Patent Abstract:
An internal-combustion engine comprises an engine housing having a first wall delimiting a first combustion chamber, a first piston also delimiting said first combustion chamber and with a first piston head, a first crankshaft, a second piston also delimiting said first combustion chamber and with a second piston head, a second crankshaft, and a second connecting rod connected between said second piston and said second crankshaft, said first wail defining at least a section of a torus, said pistons being guided along a curved path defined by said section of a torus.

Full Description:
BACKGROUND OF THE INVENTION 
   The invention concerns an internal-combustion engine with an engine housing comprising a first wall delimiting a first combustion chamber, with a first piston also delimiting said first combustion chamber by means of a first piston head and with a first crankshaft. 
   Engines of this type have been known for more than a hundred years and are used as stationary drives as well as for vehicles. In these engines, the walls delimiting the combustion chambers are of cylindrical shape and closed on one side with a cylinder head. On the other side, a piston is moveably guided in the cylinder to transfer the driving force to a crankshaft via a connecting rod as the combustion gases expand. Combustion engines operating according to this principle may function in two cycles or four cycles, such as Otto and diesel engines. The efficiency of these engines is, however, very low. 
   It is the underlying purpose of the invention to provide a combustion engine having a higher efficiency. 
   SUMMARY OF THE INVENTION 
   This object is achieved in accordance with the invention with a combustion engine of the above-mentioned type by providing a second piston also delimiting said first combustion chamber with a second piston head, a second crankshaft, and a second connecting rod connected between said second piston and said second crankshaft, said first wall defining at least a section of a torus and said pistons being guided along a curved path defined by said section of a torus. 
   In contrast to conventional combustion engines, the inventive combustion engine comprises a combustion chamber which is not only delimited by a wall of the engine housing and a first piston head of a first piston, but also by a second piston head of a second piston. The wall of the engine housing defines at least a section of a torus in which the pistons are guided, so that the pistons travel along a curved path. When the combustion gas is ignited in a combustion chamber that is delimited as described, the two pistons are driven in opposite directions, i.e. forced apart, and transmit their motion to the crankshafts via their connecting rods. The gases expanding in the combustion chamber thereby drive not only one, but two pistons to substantially increase the efficiency of the engine. This reduces fuel consumption and improves emission values. 
   Since the pistons travel along a curved path, the inventive combustion engine is very compact for a given combustion chamber volume. 
   Advantageously, the pistons move simultaneously during expansion of the combustion gases, i.e. the forces and moments generated are largely compensated for. Vibrations are thereby almost completely compensated for, such that special devices such as e.g. balancer shafts etc. are not required. 
   In a preferred embodiment, the first piston comprises a third piston head and the second piston comprises a fourth piston head, wherein the third piston head and the fourth piston head delimit a second combustion chamber. This allows for a very compact arrangement of two combustion chambers. Each piston delimits a first combustion chamber at one end and a second combustion chamber at its other end. Therefore, one stroke decreasing the size of one combustion chamber corresponds to increasing the size of the other combustion chamber and vice versa. Therefore, idle strokes of the pistons can be avoided and corresponding losses due to friction are minimized. 
   A wall having the shape of a torus can delimit the first and the second combustion chambers. It is also possible for the second combustion chamber to be delimited by a separate, second wall which also defines at least a section of a torus. It is understood that, within the scope of this invention, a torus means a ring-shaped body, which, in profile, can have any shape, e.g. circular, square, rectangular or elliptical. 
   According to a preferred embodiment of the invention, the combustion chamber can have the shape of a cone. This supports a good fuel-air mixture, thereby enhancing clean and efficient combustion. 
   Another aspect of the invention proposes that the combustion chambers have indentations extending at least partially along spiral paths. These indentations can be provided by the walls of the engine housing and/or by the piston heads delimiting a combustion chamber. The indentations create a vortex flow of the gases contained in the combustion chamber, so that the ignitable parts of the air-fuel mixture are disposed evenly in the combustion chamber. This facilitates operating the inventive internal combustion engine in a direct injection mode. 
   The two pistons can pivot around a common pivot axis. This reduces the size of the engine and minimize the number of parts needed to position the pistons. For this embodiment, a fuel injection unit and/or an intake valve and/or an exhaust valve and/or a spark plug are preferably arranged in sections of the wall of the engine housing, these sections being concentric with said pivot axis. In other words, the mentioned parts can be arranged in a direction, which is substantially radial with respect to the pivot axis. 
   The two combustion chambers and the two interposed pistons are preferably arranged in a symmetrical manner. The first connecting rod is thereby joined to the first piston at a junction comprising a first junction axis, the second connecting rod is joined to the second piston at a second junction comprising a second junction axis, and the first junction axis, the second junction axis and the pivot axis are parallel to each other and aligned in a common plane. In other words, when defining the pivot axis as the origin of a coordinate system, the junction axis is arranged on opposite sides of one axis of that coordinate system. 
   In order to transfer the motion of the pistons to the crankshafts in an efficient manner, the first crankshaft preferably comprises a first rotary axis, and the second crankshaft comprises a second rotary axis, wherein the first rotary axis and the first junction axis are parallel to each other and aligned within a first plane and the second rotary axis and the second junction axis are parallel to each other and aligned within a second plane, wherein in, midwinter position of said pistons, the first plane and the second plane are perpendicular to the common plane, as defined above. 
   The inventive combustion engine may be a two-cycle or four-cycle engine, wherein the Otto principle as well as the diesel principle may be used. 
   In accordance with the invention, the two crankshafts are coupled to a flywheel e.g. via transmission wheels and rotate in the same direction. The crankshafts may also be coupled to the flywheel using chains or toothed belts. 
   When the first crankshaft and the second crankshaft rotate in a same direction, the coupling to a flywheel is very easy, since it can be directly interposed between the two crankshafts. 
   Further advantages, features and details of the invention can be extracted from the dependent claims and the following description, which describes in detail a particularly preferred embodiment with reference to the drawing. The features shown in the drawing and mentioned in the claims and in the description may be essential to the invention either individually or in arbitrary combination. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  shows a schematic top view (or side view) of a combustion engine according to the invention; 
       FIG. 2  shows a diagram indicating various angles; 
       FIG. 3  shows an enlarged view of the region III in accordance with  FIG. 1 ; and 
       FIG. 4  shows a front view of a piston head. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows the main parts of an inventive internal combustion engine  2 . This engine comprises two combustion chambers, a first combustion chamber  4  and a second combustion chamber  6 . A first piston  8  and a second piston  10  delimit each combustion chamber. The pistons  8  and  10  have a torus shape and each comprises two piston heads. The first piston  8  comprises a first piston head  12  and the second piston  10  comprises a second piston head  14 , which is arranged opposite to the first piston head  12 . 
   At its other end, the first piston  8  comprises a third piston head  16 , which is arranged opposite to a fourth piston head  18 , provided on the second piston  10 . 
   The first combustion chamber  4  is not only delimited by the piston heads  12  and  14 , but also by a first wall  20 , which is provided by an engine housing (shown in greater detail in  FIG. 3 ). The second combustion chamber  6  is accordingly delimited by a second wall  22 . The walls  20  and  22  have the shape of a section of a torus, the ends of these sections guiding the ends of the pistons  8  and  10  on which the piston heads  12  to  18  are provided. 
   The piston  8  has a pivot arm  24 , which extends in a radial direction towards the center of the engine  2 . The piston  10  has a corresponding pivot arm  26 . The pivot arms  24  and  26  pivot around a common pivot axis  28 . The pivot axis  28  extends in a direction, which is perpendicular to the plane of the drawing. The axis  28  is also shown in  FIG. 2  as the origin of a coordinate system. 
   An end of the pivot arm  24  carries a junction with a junction axis  30  to connect a first connection rod  34  and the piston  8 . The pivot arm  26  extends in a plane behind the pivot arm  24  and is, therefore, partially shown in dashed lines. An end of the second junction axis  32  connects the second connecting rod  36  with the piston  10 . 
   The connecting rods  34  and  36  are connected via respective bearings  38  and  40 , to a first crankshaft  42  and a second crankshaft  44 , respectively. The first crankshaft  42  rotates around a first rotary axis  46 , the second crankshaft  44  rotates around a second rotary axis  48 . 
   In  FIG. 1 , pistons  8  and  10  are shown in their mid-center positions. For these positions, the arrangement of the pivot axis  28 , the junction axis  30  and  32  and the rotary axis  46  and  48  are shown in  FIG. 2 . All axes shown are parallel to each other and extend in a direction, which is perpendicular to the plane of the drawing. 
   The pivot axis  28  and the junction axes  30  and  32  lie in a common plane  50 . The distance between the pivot axis  28  and the first junction axis  30  is the same as the distance between the pivot axis  28  and the second junction axis  32 . 
   The first junction axis  30  and the first rotary axis  46  are arranged in a plane  52 , which is perpendicular to the common plane  50 . Accordingly, the second junction axis  32  and the second rotary axis  48  lie in a common plane  54 , which is also perpendicular to the common plane  50 . The distance between the axes  30  and  46  and the distance between axes  32  and  48  are the same. These distances can be the same as the distances between axes  28  and  30  and/or between axes  28  and  32 . 
   With further reference to  FIG. 1 , in which pistons  8  and  10  are shown in their mid-center positions, the piston heads  12  and  14  are spaced apart from each other by an angle  56 , which has the same value as an angle  58  corresponding to the second combustion chamber  6  between the piston heads  16  and  18 . 
   When the first piston head  12  travels between its top dead center position and its bottom dead centre position, it travels along the angle  60 . Accordingly, the third piston head  16 , also belonging to piston  8 , will travel along the angle  62 , which is equal to angle  60 . The piston heads  14  and  18  of piston  10  will also travel along angles  64  and  66 . For the embodiment shown, the size of all angles  56  to  66  is the same. 
   When piston  8  moves according to a direction indicated with reference numeral  68 , the piston head  12  moves from its bottom dead center position to its top dead center position. Accordingly, the piston head  14  moves in direction  70  from its bottom dead center position to its top dead center position. Alter both pistons  8  and  10  have reached their top dead center positions with respect to the first combustion chamber  4 , the pistons  8  and  10  will move along respective directions  72  and  74 , so that, with respect to the second combustion chamber  6 , the piston heads  16  and  18  will move from their bottom dead center positions to their top dead center positions. The pistons  8 ,  10  therefore move in opposite directions. 
   In  FIG. 3 , pistons  8  and  10  are shown in their top dead center positions with respect to combustion chamber  4 .  FIG. 3  also shows parts of an engine housing  76 , in which a wall  20  is provided, which has the shape of a section of a torus in which the torus-shaped pistons  8  and  10  are guided along a circular path. 
   The pistons  8  and  10  can be at least partially hollow or be made from a lightweight material, such as carbon composites. Adjacent to their respective piston heads  12  and  14 , the pistons  8  and  10  carry piston rings  78 , which seal the pistons  8  to  10  with respect to the wall  20  of the engine housing  76 . The piston heads  12  and  14  define a combustion chamber  4 , which has the shape of a cone. The piston head  12  of piston  8  comprises a cone wall  80 , which is also shown as a dashed line in  FIG. 1  and in a front view in  FIG. 4 . Accordingly, the piston head  14  of piston  10  has a cone wall  82 . The cone walls  80  and  82  have indentations, which extend at least partially along a spiral path. These indentations  84  are also shown in  FIG. 4 . The indentations  84  initiate a vortex flow within the combustion chamber  4 , so that a clean and efficient combustion can take place. 
   A fuel injector  86  is provided at the tip of the cone-shaped combustion chamber  4  and mounted within the engine housing  76 . A spark plug  88  is accommodated in the engine housing  76  on the side opposite to the fuel injector  86 . A double spark ignition system can also be provided. 
   An intake valve  90  and an exhaust valve  92  are provided adjacent to the spark plug  88 . The valves are integrated in a rounded bottom plate  94 , which merges with the wall  20 . 
   Lobes provided on the crankshafts  42  and  44  can drive the valves  90  and  92 . They can also be electromagnetically operated, which allows for a more flexible valve timing. 
   The engine can be operated according to the four-cycle-principle. When operating the inventive engine according to the two-cycle-principle, use of a forced air induction system is recommended. This system comprises an air compressor, an air storage tank and an intercooler. The compressor forces fresh air through the intercooler and into the air storage tank. When the air storage tank has reached its maximum capacity, pressure, and volume, a valve switches an air-return from the air storage tank to the air compressor. This causes the air to resume circulation through the intercooler system.

Technology Classification (CPC): 5