Flexible boot for driving axle joints

A flexible molded type boot for use to retain lubricant in a constant velocity joint in which the boot is formed with a series of axially related convolutions which extend from a joint housing having a large diameter through a series of progressively smaller diameters to a smallest diameter driving shaft. The convolutions are formed with expernal peaks spaced apart by inwardly recessed valleys constituted by pairs of angularly convergent walls forming valleys between the convolution peaks. The walls taper from thinnest adjacent the external ridges to thickest adjacent the valleys where the convergent walls are joined.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is concerned with convolution bellows for drive axle joints 
in which the convolutions over the length of the bellows share 
substantially more equally in flexibility. 
2. Description of the Prior Art 
Constant velocity or cv joints are used to transmit torque between the 
engine and the drive wheels for front wheel driven automobiles, and such 
joints may be used in other types of installations in the automotive field 
and elsewhere. This type of joint is protected by a bellows-type boot that 
encloses the joint and retains the grease or other lubricant, and such 
bellows must be flexible to accommodate angular cycles of motion which are 
particularly severe with front wheel drive installations. 
A continuing problem with bellows-boots is that the convolutions have been 
found to flex in such manner as to rub against each other which creates 
wear and eventual failure in the material to retain the lubricant which 
fills the boot. 
Examples of universal joint boots are seen in prior patents such as U.S. 
Pat. Nos. 4,278,262; 4,558,869; 4,673,188; and 4,786,272. These boots 
illustrate some of the designs that are intended to overcome problems in 
the automotive use of cv joint protective boots. However, problems still 
remain in regard to the life expectancy of a boot so that the cost and 
frequency of replacement of the boot can be reduced over the useful life 
of the cv joint. 
SUMMARY OF THE INVENTION 
The present flexible bellows is constructed so that it will provide longer 
life in service by adapting a series of convolutions of the bellows to 
share in the range of severity of flexure that takes place between the 
large and small ends of the bellows. 
The important object of the present invention is to construct the bellows 
so that specific changes in wall thickness in each convolution from the 
joint housing to the axle shaft will result in each convolution sharing 
more equally in the flexing requirements along the length of the bellows, 
thereby gaining longer service life. 
The bellows of the present invention is intended to have a large diameter 
end, a small diameter end and a series of convolutions interconnecting 
these ends, wherein the convolutions have inner and outer zones of 
connection which have specifically graduated wall thickness relationships 
to provide the desired sharing in the resulting flexing service.

DESCRIPTION OF THE INVENTION 
One example of the present invention is seen in FIG. 1 where the bellows 10 
is formed of suitable moldable and flexible material, such as polyurethane 
or the like. The bellows is formed with a large diameter end 11 adapted to 
fit over the housing (not shown) of a constant velocity or cv joint and be 
secured by a suitable clamping device (not shown). An example of a cv 
joint housing is illustrated in U.S. Pat. No. 4,673,188. The opposite and 
small diameter end 12 is adapted to be fitted over the driving shaft (not 
shown) which extends from the cv joint and is adapted to rotate and swing 
in an appropriate universal path which is well known in the art of cv 
joints. Attention is again directed to the Pat. No. 4,673,188 patent. 
The respective ends 11 and 12 of bellows 10 are connected by a series of 
convolutions 13, 14, 15 and 16. 
The respective convolutions progressively decrease in diameter at the peaks 
from the large end 11 to the small end 12. At the same time the wall 
thickness tapers but decreases in each convolution in order for each 
convolution to share substantially more equally in the flexing required of 
the bellows. As an example, the walls 13B and 14A in the adjacent 
convolutions 13 and 14 each taper to an increase in thickness up to the 
apex of the valley V-1. The walls 14B and 15A in the adjacent convolutions 
14 and 15 each taper in thickness up to the apex of the valley V-2, and 
these walls 14B and 15A are thinner than the walls 13B and 14A. In like 
manner, the walls 15B and 16A in the adjacent convolutions 15 and 16 are 
tapered to increase the thickness up to the apex of the valley V-3, but 
the increase is less than for the walls 14B and 15A. 
For example, where the walls 13B and 14A meet to form valley V-1, that 
joint has a thickness of 0.053 plus or minus 0.010 inches; the thickness 
of the material at peak R-2 where the walls 14A and 14B meet is less than 
for the valley V-1; the thickness of the material at valley V-2 where 
walls 14B and 15A meet is less than at the valley V-1; the thickness of 
the material where the walls 15A and 15B meet at R-3 is less than at the 
valley V-2; the thickness of the material at the valley V-3 where the 
walls 15B and 16A meet is less than at the peak 15; and finally the 
thickness of the material at the peak R-4 where the walls 16A and 16B meet 
is about 0.040 plus or minus 0.010 inches. There is a progressive thinning 
of the connections at peaks R-1, R-2, R-3 and R-4, and a progressive 
thinning of the material at the valleys V-1, V-2 and V-3. 
It can be seen in FIG. 2 that one of the important characteristics of the 
present boot is to vary the thickness of the boot wall at the respective 
hinge elements 17 at the valles V-1, V-2 and V-3 so that as the boot 
rotates and also flexes through whatever angle is followed by the shaft 
running through the boot, the walls that form the valleys in each 
rotational cycle will tend to fold toward each other, but the contact that 
does occur between convolute walls will not develop a hard compressive 
surface-to-surface abutment so that there is little or no surface stress 
induced in the walls approaching the valleys. The result is that the 
flexing of the various convolutions making up the boot share substantially 
equally in the flexure during the alternate folding and extension of the 
adjacent convolutions. The sharing in the alternate folding and extension 
of the adjacent convolutions is obtained by varying the angles the walls 
13B, 14B and 15B make with the longitudinal axis X--X of the boot. For 
example, in FIG. 3 the slope of the convolution wall 13B makes an acute 
angle A-1 with axis X--X; the slope of wall 14b makes a somewhat larger 
acute angle B-1, and the slope of wall 15B makes a still larger acute 
angle C-1 with the axis X--X. This progressive change in the slope the 
convolution walls make with the axis X--X of the boot 10 establishes the 
convolution wall flexure such that the convolutions tend to collapse 
substantially concurrently or together rather than first one convolution, 
then the next convolution, and the next convolution, such as in a 
one-after-another fashion. 
The presence of more material at the internal valleys, where the flexing is 
the most severe, takes care of the stresses and thereby provides a longer 
service life for the entire boot. As shown in FIG. 4 the thickness of the 
hinge element 17 interconnecting walls 13B and 14A is greater than the 
thickness of the hinge element 17A, and hinge element 17A is thicker than 
the hinge element 17B. Furthermore, in its position with the several 
convolutions normal to the axis X--X of the boot, the included angles 
between walls 13B and 14A is larger than the like angle between walls 14B 
and 15A, and that latter included angle is larger than the included angle 
between walls 15B and 16A. 
It should be apparent from the disclosure in FIGS. 1 and 2 that there are a 
series of convolutions 13, 14, 15 and 16 arranged in that order beginning 
at the enlarged diameter end 11 of the boot and progresses to the small 
diameter end 12 of the booth. Each convolutions is formed by a pair of 
angularly diverging walls, such as walls 13A and 13B for the convolution 
13 or the angularly divergent walls 15A and 15B for the convolution 15. 
The respective convolutions are integrally interconnected and the 
divergent walls, such as walls 13B to and including wall 16B are directed 
inwardly so that the inner ends thereof form valleys which are denominated 
V-1, V-2 and V-3. The normal construction of a constant velocity joint as 
used in the automotive field is attached to the constant velocity unit in 
a housing (not shown) to which the large diameter end 11 of the boot is 
connected, and the driving shaft (not shown) extends out of that constant 
velocity unit and runs through the small diameter end 12 of the boot where 
a case seal is located. In operation, as the shaft rotates it carries with 
it the boot and the shaft can describe a circular movement about the 
center of the universal joint. The result is that the convolution closest 
to that center will flex more than those farther away. Thus, the boot will 
periodically compress or fold portions of the convolutions on one side and 
extend the opposite side of the same convolutions in a manner that is 
illustrated in prior art Pat. No. 4,673,188. In the example of the prior 
art just noted, it is clearly illustrated that as the convolutions of the 
boot are compressed or folded, there is a compaction of the portions of 
the convolutions to such an extent that the exterior surfaces are brought 
into rubbing contact which shortens the service life of the boot. A unique 
feature of the subject invention resides in the provision (as seen in FIG. 
2) of the inner ends of the divergent walls which form the valleys (V-1, 
V-2 and V-3 having a connecting element 17 which makes a working 
connection between the divergent walls of the respective convolutions. 
That connecting element 17 is diminished in such a way as to allow the 
walls to approach each other but to maintain a slight contact. This is a 
unique way of preventing the walls of the convolutions from moving into 
destructive rubbing contact with each other when the portions of the 
convolutions are on the side where the shaft causes the boot to fold 
during its angular motion. 
It is also illustrated in FIG. 2 that the divergent walls of the 
convolutions are tapered in thickened so as to provide substantial mass in 
the walls adjacent the position of the element 17 to provide for a 
strength of material that will not work harden. The tapering thickness of 
the convolution walls which are directed into positions to form the 
valleys V-1, V-2 and V-3 have a tapered section as shown in FIG. 2 so that 
the presence of the material of the boot is strengthened in the critical 
area of the convolutions where they are periodically compressed or folded 
and extended as the shaft described its angular rotation which is a 
typical function of a constant velocity joint. 
It should be apparent from the foregoing description of the unique 
characteristics of the flexible bellows that the objects of the invention 
are adhered in a simple and unique manner.