Abstract:
A synchronous reluctance motor is described. The synchronous reluctance motor includes a core configured to rotate about a central axis and having first and second groups of flux barriers formed therein. Each flux barrier is defined as an opening in the core. Each of the first and second groups includes a first flux barrier and a second flux barrier with the second flux barrier disposed outside the first flux barrier in a radial direction from the central axis of the core. Each of the second flux barriers of the first and second groups has at least two connection parts crossing the opening of the second flux barrier.

Description:
This application claims the benefit of Korean Patent Application No. 10-2007-0053342, filed on May 31, 2007, which is incorporated by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     This document relates to a synchronous reluctance motor. 
     2. Description of the Related Art 
     In general, a synchronous reluctance motor is a motor for generating a rotary force by a variation of magnetic resistance caused by a rotation of a rotor. The synchronous reluctance motor is widely used, for example, in a compressor. A rotor of the synchronous reluctance motor includes a core having laminated steel sheets. Each steel sheet of the core has flux barriers and a steel part, where the flux barriers may comprise voids in the steel part. 
     If the rotor is activated, the flux barrier interferes with a flow of flux, which causes a difference of magnetic resistances between a “q” axis directing to the flux barrier and a “d” axis directing between respective flux barrier groups in a circumferential direction of the rotor. The difference of magnetic resistances between the “q” axis and the “d” axis generates reluctance torque. The reluctance torque is synchronized with the flux of a stator and therefore, the reluctance torque is more dominant than the inductive torque by the flux barrier. Thus, the rotor is rotated at synchronous speed by the reluctance torque. 
     In the conventional synchronous reluctance motor, stress caused by the centrifugal force is concentrated around the outer side of the core, specifically, in both side ribs of the flux barrier, thereby causing a deformation of the outer side of the core. 
     SUMMARY 
     In one general aspect, a synchronous reluctance motor is configured to decentralize a stress concentrated in an outer side of a core at the time of rotating a rotor at high speed, so as to improve a mechanical rigidity of the core. The synchronous reluctance motor includes a core configured to rotate about a central axis and having first and second groups of flux barriers formed therein. Each flux barrier is defined as an opening in the core. Each of the first and second groups includes a first flux barrier and a second flux barrier with the second flux barrier disposed outside the first flux barrier in a radial direction from the central axis of the core. Each of the second flux barriers of the first and second groups has at least two connection parts crossing the opening of the second flux barrier. 
     In another general aspect, a synchronous reluctance motor includes a core configured to rotate about a central axis and having first and second groups of flux barriers formed therein. Each flux barrier is defined as an opening in the core and each of the first and second groups includes a first flux barrier and a second flux barrier with the second flux barrier disposed outside the first flux barrier in a radial direction from the central axis of the core. The synchronous reluctance motor also includes an end plate disposed at one end of the core and a pin passing through the core and mechanically coupled to the end plate. The distance between the pin and the central axis of the core is greater than the distance between one of the second flux barriers and the central axis of the core. 
     In yet another general aspect, a synchronous reluctance motor includes a core with a flux barrier formed therein with the flux barrier dividing the core into an inner part and an outer part. The synchronous reluctance motor also includes an end plate disposed at one end of the core and a fixing member passing through the flux barrier and mechanically coupled to the end plate and the core. 
     Implementations may include one or more of the following features. For example, each of the connection parts may have a width of 0.3 mm to 0.7 mm. The core may be made of steel. The fixing member may pass through one of the second flux barriers. The fixing member may include a protrusion and the outer part of the core may include a groove to receive the protrusion of the fixing member. The connection parts in the second flux barrier through which the fixing member passes may be symmetrically disposed with respect to the fixing member. The fixing member may be a rivet and the pin may be a magnetic body. 
     The distance between one of the connection parts and the central axis of the core may be greater than the distance between the fixing member and the central axis of the core. Also, the distance between the pin and the central axis of the core may be greater than the distance between the central axis of the core and the fixing member. 
     Other features and advantages will be apparent from the following description, including the drawings and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a rotor of a synchronous reluctance motor; 
         FIG. 2  is a perspective view of the rotor of the synchronous reluctance motor shown in  FIG. 1 ; 
         FIG. 3  is a plan view of a rotor core of a synchronous reluctance motor in one implementation; 
         FIG. 4  is a diagram illustrating a degree of deformation of an outer side of a rotating core without reinforcement; 
         FIG. 5  is a diagram illustrating a degree of deformation of an outer side of a rotating core having reinforcement; 
         FIG. 6  is a plan view of a rotor of a synchronous reluctance motor in another implementation; and 
         FIG. 7  is a plan view of a rotor of a synchronous reluctance motor in another implementation. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an exploded perspective view of a rotor of a synchronous reluctance motor and  FIG. 2  is a perspective view of the assembled rotor of the synchronous reluctance motor shown in  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the rotor  100  of the synchronous reluctance motor includes the core  110 , end plates  120  and  130  disposed at each side surface of the core  110 , and a fixing member  150  for fixing the core  110  and the end plates  120  and  130 . 
     The core  110  is a laminate core formed by laminating steel sheets  111 . The steel sheet  111  is, for example, a silicon steel sheet. The core  110  has a shaft hole  111   a  at its center. 
       FIG. 3  is a plan view of a rotor core of a synchronous reluctance motor in one implementation. Referring to  FIG. 3 , the core  110  has flux barriers  113  and steel parts  114 ,  115 ,  116 , and  117 . 
     The flux barriers  113  may be formed, for example, by machine-pressing the steel sheets of the core  110 . The flux barriers  113  may be formed in regions that are equally spaced around the center of the silicon steel sheet  111 . At each of the regions, four flux barriers  113   a ,  113   b ,  113   c , and  113   d  are formed. 
     Referring to  FIG. 3 , four flux barrier groups B 1 , B 2 , B 3 , and B 4  are formed in the regions that are separated by an angle of 90° around the center of the core  110 . Each of the flux barrier groups B 1 , B 2 , B 3 , and B 4  has four flux barriers  113   a ,  113   b ,  113   c , and  113   d . The number and shape of the flux barriers and the flux barrier groups may vary according to a characteristic of a motor. 
     Among the flux barriers  113   a ,  113   b ,  113   c , and  113   d , the flux barriers  113   a  and  113   b  are of a circular arc shape in which both ends are provided to be in proximity with the circumference of the silicon steel sheet  111  and central part protrudes toward the shaft hole  111   a  at the center. 
     Referring to  FIGS. 1 and 2 , the end plates  120  and  130  are disposed at both side surfaces of the core  110  and are fixed to the core  110 . The end plates  120  and  130  have shaft holes  121  and  131 . The shaft holes  121  and  131  are provided at the centers and communicate with the shaft hole  111   a  of the core  110 . 
     The core  110  has pin holes  112  provided between the flux barrier groups B 1 , B 2 , B 3 , and B 4 . Pins  140  are inserted into the pinholes  112 . The end of each pin  140  is fitted into or passes through a pin fixing groove  132  of at least one of the end plates  120  and  130 . 
     When the core  110  is assembled, the pin  140  serves to align the silicon steel sheets  111  and serves to increase a coupling force between the core  110  and the end plates  120  and  130 . 
     The end plates  120  and  130  include balance weights  123  and  133  to prevent the eccentricity of the rotor  100 . The size of the balance weights  123  and  133  may vary depending on the motor capacity. 
     Coupling holes  124  and  134  are provided around the shaft holes  121  and  131  of the end plates  120  and  130 . The coupling holes  124  and  134  provide passage for the fixing members  150 . In one implementation, the fixing member  150  is a rivet having a body  153 , a head  151 , and an end  152 . 
     Referring to  FIG. 3 , the fixing members  150  are installed to pass through at least one of the flux barriers  113   a ,  113   b ,  113   c , and  113   d  of flux barrier groups B 1 , B 2 , B 3 , and B 4 . Specifically, the fixing member  150  is installed to pass through the flux barrier  113   b  in the middle of the flux barrier  113   b . Two supports  160  and  170  are formed to face with each other at the central flux barrier  113   b . The supports  160  and  170  have arc shaped mount grooves  161  and  171 , respectively, to accommodate the body  153  of the fixing member  150 . The head  151  and end  152  of the fixing member  150  are firmly coupled to the end plates  120  and  130 . 
     When the rotor  100  is rotated at high speed, the core  110  is subjected to a centrifugal force in a radial direction. The fixing member  150  passing through the flux barrier  113   b  and firmly coupled to the end plates  120  and  130  supports, for example, steel part  115 , thereby preventing the deformation of the core  110 . 
     In some implementations, the end plates  120  and  130 , guide pins  140 , and the fixing members  150  are made of non-magnetic material to prevent a leakage of flux through a flux path and thus are magnetically independent of the core  110 . 
     When the rotor  100  is rotated at high speed, the core  110  is subjected to a stress in a radial by the centrifugal force. In such a case, as described above, the fixing member  150  supports the steel part  115 , thereby preventing the deformation of the core  110 . 
     However, the fixing member  150  does not support the steel parts  116  and  117 . Therefore, the stress due to the centrifugal force is concentrated around both ends of the flux barrier  113   b.    
       FIG. 4  is a diagram illustrating the degree of deformation near the ends of the flux barrier  113   b . As shown in  FIG. 4 , the stress due to the centrifugal force is concentrated around both sides of ribs (R) of the flux barrier  113   b.    
       FIG. 3  illustrates a virtual circle (C) having a center at the center of the core  110  and passing through the fixing members  150 . The fixing members  150  can support portions of the core inside the virtual circle (c) but cannot support portions of the core outside the virtual circle (c), resulting in the deformation near the ends of the flux barrier  113   b , as shown in  FIG. 4 . 
     In some implementations, reinforcement is provided to support portions of the core when the core rotates at high speed. Referring to  FIG. 3 , in order to support portions of the core  110  outside the virtual circle (c), the reinforcement is provided in the form of a connection parts  180  formed at the flux barrier  113   b  and connecting steel parts  115  and  116 . 
     The connection part  180  is formed to cross the flux barrier  113   b  so that it connects between the steel part  115  positioned at an outer side of the flux barrier  113   b  in the core  110  and the steel part  116  positioned at an inner side of the flux barrier  113   b.    
     The connection part  180  is disposed at the flux barrier  113   b  where the fixing member  150  is installed. Referring to  FIG. 3 , the fixing member  150  is installed at the central flux barrier  113   b  among the plurality of flux barriers  113   a ,  113   b ,  113   c , and  113   d . Large stress is concentrated around both side ribs (R) of the central flux barrier  113   b  (shown in  FIG. 4 ). Therefore, it is desirable that the connection part  180  is formed to connect the steel parts  115  and  116  across the central flux barrier  113   b  in order to reinforce the structure against the stress. 
     The connection parts  180  are formed to extend from the steel parts  115  and  116  and may have the same material as the steel parts  115  and  116 . The connection parts  180  each are disposed one by one in symmetry with respect to the fixing member  150 . 
     As the connection parts  180  increase in number, the core  110  can be better reinforced. But, the connection part  180 , which is a magnetic body having the same material as the steel parts  115  and  116 , may also cause leakage of flux through a flux path and thus, may reduce the efficiency of the motor. Therefore, in determining the number and width of the connection parts  180 , a trade-off should be made between the degree of reinforcement and the flux leakage. For example, the width of the connection part  180  may be within a range of 0.3 mm to 0.7 mm to minimize the influence on the pattern of the flux and optimize an effect of stress decentralization. 
       FIG. 3  illustrates “d” axis and a “q” in the core  110 . The “d” axis extends from the center of the core  110  in the radial direction and passes between the respective flux barrier groups B 1 , B 2 , B 3 , and B 4 . That is, the “d” axis is a line between the center of the core  110  and a space between the respective flux barrier groups B 1 , B 2 , B 3 , and B 4 . The “q” axis extends from the center of the core  110  to a center of the fixing member  150 . That is, the “q” axis is a line between the center of the core  110  and the center of the fixing member  150 . The connection part  180  is formed in the middle region among the regions trisecting the angle between the adjacent “d” axis and “q” axis. 
     In detail, as shown in  FIG. 3 , in the core  110 , the “d” axis and the “q” axis are provided in each region equally divided at an angle of 90°. The connection part  180  can be formed in the middle region among the regions trisecting the angle between the adjacent “d” axis and “q” axis. Specifically, it is desirable that the connection part  180  is formed near a bisector bisecting the angle between the adjacent “d” axis and “q” axis. 
     This is because in case where the connection part  180  is formed close to the fixing member  150  or to the outer rib (R) of the core  110 , the reinforcement effect against the centrifugal force inflicted on the outer rib (R) of the core  110  reduces. Therefore, the connection part  180  is formed near the bisector approximately bisecting the angle between the “d” axis and the “q” axis 
       FIGS. 4 and 5  illustrate a degree of deformation of the outer side of the core when the rotor is rotated at a high speed of 120 Hz.  FIGS. 4  and  5  compares the degrees of deformation between when the connection part  180  is used and not. When the connection part is not formed as shown in  FIG. 4 , the measured maximum stress applied to the outer rib (R) of the core  110  is about 191.9 MPa, and the degree of deformation of the outer rib (R) of the core  110  is about 15.6 μm. Here, the deformation degree represents an extent that the outer rib (R) is deformed at an outer side compared to a case when the core  110  is not rotating. 
     When the connection part  180  is formed as shown in  FIG. 5 , the measured maximum stress applied to the outer rib (R) of the core  110  is about 97.6 MPa, and the degree of deformation of the outer rib (R) of the core  110  is about 6.9 μm. Thus, the addition of the connection part  180  shows 50.9% reduction of maximum stress and 44.2% reduction of deformation. 
       FIG. 6  is a plan view of a rotor of a synchronous reluctance motor in another implementation. In  FIG. 6 , the reinforcement against the centrifugal force is provided in the form of a pin  260  passing through a core  210 . The pin  260  is made of a magnetic material to allow a passage of flux. 
     The pin  260  is inserted to the steel part  216 . The steel part  216  is positioned outside the flux barrier  213   b  where a fixing member  250  is installed. The pin  260  is coupled at its both ends to end plates, for example, the end plates  120  and  130  in  FIGS. 1 and 2 . Accordingly, when the rotor is rotated at high speed, the pin  260  supports the portions of the core  210  outside of the fixing member  250  against the centrifugal force, thereby reducing a deformation of the outer side of the core  210 , specifically, a deformation of a rib (R) part outside the core  210 . 
       FIG. 7  is a plan view of a rotor of a synchronous reluctance motor in another implementation. 
     Referring to  FIG. 7 , in the synchronous reluctance motor, reinforcement may be provided in the form of a connection part  360  which couples a fixing member  350  with steel part  316 . 
     The fixing member  350  is installed in the flux barrier  313   b  of the core  310 . The connection part  360  may include a protrusion  355  and a groove  320 . The protrusion  355  is formed to protrude from the fixing member  350 . The groove  320  is formed at the steel part  316  to receive the protrusion  355 . The protrusion and groove structure couples the fixing member  350  with the steel part  316 . Since the fixing member  350  is coupled to the end plates, for example, end plates  120  and  130  in  FIGS. 1 and 2 , the fixing member  350  supports the steel part  316  against the centrifugal force when the core  310  rotates. Therefore, the deformation of the outer side of the core  310 , specifically, the deformation of the outer rib (R) of the core  310  is reduced. 
     In the above implementations of the synchronous reluctance motor, the mechanical rigidity of a core is improved and the deformation of an outer side of the core is reduced because of the reinforcement structure, when a rotor is rotated at high speed. 
     Other implementations are within the scope of the following claims.