DE102006014249A1 - Lambda value pre-controlling method for use during pre-heating phase of catalyzer, involves partially loading lambda-characteristic of lambda-pre-control, so that temporal lambda-center value is provided and lambda-value is obtained - Google Patents

Abstract

The method involves providing an internal combustion engine with catalyzers and a lambda sensor. A temporal lambda-characteristic (11) of a lambda-pre-control is partially loaded during a pre-heating phase of an exhaust gas cleaning system of the engine by a high frequent modulation in such a manner that a temporal lambda-center value (12) with lambda greater than 1 is provided in the phase and a lambda-value with lambda less than 1 is obtained.

Description

State of technology

The The invention relates to a method for the pilot control of a lambda value while the heating phase of an exhaust gas purification system of an internal combustion engine with at least one catalyst and at least one lambda probe.

Around to meet the strict emission standards for internal combustion engines, is in addition to minimizing the raw emissions during the start of the catalyst as quickly as possible to heat up to the correct operating temperature. Are known different measures, such as the increase the exhaust gas temperature by late ignition, a Mixture enrichment in connection with secondary air injection, the use a glow plug in the exhaust system in front of the catalytic converter. For turbocharged engines and boost pressure control valve, the wastegate valve for fast warming opened the catalyst become. All these measures hang on the one hand, the exhaust concept, such as fat or lean, and on the other from the available stationary hardware (e.g., charge motion flap, secondary air injection, Camshaft adjustment, etc.), and affect the exhaust quality. by virtue of Legal requirements must be effective in motor vehicles be checked with on-board diagnostics. Should while the cold start one of these measures can not be adjusted can this cause that the exhaust emission limits can not be met.

on the other hand with regard to the conversion of noxious gas components is the storage capacity of the Catalyst for Oxygen OSC (Oxygen Storage Capacity) of particular interest. The storage capacity an emission control system for Oxygen is used to absorb oxygen in lean phases and again in fat phases. This ensures that converts the pollutant gas components of the exhaust gas to be oxidized can be. As the emission control system ages, its storage capacity for oxygen decreases from. As a result, in the fat phases not enough oxygen to disposal be made to clean the exhaust gas from the noxious gas components and the lambda probe is detected behind the emission control system these components to be oxidized. Furthermore, this lambda probe detects in longer Mealy phases the oxygen that is no longer from the emission control system can be stored. In many countries, a review of the Emission control system during driving required by the engine control by law (On-board diagnostics). An active catalyst diagnosis is included the task, an inadmissible Falling of the conversion, which leads to inadmissible increase of exhaust emissions recognize and over to display a control lamp.

The oxygen-measuring catalyst diagnosis is carried out with a broadband probe according to the following procedure:
The catalyst is first freed of oxygen by a rich mixture (λ <1). After this phase, referred to as conditioning, a lean exhaust gas (λ> 1) is subsequently introduced and the amount of oxygen introduced is integrated. If, during this measurement phase, the probe behind the catalyst indicates a lean, ie oxygen-containing, mixture, the integrated amount corresponds to the current oxygen storage capacity of the catalyst, which represents a measure of the quality. This procedure is applied several times in succession.

In the DE 41 12 478 C2 describes a method for assessing the aging state of a catalyst, in which the lambda values are measured in front of and behind the catalyst. It is examined whether the lambda value behind the catalyst shows a corresponding transition at a control oscillation before the catalyst from rich to lean or vice versa, and then, if this is the case, the gas mass flow flowing through the catalyst is determined, the time integral of the product from gas mass flow and lambda value calculated before the catalyst, the time integral of the product calculated from gas mass flow and lambda value behind the catalyst and as a measure of the aging state of the catalyst either the difference between the two integrals or the quotient of the two integrals or the quotient of the difference and a the two integrals is used. A disadvantage of the method described is that the lambda value must be measured in front of the emission control system with a complex broadband lambda probe in order to determine the introduced or withdrawn amount of oxygen via the integration of the product from the current lambda value and gas mass flow.

Another method for determining the oxygen storage capacity of an emission control system describes the EP 0546 318 B1 , The system is supplied with a Lambdaverlauf whose oxygen deficiency entry is initially higher than the oxygen storage capacity of the catalyst. The sour Substance entry is chosen so that the catalyst is filled in the lean phases each to its capacity limit. To determine the oxygen storage capacity of the catalyst, the average lambda value in front of the catalyst during the lambda oscillations of the system is selectively shifted in the direction of lean, thus reducing the oxygen removal from phase to phase. By determining the number of lean-to-rich transitions that the lambda probe located behind the catalytic converter indicates, the oxygen storage capability can be determined, with an increased number of phases resulting in reduced storage capability. A disadvantage of this method is that in the lean phases unpurified exhaust gas is discharged.

The DE 10240977 A1 describes a method for operating an internal combustion engine, in particular for a motor vehicle with a direct fuel injection system, which has an exhaust system with at least one catalytic converter. For heating at least one of the catalysts is provided, the internal combustion engine cyclically in a lean operation with λ> 1 to fill the one oxygen storage of at least one catalyst, and operate in a rich operation with λ <1, not burned by the heat of reaction reaction Fuel components with the oxygen in the at least one catalyst to heat this. In this case, the oxygen storage capacity of each individual or a group of catalysts is first determined by a lambda jump and the oxygen storage capacity of the catalyst or an oxygen-based lower calorific value and taking into account an exhaust lambda and an exhaust gas mass flow of energy input and thus a temperature in at least a catalyst determined. Thereby, a regulation and control of the heating of the catalyst or catalysts on the adjustment of the fat and / or lean phases is made.

Supportive to rapid heating of the catalyst is according to the prior art after starting a slightly lean mixture with λ> 1 driven. As the dew point in particular at cold start for the lambda probe is still below, is the operational readiness the lambda probe only reached significantly after the start. The lambda value is therefore pre-controlled directly after the start to a value of λ> 1 and is usually at about 1.05. This will ensure that despite deviations caused by the series dispersion always kept a slightly lean lambda in the fuel metering can be. An undershooting of the lambda value λ = 1 would become a strong increases in CO and HC emissions and possibly a Violation of the relevant emission limit values. By the lean lambda is however also after the crossing the so-called "light-off temperature", the temperature, from which the catalyst reaches an optimum operating temperature and thus the catalyst in principle as a 3-way catalyst able to work would be, none Conversion of nitrogen oxides in the exhaust possible.

It It is therefore an object of the invention to provide a method that already during the heating phase of the catalyst an at least partial conversion ensured by NOx, without at this stage a limit violation for the consists of oxidizing components.

epiphany the invention

Advantages of invention

The Task is solved by that a temporal lambda curve of the lambda pilot control during the Heating phase of the catalyst at least temporarily by means of a higher frequencies Modulation is applied, so that in this phase, a temporal Lambda mean of λ> 1 predetermined and at least for a short time a lambda value of λ <1 is achieved. Through this targeted control strategy for the lambda is already during this Phase achieved a partial conversion of nitrogen oxides, since at least temporarily a lambda value of λ <1 is achieved. At the same time, the mean lambda value continues to be poor on average the conversion of the components to be oxidized, such as HC and CO not negatively affected. It was even observed that through to a small extent this conversion strategy also the conversion of the is supported to oxidizing components. It can by a pilot control to a lambda λ> 1, for example λ = 1.05, a series dispersion will be covered safely, so the danger a limit violation for the components to be oxidized, as described above, does not exist.

The Add up the higher Frequent modulation is done in a preferred process variant in such a way that the temporal lambda curve of the lambda pilot control with a unbalanced duty cycle piloted between phases with λ> 1 and λ <1 is, and relatively short time a lambda value of significantly less than 1 are controlled and for the lambda relatively long time at λ> 1 can remain, to be sure the conversion of the components to be oxidized, such as HC and CO to ensure. A lambda value of significantly less than 1 accelerates the Conversion of nitrogen oxides.

Farther can be provided that higher Frequency modulation in terms of amplitude and / or frequency depending on Operating point of the internal combustion engine is changed, whereby a flexible lambda pilot control can be achieved.

There For example, the oxygen storage capacity (OSC) of the or Catalysts subject to a certain aging, can be provided according to the invention be that the amplitude of the higher Frequency modulation to a current value of the oxygen storage capacity (OSC) of the catalyst (s). Through this lambda pilot control thus becomes as possible constant conversion rate for ensures the nitrogen oxides on the one hand and HC or CO on the other hand, in particular, compliance with the limit values for these pollutant components even after a certain aging.

As a general rule It makes sense and advantageous if the frequency of higher-frequency Modulation with decreasing value of oxygen storage capacity (OSC) of the catalyst or catalysts is increased. The danger of breakthrough of fat tips can be reduced with it.

The In this case, the method provides that the current value of the oxygen storage capacity (OSC) of the catalyst or catalysts by means of a diagnostic method for the Oxygen storage capacity (OSC) is determined and stored. This value can then be directly to calculate the optimal modulation in terms of frequency, amplitude and possibly the duty cycle be used between the phases with λ> 1 and λ <1.

He follows additionally for oxygen storage ability (OSC) of the catalyst or catalysts, a volumetric weighting of a Catalyst temperature, and this at the amplitude and / or Frequency modulation of the temporal lambda curve of the lambda pilot control while the heating phase of the catalyst or catalysts, it can be a effective oxygen storage capacity be determined, which is a function of the temperature in or in the Catalysts is. Since the catalyst or catalysts during the Heating up from the front to the rear (in gas flow direction) can warm up by this volumetric weighting a characteristic catalyst temperature for the entire catalyst or catalysts are determined, the for one further calculation available stands.

there provides a particularly preferred process variant that the Value for the oxygen storage capacity (OSC) of the catalyst or catalysts and the value for the volumetric weighting the catalyst temperature measured and stored in maps become. This can be advantageous even complex functional relationships represent or evaluate.

It may be provided in the method described above, that the amplitude of the modulation of the temporal lambda curve of Lambda pilot control is limited. This is especially true on the quiet sense, especially if a lean lambda value is pre-controlled.

Become the measures described above while the catalyst heating and before reaching operational readiness the lambda probe can be applied, the activity of the catalyst (s) something else be increased, so that these measures are also ahead of achievement The light-off phase is advantageous, with the increase in the activities of the or the catalysts for the conversion of the components to be oxidized (HC, CO) a modulation of the lambda from the regular λ = 1 operation is known.

Become the measures in internal combustion engines with gasoline direct injection or port injection is particularly suitable for engines with gasoline direct injection to combine the tax strategy with the well-known "homogenous split" operating because here the lean running ability is improved compared to pure homogeneous operation. in principle could also a mode change can be combined with it. For example, if the firing method allows, in the lean part of the amplitude the shift mode selected and in the fat part of the amplitude the homogeneous mode be driven. Is with a port injection the lean running ability Given in the required areas, the strategy can be here also be applied.

Short description the drawings

The Invention will be described below with reference to one shown in the figures embodiment explained in more detail. It shows:

1a a schematic representation of a symmetrical lambda pilot control,

1b a schematic representation of a single-ended lambda pilot control,

2 a schematic representation of the time course of the lambda value, the oxygen concentration and various pollutant concentrations.

embodiments the invention

The technical environment in which the inventive method runs sees an example of an internal combustion engine, consisting of an engine block and a supply air duct, which supplies the engine block with combustion air, in front. In this case, the amount of air in the supply air duct with a Zuluftmesseinrichtung be determinable. The exhaust gas of the internal combustion engine is thereby via a Emission control system led, which has as main components an exhaust passage in which flow direction of the exhaust gas, a first lambda probe in front of a catalyst and a second lambda probe is arranged behind the catalyst. The emission control system can still have a second catalyst behind the second lambda probe exhibit. The lambda probes are connected to a control device, those from the data of the lambda probes and the data of the supply air measuring device calculated the mixture and a fuel metering device for metering of fuel with appropriate injectors in the supply air duct controls.

With the arranged in the exhaust passage behind the engine block lambda probe can set a lambda value with the aid of the control device be that for the emission control system to achieve an optimal cleaning effect suitable is. The lambda probe can be used as a simple jump probe or as a sophisticated broadband probe accomplished be determined by the air ratio λ in a wide range leaves. If the lambda probe is designed as a jump probe, this is less expensive, but allows only a control to a setpoint of λ = 1. Therefore can while the determination of the oxygen storage capacity no lambda control be active. In this operating phase, only one pilot control takes place the fuel mixture with a predetermined by the controller Lambda value. The arranged in the exhaust passage behind the first catalyst second lambda probe can also be evaluated in the control device be and serves in a method according to the prior art the oxygen storage capacity to determine the emission control system.

The Control device can also with a display / storage unit be connected, with the example, a malfunction of the emission control system can be displayed. In addition, it can also be displayed if For example, in the on-board diagnosis, an oxygen storage capacity of the Catalyst is determined, which already with regard to the fulfillment of statutory emissions legislation is classified as borderline.

to Determination of oxygen storage capacity will generally while the on-board diagnosis the internal combustion engine first sufficiently long with excess fuel operated ("fat Mixture ") to all To reduce oxygen in the catalyst. In the subsequent lean operation Oxygen is stored in the catalyst, with the lambda probe behind the catalyst is detected when oxygen-rich Exhaust gas occurs because the oxygen storage capacity then exceeded OSC is.

To the prior art, a sudden change between λ <1 and λ> 1 is specified. At this Precontrol can Errors occur, for example, due to a scattering of the injectors or errors in the fill detection originate. These distort the lambda value and lead thus also errors in the determination of oxygen storage capacity.

During the Heating phase directly after the start of the engine is supportive to the fast Heating the catalyst provided, after starting a light to control lean mixture with λ> 1. There the dew point is still lower than during the cold start for the lambda probe is, the operational readiness of the lambda probe only becomes clear reached after the start.

As in 1a and 1b shown schematically, is provided during the heating phase of the exhaust gas purification system of the internal combustion engine, a temporal lambda curve 11 the lambda pilot control 10 during the heating phase of the catalyst to act on at least temporarily by means of a higher-frequency modulation, so that in this phase, a temporal lambda mean 12 of λ> 1, in the example shown λ = 1.05, given and at least briefly a lambda value of λ <1 is achieved. In 1a is a variant of the method with a sym metric lambda precontrol 10 shown. 1b shows a method variant in which the temporal lambda curve 11 the lambda pilot control 10 is precontrolled with an asymmetrical duty cycle between phases with λ> 1 and λ <1.

The areas of NOx conversion 20 lie in the range of the temporal lambda curve 11 in which λ <1, provided that the catalyst or catalysts have reached the light-off phase, ie the operating temperatures. The NOx reduced in the rich phase can not be reformed for reaction kinetic reasons in the catalysts and also afterwards in the exhaust gas line. In this context, it should be noted, however, that a NOx conversion with efficiencies of> 99%, as can be achieved in a controlled λ = 1 operation of a 3-way catalyst can not be achieved with this method, but here is not the goal of the described strategy.

According to the invention, it is provided that the higher-frequency modulation with respect to amplitude 13 and / or frequency is changed depending on the operating point of the internal combustion engine. In this case, the amplitude 13 the higher frequency modulation to a current value of the oxygen storage capacity (OSC) of the catalyst (s). Furthermore, it can be provided to increase the frequency of the higher-frequency modulation with decreasing value of the oxygen storage capacity (OSC) of the catalyst (s).

The actual value of the oxygen storage capability (OSC) of the catalyst (s) may be determined and stored using an oxygen storage capability (OSC) diagnostic method as described above. In addition to the oxygen storage capacity (OSC) of the catalyst or catalysts, a volumetric weighting of a catalyst temperature can be carried out and this in the amplitude and / or frequency modulation of the temporal lambda curve 11 the lambda pilot control 10 be considered during the heating phase of the catalyst or catalysts. To calculate the amplitude 13 and the frequency of the modulation, the value for the oxygen storage capacity (OSC) of the catalyst or catalysts and the value for the volumetric weighting of the catalyst temperature are measured in a preferred process variant and stored in maps.

The The strategy described above can be found below in different Phases of catalyst heating be used, as the following tabular compilation shows, taking the measures while the catalyst heating and before reaching operational readiness the lambda probe are applied.

An application in phase B, ie before reaching the operating temperature of the catalyst ("light-off") can be useful insofar that in addition to the improvement of NO _x conversion an increase in the activity of the catalyst or catalysts for the conversion of the oxidizing Depending on the system design or application, phase D may be omitted so that it is possible to proceed directly to normal operation without any further catalyst heating measures be carried out in the phase with regulated or unregulated lambda, depending on whether the lambda probe is ready for use or not. It is also possible to convert the control strategy into a control strategy in phase D with an operational lambda probe. The default value for the lambda is introduced directly into the lambda control as setpoint specification.

2 schematically shows the temporal lambda curve 11 , a time course of the oxygen concentration 40 as well as various pollutant concentrations 30 . 60 ,

Depending on the setting of frequency and amplitude 13 can be achieved in the example shown, compared to the pilot operation with a constant λ = 1.04, a conversion for NO _x of more than 50%. It can be seen that with increasing amplitude 13 the modulation for the lambda pilot control 10 the NO _x concentration 30 gradually decreases. It is in the 2 also to recognize that too small an amplitude 13 , in which the lambda value is not pre-controlled under one, no decrease in the NO _x concentration 30 is detected. Only with increasing amplitudes 13 the NO _x concentration decreases 30 from. The oxygen concentration 40 remains constant in wide ranges at about 0.6%. Due to the oxygen storage (OSC) always present in a 3-way catalytic converter, the grease peaks from the pilot-operated rich lambda are well intercepted, so that with proper design of frequency and amplitude 13 no appreciable breakthrough of CO and HC is expected, as is the timing of the CO concentration 50 and the HC concentration 60 demonstrate.

With The method can be achieved that still without operational Lambda control directly after the start of the internal combustion engine a Lambda pre-control is realized during the heating of the Catalyst already achieved a partial conversion of nitrogen oxides, without causing any appreciable deterioration for the oxidizing components results. Another advantage of this Strategy is that you can not exactly set a fixed value for the lambda is dependent, as required for example in λ = 1 operation, what a regular lambda probe would be required.

Claims (11)

Method for pilot control of a lambda value during the heating phase of an exhaust gas purification system of an internal combustion engine having at least one catalytic converter and at least one lambda probe, characterized in that a temporal lambda curve ( 11 ) of the lambda pilot control ( 10 ) is applied during the heating phase of the catalyst at least temporarily by means of a higher-frequency modulation, such that in this phase a temporal lambda mean ( 12 ) of λ> 1 and at least briefly a lambda value of λ <1 is achieved. Method according to Claim 1, characterized in that the temporal lambda curve ( 11 ) of the lambda pilot control ( 10 ) is precontrolled with an asymmetrical duty cycle between phases with λ> 1 and λ <1. A method according to claim 1 or 2, characterized in that the higher-frequency modulation with respect to amplitude ( 13 ) and / or frequency is changed depending on the operating point of the internal combustion engine. Method according to claim 3, characterized in that the amplitude ( 13 ) of the higher frequency modulation is adjusted to a current value of the oxygen storage capacity (OSC) of the catalyst (s). Method according to claim 3, characterized that the frequency of the higher Frequent modulation with decreasing value of the oxygen storage capacity (OSC) of the catalyst or catalysts is increased. Method according to one of claims 4 to 5, characterized that the current value of the oxygen storage capacity (OSC) of the Catalysts by means of a diagnostic method for oxygen storage capacity (OSC) is determined and stored. Method according to one of claims 3 to 6, characterized in that in addition to the oxygen storage capacity (OSC) of the catalyst or catalysts carried out a volumetric weighting of a catalyst temperature and this in the amplitude and / or frequency modulation of the temporal lambda curve ( 11 ) of the lambda pilot control ( 10 ) during the heating phase of the catalyst (s) becomes. Method according to claim 7, characterized in that that the value for oxygen storage capacity (OSC) or the catalyst and the value for the volumetric weighting the catalyst temperature measured and stored in maps become. Method according to one of claims 1 to 8, characterized in that the amplitude ( 13 ) the modulation of the temporal lambda curve ( 11 ) of the lambda pilot control ( 10 ) is limited. Application of the method according to one of claims 1 to 9, characterized in that the measures during the catalyst heating and before reaching the operational readiness of the lambda probe applied become. Application of the method according to one of claims 1 to 10, characterized in that the measures in internal combustion engines be applied with gasoline direct injection or port injection.