US3899272A

US3899272A - Rotary mechanism having apex seals with low contact pressure

Info

Publication number: US3899272A
Application number: US469594A
Authority: US
Inventors: Winthrop B Pratt
Original assignee: Curtiss Wright Corp
Current assignee: Rotary Power International Inc
Priority date: 1974-05-13
Filing date: 1974-05-13
Publication date: 1975-08-12
Anticipated expiration: 1992-08-12
Also published as: CA1022078A

Abstract

A rotary mechanism of trochoidal type, having means for limiting the gas pressure under the apex seals which urges the seals radially outwardly against the trochoidal running surface. Excessive outward pressure results in undue wear of the seals and the trochoidal surface, and in this invention the underseal gas pressure is restricted by a seal assembly which is responsive to chamber pressures of the engine.

Description

United States Patent 1191 Pratt Aug. 12, 1975 [54] ROTARY MECHANISM HAVING APEX 3,253,581 5/1966 Nallinger 418/113 SEALS WITH LOW CONTACT PRESSURE 3,369,528 2/1968 lrgens 418/61 A 3,551,080 12/1970 Feller 418/61 A 1 lnventorl Winthrop Pratt, North Haledon, 3,794,450 2/1974 Klomp 418/122 NJ. [73] Assignee: Curtiss-Wright Corporation, Primary Examinerc Husar wood Ridge, Ni Attorney, Agent, or firm-Raymond P. Wallace;

Victor D. Behn [22] Filed: May 13, 1974 [21] Appl. No.: 469,594 [57] ABSTRACT A rotary mechanism of trochoidal type, having means 52 US. Cl. 418/113; 418/123- 418/61 A for limiting the gas Pressure under the apex seals 51 Int. c1. FOIC 19/02 which urges the Seals radially outwardly ageingt the [58] Field of Search 418/111 122 123 61 A trochoidal running surface. Excessive outward pressure results in undue wear of the seals and the trochoi- [56] References Cited dal surface, and in this invention the undersea] gas pressure is restricted by a seal assembly which is re- UNITED STATES PATENTS sponsive to chamber pressures of the engine. 3.03.3,180 5/1962 Bentele 418/123 3,127,095 3/1964 Froede 418/122 8 m 6 Drawing g r is 32 1O 32 31c. s4 19 to BACKGROUND OF THE INVENTION This invention relates to rotary mechanisms of trochoidal type having a multi-apexed rotor with a sealing strip at each apex thereof sweeping a sealing surface, and more particularly to means for reducing and controlling the gas pressure under the apex seals.

In rotary mechanisms of the trochoidal type each apex of the rotor has a slot of appropriate radial depth and extending from side to side of the rotor in the longitudinal direction parallel to the axis of rotation. In each such slot is disposed a seal strip with one edge presented generally radially to the inner trochoidal surface of the peripheral housing shell, the other edge being retained in the slot with a spring between the inner edge and slot bottom urging the seal strip radially outwardly. Because of necessary clearance between the seal strip and the walls of its slot, gas pressure from the operating chamber on one side or the other of the seal enters the slot, and acting on the inner edge of the seal also urges it outwardly.

During the larger part of the seal travel along the trochoidal surface, centrifugal forces also urge the seals radially outwardly. However, when the seal is moving in the region of the cusps of the trochoid the direction of centrifugal force reverses and tends to urge the seal inwardly. The combined forces of spring pressure and gas pressure under the seal must be sufficient to oppose the inward urging of centrifugal force and hold the seal in contact with the trochoidal surface. Therefore, at such times as centrifugal force is outwardly directed the total force exerted on the seals may be excessively large, which causes rapid wear of the seals themselves and also of the trochoidal shell surface.

Various expedients have been suggested in the prior art to control the outward thrust of the apex seals, such as systems of flyweights and counterbalancing responsive to centrifugal throw, which are intended to restrain or retract the apex seals from outward movement as outward centrifugal thrust increases. However, the seal strips are small and very light in weight in comparison to the other parts of the mechanism, and such counterbalancing systems require a number of parts which are delicate, require precise calculation and manufacture, are difficult to adjust, and very expensive to produce and assemble. The present invention overcomes these prior art difficulties of multiple parts, delicacy of manufacture, and expensive production and assembly.

SUMMARY This invention provides a rotary mechanism of trochoidal type wherein the sealing means is responsive to pressure in the operating chambers to restrict and control the gas pressure under the apex seals to a moderate amount sufficient for good sealing action. The seal as sembly at each rotor apex is constructed to react to the higher chamber pressure on either side of the sea] as it alternates in operation, closing the clearance between the seal and its slot and channeling a small amount of high pressure gas to the under side of the seal.

It is an object of this invention to provide a rotary Combustion engine having improved sealing means.

It is another object to provide such an engine in which the apex seals have low contact pressure against the running surface of the peripheral housing.

A further object is to provide apex sealing means responsive to gas pressures in the operating chambers to restrict and control seal pressure against the peripheral shell.

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

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a two-lobed rotary mechanism with one side plate removed;

FIG. 2 is an enlarged view of the apex sealing means;

FIG. 3 is a fragmentary section taken on line 3-3 of FIG. 2;

FIG. 4 is an enlarged cross-section taken on line 44 of FIG. 1',

FIG. 5 is a perspective view of a portion of the apex sealing means; and

FIG. 6 is a similar view of a modification of the device shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be described principally in terms of a rotary internal combustion engine, but it is to be understood that it is equally applicable to such other trochoidal mechanisms as expansion engines, pumps, and compressors.

In FIGS. 1 and 4 there is shown a rotary combustion engine 11 having a peripheral housing shell 12 with a multi-lobed generally trochoidal inner surface 13; although shown with two lobes, the shell 12 may have any number of lobes. The shell is closed by a pair of side plates 14, of which only the rearmost is shown in FIG. 1. A shaft 16 is journaled by the side walls coaxial with the shell and has an eccentric portion 17 within the housing, on which is rotatably mounted a rotor 18 which defines with the housing a plurality of operating chambers 19 of variable volume.

As shown, the rotor 18 has three apex portions 21, but the number of apex portions will vary in accordance with the number of lobes of the epitrochoid; that is, the rotor will have one more apex portion then the number of lobes of the peripheral shell, two apex portions for a single lobe, four apex portions for three lobes, etc. Each apex portion carries sealing means 22 which effects sealing between the rotor apexes and the inner trochoidal surface 13 of the shell, and serves to keep the chambers 19 separate from each other. Gas sealing between the sides of the rotor and the side walls 14 is provided by side seals 10 carried in grooves on the sides of the rotor and near the periphery thereof. At least one oil seal ring 15 is carried by the rotor radially inward from the side gas seals.

Inlet port means is provided, which may be either the peripheral port 23 through the shell, or the side port 24 through one or both side walls, or any combination of such. Outlet port means 26 is also provided, which may be through any of the housing walls. The angular location, size, and shape of such ports may vary according to the design of the particular mechanism. When the device is a combination engine, ignition means or fuel injection means indicated by the lightning arrow 27 is provided in the compression region, generally opposite to the inlet and outlet region.

The apex sealing means 22 is shown much enlarged in FIG. 2, and positioned in its operating environment in FIG. 4. Each apex portion 21 of the rotor has acylindrical bore 28 therethrough in the axial direction from one side to the other of the rotor. A seal slot 29 in the rotor apex communicates with bore 28 and extends radially therefrom to the rotor apex, the seal slot 29 also extending axially the full width of the rotor. Disposed within bore 28 are a plurality of elements which collectively comprise a multipart generally cylindrical seal pin 31 (best shown in FIG.

The composite seal pin 31 is divided longitudinally and transversely, resulting in the four

parts

31a, 31b, 31c, and 31d shown in FIG. 5. The diameter of the seal pin is slightly less than the diameter of the bore 28 in which it is disposed. Considered as a whole, the multipart seal pin 31 has an axial slot 32 of the same transverse width as slot 29 in the rotor apex, and receiving the radially inward edge of apex seal strip 33, which extends further outwardly in the radial direction through slot 29 and makes sliding contact with the trochoidal inner surface 13. A spring 34 is positioned in the seal pin slot 32 under the seal strip 33 to urge it radially outwardly. The longitudinal division of the seal pin 31 is along the median plane of slot 32, so that when the pin is positioned within its bore with the two sides of its slot parallel, the bottom of slot 32 is closed and flat. In effect, when the elements of the sealing system are assembled in the rotor apex, slot 29 in the rotor and slot 32 in the seal pin comprise a single apex seal slot.

The conditions of the operating cycle of a trochoidal mechanism are such that pressures on opposite sides of an apex seal differ according to which portion of the cycle is being performed in the adjacent chambers. In a combustion engine, at the rotor position shown in FIG. 1 the chamber 19 at the top of the illustration has just fired, and the pressure therein is high. The chamber on the lefthand side is intaking fresh fuel and air mixture, and its pressure is therefore low. The righthand chamber is exhausting, and although open to atmosphere its pressure is still higher than that of the lefthand chamber, but lower than that of the chamber which is undergoing combustion.

For reasons of manufacturing tolerances and to accommodate thermal changes of dimension, the thickness of the apex seals is less than the width of their slots, so that they fit therein with a certain degree of looseness. Therefore the seals travel transversely from side to side of their slots toward the sides having lower pressure, and gas from the high pressure side can enter the rotor slot. Although in the prior art this high pressure gas entering the seal slot has been allowed to permeate under the seals and add its pressure to the radially outward urging of the springs, as set forth above this additional underseal pressure can sometimes be undesirable.

FIG. 2 shows the operation of the sealing means of this invention in controlling and limiting this underseal gas pressure. As shown, the high pressure chamber is at the right side of the figure. Because the diameter of pin 31 is less than that of its bore, gas pressure acts on the outer cylindrical surface of the pin and the half of the pin on the high pressure side rolls or tilts slightly within the bore so that the radially outer edge 36 of that half of the pin formed by

parts

31a and 31b tips against the plane face of apex seal 33 and prevents gas pressure from traveling inwardly along the side of the apex seal. In the operation of the mechanism, when the other side of the apex seal becomes the high pressure chamber in the next following portion of the cycle, the seal travels laterally across its slot and the corollary motion of the other half of the sealing pin, formed by parts 31c and 31d, occurs.

As is shown in FIGS. 4 and 5, pin 31 is divided transversely about midway of its length. In the gap 37 thus formed between the two end portions a generally horseshoe-shaped wave spring 38 is disposed, urging the two end portions axially outwardly against the side walls. The clearances shown in the drawings have been exaggerated for clarity of illustration. Through this gas 37 a small amount of high pressure gas bleeds into the underseal space to assist spring 34 in holding the apex seal against the trochoidal surface. The rollling motion of the tilted portion of pin 31 within its cylindrical bore is such that the bottom of the slot in the pin does not separate between right and left halves, but remains closed along the dividing line by the corner of the shoulder.

In order that the gas under the seal shall not build up to an undesirably high pressure a relief vent is provided. On at least one end face of pin 31 the corners of the bottom shoulder are chamfered or grooved at 39 along the radial dividing surfaces. The axial width of the rotor 18 is slightly less than the axial spacing between side walls 14 (best seen in FIG. 4) in order to provide suitable running clearances. There is thus a space 41 at each side of the rotor between the side gas seals 10 and the oil seal 15, so that the underseal gas bleeds through vent 39 into space 41. The relief groove 39 in the end face of the pin is axially a little deeper (shown in FIG. 3) than the nominal axial depth of space 41, so that even if the rotor should run more to one side or the other the underseal space remains in communication with space 41. Ordinarily a slight hub, thrust bearing, or other means (not shown) is provided to prevent the rotor from bearing directly against side walls 14. If desired, a vent 39 may be provided at each end face of pin 31.

The cross-sectional area of the vent means 39 is sized in proportion to the cross-section of gap 37 so that the underseal gas pressure shall not bleed off too rapidly and will always exert the desired amount of radially outward thrust against the apex seals, according to the design of the mechanism. Spaces 41 at the rotor sides are periodically vented to one of the ports, or by other convenient means.

In some engines or other trochoidal mechanisms, owing to small size of the parts or the presence of oil around the pins or to other factors, gas pressure may not readily enter the top portion of bore 28 to cause the high pressure side of the pin to tilt and press its sealing edge 36 against the apex seal. For this condition there is provided the modification of the seal pin shown in FIG. 6.

Seal pin 51 is formed of four parts, similar to those of the previously described embodiment, of which 51a and 510 are shown in FIG. 6. The top edges of each side are flatted off at 52 so that the sealing edges 36 are radially a little further inward than in pin 31. In the top quadrants of each side of the pin, grooves 53 are provided on its external diameter, running out at the cylindrical surface at one end and debouching into the flats 52 at the other end without interrupting the sealing edges 36. These grooves 53 provide gas entry to the external surface of the pin and allow the halves to tilt at appropriate portions of the cycle to present sealing edges 36 to the plane surfaces of the apex seals. The depth of grooves 53 need by only slight, and their number is not critical, although it is preferred that there be at least two such grooves in each piece of pin 51. If convenient, the gas-entry grooves 53 may be formed in the inner surface of bore 28 instead of on the sealing pin.

As shown in the present mechanism the side gas seals have their trailing ends butted against the circumference of the seal pin on its leading side. The leading ends of the side seals rest on shoulders 54 formed in the ends of the trailing halves of the seal pins. However, the mechanism may be designed to have both ends of the side gas seals butt against the pins, or both ends of the side seals resting on such shoulders. In either of the latter cases the leading and trailing halves of the seal pins are mirror images of each other.

Various elements of such trochoidal rotary mechanisms have been omitted from the drawings as not necessary to an understanding of the invention. Examples of such omissions are phasing gears for maintaining registration of the rotor within the housing lobes, certain bearings, passages within the rotor and the housing for cooling, and similar elements.

It will be apparent from the foregoing description that the present invention provides a trochoidal mechanism having apex sealing means which is automatically responsive to gas pressures within the operating chambers, restricting and controlling the amount of high pressure gas admitted to the underside of the apex seals and preventing build-up of high underseal pressures. Excessive wear of the apex seals and of the trochoidal running surface are thus prevented, and power is saved by reducing the high friction which would otherwise occur.

What is claimed is:

1. A rotary mechanism having a housing comprising a peripheral shell having an inner surface and a pair of side walls defining therein a rotor cavity, a shaft journaled by the side walls coaxially with the peripheral shell and having an eccentric portion within the cavity, a rotor having a plurality of apex portions and rotatably mounted on the shaft eccentric portion and defining with the housing a plurality of operating chambers of variable volume wherein gas pressure alternates between lower and higher pressures, wherein the improvement comprises:

a. each rotor apex portion having a radially disposed slot extending in the axial direction from one side of the rotor to the other;

b. a seal strip disposed within the slot and radially movable therein and sweeping the inner surface of the shell in sealing relation, there being an underseal space between the radially inner edge of the seal strip and the bottom of the slot;

0. each rotor apex portion having associated sealing means responsive to gas pressure to restrict entry of gas into the underseal slot space radially inward of the seal strip;

d. the associated sealing means comprising movable means disposed on each side of the apex seal strip and extending in the axial direction and of substantially the same length as the apex seal strip, each movable means having a sealing edge facing the apex seal strip and parallel therewith, the movable means on the side exposed to the operating chamber having higher pressure being responsive to gas pressure in said chamber to appose its sealing edge to the side of the apex seal strip to occlude the underseal space from entry of gas.

2. The combination recited in claim 1, wherein the sealing edge of the movable means is interrupted for a portion of its length to provide a channel for entry of a small amount of gas into the underseal space to provide underseal pressure urging the seal radially outwardly.

3. The combination recited in claim 2, wherein the underseal space is vented to prevent build-up of high pressure therein.

4. The combination recited in claim 1, wherein each apex portion has a bore therethrough from one side of the rotor to the other communicating with the slot in the rotor apex and radially inward therefrom, and the associated movable means comprises a multipart generally cylindrical pin disposed within the bore, the pin having in its radially outer portion a slot congruent with the rotor slot and receiving the radially inner edge of the apex seal and defining therewith the underseal space, the pin being divided into a leading half and a trailing half with the outermost edge of the slot portion in each half comprising the sealing edge, the half pin exposed to the chamber of higher pressure rotating within the bore in response to such pressure on its outer surface to appose its sealing edge to the leading face of the apex seal.

5. The combination recited in claim 4, wherein the generally cylindrical pin is divided across its diameter approximately midway between its ends, and a spring member is disposed between the two end portions urging them axially apart to form a midseal gap therebetween, the midseal gap forming an interruption of the sealing edges of the leading half and the trailing half for entry of gas from the chamber of higher pressure into the underseal space to urge the apex seal radially outwardly.

6. The combination recited in claim 5, wherein the axially outer face of at least one end portion of the generally cylindrical pin has a groove therein communicating with the underseal space to vent gas therefrom.

7. The combination recited in claim 4, wherein the multipart generally cylindrical pin has a plurality of gas-entry grooves formed in the radially outermost quadrant of the outer surface of the leading half and the trailing half to allow gas in the chamber of higher pressure to act on the outer surface of the pin to rotate it toward the seal.

8. The combination recited in claim 7, wherein a flat surface is formed on the radially outermost portions of the leading half and the trailing half of the multipart pin, and the gas-entry grooves have their orifices debouching in the flat surface without interrupting the sealing edges.

Claims

1. A rotary mechanism having a housing comprising a peripheral shell having an inner surface and a pair of side walls defining therein a rotor cavity, a shaft journaled by the side walls coaxially with the peripheral shell and having an eccentric portion within the cavity, a rotor having a plurality of apex portions and rotatably mounted on the shaft eccentric portion and defining with the housing a plurality of operating chambers of variable volume wherein gas pressure alternates between lower and higher pressures, wherein the improvement comprises: a. each rotor apex portion having a radially disposed slot extending in the axial direction from one side of the rotor to the other; b. a seal strip disposed within the slot and radially movable therein and sweeping the inner surface of the shell in sealing relation, there being an underseal space between the radially inner edge of the seal strip and the bottom of the slot; c. each rotor apex portion having associated sealing means responsive to gas pressure to restrict entry of gas into the underseal slot space radially inward of the seal strip; d. the associated sealing means comprising movable means disposed on each side of the apex seal strip and extending in the axial direction and of substantially the same length as the apex seal strip, each movable means having a sealing edge facing the apex seal strip and parallel therewith, the movable means on the side exposed to the operating chamber having higher pressure being responsive to gas pressure in said chamber to appose its sealing edge to the side of the apex seal strip to occlude the underseal space from entry of gas.