Abstract:
The invention relates to an oscillating piston engine comprising a housing that contains a first and at least a second piston, both of which can rotate about a fixed rotational axis in the housing and which when rotating about said axis execute counter-rotating displacements back and forth about a pivoting axis that runs perpendicular to the rotational axis through the centre of the housing. A working chamber is situated between opposing end faces of the first and at least second piston. The housing is provided with at least one gas exchange opening for admitting or discharging a gas into or from the working chamber. The pistons are arranged in such a way that the rotational axis runs through the working chamber. The pistons are mounted to slide in a piston cage, which is located in the housing, is concentric with the rotational axis, and rotates together with the pistons about said axis. The gas exchange opening is arranged eccentrically in relation to the rotational axis, on one end face of the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of pending international patent application PCT/EP2007/001488 filed on Feb. 21, 2007 which designates the United States, and which claims priority of German patent application no. 10 2006 009 198.1 filed on Feb. 22, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention generally relates to oscillating piston engines. More specifically, the present invention relates to an oscillating piston engine of the type having a housing in which a first and at least a second piston are arranged which can jointly revolve in the housing about an axis of rotation which is fixed in relation to the housing, and which perform when revolving about the axis of rotation reciprocating pivoting movements in opposite directions relative to one another about a pivot axis running through the center of the housing perpendicularly to the axis of rotation, wherein a working chamber is arranged between mutually facing end surfaces of the first and at least second piston, and which further comprise at least one gas exchange opening in the housing for admitting or discharging a gas into or from the working chamber. 
         [0003]    Oscillating piston engines and in particular an oscillating piston engine according to the present invention can be used as internal combustion engines, as pumps or as compressors. An oscillating piston engine according to the present invention is preferably used as an internal combustion engine and is described as such in the present description. 
         [0004]    In the case of the use of an oscillating piston engine as an internal combustion engine, the individual working strokes of admitting, compressing, expanding and expelling are imparted by reciprocating pivoting movements of the individual pistons between two end positions. 
         [0005]    In the case of the oscillating piston engine known from document WO 03/0670333 A1 from the same Applicant, four pistons are arranged in the spherical housing which jointly revolve about an axis of rotation which is central to the housing and fixed in relation to the housing and perform when revolving in the housing reciprocating pivoting movements about a pivot axis, each two adjacent pistons pivoting in opposite directions. In the case of this known oscillating piston engine, each two pistons diametrically opposing the center of the housing are rigidly connected to each other to form a double piston, and two such pairs of pistons are arranged crosswise in the center of the housing. A respective working chamber is formed between each two mutually facing end surfaces of the pistons of the pairs of pistons, so that the known oscillating piston engine has a total of two working chambers. Both working chambers, which are arranged diametrically opposing the center of the housing, increase and decrease in size in the same direction during the reciprocating pivoting movement of the pistons. 
         [0006]    The pistons of this known oscillating piston engine are arranged in the housing in such a way that they are located in their TDC position, in which the volumes of the two working chambers are minimal, perpendicularly to the axis of rotation. In this position, as the pistons revolve about the axis of rotation, the centrifugal forces acting on the pistons are maximal. As a result, at high rotational speeds, the expanding or the pivoting-apart of the pistons must take place counter to the centrifugal forces, because the centrifugal forces counteract the pivoting-apart movement of the pistons. In the case of this oscillating piston engine, the working chambers are located in all cases outside and perpendicularly to the axis of rotation. 
         [0007]    Furthermore, the known oscillating piston engine has in the housing two gas exchange openings, which are arranged at an angular distance of approximately 100° from one another relative to the axis of rotation. One gas exchange opening serves to admit combustion air and the other gas exchange opening serves to expel the combusted fuel/air mixture. A spark plug is arranged on the side of the axis of rotation opposing the gas exchange openings, for example on the bisector of an angle between the two gas exchange openings. 
         [0008]    An oscillating piston engine which is comparable to the above-described known oscillating piston engine is known from document WO 2005/098202 A1. As in the case of the above-described known oscillating piston engine, admission pressure chambers are associated with the backs of the pistons that are remote from the working chambers. For flooding the admission pressure chambers with atmospheric fresh gas, intake openings are provided in the housing, and for flooding the working chambers with precompressed fresh gas, the admission pressure chambers are connected to the working chambers via a connection opening and via an overflow channel. The output shaft located on the axis of rotation is provided on its end face with rotary slide valves which each have two opposing windows which can be drawn together with the intake openings and with the connection opening, wherein on rotation of the shaft through 180° alternately all four windows clear the intake openings and two of the windows clear the connection openings of the overflow channels. The actual gas exchange openings, which are associated with the working chambers, are provided with controlled valves, and this increases the design costs. This known approach of providing a control disc rotating about the axis of rotation or a rotary slide valve is known, in the case of a comparable oscillating piston engine, also from document U.S. Pat. No. 6,325,038 B1. 
       SUMMARY OF THE INVENTION 
       [0009]    The invention is based on the object of specifying an oscillating piston engine which breaks with the approach for arranging the pistons of the known oscillating piston engine, and which in this case also allows the gas exchange of the working chambers to be controlled in a simple manner in terms of design. 
         [0010]    According to the invention, an oscillating piston engine is provided, comprising a housing having a center and having an end face, 
         [0011]    a first and at least a second piston arranged in the housing, the first and at least second piston having mutually facing end surfaces, the first and at least second piston being able to jointly revolve in the housing about an axis of rotation which is fixed in relation to the housing, and to perform, when revolving about the axis of rotation, reciprocating pivoting movements in opposite directions relative to one another about a pivot axis running through the center of the housing perpendicularly to the axis of rotation, 
         [0012]    a working chamber arranged in the housing between the mutually facing end surfaces of the first and at least second piston, the axis of rotation running through the working chamber, 
         [0013]    a piston cage arranged in the housing concentrically with the axis of rotation, the first and at least second piston being slidingly mounted in the piston cage, the piston cage being able to rotate together with the first and second piston about the axis of rotation, and 
         [0014]    at least one gas exchange opening arranged in the housing for admitting or discharging a gas into or from the working chamber, the at least one gas exchange opening being arranged eccentrically with respect to the axis of rotation on the end face of the housing, the axis of rotation running through the end face of the housing, the piston cage having an end face opposing the end face of the housing and having an eccentric opening delimited in direction of revolution about the axis of rotation. 
         [0015]    In the case of the oscillating piston engine according to the invention, the at least two pistons are therefore arranged in such a way that the working chamber is located not perpendicularly to the axis of rotation, but rather on the axis of rotation or around the axis of rotation. Owing to the shorter spacing of the pistons from the axis of rotation, the centrifugal forces acting, during revolving about the axis of rotation, on the two pistons delimiting the working chamber are lower and also act in the direction of the pivoting-apart of the two pistons, i.e. the centrifugal forces assist the expanding working stroke. Furthermore, the at least one gas exchange opening is now arranged no longer, as in the case of the known oscillating piston engine, in a housing region far apart from the axis of rotation, but rather on the end face of the housing, directly associated with the working chamber located on the axis of rotation. The flow of the working gas through the at least one gas exchange opening is thus directed substantially axially to the axis of rotation. In order to achieve simple control, in particular without valves, of the exchange of gas into or from the working chamber, the piston cage in which the pistons are mounted to slide has a full-area end face which runs along the inside of the end face of the housing as the piston cage rotates. Present in the end face of the piston cage is a, viewed in the direction of revolution, delimited eccentric opening which, as the piston cage revolves about the axis of rotation, communicates or does not communicate, depending on the revolving position, with the gas exchange opening in the end face of the housing. In this way, it is advantageously not necessary to provide the at least one gas exchange opening with an actively controlled valve, because the valve function is performed by the opening in the end face of the piston cage. When the eccentric opening in the end face of the piston cage is not aligned with the gas exchange opening, the working chamber is sealed from the gas exchange opening, for example during compressing or expanding of the fuel/air mixture. 
         [0016]    In a preferred configuration, the gas exchange opening widens in opening cross section from an outside toward an inside of the end face of the housing. 
         [0017]    The advantage of this measure is that owing to the opening cross section of the gas exchange opening, which is larger on the inside at the end face of the housing, the opening in the end face of the piston cage can be kept small, and an adequate exchange of gas can nevertheless take place as the opening of the piston cage passes the gas exchange opening in the housing. 
         [0018]    In a further preferred configuration, a maximum clear width of the gas exchange opening extends, viewed in the direction of revolution about the axis of rotation, over an angle of revolution of more than 30° and less than 90°. 
         [0019]    The advantage of this measure is that a complete exchange of gas is brought about by the at least one gas exchange opening in an angle of revolution range of less than 90°. 
         [0020]    In a further preferred configuration, a second gas exchange opening is arranged eccentrically on the end face of the housing, the at least one gas exchange opening serving to discharge a gas from the working chamber and the second gas exchange opening to admit a gas into the working chamber, and the opening in the end face of the piston cage communicating when revolving about the axis of rotation successively, but without a time overlap, with the at least one and the second gas exchange opening. 
         [0021]    In the case of this configuration, two gas exchange openings are accordingly provided in the end face of the housing, one of which serves to admit a gas, for example combustion air or fuel/air mixture, and the other to discharge a gas, for example combusted fuel/air mixture. Viewed in the direction of revolution of the pistons, the opening in the end face of the piston cage runs first past the gas exchange opening for discharging the gas from the working chamber and subsequently past the gas exchange opening for admitting a gas into the working chamber. The gas exchange openings are in this case arranged in relation to the dimensions of the opening in the end face of the piston cage so as to allow the opening of the piston cage to communicate at all times only with one of the two gas exchange openings, while the other is covered by the remaining full-area end face of the piston cage. Overall, this configuration has the advantage of allowing the admission of a gas into the working chamber and the discharging of a gas from the working chamber to be controlled in a simple manner in terms of design without the need for additional control valves. 
         [0022]    In relation to the above-mentioned configuration, it is furthermore preferred if the at least one gas exchange opening for discharging gas is arranged, viewed in the direction of revolution of the piston cage, before the second gas exchange opening for admitting gas. 
         [0023]    This measure has the advantage that the arrangement of the gas exchange openings corresponds to the natural respiration principle of the working chambers defined by the two pistons. The process of the discharging or expelling of combusted fuel/air mixture is carried out, in the case of a pivoting movement of the two pistons directed toward each other, until the working chamber between the two pistons is minimized. After the expulsion of combusted fuel/air mixture, new combustion air can now be admitted or drawn into the working chamber, optionally together with fuel, as the two pistons again pivot apart from each other, during which process the working chamber again increases in size, immediately after the complete expulsion of the combusted fuel/air mixture. This combined process of expelling the combusted fuel/air mixture and admitting fresh combustion air or fuel/air mixture can advantageously take place in an angular range of less than 180° of the revolving movement of the pistons or the piston cage about the axis of rotation. 
         [0024]    Furthermore, it is preferred if the at least one gas exchange opening and the second gas exchange opening are separated from each other, viewed in the direction of revolution of the piston cage, by a web which is at least slightly broader than the breadth of the opening of the piston cage, the web extending, viewed in the direction of revolution, over an angle of from approximately 20° to approximately 60°, preferably over an angle of from approximately 40° to approximately 50°. 
         [0025]    In the case of this configuration, the two gas exchange openings are accordingly arranged, viewed in the direction of revolution about the axis of rotation, close together and separated from each other merely by the web. The breadth of the web must merely be broader than the opening of the piston cage to ensure gas-tight separation of the two gas exchange openings as the piston cage revolves about the axis of rotation. Overall, there is obtained a control mechanism which is very simple in terms of design for the exchange of gas into and from the working chamber, requiring just two openings in the end face of the housing that are eccentric with respect to the axis of rotation and one eccentric opening in the end face of the piston cage. 
         [0026]    In a further preferred configuration, between the end face of the housing and the end face of the piston cage is a sealing arrangement having at least one seal which seals the at least one gas exchange opening from the end face of the piston cage. 
         [0027]    This measure has the advantage that the at least one seal in the positions of revolution of the piston cage about the axis of rotation, in which the opening of the piston cage does not communicate with the at least one gas exchange opening, ensures that no gas is exchanged into or from the working chamber, thus allowing high working pressures to be achieved in the working chamber during compression of the fuel/air mixture and during expansion of the fuel/air mixture after ignition thereof. In the simplest case, the at least one seal is arranged on the circumference of the at least one gas exchange opening and nestles against the end face of the piston cage. 
         [0028]    It is preferred if the sealing arrangement is provided on the piston cage and has a radially outer ring seal based on the axis of rotation, optionally a radially inner ring seal and at least two at least approximately radially extending seals which are set apart from one another in the circumferential direction, are connected to the ring seals and arranged on both sides of the opening of the piston cage. 
         [0029]    The radially outer ring seal and the optionally provided radially inner ring seal cause sealing of the at least one gas exchange opening from the remaining interior of the housing, while the two approximately radially extending seals seal the opening of the piston cage from the end face of the housing. The two ring seals and the two radial seals slide along the inside of the end face of the housing as the piston cage revolves. 
         [0030]    In a further preferred configuration, the sealing arrangement has more than two at least approximately radially extending seals which are preferably distributed uniformly about the axis of rotation in the direction of revolution. 
         [0031]    The advantage of this measure is that as a result of the provision of a plurality of radial seals, the sealing effect is further improved, and that uniform abutment of the sealing arrangement as a whole against the inside of the end face of the housing is also achieved. 
         [0032]    The sealing arrangement as a whole, comprising the ring seals and the radial seals, can in particular be embodied in one piece and be introduced in a correspondingly configured groove in the outside of the end face of the piston cage. In order to achieve uniform contact pressure of the sealing arrangement against the end face of the housing, the sealing arrangement can be acted on in the end face of the piston cage with spring force which presses the sealing arrangement against the end face of the housing. 
         [0033]    In a further preferred configuration, there is present in the end face of the housing a further, centric opening and in the end face of the piston cage also a further, centric opening. 
         [0034]    There may now advantageously be inserted in the centric opening of the end face of the housing a spark plug or glow plug which can then exert an influence into the working chamber through the centric opening in the end face of the piston cage, which opening communicates with the centric opening of the end face of the housing. 
         [0035]    The aforementioned radially inner ring seal should then be provided to seal the at least one gas exchange opening from the centric opening in the end face of the piston cage. 
         [0036]    In a further preferred configuration, the end surfaces of the pistons have a trough-like depression in a region facing the end face of the piston cage. 
         [0037]    The depression causes the pistons to ensure a finite working chamber volume even in the TDC position, in which the pistons are pivoted maximally toward one another, resulting in an optimum configuration of an initial combustion trough. At the start of the working stroke after the ignition of the fuel/air mixture, the explosion which takes place in this combustion trough acts on the pistons with maximum leverage, as the depressions in the aforementioned configurations are at the greatest distance from the swivel axis and thus form a large lever arm on the piston. 
         [0038]    Further advantages and features will emerge from the following description and the appended drawings. 
         [0039]    It will be understood that the features which have been mentioned hereinbefore and will be further described hereinafter can be used not only in the respectively specified combination, but rather also in other combinations or in isolation, without departing from the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    An exemplary embodiment of the invention is illustrated in the drawings and will be described hereinafter in greater detail with reference to said drawings, in which: 
           [0041]      FIG. 1  is a perspective overall view of an oscillating piston engine; 
           [0042]      FIG. 2  is a longitudinal section of the oscillating piston engine in  FIG. 1 , the pistons being shown in a first pivoting end position (BDC position); 
           [0043]      FIG. 3  shows the oscillating piston engine in  FIG. 1  in the same section as in  FIG. 2 , the pistons now being shown in a second pivoting end position (TDC position); 
           [0044]      FIG. 4  is a further longitudinal section of the oscillating piston engine in  FIG. 1 , the sectional plane in  FIG. 4  being tilted through approximately 45° in relation to the sectional plane in  FIGS. 2 and 3 , and the pistons being shown in a pivoting position located approximately centrally between the positions in  FIG. 2  and in  FIG. 3 ; 
           [0045]      FIG. 5  is a perspective view of a piston cage of the oscillating piston engine in  FIG. 1 to 4  including pistons received therein; 
           [0046]      FIG. 6  is an external view of a housing part of the oscillating piston engine in  FIG. 1 to 4 ; 
           [0047]      FIG. 7  is an internal view of the housing part in  FIG. 6 , on an enlarged scale compared to  FIG. 6 ; and 
           [0048]      FIGS. 8 ,  9  and  10  are each a further internal view of the housing part as in  FIG. 7 , although an end face of the piston cage is additionally shown by broken lines in  FIG. 5 , and  FIGS. 8 ,  9  and  10  each showing a differing revolving position of the piston cage in relation to the end-face housing part. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0049]      FIG. 1 to 4  show an oscillating piston engine provided with general reference numeral  10 . Further details of the oscillating piston engine  10  are shown in  FIG. 5 to 10 . 
         [0050]    The oscillating piston engine  10  is generally designed as an internal combustion engine but, modified accordingly, can also be used as a pump or as a compressor. 
         [0051]    The oscillating piston engine  10  has a housing  12  which in  FIG. 1  is shown closed. The housing  12  has a central housing portion  14  which is spherical in its formation. The central housing portion  14  is composed of two housing halves  16  and  18  which are joined together via a flange  20 . 
         [0052]    The housing  12  also has a first end face  22  and a second end face  24  opposing the first end face  22 . 
         [0053]    The first end face  22  is formed by an end-face housing lid  26  and the second end face  24  by an end-face housing lid  28 . The housing lids  26  and  28  are connected to the central housing portion  14  or the housing halves  16  and  18  thereof. The housing lids  26  and  28  can be detached from the central housing portion  14 , just as the housing half  16  can be detached from the housing half  18 . 
         [0054]    According to  FIG. 2 to 4 , four pistons  30  to  36  are arranged inside the housing  12 . The pistons  30  to  36  can revolve in the housing  12  jointly about an axis of rotation  38  in the direction indicated by an arrow  40 . The axis of rotation  38  passes through the center of the spherical interior of the housing  12  and is fixed in relation to the housing, i.e. does not change its position relative to the housing  12  as the pistons  32  to  36  revolve. 
         [0055]    The pistons  30  to  36  perform as they revolve about the axis of rotation  38  a pivoting movement which is superimposed on the revolving movement. The pistons  30  and  32  perform in this case reciprocating pivoting movements about a first pivot axis  42  which perpendicularly intersects the axis of rotation  38  at the center of the interior of the housing  12 , while the pistons  34  and  36  perform as they revolve about the axis of rotation  38  reciprocating pivoting movements about a second pivot axis  44  which perpendicularly intersects the axis of rotation  38  likewise at the center of the interior of the housing  12 , but is also located perpendicularly to the pivot axis  42 . The pivot axes  42  and  44  revolve with the pistons  30  to  36  likewise about the axis of rotation  38 . The instantaneous pivot plane of the pistons  30  and  32  is in this case located at all times perpendicularly to the instantaneous pivot plane of the pistons  34  and  36 . 
         [0056]    It is however also possible for all four pistons  30  to  36  to be arranged in a common plane and for the pivot axes  42  and  44  to be parallel or coincide. 
         [0057]    Both the axis of rotation  38  and the pivot axes  42  and  44  are in this case to be understood as geometric axes. 
         [0058]    The pivoting movements of the pistons  30  and  32  or  34  and  36  are carried out between two end positions, one end position being shown in  FIG. 2  (what is known as the BDC position) and the other end position in  FIG. 3  (what is known as the TDC position). 
         [0059]    The pivoting movements of the pistons  30  and  32 , on the one hand, and the pistons  34  and  36 , on the other hand, are in all cases in the same direction, i.e. when the pistons  30  and  32  pivot apart from each other, the pistons  34  and  36  also pivot apart from each other, and vice versa. 
         [0060]    Each of the pistons has an end surface, i.e. the piston  30  has an end surface  46 , the piston  32  an end surface  48 , the piston  34  an end surface  50  and the piston  36  an end surface  52 , the view onto said end surface  52  being obscured in  FIG. 2  by another component. 
         [0061]    The pistons  30  and  32  form a first pair of pistons, the end surfaces  46  and  48  of which face each other. The end surfaces  46  and  48  define a first working chamber  54 . The pistons  34  and  36  form a second pair of pistons, the end surfaces  50  and  52  of which face each other and define a second working chamber  56 . The volumes of the working chambers  54  and  56  increase and decrease in size in accordance with the reciprocating pivoting movements of the pistons  30  and  32  or  34  and  36 , the working chambers  54  and  56  increasing or decreasing in size in all cases in the same direction. 
         [0062]    The pistons  30  to  36  are arranged in the housing  12  in such a way that the axis of rotation  38  passes through both working chambers  54  and  56 , preferably centrally in each revolving and pivoting position of the pistons  30  to  36 . 
         [0063]    In order to generate the pivoting movements of the pistons  30  to  36  during the revolving movement thereof about the axis of rotation  38 , each piston has a running element: the piston  30  a running element  58  ( FIGS. 3 and 4 ), the piston  32  a running element  60  (cf.  FIG. 2 to 4 ), the piston  34  a running element  62  (cf.  FIG. 2 ) and the piston  36  a running element  64  (cf.  FIGS. 3 and 4 ). The running elements  58  to  64  are in this case formed as rollers, each running element  58  to  64  being rotatably fastened to the associated piston  30  to  36 . A first control cam  66 , which is formed on a control cam member  68 , is associated with the running elements  58  and  60  of the pistons  30  and  32 . A second control cam  70  on the control cam member  68  is associated with the running elements  62  and  64  of the pistons  34  and  36 . 
         [0064]    The running elements  58  and  60  accordingly run along the same control cam  66 , and the running elements  62  and  64  along the same control cam  70 . 
         [0065]    The control cams  66  and  70  are formed around the axis of rotation  38  over their entire circumference and have a contour or cam guide allowing the pivoting movement of the pistons  30  and  32  or  34  and  36  to be derived from the revolving movement thereof about the axis of rotation  38 . 
         [0066]    The pistons  30  to  36  are mounted to slide in the housing  12  in a piston cage  72  which revolves about the axis of rotation  38  in conjunction with the pistons  30  to  36  and is shown in  FIG. 5  together with the pistons  30  to  36 , but without the housing  12 . In the piston cage  72 , the pistons are prevented from turning or tilting, for example by means of tongue-and-groove connections (not shown). 
         [0067]    The piston cage  72  has according to  FIG. 4  a bore  74  associated with the pistons  34  and  36  and according to  FIG. 2  a bore  76  associated with the pistons  30  and  32 . The pistons  34  and  36  are mounted to slide in the bore  74 , and the pistons  30  and  32  are mounted to slide in the bore  76 . Together with the end surfaces  46  and  48  of the pistons  30  and  32 , the bore  76  delimits the working chamber  54 , and the bore  74  delimits the working chamber  56  together with the end surfaces  50  and  52  of the pistons  34  and  36 . Owing to the arrangement, staggered through 90°, of the pistons  30  and  32  relative to the pistons  34  and  36 , bores  74  and  76  are also formed perpendicularly to each other in the piston cage  72 . 
         [0068]    The bores  74  and  76  are provided in a respective main bearing portion  78  (bore  74 ) and main bearing portion  80  (bore  76 ). Via the main bearing portions  78  and  80 , the piston cage  72  is mounted in the housing  12  so as to be able to rotate about the axis of rotation  38  via bearings  82  and  84  respectively. 
         [0069]    The piston cage  72  serves not only to mount the pistons  30  to  36 , but rather also to transmit the rotational movement from or to a drive/output shaft  86 . For this purpose, the piston cage  72  is provided at its ends with in each case a set of outer teeth  88  and  90  respectively, of which at least one set, in the exemplary embodiment shown the set of outer teeth  88 , meshes with a gear-wheel  92  connected to the output shaft  86 . The output shaft  86  is, in the case of the oscillating piston engine  10 , accordingly arranged on the axis of rotation  38  not coaxially, but rather extra-axially, thus facilitating the gas exchange control of the oscillating piston engine  10  to be described hereinafter. 
         [0070]    For operating the oscillating piston engine  10  as an internal combustion engine, it is necessary that the working chambers  54  and  56 , in which a fuel/air mixture is compressed and ignited and after ignition expanded, allow an exchange of gas, i.e. air and fuel must periodically be admitted into the working chambers  54  and  56  and combusted fuel/air mixture expelled again from the working chambers  54  and  56 . 
         [0071]    This requires gas exchange openings in the housing  12 , which will be described hereinafter. In the case of the oscillating piston engine  10 , the gas exchange openings are provided in the end faces  22  and  24  of the housing  12 , i.e. in proximity to the axis of rotation  38 , but eccentrically thereto. 
         [0072]    As the oscillating piston engine  10  has two working chambers  54  and  56  which are however formed symmetrically to each other, the gas exchange openings in the end faces  22  and  24  are formed identically to one another apart from an offset through 180° about the axis of rotation  38 , so only the gas exchange openings on the end face  22  of the housing  12  will be described hereinafter. 
         [0073]      FIG. 7  is an internal view of the housing lid  26  forming the end face  22  of the housing  12 , and  FIG. 6  is an external view of the housing lid  26 . 
         [0074]    According to  FIG. 7 , a first gas exchange opening  94  and a second gas exchange opening  96  are formed in the end-face housing lid  26 . The gas exchange opening  94  serves to admit gas, in the present case to admit combustion air into the working chamber  56 , and the gas exchange opening  96  serves to discharge or expel a gas from the working chamber  56 , in this case to expel combusted fuel/air mixture. 
         [0075]    The gas exchange opening  94  has associated with it a connecting piece  98  which in the exemplary embodiment shown is combined with an injection nozzle  100  for injecting a fuel together with the combustion air into the working chamber  56 . However, direct injection may also be provided for the oscillating piston engine  10 , i.e. the injection nozzle  100  is then arranged separately from the connecting piece  98 . 
         [0076]    The gas exchange opening  96  has associated with it a connecting piece  102  which serves to connect the oscillating piston engine  10  to an exhaust system. 
         [0077]    The gas exchange openings  94  and  96  are arranged on the end-face housing lid  28  eccentrically with respect to the axis of rotation  38 . As is apparent from  FIG. 7 , the gas exchange openings  94  and  96  are not formed as bores passing through the end-face housing lid  28  with the same opening cross section, but rather widen from the outside to the inside of the end-face housing lid  28 . The gas exchange opening  94  has for this purpose a cavernous or funnel-shaped recess  104 , while the gas exchange opening  96  has a corresponding cavernous recess  106 . The outline of the cavernous recesses  104  and  106  is approximately in the shape of a sector of a circle in its formation. 
         [0078]    The cavernous depressions or recesses  104  and  106  respectively act as funnels for the respective admission of gas or discharge of gas. 
         [0079]    A maximum clear width W of the gas exchange openings  94  and  96 , more precisely the cavernous recesses  104  and  106 , extends, viewed in the direction of revolution about the axis of rotation  38 , over an angle of revolution of more than 30° and less than 90°. For the cavernous recesses  104  and  106 , the angle of revolution in  FIG. 7  is in each case approximately 70°. 
         [0080]    The gas exchange openings  94  and  96  are separated from each other by a web  108 . 
         [0081]    The web  108  has, viewed in the direction of revolution about the axis of rotation  38 , a smaller angular extension than the two cavernous depressions or recesses  104  and  106 , in the present case of approximately 40°. 
         [0082]    Viewed in the direction of revolution of the pistons  30  to  36  or of the piston cage  72  (arrow  40  in  FIG. 7 ), the gas exchange opening  96  for discharging combusted fuel/air mixture is located before the gas exchange opening  94  for admitting the fresh fuel/air mixture. This makes allowance for the mode of operation of the oscillating piston engine  10  when performing the working strokes of expelling, drawing-in, compressing and expanding (working), as will be described hereinafter. 
         [0083]    The gas exchange openings  94  and  96  in the end-face housing lid  26  of the end face  22  are one part of the gas exchange control of the oscillating piston engine  10 . The other part of the gas exchange control of the oscillating piston engine  10  is performed by the piston cage  72 . The piston cage  72  has an end face  110  which directly opposes the end-face housing lid  26  of the end face  22  of the housing  12  and is externally convexly arched in accordance with the internally concave configuration of the end-face housing lid  26 , with the same radius of curvature. Present in the end face  110  of the piston cage  72  is an opening  112  which passes through the end face  110 . In the exemplary embodiment shown, the opening  112  has an opening cross section having substantially the shape of a sector of a circle. The breadth or maximum width of the opening  112 , viewed in the direction of revolution about the axis of rotation  38 , is in this case smaller than the minimum breadth or width of the web  108  in the end-face housing lid  26 . The opening  112  is, like the gas exchange openings  94  and  96 , arranged eccentrically to the axis of rotation  38 . 
         [0084]    As the piston cage  72  revolves about the axis of rotation  38 , the opening  112  sweeps the surface directly opposing it of the inside of the end-face housing lid  26  and, depending on the revolving position, the opening  112  sweeps successively the gas exchange opening  96  and the gas exchange opening  94  and obviously also the remaining closed region  114  of the surface of the end-face housing lid  26  that opposes the end face  110 , including the web  108 . 
         [0085]    With the exception of the opening  112  and with the exception of a central opening  116 , which is flush with a likewise central opening  118  in the end-face housing lid  26  and in which a spark plug or glow plug  120  is positioned, the end face  110  of the piston cage  72  is a full-area end face, i.e. is closed. 
         [0086]    In order adequately to seal the gas exchange openings  94  and  96  from the end face  110  when specifically no gas is to be exchanged, i.e. when the opening  112  communicates neither with the gas exchange opening  94  nor with the gas exchange opening  96 , a sealing arrangement  122  is provided, on the end face  110  of the piston cage  72  in the exemplary embodiment shown. 
         [0087]    The sealing arrangement  122  has a radially outer ring seal  124 , a radially inner ring seal  126  and a plurality of radially extending or radiantly arranged seals  128  which are arranged between and join together the radially inner ring seal  126  and the radially outer ring seal  124 . The radially inner ring seal  126  produces a seal from the central opening  116 , as does the radially outer ring seal  124  from the radially outer region of the end face  110  of the piston cage  72 . Two of the radially extending seals  128 , namely radially extending seals  130  and  132 , surround in this case, together with the corresponding portion of the radially inner ring seal  126  and the radially outer ring seal  124 , the opening  112  in the end face  110  of the piston cage  72 . 
         [0088]    All the above-mentioned seals  124  to  132  of the sealing arrangement  122  are formed in one piece with one another and received in corresponding grooves in the outside of the end face  110  of the piston cage  72 . The seals  124  to  132  are in particular mounted in the aforementioned grooves resiliently, example via compression spring elements, so that the seals  124  to  132  can be pressed against the inside of the end-face housing lid  26  by means of spring force. 
         [0089]      FIG. 8 to 10  show various relative positions between the opening  112  in the end face  110  of the piston cage  72  and the gas exchange openings  94  and  96  in the end-face housing lid  26 . 
         [0090]    Starting with  FIG. 8 , the piston cage  72  is located in a revolving position about the axis of rotation  38  in which the opening  112  communicates with the gas exchange opening  96 . While the opening  112  sweeps the gas exchange opening  96 , combusted fuel/air mixture is expelled from the working chamber  54 . During this process, the pistons  30  and  32  pivot from the BDC position shown in  FIG. 2  into the TDC position shown in  FIG. 3  via the intermediate position shown in  FIG. 4 . For this pivoting stroke, the pistons  30  and  32  require a path of revolution of 90° about the axis of rotation  38 . During the expulsion process, the gas exchange opening  94  is completely sealed from the working chamber  54  via the sealing arrangement  122 . 
         [0091]    Once the expulsion process has been terminated, or in the TDC position in  FIG. 3 , the opening  112  in the end face  110  of the piston cage  72  is flush with the web  108  of the end-face housing lid  26 . In this state, both gas exchange openings  94  and  96  are sealed from the working chamber  54 . After the TDC position according to  FIG. 3 , the pistons  30  and  32  again pivot apart from each other, into the BDC position according to  FIG. 2  via the intermediate position according to  FIG. 4 , although the pistons in the renewed BDC position have continued to revolve through 180° about the axis of rotation  38  in relation to  FIG. 2 . 
         [0092]    During the above-described pivoting-apart of the pistons  30  and  32 , the opening  112  in the end face  110  of the piston cage  72  slides, as shown in  FIG. 10 , via the gas exchange opening  94 , as a result of which fuel/air mixture is drawn into the working chamber  54  via the gas exchange opening  94 . The process of admitting or drawing in the fuel/air mixture is carried out, again, over less than 90° of the revolving movement of the pistons  30  and  32  about the axis of rotation  38 . Once the pistons  30  and  32  have reached their BDC position, the opening  112  is no longer flush with the gas exchange opening  94 , and the working chamber  54  is now again completely sealed from the gas exchange openings  94  and  96 . 
         [0093]    From this renewed BDC position, the pistons  30  and  32  again pivot, imparted by the control cam  66 , toward each other, as a result of which the previously admitted or drawn-in fuel/air mixture is compressed until the pistons  30  and  32  have returned to the TDC position. The opening  112  is located in this case approximately at the level of a point  136  in  FIG. 10 . The fuel/air mixture, which is now maximally compressed, is then ignited via the spark plug  120 , and the ensuing expansion of the fuel/air mixture is then carried out during the renewed passing of the pistons  30  and  32  from their TDC position to their BDC position via a further 90° path of revolution about the axis of rotation  38 . 
         [0094]    During the working strokes of compressing and expanding (working), which overall take place over a path of revolution of 180° about the axis of rotation  38 , the gas exchange openings  94  and  96  are tightly closed by the end face  110  of the piston cage  72  and the sealing arrangement  122 . The gas exchange openings  96  and  94  open automatically as the opening  112  of the piston cage  72  passes the gas exchange openings  96  and  94 . 
         [0095]    In  FIG. 10 , the corresponding piston positions are denoted by “OT” (TDC) and “UT” (BDC). 
         [0096]    While the control of the exchange of gas has been described hereinbefore with regard to the working chamber  54 , it should be noted that the exchange of gas for the working chamber  56  is controlled in exactly the same way, without this requiring more detailed description in the present document. There is merely a time lag between the working strokes. Just while the working stroke of drawing in fresh fuel/air mixture is taking place in the working chamber  54 , the expanding working stroke (working) takes place in the working chamber  56 . When the expelling working stroke is taking place in the working chamber  54 , the compressing working stroke takes place in the working chamber  56 , etc. 
         [0097]    The end surfaces of the pistons  30  to  36  have in their respective region facing the end face of the piston cage  72  a trough-like depression such as is denoted by reference numerals  140  and  142  for the pistons  30  and  32 . The trough-like depressions  140  and  142 , which are accordingly also provided on the pistons  34  and  36 , cause a finite volume of the working chamber  54  still to remain in the TDC position of the pistons  30  and  32 , as a result of which the pistons  30  and  32  are pressed apart from each other with optimum leverage on ignition of the fuel/air mixture which has just been compressed in the working chamber  54 . According to  FIG. 3 , the pistons  30  and  32  each have associated with them, remote from the working chamber  54 , backward chambers  150  and  152 , the volume of which decreases in size when the working chamber  54  increases in size, and vice versa. The chambers  150  and  152  can be used as admission pressure chambers for precompressing combustion air as the pistons  30  and  32  swivel apart from each other, wherein in the BDC position of the pistons  30  and  32  the precompressed combustion air can then be injected into the pistons  30  and  32  via a valve arrangement (not shown) and, through said pistons, into the working chamber  54 . Comparable backward chambers or preliminary pressure chambers can be provided accordingly for the pistons  34  and  36 . 
         [0098]    According to  FIG. 1 , an air inlet  154  and a corresponding air outlet  156  are also present on the housing  12 , cooling air for the interior of the housing  12  being supplied via the air inlet  154  and discharged again via the air outlet  156 . Also provided is a water inlet  158  via which cooling water for cooling the housing  12  itself can be admitted, the water then being discharged again via a water outlet  160 . 
         [0099]    An oil inlet  162  for lubricating and cooling the rotating parts of the oscillating piston engine  2 , in particular the piston cage  72  and the pistons  30  to  36 , and an oil outlet  164  are likewise provided on the housing  12 .