WO2010015453A1

WO2010015453A1 - Method and device for controlling an exhaust gas post-treatment

Info

Publication number: WO2010015453A1
Application number: PCT/EP2009/057499
Authority: WO
Inventors: Peter Bauer; Tahar Zrilli
Original assignee: Continental Automotive Gmbh
Priority date: 2008-08-05
Filing date: 2009-06-17
Publication date: 2010-02-11
Also published as: US20110094208A1; CN102076934B; DE102008036418B4; CN102076934A; DE102008036418A1

Abstract

Method and device for controlling an exhaust gas post-treatment for an internal combustion engine comprising at least one cylinder (Z1-Z4) and one combustion chamber (26) and one exhaust gas tract (14) in which is disposed an SCR catalyst (34). A humidity parameter (HDT EXH) of an exhaust gas in the exhaust gas tract (14) is determined upstream of the SCR catalyst (34) of the internal combustion machine. A control signal for an actuator for introducing ammonia into the exhaust gas is determined as a function of the humidity parameter (HDT_EXH) of the exhaust gas, and the actuator is adjusted accordingly.

Description

description

Method and apparatus for controlling exhaust aftertreatment

The invention relates to a method and a device for controlling an exhaust gas aftertreatment in an internal combustion engine with an SCR catalytic converter.

Ever stricter legal regulations regarding permissible pollutant emissions in motor vehicles, in which internal combustion engines are arranged, make it necessary to keep the pollutant emissions during operation of the internal combustion engine as low as possible. This can take place, on the one hand, in that the pollutant emissions which occur during the combustion of the air / fuel mixture in the respective cylinder of the internal combustion engine are reduced. On the other hand, exhaust gas aftertreatment systems are used in internal combustion engines, which convert the pollutant emissions which are generated during the combustion process of the air / fuel mixture in the respective cylinder into harmless substances. For this purpose, catalysts are used, which convert carbon monoxide, hydrocarbons and nitrogen oxides into harmless substances. Both the targeted influencing of the generation of the pollutant emissions during combustion and the conversion of the pollutant components with a high efficiency by an exhaust gas catalyst require a very precisely adjusted air / fuel ratio in the respective cylinder.

In this context, it must be ensured that the components of the exhaust aftertreatment system also function in the desired manner over a long period of operation and errors are reliably detected. In a lean-running gasoline engine and in a diesel internal combustion engine, nitrogen oxides can be produced during a combustion process in a combustion chamber of the corresponding internal combustion engine. The resulting nitrogen oxides are then part of an exhaust gas of the internal combustion engine. To reduce the nitrogen oxide content of the exhaust gas, the exhaust tract of the internal combustion engine can be metered with a reducing agent, by means of which the nitrogen oxides in an SCR catalyst can react to give acceptable nitrogen and water. The reducing agent used is preferably ammonia. The ammonia can be recovered by heating a complex salt and gaseously metered into the exhaust tract. Alternatively, the exhaust tract may be fed with an aqueous urea solution which, due to the heat in the exhaust tract, is then at least partially hydrolyzed to ammonia which reacts with the nitrogen oxides of the exhaust gas in the SCR catalyst. If the nitrogen oxides are not completely reduced, they contribute to environmental pollution. If an excess of ammonia is metered and the ammonia exits the exhaust tract, this leads to a significant odor nuisance in an environment of the internal combustion engine.

The object on which the invention is based is to provide a method and a device for controlling an exhaust gas aftertreatment in an internal combustion engine, which contribute to a particularly advantageous reduction of a pollutant content of an exhaust gas of the internal combustion engine.

The object is solved by the features of the independent claims. Advantageous embodiments of the invention are specified in the subclaims.

The invention is characterized by a method and an apparatus for controlling an exhaust gas aftertreatment for a Internal combustion engine having at least one cylinder with a combustion chamber and an exhaust tract, in which an SCR catalyst is arranged. A parameter for a water content of an exhaust gas in the exhaust tract upstream of the SCR catalytic converter of the internal combustion engine is determined, and depending on the characteristic for the water content of the exhaust gas, an actuating signal for an actuator for introducing ammonia into the exhaust gas is determined and adjusted the actuator.

Due to the water contained in the exhaust gas, there may be a buildup of water in the SCR catalyst. As a result, it is possible that a deviation of the actual time profile of the catalyst temperature from a time profile of the catalyst temperature, as it would occur without stored in the SCR catalyst water arises.

The advantage of considering the water content of an exhaust gas in the exhaust tract upstream of the SCR catalyst is that the water / moisture content in the SCR catalyst can be taken into account in the injection amount and injection timing of the reductant to be supplied. Optionally, an introduction of suitable heating measures for the catalyst is possible. This makes it easier to avoid NOx emissions. Furthermore, avoidance of blockage of the SCR catalyst by high water / moisture content in the SCR catalyst is possible. In addition, information on the moisture-dependent aging behavior of the SCR catalyst is possible.

In an advantageous embodiment, the parameter for the water content of the exhaust gas is determined as a function of the air moisture content of the ambient air supplied to the internal combustion engine. This allows an accurate determination of the water / moisture content in the SCR catalyst. In a further advantageous embodiment, the parameter for the water content of the exhaust gas is determined depending on the temperature of the ambient air supplied to the internal combustion engine. This has the advantage that an accurate determination of the moisture content of the ambient air and thus the exhaust gas is possible.

In a further advantageous embodiment, the air moisture content and / or the temperature is determined by means of one or more sensors whose measurement signal is representative or whose measurement signals are representative of the air moisture content and / or the temperature of the ambient air supplied to the internal combustion engine. This makes it possible to control the exhaust aftertreatment taking into account the water / moisture content in the SCR catalyst with simple sensors.

In a further advantageous embodiment, a position of the actuator affects an ammonia mass, which is supplied to the SCR catalyst. This is an easy way to measure the ammonia mass in a suitable manner.

Embodiments of the invention are explained in more detail below with reference to schematic drawings.

Show it:

Figure 1 shows an internal combustion engine with a control device, and 2 shows a block diagram of a method for controlling an exhaust aftertreatment for the internal combustion engine.

Elements of the same construction or function are identified across the figures with the same reference numerals.

FIG. 1 shows an internal combustion engine with an intake tract 10, an engine block 12, a cylinder head 13 and an exhaust tract 14. The intake tract 10 preferably comprises a throttle valve 15 and a suction pipe 17. The intake manifold 17 is directed towards a cylinder Z1 at the intake passage in FIG a combustion chamber 26 of the engine block 12 out. The engine block 12 includes a crankshaft 18, which is coupled via a connecting rod 20 with a piston 21 of the cylinder Zl.

The cylinder head 13 comprises a valve drive with a gas inlet valve 22 and a gas outlet valve 24. The cylinder head 13 further comprises an injection valve 28 and a spark plug 30. Alternatively, the injection valve 28 may also be arranged in the intake pipe 17.

In the exhaust tract 14, an SCR catalyst 34 is arranged for the reduction of NOx.

The internal combustion engine is further associated with a control device 35, which is associated with sensors that detect different measured variables and can each determine the value of the measured variables. The control device 35 is designed to determine manipulated variables as a function of at least one of the measured variables, which variables can then be converted into one or more actuating signals for controlling actuators by means of corresponding actuators. The control device 35 is here as a device for controlling an exhaust aftertreatment designated .

The actuators are, for example, the throttle valve 15, the gas inlet and gas outlet valves 22, 24, the injection valve 28 or the spark plug 30.

The sensors include a pedal position sensor 36, which detects an accelerator pedal position of an accelerator pedal 38. Furthermore, the internal combustion engine has a humidity sensor 40, which is arranged upstream of the throttle valve 15 and detects there a humidity of the intake air. A temperature sensor 42 upstream of the throttle valve 15 detects an intake air temperature.

Downstream of the SCR catalyst 34, a NOx sensor 44 is arranged, which detects a NOx concentration of the exhaust gas.

Depending on the embodiment of the invention, any subset of said sensors may be present, or additional sensors may be present.

In addition to the cylinder Zl further cylinders Z2 to Z4 are preferably provided, which are also associated with corresponding actuators and optionally sensors.

For carrying out the method for controlling an exhaust gas aftertreatment for an internal combustion engine, a program can be stored in a program memory of the control device 35 and executed during operation of the internal combustion engine.

The program is shown in FIG. The figure shows a temperature model 100 for the calculation of the temperature of the exhaust gas of the internal combustion engine from an exhaust gas mass flow EXH_MASS_FLOW, an exhaust gas temperature TEMP_TUR_UP before a turbine of the internal combustion engine and a total injection quantity MF_TOT of fuel. By means of the temperature model 100 for the exhaust gas of the internal combustion engine, a modeled exhaust gas temperature TEMP_EXH_MDL is determined therefrom.

Furthermore, a measured exhaust gas temperature TEMP_EXH_MES is determined and compared in a comparison block 102 with the modeled exhaust gas temperature TEMP_EXH_MDL, whereby an exhaust gas temperature TEMP_EXH is determined as output variable of the comparison block 102 in a suitable manner.

In a humidity model 104 of the exhaust gas of the internal combustion engine, a modeled water content HDT_EXH_MDL of the exhaust gas is determined from an air temperature AIR_TEMP of the ambient air, an air humidity content AIR_HDT of the ambient air, an injection quantity MF_CYL into a cylinder, a total air charge MASS_GAS_CYL in the cylinder and a combustion efficiency CMB_EFF of the internal combustion engine.

The air humidity content AIR_HDT of the ambient air is preferably detected by the humidity sensor 40, the air temperature AIR_TEMP of the ambient air is preferably detected by the temperature sensor 42 upstream of the throttle valve 15. In alternative embodiments of the method for controlling the exhaust gas aftertreatment, the air humidity content AIR_HDT and the air temperature AIR_TEMP of the ambient air may also be determined by an empirical model of weather data.

Furthermore, from a mass flow MASS_EGR of the exhaust gas recirculation by means of a first characteristic map 106, a correction FACTOR FAC_EGR_COR the exhaust gas recirculation determined and determined in a first multiplier 108, together with the determined from the humidity model 104 of the exhaust gas modeled water content HDT_EXH_MDL the exhaust gas, a water content HDT_EXH of the exhaust gas.

By determining the parameter for the water content HDT_EXH of the exhaust gas as a function of the air humidity content AIR_HDT and the temperature AIR_TEMP of the internal air supplied to the internal combustion engine, an accurate determination of the water content HDT_EXH of the exhaust gas is possible.

In a temperature model 110 of the SCR catalytic converter 34, a modeled catalyst temperature TEMP_CAT_MDL is determined as a function of the exhaust gas temperature TEMP_EXH, the exhaust gas mass flow EXH_MASS_FLOW, a vehicle speed VS, the temperature AIR_TEMP of the ambient air supplied to the internal combustion engine, a heat capacity C_CAT and a catalyst volume VOL_CAT of the SCR catalytic converter 34 and a second multiplier 114. The determined value of the water content HDT_EXH of the exhaust gas is supplied to a second characteristic map 112 and from this a correction factor FAC_HDT_COR of the moisture content is determined and likewise fed to the second multiplier 114.

In a known manner, a modeled urea injection quantity UREA_INJ_MDL for injecting urea into the exhaust gas in the exhaust gas tract 14 is determined by means of a urea injection model 116, inter alia from the exhaust gas mass flow EXH_MASS_FLOW and a NOx content NOX in the exhaust gas, and fed to a third multiplier 120.

From the values supplied to the multiplier 114, a catalyst temperature TEMP_CAT is determined and fed to a third map 118. By means of the third map 118 a correction factor UREA_INJ_COR for the urea injection amount is determined and also supplied to the third multiplier 120.

From the values supplied to the multiplier 120, the injection amount UREA_INJ of urea into the exhaust tract 14 upstream of the SCR catalyst 34 is determined.

By means of this method it is possible to take into account the actual catalyst temperature TEMP_CAT taking into account the water content HDT_EXH in the exhaust gas and / or of condensate in the SCR catalytic converter 34 for controlling the exhaust gas aftertreatment. Thus, the injection quantity and the injection timing of the reductant to be supplied, ie in particular the urea solution, can be accurately determined. Urea or another reducing agent may be supplied to the exhaust gas upstream of the SCR catalyst if and only if a predetermined catalyst temperature TEMP_CAT is actually reached. An optionally unnecessary use of urea or another reducing agent before reaching the predetermined catalyst temperature TEMP_CAT can thus be avoided. It is very possible to avoid emissions of ammonia or NOx from the SCR catalyst 34. In particular, it can also be avoided that the SCR catalytic converter 34 is impeded in its function by a high water or moisture content. Since attachment of water or moisture in the SCR catalyst 34 may result in additional aging of the SCR catalyst 34, this method further enables the aging of the SCR catalyst 34 to be accurately determined.

Claims

claims

A method for controlling exhaust aftertreatment for an internal combustion engine having at least one cylinder (Z1-Z4) with a combustion chamber (26) and an exhaust tract (14), in which an SCR catalyst (34) is arranged, in which

a characteristic value for a water content (HDT_EXH) of an exhaust gas in the exhaust gas tract (14) upstream of the SCR catalytic converter (34) of the internal combustion engine is determined, and depending on the parameter for the water content (HDT_EXH) of the exhaust gas, an actuating signal for an actuator for Introducing ammonia detected in the exhaust gas and the actuator is set.

2. The method of claim 1, wherein the characteristic for the water content (HDT_EXH) of the exhaust gas is determined depending on the air moisture content (AIR_HDT) of the internal combustion engine supplied ambient air.

3. The method of claim 1 or 2, wherein the characteristic for the water content (HDT_EXH) of the exhaust gas is determined depending on the temperature (AIR_TEMP) of the internal combustion engine supplied ambient air.

4. The method of claim 2 or 3, wherein the air moisture content (AIR_HDT) and / or the temperature (AIR_TEMP) by means of one or more sensors (40, 42) is determined, the measurement signal or the measurement signals are representative of the air moisture content (AIR_HDT) and / or the temperature (AIR_TEMP) of the ambient air supplied to the internal combustion engine.

5. The method according to any one of the preceding claims, wherein a position of the actuator on an ammonia mass, which is supplied to the SCR catalyst (34).

6. An apparatus for controlling an exhaust gas aftertreatment in an internal combustion engine having at least one cylinder (Z1-Z4) with a combustion chamber (26) and an exhaust tract (14), in which an SCR catalyst (34) is arranged, wherein the device is designed to determine a parameter for a water content (HDT_EXH) of an exhaust gas in the exhaust gas tract (14) upstream of the SCR catalytic converter (34) of the internal combustion engine,

- Determine an actuating signal for an actuator for introducing ammonia into the exhaust gas and adjust the actuator depending on the characteristic for the water content (HDT_EXH) of the exhaust gas.