The invention relates to a two-stroke engine comprising a first work cylinder, a sec ond work cylinder and a crankshaft, and the first work cylinder comprises a first work chamber and a first work piston and the second work cylinder comprises a second work chamber and a second work piston.

BACKGROUND

A two-stroke engine is a type of internal combustion engine which completes a power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time. Many two-stroke engines, such as common small gasoline-powered engines, are lubricated by a fuel mixture. Lu brication oil is mixed in with their fuel beforehand, in a ratio of around 1 :50. All that oil then forms emissions, either by being burned in the engine or as oily droplets in the exhaust. This create more exhaust emissions, particularly hydrocarbons, than four-stroke engines of comparable power output. The combined opening time of the intake and exhaust ports in some 2-stroke designs can also allow some amount of unburned fuel vapours to exit in the exhaust stream. Also, the high combustion tem peratures may also give NOx emissions. Patent publication US2807249 discloses a two-stroke engine having two work cyl inders. This kind of an engine has similar drawbacks as was described earlier.

There is a clear need for an engine where harmful emissions can be reduced and still maintain the efficiency of the engine. BRIEF DESCRIPTION

The object of the invention is a solution that can significantly reduce the disad vantages and drawbacks of the prior art. In particular, the object of the invention is a solution where a two-stroke engine is efficient and emissions are reduced.

The objects of the invention are attained with a device that is characterised by what is stated in the independent patent claim. Some advantageous embodiments of the invention are disclosed in the dependent claims. The invention is a two-stroke engine having two work cylinders: a first work cylinder and a second work cylinder, and two injection cylinders: a first injection cylinder and a second injection cylinder, for injecting air for combustion processes in the work cylinders. The work cylinders are in opposite phases when the engine is in use. The injection cylinders are adjacent to the work cylinders. The first injection cylinder com prises a first fuel compression piston and the second injection cylinder comprises a second fuel compression piston. When the first injection cylinder compress air to the first work cylinder, the first fuel compression piston compress fuel to the second work cylinder, and when the second injection cylinder compress air to the second work cylinder, the second fuel compression piston compress fuel to the first work cylinder.

When reference is made in the text to the upper or the lower parts or respective directions such as down or up, a situation is described in which the engine according to the invention is in use. Also, when reference is made to the positions of the pis tons, they are given in relation to the crankshaft. Up is away from the crankshaft, and low is near the crankshaft.

In one embodiment of the invention is a two-stroke engine comprising a first work cylinder, a second work cylinder and a crankshaft, and the first work cylinder com prises a first work chamber and a first work piston and the second work cylinder comprises a second work chamber and a second work piston. In one advantageous embodiment of the invention, the first work cylinder, the second work cylinder and the crankshaft are configured in such a way that the first work cylinder and the sec ond work cylinder are in opposite phases when the engine is in use. The engine further comprises a first injection cylinder and a second injection cylinder and the injection cylinders are configured to compress air. The first injection cylinder comprises a first injection chamber and a first injection piston and the second injection cylinder comprises a second injection chamber and a second injection piston, and the first injection cylinder is adjacent to the first work cylinder and the second injection cylinder is adjacent to the second work cylinder. The first injection cylinder, the second injection cylinder and the crankshaft are configured in such a way that the injection cylinder and corresponding adjacent work cylinder are in opposite phases when the engine is in use. Between the first injection chamber and the first work chamber is a first air channel and between the second injection chamber and the second work chamber is a second air channel. The engine further comprises a first fuel chamber and a second fuel chamber, and between the first fuel chamber and the second work chamber is a first fuel channel and between the second fuel chamber and the first work chamber is a second fuel channel. On the first injection piston is a first fuel compression piston and on the second injection piston is a sec ond fuel compression piston, and when the engine is in use the first fuel compres sion piston is configured to compress the fuel in the first fuel chamber and the sec ond fuel compression piston is configured to compress the fuel in the second fuel chamber. The fuel chambers and the fuel channels are configured in such a way that the compressed fuel flows through the first fuel channel to the second work chamber and through the second fuel channel to the first work chamber.

In one embodiment the first work cylinder and the second work cylinder are on op posite sides compared to the crankshaft. This feature increases the efficiency of the engine and makes optimization and manufacturing of the engine simpler.

In a second embodiment the first work cylinder has a top of the first work cylinder and the second work cylinder has a top of the second work cylinder, and the active area of the first work chamber is between the first work piston and the top of the first work cylinder and the active area of the second work chamber is between the sec ond work piston and the top of the second work cylinder, and the top of the first work cylinder comprises a first fuel outlet and the top of the second work cylinder com prises a second fuel outlet, and the second fuel channel is connected to the first fuel outlet and the first fuel channel is connected to the second fuel outlet. In a third embodiment the first fuel outlet comprises a first pressure valve and the second fuel outlet comprises a second pressure valve. By the term ‘the active area of the work chamber’ it is meant the area where the combustion processes take place.

In a fourth embodiment the pressure valves are mechanical.

In a fifth embodiment the pressure valves are operated electrically.

In a sixth embodiment the engine comprises a fuel transfer system, and the first fuel chamber comprises a first fuel chamber outlet and the second fuel chamber comprises a second fuel chamber outlet and the fuel chamber outlets are connected to the fuel transfer system, and the first fuel chamber outlet is configured to release fuel from the fuel transfer system into the first fuel chamber when the first fuel compression piston is moving towards the crankshaft, and the second fuel chamber out let is configured to release fuel from the fuel transfer system into the second fuel chamber when the second fuel compression piston is moving towards the crank shaft. In a seventh embodiment the first work cylinder comprises a first air inlet and a first air outlet and the second work cylinder comprises a second air inlet and a second air outlet, and the first air inlet is connected to the first air channel and the second air inlet is connected to the second air channel, and the first work piston is configured to close and open the first air inlet and the first air outlet when the first work piston is moving and the second work piston is configured to close and open the second air inlet and the second air outlet when the second work piston is moving, and the first air inlet is configured to release pressurized air into the first work chamber and the second air inlet is configured to release pressurized air into the second work chamber. In an eighth embodiment the distance between the first air outlet and the longitudinal axis of the crankshaft is greater than the distance between the first air inlet and the longitudinal axis of the crankshaft, and the distance between the sec ond air outlet and the longitudinal axis of the crankshaft is greater than the distance between the second air inlet and the longitudinal axis of the crankshaft, i.e. the air outlet opens before the air inlet opens when the work piston is moving towards the crankshaft. In a nineth embodiment the work piston is configured to close the air outlet before the fuel channel releases fuel into the work chamber.

In a tenth embodiment the opening of the first air channel in the first injection cham ber is closer to the longitudinal axis of the crankshaft than the opening of the first air channel in the first work chamber, and the opening of the second air channel in the second injection chamber is closer to the longitudinal axis of the crankshaft than the opening of the second air channel in the second work chamber.

In an eleventh embodiment the engine comprises an air transfer arrangement, and the first injection cylinder comprises a first air opening and the second injection cyl inder comprises a second air opening, and the air openings are connected to the air transfer arrangement, and the first air opening is closer to the longitudinal axis of the crankshaft than the opening of the first air channel in the first injection chamber, and the second air opening is closer to the longitudinal axis of the crankshaft than the opening of the second air channel in the second injection chamber.

In a twelfth embodiment the engine comprises a second set of work cylinders; a third work cylinder and a fourth work cylinder, and the second set of work cylinders is positioned in a corresponding manner to the first work cylinder and the second work cylinder, and the first injection cylinder is configured to compress air for the third work cylinder and fuel for the fourth cylinder, and the second injection cylinder is configured to compress air for the fourth work cylinder and fuel for the third cylin der. In a thirteenth embodiment the engine comprises a crankshaft chamber and when the engine is in use the crankshaft chamber is configured to contain lubrication oil. In a fourteenth embodiment the work chambers and the injection chambers are iso lated from the crankshaft chamber. It is an advantage of the invention that it provides a significantly cleaner engine than prior art two-strike engines.

One advantage of the invention is that it improves efficiency of the two-strike engine.

DESCRIPTIONS OF THE FIGURES In the following, the invention is described in detail. The description refers to the accompanying drawings, in which

Figure 1 shows an example of an engine according to an embodiment,

Figure 2 shows a second example of a device according to an embodiment, Figure 3a shows the engine presented in Figure 1 , Figure 3b shows an enlarged part of the engine presented in Figure 3a,

Figure 4a shows a stroke position of the engine presented in Figure 1 ,

Figure 4b shows a second stroke position of the engine presented in Figure 1 Figure 4c shows a third stroke position of the engine presented in Figure 1 , and Figure 4d shows a fourth stroke position of the engine presented in Figure 1 .

DETAILED DESCRIPTIONS OF THE FIGURES

The embodiments in the following description are given as examples only and some one skilled in the art can carry out the basic idea of the invention also in some other way than what is described in the description. Though the description may refer to a certain embodiment or embodiments in several places, this does not mean that the reference would be directed towards only one described embodiment or that the described characteristic would be usable only in one described embodiment. The individual characteristics of two or more embodiments may be combined and new embodiments of the invention may thus be provided.

Figure 1 shows an embodiment of an engine 100 that works in the two-strike cycle. The engine comprises a first work cylinder 101 , a second work cylinder 105 and a crankshaft 102. There is a crankshaft chamber 128 where the crankshaft is placed. The first work cylinder comprises a first work chamber 103 and a first work piston 104. The second work cylinder comprises a second work chamber 105 and a sec ond work piston 106. The work pistons move inside the work chambers. The first work cylinder has a top of the first work cylinder 122 and the second work cylinder has a top of the second work cylinder 123. In this embodiment the first work cylinder and the second work cylinder are on opposite sides of the crankshaft. There are embodiments where the work cylinders are positioned in a different positions. For example, the angle between the longitudinal axis of the work cylinders can be 90 degrees. The work cylinders and the crankshaft are configured in such a way that when the engine is running, the work cylinders are in opposite phases, i.e. when the first work piston is in its uppermost position (nearest the top of the first work cylin der), the second work piston is in its lowermost position (nearest the crankshaft), and also, the directions of the movements of the work pistons are opposite. When the work piston moves away from the crankshaft, it compresses air and fuel in the work chamber between the work piston and the top of the work cylinder. The compressed air-fuel mixture is ignited with an ignition device, such as a spark plug, and the resulting explosion drives the work piston towards the crankshaft. In the wall of the work cylinder is an air outlet. The air outlet is uncovered when the work piston is moving towards the crankshaft, and pressure in the work cylinder drives the ex haust gases out of the work chamber. The downward movement (i.e. towards the crankshaft) of the work piston rotates the crankshaft and this rotation can be used as a power source.

The engine 100 further comprises a first injection cylinder 108 and a second injection cylinder 111. The first injection cylinder comprises a first injection chamber 109 and a first injection piston 110 and the second injection cylinder comprises a second injection chamber 111 and a second injection piston 113. The injection pistons move inside the injection chambers. The injection cylinders are for compressing air for the work cylinders. The movement of the injection pistons is provided by the crankshaft 102, i.e. the injection pistons are connected to the crankshaft. The first injection cylinder is adjacent to the first work cylinder 101 and the second injection cylinder is adjacent to the second work cylinder 105. The longitudinal axis of the injection cylinder is parallel to the longitudinal axis of the work cylinder beside the injection cylinder, i.e. the adjacent work cylinder. The first work cylinder 101 , the second work cylinder 105, the first injection cylinder, the second injection cylinder and the crank shaft are configured in such a way that the injection cylinder and corresponding adjacent work cylinder are in opposite phases when the engine is in use.

Between the first injection chamber 109 and the first work chamber 103 is a first air channel 114. Between the second injection chamber 112 and the second work chamber 106 is a second air channel 115. The first work cylinder 101 comprises a first air inlet and a first air outlet. The second work cylinder 105 comprises a second air inlet and a second air outlet. The first air inlet is connected to the first air channel 114 and the second air inlet is connected to the second air channel 115. The first work piston 104 is configured to close and open the first air inlet and the first air outlet when the first work piston is moving. The second work piston 107 is configured to close and open the second air inlet and the second air outlet when the second work piston is moving. The first air inlet is configured to release pressurized air into the first work chamber 103 and the second air inlet is configured to release pressur ized air into the second work chamber 106. The distance between the first air outlet and the longitudinal axis of the crankshaft 102 is greater than the distance between the first air inlet and the longitudinal axis of the crankshaft, and the distance between the second air outlet and the longitudinal axis of the crankshaft is greater than the distance between the second air inlet and the longitudinal axis of the crankshaft. This means that the air outlet opens before the air inlet opens when the work piston is moving towards the crankshaft. When the air inlet opens, the pressurized air in the injection chamber is released and exhaust gases are removed from the work chamber via the air outlet. Thus the exhaust gas removing is significantly improved.

In some embodiments the opening of the first air channel 119 in the first injection chamber 109 is closer to the longitudinal axis of the crankshaft 102 than the opening of the first air channel in the first work chamber 103, and the opening of the second air channel 115 in the second injection chamber 112 is closer to the longitudinal axis of the crankshaft 102 than the opening of the second air channel in the second work chamber 106. In some embodiments the engine 100 comprises an air transfer arrangement, and the first injection cylinder 108 comprises a first air opening and the second injection cylinder 111 comprises a second air opening. The air openings are connected to the air transfer arrangement. The first air opening is closer to the lon gitudinal axis of the crankshaft than the opening of the first air channel 114 in the first injection chamber, and the second air opening is closer to the longitudinal axis of the crankshaft than the opening of the second air channel 115 in the second injection chamber. These features prevent the exhaust gases from entering into the injection chambers.

The engine 100 further comprises a first fuel chamber 116 and a second fuel cham ber 117. Between the first fuel chamber and the second work chamber is a first fuel channel 118 and between the second fuel chamber and the first work chamber is a second fuel channel 119. In some embodiments the top of the first work cylinder comprises a first fuel outlet 124 and the top of the second work cylinder comprises a second fuel outlet 125, and the second fuel channel 119 is connected to the first fuel outlet and the first fuel channel 118 is connected to the second fuel outlet. On the first injection piston 110 is a first fuel compression piston 120 and on the second injection piston 113 is a second fuel compression piston 121 . The fuel compression pistons are configured to compress fuel in the fuel chambers. The fuel chambers and the fuel channels are configured in such a way that the compressed fuel flows through the first fuel channel to the second work chamber and through the second fuel channel to the first work chamber. Because the work cylinders are in opposite phases, this means the fuel enters into work chamberwhen the work piston is rising, i.e. going towards the top of the work cylinder. The first fuel outlet 124 comprises a first pressure valve and the second fuel outlet 125 comprises a second pressure valve. In some embodiments these pressure valves release fuel to the work chamber when the pressure in the fuel channel exceeds some pressure value. In some embodiments the pressure valves are mechanical. In some embodiments the pres sure valves are operated electrically. The work pistons are configured to close the air outlets before the fuel channels releases fuel into the work chambers thus pre venting unburned fuel escaping from the work chamber. The fuel compression pis tons and fuel chambers are configured in such a way that the fuel cannot enter into the injection chambers. In this embodiment the fuel compression pistons are shaft like cylinders which are configured to fit into the fuel chambers. Of course, fuel com pression pistons can be implemented in different ways. What is essential is that the fuel compression piston produces pressure into the fuel chamberwhen the injection piston is moving away from the crankshaft and compressing air for the adjacent work cylinder. The pressurized fuel is feed to the opposing work cylinder via the fuel channel.

The engine 100 comprises a fuel transfer system, and the first fuel chamber 116 comprises a first fuel chamber outlet 126 and the second fuel chamber 117 com prises a second fuel chamber outlet 127. The fuel chamber outlets are connected to the fuel transfer system, and the first fuel chamber outlet is configured to release fuel from the fuel transfer system into the first fuel chamber when the first fuel com pression piston 120 is moving towards the crankshaft 102, i.e. away from the first fuel chamber. The second fuel chamber outlet is configured to release fuel from the fuel transfer system into the second fuel chamber when the second fuel compres sion piston 121 is moving towards the crankshaft.

Figure 2 shows a second embodiment of an engine 200. The engine comprises a first work cylinder 201 , a second work cylinder 205, a first injection cylinder 208, a second injection cylinder 211 , a first fuel channel 218 and a second fuel channel 219. The first work cylinder and the first injection cylinder are beside each other, and the second work cylinder and the second injection cylinder are beside each other. In this embodiment the first work cylinder and the first injection cylinder are on the opposing side of the engine than the second work cylinder and the second injection cylinder. The first fuel channel leads fuel to the second work cylinder and the second fuel channel leads fuel to the first work cylinder. The injection cylinders provide pres surized air to the adjacent work cylinder and pressurized fuel to the opposing work cylinder. It must be noted that in some embodiments the work cylinders may be positioned differently in relation to the crankshaft. In that case the term ‘opposing’ means the work cylinder which is in the same phase (or near the same phase) as the injection cylinder. Also, it can be defined that the injection cylinder provides fuel to the different work cylinder than the work cylinder the injection cylinder provides air. Also, it must be noted that there are many embodiments for positioning the fuel channels. What is presented in this embodiment is an example.

Figure 3a shows the engine 100 presented in Figure 1. The area A is enlarged in the Figure 3b. The area A illustrates the details of the first injection cylinder 108.

On the top of the first injection piston is the first fuel compression piston 120. In the Figure 3b the first injection piston is in the uppermost position i.e. farthest from the crankshaft 102. The first fuel compression piston has compressed the fuel from the first fuel chamber 116 via the first fuel channel 118 to the second work cylinder. The first injection piston has closed the first air channel 114. The compressed air from the first injection cylinder 108 has cleared the first work chamber 103. When the first work piston 104 rises, i.e. moves farther from the crankshaft, it closes the first air channel, for preventing air and fuel flowing backwards to the first injection chamber from the first work cylinder 101 . When the first injection piston is going downwards, the pressure inside the first fuel chamber 116 decreases and fuel starts to flow into it from the first fuel chamber outlet. The crankshaft chamber 128 is isolated from the from the work chamber 103 and the injection chamber.

Figures 4a, 4b, 4c and 4d show the phases of the engine 100. The engine comprises the first work cylinder 101 , the second work cylinder 105, the first injection cylinder 108 and the second injection cylinder. The movements of the pistons are exagger ated for making the working of the engine more clear.

In the figure 4a the first work piston of the first work cylinder 101 is in the uppermost position, and the second work piston of the second work cylinder 101 is in the lowest position. Up and low means here the position in relation to the crankshaft. The first injection piston of the first injection cylinder 108 is going upwards and air flows into it from the first air opening. The second injection piston of the second injection cylinder 111 is going downwards. The compressed air and fuel in the first work cylinder is ignited and it explodes.

In the figure 4b the first work piston moves towards the crankshaft due the explosion of fuel in the first work cylinder 101. The first injection piston rises and the first fuel compression piston compress the fuel in the first fuel chamber. At the same time air is compressed in the first injection chamber. The first air channel is still closed by the first work piston. The compressed fuel from the first fuel chamber is released to the second work cylinder via the first fuel channel. The second work piston rises and compress air and fuel in the second work chamber.

In the figure 4c the first work piston has moved to the lowest position and has opened the first air channel between the first injection cylinder 108 and the first work cylinder 101. The compressed air from the first injection cylinder has cleaned the exhaust gases away from the first work chamber. The compressed air and fuel mixture in the second work chamber is ignited. Airflows into the second injection cylin der 111 from the second air opening in the wall of the second injection chamber. The first injection piston starts to move downwards, and the second injection piston starts to move upwards and will close the second air opening.

In the figure 4d the second fuel compression piston compress the fuel in the second fuel chamber when the second injection piston moves upwards (away from the crankshaft) and when the fuel is compressed enough, the fuel flows to the second fuel channel and trough it to the first work cylinder 101 . The first work piston starts to compress air and fuel mixture in the first work chamber. The ignited air and fuel mixture in the second work chamber drives the second work piston towards the crankshaft. And thus the two-strike cycle continues.

Some advantageous embodiments of the engine according to the invention have been described above. The invention is however not limited to the embodiments described above, but the inventive idea can be applied in numerous ways within the scope of the claims.