US3782869A

US3782869A - Oil seal construction for rotary engines

Info

Publication number: US3782869A
Application number: US00281765A
Authority: US
Inventors: J Steinwart; A Bauder
Original assignee: Audi AG
Current assignee: Audi AG
Priority date: 1971-09-06
Filing date: 1972-08-18
Publication date: 1974-01-01
Anticipated expiration: 1991-01-01
Also published as: DE2144497A1; FR2152126A5; IT964019B; JPS4872505A; JPS5440688B2; GB1342215A; DE2144497B2

Abstract

A double annular oil seal disposed between the rotor and the side wall of a trochoidal rotary engine, with provision for cooling the oil seal assembly.

Description

United States Patent [i Steinwart et al. 1

[ Jan. 1, 1974 OIL SEAL CONSTRUCTION FOR ROTARY ENGINES [75] Inventors: Johannes Steinwart, Bad [56] References Cited Friedrichshall; Armin Bauder, UNITED STATES PATENTS Neckarsulm of Germany 3,400,939 9/1968 Jones 123/845 x 1 Assignees= 2:] a g" k I FOREIGN PATENTS OR APPLICATIONS lengese sc a ec arsu m;

. 1,167,078 10/1969 Great Brltam 418/142 1,333,377 6/1963 France 418/142 1221 Filed: Aug. 18, 1972 Primary Examiner-C1. Husar Assistant Examiner -LeOnard Smith 2 A l PP No 281,765 Attorney-Raymond P. Wallace et al.

[30] Foreign Application Priority Data [57] ABSTRACT Sept 11971 Germany P 21 44 497'3 A double annular oil seal disposed between the rotor V and the side wall of a trochoidal rotary engine, with provision for cooling the oil seal assembly [58] Field of Search 418/142; l23/8.0l; 7 Claims, 3 Drawing Figures I I l/ l/ V ji 1 1-10 -----L.L l. n.1,;-

7 i i 7 2 l 1' i \\\\q 2 a 1 l0 5 l 1 1 Z i 1 4 2a PATENTED JAN 1 SHEEI 2 BF 3 PATENIED 3.782.869

sum a 0i 3 OIL SEAL CONSTRUCTION FOR ROTARY ENGINES BACKGROUND OF THE INVENTION This invention relates to rotary internal combustion engines, and more particularly to engines of the trochoidal type. Such an engine comprises a housing having a peripheral wall with a generally trochoidal multilobed inner surface and a pair of parallel side walls, the housing having inlet and outlet ports and defining an engine cavity, a shaft transpiercing the side walls and having an eccentric portion disposed within the cavity, a multiapexed rotor of generally polygonal profile rotatably mounted on the eccentric with its apexes sweeping the inner peripheral surface, and appropriate sealing elements at the apexes and sides of the rotor.

The rotor commonly bears in an annular groove on each side at least one oil seal ring surrounding the eccentric and sealing against the adjacent side wall to prevent leakage of oil from the bearings into the working chambers. An example of such a seal, having either one or two scraping surfaces, is shown in U. S. Pat. No. 3,179,331. The seal ring shown there however, is too rigid to have sufficient resilience, either requiring a very delicate fit to assure contact with both the side wall and the rotor, which causes increased friction and perhaps binding when the parts are hot, or else elastomeric backings to provide resilience. The rotor has no provision for cooling.

A further development of the oil seal is shown in U. S. Pat. No. 3,171,590, showing an uncooled rotor having in an annular groove on each side either one or two seal rings resiliently urged against the side wall by elastomeric backings. It has been found that such seals become considerably heated by transfer of the heat absorbed by the rotor during the combustion cycle. Because of such heating the elastomeric backing may become brittle and lose its resilience, or even become sticky, or torn by the relative movement between the seal ring and the rotor.

Yet another example appears in U. S. Pat. No. 3,400,939, wherein the rotor is formed with internal cavities which are cooled by oil supplied through a bore in the shaft. There are two concentric oil seal rings, pressed by Belleville springs against the side wall. Nevertheless, an elastomeric O-ring is still required around the periphery of the outermost seal ring in order to provide sealing between itself and the cylindrical wall of the groove in the rotor wall. Provision is made for venting the oil which collects between the two rings, partly to a collecting cavity in the side wall and partly through a passage to the interior of the rotor, which passage is slanted in the radially outward direction so that oil is impelled therethrough by centrifugal force into the rotor interior.

The disadvantage of such an arrangement is that the oil which contacts the seal rings is hot oil which has already passed through the rotor and extracted heat therefrom, and is then being returned to the oil cooler before being recirculated. This hot oil transfers a considerable heat load to the seal rings, again with the likelihood of damage to the elastomeric O-ring and possibly causing variation in the spring force of the Belleville springs.

Another disadvantage of internally cooled rotors of the prior art is that the rotor side wall extends radially inwardly nearly to the outer diameter of the eccentric,

in order that there may be sufficient space in the rotor wall for the annular grooves bearing the seals. This results in a relatively small central opening in the rotor side walls, making the casting of the rotor difficult an expensive, since the mold cores which form the interior cavities must be very thin in various places, rendering them fragile and easily broken.

SUMMARY OF THE INVENTION This invention solves the problems of the prior art by providing an oil seal which, instead of being washed by hot oil after discharge from the rotor, is continuously cooled by the rotor internal coolant before discharge from the interior of the rotor, thus maintaining the seals cooler and improving the durability of the sealing elements. Further, the invention provides a seal assembly such that it can be applied to the rotor, thus eliminating the previous annular grooves in the rotor side walls and allowing its central opening to be made very large, almost out to the rotor periphery. This provides greater access to the interior of the rotor, making it possible to form the casting cores, which must extend through the central openings, much stronger and more stable, re ducing the expense of fabrication.

These results are accomplished by providing a support ring for the seal assembly which can be positioned within the large central opening of the rotor side wall, coaxially therewith, the support ring being mounted on the rotor hub surrounding the eccentric. The support ring is so formed as to provide communication between the seals and the rotor cavity, allowing the inner surfaces of the seals to be washed by the internal coolant within the cavity. Either a single oil sealing ring may be used, or a plurality of such rings concentrically disposed, and resilient flexible sealing elements are pro vided between the circumference of the outermost ring and the cylindrical wall of the rotor opening, and also between seal rings if more than one are used. In engines wherein indexing gears are used at one side of the rotor the ring gear mounted on the rotor may also serve as the support ring for the oil seal.

It is an object of this invention to provide a rotary combustion engine having a hollow internally cooled rotor with oil sealing means which is continuously cooled by the rotor internal coolant.

It is another object to provide for such an engine a rotor having internal cooling cavities which are easily accessible from the outside, thus making possible stronger and more stable casting cores for forming the rotor.

A further object is to provide such arotor having large central openings through the rotor side walls, in which openings oil sealing assemblies can be installed.

Other objects and advantages will become apparent on reading the following specification in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a transverse cross-section of a rotary internal combustion engine according to the invention, taken along line 1-1 of FIG. 2;

FIG. 2 is a cross-section along line 22 of FIG. 1 on an enlarged scale; and

FIG. 3 is a fragmentary section on a still larger scale of the portion of FIG. 2 within the circle A.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. 1 and 2 there is shown a rotary internal combustion engine of trochoidal design, having a housing comprising a peripheral wall 1 having a two-lobed inner surface 2, and side walls 3 and 4, which together define an engine cavity 5. A shaft 6 transpierces the side walls, being rotatably mounted therein on bearings 7, and has an eccentric portion 8 disposed within the engine cavity. A generally triangular rotor 9 is rotatably mounted on the eccentric on a bearing 10. The rotational speed of the rotor 9 is in a ratio of 1 3 relative to the rotational speed of the shaft 6. This ratio is maintained by indexing gears comprising a ring gear 11 fastened to the rotor and in mesh with a pinion l2 borne by the side wall 3.

At each apex of the rotor there is disposed a radial apex seal 13, which apex seals sweep along the inner surface 2 of the peripheral housing, whereby there are formed three variable-volume combustion chambers 14. In the peripheral housing 1 there are provided an inlet channel 15 for fresh gas, a spark plug schematically indicated at 16, and an exhaust channel 17 for burned gases. The inlet and exhaust channels may be provided in one or both the side walls, however.

The rotor 9 has interconnected internal cavities 18 through which flows a cooling fluid. This coolant is supplied through an axial bore 19 in shaft 6, and is transmitted by means of transverse bores 20 to the shaft bearings 7 and through a transverse bore 21 in the eccentric to the rotor bearing 10. The cooling and lubricating medium emerges from the ends of bearing 10 and is thrown by centrifugal force into the individual cavities 18 in the rotor. Each rotor side wall 22 has a central circular opening 23 through which the cooling fluid emerges after it has flowed through cavities 18. The coolant is then conducted away through apertures 3a and 4a in the side walls 3 and 4 respectively.

In order to prevent the coolant from passing through the gap between the rotor side walls 22 and the adjacent housing side walls 3 and 4 and entering the operating chambers 14, the rotor is provided at each side with an annular seal assembly 24. As will be seen from FIG. 3 in particular, the seal assembly 24 shown by way of example has two

seal rings

25 and 26 of L-shaped cross-section, concentrically disposed and installed in the opening 23 of each side wall. The

seal rings

25 and 26 are axially displaceable, and are urged by a common annular wave spring 27 against the inner surface of the adjacent side wall. The annular wave spring 27 is supported and backed up by a ring 28, which is fastened to the rotor hub by screws 29, the screws passing entirely through the hub and being threaded into a similar ring on the other side of the rotor. In the example shown, the ring supporting the seals on the opposite side is the ring gear 11.

Sealing between the radially outer seal ring 25 and the cylindrical wall of the rotor opening 23 is effected by a seal element 30. The seal element 30 has a C- shaped cross-section, and may be formed, for example, of a thin-walled annular metal tube, slit along one side. Removing some of the metal along the slit, or opening it up, leaves a springy annular tube which through its inherent stress bears resiliently against the cylindrical wall of the opening 23 and against the axially extending leg of seal ring 25. A similar annular resilient seal elcment 3] is positioned between the two

seal rings

25 and 26. For the purpose of decreasing friction the

annular seal elements

30 and 31 may, if desired, be coated on the exterior with a suitable substance, for example polytetrafluoroethylene.

The supporting ring 28 defines, with the rear side of seal rings 25 and 26, an annular space 32 which is in communication with the internal cavities 18 of the rotor. In this way the gap 32 has coolant continuously flowing through it and good cooling is obtained for the seal rings and for the

flexible sealing elements

30 and 31. Consequently, instead of using annular tubing as shown, the

seal elements

30 and 31 may be made of rubber or a similar elastomer. The L-shaped crosssection of

rings

25 and 26, with the

seal elements

30 and 31 surrounding the axially extending leg, allows the coolant to arrive unhindered at

elements

30 and 31, and the axial legs of the seal rings. The radially extending legs of

rings

25 and 26 maintain the seal rings in their concentric position within the rotor opening 23. The seal rings may have flat faces against the side walls 3 and 4, but for better sealing the sealing faces preferably have a slight taper as shown in FIG. 3, leaving a scraping edge at the inner circumference of each ring. The inner circumference of the rings may also be coated with a harder material 37 than the main body of the ring, in order to provide a scraping edge which does not readily wear.

The seal-supporting ring 28 comprises generally a hub portion radially inside the seal rings and extending toward the engine side wall, and a flange portion extending radially outwardly from the hub portion on the side positioned toward the rotor interior. The flange portion has an annular groove 33 on the side facing the seal rings, in which groove is positioned an annular wave spring 27 which bears against the axially extending legs of both seal rings, urging them against the engine side wall. The flange portion of supporting ring 28 has at its periphery an annular web 34 extending toward the seal assembly, which web prevents sealing element 30 from moving toward the interior of the rotor. Web 34 has a plurality of cuts or slots 35 therethrough to maintain the gap 32 in communication with the rotor cavities 18. Sealing element 31 is maintained axially in position by the undulated wave spring 27, and coolant reaches element 31 through the undulations of the spring.

The hub portion of supporting ring 28 which is disposed radially inside the seal rings 25 and 26 is extended toward the housing side wall 4 slightly beyond the plane of the rotor side wall, thus providing a running surface against the wall for axial piloting of the rotor.

The seal assembly shown in FIG. 3 is disposed on the side of the rotor opposite the indexing gears 11 and 12. However, the seal assembly on the gear side is identical with that of FIG. 3 except that the support ring comprises the ring gear 11, and has internal gear teeth on its inner circumference in engagement with the external teeth of pinion gear 12 borne by the housing side wall 3. Ring gear 11 is mounted on the rotor 9 by the same screws which hold supporting ring 28, which screws pass through the rotor hub.

Positioning the seal assemblies 24 within the central openings 23 in the rotor side walls 22 not only has the advantage of enabling the seals to be continuously cooled from the rotor interior, but has the further advantage that openings 23 can be made quite large. The large diameter of these openings makes it possible to form the cores which serve in the fabrication of the rotor much more substantially, stronger and more stable than formerly. Because of the small radial extent of the side walls 22 of the rotor, the weight of the rotor is also decreased. Finally, the invention renders it possible to build rotary engines of the trochoidal type with a greater traverse angle than heretofore, because the space previously needed for the seal grooves in engines of the prior art is saved.

What is claimed is:

1., A rotary internal combustion engine having a housing comprising a peripheral wall having a multilobed inner surface and a pair of end walls defining an engine cavity, a shaft transpiercing the end walls and having an eccentric portion within the engine cavity, a multiapexed rotor rotatably mounted on the eccentric, the rotor having internal cavities through which a cooling medium flows and having side walls each having a central circular opening therein, wherein the improvement comprises:

a. a sealing assembly disposed at each side of the rotor and having at least one axially movable seal ring disposed in the rotor side wall opening on its associated side;

b. a resilient flexible annular sealing member comprising a thin-walled split tube disposed between the cylindrical wall of the rotor opening and the outer circumference of the seal ring in sealing relation to the seal ring and the cylindrical wall;

c. a supporting ring mounted on the rotor axially inwardly of the seal ring, and spring means disposed between the supporting ring and the seal ring and urging the seal ring against the adjacent housing side wall; and the supporting ring defining with the axially inward side of the seal ring an annular space in communication with the rotor internal cavities whereby the rotor cooling medium flows through the annular space to cool the sealing assembly, the axially inward side of the flexible annular sealing member being exposed to the cooling medium and washed thereby.

2. The combination recited in claim 1, wherein the supporting ring has in the side facing the seal ring an annular channel in which the spring means is disposed, the supporting ring having at its outer periphery an annular web extending toward the seal ring and defining the outer circumference of the annular spring channel, the web having a plurality of generally radial slots therethrough providing communication between the rotor internal cavities and the annular space between the supporting ring and the seal ring.

3. The combination recited in claim 2, wherein the supporting ring has a hub portion radially inward of the seal ring and concentric therewith, the hub extending toward the adjacent housing side wall beyond the plane of the rotor side wall to provide a running surface for axial piloting of the rotor.

4. The combination recited in claim 3, wherein the engine has rotor indexing gears comprising a ring gear mounted on one side of the rotor and a pinion gear surrounding the shaft and mounted on the adjacent housing side wall and in mesh with the ring gear, the ring gear also comprising the seal supporting ring on its respective side of the rotor.

5. The combination recited in claim 4, wherein the rotor has an internal hub portion and the supporting ring on each side of the rotor is mounted on the rotor hub portion by screws extending through one supporting ring and through the rotor hub and seating in the other supporting ring.

6. The combination recited in claim 5, wherein the seal ring is of generally L-shaped cross-section, the radial leg thereof cooperating in sealing relationship with the adjacent housing side wall, and the resilient annular sealing member is disposed between the axial leg and the cylindrical wall of the rotor opening.

7. The combination recited in claim 6, wherein there are two concentric seal rings, the spring means urges both seal rings against the adjacent housing side wall, and a second resilient flexible annular sealing member is disposed between the two seal rings in sealing relation to both.

Claims

1. A rotary internal combustion engine having a housing comprising a peripheral wall having a multilobed inner surface and a pair of end walls defining an engine cavity, a shaft transpiercing the end walls and having an eccentric portion within the engine cavity, a multiapexed rotor rotatably mounted on the eccentric, the rotor having internal cavities through which a cooling medium flows and having side walls each having a central circular opening therein, wherein the improvement comprises: a. a sealing assembly disposed at each side of the rotor and having at least one axially movable seal ring disposed in the rotor side wall opening on its associated side; b. a resilient flexible annular sealing member comprising a thin-walled split tube disposed between the cylindrical wall of the rotor opening and the outer circumference of the seal ring in sealing relation to the seal ring and the cylindrical wall; c. a supporting ring mounted on the rotor axially inwardly of the seal ring, and spring means disposed between the supporting ring and the seal ring and urging the seal riNg against the adjacent housing side wall; and d. the supporting ring defining with the axially inward side of the seal ring an annular space in communication with the rotor internal cavities whereby the rotor cooling medium flows through the annular space to cool the sealing assembly, the axially inward side of the flexible annular sealing member being exposed to the cooling medium and washed thereby.