Homokinetic universal joint

A universal joint has two shafts, axially restrained, but pivotable from a common point. One shaft end is in the form of a thick-walled hollow sphere. Two axially extending grooves are cut into the wall facing each other in a circumferentially opposed relationship to form a first set. The other shaft end is in the form of a spherical bowl having a central ball. The inside surface of the bowl and the surface of the ball define an annular spherical cavity into which the hollow sphere nests. Two axially extending grooves are cut, one in each surface, in a radially opposed relationship to form a second set. Each set of grooves positively determines the line path that the center of an enclosed ball will travel. In the assembled joint, the line paths are in mirror image relationship and always intersect in the homokinetic plane. The ball, being enclosed by each set is forced to occupy the intersection. The number of balls used can be any number, odd or even.

TECHNICAL FIELD 
This invention is in the general field of homokinetic universal joints as 
classified in U.S. Patent Class 64-21. Specifically, it pertains to those 
universal joints that are axially restrained and where torque is 
transmitted by balls steered into the homokinetic plane by crossed 
grooves. 
BACKGROUND ART 
The crossed groove principle is old. It is also known as the track steering 
principle. Prior to this invention, this principle has been applied in the 
following way: 
A ball-guiding groove is made in one half of the universal joint. Another 
groove is made in the other half. Each groove is considered to have an 
imaginary line path that is generated by the center of a ball as it moves 
along the groove. In the assembled condition of the joint halves, the 
grooves are in such an opposed relationship that their imaginary line 
paths always intersect at a point, no matter what angularity the joint 
halves assume to each other. This point of intersection always lies in the 
homokinetic plane. A ball confined between the grooves tends to occupy the 
point of intersection. Whether it does so in the positive, predictable 
manner that is a critical requirement for proper operation of the joint, 
depends upon the way the grooves are opposed to each other. 
If the grooves are opposed in a radial direction, i.e. one on top of the 
other, the ball must be urged to the line path intersection by additional 
means, such as a cage. The ball can transmit torque from one joint half to 
the other in either direction of rotation. Four balls is the minimum that 
can be used for proper control. In practice, six are used. The foregoing 
is best exemplified by U.S. Pat. No. 2,046,584 issued to Rzeppa. 
If the grooves are opposed in a peripheral direction, i.e. facing each 
other side by side, the ball is steered positively into the line path 
intersection without additional means. The ball, however, can transmit 
torque from one joint half to the other in only one rotational direction. 
Four balls is the minimum that can be used. In practice, four are used. 
The foregoing is best exemplified by U.S. Pat. No. 1,522,531 issued to 
Weiss. 
Numerous other designs shown in the Prior Art use the principle in the same 
manner. It could more precisely be labeled the Crossed Dependent Groove 
principle, because one groove in one half of the joint cannot, by itself 
constrain the ball to travel along the line path associated with that half 
of the joint. It depends upon the cooperation of an opposed groove in the 
other half of the joint for ball control, and vice versa. 
In contrast, this invention introduces the concept of Crossed Independent 
Grooves. In each joint half, the grooves are so arranged that they 
constrain the enclosed ball to travel along the line path associated with 
that half of the joint independently from the grooves constraining the 
same ball in the other joint half. This results in positive confinement of 
the torque transmitting ball to the homokinetic plane by grooves alone, 
with the ball being able to transmit torque in either rotational 
direction. 
DISCLOSURE OF INVENTION 
The invention resides in the novel construction and assembly of a 
homokinetic universal joint utilizing a new method of ball control. 
The two joint halves are axially restrained to pivot at a common point by a 
double nested ball and socket joint. The torque transmitting connection 
between the halves is by means of balls. Each ball is completely 
controlled and guided by a set of circumferentially opposed grooves in one 
half of the joint, and simultaneously completely guided and controlled by 
a set of radially opposed grooves in the other half of the joint. 
The resulting interaction of the two groove sets on the enclosed ball 
positively keeps it in the homokinetic plane. 
The invention meets these objectives: 
1. Reduced cost and weight. 
2. Few parts. 
3. High torque capacity to diametral size ratio. 
4. Good lubricant distribution. 
5. Uncomplicated assembly resulting in a complete unitary driveshaft 
assembly.

BEST MODE FOR CARRYING OUT THE INVENTION 
1. Description of the Structure. 
FIG. 1 shows a preferred embodiment of the invention in a typical 
automotive front wheel drive application. 
It consists of: 
(a) Driveshaft 30. 
(b) Wheel Spindle 31. 
(c) Cap 32. 
(d) Balls 33. 
(e) Boot 34. 
(f) Driveshaft Clamp 35. 
(g) Cap Clamp 36. 
The driveshaft 30 is referred to in the claims and some parts of this 
description as the First Joint Half. The wheel spindle 31 and cap 32 form 
an integral part after assembly of the joint as will be described, and 
this integral part is referred to in the claims and some parts of this 
description as the Second Joint Half. 
The boot and clamps are shown for completeness and are not part of this 
invention. The physical structure of the remaining parts is described 
below. 
Driveshaft 30: 
Refer to FIG. 6 and FIG. 7 which show a top and end view of driveshaft 30. 
The shaft portion 37 has at its other end (not shown) means, such as a 
spline, for connection to a power source. The shaft has an axis of 
rotation 38. Using a point 39 on the axis of rotation as a center, a 
partial convex spherical surface 40 having a radius 41 is constructed. 
About the same center 39, a partial concave spherical surface 42 having a 
radius 43 is constructed, resulting in an annular spherical wall section. 
The convex spherical surface is cut away at two places 44 for weight 
reduction and lubricant access holes 45 are drilled to communicate with 
the concave spherical surface 42. 
Again using center point 39, a conical end surface 46 with an apex angle 47 
is constructed to define a stop surface. 
Two slots 48, diametrically opposite, are cut into the annular spherical 
wall. Each slot defines a set of circumferentially opposed grooves 49. The 
grooves are constructed as follows: 
Refer to FIG. 8. On the axis of rotation 38, a point 50 is located to the 
left of point 39 at a distance 51. Using this point as a center, a circle 
52 of radius 53 establishes a theoretical line path. A contoured cutter 
cuts grooves 49, such that the center of ball 33 rolling in contact with 
the grooves will follow the path. Referring to FIG. 9, the curvature 54 of 
each groove 49 closely conforms to that of ball 33. The grooves are spaced 
apart a distance 55 equal to the diameter of ball 33 plus a very small 
clearance. The grooves are cut in an axial direction to the extent shown 
by angle 56 in FIG. 8, the end surfaces 57 forming stop surfaces. The 
feather edges left by the intersection of the grooves and spherical 
surface 40 are removed by chamfers 58. 
Thus a ball 33, when inserted into either set of circumferentially opposed 
grooves 49, is positively confined to the traveling of a curved path for a 
limited angular distance. In so doing, as can best be seen in FIG. 8, the 
center of the ball describes a ball center line path of a specific 
geometrical shape, i.e. circle 52. The points of contact between ball and 
groove when the joint is under torque loading are at points 59. 
Wheel Spindle 31: 
Refer to FIG. 10 and FIG. 11 which show a top view and an end view of the 
wheel spindle 31. The shaft portion 60 is adapted for connection to a 
wheel. The shaft has an axis of rotation 61. Using a point 62 on the axis 
of rotation as a center, a partial convex spherical surface 63 having a 
radius 64 is constructed. Using point 62 as the apex of a cone, a conical 
surface 65 with an apex angle 66 is constructed connecting the spherical 
surface 63 to a flange 67. The conical surface 65 acts as a stop surface 
as later described. The flange 67 is undercut to form surface 68, 
providing clearance for driveshaft surface 40. (FIG. 6). The periphery 69 
of flange 67 is shown smooth and is intended for a shrink fit with cap 32 
at assembly. 
Refer to FIG. 12 and FIG. 13. Two grooves 70, diametrically opposite, are 
cut into surface 63 (FIG. 10) in the following manner: 
A point 71 is located to the right of point 62 at a distance 72. Using this 
point as a center, a circle 73 of radius 74 establishes a theoretical line 
path. A contoured cutter cuts a groove 70, such that the center of ball 33 
rolling in contact with the groove will follow the path. The groove cross 
section shown in FIG. 13 is preferably in the form of a gothic arch 75 
(shown exaggerated) or an ellipse rather than a circle, these curves 
providing better control of the ball to groove contact areas. The grooves 
are cut in an axial direction to stops 76 and 77 defined by angle 78. A 
chamfer 79 (FIG. 11) is provided around both grooves to remove sharp 
edges, resulting in a chordal distance 80. 
Radius 74 (FIG. 12) equals driveshaft radius 53 (FIG. 8), and distance 72 
equals driveshaft distance 51. 
Cap 32: 
Refer to FIG. 16. The cap 32 has a hole 81 with a central axis 82. The 
inside surface 83 of the hole is shown smooth. It is intended for a shrink 
fit with the wheel spindle flange at assembly. 
Using a point 84 on the axis 82 of hole 81 as a center, a partial concave 
spherical surface 85 of radius 86 is constructed. A cylindrical surface 87 
sharing axis 82 is constructed in the end of the cap opposite hole 81. The 
radius 88 of this cylindrical surface can equal radius 86 of the spherical 
surface 85 as shown in the lower half of FIG. 16, or it can be smaller as 
shown in the upper half of the figure, depending on the type of assembly 
used to join spindle and cap. For example, if the cap is heated to expand 
it for a shrink fit assembly, the radius 88 can be smaller than radius 86. 
Refer to FIG. 14. Two grooves 89, diametrically opposite, are cut into 
surfaces 85 and 87 in the following manner: 
On axis 82, a point 90 is located to the right of point 84 at a distance 
91. Using this point as a center, a circle 92 of radius 93 establishes a 
theoretical line path. A contoured cutter cuts a groove 89 such that the 
center of ball 33 rolling in contact with the groove will follow the path. 
The groove cross section, as in the spindle 31, is in the form of a gothic 
arch 94 in FIG. 15 (shown exaggerated). The grooves are cut in an axial 
direction open at both ends of the cap, having no angular limit. 
Radius 93 equals spindle radius 74 (FIG. 12), and distance 91 equals 
spindle distance 72. 
Ball 33: 
The ball 33 is a hardened ball of precise dimension, relatively large 
compared to prior art. 
2. Method of Assembly. 
Refer to FIG. 19. Wheel spindle 31 is aligned with driveshaft 30, with 
spindle grooves 70 aligned with driveshaft slots 48. The spindle is then 
inserted into the driveshaft until center point 62 aligns with center 
point 39, the width 80 (FIG. 11) being such as to allow entry into the 
driveshaft slots 48. The spindle is then turned 90.degree. to engage 
convex spherical surface 63 with concave spherical surface 42. 
Refer to FIG. 20. Driveshaft 30 is then swung to maximum angularity 95, and 
a ball 33 is inserted into a slot 48 to engage grooves 49. A second ball 
is inserted in the same manner, and the shafts are swung back into 
alignment. 
Refer to FIG. 21. Cap 32 is then placed over the spindle 31 as shown. Using 
an assembly fixture to keep grooves 89 in the cap aligned with grooves 70 
on the spindle and also with balls 33, the cap is moved towards the 
driveshaft until cap spherical surface 85 (FIG. 16) contacts driveshaft 
spherical surface 40 (FIG. 7). 
It then remains to lubricate the inside of the assembly and install the 
boot and clamps. The result is a unitary, jointed driveshaft assembly as 
shown in FIG. 1. 
3. Mode of Operation. 
Refer to FIG. 1 and FIG. 4. In the assembled joint, the shaft portion 60 of 
the second joint half and the shaft portion 37 of the first joint half can 
assume any position of angularity to each other, up to a maximum, about 
point 96, which is the center of the double ball and socket. 
Maximum angularity is limited by two stops. One stop (FIG. 3) is provided 
by contact between conical face 46 on the driveshaft and and conical 
surface 65 on the wheel spindle. The other stop (FIG. 5) is provided by 
pockets 57 on the driveshaft and pockets 77 on the wheel spindle acting 
against the ball 33. Two stops are necessary for a two ball design because 
the stop provided by the conical surfaces becomes inoperable when the two 
balls move into the plane defined by the inclined axes of rotation. 
Because of the ball and socket connection, the two joint halves are 
restrained axially and can absorb thrust from either axial direction. 
Refer to FIG. 2 and FIG. 3. Torque is transmitted from the shaft portion 37 
of the first joint half to the shaft portion 60 of the second joint half 
by balls 33, the torque being transferred from contact point 59 (FIG. 2) 
on the first joint half to contact points 97 on the second joint half when 
the direction of rotation is as shown. It is obvious that torque can be 
transferred through the balls in the opposite direction of rotation, the 
contact points reversing their positions. FIG. 2 clearly shows the 
interposed relationship of the two sets of circumferentially opposed 
grooves with the two sets of radially opposed grooves. 
In the first joint half (FIG. 8), the ball 33 is positively confined by the 
set of grooves 49 to describe circle 52 of radius 53 with center 50 
displaced a distance 51 from the center of the ball and socket. This fixed 
spatial relation of circle 52 to the center of the ball and socket that 
exists in the first joint half has its exact counterpart in the second 
point half. This is best visualized by referring to FIG. 17, which shows 
wheel spindle 31 joined with cap 32 to form an integral part with two sets 
of radially opposed grooves. 
In this FIG. 17, circle 98, radius 99, center 100, and distance 101 are the 
results of the superimposition of circles 73 and 92, radii 74 and 93, 
centers 71 and 90, and distances 72 and 91 when wheel spindle 31 was 
assembled with cap 32. Thus circle 98, radius 99, and distance 101 are 
equal to their like in the first joint half and bear the same spatial 
relationship to the center of the ball and socket. 
Put in other words, the spatial relation of the ball line path in the first 
joint half to the center of the ball and socket, is identical to the 
spatial relation of the ball line path in the second joint half to the 
center of the ball and socket. Also, the geometrical shape of the ball 
line path in the first joint half is identical to the geometrical shape of 
the ball line path in the second joint half. 
Refer to FIG. 4. The two joint halves are facing each other and have the 
common ball and socket center 96. The two line paths 52 and 98 are mirror 
images of each other about center 96 and will always intersect at a point 
102. 
By geometry, a line 103 drawn from this point 102 to point 96 will always 
bisect the angle of inclination of the axes, whether that angle be zero or 
a maximum. Furthermore, as the joint rotates and the point of intersection 
102 moves out of the plane containing both axes of rotation 38 and 61, 
when inclined to each other, line 103 will generate the homokinetic plane 
104. 
Since a ball 33 must occupy both line paths simultaneously, it can only do 
so at the intersection point 102. Thus the balls always are located in the 
homokinetic plane and the torque is transmitted with constant velocity. 
4. Comments. 
The following are additional facts that contribute to a fuller 
understanding of the invention: 
(a) A two ball design is described. Subject to practical considerations, 
any odd or even number of balls can be used. A one ball design is workable 
but impractical. It does emphasize a basic difference between the prior 
art crossed dependent groove principle which dictates a minimum of four 
balls and the new crossed independent groove principle which permits any 
number. 
(b) A solid ball is specified. A hollow ball is feasible and may result in 
better conformity with the groove profile and a lower level of hertz 
stress. Also weight and centrifugal force would be reduced. 
(c) For good ball control, the ball path radius should not be more than 
five times the displacement distance. 
(d) A shrink fit between flange circumference and cap inside surface is 
specified. It is obvious that other mechanical connections are feasible, 
such as press fit serrations, welding, et cetera, as long as they can 
resist torsional and axial stress. 
(e) The grooves on the wheel spindle and inside the cap are described as 
being cut into the surface. However, because of the two piece 
construction, the grooves could be formed by a chipless method such as 
coining or cold forming. 
The foregoing description has been very specific to best exemplify one 
preferred embodiment. Variations are possible, and some have been noted. 
Accordingly, the scope of this invention should not be determined by the 
embodiment, but by the appended claims and their legal equivalents.