Method for operating an internal combustion engine

Abstract

Method for operating an internal combustion engine of a motor vehicle with direct fuel injection, wherein the internal combustion engine has a NOx catalyst and is operated in an engine stop-start mode, and wherein, for the purpose of regenerating the catalyst, the air-fuel mixture is enriched at every nth start phase (with n greater than or equal to one) of the internal combustion engine from an automatic engine stop.

Description

[0001] The invention relates to a method for operating an internal combustion engine of a motor vehicle. The internal combustion engine has direct fuel injection for injecting fuel into the combustion chamber of individual cylinders of the engine, as well as a nitrogen oxide catalyst (NOx catalyst) for cleaning the exhaust gas of nitrogen oxides. Furthermore, the internal combustion engine is controlled by a control unit (engine control unit) such that an automatic engine stop-start operation is performed. In this process, a motor vehicle powered by the internal combustion engine is monitored for impending stop phases, e.g., at a traffic light or during stop-and-go traffic in a traffic jam, and upon detection of an impending stop phase (e.g.,If a predetermined speed limit is undershot and the brake pedal is simultaneously applied, the internal combustion engine is temporarily shut down by switching off the ignition and / or fuel supply. If a start signal is detected (e.g., pressing the accelerator pedal and not pressing the brake pedal), an automatic engine start is initiated.

[0002] In motor vehicles with direct injection internal combustion engines and nitrogen oxide catalyst systems, the internal combustion engine is usually enriched at predetermined time intervals according to a map in order to regenerate the nitrogen oxide catalyst.

[0003] Further methods for operating an internal combustion engine are known from patent documents DE 10 2004 007 220 B4 and US 2006 / 0 021 330 A1.

[0004] The invention is based on the objective of reducing the increased fuel consumption in a motor vehicle due to mixture enrichment during regeneration phases, or of improving the overall energy balance in such engine stop-start systems.

[0005] According to the invention, the problem is solved by the entirety of the features of claim 1, while preferred embodiments of the invention are specified in the dependent claims. According to the invention, the internal combustion engine is operated with a rich air-fuel mixture (lambda less than 1) during every nth start-up phase (n greater than or equal to 1) – preferably during every start-up of the internal combustion engine – after an automatic engine stop (or during every automatic start-up phase in engine stop-start operation). For this purpose, an excessive amount of fuel is injected into the combustion chambers of the cylinders of the internal combustion engine during each automatic start-up phase.

[0006] Preferably, the amount of fuel to be injected during the automatic start phase is determined as a function of an operating parameter of the internal combustion engine and / or a parameter of the engine or vehicle environment. Particularly suitable operating parameters are the current temperature of the internal combustion engine and / or the temperature of the air in the intake manifold and / or the temperature of the air outside the intake manifold and / or the position of the stationary crankshaft before the automatic engine start and / or the time elapsed since the last enrichment.

[0007] Advantageously, targeted enrichment during the automatic start phases occurs only for a predetermined duration after each automatic start of the internal combustion engine. In a particularly preferred embodiment of the invention, the enrichment occurs only for a predetermined number of crankshaft revolutions after each automatic start. Enrichment for just one crankshaft revolution may be sufficient in this case.

[0008] Another embodiment of the invention is characterized in that each cylinder, or each cylinder of a cylinder group, is individually enriched or supplied with fuel when cylinders start simultaneously. During an automatic starting process, the individual cylinders or cylinder groups are started sequentially at fixed time intervals, whereby, advantageously, an individually enriched air-fuel mixture is determined for each cylinder or cylinder group starting simultaneously, and a corresponding quantity of fuel is supplied to each cylinder to be started.

[0009] The single figure schematically depicts a driving cycle, with the current vehicle speed plotted against time. One such driving cycle is the New European Driving Cycle (NEDC), during which specific acceleration phases (B), constant speed phases (K), and driving breaks (FP) must be completed. In the illustrated example, the driving breaks (FP) are achieved through automatic engine stops at times t. Stop_1 - t Stop_n The driving breaks initiated by the engine stop-start operation of the internal combustion engine are initiated. As described above, the driving breaks (FP) initiated by the engine stops are ended by automatic engine starts at times t. Start_1 - t Start_n, wherein at each point during an automatic engine start, a correspondingly enriched air-fuel mixture is determined and the appropriate amount of fuel is supplied to the internal combustion engine or to the individual cylinders of the internal combustion engine (as described above). The invention allows fuel to be saved and / or the overall energy balance of the described engine start-stop systems to be significantly improved. By enabling the elimination of other regeneration phases for the catalytic converter using a modified start application (as explained above), an improved result is achieved in the overall energy balance of such start-stop systems.

Claims

[1] Method for operating an internal combustion engine of a motor vehicle with direct fuel injection, wherein the internal combustion engine has a NOx catalyst and is operated in an engine stop-start mode, and wherein, for the purpose of regenerating the catalyst, the air-fuel mixture is enriched at every nth start phase (with n greater than or equal to one) of the internal combustion engine from an automatic engine stop. [2] Method according to claim 1, characterized by , that the amount of fuel to be injected is determined as a function of at least one operating parameter of the internal combustion engine in order to enrich the air-fuel mixture. [3] Method according to any of the preceding claims, characterized by, that the amount of fuel to be injected during an automatic start process, in which individual cylinders or individual cylinder groups with simultaneously starting cylinders are started one after the other until all cylinders of the internal combustion engine are activated, is determined individually for each cylinder or for each cylinder of a cylinder group. [4] Method according to any of the preceding claims, characterized by , that at least one operating parameter is the temperature of the internal combustion engine and / or the temperature of the air in the intake manifold and / or the temperature of the air to be drawn in outside the intake manifold and / or the initial position or crankshaft angle of the stationary crankshaft before automatic engine start. [5] Method according to any of the foregoing claims, characterized bythat the enrichment of the air-fuel mixture only takes place for a predetermined number of crankshaft revolutions, in particular the enrichment only for the first crankshaft revolution after the automatic engine start.

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