Abstract:
An internal combustion piston engine comprises a cylinder with a cylinder bore therein; a cylinder head mounted on said cylinder; a piston reciprocably movable in said cylinder bore, and a main combustion chamber formed between the cylinder head and the piston. At least one secondary combustion chamber is arranged to be connected at least temporarily to the main combustion chamber via at least one connecting channel whereby different compressions and hence different pressure rises occur during the compression stroke or the expansion stroke of the piston in the main combustion chamber or in the secondary combustion chamber. Control means are arranged in the zone of the connecting channel to enable the flow of the gases, which are under a higher pressure, from the main combustion chamber into the secondary combustion chamber or vice versa, to generate velocity fields which improve the turbulence, in particular in the quench zones of the main combustion chamber, and hence improve the combustion.

Description:
This application is a continuation of application Ser. No. 451,223, filed Dec. 20, 1982, now abandoned, which is a continuation of application Ser. No. 177,550 filed Aug. 13, 1980, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to an internal combustion piston engine, the cylinder of which has a main combustion chamber, in which the combustion is initiated, and at least one secondary combustion chamber which is connected at least temporarily to the main combustion chamber via one or more channels. 
     Internal combustion piston engines with subdivided combustion chambers are known. Moreover, it is not novel that the combustion process can be influenced by this sub-division. Recently, an internal combustion engine of this type has been described, for example, in German Offenlegungsschrift 27 45 902. In the embodiment according to FIG. 4 of this printed publication, the main combustion chamber and the secondary combustion chamber are continuously connected to one another. Thus, approximately the same pressure prevails in the two chambers at the end of a compression stroke. The combustion process in the main combustion chamber can therefore be influenced only by moving pressure waves which are said to pass from the secondary combustion chamber into the main combustion chamber after the mixture has been ignited. In addition, heating of the thin, disc-shaped cap of the piston also plays a role in promoting combustion. It must be doubted whether it is possible substantially to improve the combustion and to reduce the emission of pollutants by means of the pressure waves which run at high velocity and only for a short time. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to improve an internal combustion piston engine of the type indicated at the outset in such a way that, by means of controlled and longer-lasting flow processes, velocity fields which substantially improve the combustion are generated between the combustion chambers. 
     To attain this object the present invention provides an internal combustion piston engine comprising a cylinder having an inner wall defining a cylinder bore; a cylinder head having a wall and being mounted on said cylinder; a piston having a head and an axis and being reciprocably movable in said cylinder bore; a main combustion chamber formed between the cylinder head and the piston and in which the combustion is initiated by a spark plug; at least one secondary combustion chamber arranged to be connected at least temporarily to the main combustion chamber via at least one connecting channel whereby different compressions and hence different pressure rises occur during the compression stroke or the expansion stroke of the piston in the main combustion chamber or in the secondary combustion chamber, and control means arranged in the zone of the connecting channel to enable the flow of the gases, which are under a higher pressure, from the main combustion chamber into the secondary combustion chamber or vice versa, to generate velocity fields which improve the turbulence, in particular in the quench zones of the main combustion chamber, and hence improve the combustion. 
     The inventive concept on which these features are based consists in providing two combustion chambers which, during the compression stroke and also during the expansion stroke, are separated from one another for a short time and are arranged in such a way that different pressures are built up therein. When the control means are actuated by the motion of the piston and the combustion chambers are again connected to one another, pressure balancing occurs due to a flow from one combustion chamber into the other combustion chamber. In this way, velocity fields are necessarily generated, which favor the advance of the flame front and, due to improved turbulence, promote the reactions behind the flame front. The velocity fields also prevent the formation of undesired quench zones on the walls. 
     Advantageous embodiments and further developments of the invention are indicated in the sub-claims. The embodiments differ in the main in that the main combustion chambers are located in the cylinder or in the cylinder head, the secondary combustion chambers are located either in the piston, in the cylinder or in the cylinder wall and the connecting channels are located between the piston and the cylinder wall or in the cylinder head. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described by way of example and with reference to the accompanying schematic drawings in which: 
     FIGS. 1a and 1b show a first embodiment with a seondary combustion chamber arranged in the piston; 
     FIG. 2 shows a diagrammatic sketch of the advance of the flame front in the cylinder of a conventional internal combustion piston engine; 
     FIGS. 3 and 4 show schematic sketches of the control of the cross-flow and of the advance of the flame front in the arrangement according to FIGS. 1a and 1b; 
     FIG. 5 shows an embodiment with a secondary combustion chamber arranged in the inner wall of the cylinder; 
     FIG. 6 shows a further embodiment in which the main combustion chamber is arranged in the end wall of the cylinder head, and 
     FIGS. 7 and 8 show, in longitudinal section and cross section along the lines VIII--VIII and VII--VII, respectively, an embodiment with a main combustion chamber arranged in the end wall of the cylinder head and with control valves in the connecting channels. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1a and 1b show a piston/cylinder arrangement comprising a piston 1 which is at its bottom dead center according to FIG. 1a and at its top dead center according to FIG. 1b. At a distance from the piston head 1a, the piston 1 has an approximately torus-shaped inward-directed cavity 1b which forms a secondary combustion chamber 2. At its end facing the main combustion chamber 4, the piston 1 is set back in the form of a step in such a way that a connecting channel 3 from the main combustion chamber 4 to the secondary combustion chamber 2 is formed by the annular gap between the cylindrical wall part 5 of reduced diameter of the step on the piston and the inner wall 6 of the cylinder. To control the flow through the connecting channel 3 as a function of the stroke of the piston 1, an annular projection is provided on the inner wall 6 of the cylinder, which annular projection can, for example, be formed by a sealing strip 7 inserted into the inner wall of the cylinder. The annular projection or the sealing strip 7 is arranged in such a way that, in interaction with the cylindrical wall part 5 of reduced diameter of the step on the piston, it blocks the connecting channel 3 when the piston 1 is at some distance from its top dead center, and reopens the connection between the secondary combustion chamber 2 and the main combustion chamber 4 when the piston 1 has approached the top dead center. 
     The mode of action of this control of the connecting channel 3 can be seen from FIGS. 2 to 4, in comparison with the conditions in a conventional internal combustion engine. 
     FIG. 2 shows the advance of the flame front in the cylinder of a conventional internal combustion engine having an undivided combustion chamber 4 1 . The lines in the combustion chamber 4 1  show the course of the flame front at various points in time. The directions of advance of the flame front are indicated by arrows. It can be seen that, from the spark plug 14, the flame front moves initially almost spherically and then approximately perpendicular towards the head 1a 1  of the piston 1 1  and towards the inner wall 6 1  of the cylinder. The flame front is extinguished in the vicinity of these walls so that quench zones are formed which contain an unburned or only partially burned mixture. Disregarding the low residual velocity in the gas, generated by the intake process, the flame front advances in virtually stagnant gas at a velocity which is caused by diffusion and heat conduction. 
     By contrast, FIGS. 3 and 4 show what happens in the cylinder of an internal combustion engine designed according to the invention. 
     In FIG. 3, the piston 1 2  is at some distance from its top dead center. The gas in the main combustion chamber 4 2  is separated from the secondary combustion chamber 2 2  by the sealing strip 7 2 , preferably without contact, opposite the cylindrical wall part 5 2  of reduced diameter of the step on the piston 1 2 . When the piston 1 2  in FIG. 3 moves upwards, the gas in the main combustion chamber 4 2  is compressed to a much greater extent than the gas in the secondary combustion chamber 2 2 . The degree of compression or of the difference in compression is essentially determined by the geometrical shape and the dimensions of the main combustion chamber 4 2 , the sealing strip 7 2  and the secondary combustion chamber 2 2  formed by the cavity 1b 2 . When the cylindrical wall part 5 2  of reduced diameter of the step on the piston 1 2  clears the sealing strip 7 2  toward the end of the compression stroke of the piston 1 2 , gas flows at high velocity from the main combustion chamber 4 2  into the secondary combustion chamber 2 2 . The flame front then forms approximately in accordance with the lines and arrows sketched in FIG. 4. 
     In contrast to the conditions in conventional internal combustion piston engines, the flame front in an embodiment according to the invention advances at a high velocity which results from the superposition of the flame front velocity in stagnant gas and the inherent velocity of the gas. In this way, the gas and flame front are moved along the walls of the cylinder chamber and of the piston at a high velocity so that very low thicknesses of the boundary layer and small quenching zone result. Moreover, the gas flowing at high velocity into the secondary combustion chamber creates strong turbulence in this combustion chamber so that complete combustion takes place in the latter. 
     During the downward stroke (expansion stroke) of the piston 1 2 , the main combustion chamber 4 2  is separated again from the secondary combustion chamber 2 2  by the sealing strip 7 2  interacting with the cylindrical wall part 5 2  of reduced diameter. For the reasons explained above in the context of compression, the expansion of the gas in the main combustion chamber 4 2  is now much greater than in the secondary combustion chamber 2 2  in which the combustion continues at approximately constant volume. The gas pressure in the secondary combustion chamber 2 2  can therefore still rise, whilst it falls in the main combustion chamber 4 2  due to the expansion. When the upper edge of the cylindrical wall part 5 2  of reduced diameter, during its downward motion, clears the sealing strip 7 2 , gas flows at high velocity from the secondary combustion chamber 2 2  into the main combustion chamber 4 2  and creates strong turbulence of the incompletely burned gas quantities which may still be present there. Thus, complete combustion in the main combustion chamber 4 2  is also promoted. 
     The arrangement of the main combustion chamber and of the secondary combustion chamber and also of the control means for the overflowing gases can also be realized constructionally in a different manner. 
     Thus, FIG. 5 shows an embodiment in which the secondary combustion chamber 2 3  is formed by an approximately torus-shaped outward-directed cavity 6b in the inner wall 6 3  of the cylinder. On the shell of the piston 1 3 , a shallow constriction 10 is provided which, together with the inner wall 6 3  of the cylinder, delimits the connecting channel 3 3  leading to the main combustion chamber 4 3 . In its upper part, the main combustion chamber 4 3  is widened radially outwards. At the end of the shallow constriction 10, towards the piston head 1a 3 , the piston 1 3  has approximately its normal external diameter corresponding to the cylinder bore so that, relative to the bottom of the shallow constriction 10, there is a collar-like annular projection 12 which interacts with that part 6c of the inner wall 6 3  of the cylinder which extends between a widening 6a of the combustion chamber 4 3  and the torus-shaped outward-directed cavity 6b, in order to control the flow through the connecting channel 3 3 , in a manner similar to that already described in connection with FIGS. 3 and 4. 
     FIGS. 6 and 8 show two embodiments of the invention, in which the main combustion chamber is arranged in the end wall of the cylinder head. 
     According to FIG. 6, the piston 1 4  shown in the vicinity of its top dead center has, on its head 1a4, a cylindrical projection 1c of a diameter which is smaller than that of the piston head. The cylinder bore is provided with an extension 8 which matches the piston projection 1c and which, together with the end face of the piston projection, forms the main combustion chamber 4 4 , whilst the secondary combustion chamber 2 4  is delimited by the shoulder parts of the piston 1 4  and the inner wall 6 4  of the cylinder. Corresponding to the piston design according to FIG. 5, the piston projection 1c is here provided with a constriction 11 which is delimited by an annular collar 13 on the side toward the main combustion chamber 4 4 . The control of the gases flowing through the connecting channel 3 4  is effected by the interaction of the annular collar 13 with the cylindrical wall section located between the secondary combustion chamber 2 4  and a widening 8a of the extension 8 of the cylinder bore. 
     In the arrangement according to FIG. 6, differential compression or expansion of the gas in the two combustion chambers 2 4  and 4 4  is achieved by the fact that the volume of the secondary or of the main combustion chamber, remaining above the piston head 1a4 or the cylindrical projection 1c at the end of the compression stroke, is of different size in relation to the associated piston area. The size of the residual volumes, remaining above the piston 1a4 or the cylindrical projection 1c at the end of the compression stroke, can, for example, be influenced by appropriate dimensioning of the distance of the front faces of these piston parts from the end faces of the associated cylinder chambers. The final compression space can also be enlarged in this sense by radial widening. However, the slight widening 8a of the main combustion chamber, shown in FIG. 6, serves only to provide a control edge for the annular collar 13. 
     In the embodiment shown in FIGS. 7 and 8, the connection between the main combustion chamber 4 5  and the secondary combustion chamber 2 5  is made via connecting channels 3 5  provided in the wall of the cylinder head. Also in this embodiment the secondary combustion chamber is delimited by the shoulder parts of the piston head 1a 5  and the inner wall 6 5  of the cylinder. To control the cross-flow processes, valves 9 are provided which are opened and closed either automatically by the pressure difference between the secondary combustion chamber 2 5  and the main combustion chamber 4 5  or by a mechanical drive. In addition to appropriate design and control of the valves 9, the gases can also be caused to flow from the secondary combustion chamber 2 5  into the main combustion chamber 4 5  by an arrangement in which the projection 1c 5  of the piston 1 5  completely leaves the cylinder extension 8 5  and thus opens a flow cross section between the combustion chambers. 
     The connecting channels 3 5  extend in the manner of a spatial helix in such a way that the gas flowing into the secondary combustion chamber 2 5  induces in this chamber a turbulent flow which promotes combustion. 
     Incidentally, a vortex in the gases flowing across can be obtained also in the embodiments according to FIGS. 5 and 6, if the constrictions 10 and 11 of the piston and of the piston projection 1c, respectively, are sub-divided by radial ribs which follow a helix about the piston axis. The connecting channels remaining between the ribs impart to the gases, flowing across in them, a velocity component in the peripheral direction and thus promote turbulence in the combustion chambers, into which the gases flow at the time. In a similar way, the same effect can also be produced in the embodiment according to FIGS. 1a and 1b, if corresponding ribs are provided on the inner wall 6 of the cylinder above the sealing strip 7. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments are therefore to be considered in all respects as illustrative and not restrictive.