Abstract:
A motor having an improved structure to enhance productivity and assemblability and a washing machine having the same includes a main body, a tub disposed in the main body, a drum rotatably disposed in the tub, and a motor mounted to a surface of the tub to rotate the drum. The motor includes a stator including a stator core and an insulator to cover the stator core, and a rotor rotatably disposed either inside or outside the stator. The insulator includes at least one support protrusion protruding from an inner circumferential surface of the insulator toward a center of the stator in order to support the stator core.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit of Korean Patent Application No. 10-2012-0085146, filed on Aug. 3, 2012 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The following description relates to a motor to generate rotational force and a washing machine having the same. 
         [0004]    2. Description of the Related Art 
         [0005]    A washing machine is an appliance that washes laundry using electric power. In general, a washing machine includes a tub to store wash water, a drum rotatably mounted in the tub, and a motor to rotate the drum. 
         [0006]    A motor includes a stator and a rotor, and generates rotational force using electric energy. The rotor is configured to electromagnetically interact with the stator, and rotates by force exerted by a magnetic field and an electric current flowing through coils. 
         [0007]    The stator includes a stator core and an insulator to receive the stator core therein. In general, the stator core has a circular shape, and the insulator has a receiving part corresponding to the circular stator core. 
         [0008]    In a manufacturing process of the stator, the stator core is inserted into the insulator. However, a center of the stator and a center of the insulator may be misaligned with each other, or a diameter of the stator core may be larger than a diameter of the receiving part of the insulator due to machining error occurring in the manufacturing process of the stator core. In this case, a worker may apply more force than necessary to insert the stator core into the insulator, which may cause damage to the insulator made of a weaker material than the stator core or may result in an inability to insert the stator core into the insulator. 
       SUMMARY 
       [0009]    It is an aspect of the present disclosure to provide a motor having an improved structure capable of enhancing productivity and assemblability and a washing machine having the same. 
         [0010]    Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
         [0011]    In accordance with an aspect of the present disclosure, a washing machine includes a main body, a tub disposed in the main body, a drum rotatably disposed in the tub, and a motor mounted to a rear surface of the tub to rotate the drum. The motor includes a stator including a stator core and an insulator to cover the stator core, and a rotor rotatably disposed either inside or outside the stator. The insulator includes at least one support protrusion protruding from an inner circumferential surface of the insulator toward a center of the stator in order to support the stator core. 
         [0012]    The support protrusion may be provided in two or more separate parts which are arranged spaced from each other along the inner circumferential surface of the insulator. 
         [0013]    The insulator may include a first insulator to cover one side of the stator core and a second insulator to cover the other side of the stator core, and the support protrusion may include a first support protrusion provided at an inner circumferential surface of the first insulator and a second support protrusion provided at an inner circumferential surface of the second insulator. 
         [0014]    At least a portion of the first support protrusion may be slanted in an insertion direction of the stator core into the first insulator, and at least a portion of the second support protrusion may be slanted in an insertion direction of the stator core into the second insulator. 
         [0015]    The first support protrusion may include a first slanted portion and a second slanted portion which have different slanted angles. 
         [0016]    The first slanted portion may protrude further than the second slanted portion toward a center of the first insulator. 
         [0017]    The slanted angle of the second slanted portion may be less than the slanted angle of the first slanted portion. 
         [0018]    The slanted angle of the second slanted portion may range from approximately 3° to approximately 10°. 
         [0019]    At least a portion of the second slanted portion may be in contact with an outer circumferential surface of the stator core when the stator core is in an inserted state in the first insulator. 
         [0020]    The stator core may include a core body having a ring shape and a plurality of core teeth extending from an inner circumferential surface of the core body toward a center of the stator core and arranged spaced apart from each other along the inner circumferential surface of the core body, and the insulator may include a first receiving part to receive the core body and a second receiving part to receive the plurality of core teeth. 
         [0021]    The support protrusion may be provided at an inner circumferential surface of the first receiving part to support an outer circumferential surface of the core body. 
         [0022]    The insulator may include a plurality of fixing ribs protruding toward the rear surface of the tub and arranged spaced apart from each other in a peripheral direction of the insulator, and a plurality of fixing holes formed through the fixing ribs in an axial direction of the stator. 
         [0023]    The stator may further include at least one sleeve inserted into the fixing holes, and the insulator may include at least one contact protrusion protruding from an inner circumferential surface of each of the fixing holes toward a center of each of the fixing holes and serving to contact an outer circumferential surface of the sleeve. 
         [0024]    The contact protrusion may be provided in two or more separate parts which are arranged spaced from each other along the inner circumferential surface of the fixing holes. 
         [0025]    The contact protrusions may be arranged equidistantly from each other. 
         [0026]    At least one of the contact protrusions may be disposed inside an imaginary circle whose diameter is a distance between a rotation center of the stator and a center of each of the fixing holes. 
         [0027]    An angle between a line connecting a center of the contact protrusion disposed inside the imaginary circle and the center of the fixing hole and a line connecting the rotation center of the stator and the center of the fixing hole may range from approximately 45° to less than approximately 90°. 
         [0028]    In accordance with an aspect of the present disclosure, a washing machine includes a main body, a tub disposed in the main body, a drum rotatably disposed in the tub, a motor to rotate the drum, and a fixing member to fix the motor to a rear surface of the tub. The motor includes a stator fixed to the rear surface of the tub, and a rotor rotatably disposed either inside or outside the stator. The stator includes at least one fixing hole through which the fixing member is inserted, a sleeve inserted into the fixing hole, and at least one contact protrusion protruding from an inner circumferential surface of the fixing hole toward a center of the fixing hole and serving to contact an outer circumferential surface of the sleeve. 
         [0029]    The stator may include a stator core and an insulator to cover the stator core, the insulator may include a plurality of fixing ribs arranged spaced apart from each other in a peripheral direction of the insulator, and the fixing hole may be formed through each of the fixing ribs in an axial direction of the stator. 
         [0030]    The contact protrusion may have a smaller length than the inner circumferential surface of the fixing hole in an axial direction of the fixing hole. 
         [0031]    The contact protrusion may include a guide portion configured to contact an end of the sleeve and guide the sleeve to be inserted into an area of the fixing hole provided with the contact protrusion. 
         [0032]    The contact protrusion may be provided in two or more separate parts which are arranged equidistantly from each other along the inner circumferential surface of the fixing hole. 
         [0033]    At least one of the contact protrusions may be disposed inside an imaginary circle whose diameter is a distance between a rotation center of the stator and a center of the fixing hole, and an angle between a line connecting a center of the contact protrusion disposed inside the imaginary circle and the center of the fixing hole and a tangent line of the imaginary circle passing the center of the fixing hole may be greater than approximately 0° and less than approximately 45°. 
         [0034]    The contact protrusion may protrude from a portion of the inner circumferential surface of the fixing hole which is located apart from an entrance of the fixing hole in an axial direction of the fixing hole. 
         [0035]    The stator may include a first insulator to cover one side of the stator core and a second insulator to cover the other side of the stator core. 
         [0036]    The fixing ribs may include a plurality of first fixing ribs arranged spaced from each other in a peripheral direction of the first insulator, and a plurality of second fixing ribs arranged spaced from each other in a peripheral direction of the second insulator. The fixing holes may include a plurality of first fixing holes formed through the first fixing ribs in an axial direction of the stator, and a plurality of second fixing holes formed through the second fixing ribs in the axial direction of the stator and respectively communicating with the plurality of first fixing holes. The contact protrusion may include at least one first contact protrusion protruding from an inner circumferential surface of each of the first fixing holes toward a center of each of the first fixing holes and serving to contact the outer circumferential surface of the sleeve, and at least one second contact protrusion protruding from an inner circumferential surface of each of the second fixing holes toward a center of each of the second fixing holes and serving to contact the outer circumferential surface of the sleeve. 
         [0037]    The first contact protrusion may protrude from a portion of the inner circumferential surface of the first fixing hole which is located apart from an entrance of the first fixing hole in an axial direction of the first fixing hole. 
         [0038]    The second contact protrusion may protrude from a portion of the inner circumferential surface of the second fixing hole which is located apart from an entrance of the second fixing hole in an axial direction of the second fixing hole. 
         [0039]    In accordance with an aspect of the present disclosure, a motor includes a stator including a stator core and an insulator to cover the stator core, and a rotor rotatably disposed either inside or outside the stator. The insulator includes at least one support protrusion protruding from an inner circumferential surface of the insulator, which opposes an outer circumferential surface of the stator core, toward a center of the stator in order to support the stator core. 
         [0040]    As is apparent from the above description, due to the support protrusions provided at the inner circumferential surface of the insulator in order to support the outer circumferential surface of the stator core, the assembly of the stator core and the insulator may be easily achieved, and defective assembly because of machining error of the stator core is prevented, thereby enhancing assemblability and productivity of the motor. 
         [0041]    In addition, due to the contact protrusions provided at the inner circumferential surface of the fixing hole configured to fix the stator to the rear surface of the tub in order to contact the outer circumferential surface of the sleeve, the sleeve may be easily inserted into the fixing hole, and defective assembly because of machining error of the sleeve is prevented, thereby enhancing assemblability and productivity of the motor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]    These and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0043]      FIG. 1  is a view showing a washing machine according to an embodiment of the present disclosure; 
           [0044]      FIG. 2  is an exploded perspective view showing a stator and a rotor of a motor and a tub in the washing machine according to the embodiment of the present disclosure; 
           [0045]      FIG. 3  is a perspective view showing the stator of the motor according to the embodiment of the present disclosure; 
           [0046]      FIG. 4  is a plan view showing the stator of the motor according to the embodiment of the present disclosure; 
           [0047]      FIG. 5  is an exploded perspective view showing the stator depicted in  FIG. 3 ; 
           [0048]      FIG. 6  is a plan view showing a second insulator depicted in  FIG. 5 ; 
           [0049]      FIG. 7  is a plan view showing engagement of the second insulator with a stator core; 
           [0050]      FIG. 8  is an enlarged view of portion “A” in  FIG. 7 ; 
           [0051]      FIG. 9  is a sectional view taken along line I-I in  FIG. 6 ; 
           [0052]      FIG. 10  is a view showing a process of engaging the stator core with the second insulator in  FIG. 9 ; 
           [0053]      FIG. 11  is an enlarged view of portion “B” in  FIG. 4 ; and 
           [0054]      FIG. 12  is a sectional view taken along line n-n in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0055]    Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. A motor according to the embodiments of the present disclosure may be used for various apparatuses using a motor as a power source, such as a washing machine, an air conditioner, an electric car, a light rail transit system, an electric bicycle, a small-sized electric generator or the like, and a washing machine will be explained for a better understanding of the present disclosure. 
         [0056]      FIG. 1  is a view showing a washing machine according to an embodiment of the present disclosure. 
         [0057]    As shown in  FIG. 1 , a washing machine  1  includes a cabinet  10  defining an appearance thereof, a tub  20  disposed in the cabinet  10 , a drum  30  rotatably disposed in the tub  20 , and a motor  40  to rotate the drum  30 . 
         [0058]    The cabinet  10  is formed with a laundry entrance hole  11  at a front portion thereof, through which a user places laundry into the drum  30 . A door  12  is provided at the front portion of the cabinet  10  in order to open and close the laundry entrance hole  11 . However, the disclosure is not limited to the above embodiment. For example, the door may be provided on a top portion of the cabinet  10 . 
         [0059]    A water supply pipe  50 , through which wash water is supplied to the tub  20 , is mounted above the tub  20 . One end of the water supply pipe  50  is connected to an external water supply source (not shown), and the other end of the water supply pipe  50  is connected to a detergent supply device  60 . The detergent supply device  60  is connected to the tub  20  by a connecting pipe  55 . The water supplied through the water supply pipe  50  flows into the tub  20  together with a detergent via the detergent supply device  60 . 
         [0060]    A drain pump  70  and a drain pipe  75  are mounted below the tub  20 , in order to discharge the water in the tub  20  from the cabinet  10 . 
         [0061]    The drum  30  is formed with a plurality of through-holes  31  for wash water flow on a peripheral surface thereof. The drum  30  is also provided with a plurality of lifters  32  on an inner circumferential surface thereof, in order to lift laundry when the drum  30  is rotated. 
         [0062]    The drum  30  and the motor  40  are connected to each other by a driving shaft  80 . The driving shaft  80  transmits rotational force of the motor  40  to the drum  30 . One end of the driving shaft  80  is connected to the drum  30 , and the other end of the driving shaft  80  extends outwardly from a rear wall  21  of the tub  20 . 
         [0063]    A bearing housing  82  is mounted to the rear wall  21  of the tub  20 , in order to rotatably support the driving shaft  80 . The bearing housing  82  may be made of aluminum alloy, and may be inserted into the rear wall  21  of the tub  20  in an injection molding process of the tub  20 . Bearings  84  are disposed between the bearing housing  82  and the driving shaft  80  so that the driving shaft  80  may smoothly rotate. However, the disclosure is not limited to the above embodiment. For example, the washing machine may comprise a top loading type washing machine where the above components are arranged to provide a top loading arrangement. 
         [0064]      FIG. 2  is an exploded perspective view showing a stator and a rotor of the motor and the tub in the washing machine according to the embodiment of the present disclosure,  FIG. 3  is a perspective view showing the stator of the motor according to the embodiment of the present disclosure,  FIG. 4  is a plan view showing the stator of the motor according to the embodiment of the present disclosure, and  FIG. 5  is an exploded perspective view showing the stator depicted in  FIG. 3 . Illustration of a coil is omitted in  FIGS. 3 and 5 . The motor according to the embodiment of the present disclosure includes both an inner rotor type motor, in which a rotor is disposed inside a stator, and an outer rotor type motor, in which a rotor is disposed outside a stator. Hereinafter, an inner rotor type motor will be explained for a better understanding of the present disclosure. 
         [0065]    As shown in  FIGS. 2 through 5 , the motor  40  is coupled outside the tub  20 , and supplies power to the drum  30  to rotate the same in both directions. The motor  40  includes a stator  100  mounted to the rear wall  21  of the tub  20 , and a rotor  200  disposed inside the stator  100  and configured to rotate by electromagnetic interaction with the stator  100 . 
         [0066]    The stator  100  is formed by engagement of a stator core  101  made of a metallic material and an insulator  102  covering the stator core  101 . The stator  100  includes a circular stator body  110 , a plurality of stator teeth  120  arranged in a peripheral direction of the stator body  110 , coils  130  wound around the plurality of stator teeth  120 , a plurality of fixing ribs  140  to fix the stator  100  to the rear wall  21  of the tub  20 , a plurality of fixing pins  142 , and a plurality of fixing holes  144 . 
         [0067]    The stator body  110  supports the plurality of stator teeth  120 . The plurality of stator teeth  120  radially protrude from an inner circumferential surface of the stator body  110  toward a center of the stator body  110 , and are arranged spaced apart from each other in a peripheral direction of the stator body  110 . 
         [0068]    The fixing ribs  140  protrude from one side surface of the stator body  110 , which opposes the rear wall  21  of the tub  20 , toward the rear wall  21  of the tub  20 , and are arranged spaced apart from each other in a peripheral direction of the stator body  110 . 
         [0069]    The fixing pins  142  protrude from one surface of the fixing ribs  140 , which opposes the rear wall  21  of the tub  20 , toward the rear wall  21  of the tub  20 . The fixing pins  142  serve to be inserted into the rear wall  21  of the tub  20  in order to set the position of the stator  100  before fixing the stator  100  to the rear wall  21  of the tub  20 . 
         [0070]    The fixing holes  144  are formed through the stator body  110  and the fixing ribs  140 . Sleeves  170  are inserted into the fixing holes  144  in order to reinforce engagement between the stator  100  and the tub  20 . Fixing members  150 , such as bolts, for example, are coupled to the rear wall  21  of the tub  20  through the sleeves  170 . 
         [0071]    The fixing ribs  140 , the fixing pins  142 , and the fixing holes  144  may be formed integrally with the insulator  102  in an injection molding process of a first insulator  102   a  and a second insulator  102   b.    
         [0072]    The rear wall  21  of the tub  20 , to which the stator  100  is coupled, is provided with support ribs  160  configured to be in contact with the fixing ribs  140  to support the stator  100  after the stator  100  is coupled to the rear wall  21  of the tub  20 , first receiving holes  161  formed at the support ribs  160 , into which the fixing pins  142  are inserted, and second receiving holes  162  formed at the support ribs  160 , into which the fixing members  150  are inserted. 
         [0073]    The support ribs  160  protrude rearward from the rear wall  21  of the tub  20 , and are positioned corresponding to the fixing ribs  140  so as to be kept in contact with the fixing ribs  140  in a state of coupling the stator  100  to the rear wall  21  of the tub  20 . 
         [0074]    The first receiving holes  161  receive the fixing pins  142  therein so that the position of the stator  100  may be set before the stator  100  is fixed to the rear wall  21  of the tub  20 . The second receiving holes  162  receive the fixing members  150 , such as bolts, therein so that the stator  100  may be fixed to the rear wall  21  of the tub  20 . 
         [0075]    The first receiving holes  161  and the second receiving holes  162  may be formed integrally with the tub  20  in an injection molding process of the tub  20 . 
         [0076]    Hereinafter, engagement between the stator core  101  and the insulator  102  will be explained. 
         [0077]      FIG. 6  is a plan view showing the second insulator depicted in  FIG. 5 ,  FIG. 7  is a plan view showing the engagement between the stator core and the second insulator,  FIG. 8  is an enlarged view of portion “A” in  FIG. 7 ,  FIG. 9  is a sectional view taken along line I-I in  FIG. 6 , and  FIG. 10  is a view showing a process of engaging the stator core with the second insulator in  FIG. 9 . 
         [0078]    As shown in  FIGS. 2 through 10 , the stator core  101  includes a ring-shaped core body  101   a,  and a plurality of core teeth  101   b  radially extending from an inner circumferential surface of the core body  101   a  toward a center of the core body  101   a  and arranged spaced apart from each other along the inner circumferential surface of the core body  101   a.  The first insulator  102   a  and the second insulator  102   b  cover both sides of the stator core  101 . The stator core  101  may be formed by laminating pressed steel plates, and the first and second insulators  102   a  and  102   b  may be made of a material having electrical insulation. 
         [0079]    The first insulator  102   a  and the second insulator  102   b  are provided with at least one first support protrusion (not shown) and at least one second support protrusion  104 , respectively, in order to support the outer circumferential surface of the stator core  101 . Because a structure of the first insulator  102   a  to receive one side of the stator core  101  and a structure of the second insulator  102   b  to receive the other side of the stator core  101  are identical, the structure of the second insulator  102   b  to receive the stator core  101  will be focused upon to avoid repetition. 
         [0080]    The second insulator  102   b  includes a first receiving part  106  to receive the core body  101   a,  and a second receiving part  107  to receive the plurality of core teeth  101   b.  The first receiving part  106  has a ring shape corresponding to the core body  101   a  to receive the core body  101   a.  The second receiving part  107  is connected to an inner side of the first receiving part  106 , and has a shape corresponding to the core teeth  101   b  to receive the respective core teeth  101   b.    
         [0081]    The inner circumferential surface of the second insulator  102   b,  which opposes the outer circumferential surface of the core body  101   a,  is provided with a plurality of second support protrusions  104  which contact the outer circumferential surface of the core body  101   a  to support the same. The second support protrusions  104  protrude from the inner circumferential surface of the second insulator  102   b  toward a center of the stator  100 . 
         [0082]    Each of the second support protrusions  104  includes a first slanted portion  108   a  and a second slanted portion  108   b  which have different slanted angles from each other. 
         [0083]    The first slanted portion  108   a  is formed at an upper portion of the second support protrusion  104  so as to temporarily support the stator core  101  before the stator core  101  is inserted into the second insulator  102   b.  Because the slanted angle of the first slanted portion  108   a  is larger than the slanted angle of the second slanted portion  108   b,  the stator core  101  may be seated on the upper portion of the second insulator  102   b  before the stator core  101  is inserted into the second insulator  102   b.    
         [0084]    The second slanted portion  108   b  is formed below the first slanted portion  108   a,  and serves to guide the stator core  101  to be inserted into the second insulator  102   b.  In addition, when the stator core  101  is in a completely inserted state in the second insulator  102   b,  at least a portion of the second slanted portion  108   b  contacts the outer circumferential surface of the stator core  101  and supports the same so that the stator core  101  may be firmly fixed to the second insulator  102   b.  To guide the stator core  101  to be inserted into the second insulator  102   b  and support the stator core  101  by contacting the outer circumferential surface of the same, the second slanted portion  108   b  may have a slanted angle ranging from approximately 3° to approximately 10°. 
         [0085]    The plurality of second support protrusions  104  are arranged spaced apart from each other along the inner circumferential surface of the second insulator  102   b  in a peripheral direction. Accordingly, although a center of the stator core  101  is slightly misaligned with a center of the second insulator  102   b  when the stator core  101  is seated on the first slanted portion  108   a  in an initial process of assembly, a relative position between the stator core  101  and the second insulator  102   b  is corrected so that the center of the stator core  101  and the center of the second insulator  102   b  are aligned with each other in the process of inserting the stator core  101  into the second insulator  102   b.    
         [0086]    The support protrusions  104  decrease a contact area between the stator core  101  and the second insulator  102   b  so that the stator core  101  may be easily inserted into the second insulator  102   b.  In addition, although an actual diameter of the stator core  101  is slightly larger than a designed diameter due to a machining error, for example, the machining error is compensated for by a process in which the second support protrusions  104  contact the outer circumferential surface of the stator core  101  and are deformed when the stator core  101  is inserted into the second insulator  102   b,  which prevents the stator core  101  from not being inserted into the second insulator  102   b.    
         [0087]    Hereinafter, engagement between the stator  100  and the sleeves  170  will be explained. 
         [0088]      FIG. 11  is an enlarged view of a B portion in  FIG. 4 , and  FIG. 12  is a sectional view taken along line n-n in  FIG. 11 . 
         [0089]    As shown in  FIGS. 2 through 5 ,  11 , and  12 , the first insulator  102   a  and the second insulator  102   b  include a plurality of first fixing ribs  140   a  and a plurality of second fixing ribs  140   b,  respectively, which compose the plurality of fixing ribs  140  when the first insulator  102   a  and the second insulator  102   b  are in a coupled state with the stator core  101 . The first insulator  102   a  and the second insulator  102   b  further include a plurality of first fixing holes  144   a  and a plurality of second fixing holes  144   b,  respectively, which compose the plurality of fixing holes  144  by communicating with each other when the first insulator  102   a  and the second insulator  102   b  are in a coupled state with the stator core  101 . 
         [0090]    Each of the first fixing holes  144   a  is provided with at least one first contact protrusion  147  which protrudes from an inner circumferential surface of the first fixing hole  144   a  toward a center of the first fixing hole  144   a  and contacts an outer circumferential surface of the sleeve  170 . Each of the second fixing holes  144   b  is provided with at least one second contact protrusion  148  which protrudes from an inner circumferential surface of the second fixing hole  144   b  toward a center of the second fixing hole  144   b  and contacts the outer circumferential surface of the sleeve  170 . 
         [0091]    The first contact protrusion  147  includes a first guide portion  147   a  which is configured to contact an end of the sleeve  170  and guide the sleeve  170  to be inserted into an area of the first fixing hole  144   a  provided with the first contact protrusion  147 , and a first contact portion  147   b  which is configured to be kept in contact with the outer circumferential surface of the sleeve  170  inserted into the first fixing hole  144   a  and support the sleeve  170 . 
         [0092]    As shown in  FIG. 12 , the first contact protrusion  147  protrudes from a portion of the inner circumferential surface of the first fixing hole  144   a  which is located apart from an entrance D 1  of the first fixing hole  144   a  in an axial direction of the first fixing hole  144   a.  That is, the first guide portion  147   a  is not located at the entrance D 1  of the first fixing hole  144   a,  but is located on the inner circumferential surface of the first fixing hole  144   a  which is spaced apart from the entrance D 1  of the first fixing hole  144   a  by a certain distance d 1 . The reason that the first contact protrusion  147  is located apart from the entrance D 1  of the first fixing hole  144   a  in an axial direction of the first fixing hole  144   a  is that an end of the sleeve  170  may be supported by a portion of the inner circumferential surface of the first fixing hole  144   a  without the first contact protrusion  147  while the end of the sleeve  170  is in contact with the first guide portion  147   a  before the sleeve  170  is inserted into the first fixing hole  144   a.    
         [0093]    The first contact protrusion  147  may be provided in two or more separate parts which are arranged equidistantly from each other along the inner circumferential surface of the first fixing hole  144   a.  The plurality of first contact protrusions  147  are arranged spaced from each other so that force exerted on the first fixing hole  144   a  is not concentrated at a specific point but is evenly dispersed while the stator  100  is fixed to the rear wall  21  of the tub  20 . 
         [0094]    For instance, as shown in  FIG. 11 , if three first contact protrusions  147  are provided at the inner circumferential surface of the first fixing hole  144   a,  an imaginary circle C 1 , whose diameter is a distance between a rotation center Cs of the stator  100  and a center Ch of the first fixing hole  144   a,  may be formed. On the basis of the imaginary circle C 1 , an angle a between a line L 1 , which connects a center Ck of two first contact protrusions  147  disposed inside the imaginary circle C 1  and the center Ch of the first fixing hole  144   a,  and a tangent line L 2  of the imaginary circle C 1 , which passes the center Ch of the first fixing hole  144   a,  is greater than approximately 0° and less than approximately 45°. Because a thickness of the first insulator  102   a  around the first fixing hole  144   a  in a peripheral direction of the first insulator  102   a  is larger than a thickness of the first insulator  102   a  around the first fixing hole  144   a  in a radial direction of the first insulator  102   a,  the plurality of first contact protrusions  147  are arranged so that force exerted on the first fixing hole  144   a  is directed toward a periphery of the first insulator  102   a  around the first fixing hole  144   a.    
         [0095]    Similar to the first contact protrusion  147 , the second contact protrusion  148  includes a second guide portion  148   a  which is configured to contact an end of the sleeve  170  and guide the sleeve  170  to be inserted into an area of the second fixing hole  144   b  provided with the second contact protrusion  148 , and a second contact portion  148   b  which is configured to be kept in contact with the outer circumferential surface of the sleeve  170  inserted into the second fixing hole  144   b  and support the sleeve  170 . 
         [0096]    The second contact protrusion  148  protrudes from a portion of the inner circumferential surface of the second fixing hole  144   b  which is located apart from an entrance D 2  of the second fixing hole  144   b  in an axial direction of the second fixing hole  144   b.  That is, the second guide portion  148   a  is not located at the entrance D 2  of the second fixing hole  144   b,  but is located on the inner circumferential surface of the second fixing hole  144   b  which is spaced apart from the entrance D 2  of the second fixing hole  144   b  by a certain distance d 2 . The reason that the second contact protrusion  148  is located apart from the entrance D 2  of the second fixing hole  144   b  in an axial direction of the second fixing hole  144   b  is that although a center of the first fixing hole  144   a  and a center of the second fixing hole  144   b  may be slightly misaligned in the insertion process of the sleeve  170 , the sleeve  170  having passed through the first fixing hole  144   a  may be easily inserted into the second fixing hole  144   b.    
         [0097]    The second contact protrusion  148  may be provided in two or more separate parts which are arranged equidistantly from each other along the inner circumferential surface of the second fixing hole  144   b.  The plurality of second contact protrusions  148  are arranged spaced from each other so that force exerted on the second fixing hole  144   b  is not concentrated at a specific point but is evenly dispersed while the stator  100  is fixed to the rear wall  21  of the tub  20 . The arrangement principle of the plurality of second contact protrusions  148  is substantially the same as that of the aforementioned a plurality of first contact protrusions  147 , and a detailed description thereof will thus be omitted. 
         [0098]    The first contact protrusions  147  and the second contact protrusions  148  decrease a contact area between the first and second fixing holes  144   a  and  144   b  and the sleeve  170  so that the sleeve  170  may be easily inserted into the first fixing hole  144   a  and the second fixing hole  144   b.  In addition, although an actual diameter of the sleeve  170  may be slightly larger than a designed diameter due to machining error, for example, the machining error is compensated for by a process in which the first contact protrusions  147  and the second contact protrusions  148  contact the outer circumferential surface of the sleeve  170  and are deformed when the sleeve  170  is inserted into the first fixing hole  144   a  and the second fixing hole  144   b,  which prevents the sleeve  170  from not being inserted into the first fixing hole  144   a  and the second fixing hole  144   b.    
         [0099]    Although a few embodiments of the present disclosure have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.