FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the Invention
METHOD FOR INTRODUCING HEAT INTO AT LEAST ONE COMPONENT OF AN EXHAUSTGAS AFTERTREATMENT DEVICE, SOFTWARE AND OPEN-LOOP OR CLOSED-LOOP
CONTROL DEVICE
2. Applicant(s)
Name Nationality Address
FRAUNHOFER-GESELLSCHAFT
ZUR FÖRDERUNG DER
ANGEWANDTEN FORSCHUNG E.V.
GERMAN Hansastraße 27c 80686 München,
Germany
3. Preamble to the description
The following specification particularly describes the invention and the manner in which it is to be performed
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The invention relates to a method for introducing heat into at least one component of an
exhaust-gas aftertreatment device of an internal combustion engine, in which a partial flow of
an exhaust-gas flow is at least partially reacted with fuel in a heated catalyst and fed back to
the exhaust-gas flow. The invention also relates to an open-loop or closed-loop control device
as well as a computer program for carrying out a method of this type.
It is known from practice to arrange in the exhaust-gas line of an internal combustion engine
at least one component which purifies the raw exhaust gas of the internal combustion engine.
This purification often comprises a catalytic post-oxidation, the filtering of particles or the
catalytic reaction of nitrogen oxides with a reducing agent. In some cases, a plurality of
components for different method steps of the exhaust-gas aftertreatment or exhaust-gas
purification can also be run through sequentially.
Insofar as this component renders possible a chemical reaction of the raw exhaust gas, the
component usually requires a certain operating temperature of, for example, more than 200°C
or even more than 300°C in order to purify the raw exhaust gas with sufficient efficiency.
Although, particulate filters can be effective even at ambient temperature, they need to be
regenerated at a certain loading, which is usually done by oxidation of the embedded particles
at high temperatures and gaseous discharge of the combustion products.
There is thus a need to heat all or at least individual components of an exhaust-gas
aftertreatment device by supplying thermal energy at least occasionally. This can be done, for
example, by means of internal engine measures which, although they adversely affect the
efficiency and/or pollutant emissions of the internal combustion engine, they raise, on the
other hand, the exhaust-gas temperature of the raw exhaust gas so that additional heat is
introduced into the components of the exhaust-gas aftertreatment device.
WO 2020/193595 A1 additionally discloses the use of a heated catalyst to which a partial
flow of the raw exhaust gas emitted by the internal combustion engine is fed. This partial flow
of raw exhaust gas is reacted with fuel. In this process, heat can be generated, on the one
hand, by an exothermic reaction independently of the operation of the internal combustion
engine and fed to the exhaust-gas aftertreatment device. In addition, this known heated
catalyst allows the production of an easily ignitable synthesis gas from the supplied fuel. This
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synthesis gas can be exothermically reacted on an exhaust-gas catalyst, thus generating heat
directly within the exhaust-gas catalyst.
However, this known device has the disadvantage that during a dynamic operation of an
internal combustion engine, in particular in motor vehicles, the exhaust-gas mass flow and its
composition vary. Since the amount of heat emitted from the heated catalyst into the
component of the exhaust-gas aftertreatment device depends nonlinearly on the amount of
exhaust gas supplied, the amount of fuel supplied, and the composition of the exhaust gas
supplied, this leads to large fluctuations in the heat emitted from the heated catalyst. In
addition, the temperature control of a component of an exhaust-gas aftertreatment device is
complicated by long dead times.
Based on the prior art, there is thus a need to more reliably control, by open-loop or closedloop control, the heat introduction into at least one component of an exhaust-gas
aftertreatment device in order, on the one hand, to prevent cooling of the exhaust-gas
aftertreatment device with subsequent emission slip and, on the other hand, not to use
unnecessary energy for heating.
According to the invention, this object is achieved by a method according to claim 1, a data
carrier having data stored thereon or a signal sequence which represents data and is suitable
for transmission by means of a computer network according to claim 12, and an open-loop or
closed-loop control device according to claim 13. Advantageous further developments of the
invention are found in the subclaims.
According to the invention, a method for introducing heat into at least one component of an
exhaust-gas aftertreatment device of an internal combustion engine is proposed. In some
embodiments of the invention, the internal combustion engine can be a spark-ignited internal
combustion engine or a gasoline engine. In other embodiments of the invention, the internal
combustion engine can be a compression-ignition internal combustion engine or a diesel
engine. The internal combustion engine used according to the invention can be part of a motor
vehicle, for example a passenger car or a truck. In other embodiments of the invention, the
internal combustion engine can be used in a construction machine or a ship. In yet other
embodiments of the invention, the internal combustion engine can also be used in stationary
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power generators or compressors. The advantages of the method according to the invention
are particularly apparent in a dynamic operation, i.e. when the load requirements of the
internal combustion engine change for a short time. This is the case, for example, with motor
vehicles, especially in city traffic.
The component of an exhaust-gas aftertreatment device used according to the invention can,
for example, be a three-way catalyst. In other embodiments of the invention, the component
can be selected from an oxidation catalyst, a storage catalyst, an SCR system, and/or a
particulate filter. In some embodiments of the invention, a plurality of such components can
also be present in an exhaust-gas
aftertreatment device and raw exhaust gas from the internal combustion engine can flow
therethrough in parallel or sequentially.
According to the invention, it is proposed that a partial flow of the exhaust-gas flow of the
internal combustion engine be at least partially reacted with fuel in a heated catalyst in order
to feed the product generated in the heated catalyst back to the exhaust-gas flow. This results
in the advantage that the device for generating heat is largely independent of the internal
combustion engine, so that the internal combustion engine does not have to be operated with
unfavorable operating conditions in order to generate additional heat. On the contrary, the
internal combustion engine can always be operated in such a way that the mechanical power
required in each case is produced with the lowest possible pollutants and/or the lowest
possible fuel consumption.
The method according to the invention now aims to determine the exhaust-gas temperature in
the direction of flow upstream and/or downstream of the component of the exhaust-gas
aftertreatment device which is provided for introducing heat, and to control, in open-loop or
closed-loop control, the amount of heat emitted by the heated catalyst on the basis of the
temperature. In this context, the heat emitted by the heated catalyst can be influenced by the
supplied fuel amount and/or the mass flow of the partial flow of the raw exhaust gas fed to the
heated catalyst as a reference variable. According to the invention, it is thus proposed to
adjust one or both influencing variables on the heat emitted by the heated catalyst per unit
time on the basis of at least one exhaust-gas temperature so that the exhaust-gas temperature
upstream and/or downstream of the component is kept constant at a predeterminable desired
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value or within predeterminable fluctuation ranges. In some embodiments of the invention,
the heated catalyst can have further reference variables, for example an ambient air supply or
an electrical heating device. They can be controlled in the same manner. In some
embodiments of the invention, the fuel fed to the heated catalyst is here completely or at least
partially liquid.
The thus controlled desired value of the exhaust-gas temperature in at least one
predeterminable spot of the exhaust-gas aftertreatment device can vary during the operation of
the internal combustion engine. For example, the desired value upstream of a particulate filter
can be temporarily increased if a differential pressure sensor detects an imadmissibly high
loading of the particulate filter and the particulate filter shall be regenerated by oxidation of
the particles. The desired value of the exhaust-gas temperature can then be lowered again as a
function of time or on the basis of measured values when the particulate filter has been
regenerated. In other embodiments of the invention, the exhaust-gas temperature can be
controlled in such a way that it does not fall below certain minimum values, for example
when operating oxidation catalysts or SCR systems, which require a minimum temperature
for operation. If this minimum temperature is not reached, for example due to partial load
operation of the internal combustion engine, additional heat can be introduced by the heated
catalyst used according to the invention.
In some embodiments of the invention, the exhaust-gas temperature upstream and/or
downstream of the component of the exhaust-gas aftertreatment device can be detected by at
least one temperature sensor. In a manner known per se, it is possible to use, as temperature
sensors, thermocouples or resistance thermometers which generate an electrical signal
corresponding to the temperature. Depending on the measured variable of the exhaust-gas
temperature that is detected in this way, the reference variables on the heated catalyst can then
be influenced in order to control, by open-loop or closed-loop control, the control variable of
the thermal power of the heated catalyst.
In some embodiments of the invention, the exhaust-gas temperature upstream and/or
downstream of the component of the exhaust-gas aftertreatment device can be determined
from the operating state of the internal combustion engine. This feature allows additional
sensor technology to be saved, thereby increasing the operational reliability. For example, the
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temperature developing at a catalyst or particulate filter can be calculated or tabulated from
the thermal power converted in the internal combustion engine, the proportion of this power
dissipated into the exhaust gas and the heat dissipation of the exhaust-gas line upstream of the
component on the basis of the outside temperature and the inflow velocity of the airstream.
This allows a heat balance to be established for the component and the ensuing temperatures
to be derived without the use of a temperature sensor in the exhaust-gas flow.
In some embodiments of the invention, a portion of the exhaust-gas temperatures can be
measured and another portion of the exhaust-gas temperatures can be calculated. For example,
a measured temperature downstream of an oxidation catalyst and the operating state of the
internal combustion engine can be used to calculate the temperature upstream of the oxidation
catalyst, or vice versa. In other embodiments of the invention, the inlet temperature or also the
outlet temperature of an SCR system located downstream of the oxidation catalyst can be
determined from a temperature downstream of the oxidation catalyst.
In some embodiments of the invention, the operating state of the internal combustion engine,
which is used to determine the exhaust-gas temperature can be determined from currently
applied characteristic map values or characteristic map ranges of the engine control unit of the
internal combustion engine. Thus, it is no longer necessary to measure, for example, the
exhaust-gas mass flow of the raw exhaust gas of the internal combustion engine. Instead, the
exhaust-gas mass flow can be determined with high accuracy from the intake air amount and
the supplied fuel amount. In some cases, the operating state of the internal combustion engine
can be determined with greater accuracy using other characteristic maps, for example the
measured values of a λ-probe, the rotational speed, the accelerator pedal position, the position
of the EGR valve, the cooling water temperature or further values which are not explicitly
mentioned here.
Heated catalysts of the type used exhibit a nonlinear behavior of heat dissipation on the basis
of the amount of fuel supplied and/or of the partial flow of raw exhaust gas fed to the heated
catalyst. According to the invention, the amount of fuel supplied to the heated catalyst and/or
the partial flow of the raw exhaust gas supplied to the heated catalyst is determined by means
of at least one heated catalyst characteristic map. The input variables of the heated-catalyst
characteristic map can, for example, be selected from the exhaust-gas mass flow of the
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internal combustion engine and/or the oxygen content of the raw exhaust gas and/or at least
one exhaust-gas temperature and/or a driving profile and/or a navigation destination and/or
position data and/or the state of charge of at least one battery. The open-loop or closed-loop
control by means of a heated-catalyst characteristic map here has in particular the advantage
that the control can also be carried out very quickly even if the operation is highly dynamic
since only the desired values of the reference variables which are currently suitable for the
operating conditions of the internal combustion engine have to be read out from the
conversion table stored in the control device and set at the heated catalyst.
In some embodiments of the invention, the exhaust-gas mass flow of the internal combustion
engine and/or the oxygen content of the raw exhaust gas of the internal combustion engine
and/or at least one exhaust-gas temperature can be determined using a first referencecontrolled synthesizer. For the purposes of the present invention, such a reference-controlled
synthesizer designates a system which reconstructs non-measurable variables from known
input variables and output variables of the internal combustion engine. For this purpose, the
synthesizer reproduces the internal combustion engine as a model and uses a controller to
reconstruct the measurable state variables, which are therefore comparable with the real
internal combustion engine. In this way, it is, for example, possible to calculate an exhaustgas mass flow of the raw exhaust gas of the internal combustion engine from the intake air
mass and the supplied fuel amount, without having to measure the exhaust-gas mass flow
with great technical effort and without generating a growing error over the operating time.
In some embodiments of the invention, the thermal power which is outputted by the heated
catalyst can be determined from the amount of fuel supplied to the heated catalyst and/or the
partial flow of the raw exhaust gas of the internal combustion engine which is supplied to the
heated catalyst and/or the oxygen content of the raw exhaust gas by means of a second
reference-controlled synthesizer. Therefore, an exact measured value of the thermal power or
the amount of heat introduced into the exhaust-gas aftertreatment by the heated catalyst is
always available for the temperature control without the need to measure this thermal power
with great technical effort.
In some embodiments of the method, the heated catalyst can have at least a second operating
state in which the air ratio λ of the heated catalyst is between about 0.75 and about 30. In
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other embodiments of the method, the heated catalyst can have at least a second operating
state in which the air ratio λ of the heated catalyst is between about 1.0 and about 10. This
first operating state can also be referred to as burner operation since the amount of fuel
supplied is largely or completely reacted in the heated catalyst with the residual oxygen of the
raw exhaust gas. In this first operating state, the heated catalyst emits a hot gas which can be
supplied to the component of the exhaust-gas aftertreatment via an exhaust-gas line and heats
the component by directly introducing heat.
In some embodiments of the invention, the heated catalyst can further have at least a fourth
operating state in which the air ratio λ of the heated catalyst is between about 0.05 and about
0.7. In this operating state, a portion of the fuel is exothermically reacted. The heat released
by this can be used to vaporize another portion of the fuel supplied and discharge it in gaseous
form into the exhaust-gas line. Alternatively or additionally, the fuel can be converted by
chemical reactions on the heated catalyst into a synthesis gas, which is also discharged into
the exhaust-gas line. The synthesis gas and/or fuel vapor can be oxidized at an exhaust-gas
catalyst, for example, where it releases thermal energy directly in the component of the
exhaust-gas aftertreatment device to be heated, such that it is heated with lower thermal losses
and/or greater thermal power.
In some embodiments of the invention, the heated catalyst can include at least one electrical
heating device that is used in a first operating state to bring the heated catalyst to an operating
temperature at which supplied fuel can be at least partially reacted on the heated catalyst. This
allows the heated catalyst to be brought to operating temperature after a cold start.
In some embodiments of the invention, the heated catalyst can contain at least one electrical
heating device which, in an eighth operating state, is used to heat a partial flow of the raw
exhaust gas of the internal combustion engine supplied to the heated catalyst. This
embodiment makes it possible, when there is a surplus of available electrical energy, for
example when the internal combustion engine is in an overrun mode and recuperating, to
introduce heat into at least one component of the exhaust-gas aftertreatment device even
without supplying fuel. In some of these embodiments, the electrical power supplied to the
heated catalyst can be made dependent on the state of charge of at least one battery, i.e. the
heated catalyst is not electrically heated until the electrical energy is not needed as a charging
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current or when position data and navigation destination allow battery charging at a later time
in a predictive view of the trip. The battery can be selected from a starter battery and/or a
high-voltage battery of a hybrid drive.
In some embodiments of the invention, the partial flow of the raw exhaust gas from the
internal combustion engine that is supplied to the heated catalyst can be between about 3 kg/h
and about 200 kg/h. In other embodiments of the invention, the partial flow of the raw exhaust
gas from the internal combustion engine, which is supplied to the heated catalyst, can be
between about 3 kg/h and about 100 kg/h. In yet other embodiments of the invention, the
partial flow can be selected between about 6 kg/h and about 80 kg/h. In yet other
embodiments of the invention, the partial flow can be selected between about 6 kg/h and
about 150 kg/h. The partial flow can be selected on the basis of the oxygen content of the raw
exhaust gas and/or on the basis of the desired operating state of the heated catalyst and/or on
the basis of the required thermal heating power.
The method proposed according to the invention can be implemented in a computer program
which carries out the method according to the invention when the computer program runs on
a microprocessor. The computer program can be available on a data carrier having data stored
thereon, or in the form of a data-representing signal sequence suitable for transmission by
means of a computer network.
In some embodiments of the invention, the invention relates to an open-loop or closed-loop
control device which is designed to carry out the method according to the invention. For this
purpose, the open-loop or closed-loop control device can have at least one microprocessor or
one microcontroller. In addition, the open-loop or closed-loop control device can contain
memories which are designed to receive a computer program. In addition, the open-loop or
closed-loop control device can contain analog or digital interfaces that can process sensor
data, for example, the oxygen content of the raw exhaust gas and/or the exhaust-gas
temperature upstream and/or downstream of the component of the exhaust-gas aftertreatment
device. Finally, the open-loop or closed-loop control device can have a digital interface which
is designed to receive data from an engine control unit of the internal combustion engine in
order to derive the operating conditions of the heated catalyst from the current operating state
of the internal combustion engine.
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The invention shall be explained in more detail below on the basis of drawings and exemplary
embodiments without restricting the general concept of the invention. In the drawings:
Figure 1 shows a first exemplary embodiment of an exhaust-gas aftertreatment device that can
be used according to the invention.
Figure 2 shows a second exemplary embodiment of an exhaust-gas aftertreatment device that
can be used according to the invention.
Figure 3 shows a block diagram of an open-loop or closed-loop control device according to
the present invention.
Figure 4 shows a structure chart of the method according to the invention in a first
embodiment.
Figure 5 shows a structure chart of the method according to the invention in a second
embodiment.
Figure 6 shows the use of the method according to the invention in a first exemplary
embodiment.
Figure 7 shows the use of the method according to the invention in a second exemplary
embodiment.
A first exemplary embodiment of an exhaust-gas aftertreatment device 1 usable according to
the invention is explained in more detail on the basis of figure 1. The exhaust-gas
aftertreatment device 1 is connected to an internal combustion engine 15 via an exhaust-gas
line. The internal combustion engine 15 can be a compression-ignition internal combustion
engine or also a spark-ignition internal combustion engine of known design. The internal
combustion engine 15 draws in ambient air and exothermically reacts it with supplied fuel. In
the process, the internal combustion engine 15 outputs mechanical power. During the
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operation of the internal combustion engine 15, a raw exhaust gas is produced which, in
addition to CO2 and H2O, can also contain pollutants, such as CHX, CO and/or NOX.
The raw exhaust gas is fed to the exhaust-gas aftertreatment device 1 by means of an exhaustgas line. Optionally, a sensor system can be installed in the exhaust-gas line, for example a λprobe for measuring the oxygen content of the raw exhaust gas. In the illustrated first
exemplary embodiment, the exhaust-gas aftertreatment device 1 includes a first SCR system
13a and a second SCR system 13b. The SCR systems are each designed to catalytically
reduce nitrogen oxides in the raw exhaust gas by adding a reducing agent. For this purpose,
temperatures above 220°C, preferably above 250°C, are required.
A particulate filter 12 is located in the flow direction between the two SCR systems 13a and
13b. The particulate filter 12 is designed to retain fine dust or soot particles produced during
the operation of the internal combustion engine 15. If the particulate filter 12 becomes
clogged with increasing use, it can be temporarily heated to high temperatures under oxygen
supply so that the embedded particles are oxidized and discharged in gaseous form.
In the first exemplary embodiment shown in figure 1, the first SCR system 13a and the
particulate filter 12 are installed close to the engine so that the thermal energy of the raw
exhaust gas is sufficient to bring these components up to operating temperature or keep them
at operating temperature. The second SCR system 13b, on the other hand, is located further
downstream in the exhaust-gas line so that it reaches the operating temperature only slowly
and/or can cool below its operating temperature during the part-load operation of the internal
combustion engine 15. Therefore, exhaust-gas purification is inadequate in part-load
operation, which is referred to as emission slip in the sense of the present description.
In order to solve this problem, a heated catalyst 2 is located upstream of the second SCR
system 13b. A partial flow of the raw exhaust gas flowing in the exhaust-gas line is fed to the
heated catalyst 2. Furthermore, a fuel is fed to the heated catalyst, which is reacted with the
exhaust gas or the residual oxygen contained in the exhaust gas. The heat generated in this
process is fed back to the exhaust-gas line in the form of a hot gas and introduced into the
second SCR system 13b. This additional heat introduction can take place both after a cold
start and during a part-load operation, thus allowing rapid heating, on the one hand, and
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preventing cooling during operation, on the other hand. At full load or near full load operating
conditions of the internal combustion engine, the heated catalyst 2 can be switched off.
With reference to figure 2, a second exemplary embodiment of an exhaust-gas aftertreatment
device which can be used according to the invention is explained in more detail. Equal
reference signs denote equal components of the invention, so that the following description is
limited to the essential differences. Figure 2 shows an oxidation catalyst 11 which is designed
to post-oxidize oxidizable components of the raw exhaust gas, for example CO and/or CHx. A
particulate filter 12 is disposed downstream of the oxidation catalyst, as described above. An
SCR system, which is used in particular to reduce NOx, is disposed downstream of the
particulate filter 12.
In the illustrated exemplary embodiment, the heated catalyst 2 is located upstream of the
oxidation catalyst 11 and downstream of the internal combustion engine 15. During operation,
a partial stream of the not previously purified raw exhaust gas from the internal combustion
engine 15 is therefore supplied to the heated catalyst 2.
Figure 11 further shows three temperature sensors 111, 112 and 132. The temperature sensors
measure the exhaust-gas temperature at the inlet to the oxidation catalyst, at the outlet from
the oxidation catalyst and at the outlet from the SCR system. These three temperature sensors
should be understood as merely exemplary. In other embodiments of the invention, the
number of temperature sensors used can be greater or less. In some cases, no temperature
sensor at all can be used, as described above with reference to figure 1. In this case, the
temperatures can be determined from the operating state of the internal combustion engine,
for example with a reference-controlled synthesizer.
It should be noted that the exhaust-gas aftertreatment devices 1 shown in figures 1 and 2
should be understood as merely exemplary. In other embodiments of the invention, other
components can be used, for example three-way catalysts or storage catalysts. Likewise,
individual components can be omitted. It is merely essential to the invention that at least one
component 11, 12, 13 is present in the exhaust-gas aftertreatment device 1.
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The object of the invention is to achieve the operating temperature of at least one component
11, 12, 13 rapidly and/or to maintain it at low exhaust-gas temperatures of the internal
combustion engine 15, which can occur in particular in the lower partial load range. An
exhaust-gas temperature upstream and/or downstream of the component can either be
measured, as shown in figure 2, or determined from the operating state of the internal
combustion engine. In this second case, too, the temperature is referred to as a "measured
value" for the purposes of the present description, even if it has not been measured directly,
for example by a thermocouple or a resistance thermometer.
The measured value of the temperature, its deviation from a predeterminable desired value,
the heat capacity of the exhaust-gas line and upstream components of the exhaust-gas
aftertreatment device, and the heat loss or gain of the raw exhaust gas on its way through the
exhaust-gas aftertreatment device lead to a required thermal power of the heated catalyst 2 as
control variable. This control variable can be influenced by the amount of fuel supplied to the
heated catalyst 2 as well as the amount of exhaust gas supplied to the heated catalyst and, in
some cases, the electrical energy supplied to the heated catalyst as reference variables. The
reference variables in turn depend on the oxygen content of the raw exhaust gas, the exhaustgas temperature and the exhaust-gas mass flow of the raw exhaust gas of the internal
combustion engine 15. The exemplary embodiment of an open-loop or closed-loop control
device 3 shown in figure 3 therefore uses a heated catalyst characteristic map 35. The heated
catalyst characteristic map 35 is supplied with the temperatures and the oxygen content of the
raw exhaust gas measured or determined via a first reference-controlled synthesizer from the
data of the engine control unit 16. Likewise, measured values optionally read out from the
engine control unit 16 are fed to the open-loop or closed-loop control device 3 by means of a
digital data link 351. Thereafter, the open-loop or closed-loop control device 3 can read and
set the reference variables with the aid of the heated catalyst characteristic map 35.
In some embodiments of the invention, further data can, in addition to the data from the motor
control unit 16, be made available to the open-loop or closed-loop control device 3, which can
then control the reference variables of the heated catalyst 2 more quickly or with greater
accuracy, either under characteristic map control or also by calculation. This further data can
be selected from a driving profile and/or a navigation destination and/or position data and/or
the state of charge of a battery. For example, the heating power of the heated catalyst 2 can
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already be proactively reduced if it is known that the vehicle is about to drive up an incline
and that a larger and also hotter exhaust-gas mass flow of the raw exhaust gas from the
internal combustion engine is available as a result. Likewise, the heated catalyst can already
be proactively activated at the end of an incline in order to prevent or reduce a drop in
temperature of the component of the exhaust-gas aftertreatment device, which results from the
fact that the internal combustion engine only operates at partial load or even in overrun mode
when driving downhill. In the same way, position data can be used to define a base load range
of the heated catalyst 2 since, for example in urban areas, a lower average load of the internal
combustion engine 15 can be expected than during highway travel. Similarly, the operation of
the vehicle in urban areas can indicate a higher dynamic range, whereas a more uniform load
demand is placed on the internal combustion engine 15 during interurban travel. Finally, a
navigation destination can also be used to control the heated catalyst 2, for example by
stopping the regeneration of a particulate filter 12 shortly before reaching the driving
destination or by postponing it until the vehicle reaches the city limit.
Figure 4 shows a structure chart of a first embodiment of the method according to the
invention. In the first embodiment, the heated catalyst 2 can be operated in seven different
operating states, which are designated by the reference signs 51 to 57. The process control
according to figure 4 should not be understood as meaning that the seven operating states are
necessarily run through sequentially. On the contrary, at least one temperature is determined
downstream of an oxidation catalyst, either directly by measurement or indirectly from the
operating state of the internal combustion engine. Depending on the temperature and
optionally further parameters, for example the operating time of the internal combustion
engine, one of the illustrated operating states of the heated catalyst 2 is then selected. If the
temperature at the outlet of the oxidation catalyst changes so that the applied operating state is
no longer appropriate, the open-loop or closed-loop control device changes to another
operating state on the basis of the temperature. In this case, a hysteresis can be used to avoid
frequent changes in the operating state of the heated catalyst 2. The individual operating states
are explained in more detail below.
The first operating state 51 denotes the start of the heated catalyst. For this purpose, the
heated catalyst can first be preheated by supplying an exhaust-gas mass flow with an optional
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electric heating device until supplied fuel is converted exothermically on the heated catalyst
and heats the heated catalyst further to its operating temperature.
In the second operating state 52, a comparatively large exhaust-gas mass flow of, for
example, about 60 kg/h to about 100 kg/h is supplied to the heated catalyst. The heated
catalyst is operated with an air ratio λ between about 0.75 and about 3.5 or between about 1.5
and about 2.5. This results in an almost complete conversion of the supplied fuel with the
residual oxygen of the exhaust gas supplied to the heated catalyst 2. In some embodiments,
the heated catalyst can deliver a thermal power of about 5 kW to about 20 kW in the form of a
hot gas.
The third operating state 53 denotes an alternating operation in which cyclic switching occurs
between a first sub-step 53a and a second sub-step 53b. In the first sub-step 53a, the operating
conditions correspond approximately to the operation in the second method step 52. In the
second sub-step 53b, the exhaust-gas mass flow is reduced by a factor of 10 to 25, for
example to about 3 kg/h to about 10 kg/h, so that the heated catalyst is operated with an air
ratio λ of between about 0.05 and about 0.5 or between about 0.1 and about 0.4. In the second
sub-step 53b, the supplied fuel is thus not completely reacted, but is partially vaporized and
partially converted into a synthesis gas, which is supplied to the oxidation catalyst via the
exhaust-gas line. The heat supplied in the first substep 53a allows the synthesis gas to ignite at
the oxidation catalyst where it can be converted exothermically so that a heating power of
about 13 kW to about 20 kW is released directly at the oxidation catalyst.
The fourth method step 54 is similar to the second sub-step 53b of the third method step 53.
However, the partial exhaust-gas flow supplied to the heated catalyst is greater and can be
between about 5 kg/h and about 20 kg/h. The control can be such that a predeterminable
proportion of the raw exhaust gas is passed through the heated catalyst. For example, between
about 2 % and about 10 % or between about 3 % and about 8 % of the exhaust-gas flow of the
internal combustion engine can be fed as a partial flow to the heated catalyst 2. In the fourth
operating state 54, the heated catalyst can supply a thermal power of from about 10 kW to
about 50 kW or from about 14 kW to about 36 kW in the form of an ignitable synthesis gas to
the oxidation catalyst 11. Therefore, the fourth operating state 54 is particularly suitable for
the rapid heating of the exhaust-gas aftertreatment device after a cold start and after the heated
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catalyst is started in the first method step 51 and some preconditioning of the exhaust-gas
aftertreatment device has taken place in the second and third process steps 52 and 53.
After the exhaust-gas aftertreatment device is heated to a predeterminable desired
temperature, the heated catalyst 2a can be cleaned in the fifth method step 55. For this
purpose, the supplied partial flow is increased again, for example to about 50 kg/h to about
100 kg/h. The amount of fuel supplied can be reduced compared with the second method step
52, so that the heat released in the heated catalyst 2 is primarily used to oxidize and vaporize
remaining deposits and residual fuel in order to prevent permanent deposits and
contamination in the heated catalyst 2.
The sixth method step 56 is suitable for a warm-keeping operation, for example if the internal
combustion engine 15 only produces low exhaust-gas temperatures in the low partial load
range or if no fuel at all is supplied to the internal combustion engine in overrun operation. In
the sixth method step 56, the thermal power of the heated catalyst can be between about 0 kW
and about 10 kW. For this purpose, a comparatively small partial flow of about 5 kg/h to
about 50 kg/h of the raw exhaust gas is supplied to the heated catalyst 2, while the heated
catalyst is operated with an air ratio λ of between about 0.75 and about 3.5 or between about
1.5 and about 2.5.
If the heated catalyst 2 is permanently not required at high exhaust-gas temperatures, it can
also be switched off in the seventh method step 57. In this case, no fuel is fed to the heated
catalyst 2 so that the heated catalyst does not emit any heat even in the event that a partial
flow of the exhaust gas permanently flows through the heated catalyst due to its installation
situation.
In some embodiments of the invention, the method steps 51, 52, 53 and 54 are run through
cyclically after a cold start, in each case switching to the next operating state when
predeterminable temperature thresholds are reached. During continuous operation of the
internal combustion engine, it is then possible to switch between the operating states 54, 55,
56 and 57 on the basis of the exhaust-gas temperature or the deviation of the desired
temperature value of the oxidation catalyst from the actual value. The temperature limit
17
values between the individual operating states can be provided with a hysteresis in order to
avoid frequent undesired changes of the operating state.
With reference to figure 5, a structure chart of a second embodiment of the method according
to the invention is explained in more detail. Equal components of the invention or equal
operating states are provided with equal reference signs so that the following description is
limited to the essential differences. After a cold start of the internal combustion engine or of
the vehicle equipped therewith, the heated catalyst is started in the first method step 51.
As soon as the heated catalyst 2 has reached its operational readiness, the open-loop or
closed-loop control device checks whether the exhaust-gas temperatures upstream and
downstream of the oxidation catalyst 11 are above predeterminable limit values and whether
the exhaust-gas mass flow of the raw exhaust gas exceeds a predeterminable minimum value.
If this is the case, the fourth operating state with comparatively low partial flow and low air
ratio can be started immediately, which allows rapid heating of the oxidation catalyst. If this
is not the case, the component of the exhaust gas aftertreatment device is first preheated in
catalytic burner mode according to the second operating state 52.
As soon as the heat front generated in the fourth method step 54 has penetrated all
components of the exhaust-gas aftertreatment device and the temperature sensor 132 at the
output of the SCR system also detects a value above a predeterminable limit value, the heated
catalyst 2 is switched to warm-keeping operation according to the above described sixth
operating state 56.
The process control according to figure 5 differs from the preceding control primarily in that
the open-loop or closed-loop control device 3 of the heated catalyst 2 reads the operating data
from the engine control unit 16 of the internal combustion engine 15 and, if necessary, uses
further data, such as the remaining driving distance, the topography and the road class, to
determine the required thermal power of the heated catalyst 2 in advance and, on the basis of
the current and/or future operating conditions of the internal combustion engine, sets the
respective optimum values for the partial flow and the fuel amount of the heated catalyst 2
using the heated-catalyst characteristic map 35. In this way, dead times of the control circuit
can be eliminated so that the desired values of the temperature of the component of the
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exhaust-gas aftertreatment can be reached more quickly or the actual temperature fluctuates to
a lesser extent.
Figure 6 shows the use of the method according to the invention in a first exemplary
embodiment of a multistage control system according to figure 4. Figure 6 a) shows the
exhaust-gas mass flow of a raw exhaust gas in curve A on the left ordinate and the oxygen
content of the exhaust gas in curve B on the right ordinate versus time in seconds. Figure 6 b)
shows on the same time axis the temperature of the temperature sensor 12 downstream of the
oxidation catalyst 11 on the right ordinate in curve C and the output power of the heated
catalyst in curve D on the left ordinate. Figure 6 b) shows measured values for a desired value
of 400°C. Figure 6 c) shows similar measured values as figure 6 b), but for a desired value of
280 °C.
As can be seen from figure 6, the output power of the internal combustion engine 15 in the
section shown from a WHTC cycle is not constant over time, but rather highly dynamic.
Accordingly, the exhaust-gas mass flow and the oxygen content of the exhaust gas also
change within a few seconds. As figures 6 b) and 6 c) both show, the heated catalyst 2 can be
controlled very rapidly with the open-loop or closed-loop control device according to the
invention, so that the heat introduced by the heated catalyst largely compensates for the
fluctuating heat introduced by the internal combustion engine, so that the output temperature
downstream of the oxidation catalyst 11 only fluctuates to a small extent. The oxidation
catalyst 11 can therefore always be used even in the part-load operation of the internal
combustion engine. Emission slip does not occur.
Figure 7 describes the use of the method according to the invention in a second exemplary
embodiment, namely the regeneration of a particulate filter 12. Figure 7 a) shows the exhaustgas mass flow in curve A.
Figure 7 b) shows in curve F the exhaust-gas temperature of the raw exhaust gas downstream
of the internal combustion engine. Curve C shows the temperature at the outlet of the
oxidation catalyst or at the inlet of the particulate filter. Figure 7 c) shows in curve E the CO
content of the raw exhaust gas and in curve G the CHx content.
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For the regeneration of the particulate filter 12, high exhaust-gas temperatures are required to
oxidize the embedded particles and discharge them in gaseous form from the particulate filter
12. According to the prior art, the exhaust-gas temperature is raised, for this purpose, by
internal engine measures, which leads to poor consumption and emission values during the
regeneration.
As Figure 7 shows, switching on the heated catalyst 2 after about 60 seconds leads to a rapid
increase in the exhaust-gas temperature from about 200°C to about 600°C. The exhaust-gas
temperature is kept constant by the heated catalyst within a narrow temperature range despite
a dynamic load demand on the internal combustion engine and correspondingly fluctuating
exhaust-gas mass flow of the raw exhaust gas over time. As curves E, F and G show, no
further in-engine measures are required for regeneration, i.e. the temperature of the rawexhaust gas remains below 250°C at all times. Similarly, the pollutant emissions shown in
curves E and G are not increased during the regeneration of the particulate filter, which is
different from the prior art.
Of course, the invention is not limited to the illustrated embodiments. Therefore, the above
description should not be considered limiting but explanatory. The below claims should be
understood as meaning that a stated feature is present in at least one embodiment of the
invention. This does not rule out the presence of further features. Where the claims and the
above description define “first” and “second” embodiments, this designation is used to
distinguish between two similar embodiments without determining a ranking order.
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WE CLAIM:
1. Method for introducing heat into at least one component (11, 12, 13) of an exhaust-gas
aftertreatment device (1) of an internal combustion engine (15), in which method a
partial flow of an exhaust-gas flow is at least partially reacted with fuel in a heated
catalyst (2) and fed back to the exhaust-gas flow, characterized in that the amount of
fuel fed to the heated catalyst (2) and/or the partial flow fed to the heated catalyst (2) is
controlled, by open-loop or closed-loop control, in accordance with the exhaust-gas
temperature upstream and/or downstream of the component (11, 12, 13), and the
amount of fuel fed to the heated catalyst (2) and/or the partial flow fed to the heated
catalyst (2) being determined by means of at least one heated-catalyst characteristic map
(35).
2. Method according to claim 1, characterized in that the exhaust-gas temperature
upstream and/or downstream of the component (11, 12, 13) is detected using at least
one temperature sensor (111, 112, 132).
3. Method according to claim 1 or 2, characterized in that the exhaust-gas temperature
upstream and/or downstream of the component (11, 12, 13) is determined from the
operating state of the internal combustion engine (15).
4. Method according to claim 3, characterized in that the operating state of the internal
combustion engine is determined from currently applied characteristic map values or
characteristic map ranges of the engine control unit (16).
5. Method according to any one of claims 1 to 4, characterized in that the input variables
(351) of the heated-catalyst characteristic map (35) are selected from the exhaust-gas
mass flow of the internal combustion engine and/or the oxygen content of the raw
exhaust gas of the internal combustion engine and/or at least one exhaust-gas
temperature and/or a driving profile and/or a navigation destination and/or position data
and/or the state of charge of at least one battery.
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6. Method according to claim 5, characterized in that the exhaust-gas mass flow of the
internal combustion engine (2) and/or the oxygen content of the raw exhaust gas of the
internal combustion engine and/or at least one exhaust-gas temperature are determined
by means of a first reference-controlled synthesizer.
7. Method according to any one of claims 1 to 6, characterized in that the thermal power
outputted by the heated catalyst (2) is determined from the fuel amount fed to the heated
catalyst (2) and/or the partial flow fed to the heated catalyst (2) by means of a second
reference-controlled synthesizer.
8. Method according to any one of claims 1 to 7, characterized in that the heated catalyst
(2) has at least a second operating state (52) in which the air ratio λ of the heated
catalyst (2) is between about 0.75 and about 30 or between about 1.0 and about 10, and
the heated catalyst (2) has at least a fourth operating state (54) in which the air ratio λ of
the heated catalyst (2) is between about 0.05 and about 0.7.
9. Method according to any one of claims 1 to 8, characterized in that the partial flow is
selected between about 3 kg/h and about 100 kg/h or between about 6 kg/h and about 80
kg/h.
10. Method according to any one of claims 1 to 9, characterized in that the heated catalyst
(2) contains at least one electrical heating device which, in a first operating state, is used
to bring the heated catalyst () to an operating temperature at which supplied fuel can be
at least partially reacted on the heated catalyst (2) and/or
in that the heated catalyst (2) contains at least one electrical heating device which, in an
eighth operating state, is used to heat a partial flow, fed to the heated catalyst (2), of the
raw exhaust gas of the internal combustion engine (15).
11. Method according to any one of claims 1 to 10, characterized in that the component (11,
12, 13) is selected from an oxidation catalyst (11) and/or a three-way catalyst and/or an
SCR catalyst (13) and/or a particulate filter (12).

12. Data carrier having data stored thereon or signal sequence which represents data and is
suitable for transmission by means of a computer network, wherein the data represents a
computer program which carries out a method according to any one of claims 1 to 11,
when the computer program is executed on a microprocessor.
13. Open-loop or closed-loop control device (3), which is designed to carry out a method
according to any one of claims 1 to 11.