CA1043831A - Piston ring system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A multiple element seal ring system comprising a pair of pressure non-deformable split rings and a deformable expander ring adapted to be received in a grooves. The split rings are provided with relatively narrow inner surfaces spaced from the groove bottom wall to provide clearance of short axial extent therebetween for restricting deformation of the expander ring within its elastic limits. The expander is provided with rounded corners adjacent to the aforesaid clearances to further retard any permanent deformation of the expander ring.

Description

~ his application is related to Canadian Patent No. 966,871, issued on April 29, 1975 entitled 'IPiston Ring System".

BACKGROUND OF THE INVENTION
This invention relates to seal ring systems for fluid actuators and, more particularly, to seal ring systems of a composite design.
In recent times, the conventional O rings and chevron ` , type packings employed in fluid actuators have been replaced -by multiple element sealing arrangements including elements -formed of both pressure deformable and non-deformable materials.
While these multiple element sealing systems offer improvements over the O ring and chevron type seals, particularly in high pressure applications they do possess certain disadvantages.
For example, in some known constructions, the deformable ;
component, such as a rubber ring, is relied upon to perform some sealing and in contacting the other part is subject to wear.
Often, metal rings, which do have a significantly long wear life, are used as the non-deformable components. However, they are sus~eptible to galling when performing the sealing function.
In those systems in which split rings are utilized, fluid leakage or bypass often occurs through the ring partings at high pressures. One attempt to overcome these disadvantages is disclosed in U.S. patent ~o. 3,612,538, on a multiple element ~iston Ring System, granted on October 12, 1971 and assigned to the same assignee as the present invention. The present invention constitutes a further improvement in such a multiple ~ 3~
element seal ring system and is directed to a constr~ction positively preventing permanent deformation of the deformable expander ring.
SUMMARY OF THE INYENTION
An object of the present invention is to provide an improved multiple element seal ring system for fluid actuators : ~ .
which will remain leak-free under high pressure conditions :
and which is not susceptible to permanent deformation. :
A primary obiect of the present invention is to provide an expander ring for use in a multiple element seal ring system which is formed as to resist undesired deformation and which tends to return to its unstressed shape after beingin a loaded condition. ~.
Broadly speaking, the present invention provides, .
in a seal assembly having a pair of non-deformable rings disposed- ~:
in an axial abutting relation adapted to be received in a peripheral groove formed in a reciprocating member and having I :: inner recesses defining a composite groove, the rings having outer bearing surfaces engagable with the surface to be sealed and inner surfaces slightly spaced from the groove bottom wall ;
to define clearances therebetween and a deformable ring received in the composite gro-ove, the inner surface on each of the non- ;^
deformable rings being of a relatively narrow axial length limiting the axial extent of the clearances available for :
displacement of portions of the deformable ring within the elastic 1imits of the deformable ring to prevent permanent distortion thereof, the deformable ring having inclined axial . .:
end faces converg~ng radially outwardly and complementary to corresponding surfaces on the non-deformable rings defining the groove, a radially inner surface adjacent the groove bottom , ~ :
wall connected to the inclined faces by a rounded corner surface immediately ad~acent each cle2rance and curving away therefrom towards the radially inner surface and the adjacent end face, .. -~ ~ .
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the radially inner surface having a central land portion, and a pair of axially spaced apart ribs defining therebetween the central land portion, each rib projecting radially inwardly ~
from the radially inner surface and having a bearing surface ;
adapted to engage the groove bottom wall, the ribs serving to . ...
space the corners and the radially inner surface radially :.
outwardly of the groove bottom wall.

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43~3 ~ -The foregoing and other obiects, advantages and characterizing features of the present invention will become -~-clearly apparent fro~ the ensuing detailed description of an illustrative embodiment thereof, taken together with the accompanying drawing wherein like reference characters denote like parts throughout the various views.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
Fig. 1 is a fragmentary, longitudinal sectional view of a portion of an hydraulic cylinder incorporating the seal ring system of the present invention, Fig. 2 is a front elevational view of the deformable ring element of the seal ring system shown in Fig. l;
Fig. 3 is a fragmentary, transverse elevational view in section of the deformable ring element af Fig. 2 as taken about on line 3-3 therein, and Fig. 4 is an enlarged detail view of the expander and split ring assembly shown in Fig. 1.
DETAILED DESCRIPTION OF AN ILLUSTRATED EMBODIMENT
Referring now in detail to the illustrative embodiment depicted in the drawing, there is shown in Fig. 1 and 4 a seal ring system or assembly, generally designated 10, constructed in accordance with this invention, and shown incorporated in a ~-piston 12 mounted for reciprocating movement in a sleeve 14 of an hydraulic cylinder 16. While the piston shown in Fig. 1 is comprised of two components bolted together, it should be understood that seal ring systems 10 can be utiliied with elther Lultiple co=ponent or unitary pi9tons. A s=all gap or :' : ` .' .. ~ .

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. , . ~`:' 3'~ ~ -1 clearance 18 exists between the inner wall of sleeve 14 and the outer peripheral surface of piston 12. A pair of axially spaced sleeve type bearings 20 are mounted a~out piston 12 in bearing relation to the inner wall surface of sleeve 14.
As further shown in Fig. 1 and 4, a groove 22 is formed in piston 12 for receiving seal ring system 10, such groove being defined by a bottom wall surface 22a and spaced-apart side wall surfaces 22b and 22c. ~f course, two or more grooves 22 with corresponding seal ring systems can be provided in piston 12, as desired.
In accord with this invention, seal ring system 10 comprises -first and second split rings 24 and 26, respectively, preferably formed of non-deformable material, such as synthetic plastic for example. Rings 24 and 26 are juxtapositioned in an axial abutting relation in groove 22 and the combined thicknesses or axial width of rings 24 and 26 is less than the axial width of groove 22. The cross sectional or radial width of each ring 24 and 26 is less than the depth of groove 22 or less than the cross sectional radial extent of groove 22.
Seal ring system 10 also includes an expander ring 28 of resiliently yieldable, pressure defoxmable material, adapted to be positioned in an annular space defined by the groove bottom wall 22a and the inner surfaces of rings 24 and 26.
Under pressure, expander ring 28 urges rings 24 and 26 radially ; outwardly to force the outer surfaces thereof into sealing engagement with the inner surface of sleeve 14.
Since rings 24 and 26 are of identical construction, although oriented in op~ositely facing directions in the assembled relation shown in Fig 1, it is believed that a ,. , ; ~
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1 detailed description of split ring 24 only will suffice, it being understood that the same reference characters designate identical parts. As shown in Fig. ~t, ring 24 has parallel axial end faces 30 and 32 and an outer, circumferential bearing surface 34, ioining faces 30 and 32 a~ sharp, right angular edges to provide an effective wiping engagement between bearing surface 34 and the inner wall surface of sleeve 14.
Ring 24 is provided with an annular recess extending inwardly of end face 32 and defined by an internal circumferential ~ -surface 36 parallel to and concentric with bearing surface 34and an inclined surface 38 tapering radially inwardly and toward end face 30. Tapering surface 38 terminates in a flat, inner surfa~e 40 concentric with surfaces 34 and 36 and definin~
the inner periphery of ring 24. ~ -Split rings 24 and 26 preferably are formed of a polyamide commonly known as Nylon and which is provided with a filler including glass fibers in an amount constituting about 30 percent by weight of the ring composition and molybdenum disulfide in an amount constituting about 5 percent by weight of the total ring material. Those glass fibers add strength tG the Nylon lengthening its useful wear life, and the molybdenum disulfide adds lubricity. While the above weight proportions of filler material are pre~erable, it has been found that the addition of glass fibers in a range of about 12 to 30 percent and molybdenum disulfide in a range of about 2 to 5 percent by total weight produces satisfactory results.
~ ylon is preferable as the basic ring material because of its non-galling property. Also, ~ylon has the capability of absorbing metallic impurities present in hydraulic fluid . . . / ,,,, , ,. -: : - ,- ~ ' ': ' 3~

1 which would otherwise score and damage the cylinder. In addition, when Nylon is prov~ded with the appropriate filler, it exhibits thermosetting characteristics, becoming permanently hard and rigid when heated or cured and will remain stable at temperatures up to 400F and pressures up to 4,000 p.s.i., these conditions being well above those normally encountered in use. Ring 24 is molded to provide a protective skin against -moisture and temperatures, which under extreme conditions, can render the rlng material deformable. Although the ring material preferably is Nylon, it should be understood that ot(her synthetic material having similar thermosetting properties and which do not exhibit "cold flow" under the temperature ; can be used in lieu of ~ylon, if desired, within the purview of this invention. As previously mentioned, split ring 26 is identical in construction to ring 24 and can be formed of the same material by the same mold.
Expander ring 28 is formed of a resiliently yieldable, pressure deformable material, such as neoprene for example. '~
As shown in Fig. 2, expander ring 28 comprises an annular, endless body provided with an outer, peripheral bearing surface 52 adapted to engage circumferential surfaces 36 of rings 24 and 26 and a pair of inclined or tapered axial end faces 54, as seen in Fig. 3, engagable with and complementary to the inclined surfaces 38 of rings 24 and 25. In addition, the expander ring has rounded corners 56 which essentially provide the intersection of inclined surfaces 38 with adjacent ribs 59 as seen in Fig. 3. ; ;
The annular ribs 59 on the radially inner surface of the expander are axially spaced from each other and have bearing surfaces 60 engageable with groove bottom wall 22a to form a ... ,, .~ , .. ,- . . . . . ~ .. : .. . . .. .

static seal therewith. An upper bead portion 64 of the expander provides in turn a static seal with the inner surfaces 36 of split rings 24 and 26. The ribs ~ define a land portion 70 radially ~, spaced from groove bottom wall surface 22a providing a clearance 62 therebetween, enabling bead 64 to radially yield inwardly somewhat, thereby offering only moderate re~ ~t~nce to radial movement and reducing the stresses on outer rings 24 and 26 while effectively resisting axial deformation. Under static sealing conditions, expander ring 28 imposes only a relatively 10 light radial load on outer ring 24, created by triangular three point contact, as opposed to the more severe initial loading that would be offered by an expander ring having a trapezoidal cross section of similar durometer rating completely filling the space defined by rings 24 and 26 and groove wall 22a, for example. However, the radial loading increases under dynamic ~;
sealing conditions in proportion to the hydraulic forces ~;
encountered. Accordingly, increased loading on outer ring 24 is obtained when needed most to provide a firmer pressure sealing engagement against inner wall surface 18 of cylinder 20 14.
When rings 24, 26 and 28 are assembled together and positioned in piston groove 22, as best shown in Fig. 1, the resulting seal ring system 10 maintains an effective fluid seal under both high and low pressure conditions while possessing low friction characteristics and no susceptibility to destructive pressure deformation. In this asse~bbled relation, split r~ngs 24 and 26 are oriented in a manner locating their respective gaps or partings between their respective split ends 180 apart so that the gap of each split -8- -~

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1 ring is adjacent the unihberrupted surface of the other split ring to eliminate any potential path f~r fluid bypass there-through. Expander ring 28 closes the small gap existing between the inner surfaces 40 of rings 24 and 26 and the groove bottom wall surface 22a and urges the bearing surfaces 34 of rings 24 and 26 radially outwardly into a fluid-tight, slidable sealing engagement with the inner wall surface of sleeve 14. The sharp, right angularly edges formed by the intersection of faces 30 and 32 with bearing surfaces 34, repsectively, enhances this sealing engagement and also provides an effective wiping edge. -End faces 30 of each of the rings 24 and 26 have a radial dimension slightly less than the distance from the groove bottom ~all surface 22a to the inner wall surface of sleeve 14 to provide a relatively large area exposed to axial loading under fluid pressure, thereby increasing the `
overall structural rigidity of seal ring system 10. This enables the plastic material of which the rings are formed to more effectively resist "cold flow" under high fluid pressure conditions. Moreover, this relatively large exposed area enhances the effectiveness of seal ring system 10 in contaminated ~
hydraulic systems. It should be understood that for a ;
hydraulic system to properly handle contaminated fluids, the width of clearance 18 between piston 12 and sleeve 14 should -be relatively large. To this end, the large exposed areas :
of rings 24 and 26 inc~ease the rigidity of seal ring system 10 against the increased axial stresses resulting from the larger clearanCe and also provide more surface area for exposure to the fluid to absorb the contaminating particles.
Since the inner surfaces 40 of rings 24 and 26 are `-t .. ..

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1 slightly spaced from the groove bottom wall surface 22a to - prevent interference therewith, a slight clearance 58 exists therebetween. A feature of this invention resides in tapering the inner portions of rings 24 and 26 by means of inclined surfaces 38 to define relatively narrow inner surfaces 40 of substantially knife edge thicknesses to provide an extremely short axial dimension to clearances 58 ~etween such surfaces 40 and groove bottom wall surface 22a. While the width of each clearance 58 is sufficiently shallow to normally preclude "nibblingl' or displacement of portions of deformable expander ring 28 into these clearances 58 under most pressure conditions, in the event such ~nibbling~ or temporary displacement does occur under adverse pressure conditions, the short axial extent of such clearances 58 will restrict stretching of the displaced portions of expander ring 28 well within the elastic limits of the material of which ring 28 is formed. In addition, an ;
important feature of the present invention resides in the nature of the7rounded corners 56. The contour thereof also retards "nib~ling" and greatly enhances the ability of the expander to maintain its initial or undeformed shape. Such a rounded corner concept is to be distinguished from prior art structures having essentially pointed corners at corresponding axial end points. Accordingly, temporarily deformed portions of the expander will not take a permanent set or deformation due to the rounded corners 56 as well as the minimal size of clearances 58 and expander ring 28 will restore itself to its initial shape upon removal of the pressures acting thereon.
In illustrating the operation of seal ring system 10, ... . ... ..
assume that fluid under pressure is applied to the right side --10- ;, ` , :~,' l of piston 12, as viewed in Fig. l, to force the latter toward - the left. Fluid pressure acting on end face 30 of spli~ ring 24 causes the entire seal ring system lO to move slightly axially to the left within groove 22. of course, the extent of axial movement will be small due to the relatively small clearances ~ -between seal ring system lO and the opposite side wall surfaces 22b and 22c of groove 22. However, this slight axial movement ~--is sufficient to allow fluid under pressure to enter clearance 58 between the split ring narrow, inner surface 40 and groove bottom wall 22A to act on deformable expander ring 28. Ring 28 expands in both a radial direction and in anuaxial direction toward the left, as viewed in Fig. 1. Consequently, split rings 24 and 26 are urged radially outwardly into pressure sealing engagement against the inner wall surface of sleeve 14. Also, the seal between the ribs of expander ring 28 and groove bottom wall 22a is made tighter. In addition, the axial and face 30 of split ring 26 is pressed into finmer contact with groove sidewall 22c as a result of the axial expansion of expander ring 28.
Since these axial stresses are distributed over the relatively large surface area of face 30 of ring 26, which surface area is several times the surface area of that portion of face 30 exposed to clearance 18, seal ring system lO is able to resist ~-cold flow into such clearance.
In the event th~t "nibbling" of expander ring 28 or the ~`
displacement of a portion thereof into clearance 58 takes place under the influence of high fluid pressures, this displaced or defonmed portion will contact groove sidewall 22c before it is stretched beyond its elastic limits because of the short extent of clearance 58 as defined by the narrow, substantially knife , . ,.. . . . ~ ............... . - . .............................. :
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1 edge thickness of ring inner surface 40. Furthermore, in addition to the ~ unded corners 56 of the expander tending to resist temporary or permanent deformation, such rounded corners readily urge the expander to return to its original shape after any temporary deformation has occurred. Accordingly, this displaced portion of expander ring 28 will not be permanently .
deformed and is restored to its natural condition upon removal of the fluid pressure. ~ -From the foregoing, it is apparent that the objects of the ;
present invention have been fully accomplished. By providing ,~t' the split rings 24 and 26 with relatively narrow inner surfaces 40 of substantially knife edge thicknesses to define short axial clearances between the latter and the groove bottom wall surface, the degree of potential expander ring "nibbling" or deformation into such clearance is restricted within the elastic limits thereof to prevent permanent deformation. ~- ;-With the expander 28 provided with rounded corners adjacent ;
to the clearances 58, any potential expander ring "nibbling" or deformation is further retarded and such rounded corners tend ~ -to maintain or urge expander 28 into its natural, unstressed shape.
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A preferred embodiment of this invention having been des-cribed in detail, it should be understood that this has been ..... ,.. ::
done by way of illustration only, without thought of limitation.
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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a seal assembly having a pair of non-deformable rings disposed in an axial abutting relation adapted to be received in a peripheral groove formed in a reciprocating member and having inner recesses defining a composite groove, said rings having outer bearing surfaces engagable with the surface to be sealed and inner surfaces slightly spaced from the groove bottom wall to define clearances therebetween and a deformable ring received in said composite groove, the inner surface on each of said non-deformable rings being of a relatively narrow axial length limiting the axial extent of said clearances available for displacement of portions of said deformable ring within the elastic limits of said deformable ring to prevent permanent distortion thereof, said deformable ring having inclined axial end faces converging radially outwardly and complementary to corresponding surfaces on said non-deformable rings defining said groove, a radially inner surface adjacent said groove bottom wall connected to said inclined faces by a rounded corner surface immediately adjacent each said clearance and curving away therefrom towards said radially inner surface and the adjacent end face, said radially inner surface having a central land portion, and a pair of axially spaced apart ribs defining therebetween said central land portion, each rib projecting radially inwardly from said radially inner surface and having a bearing surface adapted to engage said groove bottom wall, said ribs serving to space said corners and said radially inner surface radially outwardly of said groove bottom wall.

2. A seal ring assembly as set forth in claim 1 wherein said deformable ring comprises an endless annular body.