DE102019203798A1 - Emission-based control of an internal combustion engine - Google Patents

Abstract

A method is provided for controlling an internal combustion engine as a function of the current emissions of the internal combustion engine, the function of exhaust gas aftertreatment devices arranged in the exhaust gas tract of the internal combustion engine being checked and the power of the internal combustion engine being regulated so that the emissions from the exhaust gas tract remain below a threshold value. Furthermore, an arrangement for carrying out the method and a corresponding motor vehicle are provided.

Description

The invention relates to a method for controlling an internal combustion engine as a function of the current emissions of the internal combustion engine and an arrangement for carrying out the method and a corresponding motor vehicle.

Existing and future rules for limiting emissions from internal combustion engines are very strict and represent a major challenge for the development of internal combustion engines and corresponding devices for exhaust gas aftertreatment. Compared to previous requirements, the emissions are being set within increasingly narrow limits, e.g. also apply to certain outside temperatures and altitudes, so that there are now limiting requirements under almost all conditions. Furthermore, there is a tendency for cities to strive to improve the air quality, e.g. Establish environmental protection zones that have specific requirements, usually including strict emission limits.

Under previous legal regulations, it was possible to design the internal combustion engine and the exhaust gas aftertreatment system in such a way that full power of the internal combustion engine was available under all conditions and at all times. This guaranteed driver satisfaction and safety because the vehicle behavior was known and predictable. In future, however, it will hardly be technically possible to comply with the emission limits under all conditions. This would require complex installations in the exhaust tract which, for reasons of cost and space, are very difficult to implement.

The dependence of the performance of an internal combustion engine on external conditions can, however, lead to a changing vehicle behavior, which is uncomfortable for a driver of the corresponding motor vehicle, but can also lead to dangerous situations if the driver expects more performance than the machine can currently be provided due to the emission-based limitations of their performance. The task is therefore to balance the limitation of pollutant emissions and the necessary performance.

This object is achieved by a method with the features of claim 1. Further advantageous embodiments and refinements of the invention emerge from the dependent claims, the figures and the exemplary embodiments. The embodiments of the invention can advantageously be combined with one another.

• - Betreiben der Brennkraftmaschine,
• - Ermitteln einer vorgegebenen Begrenzung der Emission durch einen ersten Schwellenwert,
• - Erfassen der Funktion der Abgasnachbehandlungseinrichtung,
• - Erteilen eines ersten Steuerbefehls zum Anpassen des Betriebsmodus der Brennkraftmaschine, so dass die Stickoxid-Emission der Brennkraftmaschine unter den ersten Schwellenwert gelangt, wenn mindestens ein Kriterium der Funktion der Abgasnachbehandlungseinrichtung nicht erreicht wird,
• - Erteilen eines zweiten Steuerbefehls zum temporären Aufheben des ersten Steuerbefehls,
• - Überprüfen der Priorität des ersten und zweiten Steuerbefehls und temporäres Aufheben des ersten Steuerbefehls durch den zweiten, wenn der zweite Steuerbefehl eine höhere Priorität hat, sowie Zurückweisen des zweiten Steuerbefehls, wenn der erste Steuerbefehl eine höhere Priorität hat.

A first aspect of the invention relates to a method for controlling the operation of an internal combustion engine of a motor vehicle with an exhaust tract, in which an exhaust gas aftertreatment system is arranged, which comprises at least one exhaust gas aftertreatment device, with the steps:

• - operation of the internal combustion engine,
• - Determination of a predetermined limitation of the emission by a first threshold value,
• - Detecting the function of the exhaust gas aftertreatment device,
• - Issuing a first control command to adapt the operating mode of the internal combustion engine, so that the nitrogen oxide emissions of the internal combustion engine fall below the first threshold value if at least one criterion of the function of the exhaust gas aftertreatment device is not met,
• - Issuing a second control command to temporarily cancel the first control command,
• - Checking the priority of the first and second control command and temporarily canceling the first control command by the second if the second control command has a higher priority, and rejecting the second control command if the first control command has a higher priority.

The method advantageously enables the emission of pollutants by a motor vehicle, especially nitrogen oxides, to be limited. The power of the internal combustion engine is not permanently limited, but only when external conditions require it. Furthermore, the method advantageously enables the power limitation to be temporarily canceled under certain, particularly critical conditions, under which higher power must be provided by the internal combustion engine. In this way, the driver of the motor vehicle has more options for querying performance. The method also allows the design of vehicles with a relatively simple exhaust gas aftertreatment system of low complexity, but with the specified emissions.

Said recording of the function of the exhaust gas aftertreatment device means that, for example, the temperature conditions are recorded, since exhaust gas aftertreatment devices have a temperature window in which they function optimally. Furthermore, sensors can also be used to determine whether, for example, nitrogen oxides are being efficiently removed from the exhaust gas. Said adaptation of the operating mode of the internal combustion engine means that the output of the internal combustion engine is regulated in such a way that the pollutant emissions, especially nitrogen oxides, are reduced. Priority of the control commands means that the command with the higher priority can overwrite the other command, since it is evaluated as more important. Temporary cancellation means that the first control command of the internal combustion engine is canceled for a certain period of time, for example for 10, 20 or 30 seconds.

The exhaust gas aftertreatment device is preferably selected from the group comprising nitrogen oxide storage catalysts (LNT) and catalysts for selective catalytic reduction (SCR). These two types of catalytic converter are particularly involved in reducing the nitrogen oxide content in the exhaust gas.

LNT are used for the temporary adsorption of nitrogen oxides (NOx) from the exhaust gas of internal combustion engines. In addition, they fulfill their tasks of oxidative post-treatment of carbon monoxide (CO) and hydrocarbons (HC). Nitrogen oxides that arise when an internal combustion engine is running can be stored in an LNT; To do this, the LNT oxidizes the nitrogen monoxide (NO) contained in the lean exhaust gas to nitrogen dioxide (NO ₂ ) and then stores it in the form of nitrates. Barium and / or other oxides, for example, serve as adsorbents that are built into the coating of the LNT.

If the storage capacity of the LNT is exhausted, the LNT must be regenerated. In the case of a regeneration event (purge), rich exhaust gas conditions are provided for a few seconds, e.g. by operating the internal combustion engine with a rich, i.e. sub-stoichiometric fuel-air mixture; The stored nitrogen oxides are desorbed again and reduced to nitrogen in the catalytically active components of the LNT with the help of the rich exhaust gas components (CO, HC). In addition to a purge that is only used for regeneration, the LNT is of course also regenerated when the exhaust gas e.g. becomes richer due to a power requirement of the internal combustion engine.

The stored nitrates continue to react in the LNT with molecular hydrogen, which is created under rich exhaust gas conditions through incomplete combustion of the fuel and also through reactions in the LNT, which can also generate ammonia during regeneration. This ammonia can be used to further reduce the nitrogen oxide concentration in the exhaust gas in an SCR arranged downstream of the LNT. In the SCR, ammonia, which originates from the LNT or was introduced into the exhaust gas tract in the form of a urea solution, is used as a reducing agent to reduce nitrogen oxides.

In the method according to the invention, the criterion of the function of the exhaust gas aftertreatment device is advantageously the nitrogen oxide load and temperature of the LNT and the temperature of the SCR system. If the LNT has reached a certain charge status during normal, lean exhaust gas conditions, at which it no longer efficiently stores NOx, it must be regenerated. The achievement of the corresponding NOx loading is determined by exceeding a second threshold value for the NOx concentration in the exhaust gas tract, downstream of the LNT. If rich operation is not possible, for example because a medium or high load cannot be applied, the internal combustion engine is idling or because the internal combustion engine has just been started cold, the output of the internal combustion engine is limited according to the invention with the corresponding first control command in order to increase the amount of reduce nitrogen oxides emitted by the internal combustion engine.

It is also preferred if the criterion is the functional temperature of the exhaust gas aftertreatment device. The temperatures are provided by the exhaust gas, it also being possible to use electrical heating devices. The function depending on the temperature can e.g. can be determined by means of temperature sensors. The temperature of the exhaust gas aftertreatment device can be too high or too low. Threshold values can also be defined for evaluating the function as a function of the temperature.

All exhaust aftertreatment devices have components that require a minimum temperature for their function. The urea injection of an SCR system works e.g. not below 200 ° C. An LNT only stores nitrogen oxides inefficiently below 150 ° C and cannot be regenerated below 200 ° C. Oxidation catalysts need around 150 ° C to control hydrocarbons and carbon monoxide. The age and signs of poisoning of catalytic converters also have an influence on the function, as these catalytic converters have a higher operating temperature. If the functional temperature is not reached, e.g. During cold starts, under cold weather conditions and low loads on the internal combustion engine, the power of the internal combustion engine is reduced according to the invention in order to reduce the production of nitrogen oxides by the internal combustion engine.

This can e.g. can be achieved by slowing the transient response and limiting the possible load.

Even if the temperatures are too high, the criterion of the functional temperature of the exhaust gas aftertreatment device is not achieved. Too high a temperature, especially above 400 ° C, affects the absorption capacity for, for example, LNT Nitrogen oxides and, with SCR, the oxidation of ammonia on the reduction efficiency. With longer times of the internal combustion engine under high or full load, during which high exhaust gas temperatures arise, the efficiency of the reduction of nitrogen oxides by the LNT and / or SCR slowly decreases. Since longer high loads, especially for cars and small trucks, rarely occur, e.g. when driving uphill with a heavy load or a loaded trailer, the power of the internal combustion engine is reduced according to the invention in order to reduce the production of nitrogen oxides by the internal combustion engine, but only slowly compared to the reduction at excessively low temperatures of the exhaust gas aftertreatment device. In this way, emissions control can be ensured while achieving the current target. Alternatively, additional exhaust aftertreatment devices could be arranged in the exhaust tract for these rare cases at full load; however, this is not preferred for reasons of cost and space.

The first control command is preferably based on geofencing specifications. This means that for a certain geographic area, e.g. a city, a district or a street is declared a low emission zone. If the exhaust gas aftertreatment cannot sufficiently reduce the emissions, the power of the internal combustion engine is reduced when such a zone is reached, so that the internal combustion engine emits fewer pollutants. With this embodiment of the method, vehicles which, because of their pollutant emissions, do not have an operating license for these zones, could drive through them with reduced performance.

This concept can even advantageously be applied to entire countries.

In the method according to the invention, the driver of the corresponding vehicle is preferably informed of the current performance of the internal combustion engine. In this way, the driver advantageously has knowledge of a temporary power restriction of the internal combustion engine. Particularly preferably, the driver is informed of the reason for a restriction and of the expected duration of the restriction. The information is communicated to the driver via devices of the vehicle, e.g. numeric displays, warning lights, audio signals, voice signals, head-up displays, messages on the dashboard or a combination of the options listed.

In the method according to the invention, the second control command is preferably issued by a power request by the driver of the motor vehicle. The power request can in particular be issued by pressing the accelerator pedal, a defined threshold value of the accelerator pedal travel having to be exceeded. This is advantageous when high acceleration is desired, e.g. move the vehicle out of a dangerous traffic situation. The second control command has a higher priority than the first, so that the power of the internal combustion engine is available without restriction. The second control command issued by the driver preferably only has a higher priority for a limited number of commands. This advantageously avoids misuse which would make the use of the first control command superfluous.

Furthermore, the second control command is preferably issued by a device in the motor vehicle. The device is a control device that issues appropriate instructions. For example, be set so that during a cold start, thermal energy is used to heat the passenger compartment, which is then not available for heating the exhaust gas aftertreatment devices. Depending on the amount of heat required, the heating of the exhaust gas aftertreatment devices is delayed. The internal combustion engine then works with limited power until the exhaust gas aftertreatment devices have reached their operating temperature. The second control command, which is issued by a device in the motor vehicle, preferably has a permanently higher priority than the first. This is e.g. advantageous in vehicles of the fire brigade or rescue vehicles, which are allowed to call up a high performance even in traffic-calmed zones with low emission limits, which is associated with high emission values of their internal combustion engine in order to fulfill their purpose.

A second aspect of the invention relates to an arrangement comprising an internal combustion engine, an exhaust tract, at least one exhaust gas aftertreatment device and a control device which is designed to control a method according to the invention. The advantages of the arrangement correspond to the advantages of the method.

A third aspect of the invention relates to a motor vehicle with an arrangement according to the invention.

• 1 eine schematische Darstellung einer Ausführungsform der erfindungsgemäßen Anordnung.
• 2 ein Fließdiagramm einer Ausführungsform des erfindungsgemäßen Verfahrens.

The invention is explained in more detail with reference to the figures. Show it

• 1 a schematic representation of an embodiment of the arrangement according to the invention.
• 2 a flow diagram of an embodiment of the method according to the invention.

According to the representation of 1 has an embodiment of an arrangement according to the invention 1 an internal combustion engine 2 on that with an intake duct 3 for supplying combustion air and an exhaust system 4th is fluidly connected for discharging exhaust gas. The internal combustion engine 2 is a self-igniting internal combustion engine, but can alternatively also be an externally ignited internal combustion engine. The internal combustion engine 2 shows three cylinders 2a on, but it can also have a different number of cylinders. The internal combustion engine 2 is assigned to a motor vehicle.

In the exhaust tract 4th are a nitrogen oxide storage catalytic converter (LNT) for post-treatment of the exhaust gas 5 arranged. Downstream from the LNT 5 is a catalyst for selective catalytic reduction (SCR) 6th arranged. Instead of the LNT 5 an oxidation catalytic converter can also be installed. Further possible exhaust aftertreatment devices not shown here in the exhaust tract 4th are for example a particle filter, which can also have a catalytically active coating for selective catalytic reduction, three-way catalytic converters and further LNT, oxidation catalytic converters and SCR.

Upstream of the SCR 6th is a device for introducing an aqueous urea solution 7th arranged. The aqueous urea solution, for example commercially available AdBlue®, is thermolytically converted into ammonia and isocyanic acid in the exhaust system; the isocyanic acid reacts hydrolytically with water to form ammonia and carbon dioxide. The ammonia is in the SCR 6th stored and used to reduce nitrogen oxides in nitrogen and water.

In the exhaust tract is immediately upstream of the LNT 5 and SCR 6th one temperature sensor each 8th arranged. The temperature sensors 8th are intended for determining the exhaust gas temperature. Additional temperature sensors can be installed in the LNT 5 and SCR 6th or at other locations in the exhaust tract 4th be arranged. Downstream of the LNT 5 is a nitrogen oxide sensor 9 for measuring the nitrogen oxide concentration downstream of the LNT 5 arranged. A nitrogen oxide sensor, not shown, is arranged in the exhaust area. Further temperature sensors and nitrogen oxide sensors as well as other sensors, for example lambda probes, ammonia sensors or pressure sensors, can be installed at various points in the exhaust tract 4th be arranged. The position of the probes can be adapted to the spatial conditions. The sensors come with a control device 10 connected to which the measured values are transmitted. The measured values determined by the sensors can partly also be determined based on models.

The control device 10 is in turn with the internal combustion engine 2 connected to based on an evaluation of the measured values control commands relating to the performance of the internal combustion engine 2 granted. The power of the internal combustion engine 2 can, for example, by reducing the amount of fuel injected, throttled intake air supply by means of an in the intake tract 3 arranged throttle valve or the intake valves of the internal combustion engine 2 by recirculating exhaust gas or a combination of these measures. To recirculate exhaust gas, the arrangement 1 eg an exhaust pipe 11 a low-pressure exhaust gas recirculation system.

In one embodiment of the method according to 2 will be a first step S1 the internal combustion engine 2 operated by a motor vehicle. There is a low load, so that relatively cold exhaust gas is produced.

In a second step S2 a predetermined limitation of the emission is determined by a first threshold value C _{N1 of} a nitrogen oxide concentration which should not be exceeded. This first threshold value C _N1 is derived here from the legally prescribed maximum value of nitrogen oxides in a certain area. The legal limit value is not directly equal to C _N1 , since the latter value is engine-specific. The limit value can be, for example, an average value of 80 mg / km, which is converted into a value in NOx emissions in g / s for the engine. If there is no limit (N we No), the procedure goes to step S1 back.

If there is a limit (Y as in Yes), a third step S3 the function of the exhaust aftertreatment devices is recorded. In sub-steps S3a and S3b, the function of the LNT 5 determined. For this purpose, the nitrogen oxide sensor is used in substep S3a 9 the nitrogen oxide concentration C _N in the exhaust tract 4th measured. A specific, second threshold value C _{N2 for} the nitrogen oxide concentration is reached (C _N C _N2 ), which is why the LNT has a limited storage function 5 assumed due to excessive nitrogen oxide loading. Can the LNT 5 cannot be regenerated promptly because rich operation is not possible or the exhaust gas temperature is too low, in a fourth step S4 a corresponding first control command from the control device 10 issued, the power of the internal combustion engine 2 reduce in order to keep the nitrogen oxide emission below the first threshold value C _N1 . If the second threshold value C _{N2 is} not reached (C _N C _N2 ), the method proceeds to step S2 back.

Furthermore, a temperature sensor is used in sub-step S3b 8a the temperature T _{L of} the LNT 5 determined. The function of the LNT 5 within a temperature window, a first temperature threshold _value T _L1 (minimum functional temperature) and a second temperature threshold value T _L2 (maximum functional temperature) defined. The temperature is below the first temperature _threshold value T _L1 , which is specified here as 200 ° C., so that the LNT is not functioning efficiently 5 assumed and the power of the internal combustion engine 2 also therefore reduced in order to keep nitrogen oxide emissions below the first threshold value C _N1 . If the temperature T _{L were} above the second temperature _threshold value T _L2 , which is specified here as 400 ° C., the LNT would likewise not function efficiently 5 assumed and the power of the internal combustion engine 2 in step S4 is reduced in order to keep the nitrogen oxide emission below the first threshold value C _N1 . If the temperature were in the functional range (T _L1 <T _L <T _L2 ), the method would go to step S2 run back, provided that the second threshold value C _N2 would also not be reached (C _N <C _N2 ).

The function of the SCR is recorded in a substep S3c. This is done by means of a temperature sensor 8b the temperature Ts of the SCR 6th determined. The function of the SCR 6th within a temperature window is defined by a first temperature threshold value T _S1 (minimum functional temperature) and a second temperature threshold value T _S2 (maximum functional temperature). The temperature is below the first temperature _threshold value T _S1 , which is specified here as 200 ° C., which means that the SCR is not functioning efficiently 6th assumed and the power of the internal combustion engine 2 also therefore reduced in order to reach the first threshold value. If the temperature were to rise above the second temperature _threshold value T _S2 , which is specified here as 400 ° C., the SCR would likewise function in an inefficient manner 6th assumed and the power of the internal combustion engine 2 in step S4 decreased to meet the first threshold. If the temperature were in the functional range (T _S1 <T _S <T _S2 ), the method would go to step S2 run back.

Steps S3a, S3b and S3c can be ORed, ie if the conditions for a function are not met in one step, it is sufficient to move the method to step S4 forward. Steps S3a, S3b and S3c can also be in the form of AND links, that is to say that the conditions for a function must not be met in all steps in order for the method to go to step S4 forward. Two steps can also be AND-linked, i.e. both are present, and a third OR-linked. For example, it can be set that the method does not go from step S3c to step S2 if the method goes back to step in steps S3a and S3b S4 continues.

The driver of the motor vehicle is informed by means of a display in the dashboard that the internal combustion engine is only having a limited output 2 is available. However, a higher output is required for a short time to pass a construction site. The driver fully depresses the gas pedal, which corresponds to issuing a second control command (step S5 ). In a sixth step S6 checks the control device 10 the priority of the first and second control command. Since the driver issued the power request for the first time, the first control command is canceled by the second, as it has a higher priority. The internal combustion engine adjusts accordingly 2 normal power is ready for a certain period of time Δt, for example for 20 s. After this period of time .DELTA.t, the second control command is canceled again and the first is activated again; the procedure goes to step S4 back.

It's in the controller 10 set so that the second control command has three times higher priority. If the driver makes a power request more than three times, the second control command has a lower priority than the first, so that the first control command is not canceled and the power restriction remains. After the third time, the second control command is rejected because the first control command has a higher priority; the procedure then immediately goes to step S4 without providing normal performance.

The procedure runs from step S6 cyclical to step S2 to check if the nitrogen oxide emission restriction still exists.

List of reference symbols

1

arrangement

2

Internal combustion engine

2a

cylinder

3

Intake tract

4th

Exhaust tract

5

LNT

6th

SCR

7th

Inlet device for aqueous urea solution

8a

first temperature sensor

8b

second temperature sensor

9

Nitrogen oxide sensor

10

Control device

11

Exhaust gas recirculation line

Claims (13)

A method for controlling the operation of an internal combustion engine (2) of a motor vehicle with an exhaust gas tract (4) in which an exhaust gas aftertreatment system is arranged which comprises at least one exhaust gas aftertreatment device (5, 6), with the steps: - operation of the internal combustion engine (2), - Determination of a predetermined limitation of the emission by a first threshold value, - Detecting the function of the exhaust gas aftertreatment device (5, 6), - Issuing a first control command to adapt the operating mode of the internal combustion engine (2), so that the nitrogen oxide emission of the internal combustion engine (2) falls below a first threshold value if at least one criterion of the function of the exhaust gas treatment device (5, 6) is not met - Issuing a second control command to temporarily cancel the first control command, - Evaluating the priority of the first and second control command and temporarily canceling the first control command by the second if the second control command has a higher priority, and rejecting the second control command if the first control command has a higher priority. Procedure according to Claim 1 , wherein the exhaust gas aftertreatment device (5, 6) is selected from the group comprising nitrogen oxide storage catalysts (5) and catalysts for selective catalytic reduction (6). Procedure according to Claim 2 , the nitrogen oxide loading of the nitrogen oxide storage catalyst (5) being evaluated as the criterion. Method according to one of the preceding claims, the functional temperature of the exhaust gas aftertreatment device (5, 6) being evaluated as the criterion. Method according to one of the preceding claims, wherein the first control command is based on specifications of a geofencing. Method according to one of the preceding claims, wherein the second control command is issued by a power request by the driver of the motor vehicle. Method according to one of the preceding claims, wherein the granting of the higher priority of the second control command is limited in number. Method according to one of the preceding claims, wherein the second control command is issued by a device of the motor vehicle. Method according to one of the preceding claims, wherein the second control command has a permanently higher priority. Method according to one of the preceding claims, wherein the driver is informed about the current performance of the internal combustion engine (2). Method according to one of the preceding claims, wherein the driver is informed of the duration of the power restriction. Arrangement comprising an internal combustion engine (2), an exhaust gas tract (4), an exhaust gas aftertreatment device (5, 6) and a control device (10) which is designed according to one of the Claims 1 - 11 to control. Motor vehicle with an arrangement according to Claim 12 .

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