DE102010028371A1 - Method for controlling exhaust emission of spark ignited Otto engine, involves obtaining modified lambda nominal value by nominal lambda reference value such that dynamic correction terms are added to nominal lambda reference value - Google Patents

Abstract

The method involves measuring a lambda value at downstream after treatment of an exhaust gas device (120) i.e. nitrogen oxide storage catalyst. A feedback control is performed based on a measured lambda value and a modified lambda reference value. The modified lambda nominal value is obtained by a nominal lambda reference value such that dependent dynamic correction terms are added to the nominal lambda reference value by the operating mode of the exhaust gas after treatment device. The nominal lambda reference value is used below stoichiometric value. An independent claim is also included for a device for controlling exhaust emission of a combustion engine.

Description

The present invention relates to a method and a device for controlling the exhaust emission of an internal combustion engine.

The regulation of the lambda value in the exhaust gas of an internal combustion engine is on the one hand in the context of the general regulation of exhaust emissions, eg. B. by way of limiting the production of soot during operation under high load required. On the other hand, the regulation of the lambda value in the exhaust gas also serves to maintain the required performance of an exhaust aftertreatment device, such as when operating a three-way catalyst in conjunction with a gasoline engine with spark ignition, in the regulation of the operation of a NO _x storage catalytic converter (LNT = "Lean NO _x trap") with rich air-fuel mixture or thermal protection of an exhaust aftertreatment device during soot combustion in a diesel particulate filter by reducing the oxygen content in the exhaust to suppress the exothermic reaction.

The regulation of the lambda value may be effected by performing a "feedforward" pre-calibration of a specific combustion mode for the settings of the air-fuel path to obtain the desired lambda value. Here, a feedback control (= "feedback control") using the measured lambda value in the exhaust gas for further correction can be performed. The control can take place by influencing the fuel path to deviations of the lambda value either during transient operating phases (taking into account the air path deviation due to the relatively low response speed of the air path compared to the fuel path) or due to production-related fluctuations in the injection system (compared to the nominal Injection class) or drift of the injection system due to wear or clogging of the injectors. The lambda value in the exhaust gas is controlled essentially by adjusting the fuel path to ensure a fast response to deviations in the air path during transient operating phases. However, larger deviations of the lambda value can also be compensated by adjusting the Ansaufluftmassenstroms.

In conventional approaches, it is necessary to have a lambda sensor upstream of the NO _x storage catalyst to ensure rapid response and to operate in the integrator term in a classical governor structure, particularly at the transition from lean air-fuel ratio operation to rich air mode operation. Fuel mixture, a so-called "wind-up effect" to avoid, which can result from large deviations between the lambda setpoint and the measured lambda value. In the "wind-up effect", the I-controller assumes a value above the possibilities of the actuator and causes unwanted delays on the return. In addition, a measurement of the lambda value in the exhaust gas when exiting the internal combustion engine is carried out in order to realize a feedback control ("feedback control"). Typically, a second signal for the lambda value, which is determined downstream of the exhaust aftertreatment component, as a measure of the robustness of the control and to minimize the breakdown of reductants z. B. in the required for purifying the NO _x storage catalytic converter operation with a rich air-fuel mixture.

From the US Pat. No. 7,225,612 B2 For example, there are known a method and apparatus for converting NO _x to a NO _x storage catalyst in which NO _{x is} adsorbed from the exhaust gas at a temperature below a predetermined temperature value to a predetermined absorbance value, the NO _x storage catalyst being at the predetermined level Temperature value is heated and then carried out with the addition of a reducing agent, a regeneration process.

From the US Pat. No. 7,628,063 B2 a method for "on-board" diagnostics of a NO _x storage catalytic converter for a diesel engine is known in which a first lambda sensor upstream of the NO _x storage catalytic converter and a second lambda sensor downstream of the NO _x storage catalytic converter are used, wherein a existing difference between the output signals of these lambda sensors during the regeneration of the NO _x storage catalytic converter is correlated with an operability of the NO _x storage catalytic converter, whereas a non-existent difference in the output signals of the lambda sensors is corrected with an inoperability of the NO _x storage catalytic converter ,

From the US Pat. No. 6,823,843 B1 For example, there is known an apparatus and method for minimizing the amount of NO _x released from an NO _x storage catalyst, wherein a NO _x storage limit is determined based on the temperature and oxygen storage capacity of an NO _x storage catalyst and engine operation in lean air Fuel mixture is terminated when the stored NO _x amount reaches the limit.

From the US 2006/0075740 A1 a spark ignition internal combustion engine and a three-way catalyst with a NO _x storage component is known in which a remaining NO _x storage capacity of the three-way catalyst is determined and wherein a control unit to is programmed to return to a stoichiometric air-fuel ratio when the NO _x storage capacity falls below a predetermined value.

From the DE 44 02 850 A1 A system for monitoring and controlling the exhaust emissions of an internal combustion engine is known, wherein a first NO _x sensor upstream of the NO _x storage catalytic converter and a second NO _x sensor downstream of the NO _x storage catalytic converter are arranged. On the basis of the output signals supplied by these NO _x sensors, an efficiency of the NO _x storage catalytic converter is determined, which in turn is compared with a predetermined threshold, wherein in the event that the efficiency thus determined exceeds the threshold, an output signal is displayed.

It is an object of the present invention to provide a method and a device for controlling the exhaust emission of an internal combustion engine, which allow effective control of the lambda value with comparatively little effort.

This object is achieved by the method according to the features of independent patent claim 1 and the device according to the features of patent claim 7.

• – Messen des Lambda-Wertes stromabwärts der Abgasnachbehandlungsvorrichtung; und
• – Durchführen einer Rückführungsregelung auf Basis dieses gemessenen Lambda-Wertes und eines modifizierten Lambda-Sollwertes, wobei dieser modifizierte Lambda-Sollwert dadurch erhalten wird, dass zu einem nominellen Lambda-Sollwert ein vom Betriebszustand der Abgasnachbehandlungsvorrichtung abhängiger dynamischer Korrekturterm addiert wird.

A method for regulating the exhaust emission of an internal combustion engine, wherein an exhaust gas aftertreatment device is arranged in the exhaust system of the internal combustion engine, comprises the following steps:

• - measuring the lambda value downstream of the exhaust aftertreatment device; and
• Performing a feedback control on the basis of this measured lambda value and a modified lambda desired value, wherein this modified lambda desired value is obtained by adding to a nominal lambda nominal value a dynamic correction term dependent on the operating state of the exhaust gas averaging device.

By the present invention, a feedback control is realized, which requires only a measurement of the lambda value downstream of an exhaust aftertreatment device. In this case, the invention includes a displacement of the position for determining or setting the desired lambda value from an arrangement upstream of the exhaust gas aftertreatment device to an arrangement downstream of the exhaust gas aftertreatment device.

The exhaust aftertreatment device is preferably a NO _x storage catalyst.

In particular, the invention is based on the concept of using a modified nominal value which is obtained by adding a dynamic additive correction term to a nominal (constant) lambda nominal value, the additive correction term depending on the operating state of the exhaust gas after-treatment device. In this case, the additive correction term can correlate with a value Δλ, which corresponds to the difference between the lambda value adapted for storage / release / consumption of oxygen and reductants in the NO _x storage catalytic converter and the lambda value upstream of the exhaust gas aftertreatment device.

According to a preferred embodiment, an adjustment of the lambda value is made somewhat below the stoichiometric value (ie smaller than one) in order, on the one hand, to ensure a sufficient amount of reductants upstream of the exhaust aftertreatment device for its purification and for conversion of the NO _x stored in the exhaust aftertreatment device, and, secondly, to minimize the extent of reductant breakdown.

In particular, a value of 0.99 ± 0.02, more particularly 0.99 ± 0.01, can be used as the nominal lambda nominal value.

In a preferred embodiment, the dynamic correction term has a positive value in the case of oxygen release and a negative value in the case of reductant release by the exhaust aftertreatment device. When switching from a lean air-fuel mixture operation to a rich air-fuel mixture operation, the oxygen stored in the NO _x storage catalyst is released. In this case, the corrected lambda setpoint is higher than the nominal lambda setpoint until all stored oxygen in the NO _x storage catalyst has been consumed. This is in the inventive use of the downstream of the NO _x storage arranged lambda sensor in the feedback control of a significant advantage in that it is avoided in this way that the term used in a controller structure when switching from lean to rich operation a "Wind- up effect "shows.

The invention further relates to a device for controlling the exhaust emission of an internal combustion engine. For advantages and preferred embodiments of the device, reference is made to the above statements in connection with the method.

Further embodiments of the invention are described in the description and the dependent claims.

The invention will be explained in more detail below with reference to a preferred embodiment and with reference to the accompanying drawings.

Show it:

1 a schematic representation of a portion in the exhaust system of an internal combustion engine, in which a method according to the present invention can be realized;

2 a diagram for explaining the behavior of a conventional control using a lambda sensor arranged upstream of the NO _x storage catalytic converter; and

3 a diagram for explaining the behavior of a lambda value according to the invention arranged downstream of the NO _x storage catalytic converter and with dynamic correction of the nominal lambda nominal value.

According to 1 is in the exhaust system of an internal combustion engine 110 an exhaust aftertreatment device 120 in the form of a NO _x storage catalytic converter 120 arranged. Downstream of this NO _x storage catalytic converter 120 there is a lambda sensor 130 by means of which the lambda value downstream of the NO _x storage catalytic converter 120 is determinable.

2 shows a diagram for explaining the behavior of a conventional control, and 3 shows a diagram for explaining the behavior of a control according to the invention with dynamic adjustment of the lambda setpoint.

The meaning of the curves " 1 "-" 6 " in the 2 and 3 is each as follows: Curve " 1 ": CO emissions (in units of ppm) upstream of the NO _x storage catalyst. Curve " 2 ": HC emissions (in units of ppm) upstream of the NO _x storage catalyst. Curve " 3 ": Lambda sensor value (dimensionless) upstream of the NO _x storage catalytic converter. Curve " 4 ": Lambda sensor value (dimensionless) downstream of the NO _x storage catalytic converter. Curve " 5 ": Lambda setpoint (dimensionless) after adjustment. Curve " 6 ": Fuel correction value (in units of mg per cylinder) for closed control.

According to 2 Conventional control is carried out using a lambda sensor for feedback control arranged upstream of the NO _x storage catalytic converter and setting the lambda setpoint value to a value of 0.96, without a dynamic correction taking place.

According to 3 there is a feedback control according to the invention using a modified lambda setpoint value, wherein this modified lambda desired value is obtained by the fact that at a nominal or constant Lambda setpoint from the operating state of the exhaust aftertreatment device 120 from 1 dependent dynamic correction term is added, wherein the nominal lambda target value can be set, for example, to a value of 0.99. In this case, the region in which the dynamic adjustment of the desired lambda value according to the invention takes place is marked with "A".

The additive correction term used in the adaptation of the desired lambda value depends on the operating state of the exhaust gas aftertreatment device and can in particular correlate with a value Δλ corresponding to the difference between the lambda adapted for storage / release / consumption of oxygen and reductants in the NO _x storage catalytic converter. Value and the lambda value upstream of the exhaust aftertreatment device corresponds. Here, the dynamic correction term during a phase of the oxygen release by the exhaust aftertreatment device 120 a positive value, whereas during a phase of reductant release by the exhaust aftertreatment device 120 has a negative value.

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

• US 7225612 B2 [0005]
• US 7628063 B2 [0006]
• US 6823843 B1 [0007]
• US 2006/0075740 A1 [0008]
• DE 4402850 A1 [0009]

Claims (7)

Method for regulating the exhaust emission of an internal combustion engine, wherein an exhaust gas aftertreatment device is arranged in the exhaust system of the internal combustion engine, characterized in that the method comprises the following steps: measuring the lambda value downstream of the exhaust aftertreatment device ( 120 ), and carrying out a feedback control on the basis of this measured lambda value and a modified desired lambda value, wherein this modified lambda desired value is obtained by determining a nominal lambda nominal value from the operating state of the exhaust gas after-treatment device ( 120 ) dependent dynamic correction term is added. A method according to claim 1, characterized in that a value below the stoichiometric value is used as the nominal lambda desired value. A method according to claim 2, characterized in that a value of 0.99 ± 0.02, in particular 0.99 ± 0.01, is used as the nominal lambda desired value. Method according to one of claims 1 to 3, characterized in that the dynamic correction term during a phase of the oxygen release by the exhaust aftertreatment device ( 120 ) has a positive value. Method according to one of claims 1 to 4, characterized in that the dynamic correction term during a phase of Reduktandenfreisetzung by the exhaust aftertreatment device ( 120 ) has a negative value. Method according to one of the preceding claims, characterized in that the exhaust aftertreatment device ( 120 ) is an NO _x storage catalyst. Device for controlling the exhaust emission of an internal combustion engine, characterized in that the device is designed to carry out a method according to one of the preceding claims.

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