Abstract:
A steering apparatus includes: a rack shaft which moves steered portions based on steering by a steering portion; a cover portion covering the rack shaft; and a bearing member arranged inside the cover portion and supporting the rack shaft so that the rack shaft is movable in an axial direction of the rack shaft, and the bearing member has a reservoir portion reserving a lubricant at a contact spot with respect to the rack shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-009407 filed on Jan. 21, 2015, the content of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a steering apparatus for steering and a bearing member. 
         [0004]    2. Description of Related Art 
         [0005]    A steering apparatus for a vehicle and so on is provided with an input portion receiving a steering force input from a steering portion such as a steering wheel and an output portion transmitting the steering force to steered portions such as wheels by receiving the transmission of the steering force. Then, the steering apparatus applies a rack and pinion mechanism having a pinion shaft and a rack shaft connecting to the pinion shaft for transmitting the force from the input portion to the output portion. 
         [0006]    In the rack and pinion mechanism, a bearing member movably supporting the rack shaft is provided. For example, there is disclosed, in JP-A-2002-276654 (Patent Document 1), a bearing including an outer bush made of a synthetic resin having elasticity and an inner bush fixed inside the outer bush. In the bearing disclosed in Patent Document  1 , a region abutting on an inner peripheral surface of a gear case and a region adjusting to one end portion of the region in an axial direction and partially not abutting on the inner peripheral surface of the gear case are formed on an outer peripheral surface of the outer bush. 
         [0007]    Incidentally, there is a case where a lubricant for smoothing the movement of a rack shaft is provided in the bearing member at a contact spot with respect to the rack shaft. However, there is a danger that the lubricant between the bearing member and the rack shaft is reduced with the movement of the rack shaft. As a result, a large rubbing noise may be generated when the rack shaft moves. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the present invention is to reduce the rubbing noise generated when the rack shaft moves. 
         [0009]    According to an embodiment of the present invention, there is provided a steering apparatus including a rack shaft which moves steered portions based on steering by a steering portion, a cover portion covering the rack shaft, and a bearing member arranged inside the cover portion and supporting the rack shaft so that the rack shaft is movable in an axial direction of the rack shaft, in which the bearing member has a reservoir portion reserving a lubricant at a contact spot with respect to the rack shaft. 
         [0010]    Here, the bearing member may include a projecting portion projecting toward the rack shaft to form the contact spot with respect to the rack shaft, and the reservoir portion may be formed at the projecting portion. 
         [0011]    The reservoir portion may be at least one concave portion being concave in a side opposite to a side where the rack shaft is provided. 
         [0012]    Also, the reservoir portion may be plural convex portions projecting toward the rack shaft. 
         [0013]    Also according to an embodiment of the present invention, there is provided a bearing member for supporting a rack shaft which moves steered portions based on steering by a steering portion so that the rack shaft is movable in an axial direction of the rack shaft, which includes a contact portion projecting toward an inner side of the bearing member in which the rack shaft is to be provided and forming a contact spot with respect to the rack shaft and plural convex portions projecting toward the inner side or at least one concave portion being concave toward an outer side being opposite to the inner side which are provided at the contact portion. 
         [0014]    Here, the at least one concave portion may have a hemispherical shape. 
         [0015]    The convex portions may have a hemispherical shape. According to the embodiments of the present invention, the rubbing noise generated when the rack shaft moves can be reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic front view of a motor-driven power steering apparatus; 
           [0017]      FIG. 2  is a is a cross-sectional view of the motor-driven power steering apparatus shown in  FIG. 1  taken along II-II line; 
           [0018]      FIGS. 3A and 3B  are explanatory views of a bush according to Embodiment 1; 
           [0019]      FIG. 4  is an entire perspective view of a bush according to Embodiment 2; 
           [0020]      FIGS. 5A and 5B  are entire perspective views of bushes according to Embodiment 3 and Embodiment 4. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Hereinafter, embodiments of the present invention will be explained in detail with reference to the attached drawings. 
       Embodiment 1 
     Entire Structure of Motor-Driven Power Steering Apparatus  1   
       [0022]      FIG. 1  is a schematic front view of a motor-driven power steering apparatus  1 . 
         [0023]      FIG. 2  is a cross-sectional view of the motor-driven power steering apparatus  1  shown in  FIG. 1  taken along II-II line. 
         [0024]    The motor-driven power steering apparatus  1  according to the embodiment is a steering apparatus for arbitrarily changing a traveling direction of vehicles, and a structure in which the steering apparatus is applied to a vehicle, particularly, a motorcar is cited as an example in the embodiment. The motor-driven power steering apparatus  1  according to the embodiment is a so-called pinion assist type apparatus. 
         [0025]    As shown in  FIG. 1 , motor-driven power steering apparatus  1  includes an input portion  10  to which a steering force from a steering wheel (not shown, an example of a steering portion) operated by a driver, a rack shaft  21  connected to, for example, wheels (not shown, an example of steered portions) to change a direction of the wheels and a pinion shaft  22  (see  FIG. 2 ) receiving a torque from the input portion  10  to move the rack shaft  21  in the axial direction. 
         [0026]    The motor-driven power steering apparatus  1  also includes tie rods  23 A and  23 B provided at end portions of the rack shaft  21  and connected to, for example, the wheels through knuckle arms (not shown), a housing  30  housing various members and an assist portion  40  giving a steering assist force to the pinion shaft  22 . 
         [0027]    In the following explanation, an axial direction (right and left direction in  FIG. 1 ) of the rack shaft  21  is referred to as an “axial direction”, one side (left side in  FIG. 1 ) along the axial direction of the rack shaft  21  is referred to as “one side” and the other side (right side in  FIG. 1 ) along the axial direction of the rack shaft  21  is referred to as “the other side”. Also, a circumferential direction with respect to the central axis of the rack shaft  21  is referred to as a “circumferential direction”, a radial direction with respect to the central axis of the rack shaft  21  is referred to as a “radial direction”, a central axis side in the radial direction is referred to as an “inner side” and a side separated from the central axis in the radial direction is referred to as an “outer side”. 
         [0028]    Moreover, as shown in  FIG. 2 , the motor-driven power steering apparatus  1  includes a rack guide  24  pressing the rack shaft  21  toward the pinion shaft  22 , a torque detecting apparatus  50  detecting a steering torque of the steering wheel and an electronic control unit (ECU)  51  controlling drive of an electric motor  41  (described later) of the assist portion  40 . 
         [0029]    The input portion  10  includes an input shaft  11  to which the steering force from the steering wheel operated by a driver is transmitted and a torsion bar  12  attached to the inside of the input shaft  11 . 
         [0030]    The rack shaft  21  is a hollow bar-shaped member made of, for example, iron. The rack shaft  21  includes a rack  21 R formed by plural teeth arranged in the axial direction. The rack shaft is attached so that the rack  21 R is engaged with a later-described pinion  22 P of the pinion shaft  22 . Then, the rack shaft  21  moves in the axial direction by receiving the rotation of the pinion shaft  22 . The rack shaft  21  may be a solid bar-shaped member. 
         [0031]    The pinion shaft  22  is a member in which the pinion  22 P is formed. Then, as described above, the pinion  22 P of the pinion shaft  22  is connected to the rack  21 R of the rack shaft  21 . A rotational force of the pinion shaft  22  is converted into the movement of the rack shaft  21  in the axial direction by the pinion shaft  22  and the rack shaft  21 . 
         [0032]    The pinion shaft  22  is connected to the torsion bar  12 . Therefore, the pinion shaft  22  is rotated by receiving the steering force from the input shaft  11  through the torsion bar  12 . In the embodiment, a later-described worm wheel  43  of the assist portion  40  is connected to the pinion shaft  22 . Therefore, the pinion shaft  22  is rotated by receiving an assist steering force from the assist portion  40  in addition to the steering force from the input shaft  11 . 
         [0033]    As shown in  FIG. 1 , the housing  30  is made of, for example, aluminum or iron, including a rack housing  31 R (an example of a cover member) which mainly houses the rack shaft  21  and a pinion housing  31 P which mainly houses the pinion shaft  22  (see  FIG. 2 ). 
         [0034]    The rack housing  31 R is an approximately cylindrical member, which is formed along the axial direction of the rack shaft  21 . The rack housing  31 R has a bush  60  and an end case  80  inside the approximately cylindrical shape. 
         [0035]    The bush  60  is provided coaxially with the rack shaft  21  inside the rack housing  31 R. In particular, the bush  60  is attached to a circumferential holding groove  81  formed in the end case  80  in the embodiment. Then, the bush  60  supports the rack shaft  21  inserted into the inside so as to be slidable in the axial direction. The bush  60  will be explained in detail later. 
         [0036]    Then, in a motor-driven power steering apparatus  1  according to the embodiment, a lubricant (grease) is applied between the bush  60  and the rack shaft  21 . As the lubricant, a semisolid material or a solid material obtained by dispersing a thickener in a lubricating oil can be used. Additionally, an additive can be suitably blended with the lubricant. 
         [0037]    The end case  80  has an approximately cylindrical outline. The end case  80  is provided so as to be inserted into the rack housing  31 R at an end portion in the axial direction of the rack housing  31 R. The end case  80  is provided coaxially with the rack shaft  21  and holds the bush  60  in an inner peripheral surface (holding groove  81 ). As materials for the end case  80 , for example, metals such as aluminum can be used. 
         [0038]    The rack housing  31 R thus formed covers the rack shaft  21 , the bush  60  and the end case  80  and houses these members. 
         [0039]    The pinion housing  31 P has an approximately cylindrical outline. The pinion housing  31 P is provided in a direction where a cylindrical shaft direction crosses the axial direction of the rack housing  31 R. The pinion housing  31 P rotatably holds the pinion shaft  22  through a first bearing  35  and a second bearing  36  as shown in  FIG. 2 . A cover  33  is attached to an opening of the pinion housing  31 P. The cover  33  rotatably holds the input shaft  11  through a third bearing  37 . 
         [0040]    In the shown example, a worm wheel  43 , the first bearing  35  and the second bearing  36  are arranged in this order from the central part side toward the end portion side in the axial direction of the pinion shaft  22 . In the pinion housing  31 P, a portion housing the worm wheel  43  inside is referred to as a first outer peripheral portion  31 A, a portion housing the first bearing  35  inside is referred to as a second outer peripheral portion  31 B and a portion housing the second bearing  36  inside is referred to as a third outer peripheral portion  31 C. 
         [0041]    As shown in  FIG. 2 , the assist portion  40  includes the electric motor  41 , a worm gear  42  and the worm wheel  43 . 
         [0042]    The electric motor  41  is controlled by the electronic control unit  51  to rotatably drive the worm gear  42 . The worm gear  42  is connected to an output shaft of the electric motor  41 , rotating by receiving the drive force from the electric motor  41 . The worm wheel  43  is connected to the worm gear  42 , to which the drive force from the electric motor  41  is transmitted. Therefore, a rotational force of the electric motor  41  is transmitted to the pinion shaft  22  after decelerated by the worm wheel  43 . 
       Function/Structure of Bush  60   
       [0043]      FIGS. 3A and 3B  are explanatory views of the bush  60  according to Embodiment 1.  FIG. 3A  is an entire perspective view of the bush  60  according to Embodiment 1 and  FIG. 3B  is a schematic view for explaining the arrangement of later-described spherical concave portions  642 . 
         [0044]    As shown in  FIG. 3A , the bush  60  (an example of the bearing member) includes an approximately annular-shaped bush body  61 , a separated portion  62  forming a cut-off portion in a part of the bush body  61  in the circumferential direction, outward projecting portions  63  provided on the outer side of the bush body  61  in the radial direction, and inward projecting portions  64  (an example of a projecting portion and a contact portion) provided on the inner side of the bush body  61  in the radial direction. 
         [0045]    As materials for the bush  60  in the embodiment, synthetic resins such as polyurethane, polyacetal, polypropylene and polytetrafluoroethylene can be used. The bush  60  can be also formed by integral molding such as injection molding. 
       Bush Body  61 , Separated Portion  62   
       [0046]    The bush body  61  is fitted to the holding groove  81  (see  FIG. 1 ) of the end case  80 . 
         [0047]    The separated portion  62  is formed in a part in the circumferential direction. In the embodiment, deformation to narrow an interval of a gap in the separated portion  62  is possible at the time of attaching the bush  60  to the end case  80 . 
       Outward Projecting Portions  63   
       [0048]    Plural (three) outward projecting portions  63  are provided in the embodiment. The plural outward projecting portions  63  are arranged at equal intervals in the circumferential direction of the bush body  61  in the embodiment. 
         [0049]    Then, the outward projecting portions  63  are formed at positions facing the inward projecting portions  64  in the circumferential direction of the bush body  61 . That is, the outward projecting portions  63  and the inward projecting portions  64  are arranged side by side along the radial direction of the bush body  61 . 
         [0050]    Each outer projecting portion  63  has a curved surface  631 . The curved surface  631  is formed to be an arc shape along the circumferential direction. In the embodiment, the curved surface  631  of the outer projecting portion  63  contacts the holding groove  81  (see  FIG. 1 ) of the end case  80 . 
       Inward Projecting Portion  64   
       [0051]    Plural (three) inward projecting portions  64  are provided in the embodiment. The plural inward projecting portions  64  are arranged at equal intervals in the circumferential direction of the bush body  61  in the embodiment. Then, the inward projecting portions  64  form contact portions with respect to the rack shaft  21 . 
         [0052]    Also in the embodiment, an inner diameter of a virtual circle passing a portion contacting the rack shaft  21  in the inner projecting portion  64  is formed to be smaller than an outer diameter of the rack shaft  21 . That is, the bush  60  supports the rack shaft  21  with a predetermined interference. 
         [0053]    Each inward projecting portion  64  has a flat surface portion  641  and the spherical concave portions  642  (an example of the reservoir portion and the at least one concave portion). 
         [0054]    The flat surface portion  641  is formed on an approximately flat surface, forming a surface directed to the rack shaft  21  side. The flat surface portion  641  also projects toward the rack shaft  21  side as compared with other portions inside the bush body  61 . That is, the flat surface portion  641  has a shorter distance from the shaft center of the bush body  61  as compared with other portions. Then, the flat surface portion  641  linearly contacts (axial direction) the rack shaft  21  having a circular outer shape when not considering the spherical concave portions  642 . 
         [0055]    Plural spherical concave portions  642  are provided in the embodiment, which are arranged in a predetermined pattern. The spherical concave portions  642  are formed to have a hemispherical shape. The hemispherical shape does not mean a complete hemisphere but includes a shape shallower than the complete hemisphere or a shape of an approximately half of an ellipsoid. 
         [0056]    The arrangement of plural spherical concave portions  642  will be further explained specifically. Hereinafter, explanation will be made by adding alphabetic characters to numerals “ 642 ” for convenience to distinguish plural spherical concave portions  642 . 
         [0057]    As shown in  FIG. 3B , the plural spherical concave portions  642  are arranged so that the plural spherical concave portions  642  continue without a break in the axial direction when seeing the plural spherical concave portions  642  from the circumferential direction. For example, concerning the circumferential direction, between a spherical concave portion  642   a  and a spherical concave portion  642   b  which are adjacent on one side in the circumferential direction, a spherical concave portion  642   c  is arranged on the other side in the circumferential direction. A length L 1  between the spherical concave portion  642   a  and the spherical concave portion  642   b  is set to be the same as a diameter of the spherical concave portion  642   c  or smaller than the diameter of the spherical concave portion  642   c.    
         [0058]    Similarly, when seeing the plural spherical concave portions  642  from the axial direction, the plural spherical concave portions  642  are arranged so as to continue without a break in the circumferential direction. For example, concerning the axial direction, a spherical concave portion  642   f  is arranged on one side in the axial direction between a spherical concave portion  642   d  and a spherical concave portion  642   e  which are adjacent on the other side in the axial direction. A length L 2  between the spherical concave portion  642   d  and the spherical concave portion  642   e  is set to be the same as a diameter of the spherical concave portion  642   f  or smaller than the diameter of the spherical concave portion  642   f.    
         [0059]    The inward projecting portions  64  of the bush  60  having the above structure support the rack shaft  21  when the rack shaft  21  moves in the axial direction. Especially in the embodiment, the inward projecting portions  64  of the bush  60  form the interference and contact the rack shaft  21  with a smaller area as compared with, for example, a case where the bush  60  contacts the rack shaft  21  over the entire circumference in the circumferential direction. Accordingly, the motor-drive power steering apparatus  1  according to the embodiment can reduce the friction resistance between the bush  60  and the rack shaft  21  while positively supporting the rack shaft  21  by the bush  60 . 
         [0060]    Also in the embodiment, the inward projecting portions  64  of the bush  60  have the spherical concave portions  642 . The spherical concave portions  642  function so as to reserve the lubricant respectively, operating so as to hold the lubricant to leave from the bush  60  with the movement of the rack shaft  21  in the axial direction. As a result, in the motor-drive power steering apparatus  1  according to the embodiment, the lubricant is easily reversed in the bush  60  and generation of rubbing noise due to the movement of the rack shaft  21  can be reduced. 
         [0061]    Additionally, as described above, the bush  60  can support the rack shaft  21  with a relatively large interference as the bush  60  can reduce the sliding resistance with respect to the rack shaft  21 . As a result, generation of a hammering sound between the pinion shaft  22  and the rack shaft  21  (so called rattle sound) which can be generated due to insufficient support of the rack shaft  21  is suppressed. In particular, when the bush  60  made of a synthetic resin is used, the bush  60  may be expanded or contracted due to creep deformation or thermal history, however, good support of the rack shaft  21  can be realized in such cases. 
       Embodiment 2 
       [0062]    Next, a bush  260  according to Embodiment 2 will be explained. In Embodiment 2, the same symbols are given to the same components as other embodiments, and the detailed explanation thereof is omitted. 
         [0063]      FIG. 4  is an entire perspective view of the bush  260  according to the Embodiment 2. 
       Function/Structure of Bush  260   
       [0064]    The bush  260  (an example of the bearing member) according to Embodiment 2 includes the bush body  61 , the separated portion  62 , the outward projecting portions  63  and inward projecting portions  264  (an example of a projecting portion and a contact portion) provided in the inner side of the bush body  61  in the radial direction. That is, the bush  260  according to Embodiment 2 differs from the bush  60  according to Embodiment 1 in a structure of the inward projecting portions  264 . Hereinafter, the inward projecting portions  264  will be explained in detail. 
       Inward Projecting Portions  264   
       [0065]    Plural (three) inward projecting portions  264  are provided in the embodiment. The plural inward projecting portions  264  are arranged at equal intervals in the circumferential direction of the bush body  61  in the embodiment. Also in the embodiment 2, an inner diameter of a virtual circle passing a portion contacting the rack shaft  21  in the inner projecting portion  264  is formed to be smaller than an outer diameter of the rack shaft  21 . That is, the bush  260  supports the rack shaft  21  with a predetermined interference. 
         [0066]    Each inward projecting portion  264  has the flat surface portion  641  and spherical convex portions  643  (examples of the reservoir portion and convex portions). 
         [0067]    Plural spherical convex portions  643  are provided in Embodiment 2, which are arranged in a predetermined pattern. The spherical convex portions  643  according to Embodiment 2 are formed to have a hemispherical shape. 
         [0068]    The hemispherical shape does not mean a complete hemisphere but includes a shape shallower than the complete hemisphere or a shape of an approximately half of an ellipsoid. 
         [0069]    The arrangement of plural spherical convex portions  643  will be further explained specifically. The arrangement of the plural spherical convex portions  643  are the same as the arrangement of the plural spherical concave portions  642  explained with reference to  FIG. 3B . 
         [0070]    The plural spherical convex portions  643  are arranged so that the plural spherical concave portions  643  continue without a break in the axial direction when seeing the plural spherical convex portions  643  from the circumferential direction. For example, concerning the circumferential direction, between two spherical convex portions  643  which are adjacent on one side in the circumferential direction, a spherical convex portion  643  is arranged on the other side in the circumferential direction. A length between the two spherical convex portions  643  is set to be the same as a diameter of the other spherical convex portion  643  or set to be smaller than the diameter of the other spherical convex portion  643 . 
         [0071]    Similarly, when seeing the plural spherical convex portions  643  from the axial direction, the plural spherical convex portions  643  are arranged so as to continue without a break in the circumferential direction. For example, concerning the axial direction, a spherical convex portion  643  is arranged on one side in the axial direction between two spherical convex portions  643  which are adjacent on the other side in the axial direction. A length between the two spherical convex portions  643  is set to be the same as a diameter of the spherical convex portion  643  on one side or smaller than the diameter of the spherical convex portion  643  on one side. 
         [0072]    Also in the bush  260  according to Embodiment 2 having the above structure, plural spherical convex portions  643  function so as to reserve the lubricant between one spherical convex portion  643  and the other spherical convex portion  643 . Namely, the plural spherical convex portions  643  operate so as to hold the lubricant to leave from the bush  260  with the movement of the rack shaft  21  in the axial direction. As a result, in the motor-drive power steering apparatus  1  according to Embodiment 2, the lubricant is easily reversed in the bush  260  and generation of rubbing noise due to the movement of the rack shaft  21  can be reduced. 
       Embodiment 3 and Embodiment 4 
       [0073]    Next, a bush  360  according to Embodiment 3 and a bush  460  according to Embodiment 4 will be explained. In the following explanation, the same symbols are given to the same components as other embodiments, and the detailed explanation thereof is omitted. 
         [0074]      FIG. 5A  is an entire perspective view of the bush  360  according to Embodiment 3 and  FIG. 5B  is an entire perspective view of the bush  460  according to Embodiment 4. 
       Function/Structure of Bush  360   
       [0075]    The bush  360  (an example of the bearing member) according to Embodiment 3 includes inward projecting portions  364  (an example of a projecting portion and a contact portion) as shown in  FIG. 5A  instead of the inward projecting portions  64  of Embodiment 1. Then, each inward projecting portion  364  includes the flat surface portion  641  and groove portions  644  (an example of the reservoir portion and the at least one concave portion). Hereinafter, the groove portions  644  will be explained in detail. 
         [0076]    The plural (three in the embodiment) groove portions  644  are provided. The groove portions  644  are formed in straight lines in the flat surface portion  641 . Then, the groove portions  644  are formed so as to extend along a direction (orthogonal direction) crossing the axial direction. 
         [0077]    Also in the bush  360  according to Embodiment 3 having the above structure, groove portions  644  function so as to reserve the lubricant respectively. That is, the groove portions  644  operate so as to hold the lubricant to leave from the bush  360  with the movement of the rack shaft  21  in the axial direction. As a result, in the motor-drive power steering apparatus  1  according to the embodiment, the lubricant is easily reversed in the bush  360  and generation of rubbing noise due to the movement of the rack shaft  21  can be reduced. 
       Function/Structure of Bush  460   
       [0078]    The bush  460  (an example of the bearing member) according to Embodiment 4 includes inward projecting portions  464  (examples of a projecting portion and a contact portion) as shown in  FIG. 5B  instead of the inward projecting portions  264  of Embodiment 2. Then, each inward projecting portion  464  includes the flat surface portion  641  and ridge portions  645  (examples of the reservoir portion and convex portions). Hereinafter, the ridge portions  645  will be explained in detail. 
         [0079]    The plural (three in the embodiment) ridge portions  645  are provided. Respective ridge portions  645  project toward the inner side in the radial direction where the rack shaft  21  is provided. The ridge portions  645  are formed in straight lines in the flat surface portion  641 . The ridge portions  645  are also formed so as to extend along a direction (orthogonal direction) crossing the axial direction. 
         [0080]    Also in the bush  460  according to Embodiment 4 having the above structure, plural ridge portions  645  function so as to reserve the lubricant respectively. That is, the plural ridge portions  645  reserve the lubricant between adjacent two ridge portions  645 . The plural ridge portions  645  operate so as to hold the lubricant to leave from the bush  460  with the movement of the rack shaft  21  in the axial direction. As a result, in the motor-drive power steering apparatus  1  according to the embodiment, the lubricant is easily reversed in the bush  460  and generation of rubbing noise due to the movement of the rack shaft  21  can be reduced. 
         [0081]    Note that the bush  60  ( 260 ,  360  and  460 ) may have other shapes as long as the bush is configured to reserve the lubricant at contact spots with respect to the rack shaft  21 , and the present invention is not limited to the structures of the spherical concave portions  642 , the spherical convex portions  643 , the groove portions  644  and the ridge portions  645  according to Embodiments 1 to 4. 
         [0082]    Furthermore, the entire shape of the bush  60  ( 260 ,  360  and  460 ) is not limited to the above-described shapes of Embodiments 1 to 4. The bush  60  is also not limited to the structure of being provided inside the end case  80 , and may have other structures as long as the bush can support the rack shaft  21 . 
         [0083]    The above respective embodiments have been explained by using examples of the motor-drive power steering apparatus, however, the present invention is not limited to this. For example, the structures of the embodiments can be applied to motor-drive power steering apparatuses of other systems such as a rack assist type. Also, the structures of the embodiments can be applied to a power steering apparatus generating an assist force by hydraulic pressure or a manual steering apparatus not generating the power assist force.