DE102017218829A1 - Method for operating an exhaust aftertreatment device - Google Patents

Abstract

The invention relates to a method for operating an exhaust aftertreatment device (6) for cleaning an exhaust gas flow of a motor vehicle (2) with a hybrid drive (4) with an internal combustion engine (6) and an electric machine (8), which detects whether a danger is increased NOx emissions by the internal combustion engine (6), and is adjusted to a detected risk towards a power split between the internal combustion engine (6) and the motor-driven electric machine (8).

Description

The invention relates to a method for operating an exhaust aftertreatment device for purifying an exhaust gas flow of a motor vehicle with a hybrid drive with an internal combustion engine and an electric machine. Furthermore, the invention relates to an exhaust aftertreatment device and a motor vehicle with such an exhaust aftertreatment device.

A hybrid drive driving a motor vehicle is understood as meaning a combination of an internal combustion engine and an electric machine for driving the motor vehicle.

The hybrid drive can be designed in many different variations. It is used in mass production to improve efficiency, reduce fossil fuel consumption or increase low-speed performance.

With exhaust aftertreatment devices, combustion gases, after they have left the combustion chamber or the combustion chamber of the internal combustion engine, purified by mechanical, catalytic or chemical means, so as to be able to comply with statutory pollutant limits.

Various methods are known with which a risk of increased NOx emissions of the motor vehicle can be determined. Measures must be taken for such dangers of increased NOx emissions in order to be able to comply with statutory pollutant limits.

There is therefore a need to show ways in which the exhaust aftertreatment, in particular of a motor vehicle with a hybrid drive, can be improved in order to ensure that statutory pollutant limits are complied with.

The object of the invention is achieved by a method for operating an exhaust gas aftertreatment device for cleaning an exhaust gas stream of a motor vehicle with a hybrid drive with an internal combustion engine and an electric machine, which detects whether there is a risk of increased NOx emissions by the internal combustion engine, and to a Detected danger towards a power split between the engine and the motor-driven electric machine is adjusted. In this case, the ratio of the torque contributions of the internal combustion engine and the engine-operated electric machine to a requested target torque is understood by the power split. According to one embodiment, the power split is adjusted such that a torque request to the internal combustion engine is increased. In other words, it is e.g. at unchanged target torque for driving the motor vehicle increases the torque of the internal combustion engine and at the same time reduces the torque of the motor-driven electric machine. This measure ensures that an SCR catalytic converter of the exhaust gas aftertreatment device reaches its minimum operating temperature faster. Thus, the exhaust aftertreatment of motor vehicles can be improved with a hybrid drive in a surprisingly simple manner. It may also be provided to increase the torque of the internal combustion engine beyond the demand in accordance with the target torque. In other words, the internal combustion engine is overloaded to provide heat energy for heating an SCR catalyst of the exhaust aftertreatment device.

According to a further embodiment, excess mechanical energy supplied by the internal combustion engine is converted into electric energy by the generator-operated electric machine and stored temporarily in an energy store of the hybrid drive. Thus, the excess energy can be recuperated and the energy efficiency of the motor vehicle can be increased.

According to a further embodiment, the energy storage device is discharged by a further adaptation of the power branching if a catalyst temperature is higher than a threshold value and if there is a risk of increased NOx emissions. It is thus at e.g. unchanged target torque for driving the motor vehicle reduces the torque of the internal combustion engine and at the same time increases the torque of the motor-operated, electric machine. Thus, the catalyst temperature can be reduced again and the cached energy can be sensibly retrieved to increase the energy efficiency of the motor vehicle.

According to a further embodiment, in response to a regeneration request signal, the power split is adjusted such that a torque request to the internal combustion engine increases. Thus, for example, with unchanged target torque for driving the motor vehicle, the torque of the internal combustion engine is increased and at the same time the torque of the engine-operated, electrical machine is reduced. By this measure, a NOx storage catalyst of the exhaust gas aftertreatment device is heated, so that the NOx storage catalyst reaches its minimum operating temperature faster for efficient regeneration. It is also possible to adjust the power split in such a way that a torque request to the internal combustion engine is reduced so to reduce the temperature of the NOx storage catalyst.

In accordance with another embodiment, a regeneration operation is initiated, and during regeneration operation, the power split is adjusted such that a torque request to the internal combustion engine is maintained substantially constant. Thus, the torque request is adapted to the engine-operated electric machine such that fluctuations in the torque request are compensated, while at the same time the torque requirement is kept constant to the internal combustion engine. In this context, what is meant by being kept substantially constant is understood to mean that the operating conditions of the exhaust aftertreatment device, such as, for example, Catalyst temperatures, do not change. Thus, an efficient and effective operation of the exhaust aftertreatment device can be ensured.

• 1 eine Brennkraftmaschine und eine Abgasnachbehandlungsvorrichtung eines Kraftfahrzeugs zur Durchführung eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens.
• 2 ein Ablaufdiagramm des Betriebs der in 1 gezeigten Abgasnachbehandlungsvorrichtung.

Further, the invention includes an exhaust aftertreatment device and a motor vehicle with such an exhaust aftertreatment device. The invention will now be explained with reference to a drawing. Show it:

• 1 an internal combustion engine and an exhaust aftertreatment device of a motor vehicle for carrying out an embodiment of the method according to the invention.
• 2 a flow chart of the operation of in 1 shown exhaust aftertreatment device.

It will be initially on the 1 Referenced.

The 1 shows a hybrid drive 4 for driving a motor vehicle 2 , The hybrid drive 4 has in the present embodiment, an internal combustion engine 6 and an electric machine 8th and a rechargeable memory 10 for electrical energy.

Thus, the motor vehicle 2 formed in the present embodiment as a hybrid electric vehicle.

The internal combustion engine 6 and the electric machine 8th can work together in different ways: in parallel (the internal combustion engine 6 and the electric machine 8th act simultaneously on the part to be moved), serially (only one of the machines acts directly on the part to be moved, while the other machine provides power that is converted and fed to the direct acting machine), or as a power split hybrid.

In the present embodiment, the hybrid drive 4 designed as a power-split hybrid. In operation, part of the power of the internal combustion engine 6 mechanically on the drive wheels of the motor vehicle 2 another part of the power is transmitted to the wheels via the motor-generator combination operating as an electric transmission. The advantage of such a construction is that internal combustion engine 4 can operate in a low-consumption load range, regardless of the vehicle speed.

Combined hybrid drives can be switched between parallel and serial operation by means of an (automatically actuated) clutch. Mixed hybrids combine the serial and parallel hybrid drive (often variable) while driving according to the driving conditions. Depending on the operating mode and driving condition, either the internal combustion engine 6 with the generator-driven electric machine 8th only the electrical energy storage 10 charge and the electric machine 8th drive (serial hybrid drive) or be mechanically coupled to the drive shafts (parallel hybrid drive). In this combined hybrid drive is switched only by means of a (automatically actuated) coupling between the two modes.

The internal combustion engine 6 is in the present embodiment, a diesel engine, ie the diesel engine is operated in normal operation with an excess of oxygen (λ> 1). Deviating from this, the internal combustion engine 6 be designed as a gasoline engine in lean operation to increase the engine efficiency.

The internal combustion engine 6 is turbocharged in the present embodiment, so that in the exhaust stream of the internal combustion engine 6 a turbine 14 downstream of an exhaust gas turbocharger.

The electric machine 8th is an electric rotary machine with a rotor and a stator, which can be operated both by motor, ie as a partial traction motor, and also as a generator. The electric machine 8th For example, it can be designed as a DC machine, as an AC machine, as a synchronous machine, as an asynchronous machine, as a brushless electric machine or as a combination of machine types.

The rechargeable memory 10 for electrical energy is an accumulator in the present embodiment. Notwithstanding the present embodiment, the rechargeable memory 10 for electrical energy capacitors.

One in exhaust gas flow direction of the internal combustion engine 6 downstream exhaust aftertreatment device 12 has in the present embodiment in the exhaust gas flow direction one behind the other arranged a NOx storage catalyst 16 , a urea injection station 18 , a first SCR catalyst 20 , a second SCR catalyst 22 and a NOx sensor 24. Deviating from the present exemplary embodiment, the number of NOx sensors and / or NOx storage catalysts may vary, ie more than one NOx storage catalyst may be provided. Similarly, the number of SCR catalysts 20 . 22 vary. The first SCR catalyst 20 and / or second SCR catalyst 22 may have a coating to form them as Diesel Particulate Filter (DPF) for reducing particulates present in the exhaust stream. In the present embodiment, the first SCR catalytic converter 18 such a coating and is also designed as a diesel particulate filter or diesel particulate filter (DPF).

The first NOx storage catalyst 16 is designed to store NOx (nitrogen oxides). It has a construction with a suitable support with a noble metal catalyst such as platinum and a NOx storage component such as an alkaline earth metal such as barium. The first SCR catalyst 20 and the second SCR catalyst 22 are each designed for the selective catalytic reduction of nitrogen oxides using urea, which at the urea injection point 18 is injected into the exhaust stream. The NOx sensor 24 has a cross-sensitivity to ammonia (NH ₃ ).

Furthermore, the exhaust aftertreatment device 12 for exhaust gas recirculation (EGR) designed to reduce NOx emission. This is between the internal combustion engine 6 and the turbine 8th a high pressure exhaust gas recirculation injection site 26 and between the first SCR catalyst 20 and the second SCR catalyst 22 in the present embodiment is a low-pressure exhaust gas recirculation injection point 28 arranged. Deviating from the present embodiment, the exhaust aftertreatment device 12 even without low pressure exhaust gas recirculation injection point 28 be educated.

The internal combustion engine 6 is associated with a controller (not shown), which causes a change from an operation with excess oxygen to a stoichiometric operation and vice versa. For this purpose, the control unit on hardware and / or software components.

It is now additionally on 2 Reference is made to a flowchart of the operation of the exhaust aftertreatment device 6 shows.

The process begins with a step S100 , In the step S100 it is determined whether there is a risk of increased NOx emissions by the internal combustion engine 6 consists.

In this case, a case distinction is made as to whether the internal combustion engine 6 is in a start operation state or a cold start operation state or a normal operation state, and it is then determined whether there is a danger of increased NOx emissions in the start operation state or in the cold start operation state or in the normal operation state.

In this case, in the present embodiment under the start operating state, a state with the ignition switched on and subsequent startup of the internal combustion engine 6 understood, while under the cold start operating state, a state is understood, in which for the operation of the exhaust aftertreatment device 12 required minimum temperature has not yet been reached.

For detecting whether there is a risk of increased NOx emissions in a starting operating state, in the present exemplary embodiment, that in the exhaust gas aftertreatment device 12 stored NOx, an ambient temperature, an ambient pressure and / or an SCR exhaust aftertreatment efficiency of an SCR catalyst 22 . 24 the exhaust aftertreatment device 12 recorded and evaluated.

For detecting whether there is a danger of increased NOx emissions in a cold start operation, an input side NOx concentration, an exhaust side NOx concentration, ambient temperature, ambient pressure, and / or SCR exhaust aftertreatment efficiency of an SCR catalyst become 22 . 24 the exhaust aftertreatment device 12 as well as in the exhaust aftertreatment device 12 stored NOx is detected and evaluated.

To determine the exhaust-side NOx concentration in the present embodiment, the NOx sensor 24 used. Alternatively, it may be provided to use a NOx prediction model or measurements of the NOx sensor 24 to combine with the prediction model.

Further, in the present embodiment, an operating temperature and input NOx concentration are detected and evaluated to determine the exhaust side NOx concentration. So can be bypassed that the exhaust side arranged NOX sensor 24 no meaningful measured values shortly after start-up of the internal combustion engine 6 at low temperatures.

If the evaluation shows that there is the risk of increased NOx emissions, a power split between the internal combustion engine becomes the detected state 6 and the powered electric machine 8th customized.

In a further step S200 the power split is adapted such that a torque request to the internal combustion engine 6 is increased. In this case, the ratio of the torque contributions of the internal combustion engine under the power split 6 and the powered electric machine 8th understood to a requested target torque. In other words, it is eg at unchanged target torque to drive the motor vehicle 2 the torque of the internal combustion engine 6 increases and at the same time the torque of the motor-driven electric machine 8th reduced. By this measure it is achieved that in the present embodiment, the first SCR catalyst 20 is heated, leaving the first SCR catalyst 20 faster reaches its minimum operating temperature.

It can also be provided, the torque of the internal combustion engine 6 above the demand according to the target torque increase. In other words, the internal combustion engine 6 is operated with overload to heat energy for heating the example of the first SCR catalyst 20 provide.

Excess mechanical energy, then from the internal combustion engine 6 is supplied by the regenerative electric machine 8th converted into electrical energy and in the energy storage 10 the hybrid drive 4 cached.

There is also a detection of a catalyst temperature, for example, the first SCR catalyst 20 ,

If the detected catalyst temperature is higher than a predetermined threshold, there is a further adjustment of the power split to the energy storage 10 to unload. In other words, it is eg at unchanged target torque to drive the motor vehicle 2 the torque of the internal combustion engine 6 reduces and at the same time the torque of the motor-driven electric machine 8th elevated. Thus, the catalyst temperature can be reduced again.

Furthermore, by heating above the predetermined threshold value by utilizing the heat capacity of, for example, the first SCR catalyst 20 Thermal energy to be cached during a subsequent cold phase with insufficient heat energy output by the internal combustion engine 6 ensures that the catalyst temperature remains above the minimum operating temperature.

In a further step S300 It is monitored whether a regeneration request signal for starting a regeneration operation for regenerating the NOx storage catalyst 20 is present. When such a regeneration request signal is present, the power split is adjusted so that a torque request to the internal combustion engine 6 is increased. In other words, it is eg at unchanged target torque to drive the motor vehicle 2 the torque of the internal combustion engine 6 increases and at the same time the torque of the motor-driven electric machine 8th reduced. By this measure it is achieved that in the present embodiment of the NOx storage catalyst 16 is heated, so that the NOx storage catalyst 16 to a regeneration request signal for starting a regeneration operation to regenerate the NOx storage catalyst 20 faster reaches its minimum operating temperature for efficient regeneration.

In a further step S400 a regeneration operation is triggered upon the regeneration request signal. Furthermore, during the regeneration operation, the power split is adjusted such that a torque request to the internal combustion engine 6 is kept substantially constant. In other words, the torque request to the motor-driven electric machine 8th is adjusted to compensate for fluctuations in the torque request, while at the same time the torque request to the internal combustion engine 6 is kept constant. It is understood to mean essentially constant that the operating conditions of the exhaust aftertreatment device 12 , such as catalyst temperatures, do not change, for example, in the way they fall below the minimum operating temperature. Thus, an efficient and effective operation of the exhaust aftertreatment device 12 be guaranteed.

Thus, the exhaust aftertreatment of motor vehicles with a hybrid drive at different operating conditions can be improved in a surprisingly simple manner.

LIST OF REFERENCE NUMBERS

2

motor vehicle

4

hybrid drive

6

Internal combustion engine

8th

electric machine

10

energy storage

12

exhaust aftertreatment device

14

turbine

16

NOx storage catalytic converter

18

Urea injection point

20

first SCR catalyst

22

second SCR catalyst

24

NOx sensor

26

High-pressure exhaust gas recirculation injection point

28

Low-pressure exhaust gas recirculation injection point

S100

step

S200

step

S300

step

S400

step

Claims (13)

A method for operating an exhaust aftertreatment device (6) for cleaning an exhaust gas stream of a motor vehicle (2) with a hybrid drive (4) with an internal combustion engine (6) and an electrical machine (8), which detects whether a risk of increased NOx emissions by the internal combustion engine (6), and adapted to a detected risk, a power split between the internal combustion engine (6) and the motor-operated electric machine (8) is adjusted. Method according to Claim 1 wherein the power split is adjusted such that a torque request to the internal combustion engine (6) is increased. Method according to Claim 2 , wherein excess mechanical energy that is supplied by the internal combustion engine (6), converted by the regenerative electric machine (8) into electrical energy and stored in an energy store (10) of the hybrid drive (4). Method according to Claim 3 wherein, by further adjusting the power split, the energy storage device (10) is discharged when a catalyst temperature is higher than a threshold value. Method according to one of Claims 1 to 4 wherein, responsive to a regeneration request signal, the power split is adjusted to increase a torque request to the engine (6). Method according to Claim 5 wherein a regeneration operation is initiated, and wherein during regeneration operation, the power split is adjusted such that a torque request to the internal combustion engine (6) is kept substantially constant. Aftertreatment device (6) for cleaning an exhaust gas flow of a motor vehicle (2) with a hybrid drive (4) with an internal combustion engine (6) and an electric machine (8), wherein the exhaust aftertreatment device (6) is adapted to detect whether a risk of increased NOx Emissions by the internal combustion engine (6), and is adapted to a detected risk towards a power split between the internal combustion engine (6) and the motor-driven electric machine (8). Exhaust after-treatment device (6) according to Claim 7 wherein the exhaust aftertreatment device (6) is adapted to adjust the power split so that a torque request to the internal combustion engine (6) is increased. Exhaust after-treatment device (6) according to Claim 8 wherein the exhaust aftertreatment device (6) is adapted to convert excess mechanical energy supplied by the internal combustion engine (6) from the generator-operated electric machine (8) into electrical energy and in an energy store (10) of the hybrid drive (4). to save between. Exhaust after-treatment device (6) according to Claim 9 wherein the exhaust aftertreatment device (6) is adapted to discharge the energy store (10) by further adjusting the power split when a catalyst temperature is higher than a threshold value. Exhaust after-treatment device (6) according to one of Claims 7 to 10 wherein the exhaust aftertreatment device (6) is adapted to adjust the power split in response to a regeneration request signal so that a torque request to the internal combustion engine (6) is increased. Exhaust after-treatment device (6) according to Claim 11 wherein the exhaust aftertreatment device (6) is adapted to perform a regeneration operation, and to adjust the power split during the regeneration operation such that a torque request to the internal combustion engine (6) is kept substantially constant. Motor vehicle (2) with an exhaust aftertreatment device (6) according to one of Claims 7 to 12 ,

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