Abstract:
A piston engine ( 1 ) that can be driven using a steam power process and is used in particular for utilizing waste heat from an internal combustion engine comprises at least one cylinder bore ( 4 ), a cylinder piston ( 5 ) which is arranged in the cylinder bore ( 4 ), and a rod ( 20 ) which is connected to the cylinder piston ( 5 ). The rod ( 20 ) is guided out of the cylinder bore ( 4 ). The cylinder piston ( 5 ) delimits a first operating space ( 9 ) and a second operating space ( 10 ) in the cylinder bore ( 4 ). A crankshaft ( 22 ) is disposed in a crankshaft space ( 21 ). The rod ( 20 ) is connected to a slider crank mechanism ( 23 ) which is disposed in the crankshaft space ( 21 ), the rod ( 20 ) being effectively connected to the crankshaft ( 22 ) via the slider crank mechanism ( 23 ), thus making it possible to obtain a large expansion volume while keeping the design of the piston engine ( 1 ) compact.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a piston engine which can be driven via a steam power process. In particular, the invention relates to a piston engine which can be driven via a steam power process and which serves to use the waste heat of an internal-combustion engine. 
         [0002]    Internal-combustion engines convert the energy of the fuel into mechanical energy in order to drive vehicles and the like. However, a substantial portion of the energy is thereby released as waste heat which is directed away by the cooling system or in the exhaust gas of the internal-combustion engine. In order to use this thermal energy, it is conceivable for a steam power process to be coupled to the internal-combustion engine. The thermal energy from the internal-combustion engine can thereby be used to produce steam which is expanded in an expansion engine and which consequently provides additional energy which can be used to drive the vehicle or to produce auxiliary energy. In this instance, however, there is produced the problem that a large expansion volume of the expansion engine is necessary for a high degree of efficiency of the steam power process whereas the structural space situation in an internal-combustion engine is, however, generally very constrained. 
       SUMMARY OF THE INVENTION 
       [0003]    The piston engine according to the invention has the advantage that a good degree of efficiency can be obtained with a compact construction type. In particular, the piston engine can also be accommodated in a confined structural space situation in an internal-combustion engine, or the like, and have sufficient working volume at the same time. 
         [0004]    In an advantageous manner, the piston engine may be combined with an internal-combustion engine in order to convert the waste heat of the internal-combustion engine into additional driving energy. Such a combination is particularly efficient in order to use waste heat in a commercial vehicle because, in this instance, the internal-combustion engine discharges great power and consequently a large quantity of heat is also available in order to produce steam. The fuel consumption of the internal-combustion engine can thereby be reduced. 
         [0005]    Particularly for use in commercial vehicles having a diesel engine or a gas engine, a piston engine which is constructed as a reciprocating piston steam engine and which has a Scotch yoke crank mechanism is particularly advantageous. Substantially the same speed range can thereby be obtained for the piston engine as for the internal-combustion engine and consequently the mechanical energy discharged by the piston engine can be discharged directly to the crankshaft of the diesel engine or the gas engine. On the one hand, a small structural size of the piston engine is particularly important in this instance. On the other hand, however, an ability to be positioned as flexibly as possible in the internal-combustion engine is also necessary in order to still find, among the generally large number of auxiliary units present in the internal-combustion engine, a favorable fitting location which does not cause great complexity in terms of modifications to the internal-combustion engine. This is advantageously possible particularly in the case of a commercial vehicle by installation in the internal-combustion engine at the front, the installation being carried out between the internal-combustion engine and a radiator or a fan. In this instance, the crankshaft of the piston engine may be located precisely on the crank axis of the internal-combustion engine so that no additional structural space for power transmission via one or more toothed wheels, a chain or a belt is necessary. Therefore, it is particularly advantageous for a crank axis of a crankshaft of the piston engine to be located on a crank axis of the internal-combustion engine. 
         [0006]    It is further advantageous for the cylinder to be directed horizontally or downwards from the crank axis of the crankshaft in relation to an installation position of the internal-combustion engine. In the case of a piston engine which is constructed as a two-piston reciprocating piston engine and which has opposing cylinders with a Scotch yoke drive, a relatively compact structural form can be achieved. Owing to the cylinders located at both sides of the crankshaft, however, this structural form does not have a flexible orientation of the cylinders because the possible fitting positions are limited. Particularly in this case, only horizontal installation may be advantageous here, the remaining auxiliary units having to be adapted. 
         [0007]    In an advantageous manner, a piston engine which is constructed as a one-cylinder steam engine and which operates with the single-cycle method is fitted to the internal-combustion engine. This structural form allows a small structural size and flexible positioning. Owing to the construction as a one-cylinder engine, the single cylinder of the piston engine can be fitted to the internal-combustion engine in a flexible manner in terms of the angular position. By the single-cycle principle which is implemented by the dual-action cylinder piston being used, a cylinder diameter of the cylinder piston may nevertheless be determined so as to be relatively small. 
         [0008]    Owing to the compact structural form which is constructed at one side relative to the axis as a one-cylinder engine, it is easier to find structural space for the piston engine in a typical internal-combustion engine in the front portion between the fitted units which are already present. In particular, a crankshaft or another shaft of the piston engine may be located directly on the crank axis or shaft axis of the internal-combustion engine and the cylinder of the piston engine can be positioned in an available gap in the internal-combustion engine owing to the one-sided structural space. 
         [0009]    This combination allows a sufficiently compact structure of the piston engine with a working volume that is sufficient for a high level of efficiency. Both the fitting and a sufficient reduction in the fuel consumption are thereby possible. Consequently, the prerequisites for economical use of the piston engine in an internal-combustion engine of a motor vehicle or the like are met. 
         [0010]    Alternatively to the fitting arrangement in front of the internal-combustion engine, a compact piston engine may also be positioned at other locations, for example, in the region of the transmission bell housing between the internal-combustion engine and the transmission. Furthermore, fitting laterally to the internal-combustion engine is advantageous, the crankshaft of the piston engine (steam engine) being orientated parallel with the crankshaft of the internal-combustion engine. It is thereby possible to bring about a simple operative connection of the two crankshafts via toothed wheels or chains or belts. A very compact structural size of the steam engine is also necessary therefor. A one-cylinder structural form is advantageous, the cylinder being orientated approximately parallel with the travel direction of the cylinder of the internal-combustion engine. In this instance, these combinations also afford the necessary freedom for positioning the cylinder structural space for the drive connection. 
         [0011]    Alternatively, however, it is also advantageous for an additional cylinder bore, an additional cylinder piston which is arranged in the additional cylinder bore and an additional rod which is connected at least indirectly to the additional cylinder piston to be provided, for the additional rod to be directed out of the additional cylinder bore, for the additional cylinder piston to delimit in the additional cylinder bore, at one side, a third working space and, at the other side, a fourth operating space, and for the rod and the additional rod to be connected to each other at least indirectly. In particular, a piston engine having precisely two cylinders may be constructed. 
         [0012]    In order to obtain a good level of efficiency of the steam power process, a large expansion volume is necessary for the gaseous operating fluid in the piston engine. Owing to the constrained structural space situation, an increase in the cylinder piston or an increase in the number of cylinder pistons is generally not possible. Additional optimization of the expansion volume with a predetermined structural size of a piston engine may be brought about by an operating piston which acts at both sides in accordance with a single-cycle principle. 
         [0013]    A dual-action cylinder piston can be constructed with relatively little complexity in a piston engine in which a Scotch yoke drive and a bearing arrangement of a slider crank on the rods which act as transmission rods are provided. It is thereby possible to obtain practically double the stroke space with the same structural space being required, whereby the degree of efficiency of the piston engine is increased. 
         [0014]    Owing to the slider crank being supported on the transmission rods from the cylinder pistons to the slider crank, the return space constructed in the cylinder pistons can be used directly as additional operating space. The sealing of the additional working spaces is then brought about at the transmission rod, respectively. Consequently, additional sealing locations are not required. In order to improve the sealing at the transmission rods, there may optionally be provided in this instance additional sealing elements, in particular piston rings. 
         [0015]    In this construction, consequently, an advantageous combination of the piston engine with an internal-combustion engine may also be brought about. In spite of the compact construction of the piston engine, there can be obtained an adequate working volume which results in a high level of efficiency and consequently a substantial reduction of the fuel consumption. Consequently, the prerequisites for an economic use of the piston engine in a motor vehicle are also met in this instance. 
         [0016]    Additional optimization is possible owing to the slider crank being arranged in the oil region. It is thereby possible to achieve a long service-life and a high degree of efficiency, which is particularly significant for use in a commercial vehicle having an internal-combustion engine. In this instance, sealing for the operating fluid (operating medium) at the rods with respect to the oil region is also effective at the same time as sealing for the adjacent operating spaces. Consequently, there is produced an advantageous construction in which the number of components necessary is reduced. 
         [0017]    Owing to the piston engine being constructed as a reciprocating piston steam engine using the single-cycle principle and with Scotch yoke crank operation in conjunction with an internal-combustion engine, consequently, there can be produced a particularly low-consumption and cost-effective combination engine which comprises the internal-combustion engine and the piston engine and which complies with the requirements in terms of service-life of a commercial vehicle. 
         [0018]    Therefore, it is advantageous for the cylinder piston to have, at one side, a first lateral face and, at the other side, a second lateral face, for the first lateral face and the second lateral face to be directed away from each other, for the first lateral face of the cylinder piston in the cylinder bore to delimit the first operating space and for the second lateral face of the cylinder piston in the cylinder bore to delimit the second operating space. It is thereby possible to achieve alternating actuation of the cylinder piston owing to alternating filling of the operating spaces with vapor-like operating fluid. In this instance, it is also advantageous for the rod at the second lateral face of the cylinder piston to be connected to the cylinder piston and for the rod to extend at least approximately perpendicularly relative to the second lateral face through the second operating space. In this instance, the rod may be rigidly connected to the cylinder piston. As a result, the force acting on the cylinder piston may advantageously be transmitted via the rod to a crankshaft or the like. 
         [0019]    It is advantageous for an inlet for the first operating space and an inlet for the second operating space to be provided and for vapor-like operating fluid to be alternately directed into the first operating space and the second operating space via the inlet for the first operating space and via the inlet for the second operating space. In this instance, the inlets may be advantageously constructed as valve-controlled inlets. It is further advantageous for an outlet for the first operating space and an outlet for the second operating space to be provided and for at least partially depressurized vapor-like operating fluid to be able to be alternately discharged from the first operating space and the second operating space via the outlet for the first operating space and via the outlet for the second operating space. In this instance, the outlets may advantageously be constructed as valve-controlled outlets. In this instance, it is possible to incorporate the operating spaces advantageously in the steam power process. Gaseous operating fluid which is under relatively high pressure can be directed via the inlets into the operating spaces. The depressurized gaseous operating fluid can then be directed, for example, to a condenser via the outlets. 
         [0020]    It is also advantageous for a crankshaft which is arranged in a crankshaft space to be provided, for the crankshaft to have a crankshaft journal on which a sliding block is arranged, for the rod to be connected to a slider crank arranged in the crankshaft space and for the crank slider to have a slot-like recess, in which the sliding block is introduced. In an advantageous manner, a slider crank mechanism can thereby be constructed. In this instance, a piston engine in the form of a reciprocating piston steam engine can be constructed with a Scotch yoke crank mechanism. 
         [0021]    It is also advantageous for the cylinder bore to be directed horizontally or downwards from the crank axis of the crankshaft in relation to an installation position of the internal-combustion engine. In this region, no auxiliary units are generally arranged in the internal-combustion engine so that the structural space available can be used. 
         [0022]    In an advantageous manner, the steam power process may be constructed as an ORC process (Organic Rankine Cycle process). In this instance, the thermal energy of the waste heat is converted into mechanical energy via the ORC process. In this instance, the waste heat can advantageously be transmitted to the operating fluid of the ORC process from an exhaust gas of the internal-combustion engine or an exhaust gas return line via a heat exchanger. In this instance, the operating fluid may be based at least substantially on water. The operating fluid can be vaporized at the heat exchanger. That vapor can subsequently be depressurized in the piston engine which acts as an expansion engine, the mechanical energy being acquired. The operating fluid is subsequently cooled in a condenser and supplied to a pump. The operating fluid can thereby be compressed in the fluid phase by the pump to the pressure level for the repeated vaporization at the heat exchanger. The circuit is thereby closed. 
         [0023]    It is advantageous for the rod to be connected, on the one hand, rigidly to the cylinder piston and, on the other hand, rigidly to the slider crank. It is further advantageous for there to be provided a bearing on which the rod directed out of the cylinder bore is supported. In this instance, the bearing may advantageously be constructed by a bearing face. The bearing can further be lubricated by a lubricant from the crankshaft space. Consequently, the rod is supported displaceably on the bearing, a compact construction being made possible. 
         [0024]    It is particularly advantageous for precisely one cylinder bore to be provided. An extremely compact construction which produces a larger selection in relation to possible fitting positions thereby results. A favorable fitting position in the internal-combustion engine may thereby be selected even if constrained spatial conditions which are caused, for example, by additional units exist at that position. 
         [0025]    Therefore, fitting to the internal-combustion engine may be advantageously carried out, the piston engine forming a combination engine with the internal-combustion engine. In this instance, a steam engine is combined with an internal-combustion engine. The piston engine can be operatively connected in mechanical terms to a drive train of a vehicle. 
         [0026]    If the piston engine is fitted to an internal-combustion engine, it is advantageous for the piston engine to be fitted to the internal-combustion engine at the front, or for the piston engine to be fitted to the internal-combustion engine at the side. In the case of lateral fitting, for example, a gear casing or the like which is also required for other units may be used in order to produce the mechanical operative connection. It is also advantageous for the cylinder bore to be orientated at least approximately parallel with a cylinder of the internal-combustion engine. Particularly in the case of a single-cylinder construction of the piston engine, the cylinder is preferably directed upwards. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Preferred embodiments of the invention are explained in greater detail in the following description with reference to the appended drawings, in which corresponding elements are indicated with corresponding reference numerals. In the drawings: 
           [0028]      FIG. 1  is a schematic cross section of a piston engine in accordance with a first embodiment of the invention; 
           [0029]      FIG. 2  shows an arrangement of the piston engine of the first embodiment of the invention illustrated in  FIG. 1  in an internal-combustion engine and 
           [0030]      FIG. 3  is a schematic cross section of the piston engine illustrated in  FIG. 1  in accordance with a second embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIG. 1  is a schematic illustration of a piston engine  1  in accordance with a first embodiment of the invention. The piston engine  1  is driven via a steam power process. In this instance, the piston engine  1  can be used particularly in an internal-combustion engine of a motor vehicle in order to use the waste heat of the internal-combustion engine. The piston engine  1  then converts the waste heat into mechanical energy which can be used, for example, as additional drive energy or to drive an auxiliary unit, in particular an electrical generator. However, the piston engine  1  according to the invention is also suitable for other applications. 
         [0032]    The piston engine  1  has a housing portion  2  and a cylinder  3  which is connected to the housing portion  2 . In this embodiment, the piston engine  1  has precisely one cylinder  3 . 
         [0033]    The cylinder  3  of the piston engine  1  has a cylinder bore  4 , in which a cylinder piston  5  is arranged. The cylinder piston  5  is arranged in this instance in the cylinder bore  4  in a manner displaceable along an axis  6  of the cylinder bore  4 . 
         [0034]    The cylinder piston  5  has, at one side, a first lateral face  7  and, at the other side, a second lateral face  8 . The cylinder piston  5  delimits in the cylinder bore  4  a first operating space  9  with the first lateral face  7 . The cylinder piston  5  delimits a second operating space  10  in the cylinder bore  4  with the second lateral face  8 . When the cylinder piston  5  is displaced in a direction  11 , the volume of the first operating space  9  increases whereas the volume of the second operating space  10  decreases. Conversely, when the cylinder piston  5  is displaced counter to the direction  11 , the volume of the first operating space  9  decreases whereas the volume of the second operating space  10  increases. 
         [0035]    Valve-controlled inlets  12 ,  13  are provided in the cylinder  3 . Valve-controlled outlets  14 ,  15  are further provided in the cylinder  3 . The inlet  12  and the outlet  14  are associated with the first operating space  9 . The inlet  13  and the outlet  15  are associated with the second operating space  10 . For example, highly pressurized, vapor-like operating fluid can be introduced into the first operating space  9  via the inlet  12 . An actuating force is applied to the cylinder piston  5  in the direction  11  via the pressure of the gaseous operating fluid. The gaseous operating fluid in the first operating space  9  thereby becomes depressurized. The outlet  15  can be opened in order to discharge the already depressurized, remaining operating fluid from the second operating space  10 . After the completed travel of the cylinder piston  5  in the direction  11 , an inverse actuation of the cylinder piston  5  may be carried out counter to the direction  11 . In this instance, the valve-controlled inlet  13  is opened in order to introduce highly pressurized, gaseous operating fluid into the second operating space  10 . The inlet  11  for the first operating space  9  is closed in this instance. Furthermore, the outlet  14  for the first operating space  11  can now be opened in order to discharge the depressurized, gaseous operating fluid from the first operating space  9  when the cylinder piston  5  is actuated counter to the direction  11 . Consequently, an alternating actuation of the cylinder piston  5  is possible. 
         [0036]    The piston engine  1  has a rod  20  which acts as the transmission rod  20 . The rod  20  is connected at one side to the cylinder piston  5  at the second lateral face  8 . In this instance, the rod  20  is rigidly connected to the cylinder piston  5 . The rod  20  is orientated with respect to the axis  6  in this instance so that the rod  20  is orientated perpendicularly to the second lateral face  8 . There is provided in the housing portion  2  a crankshaft space  21  in which a crankshaft  22  is arranged. The rod  20  is connected at the other side to a slider crank  23  which is arranged in the crankshaft space  21 . The connection of the rod  20  to the slider crank  23  is also constructed in a rigid manner in this instance. Consequently, the rod  20  extends through the second operating space  10  and into the crankshaft space  21 . 
         [0037]    The cylinder bore  4  is separated from the crankshaft space  21  by a housing portion  24 . In this instance, a bearing face  25  which adjoins the crankshaft space  21  is constructed on the housing portion  24 . The bearing face  25  forms a bearing  25 ′, on which the rod  20  which is directed out of the cylinder bore  4  is supported. Lubricating oil is preferably located in the crankshaft space  21 . This lubricating oil can also be used to lubricate the bearing face  25 . Consequently, advantageous supporting of the rod  20  on the bearing face  25  is possible. In order to improve the sealing between the crankshaft space  21  and the second operating space  10  of the cylinder bore  4 , annular sealing elements  26 ,  27  which are arranged behind the bearing face  25  can be provided. Introduction of lubricating oil into the second operating space  10 , and consequently mixing of the gaseous operating fluid, on the one hand, and the lubricating oil, on the other hand, is thereby prevented. 
         [0038]    The crank mechanism of the piston engine  1  has a sliding block  28  which is arranged on a crankshaft journal  29  of the crankshaft  22 . The sliding block  28  is in this instance introduced into a slot-like recess  30  of the slider crank  23 . It is thereby possible to convert the reciprocating movement of the rod  20  into a rotational movement of the crankshaft  22 . The lubrication of the crank mechanism is brought about in this instance by means of the lubricating oil provided in the crankshaft space  21 . 
         [0039]    In this embodiment, there are further arranged, at an outer side of the cylinder piston  5 , piston rings  31 ,  32  which improve sealing between the operating spaces  9 ,  10  and, at the same time, prevent friction between the cylinder piston  5  and the cylinder bore  4 . Frictional wear can thereby be reduced and a reliable sealing action ensured at the same time. 
         [0040]    Consequently, a piston engine  1  which is in the form of a reciprocating piston steam engine and which operates with the single-cycle principle can advantageously be constructed so as to have precisely one cylinder  3 . In this instance, the cylinder piston  5  introduces its force via the rod  20  to the slider crank mechanism and consequently the crankshaft  22 . All the inlets  12 ,  13  and outlets  14 ,  15  are controlled. The reciprocating piston movement of the cylinder piston  5  is transmitted to the crankshaft  22  by the slider crank drive with the slider crank  23  and the sliding block  28  which is arranged on the crankshaft journal  29 . 
         [0041]    In this embodiment, the slider crank  23  is supported on the bearing location formed by the bearing face  25  via the rod  20 . That bearing is located in the oil region because it adjoins the crankshaft space  21 . 
         [0042]    The operating fluid is alternately depressurized in the operating spaces  9 ,  10 . Consequently, both the upward and the downward movements of the cylinder piston  5  contribute to the power production. A great expansion volume is thereby achieved in a small structural space of the piston engine  1 . In combination with the Scotch yoke crank mechanism, a small structural length is further achieved from one crank axis  33  of the crankshaft  22  as far as one end  34  of the cylinder  3 . The piston engine  1  can thereby be flexibly arranged in an internal-combustion engine or the like. 
         [0043]    Owing to the compact structural form of the single-cylinder piston engine  1  constructed at one side relative to the crank axis  33 , it is possible in particular to make use of the structural space which is available at the front in a typical internal-combustion engine between the installation units already present and in which the crank axis  33  of the piston engine  1  is arranged precisely on a crank axis of the internal-combustion engine. This arrangement is further described with reference to  FIG. 2 . 
         [0044]      FIG. 2  shows an arrangement of the piston engine  1  illustrated in  FIG. 1  in an internal-combustion engine  35 . In this instance, the individual components are schematically illustrated. The internal-combustion engine  35  has, for example, a cylinder  36  which is orientated perpendicularly or vertically relative to an installation position. This is possible, for example, in a configuration as a series cylinder. A plurality of auxiliary units  37 ,  38 ,  39  are arranged at the front side of the internal-combustion engine  35 . A crank axis  33  of the internal-combustion engine  35  is orientated perpendicularly relative to the plane of the drawing in this embodiment. The piston engine  1  can now advantageously be arranged at the front side of the internal-combustion engine  35 , the structural space left unoccupied by the auxiliary units  37  to  39  being able to be used. In this instance, the piston engine  1  is arranged at the front side of the internal-combustion engine  35  in such a manner that the crank axis  33  of the piston engine  1  corresponds to the crank axis  33  of the internal-combustion engine  35 . That fitting arrangement is particularly advantageous because the power transmission from the piston engine  1  to the internal-combustion engine  35  can be carried out without additional toothed wheels, chains and belts. In this instance, it is advantageous to have a fitting arrangement in which the axis  6  of the cylinder  4  is directed horizontally or, as is the case in the embodiment illustrated in  FIG. 2 , downwards because generally none of the auxiliary units  37  to  39  is located in the internal-combustion engine  35  in this region. 
         [0045]      FIG. 3  is a schematic cross section of the piston engine  1  illustrated in  FIG. 1  in accordance with a second embodiment. In this embodiment, the piston engine  1  has an additional cylinder  3 ′. An additional cylinder bore  4 ′, in which an additional cylinder piston  5 ′ is arranged, is constructed in the additional cylinder  3 ′. The additional cylinder piston  5 ′ can also be actuated along the axis  6  in this instance. The cylinder piston  5 ′ has a first lateral face  7 ′ and a second lateral face  8 ′. At the first lateral face  7 ′, the cylinder piston  5 ′ delimits a third operating space  40 . At the second lateral face  8 ′, the cylinder piston  5 ′ delimits a fourth operating space  41 . The cylinder piston  5 ′ can be actuated together with the cylinder piston  5  so that both cylinder pistons  5  are displaced either in the direction  11  or counter to the direction  11 . 
         [0046]    Inlets  12 ′,  13 ′ are provided in the additional cylinder  3 ′. Furthermore, outlets  14 ′,  15 ′ are provided in the additional cylinder  3 ′. The inlet  12 ′ and the outlet  14 ′ are associated with the third operating space  40  in this instance. The inlet  13 ′ and the outlet  15 ′ are associated with the fourth operating space  41 . A rod  20 ′, via which the cylinder piston  5 ′ is connected to the slider crank  23 , is further provided. In this instance, the rod  20 ′ is rigidly connected to the cylinder piston  5 ′ at the second lateral face  8 ′. Consequently, the displacement force acting on the cylinder piston  5  can be transmitted to the slider crank  23  via the rod  20 ′. The rod  20 ′ is supported on a bearing  25 ′ in this instance. In order to actuate the cylinder piston  5 ′, pressurized, gaseous operating fluid is alternately introduced into the third operating space  40  and the fourth operating space  41 . For that purpose, the inlets  12 ′,  13 ′ are alternately opened. The actuation of the inlets  12 ,  13  and the inlets  12 ′,  13 ′ for the two cylinders  3 ,  3 ′ may occur in a synchronized manner. Accordingly, the actuation of the outlets  14 ,  15  for the cylinder  3  and the outlets  14 ′,  15 ′ for the cylinder  3 ′ can also occur in a synchronized manner. 
         [0047]    Consequently, a piston engine  1  having mutually opposing cylinders  3 ,  3 ′ and consequently mutually opposing cylinder pistons  5 ,  5 ′ can be constructed, the cylinder pistons  5 ,  5 ′ introducing their forces to the crankshaft  22  via the slider crank mechanism. In this instance, the reciprocating piston movement of the two cylinder pistons  5 ,  5 ′ is transmitted to the crankshaft  22 . In this embodiment, the slider crank  23  is advantageously supported on the two bearing locations  25 ,  25 ′ which are arranged at the two sides of the crank axis  33 . The sealing of the crankshaft space  21  which is filled with lubricating oil with respect to the cylinder bores  4 ,  4 ′ is brought about in this embodiment via the bearings  25 ,  25 ′. An additional sealing may also optionally be provided by means of sealing elements. 
         [0048]    Consequently, for example, the first operating space  9  and the fourth operating space  41  can simultaneously be filled with gaseous operating fluid so that, during the expansion of the operating fluid, an actuation of the slider crank  23  in the direction  11  is brought about. Subsequently, an opposed actuation can be brought about by introducing the gaseous operating fluid, on the one hand, into the second operating space  10  and, on the other hand, into the third operating space  40 . Each of the cylinder pistons  5 ,  5 ′ is thereby acted upon at both sides. It is thereby possible to have a compact construction of the piston engine  1  with a large expansion volume being constructed at the same time. 
         [0049]    The piston engine  1  of the second embodiment illustrated in  FIG. 3  can be fitted to an internal-combustion engine  35 . For example, the piston engine  1  of the second embodiment can be arranged in the internal-combustion engine  35  illustrated in  FIG. 2  in that there is brought about a horizontal installation position in relation to the axis  6  of the piston engine  1  and a displacement, on the one hand, of the auxiliary unit  37  upwards and, on the other hand, optionally of the auxiliary unit  39  upwards. In this configuration, the crank axis  33  of the crankshaft  22  of the piston engine  1  then corresponds to the crank axis  33  of the internal-combustion engine  35 . 
         [0050]    The piston engine  1  then forms with the internal-combustion engine  35  a combination engine  1 ,  35 . In this instance, the piston engine  1  is operatively connected in mechanical terms to a drive train  33  of a vehicle. If the piston engine  1  is fitted to the internal-combustion engine  35 , the piston engine  1  can be fitted to the internal-combustion engine  35  at the front or the piston engine  1  can be fitted to the internal-combustion engine  35  at the side. In this instance, the cylinder bore  4  is preferably orientated at least approximately parallel with the cylinder  36  of the internal-combustion engine  35 . The fitting is particularly advantageous if precisely one cylinder bore  4  is provided. Owing to the compact construction, favorable fitting positions in the internal-combustion engine  35  are thereby produced. 
         [0051]    Consequently, it is advantageous for the cylinder piston  5  to have, at one side, a first lateral face  7  and, at the other side, a second lateral face  8 , for the first lateral face  7  and the second lateral face  8  to be directed away from each other, for the first lateral face  7  of the cylinder piston  5  to delimit the first operating space  9  in the cylinder bore  4  and for the second lateral face  8  of the cylinder piston  5  to delimit the second operating space  10  in the cylinder bore  4 . Consequently, it is also advantageous in this instance for the rod  20  to be connected to the cylinder piston  5  at the second lateral face  8  of the cylinder piston  5  and for the rod  20  to extend through the second operating space  10  at least approximately perpendicularly relative to the second lateral face  8 . 
         [0052]    Consequently, it is advantageous for an inlet  12  for the first operating space  9  and an inlet  13  for the second operating space  10  to be provided and for vapor-like operating fluid to be able to be directed alternately into the first operating space  9  and the second operating space  10  via the inlet  12  for the first operating space  9  and via the inlet  13  for the second operating space  10 , 
         [0053]    and/or 
         [0054]    for an outlet  14  for the first operating space  9  and an outlet  15  for the second operating space  10  to be provided and for at least partially depressurized vapor-like operating fluid to be able to be discharged alternately from the first operating space  9  and the second operating space  10  via the outlet  14  for the first operating space  9  and via the outlet  15  for the second operating space  10 . 
         [0055]    Consequently, it is advantageous for a crankshaft  22  which is arranged in a crankshaft space  21  to be provided, for the crankshaft  22  to have a crankshaft journal  29  on which a sliding block  28  is arranged, for the rod  20  to be connected to a slider crank  23  which is arranged in the crankshaft space  21  and for the slider crank  23  to have a slot-like recess  30  in which the sliding block  28  is introduced. 
         [0056]    Consequently, it is also advantageous for a crank axis  33  of the crankshaft  22  to be arranged on a crank axis  33  of the internal-combustion engine  35 . Consequently, it is also advantageous for the cylinder bore  4  to be orientated horizontally or downwards from the crank axis  33  in relation to an installation position of the internal-combustion engine  35 . 
         [0057]    The invention is not limited to the embodiments described.