DE10064665C2 - Method for controlling an internal combustion engine - Google Patents

Description

The invention relates to a method for controlling a burner engine depending on certain operating conditions gen either with an overstoichiometric, stoichiometric or sub-stoichiometric fuel / air mixture is driven.

To fuel consumption of motor vehicles with ottomoto further reducing drive, come more and more often Internal combustion engines for use, at least partially with superstoichiometric, d. H. with lean fuel / air operated mixed.

In order to meet the required exhaust gas limit values, special exhaust gas aftertreatment is necessary in such internal combustion engines. For this purpose, NOx storage catalysts are used, which due to their coating are able to adsorb the NOx compounds from the exhaust gas, which arise during combustion with a lean fuel / air mixture, in a storage phase. During a regeneration phase, the adsorbed NOx compounds are converted into harmless compounds with the addition of a reducing agent. CO, H ₂ and HC (hydrocarbons) can be used as reducing agents for lean-burn gasoline internal combustion engines. These are generated by briefly operating the internal combustion engine with a rich fuel / air mixture and made available to the NOx storage catalytic converter as exhaust gas components, as a result of which the stored NOx compounds in the NOx storage catalytic converter are desorbed.

The storage efficiency of such a NOx storage catalyst depends on numerous influencing variables described in the literature. A primary influencing variable, in addition to the temperature of the NOx storage catalytic converter, is in particular the degree of loading, that is to say the storage efficiency decreases continuously as the lean phase increases and the resulting storage of NOx takes place, so that, taking into account the exhaust gas limit values or other operating conditions, a switchover to the fat - That is, in the regeneration operation is necessary. The required duration of the fat operation for regeneration essentially depends on the stored NOx mass and the O ₂ storage capacity of the NOx storage catalytic converter.

Because the transition from lean operation to rich operation or from Fat operation for lean operation of the internal combustion engine for ver avoidance of NOx raw emission peaks must occur abruptly, is the change in air ratio preferably by changing the Injection quantity reached. The one with an air ratio change over Injection quantity change is associated torque change by an ignition angle intervention to compensate for the driving behavior of such a vehicle is not disadvantageous influences. Such a change from the superstoichiometric Be drove the engine to substoichiometric loading driven and vice versa poses with regard to the desired Driving comfort high demands on the engine control function naturalness, since this change of operating mode is torque-neutral must d. H. not noticeable to the driver of the vehicle should be.

In a torque-based engine control, in which the Torque desired by the driver as the base variable for the tax generation and control of the internal combustion engine is used, a rotation takes place for the new state of the internal combustion engine moment-neutral application of the transitions. For the new condition you know the influence of the ignition angle and the air ratio the torque output and these relationships can be in Maps are filed. That from the internal combustion engine torque delivered is subject to age and ver wear-related change, so that the saved Change relationships and the transitions are no longer torque-neutral  expire if they follow the same rules be processed. This change in torque can are insufficiently considered by a model, because this is usually insufficiently predictable and also from an undetectable number of influencing variables depending on the aging process. The changes in Torque of the internal combustion engine can in the known Procedures lead to a short-term operation change the required torque neutrality is guaranteed and the driver an unpleasant jerking of the Vehicle noticed.

DE 195 17 168 A1 and EP 0 687 809 A2 describe methods and Devices for controlling the torque at high ver Change in the air ratio by delaying the ignition timing and Return of exhaust gas described.

DE 197 44 410 A1 describes a method for monitoring known the smooth running control of an internal combustion engine. there the running smoothness is with at least one over a rule direction adjustable manipulated variable to influence the Laufru behavioral regulated. For this purpose, measurement signals are evaluated, which corresponds to at least one temperature at the catalyst chen. The preferred measurement value for monitoring smooth running is preferred the difference of the measurement signals at the catalyst inlet and at the Ka Talysatorauslaß formed. The measurement signals can be before increases from the internal resistances of the existing HEGO sensors (Heated Exhaust Gas Oxygen).

DE 199 15 793 A1 describes a method for desorption egg Described nitrogen oxide adsorber of an exhaust gas cleaning system ben. The air ratio of the exhaust gas in the nitrogen oxide adsorber Exhaust gas supplied to the cleaning system is during the respective lige desorption operation phase kept in the rich area. The exhaust air ratio at the beginning of the desorption operating phase to a predeterminable minimum initial Fat value set and from there in the course of the desorption operation phase  to a definable one, at the latest towards the end the final fat value present in the desorption operating phase lifted.

EP 0 926 327 A2 describes a device and a method Ren to regulate a lean-burn engine known in Exhaust line has a nitrogen oxide adsorber. For regeneration Ren of the nitrogen oxide adsorber, the engine is time operated wise with a rich mixture. A control device ü monitors the uneven running of the internal combustion engine during a Normal operation.

In US 5,941,211 A is a method for regenerating a Exhaust gas catalyst, e.g. B. a NOx storage catalyst wrote, in which the operating mode change depending on ei Nem sensor signal in unsteady phases, for example delay tion of the internal combustion engine.

The invention has for its object a method for Controlling an internal combustion engine to specify a Torque-neutral change of operating mode of the aforementioned Type is guaranteed.

This task is accomplished by the in the independent claims mentioned features solved.

To achieve torque neutrality when switching from Lean operation on rich operation or from rich operation on lean operation operation to control the regeneration phase for the NOx Storage catalytic converter are by evaluating uneven running Various tax measures have been initiated. Exceed the rough running values predetermined limit values, so the over walk between the individual operating modes in an instatio närvorgang the internal combustion engine, such as acceleration or Delay set. This has the advantage that this occurs torque fluctuations are hardly noticeable,  since the driver is having a torque change anyway expects.  

The transition between the individual operating modes is not placed in transient processes, it is advantageous to the Ü transition not to perform abruptly, but the air ratio to change via a ramp function. This allows Einbu owing to driving comfort, such as jerking of the internal combustion engine ne driven vehicle can be largely avoided.

If the rough running values are outside an approved range ches, it is also possible to use the so-called lean mix drove the engine to completely ban. It in this case, the internal combustion engine with stoichiometri fuel / air mixture d. H. with an air ratio λ = 1 operated.

Further advantageous embodiments are in the subclaims Chen specified.

The invention is described below with reference to the Drawing explained in more detail. The drawing shows:

Fig. 1 is a schematic representation of a Brennkraftmaschi ne with its associated control and exhaust gas after-treatment device,

FIG. 2 is a diagram of selected waveforms for ei nen regeneration cycle in perfect coordination,

Fig. 3 is a diagram of selected waveforms for egg Nener regeneration cycle with provoked incorrect coordination, which specifies wear and aging processes of the internal combustion engine and

Fig. 4 is a diagram of selected waveforms for egg NEN regeneration cycle, wherein the incorrect tuning is compensated.

In Fig. 1, an internal combustion engine with direct injection fuel injection is shown schematically with a NOx exhaust gas aftertreatment system, in which the method according to the invention is used. Only those components are shown which are necessary for an understanding of the invention. In particular, the fuel circuit is omitted.

The internal combustion engine 10 is supplied with the air required for combustion via an intake duct 11 . In the intake duct 11 , seen in the direction of flow of the sucked-in air, an air mass meter 12 and a throttle valve block 13 with a throttle valve 130 and a throttle valve sensor (not shown) for detecting the opening angle of the throttle valve 130 are provided. Further, the Brennkraftma machine 10 an exhaust duct 14, in which a close to the internal combustion engine 10 arranged pre-catalyst 15 for convergence orientation of the pollutants HC and CO, and in the flow rich of the exhaust gas processing the pre-catalyst 15 downstream NOx storage catalyst 16 is provided. The pre-catalytic converter 15 can also be accommodated together with the NOx storage catalytic converter 16 in a common housing. Furthermore, it is possible to provide only one NOx storage catalytic converter, which also has three-way properties, without the precatalyst.

The internal combustion engine 10 has a corresponding number of injectors 17 corresponding to the number of cylinders, so that each cylinder is assigned a separate injector. The fuel is injected directly into the respective cylinder of the internal combustion engine 10 .

The sensor system for the exhaust gas aftertreatment system includes an oxygen sensor 18 upstream of the pre-catalyst 15 , a temperature sensor 19 in the connecting pipe between the pre-catalyst 15 and NOx storage catalytic converter 16 close to the inlet area thereof, and a further exhaust gas measuring sensor 20 downstream of the NOx storage catalytic converter 16 . Either an oxygen measuring sensor or a NOx sensor can be used as the exhaust gas measuring sensor 20 . The signal of the exhaust gas measuring sensor 20 arranged downstream of the NOx storage catalytic converter 16 is also used to control the storage regeneration and to adapt model variables such as, for. B. the oxygen or NOx storage capacity of the NOx storage catalyst 16 is used.

Instead of the temperature sensor 19 , which detects the exhaust gas temperature and from whose signal the temperature of the NOx storage catalytic converter 16 can be calculated using a temperature model, it is also possible to measure the NOx storage catalytic converter temperature directly in the monolith of the NOx storage catalytic converter 16 .

A broadband lambda probe is preferably used as the oxygen sensor 18 , which, depending on the oxygen content in the exhaust gas, is a constant, e.g. B. outputs linear output signal. With the signal of this broadband lambda probe 18 , the air ratio is adjusted during operation of the internal combustion engine, in particular during lean operation and during the regeneration phase with a rich fuel / air mixture in accordance with the setpoint specifications. This function is performed by a lambda control device 21 known per se, which is preferably integrated into a control device 22 which controls the operation of the internal combustion engine 10 .

Such electronic control devices, which include a microprocessor in the Re and which in addition to fuel injection and ignition also perform a variety of other control tasks, including the control of the exhaust gas aftertreatment system, are known per se, so that only in the following the structure relevant to the invention and its mode of operation are discussed. In particular, the control device 22 is connected to a memory device 23 , in which, among other things, various characteristic curves or characteristic diagrams and threshold values are stored, the respective meaning of which is explained in more detail with reference to the description of the following figures.

The output signal of the air mass meter 12 and the signals from the throttle valve sensor, the oxygen sensor 18 , the exhaust gas sensor 20 and the temperature sensor 19 are supplied to the control device 22 via corresponding connecting lines.

To control and regulate the internal combustion engine 10 , the control device 22 is provided, in addition to an ignition device 24 for the fuel / air mixture, via a data and control line 25, which is only shown schematically, with further sensors, not explicitly shown, for. B. for speed and coolant temperature of the internal combustion engine and connected with wide ren actuators.

The following explains how to prevent a Loss of driving comfort by changing the torque of the Internal combustion engine can be achieved, which by the Functionality of the control device of the internal combustion engine does not or only appears when simulating the torque can be insufficiently covered.

This requires stationary operation detection to be safe to make sure that the torque change when loading drive mode change is not one of the driver of the of the Internal combustion engine driven vehicle or one of the Control device based on a torque request caused change is d. H. that of the control The specified torque to be realized must be selected be virtually constant during the change of operating mode. A ver Change in the real induced torque makes up for noticeable to the driver in the following way. The leaping aen change in injection, the moment compensating abrupt  Adjusting the ignition angle and changing the fill lung can be changed by changing the course of combustion influencing combustion parameters to a delayed, bad combustion in single bars during the over ganges from operation with a lean fuel / air mixture operation with a rich fuel / air mixture and vice versa to lead. This can be due to the occurrence of increased bump values are detected. The uneven running values can according to can be determined using any known method for example as described in WO 97/20195.

There are slight changes even when the internal combustion engine is new an appli Ornate uneven running window that determines the decision about an impermissible uneven running in such a situation specifies drive mode change. If such an impermissibly high He repeats uneven running during a change of operating mode knows, different control engineering interventions be initiated.

In the upper part of FIG. 2, the courses of the setpoint for the air ratio λ_sp, the actual air ratio λ_av, which was measured by means of the oxygen sensor 18 and the signal of the MAF of the air mass sensor 12 and in the lower part of the time t, depending on the time t Fig. 2 is a rough running value LU for all cylinders of the internal combustion engine in the case of a perfect vote. These curves thus reflect the relationships or relationships that exist in a new internal combustion engine. Starting from a lean fuel / air mixture corresponding to an air ratio λ = 1.4, a fuel / air mixture corresponding to an air ratio λ = 0.8 is set abruptly to regenerate the NOx storage catalyst 16 , without the uneven running value LU resulting from a upper threshold LU_SWO and a lower threshold LU_SWU limited uneven running window is left. The same applies at the end of the regeneration cycle, i.e. when changing from operating with a rich fuel / air mixture to operating with a lean fuel / air mixture.

In the upper part of FIG. 3, the courses of the setpoint for the air ratio λ_sp, the actual air ratio λ_av, which was measured by means of the oxygen measuring pickup 18 and the signal of the MAF of the air mass sensor 12 and in the lower part of the time t Fig. 3 of the rough running value LU for all cylinders of the internal combustion engine for a regeneration cycle in the event of provoked incorrect coordination, which specifies wear and aging processes of the internal combustion engine.

While the torque-neutral application of a new internal combustion engine ensures that the uneven running value lies within the uneven running value window even in the case of steep lambda jumps, this application, once made, on an aged internal combustion engine means that the uneven running value LU itself changes significantly in the event of a lambda jump due to changed combustion characteristics lies outside the predetermined limits LU_SWU, LU_SWO ( FIG. 3, lower part).

So that such uneven running values LU do not occur and none Losses in comfort and driveability are accepted must be vorese according to a first embodiment hen, the operating mode change, d. H. the transition between Be drove the engine with lean fuel / air mixture for operation with rich fuel / air mixture and conversely to le in transient phases of the internal combustion engine gene.

An operating mode change only takes place if the torque gradient exceeds a predefined threshold value TQI_SW. The torque gradient is recorded in the control device 22 and the threshold value TQI_SW is determined experimentally for the respective internal combustion engine and is stored in the storage device 23 . In the case of a negative speed gradient, the switchover from under- or stoichiometric fuel / air mixture to lean fuel / air mixture takes place, with a positive torque gradient there is a transition for the purpose of regeneration of the NOx storage catalytic converter 16 from lean fuel / air mixture to rich fuel - / air mixture

The regeneration of the NOx storage catalytic converter 16 begins and ends in an unsteady phase, ie in an acceleration phase or in a deceleration phase of the internal combustion engine. In these phases, the driver expects a torque reaction and if the torque fluctuates somewhat due to the change in operating state, this is far less uncomfortable than if the operating state changes during constant travel.

It is particularly advantageous if the operating mode change takes place during the switching operations, since then the internal combustion engine machine is separated from the gearbox and none or almost none Torque response to the vehicle and therefore to the driver is transmitted. This procedure applies to both manual switching gearbox, automated manual transmission as well as for Au tomatikschaltgetriebe.

Since it cannot always be ensured that the torque gradient reaches the threshold value for triggering an operating state change sufficiently frequently, for example if the vehicle is being driven on highways at a constant speed for a long time, the NOx storage catalytic converter 16 has reached its storage capacity in such cases, the transition from operation with a lean fuel / air mixture to operation with a rich fuel / air mixture and vice versa is not carried out abruptly, but the lambda setpoint λ_sp is changed continuously, for example by means of a ramp function.

The corresponding temporal signal curves are shown in FIG. 4. The slope of the ramp can vary who. The flatter the ramp, the smoother the run irregularity LU, the loss of driving comfort is compensated. This intervention has effects on the emission behavior of the internal combustion engine 10 , in particular on the NOx emissions and must be taken into account when determining the degree of loading of the NOx storage catalytic converter 16 .

In the exemplary embodiment shown, the lambda setpoint λ_sp = 1.4 ramped down to 1.0 and then makes one small leap in the direction of rich fuel / air mixture (λ_sp = 0.8), since the torque hardly changes there. The steepness of the ramp can correspond to another lau radio quiet evaluation can be adjusted.

In parallel, the fuel for the combustion of the Air mass supplied to the internal combustion engine can be lowered where can be low due to the ignition angle intervention and one thereby achieves an improvement in the efficiency of Regeneration.

As another option, no loss of driving comfort due to To suffer torque change of the internal combustion engine, be stands in the lean mix operation of the internal combustion engine entirely to prevent. The internal combustion engine is no longer with ü operated stoichiometric fuel / air mixture, son with a fuel / air mixture corresponding to λ_sp = 1. This can e.g. B. become necessary if a defect in an ignition candle occurs, which does not constantly produce dropouts, but in the operation of the internal combustion engine with lean force The mixture of substances and air does not guarantee clean combustion can be, so that no torque-neutral transition between between the operating modes.

Claims (7)

1. Method for controlling an internal combustion engine ( 10 ),
which, depending on certain operating conditions, is operated either with an over-stoichiometric, stoichiometric or under-stoichiometric fuel / air mixture, where
A NOx storage catalytic converter ( 16 ) is arranged in an exhaust gas duct ( 14 ) of the internal combustion engine ( 10 ),
depending on the operating parameters of the internal combustion engine ( 10 ) and the NOx storage catalytic converter ( 16 ) for the regeneration of the NOx storage catalytic converter ( 16 ), an operating mode change between the operating modes is carried out with an overstoichiometric, stoichiometric or substoichiometric fuel / air mixture,
Values for the uneven running (LU) of the internal combustion engine ( 10 ) are recorded,
it is checked whether the uneven running values (LU) meet specified conditions (LU_SWU, LU_SWO) and if the uneven running values (LU) do not meet these conditions,
Values for a torque setpoint of the internal combustion engine ( 10 ) are calculated, a torque gradient is determined therefrom and from the current value of the torque,
the torque gradient is compared with a threshold value (TQ_SW) and an operating mode change is made in insta tionary phases of the internal combustion engine ( 10 ) if the threshold value (TQ_SW) is exceeded. 2. The method according to claim 1, characterized in that in the case of a negative torque gradient, a switchover from a company with substoichiometric or stoichiometric fuel / air mixture for operation with overflow chiometric fuel / air mixture takes place.   3. The method according to claim 1, characterized in that with a positive torque gradient, a switchover from operation with stoichiometric fuel / Air mixture to an operation with substoichiometric Fuel / air mixture takes place. 4. The method according to any one of the preceding claims, characterized in that the operating mode change is carried out during the execution of switching operations in which the internal combustion engine ( 10 ) is at least partially decoupled from a drive train of the vehicle driven by the internal combustion engine ( 10 ). 5. Method for controlling an internal combustion engine ( 10 ),
which, depending on certain operating conditions, is operated either with an over-stoichiometric, stoichiometric or under-stoichiometric fuel / air mixture, where
A NOx storage catalytic converter ( 16 ) is arranged in an exhaust gas duct ( 14 ) of the internal combustion engine ( 10 ),
depending on the operating parameters of the internal combustion engine ( 10 ) and the NOx storage catalytic converter ( 16 ) for the regeneration of the NOx storage catalytic converter ( 16 ), an operating mode change between the operating modes is carried out with an overstoichiometric, stoichiometric or substoichiometric fuel / air mixture,
Values for the uneven running (LU) of the internal combustion engine ( 10 ) are recorded,
it is checked whether the uneven running values (LU) meet specified conditions (LU_SWU, LU_SWO) and if the uneven running values (LU) do not meet these conditions,
Both the transition from over-stoichiometric or stoichiometric fuel / air mixture to under-stoichiometric fuel / air mixture as well as the transition from under-stoichiometric fuel / air mixture to stoichiometric or over-stoichiometric fuel / air mixture takes place continuously, at least in sections, in which a setpoint for the air ratio (λ_sp) of the fuel / air mixture is changed using a ramp function. 6. The method according to claim 1, or 5, characterized in that that it is checked whether the rough running values (LU) are within one by a lower threshold (LU_SWU) and an o lower threshold (LU_SWO) limited uneven running window lie. 7. The method according to claim 6, characterized in that the threshold values (LU_SWU, LU_SWO) are determined experimentally and are stored in a memory device ( 23 ).