US3655304A

US3655304A - Sealing device for pistons of rotary piston machines

Info

Publication number: US3655304A
Application number: US73039A
Authority: US
Inventors: Hans Sturmer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1969-10-02
Filing date: 1970-09-17
Publication date: 1972-04-11
Anticipated expiration: 1989-04-11
Also published as: FR2064895A5; DE1949695A1; CH508804A; GB1327077A

Abstract

A rotary piston machine wherein the piston has several lobes and orbits in the interior of a cylinder whereby its lobes sweep along the inner surface of the cylinder. The lobes are formed with axially parallel grooves bounded by internal surfaces of gear tooth shaped profile, and each groove receives a sealing element whose outer portion has a convex external surface engaging the inner surface of the cylinder and whose inner portion has several gear tooth shaped projections which are received with some clearance in complementary sections of the groove. Channels which are formed in the sealing elements establish communication between the chamber of the cylinder and certain sections of the grooves to insure that all sides the sealing elements are subjected to substantially identical pressures which are only slightly higher than necessary to maintain the sealing elements in requisite sealing engagement with the inner surface of the cylinder.

Description

ilnite States set Stunner [21] Appl. No.: 73,039

[30] Foreign Application Priority Data Oct 2, 1969 Germany ..P 19 49 695.8

[52] 115. CL ..418/l24, 418/179 [51] Int. Cl ..F0lc 19/02, F03c 3/00 [58] Fieldo iSearch ..4l8/l24,123,113, 114,115, 41311 16, 117. 1 18. 119, 120, 121, 122

[ 56] References Cited UNITED STATES PATENTS 3,120,921 2/1964 l-lovorka ..4l8/116 X 3,323,498 6/1967 Krak et al. ..418/122 X FOREIGN PATENTS OR APPLICATIONS 7 7 1,151,413 7/1963 Gennany ..418/124 Primary Examiner-Carlton R. Croyle Assistant Examiner-Richard E. Gluck Attorney-Michael S. Striker [5 7] ABSTRACT A rotary piston machine wherein the piston has several lobes and orbits in the interior of a cylinder whereby its lobes sweep along the inner surface of the cylinder. The lobes are formed with axially parallel grooves bounded by internal surfaces of gear tooth shaped profile, and each groove receives a sealing element whose outer portion has a convex external surface engaging the inner surface of the cylinder and whose inner portion has several gear tooth shaped projections which are received with some clearance in complementary sections of the groove. Channels which are formed in the sealing elements establish communication between the chamber of the cylinder and certain sections of the grooves to insure that all sides the sealing elements are subjected to substantially identical pressures which are only slightly higher than necessary to maintain the sealing elements in requisite sealing engagement with the inner surface of the cylinder.

7 12 Claims, 3 Drawing Figures SEALING DEVICE FOR PISTONS OF ROTARY PISTON MACHINES BACKGROUND OF THE INVENTION The present invention relates to improvements in rotary piston machines in general, and more particularly to improvements in sealing means which are interposed between the in temal surface of a cylinder and the external surface of a piston which orbits or rotates in the cylinder chamber.

It is already known to utilize in a rotary piston machine an eccentrically mounted rotary piston which comprises several corner portions or lobes each of which sweeps along the internal surface of the cylinder when the piston is in motion. The lobes of the piston are provided with sealing elements which must insure a satisfactory sealing action between the inner surface of the cylinder (e.g., a surface having an epitrochoidal or an analogous outline) and the external surfaces of the sealing elements.

German printed publication No. 1,151,413 discloses sealing elements which are intended for use in the lobes of the piston in a rotary piston machine. Each such sealing element has a substantially rectangular profile and is inserted into an axially parallel groove provided in the external surface of the respective lobe. The sealing element has a strip-shaped outer portion which extends from the groove and is in sealing engagement with the inner surface of the cylinder. That part of the sealing element which is received in the piston does not completely fill the groove (either in the circumferential or in the radial direction of the piston) to define with the piston a chamber which is in communication with one of the compartments forming part of the internal space of the cylinder and being separated from each other by the lobes of the piston. The chamber communicates with that compartment which is maintained at the highest pressure. This is not entirely satisfactory because the sealing element is ressed against the inner surface of the cylinder with a force which is always much higher than the minimum force required to establish a satisfactory seal between the external surface of the sealing element and the inner surface of the cylinder. Thus, the sealing element is biased outwardly by a pressure which always corresponds to the maximum pressure in the interior of the cylinder, even if the sealing element is located in such angular position or positions that a much lower pressure would suffice to ensure a satisfactory sealing action. The sealing action is even more pronounced if the line of contact between the outer portion of the sealing element and the inner surface of the cylinder is permitted to shift to one side of the groove. If the sealing element happens to travel in an area which is maintained at a relatively low pressure, its external surface is subjected to a relatively low pressure which is but a fraction of the pressure in the chamber. Therefore, the outer portion of the sealing element is likely to be pressed against the cylinder with a force which suffices to destroy the film of lubricant along the inner surface of the cylinder. Once the lubricant film is destroyed, the metallic material of the sealing element comes into direct contact with the metallic material of the cylinder to generate excessive friction and wear and to cause premature destruction of the sealing element.

SUMMARY OF THE INVENTION An object of the invention is to provide a novel piston for rotary piston machines and to provide the piston with novel and improved sealing elements.

Another object of the invention is to provide a sealing element which is configurated and mounted in the piston of a rotary piston machine in such a way that the force with which it is urged against the cylinder of the machine when the piston rotates exceeds only slightly the minimum force which is required to insure a satisfactory sealing action.

An additional object of the invention is to provide a sealing element which is constructed and mounted with a view to avoid destruction of the film of lubricant along the inner surface of the cylinder in a rotary piston machine.

Still another object of the invention is to provide a sealing element which can be readily installed in the pistons of presently known rotary piston engines without necessitating appreciable alterations in the design of such pistons.

The invention is embodied in a rotary piston machine which comprises a cylinder having a chamber and including an inner surface which surrounds the chamber and preferably comprises two main arcuate sections, a piston which is installed in the cylinder chamber for rotation about a predetermined axis and is provided with several circumferentially spaced lobes sweeping along the inner surface of the cylinder when the piston rotates, an axially parallel groove provided in each lobe of the piston and being surrounded by an internal surface of gear tooth shaped profile, and a metallic or plastic sealing element in each groove. Each sealing element includes an outer portion having a convex external surface at least a portion of which is preferably of a circular cylindrical outline and is in sealing engagement with the inner surface of the cylinder to divide the chamber into a pair of compartments, and an inner portion having at least two gear tooth shaped projections which are received in the respective groove. Each sealing element is further provided with substantially radially extending channel means located between the projections of its inner portion and connecting the corresponding groove with one of the compartments to thus insure that the pressure against the surface of the inner portion of each sealing element does not excessively deviate from the pressure which acts against the external surface of the outer portion of each sealing element.

The sealing elements may be made of a metallic material (e.g., hardenable steel) or from a suitable synthetic plastic material (such as polytetrafluorethylene or another material which is resistant to wear and has a low coefficient of friction The metallic sealing elements are preferably made by drawing or precision rolling a ductile metallic material to form an elongated blank and by subdividing the blank into discrete sealing elements which can be surface-hardened by nitration or by an inductive hardening process. Plastic sealing elements can be produced by extrusion or in the cavity of a suitable mold.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved sealing device itself, however, both as to its construction and the method of making and mounting the same, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary transverse sectional view of a rotary piston machine whose piston is provided with sealing elements embodying one form of the invention;

FIG. 2 is a similar view of a second rotary piston machine whose piston is provided with modified sealing elements and FIG. 3 is a sectional view of the entire rotary piston machine which embodies the structure shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 3 illustrate a rotary piston machine, e.g., an internal combustion engine, including a cylinder 101 having inner surface 2 which is of epitrochoidal or similar outline and has two main arcuate portions. The internal chamber of the cylinder 101, which is surrounded by the inner surface 2, accommodates an eccentrically mounted piston I which travels about a predetermined axis and comprises several (for example, three) axially parallel corner portions or lobes which sweep along the inner surface 2 when the piston 1 rotates. One such corner portion or lobe of the piston 1 is shown in detail in FIG. 1; it is provided with an axially parallel groove 10 of gear tooth shaped outline. In the embodiment of FIG. I, the groove 10 has two outwardly diverging sections 10a each of which extends in parallelism with the axis of the piston 1. The groove 10 receives a novel sealing element 3 having an outer portion bounded by a convex external surface 6 which sealingly engages the inner surface 2 to divide the chamber of the cylinder 101 into

compartments

4 and 5. The surface 6 preferably forms part of a circular cylindrical surface and its end portions (as considered in the direction of rotation of the piston 1) are flush with the adjacent portions 7 of the outer surface of the illustrated lobe. Thus, the radius of curvature r of the external surface 6 is such that it ensures tangential transition of the ends of this surface into the surfaces 7. FIG. 3 shows that the inner surface 2 of the cylinder 10] has two main arcuate sections.

The inner portion of the sealing element 3 comprises two gear tooth shaped axially parallel projections 8 each of which is received in one of the sections 10a of the groove 10. The flanks of each projection 8 make an angle alpha which, in FIG. I, at least approximates 30, and the tips or top lands of the projections 8 are flat, as at 8a. The angle alpha is preferably between 30 and 60. The surface of the inner portion of the sealing element 3 between the adjacent flanks of the projections 8 is concave, as at 8b.

The sealing element 3 is further provided with a row of radially extending bores or passages 9 which communicate with the groove 10in the region between the projections 8 and with one of the

compartments

4, 5. The row of passages 9 is parallel to the axis of rotation of the piston 1. Each section 10a of the groove 10 has an inner end portion which is bounded by a concave surface, as at 1%. It is to be noted that each lobe of the piston 1 is provided with a groove 10 for a discrete sealing element 3.

Each end face of the piston 1 is further provided with straight recesses or cutouts 1a for inclined sealing strips 11 which bear against the adjacent inner end faces of the cylinder 101. The strips 11 are mounted on springs (not shown) located in the innermost portions of the respective cutouts 1a so that the outer portions of the strips are biased against the cylinder. It is also possible to make the strips of elastically deformable material. The purpose of the sealing strips 11 is to seal the compartments in the chamber of the cylinder from each other in the region of the respective end faces of the piston 1. The end portions of each sealing strip 11 abut at an obtuse angle against two sealing elements 3.

The sealing elements 3 are mounted in the respective grooves 10 with a certain minimal clearance so that, when the piston I rotates in the direction indicated by the arrow 13, the front or right-hand flanks of the projections 100 can respectively move away from the adjacent portions of the internal surface of the piston 1 to define

narrow gaps

12 and 12a. Such gaps develop in response to friction between the convex surfaces 6 of the sealing elements 3 and the internal surface 2 of the cylinder 101. The left-hand or trailing flanks of the projections 10a abut against and are in sealing engagement with the adjacent portions of the internal surface in the piston 1. The gap 12 is in direct communication with the compartment 4. The other gap 12a communicates with the compartment by way of the passages 9. The pressure in the compartment 4 is the same as in the front section We of the groove therefore, all sides of that part of the sealing element 3 which is located to the right of the line of contact between the

surfaces

2 and 6, as viewed in FIG. 1, are subjected to a uniform pressure. The rear part of the sealing element 3 (to the left of the line of contact between the surfaces 2 and 6) is subjected to a uniform pressure because the passages 9 communicate with the chamber 5. It will be seen that, in the position of the sealing element 3 as shown in FIG. 1, the pressure acting against the left-hand part of the surface 6 is the same as the pressure which acts on the adjacent projection 8 along the gap 12a and in the innermost part of the respective section 10a. When the passages 9 are sealed from that compartment which is maintained at a higher pressure, the total area of the surface of the sealing element 3 which is subjected to higher pressure is reduced accordingly because the

gap

12 or 12a then communicates with the compartment which is maintained at the lower pressure. It can be said that the area of the internal surface of the sealing element 3 which is subjected to pressure is reduced when the pressure acts against a smaller part of the external surface 6, and vice versa. However, there always remains a surplus force or pressure which acts between those flanks of the projections 8 which are in contact with the piston l and the respective portions of the surface bounding the groove 10. The magnitude of such surplus pressure is determined by the parameter B. The surplus pressure ensures that the sealing element 3 is held in requisite sealing engagement with the inner surface 2. The parameter E can be defined as the normal or average distance between a first plane which includes the trailing flank of the front projection 8 and a second plane which is parallel to the first plane and includes the line of contact between the

surfaces

2 and 6.

The just described construction and mounting of the sealing element 3 ensure that the pressure between the

surfaces

2 and 6 remains relatively low so as not to destroy the film of lubricant on the surface 2.

It will be understood that the pressure in the

compartments

4 and 5 varies, i.e., that the pressure in the compartment 4 at times exceeds and is at times less than the pressure in the compartment 5. Therefore, the sealing element 3 of FIG. 1 moves in the groove 10 between the illustrated position (when the pressure in the compartment 4 exceeds the pressure in the compartment 5) and a second position in which the right-hand flanks of the projections 8 abut against the adjacent surfaces in the respective sections 10a of the groove 10 (namely, when the pressure in the compartment 5 exceeds that in the compartment 4). This does not affect the aforedescribed advantageous characteristics of the sealing element 3 i.e., this sealing element then also ensures a requisite sealing action between the

compartments

4 and 5 by exertion of a relatively low pressure against the surface 2. The

gaps

12, 12a are then adjacent to the left-hand surfaces in the sections 10a.

The sealing element 3 moves between the two positions when the pressure in the compartment 4 nearly equals the pressure in the compartment 5. This is the stage of temporary absence of complete sealing action but it does not affect the operation of the rotary piston machine because the pressures in the

compartments

4, 5 are then substantially identical.

Since the convex external surface 6 of the sealing element exhibits a rather small curvature (it preferably forms part of a circular cylindrical surface, at least in the region where it touches the surface 2), its configuration deviates only slightly from that of the inner surface 2 of the cylinder 101. Also, since the line of contact between the

surfaces

2 and 6 is always located between the ends of the sealing element 3, as considered in the circumferential direction of the piston 1, only a portion of the surface 6 is subjected to high pressures at any time. These features ensure that the magnitude of surplus forces which urge the sealing element 3 against the surface surrounding the groove 10 of the piston 1 can be maintained within a rather low range.

Referring to FIG. 2, the cylinder 101 cooperates with a modified piston 1' having in each of its corner portions or lobes an axially parallel groove 10' which includes four outwardly diverging axially parallel sections 10a. The inner portion of the sealing element 3' has four projections 8' each of which extends into one of the sections 10a. The external surface 6' of the sealing element 3' engages the innersurface 2 of the cylinder 101 to separate the

compartments

4 and 5 from each other. The sealing element 3 is formed with three axially parallel rows of radially extending bores or passages 9' which respectively communicate with the second, third, and fourth sections 10a (as considered in the direction of rotation of the piston 1'--indicated by the arrow 13).

The sealing element 3 allows for an even more precise gradation of relieved and pressurized surfaces. When the piston 1 rotates in the direction indicated by the arrow 13, the projections 8 of the inner portion of the sealing element 3' define four clearances or

gaps

12, 12a, 12b, 12C. The number of projections on a sealing element depends on the size of the piston and on the dimensions and configuration of its lobes. If the nature of the operation of the rotary piston machine requires it, the sealing elements can be formed with a very large number of projections to ensure that the pressure between the external surface of each sealing element and the inner surface of the cylinder is always sumcient but does not substantially exceed the maximum desirable pressure.

Another important advantaGe of the improved sealing elements is that their characteristic mass is low (about 1/10) so that the sealing elements are subjected to relatively small centrifugal forces. Such centrifugal forces tend to press the sealing elements against the inner surface of the cylinder. Therefore, a piston which employs the improved sealing elements can be used with advantage in high-speed rotary piston engines. It is clear, however, that the sealing elements of the present invention can be used with equal advantage in many other types of radial piston machines, such as hydraulic machines, compressors, vacuum pumps, or other types of pumps, steam engines and/or others.

The sealing

elements

3 or 3 may consist of a metallic material, such as hardenable steel, or of a suitable wear-resistant synthetic plastic material having a relatively low coefficient of friction (for example, polytetrafluorethylene). If the sealing elements consist of a synthetic plastic material, they can be reinforced by the addition of filamentary materials such as glass, carbon or asbestos fibers.

If the sealing elements consist of a metallic material, they may be produced by a precision-rolling or drawing method. The surfaces of the thus obtained sealing elements can be hardened inductively or by nitration. If the sealing elements consist of a synthetic plastic material, they can be produced by extrusion or in the cavities of suitable molds. The precisionrolling, drawing or extruding method involves forming elongated blanks and severing the blanks to yield sealing elements of desired length.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

Iclaim:

1. In a rotary piston machine, a combination comprising a cylinder having a chamber and including an inner surface surrounding said chamber, a piston installed in said chamber for rotation about a predetermined axis and having a plurality of circumferentially spaced lobes arranged to sweep along said inner surface in response to rotation of the piston, each of said lobes having a substantially axially extending groove surrounded by a gear tooth shaped internal surface; and sealing elements provided in said grooves, each sealing element including an outer portion having a convex external surface abutting against said inner surface to divide said chamber into a pair of compartments and an inner portion having at least two substantially gear tooth shaped projections received in the respective groove, each sealing element further having channel means located between the projections of the respective inner portion and connecting the corresponding groove with one of said compartments.

2. A combination as defined in claim 1, wherein the number of lobes on said piston exceeds two and wherein the inner surface of said cylinder consists of several arcuate portions.

3. A combination as defined in claim 1, wherein at least a portion of each of said external surfaces forms part of a cylindrical surface and wherein said piston has an external surface portions of which flank said grooves and are flush with the adjacent portions of the respective external surfaces.

4. A combination as defined in claim 3, wherein said portion of said external surface of each sealing element forms part of a circular cylindrical surface and wherein said portion of such external surface engages said inner surface.

5. A combination as defined in claim 1, wherein each of said projections has two mutually inclined flanks making an angle of 30- 60.

6. A combination as defined in claim 1, wherein each of said grooves has a plurality of sections, one for each of said projections, and each of said internal surfaces has a concave portion in the bottom part of each of said sections, each of said projections extending into its respective section.

7. A combination as defined in claim 1, wherein each of said inner portions is received with clearance in the respective groove and wherein each of said projections has two mutually inclined flanks, said clearance consisting of a plurality of gaps provided between said internal surfaces and one flank of each of said projections.

8. A combination as defined in claim 1, wherein said sealing elements consist of metallic material.

9. A combination as defined in claim 8, wherein said metallic material is hardenable steel.

10. A combination as defined in claim 1, wherein said sealing elements consist of wear-resistant synthetic plastic material having a low coefficient of friction.

11. A combination as defined in claim 10, wherein said synthetic plastic material is polytetrafluorethylene.

12. A combination as defined in claim 10, wherein said synthetic plastic material contains reinforcing inserts selected from the group consisting of glass, carbon and asbestos fibers.

Claims

5. A combination as defined in claim 1, wherein each of said projections has two mutually inclined flanks making an angle of 30*- 60*.