Method for Introducing Heat into at Least One Component of an Exhaust-Gas Aftertreatment Device, Software and Open-Loop or Closed-Loop Control Device

Description

RELATED APPLICATIONS

This is a divisional application to U.S. Ser. No. 18/313,674 which is a Bypass Continuation of International Application No. PCT/EP2021/081092 filed Nov. 9, 2021, and published as WO 2022/096072A1, which claims priority to DE 10 2020 129 497.2 filed Nov. 9, 2020.

FIELD OF THE INVENTION

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 heating 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.

BACKGROUND OF THE INVENTION

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 heating 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 heating catalyst allows the production of an easily ignitable synthesis gas from the supplied fuel. This 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 heating 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 closed-loop 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.

SUMMARY

In one embodiment, a method for introducing heat into an exhaust-gas aftertreatment device connected to an internal combustion engine which outputs an exhaust-gas flow is disclosed. The exhaust-gas aftertreatment device may comprise one or more of an oxidation catalyst component, a particulate filter component and an SCR system component, the method comprising: at least partially reacting a partial flow of the exhaust-gas flow with fuel in a heating catalyst and feeding the reacted partial flow back into the exhaust-gas flow; and controlling the amount of fuel fed to the heating catalyst and/or the partial flow of exhaust-gas flow fed to the heating catalyst based on an exhaust-gas temperature upstream and/or downstream of said one or more components in accordance with at least one heating-catalyst characteristic map, wherein the exhaust-gas temperature upstream and/or downstream of said one or more components is indirectly determined from an operating state of the internal combustion engine, without direct measurement by temperature sensors.

In another embodiment, a method for introducing heat into an exhaust-gas aftertreatment device connected to an internal combustion engine which outputs an exhaust-gas flow is disclosed. The exhaust-gas aftertreatment device may comprise one or more of an oxidation catalyst component, a particulate filter component and an SCR system component, the method comprising: at least partially reacting a partial flow of the exhaust-gas flow with fuel in a heating catalyst and feeding the reacted partial flow back into the exhaust-gas flow; and controlling the amount of fuel fed to the heating catalyst and/or the partial flow of exhaust-gas flow fed to the heating catalyst based on an exhaust-gas temperature upstream and/or downstream of said one or more components in accordance with at least one heating-catalyst characteristic map, wherein input variables of the heating-catalyst characteristic map are selected from one or more of: (i) exhaust-gas mass flow of the internal combustion engine; (ii) oxygen content of raw exhaust gas of the internal combustion engine; (iii) at least one exhaust-gas temperature; (iv) a driving profile; (v) a navigation destination; (vi) position data; and (vii) state of charge of at least one battery.

According to one embodiment 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 one embodiment 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 power generators or compressors. The advantages of the method according to one embodiment 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 one embodiment 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 one embodiment, 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 heating catalyst in order to feed the product generated in the heating 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 one embodiment 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 openloop or closed-loop control, the amount of heat emitted by the heating catalyst on the basis of the temperature. In this context, the heat emitted by the heating 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 heating catalyst as a reference variable. According to one embodiment, it is thus proposed to adjust one or both influencing variables on the heat emitted by the heating 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 value or within predeterminable fluctuation ranges. In some embodiments of the invention, the heating 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 heating 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 heating catalyst used according to one embodiment.

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 heating 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 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 exhaustgas 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 one embodiment, the amount of fuel supplied to the heating catalyst and/or the partial flow of the raw exhaust gas supplied to the heating catalyst is determined by means of at least one heating catalyst characteristic map. The input variables of the heatedcatalyst characteristic map can, for example, be selected from the exhaust-gas mass flow of the 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 exhaust-gas 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 heating catalyst can be determined from the amount of fuel supplied to the heating catalyst and/or the partial flow of the raw exhaust gas of the internal combustion engine which is supplied to the heating catalyst and/or the oxygen content of the raw exhaust gas by means of a second referencecontrolled synthesizer. Therefore, an exact measured value of the thermal power or the amount of heat introduced into the exhaust-gas aftertreatment by the heating 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 heating catalyst can have at least a second operating state in which the air ratio λ of the heating catalyst is between about 0.75 and about 30. In other embodiments of the method, the heating catalyst can have at least a second operating state in which the air ratio λ of the heating 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 heating catalyst with the residual oxygen of the raw exhaust gas. In this first operating state, the heating 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 heating catalyst can further have at least a fourth operating state in which the air ratio λ of the heating 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 heating 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 exhaustgas 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 heating catalyst can include at least one electrical heating device that is used in a first operating state to bring the heating catalyst to an operating temperature at which supplied fuel can be at least partially reacted on the heated catalyst. This allows the heating catalyst to be brought to operating temperature after a cold start.

In some embodiments of the invention, the heating 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 heating catalyst can be made dependent on the state of charge of at least one battery, i.e. the heating catalyst is not electrically heated until the electrical energy is not needed as a charging 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 heating 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 heating catalyst and/or on the basis of the required thermal heating power.

The method proposed according to one embodiment can be implemented in a computer program which carries out the method according to one embodiment 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 closedloop control device which is designed to carry out the method according to one embodiment. 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 heating catalyst from the current operating state of the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 shows a first exemplary embodiment of an exhaust-gas aftertreatment device that can be used according to one embodiment.

FIG. 2 shows a second exemplary embodiment of an exhaust-gas aftertreatment device that can be used according to one embodiment.

FIG. 3 shows a block diagram of an open-loop or closed-loop control device according to the present invention.

FIG. 4 shows a structure chart of the method according to one embodiment in a first embodiment.

FIG. 5 shows a structure chart of the method according to one embodiment in a second embodiment.

FIGS. 6A, 6B and 6C show the use of the method according to one embodiment in a first exemplary embodiment.

FIGS. 7A, 7B and 7C show the use of the method according to one embodiment in a second exemplary embodiment.

DETAILED DESCRIPTION

A first exemplary embodiment of an exhaust-gas aftertreatment device 1 usable according to one embodiment is explained in more detail on the basis of FIG. 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 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 CH_X, CO and/or NO_X.

The raw exhaust gas is fed to the exhaust-gas aftertreatment device 1 by means of an exhaust-gas line. Optionally, a sensor system can be installed in the exhaust-gas line, for example a λ-probe 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 FIG. 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 heating 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 heating 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 preventing cooling during operation, on the other hand. At full load or near full load operating conditions of the internal combustion engine, the heating catalyst 2 can be switched off.

With reference to FIG. 2, a second exemplary embodiment of an exhaust-gas aftertreatment device which can be used according to one embodiment 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. FIG. 2 shows an oxidation catalyst 11 which is designed to post-oxidize oxidizable components of the raw exhaust gas, for example CO and/or CH_x. A particulate filter 12 is disposed downstream of the oxidation catalyst, as described above. An SCR system, which is used in particular to reduce NO_x, is disposed downstream of the particulate filter 12.

In the illustrated exemplary embodiment, the heating 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 heating catalyst 2.

FIG. 2 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 FIG. 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 FIGS. 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.

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 FIG. 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. Thus, the exhaust-gas temperatures may be indirectly determined from the operating state of the internal combustion engine, without direct measurement by temperature sensors.

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 heating catalyst 2 as control variable. This control variable can be influenced by the amount of fuel supplied to the heating catalyst 2 as well as the amount of exhaust gas supplied to the heating catalyst and, in some cases, the electrical energy supplied to the heating catalyst as reference variables. The reference variables in turn depend on the oxygen content of the raw exhaust gas, the exhaust-gas 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 FIG. 3 therefore uses a heating catalyst characteristic map 35. The heating 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 heating 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 heating 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 heating catalyst 2 can 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 heating 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 heating 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 heating 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.

FIG. 4 shows a structure chart of a first embodiment of the method according to one embodiment. In the first embodiment, the heating 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 FIG. 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 heating 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 heating 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 heating catalyst can first be preheated by supplying an exhaust-gas mass flow with an optional electric heating device until supplied fuel is converted exothermically on the heating catalyst and heats the heating 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 heating 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 heating catalyst 2. In some embodiments, the heating 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 heating 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 substep 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 heating 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 heating catalyst 2. In the fourth operating state 54, the heating 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 heating 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 heating 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 heating catalyst 2 is primarily used to oxidize and vaporize remaining deposits and residual fuel in order to prevent permanent deposits and contamination in the heating 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 heating 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 heating catalyst 2, while the heating 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 heating 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 heating catalyst 2 so that the heating catalyst does not emit any heat even in the event that a partial flow of the exhaust gas permanently flows through the heating 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 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 FIG. 5, a structure chart of a second embodiment of the method according to one embodiment 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 heating catalyst is started in the first method step 51.

As soon as the heating 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 heating catalyst 2 is switched to warm-keeping operation according to the above described sixth operating state 56.

The process control according to FIG. 5 differs from the preceding control primarily in that the open-loop or closed-loop control device 3 of the heating 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 heating 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 heating catalyst 2 using the heatedcatalyst 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 exhaust-gas aftertreatment can be reached more quickly or the actual temperature fluctuates to a lesser extent.

FIGS. 6A, 6B and 6C show the use of the method according to one embodiment in a first exemplary embodiment of a multistage control system according to FIG. 4. FIG. 6A 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. FIG. 6B shows on the same time axis the temperature of the temperature sensor 112 downstream of the oxidation catalyst 11 on the right ordinate in curve C and the output power of the heating catalyst in curve D on the left ordinate. FIG. 6B shows measured values for a desired value of 400° C. FIG. 6C shows similar measured values as FIG. 6B, but for a desired value of 280° C.

As can be seen from FIGS. 6A-6C, 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 FIGS. 6B and 6C both show, the heating catalyst 2 can be controlled very rapidly with the open-loop or closed-loop control device according to one embodiment, so that the heat introduced by the heating 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.

FIGS. 7A, 7B and 7C describe the use of the method according to one embodiment in a second exemplary embodiment, namely the regeneration of a particulate filter 12. FIG. 7A shows the exhaust-gas mass flow in curve A.

FIG. 7B 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. FIG. 7C shows in curve E the CO content of the raw exhaust gas and in curve G the CH_x content.

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 FIGS. 7A-7C show, switching on the heating 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 heating 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 raw-exhaust 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.