CN110030062B

CN110030062B - Method for reducing particulate emissions during cold start of an internal combustion engine

Info

Publication number: CN110030062B
Application number: CN201811346209.8A
Authority: CN
Inventors: D.苏德沙耶夫; G.施罗特
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2017-11-13
Filing date: 2018-11-13
Publication date: 2021-12-03
Anticipated expiration: 2038-11-13
Also published as: CN110030062A; DE102017126613A1

Abstract

The invention relates to a method for reducing particulate emissions at a cold start of an internal combustion engine, in particular to a method for reducing particulate emissions of an internal combustion engine (10) in the case of a cold start of the internal combustion engine (10). In this case, at least one combustion chamber (12) of the internal combustion engine (10) is shut off during a cold start phase of the internal combustion engine (10), so that only air is compressed in the shut-off combustion chamber. By means of compression work, the combustion chamber is heated, so that a better gasification of the fuel in the combustion chamber (12) is achieved. It is provided that when the cylinder wall of the combustion chamber (12) has reached a sufficient temperature, the initially switched-off combustion chamber (12) is switched on, so that soot formation due to the collision of unburned fuel onto the cold cylinder wall is reduced.

Description

Method for reducing particulate emissions during cold start of an internal combustion engine

Technical Field

The present invention relates to a method for reducing particulate emissions of an internal combustion engine, in particular a gasoline engine, during a cold start of the internal combustion engine, and to a control unit for carrying out such a method.

Background

The continuous tightening of exhaust gas regulations places high demands on vehicle manufacturers, which are addressed by corresponding measures for reducing the untreated emissions of the engine and by corresponding exhaust gas aftertreatment. With the introduction of the regulation class euro 6(EU6), a limit value for the quantity of particles is specified for gasoline engines, which in many cases necessitates the use of a gasoline particle filter. Such soot particles occur in particular after cold starting of the internal combustion engine as a result of incomplete combustion in combination with an over-stoichiometric combustion air ratio (verbrennungsluftver ä ltnis, sometimes referred to as excess air ratio) after cold starting, cold cylinder walls and an inhomogeneous mixture distribution in the combustion chamber of the internal combustion engine. The cold start phase is therefore decisive for complying with the legally prescribed particle limits (not only with respect to the particle quality but also with respect to the particle quantity). Furthermore, a cold start with a substoichiometric, fuel-rich combustion air ratio leads to higher emissions of carbon monoxide (CO) and unburned Hydrocarbons (HC), since the conversion to carbon dioxide and water vapor is not yet possible due to the cold catalyst. In motor vehicles with a gasoline particle filter, the latter is then further loaded with soot during driving operation. In order to not excessively raise the exhaust gas back pressure, the gasoline particulate filter must be continuously or periodically regenerated. The increase in exhaust gas back pressure can lead to additional consumption of the internal combustion engine, to a loss of power and to impairment of the smooth operation until the ignition is interrupted. In order to carry out the thermal oxidation of the soot trapped in the gasoline particle filter by means of oxygen, it is necessary in the exhaust gas system of a gasoline engine to combine a sufficiently high temperature level with the oxygen present at the same time. Since modern gasoline engines are usually operated without an excess of oxygen with stoichiometric combustion air ratios (λ =1), additional measures are necessary for this. The following measures are considered for this purpose: for example, temperature increases caused by ignition angle regulation, transient lean regulation (magervestellung) of the gasoline engine, blowing of secondary air into the exhaust system, or a combination of these measures. Preferably, the ignition angle adjustment used up to now in the retarded direction is combined with a lean adjustment of the gasoline engine, since this method can be used without additional components and can provide a sufficient oxygen amount in the majority of operating points of the gasoline engine. While the soot loading of the particle filter for diesel engines takes place essentially continuously, gasoline engines release soot particles primarily during the cold start phase of the internal combustion engine, the soot formation rising with decreasing ambient temperature. The highest proportion of soot emissions in the case of an externally ignited internal combustion engine is due to the cold combustion chamber walls and therefore inadequate gasification of the fuel, resulting from the cold start phase in the case of low ambient temperatures, in particular in the case of ambient temperatures below 0 ℃.

In order to reduce soot production during the cold start phase of an externally ignited internal combustion engine, it is known, for example, to reduce the start enrichment, to use multiple ignitions or multiple injections for avoiding combustion chamber wall wetting and for improved mixture preparation. However, these measures can be implemented in most cases only with high effort and are therefore in most cases costly.

DE 10131937 a1 discloses a device for reducing vehicle emissions and a method for reducing cold-start emissions of an internal combustion engine, in which the valve control time (sometimes referred to as valve timing), the ignition angle and the combustion air ratio are adapted in order to improve the engine temperature and the engine efficiency during the cold-start phase and to reduce the cold-start emissions.

Furthermore, it is known to shut off at least one combustion chamber, preferably at least two combustion chambers, in particular half of the cylinders of the combustion chambers present in an internal combustion engine, in order to save fuel in the case of weak engine loads or low partial loads of the internal combustion engine.

DE 102012022153 a1 discloses a method for operating an internal combustion engine, in which a cylinder shut-off of the internal combustion engine is used for increasing the exhaust gas temperature of the internal combustion engine in such a way that the non-shut-off cylinder is operated with a sub-stoichiometric mixture and the unburned fuel of the sub-stoichiometric mixture reacts exothermically there with the oxygen which is conveyed into the exhaust gas channel by the shut-off cylinder.

Disclosure of Invention

The object of the present invention is to reduce soot emissions during the cold start phase of an internal combustion engine and to overcome the disadvantages known from the prior art.

According to the invention, this object is achieved by a method for reducing the particle emissions of an internal combustion engine during a cold start of the internal combustion engine, comprising the following steps:

cold starting the internal combustion engine, wherein at least one combustion chamber of the internal combustion engine is switched off during a cold start phase of the internal combustion engine,

-switching on the at least one previously switched-off combustion chamber when the cylinder wall of the combustion chamber has reached a defined minimum temperature.

By means of the method according to the invention, at least one combustion chamber of the internal combustion engine is operated without fuel (gefeuert) during a cold start. Soot emissions of the internal combustion engine are thereby reduced, since overall fewer combustion chamber walls can come into contact with the fuel and therefore less unvaporized fuel is located in the combustion chamber, which contributes to soot formation. In the combustion chamber which is operated without fuel, air is compressed by the piston, whereby the combustion chamber is heated. If the combustion chamber has been sufficiently heated, a switch can be made from operation with cylinder shut-off to normal operation, since from this point on the intensified soot formation can no longer be expected. Furthermore, the advantages of the proposed method are: this method can be implemented cost-effectively (kostennetral) in the case of internal combustion engines with cylinder shut-off and requires no additional components.

In a preferred embodiment of the method, it is provided that an ambient temperature is determined and the method is activated when the ambient temperature lies below a threshold temperature. In the case of cold ambient temperatures, the engine block and therefore also the combustion chamber are correspondingly cooled down strongly. The soot formation is therefore particularly strongly formed in the combustion chamber by insufficiently vaporized fuel. In order to carry out the particle emission in this operating state, it is particularly advantageous to carry out the method according to the invention for reducing cold start emissions.

In one advantageous embodiment of the method, it is provided that the internal combustion engine is operated with a substantially stoichiometric combustion air ratio during a cold start. Even if enrichment of the combustion air mixture cannot be completely avoided and can be necessary during the cold start phase in order to avoid an ignition interruption and the associated non-stationary engine operation, an essentially stoichiometric combustion air ratio is sought in order to effectively convert the emissions of the internal combustion engine into harmless exhaust gas constituents by means of the three-way catalyst and/or the four-way catalyst.

Such an embodiment of the method is preferred in which case half of the combustion chamber is switched off in the cold start phase. In the case of a V engine, for example, a complete cylinder bank can be switched off, so that only half of the combustion chambers are active during the cold start phase. In the case of a 4-cylinder or 6-cylinder inline engine, it is likewise advantageous for half of the combustion chamber to be shut off, since a relatively smooth engine operation can thus be achieved and the loss of comfort can be kept within acceptable limits.

In a preferred embodiment of the invention, it is provided that the injection quantity of fuel in the combustion chamber which is not switched off is increased compared to the same operating point without cylinder switching off. By increasing the injection quantity, the loss of torque and/or power due to the switched-off combustion chamber can be compensated. In addition, the increased injection quantity results in the fueled combustion chamber heating up more quickly and thus leaving a temperature range in which a particularly large amount of particles are emitted.

Furthermore, it is advantageously provided that the injection pressure of the fuel injected into the combustion chamber which is not switched off is increased relative to the same operating point without cylinder switching off. Alternatively or in addition to the increase in the injection quantity, an increase in the injection pressure for the fueled combustion chamber in the cold start is provided. A finer atomization of the fuel is achieved by the increase in the injection pressure, so that less fuel strikes the cold cylinder walls of the combustion chamber. It is thus possible to further reduce soot formation during the cold start phase.

In an advantageous embodiment of the method, provision is made for the method to be ended after a defined time interval or a defined number of combustion cycles. In order to keep the wear of the internal combustion engine low and to improve the quiet running of the internal combustion engine, it can be provided that the method for reducing cold start emissions ends after a defined time interval or a defined number of combustion cycles.

If the load requirement of the internal combustion engine exceeds a threshold value, the initially switched-off combustion chamber is switched on in order to provide the torque necessary to meet the load requirement and/or the power necessary to meet the load requirement. However, since high loads in the case of cold internal combustion engines are known to lead to increased wear of the internal combustion engine, since in this operating range the engine oil is still cold and the lubrication of the piston by the engine oil is limited, the driver himself will try to avoid high engine loads during cold starts, in particular during cold starts in the case of cold ambient temperatures. Such switching on of the combustion chamber, which was initially switched off, can be replaced in this respect.

According to the invention, a controller for an internal combustion engine is proposed, wherein the controller is designed such that the method according to the invention is carried out when a machine-readable program code is executed by the controller. The inventive method for reducing cold start emissions, in particular particle emissions, can be realized in a simple and cost-effective manner by means of the control unit according to the invention in the case of internal combustion engines with cylinder shut-off. In this case, the solution can be implemented purely in software, so that no additional hardware is necessary. The method can therefore be carried out essentially cost-effectively at an internal combustion engine with a cylinder shut-off provided.

Furthermore, according to the invention, a motor vehicle is proposed with an internal combustion engine having at least two combustion chambers (preferably at least four combustion chambers), a control unit, and an exhaust system in which at least one particle filter or a quaternary catalyst is arranged. The proposed method can be carried out simply and cost-effectively not only on diesel engines but also on gasoline engines by means of a software program on the control unit of the internal combustion engine. However, the effectiveness of this method is limited for diesel engines, since diesel engines emit soot essentially continuously and also during normal operation of the internal combustion engine, in particular in the case of strong acceleration processes. However, the method proposed in principle leads to a reduction in cold-start emissions, in particular in the case of cold-start of the internal combustion engine.

In a preferred embodiment of the motor vehicle, it is provided that the internal combustion engine is a gasoline engine which is ignited externally by means of a spark plug and the at least one particle filter is a gasoline particle filter or a quaternary catalyst. In the case of gasoline engines, as mentioned at the outset, soot particles are emitted mainly during the cold start phase of the internal combustion engine. The proposed method for reducing cold start emissions is therefore particularly advantageous in the case of gasoline engines, since soot production is reduced not only in the fueled combustion chamber but also in the initially switched-off combustion chamber. A fueled combustion chamber benefits from the fact that the injection quantity is higher in the combustion chamber in the case of the same load demand and the combustion chamber therefore heats up more quickly after a cold start. In the case of an unfueled combustion chamber, initially only air is compressed, whereby the combustion chamber heats up, so that the particle emissions likewise decrease when the combustion chamber is switched on later. Furthermore, the method according to the invention can be combined with further measures known from the prior art for reducing cold-start emissions in the case of an externally ignited internal combustion engine, such as, for example, multiple ignition, an increase in injection pressure, multiple injection or a reduction in start-up enrichment. Thereby, a further reduction of cold start emissions, in particular of particulate emissions, is possible.

The different embodiments of the invention mentioned in the present application can advantageously be combined with one another, as long as they are not implemented differently in the individual cases.

Drawings

The invention is explained below in the examples on the basis of the drawing. Wherein:

fig. 1 shows an internal combustion engine with an air supply, a fuel injection system, an ignition system and an exhaust system, at which a method according to the invention for reducing cold start emissions can be carried out; and is

Fig. 2 shows a flowchart for carrying out the method according to the invention for reducing cold-start emissions of an exogenously ignited internal combustion engine.

REFERENCE SIGNS LIST

10 internal combustion engine

12 combustion chamber

14 cylinder wall

16 spark plug

18 fuel injection valve

20 waste gas equipment

22 particulate filter

24-four-element catalyst

26 three-way catalyst

28 NOx storage catalyst (NOx-Speicherkatalysator)

30 exhaust gas turbocharger

32 turbine

34 first oxygen sensor (Lambdasonde, sometimes referred to as lambda probe)

36 second oxygen sensor

38 temperature sensor

40 fuel injection system

42 fuel pump

44 fuel line

46 fuel tank

48 fuel filter

50 controller

52 signal line

54 temperature sensor

56 fuel

58 air inlet pipe

60 air supply system

62 air filter

64 air quality measurer

66 compressor

68 throttle valve

70 ignition distributor

80 motor vehicle

λ_ECombustion air ratio

T temperature

T_minMinimum temperature

T_SThreshold temperature

T_UMGThe ambient temperature.

Detailed Description

Fig. 1 shows an externally ignited internal combustion engine 10 for a motor vehicle 80, having an exhaust system 20 in which a particle filter 22 and a three-way catalyst 26 are arranged. In addition to the three-way catalytic converter 14, further catalytic converters and exhaust gas aftertreatment devices, in particular a NOx storage catalytic converter 28, can be arranged in the exhaust gas system. The particle filter 22 can have a coating effective in a three-way catalytic manner and is designed as a so-called four-way catalyst 24, wherein the particle filter 22 in this case combines the functions of the three-way catalyst 26 and the particle filter 22 in one component. The internal combustion engine 10 is supplied with fresh air by an air supply system 60. In the intake line 58 of the internal combustion engine 10, an air filter 62 and an air mass meter 64 are arranged. The fresh air can be compressed by means of a compressor and/or an exhaust gas turbocharger 30, wherein a turbine 32 is arranged in the exhaust gas system 20, which turbine is driven in an intake line 58 of the internal combustion engine 10The compressor 66. In this way, the fresh air which is fed to the combustion chamber 12 of the internal combustion engine 10 is compressed. In order to control the amount of fresh air supplied to the combustion chamber 12, a throttle 68 is arranged in the intake line 58. The internal combustion engine 10 furthermore has a fuel supply system, for which fuel 56 is supplied from a fuel tank 46 by means of a fuel pump 42 via a fuel line 44 to the fuel injection system 40 and is injected as required into an intake line 58 or into the combustion chamber 12 of the internal combustion engine 10. Preferably, the fuel 56 is injected into the respective combustion chamber 12 of the internal combustion engine 10 through the fuel injection valve 18 arranged at the combustion chamber 12. A fuel filter 48 is arranged in the fuel line 44 between the fuel tank 46 and the fuel pump 42 in order to remove dirt from the fuel 56 and thus protect the fuel pump 42 and the fuel injection system 40 from damage due to the dirty fuel 56. The internal combustion engine 10 furthermore has an ignition distributor, by means of which a spark plug 16 at the combustion chamber 12 can be actuated and in each case emits one or more ignition sparks into the combustion chamber 12. The combustion air mixture can be ignited in the combustion chamber 12. In the exhaust gas system 20 of the internal combustion engine 10,

oxygen sensors

34,36 are arranged downstream of the three-way catalyst 14 and upstream of the three-way catalyst 14 in the flow direction of the exhaust gas of the internal combustion engine 10 through the exhaust gas system 12, with which oxygen sensors the combustion air ratio λ of the internal combustion engine 10 can be adjusted. For this purpose, the

oxygen sensors

34,36, the fuel injection system 40 and the ignition distributor are connected via signal lines 52 to a control unit 50 of the internal combustion engine 10, by means of which the combustion air ratio λ, the fuel quantity and the ignition time are controlled, at which the spark plug 16 emits an ignition pulse accordingly. Furthermore, a temperature sensor 38 can be provided in the exhaust system 20, by means of which a temperature T of the exhaust gas can be detected_EGAnd this exhaust gas temperature can be used to control the internal combustion engine 10.

The particle filter 22 or the quaternary catalyst 24 has the task of removing particles from the exhaust gas. Here, the particles are deposited in the filter and the exhaust gas is cleaned. Due to this deposition mechanism, the particulate filter 22 or the quaternary catalyst 24 is loaded with soot. As a result of this loading, negative effects such as power losses, higher fuel consumption or also ignition failure can occur. To avoid these negative effects, the particulate filter 22 or the quaternary catalyst 24 must be regenerated periodically and/or depending on the loading. The loading of the particle filter takes place somewhat continuously for diesel engines and is particularly problematic in the case of intensive acceleration or full load, whereas gasoline engines essentially release particles during the cold start phase of the internal combustion engine 10. In the case of low ambient temperatures, in particular at ambient temperatures below 0 ℃, very high particle emissions are emitted for gasoline engines due to insufficient homogenization of the mixture and insufficient gasification of the fuel and start-up enrichment. The highest proportion of soot emissions results from the result that the fuel 56 is only insufficiently vaporized in the case of cold cylinder walls 14 of the combustion chamber 12. Due to the high soot emissions during the cold start phase, the particle filter 22 or the quaternary catalyst 24 is rapidly soot-loaded, so that frequent regeneration of the particle filter 22 or the quaternary catalyst 24 is necessary. Regeneration of the particle filter 22 or the quaternary catalyst 24 is possible in particular by over-stoichiometric operation of the internal combustion engine 10 or by introducing secondary air into the exhaust system 20. In the case of an over-stoichiometric operation of the internal combustion engine 10, an increase in the nitrogen oxide emissions also occurs, since the nitrogen oxide emissions can no longer be converted into non-toxic exhaust gas components by the three-way catalyst 26 or the four-way catalyst 24.

Fig. 2 shows a flow chart of a method according to the invention for reducing particulate emissions during a cold start of internal combustion engine 10. In this case, in a first method step<100>In checking whether the ambient temperature T is_UMGAt a threshold temperature T_SBelow, in particular below 0 ℃. In a second method step<110>In which at least one combustion chamber 12 remains switched off, i.e. is dragged together in the unfueled operation, wherein no fuel is injected into the respective switched-off combustion chamber 12. In the exemplary embodiment shown in fig. 1, the internal combustion engine 10 is embodied as a 4-cylinder inline engine, wherein preferably two combustion chambers 12 are operated in a cold start phase in a fueled mode and two further combustion chambers 12 are operated in an unfueled mode. In this case, injected into the combustion chamber 12 of the internal combustion engine 10 during the cold start phaseThe injection quantity of fuel 56 is determined in the method step<120>To present comparable power to that in normal operation with four combustion chambers 12 for combustion chambers 12 using two fuellings. In parallel at method steps<130>The injection pressure of the fuel 56 into the combustion chamber 12 can be increased in order to obtain a better atomization of the fuel 56 and thus the formation of finer droplets, thereby reducing the risk of the unburned, liquid fuel 56 hitting the cold cylinder wall 14 of the combustion chamber 12. By the fueled operation of only two combustion chambers 12, the combustion chambers 12 heat up faster during the cold start phase than with the normal operation of four fuel-fed (befeuert) combustion chambers 12, so that the defined minimum temperature T is reached faster_minFrom this minimum temperature, enhanced soot formation can no longer be expected. In parallel at method steps<140>In the combustion chamber 12 which is not fueled, whereby said combustion chamber 12 is also heated and when the cylinder wall 14 of the combustion chamber which is not initially supplied with fuel has reached a defined minimum temperature T_minCan then be switched on. If the minimum temperature T has been reached_minAt the method step<150>The internal combustion engine 10 is switched to normal operation and the combustion chambers 12 which are not fueled during the cold start phase are activated, so that the internal combustion engine 10 receives its power from all the combustion chambers 12 after the cold start.

Overall, it is to be understood that the method according to the invention makes it possible to reduce soot emissions in a simple and cost-effective manner in the cold start phase of the internal combustion engine 10, without additional components or without further modifications to the internal combustion engine 10 being required.

Claims

1. A method for reducing particulate emissions of an internal combustion engine (10) in the event of a cold start of the internal combustion engine (10), comprising the steps of:

-cold starting the internal combustion engine (10), wherein at least one combustion chamber (12) of the internal combustion engine (10) is switched off in a cold start phase of the internal combustion engine (10),

-when the cylinder wall (14) of the combustion chamber (12) has reached a defined minimum temperature (T)_min) When it is, turn on the at least oneA combustion chamber (12) which is previously shut off,

wherein the internal combustion engine (10) combusts air in a substantially stoichiometric ratio (λ) during the cold start_E=1) run.

2. Method according to claim 1, characterized in that the ambient temperature (T) is determined_UMG) And when the ambient temperature (T)_UMG) At a threshold temperature (T)_S) When so, the method is enabled.

3. Method according to claim 1, characterized in that half of the combustion chamber (12) is switched off in the cold start phase.

4. A method according to claim 1, characterized in that the injection quantity of fuel in the combustion chamber (12) not cut off is increased with respect to the same operating point without cylinder cut-off.

5. A method according to claim 1, characterized in that the injection pressure of the fuel injected into the combustion chamber (12) that is not shut off is increased relative to the same operating point without cylinder shut-off.

6. The method according to claim 1, characterized in that the method is ended after a defined time interval or a defined number of combustion cycles.

7. A controller (50) for an internal combustion engine (10), wherein the controller (50) is set up such that the method according to one of claims 1 to 6 is carried out when machine-readable program code is implemented by the controller (50).

8. A motor vehicle (80) having an internal combustion engine (10) with at least two combustion chambers (12), a control device (50) according to claim 7 and an exhaust system (20) in which at least one particle filter (22) or a quaternary catalyst (24) is arranged.

9. The motor vehicle (80) of claim 8, wherein the internal combustion engine (10) is an externally-ignited gasoline engine and the at least one particulate filter (22) is a gasoline particulate filter or a quaternary catalyst (24).