DE102014209420A1 - Method for controlling and / or regulating an internal combustion engine and engine control unit for carrying out the method - Google Patents

Abstract

The invention relates to a method for controlling and / or regulating an internal combustion engine (14) and an engine control unit for carrying out the method, wherein an exhaust gas flow (15) coming from the internal combustion engine (14) through an exhaust system (10, 11, 12, 13) an exhaust gas catalyst is passed, wherein an exhaust gas temperature to achieve a target temperature is increased by post-injection, wherein a Nacheinspritzmasse is varied, wherein for varying the post-injection at least individual post-injection are exposed in at least individual cylinders. An inadmissibly high heat input, too high fuel consumption and too low NOx conversion during the exhaust aftertreatment are avoided by the target temperature is in a temperature range between a light-off temperature of the catalytic converter and a Rußabbrandtemperatur.

Description

The invention relates to a method for controlling and / or regulating an internal combustion engine according to the preamble of claim 1. The invention further relates to a suitably configured engine control unit for controlling and / or regulating the internal combustion engine, wherein the engine control unit is adapted to perform the method.

From the DE 10 2010 030 640 A1 a method for controlling and / or regulating an internal combustion engine is known. An exhaust stream from the combustion engine is directed through an exhaust system having a corresponding exhaust passage and exhaust purifying component. As exhaust gas purification components, the exhaust system comprises an SCR catalyst for selective catalytic reduction (SCR plant), a three-way catalyst or a NOx trap or combinations of these components. As a further exhaust gas purification component, a diesel particulate filter is further provided. To perform regeneration of the diesel particulate filter, the diesel particulate filter is heated above its normal operating temperature to a soot burning temperature to oxidize or burn soot particles that have accumulated in the diesel particulate filter. During the regeneration of the diesel particulate filter, the method includes post injection of fuel into one or more cylinders of the engine at least in an exhaust stroke of an engine cycle, wherein the late post injection occurs after about 40 ° CA before top dead center, such that a portion of the fuel or all fuel is injected into a corresponding piston recess. The timing and amount of injection are controlled based on an amount of heat required to increase the temperature of the particulate filter during regeneration. In one mode of operation, a variable valve timing system is adjusted to temporarily close an exhaust valve prior to late post-injection. The variable valve timing system opens the exhaust valve before top dead center to deliver gases and fuel into an exhaust manifold and thus into the exhaust system and into the diesel particulate filter. Closing the exhaust valve before the late post-injection increases the temperature and pressure of the gas in the cylinder, which should result in a smaller amount of fuel needed for the later post-injection to increase the temperature of the diesel particulate filter. The amount of injected fuel is based on an amount of heat requested to increase the temperature of the diesel particulate filter and / or the difference between the actual temperature and the target temperature of the diesel particulate filter. Late post-injection may occur during three consecutive engine cycles. In another example, the late post-injection may occur every other engine cycle over a range of ten engine cycles. The number of engine cycles in which the injection takes place, for example, depending on the desired exothermic reaction on the catalytic converter and the exhaust gas-fuel ratio dependent.

This generic method is not yet optimally formed. The aim of the generic method is to bring about a large temperature increase to allow regeneration of the diesel particulate filter. The regeneration of a diesel particulate filter can take place at approx. 600 ° Celsius. At these temperatures, a nitrogen oxide conversion is no longer possible. During the further operation of the motor vehicle, the exhaust gas temperature may fall within a temperature range in which only a slight NOx conversion takes place, for example, by means of an SCR catalytic converter. Continuous heating would lead to unacceptably high heat input and high fuel consumption.

The invention is therefore based on the object, the above-mentioned method in such a way and further, so that an unacceptably high heat input, too high fuel consumption and low NOx conversion during exhaust aftertreatment is avoided.

This object of the invention is now achieved by a method having the features of claim 1. It is advantageous that the exhaust gas stream is heated to a desired temperature which is smaller than a Rußabbrandtemperatur. The setpoint temperature is in a temperature range below a Rußabbrandtemperatur, whereby substantially no Rußabbrannt takes place. The exhaust stream is heated to a desired temperature, wherein the target temperature is in a temperature range above a light-off temperature of the catalytic converter and below the regeneration temperature of a diesel particulate filter. The Rußabbrandtemperaturen for corresponding soot particles are in a range of more than 500 ° C, in particular of more than 550 ° C. The target temperature achieved by the method proposed here is in a range below 500 ° C. In particular, the target temperature is in a range below 300 ° C. This has the advantage that the injection quantity is reduced. This also allows a reduction in the heat loss due to the lower temperature difference from the environment. This results in a reduction of CO2 emissions.

Furthermore, a low NOx conversion is avoided in that the setpoint temperature is above a light-off temperature of Catalytic converter is located. The catalytic converter can be configured in particular as an SCR catalytic converter (SCR: selective catalytic reduction), wherein a corresponding reduction of nitrogen oxides can be carried out using ammonia, for example in the form of a urea solution. The SCR catalyst selectively converts the nitrogen oxide exhaust gas component to nitrogen and water without the formation of unwanted by-products. The internal combustion engine is designed in particular as a diesel engine. In an alternative embodiment, the catalytic converter can be configured as a NOx storage catalytic converter. Alternatively, an oxidation catalyst with an additional NOx storage coating may be used. Further, it is conceivable to use a particulate filter, in particular a diesel particulate filter, with an SCR coating.

The setpoint temperature may be, for example, in a range between 200 ° C and 250 ° C Celsius. The regulation of the heat input results in a CO2 advantage due to low heat loss heating at low temperatures. It is a fine adjustment of the exhaust gas temperature possible. This results in an emission advantage through longer, in particular lasting, keeping the catalyst temperature above the light-off temperature of the catalytic converter. The light-off temperature is also referred to as the light-off temperature.

 The heat input into the exhaust system is adjusted by post-injection and corresponding exothermic reaction that the Nacheinspritzmasse be varied per stroke and thus the heat input. The minimum injection mass of corresponding injectors, for example of solenoid valve injectors or of piezoinjectors, is limited per individual post-injection. The minimum injection mass of corresponding injectors may, for example, be limited to approximately 0.5 to 0.8 mg per working stroke. As a result, the smallest adjustable heat input per stroke is limited down. Single or multiple consecutive post-injections in one or more cylinders are now suspended to vary the average post-injection amount per heating period. Alternatively or additionally, post-injection can not be carried out in all cylinders. In a preferred embodiment, every nth post-injection is subjected to all cylinders or the post-injections on individual cylinders are suspended or every n-th post-injection on individual cylinders is suspended. In individual cylinders, for example, post-injections can be carried out continuously and at the same time in other cylinders all or only a few post-injections are suspended. The required mean Nacheinspritzmasse per time may be smaller than if over this period in all cylinders at each stroke an injection with the minimum possible injection quantity of the respective injector takes place. The delivered in a heating period Nacheinspritzmasse can thus be smaller than a given in heating in each stroke in all cylinders sum of the minimum injection masses of the injectors. The average fuel consumption for heating is thus reduced while optimizing NOx conversion. This has the advantage that the desired setpoint temperature in the exhaust system can be set more accurately without the post-injections being partially completely switched off. The post-injection takes place preferably 200 ° CA after top dead center. The exhaust system has an oxidation catalyst. Part of the method is that introduced during the post-injection Nacheinspritzmasse or fuel mass is no longer or no longer completely burned in the combustion chamber of the engine, but only implemented or burned on an oxidation catalyst. The oxidation catalyst is preferably followed by a diesel particulate filter.

Now, if a motor vehicle is started with a corresponding exhaust system, the internal combustion engine is initially cold and the exhaust system is cold. There is thus initially an initial cold start heating of the catalytic converter. In this case, the exhaust gas temperature and the surface temperature of the catalytic converter initially increase. This initial cold start heating can also be done by post injection. It is not necessarily necessary that during cold start heating at least individual post-injection are exposed to at least individual cylinders. It is conceivable that the cold start heating is heated consistently in every stroke on all cylinders. It is conceivable that after the cold-start heating, for example, after a corresponding propulsion phase, the surface temperature of the catalytic converter drops below the light-off temperature. Now only a lesser heat input into the exhaust system by Nacheinspritzen is required to achieve the one hand, the best possible nitrogen oxide conversion while preventing too high heat input and high fuel consumption. This lower heat input can be adjusted by subjecting one or more post-injections as described above. The surface temperature of the catalytic converter is controlled according to the target temperature.

Such a type of heating is also advantageous when the motor vehicle, a low-load operation is carried out and, for example, journeys are carried out low-speed urban. In the process, it is possible to heat for a longer time while the exhaust gas temperature and or the surface temperature of the corresponding catalytic converter for a long time in a lower Temperature range, especially at about 200 ° C to keep. It is possible to fine-tune the exhaust gas temperature for SCR catalysts.

A corresponding method is carried out in an engine control unit. The engine control unit is set up to carry out the method. By means of the control unit, the exhaust gas temperature for reaching the target temperature can be controlled and / or regulated by post-injection, wherein the post-injection is variable, wherein at least individual Nacheinspritzungen in at least individual cylinders can be exposed to vary the Nacheinspritzmasse. The setpoint temperature is as described in a temperature range between a light-off temperature of the catalytic converter and a Rußabbrandtemperatur.

The aforementioned disadvantages are therefore avoided and corresponding advantages are achieved.

There are now various ways of embodying and developing the method and the engine control unit according to the invention in an advantageous manner. For this purpose, reference may first be made to the claims subordinate to claim 1. In the following, a preferred embodiment of the method will be explained in more detail with reference to the drawing and the associated description. In the drawing shows:

1 three schematic diagrams, wherein the coolant temperature, the vehicle speed and the temperature in an exhaust system is plotted over time,

2 very schematically an internal combustion engine and a first exhaust system,

3 very schematically an internal combustion engine and a second exhaust system,

4 very schematically an internal combustion engine and a third exhaust system, and

5 very schematically an internal combustion engine and a fourth exhaust system.

In 2 to 5 is ever an exhaust system 10 . 11 . 12 . 13 a motor vehicle shown. The motor vehicle has an internal combustion engine 14 on. The internal combustion engine 14 is designed in particular as a diesel engine. One of the internal combustion engine 14 coming exhaust gas flow 15 is through the exhaust system 10 . 11 . 12 . 13 passed with at least one catalytic converter. It is at least an exhaust gas catalyst in the form of an oxidation catalyst 16 intended.

Furthermore, the exhaust systems 10 to 13 each a diesel particulate filter 17 for the separation of diesel soot from the exhaust stream 15 on. The diesel particulate filter 17 is downstream of the oxidation catalyst 16 arranged.

The exhaust system 10 (see. 2 ) further includes a NOx storage catalyst 18 on. The NOx storage catalyst 18 is downstream of the diesel particulate filter 17 arranged. The NOx storage catalyst 18 allows caching of nitrogen oxides (NOx), reducing nitrogen oxides and from the exhaust stream 15 be removed.

The exhaust system 11 (see. 3 ) has an oxidation catalyst 16 and a diesel particulate filter 17 on, wherein the oxidation catalyst 16 additionally has a NOx storage coating (not shown) for intermediate storage of nitrogen oxides.

The exhaust system 12 (see. 4 ) points downstream of the oxidation catalyst 16 and the diesel particulate filter 17 an SCR catalyst 19 on. The SCR catalyst 19 converts the exhaust gas component nitrogen oxide without formation of undesirable by-products selectively to nitrogen and water. The reduction of nitrogen oxides is carried out using a reducing agent, in particular in the form of a urea solution. Between the diesel particulate filter 17 and the SCR catalyst 19 is via a feeder 20 injected the reducing agent. By this injection of the reducing agent, the reducing agent is added to the exhaust gas stream and this mixture is the SCR catalyst 19 fed. The nitrogen oxide conversion can be carried out for example at about 200 ° C.

The exhaust system 13 (see. 5 ) points downstream of the oxidation catalyst 16 a diesel particulate filter 17 with an SCR coating (not shown). The reducing agent necessary for the reduction of nitrogen oxides is fed via the feed 20 between the oxidation catalyst 16 and the diesel particulate filter 17 the exhaust gas flow 15 added. About the feeder 20 the injection of the reducing agent takes place.

The exhaust gas temperature is used to reach a target temperature by injecting fuel into a combustion chamber of the internal combustion engine 14 elevated. The post-injection takes place at a crankshaft angle in such a way that the post-injection compound is not or not completely incinerated in the combustion chamber. The post-injection takes place preferably 200 ° CA after top dead center. The during the post-injection into the combustion chamber of the internal combustion engine 14 Introduced Nacheinspritzmasse is at least partially only on the oxidation catalyst 16 burned. in the oxidation catalyst 16 caused by this exothermic reaction additional heat that is used to heat the exhaust system 10 to 13 is being used. By post injection, therefore, on the one hand, the oxidation catalyst 16 and on the other hand by means of the heated exhaust gas flow 15 also the downstream components, such as the diesel particulate filter 17 , the NOx storage catalyst 18 or the SCR catalyst 19 heated. Through the post-injection, among other things, the NOx conversion can be influenced as described below.

Based on 1 Now a driving cycle of the motor vehicle will be described, wherein in the driving cycle, the inventive method can be applied. The method can be used in particular for any drive cycle for exhaust gas temperature control. It is in 1 a coolant temperature diagram 1 , a driving speed diagram 2 and a temperature diagram 3 the exhaust system 12 shown.

In the coolant diagram 1 is an engine coolant temperature 4 in ° C over time t in seconds s. In the driving speed diagram 2 is a driving speed 5 plotted over time t in seconds s. In the temperature diagram 3 are an exhaust gas temperature 6 and a surface temperature 7 of the SCR catalyst 19 and a target temperature history 8th the surface temperature of the SCR catalyst 19 applied over time t.

As from the driving speed diagram 2 is clearly visible, the motor vehicle leads several startup and stop cycles 9 by, wherein in the first two startup and stop cycles 9 a speed of about 50 km / h and about 90 km / h is reached. In the subsequent startup and stop cycles 9 a speed of about 60 km / h is reached twice until the time T3 and after the time T3, the maximum speed is about 50 m / h. The engine coolant temperature rises from initially approx. 20 ° C to approx. 90 ° C.

The exhaust gas temperature 6 becomes after the exhaust gas catalyst in the form of the SCR catalyst 19 measured by means of a corresponding sensor. The exhaust gas temperature 6 and the surface temperature of the SCR catalyst 19 rise rapidly from the initial ambient temperature of about 20 ° C. At time T1, a cold start heating begins, causing the exhaust gas temperature 6 quickly rises to about 290 ° C. The cold start heating ends at time T2, after which the exhaust gas temperature drops again to about 200 ° C. The Kaltstartheizen can be done in particular by post-injection of fuel.

Through the subsequent startup and stop cycle 9 At a relatively high speed of approx. 90 km / h, the exhaust gas temperature rises 6 again at about 275 ° C, the surface temperature 7 of the SCR catalyst until the time t = 300 s is increased to just over 250 ° C. Then fall now the exhaust gas temperature 6 and the surface temperature 7 - without additional heating by post-injection - to below 200 ° C.

However, it is beneficial to the surface temperature 7 of the SCR catalyst and / or the exhaust gas temperature 6 to bring to a higher value.

The inventive method for controlling and / or regulating the internal combustion engine can now in particular for holding the exhaust gas temperature 6 and / or to maintain the surface temperature 7 be used at this higher level.

The exhaust gas temperature 6 is increased to achieve a target temperature by post-injection. The setpoint temperature is in 1 through the target temperature profile 8th shown from the time T3. The target temperature profile 8th and thus the setpoint temperature in 1 just over 200 ° C.

To reach this target temperature and the target temperature profile 8th the surface temperature of the SCR catalyst 19 to be able to keep constant according to a Nacheinspritzmasse is now varied.

The heat input and the post-injection mass are varied in that at least individual post-injections are exposed in at least individual cylinders. The Nacheinspritzmasse can thereby be finely dosed, creating a longer heating and keeping constant the target temperature profile 8th is possible. It is a fine regulation of the exhaust gas temperature 6 for example, the SCR catalyst 19 (see. 4 ) possible. This low-temperature heating with low post-injection masses can in particular be carried out permanently, for example, for a heating period of more than 5 minutes.

In particular, every nth post-injection on individual or on all cylinders can be suspended. However, the post-injection is not completely suspended. For example, the number n may be between 5 and 15. However, it is also conceivable that every 2, 3, 4 or every 16th post-injection is suspended. Further, the post-injection amount can be varied by making post-injections in individual cylinders and simultaneously subjecting post-injections to other cylinders or no post-injections at all. As a result, it is possible for the entire post-injection mass delivered in a heating period to be smaller than a total minimum mass that is used during heating in each case Working stroke in all cylinders would be at least delivered by appropriate injectors, wherein an injector emits a minimum injection mass per stroke. The minimum injection mass can be between 0.5 and 0.8 mg per stroke.

The disadvantages mentioned above are now avoided in that the target temperature is in a temperature range between a light-off temperature of the catalytic converter and a Rußabbrandtemperatur. The setpoint temperature is in particular below 500 ° C. and preferably below 300 ° C.

The heating power is below the heating power, which is used to regenerate the diesel particulate filter 17 necessary is. This has the advantage that the injection quantity is reduced. This also allows a reduction in the heat loss due to the lower temperature difference from the environment. This results in a reduction of CO2 emissions.

The setpoint temperature is in a temperature range below a Rußabbrandtemperatur, which takes place in this temperature range substantially no Rußabbrannt. The exhaust stream is heated to a target temperature, wherein the target temperature in a temperature range above a light-off temperature of the catalytic converter and below the regeneration temperature of the diesel particulate filter 17 lies. The Rußabbrandtemperaturen for corresponding soot particles are in a range of more than 500 ° C, in particular of more than 550 ° C.

Furthermore, a low NOx conversion is avoided in that the setpoint temperature is above a light-off temperature of the catalytic converter. Because of the exhaust gas temperature 6 and / or a surface temperature 7 is kept permanently above the light-off, resulting in an emission advantage.

The internal combustion engine may alternatively be designed as a gasoline engine.

LIST OF REFERENCE NUMBERS

1

Coolant temperature chart

2

Speed Chart

3

temperature diagram

4

Engine coolant temperature

5

driving speed

6

exhaust gas temperature

7

Surface temperature of an SCR catalyst

8th

Target temperature profile of the surface temperature of an SCR catalyst

9

Startup and stop cycle

10

 exhaust system

11

 exhaust system

12

 exhaust system

13

 exhaust system

14

 internal combustion engine

15

 exhaust gas flow

16

 oxidation catalyst

17

 diesel particulate Filter

18

 NOx storage catalytic converter

19

 SCR catalyst

20

 feed

T1

Time - Start of cold start heating

T2

Time - End of cold start heating

T3

Time - start of low temperature heating

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102010030640 A1 [0002]

Claims (14)

Method for controlling and / or regulating an internal combustion engine, wherein one of the internal combustion engine ( 14 ) coming exhaust gas flow ( 15 ) through an exhaust system ( 10 . 11 . 12 . 13 ) is passed with an exhaust gas catalyst, wherein an exhaust gas temperature is increased to achieve a target temperature by post injection, wherein a Nacheinspritzmasse is varied, wherein for varying the Nacheinspritzmasse at least individual postinjections are exposed in at least individual cylinders, characterized in that the target temperature in a temperature range between a light-off temperature of the catalytic converter and a Rußabbrandtemperatur is. A method according to claim 1, characterized in that each n-th post-injection is exposed to individual cylinders. A method according to claim 1 or 2, characterized in that each n-th post-injection is subjected to all cylinders. Method according to one of the preceding claims, characterized in that post-injections are carried out in individual cylinders and at the same time post-injections are applied in other cylinders. Method according to one of the preceding claims, characterized in that the target temperature is below 500 ° C Celsius. Method according to one of the preceding claims, characterized in that the target temperature is below 300 ° C Celsius. Method according to one of the preceding claims, characterized in that the post-injection is far after top dead center, that the post-injection mass is not or only partially in the combustion chamber of the internal combustion engine ( 14 ) is burned. Method according to one of the preceding claims, characterized in that the exhaust gas catalyst as SCR catalyst ( 19 ) is trained. Method according to one of the preceding claims, characterized in that a surface temperature of the catalytic converter is controlled to the desired temperature. Method according to one of the preceding claims, characterized in that the post-injection by means of an injector a Mindesteinspritzmasse is discharged per stroke. A method according to claim 10, characterized in that the minimum injection mass is between 0.5 and 0.8 mg per stroke. Method according to one of the preceding claims, characterized in that the total delivered in a heating period Nacheinspritzmasse is smaller than a total minimum mass, which would at least be delivered by injection injectors in each stroke during each working stroke in all cylinders. Method according to one of the preceding claims, characterized in that the internal combustion engine ( 14 ) is designed as a diesel engine. Method according to one of the preceding claims, characterized in that during the post-injection into the combustion chamber of the internal combustion engine ( 14 ) introduced Nacheinspritzmasse only on an oxidation catalyst ( 16 ) is burned. Engine control unit for controlling and / or regulating an internal combustion engine, characterized in that the engine control unit is set up for carrying out the method according to one of the preceding claims.

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