Abstract:
Inner rings of bearings arranged at both ends of a rotor shaft are fixed to the rotor shaft, and outer rings of both of the bearings are arranged at bearing holding parts movably in an axial direction of the rotor. A preload imparting member is attached to one of the bearings, the preload imparting member being configured to bias the rotor shaft in one direction and to apply a biasing force to make a housing and a flange, which constitute a chassis, come close to each other.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a rotating electrical machine, and particularly to a rotating electrical machine with both ends of a rotor shaft thereof supported by bearings. 
         [0003]    2. Description of the Related Art 
         [0004]    Rotating electrical machines such as motors and generators have been used in many industrial fields. As a social trend, rotating electrical machines capable of saving energy and resources have been demanded. Therefore, many improvement technologies have been proposed to meet the demand for saving energy and resources. As a major technological subject of saving energy and resources, there is a technology for reducing the size or weight of a rotating electrical machine. 
         [0005]    For example, an in-vehicle rotating electrical machine of an automobile or the like is preferably small with excellent quietness and mountability, not to mention output performance. 
         [0006]    More specifically, a rotating electrical machine used for an electric power steering device for steering an automobile is generally arranged on a rack shaft, which is arranged in the vehicle interior or in an engine room near the vehicle interior. 
         [0007]    This naturally limits the location where the rotating electrical machine can be mounted. Therefore, noise generated upon the operation of the rotating electrical machine may make an occupant inside the vehicle feel uncomfortable. 
         [0008]    In recent years, operating noise to be generated by the components of an automobile has been attracting attention as one of the criteria for evaluating the automobile. It is required, therefore, to take some countermeasures against operating noise to be generated by the components used, in pursuit of comfort of an automobile or in terms of environmental regulations. 
         [0009]    As a result, there have been proposed various technologies for reducing noise to be generated by a motor of an electric power steering device. 
         [0010]    For example, the technology disclosed in JP 2009-201255 A (Patent Document 1) takes the following measure for reducing abnormal noise to be generated by the backlash of a rotor shaft in its axial direction. 
         [0011]    That is, in a rotating electrical machine with both ends of the rotor shaft rotatably supported by bearings, the rotor shaft is press fit and fixed into an inner ring of the bearing at one end, an outer ring of the bearing at the other end is press fit and fixed into a housing, and an outer ring of the bearing at the one end is elastically biased by a preload spring. With this configuration, the rotor shaft is moved together with the bearing at the one end and, along with this movement, the rotor shaft is moved inside an inner ring of the bearing at the other end and pushed in one direction. In this manner, the movement of the rotor shaft in its axial direction is regulated, thereby suppressing abnormal noise to be generated by the backlash of the rotor shaft. 
       SUMMARY OF THE INVENTION 
       [0012]    However, the rotating electrical machine disclosed in Patent Document 1 is not configured to be satisfactorily small for the reasons described below. 
         [0013]    In the rotating electrical machine disclosed in Patent Document 1, the rotor shaft is supported by a case-side bearing and a flange-side bearing. The case-side bearing includes an inner ring and an outer ring supported by a case. The flange-side bearing includes an inner ring and an outer ring supported by a flange. The rotor shaft is press fit and fixed into the inner ring of the case-side bearing, and the outer ring thereof is held by the case displaceably in the axial direction. 
         [0014]    On the other hand, the rotor shaft is inserted into the inner ring of the flange-side bearing displaceably in the axial direction, while the outer ring thereof is press fit and fixed into the flange. 
         [0015]    A wave washer serving as a preload imparting member is arranged outside the flange-side bearing (opposite to the rotor across the bearing arranged on the rotor shaft). This wave washer pushes the inner ring of the flange-side bearing toward the rotor. With this configuration, the elastic force of the wave washer is transmitted to the inner ring of the case-side bearing via the rotor shaft to further move the outer ring. 
         [0016]    As a result, the rotor shaft is pushed toward the case-side bearing, making it possible to suppress the generation of abnormal noise. 
         [0017]    However, the wave washer serving as a preload imparting member is arranged outside the flange-side bearing (opposite to the rotor across the bearing arranged on the rotor shaft). Therefore, with the rotor shaft pushed toward the case, the elastic force of the wave washer acts as a reaction force in the direction of separating the case and the flange. 
         [0018]    This makes it necessary to firmly fix the case and the flange with a fixing screw. Since the case and the flange are fixed with the fixing screw, the outer shape of the rotating electrical machine has a bulge corresponding to this fixing portion, making it difficult to reduce the size of the machine. 
         [0019]    On the other hand, in the case where the outer shape of the rotating electrical machine is determined so as to accommodate the machine in a limited mounting space, it is necessary to secure a fixing portion by a fixing screw. This makes it difficult to increase the dimensions of a stator and a rotor, which determine an actual torque, thus inhibiting high output. 
         [0020]    An object of the present invention is to provide a small rotating electrical machine excellent in quietness. 
         [0021]    Features of the present invention are as follows. That is, the rotor shaft is biased in one direction, and a preload imparting member is attached to one of the bearings. The preload imparting member applies a biasing force to make a housing and a flange, which constitute a chassis, come close to each other. 
         [0022]    According to the present invention, by pushing the rotor shaft in one direction with the preload imparting member, it is possible to suppress abnormal noise to be generated by the backlash of the rotor shaft in the axial direction. 
         [0023]    With a retaining force obtained to make the housing and the flange come close to each other, it is possible to enhance the effect of integrally holding the housing and the flange. This makes it possible to eliminate, or reduce the size of, the fixing screw that has been used to fix the housing and the flange. Therefore, the outer shape of the rotating electrical machine can be made small by a portion corresponding to this fixing portion, making the machine smaller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is an external view of a rotating electrical machine to which the present invention is applied; 
           [0025]      FIG. 2  is a vertical cross-sectional view of a rotating electrical machine, in its axial direction, according to an embodiment of the present invention; 
           [0026]      FIG. 3  is an external perspective view of a rotor illustrated in  FIG. 2 ; and 
           [0027]      FIG. 4  is a cross-sectional view of a bearing illustrated in  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Embodiments of the present invention will be described in detail below with reference to the drawings. The present invention, however, is not limited to the embodiments described below, and includes various modifications and applications within the technical concept of the present invention. 
         [0029]      FIG. 1  is a view of a rotating electrical machine assembly  10  used in an electric power steering device as an example. The rotating electrical machine assembly  10  includes a rotating electrical machine  11  and an inverter controller  12  for controlling the driving of the rotating electrical machine  11 . 
         [0030]    The inverter controller  12  includes, inside a chassis thereof, a power semiconductor element constituting an inverter circuit, a drive circuit for driving the power semiconductor element, and a control circuit for controlling the drive circuit. 
         [0031]    The rotating electrical machine  11  and the inverter controller  12  are firmly fixed to each other with a dedicated fixing bolt. In this state, the rotating electrical machine assembly  10  is integrated with a power steering device (not illustrated) with a through bolt, for example. 
         [0032]    Next, the detailed configuration of the rotating electrical machine  11  with the inverter controller  12  removed from the rotating electrical machine assembly  10  will be described with reference to  FIG. 2 . 
         [0033]      FIG. 2  is a cross-sectional view illustrating a vertical cross-section, in the axial direction, of the rotating electrical machine  11 . The rotating electrical machine  11  mainly includes a housing  13  and a flange  14 , which constitute a chassis, and a rotor  15  and a stator  16 , which constitute a motor. 
         [0034]    The housing  13  is formed in the shape of a bottomed cylinder (so-called cup shape) having an opening  17  at one end. The flange  14  is fixed to the housing  13  so as to cover the opening  17 . 
         [0035]    The stator  16  is fixed to the inner periphery of the housing  13 . Divided fixing cores  18  constitute the stator  16 , and are fixed through press fitting or shrinkage fitting while maintaining a circular shape. The divided fixing cores  18  are formed in the circular shape with divided surfaces thereof welded or not welded. 
         [0036]    A bobbin  19  is attached to the fixing core  18 . A coil  20  is wound around the outer periphery of the bobbin  19 . A lead wire of the coil  20  is connected to a bus bar  21 . Note that the coil  20  is wound continuously two or four times, after which the lead wire is protruded. Alternatively, the coil  20  is connected to the bus bar  21  while being wound around each fixing core  18 . The housing  13  and the bobbin  19  may interpose a gap therebetween, or may be fitted to each other. 
         [0037]    The bus bar  21  is arranged in the vicinity of the inner wall surface of the housing  13  such that a bearing holding part  31  described later is located on the inner periphery. Of course, the bus bar  21  and the housing  13  are arranged at locations separate from each other where air insulation can be ensured therebetween. 
         [0038]    The rotor  15  is rotatably arranged on the inner periphery side of the fixing core  18 . The rotor  15  includes a rotor shaft  22 , a rotating base  23 , a magnet  24 , and a magnet cover  25 . 
         [0039]    As illustrated in  FIG. 3 , the magnet  24  is covered with the magnet cover  25 , thereby preventing the magnet  24  from scattering around. An end face of the magnet cover  25  includes bent portions  25 A formed as illustrated in  FIG. 3 , thereby preventing the magnet  24  from scattering in a radial or axial direction. 
         [0040]    Note that an end portion of the bus bar  21  is connected to an input terminal  27  via a bus bar  26  that passes through the flange  14 . The bus bar  21  is wired so as to be connected to a coil of each phase. Power of U phase, V phase, and W phase, input through the input terminal  27 , is input to the bus bar  21 . 
         [0041]    The basic configuration of the rotating electrical machine  11  has been described above, and no further description thereof will be given. Next, the technical features of the present invention will be described. 
         [0042]    A housing-side bearing holding part  28  is formed in the center of a bottom  13 A of the housing  13 . The housing-side bearing holding part  28  protrudes inward (toward the rotor in the axial direction) from the bottom  13 A. 
         [0043]    With the configuration having the protrusion, the axial length of the rotating electrical machine  11  can be reduced. That is, by arranging the housing-side bearing holding part  28  closer to the end face of the rotor  15 , the space existing around the end face of the rotor  15  can be used as a space where the housing-side bearing holding part  28  is placed. 
         [0044]    A housing-side bearing  29  is housed inside the housing-side bearing holding part  28 , and includes an inner ring  29 A and an outer ring  29 B. As illustrated in  FIG. 4 , the housing-side bearing  29  includes the inner ring  29 A and the outer ring  29 B, and rolling elements  29 C, in the shape of a ball, between the inner ring  29 A and the outer ring  29 B. With this configuration, the inner ring  29 A and the outer ring  29 B can smoothly rotate relative to each other via the rolling elements  29 C. Note that the housing-side bearing  29  has a similar configuration to a flange-side bearing, described later, arranged on the side of the flange  14 . 
         [0045]    The housing-side bearing  29  is housed in the housing-side bearing holding part  28 . The housing-side bearing holding part  28  includes a small-diameter portion  28 A and a large-diameter portion  28 B. The small-diameter portion  28 A regulates the movement of the outer ring  29 B of the housing-side bearing  29  toward the rotor  15 . The large-diameter portion  28 B regulates the movement of the outer ring  29 B in the radial direction. 
         [0046]    A retaining ring  30  is engaged with the large-diameter portion  28 B on the opposite side of the small-diameter portion  28 A of the housing-side bearing holding part  28  across the housing-side bearing  29 . The housing-side bearing  29  is arranged between the retaining ring  30  and the small-diameter portion  28 A. The distance between the retaining ring  30  and the small-diameter portion  28 A is somewhat larger than the width BL of the housing-side bearing  29  illustrated in  FIG. 4 , so that the housing-side bearing  29  can move. 
         [0047]    A housing-side shaft  22 A of the rotor shaft  22  is press fit and fixed into, and firmly connected to, the inner ring  29 A of the housing-side bearing  29 . 
         [0048]    The outer ring  29 B of the housing-side bearing  29 , on the other hand, is arranged to face the large-diameter portion  28 B of the housing-side bearing holding part  28  with a gap therebetween. As a result, the housing-side bearing  29  can follow the axial movement of the rotor shaft  22  and move in the axial direction inside the housing-side bearing holding part  28 . This movement, however, is regulated by the small-diameter portion  28 A. Therefore, the housing-side bearing  29  can only move in a situation where the small-diameter portion  28 A suppresses the backlash of the rotor shaft  22  in the axial direction and the rotating electrical machine  11  is rotated. The reason for this will be described later. 
         [0049]    Next, the configuration of a flange-side bearing will be described. A flange-side bearing holding part  31  is formed in the center of the flange  14 . The flange-side bearing holding part  31  protrudes inward (toward the rotor in the axial direction) from a flange face  14 A. 
         [0050]    With this configuration having the protrusion, the axial length of the rotating electrical machine  11  can be reduced. That is, by arranging the flange-side bearing holding part  31  closer to the end face of the rotor  15 , the space existing around the end face of the rotor  15  can be used as a space where the flange-side bearing holding part  31  is placed. This configuration is similar to that of the housing-side bearing holding part  28  and, therefore, the axial length of the rotating electrical machine  11  can be even more reduced. 
         [0051]    The flange-side bearing holding part  31  also functions as a preload imparting part in which a preload imparting member is housed. The preload imparting part will be described later. 
         [0052]    A flange-side bearing  32  is housed inside the flange-side bearing holding part  31 , and includes an inner ring  32 A and an outer ring  32 B. 
         [0053]    The flange-side bearing  32  includes the inner ring  32 A and the outer ring  32 B, and rolling elements  32 C, in the shape of a ball, between the inner ring  32 A and the outer ring  32 B. Therefore, the inner ring  32 A and the outer ring  32 B can smoothly move relative to each other via the rolling elements  31 C. 
         [0054]    The flange-side bearing  32  is housed in the flange-side bearing holding part  31 . The flange-side bearing holding part  31  includes a small-diameter portion  31 A and a large-diameter portion  31 B. The small-diameter portion  31 A regulates the movement of the outer ring  32 B of the flange-side bearing  32  toward the rotor  15 . Note that this movement is regulated through the preload imparting member described later. Furthermore, the large-diameter portion  31 B regulates the movement of the outer ring  32 B in the radial direction. 
         [0055]    A preload imparting part  33  is formed on the side of the small-diameter portion  31 A of the flange-side bearing holding part  31 , that is, on the side of the rotor  15  across the flange-side bearing  32 . That is, a housing space serving as the preload imparting part  33  is formed between the small-diameter portion  31 A and the flange-side bearing  32 . 
         [0056]    The axial length of the large-diameter portion  31 B excluding the preload imparting part  33  is set larger than the width of the flange-side bearing  32 , so that the flange-side bearing  32  can move. 
         [0057]    A flange-side shaft  22 B of the rotor shaft  22  is press fit and fixed into, and firmly connected to, the inner ring  32 A of the flange-side bearing  32 . 
         [0058]    On the other hand, the outer ring  32 B of the flange-side bearing  32  is arranged to face the large-diameter portion  31 B of the flange-side bearing holding part  31  with a gap therebetween. As a result, the flange-side bearing  32  can follow the axial movement of the rotor shaft  22  and move in the axial direction inside the flange-side bearing holding part  31 . 
         [0059]    A wave washer  34  serving as the preload imparting member is arranged inside the preload imparting part  33  described above. The wave washer  34  is configured to generate an elastic force toward the opposite side of the rotor  15  across the small-diameter portion  31 A. 
         [0060]    With the elastic force, the flange-side bearing  32  is pushed rightward in the drawing, and the outer ring  29 B of the housing-side bearing  29  moves to the position regulated by the small-diameter portion  28 A of the housing-side bearing holding part  28 . This is because the flange-side bearing  32  and the housing-side bearing  29  move integrally, since the rotor shaft  22  is fixed to the inner ring  32 A of the flange-side bearing  32  and the inner ring  29 A of the housing-side bearing  29 . 
         [0061]    At this time, the wave washer  34  biases the small-diameter portion  31 A of the flange-side bearing holding part  31  toward the rotor  15  (leftward in the drawing) through a reaction force and, consequently, pushes the entire flange  14  toward the bottom  13 A of the housing  13 . 
         [0062]    Using the wave washer  34  as the preload imparting member can reduce the axial length of the rotating electrical machine  11 , because the wave washer  34  has a small thickness in the direction of generating the elastic force. Alternatively, a spring washer, for example, can be used instead of the wave washer  34  to produce a similar effect. 
         [0063]    The present embodiment is excellent in assemblability since the bearing including the wave washer  34  (preload imparting member) is formed on the side of the flange  14 . That is, the present embodiment can achieve the ease of assembly since the rotor shaft  22  can be press fit into the flange  14  after the wave washer  34  and the flange-side bearing  32  are assembled into the flange-side bearing holding part  31  of the flange  14 . 
         [0064]    The opening  17  of the housing  13  extends to the vicinity of a portion where the rotor  15  and the stator  16  are arranged. The flange  14  is fixed at this portion. 
         [0065]    It is desirable that the flange  14  and the housing  13  be basically fixed to each other through shrinkage fitting, press fitting, an adhesive or the like, that is, without using a fixing component. Even in the case where a fixing component is necessary in terms of design, the size of the fixing component can be reduced since the preload imparting member  34  has a function to hold the flange  14 . As a result, the size of the rotating electrical machine can be reduced. 
         [0066]    Next, the functions and effects of the assembled rotating electrical machine  11  according to the present embodiment will be described. 
         [0067]    In the state illustrated in  FIG. 2 , the housing  13  and the flange  14  are fixed to each other. Therefore, the wave washer  34  generates an elastic force to move the flange-side bearing  32  in a direction away from the rotor  15  (rightward in the drawing) from the small-diameter portion  31 A of the flange-side bearing holding part  31 . 
         [0068]    The outer ring  32 B of the flange-side bearing  32  can move relative to the large-diameter portion  31 B of the flange-side bearing holding part  31 . Therefore, the inner ring  32 A and the flange-side shaft  22 B of the rotor shaft  22  fixed to the inner ring  32 A also move accordingly. 
         [0069]    When the rotor shaft  22  moves rightward in the drawing, the housing-side shaft  22 A of the rotor shaft  22  and the inner ring  29 A of the housing-side bearing  29  fixed to the housing-side shaft  22 A move rightward. In addition, the outer ring  293  of the housing-side bearing  29  can move relative to the large-diameter portion  28 B of the housing-side bearing holding part  28 , and therefore, the entire housing-side bearing  29  moves rightward. 
         [0070]    When the housing-side bearing  29 , the rotor shaft  22 , and the flange-side bearing  32  move rightward, and the outer ring  29 B of the housing-side bearing  29  comes into contact with the small-diameter portion  28 A of the housing-side bearing holding part  38  and the movement of the outer ring  29 B is regulated, the rotor  15  maintains its rotation at that position. 
         [0071]    This makes it possible to suppress abnormal noise to be generated by the backlash of the rotor shaft  22  of the rotor  15  in the axial direction. 
         [0072]    Meanwhile, with the outer ring  29 B of the housing-side bearing  29  being in contact with the small-diameter portion  28 A of the housing-side bearing holding part  38  and the movement of the outer ring  29 B regulated, the wave washer  34  is located between the small-diameter portion  31 A of the flange-side bearing holding part  31  and the inner ring  32 A of the flange-side bearing  32  fixed to the flange-side shaft  22 B. Therefore, the wave washer  34  applies a reaction force toward the small-diameter portion  31 A of the flange-side bearing holding part  31  from the flange-side bearing  32 . 
         [0073]    In this manner, the force is applied to the flange  14  leftward in the drawing, making it possible to enhance the effect of integrally holding the housing  13  and the flange  14 . 
         [0074]    As a result, the housing  13  and the flange  14  can be fixed to each other with a relatively weak fixing force through mild shrinkage fitting or press fitting. This makes it unnecessary to use a fixing component, or can reduce the size of the fixing component used. 
         [0075]    This makes it possible to eliminate, or reduce the size of, the fixing screw that has been used to fix the housing and the flange. Therefore, the outer shape of the rotating electrical machine can be made small by a portion corresponding to the fixing portion, thereby reducing the size of the rotating electrical machine. Alternatively, the housing and the flange can be fixed to each other by interposing a fixing ring such as a C ring therebetween instead of the fixing screw. Also in this case, the shape of the C ring can be made small. 
         [0076]    Since the fixing component can be eliminated or the size thereof can be reduced, the outer diameter of the stator can be increased accordingly, within a constant outer shape. The increase in outer diameter of the stator may improve output performance. 
         [0077]    Furthermore, in the case where the outer diameter of the stator is increased to obtain the same output performance, the axial length of a magnetic circuit and the weight of a magnet and the like can be reduced, providing advantages in terms of weight reduction and manufacturing cost. 
         [0078]    Note that the preload imparting member  34  is provided on the side of the flange  14  in the embodiment described above. Alternatively, however, the bearing structure on the side of the flange  14  may be provided on the side of the housing  13 . 
         [0079]    In this case, the wave washer  34  serving as the preload imparting member can be interposed between the housing-side bearing  29  and the small-diameter portion  28 A of the housing-side bearing holding part  28  illustrated in  FIG. 2 , and the retaining ring  30  can be engaged with the large-diameter portion  31 B of the flange-side bearing holding part  31 .