Method and device for controlling an internal combustion engine

#This application claims priority to German Patent Application No. 10 2007 050 618.1 filed Oct. 23, 2007, the contents of which is incorporated herein by reference in its entirety.

#The invention relates to a method for controlling an internal combustion engine and a control device for carrying out said method.

#Modern engine electronics systems and associated control methods enable ever greater optimization of the efficiency of an internal combustion engine. In the case of Otto engines the timing position of the ignition point plays an essential role therein. The efficiency or torque produced by an Otto engine has a maximum which is dependent on the ignition advance angle. For the sake of protecting components, however, this optimum ignition advance angle can only be set to a few operating points. In large parts of the operating range of the internal combustion engine, operation of the internal combustion engine at this optimum ignition advance angle would lead to engine knocking and thus eventually to damage to the internal combustion engine. For this reason, in these operating ranges, the internal combustion engine must be operated with an ignition advance angle at which the efficiency is reduced. In the attempt to reach the highest efficiency level possible for each operating point, whilst simultaneously avoiding damage, modern engine control concepts include ‘knocking control systems’ which detect engine knocking and adjust the set ignition advance angle accordingly. By this means, the set ignition advance angle can be made to lie very close to the knocking limit of the engine.

#The invention will now be described in greater detail using one exemplary embodiment and by reference to the drawings, in which:

#FIG. 1 shows a schematic representation of an internal combustion engine;

#FIG. 2 shows a schematic representation of the efficiency of an internal combustion engine as a function of the set ignition advance angle at a particular operating point;

#In the method for controlling an internal combustion engine according to an embodiment, for an actual operating point of the internal combustion engine, a reference ignition advance angle at which the efficiency of the engine is at a maximum is determined. Furthermore, an actual ignition advance angle is determined with which the engine is to be operated at this operating point. Signal values which enable conclusions to be drawn concerning a knocking event in a combustion chamber of the internal combustion engine are detected from a sensor. To detect knocking, only the signal values coming from the sensor which lie within a predetermined evaluating interval are taken into account. The position of the evaluating interval is determined here as a function of the difference between the reference ignition advance angle and the actual ignition advance angle.

#In modern engine control concepts, for example, mapped engine control functions, the ignition advance angle or ignition time point that is to be set at an actual operating point is determined based upon an optimum reference ignition advance angle (point of maximum efficiency). The reference ignition advance angle is corrected to the extent that knocking is avoided as far as possible. It should be noted, however, that this anticipatory control of the ignition time point can never entirely rule out knocking. The ignition advance angle that is actually to be set therefore already includes the corrections needed to avoid knocking. The spacing or difference between the reference ignition advance angle and the actual ignition advance angle is therefore a measure of the knocking tendency of the internal combustion engine under current operating conditions. If the position of the evaluating interval is determined as a function of the difference between the reference ignition advance angle and the actual ignition advance angle, the anticipation value previously included in the length of the evaluating interval can be dispensed with or at least significantly reduced. Interfering signals are thereby largely excluded. This increases the precision of delineation and significantly improves the accuracy of detection of a knocking event.

#In an embodiment of the method, the actual ignition advance angle is determined in that the reference ignition advance angle is corrected depending on at least one operating parameter of the engine.