VALVE SEAL RETAINER

Abstract: A retainer for retaining a resilient annular oil seal element (31), surrounding the valve stem (23), to the valve guide (21) in an internal combustion engine includes an anchor sleeve (50, 50′, 50″) made from a polymeric material such as nylon, Teflon or the like, first retention means for retaining the sleeve to an outer surface of the valve guide, a tubular shell (38) surrounding the seal element, and retaining the seal element therein, and further retention means (48) for retaining the shell to the anchor sleeve. Preferably the first retention means comprises preselecting the diameter of an inner surface of the anchor sleeve (50, 50′, 50″) for interference fit with the outer surface of the valve guide (21).

Description: The present invention relates to valve seals for valves of internal combustion engines and, more particularly, to a valve seal retainer mechanism. Internal combustion engines typically have a plurality of reciprocating valves for permitting entry of the combustion mixture into, and exhaust of the combustion products out of, the cylinders. These valves have valve stems which slidably reciprocate within the valve guides - bores through the cylinder head of the engine. The valves are actuated in proper sequence by means of rocker arms, push rods, cams and the like, which are well-known in the art. There typically is provided a bath of oil surrounding the above components to minimise wear during operation of the engine. In particular, it has been found that a certain amount of oil must be allowed to work its way down between the valve stem and valve guides to provide lubrication and prevent excessive wear. However, it is undesirable to permit excessive quantities of oil to work down between the valve stems and guides since the oil will leak into the cylinder causing excessive oil usage by the engine and poor operating characteristics. Therefore, valve seals are typically provided which meter the amount of oil permitted to pass between the valve stems and the seals. These seals may be stamped from polytetrafluoroethylene, for example Teflon, and are typically positioned around the valve stems immediately above the valve guides. Because Teflon seals cannot be moulded to conform to the three-dimensional shape of the end of the valve guides, the the flat Teflon seals are held in place by deformable, metallic generally tubular retaining boots or shells such as those illustrated in US-A-3531134 which have retention means retaining the seal element within the shell and which secure the seals to the generally cylindrical outer surface of the outer wall or shoulder of the valve guides. Such boots are positioned telescopically over the valve guides and deformed to effect frictional engagement therewith. The engagement between the retaining boots and the outer surface of the valve guides should be tight to withstand the forces exerted by the reciprocating valve stems over a long period of time. It has been found, however, that the retaining boots of the type illustrated in the aforementioned US-A-3531134 may occasionally fail and pull off from the valve guide, rendering the seal ineffective. Because of such potential installation problems the valve seal retaining boot described in US-A-3531134 has found primary acceptance only in engine rebuilding operations where tolerances are closely controlled. Such boots have not found wide acceptance by engine manufacturers as original equipment because of excessive tolerance problems. This has been the case even though metallic retaining boots of this type, when properly fitted, are superior to other currently available retaining boots. An improvement to the boot described in US-A-3531134 is described in US-A-4502696 and is directed to the problem of valve guides varying within tolerances in their outside diameters. The latter patent describes a boot with at least two contiguous segments of progressively narrowing diameters. This, while being an improvement on prior metal boots, still has their problems. According to the present invention, an internal combustion engine has a valve stem which extends through a valve guide having a generally cylindrical outer surface, a resilient seal element surrounding the valve stem, a generally tubular shell retaining the seal element to the valve guide, and retention means retaining the seal element within the shell, and is characterised by a polymeric sleeve generally surrounding and frictionally engaging the outer surface of the valve guide providing first retention means retaining the sleeve on the said outer surface, and third retention means defined between a portion of the sleeve spaced from the bottom of the sleeve and the shell and retaining the shell to the sleeve the lower portion of the sleeve being free of constraint by the shell. A valve seal retainer according to the present invention provides increased retaining force on a valve guide outer surface in comparison to prior art retaining boots. A retainer according to the present invention provides such increased retaining force while accommodating valve guide walls having a wide diameter tolerance range. Accordingly, a valve seal retainer according to the present invention is capable of use by engine manufacturers with original equipment engines notwithstanding the dimension tolerance problem associated with such engines. The invention may be carried into practice in various ways but a number of valve seal assemblies constructed in accordance with the present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a central sectional elevational view of a valve assembly including a valve seal retainer according to the present invention; Fig. 2 is a sectional elevation view along the same plane as Fig. 1 illustrating the seal element and retainer in Fig. 1 assembled together without a mounting sleeve; Fig. 3 is a central sectional elevational view of a modification to the mounting sleeve in Fig. 2; Fig. 4 is a fragmentary central sectional elevational view of a further modification to the mounting sleeve in Fig. 2; Fig. 5 is a fragmentary sectional elevational view of a valve assembly including a first alternative embodiment of the invention; and Fig. 6 is a fragmentary sectional elevational view of a valve assembly including a second alternative embodiment of the invention. A representative overhead valve engine head 20 has a valve guide 21 formed therein as illustrated in Fig. 1. The valve guide 21 has a central opening 22 to reciprocatingly receive a valve stem 23. The top of the valve stem mounts a cap or plate 24 through which the upper end of the stem projects for engagement with a conventional rocker arm (not illustrated). Surrounding the valve stem 23 and compressed between the cap 24 and the engine head 20 is a spring 25. All of the preceding structure is conventional. Adjacent the upper end of the valve guide 21, surrounding the valve stem and located within the spring 25 is a valve seal assembly generally shown at 30. The valve seal assembly 30 includes a resilient annular seal element 31, a generally tubular boot or shell 38 surrounding element 31, retention means generally shown at 36 for retaining the seal element within the tubular shell, an anchor sleeve 50 surrounding and frictionally engaging the outer wall surface of the valve guide, and retention means generally shown at 48 for retaining the shell in engagement with sleeve 50. The annular seal element 31 has a flat peripheral portion 32 and a frusto-conical inner portion 33 inclined upwardly and inwardly toward the valve stem (Fig. 2). The upper edge of inner portion 33 terminates in a lip edge 34 which seats about and resiliently presses against the valve stem to act as a lubricant wiper. The seal element is made of a flexible, resilient material which is stable and not adversely affected by oil, gasoline, diesel fuel or similar hydrocarbons and also is capable of withstanding the high operating temperatures transmitted to it through both the valve stem 23 and guide 21. The selection of a material suitable for this purpose is within the knowledge of one skilled in the art to which this invention applies. The thickness of the seal element, its stiffness and the precise diameter of the opening through which the valve stem reciprocates should be such that the wiping action of the lip of the seal element will remove most of the lubricant applied to it while exposed in the valve chamber but will allow a very thin film to pass through sufficient to lubricate the stem as it reciprocates in the valve guide 21. Selection of these parameters is also within the knowledge of one skilled in the art to which this invention applies. The peripheral portion 32 of the seal element 31 is clamped between a relatively thin metallic upper washer 35a and a thicker metallic lower washer 35b. The washers 35a and 35b, with peripheral portion 32 of the element 31 pressed between them, are tightly clamped within the upper portion 37 of the tubular boot or shell 38, providing retention means generally shown at 36 for retaining the seal element within the shell. The shell 39 is formed from sheet steel and the retention means 36 may be provided by the shell wall being pressed or spun tightly around the peripheral edges of the washers and extended radially under the lower washer 35b, forming a seat 39 beneath it. The retention means 36 further includes the upper edge of the shell 39 being rolled over the top of the upper washer 35a to form a flange 40 that cooperates with the seat 39 to press the washers together to positively clamp and hold the seal element 31. A lower neck portion 41 of the shell 38 has a lower edge that is turned radially outwardly to form a shallow outwardly extending lip 42. The anchor sleeve 50 has an inner surface including a lower portion 49 and an enlarged upper portion 51 which extends through an upper end thereof. The diameter of the lower surface portion 49 in the embodiment shown in Fig. 1 is preselected to provide an interference fit with the outer surface of the valve guide 21 providing retention means for retaining the anchor sleeve to the valve guide. The diameter of the upper surface portion 51 is approximately that of the outside diameter of the neck portion 41 of the shell 38. A circumferential channel 52 is formed in the upper portion 51 immediately above its lower extent. The purpose of the channel 52 is to snap-fit receive and retain the outwardly extending lip 42 when the neck of the shell is press fitted into the anchor sleeve. The lip 42 seated in the channel 52 forms the retaining means 48 for retaining the shell 38 to the anchor sleeve 50. In a known process for renewing the valves and valve guides in an engine, the outer surface of the valve guide is machined to a precise tolerance, eliminating the high friction surface characteristics of an unmachined sand casting. However, this machining may not be routinely performed on production engine heads in the factory. The result is that production engines may include an eccentricity of the valve stem opening with respect to the valve guide outer surface up to 0.25 mm (0.010 inches). To accommodate this eccentricity, the anchor sleeve may be modified to either of those illustrated in Figs. 3 and 4. In both versions of the modified anchor sleeve, the inside diameter of the lower wall portion 49 is increased through out most of its axial length to provide clearance with the valve guide. To provide retention means for retaining the anchor sleeve to the valve guide, an in-turned bead or lip is provided at the bottom end of the anchor sleeve. In the anchor sleeve 50' illustrated in Fig. 3, this takes the form of an internal bead 53 having a generally semicircular cross section. The inside diameter of the bead 53 is selected to provide an opening which will provide an interference fit with the valve guide outer surface but which will not cause the anchor sleeve to take a significant permanent set when the valve seal assembly is installed. The modified anchor sleeve 50' can accommodate a somewhat greater valve guide eccentricity tolerance because the bead can, and in fact does, roll slightly upwardly as the sleeve is installed. This roll will permit the sleeve to pass over a somewhat enlarged portion of a valve guide without the material reaching its elastic limit. Thus, the amount of dimensional interference that can be accommodated may exceed the approximate 0.125 mm (0.005 inch) limit that would likely be imposed on anchor sleeves of the embodiment illustrated in Fig. 1. However, forces acting to remove the anchor sleeve would not only have to overcome the normal grip exerted by the bead but also the additional resistance created by the bead as it is further stretched to roll back to its original shape. In the anchor sleeve 50" illustrated in Fig. 4, the lower wall portion 49 has an inwardly rolled and upwardly turned bottom lip 54. Because of its thinner wall construction, this lip construction does not have the stiffness, and thus initial resistance to deformation, of the bead 53 in Fig. 3. However, it develops very significant resistance to removal because it is rolled to a greater degree than the bead in Fig. 3 during installation. Both bead 53 and lip 54 facilitate installation by reducing the force necessary to press the sleeve onto the valve guide without reducing the resistance to removal of the sleeve. Bead 53 and lip 54 need not be at the extreme lowermost portion of the sleeve but may be spaced essentially anywhere along the lower surface portion 49 with the same result. Multiple beads or lips, vertically spaced in the sleeve, can be utilised to provide enhanced resistance to removal. The individual beads or lips may be made thinner in order to prevent excessive resistance to assembly of the sleeve to the valve guide. The anchor sleeve 50 is fabricated of a polymeric material capable of maintaining its physical and chemical properties at the temperature normally encountered in the valve chambers of reciprocating engines, particularly overhead valve engines, while being exposed to lubricating oil and normal automative hydrocarbon fuels and the additives contained in such fuels. A preferred material for this purpose is Viton, a fluorocarbon resin, sold by E.I. DuPont de Nemours. Other acceptable materials are natural nylon and virgin Teflon, such as DuPont's commercial quality Teflon. Nylon has the desirable characteristic of being capable of injection moulding while Teflon has somewhat superior physical characteristics but can be shaped into the anchor sleeve only by machining, which is a more expensive and hence less desirable procedure. It has been found that for many applications, the wall thickness of anchor sleeve 50 is preferably approximately 1.5 mm (0.060 of an inch). An anchor sleeve made from Viton Rubber having a 1.5 mm (0.060 inch) wall telescopically press fitted over a typical valve guide 21 of about 12.7 mm (0.50 inch) diameter will develop a maximum pull resistance when the diameter of the sleeve 50 is stretched approximately from 0.051 to 0.127 mm (0.002 to 0.005 of an inch) during installation. Stretching the diameter of the anchor sleeve from 0.051 to 0.127 mm (0.002 to 0.005 of an inch) subjects the sleeve to stress without causing any significant permanent set in the material. A sleeve 50 made alternatively from nylon has an approximate 0.51 mm (0.020 inch) diametrical stretch limit before it becomes overstretched and takes a significant permanent set. Fig. 5 illustrates a first alternative embodiment of the invention in which the retention means 148 for retaining a shell 138 to a sleeve 150 includes an inwardly turned lip 142 on lower neck portion 141 of the shell is engaged with an outwardly facing channel 152 formed in an upper portion of sleeve outer surface 145. This embodiment provides enhanced versatility of application because the portion 141 of the shell is not placed between the upper end portion of the valve guide and the anchor sleeve but rather fits outside the anchor sleeve. In a second alternative embodiment of the invention, illustrated in Fig. 6, a lower portion 241 of a shell 238 is formed with an annular detent 256 at its lower edge to provide an inwardly extending embossment 257 having a semicircular cross section. A mid-portion of an anchor sleeve 250 is provided with a corresponding annular recess 258 on its outer diameter to receive the surface of embossment 257 in order to provide retention means for retaining the shell to the sleeve. The upper portion of the anchor sleeve 250 has an upwardly inwardly tapering outer wall 260 to be received in the lower portion of the shell 238. On installation, the shell 238 is pressed downwardly along the wall 260 of the anchor sleeve 250 until the embossment 257 is received in the recess 258 to lock the shell 238 to the anchor sleeve. It will be recognised that the circumferential channel 52 and outwardly extending lip 42 may be replaced by suitable adhesive, capable of withstanding the high temperatures of the environment, as a means for retaining the shell to the anchor sleeve.

Claims: An internal combustion engine having a valve stem (23) which extends through a valve guide (21) having a generally cylindrical outer surface, a resilient seal element (31) surrounding the valve stem, a generally tubular shell (38) retaining the seal element to the valve guide, and retention means (48, 148) retaining the seal element (31) within the shell (38), characterised by a polymeric sleeve (50, 50', 50") generally surrounding and frictionally engaging the outer surface of the valve guide providing further retention means retaining the sleeve on the said outer surface, and third retention means defined between a portion of the sleeve spaced from the bottom of the sleeve and the shell and retaining the shell (38) to the sleeve (50, 50', 50"), the lower portion of the sleeve being free of constraint by the shell. An engine according to Claim 1 in which the sleeve is made of nylon or polytetrafluorethylene. An engine according to Claim 1 or claim 2 in which the sleeve (50, 50', 50") has an inner surface portion which is dimensioned less than the valve guide outer surface, providing an interference fit between the said sleeve inner surface and the said valve guide inner surface to constitute the further retention means. An engine according to claim 3 in which the sleeve (50, 50', 50") has a second inner surface greater in diameter than an outer surface of the shell (38) and a recess (52) in the said second surface and in which the third retention means comprises an outwardly directed lip (42) on the shell outer surface dimensioned for snap-fit retention in the said recess (52). An engine according to Claim 3 in which the sleeve (50, 50', 50") has a recess (258) in its outer surface and the third retention means includes an inwardly directed portion (257) of the shell inner surface dimensioned for snap-fit retention in the recess (258). An engine according to Claim 5 in which the inwardly directed portion (257) comprises an annular detent (256) forming an inwardly extending embossment (257) of semicircular cross section. An engine according to Claim 5 or Claim 6 in which the sleeve outer surface has a tapered portion (260) adjacent the recess (258) to guide the inwardly directed portion (257) into the recess. An engine according to any of Claims 3 to 7 in which the said first inner surface portion is substantially shorter than the length of the sleeve (50, 50', 50"). An engine according to any of Claims 3 to 8 in which the said first inner surface comprises an inwardly directed bead (53) having a generally semicircular surface. An engine according to any of Claims 3 to 8 in which the said first inner surface comprises an inwardly rolled, upwardly turned lip (54). An engine according to any of Claims 1 to 10 in which the retention means (48,148) retaining the seal element (31) within the shell (38) comprises a wall of the shell (50, 50', 50") having an upper portion formed radially inwardly to form a flange (40) over the seal element (31) and a lower portion (41) being necked down below the seal element to form an inwardly extending seat (39) whereby the valve element is clamped between the flange and the seat. An engine according to Claim 11 in which the retention means (48,148) retaining the seal element (31) within the shell (38) further includes a first rigid washer (35a) between the seal element (31) and the flange (40) and second rigid washer (35b) between the seal element (31) and the seat (39).

Inventors: KAMMERAAD, JAMES ALLEN
Applicants: K-LINE INDUSTRIES, INC.
Application year: 1988
Main classification: F01L3
IPC codes: F01L3