DE10226873A1 - Method for controlling the mode selection of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for controlling the operating modes of an internal combustion engine (10) with a NO¶x¶ storage catalytic converter (18), the operating modes being controlled as a function of operating parameters. DOLLAR A It is provided, DOLLAR A (a) that when the operating mode of the internal combustion engine (10) changes depending on the level of the NO¶x¶ storage catalytic converter (18) and at least one second parameter of the internal combustion engine (10), the NO¶x ¶ storage catalytic converter (18) or the emission is decided whether regeneration of the NO¶x¶ storage catalytic converter (18) is requested if the change in operating mode results in increased NO¶x¶ desorption or a NO¶x¶ slip the NO¶x¶ storage catalytic converter (18), and / or DOLLAR A (b) that the change of the internal combustion engine (10) to a different operating mode depending on the operating parameters of the internal combustion engine (10), the NO¶x¶- Storage catalytic converter (18) and actual or expected emission parameters, a subsequent check whether a change in another engine operation is possible is only permitted if a minimum time (t¶min¶) elapses richen and / or a predetermined minimum change of at least one operating parameter of the internal combustion engine (10), the NO¶x¶ storage catalyst (18) or an emission parameter is present.

Description

The invention relates to a method to control the mode selection of an internal combustion engine with the features mentioned in the preamble of claim 1.

For the aftertreatment of exhaust gases from internal combustion engines, it is generally customary to catalytically clean the exhaust gas. For this purpose, the exhaust gas is passed over at least one catalytic converter, which converts one or more pollutant components of the exhaust gas. Different types of catalysts are known. Oxidation catalysts promote the oxidation of unburned hydrocarbons (HC) and carbon monoxide (CO), while reduction catalysts support a reduction of nitrogen oxides (NO _x ) in the exhaust gas. Furthermore, 3-way catalysts are used to catalyze the conversion of the three aforementioned components (HC, CO, NO _x ) at the same time. However, the use of a 3-way catalytic converter is only possible if there is a strictly stoichiometric air-fuel ratio at λ = 1.

Among other things, lean-burn internal combustion engines are used to optimize the consumption of motor vehicles. In a fuel-efficient lean-burn operation in which the internal combustion engine is operated with an excess of oxygen, that is to say with λ> 1, a complete 3-way catalytic conversion of NO _{x is} not possible. In internal combustion engines of this type, therefore, NO _x storage catalysts are used which, in addition to a catalytic component, contain a NO _x storage device which stores NO _x in the form of nitrate in the lean operating phases. In intermediate rich regeneration phases at λ <1, in which HC and CO are formed, which act as reducing agents, the nitrates are reduced to nitrogen N ₂ . A catalyst, for example a 3-way catalyst, is often connected upstream of the NO _x storage catalyst.

In simple processes for controlling the NO _x storage catalytic converter, regeneration is initiated on the basis of stored behavior models of the NO _x storage catalytic converter. The actual loading and also its other state of the NO _x storage catalytic converter remain unconsidered. It is therefore also known to use emission curves measured by means of a NO _x sensor to initiate the regeneration of the NO _x storage catalytic converter, so that the initiation of regeneration is carried out only as required with a corresponding NO _x breakthrough. Within the framework of this procedure, it is a special case if, for other reasons, motor operation is stopped, which, in the event that NO _x regeneration is not carried out at the same time, leads to increased NO _x desorption or increased NO _x slip the NO _x storage catalyst results. For example, in the case of a direct-injection, lean-burn gasoline engine, the change to homogeneous operation for performing an acceleration is such a special case for performance reasons. Usually, when the engine operation is requested, a check is therefore carried out to determine the loading condition of the NO _x storage catalytic converter. If the stored amount of nitrates exceeds a predetermined threshold value, a NO _x regeneration is triggered. If the threshold value is not exceeded, the desorption of the stored amount of nitrates can be neglected from the point of view of emissions. However, each NO _x regeneration is associated with additional fuel consumption, so that to compensate for the additional consumption, a lean operating time that is several times longer than the regeneration period is necessary. When the engine is operating dynamically, the storage capacity of the NO _x storage catalytic converter is generally not fully utilized, but there are often operating mode changes and thus regeneration requirements. Therefore, only a small amount of fuel can be saved. The fuel savings could be increased again by increasing the threshold value, but the stated threshold value cannot be chosen too high in the approval test for reasons of exhaust gas safety.

The state of the art includes continue procedures that during of the operation of the internal combustion engine decide whether in the current operating state in a more economical one - for example from the stoichiometric into a lean - engine operation can be changed. Criteria for this can be in addition to the motor Boundary conditions also the expected emissions or the current one Condition of the exhaust gas purification system, i.e. the working temperature range of the catalytic converter, the current or expected raw emissions or the exhaust gas mass flow. When asked whether for reasons of Emission security changed Motor operation currently permitted there is usually a conflict of objectives. So leads a more economical Engine operation generally has disadvantages in terms of exhaust emissions.

The invention is therefore the object based on a method for controlling the mode selection of a To provide internal combustion engine, which is an increased fuel economy as well as a reduced emission of pollutants compared to Has method according to the prior art.

This task is accomplished through a process solved with the features mentioned in claim 1.

• (a) dass bei Wechsel der Betriebsart der Verbrennungskraftmaschine in Abhängigkeit des Füllstandes des NO_x-Speicherkatalysators sowie mindestens eines zweiten Parameters der Verbrennungskraftmaschine, des NO_x-Speicherkatalysators oder der Emission entschieden wird, ob eine Regeneration des NO_x-Speicherkatalysators angefordert wird, wenn der Wechsel der Betriebsart eine erhöhte NO_x-Desorption oder einen NO_x-Schlupf aus dem NO_X-Speicherkatalysator zur Folge hat, und/oder
• (b) dass der Wechsel in eine andere Betriebsart der Verbrennungskraftmaschine (10) in Abhängigkeit von Betriebsparametern der Verbrennungskraftmaschine, des NO_x-Speicherkatalysators und tatsächlichen oder zu erwartenden Emissionsparametern zugelassen wird, wobei eine nachfolgende Prüfung, ob ein Wechsel in einen anderen Motorbetrieb möglich ist, nur zulässig ist, wenn eine Mindestzeit verstrichen ist und/oder eine vorgegebene Mindeständerung mindestens eines Betriebsparameters der Verbrennungskraftmaschine, des NO_x-Speicherkatalysators oder eines Emissionsparameters vorliegt.

The method according to the invention for controlling the operating modes of an internal combustion engine with a NO _x storage catalytic converter arranged in an exhaust gas duct of the internal combustion engine, the internal combustion engine being assigned means which allow the operating modes to be controlled by at least temporarily influencing at least one operating parameter of the internal combustion engine, and the control of the operating modes depending on the operating parameters of the internal combustion engine, the NO _x storage catalytic converter and actual or expected emission parameters,

• (a) that when the operating mode of the internal combustion engine changes depending on the fill level of the NO _x storage catalytic converter and at least one second parameter of the internal combustion engine, the NO _x storage catalytic converter or the emission, a decision is made as to whether regeneration of the NO _x storage catalytic converter is requested if the change in the operating mode results in increased NO _x desorption or NO _x slip from the NO _x storage catalytic converter, and / or
• (b) that the change to another operating mode of the internal combustion engine ( 10 ) depending on the operating parameters of the internal combustion engine, the NO _x storage catalytic converter and actual or expected emission parameters, whereby a subsequent check as to whether a change to another engine operation is possible is only permitted if a minimum time has passed and / or predetermined minimum change of at least one operating parameter of the internal combustion engine, the NO _x storage catalytic converter or an emission parameter is present.

A threshold value is preferably specified for the fill level of the NO _x storage catalytic converter, if it is exceeded a regeneration is necessary to avoid NO _x slip, which according to the invention depends on at least one second parameter of the internal combustion engine, the NO _x storage catalytic converter or the emission and is changeable accordingly. However, separate threshold values can also be defined for the other parameters, so that the regeneration is dependent on the exceeding of at least two threshold values.

• – aktuelle Katalysatortemperatur,
• – aktueller Betriebspunkt (Last, Drehzahl) der Verbrennungskraftmaschine,
• – aktuelle Fahrzeuggeschwindigkeit,
• – aktuell verwendeter Gang des Fahrzeugs,
• – aktuelle Fahrpedalstellung,
• – in der vorangegangenen Speicherphase emittierte NO_x-Emissionen und

The additional parameters that are used to check whether regeneration of the NO _x storage catalytic converter has to be carried out are preferably selected from the following group:

• - current catalyst temperature,
• - current operating point (load, speed) of the internal combustion engine,
• - current vehicle speed,
• - current gear of the vehicle,
• - current accelerator pedal position,
• - NO _x emissions emitted in the previous storage phase and

- Previous number of lean-homogeneous changes carried out without subsequent regeneration initiation, with or without taking into account the respective NO _x discharge from the NO _x storage catalytic converter.

It does that too with dynamic operation of the internal combustion engine with numerous operating mode changes, fuel consumption compared to State of the art is reduced.

After the second sub-step of the method according to the invention, the internal combustion engine is changed to an operating mode with an excess of oxygen or another operating mode depending on various operating parameters of the internal combustion engine, the NO _x storage catalytic converter and the actual or expected emission. In order to achieve a significant increase in emission safety without having to accept significant disadvantages with regard to the fuel consumption of the internal combustion engine, a re-examination of these conditions is only permitted again when a specified minimum time has passed and / or a specified minimum change an operating parameter of the internal combustion engine, the NO _x storage catalytic converter or an emission parameter is present. If the required minimum change is given, it can be expected that a change in the operating mode will be permitted after the test.

• – eine vorgegebene Mindeständerung in der Motordrehzahl seit der letzten Prüfung,
• – eine vorgegebene Mindeständerung im abgegebenen Moment des Motors,
• – eine Änderung des gewünschten motorischen Betriebsverhaltens, abhängig von beispielsweise der Betriebsart, dem Zündwinkel und der Androsselung, sowie
• – eine vorgegebene Mindeständerung im Temperaturniveau des Abgasreinigungssystems.

The preferred parameters to consider besides or alternatively at the minimum time are:

• - a predetermined minimum change in engine speed since the last test,
• - a predetermined minimum change in the given torque of the engine,
• A change in the desired engine operating behavior, depending on, for example, the operating mode, the ignition angle and the throttling, and
• - A predetermined minimum change in the temperature level of the exhaust gas cleaning system.

Further preferred configurations the invention result from the remaining, mentioned in the subclaims Features.

The invention is hereinafter in embodiments based on the associated Drawings closer explained. Show it:

1 a schematic diagram of an internal combustion engine with an exhaust system;

2 time profiles of various parameters when changing from stratified charging to homogeneous operation and

3 the time course of two parameters when the admissibility of a change in operating mode is repeatedly checked.

The in 1 illustrated internal combustion engine 10 is an exhaust system 12 downstream. The exhaust system 12 has an exhaust duct 14 on, in which a pre-catalyst arranged close to the engine 16 and a large-volume NO _x storage catalytic converter 18 are located. In addition to the pre-catalyst 16 and the NO _x storage catalyst 18 points the exhaust duct 14 Usually, various gas and / or temperature sensors for regulating the internal combustion engine, but not shown here, are used 10 on. Are shown in 1 an example of a NO _x sensor 20 , the downstream of the NO _x storage catalytic converter 18 is arranged and which provides at least one signal for the content of NO _x in the exhaust gas, and a temperature sensor 22 , which is the temperature of the NO _x storage catalytic converter 18 determined. The signals are sent to an engine control unit 24 transmitted in which this for controlling the operating modes of the internal combustion engine 10 be used. In the engine control unit 24 is also a control unit 26 integrated. Using the engine control unit 24 and the control unit 26 becomes at least one operating parameter of the internal combustion engine 10 , in particular an air-fuel mixture to be supplied (combustion lambda), as a function of the signal from the NO _x sensor 20 and the temperature sensor 22 affected.

2 shows the time course of various parameters of the internal combustion engine 10 and the exhaust system 12 before, during and after a NO _x regeneration, which is carried out when changing from stratified charge operation with λ _M > 1 to a homogeneous operation with λ _R = 1, since otherwise NO _x slip is to be expected in the case shown. The internal combustion engine is located first 10 in a lean operating mode λ _M > 1, in which an oxygen-rich air-fuel mixture is fed to it (graph 100 ). At time t, the intention is to switch to homogeneous operation based on an intended acceleration of the vehicle. Therefore, the NO _X sensor 20 and temperature sensor 22 to the engine control unit 24 transmitted values are used to check whether the operating mode of the internal combustion engine changes 10 regeneration of the NOx storage catalytic converter 18 must be carried out to maintain emission security. The NO _x loading of the NO _x storage catalytic converter 18 (Graph 120 ), which increases continuously, with the aid of the signal from the NO _x sensor 20 determined. For the initiation of regeneration of the NO _x storage catalytic converter 18 when a mode change is requested, a threshold value NO _{xs is} the NO _x loading of the NO _x storage catalytic converter 18 given that is already exceeded at time t. The temperature (graph 110 ) of the NO _x storage catalytic converter 18 included, since regeneration only in a certain temperature range of the NO _x storage catalytic converter 18 makes sense. Therefore, for the temperature of the NO _x storage catalyst 18 likewise a threshold value T _{S is} specified, which is also exceeded at time t. Since the two predetermined threshold values NO _xs , T _{s have been} exceeded, regeneration of the NOx storage catalytic converter is necessary before changing the operating mode 18 perform, in the course of loading the NO _x storage catalyst 18 naturally decreases and is reduced to zero. The temperature of the NO _x storage catalytic converter 18 increases with the initiation of regeneration and decreases again at the time t ₂ towards the end of the regeneration. After the regeneration is completed at time t ₂ , the internal combustion engine is changed 10 into homogeneous operation without NO _x slipping.

In 3 is the time course of the temperature (graph 110 ) of the NO _x storage catalytic converter 18 and the combustion lambda (graph 100 ). The internal combustion engine 10 is first in a homogeneous operating mode with λ _H = 1 (graph 100 ). To reduce fuel consumption, a check is made at time t, as to whether it is possible to switch to a lean operating mode with λ _M > 1. For this purpose, the temperature of the NO _x storage catalyst is used in a conventional manner 18 used that to the engine control unit 24 is transmitted, and determines whether it is within its working temperature range. The working temperature range is limited by two predetermined limit temperatures TG ₁ and TG ₂ . At time t, the temperature of the NO _x storage catalytic converter is 18 above the second limit temperature TG ₂ , so that the change to a lean operating mode is not carried out. A renewed check as to whether a change can take place is only permitted again at time t _II when a predetermined minimum time t _{m in has} elapsed. In this test at time t _II , the temperature of the NO _x storage catalytic converter has 18 again reaches the working temperature range, that is, the temperature is between TG ₁ and TG ₂ , so that as a result of the repeated test at time t _II, the change to the lean operating mode of the internal combustion engine 10 approved and by means of the engine control unit 24 is caused by changing the combustion lambda.

10

Internal combustion engine

12

exhaust system

14

exhaust duct

16

precatalyzer

18

NO _x storage catalytic converter

20

NO _x sensor

22

temperature sensor

24

Engine control unit

26

control unit

100

combustion lambda

110

Temperature curve of the NO _x storage catalytic converter

120

NO _x loading of the NO _x storage catalytic converter

NO _xs

Threshold value of the loading of the NO _x storage catalytic converter to initiate NO _x regeneration

t ₁

regeneration start

t ₂

regeneration end

t _I

time The examination

t _II

time the subsequent test

t _min

minimum time

TG ₁ , TG ₂

limit temperatures

TS

Threshold value of the temperature of the NO _x storage catalytic converter to initiate NO _x regeneration

λ _M

Lambda lean value

λ _F

Lambda fat value

λ _H

Lambda homogeneous value

Claims (5)

Method for controlling the operating modes of an internal combustion engine ( 10 ) with one in an exhaust duct ( 14 ) of the internal combustion engine ( 10 ) arranged NO _x storage catalytic converter ( 18 ), the internal combustion engine ( 10 ) Means are assigned which are influenced by at least temporarily influencing at least one operating parameter of the internal combustion engine ( 10 ) allow the control of the operating modes, and wherein the control of the operating modes as a function of operating parameters of the internal combustion engine ( 10 ), the NO _x storage catalytic converter ( 18 ) and actual or expected emission parameters, characterized in that (a) that when the operating mode of the internal combustion engine changes ( 10 ) depending on the level of the NO _x storage catalytic converter ( 18 ) and at least one second parameter of the internal combustion engine ( 10 ), the NO _x storage catalytic converter ( 18 ) or the emission is decided whether regeneration of the NO _x storage catalytic converter ( 18 ) is requested if the change in operating mode results in increased NO _x desorption or NO _x slip from the NO _x storage catalytic converter ( 18 ) and / or (b) that the change of the internal combustion engine ( 10 ) in a different operating mode depending on the operating parameters of the internal combustion engine ( 10 ), the NO _x storage catalytic converter ( 18 ) and actual or expected emission parameters, whereby a subsequent check as to whether a switch to another engine operation is possible is only permitted if a minimum time (t _min ) has elapsed and / or a specified minimum change in at least one operating parameter of the internal combustion engine ( 10 ), the NO _x storage catalytic converter ( 18 ) or an emission parameter is present. A method according to claim 1, characterized in that for the fill level of the NO _x storage catalyst ( 18 ) a threshold value (NO _xs ), on which the implementation of the regeneration is dependent, which is in turn dependent on the one or more parameters. A method according to claim 1, characterized in that for the fill level of the NO _x storage catalyst ( 18 ) a threshold value (NO _xs ) and threshold values are also specified for the further parameter or parameters, on which the implementation of the regeneration is dependent. Method according to one of claims 1 to 3, characterized in that the further parameters are selected from the following group: - current catalyst temperature, - current operating point (load, speed) of the internal combustion engine, - current vehicle speed, - currently used gear of the vehicle, - current Accelerator pedal position, - NO _x emissions emitted in the previous storage phase and - previous number of lean-homogeneous changes carried out without subsequent regeneration activation, with or without taking into account the respective NO _x discharge from the NO _x storage catalytic converter. A method according to claim 1, characterized in that the in addition to or as an alternative to the parameters to be used at the minimum time selected from the following group are: - given minimum change in engine speed since the last test, - predetermined minimum change at the given moment of the engine, - change the desired motor operating behavior as well - predetermined minimum change in the temperature level of the exhaust gas cleaning system.