U.S. patent application number 12/296817 was filed with the patent office on 2010-01-14 for device for monitoring an exhaust gas catalytic converter for an internal combustion engine.
This patent application is currently assigned to DAIMLER CHRYSLER AG. Invention is credited to Berthold Keppeler, Aleksandar Knezevic, Markus Paule, Detlef Scharr.
Application Number | 20100005783 12/296817 |
Document ID | / |
Family ID | 38255380 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100005783 |
Kind Code |
A1 |
Keppeler; Berthold ; et
al. |
January 14, 2010 |
DEVICE FOR MONITORING AN EXHAUST GAS CATALYTIC CONVERTER FOR AN
INTERNAL COMBUSTION ENGINE
Abstract
A device for monitoring an exhaust gas catalytic converter in
the exhaust system of an internal combustion engine, includes a
measuring apparatus that is arranged in the exhaust system in such
a way that, in the greatest part of the operating range of the
internal combustion engine, it assumes a temperature that is
correlated with a temperature of the exhaust gas catalytic
converter. The measuring apparatus has a temperature-sensitive
component with a temperature-dependent characteristic component
parameter that changes either abruptly at a predetermined
transition temperature or temperature range, or continuously in a
predetermined way as a function of the temperature. A control and
evaluation unit connected to the measuring arrangement detects the
characteristic component parameter and/or a change in the latter,
and correlates it with an aging state of the exhaust gas catalytic
converter.
Inventors: |
Keppeler; Berthold; (Owen,
DE) ; Knezevic; Aleksandar; (Friedrichshafen, DE)
; Paule; Markus; (Korb, DE) ; Scharr; Detlef;
(Leutenbach, DE) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
DAIMLER CHRYSLER AG
STUTTGART
DE
|
Family ID: |
38255380 |
Appl. No.: |
12/296817 |
Filed: |
April 3, 2007 |
PCT Filed: |
April 3, 2007 |
PCT NO: |
PCT/EP2007/002989 |
371 Date: |
September 3, 2009 |
Current U.S.
Class: |
60/277 |
Current CPC
Class: |
F01N 2560/02 20130101;
F01N 11/002 20130101; F01N 3/106 20130101; Y02T 10/47 20130101;
Y02T 10/40 20130101 |
Class at
Publication: |
60/277 |
International
Class: |
F01N 11/00 20060101
F01N011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2006 |
DE |
10 2006 016 906.9 |
Claims
1.-9. (canceled)
10. A device for monitoring an exhaust gas catalytic converter in
the exhaust system of an internal combustion engine, said device
comprising: measuring apparatus arranged in the exhaust system such
that, in at least a predominant part of the operating range of the
internal combustion engine, it assumes a temperature that is
correlated with a temperature of the exhaust gas catalytic
converter; and a control evaluation unit that is coupled in
communication with the measuring apparatus; wherein the measuring
apparatus has a temperature-sensitive component with a temperature
dependent characteristic component parameter that changes either
abruptly at a predetermined transition temperature or temperature
range, or continuously in a predetermined way as a function of
temperature; and the control and evaluation unit can detect the
characteristic component parameter and/or a change in the
characteristic component parameter.
11. The device as claimed in claim 10, wherein the measuring
apparatus is fixedly connected to one of the exhaust gas catalytic
converter, and a housing in which the exhaust gas catalytic
converter is arranged.
12. The device as claimed in claim 10, wherein the change that
occurs in the characteristic component parameter is
irreversible.
13. The device as claimed in claim 10, wherein the change that
occurs in the characteristic component parameter comprises a
structural transformation of a material constituent of the
temperature-sensitive component.
14. The device as claimed in claim 10, wherein the
temperature-sensitive component of the measuring apparatus is a
passive electrical structural element.
15. The device as claimed in claim 10, wherein the
temperature-sensitive component is produced by thick-film
technology.
16. The device as claimed in claim 10, wherein the measuring
apparatus comprises a plurality of temperature-sensitive
components, and one of the following is true: individual
temperature-sensitive components differ from one another in terms
of the transition temperature or temperature range of their
characteristic component parameter; and individual
temperature-sensitive components have characteristic component
parameters that change in time in a different way, as a function of
the temperature.
17. The device as claimed in claim 10 wherein, the
temperature-sensitive component is designed in such a way that the
transition temperature or temperature range of its characteristic
component parameter is correlated with a permissible upper
operating temperature of the exhaust gas catalytic converter, or
the change in the characteristic component parameter which occurs
in the course of time is correlated with a parallel-running aging
of the exhaust gas catalytic converter.
Description
[0001] This application is a national stage of PCT Application No.
PCT/EP2007/002989, filed Apr. 3, 2007, which claims priority under
35 U.S.C. .sctn.119 to German Patent Application No. 10 2006 016
906.9, filed Apr. 11, 2006, the entire disclosure of which is
herein expressly incorporated by reference.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] The invention relates to a device for monitoring an exhaust
gas catalytic converter in the exhaust system of an internal
combustion engine. In particular, the invention relates to such a
monitoring device having a measuring arrangement which is disposed
in the exhaust system in such a way that, at least in the
predominant part of the operating range of the internal combustion
engine, it assumes a temperature correlated with a temperature of
the exhaust gas catalytic converter.
[0003] Exhaust gas catalytic converters may partially or completely
lose their effectiveness when they are exposed to high
temperatures. In this context, temperature loads have a
particularly pronounced effect on the effectiveness of a catalytic
converter at low temperatures, for example during a cold start of
the associated internal combustion engine. It is known, in this
respect, to monitor the temperature of the exhaust gas catalytic
converter in order to detect inadmissible peak temperatures, and to
evaluate catalytic converter damage caused as a result. In
addition, devices are known which can detect a reduction in the
action of a exhaust gas catalytic converter directly.
[0004] In German patent document DE 43 08 661 A1 the temperature of
the catalytic coating and/or of the structure of an exhaust gas
catalytic converter and also the temperature of the exhaust gas, is
determined upstream of the exhaust gas catalytic converter. Based
on the time derivatives of the temperatures and their difference, a
conclusion can be drawn as to the effectiveness of the exhaust gas
catalytic converter.
[0005] International patent document WO 96/01364 discloses a device
having a catalytically coated thermal conductivity sensor, which
makes it possible to establish whether heat-delivering catalytic
reactions are taking place to the intended extent. For example, an
age-induced diminution in the catalytic converter activity can be
determined in this manner.
[0006] It is known from German patent document DE 198 05 928 A1 to
determine a physical property of the coating of a gas-storing
catalytic converter and to determine the effectiveness of the
catalytic converter on the basis of this property.
[0007] The devices described above are aimed at detecting the
catalytic converter action which may be impaired, for example, by
inadmissibly high temperatures. However, the catalytic converter
action often cannot be determined with the desired reliability in
this way. Moreover, the corresponding monitoring methods and
devices for catalytic converter monitoring are often
complicated.
[0008] One object of the invention, therefore, is to provide a
device which reliably monitors an exhaust gas catalytic converter
in as simple a way as possible.
[0009] This and other objects and advantages are achieved by the
measuring apparatus according to the invention, which has a
temperature-sensitive component with a characteristic parameter
that is temperature-dependent and changes abruptly at a
predetermined transition temperature, or in a predetermined
transition temperature range, or changes continuously in a
predetermined manner, as a function of the temperature. A control
and evaluation unit connected to the measuring arrangement can
detect the characteristic component parameter and/or its
change.
[0010] A temperature-sensitive component having a characteristic
component parameter which changes continuously in a predetermined
manner as a function of the temperature, is expediently designed
such that the change occurring over time is correlated with a
parallel-running degradation of the exhaust gas catalytic
converter. By means of such a component having a characteristic
component parameter that changes abruptly as a function of
temperature, it is possible to detect reliably whether the exhaust
gas catalytic converter has overshot a temperature critical for its
effectiveness, since a correspondingly high signal deviation occurs
which can be detected reliably. For this purpose, taking into
account the place of installation of the measuring arrangement, the
temperature-sensitive component is designed such that the
transition temperature or the transition temperature range of the
characteristic component parameter is correlated with this critical
temperature.
[0011] Thus, by means of the device according to the invention,
essentially the cause of thermal damage is determined, more
reliably and in a less complicated manner.
[0012] The changing characteristic component parameter may be a
temperature-dependent mechanical, electrical or other specific
material property of the component. The temperature-sensitive
component is therefore preferably mechanical or electrical, and may
be designed such that the material property changes reversibly
under the intended thermal conditions. A more or less pronounced
hysteresis with respect to the temperature dependence is expedient
in this case.
[0013] Examples of temperature-sensitive components with mechanical
properties changing abruptly as a function of temperature are
bimetallic switches or what are known as "shape memory components".
Examples of temperature-sensitive components with electrical
properties changing abruptly as a function of temperature are cold
conductors or hot conductors. In order to obtain a good correlation
between the component temperature and catalytic converter
temperature, it is expedient to arrange the measuring apparatus in
the immediate vicinity of the exhaust gas catalytic converter in
the exhaust system, preferably such that it assumes approximately
the same temperature as the exhaust gas catalytic converter itself
when the internal combustion engine is in operation.
[0014] In a refinement of the invention, the measuring apparatus is
fixedly connected to the exhaust gas catalytic converter or to a
housing which contains the exhaust gas catalytic converter. A fixed
connection is understood here, as is generally conventional in
connection technology, to mean a connection, upon the release of
which the separated individual parts and/or the connection means
are destroyed or damaged. In this case, connection parts of the
housing, such as inflow or outflow funnels or connection pieces,
are considered to belong to the housing.
[0015] As a result of this embodiment, the measuring apparatus
cannot be separated non-destructively from the exhaust gas
catalytic converter or from the housing of the exhaust gas
catalytic converter. The housing and measuring apparatus or the
catalytic converter and measuring apparatus thus form a unit which
cannot be separated non-destructively. Misinterpretations of the
information delivered by the measuring arrangement as a result of
an intended or unintended separation of the measuring arrangement
from the exhaust gas catalytic converter are thus prevented. This
achieves particularly high reliability in the assignment of data
which are provided by the measuring arrangement.
[0016] In a further embodiment of the invention, the change in the
characteristic component parameter is irreversible. Once it has
occurred, therefore, the change can be detected unequivocally, so
that interpretation difficulties are avoided.
[0017] In a further refinement of the invention, the change in the
characteristic component parameter is based on a structural
transformation of a material constituent of the
temperature-sensitive component. This is preferably a change in the
structure of a material constituent of the component, for example
in the form of recrystallization processes, sintering, melting,
material agglomeration, island formation or the like. This type of
transformation mostly takes place at a predetermined unambiguous
transformation temperature or in the predetermined
material-specific temperature range or as a function of the
temperature within a known time profile. A change, once it has
occurred, is therefore linked unambiguously to the corresponding
temperature or to a duration of action or to a temperature/timing
integral. Temperature action of predetermined intensity can
therefore be established unambiguously.
[0018] In yet a further embodiment of the invention, the
temperature-sensitive component of the measuring apparatus is a
passive electrical structural element, such as an electrical
resistor. However, the temperature-sensitive component may also be
a capacitively or inductively active electrical component.
Preferably, the temperature-sensitive component comprises a
material having a function-determining material property, such as
specific resistance, dielectric constant, permeability, curie
temperature or the like, which changes abruptly at a predetermined
transition temperature or in a predetermined transition temperature
range.
[0019] In a further refinement of the invention, the
temperature-sensitive component is produced by thick-film
technology. This embodiment allows a substantial miniaturization,
along with a flat set-up, resulting in simple and flexible
installation possibilities and in good heat transmission.
[0020] In still a further refinement of the invention, the
measuring apparatus includes a plurality of temperature-sensitive
components that differ from one another in terms of the transition
temperature (or range) of their characteristic component parameter,
or individual temperature-sensitive components having
characteristic component parameters that change in time in a
different way as a function of the temperature. In this manner, the
different temperatures of action and/or durations of action on the
measuring arrangement or on the exhaust gas catalytic converter can
be differentiated. Their action on an effectiveness parameter of
the exhaust gas catalytic converter can thus likewise be evaluated
in a differentiated way.
[0021] In another embodiment of the invention, the
temperature-sensitive component is designed in such a way that the
transition temperature or the transition temperature range of its
characteristic component parameter is correlated with a permissible
upper operating temperature of the exhaust gas catalytic converter,
or the change in the characteristic component parameter which
occurs in the course of time is correlated with a parallel-running
aging of the exhaust gas catalytic converter. Thus, a particularly
reliable catalytic converter diagnosis is possible. In particular,
an overshooting of a predetermined upper limit temperature of the
exhaust gas catalytic converter can be detected especially
reliably. A warning message preferably occurs in this case. The
critical data for the catalytic converter are preferably stored in
preset characteristic curves or characteristic maps.
[0022] Furthermore, according to the invention, a device as
described above is used to monitor an exhaust gas catalytic
converter, designed as an oxidation catalytic converter, in the
exhaust system of an internal combustion engine. More particularly,
it is used to monitor an oxidation catalytic converter with a
negligible capability for the storage of oxygen. It is especially
advantageous to use the device according to the invention in an
oxidation catalytic converter arranged near the engine. In this
case, other diagnostic devices often encounter installation
problems due to space limitations.
[0023] It is also highly advantageous to use the device according
to the invention to monitor an oxidation catalytic converter with a
low or absent oxygen possibility, since, in this case, monitoring
of diagnostic methods based on oxygen storability is not possible.
This advantage is beneficial particularly in connection with an
oxidation catalytic converter of a diesel engine, for which the
oxygen probes often used for diagnostic purposes in gasoline
engines do not have sufficient sensitivity, because of the high
oxygen excess in the exhaust gas.
[0024] Further features and advantages of the present invention
arise from the following description of preferred exemplary
embodiments. In this case, the features mentioned above and those
yet to be explained below can be used not only in the feature
combination specified in each case, but also in other combinations
or alone, without departing from the scope of the present
invention.
[0025] The invention is explained in more detail below by means of
drawings and accompanying examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a diagrammatic illustration of an advantageous
embodiment of the invention in connection with an internal
combustion engine having an exhaust system;
[0027] FIG. 2 is a diagrammatic illustration of the temperature
dependence of a component parameter; and
[0028] FIG. 3 is a diagrammatic illustration of the time dependence
of a component parameter in the case of different temperatures.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1 illustrates an internal combustion engine 1,
preferably a diesel engine, with an intake air line 2 with an
exhaust system A. The exhaust system A comprises an exhaust gas
line 3 in which a housing 9 encloses an exhaust gas catalytic
converter 4. The housing 9 is connected to the exhaust gas line 3
via an inflow funnel 5 and an outflow funnel 6. Furthermore, a
measuring apparatus 10, is connected to a control and evaluation
unit 7 via a signal line 8. The measuring apparatus 10 and the
control and evaluation unit 7 connected to it, monitor the exhaust
gas catalytic converter 4, in the manner described.
[0030] The exhaust gas catalytic converter, preferably an oxidation
catalytic converter, is arranged, preferably near the engine, in
the exhaust gas line 3. In particular, the exhaust gas catalytic
converter is preferably an oxidation catalytic converter with a
coating having low or negligible oxygen storability. A
characteristic curve or characteristic map for the exhaust gas
catalytic converter 4, which is stored for example in the control
and evaluation unit 7, contains temperature values critical for the
aging of the exhaust gas catalytic converter 4. The exhaust gas
catalytic converter 4 is monitored in terms of its
temperature-induced damage or aging by comparing temperature values
detected by the measuring apparatus 10 with the stored critical
temperature values.
[0031] Depending on the size of the corresponding temperature
value, different reactions may be provided by the control and
evaluation unit 7. For example, entries into a read-out fault store
or warning messages may be provided. However, if critical
temperature values occur, actions on the operation of the internal
combustion engine 1 may be provided, such that the latter is
operated to avoid high exhaust gas temperatures. If an upper peak
temperature for the exhaust gas catalytic converter 4 is exceeded,
a message relating to damage to the exhaust gas catalytic converter
4 is preferably output.
[0032] The measuring apparatus 10 is arranged in the exhaust system
A in such a way that its temperature when the internal combustion
engine is in operation is correlated in a known way with that of
the exhaust gas catalytic converter 4. This ensures that the
information from the measuring apparatus 10 regarding the
temperature of the exhaust gas catalytic converter 4 is realistic
and reliable.
[0033] In the representative embodiment of FIG. 1, the measuring
apparatus 10 is fastened to the outer surface of the housing 9 in
which the exhaust gas catalytic converter 4 is installed, making
the invention especially assembly-friendly. However, the measuring
apparatus 10 may also be mounted on the inner surface of the
housing 9, on the outside or inside of the inflow funnel 5 or
outflow funnel 6 or on the outer wall of the exhaust gas catalytic
converter 4. The measuring apparatus 10 may, for example, be
printed or glued directly on the outer surface of the exhaust gas
catalytic converter 4. This makes simple manufacture possible.
There may, however, also be provision for integrating the measuring
apparatus 10 into the exhaust gas catalytic converter 4, for
example into the duct structure of the latter. This allows an
especially reliable detection of the catalytic converter
temperature.
[0034] Preferably, the components of the measuring apparatus 10 are
attached to a mechanical carrier, and the carrier, for example in
the form of a flat ceramic substrate, is connected to the exhaust
gas catalytic converter 4 or to the housing 9. However, the
components of the measuring apparatus 10 may also be applied
directly to the exhaust gas catalytic converter 4 or to the housing
9.
[0035] The mounting of the measuring apparatus 10 preferably takes
place in such a way that good heat transmission from the exhaust
gas catalytic converter 4 to the measuring apparatus 10 is
obtained. Good heat transmission, at the same time with an
unreleasable connection, may be achieved, for example, in a
materially integral way by the adhesive bonding of a component or
component carrier of the measuring apparatus 10 or by the soldering
of the underside, provided with metallization, of a carrier
substrate of the measuring apparatus 10 to the metallic housing 9
of the catalytic converter 4. This ensures that the measuring
apparatus 10 or the components of the measuring apparatus 10 cannot
be removed non-destructively from the place of their mounting. This
prevents a loss the correlation of the temperatures to which the
measuring apparatus 10 and the exhaust gas catalytic converter 4
are exposed, due to intended or unintended mechanical actions. A
specific measuring apparatus is thus assigned permanently to a
specific example of a catalytic converter.
[0036] From experimentally obtained information, the temperature to
which the measuring apparatus 10 is exposed can be correlated with
the temperature of the exhaust gas catalytic converter 4 by the
control and evaluation unit 7. It is thus possible to correlate the
temperature of the measuring arrangement with that of the exhaust
gas catalytic converter 4, even when a measuring apparatus 10 is
not in direct heat transmission contact with the exhaust gas
catalytic converter 4.
[0037] For temperature monitoring and diagnosis of the exhaust gas
catalytic converter 4, the measuring apparatus 10 may have at least
one temperature-sensitive component with a characteristic component
parameter which changes abruptly as a function of temperature at a
predetermined transition temperature or temperature range. FIG. 2
illustrates this situation by a diagrammatic characteristic curve
graph for the temperature dependence of the characteristic
component parameter P.
[0038] The temperature-sensitive component of the measuring
apparatus 10 may be designed such that its characteristic parameter
P increases abruptly from the value P.sub.1 to the value P.sub.2
according to the curve branch 20 at a temperature of about T.sub.b.
(The change may be reversible or irreversible.) Of course, instead
of an abrupt increase in the characteristic component parameter P
at the transition temperature T.sub.b, an abrupt reduction is also
possible in a similar way, in which case the component of the
measuring apparatus 10 expediently has a transition temperature
T.sub.b that is correlated with a characteristic aging or damage
temperature of the exhaust gas catalytic converter 4.
[0039] As a result of the steep profile of the characteristic curve
20, an overshooting of the critical transition temperature T.sub.b
can be detected with high reliability. It is, of course,
advantageous if the surge occurring due to the values P.sub.1 and
P.sub.2 is as high as possible. Although preferable, the change in
the characteristic component parameter P does not necessarily have
to have an especially steep profile. A less steep rise within a
predetermined temperature range may likewise be quite sufficient.
However, the change should be such that the gradient of the
characteristic curve 20 is greater in the critical temperature
range than in the following temperature ranges. In this case, too,
a desired switching behavior of a component property characterized
by the parameter P is afforded.
[0040] In the event of an abrupt reversible change in the component
parameter P, it may be advantageous to provide the
temperature-sensitive component with a hysteresis, as illustrated
by the additional characteristic curve branch 21. In this case, a
changeover of the component property characterized by the parameter
P takes place at different temperatures T.sub.b, T.sub.a, depending
on the direction of the temperature change. Owing to this component
property, undefined states at a respective transition temperature
Tb, Ta can be avoided, and the interpretation of a useful signal
obtained from the parameter P is correspondingly reliable.
[0041] For temperature monitoring and diagnosis of the exhaust gas
catalytic converter 4, the measuring apparatus 10 may also have at
least one temperature-sensitive component with a characteristic
component parameter that changes in a predetermined way over time,
as a function of the temperature. For example, FIG. 3 illustrates a
family of characteristic curves which show the time dependence of
the characteristic component parameter P at various temperatures
T.sub.1 to T.sub.5 ordered according to size. Expediently, the
profiles of the characteristic curves assigned to the temperatures
T.sub.1 to T.sub.5 are adapted to the aging behavior of the exhaust
gas catalytic converter 4. It is preferable if the changes in the
characteristic component parameter which occur over time are
irreversible, corresponding, in general, to irreversible catalytic
converter aging, particularly when it is caused thermally.
[0042] Preferably, the component parameter P has a predetermined
upper limit P.sub.G which is correlated with an upper tolerance
limit for an aging or degradation of the exhaust gas catalytic
converter 4. As is evident from the graph of FIG. 3, the upper
limit P.sub.G reached at different times, depending on temperature.
Thus, aging of the exhaust gas catalytic converter 4 which takes
place at different rates at different temperatures can be
diagnosed. For example, a no longer acceptable impairment of the
catalytic converter behavior as a result of the short duration of
action t.sub.1 of the high temperature T.sub.5 can be detected.
However, a similarly pronounced impairment which has occurred as a
result of the longer duration of action t.sub.3 of the lower
temperature T.sub.3 can also be detected.
[0043] So that the effect of different temperatures on the
catalytic converter can be detected in an even more differentiated
way, the measuring apparatus 10 may have a plurality of
temperature-sensitive components, each with a different behavior.
For example, a plurality of temperature-sensitive components with
different transition temperatures or transition temperature ranges
may be provided. Additionally or alternatively, a plurality of
temperature-sensitive components may also be provided, the
characteristic component parameter of which changes in time in a
different way as a function of the temperature.
[0044] It is particularly preferable if the component whose
characteristic component parameter has the highest transition
temperature or temperature range, is a continuously measuring
temperature-sensitive component. It is advantageous, in this
respect, for the component to be a resistance thermometer having a
temperature-dependent electrical resistance that can be used for
continuous temperature measurement at low temperatures, but
abruptly changes (reversibly or irreversibly) at a predetermined
transition temperature. Thus, in addition to reliable detection of
the overshooting of the transition temperature, continuous
temperature measurement is made possible.
[0045] The temperature-sensitive component is preferably produced
as a passive electrical structural element by thick-film
technology. It may be printed as a conductor track or conductor
structure on a substrate by thick-film technology. The material for
this purpose is selected so that, at a predetermined temperature or
as a function of the temperature, it experiences, in a way
predetermined in time, a transformation which, as explained above,
is reflected in a change of a characteristic parameter. This is
preferably the real and/or imaginary part of the complex impedance
of the structural element.
[0046] If the temperature-sensitive component comprises a resistive
structural element, it is preferable if its characteristic
component parameter is represented by its electrical conductivity
or resistance. In the case of a capacitive structural element, its
material is preferably selected such that the dielectric constant
(and therefore the capacitance and/or the loss angle) change as a
function of temperature. The changes occurring as a function of
temperature may be caused, for example, by melting, sintering,
island formation, diffusion processes, material creep and/or crack
formation of a material constituent of the temperature-sensitive
component.
[0047] Instead of the characteristic parameters mentioned, however,
other physical, in particular electrical characteristic variable,
such as, for example, inductance, permeability, magnetization,
etc., may also be provided as critical parameters. In the case of a
mechanical temperature-sensitive, component temperature-induced
changes of mechanical variables, such as shape or length, may also
be considered as detectable characteristic parameters. These are
preferably detected by means of electrical measuring methods. In
this respect, temperature-dependent properties capable of being
utilized as a switching effect are particularly preferred.
[0048] In the cases mentioned, the control and evaluation unit 7
may have the capability to detect a temperature-induced change in
the characteristic component parameter critical in each case, and
to determine the aging state of the exhaust gas catalytic converter
4, based on characteristic curves.
[0049] The foregoing disclosure has been set forth merely to
illustrate the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
* * * * *