Patent Publication Number: US-2017366064-A1

Title: Electric motor

Description:
TECHNICAL FIELD 
     The present invention relates to an electric motor. 
     BACKGROUND ART 
     JP 2002-345211A discloses an electric motor that has a rotor rotatably supported by a heat-sink-side bearing also serving as a bracket and by a bracket-side bearing. 
     SUMMARY OF INVENTION 
     However, because the electric motor described in JP 2002-345211A requires fixing work of the bearing to the heat sink using a retaining ring or the like after the bearing is assembled to the heat sink, it takes time to perform an assembling operation. 
     The present invention has an object to shorten time required for the assembly work of an electric motor. 
     According to one aspect of the present invention, an electrical motor includes a stator, a rotor attached to an output shaft and supported within the stator, a cylindrical case housing the stator and the rotor inside, a ball bearing rotatably supporting the output shaft, and a cover member closing an opening of the case, the ball bearing being attached to the cover member. An outer ring of the ball bearing and the cover member are integrally formed of resin material. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of an electric motor according to an embodiment of the present invention; and 
         FIG. 2  is an enlarged cross-sectional view of a main part of an electric motor according to the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following describes an electrical motor  100  according to an embodiment of the present invention with reference to the attached drawings. 
     The electrical motor  100  is used as a power source for generating steering auxiliary torque, for example, in an electric power steering apparatus. 
     As shown in  FIG. 1 , the electrical motor  100  includes a case  10  that is formed in a cylindrical shape, a first cover member  20  that closes an opening on one end side of the case  10 , and a second cover member  30  that closes an opening on another end side of the case  10 . A motor housing  1  is formed by the case  10 , the first cover member  20 , and the second cover member  30 . 
     A stator  40  is fixed to an inner circumferential surface of the case  10 . The stator  40  includes a stator core  41  and a stator coil  43  that is wound around the stator core  41  via an insulator  42 . 
     A cylindrical rotor  50  is provided on an inner periphery of the stator  40  with a slight gap made between the stator  40 . The rotor  50  includes an output shaft  51 , a rotor core (not shown) that is attached to the output shaft  51 , and a permanent magnet (not shown) that is attached to an outer periphery of the rotor core. The output shaft  51  is rotatably supported by ball bearings  60  and  70  that are respectively attached to the first cover member  20  and the second cover member  30 . As such, the stator  40  and the rotor  50  are housed and held in the case  10 . 
     The output shaft  51  is projected outside through the first cover member  20  at one end and connected to a steering shaft via a not-illustrated worm reduction mechanism. 
     The ball bearing  60  that supports the one end side of the output shaft  51  is attached to the first cover member  20 . The ball bearing  60  is inserted into a recess  21  that is formed in a central part of the first cover member  20 , and held in the recess  21  by a not-illustrated beveled retaining ring. Note that it is not limited the above fixing method, any fixing means such as caulking may be applied as long as the ball bearing  60  is held in the recess  21 . 
     The ball bearing  70  that supports another end side of the output shaft  51  is attached to the second cover member  30 . The ball bearing  70  is a double-row ball bearing in which a plurality of ball bearings are disposed in the axial direction of the output shaft  51 . Specifically, the ball bearing  70  is constituted of two ball bearings  70 A and  70 B that are arranged in series in the axial direction of the output shaft  51 . The two ball bearings  70 A and  70 B are provided in the second cover member  30  in a manner that inner rings  72 A and  72 B come into contact with each other. 
     A control device  80  that controls electrical signals output to the stator coil  43  is provided on the opposite side of the second cover member  30  from the stator  40  and the rotor  50 . The control device  80  is housed in a housing case  81  that is provided adjacent to the second cover member  30 . The second cover member  30  and at least a part of the housing case  81  may also be integrated. 
     The following describes the second cover member  30  in detail with reference to  FIG. 2 . 
     As shown in  FIG. 2 , the second cover member  30  includes a base body portion  31  that is adjacent to the housing case  81  and a cylindrical portion  32  that projects from the base body portion  31  to the side of the rotor  50 . The ball bearing  70  is attached to the cylindrical portion  32 . The base body portion  31  and the cylindrical portion  32  are integrally formed of resin material. 
     As described above, the two ball bearings  70 A and  70 B are arranged in series on the inner peripheral side of the cylindrical portion  32 . The second cover member  30  that is made of resin material has strength weaker than that of a cover member that is made of a metal. However, the two ball bearings  70 A and  70 B are provided on the second cover member  30  in a manner that the inner rings  72 A and  72 B come into contact with each other. In this way, a thrust load exerted on the output shaft  51  can be supported by the two ball bearings  70 A and  70 B, even if a thrust load exerted on the output shaft  51  is large. In other words, because the second cover member  30  is provided with the two ball bearings  70 A and  70 B constituting a double-row ball bearing in which the two ball bearings  70 A and  70 B are disposed in series in the axial direction of the output shaft  51 , an allowable thrust load of the ball bearing  70  can be increased. Note that the inner rings  72 A and  72 B may also be integrated. Only either one of the ball bearings  70 A and  70 B may also be used, if sufficient strength is secured on raceway grooves  33 A and  33 B. 
     Outer rings of the ball bearings  70 A and  70 B are formed integrally with the cylindrical portion  32 . Specifically, the annular raceway grooves  33 A and  33 B are formed on the inner peripheral surface of the cylindrical portion  32 . Balls  71  of the ball bearings  70 A and  70 B respectively roll along the raceway grooves  33 A and  33 B. In this way, the cylindrical portion  32  that is formed with the raceway grooves  33 A and  33 B serves as outer rings that support the balls  71  of the ball bearings  70 A and  70 B. 
     The second cover member  30  is made of resin material such as POM (polyacetal) and PEEK (polyetheretherketone). Because such materials have excellent sliding property, there is no need for lubricant to be applied between the balls  71 , which is made of metal, and the raceway grooves  33 A and  33 B. This configuration, in which the second cover member  30  is made of resin material, can eliminate the need for maintenance work such as applying lubricant to the ball bearing  70 . 
     The plurality of balls  71  are arranged between the inner rings  72 A and  72 B and the raceway grooves  33 A and  33 B, and then, the ball bearings  70 A and  70 B can be assembled by fixing a not-illustrated retainer that retains the plurality of balls  71 . By the above assembly process, the ball bearings  70 A and  70 B are attached to the second cover member  30 . Thus, because the separate fixing work of the ball bearings  70 A and  70 B to the second cover member  30  is not required after the ball bearings  70 A and  70 B have been assembled, the simplification of the assembly work and the shortening of the assembly time can be realized. 
     The case  10  and the second cover member  30  may be formed integrally. In this case, the work for assembling the second cover member  30  and the case  10  may be eliminated. 
     The foregoing embodiment achieves the following effects. 
     In the electrical motor  100 , the outer rings of the ball bearing  70  and the second cover member  30  are integrally formed of resin material. In this way, the fixing work of the ball bearing  70  to the second cover member  30  is not required, and thus the simplification of the assembly work and the shortening of the assembly time can be realized. A groove for fixing the beveled retaining ring and the like needs not be machined, and thereby, no machining time is required. 
     Resin material has lower heat conductivity than metal material. Therefore, the second cover member  30  that is made of resin material can prevent heat generated by the stator coil  43  from being transmitted to the control device  80  and can prevent heat generated by the control device  80  from being transmitted to the stator  40  and the rotor  50 . 
     Because the second cover member  30  is made of resin material, weight of the electrical motor  100  can be reduced. Because of the weight reduction, a resonance point shifts to the higher frequency side. Thus, vibration and noise can be suppressed. Furthermore, because resin has elasticity compared to metal, a bias member that biases the rotor  50  in an axial direction may be omitted. 
     The structures, functions, and effects of the embodiment of the present invention configured as described above will be collectively described below. 
     The electrical motor  100  includes the stator  40 , the rotor  50  that is attached to the output shaft  51  and supported within the stator  40 , the cylindrical case  10  that houses the stator  40  and the rotor  50  inside, the ball bearings  60  and  70  that rotatably support the output shaft  51 , and the second cover member  30  to which the ball bearing  70  is attached and that closes the opening of the case  10 . The outer rings of the ball bearing  70  and the second cover member  30  are integrally formed of resin material. 
     According to this configuration, because the outer rings of the ball bearing  70  are formed integrally with the second cover member  30 , the fixing work of the ball bearing  70  to the second cover member  30  is not required. Thus, the simplification of the assembly work and the shortening of the assembly time can be realized. 
     The case  10  and the second cover member  30  may be formed integrally in the electrical motor  100 . 
     In this configuration, the assembly work of the second cover member  30  and the case  10  may be eliminated. 
     Furthermore, in the electrical motor  100 , the control device  80  that controls electrical signals output to the stator  40  or the rotor  50  is provided on the opposite side of the second cover member  30  from the stator  40  and the rotor  50 . 
     The second cover member  30  that is made of resin material is located between the control device  80  and the stator  40  and between the control device  80  and the rotor  50 . Therefore, the second cover member  30  can prevent heat generated by the stator  40  or the rotor  50  from being transmitted to the control device  80 . 
     Furthermore, the electrical motor  100  has a plurality of ball bearings, and the plurality of ball bearings  70 A and  70 B are disposed in the axial direction of the output shaft  51  to constitute a double-row ball bearing. 
     In this configuration, a thrust load exerted on the output shaft  51  can be supported by the two ball bearings  70 A and  70 B, even if the thrust load exerted on the output shaft  51  is large. 
     The embodiments of the present invention described above are merely illustration of some application examples of the present invention and not of the nature to limit the technical scope of the present invention to the specific constructions of the above embodiments. 
     For example, the first cover member  20  and an outer ring of the ball bearing  60  may be integrally formed of resin material in the electrical motor  100 . The case  10 , the first cover member  20 , and the outer ring of the ball bearing  60  may also be integrally formed of resin material in the electrical motor  100 . 
     In the present embodiment, although the electrical motor  100  is a brushless DC motor, a motor with brush or an AC motor may be applied as the electrical motor  100 . If the electrical motor  100  is the motor with brush, because a coil is provided in the rotor  50 , the control device  80  outputs electrical signals to the rotor  50 . 
     The present application claims a priority based on Japanese Patent Application No. 2015-143333 filed with the Japan Patent Office on Jul. 17, 2015, all the contents of which are hereby incorporated by reference.