EP1307639A1

EP1307639A1 - Method and controller for operating a nitrogen oxide (nox) storage catalyst

Info

Publication number: EP1307639A1
Application number: EP01956310A
Authority: EP
Inventors: Eberhard Schnaibel; Klaus Winkler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-07-26
Filing date: 2001-07-11
Publication date: 2003-05-07
Anticipated expiration: 2021-07-11
Also published as: JP5220258B2; US20030163987A1; DE10036453A1; DE50109223D1; EP1307639B1; US6889497B2; JP2004504539A; WO2002008582A1

Abstract

The invention relates to a method for operating a nitrogen oxide (NOx) storage catalyst (12') on an internal combustion engine (1), in particular in a motor vehicle (1). The nitrogen oxides (NOx) generated by the internal combustion engine (1) are stored in the storage catalyst (12') during a first operating phase and the nitrogen oxides stored in the storage catalyst (12') are released during a second operating phase. The beginning of the second operating phase is determined by means of a nitrogen oxide (NOx) level (mnosp) of the NOx storage catalyst (12'), which is modelled by means of a nitrogen oxide (NOx) storing model (30). According to the invention, in order to be able to determine the beginning and the end of the second operating phase as exactly and reliably as possible, a first value for nitrogen oxide (NOx) mass flow (msnonk s) behind the NOx storage catalyst (12') is determined and the NOx storing model (30) is corrected based on the determined first value (msnonk s).

Description

Method and control device for operating a nitrogen oxide (NOx) storage catalytic converter

The present invention relates to a method for operating a nitrogen oxide (NOx) storage catalyst of an internal combustion engine, in particular a motor vehicle. Here nitrogen oxides generated are stored in a first operating phase in the storage catalyst and the storage catalyst is stored nitrogen oxides in a second operating phase of the storage catalytic converter ausgespeichert..Der the beginning of the ^'second operating phase on the basis of a nitrogen oxide (NOx) of the internal combustion engine - the filling level of the NOx storage catalyst determined, the NOx level is modeled using a nitrogen oxide (NOx) storage model.

The invention also relates to a control device for an internal combustion engine, in particular a motor vehicle. The internal combustion engine can by the control device between a first operating phase, in which nitrogen oxides generated by the internal combustion engine in the nitrogen oxide (NOx) -

Storage catalytic converter are stored, and a second operating phase in which stored nitrogen oxides are stored out of the NOx storage catalytic converter are switched back and forth. The control device has first means for determining the start of the second operating phase on the basis of a nitrogen oxide (NOx) fill level modeled by means of a nitrogen oxide (NOx) storage model of the NOx storage catalytic converter. Furthermore, the present invention relates to a control element, in particular a read-only memory or a flash memory, for such a control device.

Finally, the present connection relates to an internal combustion engine, in particular a motor vehicle. The internal combustion engine has a control unit and a nitrogen oxide (NOx) storage catalytic converter. The internal combustion engine can between a first

Operating phase in which nitrogen oxides generated by the internal combustion engine are stored in the NOx storage catalytic converter, and a second operating phase in which stored nitrogen oxides are stored out of the NOx storage catalytic converter are switched back and forth by the control unit. The internal combustion engine has first means for determining the start of the second operating phase on the basis of a nitrogen oxide (NOx) fill level of the NOx storage catalytic converter modeled by means of a nitrogen oxide (NOx) storage model.

State of the art

In internal combustion engines that can be operated with a lean fuel / air mixture (lambda> 1), nitrogen oxide (NOx) storage catalysts are used to store the nitrogen oxide (NOx) emissions emitted by the internal combustion engine during a first operating phase (lean operation) , This first operating phase of the NOx storage catalytic converter is also referred to as the storage phase. With increasing duration of the storage phase, the efficiency of the NOx storage catalytic converter decreases, which leads to an increase in the NOx emissions behind the NOx storage catalytic converter. The cause of the decrease in efficiency is the increase in nitrogen oxide (NOx) -

Level of the NOx storage catalytic converter. The NOx level can be monitored and the second operating phase of the NOx storage catalytic converter (withdrawal phase) initiated after a predefined threshold value has been exceeded. A nitrogen oxide (NOx) storage model can be used to determine the NOx fill level of the NOx storage catalytic converter.

During the second operating phase, a reducing agent is added to the exhaust gas of the internal combustion engine, which reduces stored nitrogen oxides to nitrogen and oxygen. For example, hydrocarbon (HC) and / or carbon monoxide (CO) can be used as the reducing agent, which can be generated in the exhaust gas by a rich setting of the fuel / air mixture. Alternatively, urea can also be added to the exhaust gas as a reducing agent. Ammonia from the urea is used to reduce the nitrogen oxide to oxygen and nitrogen. The ammonia can be obtained from a urea solution by hydrolysis.

Towards the end of the withdrawal phase, a large part of the stored nitrogen oxide is reduced and less and less of the reducing agent meets nitrogen oxide, which it can reduce to oxygen and nitrogen. As a result, towards the end of the withdrawal phase, the proportion of reducing agent in the exhaust gas behind the NOx storage catalytic converter increases, and the proportion of oxygen in the exhaust gas behind the NOx storage catalytic converter decreases. By analyzing the exhaust gas behind the NOx storage catalytic converter using suitable exhaust gas sensors, the end of the

Withdrawal phase can then be initiated when the majority of the nitrogen oxide has been withdrawn from the NOx storage catalytic converter.

In a NOx storage model known from the prior art, the NOx fill level of the NOx Storage catalytic converter as a function of, inter alia, the NOx mass flow upstream of the NOx storage catalytic converter, the NOx mass flow downstream of the NOx storage catalytic converter and the temperature of the NOx storage catalytic converter. An efficiency of the NOx storage catalytic converter is determined from these variables, which multiplied by the NOx mass flow upstream of the NOx storage catalytic converter delivers the current NOx fill level when integrated. As soon as the NOx level exceeds the predefinable threshold value, the second operating phase is initiated. The efficiency of the NOx storage catalytic converter decreases with increasing boundary conditions with increasing NOx level.

The present invention is based on the object of being able to determine the NOx fill level of a NOx storage catalytic converter with the aid of a NOx storage model and thus the beginning and end of the second operating phase (withdrawal phase) as accurately and reliably as possible in order to ensure optimum exhaust gas quality.

To achieve this object, the invention proposes, based on the method of the type mentioned at the outset, that a first value of the nitrogen oxide (NOx) mass flow is detected behind the NOx storage catalytic converter and the NOx

Storage model is corrected as a function of the detected first value.

Advantages of the invention

According to the invention, it is therefore proposed to correct the NOx storage model by means of a measured value. A correction factor for the NOx storage model can be obtained from the measured value, which can be used for diagnostic purposes. Due to the measured value of the NOx fill and the can with

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Storage catalyst determined.

According to another preferred embodiment of the present invention that the difference between the two values of the NOx mass flow downstream of the NOx storage catalytic converter a ^'controller is supplied to the NOx storing is corrected of the regulator as a function of a manipulated variable is proposed. The controller is preferably designed as an integrating (I) controller. The output signal of the NOx arranged downstream of the NOx storage catalytic converter

The sensor is therefore not evaluated directly, e.g. via the absolute value, the slope or the like, but is used to control the NOx storage model using the I controller.

Finally, it is proposed that the NOx storage model be corrected as a control variable of the controller depending on the efficiency of the NOx storage catalytic converter.

Of particular importance is the implementation of the method according to the invention in the form of a control element which is provided for a control unit of an internal combustion engine, in particular a motor vehicle. A program is stored on the control element, which is executable on a computing device, in particular on a microprocessor, and is suitable for executing the method according to the invention. In this case, the invention is thus implemented by a program stored on the control element, so that this control element provided with the program represents the invention in the same way as the method, for the execution of which the program is suitable. In particular, an electrical storage medium can be used as the control element, for example a read-only memory or a flash memory.

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The inventive method according to a preferred embodiment.

Description of the embodiments

FIG. 1 shows a direct-injection internal combustion engine 1 of a motor vehicle, in which a piston 2 can be moved back and forth in a cylinder 3. The cylinder 3 is provided with a combustion chamber 4, which i.a. is limited by the piston 2, an inlet valve 5 and an outlet valve 6. An intake pipe 7 is coupled to the inlet valve 5 and an exhaust pipe 8 is coupled to the outlet valve 6.

In the area of the inlet valve 5 and the outlet valve 6, a fuel injection valve 9 and a spark plug 10 protrude in the combustion chamber 4. Fuel can be injected into the combustion chamber 4 via the injection valve 9. The fuel in the combustion chamber 4 can be ignited with the spark plug 10.

In the intake pipe 7, a rotatable throttle valve 11 is accommodated, via which air can be fed to the intake pipe 7. The amount of air supplied is dependent on the angular position of the throttle valve 11. In the exhaust pipe 8, a catalyst 12 is housed, which by the

Combustion of the fuel resulting exhaust gases cleans. The catalytic converter 12 is a nitrogen oxide (NOx) storage catalytic converter 12 'which is coupled to a 3-way catalytic converter 12' 'as an oxygen storage device.

A control device 18 is acted upon by input signals 19, which represent operating variables of the internal combustion engine 1 measured by sensors. The control unit 18 generates output signals 20 with which the behavior of the internal combustion engine 1 can be influenced via actuators or actuators. Among other things, the control unit 18 is for this purpose provided to control and / or regulate the operating variables of the internal combustion engine 1. For this purpose, the control unit 18 is provided with a microprocessor, which has stored a program in a storage medium, in particular in a flash memory, which is suitable for carrying out the control and / or regulation mentioned.

In a first operating mode, a so-called homogeneous operation of the internal combustion engine 1, the throttle valve 11 is partially opened or closed depending on the desired torque. The fuel is injected into the combustion chamber 4 by the injection valve 9 during an induction phase caused by the piston 2. The injected fuel is swirled by the air sucked in simultaneously via the throttle valve 11 and is thus distributed substantially uniformly in the combustion chamber 4. The fuel-air mixture is then compressed during the compression phase in order to then be ignited by the spark plug 10. The piston 2 is driven by the expansion of the ignited fuel. The resulting torque depends, among other things, on homogeneous operation. from the position of the throttle valve 11. In view of a low pollutant development, the fuel-air mixture is set to lambda = 1 if possible.

In a second operating mode, a so-called stratified operation of the internal combustion engine 1, the throttle valve 11 is opened wide. The fuel is injected from the injection valve 9 into the combustion chamber 4 during a compression phase caused by the piston 2, specifically locally in the immediate vicinity of the spark plug 10 and at a suitable time before the ignition point. Then we ignite the fuel with the help of the spark plug 10, so that the piston 2 in the now following working phase due to the expansion of the ignited Fuel is driven. The resulting torque largely depends on the injected fuel mass in shift operation. The stratified operation is essentially provided for the idle operation and the partial load operation of the internal combustion engine 1. In shift operation, lambda is usually> 1.

During a first operating phase, the internal combustion engine 1 is operated in stratified mode and the storage catalytic converter 12 'is loaded with nitrogen oxides and the 3-way catalytic converter 12' 'with oxygen (storage phase). In a second operating phase (regeneration phase), the storage catalytic converter 12 ′ and the 3-way catalytic converter 12 ″ are discharged again, so that they again generate nitrogen oxides or

Can absorb oxygen (withdrawal phase). During the regeneration phase, a reducing agent is added to the exhaust gas upstream of the catalytic converter 12. For example, hydrocarbons (HC), carbon monoxide (CO) or urea can be used as reducing agents. Hydrocarbons and

Carbon monoxide is generated in the exhaust gas by a rich mixture setting (operation of the internal combustion engine in homogeneous operation). Urea can be metered into the exhaust gas in a controlled manner from a storage container. The following processes take place during the regeneration phase of the catalytic converter 12: the reducing agent reduces the stored nitrogen oxides to nitrogen and oxygen. These substances emerge from the catalytic converter 12, so that there is an excess of oxygen behind the catalytic converter 12 during the regeneration phase, although the internal combustion engine 1 is operated with a rich fuel / air mixture (lack of oxygen).

An oxygen (02) sensor 13 is arranged in front of the catalytic converter 12 and a nitrogen (NOx) sensor 14 is arranged in the exhaust pipe 8 after the catalytic converter 12. After switching to Lack of oxygen (operation of the internal combustion engine 1 with a rich mixture) upstream of the catalytic converter 12 at the beginning of the regeneration phase, the 02 sensor 13 reacts practically without delay. Due to the excess of oxygen in the exhaust gas prevailing during shift operation, the oxygen storage locations of the catalytic converter 12 are initially almost all occupied. After switching to a lack of oxygen at the beginning of the regeneration phase, the oxygen storage locations are successively freed of oxygen, which then emerges from the catalytic converter 12. After the catalyst 12 there is therefore initially an excess of oxygen after switching over to the regeneration phase. After a period of time which is dependent on the oxygen storage capacity of the catalytic converter 12, the total nitrogen oxide stored in the storage catalytic converter 12 'is reduced and the entire oxygen stored in the oxygen storage device 12''is removed, so that oxygen deficiency also occurs behind the catalytic converter 12.

A NOx storage model 30 is shown schematically in FIG. The NOx mass flow msnovk upstream of the catalytic converter 12 and an efficiency eta_sp of the NOx storage catalytic converter • 12 'are present as input variables on the NOx storage model 30. The efficiency is eta_sp

• depending on u.a. the NOx mass flow msnovk upstream of the NOx storage catalytic converter 12 ', a NOx mass flow msnonk downstream of the NOx storage catalytic converter 12' and the temperature of the NOx storage catalytic converter 12 '. The efficiency eta_sp is a non-linear function of the NOx fill level mnosp of the NOx storage catalytic converter 12 'and decreases with increasing NOx fill level.

A product mnsospe of the NOx mass flow msnovk and the efficiency eta_sp is formed in a multiplier 31. The product mnsospe is in an integrator 32 integrated. The integrator 32 supplies the NOx fill level mnosp of the NOx storage catalytic converter 12 'as the output signal. This is compared in a comparator 33 with a predeterminable threshold value schw. If the NOx fill level mnosp exceeds the threshold value schw, a

Regeneration signal B_denox initiated the regeneration phase of the NOx storage catalyst 12 '.

A method according to the invention is shown schematically in FIG. In the method, an output signal msnonk_s of the NOx arranged behind the catalytic converter 12 is used.

Sensor 14 for regulating the NOx storage model 30.

This allows the beginning and end of the second

Operating phase (regeneration phase) of the NOx storage catalyst 12 'can be determined much more precisely and reliably, which leads to a significantly improved exhaust gas quality.

A modeled NOx mass flow msnonk_m is modeled after the catalytic converter 12. The modeled NOx mass flow msnonk_m results from the difference between the NOx mass flow msnovk upstream of the catalytic converter 12 and the product of the NOx mass flow msnovk and the efficiency eta_sp, ie. H. from msnovk • (1 - eta_sp). The NOx mass flow msnovk upstream of the catalytic converter 12 can be measured by a NOx sensor (not shown) or taken from the NOx model.

From a difference between the modeled NOx mass flow msnonk n after the catalytic converter 12 and the NOx mass flow msnonk_s measured by the NOx sensor 14 after the

Catalyst 12 forms a control difference 34 of the control circuit shown in FIG. 3. The control difference 34 is fed to an integrating I controller 35. Instead of an I controller 35, any other suitable controller can also be used. A manipulated variable 36 of the I controller 35 is passed to an actuator 37 which varies a manipulated variable 38 in order to have a targeted, regulating effect on the NOx storage model 30. The efficiency eta_sp of the NOx storage catalytic converter 12 'is used as the manipulated variable 38.

Claims

Expectations

1. Method for operating a nitrogen oxide (NOx) -

Storage catalyst (12 ') of an internal combustion engine (1), in particular of a motor vehicle, nitrogen oxides (NOx) generated by the internal combustion engine (1) being stored in the NOx storage catalyst (12') in a first operating phase and in the NOx storage catalyst (12 ') stored nitrogen oxides are stored in a second operating phase from the NOx storage catalytic converter (12 '), the beginning of the second operating phase is determined using a nitrogen oxide (NOx) fill level (mnosp) of the NOx storage catalytic converter (12') and the NOx fill level ( mnosp) is modeled on the basis of a nitrogen oxide (NOx) storage model (30), characterized in that a first value of the nitrogen oxide (NOx) mass flow (msnonk_s) is detected behind the NOx storage catalytic converter (12 ') and the NOx storage model (30 ) in

Depending on the detected first value is corrected.

2. The method according to claim 1, characterized in that the first value of the NOx mass flow (msnonk_s) behind the NOx storage catalytic converter (12 ') is measured by means of a NOx sensor (14).

3. The method according to claim 1 or 2, characterized in that a second value of the NOx mass flow (msnonk_m) behind the NOx storage catalyst (12 ') is taken from the NOx storage model (30) and the NOx Storage model (30) depending on the two values of the NOx mass flows (msnonk_s, msnonk_m) is corrected.

4. The method according to claim 3, characterized in that a difference between the two values of the NOx mass flows (msnonk_m - msnonk_s) is formed and the NOx storage model (30) is corrected as a function of the difference (msnonkjn - msnonk_s).

5. The method according to claim 3 or 4, characterized in that the NOx level (mnosp) by integrating the product of the NOx mass flow (msnovk) in front of the NOx storage catalyst (12 ') and an efficiency (eta_sp) of the NOx Storage catalyst (12 ') is determined in the NOx storage model (30).

6. The method according to claim 4 or 5, characterized in that the difference (msnonkjn - msnonk_s) of the two values (msnonk_s, msnonk_m) of the NOx mass flow downstream of the NOx storage catalytic converter (12 ') is fed to a controller (35) and that NOx storage model (30) is corrected as a function of a manipulated variable (38) of the controller (35).

7. The method according to claim 6, characterized in that the NOx storage model (30) is corrected in dependence on the efficiency (eta_sp) of the NOx storage catalytic converter (12 ') as the manipulated variable (38) of the controller (35).

8. Control element, in particular read-only memory or

Flash memory, for a control unit (18) of an internal combustion engine (1), in particular a motor vehicle, on which a program is stored which can be run on a computing device, in particular on a microprocessor, and is suitable for executing a method according to one of Claims 1 to 8 is.

9. Control device (18) for an internal combustion engine (1), in particular of a motor vehicle, the internal combustion engine (1) between a first operating phase in which nitrogen oxides (NOx) generated by the internal combustion engine (1) into the nitrogen oxide (NOx) storage catalyst (12 ') are stored, and a second operating phase, in which stored nitrogen oxides are stored out of the NOx storage catalytic converter (12'), can be switched back and forth by the control unit (18), and the control unit (18) has first means for determining the start the second operating phase using a nitrogen oxide (NOx) fill level (mnosp) of the storage catalytic converter (12 ') modeled by means of a nitrogen oxide (NOx) storage model (30), characterized in that the control device (18) has second means (14) for detecting a first value of the nitrogen oxide (NOx) mass flow (msnonk_s) behind the NOx storage catalytic converter (12 ') and third means for correcting the NOx storage model (30) in dependence of the detected first value (msnonk_s).

10. Internal combustion engine (1), in particular of a motor vehicle, the internal combustion engine (1) having a control unit (18) and a nitrogen oxide (NOx) storage catalytic converter (12 ') and the internal combustion engine (1) between a first operating phase, • in the Internal combustion engine (1) generated nitrogen oxides (NOx) are stored in the NOx storage catalytic converter (12 '), and a second operating phase, in which stored nitrogen oxides are stored out of the NOx storage catalytic converter (12'), by the control unit (18) and can be switched, and the internal combustion engine (1) has first means for determining the start of the second operating phase on the basis of a nitrogen oxide (NOx) fill level (mnosp) of the NOx storage catalytic converter modeled by means of a nitrogen oxide (NOx) - • ^** storage model (30) ( 12 '), characterized in that the Internal combustion engine (1) second means (14) for detecting a first value of the nitrogen oxide (NOx) mass flow (msnonk_s) behind the NOx storage catalytic converter (12 ') and third means for correcting the NOx storage model (30) depending on the detected has the first value (msnonk_s).