Patent Publication Number: US-2022216762-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 bent hollow shaft and a novel structure of housing and housing cover to a hollow shaft motor used in an integrated brake system, thereby allowing the hollow shaft and motor housing to be produced by a pressing process, 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 motor housing by a pressing process. Here, however, since the motor housing has the lower side closed, the assembling operation is difficult, and it is difficult to install a four-point contact ball bearing. 
     Japanese Patent Laid-open No. 2000-65179 discloses a structure of fastening covers to an upper portion and a lower portion of a motor housing, respectively, by means of bolts. This structure increases manufacturing processes, and makes it difficult to maintain the air tightness between the motor housing and the cover. 
     Korean Patent Laid-open No. 10-2017-0006535 discloses a structure of opening the lower side of a motor housing and assembling a separate cover thereto, and the technique of manufacturing a motor housing by a pressing process such as deep drawing. According to the structure, a separate cover is assembled to the lower side of the motor housing to support bearings supporting a hollow shaft, thereby supporting the load imposed on the hollow shaft. Thus, the assemblability and productivity decrease. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present invention was invented in order to solve the above-mentioned problems. It is an object of the present invention to provide a hollow shaft motor with a novel structure allowing a hollow shaft and a motor housing to be produced by a pressing process, thereby reducing manufacturing costs, and improving assemblability and productivity. 
     It is another object of the present invention to provide a hollow motor with a novel structure allowing the bearing to be coupled more stably and arranging a central position more accurately when coupled to a brake system by applying a new structure of a housing cover. 
     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 motor housing  11  having a cylindrical shape; a housing cover assembly  12  coupled to an upper portion of the motor housing  11 ; a rear cover  15  coupled to a lower portion of the motor housing  11 ; a stator assembly  20  located in the motor housing  11  and in a lower portion of the housing cover assembly  12 ; and a rotor assembly  30  located in the stator assembly  20  to rotate, wherein the housing cover assembly  12  comprises a housing cover  121 , and the housing cover  121  is formed by insert injection molding while placing a press ring  122 , a bus bar  123  and a sleeve  124  in a mold. 
     In the present invention, preferably, a ring-shaped protruding ring  121 G protruding upwardly is formed around a cavity  121 C axially penetrating the housing cover  121 . 
     In the present invention, preferably, the sleeve  124  may have a cylindrical shape vertically penetrated, and a flange  124 A radially extended may be formed in an upper portion of the sleeve  124 . 
     In the present invention, preferably, the flange  124 A is located in an upper portion of the cavity  121 C. 
     In the present invention, preferably, the press ring  122  comprises a press ring main body  122 A and a plurality of fastening holes  122 B formed to penetrate a side of the press ring main body  122 A. 
     Advantageous Effects of Invention 
     The present invention allows a hollow shaft of a motor and a motor housing to be produced by a pressing process, thereby having the effects of providing a hollow shaft motor with a novel structure capable of reducing manufacturing costs, improving assemblability and productivity, and arranging a central position more accurately when coupled to a brake system. 
    
    
     
       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 the 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 an exploded perspective view of a rotor assembly of the hollow shaft motor according to the present invention; 
         FIG. 5  is an exploded top perspective view of a housing cover assembly of the hollow shaft motor according to the present invention; and 
         FIG. 6  is an exploded bottom perspective view of a housing cover assembly 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 the hollow shaft motor  100  according to the present invention, and  FIG. 3  is a cross-sectional view taken along the A-A′ direction of  FIG. 1 . 
     As illustrated in  FIGS. 1 to 3 , the hollow shaft motor  100  according to the present invention includes a screw shaft  10 , a motor housing  11 , a stator assembly  20  coupled to an inner side of the motor housing  11 , and a rotor assembly  30  located in the stator assembly  20 . 
     The screw shaft  10  has a lower end portion coupled to the hollow shaft  31  so as to rotate with the rotor assembly  30 . A ball nut  17  is coupled to an outer circumferential surface of the screw shaft  10 , and the ball nut  17  moves up and down according to the rotation of the screw shaft  10 , thereby generating or removing the pressure in the piston (not illustrated). 
     The motor housing  11  can be manufactured by a continuous process using pressing equipment such as a transfer mold. The motor 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 motor housing  11  is an inner space part  112 , and a flange part  113  extending in the horizontal direction is formed around the upper portion of the inner space part. A housing cover assembly  12  is coupled to the inner space part  112  so as to cover an upper portion of the inner space part  112 . A flange part  113  is coupled to a block (not illustrated) of a brake system. 
     A bottom part  114  horizontally extending towards the center is formed in a lower portion of the body part  111 , and the lower end portion of the body part  111  may have a horizontal cross-section diameter reducing until reaching the bottom part  114 . A lower protruding part  115  protruding downwardly is formed in a central portion of the bottom part  114 . A lower bearing coupling part  116  to which the lower bearing  14  is coupled is formed in a space inside the lower protruding part  115 . A curved bent part  117  in which the bottom part  114  and the lower protruding part  115  are connected is formed in an upper end portion of the lower bearing coupling part  116 . In other words, the curved bent part  117  has a shape where a central portion of the bottom part  114  is bent so as to be connected to the lower protruding part  115 , which allows the curved bent part  117  to support the upper circumferential surface of the lower bearing  14  so that the lower bearing  14  could be coupled more solidly and intensively. 
     The curved bent part  117  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 the upper circumferential portion of lower bearing  14  is supported by the curved bent part  117 . The curved bent part  117  is preferably bent and extended to the inside at a position the same as or higher than the bottom part  114 , thereby stably supporting the lower bearing  14 . 
     The lower circumferential portion of the lower bearing  14  is supported by a curling part  115 A. As illustrated in  FIG. 3 , the flange part  152  of the rear cover  15  may be interposed between the curling part  115 A and the lower circumferential portion of the lower bearing  14 . The curling part  115 A is formed by subjecting a lower distal portion of the lower protruding part  115  to a curling process by the press. 
     The housing cover assembly  12  comprises a housing cover  121  produced by a plastic mold, and the housing cover  121 , preferably, is made of a plastic mold to be formed by insert injection molding while placing a press ring  122 , a bus bar  123  and a sleeve  124  in a mold. Accordingly, the housing cover assembly  12  becomes a member in which the housing cover  121 , the press ring  122 , the bus bar  123  and the sleeve  124  are integrally formed. 
     The housing cover  121  comprises a circular cover main body  121 A with a penetrating hole in the middle, a plurality of fitting protrusions  121 B formed to radially protrude in the outer circumferential surface of the cover main body  121 A, a cavity  121 C which is a hole formed to penetrate the center of the cover main body  121 A, and a terminal cover  121 D formed by protruding upwardly at one upper side of the cover main body  121 A. A fitting groove  112 A is formed around an upper portion of the inner space part  112  of the motor housing  11  corresponding to the fitting protrusion  121 B so that the fitting protrusion  121 B is fitted into and coupled to the fitting groove  112 A. The terminal cover  121 D comprises a bus bar terminal  123 B thereinside, allowing the bus bar terminal  123 B to be connected to an external power source. A ball nut  17  and a piston (not illustrated) for moving up and down by the rotation of the hollow shaft  31  and the screw shaft  10  are located inside the sleeve  124 . 
     The outer race of the upper bearing  13  is press-fitted and supportedly coupled to the inner side of the press ring  122  which is coupled to the circumference of the cavity  121 C of the housing cover  121 . The inner race of the upper bearing  13  is supported by an upper bearing coupling groove  312  formed in the upper portion of the hollow shaft  31  to support the rotation of the hollow shaft  31 . The sleeve  124  is downwardly extended from an inner space of the hollow shaft  31 , allowing the hollow shaft  31  to be independently separated from the inner space of the sleeve  124 . Accordingly, a movement space of the piston (not illustrated) which moves up and down may be independently secured. 
     The lower bearing  14  supports the rotation of a lower bearing supporting part  316  formed in a lower end portion of the hollow shaft  31 . The lower bearing  14  is coupled to the lower bearing coupling part  116  formed in a lower end of the motor housing  11 . 
     As illustrated in  FIG. 3 , the rear cover  15  is coupled to a lower inner side of the lower protruding part  115  of the motor housing  11  to cover the lower portion of the lower protruding part  115 . The rear cover  15  is coupled and fixed to the lower protruding part  115  by a curling part  115 A at a lower end of the lower protruding part  115 . A lock nut  16  is coupled to a lower end of the screw shaft  10 . 
     The stator assembly  20  comprises a stator core  21  press-fitted and fixed to an inner side of the body part  111  of the motor 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  123  of the housing cover assembly  12  coupled to an upper portion of the upper insulator  22 . The bus bar  123  is electrically connected to a bus bar terminal  123 B to supply power from an external power source. The bus bar terminal  123 B is surrounded and protected by a terminal cover  121 D. 
     The outer circumferential portion of the housing cover  121  is press-fitted and coupled to an upper portion of the inner space part  112  formed in the upper inner side of the body part  111  of the motor housing  11 . Detailed features of the housing cover  121  will be explained again with reference to  FIGS. 5 and 6  in the following. 
       FIG. 4  is an exploded perspective view of a rotor assembly  30  of the hollow shaft motor  100  according to the present invention. Referring to  FIGS. 3 and 4  together, the rotor assembly  30  of the present invention is located inside the stator assembly  20  to rotate. To this end, the rotor assembly  30  comprises a hollow shaft  31 , a rotor core  32  coupled to the outer circumference of the hollow shaft  31 , a plurality of magnets  33  attached to an outer circumference of the rotor core  32 , and a rotor can  34  coupled to an outer circumferential portion of the magnet  33 . 
     The hollow shaft  31  has a hollow shaft housing  311  having a cylindrical shape. The rotor core  32  is coupled to an outer circumferential surface of the hollow shaft housing  311 . A plurality of magnets  33  are attached to an outer circumferential surface of the rotor core  32 . As needed, the rotor core  32  may be omitted, and the plurality of magnets  33  may be directly attached to the outer circumferential surface of the hollow shaft housing  311 . The rotor  34  is press-fitted and coupled to the outer circumferential surface of the magnet  33 . 
     An upper bearing coupling groove  312  having a slightly smaller diameter than the hollow shaft housing  311  is formed in an upper portion of the hollow shaft housing  311 . The rotation of the inner race of the upper bearing  13  is supported by the upper bearing coupling groove  312 . An upper stepped part  313  bent outwardly is formed at an upper portion of the upper bearing coupling groove  312 , and a lower stepped part  314  is formed at a lower portion of the upper bearing coupling groove  312 , so as to have a groove shape for coupling the inner race of the upper bearing  13  to the upper bearing coupling groove  312 . The upper stepped part  313  may be formed by a curling process during the press molding process. 
     A reduced diameter part  315  which is a part bent and connected so that the diameter thereof is gradually reduced to the diameter of the lower bearing supporting part  316  is formed at a lower end portion of the hollow shaft housing  311 . The rotation of the lower bearing supporting part  316  protruding from the reduced diameter part  315  is supported by the lower bearing  14 . 
       FIG. 5  is an exploded top perspective view of a housing cover assembly  12  of the hollow shaft motor  100  according to the present invention, and  FIG. 6  is an exploded bottom perspective view thereof. 
     Referring to  FIGS. 5 and 6  together with  FIG. 3 , the housing cover assembly  12  of the present invention comprises a housing cover  121 , a press ring  122 , a bus bar  123  and a sleeve  124 . As mentioned in the above, since the housing cover  121  is molded by insert injection together with the press ring  122 , the bus bar  123  and the sleeve  124 , it is not possible to provide an exploded view as illustrated in  FIGS. 5 and 6 , but here, an exploded view thereof is provided for the sake of convenience in explanation. 
     The housing cover  121  comprises a cover main body  121 A, a fitting protrusion  121 B, a cavity  121 C and a terminal cover  121 D, and a settlement space  121 E, which is where the press ring  122  is coupled and which becomes an inner side surface of the cover main body  121 A, is formed. A coil connecting part  121 F has a plurality of holes towards a lower side of the cover main body  121 A, and a coil coupling part  123 A of the bus bar  123  is located inside the coil connecting part  121 F. A coil (not illustrated) wound around the stator assembly  20  is electrically connected to the coil coupling part  123 A. This connection between the coil and coil coupling part  123 A is made in the coil connecting part  121 F. 
     A ring-shaped protruding ring  121 G protruding upwardly is formed around a cavity  121 C at the upper portion of the housing cover  121 . When the hollow shaft motor  100  according to the present invention is installed in a brake system (not illustrated), the protruding ring  121 G helps the hollow shaft motor to be installed at an exact position, and helps the screw shaft  10  to be coupled to the brake system maintaining its exact center. 
     The press ring  122  is made of metal so that the upper bearing  13  can be firmly coupled, and the press ring  122  is coupled to the housing cover  121  as one part by insert injection. The press ring  122  comprises a press ring main body  122 A and a plurality of fastening holes  122 B formed to penetrate a side of the press ring main body  122 A. The outer race of the upper bearing  13  is coupled to an inner side surface of the press ring main body  122 A. The fastening hole  122 B allows a resin melted product to penetrate therethrough so that the press ring  122  is well coupled to the housing cover  121 . 
     The bus bar  123  is made of a conductive material so that coils on the same phase are electrically connected to each other to receive an external power source. The bus bar  123  comprises a plurality of coil coupling parts  123 A formed to radially protrude from the ring shape, and a bus bar terminal  123 B for connecting to the external power source. The housing cover  121  is injection molded in a state where the bus bar  123  is located inside the housing cover  121  except for some parts of the coil coupling part  123 A and the bus bar terminal  123 B. 
     The sleeve  124  has a cylindrical shape vertically penetrated, and a flange  124 A radially extended is formed in an upper portion of the sleeve  124 . The flange  124 A is located in the upper portion of the cavity  121 C of the housing cover  121 , and the flange  124 A is surrounded by a plastic resin forming the housing cover  121 . A screw shaft  10  for moving the piston (not illustrated) up and down and a ball but  17  are located in the inner space of the sleeve  124 . 
     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.