Patent Publication Number: US-2010109460-A1

Title: Motor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a motor and, more particularly, to a motor that has a dual retaining function and provides convenience of assembling. 
     2. Description of the Related Art 
     A conventional motor is described in Taiwan Patent Publication No. 200811372 (with Issue No. I304115) entitled “FAN”. Referring to  FIG. 1 , the fan includes a motor  90  having a base  91  preferably forming a casing of the fan, a sliding bearing  92 , a stator  93 , an oil end cap  94 , a rotor  95  with a shaft  951 , an upper retaining ring  96  with a first through hole  961 , and a lower retaining ring  97  with a second through hole  971 . The base  91  has a shaft tube  911  with a top and a bottom thereof open. A portion of the shaft tube  911  close to the top thereof is bent downwards and inwards to form an annular abutting flange  912  and an inner surface of the shaft tube  911  adjacent to the bottom thereof forms a thread  913 . The sliding bearing  92  is received in the shaft tube  911  and has a center hole  921 . The stator  93  is mounted around the shaft tube  911  and the oil end cap  94  is coupled inside the shaft tube  911  and engages with the thread  913 . The upper retaining ring  96  and the lower retaining ring  97  are mounted around the shaft  951  and close to two ends of the shaft  951  respectively. By this arrangement, the stator  93  is able to drive the rotor  95  to revolve around the stator  93 . And the upper retaining ring  96  and the lower retaining ring  97  jointly constitute a double retaining feature of the motor  90  to prevent the rotor  95  from disengaging from the base  91  during rotation. 
     Referring to  FIG. 2 , in assembly of the conventional motor  90 , the upper retaining ring  96 , the sliding bearing  92 , the lower retaining ring  97  and the oil end cap  94  are disposed into the shaft tube  911  in sequence through the bottom opening of the shaft tube  911 , with the oil end cap  94  engaging with the thread  913 . And then the shaft  951  of the rotor  95  sequentially passes through the top opening of the shaft tube  911 , the first through hole  961 , the center hole  921  and the second through hole  971 . Consequently, the shaft  951  can smoothly revolve in the sliding bearing  92 . Nevertheless, said conventional motor  90  has several drawbacks in assembly as the following. 
     First, as seen in  FIG. 3 , the upper retaining ring  96  is sandwiched between the annular abutting flange  912  and the sliding bearing  92  when the upper retaining ring  96  and the sliding bearing  92  are received in the shaft tube  911 , but this arrangement does not provide the upper retaining ring  96  with a reliable radial positioning effect. Because the upper retaining ring  96  is liable to move radially after being received in the shaft tube  911 , a gap “D” is formed between a central line of the first through hole  961  of the upper retaining ring  96  and a central line of the center hole  921  of the sliding bearing  92 . Thus, the gap “D” will lead to difficulty of passing the shaft  951  through the first through hole  961  and the center hole  921  in sequence. And therefore, the arrangement of the upper retaining ring  96  may need to be adjusted again for complete insertion of the shaft  951  into the shaft tube  911 . As a result, inconvenience of assembling the motor  90  is caused. 
     Second, the lower retaining ring  97  is disposed on a top of the oil end cap  94  in assembly of the motor  90  and then the oil end cap  94  is fixed to the bottom of the shaft tube  911  by engaging with the thread  913 . If the oil end cap  94  is not completely screwed into a predetermined position inside the shaft tube  911 , the lower retaining ring  97  will not be stably sandwiched between the sliding bearing  92  and the oil end cap  94 , and thus axial movement of the lower retaining ring  97  occurs. And that results in difficulty of passing the shaft  951  of the rotor  95  through the second through hole  971 . As shown in  FIG. 4 , even if the shaft  951  successfully passes through the second through hole  971 , an inner edge of the lower retaining ring  97  still will not extend into a annular groove  952  of the shaft  951  because the lower retaining ring  97  is not at a right position for assembling the motor  90 . Therefore, due to the way, screwing, by which the oil end cap  94  engages with the shaft tube  911 , a reliable radial positioning effect on the lower retaining ring  97  is probably inaccessible, and thus the lower retaining ring  97  can be at a wrong position for assembling the motor  90 . Hence, there is a high probability of an occurrence of incomplete combination of the rotor  95  and the stator  93 . Consequently, extra manpower and time to adjust the positions of the lower retaining ring  97  and the oil end cap  94  relative to the shaft tube  911  are necessary for assurance of a fine assembly of the motor  90 . 
     Third, there are too many components, such as the sliding bearing  92 , the oil end cap  94 , the upper retaining ring  96  and the lower retaining ring  97 , received in the shaft tube  911 , and these components results in a complex structure and complex steps for assembling. Besides, additional processing procedures are needed for forming the annular abutting flange  912  and the thread  913 . Thus, inconvenience of assembling the motor  90  is caused and production cost of the motor  90  is increased. 
     In conclusion, although departure of the rotor  95  from the base  91  is avoided by the upper retaining ring  96  and the lower retaining ring  97  jointly constituting the double retaining feature, problems of inconvenience of assembling and the complex structure for assembly result in extra manpower and time for adjustment of assembly of the conventional motor  90 . Hence, there is a need for an improvement over the conventional motor. 
     SUMMARY OF THE INVENTION 
     It is therefore the primary objective of this invention to provide a motor that overcomes the problems of the prior art described above to allow convenience of assembling and a simplified structure. 
     A motor according to the preferred teachings of the present invention includes a base, a stator, a retaining seat, a bearing, a retaining ring and a rotor. The base has a shaft tube with an assembling hole. Two ends of the shaft tube are an open end and a closed end respectively. The stator is mounted around the shaft tube. The retaining seat includes a first axial hole and is received in the assembling hole. The retaining seat is disposed at the closed end of the shaft tube and an outer diameter of the retaining seat is equal to a diameter of the assembling hole. The bearing has a center hole and is received in the assembling hole of the shaft tube. The bearing abuts the retaining seat. The retaining ring has a second axial hole and is received in the assembling hole of the shaft tube. An outer diameter of the retaining ring is equal to the diameter of the assembling hole. The bearing is sandwiched and positioned between the retaining ring and the retaining seat. The rotor includes a shaft having a first annular groove in a neck shape and a second annular groove in a neck shape formed in an outer periphery thereof to respectively form a first neck and a second neck of the shaft. An outer diameter of the first neck is smaller than a diameter of the first axial hole of the retaining seat and an outer diameter of the second neck is smaller than a diameter of the second axial hole of the retaining ring. The shaft passes through the second axial hole, the center hole and the first axial hole, with the retaining seat and the retaining ring surrounding and partially extending into the first annular groove and the second annular groove respectively. Accordingly, radial and axial movement of the retaining seat, the bearing and the retaining ring is avoided effectively after being mounted into the shaft tube to provide convenience of assembling and a simplified structure. 
     In an example, the assembling hole has an upper hole adjacent to the open end and a lower hole in communication with the upper hole and adjacent to the closed end, with a diameter of the upper hole being larger than a diameter of the lower hole to form a shoulder in an inner periphery of the assembling hole and between the upper hole and the lower hole, with the outer diameter of the retaining seat being equal to a diameter of the lower hole and the outer diameter of the retaining ring being equal to a diameter of the upper hole, with the retaining ring abutting against the shoulder. Accordingly, there is no axial movement of the retaining ring to reliably position the retaining ring. 
     In an example, the stator includes an abutting member on a top thereof, with the abutting member abutting against and positioning the retaining ring. Accordingly, the retaining seat, the bearing and the retaining ring disengaging from the shaft tube of the base is effectively avoided. 
     In an example, the abutting member is in the form of a plurality of pressing plates, with each pressing plate having one end fixed to the stator and another end extending into the assembling hole of the shaft tube of the base, with the ends of the pressing plates which extend into the assembling hole abutting against the retaining ring. Accordingly, the pressing plates can abut against the top of the retaining ring to provide more reliably positioning effect on the retaining ring. 
     In an example, the motor further includes a positioning ring coupled in the shaft tube of the base and abutting the retaining ring, with the retaining ring being sandwiched between the positioning ring and the bearing. Accordingly, the retaining seat, the bearing and the retaining ring disengaging from the shaft tube of the base is effectively avoided. 
     In an example, the positioning ring has an L-shape cross-section from an axial center line of the positioning ring to a radial outer edge thereof. Accordingly, a contact area between the inner periphery of the shaft tube and the positioning ring is increased to improve coupling stability of a combination of the positioning ring and the shaft tube. 
     In an example, the diameter of the second axial hole of the retaining ring is larger than the diameter of the first axial hole of the retaining seat. Accordingly, convenience of assembling is further enhanced, under retaining effect of the retaining seat and the retaining ring. 
     In an example, the shaft tube includes an annular protrusion on an outer periphery thereof, with a bottom of the stator abutting on the annular protrusion. Accordingly, the stator is supported by the annular protrusion to enhance convenience of assembling the motor. 
     Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferable embodiments of the invention, are given by way of illustration only, since various will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a cross sectional view illustrating a conventional motor; 
         FIG. 2  is a cross sectional view illustrating the conventional motor in assembly; 
         FIG. 3  is an enlarged detailed cross sectional view illustrating misalignment of central lines of a retaining ring and a bearing of the conventional motor; 
         FIG. 4  is a cross sectional view illustrating assembly failure of the conventional motor; 
         FIG. 5  is an exploded perspective view illustrating a motor in accordance with a first embodiment of the present invention; 
         FIG. 6  is a cross sectional view illustrating the motor in accordance with the first embodiment of the present invention; 
         FIG. 7  is a cross sectional view illustrating the motor in accordance with the first embodiment of the present invention in assembly; 
         FIG. 8  is an exploded perspective view illustrating a motor in accordance with a second embodiment of the present invention; 
         FIG. 9  is a cross sectional view illustrating the motor in accordance with the second embodiment of the present invention; and 
         FIG. 10  is a cross sectional view illustrating the motor in accordance with the second embodiment of the present invention in assembly. 
     
    
    
     In the various figures of the drawings, the same numerals designate the same or similar parts. Furthermore, when the terms “first”, “second”, “annular”, “axial”, “radial”, “outer”, “inner”, “section”, “portion”, “end”, “lower”, “upper”, “inwards”, “longitudinal” and similar terms are used hereinafter, it should be understood that these terms are reference only to the structure shown in the drawings as it would appear to a person viewing the drawings and are utilized only to facilitate describing the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A motor of a first embodiment according to the preferred teachings of the present invention is shown in  FIGS. 5 and 6  of the drawings. According to the first embodiment form shown, the motor includes a base  10 , a stator  20 , a retaining seat  30 , a bearing  40 , a retaining ring  50  and a rotor  60 . Optionally, the base  10  can be designed as a frame of a fan, such that the motor of the present invention can be utilized for a heat-dissipating fan. Furthermore, the stator  20  and the bearing  40  is mounted to the base  10  and the rotor  60  rotatably couples to the bearing  40 , so that the stator  20  is able to drive the rotor  60  to rotate. The rotor  60  may couple to a plurality of blades (not illustrated) on an outer periphery thereof to be jointly regarded as an impeller when the motor of the present invention is used as the heat-dissipating fan. The retaining seat  30  and the retaining ring  50  are mounted to the rotor  60  for the rotor  60  to avoid disengaging from the base  10  during packing, conveyance or utilization of the motor, wherein the retaining ring  50  can be taken as an oil leak-proof member. Therefore, the retaining seat  30  and the retaining ring  50  jointly constitute a double retaining feature of the motor according to the preferred teachings of the present invention, such that the motor has a dual retaining function to enhance convenience of assembling, provide a simplified structure and avoid oil leakage. 
     The base  10  of the first embodiment according to the preferred teachings of the present invention has a shaft tube  11  made of metal and a plate  12  for the shaft tube  11  to securely mount, wherein the shaft tube  11  and plate  12  are two separate pieces. The shaft tube  11  has an assembling hole  111  and two ends of the shaft tube  11  are an open end  112  away from the plate  12  and a closed end  113  formed by the shaft tube  11  and the plate  12  jointly, as shown in  FIG. 6 . Or the shaft tube  11  can form the closed end  113  alone. 
     The stator  20  of the first embodiment according to the preferred teachings of the present invention is mounted around the shaft tube  11  of the base  10 . 
     The retaining seat  30  of the first embodiment according to the preferred teachings of the present invention is a hollow cylindrical member having a longitudinal through-hole. An inner periphery of the retaining seat  30  radially extends a plurality of first retaining plates  31  toward a central line of the longitudinal through-hole to define a first axial hole  32 , with the first retaining plates  31  close to one end of the retaining seat  30 . Furthermore, the retaining seat  30  is received in the assembling hole  111  and disposed at the closed end  113  of the shaft tube  11 , with an outer diameter of the retaining seat  30  being equal to a diameter of the assembling hole  111  of the shaft tube  11 . Hence, the retaining seat  30  radially abuts on an inner surface defining the assembling hole  111  and thus is positioned inside the shaft tube  11  without radial movement. 
     The bearing  40  of the first embodiment according to the preferred teachings of the present invention has a center hole  41  and is also received in the assembling hole  111  of the shaft tube  11 . A bottom end face of the bearing  40  abuts against a top end face of the retaining seat  30  close to the first retaining plates  31 , with the center hole  41  of the bearing  40  being aligned with the first axial hole  32  of the retaining seat  30 . Besides, an outer diameter of the bearing  40  is preferable equal to the diameter of the assembling hole  111  of the shaft tube  11 , so that the bearing  40  also radially abuts on the inner surface defining the assembling hole  111  and is positioned inside the shaft tube  11  without radial movement. 
     An inner periphery of the retaining ring  50  of the first embodiment plurality of second retaining plates  51  toward a central line of the retaining ring  50  to define a second axial hole  52 . The retaining ring  50  is received in the assembling hole  111  of the shaft tube  11 , and a bottom end face of the retaining ring  50  abuts against a top end face of the bearing  40 , with an outer diameter of the retaining ring  50  being equal to the diameter of the assembling hole  111  of the shaft tube  11 . Therefore, the retaining ring  50  radially abuts on the inner surface defining the assembling hole  111  and is positioned inside the shaft tube  11  without radial movement, with the second axial hole  52  being aligned with the center hole  41  of the bearing  40 . In addition, the bearing  40  is positioned and sandwiched between the retaining seat  30  and the retaining ring  50 . 
     The rotor  60  of the first embodiment according to the preferred teachings of the present invention has a shaft  61  and a cap  62 , with one end of the shaft  61  securely coupling to the cap  62  and the other end of the shaft  61  as a free end rotatably extending into the shaft tube  11 . A first annular groove  611  and a second annular groove  612  are both formed on an outer periphery of the shaft  61 , with the first and second annular grooves  611 ,  612  being respectively close to two ends of the shaft  61  to form a first neck and a second neck of the shaft  61 . In addition, each of the first and second necks of the shaft  61  has an outer diameter smaller than that of two sections of the shaft  61 , with said two sections being adjacent to two end edges of each of the first and second annular grooves  611 ,  612 . A diameter of the first axial hole  32  of the retaining seat  30  is smaller than the outer diameters of the two sections adjacent to the first neck of the shaft  61  but larger than the outer diameter of the first neck of the shaft  61 . Similarly, a diameter of the second axial hole  52  of the retaining ring  50  is smaller than the outer diameters of the two sections adjacent to the second neck of the shaft  61  but larger than the outer diameter of the second neck of the shaft  61 . Besides, after the shaft  61  is forcibly inserted into the assembling hole  111  and passes through the second axial hole  52 , the center hole  41  and the first axial hole  32 , each first retaining plate  31  of the retaining seat  30  extends into the first annular groove  611  while each second retaining plate  51  of the retaining ring  50  extends into the second annular groove  612 , with free ends of the first retaining plates  31  which define the first axial hole  32  being in the first annular groove  611  and free ends of the second retaining plates  51  which define the second axial hole  52  being in the second annular groove  612 . Therefore, the dual retaining function jointly provided by the retaining seat  30  and the retaining ring  50  can avoid disengagement of the rotor  60  from the base  10  during packing, conveyance or utilization of the motor. 
     Further, referring to  FIG. 7 , the diameter of the second axial hole  52  of the retaining ring  50  is preferable larger than that of the first axial hole  32  of the retaining seat  30 . In assembly, the retaining seat  30 , the bearing  40  and the retaining ring  50  are mounted into the shaft tube  11  of the base  10 , and then the shaft  61  of the rotor  60  goes through the retaining ring  50 , the bearing  40  and the retaining seat  30 . Besides, a first portion of the shaft  61  between the second annular groove  612  and the free end of the shaft  61  has a first longitudinal distance “L 1 ”, and a second portion of the shaft  61  between the first annular groove  611  and the free end of the shaft  61  has a second longitudinal distance “L 2 ”. And it is obvious that the first axial hole  32  of the retaining seat  30  is for the second portion to forcibly go through and the second axial hole  52  of the retaining ring  50  is for the first portion to forcibly go through when the shaft  61  is projecting into the assembling hole  111 . Therefore, with the first longitudinal distance “L 1 ” being much longer than the second longitudinal distance “L 2 ” and the first axial hole  32  being merely for the second portion to pass through, it will be much easy for the rotor  60  to couple with the shaft tube  11  by designing the diameter of the second axial hole  52  being larger than that of the first axial hole  32 . Thus, in addition to offering a reliable retaining effect, the retaining seat  30  and the retaining ring  50  with said difference between the first and second axial holes  32 ,  52  can also decrease a difficulty for assembling of the rotor  60  and the shaft tube  11 . That is, by this configuration described above, the motor of the present invention can further provide convenience of assembling with allowing the retaining effect on the shaft  61 . 
     Moreover, the retaining ring  50  fixed inside the shaft tube  11  provides blocking effect to avoid disengagement of the retaining seat  30  and the bearing  40  relative to the shaft tube  11 , as well as leakproof effect to prevent oil inside the shaft tube  11  from leaking. The retaining ring  50  is fixed in the shaft tube  11  and coupled to the top of the bearing  40  with close-fit, adhesive or other methods, and it is preferable to achieve said coupling by a positioning ring  13  (seen in  FIG. 6 ). The positioning ring  13  is fixed in the shaft tube  11  of the base  10 , with the positioning ring  13  abutting against the retaining ring  50 , so that the retaining ring  50  is sandwiched and retained between the positioning ring  13  and the bearing  40 . And the positioning ring  13  preferably has an L-shape cross-section from a axial center line of the positioning ring  13  to a radial outer edge thereof, with a lateral wall of the positioning ring  13  contacting with the inner surface of the shaft tube  11  defining the assembling hole  111 , to increase a contact area between the inner surface and the positioning ring  13 , so that a combination of the positioning ring  13  and the shaft tube  11  with enhanced reliability and stability is provided. Therefore, the retaining seat  30 , the bearing  40  and the retaining ring  50  disengaging from the shaft tube  11  is prevented effectively. 
     Referring to  FIGS. 5 to 7 , the motor of the present invention is characterized in that the retaining seat  30 , the bearing  40  and the retaining ring  50  are disposed into the shaft tube  11  of the base  10  in order, in assembly. And because the outer diameters of the retaining seat  30  and the retaining ring  50  and the diameter of the assembling hole  111  are the same, the retaining seat  30  and the retaining ring  50  never move radially after being mounted into the shaft tube  11 , such that radially positioning effect is allowed. Furthermore, by the bearing  40  being sandwiched and positioned between the retaining seat  30  and the retaining ring  50 , axial and radial movement of the bearing  40  are prevented assuredly. In the case of the outer diameter of the bearing  40  being equal to the diameter of the assembling hole  111  of the shaft tube  11 , the bearing  40  is more securely positioned not to move radially. Besides, the retaining ring  50  abuts against and presses the bearing  40  to position the bearing  40  and the retaining seat  30  to axially provide a reliable positioning effect. 
     By the arrangement described above, with no radial movement of said components inside the shaft tube  11 , central lines of the first axial hole  32 , the center hole  41  and the second axial hole  52  certainly align with each other after the retaining seat  30 , the bearing  40  and the retaining ring  50  are mounted into the shaft tube  11  of the base  10 . And thereby, an unhindered passage for the shaft  61  to go through the second axial hole  52 , the center hole  41  and the first axial hole  32  is assured. Further, due to no axial movement of the retaining seat  30 , the bearing  40  and the retaining ring  50 , each first retaining plate  31  of the retaining seat  30  and each second retaining plate  51  of the retaining ring  50  can be partially and unhinderedly received in the first annular groove  611  and the second annular groove  612  respectively to provide the dual retaining function after the shaft  61  passes through the second axial hole  52 , the center hole  41  and the first axial hole  32 . Additionally, only the retaining seat  30 , the bearing  40  and the retaining ring  50  are inside the shaft tube  11  of the base  10 , and a oil end cap that is coupled inside the bottom of a shaft tube, threads for combining the oil end cap and the shaft tube, and an annular abutting flange forming on a top of the shaft tube for abutting against a retaining ring are omitted to provide a simplified structure for assembly. Therefore, the motor of the present invention has many advantages, such as enhancement of convenience of assembling and simplification of structure. 
       FIGS. 8 and 9 , show a motor of a second embodiment according to the preferred teachings of the present invention. The motor includes a base  70 , a stator  80 , a retaining seat  30 , a bearing  40 , a retaining ring  50  and a rotor  60 , wherein descriptions of the retaining seat  30 , the bearing  40 , the retaining ring  50  and the rotor  60  are omitted. 
     The base  70  of the second embodiment according to the preferred teachings of the present invention has a shaft tube  71  made of plastics and a plate  72  for the shaft tube  71  to securely mount, wherein the shaft tube  71  and the plate  72  are integrally formed in one piece. The shaft tube  71  has an assembling hole  711  and two ends of the shaft tube  71  are an open end  712  away from the plate  72  and a closed end  713  respectively. The major difference between the first embodiment and the second embodiment is shown as the following. The assembling hole  711  consists of an upper hole  711   a  and a lower hole  711   b  in communication with the upper hole  711   a,  wherein the upper hole  711   a  and the lower hole  711   b  are adjacent to the open end  712  and the closed end  713  respectively. Furthermore, a diameter of the upper hole  711   a  is larger than that of the lower hole  711   b,  such that a shoulder  714  in an inner surface of the shaft tube  71  defining the assembling hole  711  and between the upper hole  711   a  and the lower hole  711   b  is formed. Besides, the shaft tube  71  includes an annular protrusion  715  on an outer periphery thereof, with the annular protrusion  715  providing a supporting face preferably perpendicular to an axis of the shaft tube  71 . A wear-resisting plate  73  is received in the shaft tube  71 , with the wear-resisting plate  73  being disposed at the bottom of the shaft tube  71  to abut the free end of the shaft  61  to prevent the closed end  713  from wearing away by the shaft  61  during rotation of the rotor  60 . Thus, life of the base  70  is prolonged. 
     The stator  80  of the second embodiment according to the preferred teachings of the present invention is mounted around the shaft tube  71  of the base  70  and on the annular protrusion  715 , with a bottom of the stator  80  abutting on the annular protrusion  715 . The supporting face of the annular protrusion  715  is opposite to the stator  80  when the base  70  and the stator  80  are assembled, so that the annular protrusion  715  provides the stator  80  with an axial supporting force along the axis of the shaft tube  71  to facilitate the follow-up assembling process. Moreover, an abutting member  81  couples on a top of the stator  80  and is in the form of a plurality of pressing plates  811  with intervals, with two ends of each pressing plate  811  being fixed to an inner periphery of the stator  80  and extending into the assembling hole  711  of the shaft tube  71  of the base  70  respectively. And thereby, after the retaining seat  30 , the bearing  40  and the retaining ring  50  are mounted into the shaft tube  71 , the ends of the pressing plates  811  extending into the assembling hole  711  can abut against the top of the retaining ring  50  to avoid the retaining seat  30 , the bearing  40  and the retaining ring  50  disengaging from the shaft tube  71  of the base  70 . 
     In the second embodiment, the outer diameter of the retaining seat  30  is equal to a diameter of the lower hole  711   b  and the outer diameter of the retaining ring  50  is equal to a diameter of the upper hole  711   a.    
     As shown in  FIG. 10 , in assembly of the motor of the second embodiment according to the preferred teachings of the present invention, the retaining seat  30 , the bearing  40  and the retaining ring  50  are mounted into the shaft tube  71  of the base  70 . The retaining ring  50  never moves radially after being mounted into the shaft tube  71  due to the outer diameter of the retaining ring  50  the same as the diameter of the upper hole  711   a.  Further, with the retaining ring  50  abutting against the shoulder  714 , it is assured that axial movement of the retaining ring  50  is prevented and a more reliable combination of the retaining ring  50  and the shaft tube  71  is allowed. Therefore, the retaining ring  50  radially abuts on an inner surface defining the upper hole  711   a  and thus is securely positioned in the shaft tube  71  without axial and radial movement. And because the outer diameter of the retaining seat  30  and the diameter of the lower hole  711   b  are the same, the retaining seat  30  never moves radially after being mounted into the shaft tube  71 , such that radially positioning effect is allowed. Additionally, the bearing  40  is sandwiched and positioned between the retaining seat  30  and the retaining ring  50 , so that the bearing  40  moving axially and radially is avoided from. 
     By the arrangement described above, after the retaining seat  30 , the bearing  40  and the retaining ring  50  of the second embodiment are mounted into the shaft tube  71  of the base  70 , central lines of the first axial hole  32 , the center hole  41  and the second axial hole  52  certainly align with each other to ensure that convenience of mounting the rotor  60  is enhanced. Besides, after the shaft  61  of the rotor  60  passes through the second axial hole  52 , the center hole  41  and the first axial hole  32 , each first retaining plate  31  of the retaining seat  30  and each second retaining plate  51  of the retaining ring  50  can extend into the first annular groove  611  and the second annular groove  612  respectively. Therefore, convenience of assembling the motor is further improved and structure of the motor is simplified. 
     Specifically, no matter the first or second embodiment according to the preferred teachings of the present invention, the outer diameter of the retaining seat  30  and the diameter of the assembling hole  111 ,  711  of the shaft tube  11 ,  71  are the same size, and the outer diameter of the retaining ring  50  is equal to the diameter of the assembling hole  111 ,  711  of the shaft tube  11 ,  71 . In this way, with the retaining seat  30  and the retaining ring  50  being arranged in the shaft tube  11 ,  71 , there is no radial movement of the retaining seat  30  and the retaining ring  50 . It should be noted that although imperceptible difference between the outer diameters of the retaining seat  30  or the retaining ring  50  and the diameter of the assembling hole  111 ,  711 , which is a tolerance due to manufacturing errors, results in little misalignment of the central lines of the first axial hole  32 , the center hole  41  and the second axial hole  52 , it will not really affect an assembling procedure of the motor. For example, radial positions of the retaining seat  30  and the retaining ring  50  are not affected in practice, while difference between one of the outer diameters of the retaining seat  30  and the retaining ring  50  and the diameter of the assembling hole  111 ,  711 , is ±0.2 mm. 
     Moreover, as to the second embodiment according to the preferred teachings of the present invention, the diameter of the second axial hole  52  of the retaining ring  50  is larger than that the first axial hole  32  of the retaining seat  30 , so that convenience of assembling is provided and retaining effect as well. Besides, the wear-resisting plate  73 , the abutting member  81  and the annular protrusion  715  disclosed in the second embodiment also can be used in the motor of the first embodiment according to the preferred teachings of the present invention. 
     As has been discussed above, under the condition of the dual retaining function resulting from the double retaining feature, the retaining seat  30 , the bearing  40  and the retaining ring  50  can be prevented from moving radially and axially after being mounted into the shaft tube  11 ,  71 . And that leads to no misalignment of the central lines of the first axial hole  32 , the center hole  41  and the second axial hole  52 , so that each first retaining plate  31  of the retaining seat  30  and each second retaining plate  51  of the retaining ring  50  are able to unhinderedly extend into the first annular groove  611  and the second annular groove  612  respectively, with the rotor  60  coupling to the base  10 ,  70 . Consequently, the simplified structure of the motor of the present invention indeed allows convenience of assembling. 
     Although the invention has been described in detail with reference to its presently preferable embodiment, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the invention, as set forth in the appended claims.