Abstract:
A constant velocity joint comprises an outer race, an inner race, a plurality of balls and a cage. The outer race and inner race have crossed grooves of multiform length. The outer race grooves and the inner race grooves are circumfercntially spaced and paired to hold the balls. The central planes of paired grooves are inclined from the longitudinal direction and are crossed relative to one another. The outer race, inner race and cage having mating part-spherical surfaces that accommodate joint angulation while supporting the components against axial stroking about a fixed center. The grooves have a substantially uniform depth along their lengths including toward the closed end of the outer race to provide full support to the balls at high joint angles.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is based upon, and claims the benefit of, U.S. Provisional Patent Application No. 60/183,007 filed Feb. 16, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to constant velocity joints of the Rzeppa type and more particularly to those for use in front wheel drive vehicle applications. 
     2. Related Art 
     Prior art constant velocity universal joints are known from U.S. Pat. No. 2,046,584 issued Jul. 7, 1936 to A. H. Rzeppa. So-called “Rzeppa” universal joints include an outer race, an inner race, and a plurality of balls retained in each of the races in a pair of opposed arcuate groove sets formed lengthwise of the respective inner and outer races. A cage receives the balls. In a Rzeppa universal joint, the lengthwise centers of the outer race and inner race grooves are offset by substantially equal amounts on the opposite sides of a central plane of the joint, such that the joint will operate at a constant velocity through a wide range of joint angles. While suitable for their intended purpose, in present day applications the degree of angulation required of such joints can be so great that when the balls travel to the inward closed end of the joint, there is inadequate groove depth of either the outer race groove or inner race groove to properly support the balls under heavy torque loads. Such insufficient support can produce undesired large contact stresses between the balls and the grooves at high joint angles. 
     U.S. Pat. No. 3,879,960 discloses a joint where the open portion of the outer race grooves and the closed portion of the inner race grooves are made straight to accommodate a large joint angle while containing the balls. However, the outer race grooves at the closed end still have a shallow depth as in a conventional “Rzeppa” joint and the inner race groove at the closed end tends to get shallower than the conventional “Rzeppa”joint because of the straight groove configuration. 
     U.S. Pat. No. 4,589,857 discloses a joint where the centers of the outer and inner race spherical surfaces are offset by an equal amount on opposite sides of the central plane of the joint, and further where the groove centers of the inner and outer race are offset. Such a configuration provides only a modest gain in groove depth at the closed end while sacrificing cage web strength. 
     It is an object of the present invention to improve upon such joints to provide both high angularity and strength to the joint. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     A constant velocity joint constructed according to the invention includes an outer race having an inner partial spherical concave joint surface disposed about a longitudinal axis of the outer race. A first plurality of circumferentially spaced grooves are formed in the joint surface of the outer race and extend generally longitudinally of the outer race between an open end of the outer race and a closed end. An inner race is disposed in the outer race and has an outer partial spherical convex joint surface disposed about a longitudinal axis of the inner race. A second plurality of circumferentially spaced grooves are formed in the joint surface of the inner race and extend generally longitudinally of the inner race between the open and closed ends of the outer race. Each of the grooves of the second plurality are arranged opposite a corresponding one of the grooves of the first plurality to define a plurality of paired ball groove sets. A plurality of torque-transmitting balls are disposed in the plurality of ball groove sets for movement therealong during relative angulation of the inner and outer races. A ball cage is disposed between the inner race and the outer race and is formed with a plurality of windows supporting the balls in a common ball plane during movement of the balls along the groove sets. The ball cage has an outer convex partial spherical joint surface constrained against relative axial movement by the inner joint surface of the outer race. The ball cage has an inner concave partial spherical joint surface constrained against relative axial movement by the outer joint surface of the inner race. Each groove of each ball groove set has an associated lengthwise extending groove plane. The groove planes of the grooves of each of the ball groove sets are disposed in transverse crossing relation to one another. 
     The invention has the advantage of providing a fixed center, non-stroking universal joint capable of achieving high joint angulation with exceptional support of the balls at the closed end of the joint. A joint constructed according to the invention is capable of achieving a joint angle of 55°, whereas a conventional “Rzeppa” joint is limited to joint angles of about 46°. Moreover, the cross-groove joint constructed according to the invention provides substantially greater groove depth at the closed end of the joint than that of the “Rzeppa” joints for proper support of the balls at the high angles, without sacrificing the strength of the ball cage. 
     The invention has the further advantage of being simple to manufacture and of offering a variety of groove configuration alternatives which achieve the stated objectives of high joint angulation and excellent ball support at such high angles. 
     According to further advantages, the joint construction of the present invention provides a large groove depth at the open end of the outer race which remains uniform to the closed end. A characteristic ball center motion relative to cage window enables an increase in the cage internal diameter. Accordingly, the depth of the groove at the closed end of the inner race can also be adjusted to an appropriate degree by increasing the inner race sphere diameter. 
     According to a particular embodiment of the invention, the central line of each groove is a combination of an arc and a tangent straight line. At zero joint angle, the central planes of each groove pair are symmetrically inclined from the joint axis in the radial direction to ensure smooth angulation and constant velocity of the joint. 
     According to further embodiment, the groove pairs are either continuously curving or are substantially linear along their lengths to alter the characteristics of the joint while achieving the same objectives discussed above. 
    
    
     THE DRAWINGS 
     Presently preferred embodiments of the invention are disclosed in the following description and accompanying drawings, wherein: 
     FIG. 1 is an end elevation view of a constant velocity joint according to the present invention; 
     FIG. 2 is a sectional view taken generally along lines  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view like FIG. 2 but of only the outer race; 
     FIG. 4 is a sectional view taken generally along lines  4 — 4  of FIG. 1 but showing only the outer race; 
     FIG. 5 is an elevational view of the inner race; 
     FIG. 6 is a sectional view of the inner race; 
     FIGS. 7A and 7B are sectional views of an alternative groove configuration of the outer and inner races; 
     FIGS. 8A and 8B are sectional views showing an another alternative groove configuration of the outer and inner races; 
     FIG. 9 is a sectional view a the ball cage according to one embodiment thereof; 
     FIG. 10 is a sectional view like FIG. 9 but of an alternative cage configuration; 
     FIG. 11 is a sectional view of an alternative embodiment of the invention; and 
     FIG. 12 is a sectional view of another alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 2 illustrate a fixed-center, cross groove constant velocity joint  10  constructed according to a first embodiment of the invention. The joint  10  comprises an outer race  12 , an inner race  14  disposed in the outer race, and a cage  16  disposed between the outer race  12  and the inner race  14 . The components  12 ,  14 ,  16  are constrained in the longitudinal direction along an axis A of the joint  10  by mating part-spherical joint surfaces to be described below, such that the components  12 ,  14 ,  16  are non-stroking in the axial direction of the joint. 
     The cage  16  is formed with a plurality of cage windows  18  in which a corresponding plurality of load-bearing balls  15  are accommodated for constraining the balls  15  in a common ball plane B through all joint angles, such that the centers of the balls  15  always lie on a cage central plane  17  passing through the windows  18  of the cage  16  (FIGS.  9  and  10 ). 
     The outer race  12  includes an inner partial spherical concave joint surface or outer race sphere  20  disposed about a longitudinal axis  21  of the outer race  12 . A plurality of generally longitudinally directed grooves  22  are formed in the outer race sphere  20  at circumferentially spaced locations, as best shown in FIGS. 1-4. The longitudinal center of the outer race sphere  20  is shown at  41  in FIGS. 3 and 4. 
     Each groove  22  has a straight or linear section  22 A and a curving or arcuate section  22 B. The straight section  22 A extends outwardly to an open end  12 A of the outer race  12 . The arcuate section  22 B extends tangentially inwardly from the straight section at a medium point  45  toward a closed end  12 B of the outer race  12  (FIG.  3 ). The grooves  22  have a substantially uniform depth at the arcuate section  22 B between the opposite ends of the grooves  22 . 
     The inner race  14  has an outer partial spherical convex joint surface or inner race sphere  24  in which a plurality of grooves  26  are formed. Each groove  26  has a straight or linear section  26 A at the inboard end thereof that is tangent to a curving or arcuate section  26 B at the open end of the outer race  12 . The grooves  26  have a substantially uniform depth at the arcuate section  22 B. 
     An outer race central plane  43  (FIG. 4) passes through the outer race sphere center  41  and is perpendicular to the outer race axis  21 . As a ball  15  moves along the length of outer race groove  22 , a trace of the ball center defines an outer race groove central line  44  (FIG.  3 ). An outer race groove central plane D (FIG. 4) contains the outer race groove central line  44 . The outer race groove central line  44  intersects the outer race central plane  43  at a medium point  45  (FIGS.  3  and  4 ). As best shown in FIG. 4, the central plane D of each outer race groove  22  is inclined to the outer race axis  21  at a tip angle α o . In other words, when viewing the outer race  12  in section perpendicular to its longitudinal axis  21  as in FIG. 4, the grooves  22  extend cross-wise to the longitudinal axis  21  at the prescribed angle α o  and as such are transverse and non-parallel in the longitudinal direction. The cross-point, or intersection point with the longitudinal axis  21  is located at the medium point  45 . 
     The inner race  14  has a center point at  46 . An inner race central plane  48  passes through the inner race sphere center  46  and is perpendicular to a longitudinal axis  47  of the inner race  14 . As a ball  15  moves along the length of the inner race groove  26 , the trace of the ball center is defined an inner race groove central line  49  (FIG.  6 ). An inner race groove central plane E contains the inner race groove central line  49 . The inner race groove central line  49  intersects the inner race central plane  48  at a medium point  50  (FIG.  6 ). The central plane E of each inner race groove  26  is inclined to the longitudinal axis  47  of the inner race  14  at a tip angle αi which is the same value as the tip angle α o  of the outer race  12 , but oppositely directed, as best shown in FIGS. 4 and 5. In other words, the grooves  22  and  26  are inclined to the axes of the outer and inner races  12 ,  14  to the same degree when the joint  10  is at zero joint angle, but in opposing directions such that they cross one another. Each groove  22  from the outer race  12  is matched with a corresponding groove  26  from the inner race  14  to form a plurality of matched groove pairs or sets in which the balls  15  are disposed. The grooves  22 ,  26  from each groove set are angled relative to the longitudinal axes of the races, and are further angled relative to one another such that their respective groove center planes D, E are disposed in transverse crossing relation to one another. 
     As shown best in FIG. 9, the cage  16  has an outer partial spherical convex joint surface or outer cage sphere  34 , and an inner partial spherical concave joint surface or inner cage sphere  36 . The outer surface  34  confronts and is supported for relative angular movement by the inner surface  20  of the outer race  12 . The mating part-spherical surfaces  34 ,  20  cooperate to support the cage  16  against axial movement or stroking in the longitudinal direction relative to the outer race  12 . Similarly, the inner part-spherical surface  36  of the cage  16  confronts and reacts with the outer part-spherical surface  24  of the inner race  14  to support the cage  16  and inner race  14  against relative longitudinal stroking movement. As such, the joint  10  is non-stroking and has a fixed center. The cage  16  has a plurality of cage windows  18  as previously mentioned which are rectangularly shaped with curved comers and circumferentially located around a cage axis  33  as shown in FIG. 9 or FIG.  10 . The cage central plane  17  is perpendicular to the cage axis  33  and passes through the centers  19  of all cage windows  18 . The intersection of the cage central plane  17  and the cage axis  33  is at the cage center point  35 . 
     As shown in the embodiment of FIGS. 1-6, the centers of the part-spherical surfaces  20 ,  24 ,  34 , and  36  arc configured to be coincident and thus have a common center at the center point  35  of the cage  16 . The groove central planes D, E are arranged to intersect one another in the central cage plane  17  at all angles of the joint  10 . This arrangement of the planes D, E is present in the subsequent embodiments as well (FIGS.  9  and  10 ). 
     In the illustrated embodiment of FIGS. 1-6, the depths of the grooves  22 ,  26  that provide support to the balls  15  during torque transmission at all angles is substantially uniform along the length of the grooves  22 ,  26 , and particularly in the vicinity of the closed end  12 B of the outer race  12 , to provide non-varying support to the balls  15  at all joint angles, and particularly at high maximum or near-maximum joint angles approaching 55°. In contrast, the grooves of “Rzappa”-type universal joints get characteristically shallower toward the closed end of the outer race at the critical point where maximum ball groove forces occur at maximum joint angle approaching 46° for such prior joints. 
     FIGS. 7A and 7B show an alternative configuration of the inner and outer race grooves, which are substantially identical in all respects to the grooves  22 ,  26  described previously with respect to FIGS. 1-6, except that the straight sections  22 A′,  26 A′ are further angled radially toward or away from the axes  21 ′,  47 ′ of the outer and inner races  12 ′,  14 ′ by respective radial angles β o , β i . All other features are the same and thus the same reference numerals are used to identify like features, but are primed. 
     With the cage  16  of FIG. 9, the cage outer sphere  34  and the cage inner sphere  36  coincide at the cage center  35 . This arrangement results in a cage of uniform thickness in the lengthwise axial direction. In this case, all five centers (of outer race sphere  41 , cage outer sphere  34 , cage inner sphere  36  and inner race sphere  24 , as well as cage center  35 ) in the joint coincide at the common point of the cage center  35 . The medium point  45  of the outer race groove central line  44  is coincident with the medium point  50  of the inner race groove central line  49  on the cage central plane  17  under zero joint angle. 
     With the alternative cage of FIG. 10, the same reference numerals are used as those used in FIG. 9, but are double primed. The centers of the cage outer sphere  34 ″ and the cage inner sphere  36 ″ are symnmetrically offset from the cage center  35 ″ along the cage axis  33 ″. This arrangement results from a cage having a variable thickness along it length as shown. In this case, the centers of the outer race sphere  41  and the cage outer sphere  34 ″ are still superimposed. So are the centers of the inner race sphere  24  and the cage inner sphere  36 ″. Each intersection point of the outer race groove central line  44  and the inner race groove central line  49  still lies on the cage central plane  17 ″, but the medium point  45  and  50  are no longer superimposed under zero joint angle. 
     FIGS. 8A,  8 B and  11  show further alternative embodiments of a joint, wherein everything described above with respect to the first embodiment of FIGS. 1-6 and the alternative cage configurations of FIGS. 9-10 applies, except that the groove configurations  122 ,  126  and  222 ,  226  of the inner and outer races, respectively, have been altered in their longitudinal shape to be substantially continuously curving or arcuate along their entire length so as to omit the straight section of the first embodiment. Accordingly, the same reference numerals are used, but are offset by 100 in FIGS. 8A and 8B and by 200 in FIG.  11 . They are still cross grooves as previously described. By fully curving, it is meant that the grooves lack a straight section as in the first embodiment, and rather have a continuously curving shape that may be spherical, elliptical, or other curving, generally arcuate shapes. The fully curving grooves  122 , 126  and  222 ,  226  achieve the same objects of high joint angle and uniform groove depth of the first embodiment. 
     FIG. 12 shows still a further embodiment of a joint constructed according to the invention, which likewise applies in its description and operation to that described above for the first embodiment of FIGS. 1-6 and the cages of FIGS. 9 and 10, except that the groove configurations  322 ,  326  of the inner and outer races have been altered in their longitudinal shape to be substantially straight or linear along their length, although still crossed in the groove sets. Accordingly, the same reference numerals are used, but are offset by 300. 
     It will be obvious to those skilled in this field that various changes may made without departing from the scope of the present invention. The present invention is not limited to what is shown in the figures and described in the specification, but is defined by the claims.