Abstract:
A reduction gear includes a gear case, a plurality of shafts in the gear case, a fixed member, an axially movable member, and a friction applying member. The friction applying member is interposed between the fixed member and the axially movable member, to apply a frictional force to at least one of the plurality of shafts in a radial direction of the shaft.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a reduction gear capable of reducing so-called rattle noises and a frictional load application (or generation) member for the reduction gear.  
         [0003]     2. Description of the Related Art  
         [0004]     In a mechanical reduction gear, a “play” is provided between gears. The play is indispensable for smooth rotation of the gears. However, there is a problem that the presence of a play induces so-called “rattle noises” in operation under a small load.  
         [0005]     The rattle noise designates a noise generated by the repeated contact and separation between the tooth surface of a driving-side gear and the tooth surface of a driven-side gear due to the vibration or pulsation of a motor, a variation in load on the driven object side, or the like.  
         [0006]     In order to reduce such rattle noises, for example, Japanese Patent Laid-Open Publication No. 2002-115754 discloses a structure for applying a light frictional load to a gear shaft. If a frictional load is applied to the gear shaft, the tooth surface of a driven-side gear is unlikely to be separated from the tooth surface of a driving-side gear. Therefore, the generation of rattle noises can be more reduced.  
         [0007]     In the above-mentioned Japanese Patent Laid-Open Publication No. 2002-115754, for example, the structure as shown in  FIG. 5 (A) or  5 (B) has been proposed so as to apply (or generate) a frictional load to the gear shaft.  
         [0008]     In the structure shown in  FIG. 5 (A), a bearing housing  14  housing a bearing  12  of an intermediate shaft  10  therein is extended toward the interior of a gear case  16  to form an extended part  14   a . An oil seal  20  for applying a frictional load is interposed between the extended part  14   a  and the intermediate shaft  10 . The extended part  14   a  has a larger diameter than that of a part of the bearing housing  14 , in which the bearing  12  is housed, so as to house the oil seal  20  therein.  
         [0009]     In the structure shown in  FIG. 5 (B), a part of a bearing housing  30  of the bearing  12  is extended toward the gear case  16  to form an extended part  30 A. An O-ring  32  for generating a frictional load is housed in the inner space of the extended part  30 A.  
         [0010]     In the above-described structure shown in  FIG. 5 (A), however, the extended part  14   a  of the bearing housing  14 , which has a larger diameter, is extended beyond the bearing  12  toward the gear. Therefore, there is a problem that positional interference with another gear is likely to be caused. In particular, if a number of gears are present in the gear case  16  as in the case of a multistage reduction gear, it is often difficult to ensure a space where the oil seal  20  for generating a frictional load is to be provided. The design of increasing the axial length of the gear case  16  for the placement of the oil seal  20  for applying a frictional load is normally unacceptable.  
         [0011]     The structure shown in  FIG. 5 (B) has also a problem that a space is difficult to be ensured if the size is small. Therefore, it is sometimes difficult to house the O-ring  32  of desired size. Moreover, the O-ring  32  is not axially positioned yet to be simply housed between the bearing  12  and the bearing housing  30 . Therefore, a thrust load with the deformation of the O-ring  32  may possibly affect an inner ring  12 A. If the bearing  12  rotates while an axial load is being applied only to its inner ring  12 A, smooth relative rotation between the inner ring and the outer ring is inhibited, inevitably inducing a reduction of lifetime.  
         [0012]     In order to ensure that the bearing  12  does not suffer from the axial effects of the O-ring  32 , it is necessary to provide a positioning part (a thrust load supporting part) exclusively for the O-ring  32  between the O-ring  32  and the bearing  12 . As a result, the structure is more complicated. In addition, the axial length of the gear case  16  is increased in some cases.  
       SUMMARY OF THE INVENTION  
       [0013]     In view of the foregoing problems, various exemplary embodiments of this invention provide a reduction gear having a simple structure, which is capable of applying a frictional load to a shaft, and a frictional load application member which can be used for the reduction gear.  
         [0014]     The present invention solves the above problems in a reduction gear including a plurality of shafts in a gear case, the reduction gear comprising: a fixed member; an axially movable member; and a friction applying member applying a frictional force to at least one of the plurality of shafts in a radial direction of the shaft, the friction applying member being interposed between the fixed member and the axially movable member.  
         [0015]     In the present invention, the friction applying member is provided to be interposed between the specified fixed member and the specified axially movable member so as to apply a frictional force to a specific shaft in the gear case in the radial direction of the specific shaft. Therefore, the effects of reducing rattle noise can be obtained in a simple structure.  
         [0016]     Various specific structures for embodying the present invention can be conceived. For example, the following structure can be adopted. In a reduction gear including a plurality of shafts supported by bearings housed within bearing housings in a gear case, an end of at least one of the plurality of shafts is exposed outside the bearing housing of the bearing supporting the shaft, and an elastic member being interposed between an inner face of the gear case and the bearing housing to be capable of applying a radial pressing force to the shaft, is provided at the end of the shaft.  
         [0017]     According to the exemplary structure, the end of the shaft passes through the bearing housing so as to be exposed outside the bearing housing, that is, to the gear case side. The elastic member is interposed between the inner face of the gear case and the bearing housing at the end of the shaft so as to generate a radial pressing force to an intermediate shaft.  
         [0018]     The gear case and the bearing housing are existing members. A small space is actually present between the gear case and the bearing housing. By using the space as a space for placing the elastic member, there is no possibility that the elastic member and a gear interfere with each other when the elastic member is provided. Therefore, it is not necessary to extend the gear case in the axial direction.  
         [0019]     Furthermore, it is not necessary to provide an additional positioning member (a thrust load supporting part) or the like for the placement of the elastic member. In addition, a thrust force is not applied to the bearing by the elastic member. In general, in order to apply a radial frictional load to a shaft, a member for receiving a counterforce is required on the radial outer side of the elastic member for applying the frictional load. In addition, members for axially positioning the elastic member are required on both sides of the elastic members in the axial direction. For example, an O-ring is suitable as such a kind of elastic member for applying a frictional load. However, if an inner ring of the bearing is responsible for the axial positioning of the O-ring (as in the above-described conventional techniques), there is a possibility that a thrust load may be applied to the inner ring of the bearing. However, according to the above-described exemplary structure, the bearing housing is subjected to the counterforce by the deformation of the elastic member. Therefore, the bearing is not affected by the thrust force generated by the elastic member. Accordingly, the bearing itself can extremely smoothly rotate to maintain high durability. Moreover, since both the bearing housing and the gear case are existing members, it is not necessary to additionally provide a positioning member.  
         [0020]     A frictional load can be applied to a specific shaft of a reduction gear with a simple structure, thereby reducing rattle noises at low cost. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     Various exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein:  
         [0022]      FIG. 1  is an overall longitudinal sectional view of a multistage reduction gear with the application of an exemplary embodiment of the present invention;  
         [0023]      FIG. 2  is an enlarged view showing the vicinity of an end of a first intermediate shaft in  FIG. 1 ;  
         [0024]     FIGS.  3 (A) and  3 (B) are schematic views, each showing a deformation state of an elastic member in the above exemplary embodiment;  
         [0025]      FIG. 4  is an enlarged view equivalent to  FIG. 2 , showing an example of another exemplary embodiment of the present invention; and  
         [0026]     FIGS.  5 (A) and  5 (B) are enlarged views equivalent to  FIG. 2 , each showing an example of a conventional structure for applying a frictional load. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]     Hereinafter, examples of a multistage reduction gear with the application of various exemplary embodiments of this invention will be hereinafter described in detail with reference to the drawings.  
         [0028]     A multistage reduction gear  40  includes an input shaft  44 , a first intermediate shaft  46 , a second intermediate shaft  48 , and an output shaft  50 .  
         [0029]     In this exemplary embodiment, a motor shaft  52  of a motor (not shown) also serves as the input shaft  44 . The input shaft  44  is exposed in a gear case  42  in a cantilever state. A first pinion  54  is formed at the tip of the input shaft  44  by direct gear cutting. The gear case  42  is connected with a side plate  42 A forming a framework of the gear case  42  through a bolt  45 .  
         [0030]     The first intermediate shaft  46  is supported by a pair of bearings  56 A and  56 B. The bearings  56 A and  56 B are housed in bearing housings  58 A and  58 B, respectively. The first intermediate shaft  46 A has a first gear  60  meshing with the first pinion  54  and a second pinion  62 .  
         [0031]     The second intermediate shaft  48  is supported by a pair of bearings  66 A and  66 B. The bearings  66 A and  66 B are housed in bearing housings  68 A and  68 B, respectively. The second intermediate shaft  48  has a second gear  70  meshing with the second pinion  62  and a third pinion  72 .  
         [0032]     The output shaft  50  is supported by a pair of bearings  76 A and  76 B. The bearings  76 A and  76 B are housed in bearing housings  78 A and  78 B, respectively. The bearing housing  78 A of the pair of bearing housings  78 A and  78 B, which is on the side where the output shaft  50  protrudes outside the gear case  42 , is formed by the gear case  42  itself. The bearing  76 A, which is on the bearing housing  78 A side, is considerably larger than that of the bearing  76 B for a radial load applied to the output shaft  50 . The output shaft  50  has an output gear  75 .  
         [0033]     In this exemplary embodiment, frictional load application (or generation) mechanisms  80  and  82  are provided for both the first intermediate shaft  46  and the second intermediate shaft  48 , respectively. The application mechanism  80  includes an elastic member  86 , whereas the application mechanism  82  includes an elastic member  87 . Since the two application mechanisms  80  and  82  have basically a similar structure, the application mechanism  80  is mainly described herein.  
         [0034]     As shown in  FIG. 2  in an enlarged manner, the bearing housing  58 A on one side of the first intermediate shaft  46  (on the right side in  FIG. 1 ) includes a through hole  84  formed in the center in a radial direction. An end  46 A of the first intermediate shaft  46  passes through the through hole  84  to be exposed outside the bearing housing  58 A, that is, to face the gear case  42 . The elastic member (the frictional load application member)  86  for applying a frictional load to the first intermediate shaft  46  is provided for the end  46 A.  
         [0035]     The elastic member  86  includes an axially extending ring part  88 , a disc-shaped part (a planar part)  90  formed in continuation with the ring part  88  so as to extend in the radial direction, and a spreading part  92  formed in continuation with the planar part  90 . The elastic member  86  is interposed between an inner face  42 B of the gear case  42  and the bearing housing  58 A. Each of the ring part  88 , the disc-shaped part  90 , and the spreading part  92  is formed of an elastic material.  
         [0036]     More specifically, the ring part  88  axially extends along the outer circumference of the end  46 A of the first intermediate shaft  46 . The ring part  88  has a ring shape with its inner diameter being set larger than the outer diameter of the first intermediate shaft  46 . The disc-shaped part  90  extends in a disc-like shape from an end  88 A of the ring part  88  on the gear case  42  side along an outer face  58 A 1  of the bearing housing  58 A. The spreading part  92  spreads from an outer circumferential end  90 A of the disc-shaped part  90  toward the gear case  42 . An outer circumferential edge  92 A of the spreading part  92  is in contact with the inner face  42 B of the gear case  42 .  
         [0037]     With the above-described shape and arrangement, the elastic member  86  constitutes a “lever,” in which the outer circumferential edge  92 A of the spreading part  92  functions as a power point, the outer circumferential end  90 A of the disc-shaped part  90  functions as a supporting point, and an end  88 B of the ring portion  88  functions as a point of application.  
         [0038]     The functions of the multistage reduction gear  40  will be now described.  
         [0039]     A motive power input from the input shaft  44  (the motor shaft  52 ) is transmitted through the first pinion  54 , the first gear  60 , the second pinion  62 , the second gear  70 , the third pinion  72 , and the output gear  75  to the output shaft  50 .  
         [0040]     At this time, a frictional load is applied to the first intermediate shaft  46  and the second intermediate shaft  48  in the following manner.  
         [0041]      FIG. 3 (A) shows a state where the side plate  42 A is not screwed to the gear case  42  by the bolt  45  (see  FIG. 1 ) yet, that is, the elastic member  86  is not deformed yet. In this state, the elastic member  86  is simply in slight contact with the outer circumference of the end  46 A of the first intermediate shaft  46 . Therefore, a pressing force is not generated. Under this state, the side plate  42 A is screwed to the gear case  42  by the bolt  45 . Then, a distance between the inner face  42 B of the gear case  42  and the bearing housing  58 A is reduced to deform the elastic member  86  as shown in  FIG. 3 (B). As a result, the end  88 A of the ring part  88  on the gear case  42  side is lifted up by the principle of “leverage” with the outer circumferential edge  92 A of the spreading part  92  functioning as a power point, the outer circumferential end  90 A of the disc-shaped part  90  functioning as a supporting point, and the end  88 B of the ring portion  88  functioning as a point of application. Then, the end  88 B of the ring part  88  on the bearing  56 A side is pressed against the outer circumference of the end  46 A of the first intermediate shaft  46 .  
         [0042]     As a result, a radial frictional load is applied to the first intermediate shaft  46 . While the first intermediate shaft  46  is rotating, a predetermined rotational resistance is generated in the first intermediate shaft  46  at this portion. Therefore, the first gear  60  engaged on the first intermediate shaft  46  rotates while constantly applying a rotational load to the first pinion  54 . Even if some pulsation or the like is present in a driving force from the first pinion  54  side, the first gear  60  is not separated from the first pinion  54 . Therefore, the generation of rattle noises at the portion where the first pinion  54  and the first gear  60  mesh with each other is effectively prevented.  
         [0043]     Since exactly the same effects can be obtained from the frictional load application mechanism  82  for the second intermediate shaft  48 , the generation of rattle noises at the portion where the second pinion  62  and the second gear  70  mesh with each other is effectively prevented.  
         [0044]     Since the elastic member  86  can be deformed by using the assembly mechanism achieved with the bolt  45  to the side plate  42 A of the gear case  42  in this exemplary embodiment, assembly is advantageously easy. Moreover, a special (additional) moving mechanism or the like is not needed.  
         [0045]     The deformation force of the elastic member  86  is only applied to the gear case  42  and the bearing housing  58 A in addition to the end  46 A of the first intermediate shaft  46 , which is a target of the application of the deformation force, but is not applied to the bearing  56 A at all. Therefore, the bearing  56 A can rotationally support the first intermediate shaft  46  with no thrust load. Therefore, high durability can be maintained.  
         [0046]     Furthermore, the thrust load generated by the deformation of the elastic member is not applied to the first intermediate shaft  46  either. Therefore, there is no possibility that the thrust load is applied to the bearing  56 B on the opposite side through the first intermediate shaft  46 .  
         [0047]     Moreover, a user can adjust the applied frictional force at the place of use of the reduction gear simply by cutting or scraping the outer circumferential edge  92 A of the spreading part  92  or the ring part  88  of the elastic member to a predetermined length, so as to reduce the frictional force.  
         [0048]     The specific shape or arrangement of the elastic member in the present invention may be any shape other than the example given in the above exemplary embodiment. In sum, an elastic member for realizing the present invention in a simpler manner can be achieved if an elastic member in such a shape that constitutes the “lever” is prepared. The “lever” acts on the outer circumference of the end of the intermediate shaft with a part of the elastic member functioning as a point of application when a specific portion of the elastic member functions as a supporting point and a contact portion of the elastic member with the gear case functions as a power point. In this case, the outer face of the bearing housing, the inner circumferential face of the through hole in the bearing housing, or the like must function in a good manner to provide the supporting point.  
         [0049]     Furthermore, for example, if a protrusion  158 A 2  protruding toward a gear case  142  is provided for a bearing housing  158 A as shown in  FIG. 4 , an elastic member  186  can also be constituted to be deformed in the inward radial direction by a pressing force from the gear case  142  side while being in contact with an outer face  158 A 1  of the bearing housing  158 A and the protrusion  158 A 2  at an end  146 A of a first intermediate shaft  146 . In such a structure, an elastic member having a simpler structure such as an O-ring is satisfactory as the elastic member  186 .  
         [0050]     Although the protrusion of the bearing housing is integrally formed with the bearing housing in the example shown in  FIG. 4 , the protrusion may be independently formed. Moreover, instead of providing the protrusion so as to protrude from the bearing housing side, some kind of protrusion may be formed to protrude from the gear case side.  
         [0051]     The present invention can be used for a multistage reduction gear, in which rattle noises occurs, so as to reduce rattle noises.  
         [0052]     The disclosure of Japanese Patent Application No. 2004-83535 filed Mar. 22, 2004 including specification, drawing and claim are incorporated herein by reference in its entirety.