Patent Publication Number: US-6983729-B2

Title: Rotary piston machine

Description:
THIS APPLICATION IS A CONTINUATION OF INTERNATIONAL APPLICATION PCT/EP02/08898 FILED AUG. 8, 2002, WHICH CLAIMS PRIORITY OF GERMAN PATENT APPLICATION S.N. 101 39 286.9 FILED AUG. 9, 2001. 

   The invention relates to a rotary piston machine with an oval chamber and a preferably oval rotary piston guided therein. 
   In mathematics, an “oval” is a non-analytic, closed, plane convex figure, which is composed of circular arcs. The circular arcs are composed continuously and differentiably. In the points, in which the circular arcs join each other, the curve is continuous. Also the tangents in which the two circular arcs change into each other coincide. The curve is differentiable. In the points where the circular arcs join the second derivative—which determines the curvature—has a discontinuity. The oval consists, alternatingly, of circular arcs having a first, relatively small radius of curvature and a second, relatively large radius of curvature. The order of the oval is determined by the number of pairs of circular arcs with the first and the second radius of curvature. An oval of second order or bi-oval is “ellipse-like” with two diametrically opposite circular arcs of smaller diameter, which are interconnected by two circular arcs of larger diameter. 
   The invention relates to a rotary piston machine, wherein a housing forms a prismatic chamber, the cross section of which represents an oval of odd order, thus, for example, an oval of third order. The chamber forms cylindrical inner wall sections alternatingly with the first smaller and the second larger radius of curvature. A rotary piston is movable in such an oval of third (fifth or seventh and higher) order, the cross section of the rotary piston, preferably but not necessarily, being an oval, the order of which is by one lower than the order of the oval of the chamber. The oval used for the rotary piston—even if it has a higher order—has a twofold symmetry, i.e. it is mirror symmetric with respect to two mutually orthogonal axes. This rotary piston has two diametrically opposite nappe sections, the radii of curvature of which are equal to the smaller (first) radius of curvature of the oval of the chamber. If the cross section of the rotary piston forms an oval, then the second, larger radius of curvature of this oval is equal to the second radius of curvature of the oval defining the chamber. In a certain interval of movement, this cylindrical nappe section of the rotary piston is located in a cylindrical inner wall section complementary thereto of the chamber, which section has the same smaller radius of curvature. The second diametrically opposite cylindrical nappe section of the rotary piston slides along the opposite cylindrical inner wall section of the chamber, which section has the larger radius of curvature. In this way, two working chambers are defined in the chamber by the rotary piston, of which, during rotation of the rotary piston, one becomes larger and the other one becomes smaller. The rotary piston, during this motion, rotates about an instantaneous axis of rotation. This instantaneous axis of rotation coincides with the cylinder axis of the first cylindrical nappe section. Therefore, this instantaneous has a well-defined position relative to the rotary piston. In this interval of movement, this instantaneous axis of rotation, of course, also coincides with the housing-fixed cylinder axis of the cylindrical inner wall section of smaller radius of curvature, in which the rotary piston rotates. This rotation continues, until the second cylindrical nappe section of the rotary piston reaches a stop position. In this stop position, the second cylindrical nappe section is located within the smaller diameter inner wall section following the opposite inner wall section of larger radius of curvature. 
   Further rotation of the rotary piston about the axis of rotation valid up to now is no longer possible. Therefore, the instantaneous axis of rotation, for the next interval of movement, jumps into another position, namely the cylinder axis of the second cylindrical nappe section. Also this new instantaneous axis of rotation is in a well-defined position relative to the rotary piston. It coincides, during the next interval of movement, with the cylinder axis of the cylindrical inner wll section, in which now the second cylindrical nappe section of the rotary piston rotates. During this interval of movement, the “first” cylindrical nappe section again slides along the oppisit inner wall section having the larger radius of curvature. 
   With such a rotary piston machine, the rotary piston always rotates in the same direction of rotation but alternatingly about different instantaneous axes of rotation, the axes of rotation “jumping” after each interval of movement. Two such instantaneous axes of rotation are defined with reference to the piston, namely by the cylinder axes of the diametrically opposite cylindrical nappe sections. With reference to the housing and to the chamber defined therein, the instantaneous axis of rotation jumps between the “corners” of the oval, thus the cylinder axes of the inner wall sections having the smaller radius of curvature. 
   During each interval of movement, the volume of one working chamber is increased up to a maximum value, while the volume of the respective other working chamber is decreased to a minimum value. In the ideal case, when the cross section of the rotary piston is also an oval, the volume of the working chamber is increased from virtually zero to the maximum value, or is decreased to virtually zero, respectively. Such a rotary piston machine can be used as a two or four cycle combustion engine (with internal combustion). It may, however, also operate as a compressed air motor, as a hydraulic motor or as a pump. 
   PRIOR ART 
   U.S. Pat. No. 3,967,594 and U.S. Pat. No. 3,996,901 disclose rotary piston machines having an oval piston in an oval chamber. In this design, the cross section of the piston is bi-oval. This bi-oval piston is movable in a tri-oval chamber. In this prior art rotary piston machine, expensive transmissions are provided, in order to transmit the rotary movement of the rotary piston to the driving or driven shaft. 
   DE 199 20 289 C1 also describes a rotary piston machine, wherein the cross section of a prismatic chamber defined in a housing is tri-oval with first and second circular arcs of alternatingly a smaller radius of curvature and a larger radius of curvature changing into each other continuously and differentiably. A rotary piston with bi-oval cross section is guided in the chamber. The bi-oval cross section is defined, alternatingly, by first and second circular arcs having the smaller and larger, respectively, radii of curvature of the tri-oval cross section of the chamber, which again change into each other continuously and differentiably. The bi-oval rrotary piston carries out the cycles of movement described above with the jumping instantaneous axes of rotation. There, the movement of the rotary piston is picked-off in a very simple way: A driving or driven shaft carries a pinion. The rotary piston has an oval aperture with an internal toothing. The longer axis of the cross section of the aperture extends along the short axis of the bi-oval cross section of the rotary piston. The pinion continuously meshes with the internal toothing. 
   DISCLOSURE OF THE INVENTION 
   The invention is based on the following discovery: 
   With the prior art rotary piston machines of the type mentioned in the beginning, problems may arise in those moments, when the instantaneous axis of rotation, after completion of one interval of movement, and prior to the beginning of the next interval of movement jumps from one position to the other one. In this position, namely, the kinematics is not “closed”. If, at this moment, a force transverse to the connection plane of the two possible instantaneous axes of rotation is exerted on the rotary piston out of the working chamber, for example because a fuel mixture is ignited in the working chamber having minimum volume, then the rotary piston may be urged transversely into the other working chamber, which tapers like an “arcuate triangle”, and may jam therein. Then the piston does not carry out a rotary movement about the new instantaneous axis, but both axes are moved translatorily into a jamming position. This risk exists, in particular, with slow movements of the rotary piston, where the rotary piston is not yet maintained in further rotation over the jump of the axis of rotation, by the kinetic energy of its rotation. 
   It is an object of the invention to ensure, in a rotary piston machine of the type mentioned in the beginning, safe and reliable transition from one instantaneous axis of rotation to the other one, when changing from one interval of movement to the next one. 
   This object is achieved by fixing means for temporarily fixing the instantaneous axis of rotation for the subsequent interval of movement, when said changed position has been reached. 
   In this way, the kinematics is closed. It is ensured that the rotary piston during transition from one interval of movement to the other one positively carries out a rotary movement about the new instantaneous axis of rotation an cannot make translatory movement in transverse direction. Once the continuing rotation of the rotary piston has been ensured in this way, the fixing may be released again. The fixing should be released as soon as possible in order not to cause unnecessary friction. 
   The fixing means have to release the rotary piston prior to reaching the next stop position. 
   Fixing can be achieved in that coupling structures are provided on one end face of the rotary piston in the area of the possible piston-fixed instantaneous axes of rotation, and axially movable shafts having complementary coupling structures are mounted on the side of the housing and on the axes of the first cylindrical inner wall sections, which structures are moved into engagement with the coupling structures of the rotary piston to fix the respective instantaneous axis of rotation. To this end, the piston-side coupling structures may be conical recesses in the end faces of the rotary piston and the shaft-side coupling structures may be conical heads, which can be inserted into the conical recesses to establish the coupling. Because of the conical structures, the shaft and the rotary piston will be centerd to each other. 
   The shafts may be actuated by electrical actuators, for example by solenoids, which are energised .at certain moments of the interval of movement. This provides a simple design, as commercially available components can be used. Because of the electrical actuation, the actuating moments can be adjusted conveniently, and the time response of the system can be taken into account by conventional electrical or electronic means. The electrical actuators may be controlled by sensor means, which respond to the rotary motion of the driving or driven shaft. 
   Similar to the DE 199 20 289 C1, the torque can be picked off or exerted in simple way in that a driving or driven shaft with a pinion extends centrally through the chamber, and the rotary piston has an aperture which is elongated in cross section, the longer axis of the aperture being normal to the center plane of the rotary piston, and the aperture has an internal toothing which meshes with the pinion. 
   The shape of the aperture is determined by the shape of the rotary piston and the diameter of the pinion. The lateral edges of the aperture are circular arcs, which are curved about the two instantaneous axes of rotation. At both ends, the circular arcs are interconnected by circular arcs the radii of which are substantially equal to the radius of the pinion. The axis of the driving or driven shaft moves, during the revolution of the rotary piston, along a trajectory in the shape of a “two-angle”, i.e. a curve having two oppositely curved circular arcs forming two corners. 
   If the radii of the interconnecting circular arcs at the end of the aperture were smaller than the radius of the pinion, then the pinion would not have space and would jam between the circular arcs curved about the instantaneous axes of rotation. If the radii of the interconnecting circular arcs were substantially larger than the radius of the pinion, then the continuous drive would not operate. In the transition moment between the cycles of movement, the pinion would have to change over from one of the circular arcs curved about the instantaneous axes of rotation to the other one. During this change-over, cinematic problems can arise with a continuous, concave internal toothing along the edges of the aperture. 
   According to a further modification, provision is made that the internal toothing has opposite concave gear racks on both sides of the longer axis of the aperture, and the internal toothing, furthermore, comprises non-concave end toothings at the ends of the aperture. The end toothings may be linear gear racks. The end toothings may, however, also be concave gear racks. 
   Surprisingly, it can be shown that with such structure of the end toothings of the aperture the cinematic problems arising with the prior art can be solved. 
   In order to achieve high efficiency, the rotary piston ought to be guided in the oval chamber as easy-running as possible to keep friction and wear low. On the other hand, a safe seal between the working chambers has to be ensured. Leaks also reduce the efficiency. 
   To this end, advantageously, longitudinal grooves are formed in said diametrically opposite cylindrical nappe sections of the rotary piston, the grooves accommodating seals for sealing between the working chambers, the seals engaging the inner surface of the chamber, the longitudinal grooves being arranged to be connected, through a valve assembly controlled by the pressure difference between the working chambers, with the working chamber of higher pressure, if a large pressure difference occurs. The valve assembly may comprise a bore provided in the rotary piston between the working chambers adjacent the rotary piston, the bore being separated, at both ends, from the working chambers by sleeve-shaped closure pieces, and a slide valve being guided in the bore and being provided with reduced diameter sections on both sides, whereby, in end positions of the slide valve a respective reduced diameter section engages the connection bore of the adjacent closure piece. 
   If the pressure difference between the working chambers is small, then the seals can engage the inner wall of the oval chamber with small force. This reduces friction and increases the efficiency. If a large pressure difference occurs, then the pressure prevailing in the working chamber of higher pressure is directed under the seals. The seals are urged more strongly into engagement with the inner wall of the chamber. The higher pressure acting on the slide valve shifts the slide valve in the bore towards the side of lower pressure. Thereby, the connecting bore is closed by the reduced diameter section. Then the higher pressure prevails within the bore and becomes effective in the grooves under the seals. 
   In order to improve the sealing effect with low contact pressure, the seals may have a convex profile matching with the radius of curvature of one of the cylindrical inner wall sections. Preferably, this is achieved in that pairs of parallel grooves and seals are provided in the two diametrically opposite cylindrical nappe sections, and one seal of each pair has a convex profile with the first radius of curvature, and the other seal of each pair has a convex profile with the second radius of curvature. 
   Another, particularly advantageous solution is that the seals are longitudinally subdivided into (notional) strips, the radius of curvature in at least one strip is equal to the smaller radius of curvature of the first inner wall sections and in at least one strip is equal to the larger radius of curvature of the second inner wall sections. Each of the seals, in two outer strips has the smaller radius of curvature and, in the intermediate inner strip, has the larger radius of curvature. 
   Another aspect of the invention provides that the cross section of the chamber of the rotary piston machine is an oval of odd order (2n+1)&gt;3, and the cross section of the rotary piston is an oval of even order 2n, in particular a quatro-oval or a sext-oval, the rotary piston having two diametrically opposite main apexes with the two diametrically opposite cylindrical nappe surfaces, and the piston-side possible instantaneous axes of rotation are located on the center plane interconnecting the main apexes. 
   This aspect of the invention is based on the discovery that an oval of higher order than two can be used as piston without increasing the number of (piston-fixed) possible axes of rotation. 
   Rotary piston machines with chambers and rotary pistons of higher order permit realisation of drives having extremely low rotary speeds with correspondingly extremely high torques and particularly high positioning accuracy of the driven shaft. 
   In a further modification of the invention, the combustion chamber has a cross section which has the shape of a figure of equal height, and the piston has a shape adapted to the shape of the combustion chamber, wherein the piston is mirror-symmetric to the center plane, the center plane intersecting two centers of curvature of the combustion chamber which have maximum distance from each other, and the nappe of the piston, in one stop position on one side of the center plane, completely abuts the inner wall of the smaller portion of the combustion chamber resulting therefrom. 
   Embodiments of the invention are described in greater detail with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a bi-oval rotary piston rotating in a tri-oval chamber of a housing. 
       FIG. 2  shows a quarto-oval rotary piston rotating in a pent-oval chamber of a housing. 
       FIG. 3  shows a sext-oval rotary piston rotating in a sept-oval chamber of a housing. 
       FIG. 4  shows, for an arrangement according to  FIG. 1 , the single trajectory of the possible axes of rotation of the rotary piston relative to the housing as well as the trajectory of the axis of the driving shaft relative to the rotary piston. 
       FIG. 5  shows the kinematics of the power transmission system in an arrangement according to  FIG. 1  with odd toothed racks. 
       FIG. 6  shows the kinematics of the power transmission system in an arrangement of  FIG. 1  at the moment shortly after leaving the stop position with convex toothed racks. 
       FIGS. 7.1  to  7 . 12  show the motion phases of the rotary piston in the arrangement of  FIG. 1 . 
       FIG. 8  shows for the arrangement according to  FIG. 2 , the single trajectory of the possible axes of rotation of the rotary piston relative to the housing as well as the trajectory of the axis of the driving or driven shaft relative to the rotary piston. 
       FIG. 9  shows similarly to  FIG. 5 , the kinematics of the power transmission system in the arrangement of  FIG. 2  with the toothed bars. 
       FIG. 10  shows the kinematics of the power transmission system in the arrangement of  FIG. 2  similarly to  FIG. 6 , a the moment shortly after leaving the stop position with the convex toothed arcs. 
       FIGS. 11.1  to  11 . 20  show, similarly to  FIGS. 7.1  to  7 . 12 , the motion phases of the rotary piston in the arrangement of  FIG. 2 . 
       FIG. 12  shows, similarly to  FIG. 4  for an arrangement according to  FIG. 3 , the single trajectory of the possible axes of rotation of the rotary piston relative to the housing as well as the trajectory of the axis of the driving shaft relative to the rotary piston. 
       FIG. 13  shows, similarly to  FIG. 4 , the kinematics of the power transmission system in an arrangement of  FIG. 3  with the toothed racks. 
       FIG. 14  shows, similarly to  FIG. 5 , the kinematics of the power transmission system in an arrangement of  FIG. 3  a the moment shortly after leaving the stop position with convex toothed arcs. 
       FIGS. 15.1  to  15 . 28  show, similarly to  FIGS. 7.1  to  7 . 12 , the motion phases of the rotary piston in the arrangement of  FIG. 3 . 
       FIG. 16  schematically shows a design embodiment of the fixing means for temporarily fixing one instantaneous axis of rotation respectively in the stop position when the rotary piston is changing the intervals of movement. 
       FIG. 17  schematically shows a slide valve control for controlling the pressure of the seals against the inner wall of the housing. 
       FIG. 18  schematically shows an arrangement of seals the profile of which are alternatingly adapted to the radii of curvature of the alternating inner wall sections of the chamber. 
       FIGS. 19A  and B show a modified embodiment of the seals, in which each seal in outer longitudinal strips is adapted to the radius of curvature of the inner wall sections having a relatively small radius of curvature and in which each seal in interposed longitudinal strips is adapted to the radius of curvature of the inner wall sections having relatively large radius of curvature. 
       FIG. 20  shows the rotary piston machine of  FIG. 1  with the valve assembly for pressing the seals. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1  the housing of a rotary piston machine is designated by  30 . This housing  30  forms a prismatic chamber  32 . The cross section of this chamber is an oval of third order. The cross section is composed of three circular arcs  34 ,  36 ,  38  having all three the same relatively small radius of curvature and three circular arcs  40 ,  42 ,  44  having all three the same relatively large radius of curvature. The circular arcs having a small and a large radius of curvature  34 ,  36 ,  38  and  40 ,  42 ,  44 , respectively are alternating. A circular arc, for example  34  having a small radius of curvature joins a circular arc  40  having a larger radius of curvature counter clockwise in  FIG. 1 . A circular arc  36  of smaller radius of curvature joins the latter and so on. The circular arcs join each other continuously and smoothly differentially. Accordingly, the inner wall of the chamber is composed of cylindrical inner wall sections, that is three cylindrical wall sections  46 ,  48  and  50  corresponding to the circular arcs  34 ,  36  and  38 , respectively, designated herein as “first” inner wall sections, and three cylindrical inner wall sections  52 ,  54  and  56 , designated herein as “second” wall sections. One can see that the oval and therewith the chamber  32  has a threefold symmetry. There are three symmetry planes angularly offset by 120°. The symmetry planes intersect in an axis  58 . 
   A rotary piston  60  is guided in the chamber  32 . The rotary piston  60  is prismatic. The cross section of the rotary piston  60  is an oval of second order. This oval is composed of two circular arcs  62  and  64  of relatively small radius of curvature and two circular arcs  66  and  68  of relatively large radius of curvature. The small and large radii of curvature of the oval of the rotary piston  60  correspond to the small and large radii of curvature, respectively, of the oval of the chamber  32 . Also herein, the circular arcs with small and large radius of curvature are alternating. The alternating circular arcs  62 ,  66 ,  64 ,  68  join each other continuously and smoothly. The prismatic rotary piston  60  comprises, in accordance with the circular arcs, cylindrical nappe sections  70  and  72  having relatively small radius of curvature and cylindrical nappe sections  74  and  76  having relatively large radii of curvature. The cylindrical nappe sections  70  and  72  are diametrically opposite. The rotary piston has a symmetry of second order: one symmetry plane extends through the cylinder axes of the diametrically opposite cylindrical nappe sections  70  and  72  of smaller radius of curvature. A second symmetry plane extends perpendicularly thereto through the cylinder axes of the cylindrical nappe sections  74  and  76  of relatively large radii of curvature. 
   One can see that the rotary piston  60  is guided in the chamber  32  with positive fit. In  FIG. 1 , the cylindrical nappe section  70  is situated in the cylindrical inner wall section  34  of the chamber  32 , the nappe section  70  and the inner wall section  34  having the same radius of curvature. The cylindrical nappe section  72  engages the inner wall section  54  of the chamber  32  facing the inner wall section  34 . When the rotary piston  60  is rotating, as indicated, counter clockwise in  FIG. 1 , the cylindrical nappe section  70  of the rotary piston is rotating in the cylindrical inner wall section  46  of the chamber  32 . The diametrically opposite cylindrical nappe section  72  of the rotary piston  60  is sliding along the cylindrical inner wall section  54  of the chamber  32 . 
   In  FIG. 1 , the rotary piston  60  forms two working chambers  78  and  80  in the chamber  32 , which working chambers are sealed against each other by the rotary piston  60 . When the rotary piston  60  rotates counter clockwise in  FIG. 1 , the working chamber  78  in the observed working section is increased, while the working chamber  80  is decreased. 
   The rotary piston machine illustrated in  FIG. 1  is an internal combustion engine in which a fuel is ignited and burnt in the working chamber  78  and  80 , respectively, of the rotary piston machine. Accordingly, one inlet valve  82 , 84  and  86 , respectively for feeding the fuel, one outlet valve  90 ,  92  and  94  and one spark plug  96 ,  98 , and  100  are provided in each of the cylindrical inner wall surfaces  52 ,  54  and  56 , respectively, having the larger radius of curvature, these elements being known technology and, therefore, are illustrated only schematically and symbolically in  FIG. 1 . The spark plugs  96 ,  98  and  100  are located in combustion chamber cavities  97 ,  99  and  101  respectively formed in the cylindrical inner wall sections  52 ,  54 , and  56 , respectively. 
   The rotary movement of the rotary piston is picked-off or (when applying to a pump) initiated in the following way: 
   A driving or driven shaft  102  extends centrally through the chamber  32 . The driving or driven shaft  102  is mounted in closure pieces of the housing  10  which are not illustrated in  FIG. 1 . The axis of the driving or driven shaft  102  coincides with the central axis  58 . A pinion  104  is located on the driving or driven shaft  102 . Instead of one single pinion, two pinions biased in known way may be provided, the pinions suppressing the game from the driving or driven system in co-operation with the counter toothing. A longitudinal aperture  106  extends through the rotary piston  60 . The rotary piston  60  has an internal toothing described hereinafter. The large axis of the aperture is extending perpendicularly to the first symmetry plane of the rotary piston  60  into the second symmetry plane. The internal toothing is composed of two concave toothed racks  108  and  110  on opposite longitudinal sides of the aperture  106 . The toothed racks  108  and  110  are curved about the cylinder axes of the cylindrical nappe sections  62  and  64 , respectively. These cylinder axes define piston-fixed instantaneous axes of rotation  112  and  114 , respectively, of the rotary piston  60 . Linear toothed racks  116  and  118  are provided at the ends of the aperture  106 . They may also be replaced by the convex toothing arcs. 
   A seal is designated by  120 , which seal causes a sealing between the rotary piston  60  in the area of the cylindrical nappe sections  70 ,  72  and the cylindrical inner wall sections of the chamber  32 . The seals  120  will be described in greater detail hereinafter. 
   The movement of the rotary piston  60  in the chamber  32  is explained with reference to the schematic  FIG. 4 . The rotary piston  60  is moving in subsequent similar intervals of movement. The rotary piston  60  is rotating alternatingly about respectively one of two instantaneous axes of rotation  112  and  114 , defined by the cylinder axes of the cylindrical nappe sections  62  and  64 , respectively. 
   In  FIG. 4 , the rotary piston  60  is located, at the beginning of an interval of movement, in a position in which half of the two cylindrical nappe sections  70  and  72  of the rotary piston are in the inner wall sections  46  and  48 , respectively, complementary thereto. The circular arc  66  of larger radius of curvature engages the inner wall section  52  complementary thereto. From this position, the rotary piston is rotating counter clockwise in  FIG. 4  about the instantaneous axis of rotation  112 . The cylindrical nappe section  70  rotates like in a bearing in the cylindrical inner wall section  46  of the chamber  32  complementary thereto. The cylindrical nappe section  72  slides to the right in  FIG. 4  on the inner wall section  54 . This rotation about the instantaneous axis of rotation  112  is continued until the rotary piston  60  engages the face of the chamber  32  on the right side in  FIG. 4 . This is a “stop position”. Half of the cylindrical nappe section  72  is then located in the inner wall section  50  complementary thereto. The nappe section  68  engages the inner wall section  56 . Thus, the rotary movement about the instantaneous axis of rotation  112  is limited. The described movement is an “interval of movement”. 
   In the subsequent interval of movement, the rotary piston rotates in a similar way about the other instantaneous axis of rotation  114 . In the subsequent interval of movement, this instantaneous axis of rotation  114  coincides with the cylinder axis  122  of the cylindrical inner wall section  50 . The rotary piston  60  now rotates about this new instantaneous axis of rotation ( 122  referring to the chamber or  114  referring to the rotary piston). The nappe section  72  is rotating in the inner wall section  50 , while the nappe section  70  is sliding at the inner wall section. 
   Thus, each interval of movement comprises a movement into a stop position followed by a jump of the instantaneous axis of rotation  112  to  114  or vice versa.  FIG. 4  shows the trajectory  124  of the axis of rotation  112  or  114  not acting as instantaneous axis of rotation in an interval of movement: In the first interval of movement the axis  114  is moving on the arc  126  to the position defined by the cylinder axis  122 . Then, an axis jump occurs: Now, the axis  112  rotates about the instantaneous axis of rotation  114  in the position of the cylinder axis  122  along the arc  128 . In the third interval of movement, the axis  112  has reached the position of the cylinder axis of the inner wall section  48  and becomes again instantaneous axis of rotation. The axis  114  moves along the arc  130 . Then, the arrangement illustrated in  FIG. 4  is reached again, however, the instantaneous axes of rotation  112  and  114  having changed their position. Starting out herefrom, there are three other intervals of movement until the state of  FIG. 4  is reached again. The trajectory  124  thus represents an arcuate triangle, which, however, is not passed continuously. 
     FIG. 4  also shows the trajectory  132  passed by these movements of the rotary piston  60  from the axis  58  of the driving or driven shaft  102  relative to the rotary piston  60  and the aperture  106 . This trajectory is a twoangle, i.e. a geometric figure having two oppositely curved circular arcs meeting in two corners. The circular arcs are curved herein about the two possible instantaneous axes of rotation  112  and  114  of the rotary piston  60  and symmetrical to the “transversal” symmetry plane of the rotary piston. In the end position of  FIG. 4 , the transversal symmetry plane passes through the axis  58 . In the “stop position”, the axis  58  is located on one of the corners of the twoangle on the transversal symmetry plane. The curvature of the circular arcs depends on the position of the axes of rotation  112 ,  114  relative to this transversal symmetry plane and therewith on the radius of curvature of the two nappe sections  70  and  72 . The toothed racks  108  and  110  are also curved about the possible instantaneous axes of rotation  112  and  114 , respectively. Their distance from the two circular arcs  134  and  136 , respectively, is equal to the radius of the pinion  104 . In the stop position there will be a jump of the instantaneous axis of rotation from for example  112  to  114 . When the rotary piston  60  is rotating during one interval of movement for example about the instantaneous axis of rotation  112 , then the axis  58  of the driving or driven shaft  102  is moving on the circular arc  134  of the trajectory  132 , and the pinion  104  engages the concave toothed rack  108 . After having reached the stop position the instantaneous axis of rotation jumps as illustrated in  FIG. 5 . The rotation is now effected about the instantaneous axis of rotation  114 . The axis  58  of the driving or driven shaft  102  is then in one corner of the twoangle and is moving in the next interval of movement along the circular arc  136 . Correspondingly, the pinion  104  then must engage the concave toothed rack  110  curved about the instantaneous axis of rotation  114 . In the stop position the circumference of the pinion must join the concave toothed racks  108  and  110  continuously and smoothly. However, the transmission of the pinion  104  from one toothed rack to the other  108  resp.  110  must be realised without blocking. This would be the case, if the toothed racks would form an oval of second order in total with the radius of curvature about the instantaneous centers of rotation and the radius of curvature of the gearwheel. For this reason, the odd or linear tooth racks  116  and  118  are provided at the ends of the aperture  106 . Also convex toothed racks (toothed bars) might be provided instead of linear toothed racks  116  and  118 . There are gaps between the concave toothed racks  108  and  110  and the linear or convex toothed racks  116  and  118 , the pinion  104 , however, just coming out of the engagement with the concave toothed rack  108  or  110 , when engaging the linear or convex toothed rack  116  or  118 . It can be shown that the kinematics is closed and that a safe and correct transition from one concave toothed rack to the other is ensured without interruption of the driving connection. 
     FIG. 5  shows the kinematics of the power transmission exactly in the stop position.  FIG. 6  shows the power transmission shortly thereafter, when the rotation is effected about the instantaneous axis of rotation  114  and the pinion engages the concave toothed rack  110 . 
     FIGS. 7.1  to  7 . 12  show the different operational phases of a rotary piston machine according to  FIG. 1 , operating as an internal combustion engine. 
     FIG. 7.1  shows the rotary piston machine in the position of  FIG. 1 . A working chamber  78  and a working chamber  80  are formed. The combustion takes place in the working chamber  70 , i.e. fuel is introduced or injected and ignited. The combustion gases urge the rotary piston  60  counter clockwise about the instantaneous axis of rotation  112 . The working chamber  78  is expanding, the working chamber  80  is reduced. The air in the working chamber  80  is compressed. This is continued until the stop position, illustrated in  FIG. 7.2 . The working chamber  78  has a maximum volume. The volume of the working chamber  80  is zero except for the combustion chamber cavity  101 . This shall be called “first” interval of movement. 
   In this stop position, fuel is injected into the combustion chamber cavity  101  and ignited. The combustion gases urge the rotary piston  60  further counter clockwise now about the instantaneous axis of rotation  114 . In a second interval of movement, a working chamber  140  is formed, as illustrated in  FIG. 7.3 . This working chamber  140  expands. Thus, the working chamber  78  on the other side of the rotary piston  60  is reduced. The combustion gases are pressed out as waste gas. The working chamber  140  increases in the second interval of movement until the second stop position is reached, which is shown in  FIG. 7.4 . Then, the working chamber  140  has its maximum volume. The volume of the working chamber  78  is practically zero. 
   In the third interval of movement, the instantaneous axis of rotation jumps again from  114  to  112 . With further rotation of the rotary piston  60  counter clockwise, a new working chamber  142  is formed. Air is drawn into this working chamber  142 . The combustion gases are pressed out as waste gases out of the opposite working chamber  140  again reduced during the third interval of movement. This is illustrated in  FIG. 7.5 . The third interval of movement ends in the stop position illustrated in  FIG. 7.6 . In this stop position, the volume of the working chamber  142  has reached the maximum, the volume of the working chamber  140  is practically zero. 
   A fourth interval of movement illustrated in  FIG. 7.7  and  FIG. 7.8  is geometrically similar to the first interval of movement. However, the rotary piston  60  is now rotating about the piston-fixed instantaneous axis of rotation  114 . A working chamber  114  is formed in this fourth interval of movement, which working chamber is expanded with rotation of the rotary piston  60 . Air is drawn into this working chamber  144 . The air drawn in the third interval of movement into the working chamber  142  is compressed when the working chamber  142  is reduced. In the stop position illustrated in  FIG. 7.8 , the volume of the working chamber  144  has reached the maximum and the volume in the working chamber  142  is practically zero. The air earlier drawn-off is compressed in the combustion chamber cavity  101 . In this stop position of  FIG. 7.8 , fuel is again introduced or injected into the combustion chamber cavity  101  and ignited. 
   In a fifth interval of movement, illustrated in  FIGS. 7.9  and  7 . 10 , the rotary piston is again rotated about the instantaneous axis of rotation  112 . A working chamber  146  is formed, in which chamber the combustion gases expand and urge the rotary piston  60  further counter clockwise. The working chamber  144  is reduced and the air drawn-off during the fourth interval of movement is compressed. Fuel is injected into the compressed air in the combustion cavity  99  of the working chamber  144  and ignited. The instantaneous axis of rotation jumps again from the axis of rotation  112  to the axis of rotation  114 . 
   In a sixth interval of movement illustrated in the  FIG. 7.11  and  FIG. 7.12 , an expanded working chamber  148  is formed. The combustion gases expand in the working chamber  148  and urge the rotary piston  60  about the rotary axis  114  into the position of  FIG. 7.12 . The combustion gases in the newly decreased working chamber  147   146  are pressed out as waste gases. In  FIG. 7.12  the rotary piston  60  is again in the same position (with the axis of rotation  112  “at the top”) as at the beginning of the first interval of movement. The cycle is then restarted. 
   “Working strokes” of the 4-cycle version are illustrated in the  FIGS. 7.1  and  7 . 3  and in the  FIGS. 7.9  and  7 . 11 . Each working stroke is associated with a suction stroke, a compression stroke and a outlet stroke after the working stroke. Four out of eight intervals of movement comprise a “working stroke”. 
   The instantaneous axis of rotation of the rotary piston  60  is not clearly kinematically identified in the stop positions. Temporarily, the two axes of rotation  112  and  114  are equal. The kinematics is not closed yet. If the fuel is injected and ignited or a working medium as hydraulic oil or vapour is introduced during this stop position, as it is shown for example in  FIG. 7.8 , a force transverse to the connection plane S-N of the rotary piston  60  acts upon the surface of the rotary piston  60  on the right in  FIG. 7.8 . This force may press the rotary piston  60  to the left into the generally triangular working chamber  144 . The rotary piston  60  may then jam between the inner wall sections  52  and  54 . This is particularly true for slow rotations, in which the further clockwise rotary movement is not already ensured by the rotary momentum of the rotary piston  60 . 
   In order to avoid such jamming, fixing means are provided, which fixing means fix one of the two possible instantaneous axes of rotation  112  and  114 , namely, in the stop position of the rotary piston  60 , the one acting in the following interval of movement as instantaneous axis of rotation. In the mentioned case of  FIG. 7.8 , this would be the axis of rotation  112 . This piston-fixed axis of rotation  112  is temporarily fixed in a position in which it coincides with the housing-fixed cylinder axis of the inner wall section  50 . When the rotary piston  60  has made a certain rotation about this fixed axis, then it is ensured that the rotary piston  60  will further rotate clockwise about the instantaneous axis of rotation  112 . Then, the fixing may be released. The fixing of the instantaneous axis of rotation has, of course, to be released before the rotary piston  60  has reached its next stop position, that is before the end of the interval of movement. 
   A mechanical device for temporarily fixing an instantaneous axis of rotation  112  or  114  is schematically illustrated in  FIG. 16  in a longitudinal section along the line S-N of  FIG. 7.8 . 
   In  FIG. 16  the housing  10  with a chamber  12  is illustrated in a longitudinal section. The housing comprises a nappe portion  150  defining the chamber  12  and closure pieces  152  and  154 . The rotary piston  60  is movable in the chamber  12 . In  FIG. 16 , the possible instantaneous axes of rotation are designated by  112  and  114 . 
   Conical recesses  156  and  158 , respectively, are provided on the end face of the rotary piston  60  on the two possible axes of rotation  112  and  114 . Shafts are mounted in the closure piece  154  coaxial to the cylinder axes of the cylindrical inner wall sections  46 ,  48  and  50 , only two shafts  158  and  160  being illustrated in  FIG. 16 , the axes of which shafts coincide with the cylinder axes of the inner wall sections  46  and  50 , respectively. The shafts  158  and  160  are axially movably guided. Heads  162  and  164 , respectively, are located on the shafts. The heads  162  and  164  are coil-shaped with a central portion  166  and  168 , respectively, of reduced diameter and two spaced discs  170 ,  172  and  174 ,  176 , respectively, of larger diameter. The central portions  166  and  168  are guided in bores  178  and  180 , respectively, of the closure piece  154 . The bores  178  and  180  end in enlarged sections  182  and  184 , respectively, in which are guided the chamber-side discs  172  and.  176 . respectively. The chamber-side discs  172  and  176  are provided with conical surfaces  186  and  188 , respectively, which can be moved into engagement with the inner surfaces of the conical recesses  156  and  158 , respectively. The shaft-side outer discs  170  and  174  form armatures for the control solenoids  190  and  192 , respectively. The heads  162  and  164  are movable by the control solenoids between two positions. In one position on the left in  FIG. 16 , the chamber-side disc  172  is located within the enlarged section  182  of the bore. In the other position on the right in  FIG. 16 , the outer disc  174  engages the outer face of the closure piece  154 . Then, the conical surface  188  of the head engages the conical recess  156  of the rotary piston  60 . 
   The control solenoids  190  and  192  are controlled by a (non illustrated) sensor arrangement responding to the rotation of the driving or driven shaft  102 . The control solenoids are energised each time, when a stop position is reached, in which the instantaneous axis of rotation jumps from the axis of rotation  112  to the axis of rotation  114  or vice versa, such that the axis of rotation is temporarily fixed for the consecutive interval of movement. In the case of  FIG. 7.8 , this is the axis of rotation  112 . This one is mechanically determined, as illustrated in  FIG. 16  in that the head  164  engages the conical recess  156  of the rotary piston  60 . Thereby, the rotary movement according to  FIG. 7.9  is ensured. Jamming of the rotary piston  60  is avoided. 
   Longitudinal grooves  200  are provided in the cylindrical nappe sections  70  and  72 , as illustrated in  FIG. 17 . Seals  120  are located in the longitudinal grooves  200 . The seals  120  are under the action of compression springs  204  and are urged against the inner wall of the chamber  12 . Thereby an additional sealing between the rotary piston  60  and the inner wall of the chamber  12  shall be obtained. Additionally, pressure from one of the working chambers may be applied to the seals, which pressure is introduced into the longitudinal grooves  200  and urges the seals  120  against the inner wall of the chamber  12 . Such a pressure force improves the sealing effect, but causes increased friction, having a negative impact on the degree of efficiency and the wear. For this reason, the working chamber pressure is applied through a valve assembly  206  to the longitudinal grooves, the pressure difference between the working chambers for example  78  and  80  being applied to the valve assembly. If the pressure difference is large, the seals are urged against the inner wall of the chamber  12  with a bigger force than in case of a small pressure difference. Thus, a better sealing is achieved with large pressure difference between the working chambers, while accepting increased friction, whereas with small pressure difference a less strong pressure of the seals  120  is sufficient and friction is reduced. 
   In  FIGS. 17 and 20 , the valve assembly  206  comprises a bore  208  extending transversally through the rotary piston  60  and connecting the working chambers, for example  78  and  80 . A slide valve  210  is guided in the bore  208 . The slide valve  210  has a central portion  212  the diameter of which is adapted to the diameter of the bore  208 . Reduced diameter sections  214  and  216  are located on both ends of the central portion  212 . The bore is closed by sleeve-shaped closure pieces  218  and  220 , respectively, in the direction of the working chambers  78 ,  80 . The reduced diameter sections  214  and  216  can engage the bores of the sleeve-shaped closure pieces  218  or  220  and close them. 
   The slide valve  210  is centered by non illustrated means such that with low pressure difference between the working chambers  78 ,  80  it covers the connection to the longitudinal grooves  200 . When the pressure difference between the working chambers exceeds a determined measure, the slide valve  208  is moved by the pressure difference in one of its end positions, in which the respective section  214  or  216  engages the associated closure piece. Then, a connection between the working chamber with higher pressure and the longitudinal groove  200  is established. 
   It would be desirable that the profile of the seals is adapted to the respective curvature of the inner wall section adjacent the seal. Then the seal would have a surface contact with the inner wall section with lower surface pressure and better sealing effect, as it would be the case if the seal and the inner wall section had different radii of curvature and correspondingly had only line contact. However, the inner wall sections to which the seals have consecutively contact, have either the smaller first or the larger second radius of curvature. 
   This problem is solved in an assembly according to  FIG. 18  in that there are provided two types of seals, namely  222  and  224 , one of which has a profile adapted to the inner wall sections  46 ,  48 ,  50  ( FIG. 1 ) with smaller radius of curvature, thus having the same radius of curvature than those, and the other type of seal has a profile adapted to the inner wall sections  52 ,  54 ,  56  with larger radius of curvature. The two types of seals are provided alternatingly in longitudinal grooves in cylindrical surfaces  70  and  72 , for example, all in all three seals  222  and two seals  224 . Seals  222  with smaller radius of curvature form, in circumferential direction, the beginning and the end of the group of seals. Thus it is ensured that with contact to the cylindrical nappe sections  70  or  72  at least two seals engage each inner wall section, which seals have a radius of curvature equal to the radius of curvature of the inner wall section. 
   Another solution is shown by  FIGS. 19A and 19B . Therein, a seal  226  is shown, the seal having a convex profile  228 . The profile  228  is subdivided into three notional longitudinal strips  230 ,  232  and  234 . The radius of curvature of the profile in the two outer longitudinal strips  230  and  234  is equal to the smaller radius of curvature of the inner wall sections  46 ,  48 ,  50 . The radius of curvature of the profile in the central longitudinal strip  232  is equal to the larger radius of curvature of the inner wall sections  52 ,  54 ,  56 . When the seal  226  engages an inner wall section  46 ,  48 ,  50  with smaller radius of curvature the two outer longitudinal strips  230  and  234  are in surface contact with the inner wall section, for example  46 . This is illustrated in  FIG. 19A . When the seal  226  engages an inner wall section  52 ,  54 ,  56  with larger radius of curvature, then the seal in the central longitudinal strip  232  has surface contact with the inner wall section, for example  52 . 
     FIG. 2  shows a rotary piston machine in which the cross section of a chamber  252  formed in a housing  250  is an oval of fifth order. The inner wall of the chamber  252  comprises five cylindrical inner wall sections  254 ,  256 ,  258 ,  260  and  262  of smaller radius of curvature and five cylindrical inner wall sections  264 ,  266 ,  270 ,  272  and  274  of larger radius of curvature, alternating therewith. The expression “cylindrical” shall mean herein that they are sections of a cylindrical surface. The inner wall sections with smaller or larger radius of curvature join each other continuously and smoothly, i.e. with a common tangent in the connection points of the cross section. A rotary piston  276  is movable in the chamber  252 . The cross section of the rotary piston  276  is an oval of fourth order. The nappe surface of the rotary piston  276  comprises four cylindrical nappe sections  278 ,  280 ,  282 , and  284  of smaller radius of curvature and four cylindrical nappe sections  286 ,  288 ,  290  and  292  of larger radius of curvature, alternating therewith. Also herein, the nappe sections with smaller or larger radius of curvature join each other continuously and smoothly, i.e. with a common tangent in the connection points of the cross section. The smaller and larger radii of curvature of the rotary piston  276  are again equal to the smaller or larger, respectively, radii of curvature of the chamber  252 . 
   The chamber  252  has a fivefold symmetry, i.e. there are five symmetry planes extending through the cylinder axis of an inner wall section of smaller radius of curvature and the cylinder axis of the opposite inner wall section of larger radius of curvature. The symmetry planes intersect in a center axis  294 . The rotary piston  276  only has a twofold symmetry: the two symmetry axes pass on the one hand through the cylinder axes of the opposite cylindrical nappe surfaces  278  and  278  and on the other hand through the cylinder axes of the opposite cylindrical nappe sections  280  and  284 . 
   Similarly to the rotary piston machine of  FIG. 1 , two possible instantaneous axes of rotation  296  and  298  are defined at the rotary piston  276 . These axes of rotation  296  and  298  are the cylinder axes of the cylindrical nappe sections  278  and  282 , respectively, and are located on a first symmetry plane of the rotary piston  276 . 
   The rotary piston  276  comprises, similarly to the rotary piston machine of  FIG. 1 , a bi-oval central aperture  300 . The longer axis of the aperture extends into the second symmetry plane of the rotary piston  276 . The shorter axis is located in the mentioned first symmetry plane. A driving or driven shaft  302  extends along the center axis  294 . A pinion  304  is located on the driving or driven shaft  302 . The pinion  304  engages respectively one of two concave arcuate toothed racks  306  and  308 . The toothed rack  306  is curved about an instantaneous axis of rotation  298 . The toothed rack  308  is curved about the instantaneous axis of rotation  298 . Linear toothed racks  310  and  312  are located at the ends of the aperture  300 . They may be replaced by convex toothed arcs. 
   This assembly operates in general in the same way as the corresponding assembly of  FIG. 1  and establishes a driving connection between the rotary piston  276  and the driving or driven shaft  302 . 
   The rotary piston is rotating in the chamber  252  counter clockwise in general in the same way as described for the embodiment of  FIG. 2 : In consecutive intervals of movement the rotary piston is rotating about one of the two possible instantaneous axes of rotation, for example with the cylindrical nappe section  278  in the cylindrical inner wall section  254  about the axis of rotation  296 , the nappe section  282  sliding at the inner wall section  258 . When the stop position is reached, the axis of rotation is changed. 
   The rotary piston  276  rotates with relative to the chamber  252  consecutively about the chamber-fixed axes of rotation  314 ,  316 ,  318 ,  320  and  322  ( FIG. 8 ). These axes are again defined by the cylinder axes of the cylindrical inner wall sections  254 ,  260 ,  256 ,  262  and  258 , respectively. The center axis  294  passes through a trajectory  324  in the form of a two-angle relatively to the rotary piston  276 . The pinion  304  alternatingly meshes with the concave toothed rack  306  or  308 , depending on the rotary piston  276  rotating about the instantaneous axis of rotation  296  or about the instantaneous axis of rotation  298  of the rotary piston  276 . This is similar to  FIG. 4 . 
     FIGS. 9 and 10  show, for the assembly of  FIG. 2 , the change of the instantaneous axes of rotation from the axis of rotation  298  to the axis of rotation  296  and the corresponding transmission of the pinion  302  from the concave toothed rack  308  to the toothed rack  306 . This is analogous to  FIGS. 5 and 6  except for the slightly different shape of the oval aperture. 
   In the stop positions of the rotary piston, the kinematics is again not closed, and the instantaneous axis of rotation is not exactly identified. The same problems arise as already described for the rotary piston machine of  FIG. 2 , namely that the rotary piston  276  for example in the position of  FIG. 8  is not moved into further rotation by pressure in the working chamber but is pressed transversally to its first symmetry plane between the inner wall sections  268  and  272  and jams therein. This problem is again solved by the construction illustrated in  FIG. 16 , by which the instantaneous axes of rotation of the rotary piston are temporarily fixed consecutively in the chamber-fixed axes of rotation  314 ,  316 ,  318 ,  320  and  322  when the stop positions are reached. 
   The  FIGS. 11.1  to  11 . 20  show in similar form as the  FIGS. 7.1  to  7 . 12  the moving process of the rotary piston  276  during a complete revolution, the formation of working chambers, the intake and compression of air, the introduction and ignition of fuel and the expelling of the combustion gases. 
   It can be seen that a complete revolution of the rotary piston  276  comprises six working strokes with introducing, igniting and combustion of fuel, an suction and a compression stroke and after each working stroke an exhaust stroke being again associated with each working stroke. 
     FIG. 3  shows an embodiment in which a chamber  352  is formed in a housing  350 , the cross section of the chamber being an oval of seventh order. The inner wall of the chamber  352  has seven concave cylindrical inner wall sections  354 ,  356 ,  358 ,  360 ,  362 ,  364  and  366  of relatively small radius of curvature alternating with seven concave cylindrical inner wall sections  368 ,  370 ,  372 ,  374 ,  376 ,  378  and  380  of relatively large radius of curvature. The alternating inner wall sections with smaller and larger radii of curvature join each other again consecutively and smoothly. A rotary piston  382  is movable in the chamber  352 . The cross section of the rotary piston  382  is an oval of sixth order. The nappe surface of the rotary piston  382  has six convex cylindrical nappe sections  384 ,  386 ,  388 ,  390 ,  392  and  394  of relatively small radius of curvature alternating with six convex cylindrical nappe sections  396 ,  398 ,  400 ,  402 ,  404  and  406 . The smaller and larger radii of curvature of the rotary piston  382  are equal to the smaller and larger radii of curvature of the chamber  352 , respectively. The chamber  352  has a sevenfold symmetry, i.e. seven radial symmetry planes intersecting in a center axis  408 . The rotary piston has again only a twofold symmetry: A first symmetry plane extends through the cylinder axes of the opposite convex cylindrical nappe sections  384  and  390 . These two cylinder axes form again the two possible instantaneous axes of rotation  410  and  412  of the rotary piston  382 . The second symmetry axis extends perpendicularly thereto through the cylinder axes of the convex cylindrical nappe sections  398  and  404 . 
   A driving or driven shaft  414  extends longitudinally to the center axis  408 . The driving or driven shaft  414  extends through an oval aperture  416  of the rotary piston  382 . A pinion  418  is located on the driving or driven shaft  414 . The pinion  418  meshes with one of two opposite concave toothed racks  420  and  422  curved about the axes of rotation  410  and  412 , respectively. Thus, the rotary movement of the rotary piston  382  is transmitted to the driving or driven shaft or vice versa. This assembly is operating in the same way as the assembly described in detail with reference to  FIG. 1 . 
     FIG. 12  is similar to  FIG. 4  or  FIG. 8 , referring however to the embodiment according to  FIG. 3 . It shows seven chamber-fixed axes of rotation, the rotary piston  382  rotating about these axes with its instantaneous axes of rotation  410  or  412  in the consecutive intervals of movement. These are the cylinder axes of the concave cylindrical inner wall surfaces with smaller radius of curvature. The chamber-fixed axes of rotation consecutively coming into function are designated in  FIG. 12  by  424 ,  426 ,  428 ,  430 ,  432 ,  434  and  436 . The trajectory of the center axis  408  with reference to the rotary piston  382  is designated in  FIG. 12  by  438 .  440  is the trajectory, which the axis of rotation  412  or  410  traverses when rotating about the respective other one of the piston-fixed instantaneous axes of rotation  410  and  412 , respectively. This is an arcuate seven-angle which again is not traversed continuously. 
     FIGS. 13 and 14  correspond, for the embodiment according to  FIG. 3 , to  FIGS. 5 and 6  in the embodiment of  FIG. 1 , and to  FIGS. 9 and 10  in the embodiment of  FIG. 2 . The function is the same as there. However, the apertures in  FIG. 2  and  FIG. 3  are increasingly compact because the “strokes” of the pistons are smaller with each working cycle. 
   The  FIGS. 15.1  to  15 . 28  show the movement course of the rotary piston  382  in the embodiment according to  FIG. 3  for a complete revolution of the rotary piston. A solid circle marks the respective instantaneous axis of rotation. In the stop position, the kinematics does not determine exactly which axis  410  or  412  is the instantaneous axis of rotation. Therefore, two semi-solid circles mark the two axes of rotation  410  and  412 . Igniting injected fuel or an introduced working medium, as, for example, illustrated in  FIG. 15.2  could then urge the rotary piston diagonally to the right downwards in  FIG. 15.2  instead of causing a further rotation. The rotary piston may then jam between the inner wall sections  368  and  374 . For this reason, fixing means for example of the type of  FIG. 16  are again provided herein for the piston fixed instantaneous axes of rotation  410  or  412  on the chamber fixed axes of rotation  424 ,  426 ,  428 ,  430 ,  432 ,  434  and  436 . 
   The  FIGS. 15.1  to  15 . 28  show that with a complete revolution of the rotary piston  382  there are all, in all, eight working strokes, with the associated intake, compression and exhaust strokes. 
   As in the embodiments according to  FIG. 2  and  FIG. 3  there are six and eight working strokes, respectively, per revolution of the driving shaft  302  and  414 , respectively, such rotary piston machines may better operate with high torque than a rotary piston machine according to  FIG. 1 . With slowly operating rotary piston machines of the present type, the risk is particularly high that the rotary piston jams. On one hand, the rotary momentum of the rotary piston forcing a further rotation does not cure the unclear kinematics in the stop positions. On the other hand, the wedge angle between the inner wall sections between which the rotary piston may be wedged, decreases with increasing order. Thus, fixing the instantaneous axis of rotation according to  FIG. 16  should be of particular importance for the rotary piston machines with ovals of higher order. 
   The described arrangements may be modified in multiple ways. For instance, the surfaces of the rotary piston  60  curved about the possible instantaneous axes of rotation, for example  112  and  114  in  FIG. 1 , need not be curved themselves exactly cylindrically about the instantaneous axes of rotation  112  and  114 , respectively. The invention may also be realised in such a manner that the contact surfaces of the seals are located on a cylinder surface about the instantaneous axes of rotation. This shall also be covered by the term “cylindrical nappe sections”.