Abstract:
An externally ignited four cycle internal combustion engine equipped with an inlet valve and an outlet valve, both valves being positioned on one side of the cylinder. A swirl (or vortex) chamber is provided within the cylinder head, the height of the swirl chamber being substantially less than its maximum diameter. The inlet and outlet valve discs lie substantially in a same plane. A channel-like recess in the cylinder head, which creates a guide channel when the piston is in its upper dead center position, terminates approximately tangentially in the swirl chamber.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of Application Ser. No. 630,624, filed Nov. 10, 1975, now U.S. Pat. No. 4,094,272. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to an externally ignited fourcycle internal combustion engine in which the fuel-air mixture is formed outside of at least one cylinder. The present invention is concerned more particularly with such an internal combustion engine in which the inlet and outlet valves are arranged on one side of the cylinder. This engine is known as a side-valve or L-head engine. The combustion chamber of each cylinder in this engine is a volume surrounding the valve discs. It is designed to allow a substantially single vortex movement of the charge whereby the imaginary central axis of the swirl is substantially parallel to the cylinder axis. The height of the swirl chamber is typically less than its maximum diameter. A guide channel, originating approximately above the center of the piston head surface collects gases emerging from the cylinder volume when the piston approaches its top dead center position and directs them in a substantially tangential direction to the swirl chamber, thereby generating an essentially single swirl motion of the compressed charge during and toward the end of the compression stroke of the piston. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The side valve arrangement in a four cycle internal combustion engine is well known to be outdated, essentially due to the fact that the obtainable specific output power and specific fuel consumption are rather poor. Furthermore, the exhaust gases contain a high amount of undesirable components, e.g., carbon monoxide and various hydrocarbon components. 
     For these reasons, this engine type has been largely neglected and, in some fields, e.g., the automotive industry, it has been completely abandoned. 
     Nevertheless, this type of engine is still being produced because it is relatively inexpensive and these engines are in use for powering lawn mowers, small electric generators, pumps, etc. 
     It is a principal object of this invention to provide an engine of the type described above, i.e., a side valve engine, sometimes referred to as an L-head engine, which is so improved that it has clear advantages by comparison with engines without swirl (vortex) chambers, especially in having a high thermodynamic efficiency with all advantages deriving therefrom and a high degree of completeness of combustion, so that, among other things, this engine expels only a relatively small amount of toxic exhaust gas constituents. 
     It is another object of the invention to obtain such results by only slightly modifying the known engine so as not to increase the production costs appreciably. According to the invention, only the already simple cylinder head needs to be partially reshaped. 
     These and other objects are attained, according to the invention, by providing, in an engine of the type described above, that the cylinder head (and/or the top of the piston) includes a channel-like recess which becomes a guide channel for the gases when the piston approaches and reaches its top dead center position. The guide channel terminates approximately tangentially in the swirl chamber and its extent is defined by the cylinder head and the top of the piston. The height and cross section of the guide channel may both increase from its origin above and near the center of the piston in the direction leading to the swirl chamber. The guide channel is so disposed that it creates a rotational gas flow in the swirl chamber whose axis is approximately parallel to the longitudinal axis of the cylinder. The rotational gas flow takes place at the latest toward and near the end of the compression stroke of the piston. The channel-like recess in the cylinder head and/or the piston, in cooperation with the approaching piston head surface, imparts a directed impulse to fuel-air mixture toward and into the swirl chamber. The guide channel is so configured that a substantially single rotational flow is generated within the swirl chamber and that its rotational axis is approximately parallel to the cylinder axis. The rotational flow leads to rapid combustion and low flow losses during the compression stroke and during the expulsion of the combusted mixture. Furthermore, the engine may be operated with a surprisingly lean fuel-air mixture. In addition, the fluctuation of the pressure characteristics of consecutive cycles is small in steady-state operation. The engine according to the present invention exhibits low fuel consumption, high specific power and expels only small amounts of toxic constituents in the exhaust gas. In addition, the engine tends not to &#34;ping&#34; or &#34;knock&#34; so that it may be operated at relatively high compression ratios using ordinary fuels. Nevertheless, the engine is inexpensive to manufacture. Furthermore, the mass production facilities for four cycle, internal combustion engines without swirl chambers can be readily changed over to the manufacture of internal combustion engines according to the invention at relatively low cost because, in the simplest case, only the casting of the cylinder head needs to be altered. It is known that flathead pistons have a minimum heat transfer area. Therefore, it can be suitably provided that the piston used is a flat-head piston and that the channel-like recess is provided only in the cylinder head. In addition, this embodiment produces particularly low flow losses. 
     In order to further improve, i.e., to accelerate the combustion process, it may be suitably provided that, when the piston is in its top dead center position, then preferably at least 80 percent of the remaining volume of the combustion chamber is formed by the swirl chamber and by the guide channel. 
     In a preferred embodiment, the walls of the swirl chamber are continuously curved so as to form a spiraling enclosure provided with a rupture edge at the end of the spiral. It has been shown that this construction generally further improves the operational characteristics of the engine, especially when extremely lean mixtures are being used. 
     It is also generally suitable, according to the invention, to provide that the height of the swirl chamber is substantially less than its maximum diameter. It is especially advantageous if the height of the swirl chamber is approximately constant. 
     In general, the fuel mixtures which may be used in the engine can be further leaned out by providing that the spark plug is located in the vicinity of the end of the spiral enclosure. Furthermore, the propagation of combustion is enhanced if the ignition of the charge in the gap between the electrodes of the spark plug originates close to the top surface of the piston. A further improvement is achievable by concentrating the cooling around the spark plug and maintaining the squeezing or squish zone above the piston relatively hot so that the inner wall acquires temperatures in the range of from at least 120° C. to at most 350° C. during partial and full-load operation. 
     Preferably, the depth of the guide channel increases from the side adjacent to the rupture edge toward the opposite side. In a preferred embodiment, the guide channel points toward the area where the inlet valve is located, but the invention is not restricted to this embodiment. 
     The invention will be better understood as well as further objects and advantages thereof will become more apparent from the ensuing detailed description of an exemplary embodiment taken in conjunction with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIGS. 1 and 1A are bottom views of the cylinder head of a four cycle internal combustion engine according to the invention, only one cylinder being shown, although the engine may have additional cylinders; 
     FIGS. 2 and 2A are cross-sectional views of the cylinder head of FIG. 1, the section being taken along the line C-C of FIGS. 1 and 1A, and also showing a portion of the cylinder wall and a portion of the piston; 
     FIG. 3 is a cross-sectional view of a cylinder head along the line A--A of FIG. 1A; and 
     FIG. 4 is a cross-sectional view of a cylinder head along the line B--B of FIG. 1A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the preferred exemplary embodiment illustrated by FIG. 2, a piston 10 is embodied as a flat-head piston, i.e., it has a flat piston-head 9. A cylinder-block 11&#39; includes an inlet valve 12. A portion of an induction tube 15 leading to the space above a valve disc 14 of the inlet valve 12 extends approximately perpendicular to the longitudinal axis of the inlet valve 12. 
     In the similar FIG. 2A, the valve shown represents the outlet valve 13 with an outlet valve disc 17 and outlet port 19. 
     It may be seen especially clearly from FIG. 1 that, originating in the vicinity of the cylinder axis, is a channel-like recess or cavity 26 which, in the exemplary embodiment, is worked into the inwardly facing surface of the cylinder head adjacent to and facing the top of the piston 9 and which extends up to the swirl chamber 21. Its height, as can be seen in FIG. 2, increases from the origin 25 up to the swirl chamber 21. 
     In the top dead center position of the piston 10, as shown in FIG. 2, this channel-like recess or cavity 26, together with the top of the piston-head 9, reaching position 9&#39;, forms a guide channel 26 which, as may be clearly seen in FIG. 1, terminates approximately tangentially in the circumferential wall 24 of the swirl chamber 21. The guide channel 26 can be considered to provide a directed fluid communication from the cylinder volume 10&#39; to the combustion chamber surrounding the valves 12 and 13. 
     The cross-sectional area of the guide channel 26 also continually increases from its origin 25 up to the swirl chamber 21 due to its continuously increasing height. Its width increases only slightly throughout its length. The terminus of the channel-like recess or cavity 26 nearest the swirl chamber 21 merges smoothly with the latter. 
     One side of the channel-like recess or cavity 26 terminates at the circumferential wall 24 of the swirl chamber 21, in the location 23, in the manner of a breakaway or flow-separating edge so that the fluid flow entering the swirl chamber 21 out of this channel-like recess or cavity 26 during the compression stroke will break away from the wall. The other side of this channel-like recess or cavity 26 continuously extends into the circumferential wall 24 of the swirl chamber 21 at the location 22. 
     As may be understood from FIG. 2, the combustion chamber volume remaining when the piston 10 is in its top dead center position is determined substantially only by the volumes of the guide channel 26 and of the swirl chamber 21. 
     Suitably, as may be seen in FIG. 2, a spark plug 27 is inserted within the circumferential wall 24 of the swirl chamber 21 in the area of the break-away edge 23. 
     The smallest volume of the channel-like recess or cavity 26 is smaller than the volume of the swirl chamber 21. Preferably, a single swirl chamber 21 is provided in each cylinder. Except for the region containing the swirl chamber 21 and the channel-like recess or cavity 26, the remaining region of the surface of the cylinder head 11 is everywhere so close to the piston 10 in the top dead center position of the latter, that a so-called compression zone or squeezing (squish) zone is formed throughout this entire remaining region. The thickness of this squeezing zone is preferably as small as technically allowable, preferably in the range of 0.3 to 0.75 mm, depending on the size of the cylinder. 
     FIGS. 3 and 4 are cross sections of the guide channel, along the lines B--B and A--A, respectively, showing the increasing depth of the guide channel toward the side opposite the rupture edge, i.e., toward the top of FIG. 1A. In FIG. 2 the guide channel is directed toward the inlet valve area; in the alternative embodiment of FIG. 2A it is directed toward the outlet valve area. 
     The following test sets forth the manner of operation of the sectionally illustrated cylinder when forming part of an externally ignited four-cycle internal combustion engine, not shown in further detail, and whose fuel-air mixture is produced in any known manner outside of the combustion chamber of the cylinder, for example by means of a carburetor or by fuel injection into an induction tube. 
     During the suction stroke of the piston, and in known manner, the downward motion of the piston 10 aspirates a fuel-air mixture into the combustion chamber while the inlet valve 12 is open. During the subsequent compression motion of the piston 10, this mixture is compressed and a slow rotational flow in the direction of an arrowhead line B (FIGS. 1, 1A) may already be formed at this time in the swirl chamber 21, conditioned by the channel-like recess or cavity 26. The rotational axis of this flow is approximately parallel with the longitudinal axis of the cylinder 10. Toward the end of the compressional motion of the piston 10, the top 9 of the piston 10 comes closer and closer to the channel-like recess or cavity 26 so that the flow occurring therein is reinforced and a relatively intensive flow of fuel-air mixture takes place, via the guide channel 26 being formed, into the swirl chamber 21, where it generates an intensive rotational flow in the direction of the arrowheaded line B. The spark plug 27 ignites the fuel-air mixture in known manner at adjustable crankshaft angles during the compressional motion of the piston 10, i.e., before the piston 10 has reached its top dead center position. 
     Due to the concentration of the mixture in the swirl chamber 21 and in the guide channel 26 and due to the intensive and orderly rotational flow prevailing in the same sense in the swirl chamber 21, the combustion process is rapid and a high degree of fuel utilization is achieved. After the piston 10 has passed its top dead center position, it is pushed downwardly and, during the next upward motion of the piston 10 and while the outlet valve 13 is open, the combusted gas is expelled in known manner. 
     An engine constructed as described above may be operated with very lean fuel-air mixtures, preferably with 20-40% air excess. It exhibits a low specific fuel consumption and the exhaust gas contains relatively few toxic constituents, so that, in spite of its simple construction and its relatively high specific power, it is compatible with the environmental regulations. In addition, the octane number of the fuel used may be relatively low. 
     As preferably provided in the above described exemplary embodiment, the channel-like recess or cavity 26 is located only in the cylinder head. However, in many cases, it may be suitable to form the guide channel 26 by opposite cooperating cavities in the cylinder head 11 and the top 9 of the piston 10. In that case, it ought to be generally suitable to make the depth of the cavity in the cylinder head 11 greater than the depth of the cavity in the top 9 of the piston 10. This variant is also illustrated in FIG. 2A, which shows a cavity 26&#39; in the top of the piston by a dashed line. In special cases, the guide channel 26 may be formed exclusively by a depression or cavity in the top 9 of the piston 10 which is so shaped that, toward the end of the compression stroke of the piston 10, it channels gas into the swirl chamber 21 tangentially so that the gas executes a rotational flow along the circumferential wall 24 of the swirl chamber 21 or that at least a substantial component of this rotational flow lies along the circumferential extent of the swirl chamber 21. This variant is not illustrated. 
     It is to be appreciated that the exemplary embodiments of the present invention as illustrated and described in detail, and the variants mentioned have been set out by way of example and not by way of limitation. Thus, numerous other embodiments and variants are possible within the spirit and scope of the present invention, the scope being defined by the appended claims.