WO2020074292A1

WO2020074292A1 - Electrically heated catalytic converter, and method for operating such a catalytic converter

Info

Publication number: WO2020074292A1
Application number: PCT/EP2019/076352
Authority: WO
Inventors: Dietmar Ellmer
Original assignee: Vitesco Technologies GmbH
Priority date: 2018-10-08
Filing date: 2019-09-30
Publication date: 2020-04-16
Also published as: DE102018217174B4; DE102018217174A1

Abstract

The invention relates to a catalytic converter (35) having a total catalysis region (42) for catalytically treating the exhaust gas of the internal combustion engine (10). Two electric heating elements (40, 41) are provided which are arranged within the total catalysis region (42) and which are placed one behind the other at a specified distance to one another in the flow direction of the exhaust gas such that the total catalysis region (42) is divided into three catalysis regions (37, 38, 39) which follow one another in the flow direction of the exhaust gas. A first heating element (40) is arranged within the total catalysis region (42) such that a first catalysis region (37) which constitutes 5-15% of the total catalysis region (42) is formed upstream of the first heating element (40) when viewed in the flow direction of the exhaust gas, a second heating element (41) is arranged in the total catalysis region (42) such that a catalysis region (37, 38) which constitutes 60-80% of the total catalysis region (42) is formed upstream of the second heating element (41) when viewed in the flow direction of the exhaust gas, and a third catalysis region (39) is formed downstream of the second heating element (41) when viewed in the flow direction of the exhaust gas.

Description

description

ELECTRICALLY HEATED EXHAUST GAS CATALYST AND METHOD FOR OPERATING SUCH A

The invention relates to an electrically heated catalytic converter and a method for operating an electrically heated catalytic converter.

Ever stricter legal regulations make it

Motor vehicles with internal combustion engines, on the one hand, he required to reduce the raw emissions caused by the combustion of the air / fuel mixture in the cylinders as much as possible. On the other hand, exhaust gas aftertreatment systems are used in internal combustion engines, converting the pollutant emissions that are generated in the cylinders during the combustion process of the air / fuel mixture into harmless substances.

Among other things, Exhaust gas catalysts in which a chemical conversion of combustion pollutants is carried out by oxidation or reduction of the respective pollutant.

For this purpose, the catalytic converters have active catalytic areas in which the chemical conversion - catalysis - takes place.

The required operating temperature is usually in a fuel- and coating-dependent area, starting at a minimum of around 250 ° C, since the catalysis that is carried out in the catalytic area requires a certain minimum temperature, also called light-off temperature, for effective exhaust gas aftertreatment.

It is therefore necessary to quickly bring the catalytic converter up to the desired operating temperature. For this purpose, combustion-related measures can be carried out on the one hand, that is, measures in which the internal combustion engine is operated in such a way that the waste heat from the internal combustion engine can be used to quickly heat up the exhaust gas catalytic converter. However, this leads to higher fuel consumption. On the other hand, it is also possible to use an electrically heatable catalytic converter. Such catalytic converter have their own electrical heating device, which brings the gas catalytic converter from the desired operating temperature. One advantage of an electrically heatable exhaust gas catalytic converter is that the exhaust gas catalytic converter can be brought to operating temperature in a so-called catalytic converter cold phase even without the internal combustion engine operating.

An electrically heated catalytic converter (EHC = electrical heated catalyst, E-KAT), the electrical heating device being implemented, for example, in the form of one or more electrical heating disks, represents a particularly effective sub-system. The electrically heated catalytic converter, in contrast, enables this alternative measures for heating the same, heating the catalytic surface directly, that is to say on-site. This has the advantage of briefly introducing heat into the catalytic converter. The structure of such electrically heated catalytic converters are described, for example, in the publications DE 199 43 846 Al and DE 44 34 673 Al.

The problem arises, however, that the catalytic volume at the start of the internal combustion engine is comparatively low, since the heat is transported only by heat conduction and free convection. Is the heating disc, that is, the heat source as such, in the direction of flow on the front or outside of the exhaust gas catalytic converter, for example, when preheating, i.e. a heating process before the start of the internal combustion engine, a large part of the heat generated in the catalytic converter facing away Lost direction. If there is a heating disc at the outlet of the exhaust gas catalytic converter, this cannot be used to heat up a catalytic converter volume when forced convection in the flow direction (for example, the internal combustion engine is in operation). In addition, the heat sources for the temporary heating process of parts of the exhaust gas aftertreatment system should be used to minimize the absolute number in terms of the complexity of the system. For example, it may be necessary to increase the exhaust gas temperature to such an extent that a particle filter positioned downstream of the exhaust gas catalyst regenerates or switches on

NOx aftertreatment system can be activated.

With regard to the rapid availability and sufficient intensity of the local heat sources or heat generation, there are additional requirements for real ferry operations. Furthermore, emission hatching must be avoided in all aspects, since legislation increasingly focuses on short-haul operations when evaluating the emission behavior of a motor vehicle.

In principle, all local temperature increases in the exhaust gas aftertreatment system, which are based on the composition of the exhaust gas, have the disadvantage that they are accompanied by a conversion deterioration below 100%. External heat sources can largely avoid this disadvantage with the appropriate design and strategy. A disadvantage of the usual use of only a single heating disk in the end region of the exhaust gas catalytic converter is that a necessary increase in gas temperature at the end of the exhaust gas catalytic converter, that is to say always an increase in the temperature of the entire front area of the exhaust gas catalytic converter by this single heating disk at the outlet side of the exhaust gas power. In this case, depending on the heating power of this heating disk under real driving conditions, the case may arise that the heat given off is not sufficient to reach the exhaust gas temperature after the exhaust gas catalytic converter for heating the following part of the exhaust gas aftertreatment system. The heat losses are also significantly greater. If a single heating disc is positioned further downstream in the catalytic converter, the front part of the catalytic converter remains largely catalytically inactive for a long time at low exhaust gas temperatures. A single heating disc is usually located in the flow direction on the end face of the exhaust gas catalytic converter. The number of heat sources, i.e. the heating discs, can also be larger. The publication "Innovative Catalyst Substrate Components for Future Passenger Car Diesel After Treatment Systems" [Rolf Brück, Peter Hirth, Francois Jajat, Continental Emitec GmbH, Lohmar, Germany]; 26th Aachen Col loquium Automobile and Engine Technology 2017, describes a three-heater - Disc Kat shown schematically, which shows the theoretical positioning of the heating discs in a gas catalytic converter.

DE 10 2016 213 612 B3 describes an electrically heated exhaust gas catalytic converter for a vehicle with an internal combustion engine, the exhaust gas catalytic converter having the following: an active catalytic converter area for reducing and / or oxidizing at least one gas flow generated in the internal combustion engine and flowing through the active catalytic converter area along a flow direction Exhaust gas; a heating device for heating the catalytic converter area, the heating device having a first heating element and a second heating element arranged separately from the first heating element, the first heating element being arranged in the flow direction of the exhaust gas upstream of the catalytic converter area and the second heating element in the flow direction of the exhaust gas downstream of the catalytic converter area . The first heating element is thus arranged directly on the end face of the exhaust gas catalytic converter, that is to say at the gas inlet, and the second heating element is arranged directly at the opposite end of the exhaust gas catalytic converter, that is to say at the gas outlet. Furthermore, a control device is provided for controlling the heating device in such a way that only the first heating element for heating the catalytic converter area is actuated when the internal combustion engine is operating, and that only the second heating element for heating the catalytic converter area is actuated when the internal combustion engine is at a standstill.

The invention has for its object to provide an electrically heatable catalytic converter that can be operated particularly efficiently and an improved converter ensures behavior even under real driving conditions. It is also an object of the present invention to provide a method for operating such an exhaust gas catalytic converter.

These objects are achieved by an electrically heatable gas catalytic converter according to claim 1 and the method according to claims 6, 11 and 13.

Advantageous embodiments of the invention are the subject of the dependent claims.

According to a first aspect, an electrically heatable exhaust gas catalytic converter is created which has an overall catalytic area for the catalytic treatment of the exhaust gas of the internal combustion engine, two electrical heating elements being arranged within the total catalytic area, which are placed one behind the other at a predetermined distance in the flow direction of the exhaust gas, so that the total catalytic area n is divided into three successive catalytic areas in the flow direction of the exhaust gas. A first heating element is arranged within the overall catalytic area in such a way that, seen in the flow direction of the exhaust gas, a first catalytic area is formed upstream of the first heating element, which is 5-15% of the total catalytic area. A second heating element is arranged in the overall catalytic area in such a way that, seen in the flow direction of the exhaust gas, a catalytic area is formed upstream of the second heating element, which amounts to 60-80% of the total catalytic area. A third catalytic area is in

Direction of flow of the exhaust gas seen, formed downstream of the second heating element.

The specified positioning of the two heating sources of the externally heatable exhaust gas catalytic converter, so that both heating elements are surrounded by active catalytic converter areas, means that very good conversion behavior is achieved not only on the test bench, but also in real driving on the road, and that with low complexity of the exhaust gas aftertreatment system . In addition, a very rapid heating of the exhaust gas catalyst is achieved.

The advantage lies in the number of selected heating sources in relation to the commonly used electrical energy sources, the overall size of a catalytic converter for a vehicle and the design of the electrical system, taking into account an increasing complexity of the overall system as the number of heating elements increases.

According to a further aspect of the invention, methods for heating an electrically heatable exhaust gas catalytic converter according to the first aspect are proposed, which show different heating strategies for this exhaust gas catalytic converter. These correlate with the heat emission of the internal combustion engine in such a way that the exhaust gas mass flow of the internal combustion engine is used for heat transport and as available heat input into the exhaust gas aftertreatment system. The invention is based on the assumption that this heat contribution from the internal combustion engine is such that it is minimal under the current boundary conditions and thus CO 2 emissions are optimal.

When heating on the basis of free convection, the volume (catalytic converter areas) heated by the two heating elements activated in parallel is maximum. It is particularly advantageous that the heating elements are bordered by adjoining catalyst parts in an almost maximum manner. When heating on the basis of forced convection, the heated volume increases significantly over the time axis compared to an exhaust gas catalytic converter with a single heating element.

The same gas mass flow flowing through the exhaust gas catalyst transports the heat to parts of the exhaust gas catalyst at two different locations which have not yet reached the threshold temperature. The advantage here is that if the downstream catalyst volume is completely heated up prematurely, the second heat source can be deactivated before the first one. When reheating due to a cold exhaust gas mass flow or long engine downtimes is sufficient, the front in terms of flow direction

Reactivate heating element. Not only can a catalyst volume, which is inactive due to the temperature level, be activated particularly quickly, but this is done with lower electrical energy expenditure, since this can take place in a targeted manner depending on the exhaust gas mass flow and its heat contribution. The divisions made according to the invention, as well as the position of the heating elements in the cases of holistic temperature management that occur, are clearly advantageous compared to other variants with regard to the electrical energy to be used for them.

Further advantages and refinements of the exhaust gas catalytic converter according to the invention and the control method for such an exhaust gas catalytic converter are explained in more detail with reference to the following description of an exemplary embodiment with reference to the drawing.

The single FIGURE shows a schematic representation of an internal combustion engine 10, an electric machine 43 connected to the internal combustion engine 10, an intake tract 15 with an electric machine 44 arranged therein, in particular in the form of an electrically driven compressor, an engine block 20 with a plurality of cylinders, not specified and an exhaust line 25 in which an exhaust gas aftertreatment system 30 is arranged.

The exhaust gas aftertreatment system 30 has, inter alia, an exhaust gas catalyst 35 according to the invention. Downstream of the gas catalytic converter 35, further exhaust gas treatment components 50 are optionally provided, only one of which is shown. Possible exhaust gas aftertreatment components at this point are a three-way catalytic converter, an SCR catalytic converter for selective catalytic reduction, diesel particle filter, SCR-coated diesel particle filter, gasoline particle filter, NOx catalyst (lean NOx trap). The exhaust gas catalytic converter 35 is designed as an electrically heatable catalytic converter and comprises a jacket tube 36 which encloses an overall physically catalytic area 42. In the total catalytic area 42 there is a heating device, consisting of two separate heating elements 40, 41, which are placed one behind the other at a predetermined distance in the direction of flow of the exhaust gas, so that there are three successive catalytic areas 37, 38, 39.

A first heating element 40 is arranged in the total catalytic area 42 in such a way that, seen in the flow direction of the exhaust gas, a first catalytic area 37 is formed upstream of the first heating element, which amounts to 5-15% of the total catalytic area 42.

A second heating element 41 is arranged in the overall catalytic area 42 in such a way that, seen in the flow direction of the exhaust gas, a catalytic area 37, 38 is formed upstream of the second heating element 41, which is 60-80% of the total catalytic area 42. A third catalytic region 39 is located downstream of the second heating element 41.

The exact position results from the heat capacity of the downstream catalytic converter volume, the downstream path and the part of the exhaust gas aftertreatment system that is to be activated by the heat of the exhaust gas. This includes the outside temperatures to be taken into account as the lowest limit, the minimum or maximum conceivable exhaust gas mass flow and its emission properties.

The term exhaust gas catalytic converter can also be a cascade of individual bricks, provided that the distance between them is less than a few millimeters or zero and that it only results from the fact that the heating elements or the individual bricks in continuous operation show no premature wear or deactivation Experienced. The three catalytic converter areas 37, 38, 39 serve to catalytically treat or oxidize or reduce the exhaust gas present in the exhaust gas line 25 from the internal combustion engine 10 so that the exhaust gas can be discharged into the environment largely free of pollutants.

The heating devices 40, 41 are preferably designed as heating disks and can almost completely fill the interior of the casing tube 36, so that when the heating disks are heated, a large amount of thermal energy is available for heating the three catalytic converter areas 37, 38, 39. The heating devices 40, 41 are fixed, for example, to a so-called supporting catalyst volume.

If the internal combustion engine 10 is at a standstill at the beginning of the driving cycle (cold start), there is no possibility of realizing forced convection, so that only free convection leads to an enlargement of the possible catalytic area, the heating elements 40, 41 are fixed in such a way that in addition to this form of Heat transport the heat conduction is intensified as possible. The position of the exhaust gas catalytic converter in the vehicle plays a role (its axis is preferably perpendicular to the longitudinal axis of the vehicle), the nature and shape of the carrier material and the feasibility of the minimum distance between the respective heating element and the adjacent catalyst volume.

An electronic control device (ECU) 60 is provided, which is connected in terms of control to the two heating devices 40, 41 and to sensors and actuators of the internal combustion engine 10, not shown, and which can independently control the heating devices 40, 41 independently of one another depending on the signals from these sensors . The electronic control device 60 can be designed as a separate catalytic converter heating control device or can be integrated in a motor control device for the internal combustion engine 10. Are the heating devices 40, 41 are energized, they heat up and transfer their thermal energy to the three catalytic areas 37, 38, 39. The heating element 40 heats the adjacent catalytic areas 37 and 38, the heating element 41 heats the adjacent catalytic areas 38 and 39.

In the strategy of activation, i.e. The electrical control of the two heating elements 40, 41 can be differentiated into two basic cases.

On the one hand, both heating elements 40, 41 can be supplied with energy at the same time, which leads to heating of the entire physically available total catalytic area of the exhaust gas catalytic converter 35 in the shortest possible time.

Preheating the two heating elements 40, 41 with the internal combustion engine 10 at a standstill results in optimal utilization of the free convection and thermal conduction of the catalyst volume upstream of the respective heating element. If the design of the system makes it possible to force convection, for example using an electrically driven machine that delivers an air mass flow into the exhaust line, or by dragging the internal combustion engine in one of its two possible directions of rotation, the convection and heat conduction can also can be used depending on the direction. Thus the full catalyst volume, i.e. the catalytically active total area 42 can be heated. In this case, the heating elements 40, 41 are only activated until the volume that can be heated directly by the gas movement is catalytically active.

When the rotary movement of the internal combustion engine 10 begins, both heating elements 40, 41 become a heating operation controlled by ON / OFF in order to maintain the temperature level on the respective heating element 40, 41 (limited to the maximum level at which premature aging or even destruction is certain can be avoided). The ON / OFF operation depends on the amount of the locally reached catalyst temperatures and the exhaust gas mass flow. Respective deactivation of the heating elements 40, 41 when the heatable maximum catalyst volume is reached downstream.

On the other hand, due to the described placement of the two heating elements 40, 41 within the exhaust gas catalytic converter 35, these can be used to increase the temperature of the exhaust gas to activate a component of the exhaust gas aftertreatment system located downstream of the exhaust gas catalytic converter. For this purpose, only the second heating element 41 downstream of the first heating element 40 is activated, i.e. supplied with energy until the exhaust gas temperature after the exhaust gas catalyst 35 exceeds a predetermined threshold. There is a

ON / OFF operation with the heating function of the second heating element 41 to maintain the exhaust gas temperature until the downstream component of the catalytic converter has reached sufficient temperature level. If necessary, a

Continuation of the ON / OFF heating element operation until a temporary process in the downstream part of the exhaust gas aftertreatment system is completed, for example the regeneration of a particle filter has ended.

In a special embodiment of the specified cases, current information such as fuel quality, individual vehicle properties (vehicle owner, driving history, component status, etc.), environmental parameters such as outside temperature, humidity, traffic density, construction sites, prior knowledge, e.g. a known route profile , if necessary, individual driving information such as driver type, system information based on artificial intelligence to adapt all the above-mentioned temperature threshold values, heating times and setpoints.

In a special embodiment of the actuation strategy, the activation of the heating elements 40, 41 can be interrupted before the catalytically active region which can be heated to the maximum is reached, in order to use compensation process and to save electrical energy.

In a further embodiment of the control strategy of the heating elements 40, 41, the heating or temperature compensation process is predicted by models, and thus the targeted adaptation of the heating process to the space velocity of the catalytic converter is carried out.

If the ideal heating process cannot be realized with the two heating elements 40, 41 due to the course of the room speed, the control strategy is carried out as optimally as possible in accordance with the specified quality criteria. In the cases in which activation of the heating elements 40, 41 according to the invention is to take place, however, it is fundamentally to be checked whether this is possible within the scope of the still available amount of energy in the energy store.

In a special embodiment, the threshold values and setpoints specified above can be increased or decreased depending on the available amount of energy in the energy store which supplies the heating devices 40, 41 with energy, or by the requirements of comprehensive energy management.

List of terms / reference symbols

10 internal combustion engine

15 intake tract

20 engine block

25 exhaust line

30 exhaust gas aftertreatment system

35 electrically heated catalytic converter

36 casing tube

37 first catalytic converter area

38 second catalytic area

39 third catalytic area

40 first heating element

41 second heating element

42 Total catalytic range

43 electric machine

44 electrical machine in the intake tract, 50 exhaust gas aftertreatment component

60 electronic control device

Claims

1. Electrically heated exhaust gas catalytic converter (35) in a gas line (25) from an internal combustion engine (10), comprising:

- a total catalytic area (42) for the catalytic treatment of the exhaust gas of the internal combustion engine (10),

- Two electrical heating elements (40, 41) arranged within the overall catalytic converter area (42), which are placed one behind the other at a predetermined distance in the flow direction of the exhaust gas, so that the overall catalytic converter area (42) in three catalytic converter areas (37) following one another in the flow direction of the exhaust gas , 38, 39) is divided,

- A first heating element (40) in the overall catalytic range

(42) is arranged such that, seen in the flow direction of the exhaust gas, a first catalytic area (37) is formed upstream of the first heating element (40), which amounts to 5-15% of the total catalytic area (42)

- A second heating element (41) in the overall catalytic range

(42) is arranged such that, seen in the flow direction of the exhaust gas, a catalytic area (37, 38) is formed upstream of the second heating element (41), which is 60-80% of the total catalytic area (42).

- A third catalytic area (39), which is seen in the flow direction of the exhaust gas, downstream of the second heating element (41).

2. The catalytic converter according to claim 1, wherein the first catalytic region (37) and the second catalytic region (38) contact the first electrical heating element (40).

3. The catalytic converter according to claim 1 or 2, wherein, wherein the second catalytic region (38) and the third catalytic region (39) contact the second electrical heating element (42).

4. Exhaust gas catalytic converter according to one of the preceding claims 1, wherein the electrical heating elements (40, 41) are designed as heating disks.

5. Exhaust gas catalytic converter according to claim 4, wherein the exhaust gas catalytic converter (35) has a jacket tube (36) and the heating disks almost completely fill the interior of the jacket tube (36) in the radial direction and the heating disks are fixed by means of support pins to a respective catalyst volume.

6. A method of operating an electrically heated exhaust gas catalytic converter (35) according to one of claims 1 to 5, wherein at least one of the two heating elements (40, 41) is supplied with electrical energy before the start of the internal combustion engine (10).

7. The method according to claim 6, wherein and a forced convection by means of an air mass flow through the at least one heating element (40, 41) is generated.

8. The method according to claim 7, wherein the forced convection is carried out by activating an electrically driven machine (44) which is arranged in the intake tract (15) and which generates an air mass flow.

9. The method according to claim 7, wherein the forced convection is carried out by means of the internal combustion engine (10), which is towed by an electric machine (42).

10. The method of claim 9, wherein a direction-dependent forced convection is generated by the internal combustion engine (10) is rotated alternately in a first direction of rotation and then rotated in a second direction of rotation opposite to the first direction of rotation.

11. A method of operating an electrically heated gas catalyst (35) according to one of claims 1 to 5, wherein at starting rotary movement of the internal combustion engine (10), both heating elements (40, 41) are supplied with electrical energy.

12. The method according to claim 11, wherein the activation of the two heating elements (40, 41) continues until an ON / OFF controlled heating operation to maintain a predetermined temperature level on the respective heating element (40, 41).

13. A method for operating an electrically heated gas catalytic converter (35) according to one of claims 1 to 5, wherein until a predetermined threshold value for the exhaust gas temperature downstream of the exhaust gas catalytic converter (35) is finally supplied to the second heating element (42) with electrical energy .

14. The method according to claim 13, wherein after reaching the threshold value, the second heating element (41) is operated in an ON / OFF controlled heating mode to maintain the exhaust gas temperature until the downstream part of the exhaust gas catalytic converter (35) has reached a sufficient temperature level.

15. The method according to claim 14, wherein the ON / OFF controlled heating operation is maintained until a temporary process for a further exhaust gas aftertreatment component (50) downstream of the exhaust gas catalytic converter (35) is completed.

16. The method of claim 15, wherein the temporary process is a regeneration of a particle filter.