Abstract:
The invention relates constant velocity fixed universal joints A fixed constant-velocity ratio universal joint, comprising an outer joint part, an inner joint part, a ball cage and a plurality of balls. The ball cage is disposed between the inner and outer joint parts and includes windows in which respective balls are received and constrained such that their centers lie in a common plane. At least two opposing windows are wider than said outer joint part lands to accommodate receiving the lands during assembly. The cage includes substantially spherical inner and outer surfaces which engage the land surfaces on the inner and outer joint parts respectively. The ball cage also includes a relief groove between at least one pair of adjacent windows thereby providing a reduced circumference for the ball cage outer surface in the region of the groove. The groove is at least as wide as one of the outer joint part lands to accommodate introduction of the ball cage into the outer joint part when the ball cage is rotated about a transverse axis by 90° with respect to the outer joint part axis during assembly.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Application Ser. No. 60/183,598 filed Feb. 18, 2000, entitled “Constant Velocity Fixed Joint Cage Installation Grooves.” 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to constant velocity fixed universal joints and, in particular, concerns a constant velocity fixed joint of the type comprising: (1) an outer joint member of hollow configuration, having a rotational axis and in its interior, a plurality of arcuate tracks circumferentially spaced about the axis extending in meridian planes relative to the axis, and forming lands between the tracks and integral with the outer joint part wherein the lands have radially inwardly directed surfaces; (2) an inner joint member disposed within the outer joint member and having a rotational axis, the inner joint member having on its exterior a plurality of tracks whose centerline lie in meridian planes with respect to the rotational axis of the inner joint member in which face the tracks of the outer joint member and opposed pairs, wherein lands are defined between the tracks on the inner joint member and have radially outwardly directed surfaces; (3) a plurality of balls disposed one in each pair of facing tracks in the outer and inner joint members for torque transmission between the members; and (4) a cage of annular configuration disposed between the joint members and having openings in which respective balls are received and constrained so that their centers lie in a common plane, wherein the cage has external and internal surfaces each of which cooperate with the land surfaces of the outer joint member and inner joint member, respectively, to locate the cage and the inner joint member axially. 
     In joints of this kind, the configuration of the tracks in the inner and outer joint members, and/or the internal and external surfaces of the cage are such that, when the joint is articulated, the common plane containing the centers of the balls substantially bisects the angle between the rotational axes of the joint members. 
     There are several types of joint of the kind specified differing from one another, inter alia, with respect to the arrangement and configuration of the tracks in the joint members and/or to the internal and external surfaces of the cage whereby the common bisector plane is guided as described above thereby giving the joint constant-velocity-ratio operating characteristics. What such different types of joints have in common, however, is that the cage is located axially in the joint by cooperation between the external cage surface and the surfaces of the lands facing the cage surface. 
     The outer surface of the cage and cooperating land surfaces of the outer joint member are generally spherical. When torque is transmitted by the joint, the forces acting in the joint cause the cage to be urged towards one end of the joint (i.e. ball expulsion forces); which end will depend on the respective directions of the offsets of the tracks in the inner and outer joint members from the common plane when the joint is in its unarticulated position To reduce the normal forces acting on the cage as a result of these ball expulsion forces, the amount of spherical wrap by the outer joint member lands should be maximized for increased cage support. However, the more the outer joint part lands spherically enclose the spherical outer surface of the cage, the more difficult the introduction of the ball cage into the outer joint part becomes. In a disc-style constant velocity fixed joint wherein the outer joint member is open on both ends, the cage is assembled from the end opposite the end towards which the cage is urged by ball expulsion forces under articulated load conditions. Assembly of the cage into the outer joint member is typically accomplished by either incorporating cage assembly notches into one of or a pair of lands in the outer joint member, or by sufficiently increasing the bore diameter of the outer joint part to allow the ball cage to be introduced into the outer joint part. 
     In a mono-block constant velocity fixed joint wherein the outer joint part is a bell-shaped member having a closed end, the cage must be assembled from the open end of the outer joint member. To accommodate assembly of the cage into the outer joint part, again, the bore diameter of the outer joint part must be sufficiently increased to allow assembly and/or assembly notches must be incorporated into at least one opposing pair of the outer joint member lands to allow introduction of the cage. Either method is undesirable however in that both assembly methods reduce the amount of spherical wrap available for cage support. In turn, higher surface stresses are induced to the cooperating surfaces of the outer joint part and the cage resulting in greater heat generation due to increased friction. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a constant velocity fixed joint with an improved cage assembly. According to the present invention, the foregoing and other objects are obtained by a fixed constant-velocity-ratio universal joint, comprising an outer joint part, an inner joint part, a ball cage and a plurality of balls. The outer joint part has a hollow configuration and includes a rotational axis, a plurality of at least partially arcuate tracks circumferentially spaced about the axis in the interior of the outer joint part and having center lines extending in meridian planes relative to the axis, and lands defined between the tracks and which are integral with the outer joint part and have inwardly directed surfaces. The inner joint part is disposed within the outer joint part and includes a rotational axis, a plurality of at least partially arcuate tracks on the exterior of the inner joint part having center lines extending in meridian planes with respect to the rotational axis of the inner joint part and which faces the tracks in the outer joint part in opposed pairs, and lands defined between the tracks on the inner joint part having radially-outwardly directed surfaces. The plurality of balls are disposed one in each pair of facing tracks in the outer and inner joint parts for torque transmission between the parts. The ball cage is disposed between the inner and outer joint parts and includes windows in which respective balls are received and constrained such that their centers lie in a common plane. At least two opposing windows are wider than the outer joint part lands to accommodate receiving the lands during assembly. The cage includes substantially spherical inner and outer surfaces which engage the land surfaces on the inner and outer joint parts respectively. 
     The ball cage also includes a relief groove between at least one pair of adjacent windows thereby providing a reduced circumference for the ball cage outer surface in the region of the groove. The groove is at least as wide as one of the outer joint part lands to accommodate introduction of the ball cage into the outer joint part when the ball cage is rotated about a transverse axis by 90° with respect to the outer joint part axis. In one aspect of the invention, the groove is an annular groove about the circumference of the cage outer surface. In another aspect of the invention, the groove comprises two grooves centered about the central ball plane of the cage and corresponding to the outer joint part land width. 
     One advantage of the present invention is that it maximizes the spherical wrap of the outer joint member lands with respect to the outer surface of the cage. Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of this invention, reference should now be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention. 
     In the drawings: 
     FIG. 1 is an end view of a constant velocity fixed joint according to one embodiment of the present invention taken in the direction of arrow A in FIG.  2 . 
     FIG. 2 is a longitudinal section view of the joint of FIG. 1 taken along line  2 - 2 . 
     FIG. 3 shows a perspective view of a cage member according to one embodiment of the present invention. 
     FIG. 4 shows a longitudinal section of an outer joint part through the longitudinal axis of the outer joint part and a cage according to one embodiment of the present invention during assembly. 
     FIG. 5 shows a perspective axial view of an outer joint part and ball cage according to FIG.  4 . 
     FIG. 5A shows a detail of an outer joint part and the cage of FIG. 5 during assembly. 
     FIG. 6 shows a perspective view of an alternative embodiment of a cage according to the present invention. 
     FIG. 7 shows a detail of an outer joint part and the cage of FIG. 6 during assembly. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 will be described jointly. FIG. 1 is an end view of a constant velocity fixed joint according to one embodiment of the present invention taken in the direction of arrow A of FIG.  2 . FIG. 2 is a longitudinal section through the joint of FIG. 1 along line  2 — 2  of FIG.  1 . The principal components of the fixed joint are an outer joint member  10 , an inner joint member  11 , a cage  12 , and a plurality of torque-transmitting balls  13 . 
     The outer joint member  10  is a hollow bell-shaped component having an open end  14  and a closed end  16  from which a stub shaft  17  extends. The axis of rotation of the outer joint member  10  is indicated at  18 . In the interior of the outer joint member  10 , there is a number of circumferentially spaced arcuate tracks  20  which are equally angularly spaced about the joint member axis  18  and whose centerlines lay in meridian planes containing the axis  18 . Between the outer joint member tracks  20 , there are defined lands  22  which are integral with the joint member and have radially inwardly directed surfaces. The closed end  16  of the outer joint member  10  can be either integrally formed as part of the outer joint member or comprise a welded-on-base. 
     The inner joint member  11  is provided on its exterior surface with a number of arcuate tracks  24  whose centerlines lie in meridian planes containing the inner joint member axis of rotation  26  which, when the joint is in the aligned, i.e. non-articulated, condition illustrated, is coincident with the axis  18 . The tracks  24  face the tracks  20  in opposed pairs. Between the tracks  24 , the inner joint member has lands  28  which are integral with the inner joint member  11  and have radially outwardly directed surfaces. Inner joint member  11  is a cylindrical component having a splined bore  30  for torque-transmitting reception of a drive shaft  32 . Of course, the inner joint member  11  and driveshaft may be integral parts, or connected by means other than a spline such as a weld. 
     In the longitudinal cross-section shown in FIG. 2, the tracks  20 ,  24  are arcuate in configuration and the centers of curvature of such arcs are offset from one another axially with respect to the joint so that the tracks of each pair diverge from one another as they approach the open end  14  of the outer joint member  10 . Each pair of opposed tracks  20 ,  24  receives a respective torque-transmitting ball  13 . The centers of the balls  13  lie in a common plane  19 . The offset configuration of the tracks  20 ,  24  in the joint members  10 ,  11  is such that, in a known manner, when the joint is articulated, the common plane  19 , i.e. the bisector plane in FIG. 2, is caused to bisect the angle between the rotational axes  18 ,  26  of the outer and inner joint members  10 ,  11 , respectively, thereby giving the joint constant-velocity-ratio characteristics. 
     The cage  12  is an annular component innerposed between the inner joint member  11  and outer joint member  10 . It has a plurality of openings or windows  34  respectively receiving the balls  13  so that the centers of the balls lie in the common plane  19 . 
     The cage has a generally spherical external surface  36  which contacts the radially inwardly facing surfaces of the lands  22  between the tracks  20  of the outer joint member  10 . The cage also has a generally spherical internal surface  38  engageable with the radially-outwardly facing surfaces of the lands  28  between the tracks  24  of the inner joint member  11 . 
     When the joint is in use, forces acting on the balls and, in turn, on the cage, urge the cage  12  towards the open end  14  of the outer joint member  10 . Thus, the cage outer surface  36  bears on the facing surf aces of the outer joint member lands  22  primarily in the area  21  immediately adjacent the open end  14  of the outer joint member  10 . In the joint shown, the offset of the tracks in the inner joint member  11  is towards the closed end  16  of the outer joint member  10  and the offset of the tracks in the outer joint member  10  is towards the open end  14  of the outer member  10 . Thus, the cage inner surface  38  bears on the facing surfaces of the inner joint member lands  28  primarily in the area  23  immediately adjacent the closed end  16  of the outer joint member  10 . However, the direction of the offsets of the tracks  20 ,  24  can be reversed which would change the location of the contacting surface portions of the cage outer surface  36  and cage inner surface  38  to opposite positions. 
     The surfaces of the lands  22 ,  28  are preferably part-spherical, forming parts of a sphere centered on the axis of rotation  18  of the outer joint member  10  or the inner member  11 , respectively. However, the land surfaces may be formed surfaces of revolution of a circular arc about said axes but with the arc not being centered on the axis. In another arrangement, the arc is not circular. The land surfaces could be alternatively formed by surfaces of revolution of an arc, which is preferably but not necessarily circular, about an axis of revolution offset from said axes  18 ,  26 , the locus of the axis of revolution, when considering all the land surfaces, being a circle around the axis of rotation. As will be clear to one skilled in the art, any departure of the land surfaces from true part-spherical surfaces centered on the axes  18 ,  26  will be small. 
     In the embodiment of the invention shown in FIGS. 1 and 2, the cage outer surface  36  is relieved as indicated at  40 . The relief  40  is in the form of a radial groove about the equator of the cage  12 . The groove  40  extends in width on both sides of the ball plane  19  and is centered on the ball plane  19  as shown in FIG.  2 . 
     Referring now to FIG. 3, there is shown a perspective view of the cage  12  of FIGS. 1 and 2. The cage  12  shown in FIG. 3 includes six windows  34  for accommodating respective balls. Between each window  34  is a web portion  44  in which the groove  40  is formed to reduce the maximum circumference of the cage outer surface to aid in the introduction of the cage into the outer joint member. Although the groove  40  is shown extending around the entire circumference of the cage  12 , its benefits can be realized by merely reducing the thickness of one web portion  44  rather than all. For manufacturing purposes and for balance, however, it may be preferable to form the groove  40  about the entire circumference by roll-forming or turning the cage. 
     FIG. 4 shows a longitudinal sectional view of the outer joint part  10  and an axial view of the cage  12 , in part section, during assembly. Thus, the ball cage  12  is shown in a position in which it is rotated about one of its transverse axes 50 by 90° and displaced along its axis from the central axis  18  of the outer joint part. The outer joint part lands  22  comprise the guiding face for the spherical outer surface  36  of the ball cage  12 . The outer surface  36  of the ball cage  12  is interrupted by the windows  34  and the groove  40 . 
     As mentioned above, preferably the spherical wrap of the outer joint part lands  22  is maximized with respect to the spherical outer surface  36  of the cage  12  to maximize cage support during operation. The greater the spherical wrap, however, the smaller the bore diameter D 1  defined by the opening formed by opposing lands  22  in the outer joint part  10 . The relationship between the bore diameter opening D 1  of the lands  22  and the diameter of the ball cage D 2 , is such that D 2  is greater than D 1 . For this reason, the cage  12  cannot be axially inserted into the outer joint part  10 . Thus, for assembly purposes, an edge  60  of a land  22  is introduced into the forward portion  62  of one of the cage windows  34 , and the ball cage  12  is introduced into the outer joint part  10  while carrying out a displacing or rotating movement such that the opposing edge  64  is introduced into the opposing cage window  66 . Thus, the groove  40  acts to reduce the distance D 3  such that D 3  is less than D 1  thereby allowing introduction of the cage  12  into the outer joint part  10 . Once the cage  12  enters the outer joint part aperture  14 , it is returned onto the central axis  18  of the outer joint part by rotating the cage around its transverse axis  50  by 90° and translating the cage  12  with respect to the outer joint part  10  along the outer joint part axis  18 . Subsequently, the inner joint part and balls are assembled in a known matter. In order to receive the land edges  60 ,  64  into the cage windows  62 ,  66 , however, the window width must be greater than the land width. 
     Referring now to FIG. 5, there is shown a perspective view of the cage with respect to the outer joint part during the assembly process. During the assembly process, the rotational axis of the cage is transverse to the rotational axis of the outer joint part. Again, the opening  60  of a land  22  is introduced into the forward portion  62  of a cage window and the opposing cage window  66  is then moved toward the outer joint part  10  such that the opposing opening  64  passes the web portion  44  having its thickness reduced by the groove  40  and is introduced into the cage window  66 . At that point, the cage can be advanced along the central axis of the outer joint part and rotated about its transverse axis to bring the lands  22  into contact with the spherical outer surface  36  of the cage  12 . FIG. 5A shows a detail of the relationship between the groove  40  and land edge  64  during introduction of the cage into the outer joint part. As can be seen in FIG. 5A, the width W L  of the land edge  64  is less than the width W g  of the groove  40 . 
     Referring now to FIG. 6, there is shown a perspective view of an alternative embodiment of a cage for use in a fixed constant velocity joint according to the present invention. The cage  100  of FIG. 6 include relief portions  102  which permit the cage  100  to be introduced into an outer joint part between opposing lands as shown in FIG.  7 . FIG. 7 is a detail of an outer joint part  110  and the cage  100  of FIG. 6 during assembly. As shown in FIG. 7, the grooves  102  allow the points  104  defining the width of the land  122  to be introduced into the cage window  134  opposing the cage window containing the opposing land member (not shown). As shown in Figure, 7  and FIG. 5, the width of the groove  40  or the spacing between centers of the relieved portions  102  (W 2  shown in FIG. 6) must be greater than the width W L  of the lands to allow introduction of the lands into the cage window  134 . 
     From the foregoing, it can be seen that there has been brought to the art a new and improved constant velocity fixed joint. While the invention has been described in connection with one or more embodiments, it will be understood that the invention is not limited to those embodiments. For example, the improved cage design is equally applicable to constant velocity fixed joints having four ball pairs rather than three. The improved cage design is also applicable to disc-style constant velocity fixed joints wherein the outer joint part is open at both ends. Thus, the invention covers all alternatives, modifications, and equivalents as may be included within the spirit and scope of the appended claims.