DE102016218818B4 - Secondary air-dependent lambda control - Google Patents

Abstract

Method for controlling an internal combustion engine with a secondary air pump (33), an exhaust system (30) and a lambda control unit (5) for controlling a combustion chamber lambda of at least one cylinder of the internal combustion engine, in which a secondary air pump (33) in the exhaust system (30) of the internal combustion engine introduced secondary air quantity is determined and transmitted to the lambda control unit (5), and in which the combustion chamber lambda is adjusted by the lambda control unit (5) depending on the determined secondary air quantity in such a way that a specified exhaust gas lambda is set in the exhaust system (30), and in which a Control system of a control circuit used to control the lambda control unit (5) is simulated by means of a mathematical model (11, 13) of a system behavior over time of the exhaust system (30) and/or the internal combustion engine.

Description

The present invention relates to a method for controlling an internal combustion engine and an internal combustion engine.

For heating up an exhaust system, especially in combination with a coated particle filter, i. H. a 4-way catalytic converter, it may be necessary to inject secondary air into the exhaust system. In this case, an internal combustion engine supplying the exhaust system with exhaust gas is to be operated with a combustion chamber mixture that has a high proportion of fuel, i. H. with a combustion chamber mixture that is particularly rich. The rich combustion chamber mixture can react in an exothermic reaction in the exhaust system with a respective injected quantity of secondary air and heat the exhaust system, in particular the 4-way catalytic converter, accordingly, so that, for example, the 4-way catalytic converter is regenerated and soot that accumulates in accumulated on the 4-way catalyst is burned.

In order to minimize the generation of emissions during a phase in which an exhaust system is being heated, it is necessary for the exhaust system to be in stoichiometric proportions, i.e. H. a fuel-air mixture with a lambda value λ=1 is present.

In the German pamphlet DE 10 2004 006 876 A1 a method for operating a secondary air pump driven by an electric motor is disclosed, in which the secondary air pump is operated in a clocked manner, and in which a diagnosis of the secondary air pump is carried out using respective clocks for controlling the secondary air pump.

A device for controlling a supercharged Otto internal combustion engine with two throttle bodies, one throttle body being arranged in an intake line leading to a charger, is disclosed in German publication DE 198 41 330 A1 disclosed.

The German pamphlet DE 10 2004 001 330 A1 discloses a method for diagnosing a secondary air system of an internal combustion engine, in which a secondary air mass is calculated and used to provide a diagnostic signal.

From the German pamphlet DE 195 39 937 A1 discloses a method for controlling the exhaust gas ratio of fuel to oxygen in the exhaust tract of an internal combustion engine, in which secondary air is blown into the exhaust tract upstream of the catalytic converter via a pilot-controlled secondary air pump, with the amount of fuel supplied to the internal combustion engine depending on the secondary air mass delivered and on a target value for the exhaust gas ratio before the catalyst is dependent.

The German pamphlet DE 10 2006 007 417 A1 relates to an internal combustion engine with at least one cylinder and an exhaust tract that includes a component to be protected. An estimated dynamic component temperature and an estimated steady-state component temperature of the component to be protected are determined as a function of at least one operating variable of the internal combustion engine, taking into account the dynamic behavior of the route. An actual value of the component temperature of the component is determined depending on the estimated dynamic and stationary component temperature of the component to be protected. Protective measures for the component to be protected are carried out depending on the actual value of the component temperature of the component to be protected.

Against this background, it is an object of the present invention to provide a method for controlling an internal combustion engine that enables the internal combustion engine to be operated with the lowest possible pollutant emissions.

To solve the above-mentioned task, a method for controlling an internal combustion engine with a secondary air pump, an exhaust system and a lambda control unit for controlling a combustion chamber lambda of at least one cylinder of the internal combustion engine is presented, in which a quantity of secondary air introduced into the exhaust system of the internal combustion engine by means of the secondary air pump is determined and sent to the lambda control unit is transmitted, and in which the combustion chamber lambda is adjusted by the lambda control unit as a function of the determined secondary air quantity in such a way that a specified exhaust gas lambda is set in the exhaust gas system and in which a control system of a control circuit used to control the lambda control unit is calculated using a mathematical model of a time system behavior of the Exhaust system and / or the internal combustion engine is simulated.

Refinements of the presented invention emerge from the description and the dependent claims.

In the context of the present invention, a combustion chamber lambda is a mass ratio of air and fuel to be set in at least one cylinder of an internal combustion engine for a combustion process.

In the context of the present invention, an exhaust gas lambda is to be understood as meaning a mass ratio of an air-fuel mixture to be set in an exhaust system, in particular in a catalytic converter, of an internal combustion engine.

In the context of the present invention, a rich mixture is understood to be a mixture of air and fuel that has a particularly high proportion of fuel and causes a correspondingly low lambda value.

The method presented is used in particular for setting stoichiometric ratios, i. H. an exhaust gas lambda value of λ=1 in a catalytic converter of an internal combustion engine, so that minimal emissions are generated during combustion processes taking place in the catalytic converter. For this purpose it is provided according to the invention that a quantity of secondary air blown into an exhaust system is determined, i. H. is measured, for example, by means of an air mass meter. On the basis of the known quantity of secondary air, a quantity of fuel to be metered into the internal combustion engine is regulated in such a way that the internal combustion engine generates an exhaust gas which has a proportion of fuel which, together with the known quantity of secondary air, results in stoichiometric conditions being established in the exhaust system, i. H. an exhaust lambda of λ=1 is set, and generation of emissions in the exhaust system is minimized.

In particular, according to the method presented, it is provided that, in order to adjust the combustion chamber lambda, a disturbance variable determined as a function of a quantity of secondary air blown into an exhaust system by a secondary air pump is transmitted to a lambda control unit. This means that the lambda control unit receives a disturbance variable that is determined as a function of the secondary air quantity. A disturbance variable determined as a function of the secondary air quantity blown in allows very fast control of the combustion chamber lambda, i. H. fuel can be metered in very quickly by means of the lambda control unit, since the lambda control unit can take into account the quantity of secondary air directly when calculating the fuel to be metered in, and time-consuming intermediate steps for determining a fuel proportion dependent on the quantity of secondary air are avoided.

In order to increase the quantity of secondary air blown into a respective exhaust system, i. H. To determine a respective injected secondary air quantity, the secondary air quantity can be detected, for example, by means of a sensor, such as an air mass sensor or any other technically suitable sensor. Alternatively, the quantity of secondary air can be calculated using a mathematical model of a flow pattern of secondary air through a secondary air line. In particular, a respective quantity of secondary air blown into the exhaust system can be recorded or calculated over a predetermined period of time.

It is conceivable that a time window in which the secondary air quantity and the corresponding combustion chamber lambda are determined can last from a few milliseconds to a few seconds.

In one possible embodiment of the method presented, it is provided that a target value for the combustion chamber lambda of the at least one cylinder of the internal combustion engine is determined on the basis of the secondary air quantity determined, in particular in conjunction with a current combustion chamber lambda, and is set on the lambda control unit. It is provided in particular that the desired value is selected in such a way that stoichiometric ratios are established in a respective exhaust system between a quantity of secondary air introduced into the exhaust system and fuel introduced into the exhaust system.

In order to provide a fuel quantity required for generating stoichiometric ratios with a respective quantity of secondary air blown into an exhaust system of an internal combustion engine, a lambda control unit is particularly suitable which is configured to control a fuel supply unit, such as a fuel pump, in order to achieve a specified combustion chamber lambda, which is e.g Is specified as a function of the amount of secondary air to be set on the internal combustion engine. This means that the lambda control unit is used to determine a fuel quantity that is suitable for generating an exhaust gas that, together with a specified secondary air quantity in the exhaust system of a respective internal combustion engine, results in stoichiometric ratios between the secondary air quantity and a fuel quantity in the exhaust gas set.

The method presented provides in particular that a lambda control unit takes into account an air quantity sucked in by a respective internal combustion engine and involved in combustion in the internal combustion engine, as well as a secondary air quantity blown into an exhaust gas system of the internal combustion engine by a secondary air pump when calculating a fuel quantity to be metered into the internal combustion engine.

As soon as a respective quantity of secondary air blown into an exhaust system is known, it is provided according to the invention on the basis of Secondary air quantity to determine a combustion chamber lambda, which leads to stoichiometric conditions in the exhaust system, ie to a stoichiometric equilibrium of a quantity of fuel introduced into the exhaust system by exhaust gases and a quantity of air present in the exhaust system. This means that an amount of fuel to be introduced into a respective internal combustion engine is calculated, which is required to generate an exhaust gas that has exactly the amount of fuel required to generate stoichiometric ratios with the fuel blown in by the secondary air pump, ie introduced into the exhaust system , Amount of secondary air and an amount of air sucked in by a respective internal combustion engine and involved in combustion in the internal combustion engine is necessary.

In order to meter a corresponding amount of fuel into an internal combustion engine, based on a combustion chamber lambda that results in stoichiometric conditions being established in a respective exhaust gas system, provision is made for using a lambda control unit. The lambda control unit can, for example, be provided with a corrected actual value of a combustion chamber lambda, which means that the lambda control unit, which is configured to always set a current combustion chamber lambda of λ=1 on the internal combustion engine, supplies the internal combustion engine with so much fuel that the combustion chamber lambda occurs on the internal combustion engine, which leads to stoichiometric conditions in the exhaust system, d. H. set in an exhaust tract and especially in a secondary air line. This means that by means of a corrected actual value of a currently measured combustion chamber lambda, a combustion chamber lambda is generated that deviates, for example, from an ideal lambda value of λ=1 and, compared to operation with fuel with a combustion chamber lambda of λ=1, the fuel input into the exhaust system is increased he follows.

In a further possible embodiment of the method presented, it is provided that an actual value of the combustion chamber lambda of the at least one cylinder of the internal combustion engine is determined taking into account a ratio of the determined secondary air quantity and a determined combustion chamber air quantity of the at least one cylinder of the internal combustion engine.

In order to use a lambda control unit for setting a combustion chamber lambda that is suitable for setting stoichiometric ratios in a respective exhaust system, it can be provided that an actual value of a combustion chamber lambda and/or an actual value of a The amount of air in the combustion chamber provided for combustion, which is reported to the lambda control unit for calculating an amount of fuel to be metered into the internal combustion engine, is modified with a calculation factor which is determined as a function of a ratio of an amount of air present in the exhaust system, in particular a currently determined amount of secondary air. Accordingly, a lambda control that is configured to control an internal combustion engine in such a way that it is operated with a combustion chamber lambda of λ=1 can be used to set a combustion chamber lambda that is, for example, smaller in real terms A=1, resulting in an increased entry of fuel into the exhaust system.

In a further possible embodiment of the method presented, it is provided that the secondary air quantity is introduced into the exhaust system by means of a regulated secondary air pump.

By using a regulated secondary air pump, a precisely measured quantity of secondary air can be introduced into an exhaust system, so that a respective value of the quantity of secondary air determined, for example, in a predetermined period of time is not falsified by the subsequent supply of further secondary air. Accordingly, a controlled secondary air pump enables exact generation of stoichiometric ratios in the exhaust system and leads to correspondingly minimal emissions from the combustion processes taking place in the exhaust system.

The purpose of regulating the secondary air pump is to provide a secondary air mass flow that is typically 10% of a combustion chamber air mass flow. However, the secondary air mass flow can also be 5-25% of the combustion chamber air mass flow.

In another possible embodiment of the method presented, it is provided that the specified exhaust gas lambda is selected such that the exhaust system has stoichiometric ratios between the air introduced into the exhaust system and the fuel introduced into the exhaust system.

The exhaust gas lambda provided according to the invention is advantageously selected in such a way that stoichiometric conditions are present in a corresponding exhaust system, i. H. an exhaust gas lambda value of λ=1 is set and emissions caused by a heating process or "clearing out" of a catalytic converter in the exhaust system are minimized.

Of course, it is also conceivable that by means of the method presented, an exhaust gas lamb dawert is not set equal to λ=1, for example to affect combustion processes in other exhaust systems.

According to the invention, it is provided that a controlled system of a control circuit used to control the lambda control unit is simulated by means of a mathematical model of a system behavior over time of the exhaust system and/or the internal combustion engine.

In order to regulate a respective lambda control unit in such a way that it causes a fuel input into a corresponding internal combustion engine, which is suitable for generating an exhaust gas, by means of which stoichiometric ratios are generated in an exhaust gas system of the internal combustion engine, the lambda control unit can be based on a model of a time-dependent path behavior , i.e. H. be regulated in particular by gas propagation times and/or latencies in signal transmission through aged lambda probes, the internal combustion engine and/or the exhaust gas system. In particular, a mathematical model is suitable for calculating a prognosis, i. H. a behavior of the exhaust gas lambda to be expected in the future, so that depending on whether an increase or a decrease in the exhaust gas lambda is to be expected according to the mathematical model, a corresponding amount of fuel can be set using the lambda control unit, whereby the exhaust gas lambda, for example, has a lambda value of λ =1 approaches.

In a further possible embodiment of the method presented, it is provided that the mathematical model is supplied with at least one operating parameter of the internal combustion engine and/or the exhaust system, which is detected by means of at least one sensor arranged on the internal combustion engine and/or the exhaust system, with the mathematical model being used to calculate a current lambda value at an installation position of the sensor is used.

In order to assess a system behavior of the controlled system, for example a latency of a sensor for detecting an operating parameter of the internal combustion engine and/or of the exhaust system, such as a lambda probe, for example, can be detected.

Through a system model of a system behavior of a controlled system, i. H. For example, from gas running times of exhaust gas generated in a respective internal combustion engine up to an introduction point of a secondary air line, a control circuit based on a large dead time, d. H. based on long gas transit times, can achieve greater stability than would be possible with measurement-based control.

According to the method presented, it is provided in particular that a quantity of secondary air is introduced into the exhaust system upstream of a particle filter of a respective exhaust system, and a stoichiometric exhaust gas composition is regulated at the position at which the quantity of secondary air is introduced. In order to regulate the stoichiometric exhaust gas composition, a path behavior of a gas transit time with dead time can be simulated by means of a mathematical model in order, for example, to take into account aging processes of exhaust gas sensors in a corresponding regulation. A control difference, which is to be compensated for by means of a respective lambda control unit, results from a difference between a measured variable that is actually subject to dead time and a model variable that is expected according to the mathematical model.

Corresponding sensors are of course also suitable for determining input signals, on the basis of which a mathematical model of a controlled system of a control circuit used to control a lambda control unit can be calculated. Such a mathematical model can be used, for example, to predict the behavior of operating parameters determined by the sensors that is to be expected in the future. In order to minimize the influence of measurement errors, measured values determined by a respective sensor and/or values calculated using a mathematical model, for example of a future exhaust gas lambda, can be filtered using a filter, for example using a bandpass filter.

In a further possible embodiment of the method presented, it is provided that a secondary air line for introducing secondary air through the secondary air pump is arranged between a first exhaust gas aftertreatment element and a second exhaust gas aftertreatment element and a quantity of secondary air is introduced into the second exhaust gas aftertreatment element by means of the secondary air pump, the secondary air quantity being suitable for this purpose to reduce a fuel concentration in the second exhaust gas aftertreatment element compared to a fuel concentration in the first exhaust gas aftertreatment element and to enable complete oxidation of hydrocarbons and carbon monoxide in the second exhaust gas aftertreatment element, and in which the fuel concentration in the first exhaust gas aftertreatment element is selected such that a complete reduction of nitrogen oxides takes place.

By partially increasing an amount of air in an exhaust system, ie leaning part of an exhaust system, such as. A in the flow direction of a combustion engine generated exhaust gas rearmost catalytic converter, which is usually a 4-way catalytic converter, it can be achieved that there is an air-fuel ratio independent of one in front of the rearmost catalytic converter with, for example, a low fuel content is set, by means of which inflowing hydrocarbons and inflowing Carbon monoxide can be oxidized, while in a catalytic converter located in front of a respective secondary air introduction, a reduction of nitrogen oxides with an exhaust gas that has a high proportion of fuel can take place. This means that a catalytic converter for reducing nitrogen oxides and a catalytic converter for oxidizing hydrocarbons and carbon monoxide can be used through a secondary air line between two catalytic converters of an exhaust system.

Furthermore, the present invention relates to an internal combustion engine with an exhaust system, a secondary air pump configured to introduce secondary air into the exhaust system, and a control unit, the control unit being configured to generate a combustion chamber lambda of at least one cylinder of the internal combustion engine as a function of a secondary air quantity introduced into the exhaust system by means of the secondary air pump set in such a way that a specified exhaust gas lambda is set in the exhaust system, and wherein the control unit is also configured to simulate a controlled system of a control circuit to be used for controlling the lambda control unit by means of a mathematical model of a time-related system behavior of the exhaust system and/or the internal combustion engine.

The presented method serves in particular to operate the presented internal combustion engine.

In a possible embodiment of the presented internal combustion engine, it is provided that the secondary air pump is configured to meter a quantity of secondary air to be introduced into the exhaust system uniformly over an entire cross section of at least one lambda probe arranged on the exhaust system.

A uniform flow onto a lambda probe makes it possible to prevent measurement errors due to a concentration gradient of air introduced into an exhaust gas flowing onto the lambda probe.

In a further possible embodiment of the presented internal combustion engine, it is provided that a secondary air line for introducing secondary air into the exhaust gas system is arranged between a first exhaust gas aftertreatment system and a second exhaust gas aftertreatment system. It is provided that the control device is configured to use the secondary air in the second exhaust gas aftertreatment system to set a fuel concentration that is reduced compared to a fuel concentration set in the first exhaust gas aftertreatment system and to enable complete oxidation of hydrocarbons and carbon monoxide in the second exhaust gas aftertreatment element. Furthermore, it is provided that the fuel concentration in the first exhaust gas aftertreatment element is dimensioned in such a way that a complete reduction of nitrogen oxides takes place.

In a further possible configuration of the presented internal combustion engine, it is provided that the control unit is configured to set an exhaust gas lambda in the exhaust system during a heating-up phase for heating up at least part of the exhaust gas system, which corresponds to a lambda value of λ=1, and in a Set a lambda value in the exhaust system following the soot fire phase that is higher than the lambda value of λ=1.

In order to trigger a soot fire in a particle filter and thereby "clear out" the particle filter, it is necessary that after a heating phase, which takes place according to the method presented using an exhaust gas in which stoichiometric ratios between an air component of the exhaust gas and a fuel component of the exhaust gas are present, there is an increased air supply to the particle filter.

Further advantages and refinements of the invention result from the description and the accompanying drawings.

It goes without saying that the features mentioned above and those still to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

• 1 zeigt eine schematische Übersicht über ein Regelungsverfahren zum Regeln einer Brennkraftmaschine gemäß einer möglichen Ausgestaltung des erfindungsgemäßen Verfahrens.
• 2 zeigt eine schematische Darstellung einer möglichen Ausgestaltung der erfindungsgemäßen Brennkraftmaschine.
• 3 zeigt eine Übersicht eines Verhaltens verschiedener Betriebsparameter einer Brennkraftmaschine gemäß dem Stand der Technik.
• 4 zeigt die Übersicht aus 3 gemäß einem weiteren Verfahren, wie es durch den Stand der Technik vorbekannt ist.
• 5 zeigt die Übersicht aus 3 für eine Brennkraftmaschine, die gemäß einer möglichen Ausgestaltung des vorgestellten Verfahrens gesteuert wird.

The invention is shown schematically on the basis of embodiments in the drawings and is described schematically and in detail with reference to the drawings.

• 1 shows a schematic overview of a control method for controlling an internal combustion engine according to a possible embodiment of the method according to the invention.
• 2 shows a schematic representation of a possible embodiment of the internal combustion engine according to the invention.
• 3 shows an overview of a behavior of various operating parameters of an internal combustion engine according to the prior art.
• 4 shows the overview 3 according to another method previously known in the art.
• 5 shows the overview 3 for an internal combustion engine that is controlled according to a possible embodiment of the method presented.

In 1 a control loop 1 for controlling a lambda control unit 5 is shown. Lambda control unit 5 is used to determine a fuel quantity that is necessary to set a combustion chamber lambda on an internal combustion engine that is suitable for an exhaust gas lambda set in an exhaust system of the internal combustion engine, ie a ratio of a quantity introduced into the exhaust system, for example by means of a secondary air pump Amount of air to act on an amount of fuel introduced into the exhaust system by means of an exhaust gas generated by the internal combustion engine itself. In particular, it is provided that stoichiometric ratios between an amount of air introduced into the exhaust system and an amount of fuel introduced into the exhaust system are set, so that an exhaust gas lambda of λ=1 is present.

By establishing stoichiometric ratios in the exhaust system, emissions produced when combusting fuel introduced into the exhaust system by the internal combustion engine are minimized. Starting from a target value 3, which generally corresponds to a lambda value of A=1, the lambda control unit 5 controls a fuel quantity to be metered into the internal combustion engine such that the internal combustion engine, i. H. in the respective cylinders of the internal combustion engine, a combustion chamber lambda of λ=1 is set.

In order to change the combustion chamber lambda and, for example, to compensate for an increased secondary air intake into the exhaust system as quickly as possible, for example by a sluggish secondary air pump, it is provided that setpoint 3 is compared in an adder 25 with a current lambda value at a lambda probe position 21. The current lambda value at lambda probe position 21 can be measured via a sensor in the exhaust system, such as a lambda probe or an air mass meter, taking into account transmission losses in the exhaust system, i. H. a gas running time from a respective internal combustion engine to the lambda probe position 21, as indicated by blocks 17 and 19, are determined. Alternatively, the current lambda value at lambda probe position 21 can be determined using a mathematical model from a calculation element represented by a block 11 and a filter represented by a block 13, by means of which a route transmission behavior of the exhaust system is modeled. Observer control can be carried out in an adder 23 using a comparison of values of the current lambda value at lambda probe position 21 determined by a sensor and values of the current lambda value at lambda probe position 21 determined by the mathematical model.

According to the method presented, it is provided in particular that a quantity of secondary air blown into the exhaust system is treated as a disruptive factor and, via a corresponding correction value 9, which is determined as a function of the quantity of secondary air, together with other external disruptive factors 7 in an adder 27 with a current value from the lambda control unit 5 set combustion chamber lambda, i. H. an actual value of the combustion chamber lambda, is adjusted.

By comparing the current lambda value at the lambda probe position 21 with the target value 3 of the combustion chamber lambda in the additor 25, a quantity of fuel required to compensate for a quantity of secondary air introduced into the exhaust system can be metered into the internal combustion engine by the lambda control unit 5, so that the quantity of secondary air does not lead to increased emissions leads.

In 2 an exhaust system 30 is shown. The exhaust system 30 includes an exhaust line 31 which is supplied with exhaust gas from an internal combustion engine and with secondary air from a regulated secondary air pump 33 . In order to determine a quantity of secondary air blown into the exhaust branch 31 by the secondary air pump 33 , an air mass meter 37 is arranged in a secondary air line 35 .

By means of a linear lambda probe 39, an exhaust gas lambda of gas conducted through the exhaust line 31, i. H. a mixture of secondary air and exhaust gas. In order to enable a valid measurement of the exhaust gas lambda of the gas routed through the exhaust line 31, provision is made in particular for the secondary air line 35 to be connected to the exhaust line 31 in such a way that a quantity of secondary air blown in by the secondary air pump 33 is distributed as evenly as possible over a cross section of the lambda probe 39 flows into the exhaust system 31 .

On the way through the exhaust system 30, the gas passes through a 3-way catalytic converter 41, a second lambda probe 43, for example as a binary Lambda probe is configured, a temperature sensor 45 and a 4-way catalytic converter 47. After the 4-way catalytic converter 47, another temperature sensor 49 and a third lambda probe 51, which is also binary, are arranged.

Optionally, the secondary air can also be introduced into the exhaust system 30 upstream of the 4-way catalytic converter 47 or downstream of the 3-way catalytic converter 41 . Then the lambda probe 43 is to be designed as a broadband probe and a correspondingly longer gas flow path when modeling a path using a mathematical model, as shown in 1 represented by calculation element 11 and filter 13, has to be taken into account. The introduction of secondary air behind the 3-way catalytic converter 41 is largely emission-neutral, since the 3-way catalytic converter is also suitable for reducing nitrogen oxides. In order to "clean up" the 4-way catalyst 47, ie to burn a soot load accumulated in the 4-way catalyst and to restore a storage capacity of the 4-way catalyst 47 for soot, the internal combustion engine generates exhaust gas which has a high Includes fuel portion, so that the fuel portion reacts with secondary air blown through the secondary air pump 33 and heats the 4-way catalyst. It is provided that the internal combustion engine is controlled in such a way that the proportion of fuel in the exhaust gas is measured exactly such that in the exhaust system 30 stoichiometric ratios between the air quantity introduced into the exhaust gas system 30, ie an air quantity from air sucked in by the internal combustion engine and secondary air blown in, and fuel introduced into the exhaust system 30 and corresponding minimal emissions are produced.

After the exhaust system 30 by a corresponding fuel input to a for cleaning, i. H. for a soot fire, necessary temperature was heated, it is provided that in the exhaust system 30 a lean mixture composition, i. H. an exhaust gas with a low fuel content is adjusted so that the oxygen required for the soot fire is introduced into the exhaust system.

The internal combustion engine is controlled as a function of measured values of the secondary air quantity determined by the air mass sensor 37, so that exactly the quantity of fuel is metered into the internal combustion engine that leads to an exhaust gas that includes so much fuel that stoichiometric ratios, i. H. set a ratio between an amount of air introduced into an exhaust system, in particular an amount of secondary air, and fuel, which corresponds to a lambda value of λ=1, in exhaust system 30 .

In 3 are plots of various characteristic values of an exhaust system over time in [s]. The exhaust system according to 3 is supplied by an internal combustion engine that is operated without a lambda control unit. In a diagram 50, which spans the abscissa 52 over time and the ordinate 54 over an air quantity flow rate in [kg/h], a course 53 of a flow rate of a combustion chamber air quantity that is sucked in by the internal combustion engine and supplied to the respective cylinders of the internal combustion engine Combustion is supplied, and a course 55 of a flow rate of a secondary air quantity, which is blown into the exhaust system, is shown. In the present case, curve 55 of the flow of the secondary air quantity is scaled up by a factor of “10”, so that the actual secondary air quantity is reduced by a factor of “10” compared to curve 55 of the flow of the secondary air quantity and is approximately 10% of the flow of the combustion chamber air quantity according to curve 53 located.

The curve 55 of the flow of the secondary air quantity essentially follows the curve 53 of the flow of the combustion chamber air quantity. Due to the limited dynamics of a secondary air supply, such as a sluggish secondary air pump, which cannot follow the dynamics of the flow rate of the combustion chamber air quantity, as occurs, for example, with an increased power requirement and a subsequent strong reduction in the power of an internal combustion engine, delays occur Adaptation of the secondary air volume to the combustion chamber air volume, as can be seen, for example, at second 30 in diagram 50.

A profile of a ratio between the injected secondary air quantity and the measured combustion chamber air quantity is represented by a curve 59 in a diagram 60, which extends over time on the abscissa 52 and over a ratio of secondary air to combustion chamber air on the ordinate 62. At second 30, the ratio of secondary air to combustion chamber air drops to a minimum due to the increase in the quantity of combustion chamber air, e.g. This means that the secondary air pump used to introduce the secondary air cannot follow the course of the combustion chamber air quantity and reacts too sluggishly, resulting in an uneven course 59 of a ratio of secondary air quantity to combustion chamber air quantity. Due to the inertia of the secondary air pump, there are increased emissions, especially during short acceleration maneuvers or rapidly changing performance requirements presented method can be significantly reduced.

Diagram 61 that plots on the abscissa 52 over time and on the ordinate 64 over an exhaust gas lambda value, i. H. a lambda value in an exhaust system, in particular taking into account the quantity of secondary air, shows a curve 63 of a lambda value in an exhaust gas of an internal combustion engine that does not have a lambda control unit. The lambda value of the exhaust gas, i. H. the exhaust gas lambda, varies greatly between a maximum of λ=1.2 and a minimum of λ=0.9. This means that exhaust gases flow in the exhaust gas system of the internal combustion engine, which at times deviate from an exhaust gas lambda value of λ=1, as is required for ideal combustion with the lowest possible emissions. A high concentration of fuel, as is the case, for example, in phases with an exhaust gas lambda value of λ=0.9, leads to increased emissions compared to ideal combustion, as does a high concentration of air, as is the case in phases with an exhaust gas lambda value of λ =1.2 is present.

Emission output in [g] is shown in graph 65 which is plotted against time on abscissa 52 and mass in [g] on ordinate 66 . A trace 67 shows an amount of carbon monoxide emitted, which increases to a value of 0.5 grams at about second 32. To simplify the illustration, the values of the trace 67 of the amount of carbon monoxide emitted are shown divided by a value of “5”. A trace 69 represents an amount of nitrogen oxides emitted increasing at about second 37 to a value of 0.1 grams.

4 shows curves of various characteristic values of an internal combustion engine that is controlled by means of a lambda control unit without pilot control. This means that the influence of a secondary air supply is not taken into account in a pilot control for regulating the lambda control unit, but rather an influence of the secondary air supply is first measured at a lambda probe in the exhaust system, so that the lambda control unit attempts to reduce a lambda value in the exhaust system to a value of typically set to λ=1.

A curve 71 of a combustion chamber air flow rate and a curve 73 of a secondary air flow rate are shown in a diagram 70, which extends over time on the abscissa 52 and over time on the ordinate 72 over an air flow rate in [kg/h]. In the present case, curve 73 of the secondary air flow rate is scaled up by a factor of “10”, so that the actual secondary air flow rate is reduced by a factor of “10” compared to curve 73 and is around 10% of the combustion chamber air flow rate according to curve 71. Curves 71 and 73 behave analogously to curves 53 and 55 3 . The ratio of secondary air to combustion chamber air represented by curve 81 in diagram 80, which extends over time on abscissa 52 and over time on ordinate 82, behaves analogously to the curve of line 59 from the diagram 60 from 3 .

Diagram 90, which extends over time on abscissa 52 and over a lambda value on ordinate 92, shows a curve 91 of a lambda value determined by means of a lambda control unit without precontrol and a curve 93 of a lambda value measured by means of a lambda control unit with precontrol. This means that curve 93 corresponds to a lambda value that was determined using a lambda control unit, to which a disturbance variable was transmitted that takes into account a currently blown-in quantity of secondary air as part of the pilot control. In contrast, curve 91 corresponds to a lambda value that was determined by a lambda control unit, in which the secondary air quantity is determined via several intermediate steps, as a result of which the lambda control unit reacts correspondingly sluggishly to changes in the secondary air quantity.

Compared to curve 91, there are smaller deviations from a setpoint lambda value of λ=1 in curve 93, which leads to a significant reduction in emissions compared to an internal combustion engine without a lambda control unit, as can be seen in a comparison of diagram 100 from FIG 4 and Diagram 65 3 becomes evident.

Since the the 4 underlying internal combustion engine is regulated by means of a lambda control unit, emissions generated by the internal combustion engine, as shown in diagram 100, are approximately half lower than the emissions, as shown in diagram 65. Correspondingly, the scaling of the ordinate 102 of Diagram 100, which indicates a mass in [g], has been changed compared to the ordinate 66 of Diagram 65. The time is indicated on the abscissa 52 .

A curve 101 shows an emission of carbon monoxide and a curve 103 an emission of nitrogen oxides. The course of the curve 101 for the emission of carbon monoxide is also shown here divided by a value “5” for better representation with the scaling used. Analogous to Diagram 65 3 follows a course of a quantity of nitrogen oxides emitted according to curve 103 of a quantity of emitted Carbon monoxide according to curve 101, which opens into a plateau phase at about 32 seconds. The course of the curve 103, on the other hand, ends in a plateau phase at about second 37 with a time delay.

5 shows curves of various characteristic values of an internal combustion engine which is operated by means of a lambda control unit with pilot control, ie a lambda control unit which is controlled as a function of a respective quantity of secondary air blown into the exhaust system. Correspondingly, when regulating the pilot control, a quantity of air burned by the internal combustion engine and a quantity of secondary air introduced into the exhaust system by a secondary air pump are taken into account. The lambda control unit of the internal combustion engine supplies a quantity of fuel that is necessary in order to set stoichiometric ratios between the resulting quantity of air and the fuel introduced in the exhaust system. With such a control by the lambda control unit, the lambda control unit only has to compensate for precontrol errors in the precontrol, so that a curve 133 in diagram 130 compares to the curve 93 in diagram 90 3 behaves significantly more precisely, ie fluctuates significantly less around the target lambda value of λ=1. Correspondingly, the emission curves 141 and 143 shown in a diagram 140 are significantly reduced compared to the emission curves 101 and 103 shown in the diagram 100 .

A curve 111 of a combustion chamber air flow rate and a curve 113 of a secondary air flow rate are shown in a diagram 110 that spans the abscissa 52 over time and the ordinate 112 over an air flow rate in [kg/h]. In the present case, curve 113 of the secondary air flow rate is scaled up by a factor of “10”, so that the actual secondary air flow rate is reduced by a factor of “10” compared to curve 113 and is around 10% of the combustion chamber air flow rate according to curve 111. Curves 111 and 113 behave analogously to curves 53 and 55 3 . The ratio of secondary air to combustion chamber air represented by line 121 in diagram 120, which extends over time on abscissa 52 and over a ratio of secondary air to combustion chamber air on ordinate 122, behaves analogously to curve 59 from diagram 60 of FIG 3 .

Diagram 130, which extends over time on the abscissa 52 and over a lambda value on the ordinate 132, shows an effect of the pilot control of the lambda control unit. While a curve 131 of a lambda value determined by means of a lambda control unit without pre-control fluctuates greatly, a curve 133 of a lambda value determined by means of a lambda control unit with pre-control levels off around a lambda value of λ=1, which suggests that the downstream lambda control unit with pre-control arranged lambda probe stoichiometric ratios between introduced into the exhaust system amounts of air and fuel are present and a minimum of emissions is generated. In the lambda control unit with pilot control, a currently blown-in quantity of secondary air is taken into account in a pilot control unit of the lambda control unit, for example as part of a disturbance variable, so that the lambda control unit can quickly adapt the lambda values determined to a changed quantity of secondary air.

In diagram 140, which extends over time on the abscissa 52 and a mass in [g] on the ordinate 142, a curve 141 represents an emission of carbon monoxide and a curve 143 an emission of nitrogen oxides. Here is the mass of Curve 141 of the carbon monoxide emissions is also shown divided by a value “5” for reasons of clarity, ie scaled by a factor of “1/5”. Both the curve shape 141 and the curve shape 143 are compared to the emission output as shown in diagram 100 of FIG 4 is shown reduced.

Claims (12)

Method for controlling an internal combustion engine with a secondary air pump (33), an exhaust system (30) and a lambda control unit (5) for controlling a combustion chamber lambda of at least one cylinder of the internal combustion engine, in which a secondary air pump (33) in the exhaust system (30) of the internal combustion engine introduced secondary air quantity is determined and transmitted to the lambda control unit (5), and in which the combustion chamber lambda is adjusted by the lambda control unit (5) depending on the determined secondary air quantity in such a way that a specified exhaust gas lambda is set in the exhaust system (30), and in which a controlled system of a control circuit used to control the lambda control unit (5) is simulated by means of a mathematical model (11, 13) of a system behavior over time of the exhaust system (30) and/or the internal combustion engine. procedure after claim 1 , in which a target value (3) for the combustion chamber lambda of the at least one cylinder of the internal combustion engine is determined on the basis of the secondary air quantity determined and is set on the lambda control unit (5). procedure after claim 1 or 2 , in which an actual value of the combustion chamber lambda of the mind at least one cylinder of the internal combustion engine, taking into account a ratio of the determined secondary air quantity and a determined combustion chamber air quantity of the at least one cylinder of the internal combustion engine. Method according to one of the preceding claims, in which the quantity of secondary air is introduced into the exhaust system (30) by means of a regulated secondary air pump (33). Method according to one of the preceding claims, in which the specified exhaust gas lambda is selected in such a way that the exhaust system (30) has stoichiometric ratios between the respective volumes of air and fuel introduced into the exhaust system (30). Method according to one of the preceding claims, in which the mathematical model (11, 13) with at least one operating parameter of the internal combustion engine and/or the exhaust system (30) detected by means of at least one sensor (39, 43) arranged on the internal combustion engine and/or the exhaust system (30) is supplied, the mathematical model being used to calculate a current lambda value at an installation position of the sensor (39, 43). procedure after claim 6 , in which a temperature sensor (45, 49) and/or a lambda probe (39, 43) is selected as the at least one sensor. Method according to one of the preceding claims, in which a secondary air line for introducing secondary air through the secondary air pump is arranged between a first exhaust gas aftertreatment element (41) and a second exhaust gas aftertreatment element (47) and a quantity of secondary air is introduced into the second exhaust gas aftertreatment element (47) by means of the secondary air pump, and in which the quantity of secondary air is suitable for reducing a fuel concentration in the second exhaust gas after-treatment element (47) compared to a fuel concentration in the first exhaust gas after-treatment element (41) and for allowing complete oxidation of hydrocarbons and carbon monoxide in the second exhaust gas after-treatment element (47), and at in which the fuel concentration in the first exhaust gas aftertreatment element (41) is selected in such a way that a complete reduction of nitrogen oxides takes place. Internal combustion engine with an exhaust system (30), a secondary air pump (33) configured to introduce secondary air into the exhaust system (30), and a control unit, wherein the control unit is configured to control a combustion chamber lambda of at least one cylinder of the internal combustion engine as a function of a secondary air pump (33 ) set the amount of secondary air introduced into the exhaust system in such a way that a specified exhaust gas lambda is set in the exhaust system (30), and wherein the control unit is further configured to use a mathematical model (11 , 13) to simulate the behavior over time of the exhaust system (30) and/or the internal combustion engine. internal combustion engine claim 9 , wherein the control unit is configured to set an exhaust gas lambda in the exhaust system (30) during a heating-up phase for heating up at least a part of the exhaust system (30) which corresponds to a lambda value of λ=1, and in a soot fire phase following the heating-up phase To set the lambda value in the exhaust system (30), which is increased compared to the lambda value of λ=1. internal combustion engine claim 9 or 10 , wherein a secondary air line for introducing secondary air into the exhaust gas system (30) is arranged between a first exhaust gas aftertreatment system (41) and a second exhaust gas aftertreatment system (47), and wherein the control device is configured to use the secondary air in the second exhaust gas aftertreatment system (47). compared to a fuel concentration set in the first exhaust gas aftertreatment system (41) and to enable complete oxidation of hydrocarbons and carbon monoxide in the second exhaust gas aftertreatment element (47), and wherein the fuel concentration in the first exhaust gas aftertreatment element (41) is dimensioned in such a way that a complete Reduction of nitrogen oxides takes place. Internal combustion engine according to one of claims 9 until 11 , in which the secondary air pump (33) is configured to meter a quantity of secondary air to be introduced into the exhaust system (30) uniformly over an entire cross section of at least one lambda probe (39, 43) arranged on the exhaust system (30) into the exhaust system (30).

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