EP3146186A1

EP3146186A1 - Method and device for controlling the exhaust gas temperature of an internal combustion engine

Info

Publication number: EP3146186A1
Application number: EP15718963.0A
Authority: EP
Inventors: Michael Greiner
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2014-05-19
Filing date: 2015-05-04
Publication date: 2017-03-29
Also published as: WO2015176945A1; DE102014209420A1

Abstract

The invention relates to a method for controlling an engine (14) in an open-loop and/or closed-loop manner and to an engine control module for performing the method, wherein an exhaust gas flow (15) coming from the engine (14) is conducted through an exhaust system (10, 11, 12, 13) having an exhaust gas catalytic converter, wherein an exhaust gas temperature is increased by post-injection in order to achieve a target temperature, wherein a post-injection mass is varied, wherein at least individual post-injections in at least individual cylinders are suspended in order to vary the post-injection mass. Impermissibly high heat input, excessively high fuel consumption, and an excessively low NOx conversion during the exhaust gas aftertreatment are avoided in that the target temperature lies in a temperature region between a light-off temperature of the exhaust gas catalytic converter and a soot burn-off temperature.

Description

description

METHOD AND DEVICE FOR CONTROLLING THE DEFROSTING TEMPERATURE OF AN INTERNAL COMBUSTION ENGINE

The invention relates to a method for controlling and / or regulating a

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

From DE 10 2010 030 640 A1 a method for controlling and / or regulating an internal combustion engine is known. An exhaust gas flow coming from the combustion engine is passed through an exhaust system with a corresponding exhaust duct and with a

Exhaust gas purifying component passed. 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. The

During the regeneration of the diesel particulate filter, the method comprises post-injecting fuel into one or more cylinders of the engine at least in an exhaust stroke of a motor cycle, wherein the late post-injection takes place after about 40 ° CA before top dead center, so that part of the fuel or all fuel in a corresponding piston recess is injected. The timing and amount of injection will be on

Controlled based on a required to increase the temperature of the particulate filter during the regeneration amount of heat. In an operating mode becomes a variable

Valve control system adjusted so that an exhaust valve is temporarily closed before the 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. By closing the exhaust valve before the late post-injection, the temperature and the pressure of the gas in the cylinder is increased, which should lead to a smaller amount of fuel, which for the later

After-injection is needed to increase the temperature of the diesel particulate filter. The Amount of injected fuel is based on an amount of heat that is requested to increase the temperature of the diesel particulate filter and / or on 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 span of ten

Motor cycles take place. 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 goal of

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 be done at about 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 can 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 the

Exhaust gas aftertreatment is avoided.

This object of the invention is based on a method with the

Characteristics of claim 1 solved. 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, causing the

Essentially no Rußabbrannt takes place. The exhaust stream is heated to a target temperature, the target temperature 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 is also a reduction of Loss heat flow through the lower temperature difference to the environment allows. This results in a reduction of CO 2 emissions.

Furthermore, a low NOx conversion is avoided in that the setpoint temperature is above a light-off temperature of the catalytic converter. 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 converts the

Exhaust gas component nitrogen oxide without formation of undesired by-products selectively to nitrogen and water around. 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 CO 2 advantage

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

Exhaust catalyst. 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, can be continuous Post-injections are made 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 Mindesteinspntzmassen 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

Kaltstartheizen for example, after a corresponding Schubfahrtphase 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 lesser heat input can be caused by exposure to single or multiple

Post-injections are set 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 connected to the motor vehicle

Low-load operation takes place and, for example, driving in low-speed urban areas be performed. With in the process, it is possible to heat longer and thereby keep the exhaust gas temperature and or the surface temperature of the corresponding catalytic converter for a long time in a lower temperature range, in particular at about 200 ° C. 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 procedure. By means of the control unit, the exhaust gas temperature for reaching the setpoint temperature can be controlled and / or regulated by post-injection, the post-injection mass being variable, wherein at least individual post-injections in at least individual cylinders can be exposed for varying the post-injection mass. 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 various possibilities for the method according to the invention and the

Design and development of 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:

Fig. 1 shows three schematic diagrams, wherein the coolant temperature, the

Driving 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,

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

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

In Fig. 2 to 5 each an exhaust system 10, 1 1, 12, 13 of a motor vehicle is shown. The motor vehicle has an internal combustion engine 14. The internal combustion engine 14 is designed in particular as a diesel engine. An exhaust gas flow 15 coming from the internal combustion engine 14 is passed through the exhaust system 10, 11, 12, 13 with at least one

Passed catalytic converter. It is at least one catalytic converter in the form of a

Oxidation catalyst 16 is provided.

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

The exhaust system 10 (see Fig. 2) further includes a NOx storage catalyst 18. The NOx storage catalyst 18 is disposed downstream of the diesel particulate filter 17. The NO x storage catalytic converter 18 allows intermediate storage of nitrogen oxides (NO x), wherein nitrogen oxides are reduced and removed from the exhaust gas flow 15.

The exhaust system 1 1 (see Fig. 3) has an oxidation catalyst 16 and a

Diesel particulate filter 17, wherein the oxidation catalyst 16 additionally comprises a NOx storage coating (not shown) for the intermediate storage of nitrogen oxides.

The exhaust system 12 (see Fig. 4) has downstream of the oxidation catalyst 16 and the diesel particulate filter 17 an SCR catalyst 19. The SCR catalyst 19 selectively converts the exhaust gas component nitrogen oxide to nitrogen and water without the formation of undesirable by-products. 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 feed 20 the

Reducing agent injected. By this injection of the reducing agent is the

Reducing agent is added to the exhaust stream and this mixture is fed to the SCR catalyst 19. The nitrogen oxide conversion can be carried out for example at about 200 ° C.

The exhaust system 13 (see Fig. 5) has, 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 introduced via the feed 20 between the

Oxidation catalyst 16 and the diesel particulate filter 17 admixed to the exhaust gas stream 15. Via the feed 20, the injection of the reducing agent takes place.

The exhaust gas temperature is increased to reach a target temperature by injecting fuel into a combustion chamber of the internal combustion engine 14. The post-injection takes place at a crankshaft angle such that the Nacheinspritzmasse is not or not completely burned in the combustion chamber. The post-injection takes place preferably 200 ° CA after top dead center. During the post-injection into the combustion chamber of the

Internal combustion engine 14 introduced Nacheinspritzmasse is at least partially burned only on the oxidation catalyst 16. In the oxidation catalyst 16 is formed by this exothermic reaction additional heat, which is used to heat the exhaust system 10 to 13. As a result of the post-injection, the oxidation catalytic converter 16 and, secondly, the heated exhaust gas flow 15 also heat the downstream components, such as the diesel particulate filter 17, the NOx storage catalytic converter 18 or the SCR catalytic converter 19. Through the post-injection, among other things, the NOx conversion can be influenced as described below.

A driving cycle of the motor vehicle will now be described with reference to FIG. 1, wherein the method according to the invention can be used in the driving cycle. The method can be used in particular for any drive cycle for exhaust gas temperature control. It is in Fig. 1 is a coolant temperature diagram 1, a

Fahrgeschwindigkeitsdiagramm 2 and a temperature diagram 3 of the exhaust system 12 shown.

In the coolant diagram 1, an engine coolant temperature 4 in ° C is plotted over time t in seconds s. In the vehicle speed diagram 2 is a

Driving speed 5 is plotted over time t in seconds s. In the temperature diagram 3, an exhaust gas temperature 6 and a surface temperature 7 of the SCR catalyst 19 and a target temperature profile 8 of the surface temperature of the SCR catalyst 19 are plotted over time t.

As can be clearly seen from the vehicle speed diagram 2, the motor vehicle carries out several startup and stop cycles 9, wherein in the first two startup and stop cycles 9 a speed of approximately 50 km / h and approximately 90 km / h is achieved. In the subsequent start-up and stop cycles 9, a speed of about 60 km / h is still reached twice until time T3, and after 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 is measured after the exhaust gas catalyst in the form of the SCR catalyst 19 by means of a corresponding sensor. The exhaust gas temperature 6 and the

Surface temperature of the SCR catalyst 19 increases from the initial one Ambient temperature of about 20 ° C quickly. At time T1, a cold start heating begins, whereby the exhaust gas temperature 6 rises rapidly up 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 Nacheinspritzen of fuel.

By the subsequent start-up and stop cycle 9 with a relatively high speed of about 90 km / h, the exhaust gas temperature 6 rises again to about 275 ° C, wherein the

Surface temperature 7 of the SCR catalyst is increased to just over 250 ° C until the time t = 300 s. Then fall now the exhaust gas temperature 6 and the surface temperature 7 - without additional heating by Nacheinspritzen - to below 200 ° C.

However, it is advantageous to bring the surface temperature 7 of the SCR catalyst and / or the exhaust gas temperature 6 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 for holding the

Surface temperature 7 can 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 shown in FIG. 1 by the target temperature profile 8 from the point in time T3. The target temperature profile 8 and thus the setpoint temperature in Fig. 1 are just above 200 ° C.

In order to achieve this setpoint temperature and to the target temperature profile 8 of

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, whereby a longer heating and keeping constant the target temperature profile 8 is possible. A fine regulation of the exhaust gas temperature 6 is possible, for example for the SCR catalytic converter 19 (see FIG. 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 while simultaneously subjecting injections to other cylinders or none at all

Post-injections are made. This makes it possible that the entire post-injection mass delivered in a heating period is smaller than one

Total minimum mass that is due during heating in every stroke in all cylinders

corresponding injectors would at least deliver, with an injector a

Gives 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 necessary for the regeneration of the diesel particulate filter 17. 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 CO 2 emissions.

The setpoint temperature is in a temperature range below a Rußabbrandtemperatur, which takes place in this temperature range substantially no Rußabbrannt. The exhaust gas stream is heated to a desired temperature, wherein the setpoint temperature is in a temperature range above a light-off temperature of the catalytic converter and below the regeneration temperature of the diesel particulate filter 17. 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 that

Exhaust gas temperature 6 and / or a surface temperature 7 permanently above the

Light-off temperature is maintained, there is an emission advantage. The internal combustion engine may alternatively be designed as a gasoline engine.

LIST OF REFERENCE NUMBERS

1 coolant temperature diagram

2 driving speed diagram

3 temperature diagram

4 engine coolant temperature

5 driving speed

6 exhaust gas temperature

7 Surface temperature of an SCR catalyst

8 Target temperature profile of the surface temperature of an SCR catalytic converter

9 Starting and stopping cycle

10 exhaust system

1 1 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 catalyst

19 SCR catalyst

20 feeder

T1 time - start of cold start heating

T2 time - end of cold start heating

T3 time - start of low temperature heating

Claims

claims

1. A method for controlling and / or regulating an internal combustion engine, wherein one of the internal combustion engine (14) coming exhaust gas stream (15) through an exhaust system (10, 1 1, 12, 13) is passed with an exhaust gas catalyst, wherein an exhaust gas temperature to achieve a Target temperature is increased by post-injection, with a

Nacheinspritzmasse is varied, wherein for varying the post-injection at least individual post-injection are exposed in at least individual cylinders, characterized in that the target temperature is in a temperature range between a light-off temperature of the catalytic converter and a Rußabbrandtemperatur.

2. The method according to claim 1, characterized in that each n-th post-injection is exposed to individual cylinders.

3. The method according to claim 1 or 2, characterized in that every nth

Post-injection is suspended on all cylinders.

4. The method according to any one of the preceding claims, characterized in that post-injections are carried out in individual cylinders and simultaneously exposed in other cylinders Nacheinspritzungen.

5. The method according to any one of the preceding claims, characterized in that the target temperature is below 500 ° C Celsius.

6. The method according to any one of the preceding claims, characterized in that the target temperature is below 300 ° C Celsius.

7. The method according to any one of the preceding claims, characterized in that the post-injection is far after the top dead center that the Nacheinspritzmasse is not or only partially burned in the combustion chamber of the internal combustion engine (14).

8. The method according to any one of the preceding claims, characterized in that the exhaust gas catalyst is designed as an SCR catalyst (19).

9. The method according to any one of the preceding claims, characterized in that a surface temperature of the catalytic converter is controlled to the target temperature.

10. The method according to any one of the preceding claims, characterized in that the Nacheinspritzen by means of an injector a Mindesteinspritzmasse per stroke is delivered.

1 1. A method according to claim 10, characterized in that the minimum injection mass is between 0.5 and 0.8 mg per stroke.

12. The method according to any 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 be at least delivered in each cylinder after injections in each stroke by appropriate injectors.

13. The method according to any one of the preceding claims, characterized in that the internal combustion engine (14) is designed as a diesel engine.

14. The method according to any one of the preceding claims, characterized in that during the post-injection into the combustion chamber of the internal combustion engine (14) introduced Nacheinspritzmasse is burned only on an oxidation catalyst (16).

15. 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.