press Mail No. IB644548630 3489 VIC (60,680-055) -l- 211 5 9 5 ~
CYLINDER ~EAD (R~1J~tlZII~ RFTAINING ~rn6~ SPRING SeAL
The prese~t invention relates to an engine cylinder head gasket utilizin~ a ret~inin~ ring ~nd a spring energized seal disposed within an an~ular U-~haped flange ad~acent a gasket body. Th~8 application i~ ~ cont~m ~tion-in-part of Applicat~on Serial No. 07/992,678, filed December 18, 1992.
A cylinder head gasket bear6 a clamplng load from a bolted connection between a cylinder head and sn en~ine block and relies upon that load to provide ~ seal again~t the sealing elements of the gasket. The gasket includes a combustion seal to prevent the leakage of combustion gases during engine operation.
Known gaskets u6e any of several types of combustion seal rings. One type, known as a yieldable combustion 6eal ring, is essentially comprised of a wire having a generally circular cross-6ectional area. A clamping force applied to such a ring is concentrated at the point of contact, deforming the ring's circumference to effectively seal out combustion gase.
This type of seal ring, however, i~ subject to thermal crushing which produces additional plastic deformation that tends to occur under high temperature operation during the life of the ring.
Other known ga~kets use a spr~ng energized seal.
The spring energized seal extends about the cylinder bore and defines an annulus. The seal has a generally circular cross-section and compri6e6 both an outer jacket and an inner spring. As with the yieldable combustion seal ring, a clamping force applied to such a ring is concentrated at the point of contact to seal out combustion gases. The spring energized 6eal requires only a low load before sealing out combustion gase6, ~. . . : . . , :, ,:, . : , ~ : , , . . :
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,: : : : :. : , - ~ .: .,: : : : : -3489 VIC (60,680-o5' ~115~9 which i6 of particular importance in a cold engine start up condition. Such a spr~ng energized 6eal, however, i6 al60 fiubject to thermal cru~hing. Further, the Rpring energized seal tends to roll or plvot about i~6 annulsr axi~ in use, leading to undesirable fatigue under certain circum~tances.
An improved combustion 6ealing ~y~tem for a cylinder head ga~ket of an engine comprise~ a palr of seals. An inner annular spring energized combustion ~eal ic used in combination with an outer annular retaining ring, both of which are disposed within an annular metsl wrap and centered about an ax~6.
The 6pring energized seal acts as a cont~nuous or primary seal again6t combu6tion ga6es under all engine op~ratlng conditions. The retaining ring is di~po~ed bet~een the ~pring energized combustion ~eal and a gasket body. The retain~ng rine provide6 a positive mechancal stop for the ~pring energized combustion seal and provides a secondary seal again~t combustion ga~es. The retaining ring also protects the ~pring energized combustion seal from thermal crushing. The metal wrap i8 typically a generally U-6haped flange which position6 the sealŠ
relative to the gasket body.
Preferably, the retaining ring i~ po6itioned radlally outwardly of the spring energi~ed 6eal and includes a radially elongate cro~s-6ectlon hav~ng convex top and bottom surfaces 80 that an initial load app}ied to the retaining ring is a point load. Faces are formed at the radlal extremitie6 of the retaining ring having an orientation that i6 generally parallel to the axls about which the retaining r~ng 18 centered. In one preferred embodiment, a face at the radially inner extremity includes a groove adapted to receive an outer periphery of a spring energized combu6tion 6eal. The u6e of the .
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3489 VIC (60,680-~5' 3 21159~9 groove increa6es ~urface coDtact between the ring and the energized combustion seal which avolds polnt loading of the 6pring energized 6eal in the radial dimen6ion.
The ring is formed from a homogeneou~ composite powdered metal wh~ch contains zones of ~arying den6itie6 after sintering. In one preferred form, the powdered metal is composed primarily of titan~um.
B~I~F D~SCRIPTION OF TEE DRAWINGS
The $eatures and inventive a~pects of the pre6ent invention will become more apparent upon reading the following detailed descr~ption, claims, and drawings, of which the following is a brief description:
Fi~ure 1 i8 a perspective view of a portlon of a ga~ket incorporating the present invention.
Figure 2 is a cro6s-sectional view along lines 2-2 of the gasket of Figure 1 which depicts a first embodiment of a first embodiment of a retaining ring con6tructed in accordance with the present invention.
Figure 3 is a cross-sectional view of a second embodiment of a retain~ng r~ng.
D~SCRIPTLQ~_QF ~ D~TAIiED BM~QDIMe~T
An engine cylinder head gasket 20 illu6trated ~n Figure~ 1 and 2 includes ~ gssket body 22~ cylinder apertures 24, and fluid flow openln~s 26. To provide a multiple ~ealing system 28 about a cylinder bore ~not shown), gasket 20 include6 an annular U-shaped wr~p or flange 29 with an upper leg 30 and a lower leg 32. An annular spring energized seal 34 i8 di6posed .. .
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within the flange. Spring energized 6eal 34 iB ce~tered about an axi6 35 and define~ an annulu6. Spring energized seal 34 comprise6 both an inner coil spring 36 and an outer hollow 6pring or jacket 38, and acts as a primary ~eal again6t combustion ga~ leakage. a retalning ring 40, radially disposed between the spring energized combustion seal 34 and ga6kst body 22, and also centered about uKis 35, actl~ a8 a positi~e mechanical stop for ~pring energi~ed combustion fieal 34.
Ret~ining ring 40 proYides a secondary seal against combu~tion gas leakage.
A6 illustrated in Figure 2, retaining ring 40 define6 a radially elongate cro~6-section having a convex top surface 42 and a convex bottom 6urface 44. A radially outer circumferential face 46 defines an extremity which i8 perpendicular to the radial direction, and corre6pond6 to a mating surface 48 of ga~ket body 22. A generally circular concave groove S0 i6 formed on a face 51 that define~ a radially inner extremity of reta~ning ring 40 to corre~pond to and receive a mating outer convex peripheral 6urface 52 of 6pring energized combu6tion seal 34.
Retaining ring 40 provide6 support to spring energized combu6tion 6eal 34, aiding in ~aintaining 6pring 0nergized seal 34 in po6ition. Retaining ring 40 ~nd in particular, circular concave groove 50, re6~sts movement by 6pring energized seal 34 during A6sembly. Concave ~roove 50 al60 limit6 pivoting or rolling by 6pring energized 6eal 34 about it6 annulu6, re6ulting otherwi~e in unde6irable fatigue.
Stre66es imparted to retaining ring 40 include both a radial stre6s and a hoop 6tre6s from the ~pring energized seal 34. The shape of groove 50 in conjunction wlth mating surfaee 52 ~8 preferably chosen to place 6pring energize¨ seal 34 rad~ally in line with retaining r~ng 40 and to provide ~ ~light interference fit between the two parts. Such a radially in line relation6hip ,. . ~; , -, . ~ : :
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3489 VIC (60~68~-dSC
di6tr~butes radlal and hoop induced load6 over a maximum surface area, lowering the correspoading stresses. One preferred ratio between a radial di~en~ion of retaining ring 40 measured between faces 46 and 51 at the radial extremitie6, and a thickness measured between convex ~urface6 42 and 44 i8 approximately three to one. Thi6 ratio assures the necessary hoop strength to re~ist the externally applied pressure of the ~nternal combustion forces.
Spring energized seal 34 has a circular cross section while retaining ring 40 has convex top surface 42 and convex bottom surface 44. As a result, an initial axial compressive load applied to spring energized seal 34 and retaining ring 40 is a point load. Deformation~ of the spring energlze seal 34 and retaininX ring 40 will compen6ate for surface variatlon~ to provide conformabllity and a saperlor combustion seal. Both the spring energized ~eal 34 and the retaining ring 40 deform plastlcally upon initial loading.
Thereafter, during the thermal cycles which occur over their useful life, each will deform elastically. ~owever, during the latter, further plastic deformation is not precluded. Because of the shape and ~ize of retaining ring 40, excesaive thermally induced crush of spring energized seal 34 is prevented. A
primary advantage of spring energlzed seal 34 i8 that it requires only ~ low load before sealing out combustion gases.
With non-liner engine applications, spr~ng energized ~eal 34 is of particular importance under cold engine start up conditions.
Howe~er, even with liner-engine application~, the spring energized seal 34 limits 6eal leakage, particularly under hot operating conditiQns when engine components may warp.
Flange 29 plays an important role ln the proper operation of spring energi~ed seal 34 and retaining ring 40.
Flange 29 must be sufficiently strong to ~aintain proper orientations of retain~ng ring 40 and seal 34, particularly for , .- ~ . . . . . .
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3489 VIC (60,686 55 -6- 2 11 ~ 9rj(~
limitation of rolling or pivoting of spring energized 6eal 34.
Preferably, outer convex surface6 42 and 44 of retaining ring 40 and outer peripheral surface 52 of sprlng energized seal 34 abut and are supported by an inner surface 55 of one of legs 30 or 32 of flange 29.
In one preferred embodlment, f}snge 29 compri~e6 a nickel 6tainless steel such as that ~old under the re~i~tered traden~mes of "Inconel" and "Ha~slloy". A preferred high-temperature resistant coat~ng 53 is applied to both inner surface 55 and an outer 6urface 57 of leg6 30 ~nd 32 of flange 29 to avoid 6urface irregularltie6 and to provide a low coefficient of friction. Preferred coating6 include polytetrafluoroethene, sold under the regi6tered tradename Teflon, snd tung6ten disulfide. A smooth low-friction surface is preferred to permit ~pring energized seal 34 and retaining ring 40 to alter their po~itions as requ~red to as6ure proper deformation under load.
Ring 40 ifi preferably formed from a compo6ite powdered metal and include6 a high strength material zone 54 sandwiched between two outer relatively soft material zones 56.
Havlng soft material 70nes 56 at the outer vertical ex~remlties of ring 40 improve~ the ring's deformability under initial loading condit~ons. Each of the 70nes extend6 radially acrogs the ring from face 51 to face 46. Thi6 a~pect of the ring design i6 particularly important with high strength material ~one 54, which provides much of the needed hoop strength. To provide this strength, high strength material zone 54 i6 thicker than corre6ponding zones 56. ~igh strength material zone 54 preferably ha6 a porosity of approximately 0 percent and relatively soft material zones 56 have a poro6ity between 3 ~nd 60 percent and preferably between 15 and 30 percent poro6ity.
As a result, ring 40 i6 imper0eable to combu6tion ga6es.
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3489 VIC (60,680-uS5 2~1~9~9 The inventive multiple density zones provide numerou6 advantages, including the ability to vary the design strength6 of the riDg in both the vertical ~nd hoop directions.
A material yield strength for retaining ring 4ű along the vertical axis preferably has a range between 10 and 120 kpsi;
more preferably between 25 and 43 kpsi. A most preferred value is approximately 25 kpsi. This strength value provides a good secondary combustion seal around the circumference of re~aining ring 40. At the 6ame time, however, it iB preferable to have a yield strength along the hoop axi6 of between lOű and 200 kpsi, and more preferably between 100 and 160 kp6i. A 00st preferred value i6 approximately 160 kpsi to ensure that the retaining ring can withstand high internal cylinder pressures produced during engine operation, as well afi the pressures exerted upon ring 40 by sprlng energized combustion seal 34.
Another advantage of using multiple den6ity zones is that a variable spring rate may be more readily designed into the ring. Also, the stiffness along any 6elected axis may be varied as a function of retaining ring loading. Becau6e of the convex top and bottom surfaces, initial assembly will result in point loading and local yield~ng of the retaining ring. Thi6 yielding will provide ring deformability to ensure a good initial seal around the circumference of the ring.
The variable 6pring rate may also be used to reŠtrict further yielding. For example, a~ the vertlcal load is increased, ring 40 can be made to become stiffer, resi6ting thermal cruŠhing while still providing a de6irable combu6tion 6eal in a manner similar to that of a yieldable seal ring. The additional stiffness reduces the likelihood of plastic deformation, allowing the ring to recover its Šhape as a funct~on of the Modulu~ of Elasticity.
Referring now to Figure 3, a ~econd embodiment annular retaining ring 60 includes a multiple layer laminate ., : , ., ~ : . .
3489 VIC (60,68~-J55 ~-21159~
with a plurality of high strength material ~one6 62 alternating with a plurality of relatively 60ft material zones 64. A6 in the first embodiment, it i6 preferred that zone6 62 and 64 extend radially from a face 66 at a radially inner extremity to a face 68 at a radially outer extremity of se~sl 60. Agaln, a relatively soft material zone iB located at each vertical extremity 70 and 72 to assure the ring's deformabllity uDder initial loading conditions. The shape of ring 60 i8 similar to that of ring 40. ~owever, in ehe embodiment shown, face 66 does not i~clude a groove.
Preferably, retaining rings 40 and 60 are formed from a powdered metal that primarily compri~es titanium. More preferably, the powdered metal includes between 2 and 6 percent alum~num, 1 and 6 percent vanadium, O.S and 4 percent iron nnd between 1 and 6 p~rcent molybdenum. The aluminum and ~anadium add to the titanium'~ ~tructural strength. The combination of iron and molybdenum increase the strength of the powdered metal at high temperatures while simultaneously reducing the coefficient of friction of the composite metal at the retaining ring'~ outer surface. Mo6t of the iron and molybdenum react with the rest of the powder, but 60me i6 depo6ited as a re6idue providing a lubricant. The lower coefficient of friction resulting from the lubricant is beneficial in overcoming the abrasive nature of pure titaaium. On the other hand, if too much iron is used, the resulting material may be too brittle, reducing the deformability of the reta~ning ring.
One method of manufacture include6 placing the compo6ite powdered metal in a graphite fixture whlch i8 then heated using known sintering technique6. The type of fixture u6ed and the method o~ heating can be controlled, as known to tho6e 6killed in the art, to re~ult in a 6eparation of the homogeneou6 powdered metal into desired material zones.
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9 21~9~9 Typically, a homogeneou6 compo6ite metal i8 placed in a fixture and heated at preselected temperature~ and times.
Although the di6clo6ed zone6 are preferably achieved from a homogeneous material, distlnct materlals may al60 be laminated together to achieve the hard and 60ft zones.
Preferred embodiments of the present invention have been described. It `18 to be understood that var~at~on~ and modification~ may be employed without departing from the scope of the pre6ent lnvention. Accordlngly, the follow~ng claim6 should be 6tudied to determ~ne the true ~cope of the pre6ent invention.