Carburetor and method for operating an internal combustion engine having said carburetor

A carburetor has a housing wherein a control drum is rotatably mounted. A section of an intake channel is formed in the carburetor. A subsection of this section is formed in the control drum. The control drum controls the free flow cross section of the intake channel. A fuel opening is connected to a fuel chamber via an unbranched fuel channel which opens into the subsection of the intake channel. A simple configuration of the carburetor is achieved by the carburetor including an electrically actuated valve which controls the flow of fuel through the fuel channel. For a method for operating an internal combustion engine with a carburetor, a temperature (T) is determined before or during the starting of the engine and that the flow of fuel through the fuel channel during the starting of the engine is controlled in dependence upon the temperature (T).

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority of German patent application no. 10 2015 001 452.8, filed Feb. 5, 2015, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a carburetor, wherein the carburetor has a housing, wherein a section of an intake channel is formed in the carburetor, wherein a control drum, in which a subsection of the intake channel is formed, is mounted rotatably in the housing, wherein the control drum controls the free flow cross section of the intake channel, wherein the carburetor has a fuel chamber, wherein a fuel opening, which is connected to the fuel chamber via an unbranched fuel channel, opens into the subsection of the intake channel, and to a method for operating an internal combustion engine with a carburetor.

BACKGROUND OF THE INVENTION

DE 32 47 603 A1 discloses a carburetor which has a rotatable control drum. The quantity of fuel supplied is controlled via a needle which projects into a fuel opening. In order to adapt the quantity of fuel supplied during idle, an opening is provided in a wall of the control drum, the opening being configured in such a manner that a larger air opening arises on the upstream side of the control drum than on the downstream side.

During the starting, an increased quantity of fuel has to be supplied via the carburetor. For this purpose, it is known to raise the control drum via an actuating mechanism in such a manner that the free cross section of the fuel opening is increased, and at the same time to rotate the control drum in order to increase the opening cross section of the intake channel.

It is also known from WO 2007/077971 A1 to provide, for the starting operation, an additional fuel path which is controlled by an electromagnetic valve. The free cross section of the main fuel opening is controlled by a needle.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a carburetor which has a simple configuration. It is a further object of the invention to provide a method for operating an internal combustion engine with the carburetor.

This object is achieved with regard to the carburetor by a carburetor which includes an electrically actuated valve which controls the flow of fuel through the fuel channel. With regard to the method, the object is achieved by a method for operating an internal combustion engine with a carburetor, wherein a temperature is determined before or during the starting of the internal combustion engine, and wherein the flow of fuel through the fuel channel during the starting of the internal combustion engine is controlled in dependence upon the temperature.

The carburetor includes an electrically actuated valve which controls the flow of fuel through the fuel channel. Owing to the fact that the fuel channel is unbranched, the valve controls the entire quantity of fuel supplied to the intake channel. As a result, during the starting, an increased quantity of fuel can be supplied via the valve without a further additional fuel path being necessary. Owing to the fact that the increased quantity of fuel during the starting is metered by the valve, a manual adjustment of a choke position is not necessary. As a result, a corresponding actuating mechanism can be omitted.

It has been demonstrated that, for a sufficient supply of fuel during the starting of an internal combustion engine at low temperatures, a very large quantity of fuel should be supplied. Since the entire quantity of fuel supplied to the intake channel is controlled via the valve, the valve therefore has to have a comparatively large maximum volume flow rate. By contrast, the quantity of fuel to be supplied during operationally hot idle is very small. At the same time, the negative pressure at the fuel opening is comparatively large. In the case of valves with a high maximum volume flow rate, the quantity of fuel to be supplied during idle may be so small that the provided opening times of the valve lie within the order of magnitude of the switching accuracy of the valve. As a result, a reliable supply of a small quantity of fuel during idle is not readily possible. In order nevertheless to permit the use of a simply configured electromagnetic valve, it is provided that the subsection of the intake channel, which subsection is formed in the control drum, is connected in at least one rotational position of the control drum via an entry aperture to that section of the intake channel which is located upstream of the control drum and via an exit aperture to that section of the intake channel which is located downstream of the control drum, wherein, for at least one rotational position of the control drum, the flow cross section of the exit aperture is smaller than the flow cross section of the entry aperture. Owing to the fact that the flow cross section of the entry aperture is increased relative to the exit aperture, the negative pressure at the fuel opening is reduced for the rotational position of the control drum. Accordingly, by increasing the entry aperture of the control drum in relation to the exit aperture, the supplied quantity of fuel can be reduced with the flow cross section of the fuel opening remaining unchanged. This permits the use of a simply configured, electrically actuated valve in order to supply the entire quantity of fuel supplied to the intake channel both for starting at low temperatures and for operationally hot idle.

In particular in the case of a rotational position of the control drum that is assigned to the idle, the flow cross section of the exit aperture is smaller than the flow cross section of the entry aperture. In the at least one rotational position, the flow cross section of the exit aperture is advantageously at most 80% of the flow cross section of the entry aperture. The flow cross section of the exit aperture is advantageously at most 70%, in particular at most 60%, of the flow cross section of the entry aperture. A flow cross section of the exit aperture of approximately 50% of the flow cross section of the entry aperture has proven particularly advantageous.

Even at a low partial load, the quantity of fuel to be supplied to the intake channel is very small. For all of the rotational positions of the control drum, which correspond to an angle of rotation of the control drum from the idle position in the direction of the completely open position of 0° to 20°, in particular of 0° to 40°, the flow cross section of the exit aperture is advantageously smaller than the flow cross section of the entry aperture. In order to achieve a low flow resistance at full load, it is advantageously provided that the flow cross section of the exit aperture is the same size as the flow cross section of the entry aperture in the completely open position of the control drum. For all of the rotational positions of the control drum, which correspond to an angle of rotation of the control drum from the completely open position in the direction of the idle position of 0° to 5°, in particular of 0° to 10°, preferably of 0° to 20°, the flow cross section of the exit aperture is advantageously the same size as the flow cross section of the entry aperture. As a result, a high negative pressure can be achieved at the fuel opening in full load, and therefore the high quantity of fuel required for the full load operation can be delivered.

By adaptation of the flow cross sections of entry aperture and exit aperture, in particular for rotational positions of the control drum that correspond to the idle position and to the low partial load, an additional control of the flow cross section of the fuel opening is not necessary. The free flow cross section of the fuel opening is advantageously the same size for each position of the control drum. As a result, a needle for controlling the flow cross section of the fuel opening and also a mechanism which moves the control drum in the direction of the axis of rotation thereof depending on the rotational position thereof can likewise be omitted. The adjustment of the idle oiliness, which otherwise takes place by rotation of the needle mounted in the thread, can take place by means of the electrically actuated valve. The control drum is advantageously mounted in the housing in such a manner that, in the event of a rotational movement of the control drum, no lifting movement takes place in the direction of the axis of rotation of the control drum. This results in a significantly simplified configuration of the carburetor. Fewer individual parts are required for producing the carburetor. Since the quantity of fuel supplied takes place via the electrically actuated valve, the tolerances to be observed are comparatively large, thus resulting in simple production.

The fuel opening is in particular the single fuel opening opening into the intake channel in the carburetor. The fuel opening advantageously opens into the intake channel in the control drum. The valve is advantageously an electromagnetic valve. The valve is preferably a valve which is open in the currentless state.

For a method for operating an internal combustion engine with a carburetor, it is provided that a temperature is determined before or during the starting of the internal combustion engine and that the flow of fuel through the fuel channel during the starting of the internal combustion engine is controlled depending on the temperature. The temperature here is advantageously a temperature of the internal combustion engine or is correlated to the temperature of the internal combustion engine. The temperature is in particular a temperature of a crank case of the internal combustion engine or a temperature of a control device of the internal combustion engine. On the basis of the temperature, it can be determined whether cold starting conditions or hot starting conditions prevail, and a decision can be made as to whether the internal combustion engine should be started with a quantity of fuel for a cold start or with a quantity of fuel for a hot start. Since the quantity of fuel supplied is controlled depending on the temperature, a separate choke element which has to be actuated by the operator can be omitted. A simple configuration of the internal combustion engine results. The control drum is advantageously the single component controlling the flow cross section of the intake channel. This results in simple operation since the supply of a sufficient quantity of fuel during the starting is automatically undertaken by the internal combustion engine depending on the temperature. A starting position does not have to be engaged by the operator. The decision as to whether cold starting conditions or hot starting conditions prevail is also undertaken by a controlling means of the internal combustion engine itself and not by the operator. The internal combustion engine is advantageously started with an intake channel cross section which is assigned to idle. As a result, an adjustment of the control drum into a starting position with a changed, that is, increased or reduced, flow cross section of the intake channel can be omitted.

If the internal combustion engine is intended to be started even at very low temperatures, the valve must permit a comparatively large volume flow rate of the fuel. In order to avoid overly enriching the internal combustion engine during idle, and at the same time during idle and under cold starting conditions to permit the same free flow cross section of the fuel opening, it is advantageously provided that, during idle, fuel is not supplied into the intake channel in individual engine cycles. For example, during idle, it is possible for fuel not to be supplied into the intake channel during every second or every third engine cycle. The number of engine cycles in which fuel is supplied can be appropriately selected here. As a result, sufficiently long opening durations of the electrically actuated valve can be achieved in the engine cycles in which the valve opens. The internal combustion engine is advantageously a two-stroke engine, and the intake channel supplies the fuel into a crank case of the internal combustion engine. However, the internal combustion engine may also be a mixture-lubricated four-stroke engine in which the intake channel opens into the crank case. Mixing of mixture and combustion air takes place in the crank case, leading to a uniform supply of fuel, even if fuel is not supplied into the intake channel in individual engine cycles.

The supply of fuel into the intake channel only in individual engine cycles is advantageously provided for an internal combustion engine which may also be started below −5° C. In an advantageous manner, it is identified when the first combustion takes place, and, after a combustion has been identified, the quantity of fuel supplied to the internal combustion engine during starting is significantly reduced. As a result, overly enriching the internal combustion engine after the starting can be avoided in a simple manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1shows a two-stroke engine1as an embodiment for an internal combustion engine. The two-stroke engine1is configured as a single-cylinder engine. Instead of the two-stroke engine1, a mixture-lubricated four-stroke engine may also be provided. The two-stroke engine1operates with a scavenging gas shield. However, a two-stroke engine operating without a scavenging gas shield may also provided. The two-stroke engine1serves in particular for driving the tool of a handheld work apparatus, such as a motor-driven chainsaw, a brushcutter, a cutoff machine, a blower, a lawnmower or the like.

The two-stroke engine1has a cylinder2in which a combustion chamber3is formed. The combustion chamber3is delimited by a piston5mounted in a reciprocating manner in the cylinder2. The piston5drives, via a connecting rod6, a crankshaft7rotatably mounted in a crankcase4. In the region of the bottom dead center (shown inFIG. 1) of the piston5, the interior of the crankcase4is connected to the combustion chamber3via transfer channels12in the vicinity of the inlet and transfer channels15in the vicinity of the outlet. In the embodiment shown, two transfer channels12in the vicinity of the inlet and two transfer channels15in the vicinity of the outlet are in each case provided. The transfer channels are arranged symmetrically with respect to the section plane inFIG. 1. The inlet-near transfer channels12open with transfer windows13into the combustion chamber3and the outlet-near transfer channels15with transfer windows16. An outlet10controlled by the piston5leads out of the combustion chamber3.

The two-stroke engine1draws in combustion air via an air filter17and a carburetor11. In the carburetor11, fuel is supplied into an intake channel21which opens with an intake channel inlet20at the cylinder bore. The intake channel inlet20is also controlled by the piston5. In addition, the two-stroke engine1has an air channel8which is likewise controlled by the carburetor11and which opens at the cylinder2via an air inlet9. The air inlet9is also controlled by the piston5. The piston5has a piston pocket14via which the air inlet9is connected to the transfer windows13and16of the transfer channels12and15in the region of the top dead center of the piston5. A partition wall59separates the intake channel21from the air channel8. The partition wall59extends at least in the carburetor11downstream of the fuel opening19. In the embodiment shown, the partition wall59extends over the entire length of the carburetor1and downstream of the carburetor11.

The carburetor11has a housing18in which a section24of the air channel8and a section25of the intake channel21are formed. A control drum22is mounted rotatably about an axis of rotation23in the housing18of the carburetor11. The axis of rotation23extends transversely with respect to intake channel21and air channel8and extends through the two channels. A fuel opening19, which opens into the intake channel21and supplies fuel to the intake channel21, is formed on the control drum22. The fuel is drawn up into the intake channel21because of the negative pressure prevailing in the intake channel21. The combustion air and the fuel/air mixture flow in the carburetor11in a direction of flow60from the air filter17in the direction of the cylinder2. A subsection26of the air channel8and a subsection27of the intake channel21are formed in the control drum22. By rotating the control drum22about the axis of rotation23, the free flow cross section of the section24of the air channel8and of the section25of the intake channel21is adjustable.

During operation, the piston5opens the intake channel inlet20during the upward stroke. Owing to the negative pressure in the crankcase4, fuel is sucked up out of the fuel opening19in the carburetor11into the intake channel21and is drawn up as a fuel/air mixture together with the drawn-up combustion air into the crankcase4. In the region of the top dead center of the piston5, air which is low in fuel or is substantially free of fuel is drawn up via the piston pocket14from the air inlet9of the air channel8into the transfer channels12and15via the transfer windows13and16. The drawing up of the air from the air channel8also takes place because of the negative pressure in the crankcase4. During the downward stroke of the piston5, the fuel/air mixture in the crankcase4is compressed. The downwardly moving piston5opens the transfer windows13and16before the bottom dead center is reached. Then, the air which is substantially free of fuel and is stored upstream in the transfer channels12and15first of all flows into the combustion chamber3and flushes out exhaust gases from the preceding engine cycle through the outlet10. Fresh mixture subsequently flows into the combustion chamber3from the crankcase4.

During the following upward stroke of the piston5, the mixture is compressed in the combustion chamber3and is ignited in the region of the top dead center of the piston5by a spark plug58projecting into the combustion chamber3. Owing to the combustion in the combustion chamber3, the piston5is accelerated back in the direction of the crankcase4. As soon as the piston5opens the outlet10during the downward stroke, the exhaust gases begin to flow out of the combustion chamber3. The mixture drawn up during the preceding upward movement of the piston5is simultaneously compressed in the crankcase4and air from the air channel8is stored upstream in the transfer channels12and15. The air stored upstream flows into the combustion chamber3as soon as the piston5has opened the transfer windows13and16. The remaining exhaust gases are flushed out through the outlet10by the air, which is substantially free from fuel, flowing into the combustion chamber3via the transfer channels12and15.

FIG. 2shows the carburetor11in a side view. The housing18of the carburetor11includes a base body47to which a cover46is fastened. An entry aperture51for the intake channel21and an entry aperture52for the air channel8are formed on the basic body47. AsFIG. 2shows, the entry apertures51and52are separated from each other by the partition wall59. AsFIG. 2. further shows, the partition wall59is not arranged centrally, but rather is offset toward the intake channel21, thus producing a flow cross section of the intake channel that is smaller than the flow cross section of the air channel8. AsFIG. 2shows, a wall section53which reduces the flow cross section of the entry aperture52is provided at the entry aperture52for the air channel8. The wall section53is provided here in such a manner that the air channel8is closed in the idle position of the control drum22. The control drum22is mounted in the cover46with a bearing shaft50which is shown inFIG. 2.

An actuating lever49is arranged on the bearing shaft50and a throttle cable (not shown) engages with this actuating lever. The throttle cable can be connected to a throttle lever of a work apparatus. The throttle cable is advantageously a Bowden cable. For the fixing of the sheath of the Bowden cable, a holder48is provided on the cover46of the carburetor11. However, a different actuation of the bearing shaft50or of the control drum22, for example via a linkage, may also be advantageous.

FIG. 3schematically shows the configuration of the carburetor11. The control drum22is shown here in an idle position54. In the idle position54, the control drum22bears against a stop (not shown) which is advantageously adjustable in order to adjust the idle. In the schematic inFIG. 3, the direction of flow60(FIG. 1) is directed from behind the image plane forward, that is, out of the image plane. The idle position54is an end position of the control drum22. A fuel chamber28is formed in the housing18of the carburetor11. In the embodiment, the fuel chamber28is separated from a compensation chamber66via a membrane65. The compensation chamber66is open toward the ambient, and therefore ambient pressure prevails in the compensation chamber66. In order to supply fuel into the fuel chamber28, a pump, for example, in particular a diaphragm pump driven by the fluctuating crankcase pressure, can be provided. In order to flood the fuel system after a relatively long shut down prior to the starting, a feed pump is provided in the embodiment, the pump bellows57of which is shown inFIG. 3. The fuel chamber28is connected to the fuel opening19via a fuel channel29. In the embodiment, the fuel opening19is formed on a longitudinal side of a tube67which projects into the subsection27of the intake channel21. However, a different configuration of the fuel opening19, in particular on the end side of a tube67, may be advantageous. The volume flow rate of the fuel through the fuel channel29is controlled by a valve30which is configured as an electromagnetic valve. The fuel channel29is formed unbranched. An unbranched fuel channel29here is a fuel channel in which the entire quantity of fuel flowing through the fuel channel29is controlled by the valve30and opens into the intake channel21via the fuel opening19.

FIG. 3also shows the configuration of the subsection27of the intake channel21in detail. The subsection27has an entry opening61which has a height (a), measured parallel to the axis of rotation23, and an exit opening63. The height of the subsection27at the exit opening63corresponds to the height (a) at the entry opening61.

The subsection26of the air channel has an entry opening62and an exit opening64. The entry opening62and the exit opening64are identical in size.

The control drum22is mounted in the housing18in such a manner that the control drum22does not execute any lifting movement during rotation about the axis of rotation23thereof. It can be provided that the control drum22is fixed for this purpose in an axially fixed manner in the housing18. In the embodiment shown, a compression spring45is provided between the cover46and the control drum22. The compression spring presses the control drum22against a base69of a receptacle68of the housing18. The control drum22is arranged rotatably about the axis of rotation23in the receptacle68. The compression spring45compensates for tolerances. An axial movement of the control drum22during operation is not provided.

FIG. 4shows by way of example the configuration of the valve30. In the embodiment, the valve30is a valve which is open in the currentless state. The valve30has a housing31in which a coil32, surrounded in a known manner by an iron core33, is arranged. An armature plate34is arranged on the end of the iron core33. The armature plate is pulled away from the iron core33and the coil32by a spring element35. A passage opening40, which is connected to an entry opening37for fuel, opens at the armature plate34. If the coil32is energized, the armature plate34is pulled against the passage opening40by the coil32such that the armature plate34closes the passage opening40. In the open state of the valve30shown inFIG. 4, fuel can flow via the entry opening37, the passage opening40, a gap39formed on the outer circumference of the armature plate34between armature plate34and housing31and through openings36in the spring element35to one or more exit openings38for fuel. The spring element35can have any expedient configuration here. The housing31is advantageously injection-molded over the coil32and the iron core33. The valve30controls the throughput of fuel through the fuel channel29over the period of time at which the valve30is open. For this purpose, the valve30is energized advantageously in a clocked manner.

FIGS. 5 to 10show the different flow cross sections of intake channel21and air channel8in the carburetor11for different rotational positions of the control drum22.FIGS. 5 and 6show the control drum22in the idle position54. In the idle position54, the control drum22is closed as far as possible. The control drum22customarily bears against a stop in the idle position54. An actuation by the operator, for example an actuation of a throttle lever, in order to adjust the idle position54, is unnecessary.

AsFIG. 5shows, the flow cross section of the section25of the intake channel21is partially closed by the control drum22. The entry opening61of the control drum22only partly overlaps with that section25of the intake channel21which is formed in the carburetor housing18. This gives rise to an entry aperture41which connects the subsection27in the control drum22to that section25of the intake channel21which is formed upstream of the control drum22. For the sake of better clarity, the entry aperture41is not shown inFIG. 3. The entry aperture41has a width (c) measured perpendicularly to the direction of flow60and perpendicularly to the axis of rotation23of the control drum22. On the downstream side of the control drum22, the exit opening63likewise has an overlap with the downstream section25of the intake channel21. An exit aperture43is thereby formed. The exit aperture43has a width (d) measured perpendicularly to the direction of flow60and perpendicularly to the axis of rotation23. The width (d) is significantly smaller than the width (c). As a result, the negative pressure prevailing at the fuel opening19is lower than the negative pressure in the intake channel21downstream of the control drum22. The quantity of fuel drawn up into the intake channel21is thereby reduced in the idle position. The fuel is supplied to the fuel opening19under a very slight positive pressure. Fuel is delivered from the fuel opening19into the intake channel21because of the negative pressure in the intake channel21. As a result, the negative pressure in the intake channel21has a very strong effect on the quantity of fuel drawn up through the fuel opening. By reducing the negative pressure at the fuel opening19in the idle position54, the quantity of fuel supplied can thereby be reduced in a simple manner with an identical opening duration of the valve30.

FIG. 6shows the section24of the air channel8in the idle position54. In the idle position54, the control drum22closes the air channel8such that additional combustion air is not drawn up via the air channel8. AsFIG. 6also shows, the wall sections53of the carburetor housing18have the effect that the control drum22still keeps the air channel8closed in the idle position54.

FIGS. 7 and 8show the control drum22in a part load position55. In comparison to the idle position54shown inFIGS. 5 and 6, the control drum22has been rotated about an angle of rotation (a) from the idle position54in the direction of the completely open position56shown inFIGS. 9 and 10. In the rotational position of the control drum22that is shown inFIG. 7, the width (e) of entry aperture41and exit aperture43is identical in size. This results in identical flow cross sections of entry aperture41and exit aperture43at a constant height (a) and identical cross-sectional shape. The negative pressure at the fuel opening19therefore corresponds to the negative pressure in the intake channel21downstream of the control drum22. Up to the part load position55shown inFIG. 7, the flow cross section of the entry aperture41is smaller than that of the exit aperture43. The angle of rotation (α), from which entry aperture41and exit aperture43have the same flow cross section, is advantageously 20°, in particular 30°, preferably 40°, starting from the idle position54.

AsFIG. 8shows, the air channel8is also open in the part load position55. The entry opening62partially overlaps the section24of the air channel8in the carburetor housing18. The exit opening63also partially overlaps the section24of the air channel8. The overlap produces an entry aperture42into the control drum22and an exit aperture44out of the control drum22. The entry aperture42has a width (f) measured perpendicularly to the direction of flow60and to the axis of rotation23. The exit aperture44has a width (g) measured in the same direction. The widths (f) and (g) are identical in size. The widths (f) and (g) are significantly smaller than the width (e) of entry aperture41and exit aperture44of the intake channel21in the part load position55shown. This arises because of the wall sections53(FIG. 6).

FIGS. 9 and 10show the control drum22in the completely open position56thereof. The completely open position56is assigned to the full load of the two-stroke engine1. In the completely open position56, the entry aperture41and the exit aperture43of the intake channel21are completely open. The complete opening of entry aperture41and exit aperture43is advantageously provided via an angle of rotation (β), which is at least 5°, from the completely open position56, shown inFIG. 9, in the direction of the idle position54. The angle (β) is advantageously at least 10°, in particular at least 20°.

In the completely open position56, the air channel8is also completely open, asFIG. 10shows. The entry aperture42and the exit aperture44have the same width (h). The width (h) is determined by the wall sections53.

AsFIGS. 5, 7 and 9schematically show, the free flow cross section of the fuel opening19is identical in size for each rotational position of the control drum22. A needle which controls the flow cross section of the fuel opening19depending on the rotational position of the control drum22is not provided. In the idle position54, the flow cross section of the exit aperture43of the section25of the intake channel21is advantageously at most 80% in particular at most 70%, preferably at most 60% of the flow cross section of the entry aperture41. A flow cross section of the outlet aperture43which is approximately 50% of the flow cross section of the entry aperture41is considered particularly advantageous.

For starting of the internal combustion engine, advantageously, more fuel is supplied at low temperatures than at higher temperatures. This is shown schematically inFIG. 11.FIG. 11shows the quantity of fuel (x) to be supplied in dependence on the temperature T. The temperature T is advantageously a temperature of the two-stroke engine1. The temperature T can be determined, for example, via a temperature sensor70, shown schematically on the crankcase4inFIG. 1. The temperature sensor70is connected to a controlling device71of the two-stroke engine1. The temperature sensor70may also be provided on the controlling device71itself. AsFIG. 3shows, the controlling device71is connected to the valve30and activates the valve30. The controlling device71also controls the ignition time point at which an ignition spark is triggered by the spark plug58. Cold starting conditions prevail below a temperature threshold value Tsat the temperature sensor70and hot starting conditions prevail above the temperature threshold value Ts. AsFIG. 11shows, a first quantity of fuel x1is supplied below a temperature threshold value Ts. Above the temperature threshold value Ts, a second quantity of fuel x2which is less than the quantity of fuel x1is supplied. The different quantities of fuel (x1, x2) can be achieved, for example, by different opening durations of the valve30. The valve30is activated here advantageously in a clocked manner, for example via a phase-angle control.

In order to be able to supply the very high quantity of fuel x1, the valve30has to be able to ensure a comparatively large maximum volume flow rate. In contrast during the idle, only a small quantity of fuel should be supplied. AsFIG. 5shows, the quantity of fuel drawn up into the intake channel21during idle can be adapted by the different flow cross sections of entry aperture41and exit aperture43. In order further to reduce the quantity of fuel (x) supplied during idle, the valve30does not open during each engine cycle. This is shown schematically inFIG. 12. The diagram shows the quantity of fuel (x) supplied as a function of the time (t) wherein the time (t) is plotted as number of engine cycles. In the first engine cycle1, a quantity of fuel x3is supplied which is significantly less then the quantity of fuel x2supplied during the hot starting and the quantity of fuel x1supplied during the cold starting. In the second engine cycle, the valve30is kept closed, and therefore fuel is not supplied in the second engine cycle2. Only in the third engine cycle is a quantity of fuel x3again supplied. Owing to the fact that fuel is supplied only during every second engine cycle, a reduced quantity of fuel arises in the crankcase4. This corresponds to a quantity of fuel x4supplied, shown by a dashed line inFIG. 12. The effectively supplied quantity of fuel can be reduced even further by supplying fuel only every third engine cycle, only every fourth engine cycle, et cetera.

For the operation of the two-stroke engine1, the temperature T is determined before or during starting. The quantity of fuel (x) to be supplied is defined with reference to the diagram shown inFIG. 11depending on the temperature T determined. During the starting of the internal combustion engine, the defined quantity of fuel (x) is then metered via the valve30. A starting position of the control drum22is not provided here. During the starting, the control drum22is arranged in the rotational position which is shown inFIGS. 5 and 6and is assigned to idle. An additional throttle element or a choke element for reducing the flow cross section of the intake channel21during the starting is not provided. As a result, the operator does not have to engage a choke during the starting and does not have to undertake any operation. The quantity of fuel (x) to be supplied during the starting is automatically adjusted by the controlling means71with reference to the temperature T measured.