US3500797A - Reinforced rotary piston - Google Patents

Description

March 17, 1970 R. SCHEUFLER REINFORCED ROTARY PISTON 1 4v t FE mm mm fl e a S a DC "r e ISM h aw R w 3 Y B Filed April 25, 1967 ATTORNEYS.

March 17, 1970 R. SCHEUFLER 3,500,797

REINFORCED ROTARY PISTON Filed April 25, 1967 2 Sheets-Sheet 2 Inventor: ROLAND SCHEUFLER ATTORNEYS.

United States Patent 3,500,797 REINFORCED ROTARY PISTON Roland Scheufler, Neckarsulm, Wurttemberg, Germany,

assignor to Karl Schmidt G.m.b.H., Neckarsulm, Wurttemberg, Germany Filed Apr. 25, 1967, Ser. No. 633,478 Claims priority, application Germany, May 7, 1966, Sch 38,952 Int. Cl. F0211 53/00, 55/00; F16c 9/00 U.S. Cl. 123-8 12 Claims ABSTRACT OF THE DISCLOSURE A light metal bearing housing reinforced by embedded steel inserts to limit the effect of thermal expansion and contraction upon certain critical dimensions of the housing.

The present invention relates in general to the reinforcement of light metal rotary piston with embedded high strength metal inserts, and more particularly to the combination of a light metal rotary piston and a steel insert embedded within the housing light metal rotary piston to constrain the portion thereof which defines a critically dimensioned cylindrical surface against thermal strain deformation in excess of predetermined tolerance limits.

As is commonly known, the lighter metals such as aluminum, magnesium and their alloys have coeflicients of thermal expansion which are much greater than those of the heavy, high-strength metals, such as steel and various alloys thereof. Accordingly, for a given temperature range, a steel reinforcing insert which is embedded Within a light metal rotary piston, as for example by casting the piston around the reinforcing insert, will constrain the light metal of the piston against thermal strain def0rma tions in directions which depend upon the geometry of the insert in relation to the dimensions to be controlled.

For example, Where it is desired to hold the diameter of a housing bore, or the bore of a rotary piston within dimensional tolerances which would normally be exceeded by thermal strain deformations occurring over a given temperature range, such can be done in accordance with the invention by using an embedded steel insert in the form of a complete cylindrical shell, or a plurality of angularly spaced cylindrical shell segments, arranged :in concentric relation to the cylindrical surface defining the bore.

The invention is not necessarily restricted to controlling the dimensions of cylindrical light metal surfaces, but is also applicable to controlling the flatness of plane surfaces, as for example the lateral end faces of a light metal rotary piston. This can be done simply by providing embedded steel inserts which have projecting ribs extending transversely to the generating axis of the piston bore and/ or the cylindrical arc edge surfaces of a rotary piston.

It has already been proposed to embed steel rings into the housing of cast light-metal bearings, especially the bearings of internal combustion engines, such as crankshaft bearings or the bearings of the pistons of rotary internal combustion engines, for the purpose of preventing an enlargement of the bearing play in the hot running state and, preventing a reduction of bearing play in the very cold state.

The present invention, which has to do especially with the further improvement of light-metal bearings for rotary pistons, is direction to the special problem of making the bearing temperature-proof both in the radial direction and in the axial direction, i.e. assurance is to be provided that the hearings will retain their dimensions in all directions under the nfluence of temperature. Furthermore, the aim of the invention is not only to prevent thermal expansion,

3,500,797 Patented Mar. 17, 1970 but also to provide a means for influencing it in a certain, predetermined manner. This may be important, for example, in the case of the lateral surfaces of pistons in rotary internal combustion engines, or also generally in the case of light-metal bearings which have to be controlled in a certain manner when in operation under the influence of high temperatures.

To accomplish the purpose of the invention it is proposed to embed concentrically into the bearing housing when it is cast from light metal, solid or divided steel inserts in the form of hoops whose lateral margins are anchored to the bearing material. In this manner it is possible to influence or to prevent not only radial but also axial thermal expansion. The anchoring of the steel inserts of the invention to the bearing material can be accomplished by lateral flanges, by the provision of holes into which the bearing material penetrates when cast, by a dovetail-like design of the margin, or by other appropriate measures of the prior art. With reference to the invention let it be noted that a piston for a rotary internal combustion engine is directly comparable to a bearing housing, since at least one bearing is provided in its center. The invention makes it possible, for example, to make the flat sides of a Wankel rotor assume a wavy shape in operation by a merely section-wise anchoring of the steel insert or the inserted steel ring, as the case may be. In this manner, when the temperature rises, the anchored areas are held back while the unanchored areas between them can expand unhampered. However, a wavy shape on the sides of a piston to be used in rotary internal combustion engines is not generally desirable, since this impairs the lateral seal. The measure just described, however, can be applied advantageously in reverse for the purpose of keeping the sides entirely flat. In a rotary internal combustion engine piston different temperatures occur at the various points on its periphery, and it, according to the invention, only the high-temperature areas are anchored, it is possible to prevent their local expansions and to keep the lateral surfaces of the Wankel rotor flat. According to the invention, furthermore, the axial play of a bearing, such as that of a piston of a rotary internal combustion engine, can be made smaller from the beginning, eliminating the need for adaptation in operation.

In pistons of rotary internal combustion engines, especially precise bearings are important on account of the ditficulty of sealing olf the combustion chambers. For this purpose, a bearing of this kind has a plurality of tight areas which advantageously correspond in number to the number of principal points of stress that occur on the circumference, so as to achieve a mounting that is as free of play as possible. In the bearing manufacturing processes of the prior art, it is customary to create the necessary tight areas by additional working procedures. The invention makes it possible to eliminate these additional working procedures by dividing the steel rings of the invention into segments whose terminal areas are anchored in the material of the bearing housing. In this manner, when the temperature increases, an eccentric deformation of the originally circular bearing hole takes place, and in this manner the desired tight areas Within the bearing are created merely by the rising of the temperature. The tight areas occur at the points where the segments according to the invention are located. Since the tight areas are to be created prinpically in the areas of maximum stress on the piston of a rotary internal combustion engine, it is recommendable also to provide the segments accordingly in these areas. Lastly, a piston in a rotary internal combustion engine has the maximum temperatures on its outer periphery when in operation, since this is where the working surfaces are which are directly attacked by the hot combustion gases. The temperature decreases toward the center. For these reasons,

u a piston of this sort, which as already mentioned is comparable to a bearing housing, is made so as to have sides that are slightly curved or tapered in cross section in the cold state, so that flat lateral surfaces will be produced in operation on the basis of the temperature distribution. This problem, too, can be controlled or influenced by means of the inserts according to the invention.

It is, therefore, an object of the invention to provide a means for reinforcing a light metal rotary piston to maintain critical dimensions thereof within predetermined limits against the influence of thermal strain deformation.

Another object of the invention is to provide a light metal bearing housing which is reinforced against thermal strain deformation both radially and axially by an embedded steel insert.

A further object of the invention is to provide a reinforcing means which can be embedded within a light metal rotary piston to control the internal dimensions of its shaft bore and the flatness of its end faces.

Other and further objects and advantages of the invention will become apparent from the following detailed description and accompanying drawing in which:

FIG. 1 is a front view of a light metal rotary piston reinforced in accordance with a preferred embodiment of the invention.

FIG. 2 is a sectional view of the piston of FIG. 1 as taken along line 11-11 therein, and illustrating the arrangement and configuration of the reinforcing means.

FIG. 3 is a side view, partly in section, of a reinforcing member according to another embodiment of the invention, featuring dovetail portions for improved anchoring within a typical bearing housing (shown in phantom).

FIG. 4 is a side view, partly in section and taken similarly to FIG. 3, of a reinforcing member according to a further embodiment of the invention, featuring circular apertures for improved anchoring Within a typical bearing housing (shown in phantom).

FIG. 5 is a side view, partly in section, of a reinforcing member similar to that of FIG. 4 but provided with elongated slot apertures for anchoring purposes.

FIG. 6 is a front end view of a reinforcing member according to the invention and having transversely projecting ribs for axial dimension control purposes when embedded in a light metal bearing housing or the like.

FIG. 7 is a sectional view of the reinforcing member of FIG. 6 as taken along line VII-VII therein.

FIG. 8 is a side sectional view of a cylindrical shell reinforcing member according to the invention and having marginal flanges projecting radially outward and inward.

FIG. 9 is a side sectional view of a cylindrical shell reinforcing member similar to that of FIG. 8, but having only radially inward projecting marginal flanges.

FIG. 10 is a front sectional view of a rotary piston having segmental reinforcing members arranged in accordance with the invention.

FIG. 11 is a side sectional view of the rotary piston and reinforcing members shown in FIG. 10, as taken along line XIXI therein.

FIG. 12 is a front sectional view of another rotary piston having segmental reinforcing members arranged according to the invention.

FIG. 13 is a side sectional view of the rotary piston and reinforcing members shown in FIG. 12, as taken along line XIII-XIII therein.

Referring now to the several figures of the drawing, the invention essentially provides a high strength metal reinforcing means which is embedded within a light metal bearing housing and positioned in symmetrical relation to a cylindrical surface thereof to constrain the thermal strain deformation of the rotary piston in directions influencing the dimensions of such surface to maintain the surface dimensions within predetermined tolerance limits.

In general, the machine part can be in practically any form, as for example, a conventional bearing housing H, as in FIGS. 3, 4 and 5, or a rotary piston 1 of the type used in a Wankel engine, as in FIGS. 1, 2 and 10-13. The housing H or piston 1, as the case may be, is made of a light metal, such as aluminum, magnesium, or alloys thereof, and has a cylindrical surface, such as a bore B, the radial dimensions of which are to be controlled by the reinforcing means of the invention. Under certain applications, it may also be desirable to also provide the same type of dimensional control over the spacing, and/ or flatness of the lateral end faces F of the piston 1 or the end faces F of the housing H, which can be done in accordance with the invention.

Thermal strain deformation within the housing H or piston 1 can be expediently controlled by a single reinforcing member in the form of a cylindrical shell 2 as in FIGS. 1-9, which shell 2 is disposed in concentric relation to the bore B surface, or by a plurality of reinforcing members in the form of cylindrical shell segments 21 disposed in concentric relation to the bore B and in angularly spacedapart relation to one another as in FIGS. 10-13. The shell 2, shell segments 21 and any projecting portions thereof are preferably made of steel or steel alloy, but in general can be made of any material having a high strength as compared with the piston 1 or housing H material, and a relatively low coeificient of thermal expansion, as compared with whatever light metal material is used for the piston 1 or housing H. With such a choice of reinforcing material, the shell 2 or shell segments 21 as well as any projecting anchor parts thereof will experience a lesser strain deformation than the piston 1 or housing H material for any given temperature range and thereby constrain such light metal material against thermal strain deformation in directions established by the geometry and arrangement of shell 2, shell segments 21 in relation to the bore B and end faces F, F.

While in general, plain cylindrical shell reinforcing members, will be satisfactory for controlling thermal strain deformations in radial directions, it is preferable to provide the shell or shell segments 21 with some sort of anchoring means that will be effective to limit thermal deformation also in axial directions, i.e. parallel to the axis of bore B.

By so limiting axial strain deformations, as for example in the case of piston 1, the flatness of its end faces F and their axial spacing can be controlled within tolerances. Such axial strain deformation can be limited by using a shell 2 having perforations through which the machine part metal extends, as for example the circular perforations 6 shown in FIG. 4, or the slot perforations 7 of FIG. 5. The same basic result can be achieved by providing the shell 2 with axially projecting dovetail portions 5 as in FIG. 3.

Other examples of reinforcing members provided with means to control axial strain deformation in conjunction with circumferentially continuous cylindrical shells 2 are to be found in FIGS. 1, 2 and 6-9.

In FIGS. 1 and 2 the cylindrical shell 2 has a circumferentially continuous radially projecting flange 3 at each axial end which flanges 3 serve to constrain thermal strain deformation in directions parallel to the axis of bore B. FIGS. 8 and 9 illustrate that a reinforcing shell 2 can be provided with circumferentially continuous end flanges 3a that are directed radially inward as in FIG. 9, or with one radially outward and one radially inward flange 3b and 3a respectively as in FIG. 8'.

FIGS. 6 and 7 illustrate that a circumferentially continuous shell 2 need not be provided with circumferentially continuous end flanges, but alternatively, can have segmental flange parts 30 which are located in angularly spaced-apart relation to one another.

Preferably, the flange parts 3, 3a, 3b, 3c and any other similar parts that serve to anchor the shell member 2, or shell segment members 21 within the piston 1 or housing H are located at regions of principal stress therein.

Similarly, in FIGS. -13, the reinforcing shell segments 21 are provided with projecting tabs 8 (FIGS. 10 and 11) or with tabs 9 (FIGS. 12 and 13) embedded within the piston 1 metal at regions of principal stress therein.

In the case of a rotary piston 1, thermal strain reinforcement along axial directions, as provided by the end flanges 3 or the reinforcing shell 2, can be quite beneficial in establishing a desired surface contour at a predetermined temperature, as for example, the surface contour of the outward portion of piston 1 end faces can be constructed to have a slightly curved contour, as indicated in phantom at 11 in FIG. 1, when in the cold state, and by appropriate dimensioning and positioning of the flanges 3 and shell 2, such curved contour 11 can be changed into the flat tapered contour shown in solid line, so as to achieve a better end sealing action when piston 1 is installed in a rotary engine (not shown).

What is claimed is:

1. In combination; a light metal rotary piston having a cylindrical surface the dimensions of which are to be controlled within predetermined tolerance limits when the part is subjected to thermal strain deformation, and a high strength metal reinforcing means embedded within said rotary piston and positioned in symmetrical relation to said cylindrical surface thereof to constrain the thermal strain deformation of said rotary piston in directions influencing the dimensions of said cylindrical surface to maintain said surface dimensions within said tolerance limits.

2. The combination according to claim 1 wherein said reinforcing means includes a steel cylindrical shell member disposed in concentric relation to said cylindrical surface.

3. The combination according to claim 1 wherein said reinforcing means includes a plurality of steel cylindrical shell segment members disposed in concentric relation to said cylindrical surface and in angularly spaced-apart relation to one another.

4. The combination according to claim 2 wherein said cylindrical shell member is perforated and the metal of said rotary piston extends through the perforated portion of said shell member to anchor same against movement relative to the rotary piston.

5. The combination according to claim 2 wherein said cylindrical shell member has axially projecting dovetail portions embedded within the metal of said rotary piston to anchor said shell member.

6. The combination according to claim 2 wherein said cylindrical shell member has radially projecting flange portions at each axial end to constrain the thermal strain deformation of said bearing housing in directions parallel to the axis of said cylindrical surface thereof.

7. The combination according to claim 3 wherein each of said cylindrical shell segment members has a radially projecting flange portion at each axial end to constrain the thermal strain deformation of said rotary in directions parallel to the axis of said cylindrical surface thereof.

8, The combination according to claim 6 wherein said flange portions project radially outward with respect to the axis of said cylindrical surface.

9. The combination according to claim 6 wherein said flange portions project radially inward with respect to the axis of said cylindrical surface.

10. The combination according to claim 6 wherein said cylindrical shell member has at each axial end, a flange portion projecting radially outward with respect to the axis of said cylindrical surface, and a flange portion projecting radially inward with respect to the axis of said cylindrical surface.

11. The combination according to claim 6 wherein said flange portions are located at regions of principal stress within said rotary piston.

12. The combination according to claim 7 wherein said flange portions are located at regions of principal stress within said rotary piston.

References Cited UNITED STATES PATENTS 1,815,344 7/1931 Brincil 308-237 FOREIGN PATENTS 1,242,135 10/ 1960 France.

1,163,360 9/1958 France.

1,049,165 1/ 1959 Germany.

MARTIN P. SCHWADRON, Primary Examiner F. SUSKO, Assistant Examiner US. Cl. X.R. 308-237

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