DE102005058524A1 - Method for monitoring exhaust gas aftertreatment system of an internal combustion engine, uses lambda map-based pilot control that provides constant increase of lambda value from minimum to maximum lambda value within acceptable range - Google Patents

Abstract

The method involves determining the oxygen storage capacity of a catalyst (70) using a lambda map-based pilot control, where the lambda value lies between the rich and lean air fuel mixture ratios. The map-based pilot control also provides constant increase of the lambda value from minimum to maximum lambda value within an acceptable range. The constant increase of the lambda value is preferably in the form of a linear slope or ramp under servo-control. An independent claim is also included for a device for monitoring of an exhaust gas aftertreatment system of an IC engine.

Description

State of technology

The The invention relates to a method for monitoring an exhaust gas purification system an internal combustion engine with a in the emission control system arranged behind a catalyst, with a control device connected exhaust probe with jump characteristic, wherein for determination the oxygen storage capacity the catalyst targeted by means of a modeled lambda precontrol between a fat (λ <1) and a lean one (λ> 1) fuel-air mixture is changed.

The The invention further relates to a device for monitoring an emission control system of an internal combustion engine with an in the emission control system arranged behind a catalyst, with a control device connected exhaust probe with jump characteristic, being targeted to determine the oxygen storage capacity of the catalyst by means of a modeled lambda pilot control a rich (λ <1) and a lean (λ> 1) fuel-air mixture is changeable.

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 OSC (Oxygen Storage Capacity). This can be in the fat phases not enough anymore Oxygen available be made to clean the exhaust gas from the noxious gas components and the lambda probe behind the emission control system detects this to oxidizing components. Furthermore, this lambda probe detects in longer Magerphasen the oxygen 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 has the task of an inadmissible sinking the conversion that is too illegal increase the emission values leads, to recognize and over to display a control lamp.

One Known diagnostic method is the oxygen storage ability to determine the emission control system, as experience shows with the storage capacity also the conversion ability decreases.

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.

The Requirement for the accuracy of the catalyst diagnosis is such that a so-called GRENZKAT is actually diagnosed as a GRENZKAT becomes. As a CATEGORY, a catalyst is called the exhaust gas value just reached the legal limit. This one is in the Application as reference for the exhaust gas optimization and for the Diagnosis used.

to correct determination of the aging of the emission control system the amplitude of lambda oscillation behind the emission control system have to the average lambda value and the amplitude of the lambda oscillation the exhaust gas purification system, the exhaust gas mass flow and to what extent a stationary operating state the internal combustion engine is present with consideration. Special operating conditions as a coasting operation without fuel injection, in which the exhaust gas purification system the 1.5 to 2 times the storage capacity as in lean operation, must be considered.

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 as the time integral of the product from gas mass flow and lambda value before the catalyst is calculated, the temporal integral of the product of gas mass flow and lambda value is calculated 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 one of 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 integrate the introduced or withdrawn amount of oxygen via the integration of the product from the current lambda value and gas mass flow determine.

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 oxygen input 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.

• – bei dem der Sauerstoffgehalt des Abgases hinter dem Katalysator bestimmt und
• – bei dem der mittlere Sauerstoffgehalt des Abgases vor dem Katalysator in eine Richtung verändert wird, die von dem zuvor bestimmten Sauerstoffgehalt hinter dem Katalysator wegführt und
• – bei dem die aus der Änderung des mittleren Sauerstoffgehaltes resultierende Änderung des Sauerstofffüllstandes des Katalysators bestimmt wird und mit einem vorbestimmten Grenzwert verglichen wird und
• – bei der eine Fehlermeldung unterbleibt, wenn der vorbestimmte Grenzwert überschritten wird bevor sich der Sauerstoffgehalt des Abgases hinter dem Katalysator ändert.

The DE 19803828 A1 describes a method and a device for checking an exhaust gas catalytic converter in internal combustion engines,

• - Determines the oxygen content of the exhaust gas behind the catalyst and
• - In which the average oxygen content of the exhaust gas before the catalyst is changed in a direction which leads away from the previously determined oxygen content behind the catalyst and
• - In which the resulting from the change in the average oxygen content change in the oxygen level of the catalyst is determined and compared with a predetermined limit and
• - In which an error message is omitted when the predetermined limit is exceeded before the oxygen content of the exhaust gas changes behind the catalyst.

at a two-point probe in front of the catalyst can the oxygen content of the input exhaust gas can not be determined quantitatively. This applies to both the fat mixture as well the lean mixture. An approach for the realization is to start from a correct precontrol and to model the oxygen content of the input exhaust gas. The punctual tolerances of the system have no effect activities inadmissible out, so the evaluation quality can not be enough to make a catalyst better or worse to diagnose as a BORDER CAT. In addition, in the further Course an additional Set deviation of feedforward, which additionally falsifies the result. at road measurements were observed in controlled operation mixture fluctuations, the in the same order of magnitude lay like the lambda lean. this leads to very big Scattering in the OSC determination. The fundamental problem with this is that one at a time with the probe jump the lambda value measures or corrects feedforward, but then, e.g. by least change the operating point, the mixture may change inadmissible.

It It is therefore an object of the invention to provide a method that the accuracy and thus the evaluation quality of the active catalyst diagnosis significantly improved with a two-point or jumping probe. It is still the object of the invention, a corresponding device provide.

Advantages of invention

The The object relating to the method is achieved in that the modeled lambda precontrol is specified in such a way that a lambda value in its time course after a minimum Lambda value a range of steady increase or after a maximum Lambda value goes through an area of steady decrease. Advantageous across from the specification of a constant lambda value is that a punctual Fault tolerance is thereby sanded. The accuracy and thus the quality of evaluation the active catalyst diagnosis can be characterized in particular in a Two-point or jumping probe can be improved.

In a preferred variant of the method is provided that in the field the steady increase in the time course of the modeled lambda precontrol the lambda value ramped up linearly in the form of a ramp becomes. This is in terms of improved averaging advantageous, similar as in the two-step control with ramped integrator.

In a variant of the method can also be provided that in the field the steady decrease in the time course of the modeled lambda precontrol the lambda value is pre-controlled linearly decreasing in the form of a ramp becomes.

Becomes in the time course of the modeled lambda feedforward control the minimum lambda value and before the range of steady increase in lambda value first in Preceded in the form of a jump, can be achieved that the Waiting time and thus the total time for an OSC diagnosis can be shortened.

Advantageous is there when the jump of the modeled lambda feedforward via a Value λ> 1 is precontrolled, because with it a probe jump earlier can be initiated.

In Another preferred variant of the method is in temporal Course of the modeled lambda pilot control after the maximum Lambda value and before the range of steady decrease in lambda value first piloted in the form of a jump. This can result in a faster reaction.

He follows while the jump of the modeled lambda feedforward under a Value λ <1, an HC conversion can be checked.

Becomes the range of the steady increase or decrease of the lambda value limited to the modeled lambda pilot control, this results in the Advantage that in particular with a new catalyst with a still very good OSC value, the lambda feedforward control is not enough an optimal range or too big Deviations occur that lead to vibrations with impermissibly high Amplitudes during lead to on-board diagnostics can.

conveniently, becomes a limit of the lambda value of the modeled lambda precontrol at the time of a probe jump of a lambda model course (GRENZKAT) initiated, since it is already recognized at this time that the OSC value of the catalyst the limit for a fulfillment has reached the legal emissions regulations. An increase in the Lambda value over this limit would, would only to larger deviations to lead.

Becomes the diagnosis aborted when during the lambda pilot control a probe voltage of an exhaust gas probe before the catalyst for a predetermined time outside of a defined voltage band, can thus a malfunction the exhaust gas probe are detected in front of the catalyst.

A Process variant provides that a limitation of the voltage band dependent on time is given, with which an error limit, depending on the operating state, is adaptable, this being at both a constant lambda value and at a continuously increasing or decreasing lambda value is applicable.

The the object relating to the device is achieved in that the control device is a model formation stage with respect to the modeled Lambda pilot control has, with a lambda value in the way is predeterminable that he in his time course for a minimal Lambda value a range of steady increase or a maximum lambda value goes through an area of steady decline. It can with this device be achieved that a higher Accuracy of determination of oxygen storage capacity the emission control system is made possible with a simple structure. This is particularly advantageous in terms of cost reduction for one On-board diagnostics.

is the controller is connected to a display / storage unit, can be displayed in the form of a service warning lamp, for example For example, the temporal occurrence of the measured probe jump that corresponds to a lambda model history for a GRENZKAT and thus just reached the legal emissions regulations become.

In preferred embodiment can monitor the functions the emission control system in the control unit as software and / or hardware accomplished be and at least partially be part of a higher-level engine control, a program stored function is particularly simple as Subroutine integrated throughout the engine control software can be. this makes possible also very fast to perform Software updates, so that the on-board diagnosis can be adapted to the state of the art at any time or even one, depending on the version the engine used modified monitoring function can be.

drawing

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

1 a schematic representation of an internal combustion engine,

2a 3 is a schematic representation of a time profile of a lambda value according to the prior art,

2 B a schematic representation of the time course of the lambda value according to the inventive embodiment of the method.

description the embodiments

1 schematically shows a technical environment in which the inventive method runs. In the figure is an internal combustion engine 1 consisting of an engine block 40 and a supply air duct 10 that the engine block 40 supplied with combustion air, shown, with the amount of air in the supply air duct 10 with a Zuluftmesseinrichtung 20 is determinable. The exhaust gas of the internal combustion engine 1 is guided through an exhaust gas purification system, which as main components an exhaust duct 50 in which, in the flow direction of the exhaust gas, a first exhaust gas probe 60 before a catalysis gate 70 and a second exhaust gas probe 80 behind the catalyst 70 is arranged. Like in the 1 indicated, the emission control system can still a second catalyst 90 behind the second exhaust gas probe 80 exhibit.

The exhaust probes 60 . 80 are with a control device 100 connected from the data of the exhaust probes 60 . 80 and the data of the supply air measuring device 20 calculates the mixture and a fuel metering 30 for the metered addition of fuel with appropriate injectors in the supply air duct 10 controls.

With the in the exhaust duct 50 behind the engine block 40 arranged exhaust gas probe 60 can with the help of the control device 100 a lambda value can be set, which is suitable for the exhaust gas purification system to achieve optimum cleaning effect. The exhaust gas probe 60 can be designed as a simple jumping probe or as a complicated broadband probe, through which the air ratio λ can be determined over a wide range. Is the exhaust gas probe 60 formed as a jump probe, this is less expensive, but allows only a control to a setpoint of λ = 1. Therefore, no lambda control can be active during the determination of the oxygen storage capacity. In this operating phase, only a pilot control of the fuel mixture with one of the control device takes place 100 predetermined lambda value. The in the exhaust duct 50 behind the first catalyst 70 arranged second exhaust gas probe 80 can also be in the controller 100 be evaluated and used to determine the oxygen storage capacity of the emission control system in a method according to the prior art.

The control device can also, as in 1 shown with a display / storage unit 110 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 70 is determined, which is already classified as borderline with regard to the fulfillment of the legal emission regulations.

In general, during the on-board diagnosis, the internal combustion engine is determined to determine the oxygen storage ability 1 initially operated for a sufficiently long time with excess fuel ("rich mixture") to all the oxygen in the catalyst 70 to reduce. In the subsequent lean operation is in the catalyst 70 Oxygen stored, with the exhaust probe 80 is detected when oxygen-rich exhaust gas occurs, since the oxygen storage capacity OSC is then exceeded.

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

In 2a schematically is the time course of a lambda value in a modeled lambda precontrol 120 represented according to the prior art. Initially, a rich mixture with a lambda of typically λ = 0.96 is set. In the further course of the modeled lambda feedforward, this then has a jump 121 to a lambda value of λ = 1.04. In road measurements, however, mixture fluctuations were observed in this controlled operation, which were up to 4% equal to a lambda lean to λ = 1.04 (corresponding to 4%). These scatters are within a tolerance range 170 , which can lead to large inaccuracies in the OSC determination.

2a continues to show in response to the lambda feed forward 120 with the jump 121 a lambda model course 130 for the exhaust gas probe 60 in front of the catalyst 70 , The time for detecting a lean mixture becomes the exhaust gas probe 60 , which is executed in the example shown as a two-point or jump probe, a probe jump 131 assuming the change between λ <1 and λ> 1 indicates. In reality, the lambda curve for the exhaust gas probe 60 compared to the lambda model course 130 delayed in time occur.

Furthermore, in 2a the time course of a lambda actual value 140 for the exhaust gas probe 80 behind the catalyst 70 represented, whose probe jump 141 opposite the probe jump 131 the exhaust gas probe 60 delayed occurs. This time delay is a measure of the oxygen storage capacity of the catalyst 70 and may be in the controller 100 be evaluated. In addition, a lambda model course (GRENZKAT) 160 with a probe jump 161 considered, for a borderline in terms of oxygen storage capacity and thus also compliance with the exhaust gas regulations catalyst 70 is predetermined. If the occurring delay is too great, as exemplified by the time course of a lambda actual value 150 with a probe jump 151 shows, it is generally assumed that then the oxygen storage capacity of the catalyst 70 has too low a value and thus compliance with the statutory emission regulations can no longer be guaranteed.

2 B schematically shows the modeled lambda feedforward 120 in an inventive process variant. The lambda model profile is shown by way of example 130 with the probe jump 131 for the exhaust gas probe 60 in front of the catalyst 70 and the time course of the lambda actual value 140 with the probe jump 141 the exhaust gas probe 80 behind the catalyst 70 for an OSC value that is still within the allowable range and an actual lambda value 150 with the probe jump 151 for an OSC value that is out of range. The allowable range is as in 2a already shown, through the lambda model course (GRENZKAT) 160 for the exhaust gas probe 80 shown for a borderline in terms of oxygen storage capacity catalyst 70 Is accepted.

Starting from a lambda value of typically λ = 0.96 will be in one jump 121 the lambda value is initially piloted to λ> 1, in the example shown to λ = 1.02. Subsequently, the modeled lambda pilot control passes through 120 a range with a steady increase in lambda value. In the process variant shown, the lambda value increases linearly in the form of a ramp 122 up to a limit 124 at. In the example shown this is λ = 1.06. The ramp 122 is favorably to be chosen so that it occupies a not too large lambda value in a GRENZKAT. The limitation is preferred 124 the lambda value of the modeled lambda pilot control 120 at the time of the probe jump 161 Lambda model history (GRENZKAT) 160 initiated. Due to the usual tolerances of the air and fuel components, such as pressure regulators and engine parts, there is a real lambda pilot control 123 derived from the modeled lambda feedforward 120 may differ. With a linearization of the relationship between oxygen content and the lambda value, an OSC determination is possible as before.

The control device 100 in 1 according to the invention has a model formation stage with respect to the model lambda precontrol 120 on, with a lambda value can be predetermined in such a way that it has the features described above in its time course. These are in particular, starting from a minimum lambda value, first the jump 121 to λ> 1, then passing through a region with a steady increase, preferably linearly in the form of a ramp 122 , as well as the limit 124 , According to the invention, it is provided that the function of the previously described modeled lambda precontrol 120 in the control unit 100 is integrated. Preferably, this function is executed as software and / or hardware and is at least partially part of a higher-level engine control.

With the method and the corresponding device can be achieved that a higher accuracy the determination of the oxygen storage capacity of the emission control system with a simple structure allows becomes. This is particularly advantageous in terms of cost reduction for one On-board diagnostics.

Claims (14)

Method for monitoring an exhaust gas purification system of an internal combustion engine ( 1 ) with a in the exhaust gas purification system behind a catalyst ( 70 ), with a control device ( 100 ) connected exhaust gas probe ( 80 ) with jump characteristics, wherein for determining the oxygen storage capacity of the catalyst ( 70 ) by means of a modeled lambda precontrol ( 120 ) between a rich (λ <1) and a lean (λ> 1) fuel-air mixture, characterized in that the modeled lambda feedforward control ( 120 ) is predetermined such that a lambda value in its time course after a minimum lambda value passes through an area of continuous increase or after a maximum lambda value through an area of steady decrease. Method according to Claim 1, characterized in that, in the region of the steady increase in the time course of the modeled lambda precontrol ( 120 ) the lambda value increases linearly in the form of a ramp ( 122 ) is piloted. A method according to claim 1, characterized in that in the region of the steady decrease in the time course of the modeled lambda precontrol ( 120 ) the lambda value decreases linearly in the form of a ramp ( 122 ) is piloted Method according to one of claims 1 or 2, characterized in that in the time course of the modeled lambda pilot control ( 120 ) after the minimum lambda value and before the range of the steady increase of the lambda value first in the form of a jump ( 121 ) is piloted. Method according to claim 4, characterized in that the jump ( 121 ) of the modeled lambda pilot control ( 120 ) is precontrolled over a value λ> 1. Method according to one of claims 1 to 3, characterized in that in the time course of the modeled lambda pilot control ( 120 ) after the maximum lambda value and before the range of the steady decrease of the lambda value first in the form of a jump ( 121 ) is piloted. Method according to claim 6, characterized in that the jump ( 121 ) of the modeled Lambda pilot control ( 120 ) is precontrolled below a value λ <1. Method according to one of claims 1 to 7, characterized in that the range of the continuous increase or decrease of the lambda value of the modeled lambda pilot control ( 120 ) is limited. Method according to one of claims 1 to 8, characterized in that a limitation ( 124 ) of the lambda value of the modeled lambda precontrol ( 120 ) at the time of a probe jump ( 161 ) of a lambda model course (GRENZKAT) ( 160 ) is initiated. Method according to one of claims 1 to 9, characterized in that the diagnosis is aborted when during the lambda feedforward control ( 120 ) a probe voltage of an exhaust gas probe ( 60 ) in front of the catalyst ( 70 ) is outside a defined voltage band for a predetermined time. Method according to claim 10, characterized in that that a limitation of the voltage band is predetermined in terms of time becomes. Device for monitoring an exhaust gas purification system of an internal combustion engine ( 1 ) with a in the exhaust gas purification system behind a catalyst ( 70 ), with a control device ( 100 ) connected exhaust gas probe ( 80 ) with jump characteristics, wherein for determining the oxygen storage capacity of the catalyst ( 70 ) by means of a modeled lambda precontrol ( 120 ) a rich (λ <1) and a lean (λ> 1) fuel-air mixture is alternately adjustable, characterized in that the control device ( 100 ) a model formation stage with respect to the modeled lambda precontrol ( 120 ), with which a lambda value can be predetermined in such a way that it traverses a region of continuous increase in its time course after a minimum lambda value or a region of continuous decrease after a maximum lambda value. Apparatus according to claim 12, characterized in that the control device ( 100 ) with a display / memory unit ( 110 ) connected is. Device according to one of claims 12 or 13, characterized in that the function of the control unit ( 100 ) is executed as software and / or hardware and is at least partially part of a higher-level engine control.