Patent Publication Number: US-2021194317-A1

Title: Hollow shaft motor

Description:
TECHNICAL FIELD 
     The present invention relates to a motor. More specifically, the present invention relates to a motor adopting a hollow shaft having a bent shape and a novel housing structure to a hollow shaft motor used in an integrated brake system, which allows the production of a hollow shaft and a housing by a pressing process, thereby reducing manufacturing costs and improving assemblability and productivity. 
     BACKGROUND ART 
     In general, a brake system generates pressure in a master cylinder to amplify the force applied to a brake and provides the pressure to a module requiring braking. A hollow shaft motor is used as an apparatus for generating pressure in a master cylinder. Such hollow shaft motor rotates a hollow shaft by the principle of a motor, and applies a screw inside the hollow shaft to use the principle of converting rotary motion into linear motion. The linear motion of the screw actuates a piston to generate or remove the pressure required in the master cylinder. 
     Recently, an integrated dynamic brake (IDB) system mainly used a motor with a hollow shaft. Since the hollow shaft of the motor needs to generate high pressure by a screw and a piston operating in the hollow shaft, a considerable axial load is imposed on bearings supporting the hollow shaft. In this regard, four-point contact ball bearings may be used to support the rotation of the hollow shaft. 
     Korean Patent Laid-open No. 10-2016-0001681 discloses a motor having a structure that can manufacture a hollow shaft and a housing by a pressing process. Here, however, since the housing has the lower side closed, the assembling operation is difficult, and it is difficult to install a four-point contact ball bearing. 
     Korean Patent Laid-open No. 10-2017-0006535 discloses a structure of opening the lower side of a housing and assembling a separate cover thereto, and the technique of manufacturing a housing by a pressing process such as deep drawing. According to the structure, a separate cover is assembled to the lower side of the housing to support bearings supporting a hollow shaft, thereby supporting the load imposed on the hollow shaft. Thus, the assemblability and productivity decrease. 
     In order to solve the above-mentioned problems, the present inventors suggest a hollow shaft motor having a novel structure. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     It is an object of the present invention to provide a hollow shaft motor having a novel structure which allows the production of a hollow shaft and a housing by a pressing process, thereby reducing manufacturing costs and improving assemblability and productivity. 
     The object above and other objects inferred therein can be easily achieved by the present invention explained below. 
     Solution to Problem 
     The hollow shaft motor according to the present invention comprises: a housing  11  having a cylindrical shape; an upper cover  12  coupled to an upper portion of the housing  11 ; a lower cover  15  coupled to a lower portion of the housing  11 ; a stator assembly  20  located in the housing  11 ; and a rotor assembly  30  located in the stator assembly  20  to rotate, wherein the rotor assembly  30  comprises a hollow shaft  31 , a rotor core  32  coupled to an outer circumference of the hollow shaft  31 , and a plurality of magnets  33  attached to an outer circumference of the rotor core  32 . 
     In the present invention, the hollow shaft  31  may comprise a yoke coupling part  311  having a cylindrical shape, an upper bearing support part  312  having a diameter greater than that of the yoke coupling part  311 , an upper bearing receiving part  313  having a shape bent inwardly in a lower portion of the upper bearing support part  312 , and a lower bearing support part  316  protruding downwardly from the yoke coupling part  311 . 
     In the present invention, preferably, a lower sleeve  12 D extending downwardly from a central portion of the upper cover  12  is formed, and the lower sleeve  12 D extends inside the yoke coupling part  311 . 
     In the present invention, preferably, an upper bearing  13  is coupled to an upper side of the lower sleeve  12 D, and an outer race of the upper bearing  13  supports the rotation of the upper bearing support part  312 . 
     In the present invention, preferably, a lower protruding part  115  protruding downwardly is formed in a lower central portion of the housing, a space in the center of the lower protruding part  115  forms a lower opening part  116 , and a lower bearing receiving part  117  is formed such that the material of the lower protruding part  115  is bent to extend upwardly from a lower portion. 
     In the present invention, preferably, an upper portion of a lower bearing  14  is received in the lower bearing receiving part  117 , an outer circumference of the lower bearing  14  is press-fitted into an inner side of the lower protruding part  115 , and the lower bearing  14  supports the rotation of the hollow shaft  31 . 
     In the present invention, the hollow shaft motor may further comprise a lower cover  15  coupled to an outer circumferential surface of the lower protruding part  115 . 
     In the present invention, the hollow shaft motor may further comprise a stopper  16  inserted into a space between the lower bearing  14  and the lower cover  15  to support the axial load of the lower bearing  14 . 
     In the present invention, the stopper  16  may be integrally formed with the lower cover  15 . 
     Advantageous Effects of Invention 
     The present invention allows the production of a hollow shaft and a housing of a motor by a pressing process, thereby having the effects of reducing manufacturing costs and improving assemblability and productivity. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a hollow shaft motor according to the present invention; 
         FIG. 2  is an exploded perspective view of a hollow shaft motor according to the present invention; 
         FIG. 3  is a cross-sectional view taken along the A-A′ direction of  FIG. 1 ; 
         FIG. 4  is a perspective view of a hollow shaft of the hollow shaft motor according to the present invention; 
         FIG. 5  is a top perspective view of an upper cover and a housing of the hollow shaft motor according to the present invention; and 
         FIG. 6  is a bottom perspective view of an upper cover and a housing of the hollow shaft motor according to the present invention. 
     
    
    
     Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings. 
     MODE FOR THE INVENTION 
       FIG. 1  is a perspective view of a hollow shaft motor  100  according to the present invention.  FIG. 2  is an exploded perspective view of a hollow shaft motor  100  according to the present invention.  FIG. 3  is a cross-sectional view taken along the A-A′ direction of  FIG. 1 . 
     Referring to  FIG. 1  to  FIG. 3  together, the hollow shaft motor  100  according to the present invention includes a housing  11 , a stator assembly  20  coupled to an inner side of the housing  11 , and a rotor assembly  30  located in the stator assembly  20 . 
     The housing  11  can be manufactured by a continuous process using a pressing equipment such as a transfer mold. The housing  11  has a body part  111  having a cylindrical shape whose upper portion and lower portion are open. The part that is open to the upper side of the housing  11  is an upper opening part  112 , and a flange part  113  extending in the horizontal direction is formed around the upper opening part. An upper cover  12  is coupled to the upper opening part  112 . The flange part  113  is coupled to a block (not illustrated) of a brake system. A bottom part  114  extending toward the center in the horizontal direction is formed in a lower portion of the body part  111 , and a lower protruding part  115  protruding downwardly is formed in a central portion of the bottom part  114 . A space in the center of the lower protruding part  115  forms a lower opening part  116 . A lower bearing receiving part  117  is formed such that the material of the lower protruding part  115  is bent by a pressing process to extend upwardly from a lower portion. 
     The lower protruding part  115  has a structure wherein the material is bent and folded, to reinforce strength. Thus, when a great load is imposed on a lower bearing  14 , the structure can help supporting the load. The lower bearing  14  is press-fitted and coupled to an inner surface of the lower protruding part  115 , and an upper portion of the outer race of the lower bearing  14  is supported by the lower bearing receiving part  117 . A lower end portion of the hollow shaft  31  is located in an opening space in the central portion of the lower bearing receiving part  117  and the lower opening part  116 . The lower bearing receiving part  117  is preferably bent inwardly at a position higher than the bottom part  114  to extend. This leads to a structure allowing stable support of the lower bearing  14 . 
     The upper cover  12  has a disk shape, and an outer circumferential portion thereof extends downwardly. The outer circumferential surface of the extending portion is press-fitted and coupled to an inner side of the upper opening part  112  of the housing  11 . A piston (not illustrated) for moving up and down by the rotation of the hollow shaft  31  is located in a central space  12 A formed in the central portion of the upper cover  12 . A terminal space  12 B is formed at one side of the upper cover  12  to connect a bus bar terminal  25  to an external power source. A plurality of coupling projections  12 C protruding in the radial direction is formed in an upper portion of the upper cover  12 . Coupling grooves  112 A corresponding to the coupling projections  12 C are formed around the upper opening part  112  of the housing  11  so that the coupling projections  12 C are inserted and coupled to the coupling grooves  112 A. 
     The central space  12 A extends downwardly, and a lower sleeve  12 D extending downwardly from the central portion of the upper cover  12  is formed to make the central space  12 A. An upper bearing  13  is coupled to an upper side of the lower sleeve  12 D. An outer race of the upper bearing  13  is supported by an upper portion of the hollow shaft  31  to support the rotation of the hollow shaft  31 . The lower sleeve  12 D extends downwardly in a central space of the hollow shaft  31 . This structure separates the hollow shaft  31  and the central space  12 A in the inner side of the lower sleeve  12 D independently to some degree. Thereby, the piston (not illustrated) moving up and down can get an independent movement space. 
     A lower cover  15  is coupled to the lower protruding part  115  of the housing  11  to cover the lower opening part  116 . The lower cover  15  may be press-fitted to an outer side of the lower protruding part  115  or screw-coupled by tapping. A stopper  16  is located in a space of the inner circumferential surface of the lower protruding part  115 , and the stopper  16  is interposed between the lower bearing  14  and the lower cover  15  to have a structure of supporting the axial load imposed on the lower bearing  14 . The stopper  16  may be a separate member from the lower cover  15  or be formed integrally with the lower cover  15  to be one member, not a separate member. 
     The stator assembly  20  comprises a stator core  21  press-fitted and fixed to an inner side of the body part  111  of the housing  11 , an upper insulator  22  coupled to an upper portion of the stator core  21 , and a lower insulator  23  coupled to a lower portion of the stator core  21 . A coil (not illustrated) is wound around each insulator, and the coil is electrically connected to a bus bar (not illustrated) of a bus bar housing  24  coupled to an upper portion of the upper insulator  22 . The bus bar is electrically connected to a bus bar terminal  25  to supply power from an external power source. The bus bar terminal  25  is surrounded and protected by a terminal cover  26 . 
     The rotor assembly  30  is located in the stator assembly  20  to rotate. To this end, the rotor assembly  30  comprises a hollow shaft  31 , a rotor core  32  coupled to an outer circumference of the hollow shaft  31 , and a plurality of magnets  33  attached to an outer circumference of the rotor core  32 . The detailed structure of the hollow shaft  31  is explained with reference to  FIG. 4 . 
       FIG. 4  is a perspective view of a hollow shaft  31  of the hollow shaft motor  100  according to the present invention. As illustrated in  FIG. 3  and  FIG. 4 , the hollow shaft  31  of the present invention has a yoke coupling part  311  having a cylindrical shape. A rotor core  32  is coupled to an outer circumferential surface of the yoke coupling part  311 . A plurality of magnets  33  is attached to an outer circumferential surface of the rotor core  32 . The rotor core  32  may be omitted, and the plurality of magnets  33  may be attached directly to the outer circumferential surface of the yoke coupling part  311 , if necessary. 
     An upper bearing support part  312  having a diameter greater than that of the yoke coupling part  311  is formed in an upper portion of the yoke coupling part  311 . An outer race of the upper bearing  13  supports the rotation of the upper bearing support part  312 . An upper bearing receiving part  313  having a shape bent inwardly is formed in a lower portion of the upper bearing support part  312 . Further, a first reduced diameter part  314  extends downwardly from the upper bearing receiving part  313  and is bent for connection such that the diameter thereof is reduced to the diameter of the yoke coupling part  311 . A second reduced diameter part  315  is bent from a lower portion of the yoke coupling part  311  for connection such that the diameter thereof is reduced. A lower bearing support part  316  protruding downwardly from the second reduced diameter part  315  is formed in a lower portion of the yoke coupling part  311 . The rotation of the lower bearing support part  316  is supported by the lower bearing  14 . 
       FIG. 5  is a top perspective view of a housing  11  and an upper cover  12  of the hollow shaft motor according to the present invention.  FIG. 6  is a bottom perspective view thereof. 
     Referring to  FIG. 5  and  FIG. 6  together, the upper cover  12  is coupled to the upper opening part  112  of the housing  11  of the present invention. An outer circumferential surface of the upper cover  12  is press-fitted and coupled to an inner circumferential surface of the upper opening part  112 , and the plurality of coupling projections  12 C formed in the upper cover  12  is inserted and coupled to the coupling grooves  112 A formed around the upper opening part  112  of the housing  11 . A terminal space through which the bus bar terminal  25  passes and to which the terminal cover  26  is coupled is formed at one side of the upper cover  12 . The lower sleeve  12 D of the upper cover  12  extends downwardly such that a ball screw and a nut (not illustrated) for operating a piston up and down are located in the central space  12 A therein. The lower sleeve  12 D extends inside the yoke coupling part  311  of the hollow shaft  31  to separate the space where a ball screw, etc. is located, in the hollow shaft  31 . 
     The detailed description of the present invention described as above simply explains examples for understanding the present invention, but does not intend to limit the scope of the present invention. The scope of the present invention is defined by the accompanying claims. Additionally, it should be construed that simple modifications or changes of the present invention fall within the scope of the present invention.