Method for operating an internal combustion engine with multiple injections

Abstract

Method for operating an internal combustion engine operated with multiple injections (4), comprising the steps: (S100) Reading in input operating parameters (IPP) of the internal combustion engine (4), (S200) Determining at least one lambda adjustment (LA) for multiple injections based on the input operating parameters (EBP), (S300) Comparing at least one lambda adjustment (LA) with a reference criterion (RK), (S400) Suppressing at least one lambda adjustment (LA) if the at least one lambda adjustment (LA) violates the reference criterion (RK) and the at least one lambda adjustment (LA) is associated with a post-injection (NE) of the multiple injections, and (S500) Perform at least one lambda adjustment (LA) when the lambda adjustment (LA) is assigned to a main injection (HE) of the multiple injections.

Description

[0001] The invention relates to a method for operating an internal combustion engine operated with multiple injections. Furthermore, the invention relates to a computer program product, a control unit, and a motor vehicle having such a control unit.

[0002] To make combustion in internal combustion engines, such as gasoline or diesel engines, even more efficient, multiple injection is used. In this case, the fuel is not always injected into the combustion chamber all at once; instead, depending on the engine speed and load, the injection is divided into up to four individual injections.

[0003] Modern diesel engines, for example, have pre-injection, main injection, and post-injection. Pre-injection, also called pilot injection, occurs before the main injection. This is intended to make the combustion process in the diesel engine smoother. This improves running smoothness and noise levels. During the main injection, as the name suggests, the majority of the fuel is directed into the cylinder. The so-called post-injection completes the injection process. The purpose of post-injection is to further optimize combustion and thus reduce emissions.

[0004] To comply with various pollutant and other emission limits, it is necessary to precisely measure the amount of fuel to be supplied. During the heating-up of catalysts in an exhaust aftertreatment system and / or during stratified charge operation, the time between fuel injections is very short, requiring particularly high precision.

[0005] During operation, so-called lambda adjustments can be made to achieve a predetermined lambda value (also called combustion air ratio λ).

[0006] However, if lambda adjustments occur during operation, e.g., in the range of ±5%, pollutant and other emission limits can no longer be met. If, for example, the lambda adjustments are too large, compliance with emission limits, especially for particulate emissions, can no longer be guaranteed. However, if a negative lambda adjustment occurs, the amount of fuel to be injected can become so small that its value falls below the minimum required for reliable operation of an internal combustion engine's fuel injector.

[0007] DE 198 29 308 A1 discloses a control device for a direct-injection gasoline engine. The control device is intended to prevent, during two-step injection (weakly stratified combustion), in which part of the fuel is injected during the intake stroke and the remaining fuel during the compression stroke, one of the divided injection quantities from being smaller than a minimum compensation quantity of a fuel injector. To achieve this, a total injection quantity is divided, at the time a command to perform two-step injection is issued, into an injection quantity for homogeneous combustion, to be injected during the intake stroke, and an injection quantity for stratified combustion, to be injected during the compression stroke, depending on a division ratio that corresponds to a target air-fuel ratio.Furthermore, after splitting, each of the two injection quantities and is compared with a smallest compensation quantity of the fuel injector. Depending on the result of this comparison, the injection quantity with the smaller split ratio is set to zero, and the injection quantity with the larger split ratio is set to the total injection quantity if it is determined that one of the two injection quantities and is smaller than the smallest compensation quantity.

[0008] DE 10 2005 001 887 B3 discloses a method for increasing the control range for equalizing injection quantity differences, particularly in internal combustion engines with multiple injections. If the maximum injection quantity of all individual injections of an injector of the internal combustion engine is less than the minimum quantity required for cylinder equalization control, the injection pattern is modified such that the injection quantity of at least one individual injection is greater than or equal to the required minimum quantity without changing the torque output of the internal combustion engine.

[0009] DE 10 2004 054 240 A1 discloses a method for operating an internal combustion engine. Fuel is injected into a combustion chamber at least temporarily per power stroke by means of a group of individual injections. The distribution of the total fuel quantity to be injected per power stroke among the individual injections depends, at least temporarily, on a target lambda value.

[0010] DE 10 2011 078 482 A1 discloses a method for controlling a fuel injector system for injecting fuel during a working cycle of an internal combustion engine. It comprises the steps of determining a combustion state of the internal combustion engine and deriving a plurality of injection pulses with associated fuel injectors and pulse durations from the combustion state. It is determined that a fuel quantity associated with one of the fuel injectors and one of the injection pulses is below a predetermined threshold, and a reduced number of injection pulses with associated fuel injectors and pulse durations are derived from the combustion state.

[0011] DE 10 2013 213 694 A1, DE 10 2006 019 317 A1 and DE 10 2008 042 104 A1 each disclose further methods for operating an internal combustion engine operated with multiple injections.

[0012] There is therefore a need to identify ways to improve the operation of an internal combustion engine using multiple injections.

[0013] The object of the invention is achieved by a method for operating an internal combustion engine operated with multiple injections, comprising the steps: Reading input operating parameters of the internal combustion engine, Determining at least one lambda adjustment for the multiple injections based on the input operating parameters, Comparing the at least one lambda adjustment with a reference criterion, Suppressing the at least one lambda adjustment if the at least one lambda adjustment violates the reference criterion and the at least one lambda adjustment is assigned to a pre-injection and / or a post-injection of the multiple injections, and Executing the at least one lambda adjustment if the lambda adjustment is assigned to a main injection of the multiple injections.

[0014] In other words, lambda adjustments are only permitted and executed if they are assigned to the main injection, since the main injection is less sensitive to changes in the amount of fuel injected than a pre-injection or post-injection. This can improve the operation of the multiple-injection internal combustion engine.

[0015] According to one embodiment, the reference criterion is a maximum limit for a value for a fuel quantity to be injected for the lambda adjustment, and a violation of the reference criterion is concluded if the value for a fuel quantity to be injected for the lambda adjustment is greater than the maximum limit. The value is therefore representative of a fuel quantity to be injected within the scope of the lambda adjustment. If the at least one lambda adjustment leads to an excessively large fuel quantity to be injected, emission limits, in particular for particulate emissions, can no longer be met. In other words, pollutant emissions can be reduced.

[0016] According to a further embodiment, the reference criterion is a minimum limit value for a value for a fuel quantity to be injected for the lambda adjustment, and a violation of the reference criterion is concluded if the value for a fuel quantity to be injected for the lambda adjustment is less than the minimum limit value. The value is therefore representative of a fuel quantity to be injected within the scope of the lambda adjustment. If the at least one lambda adjustment results in a fuel quantity to be injected that is so small that its value lies below a minimum quantity for reliable operation of a fuel injector of the internal combustion engine, this specification cannot be implemented by the fuel injector and would merely result in an increase in pollutant emissions and other emissions.It can be provided that, in a first sub-step, a check is first carried out to determine whether a negative lambda adjustment is present, which would lead to a reduction in the fuel quantity to be injected. In a second sub-step, a check is first carried out to determine whether the fuel quantity to be injected is less than the minimum limit. This two-stage approach reduces the demand for computing resources, e.g., of a control unit for operating a motor vehicle's internal combustion engine with multiple injections.

[0017] The invention further includes a computer program product, a control unit and a motor vehicle with such a control unit.

[0018] The invention will now be explained with reference to a drawing. It shows: Fig. 1 shows a schematic representation of components of an internal combustion engine of a motor vehicle. Fig. 2 shows a schematic representation of a process flow for the operation of the Fig. 1 shown internal combustion engine.

[0019] It will initially be Fig. 1 referred to.

[0020] Shown is an internal combustion engine 4 of a motor vehicle 2, such as a car.

[0021] The internal combustion engine 4 has a cylinder 8 in which a piston 10 is displaceably arranged and drives a crankshaft (both not shown) via a connecting rod.

[0022] The cylinder 8 and the piston 10 define a combustion chamber 24 of the internal combustion engine 4 in which an ignitable mixture of fuel and air is burned.

[0023] For supplying air, an intake pipe 12 is provided which can be opened and closed by means of an inlet valve 14 in order to fill the combustion chamber 24 with air in a controlled manner.

[0024] The internal combustion engine 4 is a gasoline engine with direct injection. Therefore, an injection nozzle 16 is provided for supplying fuel to the combustion chamber 24, to which fuel, in the present embodiment gasoline, can be supplied via a fuel line 18. In contrast to the present embodiment, the internal combustion engine 4 can also be a diesel engine with direct injection.

[0025] Furthermore, an exhaust pipe 20 is provided for discharging the combustion gases from the combustion chamber 24, which exhaust pipe can be opened and closed by means of an outlet valve 22 in order to be able to discharge the combustion gases from the combustion chamber 24 in a controlled manner.

[0026] Furthermore, the internal combustion engine 4 is assigned a control unit 6, which controls, among other things, the intake valve 14, the injection nozzle 16, and the exhaust valve 22. For this purpose and for the tasks and functions described below, the control unit 6 can have hardware and / or software components.

[0027] During operation, the control unit 6 controls in particular the injection nozzle 16 in such a way that the internal combustion engine 4 is operated with multiple injections.

[0028] For this purpose, the control unit 6 is designed to read input operating parameters EBP of the internal combustion engine 4. In the present exemplary embodiment, the input operating parameters EBP are a position of an accelerator pedal of the motor vehicle 2.

[0029] The control unit 6 is further configured to determine a value for a brake mean effective pressure (BMEP) by evaluating the input operating parameters EBP, e.g., the position of an accelerator pedal. By evaluating the brake mean effective pressure, the control unit 6 determines an indicated mean effective pressure (IMEP). Using an internal efficiency of the internal combustion engine 4, the control unit 6 can then determine a fuel mass flow and, based on the determined fuel mass flow and a predetermined lambda value, an air mass flow.

[0030] In addition, the control unit 6 is designed to distribute a now determined quantity of fuel to be injected over several injection processes of a multiple injection.

[0031] In the present exemplary embodiment, the multiple injection comprises a pre-injection VE, a main injection HE, and a post-injection NE. Deviating from the present exemplary embodiment, multiple pre-injections VE and / or multiple post-injections NE may also be provided.

[0032] The control unit 6 distributes the amount of fuel to be injected between the pre-injection VE, the main injection HE and the post-injection NE in order to provide the requested torque according to the position of the accelerator pedal and to keep pollutant emissions and other emissions as low as possible.

[0033] During operation, control unit 6 can also perform a lambda adjustment LB to ensure a predetermined lambda value is achieved. The lambda adjustment LA results in a change in the amount of fuel to be injected.

[0034] Larger lambda adjustments LA, e.g., in the range of ±5%, can lead to a failure to comply with pollutant and other emission limits. On the other hand, if a negative lambda adjustment LA is present, the fuel quantity to be injected for a single injection can become so small that its value falls below the minimum quantity required for reliable operation of a fuel injector of the internal combustion engine 4.

[0035] It will now be discussed with additional reference to the Fig. 2 a method for operating the internal combustion engine 4 explains how the operation of the internal combustion engine 4 operated with multiple injections can be improved, in particular how it can be ensured that pollutant and other emission limit values ​​are complied with even in the case of lambda adjustments LA.

[0036] The method begins with a first step S100.

[0037] In the first step S100, the input operating parameters EBP of the internal combustion engine 4, ie the position of the accelerator pedal of the motor vehicle 2, are read in.

[0038] In a further step S200, at least one lambda adaptation LA for the multiple injections is determined based on the input operating parameters EBP.

[0039] In a further step S300, the at least one lambda adaptation LA is compared with a reference criterion RK.

[0040] In the present exemplary embodiment, the reference criterion RK comprises a maximum limit value MAX and a minimum limit value MIN for a value W of the lambda adjustment LA. The value W is representative of the fuel quantity to be injected within the scope of the lambda adjustment LA.

[0041] In a first substep, it is checked whether the value W of the lambda adjustment LA is greater than the maximum limit MAX. If this is the case, it is concluded that the reference criterion RK has been violated.

[0042] Furthermore, in a further sub-step, it is checked whether the value W of the lambda adjustment LA is less than the minimum limit value MIN. If this is the case, it is concluded that the reference criterion RK has been violated.

[0043] Furthermore, it can be provided that, in a first sub-step, a check is performed to determine whether a negative lambda adjustment LA is present, which would lead to a reduction in the fuel quantity to be injected. In a second sub-step, a check is first performed to determine whether the fuel quantity to be injected is less than the minimum limit. This two-step procedure reduces the computing resources required by control unit 6.

[0044] If the reference criterion RK is violated and the at least one lambda adjustment LA is assigned to the pre-injection VE and / or the post-injection NE of the multiple injections, the at least one lambda adjustment LA is suppressed in a further step S400. In other words, lambda adjustments LA are only permitted and executed if they are assigned to the main injection HE, since the main injection HE is not as sensitive to changes in the fuel quantity to be injected as compared to the pre-injection VE or the post-injection NE.

[0045] In a further step S500, the at least one lambda adjustment LA is assigned to the main injection HE. In other words, the proportion of the main injection HE to the total injection quantity, which is composed of the fuel quantity to be injected during the pre-injection VE, the main injection HE, and the post-injection NE, is increased, thus making the main injection HE more dominant. This allows the total fuel quantity to be kept unchanged, thus providing the requested torque.

[0046] Deviating from the present embodiment, individual steps or groups of steps can also be carried out in a different order or at the same time or simultaneously, such as the two sub-steps concerning the check whether the reference criterion RK is violated.

[0047] This allows the operation of the multiple-injection internal combustion engine 4 to be improved. In particular, it can ensure that pollutant and other emission limits are met even in the case of lambda adjustments LA. List of reference symbols 2 motor vehicles 4 internal combustion engine 6 Control unit 8 cylinders 10 pistons 12 Intake pipe 14 Inlet valve 16 Injector nozzle 18 Fuel line 20 exhaust pipe 22 Exhaust valve 24 combustion chamber EBP input operating parameters HE main injection LA Lambda adjustment MAX Maximum limit MIN Minimum limit NE post-injection RK reference criterion VE pre-injection W value S100 step S200 Step S300 step S400 step S500 step

Claims

[1] Method for operating an internal combustion engine (4) operated with multiple injections, comprising the steps: (S100) Reading in input operating parameters (EBP) of the internal combustion engine (4), (S200) Determining at least one lambda adjustment (LA) for the multiple injections based on the input operating parameters (EBP), (S300) comparing the at least one lambda adjustment (LA) with a reference criterion (RK), (S400) suppressing the at least one lambda adjustment (LA) if the at least one lambda adjustment (LA) violates the reference criterion (RK) and the at least one lambda adjustment (LA) is assigned to a post-injection (NE) of the multiple injections, and (S500) Executing the at least one lambda adjustment (LA) if the lambda adjustment (LA) is assigned to a main injection (HE) of the multiple injections. [2] Method according to claim 1, wherein the reference criterion (RK) is a maximum limit value (MAX) for a value (W) for a fuel quantity to be injected of the lambda adaptation (LA), and a violation of the reference criterion (RK) is concluded if the value (W) for a fuel quantity to be injected of the lambda adaptation (LA) is greater than the maximum limit value (MAX). [3] Method according to claim 1 or 2, wherein the reference criterion (RK) is a minimum limit value (MIN) for a value (W) for a fuel quantity to be injected of the lambda adaptation (LA), and a violation of the reference criterion (RK) is concluded if the value (W) for a fuel quantity to be injected of the lambda adaptation (LA) is less than the minimum limit value (MIN). [4] Computer program product designed to carry out a method according to one of claims 1 to 3, when the computer program is executed in a control unit (6) for operating the internal combustion engine (4) operated with multiple injections. [5] Control unit (6) for operating an internal combustion engine (4) of a motor vehicle (2) operated with multiple injections, wherein the control unit (6) is designed to read in input operating parameters (EBP) of the internal combustion engine (4), to determine at least one lambda adaptation (LA) for the multiple injections based on the input operating parameters (EBP), to compare the at least one lambda adaptation (LA) with a reference criterion (RK), and to suppress the at least one lambda adaptation (LA) if the at least one lambda adaptation (LA) violates the reference criterion (RK) and the at least one lambda adaptation (LA) is assigned to a post-injection (NE) of the multiple injections, and to carry out the at least one lambda adaptation (LA) if the lambda adaptation (LA) is assigned to a main injection (HE) of the multiple injections. [6] Control unit (6) according to claim 5, wherein the reference criterion (RK) is a maximum limit value (MAX) for a value (W) for a fuel quantity to be injected of the lambda adaptation (LA), wherein the control unit (6) is designed to conclude that the reference criterion (RK) has been violated if the value (W) for a fuel quantity to be injected of the lambda adaptation (LA) is greater than the maximum limit value (MAX). [7] Control unit (6) according to claim 5 or 6, wherein the reference criterion (RK) is a minimum limit value (MIN) for a value (W) for a fuel quantity to be injected of the lambda adaptation (LA), wherein the control unit (6) is designed to conclude that the reference criterion (RK) has been violated if the value (W) for a fuel quantity to be injected of the lambda adaptation (LA) is less than the minimum limit value (MIN). [8] Motor vehicle (2) with a control unit (6) according to one of claims 5 to 7.

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