Abstract:
Disclosed is an interior permanent magnet type brushless direct current (BLDG) motor including a stator having a plurality of slots wound in a distributed winding manner, and a rotor positioned in the stator, configured to rotate with respect to the stator, and having a rotor core, a plurality of permanent magnets inserted in the rotor core and a plurality of flux barriers, wherein a flux barrier angle of the rotor is determined by multiples of twenty as an electrical angle and the multiples of twenty relates to a number of slots of the stator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of priority to Korean Application No. 10-2008-0127497, filed on Dec. 15, 2008, the contents of which is incorporated by reference herein in its entirety. 
       FIELD 
       [0002]    The present disclosure relates to an interior permanent magnet type brushless direct current (BLDC) motor. 
       BACKGROUND 
       [0003]    Motors may be classified into a direct current (DC) motor and an alternating current (AC) motor depending on power used. The DC motor has a commutator and a brush. Due to a mechanical contact between the commutator and the brush, reliability of the DC motor is lowered and a lifespan thereof may be shortened. 
         [0004]    An electronic switching type brushless DC (BLDC) motor using a semiconductor device has widely been used. The BLDC motors may be classified into an interior rotor type and an exterior rotor type according to an arrangement of stator and rotor. 
         [0005]    The interior rotor type motor either uses a rotor that a rotation shaft is inserted into a center of a cylindrical permanent magnet, or uses a so-called interior permanent magnet type rotor that a rotation shaft is inserted into a center of a rotor core having electrical steel sheets stacked thereon and then a plurality of permanent magnets are inserted in the rotor core. A cogging torque is generated between the rotor having the permanent magnets and the stator when the motor operates. The cogging torque causes vibration and noise. 
       SUMMARY 
       [0006]    In one aspect, an interior permanent magnet type brushless direct current (BLDC) motor includes a stator having a plurality of slots. The BLDC motor also includes a rotor positioned in the stator, configured to rotate with respect to the stator, and having a rotor core, a plurality of permanent magnets inserted in the rotor core and a plurality of flux barriers, wherein a flux barrier angle of the rotor is determined by multiples of twenty as an electrical angle and the multiples of twenty relates to a number of slots of the stator. 
         [0007]    Implementations may include one or more of the following features. For example, the multiples of twenty are used when S n /(P×m)=3n(n=1, 2, 3 . . . ) and where Sn is the number of slots of the stator, P is the number of poles of the rotor, and m is the number of power phases. The stator has thirty-six slots, three-phase distributed winding and the rotor has four poles. 
         [0008]    In some implementations, the flux barrier angle of the rotor is in a range around 160° as the electrical angle. The flux barrier angle of the rotor is in a range between 158° and 162° as the electrical angle. The flux barrier angle is determined by a size of the flux barriers. 
         [0009]    In another aspect, an interior permanent magnet type brushless direct current (BLDC) motor includes a stator having a plurality of slots. The BLDC motor also includes a rotor positioned in the stator, configured to rotate with respect to the stator, and having a rotor core, a plurality of permanent magnets inserted in the rotor core and a plurality of flux barriers, wherein a flux barrier angle of the rotor is determined by odd multiples of ten as an electrical angle and the odd multiples of ten relates to a number of slots of the stator. Implementations may include one or more of the following features. 
         [0010]    For example, the odd multiples of ten are used when S n /(P×m)=2n(n=1, 2, 3 . . . ) where Sn is the number of slots of the stator, P is the number of poles of the rotor, and m is the number of power phases. The stator has twenty-four slots, three phase distributed winding and the rotor has four poles. The flux barrier angle of the rotor is in a range around 150° as the electrical angle. The flux barrier angle of the rotor is in a range between 148° and 152° as the electrical angle. The flux barrier angle is determined by a size of a flux barrier. 
         [0011]    In yet another aspect, an interior permanent magnet type brushless direct current (BLDC) motor includes a stator having a plurality of slots. The BLDC motor also includes a rotor positioned in the stator, configured to rotate with respect to the stator, and having a rotor core, a plurality of permanent magnets inserted in the rotor core and a plurality of flux barriers, wherein a flux barrier angle of the rotor is determined by multiples of twenty or odd multiples of ten as an electrical angle in response to a number of slots of the stator. 
         [0012]    Implementations may include one or more of the following features. For example, the flux barrier angle of the rotor is in a range around 160° when determined by multiples of twenty. The flux barrier angle of the rotor is in a range around 150° in case of determined by multiples of twenty. 
         [0013]    In yet another aspect, an interior permanent magnet type brushless direct current (BLDC) motor includes a stator having a plurality of slots. The BLDC motor also includes a rotor positioned in the stator, configured to rotate with respect to the stator, and having a rotor core, a plurality of permanent magnets inserted in the rotor core and a plurality of flux barriers, wherein a flux barrier angle of the rotor increases as a number of slots of the stator increases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a plane view of an interior permanent magnet type brushless direct current (BLDC) motor; 
           [0015]      FIG. 2  is an enlarged view of main parts of  FIG. 1 ; 
           [0016]      FIG. 3  is a view showing a cogging torque in association with changes in flux barrier angles; 
           [0017]      FIG. 4  is a view showing the changes in a back EMF in association with the changes in flux barrier angles; and 
           [0018]      FIG. 5  is a view showing a cogging torque in association with changes in flux barrier angles. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Referring to  FIGS. 1 and 2 , the interior permanent magnet type BLDC motor may include a stator  110  having a plurality of slots  114 , and a rotor  120  having a rotor core  121 . Permanent magnets  131  having a plurality of magnetic poles are positioned in the rotor core  121 . 
         [0020]    The stator  110  may include a stator accommodation hole  112  for accommodating the rotor  120 , a stator core  111  having a plurality of slots  114  and a plurality of teeth positioned around the stator accommodation hole  112 , and a stator coil wound on the plurality of slots  114 . The stator  110  may have various slot numbers, e.g., twenty-four slots, thirty-six slots, forty-eight slots, or the like. Hereinafter, as an example, the stator  110  has thirty-six slots and a coil type of the stator  110  is a distributed winding, which is coil is wound on a plurality of teeth simultaneously. 
         [0021]    The rotor  120  may include a rotor core  121  defined in a cylindrical shape and having a rotation shaft  125  positioned in a center of the rotor core  121 , and a plurality of permanent magnets  131  axially positioned in the rotor core  121 . Here, with respect to an arrangement of the permanent magnets, different poles N and S are alternately located at an outside of the rotor core  121 . 
         [0022]    The rotor core  121  may have a shaft hole  122  passed through a center of the rotor core  121  and a plurality of electric steel sheets which are insulated and stacked in the rotor with a circular shape. In addition, a plurality of permanent magnet insertion portions  124  are positioned in the electrical steel sheets. The rotor  120  may have a plurality of magnetic poles. As an example, a rotor having four poles will be described. 
         [0023]    Four permanent magnet insertion portions  124  in which four permanent magnets  131  are respectively inserted may be positioned at the rotor core  121 . Each of the permanent magnet insertion portions  124  may be axially passed through the rotor core  121  to have a rectangular section such that the corresponding permanent magnet  131  defined in a shape of a rectangular plate can be axially inserted therein. The permanent magnet insertion portions  124  may be configured to be spaced apart from one another with approximately 90-degree interval in a circumferential direction of the rotor core  121 . 
         [0024]    Flux barriers  126  for preventing a flux leakage may be positioned at both end regions of each permanent magnet insertion portion  124 . Each of the flux barriers  126  may be located from the end of each permanent magnet insertion portion  124  to a position near an outer circumference of the rotor core  121 . The flux barrier  126  may be connected to the permanent magnet insertion portion  124 . 
         [0025]    The magnetic pole of the rotor  120  defined by each permanent magnet  131  has a predetermined flux barrier angle. The flux barrier angle is an inner angle between two lines that connect a center of the rotor  120  to both ends of the magnetic pole, respectively. As the flux barriers  126  for preventing the flux leakage are positioned at both end regions of the permanent magnet insertion portion  124 , the flux barrier angle is substantially an inner angle between two lines which connect inner edges of the flux barriers  126  to the center of the rotor  120 . 
         [0026]    In this implementation, the flux barrier angle of the rotor  120  is properly changed in association with the number (P) of poles of the rotor  120 , the number (S n )) of slots  114  of the stator  110 , and the number (m) of power phases applied to the stator coil. If a motor has a proper flux barrier angle, the flux leakage is reduced and a cogging torque can be minimized without lowering the motor efficiency. Accordingly, vibration or noise is reduced when a rotor rotates. 
         [0027]    A flux barrier angle α F  of the rotor  120  can be selected as a multiple of twenty as an electrical angle or an odd multiple of ten as the electrical angle based on a result of calculation, S n /(P×m)=3n or 2n. Here, the electrical angle is defined as 360° when each of different magnetic poles N and S of the rotor  120  passes a reference point one time. For instance, if the rotor  120  has two poles, the electrical angle is 360° when a one-time rotation of the rotor  120  occurs. If the rotor  120  has four poles, the electrical angle is 720° when the one-time rotation of the rotor  120  occurs. 
         [0028]    In case of S n /(P×m)=3n(n=1, 2, 3 . . . ), the flux barrier angle α F  may be, one of multiples of twenty (θ=20×n(n=1, 2, 3 . . . )). Also, the flux barrier angle α F  may have a predetermined range ((θ-2)&lt;α F &lt;(θ-2)). For example, if the number (S n ) of the slots  114  of the stator  110  is thirty-six, the number (P) of magnetic poles of the rotor  120  is four, and the number (m) of the power phases of the stator coil is three, the calculation can be the multiple of 3 (36/(4×3)). Therefore, the flux barrier angle α F  of the interior permanent magnet type BLDC motor may be one of multiples of twenty as the electrical angle. In this implementation, as the rotor  120  has four poles and the electrical angle upon the one-time rotation of the rotor  120  is 720, so the electrical angle of a single pole may be smaller than or equal to 180°. 
         [0029]    Further, the flux barriers for reducing the flux leakage are positioned at the rotor  120  and connected to the end of permanent magnets, respectively. The flux barrier angle α F  of the rotor  120  may have an electrical angle in the range of approximately 120° to 170° in consideration of the sizes of the permanent magnet insertion portions  124  and the flux barriers  126 . Here, it is noticed that if the flux barrier angle of the rotor  120  is smaller than 120°, the flux leakage is increased. If the flux barrier angle of the rotor  12   0  exceeds 170°, the deformation and/or damage of the flux barriers  126  may be caused due to a weak mechanical strength. 
         [0030]    Referring to  FIG. 3 , the cogging torque of the interior permanent magnet type BLDC motor is extremely high when the flux barrier angle α F  is 125° as the electrical angle, and decreases until the flux barrier angle α F  becomes 140°. The cogging torque is drastically increased until the flux barrier angle α F  exceeds 140° to become 145°. The cogging torque starts to be decreased again over 145° of the flux barrier angle α F , and is minimized at 160° of the flux barrier angle α F . Then, the cogging torque is drastically increased again between 160° and 165°. 
         [0031]    Further, referring to  FIG. 4 , a back electromotive force (BEMF) of the interior permanent magnet type BLDC motor is relatively low when the flux barrier angle α F  of the rotor  120  is 125° as the electrical angle. The BEMF is increased until the flux barrier angle α F  of the rotor  120  becomes 135° and thereafter gradually decreased. The BEMF is maintained at a particular level until flux barrier angle α F  of the rotor  120  is 160°, and then decreased again. 
         [0032]    Referring to  FIGS. 3 and 4 , it can be noticed that the interior permanent magnet type BLDC motor can minimize the cogging torque without lowering the motor efficiency when the flux barrier angle α F  of one pole of the rotor  120  is in the range around 160° (for example, between 158° and 162° as the electrical angle. Accordingly, the interior permanent magnet type BLDC motor can be more silently driven owing to a reduction of vibration and noise. 
         [0033]    In addition, in case of S n /(P×m)=2n(n=1, 2, 3 . . . )), the flux barrier angle α F  may be, as an electrical angle, one of multiples of ten (θ=5×n(n=2, 6, 10, . . . )). Also, the flux barrier angle α F  may have a predetermined range ((θ-2)&lt;α F &lt;(8-2)). 
         [0034]    For example, if the number (S n ) of the slots  114  of the stator  110  is twenty-four, the number (P) of magnetic poles of the rotor  120  is four, and the number (m) of the power phases of the stator coil is three, the calculation can be the multiple of 2 (24/(4×3)). Therefore, the flux barrier angle α F  of the interior permanent magnet type BLDC motor may be one of multiples of ten as the electrical angle. 
         [0035]    Referring to  FIG. 5 , the flux barrier angle of the rotor  120  from 125° to 165° to observe the changes in the cogging torque and the BEMF, it can be seen that the cogging torque is minimized without lowering the motor efficiency when the flux barrier angle α F  of the rotor  120  is in the range around 150° (for example in the range between 148° to 152°). As a result, the interior permanent magnet type BLDC motor capable of reducing the vibration and noise upon being driven can be provided. Throughout the implementations, it is noticed that flux barrier angle may be increased as the number of slots of the number are increased. 
         [0036]    It will be understood that various modifications may be made without departing from the spirit and scope of the claims. For example, advantageous results still could be achieved if steps of the disclosed techniques were performed in a different order and/or if components in the disclosed systems were combined in a different manner and/or replaced or supplemented by other components. Accordingly, other implementations are within the scope of the following claims.