Method and apparatus for electrically heating a catalytic converter of exhaust gases

Abstract

Method and device for electrically heating an exhaust-gas catalytic converter. A method and a device for heating an exhaust-gas catalytic converter (35) are described, which is arranged in an exhaust line (25) of an internal combustion engine (10) and has an electric heating device (37), wherein a secondary air mass flow (SLM) can be conveyed into the exhaust line (25) at a location upstream of the exhaust-gas catalytic converter (35) by means of an air conveying device (70), and the electric heating device (37) is activated in time before the internal combustion engine (10) is started. The temperature of the exhaust-gas catalytic converter (35) is monitored, and no secondary air mass flow (SLM) is conveyed into the exhaust line (25) or a secondary air mass flow (SLM) is conveyed into the exhaust line (25) at a first conveying quantity until the catalytic converter temperature (KT) reaches a predetermined first threshold value (SW1), and after the catalytic converter temperature (KT) reaches the predetermined first threshold value (SW1), the secondary air mass flow (SLM) is conveyed into the exhaust line (25) at a second conveying quantity which is greater than the first conveying quantity.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method and a device for electrically heating an exhaust gas catalytic converter of an internal combustion engine. BACKGROUND

[0002] Increasingly stringent legal regulations make it necessary for motor vehicles having internal combustion engines to reduce the raw emissions resulting from the combustion of air / fuel mixtures in the cylinders as far as possible on the one hand. On the other hand, exhaust gas aftertreatment systems are used in internal combustion engines, which convert pollutant emissions produced during the combustion process of air / fuel mixtures in the cylinders into harmless substances.

[0003] To this end, in particular exhaust gas catalytic converters are used, in which chemical conversion of the combustion pollutants takes place by oxidation or reduction of the respective pollutant. For this purpose, the exhaust gas catalytic converter has an active catalytic region in which the chemical conversion, i.e. the catalysis, takes place.

[0004] The necessary operating temperatures are mostly in the fuel and coating-related range from approximately 300°C to approximately 600°C. Since the catalysis taking place in the catalytic region generally requires a specific minimum temperature, also referred to as light-off temperature, for effective exhaust gas aftertreatment, it is necessary to ensure that the catalytic converter volume to be heated is heated to at least the light-off temperature as quickly as possible in order to be able to predict further reductions in the permissible pollutant emission limits under real driving conditions, i.e. so-called "real driving emissions".

[0005] It is therefore necessary to heat the catalytic converter to the desired operating temperature as quickly as possible. To this end, on the one hand, it is possible to carry out combustion engineering measures, i.e. measures for operating the internal combustion engine in such a way that the waste heat of the internal combustion engine can be used for rapid heating of the exhaust gas catalytic converter. However, this generally leads to higher fuel consumption and can only shorten the period of time after a cold start of the internal combustion engine in which the catalytic converter is not yet working and will emit a greater amount of pollutants, but cannot eliminate this period of time.

[0006] Alternatively or additionally, it is also known to use an electrically heatable exhaust-gas catalytic converter. Such an exhaust-gas catalytic converter has its own electric heating device which is fed, for example, from the on-board electrical system of a motor vehicle equipped with an internal combustion engine and which can heat the exhaust-gas catalytic converter to the desired operating temperature. The advantage of an electrically heatable exhaust-gas catalytic converter is that it can be brought to operating temperature in a so-called catalytic converter cold phase without the internal combustion engine having to be operated, i.e. to operating temperature before the internal combustion engine is started, for example. Thereby, pollutants are already converted from the moment of starting the internal combustion engine. In order to optimally operate the exhaust-gas catalytic converter, the entire volume of the catalytic converter substrate, i.e. the entire catalytically active surface, must be brought to operating temperature, but at least to the light-off temperature. Here, the conversion of NOx emissions requires a greater catalytic converter volume than the conversion of the pollutants CO and HC.

[0007] In the case of an electrically heatable catalytic converter (EHC = Electrically Heated Catalyst or E-KAT), the electric heating device is implemented, for example, in the form of one or more electric heating discs which can be flowed through by the gas / exhaust gas, which convert the electric power into heating power and are arranged directly adjacent to the catalytic converter substrate which is not heated itself.

[0008] Due to the relatively small volume of the electric heating discs and the catalytic coating of the inner surface of the heating discs themselves, the catalytic surface is heated directly, i.e. on site, and very quickly.

[0009] The construction of such an electrically heatable exhaust-gas catalytic converter is described, for example, in the publications DE 199 43 846 A1 and DE 44 34 673 A1.

[0010] The relatively small active catalytic surface of the heating discs can be sufficient to reduce the pollutants of this phase to an allowable extent, if necessary at least in the start-up operation of the internal combustion engine characterized by low load, but it is also necessary to heat the remaining catalytic converter substrate as quickly and as completely as possible to operating temperature. This takes place almost exclusively by thermal radiation in the heating phase before the internal combustion engine is started, which allows only limited heat transfer. After the internal combustion engine is started, the heating of the remaining catalytic converter substrate is supported by the exothermic conversion reactions in the heating discs which the exhaust gas sets in.

[0011] The publication DE 10 2019 219 906 A1 discloses a method for heating a catalytic converter arranged in an exhaust gas duct of a motor vehicle, wherein secondary air can be fed into the exhaust gas duct upstream of the catalytic converter. When the internal combustion engine is running, the enrichment of the catalytic converter by the enrichment of the combustion mixture and thus also of the exhaust gas and the additional feed of secondary air causes the air ratio lambda occurring downstream of the catalytic converter to be heated to oscillate around the stoichiometric air ratio, the exothermic reaction of the enriched exhaust gas in the catalytic converter thus contributing to the rapid heating of the catalytic converter substrate.

[0012] However, given the increasing frequency of start-stop operation of the internal combustion engine and the frequent increase in load immediately after starting, it is desirable that as large a volume of the catalytic converter substrate as possible reaches the operating temperature before the internal combustion engine is started, but at least above the light-off temperature, in order to ensure complete conversion of the pollutants in the exhaust gas. Simply increasing the heating power for this purpose is not constructive, since this can quickly lead to overheating and thus to damage to the heating disc.

[0013] The part of the exhaust gas catalytic converter below the light-off temperature does not contribute to the conversion. The goal of efficient and rapid heating of the exhaust gas catalytic converter is therefore to keep the area below the light-off temperature as small as possible. Furthermore, the heating device, usually a heating disc, should be brought to the light-off temperature very quickly in order to be able to convert exhaust gas components immediately upon starting of the internal combustion engine. SUMMARY

[0014] The task on which the present application is based is therefore to provide a method and a device for heating an electrically heatable exhaust gas catalytic converter of an internal combustion engine, the cold start behavior of which is improved, so that the electrically heatable exhaust gas catalytic converter can be operated particularly quickly and efficiently and has an improved conversion behavior, in particular in the starting phase of the internal combustion engine.

[0015] This task is solved according to the features of the present application. Advantageous designs of the present application are the subject of the following description.

[0016] The invention features a method for heating an exhaust-gas catalytic converter arranged in an exhaust line of an internal combustion engine and having an electric heating device, and a device for carrying out the method. Here, a secondary air mass flow can be delivered into the exhaust line at a location upstream of the exhaust-gas catalytic converter by means of an air delivery device, and the electric heating device is activated with a predefined heating power before the internal combustion engine is started in time. The catalytic converter temperature is monitored in a region of the exhaust-gas catalytic converter close to the heating device, and no secondary air mass flow is delivered or a secondary air mass flow is delivered into the exhaust line in a first delivery quantity in a time period after activation of the heating device until the catalytic converter temperature reaches a predefined first threshold value, and the secondary air mass flow is delivered into the exhaust line in a second delivery quantity greater than the first delivery quantity after the catalytic converter temperature reaches the predefined first threshold value.

[0017] Optimal use of the electrical energy is achieved by the method according to the invention in order to heat the electrically heated exhaust-gas catalytic converter (EHC) to such an extent before the internal combustion engine is started that a high conversion rate of pollutants is already ensured at the start of the internal combustion engine. Here, a greater active catalytic converter volume (catalytic region) can be achieved in a short time compared to conventional methods.

[0018] The method opens up the possibility of being able to operate the heating device from the outset and before the internal combustion engine is started with an increased heating power without the risk of overheating and thus thermal damage to the catalytic substrate. This is achieved by not delivering a secondary air mass flow or only delivering a small secondary air mass flow until a predefined first threshold value of the catalytic converter temperature is reached in order to ensure that this threshold value is reached as quickly as possible, wherein the first threshold value is set, for example, in the range of the light-off temperature. In this case, the region of the exhaust-gas catalytic converter close to the heating device is effectively heated together by radiation and also by convection when there is a secondary air mass flow with a relatively low first delivery quantity.

[0019] In order to prevent a temperature overshoot of the electric heating device in the case of continued application of a high heating power, the delivery quantity of the secondary air mass flow is increased to a value that is significantly increased relative to the first delivery quantity when the predefined first threshold value of the catalytic converter temperature is reached, which is in any case predetermined with a safety margin below the maximum permissible catalytic converter temperature. This increases the convective heat transfer from the heating device to the remaining substrate volume of the exhaust-gas catalytic converter when the temperature has already risen, and thus heat is quickly introduced into the catalytic converter substrate.

[0020] The heat coupling between the heating device and the substrate of the catalytic converter is improved by a secondary air mass flow and thus also the measurement of the catalytic converter temperature in the region of the heating device. In addition to the electrical heating power, a predefined value of the delivery quantity of the secondary air mass flow is decisive for the size of the catalytic converter volume (catalytic region) which is activated at the starting moment of the internal combustion engine.

[0021] Compared to known heating strategies, the air mass flow introduced into the exhaust gas catalytic converter can expand the portion of the exhaust gas catalytic converter which is above the light-off temperature (typically 300°C) at the starting moment of the internal combustion engine. The portion of the catalytic converter which is below this temperature does not contribute to the conversion. Therefore, the goal of an efficient and fast heating of the exhaust gas catalytic converter is to keep the region below the light-off temperature as small as possible. Furthermore, the heating device, usually a heating plate, should reach the light-off temperature very quickly in order to be able to convert exhaust gas components immediately at the starting of the internal combustion engine.

[0022] An advantageous extension of the method is characterized in that, as soon as the catalytic converter temperature reaches an upper limit value, the heating power of the heating device is reduced and then regulated so that it is not below a predefined operating temperature of the exhaust gas catalytic converter which is greater than a predetermined first threshold value of the catalytic converter temperature and smaller than the upper limit value. In this way, it is ensured that the energy consumption of the heating device is limited to the required extent and that valuable energy (for example from the on-board power network of a motor vehicle) is not wasted.

[0023] In an extension of the above-described method, when the catalytic converter temperature is greater than or equal to the operating temperature and after the starting of the internal combustion engine, the delivery quantity of the secondary air mass flow delivered into the exhaust gas duct is regulated in accordance with a regulating sensor arranged downstream of the exhaust gas catalytic converter in the exhaust gas duct, so that the air ratio λ downstream of the catalytic converter approaches the stoichiometric value 1. Here, as a regulating sensor, for example, a nitrogen oxide sensor, a lambda sensor or an ammonia sensor arranged downstream of the catalytic converter can be used. In this way, an excess of oxygen in the exhaust gas is avoided, which can have a negative effect on the NOx emissions. Furthermore, the possibility arises of maintaining the exhaust gas catalytic converter at the operating temperature in conjunction with a change in the fuel supply during the operation of the internal combustion engine without having to draw electrical energy from the on-board power network.

[0024] An advantageous implementation of the invention is characterized in that the light-off temperature of the exhaust gas catalytic converter is predetermined as the first threshold value of the catalytic converter temperature. In this way, it is ensured that the heating device, which also has a catalytic coating, and the region of the catalytic converter substrate close to the heating device reach at least the light-off temperature quickly before the starting of the internal combustion engine.

[0025] In a further embodiment of the method according to the application, the first delivery quantity of the secondary air mass flow is adjusted in accordance with the temperature of the catalytic converter present when the heating device is activated. This has a particularly advantageous effect when the internal combustion engine is operated in "start-stop operation" (i.e. with frequent intermediate stop phases due to a partial-slip operation, full-electric operation or stopping at traffic lights of the motor vehicle). In these cases, the electric heating generally starts at a higher level than in the cold start case. In order to accelerate this heating, a higher first delivery quantity of the secondary air mass flow can be used here if necessary than in the cold start case.

[0026] In a further embodiment of the method according to the application, the first delivery quantity of the secondary air mass flow can be predefined as a value between 0.2 kg / h and 5 kg / h in accordance with the power of the electric heating device, and the second delivery quantity of the secondary air mass flow can be predefined as a value between 10 kg / h and 40 kg / h. Here, in the case of a higher rated power of the heating device and if necessary in accordance with the volume of the catalytic converter substrate, a greater first and second delivery quantity of the secondary air mass flow can in principle also be adjusted respectively. This enables the heating process to be optimized in terms of the structural and power-technical boundary conditions of the respective application case.

[0027] A further embodiment of the method according to the application is characterized in that an electrically drivable air delivery device is used as air delivery device, which can be electronically controlled or regulated in terms of its delivery power. This enables the secondary air mass flow to be used economically and precisely and the delivery quantity of the secondary air mass flow to be controlled or regulated.

[0028] This applies in particular in that, according to a further embodiment, the delivery quantity of the secondary air mass flow delivered into the exhaust tract can be varied by means of an electronically regulatable delivery power of the electrically drivable air delivery device and / or an electronically controllable air valve (71).

[0029] In a further embodiment, as an alternative to an electric air delivery device, an unignited internal combustion engine can itself be used as air delivery device, which is driven by means of an electric machine. This method makes use of the fact that a reciprocating piston machine can also be operated as a compressor, i.e. as a pump, by means of an external drive (here for example a starter generator or starter motor which is coupled to the internal combustion engine and is present in any case). While this has the disadvantage that here more electrical energy is to be expected to be consumed, since the entire internal combustion engine has to be driven, on the other hand it has the advantage that no additional aggregates and no additional installation space are required.

[0030] The device for heating an exhaust-gas catalytic converter according to the application, which is arranged in an exhaust line of an internal combustion engine and has an electric heating device and a temperature sensor arranged in a region of the exhaust-gas catalytic converter close to the heating device, wherein the device has an air delivery device by means of which a secondary air mass flow can be delivered into the exhaust line at a location upstream of the exhaust-gas catalytic converter, and the device has an electronic control device which is constructed and arranged to control the method according to the application as described above.

[0031] Like the method according to the application, the optimal use of the electrical energy is achieved by the device according to the application in order to heat the electrically heated exhaust-gas catalytic converter (EHC) to such an extent before the start of the internal combustion engine that a high conversion rate of pollutants is already ensured at the start of the internal combustion engine. Here, a larger catalytic converter volume or catalytic region 39 can be activated in a short time.

[0032] The features of the illustrated embodiments can, individually or in combination, supplement the subject matter of the independent claims and expand these subject matters, as far as the features of the illustrated embodiments are not mutually exclusive or can only be applied alternatively. BRIEF DESCRIPTION OF DRAWINGS

[0033] Further advantages and designs of the method according to the application and of the device for such an electrically heated exhaust-gas catalytic converter are explained in more detail by means of the following description of an embodiment with reference to the drawings.

[0034] Figure 1 A schematic diagram of an internal combustion engine with an exhaust-gas aftertreatment facility is shown,

[0035] Figure 2 A diagram of various operating parameters when carrying out the method according to the application is shown. DETAILED DESCRIPTION

[0036] Figure 1 An internal combustion engine 10, an electric machine 50 drivingly connected to the internal combustion engine 10, an air intake 15, an engine block 20 with a plurality of cylinders not represented in detail, and an exhaust line 25 in which an exhaust-gas aftertreatment facility 30 is arranged or through which the exhaust-gas aftertreatment facility 30 extends, are shown in a schematic diagram. An intake air mass flow ALM, which can also be referred to as a primary air mass flow, is delivered to the internal combustion engine 10 by means of the air intake 15 and fuel is delivered to the internal combustion engine 10, for example by means of a fuel injection facility (not shown here). In the individual cylinders, the fuel is combusted with the intake air mass flow ALM and is discharged from the internal combustion engine 10 into the exhaust line 25 as an exhaust gas mass flow AGM.

[0037] The exhaust gas aftertreatment facility 30 has an exhaust gas catalytic converter 35 and the like. With regard to the exhaust gas mass flow AGM downstream of the exhaust gas catalytic converter 35, optionally also further exhaust gas aftertreatment components 40 are provided in the exhaust gas line 25, of which only one is shown by way of example. As possible exhaust gas aftertreatment components 40, a three-way catalytic converter, an SCR catalytic converter for selective catalytic reduction, a diesel particulate filter, an SCR-coated diesel particulate filter, a gasoline particulate filter, a NOx catalytic converter (lean NOx trap) are listed here.

[0038] The exhaust gas catalytic converter 35 is configured as an electrically heatable catalytic converter and comprises a jacket 36 which surrounds a catalytic region 39 having a catalytic converter substrate. Arranged upstream, i.e. in front of the catalytic region 39, from the flow direction of the exhaust gas is an electric heating device 37.

[0039] The catalytic region 39 serves for catalytically treating or oxidizing or reducing the exhaust gas of the internal combustion engine 10 present in the exhaust gas line 25, so that the exhaust gas can be discharged into the environment as free as possible of pollutants.

[0040] The electric heating device 37 is preferably configured as a heating disc and can extend completely or almost completely over the diameter of the interior space of the jacket 36, i.e. over the entire or almost the entire end face of the catalytic converter substrate, so that a large amount of thermal energy is available for heating the catalytic region 39 or the catalytic converter substrate and can be transferred to the catalytic converter substrate when the heating disc is heated. In order to secure the electric heating device 37, as shown here, a so-called support catalytic converter 38 can be provided, for example, upstream of the electric heating device 37, which supports or carries the electric heating device 37 or the heating disc.

[0041] In the catalytic region 39, a temperature sensor 45 is arranged in the vicinity of the electric heating device 37, which continuously detects the temperature in the catalytic region 39 in the vicinity of the electric heating device 37 during operation and thus can provide information about the temperature of the catalytic converter substrate here or, in combination with a model calculation about the heat input and the temperature distribution, can at least approximately determine the temperature distribution in the catalytic converter substrate.

[0042] In the region of the exhaust gas line 25 between the engine block 20 and the exhaust gas catalytic converter 35, i.e. in the exhaust gas mass flow AGM upstream of the exhaust gas catalytic converter 35, an introduction point for a secondary air mass flow SLM is provided. The secondary air mass flow SLM is introduced into the exhaust gas line 25 by means of an electronically controllable, usually also electrically driven air delivery device 70 and by means of an air delivery nozzle 72. An electronically controllable air valve 71 arranged downstream of the air delivery device 70 serves to additionally release and close or meter the secondary air mass flow SLM.

[0043] Furthermore, in relation to the exhaust gas mass flow AGM downstream of the exhaust gas catalytic converter 35, an adjusting sensor 47 is arranged in the exhaust gas line 25. As adjusting sensor 47, here a lambda sensor, for example also a nitrogen oxide sensor or an ammonia sensor, arranged downstream of the exhaust gas catalytic converter 35 can be used with preference. On the basis of the measured values of the adjusting sensor 47, the secondary air mass flow can be adjusted such that the air ratio lambda downstream of the exhaust gas catalytic converter 35 approaches the stoichiometric value 1.

[0044] The electric machine 50 coupled to the internal combustion engine 10 is, for example, a starter generator or an electric motor auxiliary drive used in the context of hybrid drive solutions. In the case of the internal combustion engine 10 not being ignited, i.e. before the internal combustion engine 10 is started, the electric machine can be used to drag the internal combustion engine 10 and, if necessary, to operate as air delivery device 70 to draw in the secondary air mass flow SLM through the intake tract 15 and to blow it into the exhaust gas line 25.

[0045] Furthermore, an electronic control device (ECU) 60 is provided, which can receive input signals ES and output output signals AS in accordance with the input signals ES and a work program stored in the electronic control device 60. The input signals ES are provided, for example, by the temperature sensor 45 and the adjusting sensor 47, as is shown here with dashed arrows. In contrast, the output signals AS are output, as is shown here with dashed arrows, to the electric machine 50, to the air delivery device 70, to the air valve 71 and, quite importantly, to the electric heating device 37 for actuating or adjusting them. Furthermore, further actuators and sensors, not shown, can be provided, for example for actuating the internal combustion engine 10 and for actuating other components of the exhaust gas facility, for example an exhaust gas recirculation device. It is thereby possible for the electronic control device 60 to actively actuate at least the electric heating device 37 and the air delivery device 70 and, if necessary, the air valve 71 in accordance with the method according to the application in dependence on the signal of the temperature sensor 45. The electronic control device 60 can be designed as a separate catalytic converter heating control device or can be integrated into an engine control device for the internal combustion engine 10.

[0046] If energy is applied to the electric heating device 37, this electric heating device heats up and transfers its thermal energy to the catalytic region 39 of the exhaust gas catalytic converter 35. In accordance with the application, the electric heating device 37 is activated with a predefined heating power HL in time before the internal combustion engine 10 is started. At the same time, the catalytic converter temperature KT is monitored in the region of the exhaust gas catalytic converter 35 close to the electric heating device 37 by means of the temperature sensor 45.

[0047] The temperature increase in the entire catalytic region 39 can be determined, for example, by forming a model, wherein as input variables for this model the measured values of the temperature sensors 45 and the thermal mass of the catalytic region 39 or catalytic converter substrate and the energy for evaporating moisture, which is stored in the coating of the catalytic converter substrate, can be used. Then, in the time period after activation of the electric heating device 37 until the catalytic converter temperature KT reaches a predetermined first threshold value SW1, no secondary air mass flow SLM is delivered into the exhaust gas duct 25 or the secondary air mass flow SLM is delivered into the exhaust gas duct 25 in a first delivery amount.

[0048] The delivery of the secondary air mass flow SLM in the time period until the first threshold value SW1 is reached, for example, in a relatively small delivery amount between 0.2 kg / h and 5 kg / h, can promote the heat transfer to the catalytic converter substrate and a reliable temperature measurement in the exhaust gas catalytic converter 35 by means of the temperature sensors 45 without significantly slowing down the rapid temperature increase of the electric heating device 37 itself and its environment in the catalytic converter substrate.

[0049] After the catalytic converter temperature KT reaches a predetermined first threshold value SW1, which is, for example, at the level of the light-off temperature of the catalytic region 39, for example in the range of 300°C, the secondary air mass flow SLM is delivered into the exhaust gas duct 25 in a second delivery amount, which is significantly higher than the first delivery amount, in the order of magnitude between 10-40 kg / h.

[0050] Thereby an intensified heat transfer to the catalytic region 39, i.e. the catalytic converter substrate, takes place and the temperature increase of the exhaust gas catalytic converter as a whole is further accelerated and the volume of the catalytic converter substrate downstream of the electric heating device 37, which reaches the light-off temperature, is rapidly increased. By this process, the temperature increase in the exhaust gas catalytic converter is significantly faster than in the case where the secondary air mass flow is introduced from the outset with a large delivery amount, because the electric energy is used at the beginning mainly for heating the electric heating device itself, which quickly reaches the light-off temperature, since there is no excessive cooling by heat dissipation. The intensified heat transfer, which is caused by the increased delivery amount of the secondary air mass flow SLM, takes place only at a higher temperature level, which accelerates the heat transfer.

[0051] In Figure 2 the heating strategy for an exhaust gas catalytic converter according to the application is shown based on three time-consistent diagrams, which include the time course of the relevant operating variables - heating power HL, catalytic converter temperature KT and delivery amount of the secondary air mass flow SLM.

[0052] The upper chart shows the time-varying power of the electric heating device 37 of the exhaust gas catalytic converter 35, the middle chart shows the temperature variation of the catalytic converter in the region of the exhaust gas catalytic converter 35 near the electric heating device 37, and the lower chart shows the variation of the delivery rate of the secondary air mass flow (SLM).

[0053] Corresponding to the method for heating the exhaust gas catalytic converter 35—the exhaust gas catalytic converter is arranged in the exhaust gas duct 25 of the internal combustion engine 10 and has an electric heating device 37, wherein a secondary air mass flow SLM can be delivered to the exhaust gas duct 25 at a position upstream of the exhaust gas catalytic converter 35 by means of an air delivery device 70, the catalytic converter temperature KT is monitored in the region of the exhaust gas catalytic converter 35 near the electric heating device 37, and the electric heating device 37 is activated with a predetermined heating power HL before the internal combustion engine 10 is started.

[0054] exist Figure 2 The diagram shows the time period immediately preceding the start-up of the internal combustion engine 10. At time t1, the electric heating device 37 is activated with a pre-given heating power HL, here for example, 4 kW. Therefore, this moment marks the start of the process flow. Before this moment, the electric heating device 37 is deactivated and the heating power HL shown in the diagram above remains at a value of 0. The air delivery device 70 is also deactivated until time t1, and the secondary air mass flow rate remains at a value of 0. The catalytic converter temperature shown in the intermediate diagram has been monitored before time t1 or detected at the latest at time t1, and is at the ambient temperature level in the case of a cold start of the internal combustion engine 10, as shown here. However, the catalytic converter temperature KT at time t1 can also be at a higher level if the internal combustion engine 10 has been running recently and has not yet fully cooled down.

[0055] Time t1 can be triggered by an event indicating that the internal combustion engine 10 is about to start. Corresponding events for possible internal combustion engine start-up include preparatory measures such as the opening of the driver's door, door lock activation, and driver's seat occupancy signal, when the internal combustion engine 10 in the motor vehicle is running. The processing of corresponding signals and the operation of corresponding functions, such as those of the electric heating device 37 and the air delivery device 70, are performed by means of the electronic control unit 60.

[0056] Immediately after the activation of the electric heating device 37, the catalytic converter temperature KT begins to rise rapidly until, at the end of the first time period following the activation of the electric heating device 37, the catalytic converter temperature reaches a predetermined first threshold SW1 at time t2. This first threshold, in this example, is, for example, 300°C. This roughly corresponds to the activation temperature or ignition temperature of the catalytic region 39. Depending on the type or design of the catalytic converter to be heated, the first threshold SW1 may also be predetermined to be higher or lower.

[0057] Likewise at the time t1, the air delivery device 70 is activated, if necessary in combination with the air valve 71, such that a secondary air mass flow SLM is delivered into the exhaust gas duct 25 in a first delivery quantity, in this example 2 kg / h. This advantageously leads to an additional convective heat transfer from the electric heating device 37 into the remaining catalytic region 39 without excessively cooling the electric heating device 37. The first delivery quantity can preferably be pre-defined to have a value between 0, i.e. no secondary air mass flow, and 5 kg / h or up to 10 kg / h, depending on the available power of the electric heating device 37 and / or the starting value of the catalytic converter temperature KT at the time t1 and, if necessary, on the overall configuration of the exhaust gas catalytic converter 35. The first delivery quantity of the secondary air mass flow SLM can also be adjusted according to the gradient of the temperature increase of the catalytic converter temperature KT within the first time period (t1 to t2) to ensure a uniform increase of the catalytic converter temperature KT.

[0058] After the catalytic converter temperature KT has reached a predetermined first threshold value SW1 at the time t2, the secondary air mass flow SLM is delivered into the exhaust gas duct 25 in a second delivery quantity, which is greater than the first delivery quantity, here for example 10 kg / h, by correspondingly electronically manipulating the air delivery device 70 by means of the electronic control device 60, if necessary in combination with the air valve 71. This is shown in the diagram by a sudden increase in the delivery quantity of the secondary air mass flow at the time t2. The second delivery quantity can preferably be pre-defined to have a value between 10 kg / h and 40 kg / h or up to 60 kg / h, depending on the available power of the electric heating device 37 and, if necessary, on the overall configuration of the exhaust gas catalytic converter 35. Here too, the first delivery quantity of the secondary air mass flow SLM can be adjusted according to the gradient of the temperature increase of the catalytic converter temperature KT within the second time period (t2 to t3) to ensure a uniform increase of the catalytic converter temperature KT.

[0059] The corresponding control or adjustment of the secondary air mass flow is achieved, for example, in that the air delivery device 70 and / or, if necessary, also the air valve 71 can be electrically driven and their delivery power can be electronically controlled or adjusted.

[0060] According to the illustrated example, the catalytic converter temperature KT continues to continuously increase under the condition that the secondary air mass flow SLM is kept constant after the increase in heating power HL at time t2. However, the catalytic converter temperature KT increases from time t2 with a smaller gradient than before due to the increased heat transfer caused by the increased secondary air mass flow SLM into the catalytic region 39 until the pre-defined upper limit value OGW of the catalytic converter temperature is reached at time t3. The volume of the catalytic region or catalytic converter substrate which is heated to the light-off temperature and thus has catalytic activity increases rapidly thereby. The size of the pre-defined value of the upper limit value OGW of the catalytic converter temperature depends on the design and coating, i.e. on the type and design of the exhaust gas catalytic converter 35, and is 600°C in this example.

[0061] In order to protect the components of the exhaust gas catalytic converter 35 from thermal damage caused by overheating, the heating power of the electric heating device 37 is reduced and then adjusted so as not to fall below a pre-defined operating temperature AT of the exhaust gas catalytic converter 35 and not to exceed the upper limit value OGW when the upper limit value OGW of the catalytic converter temperature KT is reached, wherein the operating temperature KT is greater than a pre-defined first threshold value SW1 and less than the upper limit value OGW. The operating temperature AT is preferably selected such that the catalytic region 39 is operated with maximum efficiency. At the same time, the second delivery quantity of the secondary air mass flow SLM is kept at the adjusted level in order to ensure that the catalytic region 39 is quickly and as completely as possible heated to the level of the operating temperature AT.

[0062] The heating power is reduced or adjusted, for example by means of clock-controlled electrical actuation or in accordance with a pulse width modulation (PWM) mode of the electric heating device, such that the operating temperature AT is maintained or adjusted. This can be seen in the upper diagram from time t3 onwards. The delivery quantity of the secondary air mass flow SLM is also kept at the increased level beyond time t3. As a result, the catalytic converter temperature KT is reduced or adjusted to the operating temperature AT from time t3 onwards.

[0063] For example, at time t4, the internal combustion engine is started. At this time, the catalytic converter temperature KT is greater than or equal to the operating temperature AT or is at the level of the operating temperature. Under these conditions, the delivery quantity of the secondary air mass flow SLM delivered into the exhaust duct 25 is adjusted in accordance with the regulating sensor 47 arranged downstream of the exhaust gas catalytic converter 35 in the exhaust duct 25, such that the air ratio λ present downstream of the exhaust gas catalytic converter 35 approaches the stoichiometric value 1. After time t4, i.e. after the internal combustion engine 10 is started, the exhaust gas catalytic converter is kept at the level of the operating temperature AT by means of the hot exhaust gas mass flow AGM in a manner known per se by corresponding actuation of the internal combustion engine 10, and the heating power of the electric heating device 37 can be further reduced or completely deactivated, as is shown in the upper diagram in Figure 2 .

[0064] In the case of the use of a separate, electrically driven and electronically controllable air delivery device 70, the delivery quantity of the secondary air mass flow can be achieved by adjusting the rotational speed of the air delivery device 70 or by a continuously adjustable air valve 71 downstream.

[0065] In an alternative embodiment of the method or of the device, the air mass flow can be generated by the unignited internal combustion engine 10 itself instead of by a separate air delivery device. Here, the internal combustion engine 10 is driven, i.e. is powered, by an electric machine 50, i.e. a starter generator or an electric auxiliary drive, for example, and thus works approximately as a piston compressor, wherein the electric machine 50 is adjusted in its rotational speed in order to adjust the delivery quantity of the secondary air mass flow SLM. In this case, the secondary air mass flow SLM is introduced into the exhaust line 25 on the path of the intake air mass flow ALM. In this case, it is not possible to feed the secondary air mass flow SLM in parallel downstream of the exhaust gas catalytic converter 35 after the start of the internal combustion engine 10 in order to adjust the air ratio λ.

[0066] List of terms / list of reference signs

[0067] 10 internal combustion engine

[0068] 15 intake tract

[0069] 20 engine block

[0070] 25 exhaust line

[0071] 30 exhaust gas aftertreatment facility

[0072] 35 exhaust gas catalytic converter

[0073] 36 sleeve

[0074] 37 electric heating device, heating disc

[0075] 38 support catalytic converter

[0076] 39 catalytic region

[0077] 40 exhaust gas aftertreatment component

[0078] 45 temperature sensor

[0079] 47 regulating sensor

[0080] 50 electric machine

[0081] 60 electronic control device (ECU)

[0082] 70 air delivery device

[0083] 71 air valve

[0084] 72 air delivery nozzle

[0085] ES input signal

[0086] AS output signal

[0087] HL heating power

[0088] KT catalyst converter temperature

[0089] SW1 first threshold value (of the catalyst converter temperature)

[0090] OGW upper limit value

[0091] AT working temperature

[0092] ALM intake air mass flow

[0093] SLM secondary air mass flow

[0094] AGM exhaust gas mass flow

[0095] t1-t4 time 1-4.

Claims

1. A method for heating an exhaust-gas catalytic converter (35) which is arranged in an exhaust line (25) of an internal combustion engine (10) and has an electric heating device (37), wherein a secondary air mass flow (SLM) can be delivered into the exhaust line (25) at a location upstream of the exhaust-gas catalytic converter (35) by means of an air delivery device (70) and the electric heating device (37) is activated with a predefined heating power in time before the internal combustion engine (10) is started, characterized in that, a catalytic converter temperature (KT) is monitored in a region of the exhaust-gas catalytic converter (35) near the electric heating device (37) and no secondary air mass flow (SLM) or a secondary air mass flow (SLM) is delivered into the exhaust line (25) in a first delivery quantity in a time period after the electric heating device (37) is activated until the catalytic converter temperature (KT) reaches a predefined first threshold value (SW1), and after the catalytic converter temperature (KT) reaches the predefined first threshold value (SW1), the secondary air mass flow (SLM) is delivered into the exhaust line (25) in a second delivery quantity which is greater than the first delivery quantity.

2. The method of claim 1, wherein, Once the catalytic converter temperature (KT) reaches an upper limit value (OGW), the heating power of the electric heating device (37) is reduced and then regulated such that a predefined operating temperature (AT) of the exhaust-gas catalytic converter (35) is not undershot, the predefined operating temperature being greater than the predefined first threshold value (SW1) and less than the upper limit value (OGW).

3. The method of claim 2, wherein, When the catalytic converter temperature (KT) is greater than or equal to the operating temperature (AT) and after the internal combustion engine (10) is started, the delivery quantity of the secondary air mass flow (SLM) delivered into the exhaust line (25) is regulated in accordance with a regulating sensor (47) arranged downstream of the exhaust-gas catalytic converter (35) in the exhaust line (25) such that the air ratio λ downstream of the exhaust-gas catalytic converter (35) approaches the stoichiometric value 1.

4. The method according to any one of claims 1 to 3, characterized in that, The light-off temperature of the exhaust-gas catalytic converter (35) is predefined as the first threshold value (SW1) of the catalytic converter temperature (KT).

5. The method according to any one of claims 1 to 3, characterized in that, The first delivery quantity of the secondary air mass flow (SLM) is adapted in accordance with the catalytic converter temperature (KT) present when the electric heating device (37) is activated.

6. The method according to any one of claims 1 to 3, characterized in that, The first delivery quantity of the secondary air mass flow (SLM) can be predefined to a value of between 0.2 kg / h and 5 kg / h and the second delivery quantity of the secondary air mass flow (SLM) can be predefined to a value of between 10 kg / h and 40 kg / h in accordance with the power of the electric heating device (37).

7. The method according to any one of claims 1 to 3, characterized in that, The air delivery device (70) can be electrically driven and can be electronically controlled or regulated in terms of its delivery power.

8. The method of claim 7, wherein, The delivery quantity of the secondary air mass flow (SLM) delivered into the exhaust line (25) can be varied by means of an electronically adjustable delivery power of an electrically driven air delivery device (70) and / or an electronically controllable air valve (71).

9. The method of claim 1, wherein, An unignited internal combustion engine (10) is used as air delivery device (70), which is driven by means of an electric machine (50).

10. An apparatus for heating an exhaust gas catalytic converter (35) arranged in an exhaust line (25) of an internal combustion engine (10) and having an electric heating device (37) and a temperature sensor (45) arranged in a region of the exhaust gas catalytic converter (35) close to the electric heating device (37), wherein the apparatus has an air delivery device (70) by means of which a secondary air mass flow (LM) can be delivered into the exhaust line (25) at a location upstream of the exhaust gas catalytic converter (35), and an electronic control device (60) which is constructed and arranged to control a method according to any one of the preceding claims.

Images