Flexible boot for universal joint

A flexible boot of the polymeric type for use with a universal joint where the boot has a radially outermost generally tubular wall section that interconnects to the boot body by oppositely facing peaks and valleys. The thickness of the boot sidewall is controlled to effect desire bending where, in one embodiment, peaks and valleys are thicker than an adjoining sidewall of a corrugation.

BACKGROUND OF THE INVENTION 
The invention relates to joint packings or seals, but more particularly, 
the invention relates to flexible boots of the corrugated type for use 
with universal joints. 
Flexible boots have long been used to protect the operating environment for 
universal joints by retaining grease for the joints and by keeping foreign 
objects away from the joints. The accomplishment of such functions over a 
suitable flex-life operating-period, while seemingly simple, is, in 
reality, more complex because damage to the boot must be avoided as much 
as possible to avoid early failures of the universal joint. 
In use, damage to a flexible boot may be inflicted in several different 
ways such as for example by: a) external abrasion of corrugations caused 
by them rubbing against themselves as the boot is flexed and rotated with 
its ends in angular misalignment; b) internal abrasion of corrugations 
caused by the boot rubbing against part of an encased universal joint as 
the flexible boot is flexed and rotated with its ends in angular 
misalignment; and c) external abrasion and puncturing from external 
sources such as when the flexible boot is operated in a rocky or prodding 
environment. Additionally, the boot must have a requisite strength to 
inhibit ballooning when rotated while maintaining requisite flexibility 
and life over a broad temperature range and angle change. 
Flexible boots may be categorized into two general groups based on an 
orientation of the corrugations in the flexible boot. In a first category, 
the corrugations are oriented generally radially, with peaks of the 
corrugations radially outward of valleys of the corrugations. Boot flexing 
is typically concentrated at the peaks and valleys and is in response to 
an induced force of an encased joint, the boot of a harder resilient 
material such as Hytrel as sold by Dupont and disclosed in the 4,747,805 
patent, or a combination of two materials such as semirigid polymeric 
materials such as glass impregnated nylon as disclosed in the 4,627,826 
patent. However, such solutions while inhibiting damage from external 
environmental sources such as by puncturing from rocks, etc. may introduce 
new problems including flex fatigue. 
For example, the flexible boot of the '805 patent has a deflection problem 
like those boots having radially oriented corrugations in that the wall of 
the boot is pulled radially inwardly at the large diameter end of the boot 
and on the side of the boot that is flexed to an acute angle. The inward 
deflection of the boot sidewall may limit the number of degrees of 
deflection before the boot is pulled into interference with an encased 
universal joint. 
As explained in the '826 patent, the axially oriented corrugations provide 
angular movements of up to 30 degrees but thereafter, a spherical member 
of the joint in conjunction with a socket portion of the boot are required 
and cooperate with each other to permit further angular movements of the 
boot. While the design of the '826 boot may permit sufficient angular 
movements, it requires a dynamic sealing arrangement between the spherical 
surface of the joint and a spherical socket of the boot. Such an 
arrangement is not only expensive but it is not 100 percent effective in 
forming a seal to retain grease. Also, constant sliding between the parts 
can cause wear leading to seal failure. 
The present invention is primarily directed to flexible boots of the second 
category which have corrugations oriented generally axially in relation to 
the boot. The invention addresses general boot problems associated with 
self inflicted damage to corrugations, and damage associated with the boot 
contacting internal and external objects as the boot is angularly 
displaced to angles as high as 40 degrees. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a flexible boot of the polymeric type is 
provided for use with a universal joint. The boot is of a category that 
includes a corrugated sidewall with a plurality of generally tubular walls 
intermediate a large diameter end and small diameter end and wherein, the 
corrugations are generally axially oriented. The boot includes a radially 
outermost and generally tubular wall portion adjacent a large diameter end 
of the boot and is positioned intermediate oppositely facing peaks and 
valleys of corrugations such that the generally tubular wall portion forms 
a protective shell having a somewhat of a semi-toroidal shape or 
appearance. One end of the outermost tubular wall interconnects to the 
large diameter end while the opposite end of the tubular wall portion 
interconnects by way of axially oriented peaks and valleys of corrugations 
to a small diameter end of the boot. The arrangement of the corrugated 
sidewall is such that the radially outermost generally tubular wall 
portion bulges radially outwardly on the acute angle side of the boot as 
the ends thereof are positioned in angular misalignment from each other 
such as by means of an encased universal joint. 
The sidewall thickness of the corrugations is varied to control the manner 
in which the sidewall flexes as the end portions of the boot are moved in 
angular misalignment relative to each other. An optional method for 
controlling deflection during bending is to provide a boot where the peaks 
and valleys of the corrugations have a greater thickness than 
interconnecting sidewall portions of the corrugations. 
An advantage of the invention is that the boot corrugations do not rub 
against themselves to inflict self damage as the ends of the boot are 
angularly misaligned in relation to each other. Also, the radially 
outermost tubular wall portion of the boot can be made relatively thick 
and without any thinned sections for hinging, and still bulge away from an 
encased universal joint at the large diameter end of the boot on the acute 
angle side of the boot and thereby avoiding or minimizing internal 
contact. 
Another advantage of the boot of the invention is that it may be made with 
higher tensile modulus materials without the need for thin walled portions 
to enhance flexibility at highly stressed hinge points of peaks and 
valleys to avoid contact between adjacent corrugations. The higher modulus 
materials provide protection against failure from external abrasion and 
puncturing from external sources.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to FIGS. 1-3, a flexible boot 10 of the molded, polymeric type is 
provided for use with a universal joint (not shown). The boot includes a 
corrugated sidewall 12 with a plurality of generally tubular walls 
intermediate a large diameter end 14 and a small diameter end 16. The boot 
has a sidewall 18 that forms a radially outermost and generally tubular 
wall portion 20 that is interconnected with an external peak 22 and valley 
24 of the corrugated sidewall to a tubular wall portion 26 of the adjacent 
large diameter end. An internal collar 28 may be integrally molded as part 
of the tubular wall portion 26 and serve as part of a grease seal means 
for a universal joint. 
The radially outermost and generally tubular wall portion 20 may optionally 
have a convex shape 30 when viewed in axial cross-section, and forms a 
protective shell. The protective shell interconnects with an oppositely 
facing external peak 32 and valley 34 of the sidewall so as to give the 
outermost protective shell somewhat of a semi-toroidal shape. Preferably, 
but optionally, the first interconnecting valley has a larger diameter 
than the oppositely facing and coaxially aligned second valley 34. 
Corrugated sidewall 12 extends to a third generally tubular wall portion 
36, a peak 38, a valley 40, an optional conical section 42, and into a 
fourth generally tubular wall section 44 that extends to the small 
diameter end 16 where internal collars 46, 48 define part of a grease seal 
means. 
The flexible boot of the invention may be made with any suitable polymeric 
material which include the natural rubbers, synthetic rubbers, and blends 
thereof, plastics and urethanes. The boot is particularly adaptable to be 
made with higher tensile modulus material because such materials usually 
provide a toughness to inhibit puncturing while providing a satisfactory 
abrasion resistant quality. Examples of some of the higher modulus 
materials include the following thermoplastic elastomers: Estane 58206 as 
sold by The BF Goodrich Company and having a tensile modulus of 270 psi at 
30 percent elongation; Pebax 3533 as sold by Elf Atochem and having a 
tensile modulus of 535 psi at 30 percent elongation; Estane 58887 as sold 
by The BF Goodrich Company and having a tensile modulus of 660 psi at 30 
percent elongation; Estane 58134 as sold by The BF Goodrich Company and 
having a tensile modulus of 710 psi at 30 percent elongation; Pellethane 
blend (2103-80A/2103-90A) as sold by Dow Chemical Company and having a 
tensile modulus of 855 psi at 30 percent elongation; Santoprene 201-87 as 
sold by Elf Atochem and having tensile modulus of 920 psi at 30 percent 
elongation; Estane 58223 as sold by The BF Goodrich Company and having a 
tensile modulus of 1000 psi at 30 percent elongation; Estane 58223 as sold 
by The BF Goodrich Company and having a tensile modulus of 1000 psi at 30 
percent elongation. 
The flexing characteristics of the boot may be modified by changing the 
thickness of the sidewall at various locations along the corrugation. 
Different materials will require some modifications to effect a most 
desirable result. 
Referring more particularly to FIGS. 2 and 3, an exemplary sidewall is 
shown and described that is suitable for elastomers such as listed above 
having a tensile modulus from about 270 psi to about 1000 psi at 30 
percent elongation for a four inch diameter constant velocity universal 
joint that is required to flex at least 40 degrees without any substantial 
contact with the boot. The tips of the arrows in FIG. 2 are oriented 
normal to the boot surface and reference the point from which the 
dimensions listed in the table of FIG. 3 are given. For example, point "a" 
is located along the X axis at 0.895 inches and has a radius of 2.107 
inches along the y axis. The thickness at point "a" is 0.081 inches as 
measured from the point and direction of the arrowhead "a." As illustrated 
by the table, the thicknesses of the peaks and valleys of the corrugated 
sidewall are optionally but preferably thicker than the interconnecting 
tubular wall portion. It is believed that by having peaks and valleys 
thicker than the wall section, it minimizes any bending stresses at such 
points while also controlling the manner in which the boot deflects which 
will later be explained. The radially outermost, generally tubular wall 
portion 20 preferably tapers in a direction that increases from the large 
diameter end of the boot 14 toward the smaller diameter end of the boot 
16. As exemplified by the table of FIG. 3, the wall portion 20 or shell 
increases from a thickness at point d of 0.080 inches to a thickness of 
0.096 inches at point e. It is believed that tapering controls the manner 
in which the wall 20 bulges radially outwardly on the acute angle side of 
the boot when the large diameter end and small diameter end are angularly 
misaligned relative to each other. 
In use, the boot 10 is used with a universal joint 50 such as of the 
constant velocity type as illustrated in dotted outline in the schematics 
of FIG. 4 and 5. The boots of FIGS. 4 and 5 are of the same construction 
as those of FIGS. 1-3 and were made of a thermoplastic urethane material 
sold under the trade name Estane 58124 and manufactured by The BF Goodrich 
Company where the material exhibited a tensile modulus of 710 psi at 30 
percent elongation. 
Referring to FIG. 4, the boot of the invention is installed on a universal 
joint 50 having a center of movement 52. The universal joint is deflected 
to an angle C of 20 degrees which is toward the acute angle side Al of the 
deflected boot. The outermost tubular wall portion 20 is bulged radially 
outwardly and away from the circumferential edge 54 of the joint 50. Such 
movement away from the joint is opposite that of prior art flexible boots. 
The oppositely facing valleys 24, 34 in cooperation with the oppositely 
facing peaks 22, 32 act to bulge the wall portion or shell 20. 
In the preferred embodiment where the peaks and valleys have a thickness 
that is greater than an adjoining wall section, they tend to act as 
annular stiffening rings that control the manner of boot flexing. Valley 
40 with its thickened sidewall section operates to generally define an 
annular ring member of the boot having diameter Dl; peak 38 with its 
thickened sidewall section operates to generally define an annular ring 
member having a diameter D2; and valley 34 with its thickened sidewall 
operates to generally define an annular ring member having a diameter D3. 
The generally defined annular rings operate to stabilize the flexing 
process and remain somewhat telescopically positioned in relation to each 
other. On the acute angle Al side of the boot, loads are transversely 
applied to the boot by a shaft 56 as it is angularly moved with regard to 
its center of movement 52. Such movement and the acute angle direction 
imparts a transverse loading in the boot from valley 40 at diameter D1, to 
peak 38 at diameter D2, and then to valley 34 at diameter D3 whereby the 
valley 34 is lifted somewhat away from the circumferential edge 54. 
Referring to FIG. 5, the shaft 56 is deflected to an angle E of 40 degrees 
whereupon the radially outer most tubular wall section 20 or shell is 
deflected further away from the joint 50 in a direction toward the acute 
angle E side of the boot A2. The boot flexing process is substantially the 
same as described for FIG. 4 and wherein the diameters D1, D2 and D3 
although changed are substantially similar. The boot flexing process is 
such that the sidewall is actually moved away from the circumferential 
edge 54 of the joint during the bending process. 
The foregoing detailed description is made for purpose of illustration only 
and is not intended to limit the scope of the invention which is to be 
determined from the appended claims.