Internal combustion engine

Abstract

An internal combustion engine including a first set of cylinders includes: a first two-stroke compression cylinder housing a first compression piston connected to a first crank shaft; an intermediate two-stroke compression cylinder housing an intermediate compression piston, wherein the second two-stroke compression cylinder is configured to receive compressed gas from the first two-stroke compression cylinder; and a first four-stroke combustion cylinder housing a first combustion piston, wherein the first four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke compression cylinder; wherein the internal combustion engine further includes a second set of cylinders including: a second two-stroke compression cylinder housing a second compression piston connected to the first crank shaft, wherein the second two-stroke compression cylinder is configured to provide compressed gas to the intermediate two-stroke compression cylinder; and a second four-stroke combustion cylinder housing a second combustion piston, wherein the second four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke compression cylinder; wherein each one of the intermediate compression piston and the first and second combustion pistons are connected to a second crank shaft, the second crank shaft being configured to rotate with a speed of at least twice the speed of the first crank shaft.

Claims

1. An internal combustion engine comprising a first set of cylinders comprising: a first two-stroke compression cylinder housing a first compression piston connected to a first crank shaft; an intermediate two-stroke compression cylinder housing an intermediate compression piston, wherein the intermediate two-stroke compression cylinder is configured to receive compressed gas from the first two-stroke compression cylinder; and a first four-stroke combustion cylinder housing a first combustion piston, wherein the first four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke-compression cylinder; wherein the internal combustion engine further comprises a second set of cylinders comprising: a second two-stroke compression cylinder housing a second compression piston connected to the first crank shaft, wherein the second two-stroke compression cylinder is configured to provide compressed gas to the intermediate two-stroke compression cylinder; and a second four-stroke combustion cylinder housing a second combustion piston, wherein the second four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke compression cylinder; wherein each one of the intermediate compression piston and the first and second combustion pistons are connected to a second crank shaft, the second crank shaft being configured to rotate with a speed of at least twice the speed of the first crank shaft, wherein the first compression piston and the second compression piston are arranged in a 180 degrees crank angle offset in relation to each other, such that the first compression piston is configured to reach an upper end position within the first compression cylinder when the second compression piston reaches a lower end position within the second compression cylinder.

2. The internal combustion engine according to claim 1, wherein the first combustion piston and the second combustion piston are positioned to reach an upper end position within the respective combustion cylinder approximately simultaneously and in such a way that the first combustion piston is configured to be ignited at an upper end position within the first combustion cylinder when the second combustion piston is in an upper end position of the second combustion cylinder for initiation of intake of fuel therein.

3. The internal combustion engine according to claim 1, wherein each of the cylinders comprises valved inlet ports and valved outlet port for controlling fluid transportation into and out from the respective cylinders.

4. The internal combustion engine according to claim 1, wherein each one of the first and second compression cylinders are arranged in fluid communication with the intermediate compression cylinder by means of a respective first and second passageway.

5. The internal combustion engine according to claim 4, wherein each of the first, second, third and fourth passageways are provided with cooling means for cooling the fluid passing there through.

6. The internal combustion engine according to claim 1, wherein the intermediate compression cylinder is in fluid communication with the first and second combustion, cylinders by means of a respective third and fourth passageway.

7. The internal combustion engine according to claim 1, wherein the first compression cylinder and the second compression cylinder are one and the same compression cylinder, and the first compression piston and the second compression piston are one and the same compression piston, wherein the compression cylinder is configured to provide a first compression when the compression piston reaches an upper position within the compression cylinder, and to provide a second compression when the compression piston reaches a lower position within the compression cylinder.

8. A vehicle comprising the internal combustion as claimed in claim 1.

9. An internal combustion engine comprising a first set of cylinders comprising: a first two-stroke compression cylinder housing a first compression piston connected to a first crank shaft; an intermediate two-stroke compression cylinder housing an intermediate compression piston, wherein the intermediate two-stroke compression cylinder is configured to receive compressed gas from the first two-stroke compression cylinder; and a first four-stroke combustion cylinder housing a first combustion piston, wherein the first four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke-compression cylinder; wherein the internal combustion engine further comprises a second set of cylinders comprising: a second two-stroke compression cylinder housing a second compression piston connected to the first crank shaft, wherein the second two-stroke compression cylinder is configured to provide compressed gas to the intermediate two-stroke compression cylinder; and a second four-stroke combustion cylinder housing a second combustion piston, wherein the second four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke compression cylinder; wherein each one of the intermediate compression piston and the first and second combustion pistons are connected to a second crank shaft, the second crank shaft being configured to rotate with a speed of at least twice the speed of the first crank shaft, and further comprising: a first two-stroke expansion cylinder housing a first expansion piston connected to the first crank shaft, the first two-stroke expansion cylinder being configured to receive exhaust gas from the first four-stroke combustion cylinder; and a second two-stroke expansion cylinder housing a second expansion piston connected to the first crank shaft, the second two-stroke expansion cylinder being configured to receive exhaust gas from the second four-stroke combustion cylinder.

10. The internal combustion engine according to claim 9, wherein the first expansion piston and the second expansion piston are arranged in a 180 degrees crank angle offset in relation to each other, such that the first expansion piston is configured to reach an upper end position within the first expansion cylinder when the second expansion piston reaches a lower end position within the second expansion cylinder (114.

11. The internal combustion engine according to claim 9, wherein the first expansion piston and the first compression piston are arranged in a 90 degrees crank angle offset in relation to each other, such that the first compression piston is configured to reach an upper end position within the first compression cylinder when the first expansion piston is located in a mid-portion within the first expansion cylinder.

12. The internal combustion engine according to claim 9, wherein a first and a second compression con rod is connected to the first and second compression piston, respectively, and a first and a second expansion con rod is connected to the first and second expansion piston, respectively, wherein the first compression con rod and the first expansion con rod is connected to a first crank pin of the first crank shaft, and wherein the second compression con rod and the second expansion con rod is connected to a second crank pin of the first crank shaft.

13. The internal combustion engine according to claim 9, wherein the first and second compression cylinders are positioned in parallel in relation to each other and the first and second expansion cylinders are positioned in parallel in relation to each other, wherein the compression cylinders and the expansion cylinders are arranged in a V-shaped configuration in relation to each other.

14. The internal combustion engine according to claim 9, wherein the first combustion cylinder is in fluid communication with the first expansion cylinder by means of a fifth passageway.

15. The internal combustion engine according to claim 9, wherein the second combustion cylinder is in fluid communication with the second expansion cylinder by means of a sixth passageway.

16. An internal combustion engine comprising a first set of cylinders comprising: a first two-stroke compression cylinder housing a first compression piston connected to a first crank shaft; an intermediate two-stroke compression cylinder housing an intermediate compression piston, wherein the intermediate two-stroke compression cylinder is configured to receive compressed gas from the first two-stroke compression cylinder; and a first four-stroke combustion cylinder housing a first combustion piston, wherein the first four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke-compression cylinder; wherein the internal combustion engine further comprises a second set of cylinders comprising: a second two-stroke compression cylinder housing a second compression piston connected to the first crank shaft, wherein the second two-stroke compression cylinder is configured to provide compressed gas to the intermediate two-stroke compression cylinder; and a second four-stroke combustion cylinder housing a second combustion piston, wherein the second four-stroke combustion cylinder is configured to receive compressed gas from the intermediate two-stroke compression cylinder; wherein each one of the intermediate compression piston and the first and second combustion pistons are connected to a second crank shaft, the second crank shaft being configured to rotate with a speed of at least twice the speed of the first crank shaft, and wherein the intermediate compression piston and the first combustion piston are arranged in a 180 degrees crank angle offset in relation to each other, such that the intermediate compression piston is configured to reach an upper en position within the intermediate compression cylinder when the first combustion piston reaches a lower end position within the first combustion cylinder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments of the present invention, wherein:

(2) FIG. 1 is a side view of a vehicle comprising an internal combustion engine according to an example embodiment of the present invention;

(3) FIG. 2 is a perspective view of the internal combustion engine according to an example embodiment of the present invention;

(4) FIG. 3 is a schematic top view of the interconnection between the cylinders in the example embodiment depicted in FIG. 2; and

(5) FIGS. 4-7 schematically illustrate the four steps of a complete cycle of the internal combustion engine according to an example embodiment of the present invention.

DETAIL DESCRIPTION

(6) The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference character refer to like elements throughout the description.

(7) With particular reference to FIG. 1, there is provided a vehicle 1 with an internal combustion engine 100 according to the present invention. The vehicle 1 depicted in FIG. 1 is a truck for which the inventive internal combustion engine 100, which will be described in detail below, is particularly suitable for.

(8) Turning to FIG. 2 in combination with FIG. 3, which illustrate an internal combustion engine 100 according to an example embodiment of the present invention. The cylinders housing the respective piston have been omitted from FIG. 2 for simplicity of understanding the invention and the piston configuration, and can instead be found in the schematic top view of FIG. 3.

(9) The internal combustion engine 100 comprises a first compression cylinder 102 which is in fluid communication with an intermediate compression cylinder 104 by means of a first passageway 202, a second compression cylinder 106 which is in fluid communication with the intermediate compression cylinder 104 by means of a second passageway 204. The intermediate compression cylinder 104 is in turn in fluid communication with a first combustion cylinder 108 by means of a third passageway 206 and in fluid communication with a second combustion cylinder 10 by means of a fourth passageway 208. The first combustion cylinder 108 is further in fluid communication with a first expansion cylinder 112 by means of a fifth passageway 210 and the second combustion cylinder 110 is in fluid communication with a second expansion cylinder 114 by means of a sixth passageway 212. The first 202, second 204, third 206 and the fourth 208 passageways are, in the example embodiment, provided with cooling means (not shown) for cooling the gases transported there through.

(10) Furthermore, the first 102 and second 106 compression cylinder houses a first 122 and a second 126 compression piston, respectively, which both are connected to a first crank shaft 150 by means of a respective connecting rod. The first 112 and second 114 expansion cylinder houses a first 132 and a second 134 expansion piston, respectively, which both are connected to the first crank shaft 50 by means of a respective connecting rod. As depicted in FIG. 2, the first compression piston 122 and the first expansion piston 32 are connected to a first crank pin 152 of the first crank shaft 150 and arranged in 90 degrees configuration in relation to each other. Likewise, the intermediate compression piston 124 and the second expansion piston 134 are connected to a second crank pin of the first crank shaft 150 and also arranged in a 90 degrees configuration in relation to each other. It should be readily understood that the 90 degrees configuration serves as an example embodiment and other configurations are of course conceivable. Furthermore, according to the example embodiment depicted in FIG. 2, the first 122 and second 126 compression pistons are positioned in parallel in relation to each other and the first 132 and the second 134 expansion pistons are positioned in parallel in relation to each other.

(11) Moreover, the above described first 108 and second 110 combustion cylinders houses a first 128 and a second 130 combustion piston, respectively, which are both connected to a second crank shaft 154 by means of a respective connecting rod. Also, the intermediate compression cylinder 104 houses an intermediate compression piston 124 which is also connected to the second crank shaft 154 by means of a connecting rod. The first combustion piston 128, the second combustion piston 130 and the intermediate compression piston 124 are hence arranged in parallel to each other.

(12) The second crank shaft 154 is configured, in the example embodiment, to rotate with a speed of a multiple integer of at least two in comparison to the speed of the first crank shaft 150. The following will, for simplicity of understanding, only describe the case where the second crank shaft 154 rotates with twice the speed of the first crank shaft 150. The compression cylinders 102, 104, 106 and the expansion cylinders 112, 114 are two-stroke cylinders, while the combustion cylinders 108 are 110 are four-stroke cylinders. Hereby, the first 122 and second 126 compression pistons, as well as the first 132 and second 134 expansion pistons will complete a full two-stroke cycle when the first 128 and second 130 combustion cylinders completes a full four-stroke cycle. The intermediate compression piston 124 will hence complete two full two-stroke cycles during the same period.

(13) The first crank shaft 150 is connected to the second crank shaft 154 by means of a suitable transmission. The transmission is in the example embodiment depicted in FIG. 2, a gear transmission having a first gear 160 connected to the first crank shaft 150 and a second gear 162 connected to the second crank shaft 154, wherein the gears are in meshed connection with each other. The engine torque is thereafter transmitted to e.g. a gearbox of the vehicle 1.

(14) Moreover, the transmission is further connected to a cam shaft 166 of the internal combustion engine. The cam shaft controls the various valves, which function will be described below, of the different cylinders. There is one single cam shaft controlling the valves for all cylinders of the internal combustion engine in the example embodiment depicted in FIG. 2. This is achievable due to the mutual speed/stroke configurations of the pistons and their respective crank shafts.

(15) In order to describe the motion pattern of the different cylinders and the communication between the different cylinders during use of the internal combustion engine, reference is made to FIGS. 4 to 7, which illustrate a complete cycle of the internal combustion engine.

(16) Starting with FIG. 4, which illustrates a first stage of the cycle, the first compression piston 122 is positioned in a lower end position within the first compression cylinder 102 and in an upward motion towards the upper end position therein. An inlet valve 402 and an outlet valve 404 of the first compression cylinder 102 are both positioned in a closed state.

(17) The intermediate compression piston 124 is positioned in a lower end position within the intermediate compression cylinder 104 and in an upward motion towards an upper end position therein. An inlet valve 406 of the intermediate compression cylinder 104 is positioned in a closed state while an outlet valve 408 of the intermediate compression piston is positioned in an open state to allow compressed gas provided therein to be forced into the first combustion cylinder 108 during the upward motion of the intermediate compression piston 124.

(18) The second compression piston 126 is positioned in an upper end position within the second compression cylinder 106 and in a downward motion towards the lower end position therein. An inlet valve 410 of the second compression cylinder 106 is positioned in an open state allowing gas to enter the second compression cylinder 106 during the downward motion of the second compression piston 126. An outlet valve 412 of the second compression cylinder is positioned in a closed state.

(19) Furthermore, the first combustion piston 128 is positioned in an upper end position within the first combustion cylinder 108 and in a downward motion towards the lower end position therein. An inlet valve 414 of the first combustion cylinder 108 is positioned in an open state to allow compressed gas from the intermediate compression cylinder 104 to be forced into the first combustion cylinder 108 during the downward motion of the first combustion piston 128. An outlet valve 416 of the first combustion cylinder is positioned in a closed state.

(20) Still further, the second combustion piston 130 is positioned in an upper end position within the second combustion cylinder 110 and in a downward motion toward a lower end position therein. An inlet valve 418 and an outlet valve 420 of the second combustion cylinder 110 are both positioned in a closed state. The second combustion cylinder is in this state in a power stroke, i.e. an ignition of the reduced volume within the second combustion cylinder takes place at this stage forcing the second combustion piston 130 downward towards the lower end position within the second combustion cylinder 10.

(21) Moreover, the first expansion piston 132 is positioned in a mid-portion of the first expansion cylinder 112 and in a downward motion towards a lower end position therein. An inlet valve 422 and an outlet valve 424 of the first expansion cylinder are both positioned in a closed state.

(22) Finally, the second expansion piston 134 is positioned in a mid-portion of the second expansion cylinder 114 and in an upward motion towards an upper end position therein. An inlet valve 426 of the second expansion cylinder is positioned in a closed state while an outlet valve 428 of the second expansion cylinder 114 is positioned in an open state to allow expanded exhaust gases provided therein to be expelled out from the second expansion cylinder 114 during the upward motion of the second expansion cylinder 114.

(23) According, to an example embodiment, the first and second expansion cylinders only comprise an outlet valve, respectively, i.e. no inlet valve 422, 426. Hereby, the exhaust gases from the combustion cylinders 108, 110 are provided into the first expansion cylinders 112, 114 via the respective outlet valves 424, 428. Accordingly, the outlet valves 422, 426 each act as inlet valves and as outlet valves for the expansion cylinders.

(24) At a second stage of the cycle, illustrated in FIG. 5, the first compression piston 122 is positioned in a mid-portion of the first compression cylinder 102 and still in an upward motion towards the upper end position therein. The inlet valve 402 of the first compression cylinder 102 is positioned in a closed state while the outlet valve 404 is positioned in an open state to allow compressed gas provided within the first compression cylinder 102 to be forced into the intermediate compression cylinder 104 during the upward motion of the first compression piston 122.

(25) The intermediate compression piston 124 is positioned in the upper end position within the intermediate compression cylinder 104 and in downward motion towards the lower end position therein. The inlet valve 406 of the intermediate compression cylinder 104 is positioned in an open state to allow compressed gas from the first compression cylinder 102 to be forced into the intermediate compression cylinder 102 during the downward motion of the intermediate compression piston 124.

(26) Further, the outlet valve 408 of the intermediate compression piston is positioned in a closed state.

(27) Furthermore, the second compression piston 126 is positioned in a midportion of the second compression cylinder 106 and in a downward motion towards the lower end position therein. The inlet valve 410 of the second compression cylinder 106 is still in an open state to further allow gas to enter into the second compression cylinder 106 during the downward motion of the second compression piston 126. The outlet valve 412 of the second compression cylinder 106 is in a dosed state.

(28) Moreover, the first combustion piston 128 is positioned in the lower end position within the first combustion cylinder 108 and in an upward motion towards the upper end position therein. Both the inlet valve 414 and the outlet valve 416 of the first combustion cylinder 108 are in a closed state such that compression of the compressed gases that entered the first combustion cylinder 108 during the above described first stage of the cycle is compressed therein during the upward motion of the first combustion piston 128.

(29) Turning to the second combustion cylinder 110, the second combustion piston 130 therein is positioned in the lower end position and in an upward motion toward the upper end position within the second combustion cylinder 110. The inlet valve 418 of the second combustion cylinder 110 is in a closed state while the outlet valve 420 is in an open state, thereby forcing exhaust gases, produced during the power stroke described above in relation to the first stage of the cycle, into the second expansion cylinder 114 during the upward motion of the second combustion piston 130.

(30) The first expansion piston 132 is positioned in the lower end position within the first expansion cylinder 112 and in an upward motion towards the upper end position therein. The inlet valve 422 of the first expansion cylinder 112 is in a closed state while the outlet valve 424 is in an open state to allow expanded exhaust gases to be expelled out from the first expansion cylinder during the upward motion of the first expansion piston 132.

(31) The second expansion piston 134 is positioned in the upper end position within the second expansion cylinder 114 and in a downward motion towards the lower end position therein. The inlet valve 426 of the second expansion cylinder 114 is positioned in the open state to allow exhaust gases from the second combustion cylinder 110 to be forced therein during the downward motion of the second expansion cylinder 114. The outlet valve 428 of the second expansion cylinder is in a closed state.

(32) Reference is now made to FIG. 6 in order to describe the third stage of the cycle. Firstly, the first compression piston 122 is positioned in the upper end position within the first compression cylinder 102 and in a downward motion towards the lower end position therein. The inlet valve 402 is positioned in an open state to allow gas to enter the first compression cylinder 102 during the downward motion of the first compression piston 122. The outlet valve 404 of the first compression cylinder 102 is positioned in a closed state.

(33) The intermediate compression piston 124 is positioned in the lower end position within the intermediate compression cylinder 104 and in an upward motion towards the upper end position therein. The inlet valve 406 of the intermediate compression cylinder 104 is positioned in a closed state while the outlet valve 408 is positioned in an open state to allow compressed gas to be forced out from the intermediate compression cylinder 104 and into the second combustion cylinder 110 during the upward motion of the intermediate compression piston 124.

(34) The second compression piston 126 is positioned in the lower end position within the second compression cylinder 106 and in an upward motion towards the upper end position therein. Both the inlet 410 and outlet 412 valves are positioned in a closed state.

(35) Furthermore, the first combustion piston 128 is positioned in the upper end position within the first combustion cylinder 108 and in a downward motion towards the lower end position therein. Both the inlet 414 and the outlet 416 valves are positioned in a closed state and the first combustion cylinder 108 is thus in a power stroke, i.e. an ignition of the reduced volume within the first combustion cylinder 108 takes place at this stage forcing the first combustion piston 128 downward towards the lower end position within the first combustion cylinder 108.

(36) The second combustion piston 130 is positioned in the upper end position within the second combustion cylinder 110 and in a downward motion towards the lower end position therein. The inlet valve 418 of the second combustion cylinder is positioned in an open state to allow compressed gas from the intermediate compression cylinder 104 to enter the second combustion cylinder 110 during the downward motion of the second combustion piston 130. The outlet valve 420 of the second combustion cylinder 110 is positioned in a closed state.

(37) The first expansion piston 132 is positioned in a mid-portion of the first expansion cylinder 112 and in an upward motion towards the upper end position therein. The inlet valve 422 of the first expansion cylinder 112 is positioned in a closed state while the outlet valve 424 is still positioned in an open state to further allow expanded exhaust gas to be expelled out from the first expansion cylinder 112 during the upward motion of the expansion piston 132 towards the upper end position therein.

(38) The second expansion piston 134 is positioned in a mid-portion of the second expansion cylinder 114 and in a downward motion towards the lower end position therein. Both the inlet 426 and the outlet 428 valves are positioned in a closed state and the second expansion cylinder 114 thus, in the downward motion of the second expansion piston 134, expands the exhaust gases forced therein from the second combustion cylinder 110 during the second stage of the cycle.

(39) Finally, reference is made to FIG. 7 in order to describe the fourth stage of the cycle. The first compression piston 122 is positioned in the mid-portion of the first compression cylinder 102 and in a downward motion towards the lower end position therein. The inlet valve 402 of the first compression cylinder 102 is still in the open state to further allow gas to enter the first compression cylinder 102 during the downward motion of the first compression piston 122. The outlet valve 404 is positioned in the closed state.

(40) The intermediate compression piston 124 is positioned in the upper end position within the intermediate compression cylinder 104 and in a downward motion towards the lower end position therein. The inlet valve 406 of the intermediate compression cylinder 104 is positioned in the open state to allow compressed gas from the second compression cylinder 106 to be forced into the intermediate compression cylinder 104 during the downward motion of the intermediate compression piston 124. The outlet valve 408 of the intermediate compression cylinder is positioned in the closed state.

(41) The second compression piston 126 is positioned in a mid-portion of the second compression cylinder 106 and in an upward motion towards the upper end position therein. The inlet valve 410 of the second compression cylinder 106 is positioned in the closed state while the outlet valve 412 is positioned in the open state to allow compressed gas in the second compression cylinder 106 to be forced into the intermediate compression cylinder 104 during the upward motion of the second compression piston 126.

(42) Turning to the combustion cylinders, the first combustion piston 128 is positioned in the lower end position within the first combustion cylinder 108 and in an upward motion towards the upper end position therein. The inlet valve 414 of the first combustion piston is positioned in a closed state while the outlet valve 416 is positioned in the open state to allow exhaust gases from the power stroke described above to be forced into the first expansion cylinder 112 during the upward motion of the first combustion piston 128.

(43) The second combustion piston 130 is positioned in the lower end position within the second combustion cylinder 110 and in an upward motion therein. Both the inlet 418 and the outlet 420 valves are positioned in the closed state. The second combustion piston 130 is hence in an initial compression stage within the second combustion cylinder 110.

(44) The first expansion piston 132 is positioned in the upper end position within the first expansion cylinder 112 and in a downward motion towards the lower end position therein. The inlet valve 422 of the first expansion cylinder 112 is positioned in the open state to allow exhaust gases from the second combustion cylinder 108 to be forced therein and expanded during the downward motion of the first expansion piston 132. The outlet valve 424 is positioned in the closed state.

(45) Finally, the second expansion piston 134 is positioned in the lower end position within the second expansion cylinder 114 and in an upward motion towards the upper end position therein. The inlet valve 426 of the second expansion cylinder 114 is positioned in a closed state while the outlet valve 428 of the second expansion cylinder 114 is positioned in the open state to, during the upward motion of the second expansion piston 134, expel the exhaust gases that was expanded in the second expansion cylinder 114 during the third stage described above.

(46) Although FIGS. 5-7 illustrates that combustion gases from the first 108 and second 110 combustion cylinder are forced into the respective expansion cylinders 112, 114 via the inlet valves 422 and 426, the present invention is equally applicable by having expansion cylinder comprising only one valve. Hereby, the valves 422 and 426 are removed and the combustion gases are provided into the respective expansion cylinder via the outlet valves 424 and 428, which still further expels the expanded gases out from the respective expansion cylinders 112, 114.

(47) It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims. For example, the described opening and closing of the different valves is not strictly limited to the above description, the valve may be arranged in an opened state and in a closed state at either an earlier point in time in relation to the position of the respective piston, or later. Furthermore, it should be readily understood that the gas entering the first or second compression cylinders described above may, for example, be ambient air or other suitable gas.