Abstract:
A motor having a motor portion and a speed-reducing portion includes a gear housing disposed on the motor portion, a bearing press-fitted in the gear housing, a worm shaft rotatably held in the bearing, a worm wheel rotatably held in the gear housing with engagement to the worm shaft. The gear housing has a bearing hole for accommodating the bearing. An inner circumference of the bearing hole includes a contact portion for press-fittingly holding the bearing. A circumferential dimension of the contact portion is different at a different circumferential position, and at least one contact portion is positioned in an opposite side to a worm wheel engagement side of the worm shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on and claims the benefit of priority of Japanese Patent Application No. 2004-282499 filed on Sep. 28, 2004, the disclosure of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention generally relates to a motor device for actuating an automotive apparatus.  
       BACKGROUND OF THE INVENTION  
       [0003]     Conventionally, a motor used for a power window system or the like includes a motor portion having a rotation shaft and a speed-reducing portion connected to the motor portion. The speed-reducing portion includes a gear housing, a worm shaft, and a worm wheel for decelerating rotation of the rotation shaft. The speed-reducing portion may include a press-fitted bearing in a bearing hole of the gear housing. The press-fitted bearing rotatably holds the worm shaft.  
         [0004]     The bearing hole in a motor without having the speed-reducing portion has contact portions toward the bearing on an inner circumference of the bearing hole formed at an equiangular distance for press-holding the bearing (refer to Japanese Patent Document JP-U-H6-44364). In this scheme of structure, the bearing is held by a plurality of small contact portions positioned equidistantly on an inner circumference of the bearing hole, thereby enabling appropriate assembly of the press-fitted bearing in the bearing hole even when dimensional accuracy of the assembly is moderate.  
         [0005]     However, this scheme of structure described above causes a problem when it is applied in the motor having a speed-reducing portion. That is, a reaction force from the worm shaft being engaged with the worm wheel to the press-fitted bearing concentrates on the small contact portions between the press-fitted bearing and the bearing hole on the other side of the worm shaft relative to the worm wheel. Therefore, the concentrated reaction force causes, for example, breakage and/or deformation of the bearing/bearing hole. The concentrated reaction force may cause a squeaky sound when an oil film normally formed on a sliding surface between an oil-impregnated bearing and the worm shaft is broken.  
       SUMMARY OF THE INVENTION  
       [0006]     In view of the above-described and other problems, it is an object of the present invention to provide a motor that has a speed-reducing portion being protected from the concentration of a mechanical force on a small portion without having a high accuracy of structure for press-fitting of a bearing.  
         [0007]     The motor in an embodiment of the present invention includes a motor portion and a speed-reducing portion connected thereto. The speed-reducing portion has a gear housing fixed on the motor portion, a bearing fixed on the gear housing, a worm shaft being rotatably held by the bearing, a worm wheel being rotatably held by the bearing having engagement to the worm shaft. The gear housing has a bearing hole for accommodating the bearing press-fittingly held therein. An inner circumference of the bearing hole has a small contact portion that holds the bearing at a small circumferentially extending portion (small contact portion) and a large contact portion that holds the bearing by an area that is circumferentially larger than the small contact portion. The large contact portion is formed axially on an opposite side to the worm wheel engagement side of the worm shaft. In this manner, dimension of the bearing hole does not have to be highly accurate for appropriate assembly. Further, breakage, deformation, and/or a squeaky operation sound from the bearing/bearing hole are prevented because a reaction force from the worm shaft and/or the worm wheel is evenly borne by the large contact portion of the bearings without concentration to a small area in the bearing.  
         [0008]     According to one aspect of the present invention, the bearing used in the motor is an oil-impregnated bearing. That is, the oil-impregnated bearing forms an oil film on its surface. The oil film formed on the surface is maintained when the pressure between the bearing and the worm shaft is evenly distributed. In an embodiment of the present invention, the large contact portion better serves for evenly distributing the pressure than the small contact portions that is conventionally used to press-fittingly hold the bearing, because no gap is formed between the bearing and the bearing hole when the large contact portion is used. Therefore, the squeaky operation sound is prevented by the oil film formed between the bearing and the worm shaft.  
         [0009]     According to another aspect of the present invention, the small contact portion is formed at plural positions along an inner circumference of the bearing hole in the gear housing. In this manner, the bearing is held securely and evenly from all directions.  
         [0010]     According to yet another aspect of the present invention, the large contact portion extends substantially over a center angle of 180 degrees in a circumferential direction for holding the bearing.  
         [0011]     According to still another aspect of the present invention, the small contact portion has following characteristics. That is, the small contact portion may have a surface that is a tangent plane of a circle that is diametrically smaller than an outer circumference of the bearing. The small contact portions may also be positioned equidistantly on the circumference of the bearing. The small contact portion may also be positioned equiangularly substantially at every 45 degrees along the circumference of the bearing.  
         [0012]     According to further aspects of the present invention, a pair of the bearings are disposed at both ends of the worm shaft. Both ends of the worm shaft are held by the pair of bearings.  
         [0013]     According to yet still another aspect of the present invention, the small contact portion and the large contact portion may be disposed on an outer circumference of the bearing that is press-fitted in the bearing hole. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which:  
         [0015]      FIG. 1  is a cross-sectional view of a motor in an embodiment of the present invention;  
         [0016]      FIG. 2  is a portion of the cross-sectional view of the motor in the embodiment;  
         [0017]      FIG. 3  is an illustration of a gear housing in the embodiment;  
         [0018]      FIG. 4  is an illustration of a bearing hole in the embodiment;  
         [0019]      FIG. 5  is a cross-sectional view of the bearing hole in another embodiment; and  
         [0020]      FIG. 6  is a cross-sectional view of the bearing hole in yet another embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     A motor of the present invention is described with reference to the drawings.  
         [0022]      FIG. 1  shows a cross-sectional view of a motor  1  in an embodiment of the present invention. The motor  1  includes a motor portion  2  and a speed-reducing portion  3 .  
         [0023]     The motor portion  2  has a yoke housing (referred to as a yoke hereinafter)  4  that is generally formed in a flat cylinder shape with a bottom, a pair of magnets  5  fixed on an inner surface of the yoke  4 , an armature  6  rotatably held in the yoke  4 , and a brush holder  7 .  
         [0024]     The brush holder  7  is made of a resin, and is disposed on an opening of the yoke  4 . The brush holder  7  holds a bearing  8  and a brush  9 . A rotation shaft  10  of the armature  6  is rotatably held by the bearing  8  and a bearing  11  that is fixed at a bottom of the yoke  4 . The brush  9  is press-contacted against a rectifier  12  of the armature  6 .  
         [0025]     The speed-reducing portion  3  includes a gear housing  21 , a pair of bearings  22 ,  23 , a worm shaft  24 , a worm wheel  25 , and a clutch  26 . The speed-reducing portion  3  is shown in  FIG. 2 . The gear housing  21  is made of a resin. The gear housing  21  has a fixed portion  21   a,  a worm housing  21   b,  and a wheel housing  21   c.    
         [0026]     The fixed portion  21   a  is formed in a shape that is fitted to a flange  4   a  at the opening of the yoke  4 . The fixed portion  21   a  is shown in  FIG. 3 . The fixed portion  21   a  is fixed by a screw on the flange  4   a.  The brush holder  7  is held between the fixed portion  21   a  and the flange  4   a.  The fixed portion  21   a  in  FIG. 3  is the gear housing  21  shown in an axial direction of the rotation shaft  10 . The fixed portion  21   a  shown in  FIG. 3  is in a form without the worm shaft  24  and the clutch  26  being fitted therein.  
         [0027]     The worm housing  21   b  is formed in a cylindrical shape extending on an extension of the rotation shaft  10 , and rotatably holds the worm shaft  24  in its body by using the bearings  22 ,  23 . The worm housing  21   b  has the clutch  26  on a motor  2  side for connectably driving the worm shaft  24  and the rotation shaft  10 . The clutch  26  transfers a driving force from the rotation shaft  10  to the worm shaft  24 , and prevents backlash of the driving force from being transferred from the worm shaft  24  toward the rotation shaft  10  by locking the rotation of the worm shaft  24 . That is, the clutch  26  prevents the motor  1  from being driven by a force from a driven mechanism.  
         [0028]     The wheel housing  21   c  is formed in a flat disk shape, and is disposed perpendicularly to the worm housing  21   b.  The wheel housing  21   c  rotatably holds a worm wheel  25  in its body. An inside space of the worm housing  21   b  and an inside space of the wheel housing  21   c  communicate with each other at a connecting portion, and the worm shaft  24  is engaged with the worm wheel  25  at the connecting portion. An output axis (not shown in the figure) is engaged with the worm wheel  25  to actuate a window through a regulator or the like (not shown in the figure).  
         [0029]     The bearings  22  and  23  are fixed in the bearing holes  31  and  32  formed in the gear housing  21  (worm housing  21   b ). Specifically, the bearings  22  and  23  are oil-impregnated bearings, and have a cylindrical shape for both of inner/outer circumferential surfaces. The gear housing  21  has the bearing hole  31  on a motor  2  side in the worm housing  21   b  as shown in FIGS.  2  to  4 . The bearing hole  31  has a small contact portion  31   a  and a large contact portion  31   b  formed on its inner circumference as shown in  FIG. 4 . The small contact portion  31   a  and the large contact portion  31   b  hold the bearing  22  by its outer circumference. The area of contact of the large contact portion  31   b  is larger than that of the small contact portion  31   a  in terms of the length in a circumferential direction of the bearing  22 . The large contact portion  31   b  holds an opposite side of the worm shaft  24  relative to a worm wheel  25  engagement side (lower side in  FIG. 4 ). The large contact portion  31   b  covers half of the outer circumference of the bearing  22 , that is, the large contact portion  31   b  substantially has a center angle of 180 degrees. In addition, the small contact portion  31   a  is formed at plural positions along the inner circumference of the bearing hole  31 . The number of the small contact portions  31   a  is three in this embodiment. The small contact portions  31   a  are formed symmetrically relative to a center line L at an angular interval of 45 degrees. The small contact portions  31   a  are formed on the worm wheel  25  engagement side of the worn shaft  24 , and the large contact portion  31   b  is formed on the opposite side of the small contact portions  31   a  on the worm shaft  24 . More specifically, the small contact portions  31   a  are formed as tangent planes  31   c  of a circle that has a slightly smaller radius than the outer circumference of the bearing  22 . The tangent planes  31   c  as small contact portions  31   a  are formed on an inner circumference  31   d  of the bearing hole  31  that has a slightly larger radius than the outer circumference of the bearing  22 .  
         [0030]     The worm shaft  24  is drawn smaller than an actual proportion to the bearing  22  for illustration purpose in  FIG. 4 . The bearing  23  and the bearing hole  32  are not shown in the figure because they are functionally identical to the bearing  22  and the bearing hole  31  only with the difference of dimensions. That is, the bearing hole  32  has the small and large contact portions.  
         [0031]     The small contact portions  31  a disposed on the inner surface of the bearing hole  31  creates gaps between the bearings  22 ,  23  and the bearing hole  31 . These gaps prevents the pressure between the worm shaft  24  and the bearings  22 ,  23  to be evenly distributed in a circumferential direction of the bearings  22 ,  23 . That is, an oil film formed on the surface of an oil-impregnated bearings  22 ,  23  may be broken when the distribution of the pressure is uneven. However, the bearing hole  31  holds the bearings  22 ,  23  by the large contact portion  31   b  in the present invention, thereby enabling the oil film suitably maintained on the surface of the bearings  22 ,  23 . Therefore, the squeaky operation sound, for example, is prevented. Further, leakage of oil that forms the oil film on the surface of the bearings  22 ,  23  is prevented by the large contact portion  31   b.  Therefore, an outer circumferential surface of the oil impregnated bearings  22 ,  23  does not have to be processed to have a precise size for press-fitting.  
         [0032]     Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.  
         [0033]     The bearing holes  31  and  32  have the small contact portions  31   a  and the large contact portion  31   b  on its inner circumference in the embodiment described above. However, the small contact portions  31   a  and the large contact portion  31   b  may be formed differently as long as the large contact portion  31   b  holds the opposite side of the worm shaft  24  relative to the worm wheel  25  engagement side.  
         [0034]     For example, the bearing hole  31  may be formed in a shape of a bearing hole  41  as shown in  FIG. 5 . In this case, planes  41   a  as the small contact portions are connected each other to form a octagon.  
         [0035]     Further, the bearing hole  31  may be formed in a shape of a bearing hole  51  as shown in  FIG. 6 . In this case, planes  51   a  as the small contact portions are formed as convex portions between two arc shape concave portions on an inner circumference that has a slightly smaller radius than the outer circumference of the bearing  22 .  
         [0036]     Furthermore, the number of small contact portions  31   a  may be more than three, or may be less than three.  
         [0037]     Furthermore, the large contact portion  31   b  may have a different center angle from the one in the above-described embodiment. That is, the center angle of the large contact portion  31   b  may be 90 degrees, or 120 degrees as far as the large contact portion  31   b  is formed on the opposite side of the worm shaft  24  relative to the worm wheel  25  engagement side of the worm shaft  24 .  
         [0038]     Furthermore, the small contact portions  31   a  and the large contact portion  31   b  may only be formed on one of the pair of bearings  22  and  23 .  
         [0039]     Furthermore, the oil-impregnated bearings  22 ,  23  may be other types of bearings. For example, ball bearings may be used to have a same functional effect, that is, prevention of the breakage, deformation, and/or a squeaky operation sound.  
         [0040]     Furthermore, the clutch  26  may be omitted in a connecting portion between the rotation shaft  10  and the worm shaft  24 . That is, the rotation shaft  10  and the worm shaft  24  may be connected by a joint or the like.  
         [0041]     The inner circumference of the bearing holes  31 ,  32  may not necessarily be in a round shape. That is, the inner circumference of the bearing holes  31 ,  32  may be a tangent plane of a certain circle to be press-fitted to the bearing  22 ,  23  as shown in the embodiment in  FIG. 5 .  
         [0042]     The motor  1  in the embodiment is used to actuate a power window system. However, the motor of the present invention may be used to actuate and operate other type of apparatus. For example, the motor  1  may be used to operate a sun roof, a wiper or the like. The motor  1  may be used in an automobile, or may be used in other type of vehicle.  
         [0043]     Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.