Static sealing arrangement

Details Static sealing arrangement Static sealing arrangement

1998-08-12

2001-05-01

Knight, Anthony (Department: 3626)

Seal for a joint or juncture

Process of static sealing

Between parts of internal combustion engine

C277S316000, C277S598000, C277S934000

Reexamination Certificate

active

06224058

ABSTRACT:

The instant invention relates to a static sealing arrangement comprising the features as recited in the preamble of claim
1
.
Sealing arrangements of the kind in question are suitable for use in sealing valve bonnets of internal combustion engines both when mounted rigidly on the cylinder head or floatingly so as to provide insulation from structure-borne noise. They are likewise suitable as seals for oil sumps in internal combustion engines, heat exchangers, gear transmissions, axles and shafts of motor vehicles and the like.
FIG. 1
illustrates a conventional seal in cross sectional elevation. The shape of the seal is that of an inverted T, having a transverse or cross bar
2
and a stem or vertical bar
3
. A rib
4
each projects from the bottom of the cross bar
2
at either side of the plane of symmetry S. The ribs
4
serve to generate pressure peaks against a surface to be sealed off.
FIG. 2
shows the seal when installed in the groove
5
of a valve bonnet
6
, the ribs
4
being pressed by means of screws
9
against a planar horizontal sealing surface
7
of a cylinder head
8
in an internal combustion engine. The screws
9
keep a horizontal circumferential flange
10
of the valve bonnet
6
pressed into contact with the sealing surface
7
. The seal
1
is shown here, as in
FIG. 1
, in a free, non-deformed condition in which its total height is greater than the depth of the groove
5
formed in the valve bonnet
6
, and the thickness of its vertical bar
3
is smaller than the width of the groove
5
. The pressure exerted by the screws, in the assembled state, subjects the seal to such upsetting on the sealing surface
7
of the cylinder head
8
, between the bottom of the groove
5
and the lower end of the vertical bar
3
as well as the ends of the ribs
4
formed at the bottom of the transverse bar
2
, that the highest local compression occurs at these locations. Sealing thus is obtained substantially along the lines of maximum compression at the head of the transverse bar
2
and the ribs
4
, and these lines are closed all along the circumference of the seal. As may be gathered from
FIG. 2
, the material displaced by the upsetting largely fills the free volume of the groove since the elastomeric material is not compressible.
As a consequence of the sealing mechanism described, with the closed peripheral lines, it is impossible to keep the seal according to
FIG. 1
inside the groove such that it will not fall out under the influence of gravity. Mounting a valve bonnet provided with this kind of seal at reasonable cost would not be possible.
Often a way out is chosen by making the cross bar of the T less slender so that it will get caught in the groove. Then the seal is compressed in contact with the sidewalls of the groove. As a rule, the profile thus becomes wedged inside the groove so that the compression which is so important for the sealing function at the top end of the vertical bar of the T hardly can be proven to exist.
The valve bonnet
6
being a molded article, its sidewalls defining the groove must be divergent in the direction of the open end of the groove so as to permit removal from the mold. As a result of this inclination of the mold pressure acts at the places of contact between the seal and the sidewalls of the groove, attempting to push the seal out of the groove.
To overcome that difficulty, the vertical bar of the T was provided at regular intervals with lateral thickened portions extending from the superior foot end of the vertical bar all the way down to the cross bar. This has the disadvantage that insertion of the seal into the groove requires a distinctly greater force at the thickened portions and yet the contact pressure between the upper end of the vertical bar and the bottom of the groove, which pressure is decisive for reliable sealing, is smaller than at the places where no such thickening exists.
When the known seal described above is pressed into the groove the friction between the elastomeric material of the seal and the material of the valve bonnet (metal or impact resistant plastics) must be overcome. During pre-assembly, the seal is upset and it bounces back somewhat when the mounting force is removed. Therefore, it is easy to pull the pre-assembled seal out of the valve bonnet groove, and it may even fall out by itself.
It would be satisfactory from the technical point of view to fix the seal to the valve bonnet by cementing or vulcanizing, but that would be very expensive, especially so because of the pretreatment of the cap with a primer which usually is needed.
The known seal
1
offers a relatively great surface area for attack of the medium. Where the swelling of the elastomeric material under the influence of the medium is great, the effect of the seal may be impaired. For instance, oil may be exuded, the compression may be uneven, resulting in local leaks and the like.
It is, therefore, an object of the invention to provide a sealing arrangement of the kind defined in the preamble of claim
1
with which an elastomeric material can be used that is capable of great swelling and suitable for direct molding of the seal in the groove formed for this purpose in a first structural member, such as a valve bonnet or cap of an internal combustion engine. The seal is to be designed in such a way that the actual swelling is only minor and will not have a deleterious effect on the sealing function.
The object is met by a static sealing arrangement as defined in claim
1
.
An elastomeric material of great swelling capability, preferably a silicone rubber of the MVQ type can be used for a sealing arrangement according to the invention because of the configuration of the seal as claimed. This kind of material permits application by direct molding-on to the first structural member which is made in particular of plastics, such as a valve bonnet or cap of an internal combustion engine. The preferred silicone rubber, type MVQ, used for making the seal is very advantageous because of its temperature and oil resistances and also because it adheres well without any primer when the seal is molded on to a valve bonnet or cap made of plastics. A module ready to be installed, with a seal attached to it which cannot get lost, is obtained by a process of joining the seal to a valve bonnet or cap by molding or vulcanizing. This means that additional costs for pretreatment with a primer can be saved since the seal consists of an elastomer of sufficiently great bonding strength to the material of the valve bonnet or cap so that it can be molded integrally with the valve bonnet or cap. The high degree of swelling of the preferred silicone rubber causes no problem in view of the structural design claimed of the sealing arrangement.
The cross sectional profile of the seal is asymmetric, the contact portion being offset towards that side of the seal which faces air. That wall of the groove formed in the first structural member which faces the medium is extended farther towards the sealing surface of the second structural member than the wall of the groove facing air, the extension being selected such that the wall facing the medium comes to lie adjacent the sealing surface when the sealing arrangement is fully assembled. In this manner the seal offers but a very small surface for attack of the medium to be sealed off and that, in turn, at least delays the swelling for quite some time. Especially in cases where rigid compression of the seal between the two structural members is desired, the wall of the groove facing the medium is drawn down until it touches the sealing surface of the second structural member in the final assembled state of the sealing arrangement. Hereby the seal surface area exposed to attack by the medium at the wall facing the medium is reduced practically to zero.
Even if a floating compression of the sealing arrangement is aimed at in order to obtain insulation from structure-borne noise, the remaining gap between the limitation of the groove at the side facing the medium and the sealing surface at the second structural

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