DE102016219689A1 - Method and control device for controlling an oxygen loading of a three-way catalytic converter - Google Patents

Abstract

The invention relates to a method for controlling an oxygen loading of a three-way catalytic converter in an exhaust gas duct of an internal combustion engine leading exhaust gas, wherein an oxygen content of the exhaust gas is determined in front of the three-way catalyst with a first jump lambda probe, wherein tolerance and aging effects, resulting in a shift an actual probe characteristic versus a reference probe characteristic, taken into account and corrected and wherein the oxygen loading of the three-way catalyst is modeled. The invention further relates to a control device for carrying out the method. According to the invention, it is provided that an oxygen input into the three-way catalytic converter and / or an oxygen discharge from the three-way catalytic converter are determined from the corrected output signal of the first jump lambda probe and that the oxygen charge of the three-way catalytic converter is modeled therefrom , By modeling the loading of the three-way catalyst whose level can be controlled so that it can be operated in the range of its optimal conversion capability even with dynamically occurring lean or rich phases due to its oxygen storage capacity.

Description

State of the art

The invention relates to a method for controlling an oxygen loading of a three-way catalytic converter in an exhaust gas duct of an internal combustion engine leading exhaust gas, wherein an oxygen content of the exhaust gas before the three-way catalytic converter with a first jump lambda probe is determined, with tolerance and aging effects that cause a shift of an actual probe characteristic with respect to a reference probe characteristic, taken into account and corrected, and wherein the oxygen loading of the three-way catalyst is modeled.

The invention further relates to a control device for controlling an oxygen loading of a three-way catalytic converter in an exhaust gas channel leading an internal combustion engine, wherein for determining an oxygen content of the exhaust gas in front of the three-way catalyst, a first jump lambda probe is provided, wherein a voltage offset in an output signal of the first A jump lambda probe is detected and corrected, wherein a shift of the lambda = 1 - point and a temperature-related shift of the probe characteristic are taken into account cross-sensitivities of the first jump lambda probe to exhaust gas components and wherein in the controller, a model for modeling a three-way oxygen loading Catalyst is provided.

In incomplete combustion of an air-fuel mixture in an internal combustion engine, in addition to nitrogen (N ₂ ), carbon dioxide (CO ₂ ) and water (H ₂ O), a variety of products of combustion are emitted, of which hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) are legally limited. The current exhaust emission limits for motor vehicles can be met according to the current state of the art only with a catalytic exhaust aftertreatment. By using a three-way catalyst in an exhaust passage of the internal combustion engine, said pollutant components can be converted to nitrogen, carbon dioxide and water.

A simultaneously high conversion rate for HC, CO and NO _x is achieved in three-way catalysts only in a narrow lambda range around the stoichiometric operating point (lambda = 1), the so-called catalyst window. Only here is there a balance between the oxygen demand for the oxidation of HC and CO and the supply of oxygen through the reduction of NO _x . For operating the catalyst in the catalyst window, current lambda control systems typically employ lambda control based on the signals from lambda probes in front of and behind the three-way catalyst. For the regulation of the lambda upstream of the catalytic converter, the oxygen content of the exhaust gas upstream of the catalytic converter is measured with the lambda probe. Depending on this measured value, the control adjusts the fuel quantity from the pilot control. For a more precise control, the exhaust gas behind the catalytic converter is additionally analyzed with another lambda probe. This signal is used for a master control, which is superimposed on the lambda control in front of the catalytic converter. As a lambda probe behind the catalyst, a jump lambda probe is generally used, which has a very steep characteristic at lambda = 1 and therefore lambda = 1 can display very accurately.

Current control concepts have the disadvantage that they detect a late exit of the catalyst window based on the signal of the jump lambda probe behind the catalyst. An alternative to controlling the three-way catalyst based on the signal of the lambda probe behind the catalyst is a control of the oxygen level of the catalyst. In currently used catalysts, ceria is located on the porous carrier material of the catalyst, which can be present in different oxidation states, depending on the presence of oxygen. While it comes in the lean operation of the engine to oxidize the oxygen storage material, this is reduced again in rich operation. Thus, an oxygen excess or a lack of oxygen in the exhaust gas mixture can be compensated in whole or in part depending on the oxygen storage capacity and current oxygen loading of the catalyst, which leads to a significantly increased conversion performance of the catalyst in non-stoichiometric exhaust gas compositions. A regulation of the oxygen loading of the three-way catalyst therefore leads to an increased cleaning performance.

Since the oxygen load or oxygen level of the three-way catalyst can not be measured, these quantities are modeled. For the modeling of the filling level, a measurement of the exhaust gas lambda in front of the catalytic converter in a wide range around lambda = 1 is necessary. Therefore, a broadband lambda probe is usually used in front of the catalytic converter.

From the Scriptures DE102013 017260 B3 is a method for operating a drive device ( 1 ) with an internal combustion engine and a catalytic converter ( 3 ) for cleaning exhaust gas of the internal combustion engine, wherein upstream of the catalyst ( 3 ), a first lambda signal providing the first lambda probe ( 5 ) and downstream of the catalyst ( 3 ), a second lambda signal providing second lambda probe ( 6 ) intended is, and wherein on the basis of the first lambda signal, a Lambda control and on the basis of the second lambda signal one of the lambda guidance control superimposed Lambda trim control is performed. It is provided that for the lambda trim control a controller ( 7 ) and a catalyst ( 3 ) modeling observer ( 8th ), whereby the controller ( 7 ) a setpoint as well as by means of the observer ( 8th ) model error as input variables and the observer ( 8th ) one by means of the controller ( 7 ) determined manipulated variable are supplied as an input variable. The invention further relates to a drive device ( 1 ).

The font DE102006 061684 A1 discloses a method for controlling an oxygen level of an exhaust gas purification system of an internal combustion engine, wherein measured in the flow direction of the exhaust gas before the exhaust gas purification system, the exhaust gas compositions with a first exhaust gas probe and behind the exhaust gas purification system with a second exhaust gas probe, wherein an oxygen entry into the Emission control system is determined and summed or integrated into an amount of oxygen and wherein the exhaust gas composition is modulated before the emission control system between predetermined limits. According to the invention it is provided that the modulation of the exhaust gas composition before the exhaust gas purification plant ( 16 ) is performed so that a lean adjustment of the exhaust gas composition is terminated when the oxygen amount reaches a predetermined upper limit value and a rich adjustment is terminated when the oxygen amount reaches a predetermined lower limit value.

The font DE010339063 A1 describes a method for mixture control in an internal combustion engine with an arranged in an exhaust system of the internal combustion engine oxygen storage capability catalyst and an oxygen sensor disposed downstream of the catalytic converter, wherein a model of the oxygen storage capability is provided, which depending on input lambda values and catalyst parameter values a value calculated an oxygen loading of the catalyst. It is provided that a mixture change is initiated as a function of the calculated value of the oxygen loading and of a fat or lean breakthrough on the catalyst determined by means of the oxygen sensor. In the DE010339063 A1 is a modeling of the oxygen level of the catalyst provided, but not the use of a corrected output of a jump lambda probe before the catalyst.

The font DE102014 211941 A1 describes a method for the evaluation of the lambda sensor ( 18 ) lambda signal (lam_2) provided with an arcuate characteristic which downstream of one in the exhaust gas channel ( 12 ) an internal combustion engine ( 10 ) arranged catalyst ( 14 ) is arranged. According to the invention, it is provided that the lambda signal (lamb_2) is differentiated, that the absolute value of the differentiated signal ( 36 ) is formed, that the magnitude signal ( 40 ) of the differentiated signal ( 36 ) is integrated over a period of time such that the integration result ( 44 ) is compared with an integration threshold (I_SW) and that at a threshold exceeding the fuel fraction of the internal combustion engine ( 10 ) is added increased air-fuel mixture. In Scripture DE102014 211941 A1 is the jump probe whose signal is evaluated improved arranged after the catalyst.

From the Scriptures DE10 2012 211 687 A1 is a method for detecting a voltage offset at least in a range of a voltage lambda characteristic of a arranged in an exhaust passage of an internal combustion engine jump lambda compared to a reference voltage lambda characteristic of the jump lambda probe known, the jump lambda probe part of a controlled system for adjusting an air / fuel mixture supplied to the internal combustion engine, wherein a characteristic deviation of the voltage lambda characteristic is corrected to the reference voltage lambda characteristic at lambda = 1, wherein, starting from a value pair to be checked on the reference voltage Lambda characteristic with a lambda to be checked and a voltage to be tested, a change in the composition of the internal combustion engine supplied air / fuel mixture to lambda = 1 is carried out and wherein from the change in the composition of the air / fuel mixture until reaching lambda = 1 to the actual value closed by Lambda. According to the invention, a delay time of the controlled system is determined in a first method step, that in a second method step, starting from the value pair to be checked, the composition of the air / fuel mixture changes to lambda = 1, that the change in composition is corrected with the delay time of the controlled system that the actual value of lambda in the pair of values from the corrected change in the composition of the air / fuel mixture is determined and that from a deviation of the actual value of lambda from the value of lambda to be checked, a voltage offset of Voltage lambda characteristic is detected.

The font DE 10 2014 210442A1 describes a method for correcting a voltage-lambda characteristic ( 36 ) one in an exhaust passage ( 17 ) an internal combustion engine arranged jump lambda probe ( 15 . 18 ) in case of deviation from one Reference voltage lambda characteristic ( 35 ) by adaptation. According to the invention, the adaptation is performed when the internal combustion engine is not operated, wherein a temperature-dependent nominal value of the leaky lambda probe ( 15 . 18 ) is checked under supply of heating power.

It is an object of the invention to provide a method which allows a model-based control of an oxygen level of a three-way catalyst with an output signal of a low-cost jump lambda probe before the three-way catalyst.

It is a further object of the invention to provide a control device suitable for carrying out the method.

Disclosure of the invention

• – Adaption eines konstanten Offsets der Sondenkennlinie
• – Kompensation einer Verschiebung des Lambda = 1 – Punktes der Sondenkennlinie
• – Kompensation einer temperaturbedingten Verschiebung der Sondenkennlinie
• – Berücksichtigung der aktuellen Abgaszusammensetzung und von unterschiedlichen Querempfindlichkeiten der Abgassonde gegenüber verschiedenen Abgaskomponenten

The object of the invention relating to the method is achieved by determining from the corrected output signal of the first jump lambda probe an oxygen input into the three-way catalytic converter and / or an oxygen discharge from the three-way catalytic converter and from this the oxygen sensor. Loading the three-way catalyst is modeled. The correction of the output signal of the first jump lambda probe with regard to tolerance and aging effects, which lead to a shift of an actual probe characteristic relative to a reference probe characteristic of an unaged jump lambda probe with a voltage lambda characteristic according to the data sheet, results in a wide lambda range Relationship between the probe signal and the lambda value of the exhaust gas. Therefore, a low-cost, leaky lambda probe can be used to account for oxygen input and output to / from the three-way catalyst, and the oxygen load or oxygen level of the three-way catalyst can be modeled from these values. In particular, it is not necessary to use the output signal of a jump lambda probe arranged downstream of the three-way catalytic converter, which can only show a reaction when a lean or rich breakthrough has occurred and the conversion capability of the three-way catalytic converter is already greatly reduced. The correction of the tolerance and aging effects takes place by known methods individually or combined in the following steps:

• - Adaptation of a constant offset of the probe characteristic
• - Compensation of a shift of the lambda = 1 - point of the probe characteristic
• - Compensation of a temperature-related shift of the probe characteristic
• - Consideration of the current exhaust gas composition and of different cross sensitivities of the exhaust gas probe to different exhaust gas components

A suitable correction of the probe characteristic can be carried out by detecting and correcting a voltage offset in an output signal of the first jump lambda probe in order to correct for tolerance and aging effects, correcting a displacement of the lambda = 1 point and a temperature-dependent shift of the probe characteristic that cross-sensitivities of the first jump lambda probe to exhaust gas components are taken into account

A preferred embodiment of the method provides that the oxygen loading of the three-way catalyst is controlled so that a leaving a predeterminable loading window is avoided. The load window is selected so that, for rich or lean exhaust gas inputs, during dynamic changes in engine operating conditions due to the oxygen storage capability of the three-way catalyst, there is a buffer capable of absorbing oxygen under lean conditions and rich exhaust gas on the other hand Oxygen can give off, so that the exhaust gas purification in the three-way catalyst at lambda = 1 can take place. With the known from the model current oxygen level of the three-way catalytic converter, the exhaust gas composition can be readjusted early, so that always sufficient buffer is available.

In one embodiment of the method it is provided that the three-way catalyst is divided into two or more zones, for each of which the oxygen loading is modeled. As a result, filling and emptying processes can be modeled with greater accuracy. Advantageously, the levels of the individual zones are normalized to the current oxygen storage capacity of the respective zone. The fill levels of the individual zones are - if necessary after a weighting - converted into a medium level. With the weighting can be considered that for the current exhaust gas composition behind the three-way catalyst, the level in a relatively small area at the outlet of the catalyst is crucial. For the development of the level in this small area at the outlet of the catalyst, the level in the preceding volume and its development is decisive. This medium level is controlled to a setpoint that minimizes the likelihood of lean and rich breakthroughs, resulting in minimal emissions.

In a further embodiment of the method, it is provided that the Catalyst model of the three-way catalyst is calibrated using an output signal of a arranged after the three-way catalyst second jump lambda probe. The second jump lambda probe indicates when the three-way catalyst is completely filled with oxygen or completely exhausted. This is exploited to match the modeled oxygen level with the actual oxygen level after lean or rich phases and, if necessary, to adapt the catalyst model.

The object of the invention concerning the control device is achieved by providing in the control device a balance of an oxygen input into the three-way catalyst and / or an oxygen discharge from the three-way catalyst from the corrected output signal of the first jump lambda probe and from this the determination of the oxygen loading of the three-way catalyst is provided.

The invention will be explained in more detail below with reference to an embodiment shown in FIGS. Show it:

1 a schematic representation of the technical environment in which the method can be used,

2 a scheme of the control according to the invention.

1 schematically shows the technical environment in which the method according to the invention can be applied. An internal combustion engine 10 , which is designed as externally ignited gasoline engine, gets combustion air via an air supply 11 fed. In this case, the air mass of the combustion air by means of an air mass meter 12 in the air supply 11 be determined. The supplied air mass serves to determine the amount of fuel to be metered at a lambda value to be preselected. Furthermore, exhaust gas parameters, in particular an exhaust gas mass flow and, derived therefrom, an exhaust gas mass are determined with the aid of the air mass. The exhaust gas of the internal combustion engine 10 is via an exhaust duct 15 dissipated, in which a three-way catalyst 16 is arranged. Furthermore, in the exhaust duct 15 a first jump lambda probe 14 in front of the three-way catalyst 16 and a second jump lambda probe 17 after the three-way catalyst 16 arranged, the signals of a control device 20 be supplied. The control device 20 continues to be the signal of the mass air flow sensor 12 fed. On the basis of the thus determined air mass and the signals of the jump lambda probes 14 . 17 is in the controller 20 The fuel mass determined over a fuel dosage 13 the internal combustion engine 10 is supplied. The control device 20 includes a pilot control and a control device for controlling the composition of the air-fuel mixture based on the signals of the jump lambda probes 14 . 17 ,

2 shows a scheme of the control according to the invention. Already in 1 used identifiers are in 2 marked with equal numbers. The internal combustion engine 10 is over the exhaust duct 15 with the three-way catalyst 16 and then connected to the outside world. Between the internal combustion engine 10 is in the exhaust duct 15 the first jump lambda probe 14 arranged. After the three-way catalyst 16 is in the exhaust duct 15 the second jump lambda probe 17 arranged. The control of the internal combustion engine 10 is in a control device 20 summarized. In known lambda controls is in the control device 20 the output signal of the first jump lambda probe 14 in a signal processing 29 corrected for a constant offset of the probe characteristic. Furthermore, a shift of the lambda = 1 - point and a temperature-related shift of the probe characteristic are compensated. Finally, the current exhaust gas composition and cross sensitivities of the exhaust gas probe against different exhaust gas components are considered. The thus corrected signal becomes a lambda control 24 supplied, which controls the composition of the air-fuel mixture, that of the internal combustion engine 10 is supplied. In a management regulation 21 becomes the output signal of the second jump lambda probe 17 evaluated by the lambda control 24 be corrected so that on average the desired lambda value of lambda = 1 is maintained.

A level control according to the invention 30 within the control device 20 regulates the oxygen level of the three-way catalyst 16 , For this purpose, the output signal of the signal conditioning 29 after correction with the signal of the command control 21 in a differential step 28 an emission model 27 fed. In the emission model 27 The corrected probe signal is converted into a lambda value or one or more variables derived therefrom. Advantageously, the lambda value is converted into a concentration of one or more exhaust gas components. By way of example, the lambda value may be in values for the concentrations of oxygen and carbon monoxide before the three-way catalyst 16 be converted. Initial values of the emission model 27 or directly the corrected lambda value become a catalyst model 25 fed. In the catalyst model 25 becomes the level of the three-way catalyst 16 modeled. In particular, an accounting of the oxygen input and output is provided to model the oxygen level. It is beneficial to the To consider the reaction kinetics of the exhaust components calculated by the emission model during the modeling. Furthermore, it is advantageous to use the three-way catalyst 16 into several zones, in each of which the level is modeled. As a result, filling and emptying processes can be depicted more realistically. For the control of the catalyst level, it is advantageous to normalize the levels of the individual zones. The levels of the individual zones are - possibly after a weighting - in a middle level of the three-way catalyst 16 converted. With the weighting can be considered that for a momentary exhaust gas composition behind the three-way catalyst 16 the level in a relatively small area at the exit of the three-way catalyst 16 is crucial. The development of the level in this small area is influenced by the preceding catalyst volume and its evolution. The mean level of the three-way catalyst 16 is from the level control 30 regulated to such a setpoint that the likelihood of breakthroughs for lean and fat at the output of the three-way catalyst 16 is minimized. As a result, the emissions of the internal combustion engine 10 that reach the outside world minimizes.

If necessary, the catalyst model 25 with the help of the output signal after the three-way catalyst 16 arranged second jump lambda probe 17 about a calibration 26 be calibrated. The output signal of the second jump lambda probe 17 indicates when the three-way catalyst 16 completely filled with oxygen or completely emptied of oxygen. This can be used to match the modeled oxygen level with the actual oxygen level after a lean or rich phase and, if necessary, the catalyst model 25 to adapt. This allows the reliability of the catalyst model 25 be increased.

From the catalyst model 25 becomes the level of the three-way catalyst 16 to a level controller 22 passed through a summation level 23 together with the output signal of the command control 21 the setpoint for the lambda control 24 adapts ..

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013017260 B3 [0007]
• DE 102006061684 A1 [0008]
• DE 010339063 A1 [0009, 0009]
• DE 102014211941 A1 [0010, 0010]
• DE 102012211687 A1 [0011]
• DE 102014210442 A1 [0012]

Claims (6)

Method for controlling the oxygen loading of a three-way catalyst ( 16 ) in an exhaust gas leading exhaust channel ( 15 ) an internal combustion engine ( 10 ), wherein an oxygen content of the exhaust gas before the three-way catalyst ( 16 ) with a first jump lambda probe ( 14 ), whereby tolerance and aging effects, which lead to a shift of an actual probe characteristic with respect to a reference probe characteristic, are taken into account and corrected, and wherein the oxygen charge of the three-way catalyst ( 16 ) is modeled, characterized in that from the corrected output signal of the first jump lambda probe ( 14 ) an oxygen entry into the three-way catalyst ( 16 ) and / or an oxygen discharge from the three-way catalyst ( 16 ) and that from this the oxygen loading of the three-way catalyst ( 16 ) is modeled. A method according to claim 1, characterized in that for the correction of tolerance and aging effects, a voltage offset in an output signal of the first jump lambda probe ( 14 ) is detected and corrected, that a shift of the lambda = 1 - point and a temperature-related shift of the probe characteristic are corrected and that cross-sensitivities of the first jump lambda probe ( 14 ) are taken into account with respect to exhaust gas components A method according to claim 1 or 2, characterized in that the oxygen loading of the three-way catalyst ( 16 ) is regulated so that a leaving a predefinable loading window is avoided. Method according to one of claims 1 to 3, characterized in that the three-way catalyst ( 16 ) is divided into two or more zones, for each of which the oxygen loading is modeled. Method according to one of claims 1 to 4, characterized in that the catalyst model ( 25 ) of the three-way catalyst ( 16 ) with the aid of an output signal after the three-way catalyst ( 16 ) arranged second jump lambda probe ( 17 ) is calibrated. Control device ( 20 ) for controlling an oxygen loading of a three-way catalyst ( 16 ) in an exhaust gas leading exhaust channel ( 15 ) an internal combustion engine ( 10 ), wherein for determining an oxygen content of the exhaust gas before the three-way catalyst ( 16 ) a first jump lambda probe ( 14 wherein tolerance and aging effects which lead to a displacement of an actual probe characteristic with respect to a reference probe characteristic are considered and corrected, and wherein in the control device a model for modeling an oxygen charge of the three-way catalyst ( 16 ), characterized in that in the control device balancing of an oxygen entry in the three-way catalyst ( 16 ) and / or an oxygen discharge from the three-way catalyst ( 16 ) from the corrected output signal of the first jump lambda probe ( 14 ) and that the determination of the oxygen loading of the three-way catalyst ( 16 ) is provided.

Images