US3712767A

US3712767A - Sealing arrangement for rotary combustion engine

Info

Publication number: US3712767A
Application number: US00145442A
Authority: US
Inventors: K Beutter
Original assignee: Audi AG
Current assignee: Audi AG
Priority date: 1970-06-03
Filing date: 1971-05-20
Publication date: 1973-01-23
Anticipated expiration: 1990-01-23
Also published as: DE2027115B2; DE2027115A1; JPS548802B1; FR2095816A5; GB1334605A; CA939272A

Abstract

A sealing arrangement for the apexes of the rotor of a rotary combustion engine, wherein the inner surface of the peripheral housing, the end walls, and the parts of the seal are of different graduated hardnesses, whereby the seal rapidly wears into a perfect fit and sealing engagement without danger of scoring or abrading the housing.

Description

Unite States Patent 1191 Beutter 1 Jan. 23, 1973 [541 SEALING ARRANGEMENT FOR ROTARY COMBUSTION ENGINE Karl Beutter, l-leilbronn, Germany Assignees: Audi NSU Auto Union Aktiengesellschatt, Neckarsulm; Wankel G.m.b.H., Lindau, Bodensee, Germany Filed: May 20, 1971 Appl. No.2 145,442

Inventor:

[30] Foreign Application Priority Data June 3, 1970 Germany ..P 20 27 115.2

US. Cl. ..418/l21, 418/122, 418/178, 418/179 Int. Cl ..F01c 19/02, F036 3/00, F046 27/00 Field 01 Search ..418/121, 122,178,179, 113,

[56] References Cited UNITED miss 1min;

3,554,677 1/1971 Zapf et a1. ..4l8/l78 3,263,912 8/1966 Frenzel ..41s 179' 3,281,064 10/1966 Springer ..41s 179 3,318,515 5/1967 Jones ..4l8/l78 3,608,535 9/1971 Winston et a1. ....41s 17s 3,394,877 7/1968 l-lantzsche et al. ..4l8/178 Primary ExaminerCarlton R. Croyle Assistant Examiner.lohn J. Vrablik Attorney-Raymond P. Wallace and Victor D. Behn [57] ABSTRACT A sealing arrangement for the apexes of the rotor of a rotary combustion engine, wherein the inner surface of the peripheral housing, the end walls, and the parts of the seal are of different graduated hardnesses, whereby the seal rapidly wears into a perfect tit and sealing engagement without danger of scoring or abrading the housing.

7 Claims, 2 Drawing Figures SEALING ARRANGEMENT FOR ROTARY COMBUSTION ENGINE BACKGROUND OF THE INVENTION This invention relates to an improved apex sealing means for the rotor of a rotary engine.

There is known in the prior art, as shown by U. S. Pat. No. 3,400,691, a three-piece apex seal for rotary engines, wherein there is a main seal piece of trapezoidal form and two triangular end pieces, the end pieces meeting the main piece along diagonal lines passing substantially through the radially outward corners of the assembly. The edge of the main piece sweeps along the surface of the peripheral housing and the edges of the end pieces slide on the inner faces of the side walls of the engine. The object of this arrangement is that the length of the main seal piece shall be accommodated between the side walls when the engine is cold, with the end pieces held radially and axially in contact along their sliding plane lines with the main piece. When the engine is hot and the length of the operating chamber expands, the end pieces are forced radially outward by their spring loading, and also longitudinally outward along the inclined planes, thus maintaining sealing contact with the side walls and at least in part filling the gaps at the comers of the main seal piece. If the axial spacing between the side walls varies from place to place in the periphery of the engine, as between a hot zone and a relatively cool zone, the triangular end seal pieces are squeezed in and out as the rotor turns.

The disadvantage of this arrangement is that at times when the axial spacing of the side walls is minimal, because of manufacturing tolerances the corners of the main seal piece may gouge the surface of the side walls, or the delicate corners of the seal are rapidly worn off, permanently enlarging the leakage gap at the corners. At other times, when axial spacing of the side walls is greater than the length of the seal members in their optimum position, the corners of the triangular end seal pieces may gouge the peripheral housing surface, or again, their delicate comers may be rapidly worn down, so that the corner gap is again enlarged. Also, these difficulties are not due solely to manufacturing tolerances and to varying engine conditions, but in addition they may arise from uneven wear of the seal parts owing to minute variations in hardness.

SUMMARY The present invention results in optimum sealing over a long period of time, and keeps as small as possible the wear of the inner surfaces of the housing and of the seal parts.

To achieve this result, the invention provides a threepiece seal assembly with a trapezoidal main part sweeping the peripheral housing, and a pair of end pieces likewise substantially trapezoidal in form, but having surfaces sweeping both a side wall and a portion of the peripheral housing, and mating with the main part along an inclined plane. Further, the inner surface of the peripheral housing is formed of a harder material than the inner faces of the side walls, and the middle piece of the seal assembly is formed of a harder material than the end pieces. By this means the wear of the individual parts is systematically correlated so as to maintain good sealing and fit throughout all engine conditions, as will be explained in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial cross-section of an engine, showing the hard facing of the peripheral housing and an apex seal assembly in place; and

FIG. 2 is a fragmentary cross-section showing the position of the seal parts at installation.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a rotary combustion engine 1 having a peripheral housing 2 and

side walls

3 and 4, which together define an internal cavity 5. A generally polygonal, multi-apexed rotor 6 is rotatably mounted within the cavity on an eccentric portion 7 of a shaft 8 which transpierces the end walls. The rotor 6 is provided at each apex with an axially-extending groove 9, in which is disposed an apex seal assembly 10, comprising a trapezoidal middle part 11 and two smaller trapezoidal end parts 12. The positioning of the seal parts is such that the longest edge of the middle part 1 1 sweeps along the inner peripheral surface 13, while the end parts 12 have their shortest edges sweeping the peripheral surface 13 and their end edges, at to their shortest edges, sweeping the inner faces 14 of the

side walls

3 and 4. The middle seal part and the end parts meet along sloping edges 16 disposed at an angle to the longitudinal axis of the shaft.

A leaf spring 15 is disposed in the groove 9 under the seal assembly, with its ends bearing against the undersides of the end parts 12 and urging them radially outward, whereby through the wedging action of the oblique abutment surfaces 16 between the middle part and the end parts there occurs a simultaneous pressing of the middle part 11 against the inner peripheral surface 13 and of the end parts 12 against the inner. faces 14 of the

side walls

3 and 4.

The peripheral housing 2 is provided with an inner coating layer 13 of hard material, as for instance a deposit of nickel containing a distribution of 2 to 8 percent silicon carbide particles having an average grain size of approximately 1 micron. This material is harder than the inner faces 14 of the side walls, which may be of nitrided hardened cast iron.

The middle part 1 l of the apex seal is harder than the end parts 12, the middle part having a Vickers hardness (l0 kilogram load) of at least 600 and preferably of more than 1,000, and the end pans having a hardness of 300 to 500.

The material for the middle part consists of an iron alloy containing at least 30 percent by weight of titani um carbide, and the end parts are formed of a cast iron alloy of the type used for piston rings. Nominal compositions for suitable alloy materials for the middle seal part areas follows.

EXAMPLE I Titanium carbide 34.5% Nickel 0.2 Carbon 0.55 Molybdenum 2.0 Chromium 6.5 Iron Balance EXAMPLE II Titanium carbide 33% Nickel 15 Molybdenum 5 Cobalt 9 Titanium 0.7

Aluminum 0.7 Copper 0.5 Iron Balance The Vickers hardness of the alloy of Example I amounts to approximately 1,030 to 1,090, and the hardness of the alloy of Example 11 amounts to approximately 700 to 750.

The material of the end parts of the seal strip may be a cast iron alloy having the nominal composition given below, with a Vickers hardness of approximately 350 to 450.

EXAMPLE III Carbon 3.4 3.8% Silicon 2.5 3.2 Molybdenum 0.8 1.3 Manganese Chromium Vanadium less than 1% each Copper Nickel lron Balance FIG. 2 shows the method of installing the seal assembly. At installation, only the end parts 12 are pressed by the spring against the inner peripheral surface 13, with the main seal piece 11 resting between them against the slanted edges 16. The gap between the main seal piece and the surface 13, however, is much exaggerated in the drawing for clarity of illustration. Because the end parts are formed of a relatively soft material compared to the inner peripheral surface, in operation their short edges rapidly wear down to the height of the middle part 11, so that after a short run-in period the condition shown in FIG. 1 is reached, in which the middle part and the end parts bear against the peripheral surface 13 across its entire width, while the end parts continue to maintain sealing abutment against the side walls.

With the arrangement described, and the proper hardness relations between the various parts, the seal assembly will continue to run true and maintain good sealing over a long period of time. The hard material of the main seal piece 11 wears very slowly, and the end parts 12 being softer they will always wear to at least the same amount and thus not protrude, with the danger of abrading the housing. Further, since the end parts have only a small bearing portion against the peripheral housing, the major part of seal wear is taken up by the center piece, and the end parts will not wear to a lower level and leave a gap.

What is claimed is:

l. A rotary internal combustion engine having a peripheral housing and a pair of side housings defining an internal cavity and a rotor rotatably mounted within the cavity, the rotor having a plurality of apex portions with a sealing arrangement positioned in a slot at each apex portion to sweep the inner surface of the peripheral housing and the inner faces of the side housings in sealing relationship, wherein the improvement comprises:

a. The inner peripheral surface being formed of a harder material than the inner faces of the side housings;

b. each sealing arrangement comprising a middle part and two end parts; the middle seal part being generally trapezoidal and having a longside disposed radially outwardly and sweeping t e inner peripheral surface, a

shorter side parallel with the long side and disposed radially inwardly, and two short ends slanting from the long side to the shorter side;

. the two end parts each being generally trapezoidal and having a short side disposed radially outwardly and sweeping the inner peripheral surface, a longer side parallel with the shorter side and disposed radially inwardly, one end perpendicular to the short side and to the long side and sweeping the adjacent side housing, and an opposite end slanting from the short side to the longer side and juxtaposed in mating relationship to the slanting end of the middle seal part in such a manner that the sealing assembly of the three seal parts has a generally rectangular outline;

. the middle seal part being formed of a harder material than the end seal parts but less hard than the inner peripheral surface of the housing;

f. the end seal parts being urged resiliently outwardly and exerting a wedging action outwardly against the middle seal part to maintain the radially outward edges of the three seal parts in sealing contactwith the inner peripheral surface with seal wear thereagainst being preferentially absorbed by the end seal parts.

2. The combination recited in claim 1, wherein the inner peripheral surface is formed of a layer of nickel having hard particles incorporated therein, the middle seal part consists of a material having a Vickers hardness of at least 600, and the seal end parts consist of a material having a Vickers hardness of at least 300.

3. The combination recited in claim 2, wherein the nickel layer has incorporated therein from 2 to 8 percent of silicon carbide particles having an average particle size of approximately 1 micron.

4. The combination recited in claim 3, wherein the middle seal part consists of an iron alloy containing at least 30 percent titanium carbide, and the end seal parts consist of piston-ring cast iron.

5. The combination recited in claim 4, wherein the end seal parts are formed of an alloy consisting of 3.4 to 3.8 percent carbon; 2.5 to 3.2 percent silicon; 0.8 to 1.3 percent molybdenum; less than 1 percent each of manganese, chromium, vanadium, copper, and nickel; and the balance iron, the alloy having a Vickers hardness of at least 350.

6. The combination recited in claim 5, wherein the middle seal part is formed of an alloy having the nominal composition of 34.5 percent titanium carbide, 0.2 percent nickel, 0.55 percent carbon, 2 percent molybdenum, 6.5 percent chromium, and the balance iron, the alloy having a Vickers hardness over 1,000.

7. The combination recited in claim 5, wherein the middle seal part is formed of an alloy having the nominal composition of 33 percent titanium carbide, 15 percent nickel, 5 percent molybdenum, 9 percent cobalt, 0.7 percent titanium, 0.7 percent aluminum, 0.5 percent copper, and the balance iron, the alloy having a l l 4 4' I

Claims

1. A rotary internal combustion engine having a peripheral housing and a pair of side housings defining an internal cavity and a rotor rotatably mounted within the cavity, the rotor having a plurality of apex portions with a sealing arrangement positioned in a slot at each apex portion to sweep the inner surface of the peripheral housing and the inner faces of the side housings in sealing relationship, wherein the improvement comprises: a. The inner peripheral surface being formed of a harder material than the inner faces of the side housings; b. each sealing arrangement comprising a middle part and two end parts; c. the middle seal part being generally trapezoidal and having a long side disposed radially outwardly and sweeping the inner peripheral surface, a shorter side parallel with the long side and disposed radially inwardly, and two short ends slanting from the long side to the shorter side; d. the two end parts each being generally trapezoidal and having a short side disposed radially outwardly and sweeping the inner peripheral surface, a longer side parallel with the shorter side and disposed radially inwardly, one end perpendicular to the short side and to the long side and sweeping the adjacent side housing, and an opposite end slanting from the short side to the longer side and juxtaposed in mating relationship to the slanting end of the middle seal part in such a manner that the sealing assembly of the three seal parts has a generally rectangular outline; e. the middle seal part being formed of a harder material than the end seal parts but less hard than the inner peripheral surface of the housing; f. the end seal parts being urged resiliently outwardly and exerting a wedging action outwardly against the middle seal part to maintain the radially outward edges of the three seal parts in sealing contact with the inner peripheral surface with seal wear thereagainst being preferentially absorbed by the end seal parts.

7. The combination recited in claim 5, wherein the middle seal part is formed of an alloy having the nominal composition of 33 percent titanium carbide, 15 percent nickel, 5 percent molybdenum, 9 percent cobalt, 0.7 percent titanium, 0.7 percent aluminum, 0.5 percent copper, and the balance iron, the alloy having a Vickers hardness of at least 700.