Abstract:
Disclosed is a rotary piston machine comprising a housing which is provided with a cylindrical inner wall and at least one piston which is disposed inside said housing and rotates around a longitudinal central axis of the housing while moving back and forth in a linear manner by means of a control mechanism so as to periodically enlarge and reduce the size of at least one chamber that is associated with the piston. Linear movement of the at least one piston occurs parallel to the longitudinal central axis of the housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation of pending international patent application PCT/EP03/04067 filed on Apr. 17, 2003 which designates the United States and which claims priority of European patent application 02008814.2 filed on Apr. 19, 2002. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a rotary piston machine, comprising a housing which has a cylindrical housing inner wall, and at least one piston which is arranged in the housing and which can rotate about a longitudinal mid-axis of the housing and at the same time executes, by means of a control mechanism, a to-and-fro linear movement which serves for periodically enlarging and reducing at least one chamber assigned to the piston.  
         [0003]     A rotary piston machine of this kind is known from DE 100 01 962 A1.  
         [0004]     Such a rotary piston machine is used preferably as an internal combustion engine.  
         [0005]     Rotary piston machines belong, in general, to a type of machine in which one or more pistons rotate in a housing, a further type of movement normally being superimposed on the rotational movement of the piston or pistons, in order periodically to enlarge and reduce in volume the one or more chambers which are assigned to the piston or pistons and which conventionally form the working chambers for a Carnot cycle.  
         [0006]     In the rotary piston machine known from DE 100 01 962 A1, a plurality of pistons are arranged so as to be distributed circumferentially about the housing mid-axis of the housing. The pistons are mounted radially moveably in the housing, the control mechanism deriving the radially directed to-and-fro stroke movement of the pistons from the rotational movement of the pistons.  
         [0007]     When the known rotary piston machine is used as an internal combustion engine, the individual working strokes of admission, compression, expansion and expulsion are therefore implemented by means of the radially directed to-and-fro stroke movement of the individual pistons.  
         [0008]     The control mechanism of the known rotary piston machine has a fixed cam piece arranged approximately in the centre of the housing, the pistons each having at least one running member on their side facing the housing mid-axis, the pistons being guided along the control cam by means of the said running members. Furthermore, the control mechanism is designed in such a way that in each case adjacent pistons of the radially moveable pistons execute an oppositely directed stroke movement. The pistons of the known rotary piston machine have in each case a toothing on their end faces leading and trailing in the direction of rotation of the pistons, and between the end faces of adjacent pistons in each case is arranged a co-rotating shaft which is provided with a toothing and which is in meshing engagement with the toothings of the two adjacent end faces of the pistons.  
         [0009]     One disadvantage of this known rotary piston machine may be seen in that the radially directed linear movement of the pistons takes place alternately in the direction of and counter to the action of the centrifugal force and the action of the centrifugal force. In this case, because of the radially directed stroke movement of the individual pistons, the mass distribution with respect to the longitudinal mid-axis of the housing and consequently also the moment of inertia of the pistons change constantly. Moreover, because of the centrifugal forces and the mechanical coupling in each case of adjacent pistons moving radially in opposition, the cam piece which is located in the centre of the housing and is fixed relative to the housing and which serves for guiding the pistons is subjected to load exerted by forces.  
         [0010]     Another type of rotary piston machine is known from WO 98/13583, in which the individual pistons rotating in the housing are designed as pivoting pistons which, during their rotational movement, additionally execute rocker-like to-and-fro pivoting movements in the housing. The control mechanism for controlling the rocker-like to-and-fro pivoting movements of the individual pistons corresponds virtually identically to the control mechanism of the abovementioned known rotary piston machine with pistons radially moveable linearly.  
         [0011]     In this pivoting piston machine, too, a disadvantage may be seen in the mass distribution which is not optimum with respect to the longitudinal mid-axis of the housing or in the incomplete cancellation of the resultant centrifugal forces of the individual pistons.  
         [0012]     The invention is based on the object to provide a new kind of a rotary piston machine in which the periodic alteration of the volume of the at least one chamber is achieved in another fashion.  
       SUMMARY OF THE INVENTION  
       [0013]     According to an aspect of the invention, a rotary piston machine is provided, comprising a housing having a cylindrical housing inner wall and a longitudinal mid-axis; at least one piston arranged in said housing which can rotate about said longitudinal mid-axis and at the same time executes, by means of a control mechanism, a to-and fro linear movement parallel to said longitudinal mid-axis; at least one chamber in said housing assigned to said at least one piston which periodically enlarges and reduces due to said to-and-fro linear movement of said at least one piston.  
         [0014]     In the rotary piston machine according to the invention, the at least one piston, during rotation about the longitudinal mid-axis of the housing, executes a linear movement directed parallel to the longitudinal mid-axis of the housing. The at least one piston thus does not possess a radially directed movement component. This affords the advantage that the distance of the mass centre of gravity of at least one piston from the longitudinal mid-axis of the housing, which forms the axis of rotation of the piston, is invariable. The advantage of improved quiet running of the rotary piston machine is thereby achieved.  
         [0015]     A further advantage, as compared with the known piston machine, is that the rotary piston machine according to the invention may be designed with a radially small build, since the at least one piston does not have to execute any radial movement or a movement with a radial movement component. The rotary piston machine according to the invention is suitable, in particular, as an internal combustion engine, in which case the at least one chamber then serves as a working chamber for a Carnot cycle, in which the working strokes of admission, compression, expansion and expulsion take place.  
         [0016]     It is to be understood that the rotary piston machine according to the invention preferably comprises more than one piston, wherein then the plurality of pistons all execute, during rotation in the housing, linear movements which are directed parallel to the longitudinal mid-axis of the housing, as is described hereafter with reference to preferred embodiments.  
         [0017]     In a preferred embodiment, the piston is arranged eccentrically with respect to the longitudinal mid-axis of the housing, and the housing has arranged in it at least one further piston which rotates about the longitudinal mid-axis and which is arranged, with respect to the longitudinal mid-axis of the housing, on the side facing away from the first piston.  
         [0018]     In this embodiment, the rotary piston machine according to the invention can be implemented as an at least two-cylinder internal combustion engine, in which case, by the at least two pistons, which do not necessarily have to lie at the same height axially, being arranged opposite one another with respect to the longitudinal mid-axis, and with the pistons being designed identically, a mass distribution which is axially symmetrical with respect to the longitudinal mid-axis can be achieved. The centrifugal forces acting on the two pistons advantageously cancel one another during rotation in the housing. The two pistons may in this case be arranged in such a way that the linear movements take place in the opposite direction to one another by means of the control mechanism, or the linear movement of the two pistons may be in the same direction.  
         [0019]     In this context, it is further preferred, if the further piston is arranged opposite the first piston at the same height axially.  
         [0020]     In this embodiment, too, the advantage is achieved that the centrifugal forces of the two pistons can cancel one another due to their axially symmetrical arrangement with respect to the longitudinal mid-axis. As in the abovementioned embodiment, in this arrangement, two chambers may be formed, which are arranged so as to be offset at 180° to one another about the longitudinal mid-axis, so that two full working cycles are completed over one full revolution of the piston arrangement.  
         [0021]     Within the scope of the previously mentioned embodiment, it is preferred, furthermore, if the further piston is connected fixedly to the first piston.  
         [0022]     In this case, it is advantageous that the two pistons located opposite one another are supported relative to one another against the centrifugal forces acting on them during rotation, and surface friction of the pistons against the housing is thereby eliminated.  
         [0023]     In a further preferred embodiment the at least one piston is arranged centrically about the longitudinal mid-axis and rotates about a piston mid-axis coinciding with the longitudinal mid-axis in the housing.  
         [0024]     With this embodiment, the advantage of a structurally particularly simple embodiment of the rotary piston machine according to the invention is achieved. In this embodiment, centrifugal forces are eliminated without an additional piston arranged on axially equal height.  
         [0025]     In a further preferred embodiment, the housing has arranged in it at least one further piston which rotates about the longitudinal mid-axis and which is arranged in the rectilinear prolongation of the first piston.  
         [0026]     The advantage of this measure is that a plurality of chambers can be implemented in the longitudinal direction of the housing, so that a multi-cylinder rotary piston machine can likewise be implemented in this way.  
         [0027]     In this connection, it is preferred if the at least one chamber is formed by the space between mutually confronting end faces of the first piston and of the further piston.  
         [0028]     In this case, it is advantageous that, with the two pistons moving in opposite directions, the individual strokes of the two pistons add up to form a total stroke, as a result of which, when the rotary piston machine according to the invention is used in the internal combustion engine, the fuel/air mixture can be compressed with a higher pressure in the common chamber between the two pistons.  
         [0029]     In a further preferred embodiment, the linear movement of the first piston is directed opposite to the linear movement of the second piston, and the space between the mutually confronting end faces of the first piston and of the further piston forms a common chamber.  
         [0030]     The advantage of this measure is that the rotary piston machine according to the invention is thereby compensated in mass also with regard to the linear movement of the at least two pistons, as a result of which vibrations of the rotary piston machine in the longitudinal direction are eliminated.  
         [0031]     In a combination of the abovementioned embodiments, it is particularly preferred if the housing has arranged in it at least four pistons, of which in each case two are arranged opposite one another at the same height axially with respect to the longitudinal mid-axis of the housing and in each case two are arranged in the rectilinear prolongation of one another.  
         [0032]     In this embodiment of the rotary piston machine according to the invention with four pistons, the two pistons arranged opposite one another at the same height axially with respect to the longitudinal mid-axis of the housing form in each case a preferable rigid double piston, the two double pistons then being arranged in the axially rectilinear prolongation of one another and rotate jointly in the housing about the longitudinal mid-axis and execute linear movements directed opposite to one another. In this embodiment, one double piston and the other double piston are preferably assigned in each case an own control mechanism for controlling the to-and-fro linear movement during rotation in the housing.  
         [0033]     In a preferred embodiment, the control mechanism comprises at least one guide member arranged on the at least one first piston and at least one control cam curve which is formed in the housing inner wall and along which the guide member runs.  
         [0034]     Such a control mechanism has the advantage, as compared with the control mechanism of the known rotary piston machine, that it is less susceptible to wear, because, in contrast to the control mechanism of the known rotary piston machine which comprises a cam piece arranged centrally in the housing and running members provided on the pistons, it is not subject to the action of the centrifugal forces caused by the rotational movement of the pistons. Provided as a guide member, on the at least one first piston, is preferably an axle which projects radially from the side of the latter facing the housing inner wall and on which one or two running rollers are arranged, while the control cam is preferably designed as a guide groove which is formed in the housing inner wall and into which the running rollers engage and roll in the housing during the rotation of the piston.  
         [0035]     In connection with one or more of the above-mentioned embodiments, according to which a further piston is arranged opposite the first piston with respect to the longitudinal mid-axis at the same height axially and the two pistons are firmly connected to one another, it is further preferred if a guide member is arranged in each case on the first piston and the further piston, the two guide members running along the same control cam curve.  
         [0036]     In this case, it is advantageous that the mass centre of gravity of the two pistons located opposite one another at the same height lies on the longitudinal mid-axis, that is to say the axis of rotation, which would not be the case if there were a running member on only one of the two pistons. The latter embodiment may, however, likewise be taken into consideration, in which case the piston which has no guide members may have a corresponding additional mass for mass compensation with respect to the longitudinal mid-axis.  
         [0037]     In a further preferred embodiment, one side of the at least one piston, the said side facing the housing inner wall, is designed in the form of a part-circle in cross section.  
         [0038]     The advantage of this measure is that that side of the at least one piston which faces the housing inner wall is adapted to the circular inner contour of the housing inner wall, with a result that the piston can be sealed off in an advantageously simple way by means of seals in the form of segments of a circle. Preferably, that side of the at least one piston which faces the housing inner wall extends over approximately 90°.  
         [0039]     It is further preferred, if the at least one piston is guided in its linear movement by a rotor which rotates about the longitudinal mid-axis jointly with the piston and which is axially immovable.  
         [0040]     The provision of a rotor has the advantage that the rotational movement of the at least one piston in the housing can be picked up by the rotor via an output shaft connected to the rotor, for example when the rotary piston machine according to the invention is used as an internal combustion engine in a motor vehicle. In this way, the rotational movement can be picked up centrally on the longitudinal mid-axis of the housing of the rotary piston machine, without complicated transmission shafts or countershafts being necessary. In this way, the rotary piston machine according to the invention can simulate a conventional reciprocating-piston engine, as compared with which, however, the rotary piston machine according to the invention has the considerable advantage that, by virtue of the rotational movement of the at least one piston, the rotational energy can be derived via the rotor, which is axially immoveable.  
         [0041]     In preferred embodiments, the rotor can be configured as a sleeve or as an axle.  
         [0042]     In connection with one of the previously mentioned embodiments, according to which at least two pistons are arranged opposite with respect to the longitudinal mid-axis, whether on axially equal height or on axially different position, it is further preferred, if the rotor has a middle portion which lies on the longitudinal mid-axis of the housing and which separates the chamber assigned to the first piston from the chamber assigned to the further piston.  
         [0043]     In this way, without additional complicated structural measures, the rotor also assumes the function of separating the at least two chambers which, for example with regard to the use of the rotary piston machine as an internal combustion engine, form working chambers for a Carnot cycle.  
         [0044]     In a further preferred embodiment, each of the two end faces of the at least one piston is assigned a chamber, the said chambers being reduced and enlarged in opposite directions, in which case one chamber serves as a working chamber for a Carnot cycle and the other chamber as a boost-pressure chamber for generating a boost pressure, in order to supply the working chamber with a boost pressure.  
         [0045]     In this case, it is advantageous that, with the rotary piston machine according to the invention being used as an internal combustion engine, self-charging of the working chambers is achieved without external devices, such as a compressor or a turbocharger, and without enlarging the construction space of the rotary piston machine. While the working chamber is being reduced, for example, in volume, the boost-pressure chamber, into which fresh air can be sucked, is enlarged correspondingly. During the expansion of the working chamber after the ignition of the fuel/air mixture, the fresh air previously sucked into the boost-pressure chamber is correspondingly compressed and, after the expulsion of the burnt fuel/air mixture out of the working chamber, can then be forced under pressure into the latter, with the result that the fuel/air mixture can be compressed with higher pressure in the next cycle. Particularly with the preferred embodiment of the rotary piston machine with four pistons, a particularly effective self-charging effect can be achieved. In this embodiment, the rotary piston machine according to the invention is suitable, in particular, as an internal combustion engine for operation with diesel or even biodiesel fuels.  
         [0046]     In a further preferred embodiment, the middle portion of the rotor is absent or configured such on the sides of the chambers serving as boost-pressure chambers that in each case two of the chambers serving as boost-pressure chambers communicate with one another.  
         [0047]     In this case, the advantage is that the chambers serving as boost-pressure chambers form together a boost-pressure chamber having a total volume which is larger, preferably four times as large as the volume of the at least one working chamber, whereby the air precompressed in the boost-pressure chambers can be fed into the at least one working chamber with an even higher boost-pressure.  
         [0048]     In a first preferred design variant, the boost-pressure chamber is connected to the working chamber via a line which is located outside the housing and in which a valve, in particular a controllable valve, is preferably arranged.  
         [0049]     The controllable valve may be, for example, a solenoid valve which is opened when a maximum boost pressure has been generated in the admission-pressure chamber.  
         [0050]     Alternatively to the abovementioned embodiment, however, the boost-pressure chamber may also be connected directly to the working chamber through the piston, at least one valve, preferably an automatic valve, then being arranged in the piston.  
         [0051]     The advantage of this measure is that a connecting line, located outside the housing, between the boost-pressure chamber and the working chamber may be dispensed with, with the result that the rotary piston machine occupies a smaller amount of space. The abovementioned automatic valve may be, for example, a flutter valve.  
         [0052]     As an alternative or in combination with the previously mentioned embodiment of the rotary piston machine with at least one boost-pressure chamber and at least one working chamber it is, however, also preferred, if both end faces of the at least one piston is assigned a chamber in each case, which mutually reduce and enlarge in the opposite sense, wherein both chambers serve as working chambers for a Carnot-cycle.  
         [0053]     This measure has the advantage that, for example, two cylinders of a conventional engine can be reproduced with only one piston, wherein a further particular advantage is that the expansion of the one working chamber after the ignition of the fuel/air mixture supports the compression of the other working chamber, which has just intaken new fuel/air mixture. In one of the previously mentioned preferred embodiments, according to which the rotary piston machine comprises four pistons in total, this embodiment is capable of reproducing a conventional six-cylinders-engine.  
         [0054]     The rotary piston machine according to the invention may be used as an internal combustion engine or else as a compressor.  
         [0055]     Further advantages and features may be gathered from the following description and the accompanying drawing.  
         [0056]     It goes without saying that the features mentioned above and those still to be explained below may be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0057]     Exemplary embodiments of the invention are illustrated in the drawing and are described in more detail hereafter, with reference to the drawing in which:  
         [0058]      FIG. 1  shows a perspective, partially sectional illustration of a rotary piston machine according to a first exemplary embodiment in a first operating position;  
         [0059]      FIG. 2  shows the rotary piston machine in  FIG. 1  in a second operating position;  
         [0060]      FIG. 3  shows the rotary piston machine in  FIGS. 1 and 2  in a third operating position;  
         [0061]      FIG. 4  shows the rotary piston machine in the operating position illustrated in  FIG. 3 , in a partially cut-away illustration;  
         [0062]      FIG. 5  shows a perspective illustration of an individual part of the rotary piston machine in FIGS.  1  to  4 ;  
         [0063]      FIGS. 6   a ) to d) show a longitudinal section through the rotary piston machine in FIGS.  1  to  4  in four different operating positions;  
         [0064]      FIGS. 7   a ) to d) show in each case a section along the line VII-VII in  FIGS. 6   a ) to d);  
         [0065]      FIGS. 8   a ) to d) show sections along the lines VIII-VIII in  FIGS. 6   a ) to d);  
         [0066]      FIGS. 9   a ) and b) show longitudinal sections, corresponding to  FIGS. 6   a ) and  6   b ), of a rotary piston machine according to a further exemplary embodiment, in two operation positions;  
         [0067]      FIGS. 10   a ) and b) show in each case a section along the line X-X in  FIGS. 9   a ) and b);  
         [0068]      FIGS. 11   a ) and b) show in each case a section along the line XI-XI in  FIGS. 9   a ) and b);  
         [0069]      FIGS. 12   a ) to d) show a longitudinal section corresponding to  FIGS. 6   a ) to  6   c ) through a rotary piston machine according to another embodiment in four different operating positions;  
         [0070]      FIGS. 13   a ) to d) show in each case a section along the line XIII-XIII in  FIGS. 12   a ) to d);  
         [0071]      FIGS. 14   a ) to d) show in each case a section along the line XIV-XIV in  FIGS. 12   a ) to d);  
         [0072]      FIGS. 15   a ) to d) show in each case a section along the line XV-XV in  FIGS. 12   a ) to d).  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0073]     FIGS.  1  to  8  illustrate a rotary piston machine, given the general reference symbol  10 , according to a first exemplary embodiment.  
         [0074]     The rotary piston machine  10  is used in the present case as an internal combustion engine.  
         [0075]     The rotary piston machine  10  has a housing  12  which has an essentially cylindrically symmetrical basic shape. At its longitudinal ends, the housing  12  is closed by means of a housing cover  14  and a housing cover  16 , although a different division of the housing  12  may also be considered, as may be gathered, for example, from  FIG. 6   a ).  
         [0076]     The housing  12  has a cylindrical housing inner wall  18  which therefore has a circular design in cross section.  
         [0077]     A longitudinal mid-axis  20  forms the cylinder axis of the housing inner wall  18 .  
         [0078]     The housing  12  has arranged in it at least one first piston  22  and, in the exemplary embodiment shown, a further second piston  24 , which can be seen in the perspective illustrations in  FIG. 4  only, a further third piston  26  and a further fourth piston  28 , which likewise can be seen in the perspective illustration in  FIG. 4  only.  
         [0079]     Of the four pistons  22  to  26 , in each case two pistons are firmly connected to one another to form a double piston, specifically these being the first piston  22  and the third piston  24 , which form a first double piston, and the second piston  26  and the fourth piston  28 , which form a second double piston. The first piston  22  is firmly connected to the third piston  24  via a first connection piece  30 , and the third piston  26  is firmly connected to the fourth piston  28  via a second connection piece  32 . The connection pieces  30  and  32  in each case make a rigid connection between the pistons  22 ,  24  and  26 ,  28  respectively.  
         [0080]     The first piston  22  and the further pistons  24  to  28  rotate in the housing  12  jointly about the longitudinal mid-axis  20  according to an arrow  34 , so that the longitudinal mid-axis  20  may also be designated as the axis of rotation.  
         [0081]     During rotation about the longitudinal mid-axis  34  of the housing  12 , the first piston  22  and the further pistons  24  to  28  execute to-and-fro linear movements by means of a control mechanism still to be described later, these linear movements being directed parallel to the longitudinal mid-axis  34 , as is indicated by a double arrow  36 .  
         [0082]     The four pistons  22  to  28  are in each case arranged eccentrically with respect to the longitudinal mid-axis  20  of the housing  12 , as may be gathered from the cross-sectional illustrations in  FIGS. 7   a ) to  7   d ).  
         [0083]     The further second piston  24  and the further fourth piston  28  are arranged opposite the first piston  22  with respect to the longitudinal mid-axis  20 , that is to say on that side of the longitudinal mid-axis  20  which faces away from the first piston  22 . In this case, the further second piston  24  is arranged opposite the first piston  22  at the same height axially, whilst the further fourth piston  28  is arranged opposite the first piston  22  with an axial offset. The further third piston  26  is arranged in the housing in the rectilinear prolongation of the first piston  22 , that is to say is located in the same circumferential position as the first piston  22  with respect to the longitudinal mid-axis  20 . By contrast, the second piston  24  and the fourth piston  28  are arranged with an offset of 180° in the circumferential direction with respect to the first piston  22  and to the third piston  26 .  
         [0084]     Since the first piston  22  is firmly connected to the further second piston  24 , the first piston  22  and the second piston  24 , during rotation in the housing  12 , execute linear movements in the same direction parallel to the longitudinal mid-axis  20 . Likewise, by virtue of their firm connection by means of the connection piece  32 , the further third piston  26  and the further fourth piston  28 , during rotation in the housing  12 , execute linear movements directed in the same direction.  
         [0085]     By contrast, the relative linear movements between the first piston  22  and the second piston  24 , on the one hand, and the third piston  26  and the fourth piston  28 , on the other hand, are directed opposite to one another. In other words, the pistons  22 ,  24 , on the one hand, and the pistons  26  and  28 , on the other hand, move either towards one another or away from one another. However, all four pistons  22  to  28  do not change their rotary position in relation to one another during rotation about the longitudinal mid-axis  20 .  
         [0086]     The four pistons  22  to  28  are designed identically to one another in terms of their geometry and dimensions. By the four pistons  22  to  28  being arranged axially symmetrically with respect to the longitudinal mid-axis  20 , the centrifugal forces occurring during the rotation of the pistons  22  to  28  about the longitudinal mid-axis  20  compensate one another completely. Furthermore, in the rotary piston machine  10 , the inertias occurring during the linear movement of the pistons  22  to  28  also compensate one another, because the first double piston formed from the pistons  22  and  24  moves in the housing  12  linearly in the opposite direction to the second double piston formed from the pistons  26  and  28 .  
         [0087]     As already mentioned, to derive the linear movement of the individual pistons  22  to  28  from their rotational movement about the longitudinal mid-axis  20 , a control mechanism is provided, which is given the general reference symbol  40  in FIGS.  1  to  4  and  6  and is described below solely with regard to the piston  22 .  
         [0088]     The control mechanism  40  comprises a guide member  42  arranged on the first piston and a control cam curve  44  which is formed in the housing inner wall  18  and along which the guide member  42  runs.  
         [0089]     The guide member  42  is connected firmly to the first piston  22  and has an axle journal  46  and also a first running roller  48  fastened to the axle journal  46  and a second running roller  50 . The running roller  48  has a smaller outside diameter than the running roller  50 .  
         [0090]     The control cam curve  44  is designed in the form of a guide groove  52  formed in the housing inner wall  18 . The guide groove  52  in this case has a portion  54  of smaller diameter and a portion  56  of larger inside diameter, corresponding to the outside diameter of the running roller  48  and to the outside diameter of the running roller  50 . The provision of two running rollers  48  and  50  of different diameter, which run in the corresponding portions  54  and  56  of the guide groove  52 , ensures that each running roller  48  and  50  has only one direction of rotation about the axle journal  46  when it runs in the guide groove  52 , that is to say that the running roller  48  and the running roller  50 , which correspondingly come to bear on only one side of their respectively assigned portion  54  and  56 , do not experience any reversal of rotation while they are rotating in the guide groove  52 .  
         [0091]     The control cam curve  44  in the form of the guide groove  52  extends over the full circumference about the longitudinal mid-axis  20  and constitutes a closed control cam curve which, in order to derive the linear movement of the pistons  22  to  28  from the rotational movement of the latter about the longitudinal mid-axis  20 , has a correspondingly curved shape which is approximately in the form of a circle curved about a diameter. The lead of the control cam curve  44  along the longitudinal mid-axis  20  determines the stroke of the piston  22 .  
         [0092]     As will be gathered from  FIG. 6   a ), the second piston  24  is equipped with a guide member which is designed identically to the guide member  42  and on which two running rollers are arranged correspondingly, the guide member  42  running along the same control cam curve  44 , that is to say in the same guide groove  52 . The control mechanism  40  thus constitutes a common control mechanism for the double piston formed from the pistons  22  and  24 .  
         [0093]     As may likewise be gathered from  FIG. 6   a ), the running rollers  48  and  50  and, correspondingly, the guide groove  52  may also be designed conically.  
         [0094]     A corresponding control mechanism  58  is provided for the further double piston formed from the pistons  26  and  28  and differs from the control mechanism  40  merely in that a control cam curve  60  is formed mirror-symmetrically in relation to the control cam curve  44  of the control mechanism  40 , with respect to the cross-sectional mid-plane of the housing  12 .  
         [0095]     The pistons  22  to  28  are guided in their linear movement by a rotor  62  which is illustrated alone in  FIG. 5 .  
         [0096]     The rotor  62  has, in general, a cylindrical shape which is adapted to the inner wall  18  of the housing  12  of the rotary piston machine  10 .  
         [0097]     For receiving the pistons  22  to  28 , the rotor  62  has two trough-like recesses  64  and  66  (cf., for example,  FIG. 8   a )) which are offset at 180° with respect to the longitudinal mid-axis  20  and only the recess  64  of which can be seen in  FIG. 5 . Those walls of the trough-like recesses  64  and  66  which are located opposite one another are designed in the form of a part-circle in cross section. Between the recesses  64  and  66 , the rotor  62  has a base or a middle portion  68  which separates the recesses  64  and  66  from one another. Furthermore, two long holes  70  and  72 , through which the connection pieces  30  and  32  (cf.  FIG. 4 ) pass, are cut out in the middle portion  68 . Instead of the long holes  70  and  72 , the middle portion  68  can also have otherwise shaped cut-outs there, or the middle portion  68  can be completely absent in this region, i.e. it can extend only through an intermediate partial region with respect to the longitudinal direction of the rotor  62 .  
         [0098]     The rotor  62  is circular, as seen in cross section, the two recesses  64  and  66  extending approximately over 90° in the circumferential direction with respect to the longitudinal mid-axis  20 . The middle portion  68  of the rotor  62  likewise extends at each of its wide ends approximately over 90° or a quarter of the full circumference.  
         [0099]     The middle portion  68  of the axially immovable rotor  62 , by means of which the pistons  22  to  28  rotate jointly, lies centrically on the longitudinal mid-axis  20  of the housing  12 . Provided on the rotor, on the end faces, are shaft extensions  74  and  76 , via which the rotor  62  is mounted rotatably in the housing  12 , more precisely in the housing covers  14  and  16 . In the exemplary embodiment shown, the shaft extension  74  projects with a toothed end piece  78  out of the housing  12 , and the shaft extension  76  likewise projects with a toothed end piece  80  out of the housing. There may also be provision, however, for the end piece  80  to be omitted and for the housing cover  16  to be designed to be closed via the shaft extension  76 . The rotational movement of the rotor  62  can be picked up as rotational energy via the end piece  78  and/or the end piece  80 , that is to say the end piece  78  and/or the end piece  80  may serve as an output shaft.  
         [0100]     Moreover, measures, for example supporting rollers, may be provided on the rotor  62 , in order, in the case of a long overall length, to support the rotor  62  against transverse forces in the housing  12 .  
         [0101]     As described below with regard to the piston  22 , each of the pistons  22  to  28  has a side  82  which faces the housing inner wall  18  and which is designed in cross section in the form of a part-circle, so that each of the pistons  22  to  28  is adapted on the outside to the housing inner wall  18 . The side  82  in this case extends over an angle of circle of about 90°.  
         [0102]     One side  85  of each piston  22  to  28 , the said side facing away from the side  82  and facing the longitudinal mid-axis  20 , is likewise designed in cross section in the form of a part-circle, the circle centre of which is spaced apart from the circle centre of the part-circle which in each case forms the side  82  of the pistons  22  to  28 . Each piston  22  thus has in cross section an approximately almond-shaped or lenticular shape.  
         [0103]     Each of the pistons  22  is assigned at least one chamber which is periodically reduced and enlarged in volume as a result of the to-and-fro linear movement of the pistons  22  to  28 .  
         [0104]     A first chamber  86  is assigned to the first piston  22  on one end face  84 . A second chamber  90  is assigned to the piston  22  on an end face  88  arranged opposite the end face  84 . The chamber  86  is assigned, in turn, to the third piston  26  on an end face  92  facing the end face  84  of the first piston  22 , so that the chamber  86  is assigned jointly to both pistons  22  and  26 . A further chamber  96  is assigned to the piston  26  on an end face  94  facing away from the end face  92 . By virtue of the oppositely directed linear movements of the pistons  22  and  26  in relation to one another, the volumes of the chambers  90  and  96  are reduced when the volume of the chamber  86  is enlarged, and vice versa.  
         [0105]     Correspondingly, the pistons  24  and  28  are assigned chambers  98 ,  100  and  102  which are arranged with an offset of 180° in relation to the chambers  86 ,  90  and  96  with respect to the longitudinal mid-axis  20 .  
         [0106]     The chambers  86  and  98  are separated from one another completely by the middle portion  68  of the rotor  62 . The chamber  86  is separated completely from the chambers  90  and  96  by means of a seal  104 , which seals off the piston  22  relative to the housing inner wall  18  and to the middle portion  68  of the rotor  62 , and a seal  106 , which seals off the piston  26  relative to the housing inner wall  18  and to the middle portion  68  of the rotor  62 .  
         [0107]     Correspondingly, the chamber  98  is separated completely from the chambers  100  and  102  via seals  108  and  110  on the pistons  24  and  28 .  
         [0108]     By contrast, the chambers  90  and  100  communicate with one another via the long hole  70 , and the chambers  96  and  102  also communicate with one another via the long hole  72 ; this, however, can also be modified according to an embodiment to be described later in such a way that the chambers  90  and  100  or  96  and  102 , respectively, do not communicate with one another. As already mentioned above, the long holes  70  and  72  can also be shaped differently, or the middle portion  68  can be absent at these locations, whereby the chambers  90  and  100  as well as  96  and  102  also communicate with one another and, in each case, form a double total volume.  
         [0109]     In the exemplary embodiment illustrated in FIGS.  1  to  6 , the chambers  86  and  98  serve as working chambers for a Carnot cycle, and the chambers  90 ,  100  and  96 ,  102  serve as boost-pressure chambers for generating a boost pressure which can act upon the working chambers  86  and  98 .  
         [0110]     For this purpose, the chambers  90  and  100  are connected to the chambers  86  and  98  via an orifice  104  in the housing  12  and a connecting line  106 , depending on which of the chambers  86  or  98  is exactly opposite an inlet orifice  108  during the rotational movement of the pistons  22  to  28  about the longitudinal mid-axis  20 . Arranged in the inlet orifice  108  is a valve  110  which is designed as a controllable valve, in particular a solenoid valve,  112 . The chambers  96  and  102  are correspondingly connected to the inlet orifice  108 , with the valve  110  interposed, via an orifice  114  and a connecting line  116 .  
         [0111]     The chambers  86  and  98  serving as working chambers are assigned, overall, a spark plug  118  for the discharge of ignition sparks and an injection nozzle  120  for the injection of a fuel, for example petrol, diesel or biodiesel.  
         [0112]     According to  FIGS. 7   a ) to d), an outlet orifice  122  for the expulsion of the burnt fuel/air mixture is also assigned to the chambers  86  and  98  in the housing.  
         [0113]     According to  FIGS. 8   a ) to d), the chambers  96  and  102  serving as boost-pressure chambers are assigned, furthermore, a common intake orifice  124 , a corresponding intake orifice, not illustrated in any more detail, in the housing  12  being assigned to the chambers  90  and  100  likewise serving as boost-pressure chambers.  
         [0114]     The functioning of the rotary piston machine  10  is described in more detail below with reference to FIGS.  6  to  8 .  
         [0115]      FIGS. 6   a ),  7   a ) and  8   a ) illustrate the rotary piston machine in a first operating position which corresponds to the operating position in  FIG. 3  and  FIG. 4 . The fuel/air mixture, which is compressed to the maximum extent, is just being ignited in the chamber  86  via the spark plug  118 . Burnt fuel/air mixture has just been expelled completely from the chamber  98 . The chambers  96 ,  102  serving as boost-pressure chambers have been filled completely with air through the intake orifice  124 , in which a corresponding valve, preferably an automatic valve, for example a flutter valve, may be arranged. The chambers  90  and  100  serving as boost-pressure chambers have likewise been filled completely with fresh air through a corresponding intake orifice.  
         [0116]     Starting from  FIGS. 6   a ),  7   a ) and  8   a ), the pistons  22  to  28  rotate clockwise, together with the rotor  62 , about the longitudinal mid-axis  20  and have been rotated through about 45° with respect to the operating position in  FIG. 6   b ),  7   b ) and  8   b ) (cf.  FIG. 1 ). The fuel/air mixture previously ignited in the chamber  86  then expands in the chamber  86  which is enlarged in volume, whilst fresh air is forced into the chamber  98  from the boost-pressure chambers  90 ,  100  and  96 ,  102 , which are reduced in volume and thereby compress the fresh air previously introduced. As illustrated in  FIG. 6   b ), the valve  110  is opened, in order to admit the precompressed fresh air into the chamber  98  from the chambers  90 ,  100  and  96 ,  102  serving as boost-pressure chambers. Since the maximum volume of the chambers  90 ,  96 ,  100 ,  102  together is larger than the maximum volume of the chamber  98 , namely about four times as large, a (pre)compression of the air forced into the chamber  98  occurs.  
         [0117]     Meanwhile, the pistons  22  and  24  move parallel to the longitudinal mid-axis  22  according to an arrow  126  and the pistons  26  and  28  move in the opposite direction parallel to the longitudinal mid-axis  20  according to an arrow  128 . The longitudinal movement of the pistons  22 ,  24  and  26 ,  28  is imparted by means of the control mechanisms  40  and  58 .  
         [0118]     After a further rotation of the pistons  22  to  28  through 45° about the longitudinal mid-axis  20 , the operating position illustrated in  FIGS. 6   c ),  7   c ) and  8   c ) (cf.  FIG. 2 ) is reached, in which the chamber  98  has attained its maximum volume and is filled with precompressed fresh air, whilst, after the complete expansion of the previously ignited fuel/air mixture, the opposite chamber  86 , which cannot be seen in the drawing, likewise assumes its largest volume. By contrast, the chambers  90 ,  100  and  96 ,  102  then have their minimum volume.  
         [0119]     As a result of a further rotation of the pistons  22  to  28  through 45°, the operating position assumed in  FIGS. 6   d ),  7   d ) and  8   d ) is reached, in which the fresh air previously admitted into the chamber  98  is then further compressed continuously, in that the pistons  24 ,  28  move towards one another again in opposite directions according to the arrows  130  and  132 . In the chamber  86 , which cannot be seen in  FIGS. 6   d ),  7   d ) and  8   d ) and which is then likewise reduced in volume again because the pistons  22  and  26  likewise move towards one another according to the arrows  130 ,  132 , the completely expanded fuel/air mixture is then expelled from the outlet orifice  122  as a result of a reduction in volume of the chamber  86 . Fresh air is correspondingly sucked from outside into the chambers  90 ,  100  and  96 ,  102 , which are then enlarged in volume again.  
         [0120]     After a further rotation of the pistons  22  to  28  through 45°, starting from  FIGS. 6   d ),  7   d ) and  8   d ), the state illustrated in  FIGS. 6   a ),  7   a ) and  8   a ) is assumed again, but the pistons  24  and  28  then lie “at the top” and the pistons  22  and  26  lie “at the bottom”. In other words, up to then, the pistons  22  to  28  have executed, overall, a rotation through 180° about the longitudinal mid-axis  20 , and at the same time have passed once through the four working strokes of admission, compression, expansion and expulsion. Accordingly, during one full revolution of the pistons  22  to  28  through 360° about the longitudinal mid-axis  20 , two full working cycles are completed.  
         [0121]      FIGS. 9   a ) and b),  10   a ) and b) and  11   a ) and b) illustrate an exemplary embodiment of a rotary piston machine  10 ′ which is slightly modified in relation to the exemplary embodiment described above and which differs from the rotary piston machine  10  in the following features.  
         [0122]     The chambers  90 ′ and  100 ′ which are assigned to the pistons  22 ′ and  24 ′ and which again serve as boost-pressure chambers for acting upon the chambers  86 ′ and  98 ′ with a boost-pressure generated in the chambers  90 ′ and  100 ′, the chambers  90 ′ and  100 ′ again communicating with one another, are not connected to the chamber  86 ′ and  98 ′ via lines located on the outside of the housing, but directly via the pistons  22 ′ and  24 ′. For this purpose, the pistons  22 ′ and  24 ′ have a hollow design, and the pistons  22 ′ and  24 ′ have arranged in them in each case a valve  138  which is designed as an automatic valve, preferably as a flutter valve.  
         [0123]     Correspondingly, the chambers  96 ′ and  102 ′ assigned to the pistons  26 ′ and  28 ′ and likewise communicating with one another are connected directly to the chambers  86 ′ and  98 ′ via valves  140  present in the pistons  26 ′ and  28 ′.  
         [0124]     Whilst the valves  138 ,  140  are shown in their closing position in  FIG. 9   a ), the pistons  22 ′ to  28 ′ moving into their position displaced to the greatest possible extent towards the middle of the housing  12 ′, the valves  138  and  140  are shown in their open position in  FIG. 9   b ), when the pistons  22 ′ to  28 ′ move apart from one another in opposite directions and the chambers  90 ′,  100 ′ and  96 ′ and  102 ′ are reduced in volume. In this way, the chamber  96 ′ provided for intake between the pistons  24 ′ and  28 ′ can be supplied with precompressed air from the chambers  90 ′,  100 ′ and  96 ′,  102 ′.  
         [0125]      FIGS. 12   a )-d) to  15   a )-d) show another embodiment of a rotary piston machine labelled with the general reference symbol  10 ″ which differs from the rotary piston machine  10  with respect to the following features.  
         [0126]     The rotary piston machine  10 ″ likewise comprises four pistons  22 ″ to  28 ″ which are assigned chambers  86 ″,  90 ″,  96 ″,  98 ″,  100 ″ and  102 ″. Differently from the rotary piston machine  12  and also from the rotary piston machine  10 ′, however, the chambers  90 ″,  96 ″,  100 ″ and  102 ″ do not serve as boost-pressure chambers, but also as working chambers for a Carnot-cycle like the chambers  86 ″ and  98 ″.  
         [0127]     As a further difference to the previous embodiments, the chambers  90 ″ and  100 ″ do not communicate with one another, but are completely separated from one another by the middle portion  68 ″ of the rotor  62 ″. Likewise, the chambers  96 ″ and  102 ″ are completely separated from one another by the middle portion  68 ″ of the rotor  62 ″ and also serve as working chambers for a Carnot-cycle.  
         [0128]     The chambers  90 ″ and  100 ″ are assigned an inlet channel  142  for fresh air and an outlet channel  144  for expelling the burnt fuel/air mixture, accordingly. Further the chambers  90 ″ and  100 ″ are assigned another spark plug  146  and another injection nozzle  148 , in common. The inlet channel  142 , the outlet channel  144 , the spark plug  146  as well as the injection nozzle  148  are arranged offset by 90° about the longitudinal mid-axis  20 ″ with respect to the corresponding inlet channel  108 ″, outlet channel  122 ″, the spark plug  118 ″ and the injection nozzle  120 ″, which are assigned to the chambers  86 ″ and  98 ″.  
         [0129]     In the same way, the chambers  96 ″ and  102 ″ are assigned another inlet channel  150 , outlet channel  152 , a spark plug  154  and an injection nozzle  156 , which are situated on the same peripherical position as the inlet channel  142 , the outlet channel  144 , the spark plug  146  and the injection nozzle  148  which are assigned to the chambers  90 ″ and  100 ″.  
         [0130]     With this construction, a six-cylinder-engine is reproduced by the rotary piston machine  10 ″, wherein the working strokes of admission, compression, expansion and expulsion are offset by 90° in the chambers  90 ″,  100 ″ as well as  96 ″,  102 ″ with respect to the corresponding working strikes in the chambers  86 ″ and  98 ″.  
         [0131]      FIGS. 12   a )-d) to  15   a )-d) show four operational positions of the rotary piston machine  10 ″ in which the pistons  22 ″ to  28 ″ have moved by 135° in total about the longitudinal mid-axis  20 ″. Upon a full revolution of the pistons  22 ″ to  28 ″ by 360° about the longitudinal mid-axis  20 ″ a full working stroke in each case is carried out in the chambers  86 ″ and  98 ″, and also in each case in the chambers  90 ″ and  100 ″ as well as  96 ″ and  102 ″ so that altogether six complete working strokes are performed in the rotary piston machine  10 ″ upon a full revolution.  
         [0132]     It is to be understood that further modifications of the rotary piston machine  10 ,  10 ′ or  10 ″ are possible within the scope of the present invention.  
         [0133]     For example, it is conceivable to provide only the pistons  22  and  24  as a double piston in the rotary piston machine  10 , whereas the pistons  26  and  28  may be omitted. In this case, however, the linear movement of the pistons  22  and  24  would not be mass-compensated. On the other hand, only the piston  22  and the piston  28  may be provided, whilst the pistons  24  and  26  would be omitted, corresponding transverse walls for delimiting the chambers  86  and  98  being provided in the rotor  62 . Such an arrangement would again lead to a mass-compensated configuration also with respect to the linear movement of the pistons  22  and  28 .