Method for operating an internal combustion engine

Description

[0001] The invention relates to a method for operating an internal combustion engine of the type specified in the preamble of claim 1.

[0002] DE 23 48 638 C3 discloses a carburetor for an internal combustion engine that features an electromagnetically actuated valve. The valve opens in sync with the cylinder intake phases. To adjust the fuel supply, the opening times are adjusted depending on the engine's operating parameters.

[0003] It is known that the intake port of mixture-lubricated internal combustion engines, particularly two-stroke or mixture-lubricated four-stroke engines, is connected to the crankcase of the internal combustion engine via a valve controlled by the piston skirt of a piston of the internal combustion engine. If the fuel is supplied via the fuel valve synchronously with the intake stroke, very short valve switching times result, especially at high engine speeds. This requires a valve that responds very quickly. Due to the very frequent switching operations, especially at high engine speeds, the service life of the valve is shortened.

[0004] From the GB 2 462 657 A A method for fuel injection in an internal combustion engine is known, in which fuel and oil are fed into the intake port. The intake port opens into the crankcase interior via a check valve. Fuel and oil are supplied via injection valves, with the supplied quantity of fuel and oil being determined by the number of valve opening cycles. This document also discloses an internal combustion engine in which the intake port opens into the combustion chamber via a valve, and fuel flows into the intake port via a fuel valve. The number of opening cycles that the fuel valve opens per engine cycle is calculated and rounded to an integer value.

[0005] From the DE 28 02 634 A1 A fuel supply system for an internal combustion engine is disclosed, which has an electronic circuit that operates depending on the engine speed. An electrical frequency dependent on the engine speed is compared with a reference frequency manually selectable by the operator. Based on the comparison result, a control valve of the injection device is controlled to adjust the engine speed to the predetermined maximum speed.

[0006] From the AT 408 250 B A two-stroke internal combustion engine is developed in which fuel is injected into the combustion chamber. The amount of fuel injected per working cycle is periodically adjusted for individual working cycles during partial load.

[0007] The invention is based on the object of creating a method for operating an internal combustion engine of the generic type which enables advantageous operation of the internal combustion engine.

[0008] This object is achieved by a method having the features of claim 1.

[0009] It is provided that in a first operating state the frequencies at which the valve that supplies the fuel and the valve that connects the intake port to the crankcase are opened are coordinated with one another. This ensures in particular that in the region of the intake port to which the second valve supplies the fuel, at the times at which the second valve is open, there is a sufficient negative pressure to actually achieve a flow of fuel into the intake port. This is provided in particular in an operating state in which the pressure in the intake port fluctuates greatly. However, such control of the fuel supply can also be advantageous for other operating states. In a second operating state it is provided that the second valve is opened independently of the first frequency at which the first valve connects the intake port to the crankcase. This makes it possible to achieve simple control.At the same time, since the frequencies are not matched, the number of switching cycles can be reduced by selecting the second frequency accordingly. This increases the service life of the second valve.

[0010] The first frequency is advantageously tuned to the second frequency by the first frequency being the same as the second frequency, by the first frequency being an integer multiple of the second frequency, or by the second frequency being an integer multiple of the first frequency. It is particularly advantageous if the two frequencies are the same or the second frequency is lower than the first frequency, so that the number of switching cycles of the second valve is reduced. In the second operating state, the second valve is opened independently of the first frequency. The second frequency is therefore not tuned to the first frequency in the second operating state. Advantageously, the ratio of the first frequency to the second frequency is not constant in the second operating state. This results in shifts between the opening times of the two valves, which change from engine cycle to engine cycle.The second frequency is advantageously lower than the first frequency. This can increase the service life of the second valve.

[0011] In the first operating state, the first frequency and the second frequency are advantageously dependent on the speed of the internal combustion engine. In the first operating state, the time period during which the second valve is opened by the control device for supplying fuel advantageously lies at least partially in a time period during which the first valve is open. This makes it easy to ensure that there is sufficient negative pressure in the region of the intake duct into which the fuel is supplied, and thus that a sufficient quantity of fuel is supplied to the intake duct. The fuel is advantageously supplied due to the negative pressure prevailing in the intake duct. The pressure of the supplied fuel is advantageously low and is in the range of the crankcase pressure or slightly higher. The fuel pressure is advantageously less than 2 bar overpressure.At low fuel pressures, the amount of fuel supplied is highly dependent on the negative pressure in the intake manifold. If the valve opening frequencies and the opening timing are not coordinated, the amount of fuel supplied can fluctuate significantly from engine cycle to engine cycle, resulting in rough running of the internal combustion engine.

[0012] Advantageously, at least one fuel channel opens into the intake channel. The second valve controls in particular the amount of fuel supplied to the intake channel via the at least one fuel channel. The second valve is therefore not an injection valve that supplies the fuel directly to the intake channel, but rather a switching valve that opens or closes a fuel channel leading into the intake channel. The first valve is formed by a piston skirt of a piston that reciprocates in a cylinder of the internal combustion engine and interacts with an inlet opening of the intake channel in the crankcase. The control times of the first valve are therefore dependent on the engine speed and fixed within each engine cycle in relation to the crankshaft angle. The valve opens and closes exactly once during each engine cycle. The second valve advantageously has exactly two switching states, namely a fully open and a fully closed switching state.The second valve is therefore a digitally switching valve. Partially opening the second valve, for example, to reduce the supplied fuel quantity compared to a fully open valve, is not possible with a valve with exactly two switching states. The fact that the valve only has two switching states results in simple control of the valve. A simply constructed valve can be used. The supplied fuel quantity is controlled exclusively by the time period during which the second valve is open or closed. The quantity of fuel sucked into the intake port per unit of time varies depending on the negative pressure prevailing in the intake port. The second valve is advantageously an electromagnetic valve.

[0013] The first and second operating states comprise different speed ranges, wherein the speeds of the first speed range of the first operating state are lower than the speeds of the second speed range of the second operating state. The first speed range is therefore a lower speed range than the second speed range. The first operating state advantageously comprises starting operation. Starting operation is the operation of the internal combustion engine from the beginning of the starting process until the first combustion. The first operating state advantageously comprises idling operation. The second operating state advantageously comprises full-load operation. The control of the second valve advantageously switches at speeds in the order of magnitude of approximately 3,500 to approximately 4.000 revolutions per minute from the control of the second valve according to the first operating state to the control of the second valve according to the second operating state in which the second valve is opened independently of the first frequency.

[0014] Advantageously, the supplied fuel quantity is increased or reduced to limit the engine speed in an upper speed range. The first operating state advantageously covers the upper speed range. In the upper speed range, the second valve is advantageously only opened when the first valve is also open. This enables very precise fuel metering. The speed limitation can be achieved either by increasing the supplied fuel quantity (i.e., by over-enriching the fuel), or by reducing the supplied fuel quantity (i.e., by leaning the fuel).

[0015] Embodiments of the invention are explained below with reference to the drawings. They show: Fig. 1a schematic longitudinal section through a chainsaw, Fig. 2a schematic section through the chainsaw from Fig. 1 along line II-II in Fig. 1 , Fig. 3a schematic representation of the carburettor of the chainsaw from the Figures 1 and 2 , Fig. 4 a diagram that schematically shows the pressure curve in the crankcase of the internal combustion engine of the chainsaw, Fig. 5 a diagram that schematically shows the pressure curve in the intake channel of the chainsaw in different operating states, Fig. 6 a diagram that shows the opening times of the valves of the internal combustion engine in a first operating state, Fig. 7 a diagram that shows the opening times of the valves of the internal combustion engine in a second operating state, Fig. 8 a diagram that shows the curve of the frequencies with which the valves are opened for several embodiments.

[0016] Fig. 1 shows a chainsaw 1 with an internal combustion engine 4 as an exemplary embodiment of a hand-held tool. However, the method according to the invention can also be used in internal combustion engines of other hand-held tools, such as power cutters, brush cutters, harvesters, vacuum / blowers, lawn mowers, or the like. The chainsaw 1 has a housing 2 to which a rear handle 3 is attached. A throttle lever 5 and a throttle lever lock 6 are pivotally mounted on the rear handle 3. On the side of the housing 2 facing away from the rear handle 3, a guide rail 7 projects forward, on which a saw chain 8 driven by the internal combustion engine 4 is arranged circumferentially.

[0017] The internal combustion engine 4 draws in combustion air via an air filter 9 through an intake duct 17. A section of the intake duct 17 is formed in a carburetor 10, in which a throttle element 11 is pivotally mounted. The throttle lever 5 acts on the position of the throttle element 10 and thus controls the amount of combustion air drawn in. The intake duct 17 opens into an inlet port 16 on a cylinder 12 of the internal combustion engine 4. A piston 19 is reciprocatingly mounted in the cylinder 12. The piston 19 defines a combustion chamber 14 formed in the cylinder 12, into which a spark plug 15 projects.

[0018] In the exemplary embodiment, the internal combustion engine 4 is designed as a single-cylinder, specifically a two-stroke engine. However, the internal combustion engine 4 can also be a mixture-lubricated four-stroke engine. The internal combustion engine 4 has a crankcase 13 into which the inlet opening 16 opens. The connection of the inlet opening 16 to the interior of the crankcase 13 is controlled by a piston skirt 20 of the piston 19. The piston skirt 20, together with the inlet opening 16, forms a first valve 24, which opens and closes depending on the speed of the internal combustion engine 4 at predetermined positions of the piston 19 and a crankshaft 31 rotatably mounted in the crankcase 13. During its up-and-down movement, the piston 19 drives the crankshaft 31 via a connecting rod 21.

[0019] The first valve 24 is open in the region of top dead center of piston 19. When the first valve 24 is open, the intake port 17 is connected to the interior of the crankcase 13 via the inlet opening 16. In this position of the piston 19, combustion air and fuel supplied to the combustion air in the carburetor 10 are sucked into the interior of the crankcase 13. During the downward stroke of the piston 19, i.e. when the piston 19 moves towards the crankcase 13, the fuel / air mixture in the interior of the crankcase 13 is compressed and, in the region of bottom dead center of the piston 19, passes into the combustion chamber 14 via transfer channels (not shown). During the subsequent upward stroke of the piston 19, i.e. when the piston 19 moves away from the crankcase 13, the mixture in the combustion chamber 14 is compressed and ignited by the spark plug 15 in the area of ​​the top dead center of the piston 19.An exhaust port 18 leads from the combustion chamber 14, which is opened by the piston skirt 20 during the downward stroke of the piston 19. This allows exhaust gases to flow out of the combustion chamber 14. An exhaust silencer 22 is arranged on the cylinder 12, into which the exhaust gases flow.

[0020] How Fig. 2shows, the chainsaw 1 has a starting device 23 for starting the internal combustion engine 4, which can be, for example, a pull-cord starter or an electrically driven starting device. A flywheel 25 is fixed to the crankshaft 31 and, in the exemplary embodiment, is arranged between the crankcase 13 and the starting device 23. The flywheel 25 can, for example, be a fan wheel. Magnets 27 are arranged on the outer circumference of the flywheel 25 and induce a voltage in an ignition module 26 arranged adjacent to the outer circumference of the flywheel 25. The ignition module 26 is connected to the spark plug 15 and supplies the spark plug 15 with the energy induced in the ignition module 26 to provide an ignition spark. A control device 28 is also connected to the ignition module 26. The control device 28 can also be integrated into the ignition module 26. The control device 28 determines the time at which the ignition is triggered by the spark plug 15.The control device 28 also controls the amount of fuel supplied to the internal combustion engine 4 by controlling a . Fig. 3 shown second valve 39. On the side of the crankcase 13 facing away from the flywheel 25, the crankshaft 31 is connected to a centrifugal clutch 29. On the output side of the centrifugal clutch 29, a drive pinion 30 for driving the saw chain 8 is fixed.

[0021] Fig. 3shows the carburetor 10 schematically. In the exemplary embodiment, the carburetor 10 is designed as a conventional diaphragm carburetor. The carburetor 10 has a fuel pump 34, which can, for example, be a diaphragm pump driven by the pressure in the interior of the crankcase 13. The fuel pump 34 delivers fuel to a control chamber 35 of the carburetor 10. At the inlet of the control chamber 35, an inlet valve 38 is arranged, which controls the amount of fuel entering the control chamber 35. The control chamber 35 is separated from a compensation chamber 36 by a control diaphragm 37. A reference pressure prevails in the compensation chamber 36, which can, for example, be the pressure in the clean chamber of the air filter 9. The position of the inlet valve 38 is linked to the position of the control diaphragm 37. If there is a negative pressure in the control chamber 35 compared to the compensation chamber 36, the inlet valve 38 opens.If the pressure is equalized or if there is an overpressure in the control chamber 35 compared to the compensation chamber, the inlet valve 38 closes. The inlet valve 38 can be spring-loaded in order to change and adjust the pressure level in the control chamber 35 compared to that in the compensation chamber 36 and to adapt the opening characteristic of the inlet valve 38.

[0022] At least one fuel channel 45 leads from the control chamber 35. In the exemplary embodiment, exactly one fuel channel 45 is provided. The amount of fuel flowing through the fuel channel 45 is controlled by the second valve 39. The second valve 39 is designed as an electromagnetic valve. The second valve 39 is controlled by the control device 28. In the exemplary embodiment, the second valve 39 has exactly two switching states: a fully open and a fully closed state. The control device 28 controls the amount of fuel supplied to the intake channel 17 by controlling the period of time during which the second valve 39 is open.

[0023] The fuel channel 45 opens into the intake channel 17 via a throttle 40 and a check valve 41 at a main fuel opening 42. The main fuel opening 42 is arranged in the region of a venturi 52. The fuel is sucked into the intake channel 17 due to the negative pressure prevailing in the intake channel 17. A fuel channel 66 branches off from the fuel channel 45. An adjusting valve 48 is provided in the fuel channel 66. The fuel channel 66 opens into a fuel chamber 47, which is designed as an idling chamber. The amount of fuel supplied to the intake channel 17 at idle can be adjusted via the adjusting valve 48. The adjusting valve 48 is preferably a needle valve. Three fuel channels 50, each having a throttle 51, lead from the fuel chamber 47. Each fuel channel 50 opens into the intake channel 17 at an idle fuel opening 44. The idle fuel openings 44 are arranged in the region of the throttle element 11.In the exemplary embodiment, the throttle element 11 is designed as a throttle valve. If the throttle element 11 is completely closed, two of the idle fuel openings 44 are arranged upstream of the throttle element 11 with respect to a flow direction 33 in the intake duct 17, and one of the idle fuel openings 44 is arranged downstream of the throttle element 11. The flow direction 33 is the direction in which combustion air flows from the air filter 9 to the inlet opening 16. In the exemplary embodiment, a dependent idle system is shown. The amount of fuel supplied to the fuel channel 66 and to the idle fuel openings 44 is controlled by the second valve 39. However, it can also be provided that the fuel channel 66 branches off directly from the control chamber 35, and the amount of fuel supplied to the idle fuel openings 44 is not controlled by the second valve 39.

[0024] How Fig. 3also shows, a fuel channel 49 branches off from the fuel channel 66, which opens via a throttle 46 at a secondary fuel opening 43. As Fig. 3 As also shown, a choke element 32 is arranged upstream of the throttle element 11 in the intake duct 17, which in the exemplary embodiment is designed as a choke flap. When the internal combustion engine 4 is started, the choke element 32 is at least partially closed.

[0025] Fig. 4shows the curve of the crankcase pressure p KGH over several engine cycles x. In the exemplary embodiment, each engine cycle x extends from one top dead center TDC of the piston 19 to the following top dead center TDC of the piston 19. As the line 59 shows, the crankcase pressure p KGH fluctuates greatly. At the top dead center TDC of the piston 19, the crankcase pressure p KGH is at its lowest. Compared to the ambient pressure, there is a vacuum in the crankcase 13. At the bottom dead center BDC of the piston 19, the crankcase pressure p KGH is at its greatest. The crankcase pressure p KGH is plotted as the difference compared to the ambient pressure. At the bottom dead center BDC of the piston 19, the crankcase pressure p KGH is greater than the ambient pressure. Fig. 4 also shows the opening time t 1 and the closing time t 2 of the first valve 24.

[0026] The first valve 24 opens at an opening time t 1 , which lies before top dead center (TDC), and closes at a closing time t 2 after top dead center (TDC). The opening time t 1 and the closing time t 2 respectively indicate the time at which the intake port 16 begins to open or begins to close. The first valve 24 is open for a time period 56 extending from the opening time t 1 to the closing time t 2 .

[0027] Fig. 5shows the curve of the intake port pressure p A . Line 60 shows the pressure curve at low speeds. At low speeds, the negative pressure from the crankcase 13 can continue into the intake port 17 as long as the first valve 24 is open. During the periods in which the first valve 24 is closed, approximately ambient pressure is established in the intake port 17 via the air filter 9. The pressure in the intake port 17 corresponds approximately to the pressure curve of the crankcase pressure p KGH from the opening time t 1 to the closing time t 2. From the closing time t 2 to the subsequent opening time t 1, the intake port pressure p A corresponds approximately to the ambient pressure.

[0028] At high engine speeds, pressure equalization between ambient pressure and intake port pressure p A via air filter 9 cannot occur, or only partially, because there is insufficient time for pressure equalization. The approximate pressure curve occurring in intake port 17 is shown schematically by a line 61. A fluctuating pressure occurs, alternating between periods in which the pressure is above ambient pressure and periods in which the pressure is below ambient pressure. The pressure fluctuates around the ambient pressure, although the fluctuations can vary depending on the engine and engine speed. Fig. 5 shows an example of a possible pressure curve at high speeds.

[0029] Fig. 6shows the opening and closing times for the first valve 24 and the second valve 39 for a first operating state. The first operating state advantageously comprises low speeds, at which the pressure curve in the intake port 17 corresponds approximately to the line 60 in Fig. 5 The first valve 24 opens at opening times t 1 and closes at closing times t 2 , which correspond to the pressure curve indicated in Fig. 4 and 5correspond to the times t 1 and t 2 shown. The second valve 39 is advantageously controlled such that the time period 57 at which the second valve 39 is open lies at least partially within the time period 56. In the exemplary embodiment, the time period 57 lies completely within the time period 56. The second valve 39 opens simultaneously with the first valve 24 at the opening time t 1 . The second valve 39 closes at a closing time t 3 , which lies before the closing time t 2 . In the exemplary embodiment, the closing time t 3 lies approximately at top dead center TDC. The closing time t 3 is advantageously controlled by the control device 28 depending on the amount of fuel to be supplied. As Fig. 6 shows, both the first valve 24 and the second valve 39 are either completely closed or completely open. Both valves have exactly two switching states. In Fig. 6the first, fully closed switching state is designated "0" and the second, fully open switching state is designated "1".

[0030] Fig. 7 shows an embodiment for the control of the second valve 39 in a second operating state, in which the pressure curve in the intake channel 17 corresponds approximately to that in Fig. 5 corresponds to the curve indicated by line 61. The pressure fluctuates around the ambient pressure when the first valve 24 is closed, so that when the first valve 24 is closed, periods of negative pressure and periods of positive pressure alternate in rapid succession. Due to the periods of negative pressure, fuel can be sucked into the intake port 17 even when the first valve 24 is closed.

[0031] In the embodiment according to Fig. 7three opening and closing processes of the second valve 39 are shown. In a first engine cycle x 1 , the second valve 39 opens at the same time as the first valve 24 at the opening time t 1 and closes at the same time as the first valve 24 at the closing time t 2 . The second valve 39 is open for a time period 58 which is exactly as long as the time period 56 for which the first valve 24 is open and coincides with this. In a second engine cycle x 2 , the first valve 24 opens at an opening time t 1 . The second valve 39 only opens in the following engine cycle x 3 , specifically shortly after top dead center TDC at an opening time t 4 . The first valve 24 then closes at a closing time t 2 . Only then does the second valve 39 close at a closing time t 5 . The time periods 56 and 58, during which the first valve 24 and the second valve 39 are open, are of equal length but only partially overlap.At the end of the third engine cycle x 3 , the first valve 24 opens at opening time t 1 and closes in the fourth engine cycle x 4 at closing time t 2 . During the time period 56, the second valve 39 is not open. The second valve 39 opens at an opening time t 6 , which lies after the closing time t 2 of the first valve 24, and closes at a closing time t 7 , which in the exemplary embodiment lies after bottom dead center BDC. In this engine cycle, the time periods 56 and 58 do not overlap. Due to the temporary negative pressure prevailing in the intake port 17 even when the first valve 24 is closed, fuel is still supplied to the intake port 17 during the time period 58.

[0032] At the Fig. 6With the wiring of the second valve 39 shown, the first valve 24 and the second valve 39 open at the same frequency, which corresponds exactly to the speed of the internal combustion engine 4. The two valves 24, 39 are advantageously opened simultaneously. However, it can also be provided that a time offset is provided between the opening times t 1 of the two valves 24 and 39. This is particularly expedient when the negative pressure from the interior of the crankcase 13 only reaches the main fuel opening 42 of the intake channel 17 with a time delay, for example due to a correspondingly large length of the intake channel 17. The second valve 39 advantageously opens when the negative pressure from the interior of the crankcase 13 prevails at the main fuel opening 42.

[0033] At the Fig. 7In the wiring of the second valve 39 shown, the frequency with which the second valve 39 is opened is lower than the frequency of the first valve 24. The frequency of the second valve 39 is less than half the frequency of the first valve 24. When the second valve 39 is opened and closed is determined solely on the basis of the amount of fuel to be supplied. The frequency with which the first valve 24 is opened is not taken into account. This results in shifts between the time periods 56 at which the first valve 24 is open and the time periods 58 at which the second valve 39 is open, with the shifts changing from engine cycle to engine cycle. The frequency with which the second valve 39 is opened is advantageously lower than the frequency with which the first valve 24 is opened. This can increase the service life of the second valve 39.Because a temporary vacuum prevails in the intake port 17 even when the first valve 24 is closed, a sufficiently large amount of fuel can be supplied. Particularly at high engine speeds, such as at full load, the inaccurate fuel metering resulting from the phase shift in the opening times of valves 24 and 39 is tolerable.

[0034] Fig. 8shows schematically the curve of a first frequency f 1 , with which the first valve 24 is opened, versus the speed n. The frequency f 1 is proportional to the speed n. The internal combustion engine 4 has a first speed range 53, which includes a starting speed range 62 and an idling speed range 63. The internal combustion engine 4 has a second speed range 54, which lies above the first speed range 53 and which includes a partial load speed range 64 and a full load speed range 65. The internal combustion engine 4 also has an upper speed range 55, which lies above the second speed range 54. In the upper speed range 55, the speed n of the internal combustion engine 4 is limited by the control device 28. The partial load speed range 64 advantageously begins at a speed of approximately 3,500 to approximately 4,000 revolutions per minute. The full load speed range 65 advantageously includes, at least in part, speeds of approximately 8,000 to approximately 12,000.000 revolutions per minute.

[0035] In Fig. 8 An exemplary curve of a second frequency f 2 is shown schematically with a dashed line. The second frequency f 2 corresponds to the frequency with which the second valve 39 is opened. In the first speed range 53, the second frequency f 2 is proportional to the speed n. The second frequency f 2 is exactly half as large as the first frequency f 1 for each speed n of the first speed range 53. The second valve 39 is therefore opened every other engine cycle x.

[0036] In the second speed range 54, the second frequency f 2 is constant. As a result, the ratio between the first frequency f 1 and the second frequency f 2 in the second speed range 54 changes depending on the speed n. The two valves 24 and 39 therefore open uncontrolled, either simultaneously or with a time delay, depending on the engine cycle. The time periods 56 and 58 during which the valves 24 and 39 are open are simultaneous, partially overlapping, or completely offset, depending on the engine cycle. The frequencies f 1 and f 2 are not coordinated with one another.

[0037] In the upper speed range 55, the second frequency f 2 is proportional to the first frequency f 1 . The second frequency f 2 is a quarter of the first frequency f 1 . In the upper speed range 55, fuel is supplied via the second valve 39 every fourth engine cycle x. The two valves 24 and 39 are advantageously opened at least partially simultaneously. This enables very precise fuel metering in the upper speed range 55. This is particularly advantageous when limiting the speed of the internal combustion engine 4 by enriching or leaning the supplied fuel / air mixture.

[0038] In Fig. 8, a further profile of a second frequency f 3 for the second valve 39 is shown as an example. In the first speed range 53, the second frequency f 3 corresponds to the first frequency f 1 . In the second speed range 54, the second frequency f 3 fluctuates. The second frequency f 3 can be set as a function of the speed n. However, it can also be provided that the second frequency f 3 is additionally set based on further parameters, for example based on the engine load, before the control device 28 and there is no fixed relationship between the speed n and the second frequency f 3 , as is the case in Fig. 8is indicated. In the upper speed range 55, the second frequency f 3 is proportional to the first frequency f 1 . The second frequency f 3 is in the upper speed range 55 half as large as the first frequency f 1 . It may also be advantageous to open the second valve 39 in the second speed range 54 with a constant frequency f 5 . This is shown in Fig. 8 shown with a dotted line. The curve of the fifth frequency f 5 corresponds to that of the first frequency f 1 in the first speed range 53 and to that of the third frequency f 3 in the upper speed range 55.

[0039] Another exemplary curve is represented by a second frequency f 4 in Fig. 8shown. In the first speed range 53, the second frequency f 4 is proportional to the speed n and twice as large as the first frequency f 1 . In the second speed range 54, the second frequency f 4 is constant. The second frequency f 4 corresponds to the highest frequency f 4 in the first speed range 53. The ratio between the first frequency f 1 and the second frequency f 4 therefore changes continuously in the second speed range 54 as the speed n increases. In the upper speed range 55, the second frequency f 4 decreases abruptly to a frequency value that corresponds to one third of the first frequency f 1 . As a result, the second valve 39 in the upper speed range 55 is only opened every third engine cycle. The frequencies f 1 and f 4 are also coordinated with one another in the first speed range 53 and in the upper speed range 55, and independent of one another and not coordinated with one another in the second speed range 54.

[0040] How Fig. 8shows, the first speed range 53 lies below the second speed range 54, thus comprising speeds that are lower than those of the second speed range 54. In the first speed range 53, there is advantageously a constant ratio between the first frequency f 1 and the second frequency f 2 , f 3 , f 4 . In this case, the first frequency f 1 is advantageously the same as the second frequency f 3 , an integer multiple of the second frequency f 2 , or the second frequency f 4 is an integer multiple of the first frequency f 1 . As a result, the two valves 24 and 39 are opened in regularly recurring engine cycles x simultaneously or with a desired time offset from one another. The two valves 24 and 39 are also advantageously open in the upper speed range 55 according to the illustration in Fig. 6opened simultaneously, whereby the second valve 39 does not open during every engine cycle x, but rather every two, every three, or every four engine cycles. A different ratio of the first frequency f 1 to the second frequency f 2 , f 3 , or f 4 in the upper speed range 55 can also be advantageous. By coordinating the frequencies in the first speed range 53 and / or in the upper speed range 55, precise metering of the fuel can be achieved. This ensures smooth running of the internal combustion engine 4, particularly in the first speed range 53.

Claims

1. Method for operating an internal combustion engine, wherein the internal combustion engine (4) has an intake duct (17) which opens via a first valve (24) into a crankcase (13) of the internal combustion engine (4), wherein the first valve (24) opens with a first frequency (f1), and wherein the internal combustion engine (4) has a second valve (39) which controls the amount of fuel supplied to the intake duct (17), wherein the amount of fuel supplied is controlled by controlling a period of time (57, 58), during which the second valve (39) is open in each engine cycle (x), wherein a control device (28) is provided to control the amount of fuel supplied, characterized in that the first valve (24) is formed by a piston skirt (20) of a piston (19) which is mounted reciprocally in a cylinder (12) of the internal combustion engine (4) and which interacts with an inlet opening (16) of the intake duct (17) into the crankcase (13), in that, in a first operating state, the second valve (39) is opened with a second frequency (f2, f3, f4), which is matched to the first frequency (f1), and in that, in a second operating state, the second valve (39) is opened independently of the first frequency (f1), wherein the first operating state comprises a first speed range (53), and wherein the second operating state comprises a second speed range (54), wherein the speed ranges do not overlap and speeds (n) of the first speed range (53) are lower than the speeds (n) of the second speed range (54).

2. Method according to Claim 1, characterized in that, in the first operating state, the first frequency (f1) is the same as the second frequency (f3), in that the first frequency (f1) is an integer multiple of the second frequency (f2), or in that the second frequency (f4) is an integer multiple of the first frequency (f1).

3. Method according to Claim 1 or 2, characterized in that, in the second operating state, the ratio of the first frequency (f1) to the second frequency (f2, f3, f4) is not constant.

4. Method according to one of Claims 1 to 3, characterized in that the first frequency (f1) and the second frequency (f2, f3, f4) in the first operating state are dependent on the speed (n) of the internal combustion engine (4).

5. Method according to one of Claims 1 to 4, characterized in that, in the first operating state, the period of time (57), during which the second valve (39) is opened by the control device (28) for supplying fuel, lies at least partially in a period of time (56), during which the first valve (24) is open.

6. Method according to one of Claims 1 to 5, characterized in that at least one fuel duct (45, 49, 50) opens into the intake duct (17), and in that the second valve (39) controls the amount of fuel supplied to the intake duct (17) via the at least one fuel duct (45, 49, 50).

7. Method according to one of Claims 1 to 6, characterized in that the second valve (39) has exactly two switching states, namely a fully open and a fully closed switching state.

8. Method according to one of Claims 1 to 7, characterized in that the second valve (39) is an electromagnetic valve.

9. Method according to one of Claims 1 to 8, characterized in that the first operating state includes the start-up mode.

10. Method according to one of Claims 1 to 9, characterized in that the first operating state includes the idling mode.

11. Method according to one of Claims 1 to 10, characterized in that the second operating state includes the full load mode.

12. Method according to one of Claims 1 to 11, characterized in that the amount of fuel supplied is increased or reduced to limit the speed (n) of the internal combustion engine (4) in an upper speed range (55).

13. Method according to Claim 12, characterized in that the second valve (39) is only opened in the upper speed range (55) if the first valve (24) is also open.