Method for quantity correction of a pre-injection of an internal combustion engine

Abstract

Method for quantity correction of a pre-injection of an internal combustion engine, characterized in that a distinction (4) is made in a speed-based quantity compensation control as to whether a correction quantity (3) is positive or negative, that the correction quantity (3) of the speed-based quantity compensation control is distributed between at least one pre-injection quantity and a main injection quantity if the correction quantity (3) is positive, and that the correction quantity (3) is applied only to the main injection quantity if the correction quantity (3) is negative.

Description

[0001] The present invention relates to a method for correcting the quantity of a pre-injection in an internal combustion engine. Furthermore, the present invention relates to a computer program that executes all steps of the method according to the invention when run on a computer or control unit. The present invention also relates to a computer program product with program code stored on a machine-readable medium for carrying out the method according to the invention when the program is executed on a computer. Finally, the invention relates to a control unit configured for carrying out the method according to the invention. State of the art

[0002] To meet the emission limits stipulated by current legislation, the mixture formation of diesel engines is being further developed, among other things, by lowering the compression ratio towards homogeneous combustion. This means that, particularly in the cold state of the diesel engine immediately after starting, high demands are placed on the application and the injection system to ensure the necessary stability during cold idling and cold start-up. In a multi-injection scenario, for example, two pre-injections and one main injection are delivered during this start-up phase. The pre-injection quantities play a crucial role in mixture formation and combustion. An insufficient pre-injection quantity results in impaired combustion, which in the worst case can lead to a complete failure of the combustion reaction.

[0003] A pre-injection correction function, such as zero-quantity calibration (ZFC), which ensures a narrow tolerance band for pre-injection quantities over the operating time when the diesel engine is warm, can only be applied to a limited extent when the engine is cold. The lack of correlation between the pre-injection quantity when warm and cold is problematic in this case. Furthermore, when the engine is cold, the viscosity of the fuel has a dominant influence on the injection quantity.

[0004] The speed-based fuel quantity control (FBC) detects a "weak" cylinder even when the diesel engine is cold and adjusts the injection quantity for that cylinder accordingly. Modern FBC systems distribute the correction quantity between the pre-injection and main injection quantities using a map, thereby increasing the insufficient pre-injection quantity of a cylinder. To maintain quantity neutrality, the same amount must be subtracted from the total pre-injection quantity of the other cylinders in the diesel engine. This quantity reduction can lead to a deterioration of combustion in another cylinder. In the worst case, the speed-based fuel quantity control will learn up to its control threshold, which must be diagnosed as a fault according to OBDII regulations.

[0005] DE 10 2008 042 104 A1, DE 10 2012 206 781 A1, and DE 199 31 823 A1 concern the different weighting of correction quantities when distributing them among the individual partial injection quantities, whereby a reduction of partial injection quantities below a minimum quantity is to be avoided, particularly during pre-injection. DE 103 15 817 A1 and DE 10 2004 030 757 A1 concern the adjustment of the pre-injection quantity for thermodynamically effective pre-injection. DE 101 52 084 A1 and DE 10 2012 020 706 A1 describe a corrective intervention on the pre-injection quantity at low temperatures. Disclosure of the invention

[0006] In the inventive method for quantity correction of a pre-injection in an internal combustion engine, a speed-based quantity compensation control distinguishes between positive and negative correction quantities. This enables a differential distribution of negative and positive FBC correction quantities between at least one pre-injection quantity and one main injection quantity when the internal combustion engine is cold. The quantity neutrality of the quantity compensation control can be maintained to avoid compromising the conventional safety concept of FBC. Unintended torque increases of the internal combustion engine can thus be avoided. The increased robustness of the cold-start application of the inventive method enables a reduction in the potential FBC failure rate, particularly for Bin5 applications.By increasing the stability of the idling and start-up phases of the internal combustion engine in cold conditions, both when new and over its service life, improved driving performance of a motor vehicle powered by an internal combustion engine can be achieved. Emissions from the internal combustion engine in cold conditions due to poor combustion or misfires can be reduced by the method according to the invention.

[0007] The correction quantity of the speed-based quantity balancing control is distributed between at least one pre-injection quantity and one main injection quantity when the correction quantity is positive, and the correction quantity is applied only to the main injection quantity when the correction quantity is negative. This allows for a differential distribution of the negative and positive FBC correction quantities between the pre-injection quantity and the main injection quantity when the internal combustion engine is cold.

[0008] It is particularly preferred that the distribution of the positive correction quantity between the pre-injection quantity and the main injection quantity is carried out according to a first map, and that the application of the negative correction quantity to the main injection quantity is carried out according to a second map. These two maps complement the map for the correction quantity distribution in the conventional application of speed-based quantity compensation control. The mapping of the maps can be carried out and validated, for example, during an application phase on an engine test bench and / or on a motor vehicle powered by the internal combustion engine.

[0009] Furthermore, it is preferred that the distinction between positive and negative correction quantities is only made when a release value fulfills a release condition. This ensures that the inventive distinction between positive and negative correction quantities is only performed when necessary due to the condition of the internal combustion engine. It is particularly preferred that the correction quantity is distributed between the pre-injection quantity and the main injection quantity according to a third characteristic map when the release condition is not met. This third characteristic map can correspond to the characteristic map for a conventional application of speed-based quantity compensation control. This also creates the possibility of neutral data for a conventional quantity compensation control system.

[0010] In one embodiment of the invention, it is particularly preferred that the release value is the temperature of the internal combustion engine and that the release condition is met when this temperature falls below an applicable first threshold. The temperature can, in particular, be the temperature of the internal combustion engine before it is started. It can be further specified that, after the temperature exceeds a second threshold, during a coasting phase, or, if the internal combustion engine has a start-stop system, during a stop phase, a switch is made to an operating strategy of the internal combustion engine in which no distinction is made as to whether the correction quantity is positive or negative.

[0011] In another embodiment of the invention, in which an ITC function is used to control and / or regulate the internal combustion engine, it is particularly preferred that the enable value is the ITC enable status and that the enable condition is met when the ITC enable status is positive. The ITC function increases the actuation time of an injector of the internal combustion engine depending on the fuel viscosity and / or temperature.

[0012] According to the invention, it is also possible to forego the distinction between whether the correction quantity is positive or negative, which is only made when the release value meets the release condition, in order to apply the method according to the invention even when the engine is warm or in other operating modes. This is particularly advantageous when the pre-injection quantity plays a crucial role in combustion and the correction functions available in a control unit of the internal combustion engine cannot affect the pre-injection quantity more effectively than the method according to the invention.

[0013] The computer program according to the invention executes all steps of the method according to the invention when it runs on a computer or control unit. It enables a simple and cost-effective implementation of the method according to the invention into basic software or into customer-specific software for controlling and / or regulating the internal combustion engine. For this purpose, the computer program product according to the invention includes program code that is stored on a machine-readable medium and serves to carry out the method according to the invention when the program is executed on a computer or control unit. By uploading the computer program according to the invention to a control unit, the control unit according to the invention is obtained, which is configured to perform a quantity correction of a pre-injection of an internal combustion engine using the method according to the invention. Brief description of the drawing

[0014] An embodiment of the invention is shown schematically in the drawing and explained in more detail in the following description. Fig. Figure 1 is a flowchart of a process according to an embodiment of the invention. Exemplary embodiment of the invention

[0015] In one embodiment of the invention, the inventive method is used for quantity correction of a pre-injection of a diesel engine that has an electronically controlled common-rail injection system. According to the Fig. In the schematic representation of the procedure shown in Figure 1, the temperature of the diesel engine is first determined as the release value 1.

[0016] Then, it is checked whether a release condition 2 of the inventive method is fulfilled, which consists of the engine temperature falling below a threshold value. This threshold value marks the transition from a cold state of the diesel engine, in which the viscosity of the diesel fuel plays a dominant role in determining the injection quantity, to a warm state of the diesel engine. The diesel engine is operated with a multiple injection strategy in which the pre-injection quantities in the warm and cold states are not correlated with each other.

[0017] If the release condition 2 for the method according to the invention is met, a correction quantity 3 is determined using FBC, and a distinction 4 is then made as to whether this correction quantity is positive or negative. If the correction quantity 3 is positive, a correction quantity distribution is carried out according to a first characteristic map 5 such that the correction quantity acts on the pre-injection quantity and the main injection quantity. If, on the other hand, the correction quantity is negative, it is applied according to a second characteristic map, which is programmed such that the correction quantity only acts on the main injection quantity of the internal combustion engine.

[0018] If the release condition 2 is not met, the correction quantity 3 is determined using FBC and applied to the injection strategy of the internal combustion engine in the conventional manner. For this purpose, it is distributed between the pre-injection quantity and the main injection quantity according to a third map 7, which corresponds to the map for a conventional application of speed-based quantity compensation control.

[0019] The method according to the invention reduces the risk of an excessively high pre-injection quantity being delivered to a cylinder of the internal combustion engine. While in conventional applications the pre-injection quantity must be applied significantly above its optimum when the diesel engine is cold in order to ensure a sufficient margin to the combustion limit of the high injection quantity, this margin can be reduced in the method according to the invention, since an excessively low pre-injection quantity, which can occur, for example, due to injector-to-injector flow, can be corrected upwards in the method according to the invention.

Claims

[1] Method for correcting the quantity of a pre-injection of an internal combustion engine, characterized by that in a speed-based quantity compensation control a distinction (4) is made as to whether a correction quantity (3) is positive or negative, that the correction quantity (3) of the speed-based quantity compensation control is distributed between at least one pre-injection quantity and a main injection quantity if the correction quantity (3) is positive, and that the correction quantity (3) is only applied to the main injection quantity if the correction quantity (3) is negative. [2] Method according to claim 1, characterized by that the distribution of the positive correction quantity between the at least one pre-injection quantity and the main injection quantity takes place according to a first characteristic map (5), and that the application of the negative correction quantity to the main injection quantity takes place according to a second characteristic map (6). [3] Method according to one of claims 1 or 2, characterized bythat the distinction (4) as to whether the correction quantity (3) is positive or negative only occurs if a release value (1) fulfills a release condition (2). [4] Method according to claim 3, characterized by that the correction quantity (3) is distributed according to a third characteristic map (7) between at least one pre-injection quantity and the main injection quantity if the release condition (2) is not fulfilled. [5] Method according to claim 3 or 4, characterized by that the release value (1) is the temperature of the internal combustion engine, and that the release condition (2) is met when this temperature falls below an applicable threshold. [6] Method according to claim 3 or 4, characterized bythat the release value (1) is the ITC release status in an ITC function which is used for controlling and / or regulating the internal combustion engine, wherein the ITC function increases the activation duration of an injector of the internal combustion engine as a function of the fuel viscosity and / or the temperature, and that the release condition (2) is met when the ITC release status is positive. [7] A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method of any one of claims 1 to 6. [8] A computer program product comprising computer-readable instructions which, when loaded onto and executed on a suitable system, perform the steps of a method according to any one of claims 1 to 6. [9] Computer program product control unit which is designed to carry out a quantity correction of a pre-injection of an internal combustion engine by means of a method according to one of claims 1 to 6.

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