Compliant grooved sealing ring for threadably secured assembly

In an assembly of two members that are threadably secured and have opposed radially extending sealing surfaces that may experience forced relative tilting there is provided an elastomeric sealing ring that engages these surfaces and has a radially facing circumferential V-shape groove providing lips that are preloaded between the sealing surfaces but do not touch each other on application of a predetermined securing torque and then on forced relative tilting of the members which tends to unseat the ring at some circumferential location the lips at this location remain preloaded while flexing to maintain sealing while at the diametrically opposite location the lips are forced toward full contact.

This invention relates to a complaint grooved sealing ring for providing a 
sealed joint between two threadably secured members and more particularly 
to such a sealing ring whose groove is formed with a V-shape so as to 
provide high compliance during tightening of the mating parts and then on 
subsequent relative tilting therebetween the ring can follow their 
movement without parting therefrom. 
In a threadably secured assembly such as gas cap for closing the filler 
neck on an automotive vehicle fuel tank, it is common practice to employ a 
solid elastomeric O-ring to seal their connection. An example of such an 
arrangement including a torque limiter mechanism is disclosed in U.S. 
patent application Ser. No. 516,032 assigned to the assignee of this 
invention. Typically, the O-ring provides satisfactory sealing under the 
preload determined by the torque limiter mechanism so long as the opposing 
seats on the cap and filler neck remain parallel which is the normal case. 
However, it has been found that such a sealing ring configuration is too 
limited by its inherent compliance characteristics in maintaining sealing 
should there occur some forced substantial tilting between the cap and 
filler neck on the occasion of a severe impact providing a large moment on 
the cap about an axis transverse to that of the cap and neck. 
One well known method of increasing the compliance is to make the O-ring of 
a softer compound but this is limited by molding defects, swell, 
compression set and/or long-term heat aging and was found not adequate to 
the task at handle. It is also known that the actual compression and thus 
the effective compliance of the O-ring can be further increased by 
reducing the coefficient of sliding friction between the filler neck 
sealing surface and the sealing ring which turns with the cap. But even 
then it was found that the increase in compliance of the conventional 
solid O-ring could not be made adequate to maintaining sealing in the 
extreme condition. 
The present invention substantially adds to the compliance that can be 
gained with a softer compound and a lower coefficient of sliding friction 
by simple modification of the cross-section of the present O-ring but 
without substantially reducing its cross-sectional strength to the point 
where the seal could roll and thereby lose its effectiveness in this 
environment. This is accomplished by a radially outwardly facing 
circumferential V-shape groove formed in the O-ring having a depth 
substantially greater than half the thickness of the ring and an included 
acute angle that provides lips between the seats such that when the 
predetermined securing torque load occurs and the ring is thereby squeezed 
between the seats, the lips are forced toward but do not touch each other 
with the seat parallel. But then on forced substantial tilting of the cap 
which tends to unseat the ring at some circumferential location the lips 
at this location remain preloaded to maintain sealing while at the 
diametrically opposite location the lips are forced toward direct contact. 
An object of the present invention is to provide a new and improved 
compliant grooved sealing ring for a threadably secured assembly. 
Another object is to provide in a threadably secured assembly a sealing 
ring of circular cross-section having a V-shape compliant groove with an 
included acute angle and a depth substantially greater than half the 
thickness of the ring to maintain sealing between normally parallel seats 
when they are forced into a substantially non-parallel condition.

Referring to FIG. 1 there is shown a fuel filler cap assembly 10 for the 
filler neck 12 of an automotive fuel tank (not shown) whose details but 
for the compliant grooved sealing ring 14 according to the present 
invention are disclosed in the afore-indentified U.S. patent application 
Ser. No. 516,032 which is hereby incorporated by reference. The fuel 
filler cap assembly 10 comprises a sheet metal cover 16 and skirt 18 which 
are secured together and contain a torque limiter mechanism 20 by means of 
which the cap is releasably connected to a plastic closure 22. The closure 
22 has an external thread 24 which engages an internal thread 26 formed in 
the filler neck 12, these engaging threads thus providing the means by 
which the cap is detachably secured to the neck. The torque limited 
mechanism 20 operates to drivingly connect the cap 10 to the closure 22 in 
the closing or tightening direction of cap turning up to a predetermined 
torque load and thereafter permits the cap to free wheel. Alternatively, 
the torque limiter operates to provide a positive drive connection between 
the cap and closure in the opening direction of turning to unthread the 
closure and thus the cap from the filler neck. For a more detailed 
understanding of the structure and operation of the fuel filler cap 
assembly including torque limiter, reference may be made to the 
afore-indentified U.S. patent application Ser. No. 516,032. The cap 
assembly may further include a pressure vacuum control valve assembly as 
disclosed in U.S. Pat. No. 3,937,358 but its structure and operation is 
not necessary to an understanding of the present invention. 
In such an arrangement the closure 22 is provided with a circumferential 
radially outwardly facing groove 30 which provides a radially outwardly 
extending sealing surface or seat 32 opposite a filler neck sealing 
surface or seat 34 formed by flaring the edge of the open end of the neck. 
Typically, a solid O-ring of elastomeric material is mounted in a slightly 
streched condition in the groove 30 on the cap and on threaded engagement 
of the cap with the filler neck the O-ring is held by the cap and squeezed 
between the seats 32 and 34 to seal this joint and thereby prevent leakage 
of any fumes and liquid from the fuel tank. 
According to the present invention and instead of the typical solid O-ring 
used for sealing, the sealing ring 14 is formed with a radially outwardly 
facing circumferential V-shape groove 36 that is bisected by a radial 
plane through the circular centerline of the seal and has a depth 
substantially greater than half the thickness or diameter of the ring's 
circular cross-section and has an included acute angle that provides lips 
38 and 40 of substantial length extending radially outward between the 
respective seats 32 and 34 of the cap and neck. The depth and angle of the 
groove 36 are determined so that when the release torque load is 
encountered and the sealing ring is thereby squeezed or preloaded between 
the seats as shown in FIG. 2, the lips are forced toward but do not touch 
each other at their ends in the normal preload condition with the 
substantial cross-sectional resistance to axial loading left by the 
compliant groove taking the squeeze to assure sealing of the small 
disparities typically found in the filler neck sealing surface. But then 
on forced substantial tilting of the cap relative to the filler neck which 
tends to unseat the sealing ring at some circumferential location, the 
lips at this location remain preloaded to maintain sealing while at the 
diametrically opposite location the lips are forced together as shown in 
FIG. 3, the long cantilevered lips with their cross-sections which 
gradually taper to the end accommodating such tilt while preventing the 
seal from rolling. 
In an actual usage of the invention it was found that excellent results 
were obtained where the sealing ring was made of butadiene acrylonitrile 
base with polyvinyl chloride added sold under compound number E-7-1 by 
International Packing Corporation, Bristol, New Hampshire. This ring had a 
hardness range of 60-70 Shore A and had a cross-section diameter of 0.250 
inches with the V-shape groove 36 then formed with a 65-75.degree. 
included angle and provided with a depth of 0.138-0.158 inch, such an 
arrangement preventing leakage up to and beyond where a 200 pound force 
was applied at the outside diameter of the cap at a 45.degree. angle to 
the cap centerline as shown in FIG. 3. 
The afore-described preferred embodiment is illustrative of the invention 
which may be modified within the scope of the appended claims.