DE102008036418B4 - Method and apparatus for controlling exhaust aftertreatment - Google Patents

Abstract

A method for controlling an exhaust gas 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 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 is determined, and
- Is determined depending on the characteristic of the water content (HDT_EXH) of the exhaust gas, a catalyst temperature (TEMP_CAT) to determine a control signal for an actuator for introducing ammonia into the exhaust gas and the actuator is set.

Description

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

always stricter legal regulations regarding permissible pollutant emissions in motor vehicles, in which internal combustion engines are arranged, make it necessary to pollutant emissions in one operation Keep the internal combustion engine as low as possible. This can on the one hand done by reducing the pollutant emissions be that while the combustion of the air / fuel mixture in the respective Cylinder of the internal combustion engine arise. On the other hand are in internal combustion engines Exhaust aftertreatment systems in use, the pollutant emissions, the while the combustion process of the air / fuel mixture in the respective cylinders are generated, convert into harmless substances. To For this purpose catalysts are used, the carbon monoxide, Convert hydrocarbons and nitrogen oxides into harmless substances. Either the targeted influencing of the generation of pollutant emissions while combustion as well as the conversion of pollutant components with a high efficiency through a catalytic converter set a very precise adjusted air / fuel ratio in the respective cylinder ahead.

In In this context, it must be ensured that the components the exhaust aftertreatment system also in the desired manner via a long operating time and error detected reliably become.

at a lean-running gasoline engine and a diesel internal combustion engine can in a combustion process in a combustion chamber of the corresponding Internal combustion engine Nitrogen oxides are formed. The resulting nitrogen oxides are then part of an exhaust gas of the internal combustion engine. To the Reducing the nitrogen oxide content of the exhaust gas can the exhaust tract the engine are assigned a reducing agent, by the nitrogen oxides in an SCR catalyst to harmless nitrogen and water can react. The reducing agent used is preferably ammonia. The ammonia can by heating a complex salt are obtained and gaseous attributed to the exhaust tract become. Alternatively, an aqueous urea solution may be added to the exhaust tract then, due to the heat in the exhaust system at least partially hydrolyzed to ammonia, which in the SCR catalyst with the nitrogen oxides of the Exhaust gas reacts. If the nitrogen oxides are not completely reduced contribute to environmental pollution. If there is a surplus is added to ammonia and the ammonia from the exhaust tract exit, so leads This leads to a significant odor nuisance in an environment of the internal combustion engine.

The DE 10 2004 043 933 A1 discloses an exhaust system of an internal combustion engine of a motor vehicle, with an exhaust gas catalyst arranged in an exhaust pipe and a sensor exposed to the exhaust gas of the internal combustion engine and monitoring the exhaust gas system. The sensor is a humidity sensor.

The DE 10 2006 058 880 A1 discloses a method for correcting an output signal of a lambda sensor of an internal combustion engine, comprising the steps of: detecting a fuel cut-off phase of the internal combustion engine, detecting an exhaust gas composition by means of the lambda sensor during the fuel cut-off phase, detecting a temperature which represents a measure for the intake air of the internal combustion engine and calibrating the lambda sensor based on the sensed temperature.

The DE 103 01 977 A1 discloses a device for controlling moisture removal for an exhaust gas purification device for use with an internal combustion engine. The apparatus has means for estimating the amount of trapped moisture that estimates the amount of moisture leaked from an internal combustion engine and trapped in a catalyst, a judging means that judges whether the estimated value of the trapped moisture exceeds a predetermined amount, and a means for controlling the removal of moisture trapped in the catalyst.

The The object of the invention is based, a method and an apparatus for controlling an exhaust aftertreatment in an internal combustion engine to create, which leads to a particularly advantageous reduction of a Contribute pollutant content of an exhaust gas of the internal combustion engine.

The Task is solved by the characteristics 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 exhaust gas aftertreatment for an internal combustion engine having at least one cylinder with a combustion chamber and an exhaust gas tract, in which an SCR catalytic converter is arranged. A parameter for a water content of an exhaust gas in the exhaust gas 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, a catalyst temperature is determined to determine a control signal for an actuator for introducing ammonia into the exhaust gas and the actuator is set.

by virtue of of the water contained in the exhaust gas can lead to a storage of Water come in the SCR catalyst. This makes it possible for that a deviation of the actual Time course of the catalyst temperature of a temporal Course of the catalyst temperature, as he without into the SCR catalyst embedded water would occur arises.

Of the Advantage of consideration 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 at the injection amount and the injection timing of the supplied Reducing agent taken into account can be. If appropriate, an introduction of suitable heating measures for the Catalyst possible. With that you can NOx emissions lighter be avoided. Furthermore, avoiding a blockage the SCR catalyst by a high water / moisture content possible in the SCR catalyst. About that In addition, information on the moisture-dependent aging behavior of the SCR catalyst possible.

In In an advantageous embodiment, the parameter for the water content dependent on the exhaust gas from the air moisture content of the internal combustion engine supplied ambient air determined. This is an accurate determination of the water / moisture content possible in the SCR catalyst.

In In another advantageous embodiment, the parameter for the water content dependent on the exhaust gas from the temperature of the internal combustion engine supplied ambient air determined. This has the advantage that an accurate determination of the Moisture content of the ambient air and thus the exhaust gas is possible.

In In a further advantageous embodiment, the air moisture content and / or the temperature is determined by means of one or more sensors, its measurement signal representative or whose measuring signals are representative are for the humidity and / or the temperature of the internal combustion engine supplied Ambient air. this makes possible the regulation of the exhaust aftertreatment taking into account the water / moisture content in the SCR catalyst with simple sensors.

In a further advantageous embodiment, a affects Position of the actuator to an ammonia mass, the SCR catalyst supplied becomes. This is a simple way, the ammonia mass to measure appropriately.

embodiments The invention are explained in more detail below with reference to schematic drawings.

It demonstrate:

1 an internal combustion engine with a control device, and

2 a block diagram of a method for controlling an exhaust aftertreatment for the internal combustion engine.

elements same construction or function are cross-figurative with the same Reference number marked.

In 1 An internal combustion engine is shown with an intake tract 10 , an engine block 12 a cylinder head 13 and an exhaust tract 14 , The intake tract 10 preferably includes a throttle 15 and a suction tube 17 , The suction tube 17 is toward a cylinder Z1 at the inlet port into a combustion chamber 26 of the engine block 12 guided. The engine block 12 includes a crankshaft 18 , which has a connecting rod 20 with a piston 21 of the cylinder Z1 is coupled.

The cylinder head 13 includes a valvetrain 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 also in the intake manifold 17 be arranged.

In the exhaust tract 14 is an SCR catalyst 34 arranged to reduce NOx.

The internal combustion engine is also a control device 35 assigned, the sensors are assigned, which detect different parameters and each can determine the value of the measured variables. The control device 35 is designed to determine in response to at least one of the measured variables manipulated variables, which can then be converted into one or more actuating signals for controlling actuators by means of corresponding actuators. The control device 35 is referred to herein as an exhaust aftertreatment control device.

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

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

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

ever according to embodiment The invention may be any subset of said sensors be present or it can also additional Sensors be present.

Next the cylinder Z1 are preferably further cylinders Z2 to Z4 provided which also corresponding actuators and optionally sensors assigned.

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

The program is in 2 shown.

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 amount MF_TOT of fuel. By means of the temperature model 100 for the exhaust gas of the internal combustion engine from a modeled exhaust gas temperature TEMP_EXH_MDL is determined.

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

In a moisture 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 determined by the humidity sensor 40 detected, the air temperature AIR_TEMP of the ambient air is preferably by the temperature sensor 42 upstream of the throttle 15 detected. In alternative embodiments of the method for controlling the exhaust 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 the exhaust gas recirculation by means of a first map 106 a correction factor FAC_EGR_COR of the exhaust gas recirculation is determined and in a first multiplier 108 along with the one from the moisture model 104 of the exhaust gas modeled water content HDT_EXH_MDL of the exhaust gas determined a water content HDT_EXH of the exhaust gas.

By the determination of the parameter for the water content HDT_EXH of the exhaust gas depending on the air humidity AIR_HDT and the temperature AIR_TEMP supplied to the internal combustion engine Ambient air is an accurate determination of the water content HDT_EXH the exhaust gas possible.

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

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

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

From the multiplier 120 supplied values, the injection amount UREA_INJ of urea in the exhaust tract 14 upstream of the SCR catalyst 34 certainly.

By means of this method it is possible, 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 catalyst 34 to consider for the control of exhaust aftertreatment. Thus, the injection quantity and the injection timing of the reductant to be supplied, so 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, emissions of ammonia or NOx from the SCR catalyst 34 to avoid. In particular, it can also be avoided that the SCR catalyst 34 is hampered in its function by a high water or moisture content. As an accumulation of water or moisture in the SCR catalyst 34 to additional aging of the SCR catalyst 34 This method further allows the aging of the SCR catalyst 34 to be determined exactly.

Claims (6)

Method for controlling exhaust gas 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 ), in which - a parameter for a water content (HDT_EXH) of an exhaust gas in the exhaust gas tract ( 14 ) upstream of the SCR catalyst ( 34 ) of the internal combustion engine is determined, and - depending on the characteristic of the water content (HDT_EXH) of the exhaust gas, a catalyst temperature (TEMP_CAT) is determined to determine a control signal for an actuator for introducing ammonia into the exhaust gas and the actuator is adjusted. The method of claim 1, wherein the characteristic for the water content (HDT_EXH) of the exhaust gas dependent from the air humidity content (AIR_HDT) of the internal combustion engine supplied ambient air is determined. The method of claim 1 or 2, wherein the characteristic for the water content (HDT_EXH) of the exhaust gas dependent from the temperature (AIR_TEMP) of the internal combustion engine supplied ambient air is determined. Method according to Claim 2 or 3, in which the air humidity content (AIR_HDT) and / or the temperature (AIR_TEMP) are determined by means of one or more sensors ( 40 . 42 ) whose measurement signal or its 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. Method according to one of the preceding claims, in which a position of the actuator has an effect on an ammonia mass which corresponds to the SCR catalyst ( 34 ) is supplied. Device for controlling 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 ), wherein the device is designed to: a parameter for a water content (HDT_EXH) of an exhaust gas in the exhaust gas tract (FIG. 14 ) upstream of the SCR catalyst ( 34 ) of the internal combustion engine to determine, depending on the characteristic for the water content (HDT_EXH) of the exhaust gas to determine a catalyst temperature (TEMP_CAT) for determining an actuating signal for an actuator for introducing ammonia into the exhaust gas and adjust the actuator.