DE102020003875A1 - Method for operating a gasoline engine within a hybrid electric motor vehicle to reduce consumption and emissions - Google Patents

Abstract

The invention relates to a method for operating a gasoline engine of a hybrid-electric motor vehicle in catalytic converter heating mode for the targeted heating of at least one exhaust gas aftertreatment device arranged in an exhaust gas duct of the internal combustion engine through which exhaust gas from the internal combustion engine can flow, with the ignition angle of the internal combustion engine being adjusted compared to that set during normal driving operation in order to carry out the catalytic converter heating mode Basic ignition angles are not retarded, the speed of the internal combustion engine is increased in a targeted manner and a maximum valve overlap is set (step S2).

Description

The invention relates to a method for operating an internal combustion engine, in particular the gasoline engine within a hybrid electric vehicle with an electrical system, according to the preamble of claim 1. The electrical system comprises, for example, at least or precisely one electrical machine, by means of which, for example, the motor vehicle is electrically driven or the load point of the internal combustion engine can be manipulated.

Such methods for operating internal combustion engines during catalytic converter heating operation, in particular of motor vehicles, are already sufficiently known from the general prior art. In the method, the internal combustion engine is operated in a catalytic converter heating mode for the targeted heating of at least one exhaust gas aftertreatment device, which is arranged in an exhaust tract of the internal combustion engine through which exhaust gas from the internal combustion engine can flow and consequently the exhaust gas can flow through it. The exhaust gas can be aftertreated by means of the exhaust gas aftertreatment device. For example, the exhaust gas aftertreatment device comprises at least one catalytic converter, which is heated in a targeted manner by means of the catalytic converter heating mode.

The object of the present invention is to further develop a method of the type mentioned at the beginning and to optimize it with regard to operation within a hybrid electric motor vehicle in such a way that the exhaust gas aftertreatment device is heated particularly efficiently and thus with low fuel consumption and emissions and optimum operation with regard to consumption and emissions can be implemented.

This object is achieved by a method with the features of claim 1. Advantageous configurations with expedient developments of the invention are specified in the remaining claims.

In order to further develop a method of the type specified in the preamble of claim 1 in such a way that the exhaust gas aftertreatment device can be heated particularly efficiently and thus with particularly low fuel consumption and emissions, it is provided according to the invention that the ignition angle of the internal combustion engine is not retarded to carry out the catalyst heating operation, the speed of the internal combustion engine is increased in a targeted manner and a maximum valve overlap is set and the internal combustion engine load is adjusted accordingly via an electric machine. In addition, provision is made for fuel injection to take place as early as possible only in the intake stroke.

The invention is based in particular on the following findings: Usually, by means of a respective operating strategy for operating motor vehicles designed as hybrid vehicles, for example, which each have an internal combustion engine, which is also known as an internal combustion engine and, for example, an Otto engine, an attempt is made to largely convert the internal combustion engine, which is also simply referred to as an engine Area of high efficiency, based on fuel consumption, i.e. to operate outside of their partial load range. The cold start or the catalytic converter heating mode, also known as catalytic converter heating, is therefore a particularly critical point in time from an efficiency point of view must result in comparable emissions, but also very high fuel consumption, also referred to simply as consumption, since the engine is operated in the inefficient partial load range. As a result of the low power of the engine, various methods have been established which enable the exhaust gas aftertreatment device comprising at least exactly one catalytic converter to be heated up quickly. For this purpose, it is usual to adjust the ignition angle, i.e. the point in time at which the ignition of the fuel-air mixture takes place, in the direction of retardation compared to the ignition angle of the most efficient operation, which, however, reduces the efficiency of the internal combustion engine but results in an increase in the exhaust gas temperature. Such an increase in the exhaust gas enthalpy flow can shorten the heating-up time, that is to say the period of time until the temperature of the catalytic converter exceeds a threshold value known as the light-off temperature.

Due to the low-load operation of the internal combustion engine when the vehicle is at a standstill or when starting up or leaving a parking space, the catalyst heating takes a long time even with increased exhaust gas enthalpy due to the late ignition point The operating point of the internal combustion engine is fixed, the required transmission input torque must be set by adapting the electrical machine. This also sets the load point of the electrical machine and can deviate significantly from the optimal operating point that is actually aimed at by the operating strategy. The consequences may be poor electrical system efficiency. During low-load operation at low engine speed and later ignition, a minimum valve overlap is usually set in camshaft adjustment systems (low-level phasers) in order to extract as little enthalpy as possible from the exhaust gas and homogeneous split injection (HSP injection) with a compared to the main injection in the intake stroke additional, short injection directly before ignition in order to obtain stable combustion and thus smooth running under these conditions.

Hybrid electric motor vehicles, the drive train of which has at least one electrical machine in addition to the internal combustion engine, have the option of setting the operating point of the internal combustion engine, depending on the drive configuration, at least partially independently of the driving performance. These are, for example, the US 2019/047547 A1 and the DE 10 2018 119 428 A1 known. In particular, a load point of the internal combustion engine that is as constant as possible should be set, and the remaining required torque should be provided by means of the electrical machine, so that a low-load internal combustion engine operation is provided. Furthermore is DE 10 2015 114 525 A1 known. Here, the load point of the internal combustion engine is selected as a function of the speed so that a constant air mass flow and a constant ignition point can be set.

In order to counteract the problems mentioned above, it is basically known and possible to implement a targeted increase in the load point of the internal combustion engine in order to provide an increased exhaust gas enthalpy flow. Excess power from the internal combustion engine can be used to charge a battery in the motor vehicle. This leads to a higher efficiency of the system, since the exhaust gas enthalpy flow is generated by increasing the internal combustion engine power and a retarded adjustment of the ignition angle is not necessarily necessary. However, nitrogen oxide (NO _x ) and particulate emissions, which increase sharply during this operation, are particularly problematic. This is for example from the US 2017/355373 A1 , the US 2019/118793 A1 and the EP 3 476 680 A1 known. The above-mentioned, basically possible and known procedure therefore results in either poor consumption with cold start emissions comparable to conventional vehicles due to the artificially set low-load operation or better consumption with poorer nitrogen oxide and particle emissions due to a load increase.

The above-mentioned disadvantages and problems can be avoided by the invention. The aim of the invention is, in particular, to carry out the catalytic converter heating with increased internal combustion engine power in order to be able to dispense with an ignition angle retardation. For this purpose, a targeted increase in the engine speed, also referred to as the engine speed, of the internal combustion engine, for example by adapting a shift strategy, with the same moderate load on the internal combustion engine, since this does not have a negative effect on nitrogen oxide and particle emissions compared to a load increase. The shift strategy is to be understood in particular as a strategy on the basis of which gear ratio or gear changes are carried out in a transmission of the motor vehicle. The speed of the internal combustion engine can thus be increased in a targeted manner by adapting the shift strategy accordingly. As a result, due to the higher mechanical power, a significantly earlier ignition angle can be selected with the internal combustion engine torque still the same, which already results in a higher degree of efficiency. In addition, an early ignition angle has a positive effect on particle emissions during a cold start, since the combustion chambers of the internal combustion engine then heat up more quickly.

• - Die Temperatur nach Einlassschluss wird durch die hohe Abgasrückführung angehoben. Hierdurch wird eine bessere Gemischaufbereitung bei noch kaltem Motor erreicht. Hierdurch sinken insbesondere die Emissionen an unverbrannten Kohlenwasserstoffen (HC) und Partikeln.
• - Das Restgas fungiert als Inertgas und senkt somit die Spitzentemperatur im Brennraum. Hierdurch wird die Bildung von thermischen Stickoxiden (NO_x) drastisch herabgesetzt

In order to further increase efficiency, depending on the power requirement, a further increase in the internal combustion engine load can be expedient in order to avoid inefficient operation of the internal combustion engine under partial load. In order to be able to keep emissions low, a high residual gas rate or exhaust gas recirculation is expedient:

• - The temperature after the inlet closes is increased by the high level of exhaust gas recirculation. This results in better mixture preparation when the engine is still cold. This in particular reduces the emissions of unburned hydrocarbons (HC) and particles.
• - The residual gas acts as an inert gas and thus lowers the peak temperature in the combustion chamber. This drastically reduces the formation of thermal nitrogen oxides (NO _x)

If the engine does not have an external exhaust gas recirculation, it is therefore advisable to set the valve control times to maximum overlap immediately after starting in order to enable a high residual gas rate. The problem of increased uneven running in the low speed range is countered by increasing the speed, for example based on the changed shift strategy.

With these two adaptations, an HSP injection can also be dispensed with. Combustion stabilization is no longer necessary here, since the catalyst heating,, is now carried out outside the speed range that is close to idling. Injection into the intake stroke alone enables better mixture preparation and lowering of the emissions of particles and unburned hydrocarbons. This also prevents the risk of fuel being applied to the cold piston.

Conventional catalytic converter heating is usually carried out with a lean combustion air ratio or air-fuel ratio. In the process according to the invention, however, stoichiometric catalyst heating is carried out. This results in a further reduction in the raw nitrogen oxide emissions and a better conversion of the emissions with the aid of the catalytic converter through stoichiometric operation. The measures according to the invention result in very low raw emissions. The load can be increased to high loads just a few seconds after starting. Investigations have shown that this can take place shortly before the light-off temperature of the catalytic converter, known as the light-off temperature, is reached, so that the operating strategy is influenced much more quickly by the catalytic converter heating operation and fuel-optimized operation can be set earlier to increase overall efficiency. The method according to the invention is thus a load point setting of the internal combustion engine while the catalytic converter is being heated, the internal combustion engine preferably being a gasoline engine and a component of a motor vehicle designed as a hybrid vehicle.

• - Drehzahlanhebung, beispielsweise durch Anpassung der Schaltstrategie:
  • Erhöhung der mechanischen Leistung und damit des Abgasenthalpiestroms insbesondere über eine Erhöhung der Drehzahl und somit ohne eine Erhöhung der Stickoxid- und Partikelemissionen; hierdurch ist bereits kein später Zündwinkel mehr nötig, und es ergibt sich ein höherer Wirkungsgrad.
• - In Abhängigkeit der Fahranforderungsleistung eine über die Drehzahlanhebung hinausgehende Anhebung der verbrennungsmotorischen Last zur Vermeidung des Teillastbetriebs und zu einer zusätzlichen Effizienzsteigerung.
• - maximale Ventilüberschneidung (hohe Restgasrate zur besseren Gemischaufbereitung bei kaltem Motor durch höhere Brennraumtemperatur nach Einlassschluss (Absenkung HC- und Partikel-Emissionen) und niedrigere Spitzentemperatur durch die Erhöhung des Inertgasanteils im Brennraum (Absenkung Bildung von thermischen Stickoxiden))
• - Weitere Emissionsreduktion durch:
  • ◯ früher Zündwinkel: Absenkung von Emissionen an unverbrannten Kohlenwasserstoffen (HC) und von Partikelemissionen durch schnellere Brennraumaufheizung, bessere Gemischbildung
  • o Stöchiometrisches Luft-Kraftstoff-Gemisch beziehungsweise Verbrennungsluftverhältnis: niedrigere Stickoxid-Rohemissionen und bessere Konvertierung des Katalysators
  • ◯ keine HSP- sondern Saughubeinspritzung (Reduktion von Emissionen an unverbrannten Kohlenwasserstoffen und Partikeln durch längere Gemischbildungsdauer und geringere Benetzung des Kolbens)
• - Lastanhebung in Abhängigkeit der jeweiligen Lastanforderung bei beziehungsweise kurz vor der Light-Off-Temperatur am Eingang des Katalysators zur weiteren Absenkung von CO₂-Emissionen und Erhöhung des Wirkungsgrads

The invention can in particular be summarized as follows:

• - Speed increase, for example by adapting the shift strategy:
  • Increasing the mechanical power and thus the exhaust gas enthalpy flow, in particular by increasing the speed and thus without increasing the nitrogen oxide and particle emissions; as a result, a later ignition angle is no longer necessary, and a higher degree of efficiency results.
• - Depending on the driving demand, an increase in the internal combustion engine load beyond the speed increase to avoid partial load operation and to increase efficiency.
• - Maximum valve overlap (high residual gas rate for better mixture preparation when the engine is cold due to higher combustion chamber temperature after the inlet closure (lowering of HC and particle emissions) and lower peak temperature due to the increase in the proportion of inert gas in the combustion chamber (lowering of the formation of thermal nitrogen oxides))
• - Further emission reduction through:
  • ◯ earlier ignition angle: lowering of emissions of unburned hydrocarbons (HC) and particle emissions through faster combustion chamber heating, better mixture formation
  • o Stoichiometric air-fuel mixture or combustion air ratio: lower raw nitrogen oxide emissions and better conversion of the catalytic converter
  • ◯ No HSP injection but suction stroke injection (reduction of emissions of unburned hydrocarbons and particles due to longer mixture formation time and less wetting of the piston)
• - Load increase depending on the respective load requirement at or shortly before the light-off temperature at the inlet of the catalytic converter to further reduce CO ₂ emissions and increase efficiency

The invention enables the following advantages in particular to be achieved: The exhaust gas enthalpy required to heat up the catalytic converter is represented by the increased mechanical power, instead of the retarded ignition angle to increase the exhaust gas enthalpy (the exhaust gas enthalpy is, in a first approximation, proportional to the mechanical power at comparable ignition times) . This avoids retarding the ignition angle, and heating the catalytic converter becomes significantly more efficient with regard to fuel consumption and CO _{2 emissions.} The fact that the power is initially increased via the speed results in significantly lower nitrogen oxide emissions than with a simultaneous or sole increase in load. Due to the increased speed, the engine can be operated with control times that lead to maximum exhaust gas recirculation, which means that nitrogen oxide emissions (NO _x emissions) can be greatly reduced, since the peak combustion chamber temperature drops due to the high proportion of inert gas. The stoichiometric operation also leads to low NO _x emissions and a better conversion of the catalytic converter, which is designed, for example, as a three-way catalytic converter.

The inactive HSP injection or only early injection in the intake stroke increases the time available for mixture preparation. Due to the high exhaust gas recirculation rate and the resulting higher combustion chamber temperatures (the temperature during compression is increased, but the peak temperature is greatly reduced due to the high proportion of inert gas), better mixture preparation is also achieved when the engine is cold. This also reduces the emissions of unburned hydrocarbons (HC emissions) and particulate emissions. The fact that the catalyst heating is carried out with a comparatively high mechanical power, initially only via the increased speed and then via an additional positive torque gradient, results in a significantly reduced duration of the catalyst heating operation. The operating strategy is only influenced to a small extent and can select a fuel-efficient operating point much earlier. The catalyst heating can also be carried out without a torque ramp after the first 7 to 8 seconds. This results in an even lower level of emissions with a slight disadvantage in terms of consumption and time. Results compared to the reference setting (overstoichiometric at lambda = 1.07, HSP injection active, minimal overlap, ignition angle efficiency of around 55 to 65 percent, load constant at around 30 percent naturally aspirated engine full load) are listed in the following table. The method provides, for example, a mechanical combustion engine output of around 20 kilowatts, so it can also be carried out with 48-volt HEV (HEV - hybrid electric vehicle) while driving. KH duration HC at KH NOX at KH Particles at KH Consumption WLTC reference 100% 100% 100% 100% 100% New, moment const. 63% 52% 53% 17% 96.3% New, moment ramp after 7-8s 43% 54% 43% 33% 96.7%

Further advantages, features and details of the invention emerge from the following description of a preferred exemplary embodiment and with reference to the drawing. The features and combinations of features mentioned above in the description can be used not only in the respectively specified combination, but also in other combinations or on their own, without departing from the scope of the invention.

The single figure of the drawing shows a flow diagram to illustrate a method according to the invention for operating an internal combustion engine of a motor vehicle in a catalytic converter heating mode.

A method for operating an internal combustion engine of a motor vehicle in a catalytic converter heating mode is described below with reference to the single figure. The motor vehicle is preferably designed as a motor vehicle, in particular as a passenger vehicle. The motor vehicle is necessarily a hybrid vehicle which has the internal combustion engine and at least or precisely one electrical machine. The internal combustion engine is also referred to as an engine or internal combustion engine, whereby the motor vehicle can be driven by the internal combustion engine or the battery can be charged. The motor vehicle can, for example, be electrically drivable by means of the electrical machine. The catalyst heating mode is also referred to as a catalyst heating mode, catalyst heating or catalyst heating and is carried out for the targeted heating of at least one exhaust gas aftertreatment device. The exhaust gas aftertreatment device is arranged in an exhaust gas tract of the internal combustion engine, the exhaust gas tract of which can be flowed through by exhaust gas from the internal combustion engine. The exhaust gas aftertreatment device comprises, for example, at least one catalytic converter, which is designed, for example, as a three-way catalytic converter. The internal combustion engine has combustion chambers in which combustion processes take place during a fired operation of the internal combustion engine. The aforementioned exhaust gas results from the combustion processes. For example, combustion processes take place in the combustion chambers while the catalyst is being heated.

With a first step S1 the internal combustion engine is started during the process. A short time after starting the internal combustion engine or immediately after starting the internal combustion engine, in a second step S2 of the method of the catalyst heating operation carried out. To carry out the catalyst heating operation, i.e. to start the catalyst heating operation and then carry it out without interruption for a certain period of time, the ignition angle of the internal combustion engine is not adjusted late, the speed of the internal combustion engine is increased in a targeted manner and a maximum valve overlap of the internal combustion engine is set. The fuel injection is carried out solely during the intake stroke and as early as possible in order to avoid wetting the piston with fuel. As a result, the catalytic converter can be heated up efficiently and effectively and thus with low fuel consumption and emissions. In addition, as a result, the period during which the catalyst heating operation is performed can be shortened significantly.

List of reference symbols

S1

First step

S2

Second step

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• US 2019047547 A1 [0008]
• DE 102018119428 A1 [0008]
• DE 102015114525 A1 [0008]
• US 2017355373 A1 [0009]
• US 2019118793 A1 [0009]
• EP 3476680 A1 [0009]

Claims (5)

A method for operating a gasoline engine of a hybrid electric motor vehicle in a catalytic converter heating mode for the targeted heating of at least one exhaust gas aftertreatment device arranged in an exhaust gas tract of the internal combustion engine through which exhaust gas from the internal combustion engine can flow, characterized in that, in order to carry out the catalytic converter heating operation, the ignition angle of the internal combustion engine is adjusted with respect to the basic ignition angles set during normal driving after late does not occur, the speed of the internal combustion engine is increased in a targeted manner and a maximum valve overlap is set (step S2). Procedure according to Claim 1 , characterized in that, in order to carry out the catalyst heating operation, a retarded adjustment of the ignition angle compared to the ignition angle is avoided when operating outside the catalyst heating operation and the catalyst heating operation is thus carried out with the ignition angles of normal driving operation or with ignition angles that are comparable therewith. Procedure according to Claim 1 or 2 , characterized in that the internal combustion engine is operated stoichiometrically during the catalyst heating operation. Internal combustion engine according to one of the preceding claims, characterized in that, during the catalytic converter heating operation, fuel is injected into combustion chambers of the internal combustion engine exclusively during a respective suction stroke of the respective combustion chamber. Internal combustion engine according to one of the preceding claims, characterized in that a load increase takes place depending on a respective load requirement at and / or shortly before the light-off temperature at an input of the exhaust gas aftertreatment _{device to further reduce CO 2} emissions and increase efficiency.

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