DE102021123030A1 - Method for reducing particulate formation in an internal combustion engine, control unit and internal combustion engine - Google Patents

Abstract

A method 100 for reducing particle formation in an internal combustion engine 1 is specified. The method 100 has the following steps: S2: operating the internal combustion engine 1 in a DFSO mode, S3: terminating the DFSO mode, and S4: operating the internal combustion engine 1 in a combustion mode, the timing of the fuel injection compared to a combustion mode with a regular fuel injection timing is shifted to a later timing.
In addition, a control unit 13 for controlling fuel injection into a combustion chamber 2 of an internal combustion engine 1, an internal combustion engine 1, a motor vehicle 200 and a computer program are specified.

Description

The invention relates to a method for reducing particle formation in an internal combustion engine, a control unit for controlling fuel injection into a combustion chamber of an internal combustion engine, an internal combustion engine, a motor vehicle and a computer program.

Known operating methods of internal combustion engines can provide for a temporary shutdown of the fuel supply if the internal combustion engine is not supposed to deliver any power, e.g. B. when braking, and a predetermined temperature of the engine, z. B. the engine operating temperature is reached, the temperature can be determined, for example, indirectly based on the temperature of the engine coolant. This process is also referred to in German as overrun cut-off and in English as deceleration fuel shut off (DFSO mode) or deceleration fuel cut-off. If engine power is requested again, for example by pressing the accelerator pedal, the DFSO mode can be ended so that fuel is injected into the combustion chamber of the internal combustion engine again. The combustion chamber is formed by the volume enclosed by the cylinder, piston and cylinder head, with the cylinder head closing off the combustion chamber from the point of view of the oscillating piston.

Since no fuel combustion takes place during the DFSO mode, in contrast to the combustion mode, the wall of the combustion chamber, in particular the cylinder wall, increasingly cools down, since air continues to be conducted through the combustion chamber and the engine cooling also continues to operate.

In the case of a subsequent renewed fuel injection, this has the effect that fuel penetrates further into the combustion chamber than would be the case with a combustion chamber in a non-cooled state. As a result, the at least partially liquid fuel comes into contact with the piston surface. This promotes the formation of undesirable particles until a higher temperature is reached again, e.g. B. the engine operating temperature.

The increasingly formed particles have a negative effect on the pollutant emissions of the combustion engine. In addition, exhaust gas after-treatment devices such as particle filters can be impaired in their function or an earlier regeneration of the affected exhaust gas after-treatment devices is required, which is usually associated with increased fuel consumption.

Against this background, it is the object of the invention to specify possibilities with which the disadvantages described above can be reduced or even completely avoided. In particular, a reduction in particle formation after exiting DFSO mode would be desirable.

This problem is solved by the subject matter of the independent claims. The dependent claims relate to developments of these solutions according to the invention.

A first aspect of the invention relates to a method for reducing particle formation in an internal combustion engine. An internal combustion engine, sometimes also referred to as an internal combustion engine, is to be understood as meaning an internal combustion engine for converting chemical energy contained in the fuel into mechanical work. During the combustion process required for this, exhaust gas is formed, which is introduced into an exhaust line connected to the internal combustion engine. The intake air required for the combustion process is supplied to the combustion engine from outside via an intake air line. Exhaust gas recirculation can optionally be assigned to the internal combustion engine, so that a proportion of exhaust gas can be admixed to the intake air. The internal combustion engine can be designed, for example, as a self-igniting or spark-ignited internal combustion engine. Motor petrol or diesel can be used as fuel, for example. The internal combustion engine can consequently be designed as an Otto engine or a diesel engine. For example, the internal combustion engine can be operated or operated in a mode with homogeneous distribution of the fuel in the combustion chamber (homogeneous operation).

The method according to the invention has the following method steps: operating the internal combustion engine in a DFSO mode, terminating the DFSO mode and operating the internal combustion engine in a combustion mode, the timing of the fuel injection compared to a combustion mode with a regular timing of the fuel injection to a later time is postponed.

In other words, the internal combustion engine is initially operated in a DFSO mode or under fuel cut-off, i.e. without fuel supply when the transmission is engaged, so that the crankshaft of the internal combustion engine continues to rotate, e.g. by the rotational movement of the wheels of a vehicle equipped with the internal combustion engine, and the pistons consequently perform an up and down movement in the cylinders as usual. The internal combustion engine can In order to save fuel, the vehicle can be operated in DFSO mode when driving the vehicle downhill, with the movement of the pistons being maintained by the momentum of the vehicle mass.

Prior to operating the engine in DFSO mode, the engine may be operated in regular combustion mode, i. H. with fuel injection into the combustion chamber at regular operating parameters, e.g. B. regular operating temperature, regular timing of fuel injection, etc.

For example, the regular combustion mode may have four strokes, an intake stroke, a compression stroke, a power stroke and an exhaust stroke, wherein the piston of the cylinder is at a top dead center of the cylinder at the beginning of the intake stroke and at the beginning of the power stroke and at a top dead center of the cylinder at the beginning of the compression stroke and at the beginning of the exhaust stroke Exhaust stroke is at a bottom dead center of the cylinder.

The term "fuel injection timing" refers to the position of the crankshaft when fuel injection begins. The position of the crankshaft can be described using the crank angle. The crank angle is the angle of the crankshaft in relation to the top dead center (TDC) of the piston and can be between 0 °CA and 720 °CA. At top dead center, the crank angle is 0 °CA or 720 °CA and 360 °CA. At bottom dead center, the crank angle is 180 °CA and 540 °CA. The crank angle is 0 °CA at ignition TDC and 360 °CA at gas exchange TDC. The regular point in time of the fuel injection can, for example, correspond to a point in time at which the crank angle is approximately 290° CA.

The DFSO mode is then terminated, for example if the speed of the combustion engine approaches idle speed and/or engine power is requested, e.g. B. to increase the speed of the vehicle. As air is pumped through the combustion chamber during DFSO mode, the combustion chamber cools down over time, such that when DFSO mode is terminated, the temperature in the combustion chamber is typically below the regular operating temperature of the internal combustion engine.

In a further method step, the internal combustion engine is (again) operated in a combustion mode. However, unlike the regular combustion mode in which the fuel injection timing is regular, the fuel injection timing is shifted to a later timing. Later point in time means that the piston is further in the downward movement, i. H. compared to the regular point in time, is further away from top dead center and consequently also further away from the fuel injection device arranged in the cylinder head. The later point in time can correspond, for example, to a crank angle between 260° CA and 250° CA.

After a certain period of time, e.g. B. depending on the temperature in the combustion chamber, can then be returned to the regular combustion mode, i. H. the fuel injection timing is shifted back to the regular timing.

A basic idea of the invention is therefore the timing of the fuel injection, engl. start of injection (SOI) after exiting DFSO mode to a later point in time, e.g. B. until a predetermined temperature in the combustion chamber (again) is reached. As a result, the fuel injection takes place at a time when the piston and consequently also the piston surface are further away from the fuel injector.

If the internal combustion engine is designed as a stratified charge engine or is operated in stratified charge mode, the point in time of the fuel injection is shifted to a point in time shortly before the ignition point when top dead center is reached. The amount of fuel required for this should be very small, as otherwise unwanted wetting of the piston can occur, which can result in the formation of particles.

Consequently, contact of the at least partially liquid fuel with the piston surface can be reduced or even avoided, so that particle formation is reduced. The negative effects associated with particle formation on the pollutant emissions of the internal combustion engine and the exhaust gas after-treatment devices in the exhaust system of the internal combustion engine can also be reduced.

As a result, the emission of pollutants can be reduced and the fuel consumption can be lowered by means of the proposed method. Furthermore, the service life of the internal combustion engine and the exhaust gas aftertreatment devices can be extended.

The method can be carried out in a computer-implemented manner, i. H. at least one method step, preferably several or all method steps, can be carried out using a computer program.

According to various embodiment variants, the time of the fuel injection can be postponed to a later time until a predefinable temperature is reached in a combustion chamber of the internal combustion engine, and when the predefinable temperature is reached to the regular time of the fuel injection.

The predefinable temperature can correspond, for example, to the regular operating temperature of the internal combustion engine, ie that temperature or a temperature in that temperature range which is optimal for the operation of the internal combustion engine. A specific temperature depends on the specific design of the internal combustion engine and can u. Consider parameters such as compression ratio, stroke, bore, operating condition of piston cooling (on/off), piston material composition.

This allows the internal combustion engine to be operated in the regular combustion mode over a long period of time, so that the advantages associated with regular combustion operation can be realized to the greatest possible extent. For example, in the regular combustion mode, the homogenization time in the combustion chamber for mixing fuel and air can be as long as possible in order to achieve better combustion of the fuel.

Reaching the specifiable temperature can be determined, for example, based on a period of time in the DFSO mode.

In other words, reaching the specifiable temperature can be estimated based on the duration of the DFSO mode. As the time in the DFSO mode increases, the time it takes for the predefinable temperature to be reached also increases, since the temperature in the combustion chamber falls as the time in the DFSO mode increases, and consequently a longer time is required in the combustion mode to reach the predefinable temperature.

The duration of the DFSO mode can be determined based on the number of work cycles and/or the speed, for example.

According to further embodiment variants, the later point in time can be defined as a function of the duration of the DFSO mode and/or the temperature in the combustion chamber of the internal combustion engine when the DFSO mode ends.

Since the temperature in the combustion chamber decreases as the duration of the DFSO mode increases, determining the later point in time as a function of the duration of the DFSO mode can on the one hand allow the later point in time to deviate as little as possible from the regular point in time, and on the other hand the later point in time can be selected sufficiently late in order to prevent the fuel from coming into contact with the piston surface and the associated formation of particles as far as possible. In the case of a longer DFSO mode, an even later, later point in time can therefore be selected than in the case of a shorter DFSO mode.

Alternatively or in addition to the duration of the DFSO mode, the later point in time, taking into account the temperature in the combustion chamber of the internal combustion engine when the DFSO mode ends, e.g. B. the temperature of the surface of a piston of the internal combustion engine.

It can also be achieved in this way that the later point in time deviates as little as possible from the regular point in time, but particle formation can still be largely prevented.

Provision can optionally be made for the later point in time to be varied as a function of the duration of the DFSO mode and/or the temperature in the combustion chamber.

In other words, it is not only possible to set a specific later point in time and this optionally depending on the duration of the DFSO mode and/or the temperature in the combustion chamber, but the later point in time can also be varied during the process and thus adapted to the changing temperature conditions become. For example, after the end of the DFSO mode, a later later time can first be specified. As the duration of the combustion mode increases, the later point in time can be shifted forward again in the direction of the regular point in time until the regular point in time is reached again.

As a result, abrupt changes in fuel injection timing can be avoided. By gradually adapting the fuel injection timing to the changing temperature conditions in the combustion chamber, engine performance and particle formation can be improved at the same time.

A further aspect of the invention relates to a control unit for controlling fuel injection into a combustion chamber of an internal combustion engine. The control unit is designed to generate control signals and to output them to a fuel injection device, the control signals shifting a point in time of the fuel injection to a later point in time compared to a regular point in time of the force bring about fuel injection after, preferably immediately after, operation of the internal combustion engine in a DFSO mode has ended.

The control unit can be used, for example, to control the above-described method steps of the method for reducing particle formation in an internal combustion engine. Variants of the method can also be implemented accordingly by means of the control unit. In this respect, the above explanations for explaining the method also serve to describe the control unit according to the invention. The advantages of the method are associated with the control unit accordingly.

The control unit can input data, e.g. from sensors, which process input data and trigger actuators in response to the processed input data based on instructions or code programmed into the controller according to one or more routines. The control unit can be realized in terms of hardware and/or software and can be designed physically in one or more parts. In particular, the control unit can be part of a controller for the internal combustion engine or can be integrated into it. In a typical embodiment, the engine control of a motor vehicle functions as a control unit.

Another aspect of the invention relates to an internal combustion engine. The internal combustion engine has a combustion chamber, a fuel injection device for injecting fuel into the combustion chamber and a control unit as described above. In addition, the internal combustion engine can have other usual components, e.g. B. intake valves, exhaust valves, an ignition device, etc. have.

In this respect, the above explanations for explaining the method and the control unit also serve to describe the internal combustion engine according to the invention. The advantages of the method and the control unit are associated with the internal combustion engine accordingly.

A further aspect of the invention relates to a motor vehicle with an internal combustion engine as described above. In this respect, the above statements serve to explain the internal combustion engine and the method and the control unit and also to describe the motor vehicle according to the invention.

The advantages of the internal combustion engine and the method and the control unit are associated with the motor vehicle accordingly. In addition, the invention has a particularly advantageous effect in a motor vehicle, since it enables compliance with strict legal requirements with regard to the permissible emission of air pollutants.

A motor vehicle is a motor-driven vehicle, e.g. B. a land, air or water vehicle to understand. The motor vehicle can be designed as a passenger car, for example.

A further aspect of the invention relates to a computer program comprising instructions which cause an internal combustion engine or a motor vehicle as described above to execute a method as described above.

A computer program can be understood as meaning a program code that can be stored on a suitable medium and/or can be called up via a suitable medium. Any medium suitable for storing software, for example a non-volatile memory installed in a control unit, a DVD, a USB stick, a flash card or the like, can be used to store the program code. The program code can be retrieved, for example, via the Internet or an intranet or via another suitable wireless or wired network.

In this respect, the above statements serve to explain the internal combustion engine, the motor vehicle and the method, and also to describe the computer program according to the invention. The advantages of the internal combustion engine, the motor vehicle and the method are associated with the computer program accordingly.

• 1 ein Ablaufschema eines beispielhaften Verfahrens zum Verringern der Partikelbildung;
• 2a eine schematische Darstellung eines Verbrennungsraums im regulären Verbrennungsmodus;
• 2b eine schematische Darstellung des Verbrennungsraums im regulären Verbrennungsmodus nach Beenden eines DFSO-Modus gemäß dem Stand der Technik;
• 2c eine schematische Darstellung des Verbrennungsraums im Verbrennungsmodus mit späterem Zeitpunkt der Kraftstoffeinspritzung nach Beenden eines DFSO-Modus;
• 3 eine schematische Darstellung eines beispielhaften Kraftfahrzeugs.

The invention is explained in more detail below with reference to the figures and the associated description. Show it:

• 1 a flowchart of an exemplary method for reducing particulate formation;
• 2a a schematic representation of a combustion chamber in the regular combustion mode;
• 2 B a schematic representation of the combustion chamber in the regular combustion mode after ending a DFSO mode according to the prior art;
• 2c a schematic representation of the combustion chamber in combustion mode with later timing of fuel injection after exiting a DFSO mode;
• 3 a schematic representation of an exemplary motor vehicle.

1 shows a flow chart of an exemplary method 100 with the method steps S1 to S5. The method 100 is used to reduce particle formation in an internal combustion engine 1, z. B. in an internal combustion engine 1 of a motor vehicle 200.

After the start of method 100, internal combustion engine 1 is first operated in regular combustion mode, ie. H. with regular operating parameters, e.g. B. regular time of fuel injection and at regular operating temperature operated. If the internal combustion engine 1 is designed as a four-stroke engine, the regular combustion mode comprises four strokes in which the piston 5 in the cylinder formed by the cylinder head 3 and the cylinder wall 4 moves up and down between top dead center OT and bottom dead center. This movement is transmitted to the crankshaft via the piston rod 7 connected to the piston 5 .

The four strokes are the intake stroke, the compression stroke, the power stroke and the exhaust stroke, with fuel injection taking place directly into the combustion chamber 2 during the intake stroke, i.e. while the piston is moving from top dead center to bottom dead center. The fuel injection begins at a crank angle of approx. 290 °CA, i. H. fuel injection timing is 290° CA. The fuel 12 is injected in liquid form and forms a fuel cloud in the combustion chamber 1 .

In the subsequent method step S2, the internal combustion engine 1 is operated in the DFSO mode, i. H. under fuel cut-off, i.e. without fuel supply. This can be the case, for example, when driving downhill. During DFSO mode, combustion chamber 1 cools down as air continues to be pumped through combustion chamber 1 and engine cooling is also still active.

In method step S3, the DFSO mode is terminated, for example based on an engine power requirement by actuating the accelerator pedal.

In method step S4, internal combustion engine 1 is again operated in a combustion mode. In contrast to the regular combustion mode, however, the fuel injection timing is shifted to a later timing. In other words, the fuel injection no longer begins at approximately 290° CA, but at a crank angle between, for example, 260° CA and 250° CA.

Since the fuel cloud forms further into the combustion chamber 2 in this modified combustion mode due to the cooling during the DFSO mode, i.e. advances further in the direction of the piston 5, there would be contact between the fuel 12 and the surface of the piston 6 if the injection timing were not adjusted . This would cause unwanted particle formation.

In order to largely prevent the formation of particles, the injection timing is therefore shifted to a later point in time at which the piston 5 is still moving downwards as viewed from the top dead center TDC, so that more space is created for the spread of the fuel cloud.

The internal combustion engine 1 is operated in this modified combustion mode with a later point in time for the fuel injection until a predetermined temperature, e.g. B. the regular operating temperature is reached again. Reaching this temperature can be estimated based on the duration of the DFSO mode in method step S2. If the DFSO mode lasts for a long time, a correspondingly strong cooling and consequently a long time until the predefinable temperature is reached is to be expected.

There is the option of specifying the later point in time, i.e. the crank angle at the start of fuel injection, as a function of the duration of the DFSO mode, since the longer the DFSO mode lasts and thus the greater the cooling, the greater the distance between the fuel injection device and the surface of the piston 6 should, in order to avoid contact of the liquid fuel with the surface 6 and the associated formation of particles.

In method step S5, internal combustion engine 1 is then operated again in the regular combustion mode, as explained for method step S1. The change from the modified combustion mode to the regular combustion mode, ie from method step S4 to method step S5, can take place when the predefinable temperature is reached. This ends the method 100.

The 2a until 2c show the combustion chamber 2 in different operating modes of the internal combustion engine 1 schematically.

2a shows the combustion chamber 2 in the regular combustion mode, as can be carried out, for example, in the method steps S1 and S5 explained above. The combustion chamber 2 is that volume which is enclosed by the cylinder head 3, the cylinder wall 4 and the piston 5. The piston has a directed in the direction of the cylinder head 3 upper surface 6 and is connected to the crankshaft (not shown) via the piston rod 7 .

An inlet valve 8 and an outlet valve 9 are arranged in the cylinder head 3 in order to be able to supply air to the combustion chamber 2 and to discharge combustion gases from the combustion chamber 2 . In addition, the fuel injection device 11 is arranged in the cylinder head 3, by means of which fuel 12 can be injected into the combustion chamber 2, forming a fuel cloud. Also arranged in the cylinder head 3 is a spark plug 10 for igniting the air-fuel mixture forming in the combustion chamber 2 . During the combustion process, the piston 5 performs the up and down movement described above.

In the regular combustion mode, the combustion chamber 2 is at the regular operating temperature, i. H. the combustion chamber 2 is comparatively warm. Consequently, after the fuel 12 has been injected, the fuel 12 evaporates quickly and the fuel cloud formed from liquid fuel 12 cannot spread far into the combustion chamber 2 . Contact of the liquid fuel 12 with the surface of the piston 6 can be avoided.

2 B shows the combustion chamber 2 after exiting the DSFO mode according to the prior art. By cooling down the combustion chamber 2 during the DFSO mode, the fuel 12 evaporates less quickly after its injection and the fuel cloud that forms can spread further into the combustion chamber 2 . This results in undesired contact of the liquid fuel 12 with the surface of the piston 6 and consequently in the formation of particles.

2c shows the combustion chamber 2 after the end of the DFSO mode according to the method according to the invention. In the modified combustion mode, in order to prevent the liquid fuel 12 from contacting the surface of the piston 6, the fuel injection is carried out at a later timing, namely at a timing when the piston 6 is farther from the top dead center TDC.

In 3 an exemplary motor vehicle 200, which is designed as a passenger car, is shown schematically. Motor vehicle 200 has an internal combustion engine 1, which in the exemplary embodiment is designed as a gasoline-powered four-stroke engine with direct injection of the gasoline. The internal combustion engine 1 has four cylinders, of which 3 only the combustion chamber 2 of a cylinder is shown schematically. The invention is not limited to a specific number of cylinders, and the internal combustion engine 1 could also have six or eight cylinders, for example.

A fuel injection device 11 is assigned to the combustion chamber 2 . This fuel injection device 11 serves to inject the fuel 12 into the combustion chamber 2 . The injection of the fuel 12 is controlled by means of control signals 14 which are generated by the control unit 13 and output to the fuel injection device 11 . For this purpose, the fine fuel injection device 11 and the control unit 13 are in an active signaling connection.

The control signals 14 cause a timing of fuel injection to be shifted to a later timing compared to a regular timing of fuel injection after operation of the internal combustion engine 1 in a DFSO mode has ended. In other words, the control unit 13 is designed to recognize the end of a DFSO mode and then to generate and output control signals 14 that cause the point in time of the fuel injection to be shifted to a later point in time. The later point in time can be defined depending on the duration of the DFSO mode. If the regular operating temperature is reached again in the combustion chamber 2, control signals 14 are generated and output to the fuel injection device 11, which bring about a shift in the point in time of the fuel injection to the regular point in time.

Reference List

1

combustion engine

2

combustion chamber

3

cylinder head

4

cylinder wall

5

Pistons

6

surface of the flask

7

piston rod

8th

intake valve

9

outlet valve

10

spark plug

11

fuel injector

12

fuel

13

control unit

14

control signal

100

Proceedings

200

motor vehicle

OT

Top Dead Center

S1

Operating the internal combustion engine in the regular combustion mode

S2

operating the internal combustion engine in a DFSO mode

S3

Exit DFSO mode

S4

operating the internal combustion engine in a combustion mode with retarded fuel injection timing

S5

Operating the internal combustion engine in the regular combustion mode

Claims (10)

Method (100) for reducing particle formation in an internal combustion engine (1), the method (100) having the following steps: - S2: operating the internal combustion engine (1) in a DFSO mode, - S3: Exit DFSO mode and - S4: Operating the internal combustion engine (1) in a combustion mode in which the fuel injection timing is shifted to a later timing compared to a combustion mode with a regular fuel injection timing. Method (100) according to claim 1 , wherein the point in time of the fuel injection is shifted to the later point in time until a predeterminable temperature is reached in a combustion chamber (2) of the internal combustion engine (1) and when the predeterminable temperature is reached it is shifted to the regular point in time of the fuel injection. Method (100) according to claim 2 , wherein reaching the predefinable temperature is determined based on a period of time of the DFSO mode. Method (100) according to claim 2 or 3 , wherein the predeterminable temperature corresponds to a regular operating temperature of the internal combustion engine (1). Method (100) according to one of the preceding claims, wherein the later point in time is determined as a function of the duration of the DFSO mode and/or the temperature in the combustion chamber (2) of the internal combustion engine (1) when the DFSO mode ends. Method (100) according to claim 5 , the later point in time depending on the duration of the DFSO mode and/or the temperature in the combustion chamber (2) being varied. Control unit (13) for controlling fuel injection into a combustion chamber (2) of an internal combustion engine (1), the control unit (13) being designed to generate control signals (14) and to output them to a fuel injection device (11), the control signals (14 ) cause a fuel injection timing to be shifted to a later timing compared to a regular fuel injection timing after the internal combustion engine (1) stops operating in a DFSO mode. Internal combustion engine (1), comprising: - a combustion chamber (2), - a fuel injection device (11) for injecting fuel into the combustion chamber (2) and - a control unit (13). claim 7 . Motor vehicle (200) with an internal combustion engine (1). claim 8 . Computer program comprising instructions that cause an internal combustion engine (1) to claim 8 or a motor vehicle (200). claim 9 a method (100) according to any one of Claims 1 until 6 executes

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