US3887307A

US3887307A - Rotary mechanism with die-cast trochoidal housing

Info

Publication number: US3887307A
Application number: US465477A
Authority: US
Inventors: Winthrop B Pratt
Original assignee: Curtiss Wright Corp
Current assignee: Rotary Power International Inc
Priority date: 1974-04-30
Filing date: 1974-04-30
Publication date: 1975-06-03
Anticipated expiration: 1992-06-03
Also published as: CA1035283A

Abstract

A rotary mechanism in which the generally trochoidal peripheral housing is die-cast to its final form and finish. The trochoidal running surface has a slight taper in the axial direction from one side to the other of the housing as a result of the draft angle necessary in the casting die, and the rotor and apex seals are constructed to accommodate such taper.

Description

United States Patent Pratt June 3, 1975 [54] ROTARY MECHANISM WITH DIE-CAST 3,206,109 9/1965 Paschke 418/61 A TROCHOIDAL HOUSING 3,259,114 7/1966 Gassmann 418/61 A [75] Inventor: Winthrop B. Pratt, North Haledon,

NJ. Primary Examiner-C J Husar Assistant Examiner-Leonard Smith [73] Assignee: Curtiss-Wright Corporation, P w

woodRidge NJ. Attorney, Agent, or trm Raymond allace [22] Filed: Apr. 30, 1974 21 Appl. No.: 465,477 [57] ABSTRACT A rotary mechanism in which the generally trochoidal 52 0.5. CI 418/61 A Peripheral housing is die-cast to its final form and 51 1m. (:1. F0lc 1/02 The trochoidal running Surface has a Slight p 5 Field of Search 413 1 A, 61 3; 23 45; in the axial direction from one side to the other of the 29/1564 R 1564 w housing as a result of the draft angle necessary in the casting die, and the rotor and apex seals are con- [56] References Ci d structed to accommodate such taper.

UNITED STATES PATENTS 7 Claims, 8 Drawing Figures 2,134,153 10/1938 Seyvertsen...1.................. 418/206 X ROTARY MECHANISM WITH DIE-CAST TROCHOIDAL HOUSING BACKGROUND OF THE INVENTION This invention relates to rotary mechanisms of the trochoidal type such as internal combustion engines, pumps, compressors, and expansion engines. Such devices have a housing including a peripheral shell of generally trochoidal internal profile, with a rotor disposed therein and sweeping the inner trochoidal surface in sealing relation and defining therewith chambers of variable volume. Devices of this type are well known in the prior art and are exemplified generally by US. Pat. No. 2,988,008 to Felix Wankel, issued June 13, I961, and US Pat. No. 2,988,065 to Felix Wankel and Ernst Hoeppner, issued June 13, 1961.

In the prior art the trochoidal peripheral shell has commonly been fabricated by conventional sand casting, and the inner surface then ground and honed to its final dimension and surface finish. It has not been possible to take advantage of the speed and low cost of diecasting processes, because of the necessary draft angle to remove the core from the internal curvature of the shell. Although a die-casting could be ground in the same way as a sand casting to render the longitudinal extent of the inner surface parallel to the shaft axis of the mechanism, such grinding exposes a porous underlayer which is typical with die-casting materials, leaving an exposed surface which is unsuitable without subsequent plating or other treatment. Such further processing would increase the cost and reduce production rate, and thus lose the advantage of die-casting.

It is also possible to fabricate a taper-free die-casting having a suitable inner surface as it comes from the die, by the transplant process disclosed in US. Pat. No. 3,083,424 to Alfred F. Bauer, issued Apr. 2, 1963. In this procedure a mandrel of appropriate finish is given a coating of the metal which will form the surface of the completed part, the body of the part is then die-cast around the coated mandrel, and the mandrel then removed by differential expansion. However, this is again a slow process of high cost.

SUMMARY The present invention overcomes these difficulties of the prior art by providing a rotary mechanism of trochoidal type having a die-cast peripheral shell in which the inner surface has a minimal taper and a satisfactory finish direct from the die. The rotor and the apex sealing stripes may be given a matching taper, and the seal slots in the rotor apexes may be angled from parallelism with the shaft axis; or any single one of these expedients or any combination of them may be adopted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a view along the shaft axis, with one side plate removed, of a rotary mechanism constructed in accordance with the invention;

FIG. 2 is a cross-sectional elevation taken on line 22 of FIG. 1;

FIG. 3 is a fragmentary cross-section on an enlarged scale of a portion of a peripheral shell for such a mechanism;

FIG. 4 is a fragmentary view partly in section of a rotor apex portion;

FIG. 5 is a similar view of a slightly modified rotor apex portion;

FIG. 6 is a side elevation of an apex seal according to the invention;

FIG. 7 is a similar view of another embodiment of an apex seal; and

FIG. 8 is a similar view of a modification adaptable to the seals of either FIG. 6 or FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be described in terms of an internal combustion engine, but it is to be understood that with minor modification of the structure the invention may be used also as a pump, a compressor, or an expansion engine.

In FIGS. 1 and 2 there is shown a rotary mechanism 11 having a peripheral housing shell 12 with a multilobed generally trochoidal inner surface 13; although shown with two lobes, the shell 12 may have any desired number of lobes. The shell is closed by a pair of side plates 14. A shaft 16 is journaled by the side walls coaxial with the shell and bears an eccentric portion 17 within the housing on which is rotatably mounted a rotor 18 which defines with the housing a plurality of 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 than 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 21 has a longitudinally extending seal slot 22 in which is disposed a seal strip 23 extending between the side walls 14 and resiliently pressed into sealing relation with the trochoidal surface 13 by a spring 24.

One side wall 14 bears a fixed gear 26 projecting into the housing cavity and in engagement with a ring gear 27 borne by the rotor, either integral therewith or affixed thereto by any convenient means. These gears serve to maintain the rotor in registry with the housing shell during relative rotation of the two elements.

An intake port 28 and an exhaust port 29 are pro vided, which may be in the peripheral shell 12 as shown, or in one or both side walls 14. The angular location, size, and shape of such ports may vary according to the use of the mechanism. When it is an internal combustion engine, ignition means or fuel injection means indicated by the lighting arrow 31 is provided in the compression region, generally opposite to the intake and exhaust region.

As shown in FIG. 2, the inner trochoidal surface 13 of shell 12 tapers in the axial direction from one side to the other of the shell. When the shell is pressure diecast or cast in other types of permanent mold its inner surface is formed by a mandrel having an appropriate finish and forming a part of the assembled mold, and which must be subsequently pulled free from the casting. It is customary for such a mandrel to have a slight taper to aid in pulling it free, and it is pulled toward the side having the larger dimension, that is, the lefthand side as the shell is oriented in FIG. 2.

Although pressure die-casting in a ram-fed permanent mold is the preferred method of forming the shell, die-casting in other types of permanent mold is satisfactory, such as centrifugal casting, or casting in a gravityfed permanent mold wherein the necessary pressure is obtained from a head of molten metal in a reservoir. In any of these modes of die-casting the parts of the mold have a surface finish such that the shell may be used as cast. If desired, the inner surface of the shell may be polished subsequent to casting, without substantial removal of metal.

The taper shown in the drawings is much exaggerated for clarity of illustration. For peripheral shells having an axial dimension of the order of 1 inch, a taper of /z between the longitudinal axis and the inner surface is sufficient. A shell of this size would be appropriate for small internal combustion engines such as might be used in lawnmowers, portable power tools, motor cycles, or for other light duty purposes. Axial dimensions of the same order would also serve for rotary mechanisms used as small pumps, compressors, or expansion engines.

For peripheral shells of greater axial dimension the amount of taper of the mandrel may be increased appropriately. For an axial dimension of approximately 3 inches a taper of about l between the axis and the inner surface is suitable. For greater axial dimensions a taper of about 1- /2 may be employed, but it is more usual that large machines would be multi-rotor mechanisms.

Although the showing of FIGS. 1 and 2 does not indicate internal passages in the housing members for liquid cooling, such passages are commonly provided in conventional sand casting and can be quite readily provided by the die-casting mold. External fins for air cooling may also be provided, as shown in FIG. 3. A peripheral shell 120 has fins 32 extending outwardly from its exterior surface, the fins being oriented circumferentially as shown, axially, or in other convenient dispo sition. The angle of the taper of the inner surface 13 may be whatever is required for ready removal of the mandrel, from a fraction of a degree to about l- It may be intended to gage the nominal dimensions of the trochoid of a peripheral shell fabricated according to the invention from one side or the other of the shell, or from the axial midplane indicated by the centerline shown in FIG. 3. The mandrel will therefore be formed according to whichever gage point is to be used. That is, when the larger side of the trochoid is to be used as the gage dimension, the mandrel is tapered from its larger end to its smaller end at the selected angle. When the smaller side is to be gaged, the mandrel is tapered at the selected angle from its smaller end toward the larger end, and when the center of the shell is to be used for gaging the mandrel will taper therefrom in both directions.

The rotor 18 of the trochoidal mechanism may also be a die casting, and as shown in FIG. 2, it may be provided with a taper from one side to the other matching that of the peripheral shell, so that the rotor apex portions will be generally parallel to the inner trochoidal surface. The radially outer edge of the seal strip 23 carried in the slot 22 at each rotor apex 21 must sweep the inner peripheral surface 13 in sealing relation. The slot 22 which receives the radially inner edge of the seal strip also contains a spring 24 which urges the seal strip radially outwardlyjnto sealing contact. The slot 22 may be formed with its bottom parallel to the rotor axis, as shown in FIG. 4, and therefore the slot is radially deeper at the larger side of the rotor than at the smaller side. In this case, the seal strip 23 may be fabricated with a slightly trapezoidal profile, as shown in FIG. 6, with one end slightly wider in the radial direction than the other, and disposed in the slot with the wide end of the seal in the deeper portion of the slot, that is, at the larger side of the rotor, so that the radially outer sealing edge of the strip is parallel to the taper of the inner shell surface 13, and the radially inner edge of the strip is parallel to the slot bottom and to the rotor axis.

However, it may be convenient to form the rotor slots as shown in FIG. 5, wherein the slot 22a has its bottom sloped to be parallel with the inner shell surface, the slot therefore being of constant radial depth across the rotor. In that event the seal strip may be formed as shown in FIG. 7, wherein the apex seal 23a is generally rhomboidal in outline, and its two long sides will both be parallel to the slope of the inner surface 13, while the short sides remain parallel to the side walls 14.

In some instances it will be unnecessary to give any special geometry to the seal. As an example, when the longitudinal dimension of the peripheral shell is I inch and the taper is #2", the radius of the trochoid at its large end will be only 0.009 inch greater than at its smaller end. In such a case, a seal strip 23b of generally rectangular outline, either in a single piece or in two parts as shown in FIG. 8, may be used in the rotor slots of FIG. 4, since the spring 24 which urges the seal radially outwardly will cock it in the slot sufficiently to maintain sealing relation between the edge of the seal strip and the trochoidal inner surface 13. There may be a very trifling leakage at the seal corners because of its cocked position, but for many noncritical uses such an amount of leakage may be disregarded.

The rectangular seal 23b may also be used in the rotor slots of FIG. 5, where again there may be a very slight leakage because the ends of the seal will be out of parallelism with the end walls by an immaterial amount.

Seal member 23b is shown in FIG. 8 in two parts, with one generally triangular end separated from the major portion along a lined angled from the radially inner edge toward the outer corner of the seal, which angle serves as a wedging surface. Since the spring 24 presses by one end against the base of the small triangular piece, the wedging action urges both pieces axially outwardly as well as radially outwardly, to maintain sealing against the side walls 14. This modification may also be practiced with either of the seals shown in FIGS. 6 and 7.

In rotary mechanisms wherein the taper of the inner surface 13 is slight, it is unnecessary that the rotor be tapered. The bottom of the rotor slots may be parallel to the axis or slanted as in FIG. 5, and the seal strips may be of any of the forms shown in FIGS. 6-8. In such a case the normal resilient radial movement of the seals within their slots will be adequate to maintain sealing contact.

Various elements of such trochoidal mechanisms have been omitted from the drawings as not necessary to an understanding of the invention. Examples of such omissions are side Seals between the rotor and the side walls for oil and gas sealing, passages within the housing for cooling, attaching means for the ring gear when it is not an integral part of the rotor, and similar elements. Such elements will vary according to the use of the mechanism as an internal combustion engine, pump, compressor, or expansion engine, and are not a part of the invention herein disclosed, which exemplifies a mode of using inexpensive die castings adapted to high production rates for such mechanisms.

What is claimed is:

l. A rotary mechanism having a housing comprising a peripheral shell having a generally trochoidal 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 rotor cavity, a rotor of generally polygonal profile having a plurality of apex portions and rotatably mounted on the shaft eccentric portion, the rotor apex portions sweeping the inner trochoidal surface in sealing relation thereto, wherein the improvement comprises:

a. the peripheral shell being a die-cast member, the inner trochoidal surface thereof being tapered in the axial direction from the side adjacent one side wall to the side adjacent the opposite side wall, the amount of taper being from about 7& to about 1V2 and b. the rotor having at each apex portion sealing means sweeping the inner trochoidal surface of the peripheral shell, the sealing means comprising a slot having radial depth and axial extent in each rotor apex portion, and a sealing strip disposed in each slot with the radially outer edge of the sealing strip parallel to the tapered inner trochoidal surface and resiliently urged into sealing contact therewith.

2. The combination recited in claim 1, wherein the sealing strip has a greater radial dimension at its end in the region of the larger side of the trochoidal inner surface than at its other end.

3. The combination recited in claim 1, wherein the sealing strip has a generally rhomboidal profile, its radially inner edge is parallel to its radially outer edge, and its end edges are parallel to the side walls.

4. The combination recited in claim 1, wherein the strip has a generally rectangular profile.

5. The combination recited in claim 1, wherein the rotor is tapered in the axial direction from one side to the other and disposed within the cavity with its apex portions approximately parallel to the inner trochoidal surface.

6. The combination recited in claim 5, wherein the slot in each rotor apex portion has its bottom parallel to the rotor axis.

7. The combination recited in claim 5, wherein the slot in each rotor apex portion has its bottom approximately parallel to the inner trochoidal surface.

Claims

1. A rotary mechanism having a housing comprising a peripheral shell having a generally trochoidal 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 rotor cavity, a rotor of generally polygonal profile having a plurality of apex portions and rotatably mounted on the shaft eccentric portion, the rotor apex portions sweeping the inner trochoidal surface in sealing relation thereto, wherein the improvement comprises: a. the peripheral shell being a die-cast member, the inner trochoidal surface thereof being tapered in the axial direction from the side adjacent one side wall to the side adjacent the opposite side wall, the amount of taper being from about 1/2 * to about 1 1/2 * and b. the rotor having at each apex portion sealing means sweeping the inner trochoidal surface of the peripheral shell, the sealing means comprising a slot having radial depth and axial extent in each rotor apex portion, and a sealing strip disposed in each slot with the radially outer edge of the sealing strip parallel to the tapered inner trochoidal surface and resiliently urged into sealing contact therewith.