DE102008054866A1 - Exhaust gas after-treatment device e.g. nitrogen oxide catcher, operation controlling method for internal combustion engine, involves comparing concentration reference value and temperature reference value with calibration threshold value - Google Patents

Abstract

The method involves determining a concentration reference value of oxygen concentration in an upstream part of an exhaust gas after-treatment device corresponding to highest temperature. A temperature reference value of exhaust temperature of the exhaust gas after-treatment device is determined corresponding to highest temperature based on a thermal mode of the exhaust gas after-treatment device. The concentration reference value and the temperature reference value are compared with a calibration threshold value under multiple situations to trigger protection mode. An independent claim is also included for a device for controlling operation of an exhaust gas after-treatment device of an internal combustion engine.

Description

The The invention relates to a method and a device for controlling the operation of an exhaust aftertreatment device.

exhaust aftertreatment devices be used to treat from burning fuel with Air resulting exhaust gas streams either inside the cylinder or externally in the exhaust stream. It can it intentionally or unintentionally in repeated and particular periodically increased be exposed to thermal level. This is done, for example in the regeneration of a diesel particulate filter (DPF) or a Operating phase of a for the lean operation designed nitrogen oxide trap with a rich air / fuel mixture.

such Exhaust aftertreatment devices have an upper temperature limit, not exceeded so that the filter integrity of the filter substrate and thus Ensures the efficiency of the exhaust aftertreatment device stay. To ensure that this upper temperature limit is not exceeded it is known, in the pre-calibration of the different Combustion modes to use a tolerance limit and a feedback control To make the system robust against manufacturing tolerances, aging processes and associated drifts as well as undiagnosed malfunctions. In this way it should be ensured that in case of a unforeseen or undesirable Increase of the heat level and an approach appropriate measures can be taken to the upper temperature limit. Such activities can For example, switching to another pre-calibration (eg. B. another combustion mode) or switching to a other feedback control with higher Bandwidth, z. B. switching from a temperature control a lambda control.

conventional Method for activating a thermal protection mode in an exhaust aftertreatment device are based either on measured or estimated Values of the temperature of the filter substrate. Here, however, occur Problems with, in particular, with the transport delay in the System at low mass flow rates and with the time delay of Temperature measurement at high mass flow rates are connected. The Temperature measurement to detect dangerous thermal levels typically runs slowly. The triggering time for the Switching of the combustion mode is however of great importance because, for example, a delay only a few seconds to irreversible damage to the exhaust aftertreatment component to lead can, for example, a thermally uncontrolled combustion from soot in a particle filter for the case of over-loading of the soot particle filter or a transition in the idle.

In front In the above background, it is an object of the present invention to a method and apparatus for controlling the operation of a To provide exhaust aftertreatment device, by means of which the Danger of thermal damage reduced or minimized in the exhaust aftertreatment device can be.

These The object is achieved by the method according to the features of the independent claim 1 or the device according to the features of the independent Claim 6 solved.

• – Ermitteln eines Konzentrationssollwertes für eine stromaufwärts der Abgasnachbehandlungsvorrichtung vorliegende Sauerstoffkonzentration und eines Temperatursollwertes für eine stromaufwärts der Abgasnachbehandlungsvorrichtung vorliegende Temperatur;
• – Vergleichen des Konzentrationssollwertes und des Temperatursollwertes mit jeweils einem kalibrierbaren Schwellenwert; und
• – Aktivieren oder Deaktivieren eines Wärmeschutzmodus im Betrieb der Abgasnachbehandlungsvorrichtung auf Basis dieses Vergleiches.

A method of controlling the operation of an exhaust aftertreatment device for after-treatment of exhaust gases of an internal combustion engine comprises the following steps:

• Determining a concentration target value for an oxygen concentration present upstream of the exhaust gas aftertreatment device and a temperature target value for a temperature present upstream of the exhaust gas aftertreatment device;
• - comparing the concentration setpoint and the temperature setpoint, each with a calibratable threshold value; and
• Activating or deactivating a thermal protection mode during operation of the exhaust aftertreatment device based on this comparison.

The inventive method provides a predictive algorithm by means of which a heat protection mode of the exhaust gas aftertreatment device is triggered or terminated. The invention is based on the concept for a maximum substrate temperature, ie an upper temperature limit not to be exceeded by the substrate, by means of the inversion of the thermal model for the exhaust aftertreatment device, a concentration target value for the oxygen concentration and a temperature setpoint for the inlet temperature as a function of the present combustion heat release and to determine the upstream measured temperature. The calculated setpoints are then each compared to a previously calibrated threshold and, preferably after expiration of an acknowledgment period, used to either enable or disable a request for a thermal protection mode of the exhaust after-treatment device depending on the result of the comparison.

Further Embodiments of the invention are the description and the dependent claims to remove.

The Invention will be described below with reference to a preferred embodiment with reference to the attached Illustrations explained.

It demonstrate:

1 a block diagram for explaining the strategy of the method according to the invention;

2 a block diagram for explaining the determination according to the invention of the concentration target value for the oxygen concentration;

3 a block diagram for explaining the determination of the temperature setpoint according to the invention;

4 a graph showing the concentration set point for the oxygen concentration for the heat protection mode at different temperature setpoints for a transition to the idle at a soot loading of 10.6 g / l;

5 a diagram for explaining a request for a heat protection mode at different temperature setpoints for a transition to the idle at a soot loading of 10.6 g / l; and

6 Charts to explain a request for a heat protection mode for a transition to idle at different initial soot loadings.

In 1 FIG. 2 shows a block diagram of the strategy according to the invention, wherein the functionality of function blocks used in this strategy is described below 110 to 150 is explained. A compilation of in 1 and the following formulas used signal designations for directly or indirectly measured signals is given in Table 1a, and other sizes used therein are given in Table 1b. Signals calculated from these signals and quantities as well as some other quantities are given in Table 2.

In a functional block 110 Based on the maximum filter temperature (= temperature of the filter substrate) PFlt_tMaxPFlt and other input variables PFlt_vVeh (= vehicle speed) and PFlt_tAmbMes (= measured ambient temperature), the heat loss to the environment is calculated based on the function block 110 as a starting size delivered heat loss in 1 with PFlt_wActAmbLoss_tPFltMax. Special is: PFlt_wActAmbLoss_tPFltMax = PFlt_tMaxPFlt - PFlt_tAmbMes) × PFlt_hCnvAmbPFlt_M × PFlt_arSurfPFlt_C · PFlt_rRateAmbLossPFlt_M

In a functional block 120 Based on the maximum filter temperature PFlt_tMaxPFlt used as input variable, the heat output (= heat release) is calculated taking into account the rate of change of the maximum filter temperature, which is calculated by the function block 120 delivered as output heat dissipation in 1 with PFlt_wAct_tRatePFltMax. Special is: PFlt_wAct_tRatePFltMax = d (PFlt_tMaxPFlt) / dt × PFlt_wSubstrateSpcHeatPFlt_C × PFlt_mSubstrateEfcPFlt_C × PFlt_rAdapt_tPFltEstim_M

In a functional block 130 Based on the maximum filter temperature PFlt_tMaxPFlt used as the input variable, and using the further input variables PFlt_tUsPFlt (= upstream temperature of the particulate filter) and PFlt_mfEg_ExtInj (= exhaust gas mass flow rate after external injection), the net enthalpy fed to the filter substrate is calculated 130 delivered outputs the net enthalpy for the maximum temperature in the filter substrate 1 With PFlt_wActNetInp_tPFltMax and the associated specific enthalpy heat are labeled PFlt_wSpecNetInp_tPFltMax. Special is: PFlt_wActNetInp_tPFltMax = PFlt_mfEg_ExtInj × PFlt_cEgSpcHeat_M × (PFlt_tMaxPFlt - PFlt_tUsPFlt) Table 1a: signal name unit description PFlt_tMaxPFlt ° C Maximum substrate temperature PFlt_vVeh km / h vehicle speed PFlt_tAmbMes ° C Measured ambient temperature PFlt_tUsPFlt ° C Temperature upstream of the substrate (not delayed in time) PFlt_mfEg_ExtInj kg / s Exhaust gas mass flow rate after external injection PFlt_concO2_UsPFlt % Measured oxygen concentration in the exhaust stream upstream of the particulate filter PFlt_wCmbPFltTot watt Total exothermic heat release in the substrate due to reductant and soot combustion Table 1b: size designation unit description PFlt_hCnvAmbPFlt_M W / m ² / K Convective heat transfer coefficient to the environment as a function of ambient temperature and vehicle speed PFlt_arSurfPFlt_C m ² Surface of the substrate PFlt_rRateAmbLossPFlt_M - Factor to account for model inaccuracies in estimating ambient heat losses as a function of exhaust mass flow PFlt_wSubstrateSpcHeatPFlt_C J / kg / K Specific heat of the substrate PFlt_mSubstrateEfcPFlt_C kg Mass of the substrate PFlt_rAdapt_tPFltEstim_M - Factor to account for model inaccuracies in estimating substrate temperature as a function of exhaust mass flow PFlt_cEgSpcHeat_M J / kg / K Specific heat of the exhaust gas at constant pressure as a function of the air / fuel ratio and the temperature of the exhaust gas

In a functional block 140 For example, a concentration target value for the oxygen concentration is calculated to prevent the filter temperature from exceeding the maximum substrate temperature. This concentration setpoint is in 1 and 2 also referred to as PFlt_concO2_UsPFltProtDes. In this calculation, in particular the means of the function block 110 calculated heat loss to the environment at maximum temperature of the particulate filter as input variables (= PFlt_wActAmbLoss_tPFltMax), which by means of the function block 120 Calculated heat output taking into account the rate of change of the maximum filter temperature (PFlt_wAct_tRatePFltMax) and the net enthalpy fed to the filter substrate (= PFlt_wActNetInp_tPFltMax). Furthermore, in this calculation, the total combustion heat release rate in the particulate filter (= PFlt_wCmbPFltTot) and the oxygen concentration in the exhaust gas flow upstream of the particulate filter (= PFlt_concO2_UsPFlt) are used as input variables. Special is: PFlt_concO2_UsPFltProtDes = (PFlt_wActAmbLoss_tPFltMax + PFlt_wAct_tRatePFltMax + PFlt_wActNetInp_tPFltMax) / (PFlt_wCmbPFltTot)) × PFlt_concO2_UsPFlt

The function block 140 is in 2 shown in more detail. Compilations of in 2 and characteristic terms used for the above formula are given in Table 2 and Table 3. In the in 2 (and later described 3 ), the operations indicated in the individual blocks by +, -, x, /, max, min are performed. It can be seen that the calculation is performed according to the above formula, with lower limit values (eg, sizes (4) and (5) in 2 set to at least 10 ^-12 ) and upper extreme cases. The block denoted by PT1 is a so-called PT1 element, a control circuit which acts as a low pass or averaging element, namely, an LZI transfer element in the control technique, which has a proportional first order lag response. The way of working and the in 2 and 3 Plotted connections of the PT1 element are known in the art. Table 2: signal name unit description PFlt_wActAmbLoss_tPFltMax watt Heat loss to environment at maximum temperature for particulate filter PFlt_wAct_tRatePFltMax watt Heat to the substrate at maximum temperature for particulate filters PFlt_wActNetInp_tPFltMax watt Enthalpy heat to substrate at maximum temperature for particulate filter PFlt_wSpecNetInp_tPFltMax Watts / K Specific enthalpy heat at substrate at maximum temperature for particulate filter PFlt_concO2_UsPFltProtDes % Setpoint for oxygen concentration upstream of the particulate filter for thermal protection mode PFlt_tUsPFltProtDes ° C Setpoint of the substrate temperature for thermal protection mode Table 3: parameter name value unit description PFlt_concO2_MaxUsPFltProtDes_C 5 % Maximum limit for setpoint of oxygen concentration in thermal protection mode PFlt_concO2_MinUsPFltProtDes_C 1 % Minimum limit for setpoint of oxygen concentration in thermal protection mode PFlt_tiFil_concO2_PFltProt_C 1 s Time constant for low pass filter applied to the set point of oxygen concentration in heat protection mode

In a functional block 150 For example, a temperature setpoint for the temperature upstream of the particulate filter is calculated to ensure that the maximum temperature of the particulate filter substrate is not exceeded. This temperature setpoint is in 1 and 3 also referred to as PFlt_tUsPFltProtDes.

In this calculation, in particular the means of the function block 110 Calculated heat release to the environment at maximum temperature of the particulate filter (= PFlt_wActAmbLoss_tPFltMax), which by means of the function block 120 Calculated heat output taking into account the rate of change of the maximum filter temperature (= PFlt_wAct_tRatePFltMax) and the specific enthalpy heat supplied to the filter substrate (= PFlt_wSpecNetInp_tPFltMax). Furthermore, in this calculation, the total combustion heat release rate in the particulate filter (= PFlt_wCmbPFltTot) and the maximum filter temperature (= PFlt_tMaxPFlt) are used as input variables.

The function block 150 is in 3 shown in more detail. In the 3 used further parameter designations and typical values are given in Table 4. Special is: PFlt_tUsPFltProtDes = PFlt_tMaxPFlt + (PFlt_wActAmbLoss_tPFltMax + PFlt_wAct_tRatePFltMax - PFlt_wCmbPFltTot) / PFlt_wSpecNetInp_tPFltMax Table 4: parameter name value unit description PFlt_tUsPFltDesMaxThd_C 700 ° C Maximum limit for set point of the temperature upstream of the filter PFlt_tUsPFltDesMinThd_C 500 ° C Minimum limit for setpoint of the temperature upstream of the filter PFlt_tiFil_tUsPFltDes_C 30 s Time constant for low pass filter applied to the set point of the temperature upstream of the filter

The calculated setpoints for the oxygen concentration (PFlt_concO2_UsPFltProtDes) and the substrate temperature (PFlt_tUsPFltProtDes) upstream of the particulate filter are those values that are necessary to keep the substrate temperature does not exceed the maximum threshold (PFlt_tMaxPFlt). The calculated setpoint for The oxygen concentration is then fixed with a calibratable Threshold of z. B. 1 to 2% compared, and if the calculated Setpoint for the oxygen concentration for a short time is smaller than the threshold, becomes the combustion mode switched to a mode in which the air and fuel path for low Oxygen content is pre-calibrated. Similarly, when the calculated Setpoint for the substrate temperature for a short time less than a calibratable fixed threshold is the combustion mode switched to a mode in which the air and fuel path for weaker Combustion is pre-calibrated.

The Criteria for the thresholds for the oxygen concentration are the minimum levels that come with a given combustion mode can be achieved, d. H. the air and fuel path is for a high temperature calibration as a target and an oxygen concentration of at least 3 to 5% pre-calibrated to good soot regeneration to ensure. Meanwhile, a protection mode for a low oxygen concentration (less than 1 to 2%) and for low temperature level calibrated to delete to ensure combustion in the substrate. Is therefore the value for PFlt_concO2_UsPFltProtDes less than 2%, the combustion mode switches to protection mode and when PFlt_concO2_UsPFltProtDes is greater than 3%, the high-temperature combustion mode becomes activated.

The implementation of the algorithm according to the invention is in 4 and 5 in the event that at a high soot loading of 10.6 g / l, a transition to idle takes place.

4 shows the course of the concentration set point for the oxygen concentration for the heat protection mode at different temperature setpoints.

The oxygen concentration set point falls below the nominal threshold of 3% when the substrate temperature approaches the temperature setpoint. As expected, the lower the temperature set point of the substrate compared to a maximum temperature of 900 ° C, so z. B. at a value of 750 ° C, a so earlier decrease in the concentration setpoint for the oxygen concentration instead. Also in 4 and 5 Shown are the maximum and minimum temperature values measured by field dependent temperature measurement at different positions of the filter substrate and the model estimated estimated temperature.

The predictive character of the algorithm according to the invention is out 6 clear. Shown is the time period between the time the thermal protection mode is triggered and the time when either the measured temperature or the model-aided estimated temperature reaches the maximum value. The algorithm is able to predict the temperature rise up to the maximum value within a time range of 5-20 s at the temperature values used.

To demonstrate the robustness of the algorithm of the invention, a transition to idle was performed for different soot loading conditions in the range of 6 g / l to 11 g / l. For a maximum substrate temperature of 900 ° C, see 6 calculates a concentration setpoint of the oxygen concentration upstream of the particulate filter by means of the algorithm according to the invention. The algorithm is in all cases able to trigger the thermal protection mode at least 20 s before reaching the maximum temperature of 900 ° C.

The above based on the function blocks 110 . 120 . 130 . 140 and 150 and the figures detailed in the figures consists in that based on a thermal model of the exhaust aftertreatment device one of the maximum temperature corresponding concentration setpoint for the oxygen concentration upstream of the exhaust aftertreatment device and a maximum temperature corresponding temperature setpoint for the exhaust gas temperature upstream of the exhaust aftertreatment device are determined. By comparing the concentration setpoint and the temperature setpoint after a minimum confirmation time with a calibrated, ie adjusted to the current operating condition of the engine threshold, as described above by way of examples, a temperature increase in the exhaust aftertreatment device to the maximum allowable value can be predicted very early, and according to the thermal protection mode triggered or canceled again.

Claims (8)

A method for controlling the operation of an exhaust aftertreatment device for the aftertreatment of exhaust gases of an internal combustion engine, wherein the exhaust aftertreatment device is associated with a maximum temperature, which must not be exceeded to avoid thermal damage in the operation of the exhaust treatment device, and wherein the exhaust aftertreatment device is converted into a protection mode depending on the operating state to avoid exceeding the maximum temperature, characterized in that the method comprises the steps of: a) determining, based on a thermal model of the exhaust aftertreatment device, a concentration set point corresponding to the maximum temperature (PFlt_concO2_UsPFltProtDes) for the oxygen concentration upstream of the exhaust aftertreatment device and one of the maximum temperature Temperature setpoint (PFlt_tUsPFltProtDes) for the exhaust gas temperature upstream of the Abgasnac hbehandlungsvorrichtung; b) comparing the concentration setpoint and the temperature setpoint, each with a calibratable threshold; and c) enable or disable the protection mode based on this comparison. Method according to claim 1, characterized in that that activating or deactivating the heat protection mode only after expiration a confirmation period he follows. Method according to claim 1 or 2, characterized determining the concentration setpoint and / or the temperature setpoint dependent on from one for the maximum temperature determined heat output (PFlt_wAct_tRatePFltMax) the exhaust aftertreatment device takes place to the environment. Method according to one of claims 1 to 3, characterized determining the concentration setpoint and / or the temperature setpoint dependent on from one for the maximum temperature determined enthalpy supply (PFlt_wSpecNetInp_tPFltMax; PFlt_wActNetInp_tPFltMax) to the exhaust aftertreatment device he follows. Method according to one of the preceding claims, characterized in that the determining the concentration setpoint and / or the temperature setpoint is a function of the total combustion heat release rate (PFlt_wCmbPFltTot) in the exhaust aftertreatment device. Apparatus for controlling the operation of an exhaust aftertreatment device for the aftertreatment of exhaust gases of an internal combustion engine, thereby characterized in that it is adapted to a method according to one of the preceding claims perform. Device according to claim 6, characterized in that the exhaust aftertreatment device is a diesel particulate filter is. Device according to claim 6, characterized in that the exhaust aftertreatment device is a nitrogen oxide trap.