to fit the stator  12  into the shell  11 , the shell  11  is heated to 200° C. to 230° C. such that it is thermally expanded somewhat. Thereafter, the stator  12  is fitted into the shell  11 , the diameter of which has been increased. To fit the rotating shaft  14  into the rotor  13 , the rotor  13  is also heated at 200° C. to 230° C. such that it is thermally expanded somewhat. Thereafter, the rotating shaft  14  is fitted into the rotor  13 , which has been increased in diameter.  
      However, in the case where the motor  10  is assembled through the above-mentioned heat-shrink fitting process, the assembly process is complicated, and a separate apparatus for heat-shrink fitting is required. Hence, there are problems in that the productivity is reduced and the cost of manufacturing the motor  10  is increased.  
      Although the above-mentioned problems have been illustrated as being caused in the motor  10  provided in the compressor  1  of the refrigerator, the problems are not limited thereto, but are caused in any motor which is manufactured through a heat-shrink fitting process.  
      Therefore, the development of a stator and rotor for motors, which can be assembled through a simple force-fitting process and do not cause physical damage during the force-fitting process, is required.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a stator for a motor which is made of soft magnetic powder material so that, when a motor assembly process is conducted, the stator can be easily assembled with a shell of the motor through a force-fitting process without causing physical damage upon force-fitting, thus the motor assembly process is simplified, thereby increasing productivity and reducing the cost of manufacturing the motor.  
      Another object of the present invention is to provide a rotor for a motor which is made of soft magnetic powder material so that, when a motor assembly process is conducted, the rotating shaft of the motor can be easily assembled with the rotor through a force-fitting process without physical damage caused by force-fitting, thus the motor assembly process is simplified, thereby increasing productivity and reducing the cost of manufacturing the motor.  
      In an aspect, the present invention provides a stator for a motor which is adapted to be fitted into a shell of the motor and is made of compressed soft magnetic powder. The stator includes a stator body, and a plurality of compression beads, which are formed on an outer surface of the stator body to reduce a contact surface between the stator body and an inner surface of the shell. The compression beads are compressed by the inner surface of the shell and thus held therein when the stator is fitted into the shell.  
      In another aspect, the present invention provides a rotor for a motor into which a rotating shaft of the motor is fitted, and which is made of compressed soft magnetic powder. The rotor includes a rotor body, which has in a central portion thereof a fastening part, into which the rotating shaft is fitted, and a plurality of compression beads, which are formed on an inner surface of the fastening part of the rotor body to reduce a contact surface between the fastening part and the rotating shaft and are compressed by the rotating shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a sectional view showing a motor according to a conventional technique;  
       FIGS. 2A and 2B  are sectional views of a motor having a stator made of soft magnetic powder material, according to the present invention;  
       FIG. 3  is a sectional view taken along line A-A′ of  FIG. 2A ;  
       FIGS. 4A  to  4 C are sectional views of a motor having a rotor made of soft magnetic powder material, according to the present invention; and  
       FIG. 5  is a sectional view taken along line A-A′ of  FIG. 4A . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings, such that those skilled in the art can easily implement the present invention.  
     FIRST EMBODIMENT  
       FIGS. 2A and 2B  are sectional views of a motor  100  having a stator  110  made of soft magnetic powder material, according to the present invention. As shown in the drawing, the stator  110  made of soft magnetic powder material according to the present invention includes a stator body  111  and a plurality of compression beads  112 , which are formed on the outer surface of the stator body  111 . The stator  110  is formed by compressing soft magnetic powder.  
      The stator body  111  is fastened to the inner surface of a shell  120  of the motor  100 . A coil  111   a  is wound around the stator body  111 , and a through hole  111   b  is longitudinally formed through the stator body  111  so that a rotor  130  fitted over a rotating shaft  131  is rotatably installed in the through hole  111   b . Furthermore, the stator body  111  has a cross-section, which has a circular or polygonal shape or the shape of a figure comprising a curved line and a straight line. Several compression beads  112  are formed on the outer surface of the stator body  111 .  
      Preferably, as shown in  FIG. 3 , the several compression beads  112  are formed on the outer surface of the stator body  111  at positions spaced apart from each other by predetermined intervals. The compression beads  112  serve to reduce the contact area between the outer surface of the stator body  111  and the inner surface of the shell  120  such that the stator body  111  can be smoothly force-fitted into the shell  120 . When the stator body  111  is force-fitted into the shell  120 , the compression beads  112  are compressed by the inner surface of the shell  120 , so that the stator body  111  is reliably fastened to the inner surface of the shell  120 .  
      The compression beads  112  are formed on the outer surface of the stator body  111  in the longitudinal direction of the stator body  111 , that is, in the direction in which the stator body  111  is inserted into the shell  120 , such that the stator body  111  can be easily force-fitted into the shell  120 . Furthermore, each compression bead  112  has a guide part  113  on the end corresponding to the end of the stator body  111  that is first inserted into the shell  120 .  
      The guide parts  113  have inclined shapes such that the compression beads  112  smoothly compress the inner surface of the shell  120  when the stator body  111  is fitted into the shell  120 , thus serving to guide forcible insertion of the stator body  111  into the shell  120 .  
      The stator  110  of the present invention is made of compressed soft magnetic powder. The soft magnetic powder mainly comprises iron-based grains. Each grain of the soft magnetic powder is coated with predetermined material for electrical insulation.  
      To form the stator  110  using soft magnetic powder through a compression molding process, a compression molding machine, in which a molding cavity having a shape corresponding to the stator  110  is defined, is provided. Thereafter, soft magnetic powder is charged into the molding cavity and is compressed by a compressing unit such as a press, thus being manufactured into the shape of the stator body  111  having the compression beads  112 . Here, a lubricant and/or binder may be added to the soft magnetic powder before the compressing process is conducted.  
      As such, the stator  110  comprises a soft magnetic composite (SMC), which has a three-dimensional shape and is manufactured through the process of compressing soft magnetic powder. Therefore, a degree of freedom higher than the conventional art, which uses silicon steel plates, is possible.  
      Meanwhile, in this embodiment, the motor  100  provided in the compressor  1  (see,  FIG. 1 ) of a refrigerator has been illustrated as a representative example, but the present invention is not limited to this. That is, the present invention can be applied to any motor in which a stator is force-fitted into a shell.  
      The operation of the stator, which has the above-mentioned structure and is manufactured using soft magnetic powder material, will be described herein below.  
      The stator  110  of the present invention can be force-fitted into the shell by the compression beads  112 , which contact the inner surface of the shell  120  to reduce the contact area between the stator  110  and the inner surface of the shell  120 . Therefore, in the installation of the stator  110  in the shell  120 , the present invention does not require a heat-shrink fitting process and equipment for heat-shrink fitting, unlike the conventional art.  
      Furthermore, when the stator  110  is force-fitted into the shell  120 , because the several compression beads  112  are compressed by the inner surface of the shell  120 , the stator  110  can be firmly fastened to the inner surface of the shell  120 . Particularly, the compression beads  112  are oriented in the longitudinal direction of the stator body  111 , that is, in the direction in which the stator  110  is inserted into the shell  120 . Thus, the stator body  111  is reliably prevented from being undesirably rotated with respect to the shell  120 .  
      As well, because the stator  110  comprises an SMC, even though it is force-fitted into the shell  120 , a problem with the conventional layered silicon steel plate structure, in which portions of the layered silicon steel plates are damaged by torsion caused by stress concentration, is avoided. Furthermore, because the stator  110  comprises the SMC, it is possible to include the compression beads  112 , which cannot be formed in the conventional layered silicon steel plate structure.  
      In addition, because the guide parts  113  are provided on the respective compression beads  112  of the stator  110 , the stator  110  can be smoothly inserted into the shell  120  without requiring excessive force at an initial stage of the process of force-fitting the stator  110  into the shell  120 .  
      As described above, in the first embodiment of the present invention, the stator  110  made of soft magnetic powder material can be provided with the compression beads  112  having the guide parts  113 , unlike the conventional structure, in which silicon steel plates having the same shape are layered, so that the stator  110  can be smoothly and force-fitted into the shell  120  without damaging the shell  120  during the process of assembling the motor  100 , thus increasing productivity and reducing the cost of manufacturing the motor  100 .  
     SECOND EMBODIMENT  
       FIGS. 4A  to  4 C are sectional views of a motor  200  having a rotor  210  made of soft magnetic powder material, according to the present invention. As shown in the drawing, the rotor  210  made of soft magnetic powder material includes a rotor body  211 , and a plurality of compression beads  212 , which are provided on the inner surface of the rotor body  211 . The rotor  210  is formed by compressing soft magnetic powder.  
      The rotor body  211  is rotatably provided in a stator  220  installed in a shell  240  of the motor  200 . The rotor body  211  is cylindrical and has in a central portion thereof a fastening part  211   a , into which a rotating shaft  230  is force-fitted.  
      In the case of the conventional art, in which a rotor body is manufactured by layering a plurality of silicon steel plates, a fastening part must be formed into a simple hole shape. However, in the present invention, because the rotor body  211  is made of compressed soft magnetic powder, it is not limited to any particularly shape. Furthermore, the hole defining the fastening part  211   a  may be closed at one end thereof. The compression beads  212  are formed on the inner surface of the fastening part  211   a.    
      Preferably, as shown in  FIG. 5 , the compression beads  212  are formed on the inner surface of the fastening part  211   a  of the rotor body  211  at positions spaced apart from each other by predetermined intervals.  
      The compression beads  212  serve to reduce the contact area between the inner surface of the fastening part  211   a  and the outer surface of the rotating shaft  230 , such that the rotating shaft  230  can be smoothly force-fitted into the fastening part  211   a . When the rotating shaft  230  is force-fitted into the fastening part  211   a , the compression beads  212  are compressed by the outer surface of the rotating shaft  230 , so that the rotating shaft  230  can be reliably fastened to the fastening part  211   a.    
      The compression beads  212  are oriented in the direction in which the fastening part  211   a  is formed, that is, in the direction in which the rotating shaft  230  is inserted into the fastening part  211   a , such that the rotating shaft  230  can be easily force-fitted into the fastening part  211   a . Furthermore, each compression bead  212  has a guide part  213  on an end corresponding to the end of the fastening part  211   a  into which the rotating shaft  230  is inserted.  
      The guide parts  213  have inclined shapes such that the compression beads  212  smoothly compress the outer surface of the rotating shaft  230  when the rotating shaft  230  is fitted into the fastening part  211   a , thus serving to guide forcible insertion of the rotating shaft  230  into the fastening part  211   a.    
      The rotor  210  of the present invention is made of compressed soft magnetic powder. The soft magnetic powder mainly comprises iron-based grains. Each grain of the soft magnetic powder is coated with predetermined material for electrical insulation.  
      To form the rotor  210  using soft magnetic powder through a compression molding process, a compression molding machine, in which a molding cavity having a shape corresponding to the rotor  210  is defined, is provided. Thereafter, soft magnetic powder is charged into the molding cavity and is compressed by a compressing unit such as a press, thus being formed into the shape of the rotor body  211 , the fastening part  211   a  of which has the compression beads  212 . Here, a lubricant and/or binder may be added to the soft magnetic powder before the compressing process is conducted.  
      As such, the rotor  210  comprises a soft magnetic composite (SMC), which has a three-dimensional shape and is manufactured through the process of compressing soft magnetic powder. Therefore, a degree of freedom higher than the conventional art, which uses silicon steel plates, is possible.  
      Although, in this embodiment, the motor  200  provided in the compressor  1  (see,  FIG. 1 ) of a refrigerator has been illustrated as a representative example, the present invention is not limited to this. That is, the present invention can be applied to any motor in which a rotating shaft is force-fitted into a rotor.  
      The operation of the rotor, which has the above-mentioned structure and is manufactured using soft magnetic powder material, will be described herein below.  
      In the rotor  210  of the present invention, the rotating shaft  230  can be force-fitted into the fastening part  211   a  of the rotor  210  by the compression beads  212 , which contact the outer surface of the rotating shaft  230  to reduce the substantial contact area between the fastening part  211   a  and the rotating shaft  230 . Therefore, in the coupling process between the rotor  210  and the rotating shaft  230 , the present invention does not require a heat-shrink fitting process or equipment for heat-shrink fitting, unlike the conventional art.  
      Furthermore, when the rotating shaft  230  is force-fitted into the fastening part  211   a  of the rotor  210 , because the several compression beads  212  are compressed by the outer surface of the rotating shaft  230 , the rotating shaft  230  can be firmly fastened to the fastening part  211   a . Particularly, the compression beads  212  are formed on the fastening part  211   a  in the longitudinal direction of the rotor body  211 , that is, in the direction in which the rotating shaft  230  is inserted into the fastening part  211   a . Thus, the rotating shaft  230  is reliably prevented from being undesirably rotated with respect to the fastening part  211   a.    
      As well, because the rotor  210  comprises an SMC, even though the rotating shaft  230  is force-fitted into the fastening part  211   a , a problem with conventional layered silicon steel plate structure, in which portions of the layered silicon steel plates are damaged by torsion caused by stress concentration, is avoided. Furthermore, the rotor  210 , which comprises the SMC, makes it possible to have the compression beads  212  which cannot be formed in the conventional layered silicon steel plate structure.  
      In addition, because the guide parts  213  are provided on the respective compression beads  212  of the rotor  210 , the rotating shaft  230  can be smoothly inserted into the fastening part  211   a  without requiring excessive force at an initial stage of the process of force-fitting the rotating shaft  230  into the fastening part  211   a.    
      As such, in the second embodiment of the present invention, the rotor  210  made of soft magnetic powder material can be provided with the compression beads  212  having the guide parts  213 , unlike the conventional structure, such that silicon steel plates having the same shape are layered, so that the rotating shaft  230  can be smoothly force-fitted into the rotor  210  without physical damage during the process of assembling the motor  200 , thus increasing the productivity, and reducing the cost of manufacturing the motor  200 .  
      As described above, the present invention provides a stator and rotor for a motor which are made of soft magnetic powder material so that a force-fitting process can be smoothly conducted without physical damage during a process of assembling a motor, thus the motor assembly process is simplified, thereby increasing productivity and reducing the cost of manufacturing the motor.  
      Although the preferred embodiments of the stator and motor for motors made of soft magnetic powder material have been disclosed, these are only illustrative examples. The present invention is not limited to the preferred embodiments. Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.