Patent Publication Number: US-2015076956-A1

Title: Motor shaft

Description:
TECHNICAL FIELD 
     The present invention relates to a motor shaft which integrally rotates with a rotor of a motor. 
     BACKGROUND ART 
     There is known a motor shaft onto which a rotor of a motor is to be press-fitted and which is integrally rotatable with the rotor. 
     JP2012-10425A discloses to construct a motor by press-fitting a rotor, a bearing, a resolver and the like from both sides of a motor shaft. 
     SUMMARY OF INVENTION 
     However, if a certain member is mounted in advance at one side of the motor shaft, it is not possible to press-fit the rotor, the bearing, the resolver and the like onto the motor shaft from the both sides. 
     This invention aims to provide a motor shaft onto which members can be press-fitted from one direction. 
     According to one aspect of the present invention, a motor shaft onto the outer periphery of which a plurality of members are to be press-fitted includes a plurality of step portions which successively expand the outer diameter of the motor shaft from one end side and a plurality of press-fit portions which are arranged adjacent to one end sides of the respective step portions and onto which the members are to be press-fitted. 
     The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view showing a motor shaft in the present embodiment. 
         FIG. 2  is a sectional view schematically showing a state where members are press-fitted on the motor shaft. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     Hereinafter, an embodiment of the present invention is described with reference to the accompanying drawings. 
       FIG. 1  is a view showing a motor shaft  10  in the present embodiment.  FIG. 2  is a sectional view schematically showing a state where constituent members of a motor  30  are mounted on the motor shaft  10 . The motor shaft  10  is integrally fixed to a rotor  31  of the motor  30  by press-fitting and rotates with the rotation of the rotor  31 . 
     As shown in  FIG. 1 , the motor shaft  10  includes a plurality of step portions  11  to  13  which successively expand the outer diameter of the motor shaft  10  from one end side (left end side of  FIG. 1 ) and a plurality of press-fit portions  14  to  16  which are arranged adjacent to one end sides of the respective step portions  11  to  13  and onto the outer peripheries of which members are to be press-fitted. 
     The step portions  11  to  13  are composed of three step portions of a first step portion  11 , a second step portion  12  and a third step portion  13  successively arranged from the one end side of the motor shaft  10 . 
     The press-fit portions  14  to  16  are composed of a first press-fit portion  14  formed at a position closer to the one end side than the first step portion  11  and adjacent to the first step portion  11 , a second press-fit portion  15  formed at a position closer to the one end side than the second step portion  12  and adjacent to the second step portion  12  and a third press-fit portion  16  formed at a position closer to the one end side than the third step portion  13  and adjacent to the third step portion  13 . 
     Accordingly, the second press-fit portion  15  is formed to have a larger diameter than the first press-fit portion  14 , the third press-fit portion  16  is formed to have a larger diameter than the second press-fit portion  15  and the motor shaft  10  is formed to have the outer periphery whose diameter is expanded stepwise from the one end side toward the other end side (right end side of  FIG. 1 ). 
     The motor shaft  10  further includes a small-diameter portion  17  having a diameter slightly smaller than the first press-fit portion  14  on a side closer to the one end side than the first press-fit portion  14 . The third press-fit portion  16  and the second step portion  12  are arranged at a distance from each other in an axial direction of the motor shaft  10 . 
     Next, a mounting procedure of the constituent members of the motor  30  onto the motor shaft  10  is described. 
     It should be noted that since a component  50  having a diameter larger than the inner diameters of the members to be mounted on the motor shaft  10  is mounted in advance on the other end side (right end side of  FIG. 2 ) of the motor shaft  10  as shown in  FIG. 2 , the constituent members of the motor  30  cannot be press-fitted from the other end side of the motor shaft  10 . 
     Accordingly, a first bearing  32  is first fitted from the one end side (left end side of  FIG. 2 ) of the motor shaft  10 . Since the inner diameter of the first bearing  32  is set larger than the outer diameters of the first and second press-fit portions  14 ,  15 , the first bearing  32  is press-fitted onto the third press-fit portion  16  after passing the first and second press-fit portions  14 ,  15 . 
     At this time, the front surface (right side surface in  FIG. 2 ) of the first bearing  32  in a press-fitting direction comes into contact with the third step portion  13 , whereby the first bearing  32  is positioned. That is, the first bearing  32  is press-fitted at a suitable position by being press-fitted onto the third press-fit portion  16  and pressed to a position where the first bearing  32  stops. 
     As shown in  FIG. 2 , a predetermined interference avoidance gap  33  is defined between the second step portion  12  and one end side of the first bearing  32  in a state where the first bearing  32  is press-fitted on the third press-fit portion  16 . This prevents the interference of the rotor  31  and the first bearing  32  during the rotation of the rotor  31  and prevents the generation of rotational resistance in the rotor  31  due to the formation of a magnetic path in the first bearing  32 . 
     Subsequently, the rotor  31  of the motor  30  is fitted from the one end side (left end side of  FIG. 2 ) of the motor shaft  10 . Since the inner diameter of the rotor  31  is set larger than the outer diameter of the first press-fit portion  14 , the rotor  31  is press-fitted onto the second press-fit portion  15  after passing the first press-fit portion  14 . 
     At this time, the front surface (right side surface in  FIG. 2 ) of the rotor  31  in the press-fitting direction comes into contact with the second press-fit portion  12 , whereby the rotor  31  is positioned. That is, the rotor  31  is press-fitted at a suitable position by being press-fitted onto the second press-fit portion  15  and pressed to a position where the rotor  31  stops. 
     Subsequently, a second bearing  34  is fitted from the one end side (left end side of  FIG. 2 ) of the motor shaft  10 . Since the inner diameter of the second bearing  34  is set larger than the outer diameter of the small-diameter portion  17 , the second bearing  34  is press-fitted onto the first press-fit portion  14  after passing the small-diameter portion  17 . 
     At this time, the front surface (right side surface in  FIG. 2 ) of the second bearing  34  in the press-fitting direction comes into contact with the first step portion  11 , whereby the second bearing  34  is positioned. That is, the second bearing  34  is press-fitted at a suitable position by being press-fitted onto the first press-fit portion  14  and pressed to a position where the second bearing  34  stops. 
     Subsequently, a resolver rotor  36  of a resolver  35  for detecting a rotation angle of the motor  30  is press-fitted onto the small-diameter portion  17  from the one end side (left end side of  FIG. 2 ) of the motor shaft  10 . The resolver rotor  36  is positioned at a position set in advance between the small-diameter portion  17  and the first press-fit portion  14 . 
     A housing  39  is provided on the outer periphery of the motor shaft  10  to surround from the first bearing  32  to the second bearing  34  in the axial direction. A stator  38  of the motor  30  is provided at a position on the inner periphery of the housing  39  facing the outer periphery of the rotor  31 . 
     The motor shaft  10  projects toward the other end side from an other-end side opening  39   a  of the housing  39 . On the other hand, the motor shaft  10  projects toward the one end side from a one-end side opening  39   b  of the housing  39 . A flange cover  40  including a hole  40   a , which allows the motor shaft  10  to project, in the center is mounted on the one-end side opening  39   b  of the housing  39 . 
     A resolver stator  37  is provided at a position on the inner periphery of the flange cover  40  facing the outer periphery of the resolver rotor  36 . The inner periphery of the flange cover  40  is further in contact with the outer periphery of the second bearing  34 . 
     This causes the motor shaft  10  to support the housing  39  and the flange cover  40  via the bearings  32 ,  34  and rotates with the rotation of the rotor  31  of the motor  30 . The rotation angle of the motor shaft  10  is detected by the resolver  35 . 
     According to the above embodiment, the following effects are achieved. 
     Since the press-fit portions  14  to  16  formed on the outer periphery of the motor shaft  10  are formed from the one end side of the motor shaft  10  while the diameters thereof are successively expanded, the rotor  31 , the first bearing  32 , the second bearing  34  and the resolver  35  that are constituent members of the motor  30  can be press-fitted onto the motor shaft  10  from one direction. 
     Further, since the respective press-fit portions  14  to  16  are arranged adjacent to the one end sides of the respective step portions  11  to  13  that expand the outer periphery of the motor shaft  10  from the one end side, when the constituent members of the motor  30  are press-fitted onto the respective press-fit portions  14  to  16 , the front surfaces in the press-fitting direction come into contact with the respective step portions  11  to  13 , whereby each constituent member can be positioned. 
     Furthermore, since the first bearing  32  is press-fitted onto the third press-fit portion  16 , the rotor  31  is press-fitted onto the second press-fit portion  15  and the second bearing  34  is press-fitted onto the first press-fit portion  14 , the rotor  31  and the first and second bearings  32 ,  34  arranged at the both sides of the rotor  31  can be fixed to the motor shaft  10  by being successively press-fitted onto the motor shaft  10 . 
     Furthermore, since the interference avoidance gap  33  is defined between the third press-fit portion  16  and the second step portion  12 , the interference of the rotor  31  and the first bearing  32  during the rotation of the rotor  31  can be prevented and the generation of rotational resistance in the rotor  31  due to the formation of a magnetic path in the first bearing  32  can be prevented. 
     Embodiments of this invention were described above, but the above embodiments are merely examples of applications of this invention, and the technical scope of this invention is not limited to the specific constitutions of the above embodiments. 
     Although three step portions  11  to  13  and three press-fit portions  14  to  16  are, for example, respectively provided in the present embodiment, two or less of them, or four or more of them may be provided and the number of them can be set as appropriate according to the number of members to be mounted on the motor shaft  10 . 
     This application claims priority based on Japanese Patent Application No.2012-81101 filed with the Japan Patent Office on Mar. 30, 2012, the entire contents of which are incorporated into this specification.