U.S. patent application number 15/635334 was filed with the patent office on 2017-12-28 for method and device for controlling and/or monitoring the function of a secondary air supply in an emission control system.
The applicant listed for this patent is Robert Bosch GmbH. Invention is credited to Matthias Blei, Michael Fey, Frank Meier, Michael Pfeil.
Application Number | 20170370264 15/635334 |
Document ID | / |
Family ID | 60579342 |
Filed Date | 2017-12-28 |
United States Patent
Application |
20170370264 |
Kind Code |
A1 |
Meier; Frank ; et
al. |
December 28, 2017 |
METHOD AND DEVICE FOR CONTROLLING AND/OR MONITORING THE FUNCTION OF
A SECONDARY AIR SUPPLY IN AN EMISSION CONTROL SYSTEM
Abstract
In a method and device for controlling and/or monitoring the
function of a secondary air supply in an emission control system of
an internal combustion engine, the emission control system includes
at least two catalytic converters situated in succession in an
exhaust duct, it being possible for the second catalytic converter
to be implemented as a combination of catalytic converter and
particulate filter. For a secondary air diagnosis and for secondary
air control, a two-point lambda probe is situated, with respect to
a direction of flow of exhaust gas, downstream of the first
catalytic converter. Measures are applied for compensating
tolerance and aging effects of the two-point lambda probe. This
results in particular in cost advantages in emission control
systems for fulfilling stricter emission requirements. In
particular, this makes it possible to operate the particulate
filter in optimized fashion.
Inventors: |
Meier; Frank; (Stuttgart,
DE) ; Blei; Matthias; (Ilsfeld, DE) ; Fey;
Michael; (Wiernsheim, DE) ; Pfeil; Michael;
(Marbach Am Neckar, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch GmbH |
Stuttgart |
|
DE |
|
|
Family ID: |
60579342 |
Appl. No.: |
15/635334 |
Filed: |
June 28, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02T 10/40 20130101;
F01N 11/007 20130101; F01N 3/30 20130101; F01N 2900/1804 20130101;
F01N 9/00 20130101; F01N 3/021 20130101; F01N 3/22 20130101; F01N
2560/025 20130101; F01N 2560/12 20130101; F01N 2560/14 20130101;
F01N 2900/08 20130101; F01N 3/035 20130101; Y02T 10/47 20130101;
F01N 11/00 20130101; F01N 2550/14 20130101; F01N 13/009 20140601;
F01N 2900/1402 20130101; F01N 2900/1602 20130101 |
International
Class: |
F01N 3/30 20060101
F01N003/30; F01N 11/00 20060101 F01N011/00; F01N 13/00 20100101
F01N013/00; F01N 3/021 20060101 F01N003/021 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2016 |
DE |
102016211595.2 |
Claims
1. A method for at least one of controlling and monitoring a
function of a secondary air supply in an emission control system of
an internal combustion engine, the emission control system, in its
central section, including a first catalytic converter and a second
catalytic converter situated in an exhaust duct in succession, a
first lambda probe being situated, with respect to a direction of
flow of exhaust gas, downstream of an engine block and upstream of
the first catalytic converter, an exhaust gas probe being situated
upstream of the second catalytic converter, air being introducible
between the first and second catalytic converters by the secondary
air supply for an optimized operation of the second catalytic
converter, wherein a two-point lambda probe is situated downstream
of the first catalytic converter and of the secondary air supply,
the method comprising: using the two-point lambda probe for at
least one of a secondary air diagnosis and a secondary air control;
and applying to the two-point lambda probe measures that compensate
tolerance and aging effects.
2. The method of claim 1, wherein: at least one particulate filter
is situated downstream of the first catalytic converter and the
secondary air supply or is part of the second catalytic converter;
and the at least one of the secondary air diagnosis and the
secondary air control is performed using the secondary air supply
and the two-point lambda probe for the a least one particulate
filter.
3. The method of claim 1, wherein the applying of the measures
includes adapting an offset of a probe characteristic of the
two-point lambda probe by an adjustment at high excess air while
the internal combustion engine is running or is at a
standstill.
4. The method of claim 3, wherein the applying of the measures
includes applying a correction of a temperature-related shift of
the probe characteristic with the aid of an active measurement of a
sensor element temperature while the internal combustion engine is
running or is at a standstill.
5. The method of claim 3, wherein the applying of the measures
further includes applying a correction of a calculation of a lambda
value, thereby taking into account a current exhaust-gas
composition and a varying cross sensitivity vis-a-vis different
exhaust-gas components.
6. The method of claim 1, wherein the applying of the measures
includes shifting a lambda-one point of a probe characteristic of
the two-point lambda probe via a tracking control of the second
two-point lambda probe.
7. The method of claim 6, wherein the applying of the measures
includes applying a correction of a temperature-related shift of
the probe characteristic with the aid of an active measurement of a
sensor element temperature while the internal combustion engine is
running or is at a standstill.
8. The method of claim 1, wherein the applying of the measures
includes: adapting an offset of a probe characteristic of the
two-point lambda probe by an adjustment at high excess air while
the internal combustion engine is running or is at a standstill;
shifting a lambda-one point of the probe characteristic via a
tracking control of the second two-point lambda probe; applying a
correction of a temperature-related shift of the probe
characteristic with the aid of an active measurement of a sensor
element temperature while the internal combustion engine is running
or is at a standstill; and applying a correction of a calculation
of a lambda value, thereby taking into account a current
exhaust-gas composition and a varying cross sensitivity vis-a-vis
different exhaust-gas components.
9. The method of claim 1, wherein the internal combustion engine is
part of a vehicle.
10. An emission control system of an internal combustion engine,
the emission control system comprising: an engine control unit that
includes a least one of a storage device and a comparator unit; and
in a central section of the emission control system: a first
catalytic converter situated in an exhaust duct; a second catalytic
converter situated in the exhaust duct in sequence with the first
catalytic converter; a lambda probe that is situated, with respect
to a direction of flow of exhaust gas, downstream of an engine
block and upstream of the first catalytic converter and that is
configured to supply signals to the engine control unit; an
exhaust-gas probe that is downstream of the first catalytic
converter and of the second catalytic converter; a secondary air
supply configured to introduce air between the first and second
catalytic converters for optimized operation of the second
catalytic converter; and a two-point lambda probe that is situated
downstream of the first catalytic converter and of the secondary
air supply and is configured to supply signals to the engine
control unit; wherein the engine control unit is configured to:
perform a catalytic converter diagnosis; use the signals from the
two-point lambda probe to perform at least one of a secondary air
diagnosis and a secondary air control of the secondary air supply;
and apply to the two-point lambda probe measures that compensate
tolerance and aging effects of the two-point lambda probe.
11. The device of claim 10, wherein at least one of the emission
control system further comprises a particulate filter downstream of
the first catalytic converter and of the secondary air supply.
12. The device of claim 10, wherein the second catalytic converter
includes a particulate filter.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C.
.sctn.119 to DE 10 2016 211 595.2, filed in the Federal Republic of
Germany on Jun. 28, 2016, the content of which is hereby
incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for controlling
and/or monitoring the function of a secondary air supply in an
emission control system of an internal combustion engine, which in
its central section includes at least two catalytic converters
situated in succession in an exhaust duct, it being possible for
additional exhaust gas-purifying components to be situated upstream
or downstream from this central section, a lambda probe being
situated, with respect to the direction of flow of the exhaust gas,
downstream of an engine block and upstream of the first catalytic
converter, and an additional exhaust gas probe being situated
upstream from an additional catalytic converter, air being
introduced between the first and the additional catalytic converter
by the secondary air supply for the optimized operation of the
additional catalytic converter. The present invention furthermore
relates to a device, in particular an engine control unit, for
implementing the method.
BACKGROUND
[0003] In today's engine control systems, lambda probes are used
for detecting the concentration of oxygen in the exhaust gas and
for the lambda control of the engine. Wide-band lambda probes and
two-point lambda probes are used for this purpose.
[0004] A wide-band lambda probe makes it possible to control the
exhaust-gas lambda continuously in a broad lambda range. By a
linearization of the probe characteristic, a continuous lambda
control is also possible using a more cost-effective two-point
lambda probe, even if in a limited lambda range.
[0005] Compared to a wide-band lambda probe, a two-point lambda
probe has a significantly higher accuracy in a narrow range around
lambda=1 due to its stepwise probe characteristic. Outside of this
narrow range, at rich or lean lambda, the accuracy of a two-point
lambda probe is normally less than that of a wide-band lambda probe
due to tolerance and aging effects.
[0006] Normally, for this reason, wide-band lambda probes are used
in engine control systems where rich or lean lambda values are to
measured accurately or where a measurement in the range around
lambda=1 with limited accuracy is sufficient. Two-point lambda
probes are used where the exhaust-gas lambda in the range around
lambda=1 is to be measured with great accuracy.
[0007] Typical applications for a wide-band lambda probe are the
lambda control upstream from the catalytic converter and the
balancing of the oxygen input and discharge in the diagnosis of the
catalytic converter. Typical applications of a two-point lambda
probe are the very accurate lambda=1 control downstream from the
catalytic converter and the detection of the breakthrough of rich
or lean exhaust gas in the diagnosis of the catalytic
converter.
[0008] A typical exhaust system of a gasoline system for today's
strict emission and diagnostic requirements, e.g., in so-called
"super ultra-low emission vehicles" (SULEV), is made up of a
wide-band lambda probe, a first three-way catalytic converter, a
two-point lambda probe, and a second non-monitored three-way
catalytic converter.
[0009] Even stricter future emission and diagnostic requirements
(e.g., probably China 6) require exhaust systems, in which not only
the second catalytic converter is also monitored, but in which also
the particulate quantity in the exhaust gas is limited. The second
three-way catalytic converter must therefore be combined with a
particulate filter or must be replaced by a coated particulate
filter, which is also called a four-way catalytic converter.
[0010] For an optimized operation of the particulate filter, in
particular with respect to reaching the operating temperature
quickly and with respect to the regeneration, an introduction of
secondary air upstream from the particulate filter may become
necessary. This also applies to other components of the emission
control system (e.g., NCS or SCR catalytic converter).
[0011] Such a secondary air introduction is known, for example,
from DE 102009043087 A1. It describes an internal combustion
engine, in particular a diesel engine, having a catalytic converter
and a particulate filter in its exhaust system, at least one
secondary air line for supplying secondary air into the exhaust
system being developed and situated in such a way that the
secondary air line discharges into the exhaust system downstream
from the catalytic converter and upstream from the particulate
filter, at least one secondary air line being developed and
situated in such a way that it branches off from a combustion-air
system. For regenerating the particulate filter, the quantity of
the secondary air introduced into the exhaust system is selected in
such a way that a lambda value for the air-fuel ratio in the
particulate filter .lamda..sub.DPF has a value of
1<.lamda..sub.DPF<x, where 1.4.gtoreq.x.gtoreq.1, in
particular 1.4.gtoreq.x.gtoreq.1.05. This ensures that the
regeneration occurs reliably, without an exhaust gas temperature in
the particulate filter falling below 600.degree. C.
[0012] From the perspective of an optimized operating strategy of
the particulate filter, it seems expedient to use a wide-band
lambda probe instead of a two-point lambda probe for controlling
the introduced secondary air quantity upstream from the secondary
air supply and the particulate filter.
[0013] In this connection, currently discussed (and in principle
also known from DE 102013226083 A1) are exhaust systems with the
following arrangement in the direction of flow of the exhaust gas
in the exhaust duct behind the engine block: a first wide-band
lambda probe, a first catalytic converter (implemented as a
three-way catalytic converter), a second wide-band lambda probe, a
second catalytic converter including a particulate filter
(implemented e.g., as a coated particulate filter), and a two-point
lambda probe.
[0014] The first wide-band lambda probe is used for the lambda
control as well as for balancing for the diagnosis of the first
catalytic converter. The second wide-band lambda probe is used for
tracking control and for breakthrough detection in the diagnosis of
the first catalytic converter as well as for the balancing for the
diagnosis of the second catalytic converter. In addition, there is
the task of controlling the introduction of secondary air. The
two-point lambda probe downstream from the second catalytic
converter that includes the particulate filter is used for
breakthrough detection for diagnosing the second catalytic
converter. In this system, however, the second wide-band lambda
probe has functional disadvantages vis-a-vis a two-point lambda
probe in this installation position. These are on the one hand a
lower accuracy of the tracking control in the range around lambda=1
and on the other hand a poorer suitability for detecting lambda
breakthroughs for the diagnosis of the first catalytic
converter.
SUMMARY
[0015] It is therefore an objective of the present invention to
provide a method that makes it possible to use a more
cost-effective two-point lambda probe in the direction of flow of
the exhaust gas behind the first catalytic converter, instead of a
second wide-band lambda probe, in an emission control system having
at least two catalytic converters and a particulate filter or a
first catalytic converter and a coated particulate filter as a
second catalytic converter in combination with a particulate filter
and including a secondary air supply downstream from the first
catalytic converter. This is to make possible a lambda control to a
setpoint value of .lamda.=1 and .lamda.>1 in active secondary
air operation in order to be able to operate the particulate filter
in optimized fashion. Additionally, using this two-point lambda
probe instead of a second wide-band lambda probe is also to allow
for a diagnosis of the secondary air pump or the secondary air
system. At the same time, a more accurate tracking control in the
range around .lamda.=1, a more accurate diagnosis of the first
catalytic converter and, if necessary, a sufficiently accurate
diagnosis of the second catalytic converter are to be achieved (see
also DE 10 2016 21 506.5, filed by the applicant in the Federal
Republic of Germany on Jun. 27, 2016, and U.S. patent application
Ser. No. 15/634,280, filed by the applicant on Jun. 27, 2017, the
contents of each of which are hereby incorporated by reference
herein in their entireties).
[0016] It is also an objective of the present invention to provide
a corresponding device for executing the method.
[0017] The objective with respect to the method is achieved in that
downstream from the first catalytic converter and the secondary air
supply, a two-point lambda probe is used for secondary air
diagnosis and/or for secondary air control and in that for this
two-point lambda probe, specific measures are used for compensating
tolerance and aging effects.
[0018] One variant of the method also provides that downstream from
the first catalytic converter and the secondary air supply at least
one particulate filter is situated or that the particulate filter
is part of the additional catalytic converter and that the
secondary air diagnosis and/or the secondary air control is/are
performed for the particulate filter using the secondary air supply
and the two-point lambda probe.
[0019] This makes it possible to provide a comparatively simple and
cost-effective emission control system. Normally, an engine control
unit for an exhaust-gas bank does not offer the possibility of
using it to operate a second wide-band lambda probe. On the other
hand, the possibility of operating a wide-band lambda probe and two
two-point lambda probes normally already exists such that no change
is required in the hardware of the control units. The use of a
two-point lambda probe for the lambda control with secondary air at
.lamda.=1 and at lean exhaust gas lambda (.lamda.>1)
presupposes, however, that there exists a definite correlation
between the probe voltage and the exhaust gas lambda. It is
important that this correlation be definite over the entire service
life of the probe since otherwise an erroneous lambda value is set,
which may result in an unnecessarily slow soot burn-off by an
unnecessarily slow heating of the particulate filter or in its
being damaged and in increased emissions. This precondition is
usually not fulfilled. Instead, the actual probe characteristic may
be shifted with respect to a reference probe characteristic by
tolerance and aging effects. For this reason, the application of
specific measures for compensating for tolerance and aging effects
is particularly important. With the aid of a lambda signal
corrected in this manner, a lambda control at an active secondary
air operation and a diagnosis of a secondary air pump or the
secondary air system are made possible with sufficiently high
accuracy.
[0020] The use of the first two-point lambda probe in this
installation position for balancing the storage capacity of oxygen
or rich gas of the second catalytic converter is described in DE 10
2016 21 506.5. The exhaust system according to the present
invention is better able to fulfill the requirements regarding the
accuracy of the tracking control and the diagnosis of the first
catalytic converter than the exhaust system mentioned at the
outset. In the exhaust system of the present invention, the
accuracy of the diagnosis of the second catalytic converter is
sufficient in order to allow for a reliable distinction between a
catalytic converter that is still in good condition and one that is
defective. The accuracy is likewise regarded as sufficient for the
lambda control with secondary air at lambda.noteq.1 as well as for
a diagnosis of the secondary air pump or the secondary air system.
The exhaust system of the present invention therefore makes
possible the fulfillment of stricter emission and diagnostic
requirements in a cost-effective manner.
[0021] This central section of the emission control system can be
part of a more complex emission control system, in which additional
exhaust gas-purifying components are installed upstream or
downstream from this central section. Thus, for example, the
following arrangements are conceivable: (a) wide-band lambda
probe/1st catalytic converter/wide-band lambda probe/2nd catalytic
converter/two-point lambda probe/3rd catalytic converter/two-point
lambda probe; (b) wide-band lambda probe/1st catalytic
converter/two-point lambda probe/2nd catalytic converter/NO.sub.x
catalyst/two-point lambda probe; or (c) wide-band lambda probe/1st
catalytic converter/two-point lambda probe/2nd catalytic
converter/wide-band lambda probe/3rd catalytic converter/two-point
lambda probe/4th catalytic converter/two-point lambda probe.
[0022] For the purpose of compensating for tolerance and aging
effects, a particularly preferred variant of the method provides
for an offset of the probe characteristic of the first two-point
lambda probe to be adapted by an adjustment at high excess air when
the internal combustion engine is running or is at a standstill.
This makes it possible to adapt a two-point lambda probe for the
above-mentioned measuring tasks in a particularly cost-effective
manner.
[0023] In order to increase the accuracy of the secondary air
diagnosis and/or the secondary air control, there can be a
provision that for adapting an offset, a compensation is performed
by shifting the lambda-one point of the probe characteristic of the
first two-point lambda probe via a tracking control of the second
two-point lambda probe.
[0024] An extended compensation of tolerance and aging effects can
be achieved if a correction of a temperature-related shift of the
probe characteristic is applied with the aid of an active
measurement of the sensor element temperature while the internal
combustion engine is running or is at a standstill.
[0025] Additionally, there can be a provision for applying a
correction of the calculation of the lambda value for adapting an
offset by taking into account a current exhaust-gas composition and
a varying cross sensitivity vis-a-vis different exhaust-gas
components.
[0026] Depending on the required accuracy, there can also be a
provision to use previously described corrective measures in
combination.
[0027] A particularly preferred application of the method with its
previously described method variants provides for its use for
vehicles having at least two successive catalytic converters in an
emission control system for adhering to particularly strict exhaust
gas guidelines. By applying the method of the present invention
with the method variants for compensating the tolerance and aging
effects, it is, in particular, possible to reduce the particulate
emission significantly since it is possible to operate the
particulate filter in an optimized range when introducing secondary
air.
[0028] The objective with respect to the device is achieved in that
for the secondary air diagnosis and/or for the secondary air
control, a first two-point lambda probe is situated downstream from
the first catalytic converter and the secondary air supply, and in
that an engine control unit is provided for carrying out the method
of the present invention, to which the signals of the various
lambda probes are supplied and which includes devices, such as
storage and/or comparator units, which in addition to a catalytic
converter diagnosis allow for a secondary air diagnosis and/or
secondary air control as well as measures for compensating
tolerance and aging effects of the first two-point lambda probe in
accordance with the previously described method variants. The
functionality of these functions can be implemented at least in
part on the basis of software, e.g., in the form of a control
software, it being possible for the control unit to be provided as
a separate unit or as part of a higher-order control unit.
[0029] To reduce the particulate emission, a particulate filter can
be situated downstream from the first catalytic converter and the
secondary air supply, or the particulate filter can be implemented
as part of the additional catalytic converter. These can be
implemented as catalytically coated particulate filters.
[0030] The present invention is explained in more detail below with
reference to an exemplary embodiment depicted in the FIGURE.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The FIGURE is a schematic representation of an internal
combustion engine having an emission control system by which the
method of the present invention may be implemented, according to an
example embodiment of the present invention.
DETAILED DESCRIPTION
[0032] The FIGURE shows in a schematic representation an internal
combustion engine 1 that includes an engine block 10, an exhaust
duct 20, a lambda probe 30 that is, with respect to the direction
of flow of exhaust gas, downstream of the engine block 10 and that
is, in an example embodiment, implemented as a wide-band lambda
probe, and a first catalytic converter 40 situated downstream of
the lambda probe 30. Lambda probe 30 makes possible lambda control
100 and is used for a first balancing 110 for diagnosing the
storage capacity of the first catalytic converter.
[0033] The internal combustion engine 1 further includes,
downstream from first catalytic converter 40, a first two-point
lambda probe 50 used for catalytic converter diagnosis-tracking
control and for breakthrough detection for the diagnosis of first
catalytic converter 40. The internal combustion engine 1 further
includes a second catalytic converter 60 downstream of the first
two-point lambda probe 50. The first two-point lambda probe 50 is
additionally used for a balancing of the storage capacity of the
second catalytic converter 60. The second catalytic converter 60
can be implemented as a combination block made up of the catalytic
converter and the particulate filter or as a coated particulate
filter. A separate particulate filter is also conceivable.
[0034] Downstream of the additional catalytic converter 60, the
internal combustion engine 1 further includes a second two-point
lambda probe 70 for breakthrough detection for the catalytic
converter diagnosis 140 of the additional catalytic converter 60.
Lambda probes 30, 50, and 70 are connected to an engine control
unit 80, in which on the one hand the lambda control and on the
other hand the diagnostic methods regarding the monitoring of the
operability of the emission control system are implemented in
hardware and/or software.
[0035] Additionally, a secondary air supply 90 into exhaust duct 20
is provided in this system between first catalytic converter 40 and
first two-point lambda probe 50. In an example embodiment, the
first two-point lambda probe 50 is used additionally for the
secondary air diagnosis as well as for the air supply control (in
the combination: tracking control/secondary air diagnosis 120 and
second balancing/secondary air control 130).
[0036] For quicker heating of catalytic converter 60 having the
particulate filter function to its operating temperature, an
exothermic reaction is brought about in the coated particulate
filter at a rich combustion chamber mixture by introducing
secondary air via the secondary air supply 90 upstream from the
particulate filter. In order to avoid unnecessary emissions, it is
important for an average exhaust gas lambda of at least 1 to be
maintained upstream from the particulate filter. At a sufficiently
high temperature of the particulate filter, a burn-off of the soot
charge and thus the regeneration of the particulate filter can be
achieved by excess oxygen. For this purpose, a defined lean exhaust
gas lambda is to be maintained upstream from the particulate
filter.
[0037] A lambda probe is then suitable as a probe upstream from the
coated particulate filter for adjusting the lambda in the event of
the introduction of secondary air and for a diagnosis of the
secondary air pump or the secondary air system if it has a
sufficiently accurate lambda signal in a broad lambda range
(typically at least between .lamda.=1 und .lamda.-1.2). A two-point
lambda probe 50, 70 does not fulfill this requirement without
additional measures.
[0038] This limitation applies also if the two-point lambda probe
50, as described in DE 10 2016 211 506.5, is to be used as a probe
upstream from the catalytic converter for adjusting the lambda
value in the rich preconditioning and for adjusting the lean lambda
value as well as for balancing the entered oxygen quantity when
measuring the oxygen storage capacity of the catalytic converter.
Here in particular a sufficiently accurate lambda signal is
required in a lambda range of typically between .lamda.=0.95 und
.lamda.=1.05.
[0039] The use of a first (as shown in the FIGURE) two-point lambda
probe 50 for the lambda control using secondary air or for its
diagnosis presupposes the compensation of tolerance and aging
effects, which result in a shift of the actual probe characteristic
vis-a-vis the reference probe characteristic stored in the control
unit or the engine control unit 80. Only then will the lambda
signal of this first two-point lambda probe 50 fulfill the
mentioned requirements regarding accuracy.
[0040] DE102012211687A1, DE102012211683A1, DE102013216595A1,
DE102014210442A1, and DE102012221549A1 describe methods that allow
for a compensation of tolerance and/or aging effects that result in
such a characteristic curve shift. The methods described there, one
or more of which, according to example embodiments of the present
invention, are applied to the first two-point lambda probe 50
individually or in combination, include: adaptation of a constant
offset of the probe characteristic by an adjustment at high excess
air while the engine is running or is at a standstill; compensation
of the shift of the lambda-one point of the probe characteristic
via a tracking control using the second two-point lambda probe 50;
compensation of a temperature-related shift of the probe
characteristic with the aid of an active measurement of the sensor
element temperature while the engine is running or is at a
standstill; and taking into account the current exhaust-gas
composition and different cross sensitivities of the probe
vis-a-vis various exhaust-gas components in the conversion of the
probe voltage into a lambda value.
[0041] In a particularly preferred variant of the method of the
present invention, only a constant offset of the probe
characteristic is adapted. This is possible to achieve in a
comparatively simple manner by an adjustment at high excess air,
such as occurs for example at an overrun fuel cutoff, and in many
cases already results in a sufficient accuracy of the lambda signal
so as to be able to use it for balancing the oxygen input and
discharge for diagnosing the catalytic converter 60. At the same
time, this adaptation improves the accuracy of the breakthrough
detection in the diagnosis of first catalytic converter 40 and the
accuracy of the tracking control 120 with the aid of the first
two-point lambda probe 50.
[0042] By combining the adaptation of a constant offset of the
probe characteristic with one or more of the above-mentioned
methods, it is possible to improve the accuracy of the lambda
signal of the first two-point lambda probe 50 downstream from first
catalytic converter 40 further, in the event that even higher
requirements are placed on the accuracy of this lambda signal.
[0043] Following the compensation, the lambda signal of the first
two-point lambda probe 50 is used, as described above, for the
lambda control using secondary air, in order to operate the
particulate filter in optimized fashion. In addition, a
corresponding diagnosis of a secondary air pump or of the secondary
air system can be performed.
[0044] It is possible to apply the method according to the present
invention analogously also to emission control systems that include
more than two monitored catalytic converters or coated particle
filters.
* * * * *