Method for a combustion machine with two times three strokes

Abstract

A method for a combustion engine has a working cycle of three revolutions of the crankshaft. The method includes: feeding a fuel mixture into a combustion chamber of a cylinder while moving a piston from a second top dead-center to a first bottom dead-center; compressing an air-fuel mixture in the combustion chamber while moving the piston from the first bottom dead-center to a first top dead-center; burning the air-fuel mixture while moving the piston from the first top dead-center to a second bottom dead-center; compressing a gas mixture in the combustion chamber while moving the piston from the second bottom dead-center to the first top dead-center; burning the gas mixture while moving the piston from the first top dead-center to the first bottom dead-center; and expelling the gas mixture from the combustion chamber while moving the piston from the first bottom dead-center to the second top dead-center.

Claims

1. A method for operating a combustion machine, where a working cycle comprises three revolutions of a crankshaft (60) of the combustion machine, and a piston (20) of the combustion machine reaches a first top dead center (OT) twice and a second top dead center (OT) once and reaches a first bottom dead center (UT) twice and a second bottom dead center (UT) once during a working cycle, the first top dead center (OT) and the first bottom dead center (UT) are farther from the crankshaft (60) than the second top dead center (OT) and the second bottom dead center (UT), respectively, the method comprising: feeding a fuel mixture into a combustion chamber (14) of the cylinder (10) during a movement of the piston (20) from the second top dead center (OT) to the first bottom dead center (UT); compressing the air-fuel mixture in the combustion chamber (14) of the cylinder (10) during a movement of the piston (20) from the first bottom dead center (UT) to the first top dead center (OT); burning the air-fuel mixture during a movement of the piston (20) from the first top dead center (OT) to the second bottom dead center (UT); compressing a gas mixture located in the combustion chamber (14) during a movement of the piston (20) from the second bottom dead center (UT) to the first top dead center (OT); burning the gas mixture during a movement of the piston (20) from the first top dead center (OT) to the first bottom dead center (UT); expelling the gas mixture located in the combustion chamber (14) during a movement of the piston (20) from the first bottom dead center (UT) to the second top dead center (OT); and scavenging at least some of the gas mixture from the combustion chamber (14) as the piston (20) passes through the second bottom dead center (UT).

2. A combustion machine having the cylinder arrangement (1) of claim 1.

3. The method of claim 1, further comprising injecting a fuel mixture into the combustion chamber (14) during compression that occurs during the movement of the piston (20) from the second bottom dead center (UT) to the first top dead center (OT) while scavenging after the piston (20) passes through the second bottom dead center (UT).

4. The method of claim 1, wherein an exhaust valve (13) is opened during passage of the piston (20) through the second bottom dead center (UT).

5. A cylinder arrangement (1) of a combustion machine, comprising: a piston (20) that moves backward and forward in translation in a cylinder (10), the piston (20) and the cylinder (10) delimiting a combustion chamber (14); a connecting rod (30) connecting the piston (20) to a planet wheel (40) by means of a connecting element (42), the connecting element (42) being arranged eccentrically on the planet wheel (40), the planet wheel (40) engaging an annulus (50) and rotates in the annulus (50), and the planet wheel (40) further being connected to a crankshaft (60), wherein: dimensioning of the planet wheel (40) and the eccentric arrangement of the connecting element (42) are designed so that, in three revolutions of the planet wheel (40) in the annulus (50), the piston (20) reaches a first top dead center (OT) twice and a second top dead center (OT) once and reaches a first bottom dead center (UT) twice and a second bottom dead center (UT) once, the first top dead center (OT) and the first bottom dead center (UT) are farther from an axis of the annulus than the second top dead center (OT) and the second bottom dead center (UT).

6. The cylinder arrangement (1) of claim 5, wherein the cylinder (10) has at least one scavenging port (11) between the first bottom dead center (UT) and the second bottom dead center (UT), the scavenging port accommodating a discharge of a gas mixture from the combustion chamber (14).

7. The cylinder arrangement (1) of claim 5, wherein the connecting element (42) between the connecting rod (30) and the planet wheel (40) is formed by an eccentrically arranged cylindrical element that is surrounded by a connecting rod eye (31) arranged at an end of the connecting rod (30).

8. The cylinder arrangement (1) of claim 5, wherein the cylinder arrangement (1) has at least one inlet valve (12) for feeding a fuel-air mixture into the combustion chamber (14) and one exhaust valve (13) for letting a gas mixture out of the combustion chamber (14).

9. The cylinder arrangement (1) of claim 5, wherein the annulus (50) is rotatable around the crankshaft (60).

10. The cylinder arrangement (1) of claim 9, wherein an external thread (51) is arranged on an outside of the annulus (50) to rotate the annulus (50) around the crankshaft (60).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of a piston arrangement according to an embodiment of the invention.

(2) FIG. 2 is a detail view of a planet wheel of a piston arrangement.

(3) FIG. 3 is a cross section of a cylinder and a motion profile of the central point of the connecting element for fastening the connecting rod on the planet wheel.

(4) FIG. 4a is a detail view of the piston arrangement where the piston is in the second bottom dead center.

(5) FIG. 4b is a detail view of the cylinder where the piston is in the second bottom dead center.

(6) FIG. 5a is a detail view of the piston arrangement 1 of FIG. 1 where the piston is in the first bottom dead center.

(7) FIG. 5b is a detail view of the cylinder 10 where the piston 20 is in the first bottom dead center.

(8) FIG. 6 illustrates the motion profile of a piston in a piston arrangement plotted against the crank angle.

(9) FIG. 7 is a schematic view of a piston arrangement according to a second embodiment with variable timings of the inlet valve.

DETAILED DESCRIPTION

(10) FIG. 1 is a perspective view of a piston arrangement 1 that has a cylinder 10, in which a piston 20 performs a linear motion. The cylinder 10 is cut away for clarity. The cylinder 10 and the piston 20 enclose a combustion chamber 14 with a volume that changes as a function of the movement of the piston 20 in the cylinder 10. An inlet valve 12 and an exhaust valve 13 are arranged at one end of the cylinder 10, i.e. the top, to pass a gas mixture into the combustion chamber 14 and to discharge the gas mixture from the combustion chamber 14. The valves are controlled by a camshaft 70 and by inlet cams 71 and exhaust cams 72 secured thereon. Embodiments having plural inlet valves 12 and exhaust valves 13 controlled by plural camshafts 70 are conceivable. The cylinder 10 has, at a defined height, radial scavenging ports 11, by means of which the combustion chamber can be scavenged, given an appropriate position of the piston 20.

(11) The piston 20 is connected by a connecting rod 30 to two planet wheels 40 that rotate in an annulus 50. It is possible to provide just one planet wheel 40 and one annulus 50. For the sake of simplicity, only one planet wheel 40 and one annulus 50 are discussed below since the motion of the two planet wheels 40 takes place synchronously. A crankshaft 60 is connected to the planet wheel 40. The crankshaft 60 makes available the power of the engine and connects different piston arrangements 1 to one another. The connecting rod 30 is connected eccentrically to the planet wheel 40, i.e. not in the geometrical center of the planet wheel 40, and this will be explained in greater detail with reference to FIG. 2.

(12) FIG. 2 is a detail view of the planet wheel 40 that can be used in the embodiment of the piston arrangement 1 of FIG. 1. The planet wheel 40 has external toothing 43 that engages with the toothing of the annulus 50. The connection of the connecting rod 30 to the planet wheel 40 is accomplished via a cylindrical connecting element 42 arranged on the side face of the planet wheel 40. The socket 41 for the crankshaft 60 is arranged in the geometrical center of the planet wheel 40.

(13) The geometrical center M of the cylindrical connecting element 42 does not coincide with the geometrical center K of the planet wheel 40. Thus, the connecting element 42 is arranged eccentrically on the side face of the planet wheel 40. The eccentricity e, that is the distance between the geometrical center M of the connecting element and the geometrical center K of the planet wheel 40, represents an important parameter for the piston motion, as explained in greater detail with reference to FIG. 3.

(14) FIG. 3 shows a cross section of the cylinder 10 and the motion profile of the geometrical center M of the connecting element 42. The motion profile of a point on the piston corresponds to the motion profile of the geometrical center M of the connecting element 42 in the y direction of the diagram. The cylinder 10 corresponds to the cylinder 10 of FIG. 1. Due to the eccentricity e explained with reference to FIG. 2, the linearly oscillating axial motion of the piston 20 within the cylinder 10 does not always take place between the same two end points, as in the prior art. These are referred to conventionally as top and bottom dead center (OT, UT) and each marks the point of reversal of the piston 20 during the axial motion. Due to the eccentricity e in the piston arrangement 1 according to the invention, the motion takes place between two upper and two lower dead centers. As explained in greater detail below with reference to FIG. 6, a working cycle (overall cycle comprising two operating cycles/power strokes) of the piston arrangement of the invention comprises three revolutions of the crankshaft 60. This means that the planet wheel 40 also rotates three times within the annulus 50. Owing to the eccentricity e, the geometrical center M of the connecting element 42 does not travel on a circular path during a revolution. However, after three revolutions of the crankshaft 60, the geometrical center M is once more at the same point. The motion profile of the geometrical center M of the connecting element 42 is depicted on the right-hand side of FIG. 3, where the motion profile of an upper point of the piston 20 corresponds to the motion profile of the geometrical center M of the connecting element 42 and thus the diagram can be applied in the y direction to an upper point of the piston 20.

(15) This hypocycloidal curve has three maxima, which can be interpreted as top dead centers, and three minima, which can be interpreted as bottom dead centers. Two maxima are higher than the third maximum, and one minimum is lower than the two other minima. As a result, therefore, the two higher maxima form the first top dead center OT, and the lower maximum forms the second top dead center OT. Similarly, the two higher minima form the first bottom dead center UT, and the one lower minimum (as it were the global minimum of the motion curve) forms the second bottom dead center UT.

(16) Owing to the conversion of the hypocycloidal motion profile of the geometrical center M of the connecting element 42 to a linear axial alternating motion of the piston 20, the piston moves between the second bottom dead center UT and the first top dead center OT during a working cycle, wherein the first top dead center OT is reached twice and the second top dead center OT once. Similarly, the first bottom dead center UT is reached twice and the second bottom dead center UT once. The scavenging ports 11 are arranged in the cylinder 10 in such a way that they are only exposed by the piston 20 as the latter passes through the second bottom dead center UT. The greater the eccentricity e chosen, the more the hypocycloidal motion profile of the geometrical center M of the connecting element 42 deviates from a circular path and, consequently, the greater is the difference between the respective first and second dead centers. The aim is to achieve as uniform as possible compression for both operating cycles.

(17) The formation of different top and bottom dead centers is further shown in greater detail in FIGS. 4a, 4b and 5a and 5b. FIGS. 4a and 5a show the piston arrangement 1 in different positions of the working cycle. In FIG. 4a, the planet wheel 40 is in the position farthest away from the cylinder 10 within the annulus 50. At the same time, the planet wheel 40 is oriented in such a way that the eccentricity e points down in the plane of the drawing, i.e. the connecting element 42 is farther away from the cylinder 10 than the geometrical center of the planet wheel 40. Thus, the piston 20 is at the second bottom dead center UT, i.e. the global minimum in the motion profile from FIG. 3. As a result, as illustrated schematically in FIG. 4b, the radial scavenging ports 11 in the cylinder 10, which is here illustrated in a cutaway view, are exposed by the piston 20.

(18) In FIG. 5a, the planet wheel 40 is again at the point farthest away from the cylinder 10 in the annulus 50, more specifically precisely one revolution of the planet wheel 40 later in the annulus 50. However, the geometrical center M of the connecting element 42 is not at the same point again after one revolution of the planet wheel 40 in the annulus 50, but has shifted upward to the left in the plane of the drawing in FIG. 5a. As a result, the piston 20 is at the first bottom dead center UT in the cylinder 10, where it covers the scavenging ports 11 and thus does not allow escape of the gas mixture from the combustion chamber 14 through the scavenging ports 11, as illustrated in FIG. 5b.

(19) FIG. 6 illustrates the motion profile of the piston 20 in the cylinder 10 of a piston arrangement 1. By means of FIG. 6, the working cycle of the piston arrangement 1 according to the invention and thus the method according to the invention is described in greater detail in conjunction with FIG. 1.

(20) The overall cycle comprises a crankshaft rotation of 1080, which corresponds to 3 full crankshaft revolutions. It is divided into a total of six strokes, which each comprise 180, i.e. half a crankshaft revolution. The diagram shows the angle of the crankshaft 60 on the x axis, i.e. the crankshaft rotation, and the travel of the piston 20 within the cylinder 10 on the y axis. The specific numerical values will only be mentioned by way of example at this point.

(21) In the initial position, the piston 20 is at the second top dead center OT. From there, it moves toward the first bottom dead center UT in the first stroke. During this movement, the inlet cam 71 on the camshaft 70 (see FIG. 1) opens the inlet valve 12, and an air-fuel mixture enters the combustion chamber 14. In an alternate embodiment, it is possible only for fresh air to enter the combustion chamber through the inlet valve and to mix with an injected fuel to form a fuel-air mixture in the subsequent compression stroke.

(22) After reaching the first bottom dead center UT, the volume of the combustion chamber 14 is reduced again by the motion of the piston 20 toward the first top dead center OT. During this process, the gas mixture in the combustion chamber 14 is compressed, and thus this stroke can be described as a compression stroke. During this stroke, the inlet valve 12 is closed again to prevent the gas mixture from escaping. The first two strokes are thus known from a four-stroke engine, but, in contrast to the four-stroke engine, the piston motion comprises two different top dead centers.

(23) The gas mixture is ignited when or shortly before the first top dead center OT is reached. For this purpose, a spark plug like that in conventional combustion machines is used in the case of spark-ignition engines while, in the case of diesel engines, the compression is so great that the gas mixture ignites spontaneously due to the high pressure and the associated increase in temperature. The ignition of the gas mixture greatly increases the pressure in the combustion chamber 14 so that the piston 20 accelerates from the first top dead center OT to the second bottom dead center UT during the movement in the third stroke. The power can thus be transmitted to the crankshaft 60 via the connecting rod 30.

(24) Once the piston 20 reaches the first bottom dead center UT, it exposes the scavenging ports 11 arranged radially in the cylinder 10 so that the combustion chamber 14 is scavenged. During the passage through the second bottom dead center UT of the piston 20, the scavenging ports 11 are opened until, in the fourth stroke, the piston 20 once again passes the first bottom dead center UT and the scavenging ports 11. During scavenging that takes place at the transition between two strokes, it is possible but not necessary that the inlet valve 12 will open and hence that fresh gas mixture will flow into the combustion chamber from the cylinder top if the pressure in the combustion chamber 14 is lower than the pressure at which the fresh gas mixture flows into the combustion chamber 14. The exhaust valve 13 preferably opens at least partially during the scavenging process (see FIG. 3), thus enabling the gas mixture to escape at least partially via the exhaust valve during the scavenging process. The scavenging process preferably takes place so that a fresh gas mixture flows in through scavenging ports 11 in the bottom of the combustion chamber 14 while the gas mixture in the combustion chamber 14 is expelled through the exhaust valve 13. The use of plural exhaust valves 13, with only some of them being used for scavenging, is conceivable, as are embodiments in which both the outflow and the inflow of the gas mixture during the scavenging process are at least partially achieved via correspondingly arranged scavenging ports 11.

(25) As soon as the piston 20 closes the scavenging ports 11 in its movement back in the direction of the first top dead center OT during the fourth stroke, scavenging is complete (with the optionally opened exhaust valve 13 also closing) and the remaining gas mixture in the combustion chamber 14 is compressed again and then ignited again, that is for a second time within a working cycle. During the compression process, the optionally opening valves are closed again. The fourth and the fifth stroke thus correspond very largely to the strokes known from a two-stroke engine.

(26) On account of the repeated, i.e. second, ignition of the gas mixture, there is a second power output to the crankshaft 60 in the fifth stroke within the working cycle so that the piston 20 gets only as far as the first bottom dead center OT. In this second combustion stroke (power output), the remaining combustion constituents in the gas mixture are burned fully, thereby achieving particularly clean and complete combustion.

(27) After the passage through the first bottom dead center UT, a valve disk 131 of the exhaust valve 13 is raised from its valve seat 132, and the burned gas mixture that has remained in the combustion chamber 14 is expelled through the exhaust valve 13. For this purpose, the exhaust cam 72 (see FIG. 1) in the embodiment shown has two lobes to open the exhaust valve 13 during the scavenging process and the exhaust stroke (stroke 6). After the second top dead center OTE has been reached, one working cycle has been completed, and the strokes begin once again from the beginning. Of course, embodiments of the invention with independently controllable valve trains and embodiments without a camshaft are also conceivable to provide variable timing of the opening and closing times of the inlet valve 12 and of the exhaust valve 13.

(28) Owing to the fact that two combustions and thus power outputs take place during one working cycle, i.e. the overall cycle of 6 strokes, the engine is a 3-stroke engine, with two different 3-stroke sequences being carried out alternately. It would therefore also be possible to refer to a two-times-three-stroke engine. Here, both compression strokes take place between the first bottom dead center UT and the first top dead center OT, thus making it possible to ensure a constant compression ratio for the respective combustions that follow.

(29) FIG. 7 essentially shows the crankshaft arrangement of FIG. 1, and therefore only the differences will be explored at this point. In contrast to the embodiment of FIG. 1, the embodiment of FIG. 7 also has an external thread 51 that extends over half the circumference on the outside of the annulus 50.

(30) By rotating the gearwheel 80, the annulus 50 can be rotated around the crankshaft 60. As a result, the planet wheel 40 likewise rotates so that the eccentricity with which the connecting element 42 connects the connecting rod 30 and the planet wheel 40 is shifted slightly. Consequently, there is also a shift in the dead centers since, owing to the shift in the eccentricity, the extremes of the piston motion are no longer identical. On the one hand, this has the effect that the volume that is available within the combustion chamber 14 for compression, and thus the compression ratio of the gas mixture in the combustion chamber 14, is modified and also the opening and closing times of the inlet valve, are modified, and control of these times can thus be achieved by rotating the annulus 50.