Tapered Seal for Engines or the Like

Technical Field

This invention relates to mechanisms such as engines, compressors, expanders, pumps, etc., whether reciprocating or rotary. More particularly, it re¬ lates to seals in such mechanisms.

Background Art

Many mechanisms of the type mentioned em- ploy so-called "gas energized seals" carried by pistons to isolate the high pressure, working volume from some other part of the mechanism to promote good sealing and thereby increase the efficiency of the mechanism. In the usual gas energized seal construc- tion, the seal is carried in a groove which is slightly wider than the seal so that the seal may laterally shift within the groove. High pressure gas on one side of the seal may thus act against a side of the seal to move the same laterally within the groove to provide an entry path for the gas to the bottom of the seal. The pressurized gas acting on the bottom of the seal provides a force which tends to push the seal out of the groove and into good sealing engage¬ ment with the wall of the operating chamber of the mechanism. At the same time, the gas under pressure acting against one side of the seal tends to firmly urge the seal against the opposite side of the groove to eliminate any leakage path at that point.

In many such mechanisms, the seal and groove geometry *Ls such that a far greater gas energizing force is applied to the seal than is required to achieve good sealing. As a consequence, seal wear is increased and scuffing of the wall of the operating

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chamber engaged by the seal is encountered at a rela¬ tively rapid rate. The ultimate result is a decrease in the useful life of the mechanism.

Exemplifying the prior art in the field of gas energized seals are U.S. Patent Nos. 2,466,389 issued April 5, 1949 to G. G. Davis; 3,139,233 issued June 30, 1964 to N.C. Simonsen; 3,357,412 issued December 12, 1967 to H. Sabet; 3,899,272 issued August 12, 1975 to W.B. Pratt; 3,966,368 and 3,999,906 issued June 29, 1976 and December 28, 1976, respec¬ tively, to A. Goloff; and British Specification No. 1,329,371, published September 5, 1973, issued to Daimler-Benz Aktiengesellschaft.

Disclosure of the Invention According to the present invention, there is provided, in a mechanism such as an engine, com¬ pressor, expander, pump, or the like, a housing de¬ fining an operating chamber. A piston is disposed within the housing and is mounted for movement therein. The piston has a first surface within the chamber which is adapted to be subjected to gas at elevated pressure and a second, adjacent surface, at least part of which is not subjected to gas at elevated pressure. A seal receiving groove is located within the piston second surface adjacent the part not subjected to gas at elevated pressure and has opposed side walls. One of the side walls is nearer the first surface of the piston and the other is nearer the part of the second surface not subjected to gas at elevated pressure. The latter side wall diverges away from the first mentioned side wall. A seal is ^Located within the groove and has a sealing surface sealingly engaging the housing. An opposed surface of the seal is disposed within the groove and a further surface interconnects the sealing sur¬ face and the opposed surface and faces the diverging

side wall and is adapted to substantially abut the same and seal against it. The seal is narrower at the opposed surface than at the sealing surface and further is sized to be somewhat laterally shiftable within the groove.

Because of the relative narrowness of the opposed surface of the seal versus the relative wide- ness of the sealing surface of the seal, forces at the point of sealing engagement of the seal with the operating chamber wall are reduced from the gas energizing forces applied to the opposed surface at least proportionally to the difference in widths of the two surfaces.

Brief Description of Drawings Other features and advantages will be under¬ stood by reference to the following specification taken in connection with the accompanying drawing in which:

Fig. 1 is a cross-sectional view of a rotary mechanism such as an engine, expander, com¬ pressor, pump or the like, and is more specifically, a slant axis rotary mechanism;

Fig. 2 is an enlarged, sectional view illus¬ trating the seal construction of the mechanism of Fig. 1;

Fig. 3 is a fragmentary, sectional view of a reciprocating mechanism; and

Fig 4 is an enlarged, sectional view of the seal construction of the mechanism of Fig. 3.

Best Modr for Carrying out the Invention

* An exemplary embodiment of a mechanism is illustrated in Fig. 1 in the form of a slant axis rotary mechanism of the four-cycle type which may be an engine, pump, compressor, expander, or the like.

However, the invention is not limited to slant axis rotary mechanisms but may be utilized with efficacy in trochoidal type rotary mechanisms or in recipro¬ cating mechanisms. With reference to Fig. 1, the mechanism includes a housing, generally designated 10, defining an operating chamber 12. The operating chamber 12 is delineated by a radially inner spherical wall 14, a radially outer spherical wall 16, and interconnecting, opposed, generally radially extending side walls 18. A shaft 20 is journalled within the housing 10, as by bearings 22, and within the operating chamber 12 includes an eccentric 24. The eccentric 24, by means of journal bearings 26 and thrust bearings 28, journals a rotor 30 for rotation and translation within the housing 10. The rotor 30 includes a gen¬ erally spherical hub 32 and a radially outwardly directed, peripheral flange 34. Opposed sides 36 of the flange 34 will be subjected to gas at elevated pressure at varying stages in the operating cycle of the mechanism.

The flange 34 includes an end surface 38 extending between the side surfaces 36, and peripher¬ ally about the end surface 38 are first and second seal receiving grooves 40 and 42. The grooves 40 and 42 receive seals 44 and 46, respectively, and that part 48 of the end surface 38 between the seals 44 and 46 will not be subjected to gas under pressure. In particular, one or more ports (not shown) will be disposed in the radially outer spherical surface 16 and at all times during operation of the mechanisms, the annular space between seals 44 and 46 and the part 48 "*όf the surface 38 as well as the radially outer spherical surface 16 will be in fluid communi- cation with such a port to vent the same to a pres- ^• sure less than that encountered by the surfaces 36.

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Within the operating chamber 12, a timing gear 50 is disposed and the same is in engagement with a ring gear 52 formed on one side of the hub 32 of the rotor 30 for the usual timing purpose. Referring now to Fig. 2 , the low pressure annular space mentioned previously is designated A, while the areas adjacent the seals 44 and 46 which receive gas under high pressure are designated B.

Each of the grooves 40 and 42 has opposed side walls 60 and 62. The side walls 60 are adjacent the high pressure side of the system, that is, nearer to the respective surfaces 36 while the side walls 62 are adjacent the part 48 of the surface 38 not subjected to the relatively high gaseous pressures. It will be observed that the surfaces 60 are generally perpendicular to the surface 38 and that the surfaces 62 diverge away from the surfaces 60 toward the part 48 of the surface 38.

The width of the grooves 40 and 42 at their narrowest parts is limited only by any requirement the mechanism might have for biasing springs, such as biasing springs 64, which ^" are operative to provide a small biasing force to the respective seals 44 and 46 to urge the same out of the respective grooves 40 and 42 into sealing engagement with the radially outer spherical wall 16. In most mechanisms, such biasing springs 64 are required to provide a nominal sealing force against the seals 44 and 46 at the initiation of operation of the mechanism and before high pressure gas is generated by operation thereof sufficient to gas energize the seals 44 and 46.

Conceivably, the sides 60 and 62 of the grooves*-40 and 42 could intersect at the bottom of the groove where biasing springs 64 are not required, reliance being placed on centrifugal force present

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during startup of the mechanism to throw the seals 44 and 46 outwardly and into sealing engagement with the surface 16.

Each seal 44 and 46 has a sealing surface 66 in sealing engagement with the radially outer spherical wall 16 and an opposed surface 68 within the associated groove 40 or 42 which is engaged by the biasing spring 64. An interconnecting surface 70 on each seal extends between the surfaces 66 and 68 and faces the groove wall 62 and is such as to be in substantial abutment therewith to seal against the same to prevent any gas within the groove 40 or 42 from escaping along the interface of the surface 70 and the groove wall 62. Finally, an opposite inter- connecting surface 72, on the high pressure side of each seal 44 and 46, also interconnects the surfaces 66 and 68.

It will be observed from Fig. 2 that the surface 68 of each seal is narrower than the surface 66.

Unit sealing pressure at the interface of the surface 66 and the wall 16 is reduced from the gas energizing pressure by the ratio of the widths of the surfaces 66 and 68. For example, referring to the seal 46, if it be assumed that the surface 66 thereof is twice the width of the surface 68, the force at the interface of the surface 66 and the wall 16 will be one-half of the force provided by gas energization (assuming spring force provided by the spring 64 can be neglected due to its relatively small value) , because the surface 68 subject to gas under pressure is only half as wide as the surface 66.

*- It will also be recognized that the seal 46 retains the advantage of so-called "Keystone" seal configurations in terms of not being prone to

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stick within the groove 42. Of course, greater re¬ duction in unit sealing pressure can be achieved by increasing the width of the surface 66 relative to the width of the surface 68 or decreasing the width of the latter relative to the width of the former.

In some instances, it is desired that the area of contact between the sealing surface 66 and the wall 16 be decreased to achieve better lubrication. In such a case, a plurality of reliefs 80 (only one of which is shown) may be provided in the surface 66 along the length of the seal, such as the seal 44 shown in Fig. 2. The reliefs 80 open to the high pressure side of the seal, that is, are formed jointly in the surface 66 at the surface 72. Assuming that the area of the surface 66 is reduced by one-fourth due to the presence of the re¬ liefs 80, then one-half of the gas energizing force applied to the surface 68 is counterbalanced by gas acting against the surface 82 of each relief 80 in bucking relation to gas acting against the surface 68. As a result, unit loading at the interface of the sur¬ face 66 and the wall 16 will be one-third of the unit gas energization pressure applied to the surface 66. By suitably configuring the reliefs 80 and appropriately adjusting the percentage of the sur¬ face 66 removed by the presence of the reliefs 80, greater or lesser reductions in gas energization can be achieved and, at the same time, provide a lesser sealing surface to promote a better oil film, as is known.

While the seal construction has been descri¬ bed in connection with so-called peripheral seals in a slant*axis rotary mechanism, it may also be utilized in hub seal constructions for such mechanisms as well as in end seal constructions in trόchoidal mechanisms.

The invention may also be used in recipro¬ cating mechanisms, as illustrated in Figs. 3 and 4. As seen in Fig. 3, the mechanism includes a housing, generally designated 100, including an operating or combustion chamber 102 in which a piston 104 is reciprocally received. The piston 104 has an end surface 106 adapted to be exposed to gases at ele¬ vated pressure and an adjoining cylindrical surface or skirt 108. The upper part 110 of the surface 108 will be subjected to gas at elevated pressure, while the lower portion 112 will not. The two are isolated by a seal 116 received in a peripheral groove 118 in the surface 108.

The seal 116 will be a so-called compression ring and the groove 118 has opposed sides 120 and 122. The side 120 diverges away from the side 122 and is adjacent the low pressure part 112 of the piston 104. The side 122 is generally transverse to the surface 108 and would be adjacent, or nearer to the surface 106 of the piston 104 subject to high pressure.

The seal 116 includes a sealing surface 126 which seals against the cylinder wall 128 of the operating chamber and an opposed surface 130. The sur¬ face 13Q is narrower than the surface 126, as seen. The low pressure side of the seal 116 is defined by a surface 132 interconnecting the surfaces 126 and 130 and which is adapted to be in substantial abutment with the wall 120 of the groove 118 to seal against the same. A further interconnecting surface 134 on the high pressure side of the seal 116 inter¬ connects the surfaces 126 and 130 and will generally be parallel to the groove wall 122. Finally, the seal ll ^' β will be sized so as to laterally shift within the groove 118 so as to enable gas from the high pressure side of the seal to enter the groove to act against the surface 130.

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Control over unit sealing pressure at the interface of the surface 126 and the wall 128 is achieved by suitably fashioning the widths of the surface 126 and 130, as mentioned previously. In a typical reciprocating mechanism, a compression seal will be a ring formed with a gap in it. Prior to installation, it will be slightly non- circular and have a greater "diameter" than the cylinder in which it is to be received. During installation, the ring is spread at the gap against its inherent resilience and placed on the piston to be received in a groove therein, at which time the ring is allowed to spring back to its original configuration.

When the piston with the ring thereon is in- stalled in the cylinder, the ring is compressed to narrow the gap. It is, of course, stressed at this time and tends to warp due to internal stress.

In the usual case, one edge of the contact or sealing surface will be in abutment with the cylin- der while the opposite edge will be spaced from the cylinder. Thus, the ring will make line contact with the wall of the cylinder rather than contact over the entire width of the sealing surface. This can result in increased oil consumption and high rates of wear.

In a piston ring made according to the pre¬ sent invention, the junction of the surfaces 126 and 134 would be the edge making such line contact. In order to avoid such line contact and the attendant disadvantages thereof, a ring made according to the present invention, when in its unstressed state, is provided with a slightly frusto-conical sealing sur¬ face 126^. Fig. 4 illustrates the configuration of the sealing surface 126 when in an unstressed state in dotted lines at 140. It will be appreciated that the surface 126, when unstressed, is defined by an

increasing buildup from a cylindrical surface from the high pressure side to the low pressure side of the ring 116.

From the foregoing, it will be appreciated that seals can be fabricated to achieve gas energized seals with virtually any desired unit loading at the interface of the seal and the operating chamber, which unit loading will be just sufficient to achieve good sealing so that seal wear may be reduced and scuffing of the housing minimized to promote long life of the mechanism.