CN112709645A

CN112709645A - Method for controlling a valve for rapid heating of an exhaust system

Info

Publication number: CN112709645A
Application number: CN202011148930.3A
Authority: CN
Inventors: A·施瓦兹; D·康策尔曼; G·斯格罗伊; G·科姆蒂
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-10-24
Filing date: 2020-10-23
Publication date: 2021-04-27
Also published as: DE102019216361A1

Abstract

The present invention relates to a method for valve control in a four-stroke reciprocating motor, comprising the feature of operating at least one of the existing cylinders and at most half of the cylinders of said reciprocating motor in a heating mode, wherein the remaining cylinders are operated in a firing mode, and wherein said heating mode for the respective cylinder comprises opening at least one exhaust valve during the compression stroke.

Description

Method for controlling a valve for rapid heating of an exhaust system

Technical Field

The invention relates to a method for valve control in a reciprocating motor, a computing unit and a computer program for carrying out said method.

Background

The combustion motor functions on the basis of a cylinder in which the gas/fuel mixture is sucked in via a corresponding valve, compressed and then ignited. Work is performed on the piston by expansion of the heated gas, which thereby moves the crankshaft. Today, four-stroke motors are first of all common, for which one complete working cycle comprises two crankshaft revolutions. Valve control, that is to say the opening and closing of the inlet and outlet valves at the appropriate times, is usually effected by means of a camshaft, on which a correspondingly shaped cam is arranged for each valve.

It is possible to use the braking torque acting on the piston in the form of a motor brake during the compression stroke in order to support the braking action of the mechanical brake. In particular for commercial vehicles, motor brake systems are common here, for which the braking action is increased by further intervention of the valve control. For a pressure-reducing brake, for example, the exhaust valve is opened for a short time after compression, so that the prevailing pressure escapes and no further torque is applied to the piston. A great disadvantage of such motor brakes is the severe noise emissions which are produced above all by the sudden expansion of the severely compressed gas. A continuous step-down brake for which the additional throttle is kept open constantly throughout the braking phase offers another possibility for utilizing the braking action in the motor. The pressure in the cylinder is thereby reduced, in particular in the expansion phase, whereby a braking action is produced.

Furthermore, increasingly stringent exhaust gas standards have led to high-level values for the exhaust gas treatment of combustion motors. Many exhaust gas treatment systems, in particular oxidation and SCR catalysts (selective catalytic reduction), rely on reaching and continuously complying with a specific minimum temperature in order to be able to effectively convert a sufficient amount of pollutant substances. Therefore, different methods are used for heating the exhaust gas treatment system and the exhaust gas stream.

Disclosure of Invention

According to the invention, a method for valve control in a four-stroke reciprocating motor, a computing unit and a computer program for implementing the method are proposed with the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims and the following description.

In particular, a method for controlling a valve is therefore proposed, which comprises the following features: operating at least one of the existing cylinders and at most half of the cylinders of the reciprocating motor in a heating mode, wherein the heating mode comprises, for the respective cylinder, opening at least one exhaust valve during a compression stroke. By opening this, a decompression of the mixture is achieved, which prevents the action of the drive torque and leaves the previously compressed gas at an increased temperature level. In this way, the exhaust gas treatment system can quickly reach temperature values which enable high conversion rates of pollutants, such as high NOx conversion efficiencies in scr (selective Catalytic reduction) catalysts, and furthermore the exhaust gas treatment system can be permanently maintained in these temperature ranges.

In addition, the heating pattern preferably includes opening at least one exhaust valve of the cylinder during an exhaust stroke, wherein a valve stroke at which the at least one exhaust valve is opened during the compression stroke is less than a normal valve stroke at which the at least one exhaust valve is opened during the exhaust stroke. For example, the valve stroke during the compression stroke when opening the at least one exhaust valve may be at most half, preferably one third to one quarter, of the normal valve stroke during the exhaust stroke when opening.

In one possible embodiment, the heating mode furthermore comprises closing of at least one exhaust valve which is opened during the compression stroke after the beginning of the expansion stroke. The opening duration of the valve positively influences the cooling possibilities of the valve and also reduces the noise emissions.

According to another embodiment, the at least one exhaust valve which is opened during the compression stroke can be kept open until all exhaust valves are opened during the exhaust stroke. This particularly favorably affects the noise emission caused by the pressure reduction; furthermore, a small valve stroke can already be sufficient to achieve the desired effect.

In a further variant, the following control can also be carried out in the heating mode: opening at least one exhaust valve of the cylinder during a compression stroke and closing the at least one exhaust valve immediately thereafter during an expansion stroke, thereafter opening at least one exhaust valve during the expansion stroke and closing the at least one exhaust valve immediately thereafter after the beginning of an exhaust stroke, and re-opening at least one exhaust valve during an exhaust stroke and closing the at least one exhaust valve immediately thereafter after the beginning of an intake stroke, wherein the valve stroke at the time of opening during the expansion stroke is greater than the corresponding valve stroke at the time of opening during the exhaust stroke and during the compression stroke. In this way, a "two-stroke heating mode" is achieved, which achieves a higher heating of the exhaust gas, but in addition provides low noise emissions. In this variant, it is also preferred that all exhaust valves can be opened and closed at the mentioned control times, respectively.

The opening and closing of the at least one exhaust valve is advantageously brought about by a fixed or adjustable camshaft base. In this way, each embodiment can be realized in a very simple manner by means of a common variable valve control. In particular, for many embodiments, a change in the actuation time of only one valve on half of the cylinders is necessary, so that the camshaft changes only slightly. The variable camshaft based version enables a suitable heating pattern in any operating situation.

Furthermore, the heating mode can comprise at least temporarily increasing the charging pressure by means of an adjustable closing of the turbocharger, so that higher exhaust gas temperatures and exhaust gas enthalpies can be achieved. Furthermore, the embodiment can be supplemented by late injection of fuel into cylinders that are not operated in the heating mode. Thereby, the exhaust gas temperature and the exhaust gas enthalpy are also further increased.

According to one specific embodiment, for example, the temperature of the exhaust gas flow and/or of the exhaust gas treatment system can be detected, and the heating mode for at least one cylinder can then be activated or deactivated as a function of the detected temperature.

The computing unit according to the invention, for example, a control unit of a motor vehicle, is designed in particular by program technology for carrying out the method according to the invention.

The implementation of the method according to the invention in the form of a computer program or a computer program product with program code for implementing all method steps is also advantageous, since this results in particularly low costs, in particular if the controller used for execution is also used for other tasks and is therefore already present. Suitable data carriers for supplying the computer program are, inter alia, magnetic memories, optical memories and electrical memories, like for example hard disks, flash disks, EEPROMs, DVDs etc. The program can also be downloaded via a computer network (internet, intranet, etc.).

Further advantages and embodiments of the invention emerge from the description and the dependent claims.

Drawings

The invention is schematically illustrated in the drawings by means of embodiments and described below with reference to the drawings. Wherein:

FIG. 1a shows a graph of valve control times for fired cylinders in a four-stroke reciprocating motor according to the prior art;

FIG. 1b shows the associated cylinder pressure for the diagram of FIG. 1 a;

FIG. 2a shows a graph of valve control time for the first embodiment with a pressure relief stroke on at least one valve;

fig. 2b shows the associated cylinder pressure for the diagram of fig. 2 a;

FIG. 3a illustrates a graph of valve control time with constant throttling of at least one valve according to an embodiment;

fig. 3b shows the associated cylinder pressure for the diagram of fig. 3 a;

FIG. 4a shows a graph of valve control time with reduced noise loading and component loading for one embodiment;

FIG. 4b shows the associated cylinder pressure for the diagram of FIG. 4 a;

FIG. 5a shows a graph of valve control time for one embodiment with a second pressure reduction phase; and is

Fig. 5b shows the associated cylinder pressure for the diagram of fig. 5 a.

Detailed Description

Fig. 1 shows a diagram of valve control times for a fired cylinder of a four-stroke motor according to the prior art. The valve stroke is plotted in fig. 1a with respect to the crankshaft angle in ° KW (crankshaft angle). Here, the crankshaft angle describes the angle of the crankshaft relative to the top dead center (ZOT) of the piston. The corresponding working stroke of the cylinder is schematically shown by the diagram. After 720 KW, one working cycle of the four-stroke motor is completed and restarted.

At 0 ° KW, the piston is at top dead ignition (ZOT). The previous compression stroke 8 is also partially shown in the diagram. Ignition point 1 can be initiated by external ignition or by self-ignition. Expansion stroke 2 or the working stroke follows, until the bottom dead center of the piston, at 180 ° KW, in which work is usually performed on the crankshaft. Approximately with the beginning of the following exhaust stroke 4, the exhaust valve of the cylinder is opened, as can be seen on the valve control diagram with the first valve stroke 10, and closed again at the end of the stroke (360 ° KW). At this new top dead center (gas dead center, GOT) or shortly before it, the intake valve is opened for the intake stroke 6, curve 12, for the intake of air, an air-exhaust gas mixture or such a mixture with atomized or vaporized fuel. At the end of the stroke at bottom dead centre of 540 deg.kw the inlet valve is closed and a new compression stroke 8 is performed.

Fig. 1b shows the resulting pressure profile inside the cylinder, again for the valve control of fig. 1a over a working cycle, with respect to the crankshaft angle in 0 ° KW. An increased pressure 14 is formed during compression stroke 8, which pressure becomes maximum with combustion. By the subsequent expansion 2, the cylinder pressure 16 is reduced again and is minimal after opening the exhaust valve. Pressure is then built up again in the cylinder with the next compression stroke 8. The first hatched region in the compression stroke 8 shows the region in which the braking torque acts on the crankshaft, and the second hatched region from the ignition 1 in the expansion stroke 2 shows the region in which the drive torque acts on the crankshaft.

In fig. 2, an embodiment is now shown in which a camshaft-based version is utilized in the heating mode, which opens at least one exhaust valve on at least one cylinder outside of exhaust stroke 4. In this embodiment, as shown for the valve control profile in fig. 2a, at least one exhaust valve is partially opened at the end of compression stroke 8 and closed again shortly after the beginning of expansion stroke 2, similar to in a compression-release brake. The valve stroke 24 in this phase can be significantly smaller than the normal valve stroke 20 during the exhaust stroke 4, for example the normal stroke 20 can be approximately three to four times as large as the valve stroke 24 for pressure reduction. The set degree of the valve stroke can be selected in particular as a function of the duration of the valve opening and as a function of the existing geometry. In rare cases it may be sufficient to open only a single exhaust valve of a single cylinder, while the remaining valves remain closed during this phase as in normal operation. Thereby, the variation can be kept as small as possible compared to conventional camshaft arrangements. Preferably, one valve per cylinder can be opened and the heating mode can be applied to half of the cylinders present; it is therefore possible and sufficient for four cylinders to provide two cylinders with a pressure reduction stroke 24 on one exhaust valve, while the remaining two cylinders are operated in the normal ignition mode and exert the necessary total torque by means of a correspondingly increased injection quantity. In this way, a smooth motor operation can always be ensured and the exhaust gas is nevertheless heated.

In this embodiment, the remaining valve control time is the same as for normal operation in FIG. 1, that is, all exhaust valves of the cylinder are opened 20 between bottom dead center and top dead center during exhaust stroke 4 and then the intake valve is opened 22 as shown during the immediately subsequent intake stroke 6. The intake valve can remain closed for the remainder of the stroke.

Fig. 2b again shows the associated pressure profile in the cylinder during a working cycle. As can be seen in comparison with fig. 1b, a pressure 26 is first built up in the compression stroke 8 as usual. The opening of the at least one exhaust valve then causes a severe pressure drop 28. A braking torque is also always generated in the compression phase 8, but this braking torque is smaller than in normal operation (see fig. 1). However, the generation of positive drive torque acting on the crankshaft is completely dispensed with by the exhaust pressure.

A disadvantage of such an embodiment can be increased noise emissions which are caused by the valve opening 24 when the cylinder pressure is high and which then have to be reduced by corresponding damping measures.

Thus, according to a further variant, a valve control scheme can be used in which at least one exhaust valve of the cylinder remains partially open for a longer time, as shown in fig. 3 a. The at least one exhaust valve is partially re-opened 34 shortly after the start of compression stroke 8 at approximately 560 ° KW and is held in this position. In this case, similar to fig. 2, the valve can be closed again after some time or, as in fig. 3a, can remain open until the exhaust stroke 4 is reached at the bottom dead center. Thereafter, all exhaust valves are opened during the exhaust stroke as already in the previous embodiment, trying to compare the valve stroke 30. The opening time 34 of the at least one outlet valve can be selected as required and can also be carried out earlier or later in the compression stroke 8 than is shown in the exemplary embodiment.

Alternatively, the exhaust valve can be kept open continuously in the heating mode. The valve travel 34 for this constant opening is in turn preferably much smaller than the normal valve travel 30 in the exhaust stroke 4. The control profile 32 of the inlet valve remains unchanged as in the previous embodiment. Fig. 3b shows in the associated pressure curve that during the compression, only a small pressure 36 is still being built up by the early opening of the valve and no drive work is being performed. The lower pressure and early opening serve to significantly reduce noise emissions.

Fig. 4 shows a further embodiment in which the features of the previously described variants are combined. Here, as shown in fig. 4a, the exhaust valve can be opened shorter than in the previous exemplary embodiment of fig. 3, but already earlier than in the exemplary embodiment of fig. 2 and also longer overall than in this exemplary embodiment. Early opening significantly reduces noise emissions. As can be seen from fig. 4a, the at least one exhaust valve is partially opened approximately in the middle of compression stroke 8 (here approximately at-90 ° KW or 630 ° KW), only a small valve stroke 44 being provided again, and is closed again approximately at 90 ° KW. These values should serve merely as examples and can be adapted accordingly to a still flatter time control profile or still earlier valve opening. In particular, valve stroke 44 can again be significantly smaller by early opening than in the second exemplary embodiment, in which the exhaust valve is not opened until shortly before the end of compression stroke 8. For example, the valve stroke 44 used in the compression and expansion strokes may be only about 1/8 of the full lift 40 in the exhaust stroke 4, but the stroke may have a greater or lesser value. In the exemplary embodiment of fig. 3, the at least one valve remains open for a large part of the compression stroke 8 or permanently, but a shorter valve opening is provided here compared to the exemplary embodiment of fig. 3, which has the advantage that a better cooling of the outlet valve is possible, in particular via the valve seat. This significantly reduces the load on the component. The opening 40 of all exhaust valves in exhaust stroke 4 and the opening 42 of all intake valves in intake stroke 8 also remain substantially unchanged in this embodiment.

The associated pressure curve in fig. 4b is similar to the pressure curve in fig. 2b with a shorter decompression opening time, but for this purpose the advantages mentioned for the component loading and the noise loading are provided. The

smaller pressure buildup

46, 48 in this embodiment serves to generate a smaller braking torque and thus also a smaller heat generation, but for this reason also a smaller fuel consumption.

Since for the application it is here mainly the heating in the exhaust gas flow that is relevant, it is also possible to use other valve control profiles. Such an embodiment is shown in fig. 5. There, as in the exemplary embodiment according to fig. 2 or 4, the exhaust valve opening 54 takes place at the end of the compression stroke 8 with a small valve stroke 54, wherein all exhaust valves are then opened with a large lift 50 directly in the expansion stroke 2 and then closed again approximately at the beginning of the actual exhaust stroke 4 or shortly thereafter. Thereby drawing the exhaust gas or gases in the expansion stroke 2 back into the combustion chamber. At the beginning of the actual exhaust stroke 4, all exhaust valves of the respective cylinder remain closed in comparison with normal operation, so that the intake gas mixture is compressed again in the exhaust stroke 4. Thereafter, the exhaust valve is opened approximately in the middle of exhaust stroke 4, i.e. approximately at 270 ° KW with a low stroke 55, which can correspond approximately to first opening 54 in compression stroke 8 with regard to opening duration and valve stroke, but can also be carried out differently, for example with a shorter opening duration or with other valve strokes. During the intake stroke 6, the intake valve is opened and closed again for replacing the gas that has been heated up severely by the process by fresh, cooler gas. Thus, a second compression is achieved within one complete duty cycle.

In comparison to the preceding exemplary embodiment, the control times for all exhaust valves of the cylinders are preferably completely changed in the heating mode, so that a greater intervention in the camshaft is necessary. The control profile of the inlet valves remains unchanged, i.e. continues to include the opening 52 of all inlet valves at the beginning of the intake stroke 6, and all inlet valves are closed at the end of this stroke.

The associated pressure profile during the working cycle is again shown in fig. 5b, where after the first pressure buildup 56 and the decompression 59, the second compression 58 and decompression can be clearly seen in the next stroke, as in fig. 2 and 4. The dashed area represents the development of the braking torque. This control profile makes it possible to exert a higher braking force and thus also an improved heating action than in the previous embodiment from fig. 4 with similar noise emissions.

In all exemplary embodiments, it is sufficient to keep approximately half of the cylinders present or also fewer cylinders in one of the described operating modes for the heating operation, while the other cylinders ensure the drive action. In this case, the cylinders braked or in heating mode exhaust gas at a moderate temperature, while the ignited cylinders likewise cause a significantly higher exhaust gas temperature by means of the higher injection quantities necessary for compensation. Thus, although in principle all valves of the cylinder can be controlled as described, it is sufficient to actuate at least one exhaust valve according to the invention as cited in the exemplary embodiment (apart from fig. 5), while the other valves follow the control profile of the ignited operating mode.

There is at least one inlet valve and one outlet valve for each cylinder, but there can also be a plurality of valves, in particular 3 or 4 or more valves per cylinder. As already described, in order to achieve the concept according to the invention, it is sufficient to vary the valve control time for only one (exhaust) valve per cylinder in the heating mode, wherein preferably at most half of the cylinders present are operated in the heating mode.

All embodiments can be applied to any combustion motor, including motors for passenger cars (PKW), commercial vehicles, industrial motors, off-road motors, large motors, such as train or ship motors, and others.

For activating the heating operation, different methods can be used. For example, the heating operation can be selected manually or can always be used after the torque requested by the driver is below a certain predetermined limit, so that a part of the cylinders can also be supplied with sufficient power and there is the risk, in particular with minor demands, that: the exhaust gas temperature drops too much, for example in a parking operation at a traffic light. In addition or alternatively, the temperature, the different exhaust gas values or other parameters can be detected and evaluated by means of suitable sensors in the exhaust system and/or in the exhaust gas aftertreatment system in order to determine on the basis thereof whether a heating operation is currently required in order to achieve or maintain the required exhaust gas temperature.

In this case, if no or only a small motor braking force is desired, such a profile is also used in a defined manner, so that the additional opening of the valve can be used in particular to bring about an increase in the exhaust gas temperature.

Switching to heating operation can be effected by Variable Valve Timing (VVT), for example, by the provision of different cam patterns arranged next to one another, which can be moved accordingly. Since a change in the valve control times is already sufficient for a valve of each cylinder, it is only necessary to change a cam on the camshaft or to add a cam for switching, respectively, accordingly, so that improvements can be easily and cost-effectively achieved. As an example, for a motor with four cylinders, each with four valves, a change in the control times of only two of the sixteen valves can be sufficient to achieve operation according to the invention.

For all the aforementioned alternatives, further variants and developments can be used as follows for improving the heating function.

According to one specific embodiment, for example, the inlet valves of one or more cylinders can be deactivated during a warm-up operation. To this end, the valve control profile of the inlet valve (or of at least one inlet valve) can be copied to at least one exhaust valve such that the exhaust valves have substantially the same control times. The opening time does not have to be as wide as the opening time for the inlet valve, but can also be lower than the latter, provided that in principle the control profile follows the inlet valve.

This can be achieved in this way, namely: no mass flow into the exhaust system occurs due to this deactivated cylinder. Such an alternative can be advantageous if the exhaust system is already sufficiently hot, but cooling of the aftertreatment system should be prevented, which can be achieved in this way by reducing the mass flow while increasing the exhaust gas temperature.

In all embodiments, it is furthermore possible to selectively shut down an exhaust gas turbocharger, such as a vtg (variable Geometry turbocharger), in order to increase the charging pressure. Such turbochargers usually have an adjustable turbine geometry on the exhaust gas side. The resulting increased boost pressure can then cause an increased braking force by the braked cylinder, which is compensated by the ignited cylinder for generating the required total power, and the resulting increased boost pressure can thus cause an increased exhaust gas temperature in the heating mode. The enthalpy of the exhaust gas is also significantly increased. However, since compensation needs to be made by the increased injection quantity for the cylinder being ignited, the fuel consumption will thereby also increase.

This increase in the charging pressure, which can additionally be used to increase the exhaust gas recirculation rate, is brought about by the closing of the turbocharger. In this case, at least a portion of the exhaust gas flow is conducted back into the intake air flow and thus into the combustion chamber. The exhaust gas flow is either taken upstream of the turbine and fed in again upstream of the cylinders (high-pressure exhaust gas recirculation, HD-AGR), or is branched off after the turbocharger and preferably the particle filter and fed in again upstream of the turbocharger to the intake air flow (low-pressure exhaust gas recirculation, ND-AGR).

When the boost pressure is increased with high-pressure exhaust gas recirculation, nitrogen oxide (NOx) emissions can be significantly reduced. In simulations, it may have been shown that the nitrogen oxide emissions in this case are also lower than in the pure use of the preceding exemplary embodiment with heating operation, and the additional advantage of an increased exhaust gas temperature and an increased exhaust gas enthalpy is also provided here.

When low-pressure exhaust gas recirculation is used, nitrogen oxide emissions can also be reduced in the heating mode by increasing the boost pressure to a similar extent to when high-pressure exhaust gas recirculation is used. The advantage of the low-pressure variant is that there are no restrictions due to problems like "surge" of the turbocharger when the mass flow is small. In addition, the enthalpy flow via the turbine is thereby increased again, which, depending on other conditions, such as the operating point, can lead to a still higher charging pressure than in the case of the high-pressure variant.

In addition to this, in all variants and embodiments, the shift of the injection time in the cylinder being ignited towards a late injection of fuel can additionally be selected. This measure can also be used individually, which serves to reduce NOx emissions and at the same time to increase the exhaust gas temperature and the exhaust gas enthalpy.

The described embodiments can be combined with one another and can be used as a supplement on all embodiments of the invention for achieving the described effects.

Claims

1. A method for valve control in a four-stroke reciprocating motor, comprising:

operating at least one of the existing cylinders and at most half of the cylinders of the reciprocating motor in a heating mode, wherein the remaining cylinders are operated in a firing mode, and wherein the heating mode for the respective cylinder comprises:

at least one exhaust valve is opened (24, 34, 44, 54) during a compression stroke (8).

2. The method of claim 1, wherein the heating mode further comprises:

-opening (20, 30, 40) at least one exhaust valve of the cylinder during an exhaust stroke (4), wherein a valve stroke (24, 34, 44) when opening at least one exhaust valve during the compression stroke (8) is smaller than a valve stroke (20, 30, 40) when opening during the exhaust stroke (4).

3. Method according to claim 2, wherein the valve stroke (24, 34, 44) when opening the at least one exhaust valve during the compression stroke (8) is at most half, preferably one third to one quarter, of the normal valve stroke (20, 30, 40)) when opening during the exhaust stroke (4).

4. A method according to claim 2 or 3, wherein the heating mode further comprises:

-keeping open (34) at least one exhaust valve that was opened during a compression stroke (8) until opening (30) said at least one exhaust valve during said exhaust stroke (4).

5. A method according to any of claims 2-4, wherein all exhaust valves of the cylinder are opened during the exhaust stroke (4).

6. A method according to any of claims 1 to 3, wherein the heating mode further comprises:

-closing the at least one exhaust valve which is opened during the compression stroke (8) after the beginning of the expansion stroke (2).

7. The method of claim 1, wherein the heating mode comprises:

opening (50) at least one exhaust valve during the expansion stroke (2) and closing at least said one exhaust valve immediately after the start of the exhaust stroke (4), and

re-opening (55) at least one exhaust valve during the exhaust stroke (4) and closing the at least one exhaust valve immediately after the start of an intake stroke (6),

wherein the valve stroke (50) when open during the expansion stroke (2) is greater than the respective valve stroke (54, 55) when open during the exhaust stroke (4) and during the compression stroke (8).

8. The method of claim 1, wherein the heating mode comprises:

opening (54) all exhaust valves of the cylinder during the compression stroke (2) and closing all exhaust valves immediately thereafter during the expansion stroke (2), and

re-opening (50) all exhaust valves during the expansion stroke (2) and closing all exhaust valves immediately after the start of the exhaust stroke (4), and

re-opening (55) all exhaust valves during the exhaust stroke (4) and closing all exhaust valves immediately thereafter after the start of the intake stroke (6),

9. A method according to any preceding claim, wherein the heating pattern comprises de-activation of the inlet valve.

10. The method according to any of the preceding claims, wherein the heating mode further comprises:

the charging pressure is increased at least temporarily by the closing of the adjustable turbocharger.

11. The method according to any of the preceding claims, further comprising:

late injection of fuel into cylinders that are not operated in the heating mode.

12. The method according to any of the preceding claims, further comprising:

sensing the temperature of the exhaust gas stream and/or the exhaust gas treatment system, and

activating or deactivating a heating pattern for at least one cylinder based on the detected temperature.

13. A computing unit which is set up to carry out all method steps of the method according to one of the preceding claims.

14. Computer program which, when executed on a computing unit, causes the computing unit to carry out all the method steps of the method according to any one of claims 1 to 12.

15. A machine-readable storage medium having stored thereon a computer program according to claim 14.