A TWO-STROKE ENGINE

Abstract: A two-stroke internal combustion engine that comprises a cylinder, a piston, a connecting rod connected between a crankshaft and said piston, an inlet (5) to a crank-housing (6) for fuel mixture from a carburettor, and a passage between crank-housing and an induction port in the cylinder wall, and an exhaust port in said cylinder wall, said exhaust port being in connection with the surroundings, wherein the engine includes a cylinder (1) which is common to two pistons (2, 12) which move towards and away from each other, wherein the engine includes a crank-housing (6, 10) at both ends of the cylinder (1), wherein each crank-housing (6, 10) accommodates a crankshaft (4, 11) which is connected to respective pistons (2, 12) through the medium of a piston rod (3, 13), wherein the crankshafts (4, 11) are interconnected mechanically so that both pistons (2, 12) will move simultaneously towards their top centre positions and also move simultaneously to their bottom centre positions, and wherein a carburettor (32) is connected to the first crank-housing (6). The invention is characterized by the combination in which only a second (10) of the crank-housings is connected to said induction port (8) via a passage (7); in that said exhaust port (9) is positioned for coaction with the piston (2) that belongs to the first of said crank-housings (6); in that a pipe (33) extends between the first crank-housing (6) and the second crank-housing (10) for transportation of fuel mixture from the first crank-housing to the second crank-housing; and in that a check valve (34) is provided between the first crank-housing (6) and the inlet end of the pipe (33).

Description: A two-stroke engine The present invention relates to a two-stroke engine. Two-stroke engines have many advantages over four-stroke engines. One distinct advantage is that the two-stroke engine has far fewer movable parts than a four-stroke engine. Another advantage is that fuel is combusted each time the piston reaches the top of the cylinder, i.e. a working stroke takes place with each revolution of the piston, via the crankshaft coupled to the piston rod. A decisive drawback with the two-stroke engine is that combustion of the fuel mixture is poor, due to the fact that fresh fuel mixture is delivered to the cylinder at the same time as the exhaust gases are ventilated, which results in non-combusted fuel mixture departing with the exhaust gases. The most common type of two-stroke engine includes passages for leading fuel mixture into the cylinder space in the cyl- inder wall, at a distance from the cylinder combustion chamber that slightly exceeds the distance from the combustion chamber to an exhaust port in the cylinder wall. When fuel is combusted in the combustion chamber, the piston moves downwards and the upper surface of the piston will thus first pass the exhaust port, wherewith the exhaust gases flow out through said port. The upper surface of the piston will then pass the passageways through which fuel mixture flows into the cylinder. However, this inflow of fuel mixture takes place whilst the exhaust port is still open. Thus, as the piston moves upwards, it will first pass the passageways that are closed and thereafter passes the exhaust port so as to close the same. A certain part of the fuel mixture will be pressed out through the exhaust port, partly while fuel mixture is being injected into the cylinder and partly during upward movement of the piston. It is known to avoid this problem by direct injection of fuel through the cylinder head of the engine, and by injecting air into the cylinder, via a valve mounted in the cylinder head, subsequent to the exhaust port having been closed by the piston as it moves up in the cylinder. However, this solution necessitates providing the engine with electronic means for controlling the injection nozzle and also with a compressor for delivering combustion air. The present invention solves the problem of achieving a high degree of combustion in two-stroke engines without requiring the provision of additional movable parts or other control equipment for delivering a fuel mixture. The present invention thus relates to a two-stroke internal combustion engine that includes a cylinder, a piston, a connecting rod connected between a crankshaft and the piston, a crank-housing inlet for fuel mixture from a carburettor, a passageway between the crank-housing and an induction or inlet port in the cylinder wall, and an exhaust port in said cylinder wall, wherein the exhaust port communicates with the surroundings, wherein there is included a cylinder which is common to two oppositely moving pistons, wherein a crank- housing is provided at both ends of the cylinder, wherein each crank-housing includes a crankshaft which is connected to respective pistons through the medium of a piston rod, wherein the crankshafts are interconnected mechanically so that both pistons will move simultaneously to their top centre positions and also move simultaneously to their bottom centre-positions, and wherein a carburettor is connected to the first crank-housing, said engine being characterized by the combination where only a second of said crank-housings is connected to said induction port via a passageway, in that said exhaust port is positioned for coaction with the piston belonging to the first of said crank-housings, in that a pipe extends between the first crank-housing and the second crank- housing for transporting fuel mixture from the first crank- housing to the second crank-housing, and in that a check valve is provided between the first crank-housing and the inlet end of said pipe. The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings, in which Figure 1 is a longitudinal section view of an engine constructed in accordance with the invention; Figure 2 is a more schematic, longitudinally sectioned view corresponding to Figure 1, but turned through 90°; Figures 3a-3e illustrate a working cycle in which the crankshafts of the engine rotate in opposite directions; Figures 4a-4e illustrate a working cycle in which the crank- shafts of the engine rotate in the same direction; Figure 5 is a schematic sectioned view corresponding to the section shown in Figure 1, with an alternative connection between the crankshafts; and Figure 6 is a schematic sectioned view corresponding to the section shown in Figure 1 with another alternative connection between the crankshafts. Figures 1 and 2 illustrate a two-stroke internal combustion engine that includes a cylinder 1, a piston 2 and a connect- ing rod 3 connected between a crankshaft 4 and the piston 2. The engine also includes an inlet 5 to a crank-housing 6 for fuel mixture from a conventional carburettor 32, said nlet including a leaf spring 35 or corresponding valve. Air is delivered via an inlet 36. The cylinder 1 is common to two pistons 2, 12 that move towards and away from each other. In addition to the crank- housing 6, the engine includes a further crank-housing 10 in the other—end of the cylinder ^ —Eac—erank-housing 6-,—1O ac- commodates a respective crankshaft 4, 11 which are each connected to a respective piston 2, 12 via respective piston rods 3, 13. The crankshafts 4, 11 are interconnected mechani- cally, so that both pistons 2, 12 will move to their top centre positions simultaneously, and also move simultaneously down to their bottom centre positions. In the Figure 1 embodiment, the crankshafts are interconnected by means of a toothed belt 14 with associated belt wheels 15, 16 on each crankshaft. Alternatively, the connection may correspondingly consist of a chain and a sprocket wheel on each crankshaft. As a result of this arrangement, when the pistons are in their top centre positions, the respective upper sides of the pistons will define a combustion chamber 17 together with the cylinder wall, as shown schematically in Figure 4a. A passageway 7 is located between the crank-housing 10 and an induction port 8 in the wall of the cylinder 1. An exhaust port 9 is provided in the cylinder wall, said exhaust port communicating with the surroundings. The cylinder includes a sparking plug hole 18 which is posi- tioned at the location of the combustion chamber defined by the upper surfaces of both pistons and the cylinder wall when said pistons are in their respective top centre positions. The hole is adapted to receive a conventional sparking plug (not shown) . The engine may include two mutually opposing sparking-plug holes, so as to obtain more positive ignition of the fuel in the combustion chamber defined by the pistons. Figure 1 shows a flywheel 37 mounted on the first crankshaft 4. The invention is comprised of the combination in which solely a second 10 of the crank-housings is connected to said induction port 8, via a passageway 7, and in which said exhaust port 9 is positioned for cooperation with the piston that belongs to the first crank-housing 6, and in which a pipe 33 extends between the first crank-housing 6 and the second crank-housing 10 for transporting fuel mixture from the first crank-housing to said second crank-housing, and in which a check valve 34 is provided between the first crank-housing 6 and the inlet end of the pipe 33. Figures 4a-4e illustrate a working cycle of the embodiment in which the crankshafts rotate in mutually the same direction. Figure 4a illsutrates the top centre position, in which the fuel is ignited. Upon ignition of the fuel, the pistons are moved away from each other, see Figure 4b, until they reach their respective bottom centre position, shown in Figure 4c. As the first piston 2 moves, it presses out fuel mixture in the pipe 33, through the check valve 34. The fuel mixture in the pipe 33 is therewith pressed into the second crank- housing 10. Both the induction port 8 and the exhaust port 9 are exposed in the bottom centre position. Fresh fluid mixture then flows in a known manner from the crank-housing 10, through the passageway 7 and into the cylinder through the induction port 8, at the same time as the exhaust gases are caused to flow out of the exhaust port 9 by the inflowing fuel mixture. The pistons then move towards one another, see Figure 4d, under the influence of a flywheel 20, 21; 37 on one or both of said crankshafts, until the top centre position is again reached, see Figure 4e, whereafter the cycle is repeated. No reference numerals or signs have been included in Figures 4b- 4e, for the sake of clarity. This engine design has been found to generate extremely low emissions of CO and HC. The reasons why these low emissions are achieved is not fully understood, but is thought to be the result of several mutually coacting factors. One factor is that the first crank-housing presses the fuel mixture out into the pipe once with each revolution, at the same time as the check valve 34 prevents the generation of a subpressure in the pipe 33 as the first piston moves towards its top centre position. This means that as the second piston moves towards its top centre position it will be supplied with fuel mixture of higher pressure than would be the case if the check valve was not present. It is assumed that this higher pressure results in more effective purging or flushing of the cylinder as the second piston moves towards its bottom centre position and both the induction port 8 and the exhaust port 9 are opened in conjunction therewith. Another contributing factor is that because the fuel mixture produced in the carburettor 36 flows through the pipe 33 in addition to flowing through the first crank-housing, the second crank-housing will receive a highly homogenous fuel/air mixture. According to one preferred embodiment of the invention, an air supply passage 39 extends along the length of the pipe 33 and functions to deliver air at atmospheric pressure to the fuel mixture in the pipe 33. The air supply passage 39 will conveniently include a valve 40 for regulating the air pressure. The air pressure will preferably be in the order of 1.05 to 1.5 bar. According to a further embodiment, the engine includes a compressor 38, or an impeller, which functions to generate said compressed air and which is driven by the engine. The compressor 38 is suitably mounted adjacent the flywheel of the engine. An outlet passage 41 extending from the compressor is connected to an inlet passage 42 of the valve 40. It has been found that emissions are markedly reduced, when compressed air is delivered to the pipe 33 containing the gas mixture. It is thought the reason for this is the same as that explained above, namely that purging or flushing of the cylinder is improved. According to one preferred embodiment, the induction port 8, or induction ports, is/are positioned so as to be fully open when the first piston 2 belonging to the first crank-housing 6 is closed to or is at its bottom centre position. According to another preferred embodiment, the exhaust port 9, or exhaust ports, is/are positioned so as to be fully open when the second piston 12 belonging to the second crank- housing 10 is closed to or in its bottom centre position. Because the crankshafts are interconnected, a flywheel 37 may be mounted on solely one of the crankshafts 4, in accordance with a further embodiment. In another embodiment, one of said crankshafts may form a drive shaft. Figure 5 illustrates an alternative embodiment with respect to the connection between the crankshafts. This embodiment includes two cog belts 22, 23 which each coacts with a crankshaft and a belt wheel 24, 25 which is fixed to an output drive gear 26. The crankshafts rotate in mutually the same direction in this embodiment. Figure 6 shows another embodiment with respect to the connection of the crankshafts. In the Figure 6 embodiment, the crankshafts are connected mechanically by means of respective cog wheels 27, 28 and cog wheels 29, 30 and a common shaft 31 extending between the cog wheels 28, 29. The cog wheels are bevelled and the crankshafts rotate in mutually opposite directions in the case of this embodiment. Depending on design, it is conceivable to provide a cog wheel on each crankshaft and for said cogs to be in immediate engagement with each other. The crankshafts will also rotate in opposite directions in this case. Figures 3a-3e illustrate a cycle that corresponds to the cycle illustrated in Figures 4a-4e, but with the sole difference that the crankshafts rotate in mutually opposite direc- tions. These Figures have not been provided with reference numbers or signs, for the sake of simplicity. In the case of the inventive engine, the distance between induction port and exhaust port is very long in comparison with conventional two-stroke engines, and there is delivered to the cylinder an homogenous fuel mixture at a pressure that is higher than that used with conventional two-stroke engines. This results in very low emissions of non-combusted fuel mixture and of CO and HC, or completely eliminates such emissions. This means, in turn, that a two-stroke engine can be made to achieve essentially complete combustion, by the person skilled in this art making typical optimizations with respect to the design of the induction port(s) and exhaust port(s) , the shape of the upper side of the piston, sparking plug positions, the optional addition of compressed air, etc. In addition, the construction of an inventive two-stroke engine is simpler than that of a conventional two-stroke engine that includes two cylinders. Furthermore, the engine is balanced-out, due to movements of the pistons towards and away from each other. Both crank-housings will be lubricated, by virtue of the fact that fuel mixture containing two-stroke oil will flow in through the first crank-housing 6 from the carburettor, and from there to the second crank-housing 10, via said pipe, and then into the cylinder. Although the invention has been described above with reference to a number of schematically illustrated drawings, it will be understood that the person skilled in this art will be able to make many modifications without departing from the inventive concept. The invention shall not therefore be considered restricted to the aforedescribed exemplifying embodiments, since variations can be made within the scope of the following claims.

Claims: Claims 1. A two-stroke internal combustion engine that comprises a cylinder, a piston, a connecting rod connected between a crankshaft and said piston, an inlet (5) to a crank-housing (6) for fuel mixture from a carburettor, and a passage between crank-housing and an induction port in the cylinder wall, and an exhaust port in said cylinder wall, said exhaust port being in connection with the surroundings, wherein the engine includes a cylinder (1) which is common to two pistons (2,12) which move towards and away from each other, wherein the engine includes a crank-housing (6,10) at both ends of the cylinder (1), wherein each crank-housing (6,10) accommodates a crankshaft (4,11) which is connected to respective pistons (2,12) through the medium of a piston rod (3,13), wherein the crankshafts (4,11) are interconnected mechanically so that both pistons (2,12) will move simultaneously towards their top centre positions and also move simultaneously to their bottom centre positions, and wherein a carbu- rettor (32) is connected to the first crank-housing (6), characterized by the combination in which only a second (10) of the crank-housings is connected to said induction port (8) via a passage (7) ; in that said exhaust port (9) is positioned for coaction with the piston (2) that belongs to the first of said crank-housings (6) ; in that a pipe (33) extends between the first crank-housing (6) and the second crank- housing (10) for transportation of fuel mixture from the first crank-housing to the second crank-housing; and in that a check valve (34) is provided between the first crank- housing (6) and the inlet end of the pipe (33) . 2. An internal combustion engine according to Claim 1, characterized by a supply air passage (39) which extends along the length of the pipe (33) and which functions to supply air to the fuel mixture in said tube at a pressure above atmospheric pressure. 3. An internal combustion engine according to Claim 2, characterized in that said compressed air has a pressure of about 1.05 to 1.5 bar. 4. An internal combustion engine according to Claim 2 or 3 , characterized by a compressor (38) , or an impeller, for generating said compressed air, said compressor being driven by the internal combustion engine. 5. An internal combustion engine according to Claim 1, 2, 3 or 4, characterized in that said induction port (8), or induction ports, is/are positioned so as to be fully open when said second piston (12) belonging to said second crank- housing (10) is close to or in its bottom centre position. 6. An internal combustion engine according to Claim 1, 2, 3, 4 or 5, characterized in that said exhaust port (9), or exhaust ports, is/are positioned so as to be fully open when said first piston (2) belonging to said first crank-housing (4) is close to or in its bottom centre position. 7. An internal combustion engine according to Claim 1, 2, 3, 4, 5 or 6, characterized in that said crankshafts (4,11) are interconnected mechanically by means of a cog belt (14) or chain. 8. An internal combustion engine according to Claim 1, 2,3,4, 5 or 6, characterized in that said crankshafts (4,11) are connected mechanically by means of cog wheels (27-30) and a possible shaft (31) .

Inventors: KARLSSON HANS, KARLSSON, HANS
Applicants: KARLSSON HANS, KARLSSON, HANS
Application year: 1998
Main classification: F02B25
IPC codes: F02B25, F02B75