EP1299630B1 - Method of ignition - Google Patents

Description

STATE OF THE ART

The present invention relates to an ignition method for an internal combustion engine, wherein an injection is performed alternatively at least in a first operating mode or in a second operating mode and wherein the charging of the ignition coil is performed depending on the current operating mode, and a corresponding ignition device.

Although applicable to any fuels and engines of any vehicle, the present invention and its underlying problem with respect to a direct gasoline injection of an internal combustion engine of a passenger car will be explained.

4 illustrates the dependence of the torque M on the rotational speed N for different operating modes of an internal combustion engine.

In the so-called homogeneous normal operation H1 of the gasoline direct injection, the entire combustion chamber with a stoichiometric air / fuel mixture is homogeneous (lambda value λ = 1), which is ignited at the ignition by the ignition spark. Here exist at high energy density of the mixture no ignition problems.

The homogeneous operation can also be realized lean and / or exhaust gas recirculation (EGR) as a homogeneous operation H2. Here, in general, in order to achieve sufficiently fast burn-through at the low energy densities of the mixture in the combustion chamber, a high flow level is required. This deflects the spark plasma until it breaks off and reignites occur.

As a result, the spark energy distributed in a coil ignition with typical spark duration under these circumstances of typically about 1 ms to numerous secondary sparks, each reaching new mixture ranges.

However, since lean operation or so-called high-EGR operation is only achieved when the entire energy of the ignition coil is introduced into a single flame core, the entire energy stored in the ignition coil must be supplied in such a short time that within this time period ( typically approx. 0.3 - 0.6 ms), the spark has not yet been torn off.

This results in a requirement for the highest possible energy and very short spark duration (about 0.3-0.6 ms) for this operation H2, which results in a high initial current requirement of 150-200 mA.

In internal combustion engines with gasoline direct injection, a so-called charge stratification is realized in the combustion chamber for full utilization of the consumption advantage in certain operating ranges, which is referred to below as shift operation S.

In shift operation S, by contrast, only a small stoichiometric cloud is introduced into the combustion chamber, which is locally ignitable, whereas the remaining contents of the combustion chamber can not be ignited. The advantage of this shift operation S lies in an extended lean operation of the internal combustion engine and thus ultimately in a fuel economy. It is therefore desirable to make the operating range of the stratified operation S as large as possible, that is, in particular to expand to the highest possible loads and high speeds.

In shift operation S, significant local and / or temporal lambda fluctuations may exist at the location of the spark at high average energy density in the mixture cloud. In order to achieve safe ignition, the spark should burn for a long time (typically approx. 5 - 10 ° CA (KW = crank angle)), so that flame nucleation can be started within this time whenever a combustible mixture area is detected by the spark plasma becomes.

In this case, depending on the flow of the mixture on the spark plug, it may only be possible with increasing spark duration Still a steadily decreasing small portion of the introduced from the ignition coil energy of flame nucleation available, which is why it was known to suggest within the above KW interval to generate a pulse train, so the ignition coil several times to charge and discharge.

Thus, this layered mode of operation is a single spark lasting as long as possible at an initial current of typically about 50-80 mA and a secondary energy of typically about 80-100 mJ or a pulse train of adjustable length with an initial current of about 100 mA from a coil with about 30 mJ secondary energy just.

Since the requirements for the operating areas stratified S and homogeneous H1 or H2 thus differ significantly, in a conventional system design with single spark a conflict of objectives exists, which so far can only be approached as a compromise. An ignition coil can be designed either for long spark duration (high secondary inductance, ie high secondary winding number) with moderate starting current or for short spark duration (low secondary inductance, ie low secondary winding number). A decision for a discrete interpretation as a compromise is therefore absolutely necessary.

US-A-5 170 760 discloses an internal combustion engine with direct injection of fuel into the combustion chambers, wherein in a first mode a stratified charge is ignited with two or more ignition pulses in the ignition primary circuit;
a second mode of operation is also provided with homogeneous charge in the combustion chamber, with fewer firing pulses than in stratified operation
This triggers a different number of firing pulses / sparks or a longer burning spark, or higher energy firing pulses are used in the first stratified charge mode

ADVANTAGES OF THE INVENTION

The ignition method according to the invention with the features of claim 1 has the advantage over the known approaches that an adapted to the problem of gasoline direct injection engines function optimal flame both stratified operation in homogeneous lean operation and / or with EGR and cold start or other critical engine conditions allows.

Control of the operation can be done as needed. Only as much energy as is required to ignite is introduced. As a result, unnecessary Kerzenabbrand is avoided.

A smaller coil space due to lower number of turns on the secondary side or larger iron cross-section is possible with the same installation space. Thus, a cost advantage by saving of magnets for biasing the iron circuit can be achieved.

For the respective operating mode, the appropriate type of ignition is provided via a control pulse coding. A pulse train ignition suitable for stratified operation is combined with the step of charging the ignition coil with significantly higher energy in homogeneous operation by increasing the primary current so that it can but nevertheless still discharges within the desired burning time of eg approx. 0, 3 = 0, 6 ms.

In the dependent claims are advantageous developments and improvements of the respective subject of the invention.

According to a preferred development, the first operating mode is a homogeneous normal operation, which is subdivided into the submodes stoichiometric normal operation and substoichiometric normal operation, and the second operating mode is an inhomogeneous stratified operation.

According to a further preferred development, the control pulse courses have different pulse times and / or pulse counts. In this way, virtually any number of operating states can be coded with simple means.

According to a further preferred development, the iron circuit of the ignition coil is driven to an onset of saturation in an operating mode which requires a high spark initial current. This design has the advantage that More energy can be stored and the voltage slew rate increased due to the initially lower secondary inductance.

DRAWINGS

Fig. 1

eine Darstellung des Funkenstromverlaufs i_F über der Zeit t gemäß einer ersten Ausführungsform der vorliegenden Erfindung;

Fig. 2

eine Darstellung des Funkenstromverlaufs i_F über der. Zeit t gemäß einer zweiten Ausführungsform der vorliegenden Erfindung;

Fig. 3

eine schematische Darstellung einer Ansteuereinrichtung zur Realisierung der ersten bzw. zweiten Ausführungsform; und

Fig. 4

für verschiedene Betriebsarten einer Brennkraftmaschine die Abhängigkeit des Drehmoments M von der Drehzahl N.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

Fig. 1

a representation of the spark current waveform i _F over time t according to a first embodiment of the present invention;

Fig. 2

a representation of the spark current waveform i _F on the. Time t according to a second embodiment of the present invention;

Fig. 3

a schematic representation of a drive device for implementing the first or second embodiment; and

Fig. 4

for different operating modes of an internal combustion engine, the dependence of the torque M on the rotational speed N.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a plot of the spark current waveform i _F versus time t according to a first embodiment of the present invention.

In FIG. 1, the curve a) represents the spark current profile as a discharge of the ignition coil (secondary energy approx. 30 mJ, primary deactivation current approx. 10 A) without the pulse train characteristic. The secondary spark spark current amounts to approx. 110 mA with a burning time of approx , 35 ms at a spark ignition voltage of 1500 V.

The curve b) shows this ignition coil in the realization of a pulse train with four pulses, in which the primary-side reconnection of the ignition coil takes place in each case when the spark current has dropped to about 50 mA. To realize the short recharging time, a battery voltage of 42 V is assumed.

It should be noted in general that the short recharging time can be achieved by increasing the primary current from 10 A to 30 A at a previously common battery voltage of 14 V.

The curve c) shows the spark current characteristic for the homogeneous operation H1 or H2, namely, when the coil was charged by increasing the primary side shutdown current (from about 10 A to 15 A) to about twice the energy of 60 mJ.

This results in a now increased to about 160 mA initial current spark duration of about 0, 5 ms.

This first embodiment assumes that the coil is in the linear range of magnetizability.

FIG. 2 is a plot of the spark current waveform i _F versus time t according to a second embodiment of the present invention. FIG.

In this second exemplary embodiment according to FIG. 2, it is assumed that a linear increase in the magnetizability can no longer be achieved due to limited installation space (bar coil), but the nonlinearity of the magnetization is deliberately included.

The curve a) represents the spark current characteristic as a discharge of the ignition coil (bar coil, secondary energy approx. 30 mJ, primary switch-off current approx. 10 A) without the pulsing characteristic. The secondary-side spark starting current, as in the above first example, is approx. 110 mA with a burning time of approx 0.35 ms.

The curve b) shows this ignition coil when implementing a pulse train with four pulses as in the above first example, in which the primary side reconnection of the ignition coil takes place in each case when the spark current has dropped to about 50 mA. To realize the short recharge time Here, too, a battery voltage of 42 V is assumed.

Curve c) shows the spark current profile for homogeneous operation, namely when the coil is charged to approximately twice the energy of 60 mJ by increasing the primary-side switch-off current (from approx. 10 A to 20 A). This results in an increased spark starting current of 200 mA, which is non-linear, i. initially steeper, falls off, since initially there is a lower inductance due to the saturation property. Again, a sufficiently short spark duration of about 0.5 ms.

This design has two advantages. With limited space (rod coil) can save more energy when the iron circuit is controlled to the beginning of saturation. The voltage slew rate increases because of the initially lower secondary inductance. The increased rate of voltage rise has a positive effect on candle shunts, i. at sooty candles (cold start) off.

FIG. 3 shows a schematic representation of a drive device for realizing the first or second embodiment.

Specifically, MS designates an engine control unit, L a control logic and ES an output stage, which as essential components a power transistor LT, a spark plug ZK and an ignition coil ZS includes. It is assumed that the pulse train generating electronics, so the control logic L and the output stage ES, is located on / in the ignition coil ZS.

From the engine control unit MS, a control pulse SI is supplied depending on the current injection mode, which has a coding from which the control logic L can detect locally, whether a pulse train at low energy or ein.Pulszug at high energy, a single pulse at low energy or a single pulse is desired at high energy.

• a) ein einziger kurzer Steuerimpuls SI (ca. 10 - 100 µs): Einzelfunke 30 mJ bei homogenem Betrieb mit λ = 1;
• b) zwei kurze Steuerimpulse SI (je ca. 10 - 100 µs).: Einzelfunke 60 mJ bei homogenem Magerbetrieb ggfs. mit AGR;
• c) ein langer Steuerimpuls SI (ca. 1 - 5 ms): Pulszug Basis 30 mJ bei Schichtbetrieb;
• d) ein langer Steuerimpuls SI (ca. 1 - 5 ms) nach einem kurzem Steuerimpuls SI (ca. 10 - 100 µs): Pulszug Basis 60 mJ bei Kalt- und/oder Rangierstarts oder bei sonstigen besonders kritischen Motorbedingungen.

FIG. 3 shows by way of example suitable codings:

• a) a single short control pulse SI (about 10 - 100 μs): single field 30 mJ in homogeneous operation with λ = 1;
• b) two short control pulses SI (each approx. 10 - 100 μs) .: single field 60 mJ in homogeneous lean operation, if necessary with EGR;
• c) a long control pulse SI (about 1 - 5 ms): pulse train basis 30 mJ during shift operation;
• d) a long control pulse SI (about 1 - 5 ms) after a short control pulse SI (about 10 - 100 μs): pulse train basis 60 mJ during cold and / or shunting starts or other particularly critical engine conditions.

Although the present invention has been described above with reference to preferred embodiments, it is not limited thereto.

In particular, the invention is not limited to the illustrated pulse shapes, energies and burning times or the like. limited. Also, further injection modes may be provided.

Claims (4)

1. Method of ignition for an internal combustion engine, injection alternatively being carried out at least in a homogeneous normal operating mode (H1, H2) or in a non-homogeneous stratified operating mode (S), an ignition coil being charged with ignition energy by a primary current, a control pulse profile (SI) which is characteristic of the current operating mode being provided, the charging of the ignition coil (ZS) being carried out by control logic (L) in the non-homogeneous stratified operating mode (S) in the form of a pulse train ignition with a predetermined primary current and in the homogeneous normal operating mode (H1, H2) by increasing the primary current in comparison with the non-homogeneous stratified operating mode in the form of individual pulse ignition.
2. Method according to Claim 1, characterized in that the homogeneous normal operating mode is divided into the submodes of stoichiometric normal operating mode (H1) and sub-stoichiometric normal operating mode (H2).
3. Method according to Claim 1 or 2, characterized in that the control pulse profiles (SI) have different pulse times and/or numbers of pulses.
4. Method according to one of the preceding claims, characterized in that the spark plug has an iron circuit with a linear range of magnetizability, and in that in an operating mode in which ignition sparks with a high initial spark current are required, the ignition coil is actuated in such a way that the iron circuit is actuated as far as the point where saturation of the magnetization begins.

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