Method for warming up a catalytic converter arranged downstream from a spark-ignition, direct injection internal combustion engine

Abstract

The invention relates to a method for warming up at least one catalytic converter that is arranged downstream from a spark-ignition, direct injection internal combustion engine. To this end, an exhaust gas temperature is at least temporarily increased by at least one measure, which is executed by the engine, after the conclusion (t1) of the engine start of the internal combustion engine. The measures, which are executed by the engine, consist of a multiple injection during which at least two fuel injections into the cylinder are carried out within an induction cycle and compression cycle of a cylinder of the internal combustion engine, and/or said measures consist of a spark retarding. The invention provides that the measure executed by the engine or a combination of measures having the strongest heating action is available, at the earliest, after a retardation of at least two working cycles of the internal combustion engine after the conclusion (t1) of the engine start. The method makes it possible to keep jumps in torque low, which result from the initiation of heating measures, and to provide these in a manner that can be reproduced and easily regulated. Moreover, a reliable ignition and combustion can be guaranteed during the entire warming up phase.

Description

[0001] The invention relates to a method for warming up at least one catalytic converter arranged downstream of a spark-ignition, direct injection internal combustion engine, in particular after an engine start of the internal combustion engine, with the features of the preambles of the independent claims.

[0002] Catalytic converters are used in exhaust gas ducts of internal combustion engines for converting pollutants contained in the exhaust gases of the internal combustion engine into substances that are less harmful to the environment. The catalytic converters must be warmed up to at least a start or light-off temperature specific for catalytic converter in order to maintain their service readiness. The term start temperature hereby refers to a temperature where the catalytic converter has a conversion efficiency of 50%. Until the time after an engine cold start when the catalytic converter reaches its start temperature, pollutants in the exhaust gas can enter the atmosphere essentially unconverted. Several strategies are known for increasing an exhaust temperature and thereby accelerating catalytic converter warm-up.

[0003] It is known to retard an ignition angle, i.e., the time when an air-fuel mixture in a cylinder is ignited, relative to an ignition angle that provides the highest efficiency during the warm-up phase. Retardation of the ignition angle reduces the efficiency of the combustion while simultaneously increasing an exhaust gas temperature. The hotter exhaust gas causes the catalytic converters to heat up faster. The method of retarding ignition reaches its limits at ignition angles where the internal combustion engine begins to run unacceptably rough and reliable ignition can no longer be guaranteed.

[0004] Another method for increasing the exhaust gas temperature includes so-called multiple injection which has recently been described for direct-injection, spark-ignition internal combustion engines, where the fuel is injected directly through injection valves into a combustion chamber of a cylinder (WO 00/08328, EP 0 982 489 A2, WO 00/57045). In this case, a total fuel quantity to be supplied during an operating cycle of a cylinder is divided into two parts and supplied in two injection processes to the combustion chamber of the cylinder. A first early injection (homogeneous injection) takes place during an intake stroke of the cylinder so that the injected fuel quantity is at the following ignition time at least substantially homogeneously distributed in the combustion chamber. On the other hand, a second late injection (stratified injection) is carried out during a following compression stroke, in particular during the second half of the compression stroke, resulting in a so-called stratified charge where the injected fuel cloud is essentially concentrated in the region surrounding a spark plug of the cylinder. Accordingly, multiple injection operation of the internal combustion engine involves a mixed operation of stratified charging and homogeneous charging. The particular ignition characteristic of the multiple injection operation results in an increased exhaust gas temperature compared to a completely homogeneous operation. In addition to increasing the exhaust gas temperature, multiple injection advantageously also reduces raw emission of nitric oxides NOx and unburned hydrocarbons HC, thereby reducing pollutant breakthrough during the warm-up phase.

[0005] Initiating and terminating the multiple injection, in other words the transition from single to multiple injection operation and back, poses problems. In particular, the late stratified injection causes the fuel to be partial knocked off the piston head, the cylinder walls and the spark plug due to the low-temperature of the internal combustion engine after engine start. The fuel that does not evaporate at the cold engine temperature is not available for the subsequent combustion process. As a result, misfirings and rough combustion processes occur. Another problem is the early ignition angle at the time of the changeover to multiple injection which lies in particular before the upper dead center U.D.C. Since an injection end of the late injection is also located in or shortly before this range, the mixture cannot be optimally conditioned since there is not enough time available for transporting the stratified cloud from the injector to the spark plug. As a result, higher HC raw emissions are observed.

[0006] It is an object of the present invention to develop a method for warming up a catalytic converter whereby engine-related heating measures, in particular a changeover into a multiple injection operation and back, occurs with the lowest possible emission of pollutants and minimal torque variations.

[0007] The object is solved by a method with the characterizing features of the independent claims 1, 3 and 4.

[0008] According to the invention, the engine-related measure or combination of measures implemented during a warm-up with the most profound heating effect occurs at the earliest after a delay of at least two operating cycles of the internal combustion engine, in particular of at least three, preferably at least five operating cycles, after the conclusion of the engine start. The term conclusion of the engine start indicates here in the point in time where the engine speed, after a rotation speed overshoot during the starting process, lies for the first time in a rotation speed range of 95 to 105% of a nominal idle rotation speed. If no pronounced rotation speed overshoot occurs during the startup phase due to the employed principle, then the conclusion of the engine start is interpreted as the point in time where the engine rotation speed is for the first time continuously for at least 0.5 seconds in the rotation speed range of 95 to 105% of the nominal idle rotation speed. Moreover, the term operating cycle is to be understood as performing once all operational processes of an internal combustion engine on one cylinder. In a four-cycle engine, these represent two crankshafts revolutions.

[0009] Since an increasing heating effect, i.e., an increasing exhaust gas temperature, is necessarily associated with a decrease in the engine efficiency and therefore with an increasing torque loss, the method of the invention makes it possible to keep torque discontinuities small by, for example, switching and/or enhancing the heating measures successively in the order of their potential heating effect. Even if the heating measure or measures are introduced in a single stage after a delay, the initial operation still causes the internal combustion engine to warm up and stabilize, so that the subsequent torque discontinuity becomes more reproducible and more easily controllable, thereby maintaining a reliable ignition and combustion.

[0010] In particular, a single injection operation is performed during a first phase of the warm-up after the conclusion of the engine start, wherein the ignition angle is at least temporary retarded, and a changeover to a multiple injection operation occurs during a subsequent second phase. The term retardation of the ignition angle is to be understood as each ignition point that occurs after an ignition point with the highest engine efficiency, which in particular results in a reduced engine efficiency by at least 5%. The cylinder is therefore already warmed up due to the ignition angle retardation during the first phase, thereby effectively reducing so-called wall film problems that occur as a result of fuel condensation from the late injection in multiple injection operation.

[0011] According to another modified embodiment of the method, an operation with 30 to 100% of an injected fuel quantity occurs after the conclusion of the engine start with an essentially homogeneous mixture preparation at an ignition time during a first phase, and a multiple injection operation occurs in a subsequent second phase where at the ignition time at least 35% of an injected fuel quantity are present as a stratified charge and at least 20% of the fuel quantity in a homogeneous distribution. Preferably, the first phase occurs during a completely homogeneous operation, whereby the total injected fuel quantity is available at the ignition time in form of an essentially homogeneous mixture. In the context of this invention, homogeneous operation is to be understood as representing a fuel density distribution in the combustion chamber at the time of ignition, where the highest fuel density at a point in the combustion chamber deviates from the lowest fuel density at another location in the combustion chamber by less than 30%. Such homogeneity can be achieved in a known manner by an injection during an intake stroke of the cylinder, in particular within the first half of the intake stroke.

[0012] The multiple injection preferably includes two injections, whereby a first, early injection occurs essentially during an intake stroke of a cylinder, preferably during a first half of the intake stroke, and a second, late injection occurs during a subsequent compression stroke, preferably during a second half of the compression stroke. In this way, an essentially homogeneous distribution of the fuel supplied in the early injection at the ignition time is achieved as well as a stratified charge of the fuel supplied in the late injection which is concentrated essentially in a region around a spark plug of the cylinder. Accordingly, the early injection will be referred to as homogeneous injection and the late injection as stratified injection. As already described above, such mixed fuel processing simultaneously increases the combustion and/or exhaust gas temperature and reduces a raw emission of unburnt hydrocarbons and nitric oxides. The fuel fractions of the two injections are preferably selected so that the homogeneous injection results in a very lean fuel mixture that cannot be ignited by itself and can only be combusted with the help of the stratified charge of the second injection. To guarantee a completed combustion of the homogeneous charge, the fuel quantity supplied during homogeneous injection should be no less than 20% of the total supplied fuel quantity. Preferably, a slightly lean to stoichiometric air-fuel mixture with a lambda value between 1 and 1.2 is set during warm-up. The lambda value during the multiple injection phase can be more strongly shifted towards lean than during the preceding first phase of the warm-up, taking advantage of the fact that the catalytic converter has a lower startup temperature in a lean exhaust gas atmosphere than in a stoichiometric atmosphere.

[0013] According to a particular advantageous embodiment of the invention, the first phase is initially started with an early ignition angle, in particular with an ignition angle before the upper dead center (U.D.C.), which preferably corresponds to the ignition angle selected during the engine start. This early ignition angle is thereafter progressively retarded, in particular past the U.D.C. The progressive retardation of the ignition angle can be continuous and/or stepwise. Preferably, when changing over to a multiple injection operation by taking into consideration a torque compensation at the switching point, the approximate last ignition angle of the first phase is adopted and continuously and progressively retarded further. Preferably, the changeover occurs at an ignition angle where a completely homogeneous operation is still possible. In particular, the changeover should occur around 6°, in particular around 4°, preferably around 2° before this critical ignition angle so as to permit corrections in the ignition angle to compensate the torque change that occurs during the changeover into the multiple injection operation. The changeover to multiple injection operation can occur preferably at an ignition angle of between 0 and 20° after U.D.C., in particular of 10° after U.D.C., taking into account the torque reserve. After changeover to the multiple injection operation, the ignition point should be progressively shifted towards the latest possible ignition angle that depends on the engine design. A maximum ignition angle of 20 to 45° after U.D.C., in particular of 35° after U.D.C., should not be exceeded.

[0014] According to another improvement of the method, an injection angle, or injection time, of the late stratified injection is also progressively retarded after changeover into the multiple injection operation, which can take place essentially synchronously with the progressive retardation of the ignition angle. Preferably, an injection end of the late injection is shifted with an essentially constant difference to the ignition angle of 50 to 100°, in particular of 60 to 80°. This difference can also be varied as a function of the engine rotation speed and/or the injection pressure, which ensures a consistent optimized time for mixture preparation of the stratified injection and transport of the fuel cloud to the spark plug.

[0015] Advantageously, the multiple injection, for example after at least partial warm-up of at least a first catalytic converter, can be terminated depending on an actual operating point of the internal combustion engine. If the internal combustion engine is at that time at the beginning of a load demand phase, for example in a startup and/or or acceleration phase, then the torque reserve expended for the heating measure can be utilized immediately; the multiple injection and/or the retardation of the injection angle can be immediately terminated, and the internal combustion engine can be switched over to a homogeneous or stratified operation. Conversely, if the internal combustion engine is in a constant load phase, for example in idle, after completing warm-up, then the heating measures are preferably reduced in the reverse order of their initiation. In particular, the injection angle of the stratified injection and/or the ignition angle are progressively advanced, and a changeover into the single injection operation takes place as soon as the ignition angle permits a homogeneous operation.

[0016] The time diagrams of all the aforedescribed methods, in particular the initiation of those engine-related measures or combination of measures with the most profound heating effect, the changeover to multiple injection operation and/or or the identification of the completed warm-up and reduction of the measures, can occur based on a measured and/or or modeled engine and/or or exhaust gas and/or catalytic converter temperature, and/or based on a time elapsed after-the conclusion of the engine start and/or completed crankshaft revolutions and/or a distance traveled and/or a cumulative exhaust gas heat flow.

[0017] Additional advantageous embodiment of the invention are recited in the dependent claims.

[0018] Embodiments of the invention will be described hereinafter in more detail with reference to the appended drawings. It is shown in:

[0019] FIG. 1 a time diagram of engine rotation speed, ignition angle and injection angle during a warm-up phase according to a conventional method;

[0020] FIG. 2 a time diagram of raw emission of unburnt hydrocarbons during a warm-up phase according to two methods that do not correspond to the invention;

[0021] FIG. 3 a time diagram of engine rotation speed, ignition angle and injection angle according to a method for warming up a catalytic converter according to a first embodiment of the invention;

[0022] FIG. 4 a time diagram of engine rotation speed, ignition angle and injection angle according to a second embodiment of the invention;

[0023] FIG. 5 a time diagram of engine rotation speed, ignition angle and injection angle according to a third embodiment of the invention;

[0024] FIG. 6 a time diagram of engine rotation speed, ignition angle and injection angle during a termination of the warm-up according to a fourth embodiment of the invention; and

[0025] FIG. 7 a time diagram of engine rotation speed, ignition angle and injection angle during a termination of the warm-up according to a fifth embodiment of the invention.

[0026] FIG. 1 shows a method for warming up a catalytic converter located downstream of conventional a direct-injection internal combustion engine. The starter motor is energized before a time t0, during which time the starter motor starts up, couples to the internal combustion engine and drives the engine initially to a minimum rotation speed. An engine start phase takes place between t0 and t1, during which the engine rotation speed n of the internal combustion engine increases and thereafter settles in a range of a substantially constant nominal idle rotation speed. The internal combustion engine operates in homogeneous operation until the begin of the engine start t0, wherein a total fuel quantity to be supplied is injected in a single injection process during an intake stroke of a cylinder (single injection). The ignition angle &agr;Z is hereby set to a crankshaft angle KWW before the upper dead center U.D.C., in particular to an ignition angle that ensures the highest engine efficiency and/or or the highest starting reliability.

[0027] According to known methods, the internal combustion engine changes over to a multiple injection operation already at the beginning of the engine run-up at the time t0 in order to increase an exhaust gas temperature and accelerate the warm-up of the downstream catalytic converter. A fraction of the fuel quantity is hereby injected during the intake stroke and hence is present as a homogeneous mixture at the ignition time (homogeneous injection). The remaining fuel quantity is injected in a second, late injection during a compression stroke, in particular during the second half of the compression stroke (stratified injection). According to the illustrated method, the injection angle &agr;EE for the late injection (stratified injection) is kept constant during the warm-up. When the multiple injection begins, the ignition angle &agr;Z is typically retarded, typically into the range around the upper ignition dead center U.D.C.

[0028] The aforedescribed approach provides, on one hand, only a short time interval between the injection time of the late stratified injection and the ignition time and, on the other hand, a small distance between the injection valve and the piston head at the time of injection. As a result, the late injected fuel cannot be optimally formed as a stratified cloud and transported into the region of the spark plug before the ignition time. Instead, the fuel is concentrated at the ignition time mainly in the region of the piston head in the form of a stratified cloud. Moreover, mixture preparation is adversely affected by the late injection in the multiple injection operation which begins immediately at the beginning of the engine start t0, because the engine, in particular the piston head, is still cold and causes the late injected fuel to condensate on the piston head, the cylinder walls and the spark plug, by preventing complete evaporation due to the cold temperatures. As a result of the insufficiently short conditioning time for the mixture and the cold combustion chamber, the internal combustion engine runs increasingly rough, shows noticeably higher HC raw emission, misfires and can even shut down. The heating measures are conventionally terminated at the time tE when they catalytic converter has reached its light-off temperature. A noticeable torque discontinuity is observed at this time, as described above in conjunction with the initiation of the multiple injection operation.

[0029] FIG. 2 depicts measured curves of the raw emission of unburnt hydrocarbons HC when the internal combustion engine is operating according to two methods for warming up the catalytic converter that are not part of the invention. The measurements are performed after an engine cold start at 20° C. and with the depicted vehicle speed profile vFZG conforming to the “New European Driving Cycle” NEFZ. The starting point of the time axis corresponds to the conclusion of the motor (time t1 in FIG. 1), i.e., the time where the engine rotation speed, after a rotation speed overshoot, lies during the start process for the first time in the range of a nominal idle rotation speed ±5%. The air-fuel ratio was in both cases controlled to a slightly lean lambda value between 1.0 and 1.1. The curve HCSZ shows the HC raw emission of the internal combustion engine with conventional retarded ignition with a latest ignition angle of approximately 10° after U.D.C. in single injection operation with homogeneous mixture conditioning. The curve HCME, on the other hand, shows the HC raw emission in multiple injection operation with 50% of the injected fuel quantity in homogeneous and 50% in stratified fuel conditioning. The control end of the late injection was about 40° before U.D.C. with a latest ignition angle of 27° after U.D.C. In both measurements, the respective heating measures, i.e. late ignition (HCSZ) and multiple injection/late ignition (HCME), where initiated immediately after the conclusion of the motor start t1. Most curves show profound HC emission maxima at approximately 3 to 4 seconds. This indicates that a multiple injection operation causes a much higher observable pollutant emission that a conventional retarded ignition. When the heating measures are initiated, the ignition angle is still relatively early at approximately 10° before U.D.C. During a time interval of approximately 1.5 to 3 seconds the ignition angle is shifted to the latest ignition angle commensurate with the heating measures. In conventional late ignition, the essentially homogeneous mixture preparation provides a sufficiently high ignition reliability over the entire ignition angle window between 20° before U.D.C.. and 10° after U.D.C., so that a maximum HC emission of only approximately 100 g/h is reached. Conversely, if the heating measure includes multiple injection, then no ignition-safe mixture preparation is possible at the beginning of the heating measure, i.e., at an ignition angle of 10° before U.D.C. The mixture preparation is improved only during the shift of the ignition angle to the latest possible ignition angle, with the HC emissions decreasing due to the higher likelihood of ignition. The maximum HC emission is with 190 g/h significantly higher and also extends over a longer time than HC emission with conventional late ignition. As also indicated, beneficial mixture preparation is not possible with conventional ignition angles in a range around the U.D.C. (see FIG. 1).

[0030] FIG. 3 shows the initiation of the engine heating measures according to a first embodiment of the invention. Shortly after the conclusion of the engine start (t1), a heat demand for a catalytic converter is identified at a time t2, for example based on a measured or modeled catalytic converter temperature. The multiple injection operation is then initiated with an early homogeneous injection during the intake stroke and a late stratified injection during the compression stroke, whereby the control end of the stratified injection &agr;EE is initially set to a very early time, for example to 60 to 80° before U.D.C. The control end &agr;EE of the stratified injection is thereafter continuously retarded. When the multiple injection operation begins at time t2 the ignition angle &agr;Z, which was located at the conclusion of the engine start, for example, at 10°. before U.D.C., is progressively retarded. The injection angle &agr;EE and the ignition angle &agr;Z are essentially retarded synchronously, preferably with a constant separation relative to each other of the 50 to 100°, in particular 60 to 80°, wherein this separation can be varied depending on the engine rotation speed n and/or and injection pressure. This provides sufficient time for conditioning the mixture. At a time t4 the injection angle &agr;EE and the ignition angle &agr;Z have reached their allowed maximum values for a particular heating power. These settings are, for example, for the control end of the injection angle &agr;EE at 40° before U.D.C. and for the ignition angle &agr;Z of 20 to 30° after U.D.C. The heating measures have therefore the most profound heating effect after the time t4. The progressive increase of the heating effect between the times t2 and t4 make it possible to obtain a stronger maximum heating effect compared to the state-of-the-art. The slowly decreasing efficiency, starting at the time t2, effectively prevents strong torque variations. The initially very early injection angle &agr;EE also counteracts precipitation on the piston head of the fuel injected during the second injection. The piston head is at this time located far away from the injection valve.

[0031] The formation of the stratified charge of the late injection in multiple injection operation as well as its transport to the spark plug can be promoted by suitably shaping the surface of the piston head, in particular by forming troughs in the piston head, as well as by generating suitable air current conditions in the combustion chamber. These measures are known from stratified direct-injection internal combustion engines and will therefore not be further explained. The embodiment of the method depicted in FIG. 3 is particularly advantageous for internal combustion engine which generate the stratified operation predominantly through a tumble gas flow. This method is only sub-optimal for direct injection engines that operate with a mixture conditioning process with a high swirl flow ratio, since with the piston located near the bottom, the injection cloud in the stratified injection is not perfectly diverted towards the spark plug and unravels at the time of ignition, preventing an ideal combustion process and increasing HC emissions.

[0032] An advantageous improvement of the method is depicted in FIG. 4. In this embodiment, the ignition angle &agr;Z is first progressively retarded during a first phase at the time t2 when the heat demand of the catalytic converter is identified. This represents a first heating measure. The internal combustion engine is hereby operated with a main fuel fraction, preferable the entire fuel, homogeneously distributed in the combustion chamber, whereby the fuel is preferably injected during the intake stroke. The multiple injection operation is initiated at a time t3 at an ignition angle of 0° to 20° after U.D.C., preferably at 10° after U.D.C. This range of ignition angles also represents a limit up to which a stable homogeneous operation is still possible. Particularly advantageously, changeover into the multiple injection operation occurs several degrees before the latest possible homogeneous ignition angle in order to retain a torque reserve for an eventually required adjustment of the ignition angle after a changeover to multiple injection. The ignition angle &agr;Z during the single injection operation is adopted for multiple injection operation, taking into consideration the above ignition angle adjustment. The ignition angle &agr;Z is also progressively retarded after the changeover at time t3, until a latest possible injection angle &agr;Z is reached at the time t4. This injection angle is at most approximately 35° after U.D.C. Certain torque reserves should also be considered (approximately ±2°) for adjusting the torque, for example, in idle. The control end &agr;EE of the stratified injection is in this case set from the start to a desired setting of, for example, 40° before U.D.C. and then kept unchanged, since the separation between the ignition angle &agr;Z and the injection angle &agr;EE is adequate from the beginning (t3) of the multiple injection. This ensures a sufficient mixture preparation and optimal combustion, also during the multiple injection operation. A maximum exhaust gas temperature in this example is reached at the time t4 with a delay of several operating cycles after the conclusion of the engine start at time t1.

[0033] Another advantageous improvement of the method is depicted in FIG. 5. The ignition angle &agr;Z is hereby controlled essentially in the same manner as in the preceding example. The multiple injection operation is again initiated at an ignition angle &agr;Z of approximately 10° after U.D.C. A control end of the injection angle &agr;EE for the stratified injection is preferably initially set at 50 to 70° before U.D.C.. The ignition angle &agr;EE is then progressively retarded in synchronism with the injection angle &agr;Z, until the injection angle &agr;EE and the ignition angle &agr;Z have reached their desired ranges at the time t4, providing maximum heating power. From this time on, both angles are held at a constant value. During the entire multiple injection operation, the injection end &agr;EE and the ignition angle &agr;Z have an essentially constant separation of 50 to 100°, preferably 60 to 80°, optionally depending on the engine rotation speed and/or the injection pressure, so that an optimal mixture preparation is achieved. The exemplary embodiment depicted FIG. 5 represents an optimized solution with respect to torque neutrality, pollutant emission and smoothness of running.

[0034] The respective engine-related heating measures are preferably decreased in the reverse order in which they were initiated, as long as the internal combustion engine operates mostly with constant load demand, preferably in idle. A corresponding embodiment is shown in FIG. 6. At the time t5, a sufficient warm-up of the catalytic converter, preferably a pre-catalytic converter, is identified based on a measured and/or modeled catalytic converter temperature. Alternatively, this point can also be identified based on an elapsed time after the conclusion of the engine start t1, a number of revolutions since the conclusion of the engine start, a traveled distance and/or and introduced heat flow. At the time t5, both the control end &agr;EE of the stratified injection and the ignition angle &agr;Z are steadily advanced with an essentially constant separation that can depend on the operating point. As soon as an ignition angle &agr;Z is reached that permits, for example, a homogeneous operation, the multiple injection is terminated (time t6). The ignition angle &agr;Z is thereafter progressively farther advanced until a desired ignition angle that depends on the actual operating point of the internal combustion engine is approximately reached.

[0035] Conversely, if the end of the warm-up is reached at a time when a positive load demand has built-up, for example at the beginning of a start up or an acceleration phase, then all heating measures can be immediately decreased at time tE, as shown in FIG. 7, and the available charge can be used directly for changing the load demand. More particularly, the multiple injection operation is terminated and the ignition angle &agr;Z is set to the optimal range for the actual operating point.

LIST OF REFERENCE NUMERALS

[0036] &agr;Z ignition angle

[0037] &agr;EE controlling stratified injection (injection angle)

[0038] HCME HC raw emission with catalytic converter warm-up according to conventional multiple injection

[0039] HCSZ HC raw emission with catalytic converter warm-up according to conventional retarded ignition

[0040] KWW crankshaft angle

[0041] n engine rotation speed

[0042] t time

[0043] t1 engine start end

[0044] vFZG vehicle speed

[0045] U.D.C. upper dead center

Claims

1. Method for warming up at least one catalytic converter arranged downstream of a spark-ignition, direct injection internal combustion engine, whereby after a conclusion of an engine start (t1) of the internal combustion engine an exhaust gas temperature is increased at least temporarily by at least one engine-related measure, and whereby the engine-related measures comprise a multiple injection, wherein at least two fuel injections into the cylinder are performed within an intake and compression stroke of a cylinder of the internal combustion engine and/or a retardation of an ignition angle, characterized in that the engine-related measure or combination of measures with the most profound heating effect occurs at the earliest after a delay of at least two operating cycles of the internal combustion engine after the conclusion of the engine start (t1).

2. Method according to claim 1, characterized in that the engine-related measure or the combination of measures with the most profound heating effect occurs at the earliest after a delay of at least three, in particular of at least five, operating cycles of the internal combustion engine after the conclusion of the engine start (t1).

3. Method for warming up at least one catalytic converter arranged downstream of a spark-ignition, direct injection internal combustion engine, whereby after an end of an engine start (t1) of the internal combustion engine an exhaust gas temperature is increased at least temporarily by at least one engine-related measure, and the engine-related measures comprise a multiple injection, wherein at least two fuel injections into the cylinder are performed within an intake and compression stroke of a cylinder of the internal combustion engine, and/or a retardation of an ignition angle, characterized in that after the conclusion of the engine start (t1), a single injection operation with at least temporary retardation of the ignition angle is performed during a first phase, and a changeover into a multiple injection operation occurs during a subsequent second phase.

4. Method for warming up at least one catalytic converter arranged downstream of a spark-ignition, direct injection internal combustion engine, whereby after an end of an engine start (t1) of the internal combustion engine an exhaust gas temperature is increased at least temporarily by at least one engine-related measure, and the engine-related measures comprise a multiple injection, wherein at least two fuel injections into the cylinder are performed within an intake and compression stroke of a cylinder of the internal combustion engine, and/or a retardation of an ignition angle, characterized in that after the conclusion of the engine start (t1), an operation with 30 to 100% of an injected fuel quantity occurs during a first phase with an essentially homogeneous mixture preparation at an ignition time, and a multiple injection operation occurs in a subsequent second phase, wherein at the ignition time at least 35% of an injected fuel quantity is present as stratified charge and at least 20% of the fuel quantity is present in homogeneous distribution.

5. Method according to one of the preceding claims, characterized in that the multiple injection comprises two injections, wherein a first early injection occurs essentially during an intake stroke and a second, late injection occurs during a subsequent compression stroke, and that the fuel supplied during the early injection has at the ignition time an essentially homogeneous distribution in the combustion chamber of the cylinder and the fuel supplied during the late injection is concentrated at the ignition time essentially as a stratified charge in a region around a spark plug.

6. Method according to claim 5, characterized in that the early injection takes place in particular during a first half of the intake stroke and the late injection during a second half of the compression stroke.

7. Method according to one of the claims 3 to 6, characterized in that the first phase is started initially with an early ignition angle (&agr;Z), in particular with an ignition angle (&agr;Z) before the upper dead center (U.D.C.), and that thereafter the ignition angle is adjusted progressively, continuously and/or stepwise towards a later ignition point, in particular up to an ignition angle (&agr;Z) after the upper dead center (U.D.C.).

8. Method according to claim 7, characterized in that the changeover to a multiple injection operation occurs at an ignition angle (&agr;Z) of between 0 and 20° after U.D.C., in particular of 10° after U.D.C.

9. Method according to claim 8, characterized in that the changeover into a multiple injection operation occurs around 4°, in particular around 2° before an ignition angle (&agr;Z) at which an exclusively homogeneous operation is still barely possible.

10. Method according to one of the claims 7 to 9, characterized in that at the changeover to the multiple injection operation the last ignition angle (&agr;Z) of the first phase is adopted and the progressive retardation of the injection angle is continued after the changeover to the multiple injection operation.

11. Method according to claim 10, characterized in that the progressive retardation of the injection angle occurs at a maximum ignition angle (&agr;Z) of 20 to 45° after U.D.C., in particular at a maximum ignition angle (&agr;Z) of 35° after U.D.C.

12. Method according to one of the preceding claims, characterized in that an injection angle (&agr;EE) of the late injection of the multiple injection is retarded essentially synchronously with the progressive retardation of the ignition angle.

13. Method according to claim 12, characterized in that an injection end (&agr;EE) of the late injection is adjusted with an essentially constant difference of 50 to 100°, in particular of 60 to 80°, relative to the ignition angle (&agr;Z).

14. Method according to claim 13, characterized in that the difference between the injection end (&agr;EE) of the late injection and the injection angle (&agr;Z) is varied as a function of the engine rotation speed (n) and/or an injection pressure.

15. Method according to one of the claims 12 to 14, characterized in that the injection end of the late injection is initially set to an angle (&agr;EE) of 40 to 90° before U.D.C., in particular 50 to 80° before U.D.C., and subsequently adjusted to an angle (&agr;EE) of 30 to 50° before U.D.C., in particular 40° before U.D.C.

16. Method according to one of the preceding claims, characterized in that the initiation of the engine-related measure or the combination of measures with the most profound heating effect and/or the changeover to the multiple injection operation is identified based on a measured and/or or modeled engine and/or exhaust gas and/or catalytic converter temperature, and/or a time elapsed after the conclusion of the engine start and/or since a number of crankshaft revolutions after the conclusion of the engine start and/or a distance traveled after the conclusion of the engine start and/or a cumulative exhaust gas heat flow since the conclusion of the engine start.

17. Method according to one of the preceding claims, characterized in that when the internal combustion engine is in a phase with an essentially constant load, in particular in idle, after at least partial warm-up of at least a first catalytic converter, the ignition angle (&agr;Z) and/or the injection angle (&agr;EE) is progressively advanced and the multiple injection is terminated and a changeover to the single injection operation occurs as soon as the ignition angle (&agr;EE) permits a homogeneous operation.

18. Method according to claim 17, characterized in that the changeover to the single injection operation occurs at an ignition angle (&agr;Z) of 5 to 15° after U.D.C., in particular 10° after U.D.C.

19. Method according to claim 17 or 18, characterized in that the progressive advancement of the ignition angle continues after the changeover to the single injection operation.

20. Method according to one of the preceding claims, characterized in that when the internal combustion engine is in a load demand phase, in particular in a startup and/or acceleration phase, after at least partial warm-up of at least a first catalytic converter, the multiple injection and/or the retardation of the ignition angle is immediately terminated and a changeover to a single injection operation occurs.

21. Method according to one of the claims 17 to 20, characterized in that the completed warm-up is identified based on a measured and/or or modeled exhaust gas and/or catalytic converter temperature and/or a time elapsed after the conclusion of the engine start and/or since a number of crankshaft revolutions after the conclusion of the engine start and/or a distance traveled after the conclusion of the engine start and/or a cumulative exhaust gas heat flow since the conclusion of the engine start.