DE102019219892A1 - Method and device for the regeneration of a coated particle filter in the exhaust tract of a gasoline-powered motor vehicle - Google Patents

Abstract

The invention relates to a method for regenerating a coated particle filter in the exhaust gas tract of a gasoline-powered motor vehicle, in which a regulation of an amount of secondary air directed into the exhaust gas tract is carried out, in which an actual value for the regulation is provided by a sensor arranged downstream of the particle filter and in which the regulation it is carried out in such a way that the air ratio present downstream of the particle filter oscillates around the stoichiometric air ratio. The invention also relates to a device for regenerating a coated particle filter in the exhaust tract of a gasoline-powered motor vehicle.

Description

The invention relates to a method and a device for regenerating a coated particle filter in the exhaust tract of a gasoline-powered motor vehicle.

Increasingly stricter statutory emission limit values are placing ever higher demands on the exhaust system of motor vehicles. In order to be able to meet such requirements, various exhaust emission reduction strategies must be applied simultaneously. These different exhaust emission reduction strategies use different components including a respective associated sensor system.

In addition to reducing fuel consumption and thus CO ₂ emissions, reducing gaseous emissions CO, NOx and HC by means of one or more catalytic converters and reducing particulate emissions with the aid of particle filters is an essential development goal.

Particle filters, often also referred to as soot filters, have been in use for diesel internal combustion engines for a long time and have proven themselves in practice.

Furthermore, it is already known that particles are also formed in the exhaust tract of a gasoline-powered internal combustion engine, in particular in internal combustion engines with direct fuel injection, in which the fuel is introduced directly into the combustion chambers at high pressures and is very finely atomized. For this reason, the legislator is also increasing the limit values for particle emissions from gasoline-powered internal combustion engines that are operated with direct fuel injection. With the introduction of the Euro 6d pollutant standard, the then applicable limit value of a maximum of 6 × 10 ¹¹ particles / km must be complied with.

The particle filters used for this purpose essentially consist of a housing (the so-called can) and a monolith inserted into the housing. This filters most of the particles produced during combustion, mostly soot particles, out of the exhaust gas. The separated particles remain in the particle filter, provided that the conditions present in the particle filter, for example increased temperature, oxygen in the exhaust gas, do not lead to regeneration of the particle filter.

For the regeneration of a coated particle filter, temperatures above 550-600 ° C are required. The higher the temperature, the faster the oxidation of the soot takes place.

It is already known to arrange the particle filter close to the engine or in the underbody of a motor vehicle. In the case of an underbody arrangement of the particle filter, the particle filter is arranged, for example, about 800 mm further away from the engine compared to a particle filter arranged close to the engine. One consequence is that in the case of an underbody arrangement of the particle filter in the particle filter, exhaust gas temperatures are approximately 140 ° C. lower than in the case of a particle filter arranged close to the engine.

For this reason, if the particulate filter had an underbody arrangement, the required particulate filter regeneration temperature could only be achieved without heating measures in the exhaust tract in an "Extra High Phase" of the WLTP (Worldwide Harmonized Light Vehicles Test Procedure), in which a comparatively high driving speed is present. If the vehicle is driven for a long time at low speed, the required particle filter regeneration temperature of 600 ° C cannot be achieved.

In order to avoid these disadvantages, the applicant has developed a system in which secondary air is blown into the exhaust gas tract upstream of a coated particle filter and the energy for heating the particle filter from the unburned components CO and HC is provided by a rich engine operation. The algorithm used here calculates the air ratio that is required for heating the particle filter as a function of the exhaust gas temperature upstream of the particle filter. The secondary air source is set in such a way that the air ratio downstream of the particle filter is in the lean range in order to ensure soot oxidation in the particle filter. With this system, particle filter temperatures of around 800 ° C can be reached even when idling, which is well above the minimum temperature required for particle filter regeneration.

If the particulate filter is arranged remote from the engine and the exhaust system has a high level of thermal inertia up to the underbody particulate filter, the temperature required for regeneration of the particulate filter cannot be reached at a late ignition point for the low-speed range without sacrificing comfort. Since the heating measures have to be much stronger than those required to quickly reach the light-off temperature of a particle filter close to the engine, a limiting factor is the misfire detection in the engine control. The particle filter regeneration temperature for an underbody arrangement of the particle filter is only reached without heating measures through acceleration in the high speed range.

Because of the energy required to heat up the particle filter through substoichiometric operation, there is an additional fuel consumption of 10% during the regeneration of the particle filter. Since only the particle filter is heated up and the thermal mass of the exhaust gas turbocharger of the motor vehicle and the catalytic converter close to the engine play no role, the additional fuel consumption is minimized during the regeneration. In the case of catalyst heating by retarding the ignition timing and lean operation to regenerate the particle filter, there is an increase in consumption of 33% without the temperature required for regeneration being reached. In addition, nitrogen oxide conversion of the catalytic converter is deactivated by the lean engine operation, which results in a massive increase in nitrogen oxide emissions.

If the particulate filter is regenerated with secondary air heating, there is an increase in nitrogen oxide emissions. When the internal combustion engine is operating below stoichiometric levels, Pt / Rh catalysts form NH ₃ , which is oxidized again to nitrogen oxide in the Pt / Rh-coated particle filter when there is excess oxygen, so that an undesirable increase in nitrogen oxide occurs during regeneration.

The object of the present invention consists in specifying a method and a device with which a coated particle filter of an internal combustion engine can be regenerated in a reliable manner without increased pollutant emissions occurring.

This object is achieved by a method with the features specified in claim 1. Advantageous refinements and developments are specified in the dependent claims 2-16. Claim 17 relates to a device for the regeneration of a coated particle filter in the exhaust gas tract of a gasoline-powered motor vehicle.

In a method with the features specified in claim 1, for the regeneration of a coated particulate filter in the exhaust gas tract of a gasoline-powered, regulation of a secondary air quantity directed into the exhaust gas tract is carried out, in which an actual value for the regulation is provided by a sensor arranged downstream of the particle filter and in which the Control is carried out in such a way that the air ratio present downstream of the particle filter oscillates around the stoichiometric air ratio (λ = 1).

According to one embodiment of the invention, the actual value is provided by a nitrogen oxide sensor arranged downstream of the particle filter.

According to a further embodiment of the invention, the actual value is provided by a lambda sensor arranged downstream of the particle filter.

According to a further embodiment of the invention, the actual value is provided by an ammonia sensor arranged downstream of the particle filter.

According to one embodiment of the invention, the amount of secondary air is increased when a change in the lambda value in the direction of rich is detected.

According to one embodiment of the invention, the amount of secondary air is increased when an increase in the ammonia content in the exhaust gas is detected.

According to one embodiment of the invention, the amount of secondary air is increased if a calculated negative amount of oxygen dioxide, which was withdrawn from the particle filter during a phase in which the secondary air injection was switched off, falls below a predetermined threshold value.

According to one embodiment of the invention, the amount of secondary air is reduced when a change in the lambda value in the direction of lean is detected.

According to one embodiment of the invention, the amount of secondary air is reduced when an increase in nitrogen oxide emissions is detected.

According to one embodiment of the invention, the amount of secondary air is reduced when a calculated amount of oxygen dioxide, which is present during a phase with active secondary air injection, exceeds a predetermined threshold value.

According to one embodiment of the invention, the respectively required amount of secondary air is provided by a secondary air source.

According to one embodiment of the invention, the secondary air source is an air pump.

According to one embodiment of the invention, the secondary air source is a scavenging air pump.

According to one embodiment of the invention, the respectively required amount of secondary air is set by changing the speed of the air pump.

According to one embodiment of the invention, the required amount of secondary air is provided by an e-compressor.

According to one embodiment of the invention, the respectively required amount of secondary air is provided by clocking a secondary air valve or a variable opening cross section of a secondary air valve.

The advantages of the invention are in particular that it enables the particulate filter to be regenerated even at low driving speeds without any loss of driveability. Another advantage of the invention is that the pollutant emissions that occur are kept small, in particular the nitrogen oxide emissions. Further advantageous properties of the invention emerge from the following exemplary explanation based on the figures

• 1 eine Skizze einer Vorrichtung zur Regeneration eines beschichteten Partikelfilters im Abgastrakt eines benzinbetriebenen Kraftfahrzeugs,
• 2 eine schematische Darstellung eines Teils eines Abgastrakts eines benzinbetriebenen Kraftfahrzeugs,
• 3 ein erstes Diagramm zur Veranschaulichung eines Verfahrens zur Regenerierung eines Partikelfilters und
• 4 ein zweites Diagramm zur Veranschaulichung eines Verfahrens zur Regenerierung eines Partikelfilters.

It shows

• 1 a sketch of a device for the regeneration of a coated particle filter in the exhaust tract of a gasoline-powered motor vehicle,
• 2 a schematic representation of part of an exhaust tract of a gasoline-powered motor vehicle,
• 3 a first diagram to illustrate a method for regenerating a particulate filter and
• 4th a second diagram to illustrate a method for regenerating a particulate filter.

The 1 shows a sketch of a device for the regeneration of a coated particle filter in the exhaust tract of a gasoline-powered motor vehicle.

To the one in the 1 The device shown includes one with a fuel tank 5 connected activated charcoal canister 1 . This activated charcoal canister 1 is via an air filter 8th Fresh air supplied. Furthermore, there is the activated charcoal canister 1 via a purge air pump 2 to a tank ventilation valve 4th connected. In the line between the purge air pump 2 and the tank vent valve 4th is a pressure sensor 3 positioned.

The one through the tank vent valve 4th flowing mass flow is upstream of a compressor 10 in the air path 9 of the motor vehicle and mixed there with fresh air to be compressed, the air path 9 via another air filter 7th is fed.

The compressor 10 is part of an exhaust gas turbocharger, to which a turbine is added 17th heard that with the compressor 10 is connected via a shaft indicated by a dashed line.

The by means of the compressor 10 compressed mass flow to which the air filter 7th provided fresh air flow and that through the tank ventilation valve 4th Flowing mass flow belong, is in the further course of the air path 9 via a charge air cooler 11 and a throttle 13 the crankcase 15th of the motor vehicle and injected there together with fuel into the combustion chambers of the motor vehicle.

Between the intercooler 11 and the throttle 13 is in the air path 9 a pressure sensor 12 intended. Between the throttle 13 and the crankcase 15th is in the air path 9 another pressure sensor 14th intended. The exhaust gas formed during the combustion process is passed through an exhaust system 16 the turbine 17th and is used in the turbine to drive the turbine wheel, which drives the compressor wheel provided in the compressor via the shaft. That from the turbine 17th Exhaust gas is output via a three-way catalyst 18th and a four-way catalyst 19th , which has a particle filter, is fed to an exhaust tailpipe (not shown) of the motor vehicle and output via this to the environment.

An engine controller is used to control the combustion process 6th provided based on the input signals supplied to it 20th and a stored working software output signals 21st provides. With the engine control 6th applied input signals 20th it is in particular sensor signals and data signals provided by a higher-level controller. The sensor signals include, for example, pressure sensor signals, temperature sensor signals and accelerator pedal position signals. To the output signals 21st the engine control 6th include in particular control signals for the injection valves and the tank ventilation valve 4th .

Furthermore, the 1 Device shown a secondary air path 29 based on the purge air pump 2 via a secondary air valve 24 upstream of the four-way catalyst 19th leads into the exhaust tract. Consequently, in this exemplary embodiment, the scavenging air pump serves as the secondary air source. Downstream of the turbine 17th several sensors are provided in the exhaust tract. These sensors include a differential pressure sensor 22nd , wherein one of the connections of the differential pressure sensor is connected upstream of the four-way catalytic converter and the other connection of the differential pressure sensor is connected to the exhaust tract downstream of the four-way catalytic converter. To the The sensors mentioned also include a control sensor 25th , the downstream of the four-way catalyst 19th in the exhaust tract 16 is arranged. The output signals of the sensors mentioned are used by the engine control 6th as input signals 20th fed. The engine control 6th calculates its output signals according to stored algorithms 21st which are fed as control signals to the actuators of the device shown.

These actuators include the scavenging air pump 2 and the secondary air valve 24 by the engine control 6th with respective control signals are applied, based on which a regulation of the in the exhaust tract 16 conducted secondary air takes place.

A regulation of the in the exhaust tract 16 Secondary air conducted is carried out in particular during a regeneration of a coated particle filter arranged in the exhaust tract, which is part of the four-way catalytic converter 19th is. To carry out this regeneration of the particulate filter is in the engine control 6th a control algorithm is stored which, through an evaluation of the output signals of the downstream of the four-way catalytic converter, which form an actual value for the control 19th arranged control sensor 25th carries out a regulation in such a way that the air ratio λ present downstream of the four-way catalytic converter and thus downstream of the particle filter oscillates around the stoichiometric air ratio λ = 1.

With the control sensor arranged downstream of the particle filter 25th It can be a nitrogen oxide sensor, a lambda sensor or an ammonia sensor, whereby each of these sensors can also be a combination sensor which, for example, performs both the function of a nitrogen oxide sensor and the function of an ammonia sensor or both the function of a lambda sensor and the function of an ammonia sensor exercises.

About the aforementioned oscillation of the air ratio around its stoichiometric value 1 To achieve this, the amount of secondary air is increased, for example, if a change in the lambda value in the rich direction is detected or if an increase in the ammonia content in the exhaust gas is detected. Alternatively, there is also the possibility of increasing the amount of secondary air if a calculated negative amount of oxygen dioxide, which was withdrawn from the particle filter during a phase with secondary air injection or reduced amount of secondary air, falls below a predetermined threshold value.

About the aforementioned oscillation of the air ratio around its stoichiometric value 1 To achieve this, the amount of secondary air is reduced if a change in the lambda value towards lean is detected or an increase in nitrogen oxide emissions is detected or a calculated amount of oxygen dioxide, which is present during a phase with active secondary air injection, exceeds a predetermined threshold value.

With the 1 The described embodiment is the scavenging air pump as the secondary air source 2 used. This consequently has a double function. On the one hand, it supports the venting process of the fuel tank 5 . On the other hand, it serves as a secondary air source for the regeneration of the particle filter.

As an alternative to the one in the 1 An electrically operated air pump can also be used as the secondary air source.

An introduction of the required amount of secondary air into the exhaust tract can be achieved by a suitable setting or change in the speed of the air pump and / or by a suitable setting or change in the passage cross section of the secondary air valve 24 .

An alternative option is to provide the required amount of secondary air using an e-compressor.

The 2 shows a schematic representation of part of an exhaust tract of a gasoline-powered internal combustion engine, from which the basic mode of operation of the invention can be seen. This representation shows that in the exhaust tract 16 of the motor vehicle a three-way catalytic converter 18th and downstream of this three-way catalyst 18th a four-way catalyst 19th are arranged, this four-way catalyst containing a coated particulate filter with a three-way catalyst coating. Furthermore, from the 2 show that by means of a secondary air source 28 secondary air provided via a secondary air path 29 , in which a secondary air valve 23 is arranged in the exhaust tract 16 is conducted, namely in the area between the three-way catalyst 18th and the four-way catalyst 19th , ie upstream of the particulate filter. Finally from the 2 can be seen that downstream of the four-way catalyst 19th and thus a control sensor downstream of the particle filter 25th is arranged. The output signal of this control sensor 25th serves as an actual value for regulating the air ratio λ, which is carried out in such a way that the air ratio λ present downstream of the particle filter oscillates around the stoichiometric air ratio λ = 1.

The temperature in the four-way catalytic converter, which is a coated particulate filter with a three-way catalytic converter coating, becomes controlled by a model in which the enrichment upstream of the four-way catalytic converter is calculated in such a way that the target temperature for the particulate filter regeneration is reached.

The 3 shows a first diagram to illustrate the above-described method according to the invention for regenerating a particle filter. In this diagram, the time t in s is plotted to the right and the courses of the nitrogen oxide emissions NOx in mg / km, the temperature T in ° C, the carbon dioxide emission CO ₂ in g / km and the vehicle speed v in km / h are plotted upwards, and although for the case of a regeneration of the particle filter with a lean air number λ and delayed ignition point (curves a), a conventional regeneration of the particle filter with injection of secondary air (curves b), a regeneration of the particle filter according to the invention with injection of secondary air (curves c) and the case no regeneration of the particle filter (curves d). In particular, it can be seen from the curves shown that with a regeneration of the particle filter according to the invention, the high temperature required for the regeneration is reached after a short time, that this high temperature is reached despite a relatively low driving speed and that the nitrogen oxide emissions compared to a conventional regeneration with Injection of secondary air is significantly reduced.

The 4th shows a second diagram to illustrate the above-described method according to the invention for regenerating a particulate filter. In this diagram, to the right are the time t in s and to the top are the curves of lλ TWC (this is the air ratio with which the combustion engine must be operated in order to reach the regeneration temperature in the four-way catalytic converter, measured with a linear lambda sensor), lλ GPF (this is the linear lambda probe signal of a NOx sensor or an additionally arranged linear lambda sensor after the four-way catalytic converter), bλ GPF (this is the binary signal of a NOx sensor or a binary lambda probe after the four-way catalytic converter) and FI (FI is the amount of secondary air which is before the Four-way catalytic converter is blown in) applied in l / min, specifically for a conventional regeneration with injection of secondary air (curves b) and a regeneration according to the invention with injection of secondary air (curves c). From these curves it can be seen in particular that the air ratio λ oscillates during the regeneration according to the invention

In the present invention - as can be seen from the above description - the secondary air quantity is determined as actual values using the output signals of a control sensor arranged downstream of the particle filter. In particular, the output signals of a nitrogen oxide sensor, a binary lambda sensor, a linear lambda probe or an ammonia sensor can be used as actual values.

• - einer Veränderung des binären Lambdasignals in Richtung fett;
• - einer Veränderung des linearen Lambdasignals in Richtung fett;
• - einem Anstieg der Ammoniakemissionen;
• - einer berechneten negativen Sauerstoffdioxidmenge, welche während der Phase mit abgeschalteter Sekundärlufteinblasung dem Partikelfilter entzogen wurde, wenn diese einen vorgegebenen Schwellwert unterschreitet.

The secondary air injection can be switched on according to one or more of the following criteria:

• - a change in the binary lambda signal in the rich direction;
• - a change in the linear lambda signal in the rich direction;
• - an increase in ammonia emissions;
• - a calculated negative amount of oxygen dioxide, which was withdrawn from the particle filter during the phase with the secondary air injection switched off, if this falls below a predetermined threshold value.

• - einer Veränderung des binären Lambdasignals in Richtung mager;
• - einer Veränderung des linearen Lambdasignals in Richtung mager;
• - einem Anstieg der Ammoniakemissionen;
• - einer berechneten Sauerstoffdioxidmenge, welche während der Phase mit aktiver Sekundärlufteinblasung dem Partikelfilter zugeführt wurde, wenn diese einen vorgegebenen Schwellwert überschreitet.

Switching off the secondary air injection or reducing the amount of secondary air can be done variably based on one or more of the following criteria:

• - A change in the binary lambda signal in the direction of lean;
• a change in the linear lambda signal in the lean direction;
• - an increase in ammonia emissions;
• - A calculated amount of oxygen dioxide which was fed to the particle filter during the phase with active secondary air injection when this exceeds a predetermined threshold value.

The amount of secondary air required in each case can be adjusted by changing the speed of a scavenging air pump used as a secondary air source. This has a positive effect on low carbon monoxide and ammonia emissions.

Alternatively, the required amount of secondary air can be provided by clocking a secondary air valve, i. E. by opening and closing the secondary air valve, to which secondary air supplied by a scavenging air pump is supplied, in such a way that an air ratio oscillating around the stoichiometric air ratio is present downstream of the particle filter. In this case, however, the disadvantage would have to be accepted that higher carbon monoxide and ammonia emissions occur compared to regulating the amount of secondary air by changing the speed of the scavenging air pump or changing the cross section of the secondary air valve.

In the invention described above, after all of this, the air ratio for a coated particle filter is regulated, in which the amount of secondary air blown into the exhaust tract is regulated using a control sensor arranged downstream of the particle filter, and the amount of fuel is not regulated, as is the case with conventional air ratio control for a three-way catalyst is made.

The amount of fuel (lambda of the internal combustion engine) is used as a manipulated variable for a temperature model of the particle filter.

List of reference symbols

1

Activated charcoal canister

2

Irrigation pump

3

Pressure sensor

4th

Tank vent valve

5

Fuel tank

6

Engine control

7th

Air filter

8th

Air filter

9

Air path

10

compressor

11

Intercooler

12th

Pressure sensor

13

throttle

14th

Pressure sensor

15th

Crankcase

16

Exhaust tract

17th

turbine

18th

Three-way catalytic converter

19th

Particle filter

20th

Input signals

21st

Output signals

22nd

Differential pressure sensor

23

Secondary air valve

24

Secondary air valve

25th

Control sensor

26th

Valve

27

Pressure and temperature sensor

28

Secondary air source

29

Secondary air path

Claims (17)

Method for the regeneration of a coated particle filter arranged in the exhaust gas tract of a gasoline-powered motor vehicle, characterized in that a regulation of an amount of secondary air directed into the exhaust gas tract (16) is carried out, in which an actual value for the control is carried out by a control sensor (25) arranged downstream of the particle filter (19) ) is provided and in which the regulation is carried out in such a way that the air ratio present downstream of the particle filter (19) oscillates around the stoichiometric air ratio. Procedure according to Claim 1 , characterized in that the actual value is provided by a nitrogen oxide sensor arranged downstream of the particle filter. Procedure according to Claim 1 , characterized in that the actual value is provided by a lambda sensor arranged downstream of the particle filter. Procedure according to Claim 1 , characterized in that the actual value is provided by an ammonia sensor arranged downstream of the particle filter. Method according to one of the Claims 1 - 3 , characterized in that the amount of secondary air is increased when a change in the lambda value in the rich direction is detected. Procedure according to Claim 4 , characterized in that the amount of secondary air is increased when an increase in the ammonia content in the exhaust gas is detected. Method according to one of the Claims 1 - 3 , characterized in that the amount of secondary air is increased when a calculated negative amount of oxygen dioxide, which was withdrawn from the particle filter during a phase in which the secondary air injection was switched off, falls below a predetermined threshold value. Method according to one of the preceding claims, characterized in that the amount of secondary air is reduced when a change in the lambda value in the direction of lean is detected. Method according to one of the Claims 1 - 7th , characterized in that the amount of secondary air is reduced when an increase in nitrogen oxide emissions is detected. Method according to one of the Claims 1 - 7th , characterized in that the amount of secondary air is reduced when a calculated The amount of oxygen dioxide that is present during a phase with active secondary air injection exceeds a predetermined threshold value. Method according to one of the preceding claims, characterized in that the respectively required amount of secondary air is provided by a secondary air source (2). Procedure according to Claim 11 , characterized in that the secondary air source is an air pump. Procedure according to Claim 12 , characterized in that the secondary air source is a purge air pump. Procedure according to Claim 12 or 13 , characterized in that the required amount of secondary air is set by changing the speed of the air pump. Method according to one of the Claims 1 - 10 , characterized in that the required amount of secondary air is provided by an e-compressor. Method according to one of the Claims 1 - 10 , characterized in that the respectively required amount of secondary air is provided by clocking a secondary air valve (24) or a variable opening cross-section of the secondary air valve (24). Device for regeneration of a coated particle filter arranged in the exhaust tract of a gasoline-powered motor vehicle, characterized in that it has an engine control (6) which is designed to control a method according to one of the preceding claims.

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