Abstract:
The present invention provides a fixed type constant velocity universal joint suitable for applications where vibration is harmful. A fixed-type constant velocity universal joint ( 1 ) includes an inner member ( 20 ) fitted in an outer member ( 10 ) with a retainer ( 40 ) therebetween, and balls ( 30 ) provided between track grooves ( 14, 24 ) of the outer member ( 10 ) and the inner member ( 20 ) as well as retained by the retainer ( 40 ). The outer member ( 10 ) is constructed as a multilayer structure of three or more layers formed of an outside member ( 15 ), one or a plurality of intermediate members ( 16 ), and an inside member ( 17 ), and at least one of the intermediate members ( 16 ) is constructed of an elastic material. Cushioning action of the intermediate members ( 16 ) can reliably absorb vibration transmitted from either of the outer member ( 10 ) and the inner members ( 20 ) with the members ( 10, 20 ) set to a predetermined operation angle.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fixed type constant velocity universal joint and, more particularly, to a fixed type constant velocity universal joint suitable for applications where vibration is harmful as in a case of an automotive steering device. 
     BACKGROUND OF THE INVENTION 
     Constant velocity universal joints are roughly classified into fixed type joints which solely allow angular displacement between input and output shafts and slide type joints in which angular displacement and axial displacement are permissible, and the kind of the joint to be used is selected according to its application, condition of use, etc. As the fixed type constant velocity universal joints, Rzeppa type joints and undercut free type joints are widely known. 
       FIG. 7  shows, by way of example, a Rzeppa type joint  1 ′ (hereinafter referred to as joint  1 ′), which is a kind of the fixed type constant velocity universal joint. The joint  1 ′ is mainly composed of: an outer member  10  having at one end of a first shaft portion  11   a  cup portion  13  with a spherical inner surface  12 , with a plurality of track grooves  14  being formed in the spherical inner surface  12  of the cup portion  13 ; an inner member  20  having at one end of a second shaft portion  21  an inner ring  23  with a spherical outer surface  22 , with a plurality of track grooves  24  being formed in the spherical outer surface  22  of the inner ring  23 ; a plurality of balls  30  arranged between the track grooves  14  and  24 ; and a retainer  40  having a spherical outer surface  42  corresponding to the spherical inner surface  12  of the outer member  10  and a spherical inner surface  44  corresponding to the spherical outer surface  22  of the inner member  20  and equipped with a plurality of ball pockets  46  for retaining the balls  30  arranged at predetermined circumferential intervals (see, for example, JP 2003-130082 A). 
     In the above-described joint  1 ′, sphere centers O of the spherical inner surface  12  of the cup portion  13  of the outer member  10  and of the spherical outer surface  22  of the inner ring  23  of the inner member  20  substantially coincide with each other. A center O 1  of the track grooves  14  of the outer member  10  and a center O 2  of the track grooves  24  of the inner member  20  are axially offset in opposite directions by substantially the same distance with respect to the sphere centers O. As a result, the ball track formed by the track grooves  14  and  24  assume a wedge-like shape diverging from a depth side toward an opening side of the outer member  10 . In the Rzeppa joint  1 ′, longitudinal sectional configurations of the track grooves  14  and  24  are curved over their entire regions, with the centers of the curved portions being the centers O 1  and O 2  of the track grooves  14  and  24 , respectively. In contrast, in the undercut free type joint, the opening side end portion of each track groove is formed in a configuration extending straight in the axial direction. 
     As shown in  FIG. 8 , in the above-described joint  1 ′, when rotational torque is applied to one of the outer member  10  and the inner member  20 , with the outer member  10  and the inner member  20  being at an operation angle of θ, the balls  30  are caused to reciprocate in the ball track, with the track grooves  24  of the inner ring  23  rocking relative to the track grooves  14  of the outer member  10 , whereby the rotational torque is transmitted to the other member. 
       FIG. 9A  shows an example of the above-mentioned joint  1 ′ as applied to a steering device  71  of an automobile. In the steering device  71 , one or a plurality of intermediate shafts  75  are arranged between an input shaft  73  connected to a steering wheel  72  and a steering gear  74 , and these members are connected by the joints  1 ′. In the steering device  71 , when vibration is transmitted to the steering wheel  72  from the wheels (not shown) during traveling, there is a fear of the driver experiencing discomfort and an operational error being induced. Thus, it is necessary for the steering device  71  to be capable of preventing transmission of vibration to the steering wheel  72 . Conventionally, as a means for absorbing such the vibration, there is provided between the input shaft  73  and the intermediate shafts  75  an elastic shaft coupling  76  as shown in  FIGS. 9B and 9C  (see, for example, JP 1996-133097 A and JP 2002-310182 A). In the elastic shaft coupling  76  of  FIGS. 9B and 9C , an inner shaft  76   a  and an outer shaft  76   b  are fit-engaged with each other through the intermediation of a cushioning member  76   c.    
     It should be noted, however, that if not only the elastic shaft coupling  76  but also the joints  1 ′ can absorb vibration, it is more effective in cutting off transmission of vibration to the steering wheel  72 . As shown in  FIGS. 7 and 8 , in the above-described joint  1 ′, there is provided a pressing portion  21   a  for axially applying an elastic pressing force to an end portion of the second shaft portion  21  constituting the inner member  20 , and the retainer  40  is provided with a receiving portion  48  for receiving the pressing force from the pressing portion  21   a . However, in a state where the outer member  10  and the inner member  20  are at an operation angle of θ, as shown in  FIG. 8 , the direction of the vibration transmitted axially from the outer member  10  and the direction in which the elastic action of the pressing member  21   a  is exerted differ from each other, so it is impossible to effectively absorb the vibration transmitted from the outer member  10  to the inner member  20 . 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above problem in the prior art. It is an object of the present invention to provide a fixed type constant velocity universal joint suitable for applications where vibration is harmful as in a case of an automotive steering device. 
     To achieve the above-mentioned object, according to the present invention, a fixed type constant velocity universal joint includes: an outer member having a spherical inner surface with a plurality of track grooves formed therein; an inner member having a spherical outer surface with a plurality of track grooves formed therein; a ball arranged in a wedge-shaped ball track formed by the track grooves of the outer member and the track grooves of the inner member; and a retainer arranged between the spherical inner surface of the outer member and spherical outer surface of the inner member and adapted to retain the ball, in which the outer member is formed in a multi-layer structure of three or more layers formed of an outside member, one or a plurality of intermediate members, and an inside member, and in which at least one of the intermediate members is formed of an elastic material. 
     More specifically, as shown, for example, in  FIG. 1 , the outer member  10  is formed in a three-layer structure composed of an outside member  15 , an intermediate member  16 , and an inside member  17 , with the intermediate member  16  being formed of an elastic material. Instead of providing only one intermediate member  16 , it is also possible to provide a plurality of the intermediate members  16 , with at least one of the plurality of intermediate members  16  being formed of an elastic material. By thus forming the outer member  10  in a multi-layer structure, due to the cushioning action of the intermediate member  16 , it is possible to reliably absorb vibration transmitted from whichever of the outer member  10  and the inner member  20 . Thus, it is possible to provide the fixed type constant velocity universal joint suitable for applications where vibration is harmful. 
     When forming the outer member in a multi-layer structure as described above, it is possible to effect torque transmission between the outer member and the inner member by providing an engagement portion on both the inner side of the outside member and the outer side of the inside member. 
     In the outer member, the inside member is fit-engaged with the outside member through the intermediation of the intermediate member, and the outside member, the intermediate member, and the inside member are integrally fixed together by a fixing device. 
     When fit-engaging the inside member with the outside member through the intermediation of the intermediate member, there is provided a fixing device for integrally fixing together the outside member, the intermediate member, and the inside member to prevent detachment of the intermediate member and the inside member from the outside member. Examples of the fixing device include one which is formed as a member separate from the outside member, or the like, and which is integrally mounted to the outside member to be locked to an end portion of the inside member, and one which is locked to an end portion of the inside member through plastic deformation of a predetermined portion of the outside member. 
     While it is desirable to use a rubber material for the elastic material forming the intermediate member from the viewpoint of workability and availability, any other material will do as long as it provides a desired cushioning action. 
     Further, when used, in particular, as a constant velocity universal joint for a steering device arranged between the steering wheel and the steering gear of a vehicle, the above-described fixed type constant velocity universal joint effectively provides a vibration absorbing effect as mentioned above, making it possible to prevent vibration of the steering wheel. The steering device may be an electric power steering device (EPS) imparting an assistant force by a motor, or a hydraulic power steering device imparting an assist force through oil pressure. 
     In the present invention, the outer member is provided with an elastic member as described above, whereby it is possible to absorb vibration with a simple structure. Thus, it is possible to provide the fixed type constant velocity universal joint suitable for applications where vibration is harmful as in the case of a steering device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view showing the present invention as applied to a Rzeppa type joint, which is a kind of fixed type constant velocity universal joint; 
         FIG. 2  is a cross-sectional view of an outer member taken along the line A-A of  FIG. 1 ; 
         FIG. 3  is an end view of an opening of the outer member as seen in a direction of the arrow B of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view, taken along the line A-A of  FIG. 1 , of an outer member according to a modification of the present invention; 
         FIG. 5  is a longitudinal sectional view of the outer member according to a modification of the present invention; 
         FIGS. 6A through 6D  are diagrams showing modifications of a fixing device, in which  FIG. 6A  is an end view of an opening of the outer member,  FIG. 6B  being an enlarged longitudinal sectional view of a main portion of the outer member,  FIG. 6C  is an end view of the opening of the outer member, and  FIG. 6D  is a longitudinal sectional view of a main portion of the outer member; 
         FIG. 7  is a longitudinal sectional view of a conventional fixed type constant velocity universal joint; 
         FIG. 8  is an explanatory view illustrating an operation of a conventional fixed type constant velocity universal joint; and 
         FIGS. 9A through 9C  are schematic views of the conventional fixed type constant velocity universal joint as applied to a steering device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, a fixed type constant velocity universal joint according to a preferred embodiment of the present invention will be described with reference to  FIGS. 1 through 6D . The components that are the same as those of a conventional joint  1 ′ shown in  FIGS. 7 and 8  are indicated by the same reference symbols, and a detailed description thereof will be omitted. 
       FIG. 1  shows the present invention as applied to a Rzeppa type joint  1  (hereinafter referred to as joint  1 ), which is a kind of the fixed type constant velocity universal joint. As shown in  FIG. 1 , the joint  1  is mainly composed of an outer member  10 , an inner member  20 , balls  30 , and a retainer  40 ; the outer member  10  has a cup portion  13  formed in a three-layer structure composed of an outside member  15 , an intermediate member  16 , and an inside member  17 , with the intermediate member  16  being formed of an elastic material. 
     As shown in  FIGS. 1 and 2 , the outside member  15  is a member constituting a main body of the outer member  10 , and is formed by providing an outer layer portion of the cup portion  13  at an end of a first shaft portion  11 . As shown in  FIG. 2 , an inner surface of the outside member  15  is formed in a spherical configuration corresponding to a spherical inner surface  12  of the cup portion  13 , and engagement grooves  15   a  as engagement portions for engagement with the inside member  17  are provided at positions corresponding to a plurality of track grooves  14 . 
     As shown in  FIGS. 1 and 2 , the intermediate member  16  is a member provided between the outside member  15  and the inside member  17  and formed of an elastic material, such as rubber or a resin. The intermediate member  16  is formed in a cup-like configuration corresponding to a configuration of a gap between the outside member  15  and the inside member  17 , and is arranged so as to be in intimate contact with the entire inner surface of the outside member  15  and the entire outer surface of the inside member  17 . 
     As shown in  FIGS. 1 and 2 , the inside member  17  is a member constituting the spherical inner surface  12  of the cup portion  13  of the outer member  10 . The outer surface of the inside member  17  is formed in a spherical configuration corresponding to the spherical inner surface  12 , and its outer diameter is somewhat smaller than the inner diameter of the outside member  15 . As shown in  FIG. 2 , on an outer surface of the inside member  17 , there are formed, at positions corresponding to the plurality of track grooves  14  formed on the inner surface side, ridges  17   a  as engagement portions for engagement with the engagement grooves  15   a  of the outside member  15 . The ridges  17   a  have a width somewhat smaller than a width of the engagement grooves  15   a  of the outside member  15 , and are formed so as to protrude into the engagement grooves  15   a  of the outside member  15  to be engaged with the engagement grooves  15   a  of the outside member  15  through the intermediation of the intermediate member  16 . With this construction, torque transmission is possible between the outside member  15  and the inside member  17 . 
     In  FIGS. 1 through 3 , reference numeral  60  indicates a fixing member as a fixing device, and the fixing member  60  serves to prevent the intermediate member  16  and the inside member  17  from being detached from the outside member  15 . As shown in  FIGS. 1 and 3 , the fixing member  60  has a cylinder portion  61  to be fit-engaged with the outer side of the opening end portion of the outside member  15 , and a plurality of lock portions  62  extending radially inwards in a tongue-like configuration from positions at the end of the cylinder portion  61  corresponding to the track grooves  14  of the outer member  10 . As shown in  FIG. 1 , the depth-side end portion (end portion on the opposite side of the lock portions  62 ) is inwardly caulked to form a caulked portion  63 , which is engaged with the outer portion of the outside member  15 . As shown in  FIG. 3 , the lock portions  62  are locked to the respective opening side end portions of the outside member  15 , the intermediate member  16 , and the inside member  17  at positions corresponding to engagement positions of the outside member  15  and the inside member  17 . As a result, the outside member  15 , the intermediate member  16 , and the inside member  17  are integrally fixed together to form the outer member  10 . 
     As described above, in the joint  1  of the present invention, the outer member  10  is formed in a three-layer structure by providing the intermediate member  16 , which is formed in a cup-like configuration of an elastic material, such as rubber or resin, between the outside member  15  and the inside member  17 , so vibration transmitted from whichever of the outer member  10  and the inner member  20 , with the outer member  10  and the inner member  20  being at a predetermined operation angle of θ (see  FIG. 8 ), can be absorbed by the cup portion  13  of the outer member  10 . 
     As described above, the description has been made of one embodiment of the present invention, however the present invention is not restricted to the above-described embodiment but allows various modifications. For example, as shown in  FIG. 4 , the engagement grooves  15   a  of the outside member  15  and the ridges  17   a  of the inside member  17  may be of any other configuration, such as an arcuate cross-sectional configuration, in correspondence with the track grooves  14  of the cup portion  13  as long as it allows torque transmission between the outside member  15  and the inside member  17 . 
     The configuration of the intermediate member  16  is not restricted to a cup-like one. For example, as shown in  FIG. 5 , the intermediate member  16  may be formed in a cylindrical configuration. The cylindrical intermediate member  16  is suitable for a case in which as shown, for example, in  FIG. 5 , the outer member  10  is composed of the two members of the first shaft portion  11  and the cup portion  13  (outer ring). The first shaft portion  11  and the cup portion  13  (outer ring) of  FIG. 5  are connected together by an appropriate method, such as screw connection, plastic connection, welding, adhesion, press-fitting, or shrink fitting. In the case of  FIG. 5 , the inside member  17  may also be formed in a cylindrical configuration, locking the depth-side end portion of the inside member  17  by a step portion  15   b  provided on the inner surface of the outside member  15 . 
     As shown in  FIG. 6A , the lock portions  62  of the fixing member  60  may be formed over an entire periphery of the cylindrical portion  61 . In this case, if the fixing member  60  slides circumferentially relative to the outer member  10 , it is always possible to prevent detachment of the intermediate member  16  and the inside member  17 . 
     Further, as shown in  FIGS. 6B and 6C , the fixing device may be formed by a lock portion  15   c  formed of an axial notch formed at the opening end of the outside member  15 . As shown in  FIG. 6C , the lock portion  15   c  is formed through formation of the outer configuration of the outside member  15  in correspondence with the inner configuration thereof. The lock portion  15   c  is formed in a small diameter portion  15   d  between the engagement grooves  15   a , and is locked with the end portions of the intermediate member  16  and the inside member  17  through plastic deformation toward the inner side of the outside member  15 . Apart from the notch formed at the end of the outside member  15 , the lock portion  15   c  may also be a tongue-like protrusion formed at the end of the outside member  15  like the lock portions  62  of the fixing member  60  shown in  FIGS. 1 and 3 . 
     Further, as shown in  FIG. 6D , it is also possible for the fixing device to be formed by a caulked portion  15   e  formed through plastic deformation toward the inner side of a part or all of the opening end portion of the outside member  15 . In this case, there is formed a swollen portion  17   b , which makes the outer diameter of the opening end portion of the inside member  17  substantially equal to the inner diameter of the opening end portion of the outside member  15 , with the caulked portion  15   e  of the outside member  15  being locked to the swollen portion  17   b  of the inside member  17 . The intermediate member  16  is arranged in the gap between the depth-side portions of the outside member  15  and the inside member  17 , with the outer diameter of the depth-side portion of the inside member  17  being smaller than the inner diameter of the depth-side portion of the outside diameter  15 . 
     Furthermore, it is also possible for the outside member  15 , the intermediate member  16 , and the inside member  17  to be integrated through baking and sticking the intermediate member  16  to the outside member  15  and the inside member  17 . When the outside member  15 , the intermediate member  16 , and the inside member  17  are thus integrated through plastic deformation of the outside member  15  or baking and sticking the intermediate member  16 , the number of components of the outer member  10  is reduced to thereby facilitate the assembly and suppress the production cost as compared with the case in which the fixing member  60  and the outside member  15  are formed as separate members. 
     It suffices for the outer member  10  to be of a multi-layer structure of three layers or more; when a plurality of intermediate members  16  are provided, it is possible to form the intermediate members  16  of different kinds of elastic material instead of forming them of the same kind of elastic material. Alternatively, it is also possible to form at least one intermediate member  16  of an elastic material, while forming the other intermediate members  16  of a non-elastic material. 
     While the above-described embodiment of the present invention is applied to a Rzeppa type joint  1 , in which the pressing portion  21   a  is formed at an end of the second shaft portion  21  of the inner member  20  and in which the retainer  40  is provided with a receiving portion  48 , the present invention is also applicable to any other fixed type constant velocity universal joint including an undercut free type joint.