Abstract:
A piston engine ( 1 ) that can be driven using a steam power process and is used in particular for utilizing the waste heat from an internal combustion engine comprises a cylinder bore ( 5 ), a cylinder piston ( 6 ) which is arranged in the cylinder bore ( 5 ) and delimits an operating space ( 8 ) in the cylinder bore ( 5 ), a rod ( 21 ) which is connected to the cylinder piston ( 6 ), and a bearing point ( 37 ) on which the rod ( 21 ) and the cylinder piston ( 6 ) connected to the rod ( 21 ) are mounted. A peripheral gap ( 28 ) is predefined between the cylinder piston ( 6 ) and the cylinder bore ( 5 ), thus preventing frictional wear between the cylinder piston ( 6 ) and the cylinder bore ( 5 ), which is particularly advantageous when a water-based working fluid is conducted through the operating space ( 8 ) since steam has no lubricity.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a piston engine that can be driven using a steam power process. In particular, the invention relates to a piston engine that can be driven using a steam power process and that is used to utilize the waste heat of an internal combustion engine. 
         [0002]    Internal combustion engines convert the energy of the fuel into mechanical energy for driving vehicles and similar. However, a considerable portion of the energy is released as waste heat, which is carried away from the internal combustion engine by the cooling system or in the exhaust gas. In order to utilize this thermal energy, it is conceivable that a steam power process is coupled to the internal combustion engine. By this means the thermal energy from the internal combustion engine can be used to generate steam, which is expanded in an expansion machine and thus provides additional energy, which can be used for driving the vehicle or for generating auxiliary energy. Here, however, the problem arises that the steam engine is driven by steam or a similar fluid from the steam power process, which has no lubrication capability, which promotes wear of the steam engine. 
       SUMMARY OF THE INVENTION 
       [0003]    The piston engine according to the invention has the advantage that advantageous operation of the piston engine is possible, even when using water or other poorly lubricating working fluids. This has the effect, inter alia, of reduced wear on the cylinder piston and of a longer service life of the piston engine. 
         [0004]    It is advantageous that the piston engine, which can be driven using the steam power process, is combined with an internal combustion engine in order to convert the waste heat of the internal combustion engine into additional drive energy using the steam power process. Such a combination is particularly efficient for waste heat utilization in a commercial vehicle, because here the internal combustion engine produces great power and there is thus a large quantity of heat available for generating steam. This enables the fuel consumption to be reduced. 
         [0005]    A piston engine with a Scotch-Yoke crank drive configured as a reciprocating piston steam engine is of particular advantage, especially for use in commercial vehicles with diesel engines or gas engines. This enables approximately the same revolution rate range to be achieved for the piston engine as for the internal combustion engine and thus the mechanical energy produced by the piston engine can be delivered directly to the crankshaft of the diesel engine or gas engine. Such a piston engine can also be conveniently mounted in the limited installation space on an internal combustion engine. 
         [0006]    The steam process is configured as an ORC process (Organic Rankine Cycle Process) in an advantageous manner. Here the thermal energy of the waste heat is converted into mechanical energy using the ORC process. This enables the waste heat from an exhaust gas of the internal combustion engine or an exhaust gas recovery means to be transferred via a heat exchanger to the working fluid of the ORC process in an advantageous manner. Here the working fluid can be based at least substantially on water. The working fluid can be evaporated at the heat exchanger. This steam can then be expanded in the piston engine acting as an expansion machine, whereby the mechanical energy is obtained. The working fluid is then cooled in a condenser and supplied to a pump. The working fluid can thus be compressed in the liquid phase by the pump to the pressure level for renewed evaporation at the heat exchanger. This closes the circuit. 
         [0007]    By mounting the rod on the bearing point, the load on the cylinder piston can be reduced in an advantageous manner. In particular, transverse forces on the cylinder piston can be reduced by said mounting, because they are absorbed by the bearing parts. An external diameter of an exterior of the cylinder piston is specified to be smaller than an internal diameter of the cylinder bore in an advantageous manner here. This ensures that the cylinder piston is not in direct contact with the cylinder bore acting as the cylinder working surface and no force is transferred between the cylinder piston acting as the working piston and the cylinder bore (cylinder wall). The cylinder piston comprises an adequate circumferential gap to the cylinder bore. A stable and well-guided mounting for the cylinder piston can be achieved in connection with the mounting on the rod, which also acts as transmission rod. 
         [0008]    The occurrence of wear on the cylinder piston is particularly critical, because it is operating with a poorly lubricating working fluid (working medium). In particular, the working piston can operate with steam, which has no lubrication capability. The occurrence of such wear is prevented or at least reduced by the gap between the cylinder piston and the cylinder bore. At least one sealing element is advantageously arranged on the exterior of the cylinder piston. Here it is also advantageous that a circumferential recess is formed on the exterior of the cylinder piston, that the sealing element is formed as an annular sealing element and that the annular sealing element is inserted into the circumferential recess on the exterior of the cylinder piston. In particular, the circumferential recess on the exterior of the cylinder piston can be formed by a circumferential annular groove. This enables the sealing on the cylinder piston to be advantageously enhanced in order to prevent or at least reduce unwanted dispersal of the gaseous working fluid, especially the steam, through the gap between the cylinder piston and the cylinder bore. In order to enhance the sealing on the piston, special additional sealing elements in the form of piston rings or similar can be used here. 
         [0009]    It is also advantageous that the rod is at least substantially rigidly connected to the cylinder piston, that the bearing point is formed by a bearing bore in which the rod is guided and that the cylinder piston is centrally orientated at least approximately on a longitudinal axis of the cylinder bore by the guidance of the rod in the bearing bore. This enables an advantageous support of the cylinder piston with respect to the cylinder bore on the bearing parts by means of the rod. Wear on the working piston can thereby be prevented over the service life of the piston engine. The bearing bore can, for example, be formed on a housing part that is arranged between the cylinder bore and a crankshaft chamber. This enables an advantageous media separation over the bearing bore. In particular, lubricating oil can be provided in the crankshaft chamber in order to lubricate a crankshaft and other components arranged in the crankshaft chamber. 
         [0010]    It is also advantageous here that the rod is led out of the cylinder bore through the bearing point into the crankshaft chamber, that the crankshaft is arranged in the crankshaft chamber and that the rod works in conjunction with the crankshaft by means of a crank loop. 
         [0011]    It is also advantageous that at least one further cylinder bore, a further cylinder piston arranged in the further cylinder bore, which bounds a further working chamber in the further cylinder bore, a further rod, which is at least indirectly connected to the further cylinder piston, and at least one further bearing point are provided, wherein the further rod is supported on the further bearing point and wherein a circumferential gap is defined between the further cylinder piston and the further cylinder bore. It is also advantageous that the further rod is essentially rigidly connected to the further cylinder piston, that the bearing point is formed by a further bearing bore, in which the further rod is guided, and that the further cylinder piston is at least approximately centrally orientated on a longitudinal axis of the further cylinder bore by the guidance of the further rod in the further bearing bore. Here the further rod is preferably connected to a crank loop arranged in the piston chamber. This enables an advantageous crank loop drive to be implemented. In particular, it is advantageous if both bearing points are lubricated with oil as is the entire rest of the crank drive. In the oil region a stable and well-guided bearing can thus be achieved. Here an additional media separation can be provided that is directly connected to the bearing points. An improved separation of the oil from the working fluid can thus be achieved. Hence a particularly low-wear piston engine with an oil-lubricated crank loop and with direct contact between the cylinder piston and the cylinder wall of the cylinder bore can be implemented. The mounting of the working piston on a respective transmission rod without respective contact with the cylinder bore can be used in an advantageous manner in piston engines configured as reciprocating piston steam engines. However, this design is particularly advantageous in a piston engine configured as a reciprocating piston-steam engine with a crank loop drive (Scotch Yoke). 
         [0012]    An external diameter of an exterior of the further cylinder piston is advantageously defined to be smaller than an internal diameter of the further cylinder bore. It is also advantageous that at least one sealing element is arranged on an exterior of the further cylinder piston. A suitable design can be provided here, as is also implemented with the cylinder piston. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]    Preferred example embodiments of the invention are explained in detail in the following description with reference to the accompanying drawing. It shows: 
           [0014]      FIG. 1  a piston engine in a schematic sectional illustration corresponding to an example embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows a piston engine  1  in a schematic illustration corresponding to an example embodiment of the invention. The piston engine  1  is driven using a steam power process. The piston engine  1  can, for example, be used with an internal combustion engine of a motor vehicle, in order to utilize the waste heat of the internal combustion engine. The piston engine  1  converts the waste heat into mechanical energy, which can be used, for example, as additional drive energy for driving an auxiliary assembly, in particular an electrical generator. The piston engine  1  according to the invention is, however, also suitable for other applications. The piston engine  1  of the example embodiment comprises a housing part  2  and cylinders  3 ,  4  connected to the housing part  2 . A cylinder bore  5 , in which a cylinder piston  6  is arranged, is formed on the cylinder  3 . The cylinder bore  5  has a longitudinal axis  7 , along which the cylinder piston  6  can be displaced. The cylinder piston  6  bounds a working chamber  8  in the cylinder bore  5  on one side and a depressurized chamber  9  on the other side. 
         [0016]    A valve-controlled inlet  10  and a valve-controlled outlet  11  for the working chamber  8  are provided on the cylinder  3 . Compressed gaseous working fluid, in particular steam, can be fed into the working chamber  8  via the valve-controlled inlet  10 . During expansion of the gaseous working fluid in the working chamber  8 , an operating force is exerted on the cylinder piston  6 , which leads to a displacement of the cylinder piston  6  in a direction  12  along the longitudinal axis  7 . The volume of the working chamber  8  thus increases, whereas the volume of the depressurized chamber  9  decreases. The depressurized chamber  9  is connected via an outlet  13  to a low pressure region of the steam circuit, so that working fluid passing into the depressurized chamber  9  is fed back into the steam circuit. 
         [0017]    A crankshaft chamber  15  is provided within the housing part  2 . A crankshaft  16  with a crankshaft journal  17  is arranged in the crankshaft chamber  15 . A rotation axis of the crankshaft  16  is orientated perpendicularly to the longitudinal axis  7  in this case. 
         [0018]    Moreover, a crank loop  18  is arranged in the crankshaft chamber  15 . The crank loop  18  comprises an oblong hole-shaped recess  19 , in which a slide block  20  is inserted. The slide block  20  is arranged on the crankshaft journal  17  in this case. The cylinder piston  6  is connected via a rod  21  to the crank loop  18 . This forms a working connection between the cylinder piston  6  and the crankshaft  16 , so that the reciprocal movement of the cylinder piston  6  is converted into a rotational motion of the crankshaft  16 . 
         [0019]    Moreover, the cylinder  4  of the piston engine  1  comprises a further cylinder bore  5 ′, in which a further cylinder piston  6 ′ is arranged. In this case the further cylinder piston  6 ′ is guided along the longitudinal axis  7  of the cylinder bore  5 ′. The longitudinal axis  7  acts here as a common longitudinal axis  7  for the two cylinder bores  5 ,  5 ′ of the cylinders  3 ,  4 . 
         [0020]    The cylinder piston  6 ′ bounds a further working chamber  8 ′ and a further depressurized chamber  9  in the cylinder bore  5 ′. In this case a valve-controlled inlet  10 ′ and a valve-controlled outlet  11 ′ for the further working chamber  8 ′ are provided on the cylinder  4 . An outlet  13 ′ for the depressurized chamber  9 ′ is also provided in order to feed back working fluid that is passing from the working chamber  8 ′ into the depressurized chamber  9 ′ into the steam circuit. 
         [0021]    Gaseous working fluid can thus also be led through the working chamber  8 ′. During the expansion of the gaseous working fluid in the working chamber  8 ′, the cylinder piston  6 ′ is operated opposite to the direction  12 . The reciprocating motion of the cylinder piston  6 ′ is thus transferred via a further rod  21 ′ to the crank loop  18 . Here the further rod  21 ′ connects the cylinder piston  6 ′ to the crank loop  18 . 
         [0022]    The crank loop  18  is thus connected via the rod  21  to the cylinder piston  6  on the one hand and via the rod  21 ′ to the cylinder piston  6 ′ on the other hand. This makes possible the optional operation of the crank loop  18  in and opposite to the direction  12 . A Scotch Yoke drive can thus be implemented in an advantageous manner. 
         [0023]    The cylinder piston  6  has an exterior  25 . The cylinder piston  6  has an external diameter  26  on the exterior  25 . Moreover, an internal diameter  27  of the cylinder bore  5  is defined. The external diameter  26  of the cylinder piston  6  and the internal diameter  27  of the cylinder bore  5  are matched to each other. The external diameter  26  of the exterior  25  of the cylinder piston  6  is hereby smaller than the internal diameter  27  of the cylinder bore  5 . In this way, a gap  28  is defined between the exterior  25  of the cylinder piston  6  and the cylinder bore  5 . The defined gap  28  ensures a certain distance of the cylinder piston  6  from the cylinder bore  5  during operation. A contact between the cylinder piston  6  and the cylinder bore  5  is hereby prevented over the entire stroke of the cylinder piston  6 . 
         [0024]    During operation of the piston engine  1  there is the problem that the gaseous working fluid provided in the working chamber  8 , in particular the steam, has no or only poor lubrication properties. Adequate lubrication of the cylinder piston  6  in the cylinder bore  5  to prevent frictional wear cannot be guaranteed in this way. However, frictional wear is prevented by the defined gap  28 . Vaporous working fluid can thus pass from the working chamber  8  into the depressurized chamber  9  through the gap  28 . However, said working fluid is fed back through the outlet  13  into the steam circuit. 
         [0025]    Moreover, the cylinder piston  6  in this example embodiment comprises annular circumferential recesses  29 ,  30 . The circumferential recesses  29 ,  30  are in the form of annular grooves in this case. Annular sealing elements  31 ,  32  are inserted in the annular grooves  29 ,  30 . The annular sealing elements  31 ,  32  form a seal between the working chamber  8  and the depressurized chamber  9  in relation to the defined gap  28 . 
         [0026]    In this example embodiment a housing part  35  is provided that is connected to the cylinder  3 . The housing part  35  is arranged between the cylinder bore  5  of the cylinder  3  and the crankshaft chamber  15 . A bearing bore  36  is formed on the housing part  35 , which forms a bearing point  37  for the rod  21 . The rod  21  is thus supported in the bearing bore  36 , wherein the bearing bore  36  allows a movement of the rod  21  along the longitudinal axis  7 . Transverse forces that occur are absorbed by supporting the rod  21  on the bearing point  37 . The sealing elements  31 ,  32  are thus relieved of load and contact between the cylinder piston  6  and the cylinder bore  5  is thus prevented. The cylinder piston  6  is additionally guided by the sealing elements  31 ,  32  in the cylinder bore  5 . If there is a rigid connection of the rod  21  to the cylinder piston  6 , guidance by the sealing elements  31 ,  32  is not necessary. 
         [0027]    Accordingly the cylinder piston  6 ′ also has an exterior  25 ′ having an external diameter  26 ′. Furthermore, the cylinder bore  5 ′ has an internal diameter  27 ′. In this example embodiment the external diameters  26 ,  26 ′ of the cylinder pistons  6 ,  6 ′ are specified to be equal. Moreover, the internal diameters  27 ,  27 ′ of the cylinder bores  5 ,  5 ′ are also specified to be equal. A gap  28 ′ is thus also formed on the cylinder piston  6 ′ between the exterior  25 ′ and the cylinder bore  5 ′. The gap  28 ′ prevents a direct contact of the cylinder piston  6 ′ and the cylinder bore  5 ′. Moreover, circumferential recesses  29 ′,  30 ′ are provided on the cylinder piston  6 ′, in which annular sealing elements  31 ′,  32 ′ are inserted. Furthermore, a housing part  35 ′ is also provided, which is arranged between the cylinder bore  5 ′ and the crankshaft chamber  15 . A bearing bore  36 ′, in which the rod  21 ′ is supported, is formed on the housing part  35 ′. The bearing bore  36 ′ thus forms a bearing point  37 ′ for the rod  21 ′. An advantageous support for the cylinder piston  6 ′ can thus take place on the cylinder  4  by means of the rod  21 ′ on the bearing point  37 ′. 
         [0028]    In this example embodiment the two rods  21 ,  21 ′ are rigidly connected to the crank loop  18 . A bilateral support of the crank loop  18  on the bearing points  37 ,  37 ′ is thus formed. Transverse forces occurring during the transfer of the reciprocating motion of the cylinder piston  6 ,  6 ′ to the crankshaft  16  can thus be advantageously absorbed at the bearing points  37 ,  37 ′. 
         [0029]    This enables optimized support of the cylinder pistons  6 ,  6 ′ acting as working pistons  6 ,  6 ′ of the piston engine  1 , which is in the form of a reciprocating piston-steam engine. Thus the cylinder pistons  6 ,  6 ′ are arranged opposite each other relative to the crankshaft  16  in this example embodiment. The cylinder pistons  6 ,  6 ′ apply their force to the crankshaft  16  via the crank loop drive. The inlet  10  and the outlet  11  for the cylinder  3  and the inlet  10 ′ and the outlet  11 ′ for the cylinder  4  are preferably valve-controlled. The reciprocating piston movement of the cylinder pistons  6 ,  6 ′ is transferred to the crankshaft  16  by the crank loop drive with the crank loop  18  and the slide block  20 , which sits on the crankshaft journal  17 . The crank loop  18  of the crank loop drive is supported by the rods  21 ,  21 ′ on the bearing points  37 ,  37 ′, wherein said support absorbs the transverse forces occurring. 
         [0030]    The support is formed in such a way that the cylinder pistons  6 ,  6 ′ do not contact their respective cylinder contact surfaces, which are specified in the cylinder bores  5 ,  5 ′, and do not transfer any forces there. Thus critical wear is prevented on these non-oil lubricated points. The piston engine  1  can thus achieve the necessary service life expectancy. 
         [0031]    In order to reliably prevent frictional wear, adequately dimensioned gaps  28 ,  28 ′ in relation to the cylinder working surfaces are provided. On the other hand, in order to further enhance the sealing on the cylinder pistons  6 ,  6 ′, in this example embodiment additional sealing elements  31 ,  32 ,  31 ′,  32 ′, in particular piston rings  31 ,  32 ,  31 ′,  32 ′, are arranged on the cylinder pistons  6 ,  6 ′. 
         [0032]    Moreover, in this example embodiment the bearing bores  36 ,  36 ′ are oil-lubricated. For this purpose the bearing bores  36 ,  36 ′ are provided immediately adjacent to the crankshaft chamber  15 , so that lubricating oil from the crankshaft chamber  15  can be used to lubricate the bearing points  37 ,  37 ′. In order to prevent the ingress of lubricating oil into the depressurized chambers  9 ,  9 ′, one or a plurality of sealing elements  38 ,  39 ,  38 ′,  39 ′ can be placed adjacent to each bearing point  37 ,  37 ′. This can ensure good, low-wear support of the crank loop  18 . 
         [0033]    The invention is not limited to the described example embodiments.