EP0494912A1

EP0494912A1 - Rotary piston machine seal

Info

Publication number: EP0494912A1
Application number: EP90914647A
Authority: EP
Inventors: Helmuth Richard Uebel
Original assignee: Archimedes Associates Inc
Current assignee: Archimedes Associates Inc
Priority date: 1989-10-04
Filing date: 1990-10-04
Publication date: 1992-07-22
Also published as: BR9007710A; CN1051777A; JPH05505007A; KR920703965A; WO1991005144A1; CA2067345A1; EP0494912A4; AU6502890A

Abstract

La machine à piston rotatif décrite (160) comprend un carter (12'), ainsi qu'un piston à trajectoires en trochoïdes (36') formé avec une enveloppe externe et rotatif à l'intérieur du carter entre des parois latérales opposées (172, 174). Un joint d'étanchéité radial (48') pour le piston (36') est monté dans un évidement (176) ménagé dans le module (20') du carter. Dans un premier mode de réalisation, le joint d'étanchéité radial comporte plusieurs éléments scellants (182, 184, 186) qui forment ensemble une surface scellante (180) en prise avec la périphérie (37') du piston et qui sont sollicités en direction du piston (36'), un élément scellant intermédiaire (186) étant sollicité élastiquement et étant conçu en forme de coin, de façon à obliger les éléments scellants (182, 184) des extrémités opposées à entrer en contact étanche avec les extrémités respectives de l'évidement formées par les parois latérales opposées (172, 174). Dans un second mode de réalisation, un joint d'étanchéité périphérique axial (210) s'étend autour d'une paroi latérale du piston (36') et un dispositif scellant latéral (178) forme une saillie à partir de la paroi latérale correspondante (172, 174) du carter (12') à proximité du joint d'étanchéité radial (48) et est sollicité élastiquement de façon à entrer en contact étanche avec la paroi latérale du piston, ce qui permet de sceller les espaces libres éventuels compris entres le joint d'étanchéité radial (48') et le joint d'étanchéité périphérique axial (210).The rotary piston machine described (160) comprises a housing (12 '), as well as a piston with trochoid trajectories (36') formed with an external and rotary envelope inside the housing between opposite side walls (172 , 174). A radial seal (48 ') for the piston (36') is mounted in a recess (176) formed in the module (20 ') of the housing. In a first embodiment, the radial seal comprises several sealing elements (182, 184, 186) which together form a sealing surface (180) engaged with the periphery (37 ') of the piston and which are biased in the direction of the piston (36 '), an intermediate sealing element (186) being resiliently biased and being designed in the form of a wedge, so as to force the sealing elements (182, 184) of the opposite ends to come into sealing contact with the respective ends of the recess formed by the opposite side walls (172, 174). In a second embodiment, an axial peripheral seal (210) extends around a side wall of the piston (36 ') and a side seal device (178) protrudes from the corresponding side wall (172, 174) of the casing (12 ') near the radial seal (48) and is resiliently biased so as to come into tight contact with the side wall of the piston, which makes it possible to seal the possible free spaces included between the radial seal (48 ') and the axial peripheral seal (210).

Description

"ROTARY PISTON MACHINE SEAL"

The present invention relates to rotary piston machines and is particularly concerned with sealing the working chamber(s) of such a machine. While the invention is applicable to rotary piston pumps and gas pressure machines it is particularly appropriate to the sealing of compression gases in rotary piston engines and will hereinafter be described in relation to this use without intending to exclude other rotary piston machines.

Rotary piston engines are commonly provided with radial seals which control the leakage of compression gases around the radial periphery of the piston and with axial seals which control the leakage of compression gases around the axial surfaces of the piston.

Rotary engine seal leakage is primarily responsible for the measured performance difference between rotary and reciprocating piston internal combustion engines and rapid wear of the radial seal and its corresponding rubbing surfaces have presented problems in rotary engines. It has been shown that 2/3 to 3/4 of the leakage in known rotary piston engines is from the radial seal with the balance being around the axial sides of the piston. It is well known that reduction in seal leakage can produce substantial improvements in engine performance.

In a rotary piston engine, the radial seal must be able to move radially in order to maintain optimum sealing contact between the sealing surface of the seal and the rubbing surface- on the piston or housing, which means that the radial seal must not be a tight fit in its mounting recess. Thus, one of the main areas of leakage in a radial seal is around the axial ends of the seal. Likewise, it is commonly not appropriate to locate the axial seals immediately adjacent the radial peripheral surface of the piston, with the result that leakage of compression gases may occur around the axial sides of the piston between the axial seals and the radial seal.

It is an object of the present invention to alleviate^" leakage in a rotary piston machine of the type in which the radial seal is mounted in the housing rather than in the piston.

According to a first aspect of the present invention there is provided a rotary piston machine comprising a casing, a piston having a peripheral working surface of trochoidal type- ith an outer envelope and being eccentrically rotatably mounted in the casing between opposed side walls, the casing having a cooperating working surface which substantially conforms to the outer envelope of the trochoid and having mounted in a recess at a convex inflexion of the cooperating working surface a radial seal having a sealing surface which extends across the peripheral working surface of the piston, the radial seal comprising a plurality of seal members which together define the sealing surface and which are biased towards the peripheral working surface of the piston, an intermediate seal member being resiliently biased and wedge shaped whereby under the resilient biasing action of the said intermediate seal member opposed wedging surfaces thereof cooperate with adjacent seal members to urge opposed end seal members into sealing contact with respective ends of the recess.

By the first aspect of the present invention, the wedge shaped intermediate seal member acts by virtue of its resilient biasing towards the peripheral working surface of the piston to urge the radial seal into sealing contact with respective ends of the recess in which the radial seal is mounted.

The rotary piston machine defined in the two immediately preceding paragraphs may have more than one convex inflexion in the cooperating working surface of the casing for the or each piston, with a radial seal at each such inflexion, and each such radial seal is conveniently in accordance with the first aspect of the present invention.

The seal members other than the intermediate seal member may be biased towards the peripheral working surface of the piston by appropriate wedging surfaces of the recess, but conveniently all of the seal members are resiliently biased towards the piston.

The resilient biasing may be by means of, for example, fluid pressure behind the radial seal in the recess and/or spring means. The resilient biasing may also act directly on the seal members other than the intermediate seal member to urge the end seal members axially outwardly into abutment with the ends of the recess, thereby assisting the action of the intermediate seal member .

The wedge shaped intermediate seal member tapers towards the peripheral working surface of the piston and preferably the opposed wedging surfaces of the intermediate seal member are inclined to the radial direction, thereby assisting the biassing of the seal members other than the intermediate seal member into contact with the peripheral working surface of the piston. For an inclined wedging surface the angle of inclination to the radial direction may be in the range of about 1° to about 45°, preferably 5 to 20°, and advantageously the angles of inclination of the two wedging surfaces are equal.

The intermediate seal member may comprise only a small part of the complete sealing surface of the radial seal, for example from 0.1 to 10%. Thus the axial length of the sealing surface on the intermediate sealing member may be less than 1mm when the radial seal is new." The intermediate seal member is conveniently formed of a slightly softer material than that of the remaining seal members. If the intermediate seal member is softer than the remaining seal members and the end portion thereof defining the respective part of the sealing surface projects slightly beyond the remaining seal members towards the peripheral working surface of the piston when the radial seal is new, it will be worn down quickly to the level of the sealing surface on the remaining sealing members. All of the seal members may be of known materials such as a composite of cast iron and graphite or ceramic.

In one embodiment, there are only three sealing members in the radial seal, the intermediate and opposed end seal members, so that the opposed wedging surfaces of the intermediate seal member cooperate directly with the end seal_* members.

The arrangement of the seal members in the recess therefor is advantageously such that pressurized combustion gases from an adjacent combustion chamber can act on the seal members to bias them towards the peripheral working surface of the piston. In one embodiment, the seal members have at least one rebate in the side thereof facing towards the adjacent combustion chamber and a space is provided in the recess radially behind the seal members whereby pressurized gases can be received in the recess from the open end thereof adjacent the sealing surface of the seal members and pass between the seal members and the adjacent recess side wall into the rebate, and then into the space behind the seal members. The same pressurized gases urge the seal members into sealing engagement with the opposite side wall of the recess. In the case where the radial seal is in communication with two combustion chambers, one on each side thereof, at least one rebate may be provided on each side of the seal members.

According to a second aspect of the present invention which may be used with or independently of the first aspect of the present invention, there is provided a rotary piston machine comprising a casing, a piston having a peripheral working surface of trochoidal type with an outer envelope and being eccentrically rotatably mounted in the casing between opposed side walls, the casing having a cooperating working surface, which substantially conforms to the outer envelope of the trochoid, the piston having a respective peripheral axial seal extending around each side wall thereof adjacent the peripheral working surface and in sealing contact with the adjacent side wall of the casing, the casing having at a convex inflexion of the cooperating working surface a radial seal having a sealing surface which extends across the peripheral working surface of the piston, and wherein side sealing means projects from at least one of the side walls of the casing adjacent the radial seal and is resiliently biased into sealing contact with the respective side wall of the piston to at least substantially seal a gap between the radial seal and the respective peripheral axial seal.

By the second aspect of the present invention, any radial gap between the annular axial seal and the radial seal on the axial side of the piston is at least substantially.sealed by the side sealing means, with wobble of the piston being able to be absorbed by the resilient biasing of the side sealing means.

Preferably a side sealing means as described in the two immediately preceding paragraphs is provided in each of the opposed side walls of the casing to engage the piston on both sides. The casing may have more than one radial seal for the or each piston, at respective inflexions, and each such radial seal preferably has a pair of side sealing means associated therewith.

The resilient biassing of the side sealing means into sealing contact with the piston may be by way of, for example, spring means and/or fluid pressure. In a preferred embodiment the side sealing means is resiliently. biased by a compression spring but the side sealing means is also biased by compression gas pressure in the adjacent combustion chamber which may be communicated to the side sealing means by way of a passage extending from a space behind the radial seal which receives the combustion gas. Alternatively the fluid pressure may be provided by other fluid compressed in the machine.

The portion of the side sealing means in engage ent with the piston is advantageously positioned approximately with one part of its surface tangential to the peripheral working surface of the piston and the tip of the radial seal, and another part of its surface tangential to the adjacent surface of the peripheral axial seal.

The portion of the side sealing means in contact with the piston is preferably formed of a material softer than that of the adjacent portion of the radial seal so as to alleviate the possibility of the adjacent portion of the radial seal preventing the side sealing means from being resiliently biased into sealing contact with the piston. The adjacent portion of the radial seal may be formed of, . for example, a ceramic or a composite of cast iron and graphite in which case the portion of the side sealing means in contact with the piston may be formed of, for example, lead bronze.

The side sealing "means may be positioned slightly offset to a combustion chamber side of the housing, for example about 10 to 21° offset from the radial seal axial centre plane towards the combustion space. Such an arrangement is suitable for an engine with a combustion space at only one end of the housing. In an engine with a combustion space at each end of the housing, the one side sealing means can be located on the radial seal centre line or, alternatively, two side sealing means can be positioned such that each is offset towards its respective combustion chamber as described above. Preferably in the aforementioned arrangements, the portion of the side sealing means in contact with the piston is of circular cross-section, but in an alternative arrangement for twin combustion chambers, the cross-section may be substantially kidney-shaped with the plunger centered on the axial centre plane of the radial seal and with part circular ends of the kidney-shaped cross-section extending to respective sides of the centre plane.

The first and second aspects of the present invention are particularly, but not essentially, applicable to a rotary piston machine of trochoidal design of the epitrochoidal type with the piston defined by 1:1 generating circles with an outer envelope, and with the peripheral working surface of the piston and/or the cooperating working surface of the casing being substantially equidistant- to the mathematically exact trochoid, and will be further described, in non-limiting manner, in relation to such an engine.

One embodiment of a rotary piston engine in accordance with each aspect of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is an axial section through a schematic representation of a rotary piston machine; Figure 2 is a part-sectional view along the line 2-2 in Figure 1;

Figure 3 is an axial sectional view of part of a multi-piston rotary piston engine illustrating the radial and side sealing means;

Figure 4 is an enlarged partial view of Figure 3 illustrating in detail one radial seal and one side seal;

Figure 5 is a cross-sectional view taken on the line A-A of Figure 4 showing an arrangement in which the radial seal communicates with only a single combustion chamber;

Figure 6 is a view similar to part of Figure 5 except that it illustrates one proposal for a dual combustion chamber arrangement; and

Figure 7 is a view similar to Figure 5 except that it shows a further proposal .for a dual combustion chamber arrangement.

Referring to Figures 1 and 2, a rotary piston machine 10 comprises a housing 12 with a crank shaft 14 supported for rotation about axis 15 in axially spaced plain bearings 16 and 18. The housing 12 is in modular form comprising a first module 20, a second module 22 and end modules 24 and 26 in which the bearings 16 and 18, respectively, are mounted.

The crank shaft 14 has a stepped crank pin 28 comprising a first portion 30 of relatively large diameter and a second portion 32 of relatively small diameter extending between the first portion 30 and a crank web 34. The crank pin 28 has an axis 29 which has an eccentricity a relative to the axis 15 of the crank shaft 14.

The large diameter portion 30 of the crank pin 28 carries* a rotary piston 36 within the first module 20 of the housing 12. The piston 36 is rotatably mounted on the crank pin portion 30 by means of a bearing 38. The piston 36 is essentially of cardioidal shape as illustrated schematically by a chain dotted line in Figure 2. Thus, the piston is of epitrochoidal type with 1:1 generating circles defined with an outer envelope. The piston is shown with an inflexion free side 40 of the peripheral working surface but that side may incorporate an inflexion.

The piston 36 rotates about the rotating crank shaft 14 in a working volume 44 defined at the periphery by the module 20 and at the sides by the modules 22 and 24 respectively of the housing 12. The module 20 defines a cooperating working surface 46 for the piston which substantially conforms to the outer envelope of the eccentrically rotatable cardioidal piston 36. The periphery 37 of the piston 36 conforms substantially to the mathematically exact trochoid and the cooperating working surface 46 is correspondingly shaped. As the piston 36 rotates about the crank pin 28 it remains permanently in contact with opposed radial seals 48 each mounted in a recess in the housing module 20 at respective inflexions in the cooperating working surface 46.

The described shapes of the piston 36 and cooperating working surface 46 require that the piston rotates on the crank shaft 14 at twice the angular velocity of the crank shaft but in the opposite direction. The required synchronised motion may be achieved by a variety of systems, including direct and indirect drive mechanisms, but as illustrated is achieved by an eccenter mechanism, which along with other aspects of this and modified such machines, comprises the subject matter of our co-pending patent application, entitled "Rotary Piston Machine" . The disclosure of said co- pending patent application is incorporated herein by reference.

The eccenter mechanism comprises an eccenter assembly 50 connected directly with the piston 36 and comprising a pair of axially spaced angularly offset eccenters 52 and 54 mounted for rotation about the drive shaft 14 with the piston 36 on respective axes. Each of the eccenters 52 and 54 has an axis which is spaced from the crank pin axis 29 by the distance a equal to the eccentricity of the crank pin 28 from the crankshaft axis 15. Thus, eccenter 54 has an axis 42 and, coincidentally, eccenter 52 is shown on the axis 15 of the crank shaft. The eccenter assembly 50 is disposed immediately axially adjacent the piston thereby ensuring that the axial distance between the main bearings 16 and 18 is minimal. By the term "axially spaced" as used in relation to the eccenters is meant merely that they are not radially aligned. The eccenters may be immediately axially adjacent or spaced slightly as shown.

The eccenter 52 is rotatably received in a first guide block 56 which is constrained to reciprocate rectilinearly in a horizontal direction (in Figures 1 and 2) by opposed guide surfaces 58 in the module 22 of the housing. The eccenter 54 is rotatably received in a corresponding guide block 60 which is constrained to reciprocate rectilinearly in a vertical direction (in Figures 1 and 2) by opposed guide surfaces 62 (only one shown in Figure 1) in the module 26 of the housing 12. Because they are provided in respective modules the opposed guide surfaces 58 and 62 may be readily machined as desired.

The guide blocks 56 and 60 are able to reciprocate linearly along their respective paths because the associated eccenter is caused to rotate about an axis which is at a distance of one crank pin eccentricity a from the axis 29 of the crank pin 28. It is not necessary that the guide blocks 56 and 60 reciprocate linearly along the major and minor axes of the piston outer envelope defining the cooperating working surface 46, but this is preferred as shown in Figure 2 because it provides the optimum accuracy in the positioning of the piston, the greatest amount of support to the crank shaft from the eccenter assembly 50 and may result in the most compact engine. It is also hot necessary that the guide blocks 56 and 60 reciprocate perpendicularly to each other.

It will be appreciated that in order for the rotary piston machine 10 of Figures 1 and 2 to be assembled, either the crank shaft 14 must be separable into two parts at one or other end of the small diameter crank pin portion 32 or the eccenter assembly 50 must be separable from the piston 36 and must divide generally parallel to the axis. For convenience, the porting for the rotary piston machine has not been shown in Figures 1 and 2, but the machine 10 can be readily adapted for use as a driven or driving machine such as a pump, an internal combustion engine or a pneumatic engine.

The eccenter assembly 50 is mounted for rotation on the reduced diameter portion 32 of the crank pin 28 which enables the motor to be more compact radially than would be the case without the stepped crank pin. However, without the stepped crank pin the eccenter assembly could be integral with the piston 36 yet still provide the advantage of axial compactness by ensuring that the eccenter assembly is immediately adjacent the piston, thereby allowing for a minimal separation of the crank shaft bearings 16 and 18.

Figures 1 and 2 illustrate schematically a single piston rotary piston machine in which the piston is of the epitrochoidal type with 1:1 generating circles and an outer envelope. Figure 2 particularly illustrates the location of the two convex inflexions in the cooperating working surface of the casing at which the radial seals 48 are disposed and adjacent which a side sealing means would be provided in accordance with the second aspect present invention.

Further embodiments of a single and multiple piston rotary piston engine in which the or each piston is of the epitrochoidal type with 1:1 generating circles and an outer envelope are described in greater detail in our aforementioned co-pending patent application entitled "Rotary Piston Machine", all incorporating the eccenter mechanism described above in relation to Figures 1 and 2 for providing the required synchronised motion of the piston.

Figure 3 is an axial sectional view through the assemblies of the spaced radial seals 48 of part of a multi-piston rotary piston engine 160 described in detail in the aforementioned co-pending patent application and, for convenience, whose operation and assembly will not be described again in detail herein except in so far as it is applicable to the sealing of the working volume.

The engine 160 is similar in operating principle to the rotary piston machine 10 of Figures 1 and 2 and, again for convenience only, the same or similar parts will be given the same reference numeral followed by a prime " ' " .

Referring to Figures 3 and 4, the housing 12' is of modular construction and the one-piece crank shaft 14' is supported in plain bearings 162 by means of respective bearing seats 164 bolted to intermediate modules 166. The crank shaft 14' has a plurality of throws which are offset by 180° and are not visible in Figure 3. Each throw is defined by a stepped crank pin 28' having a first portion 30' of relatively large diameter and a second portion 32' of relatively small diameter.

A respective piston 36' is mounted for eccentric contra rotation on the first crank pin portion 30' by means of a bearing 38' within a working volume 44' substantially conforming to the outer envelope of the cardioidal piston 36'. The working volume 44' is defined at a working surface 46', which cooperates with the peripheral working surface 37' of the piston, by t^*he associated first module 20' of the casing 12'.

A respective eccenter assembly 50' is bolted to the associated piston 36' through a securing ring 168 with which it is screw-threadedly engaged and is supported for eccentric rotation with the piston on the second crank pin portion 32' by means of a bearing 170. The offset eccenters 52' and 54' are rotatably received in respective guide blocks 56' and 60' which are constrained to reciprocate rectilinearly perpendicularly to each other by respective pairs of opposed guide surfaces 58' and 62' . The guide surfaces 58' are defined on the respective module 22' of the casing 12' and the guide surfaces 62' are defined on an adjacent one of the intermediate modules 166.

The opposed side walls 172 and 174 of the^' working volume 44' within which each piston 36' rotates eccentrically are respectively defined by the adjacent module 22' and the adjacent module 166 (not the intermediate module 166 on which the guide surfaces 62' for the eccenter 54' associated with that piston are defined).

•As described with reference to Figures 1 and 2 each substantially cardioidal piston 36' during its rotation around the crank shaft 14 remains in sealing contact at all times with the cooperating working surface 46* of the respective module 20' defining the working volume 44' at two locations, the opposed inflexions of the outer^' envelope of the cardioid, and the radial seals 48' are provided at these locations to provide this sealing contact. Thus each substantially cardioidal piston 36' has associated with it two radial seals 48' disposed in respective recesses 176 in the associated module 20' . Furthermore each radial seal 48' has associated, with its two opposed side seal assemblies 178.

All of the radial seals 48' are identical and all of the side seal assemblies 178 are identical and Figure 4 is an enlarged portion of Figure 3 showing one of the radial seals 48' and one complete side seal assembly 178. The piston 36' has a peripheral working surface 37 ' of linear cross-section all around its periphery and the radial seal 48' projects into the working volume 44 ' and has a corresponding sealing surface 180 which extends substantially the full width of the working volume 44 ' in the housing module 20' between adjacent modules 166 and 22'. This is ensured by means of a seal assembly which comprises a pair of outer end^' seal components 182 and 184 interspaced by an intermediate wedge shaped seal component 186. Each- of the components 182, 184 and 186 has a narrow generally rectangular cross-section as illustrated in Figures 5 to 7 and, the aligned components 182, 184 and 186 are received in the correspondingly narrow recess 176^* in the module 20'. The recess 176 is open at the sides to the adjacent modules 22' and 166. The sealing surface 180 of the radial seal 48' is preferably convex in cross-section as also suggested in Figures 5 to 7.

The end components 182 and 184 have opposed inclined inner end surfaces 188 and 190 with the angle of inclination corresponding to the taper of the respective wedging surfaces 192 and 194 of the intermediate component 186. The angle of inclination α of each inner end surface 188 and 190 to the radial direction may be in the range of, for example, 1 to 45°, preferably as shown about 10 to 12° and equal to each other. The length of the sealing surface 180 defined by the components 182 and 184 is such that, at least when the seal is new, the spacing between these components at the sealing surface is minimal, for example about 1mm. The portion of the sealing surface 180 not made up by the end components 182 and 184 is made up by the wedge shaped intermediate component 186. A leaf spring 196 is received in the closed end portion 198 of the recess 176 between the seal components 182, 184 and 186 and the housing module 20' extends between opposed shoulders 200 on the end components 182 and 184. The leaf spring is shaped so as to also engage both the housing module 20' at the closed end 198 of the recess and the wedge shaped intermediate component 186 and thereby urge all of the components into engagement with the peripheral working surface 37' of the piston 36' and at the same time, urge the seal end components 182 and 184 laterally into sealing engagement with the respectively adjacent modules 166 and 22'.

While the action of the leaf spring 196 on the opposed shoulder 200 of the seal end components 182 and 184 does provide some biassing of those components towards the opposed ends of the recess 176 defined by the modules 166 and 22 ' , the principal lateral bias is by virtue of the resilient biassing of the wedge shaped intermediate seal component 186 towards the peripheral working surface 37' of the piston whereby the wedging surfaces 192 and 194 urge the end seal components 182 and 184 into the sealing contact with the ends of the recess 176. Thus the continuous sealing surface 180 is maintained along the end and intermediate seal components.

The ends of the recess 176 defined by the modules 166 and 22' extend in respective radial planes perpendicular to the axis of rotation 15' of the crank shaft 14' and to the peripheral working surface 37' of the piston, and the end sealing surfaces 202 and 204 of the seal end components 182 and 184 are parallel to the ends of the recess and therefore also perpendicular to the sealing surface 180 of the radial seal 48'. The end sealing surfaces 202 and 204 intersect the radial sealing surface 180 at respective right angles to thereby provide a seal fully across the working volume 44'.

The seal components 182, 184 and 186 may be made of known seal materials such as cast iron incorporating spheroidal graphite or appropriate ceramic or sintered materials, but the wedge shaped intermediate component 186 is preferably less wear resistant than the end seal components 182 and 184 so that any part protruding from the main sealing surface 180, for example when the seal is new, will be quickly worn down to the correct shape by rubbing on the peripheral working surface 37' of the piston.

During its rotation, the piston 36' may tend to wobble slightly, and as it wobbles it may slide across the sealing surface 180 without tending to lift the end seal components out of sealing contact with the ends of the recess.

The seal components 182" and 184 have rebates

206 in their sides facing towards the adjacent combustion chamber (not shown) in the housing module 20' (or, in the case of two combustion chamber in the one housing module on both sides of the seal components as shown in Figures 6 and 7) to facilitate rapid build up of gas pressure from the combustion chamber in the closed end portion 198 of the recess 176 behind the seal components by passage of the combustion gases between the adjacent recess wall

207 (Figure 5) and that side of the seal components. The direction towards the adjacent combustion chamber is indicated by the arrow X in Figure 5. The build up of pressure in the closed end portion 198 biases the seal components against the piston surface 37' and, by virtue of the wedging effect of the intermediate seal component 186, also against the ends of the recess 176 defined by the adjacent modules 22' and 166, thus improving the sealing effect. This pressurizing effect is intermittent, with combustion in the working volume 44'.

A passage 208 extends through each of the adjacent casing modules 166 and 22' from the closed end portion 198 of the recess to each of the opposed side sealing assemblies 178 to permit combustion gas pressure to also urge those seals into better engagement with the respective side wall of the piston.

In Figure 4, only one of the associated side seal assemblies 178 has been shown complete, but the two opposed seal assemblies 178 are mirror images of each other and for convenience only the one will be described in detail.

The piston 36' has peripheral side seals 210 of known design disposed in outer annular grooves 212 in the side walls there of to engage the adjacent side wall of the working volume 44 defined by the respective modules 22' and 166. Each of the peripheral side seals 210 comprises two seal members 214 and 216 supported side by side in the associated groove 212 on an annular channel- shaped support member 218 which by means of a wave-spring 220 received in the channel of the support member within the groove biases the seal members axially outwardly into engagement with the side wall of the working volume.

The seal members 214 and 216 may be formed of cast iron while the support member 218 may be formed of a high temperature elastomer or, for example, stainless steel.

The peripheral side seals 210 are intended to prevent leakage of combustion gases from the or each combustion chamber around the side of the piston 36' to the opposite, low-pressure side of the working volume 44'. For this purpose, since the or each combustion chamber is disposed adjacent the peripheral working surface 37' of the piston, the peripheral side seals 210 should be disposed in the side walls of the piston as close as possible to the peripheral working surface. However, for practical reasons it is necessary for the peripheral side seals 210 to be slightly set back from the peripheral working surface of the piston, which tends to permit the combustion gases to leak along the side walls of the piston between the peripheral side seals 210 and the associated radial seal 48' . The side seal assemblies 178 are designed to alleviate this leakage.

Each side seal assembly 178 comprises a plunger 222 which is biased into contact with the respective side wall of the piston 36' between the peripheral side seal 210 and the radial seal 48 ' . The plunger may be formed of known sealing materials, including the aforementioned materials of the radial seal components 182, 184 and 186, but preferably is formed of a material softer than that of the radial"seal end components 182 and 184. The plunger extends through a passage 224 in the respective module 22' or 166, which passage extends in stepped manner wholly through the module parallel to the axis of rotation 15' of the crank shaft 14'. Adjacent the piston 36', the passage 224 provides a close sliding fit for the plunger 222 and is then stepped at 226 to seat an O-ring seal 228. Moving away from the piston 36', the passage 224 is stepped again to receive an end plate 230 through which the plunger 222 projects, from where the passage 224 opens into a main chamber 232 which is internally screw threaded. The passage 208 from the closed end portion 198 of the recess behind the radial seal 48' opens into the main chamber 232 adjacent the end plate 230. The plunger 222 projects into the chamber 232 and at that end is frictionally engaged with a flanged element 234, from which it may be separated, which provides a seat for a compression spring 236. The other end of the spring bears against the blind end 238 of a hollow externally screw threaded stud 240 which is screwed down onto the internal screw thread of the main chamber 232 to compress the spring 236 and bias the plunger 222 into engagement with the piston side wall.

The stud 240 has a hexagonal head clearly shown in Figure 3 but which has been partly omitted for clarity in Figure 4.

As the piston 36' wobbles in the housing module

20' the side seal assemblies 178 will move in and out to compensate for the piston sideways movement. The peripheral side seals 210 also tend to adjust to any sideways movement to the piston. As pressure builds up in the closed end portion 198 of the recess 176 behind the radial seal 48', as previously described,^' the increased pressure will be transmitted along the passage 208 into the main chamber 232 of the passage 224 and into the hollow portion of the stud 240 where the increased pressure will bear against the plunger flange element 234 and increase the bias on the plunger against the piston side wall.

It will be understood particularly from Figure 3, that access to the stud 240 to secure the side seal assembly 178 in place may be from the opposite side of the respective module 22' or 166 to that from which the plunger 222 projects. Without the piston 36' in the working volume 44' the plunger 222 may be removed and replaced by separating it from the flange element 234 and drawing it through the passage 224 into the working volume 44' . ^*

Referring to Figure 5 the plunger 222 is of cylindrical cross-section and is positioned at least approximately with one part of its peripheray tangential to the peripheral working surface 37' of the piston and to the corresponding sealing surface 180 of the radial seal 48' and with another part of its surface tangential to the adjacent surface of the peripheral side seal 210 so as to bridge the gap between the radial seal 48' and the peripheral side seal 210. The plunger 222 may^' have it axis extending along the central pla * 242 of the radial seal 48' , particularly for a twin combustion chamber arrangement such as is described in our aforementioned co-pending patent application. Ideally in a single combustion chamber arrangement, as shown in

Figure 6 the plunger 222 is disposed slightly offset to the combustion chamber side (X) of the housing module 20' to provide maximum sealing effect at the same time as the highest pressures occur in the working volume 44' . This will usually occur at about 10° to 21° from the central plane 242 of the radial seal 48' towards the combustion ^* chamber in the direction X and the selected offset is shown at 244.

In Figure 5, the corresponding portion of the piston 36' and of the peripheral side seal 210 is shown in outline only, and the dashed line 24'6 illustrates the path of the peripheral working surface 37' as the piston moves around the working volume 44' .

Neither the piston peripheral working surface 37' nor the cooperating working surface 46' of the working volume 44' in fact define a true trochoid, and the true trochoid is shown in part at 248. Arrow 250 indicates what is known as the equidistant of the true trochoid 248 to the inside envelope of the housing module 20' , which corresponds to the cooperating working surface 46', and arrow 252 indicates what is known as the equidistant of the true trochoid 248 to the piston envelope, which corresponds to the path 246 of the peripheral working surface 37' of the piston. The sealing surface 180 of the radial seal 48' ha"s a central tip 254 which is arcuate and has a radius centered on the intersection of the true trochoid 248 with the central plane 242 of the radial seal. The angle β defines the angular extremity of the tip radius from the central plane 242 and is generally in the range of about 10 to 21% corresponding to the normal to the tangent of the piston surface portion at top dead centre. At the top dead centre, or extreme position, of the piston 36', the tip radius on the seal 48' is equal to the equidistant 252 of the true trochoid to the piston envelope.

Outwardly of the central tip 254, the sealing surface 180 corresponds in shape generally to the peripheral working surface 37' of the piston.

In an alternative embodiment, shown in Figure

6, for a twin combustion chamber arrangement, two side seal assemblies 178 incorporating respective plungers

222, or one side seal assembly 178 incorporating dual plungers 222, which may be independently or jointly spring biassed, may be disposed adjacent each of the opposed sides of the piston 36' with the two plungers respectively offset as described above towards the associated combustion chambers. As may be seen in Figure 6 the radial seal 48 ' has rebates 206 on both sides of the seal components.

In an engine with two combusτion chambers at respective ends of the housing module 20 ' , an even more efficient but slightly more expensive to manufacture form of the side sealing assembly plunger 222 is shown in Fig.

7. In this case the cross section of the plunger is essentially kidney-shaped and comprises two substantially semi circular ends 256, a concave section 258 of radius equal to the distance 252 between the true trochoid 248 and the piston envelope and a convex section 260 of radius equal to the distance between the true trochoid 248 and the radially outer edge of the peripheral side seal 210. The kidney-shaped plunger 222 extends across the central plane 242 of the radial seal 48 ' so that the substantially semi circular ends 256 of the plunger correspond essentially to the two individual plungers 222 described with reference to Figure 6. This shape of plunger 222 effectively seals the gap between the piston 36' and the side walls of the adjacent housing modules 22' and 166 between the peripheral working surface 37' piston and the peripheral side seals 210. With this configuration of plunger 222 this gap is sealed at all positions of the piston and not mainly at the same time as the highest pressures apply in the working volume 44 ' .

The plunger 222 is preferably of a material such as lead bronze softer than the adjacent portion of the radial seal 48' so that, as the radial seal wears with use of the engine, if the end portion of the seal 48' which overlies the gap between the piston side wall and adjacent housing module 166 on 22' (clearly visible in Figure 4) does not wear as quickly, the end portion of "^"the radial seal wils embed into the material of the plunger 222, thereby ensuring continued effective sealing across the peripheral working surface 37' of the piston 36' by the radial seal 48'.

It will be readily .appreciated that the side sealing assembly 178 may be used with many different forms of radial seal, including a one piece seal component.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modi_fications which fall within its spirit and scope.

Claims

1. A rotary piston machine comprising a casing, a piston having a peripheral working surface of trochoidal type with an outer envelope and being eccentrically rotatably mounted in the casing between opposed side walls, the casing having a cooperating working surface which substantially conforms to the outer envelope of the trochoid and having mounted in a recess at a convex inflexion of the cooperating working surface a radial seal having a sealing surface which extends across the peripheral working surface of the piston, the radial seal comprising a plurality of seal members which together define the sealing surface and which are biased towards the peripheral working surface of the piston, an intermediate seal member being resiliently biased and wedge shaped whereby under the resilient biasing action of the said intermediate seal member opposed wedging surfaces thereof cooperate with adjacent seal members to urge opposed end seal members into sealing contact with respective ends of the recess.

2. A rotary piston machine according to Claim 1 wherein the cooperating working surface has two or more convex inflexions and wherein a radial seal is mounted in a respective recess at each convex inflexion.

3. A rotary piston machine according to Claim 1 wherein all of the seal members are resiliently biased towards the piston.

4. A rotary piston machine according to Claim 1 wherein the seal members are resiliently biased into engagement with the ends of the recess.

5. A rotary piston machine according to Claim 1 wherein the resilient biasing is achieved by fluid pressure behind the radial seal in the recess.

6. A rotary piston machine according to Claim 5 wherein the location of the seal members in the recess is such that fluid pressure in the casing between the piston and the cooperating working surface may enter the recess to urge the seal members into contact with the peripheral working surface of the piston.

7. A rotary piston machine according to Claim 1 wherein the resilient biasing is performed by spring means.

8. A rotary piston machine according to Claim 7 wherein the spring means comprises a leaf spring.

9. A rotary piston machine according to Claim 1 wherein the opposed wedging surfaces of the intermediate seal member are inclined to the radial direction.

10. A rotary piston machine according to Claim "9 wherein surfaces of the seal members other than the intermediate seal members which cooperate with the opposed wedging surfaces are correspondingly inclined.

11. A rotary piston machine according to Claim 9 wherein the opposed wedging surfaces are equally and oppositely inclined.

12. A rotary piston machine according to Claim 9 wherein the angle of inclination to the radial direction of each of the opposed wedging surfaces is in the range 1 to 45°, preferably about 10 to 12°.

13. A rotary piston machine according to Claim 1 wherein the intermediate seal member comprises from 0.1 to 10% of the length of the sealing surface.

14. A rotary piston machine according to Claim 1 wherein the intermediate seal member is less wear resistant than the remaining seal members.

15. A rotary piston machine according to Claim 1 wherein the opposed wedging surfaces of the intermediate seal member cooperate directly with the end seal members.

16. A rotary piston machine according to Claim 1 wherein the casing is of modular construction with the piston being rotatable in a first module in which the recess is also provided, said recess being axially open-ended in said first module and wherein the ends of the recess are defined by adjacent modules.

17. A rotary piston machine comprising a casing, a piston having a peripheral working surface of trochoidal type with an outer envelope and being eccentrically rotatably mounted in the casing between opposed side walls, the casing having a cooperating^'working surface, which substantially conforms to the outer envelope of the trochoid, the piston having a respective peripheral axial seal extending around each side wall thereof adjacent the peripheral working surface and in sealing contact with the adjacent side wall of the casing, the casing having at a convex inflexion of the cooperating working surface a radial seal having a sealing surface which extends across the peripheral working surface of the piston, and wherein side sealing means projects from at least one of the side walls of the casing adjacent the radial seal and is resiliently biased into sealing contact with the respective side wall of the piston to at least substantially seal a gap between the radial seal and the respective peripheral axial seal.

18. A rotary piston machine according to Claim 17 wherein side sealing means project from respective side walls of the casing and are resiliently biased into sealing contact with the respective side walls of the piston.

19. A rotary piston machine according to Claim 17 wherein the resilient biasing is by spring means.

20. A rotary piston machine according to Claim 19 wherein the spring means comprises a helical spring.

21. A rotary piston machine according to Claim 17 wherein at least part of the resilient biasing is provided by fluid pressure.

22. A rotary piston machine according to Claim 21 wherein a passage provides communication between the side sealing means and a recess in the casing in which the radial seal is received, said fluid pressure being developed in said recess and communicated with the side sealing means by way of the p'assage.

23. A rotary piston machine according to Claim 17 wherein the casing is of modular construction with the piston and radial seal disposed in a first module and the side sealing means mounted in an adjacent module.

24. A rotary piston machine according to Claim 17 wherein the portion of the side sealing means in engagement with the piston is positioned approximately with one part of its surface tangential to the peripheral working surface of the piston and the tip of the radial seal, and another part of its surface tangential to the adjacent surface of the peripheral axial seal.

25. A rotary piston machine according to Claim 17 wherein the portion of the side sealing means in contact with the piston is formed of a material softer than that of the adjacent portion of the radial seal.

26. A rotary piston machine according to Claim 17 in which a combustion chamber is provided in the cooperating working surface and wherein the side sealing means is angularly offset from the radial seal axial centre plane towards the combustion chamber.

27. A rotary piston machine according to Claim 26 wherein said angular offset is in the range 10 to 21°.

28. A rotary piston machine according to Claim 17 wherein two opposed combustion chambers are provided in the cooperating working surface and wherein two resiliently biased side sealing means are provided, each angularly offset from the radial seal axial centre plane towards the respective combustion chambers.

29. A rotary piston machine according to Claim 17 wherein two opposed^' combustion chambers are provided in the cooperating working surface and wherein the cross- section of the portion of the side sealing means in contact with the piston is substantially kidney-shaped with said portion centred on the radial seal axial centre plane and with part circular ends of the kidney-shaped cross-section extending to respective sides of the centre plane.

30. A rotary piston machine according to Claim 17 wherein the radial seal is according to Claim 1.