EP1280993B1 - Ignition system for an internal combustion engine - Google Patents

Description

The invention relates to an ignition system for an internal combustion engine with the features mentioned in the preamble of claim 1.

State of the art

From GB 1557046 an ignition system with two ignition coils and a spark plug is already known.

Ignition systems of the generic type are known. These serve to ignite a compressed fuel-air mixture in the internal combustion engine. For this purpose, an arc discharge between two electrodes of the spark plug is generated by means of an ignition device, usually a spark plug. To generate this arc discharge, an ignition voltage in the high voltage range is to be provided. To provide this required high voltage is known to connect the spark plug to the secondary winding of an ignition coil whose primary winding with a voltage source, in motor vehicles usually the motor vehicle battery, is connectable. The ignition coil works here as energy storage and as a transformer. During the closing time of the primary-side switching means is in the magnetic field of the ignition coil provided from the voltage source electrical Energy stored and provided at the ignition as Hochspannungszündimpuls.

To ignite the compressed fuel-air mixture, a certain minimum ignition energy is necessary. The amount of this minimum ignition energy depends on the stoichiometric composition of the fuel-air mixture. Especially with lean fuel-air mixtures, that is, air is in the stoichiometric excess, an increased minimum ignition energy is necessary. Failure to provide this minimum ignition energy may result in incomplete combustion of the fuel-air mixture or misfires. Known possibilities for influencing the burning process consist in the variation of the spark-burning time and / or the spark-burning current. To increase the spark-burning time and / or the spark-burning current, it is known to increase the energy stored in the ignition coil on the primary side, for example by increasing the primary current at the primary side. However, there is the disadvantage that a correspondingly large design of an ignition coil is to be selected. This precludes optimization of the installation volume.

Advantages of the invention

The ignition system according to the invention with the features mentioned in claim 1 offers the advantage that in a simple manner, a high ignition energy can be provided, in particular for igniting lean fuel-air mixtures in any operating situation the internal combustion engine is sufficiently dimensioned. Characterized in that two ignition coils are provided, the secondary windings are each connected to a spark plug and whose primary windings are acted upon by a respective switching means with the supply voltage, and a drive circuit is provided via which a staggered control of the switching means and thus the ignition coils, is advantageously possible to turn on the second ignition coil at exactly the time by the switch-off voltage leads to the secondary side formation of the high voltage in the voltage circuit of the first ignition coil. As a result, an positive turn-on voltage is formed on the high-voltage side of the second ignition coil, which adds to the negative burning voltage of the ignition spark generated by the first ignition coil and thus increases the burning voltage applied to the ignition electrodes of the spark plug, in particular more than doubled. As a result, a higher spark duration and a higher spark current is obtained, which leads to the overall provision of a higher ignition energy. This high ignition energy is suitable for safely igniting lean fuel-air mixtures at any time. By alternately connecting the respective other ignition coil in the shutdown phase of the previously switched on ignition coil can be repeatedly extend the spark burning to a longer period.

Preferred embodiments of the invention will become apparent from the remaining features mentioned in the subclaims.

drawings

Figur 1

schematisch eine Zündanlage in einem Schaltbild;

Figuren 2 bis 7

verschiedene Kennlinien der Zündanlage und

Figuren 8 bis 9

Schaltbilder von Zündanlagen in weiteren Ausführungsvarianten.

The invention will be explained in more detail in embodiments with reference to the accompanying drawings. Show it:

FIG. 1

schematically an ignition system in a circuit diagram;

FIGS. 2 to 7

different characteristics of the ignition system and

FIGS. 8 to 9

Schematics of ignition systems in further embodiments.

Description of the embodiments.

FIG. 1 shows a total of 10 designated ignition system in an equivalent circuit diagram. The ignition system 10 comprises a spark plug 12, to which a first ignition coil 14 and a second ignition coil 16 are assigned. An electrode 18 of the ignition coil 12 is connected to the secondary winding 20 of the first ignition coil 14. The second electrode 22 of the spark plug 12 is connected to the secondary coil 24 of the second ignition coil 16. Between the electrodes 18 and 22, an ignition gap 26 is formed. Between the electrodes 18 and 22 and the secondary coils 20 and 24 respectively, a resistor R ₁ and R _{2 is} connected. The primary coil 28 of the first ignition coil 14 is on the one hand with a supply voltage _source U _BATT , in motor vehicles in the Rule of the motor vehicle battery, connected. On the other hand, the primary winding 28 is connected to the secondary winding and a switching means 30. The switching means 30 is a three-stage Darlington transistor. Alternatively, the secondary winding 20 may also be connected via a turn-on suppression diode D with the anode to the secondary winding and the cathode to ground. The emitter of the switching means 30 is grounded. The base of the switching means 30 is connected to a drive circuit not shown in detail and acted upon by a control signal 32 schematically indicated here. The primary winding 34 of the second ignition coil 16 is also connected to the supply voltage _source U _BATT on the one hand and on the other hand to a switching means 36, which is also designed as a three-stage Darlington transistor. The emitter of the switching means 36 is grounded, while the base of the switching means 36 is connected to the drive circuit and can be acted upon by a control signal 38.

The function of the ignition system 10 will be explained with reference to the characteristic curves shown in FIGS. 2 to 9:

The structure and function of ignition coils controlled via Zünddarlington transistors and the generation of a spark thereby produced are generally known, so that in the context of the present description only the features according to the invention will be discussed. The control of the switching means 30 and 36 takes place with the control signals 32 and 38, whose course is shown in Figure 2. The Control signals 32 and 38 are provided by the control circuit with a time delay. That is, the turn-off time of the control signal 32, that is, when this falls from the level "HIGH" to the level "LOW", the drive signal 38 is switched on, that is, this rises from its level "LOW" to the level "HIGH" at. It can be provided that each of the switching means 30 and 36 is acted upon by a control pulse or the switching means 30 and 36 are alternately applied in each case with their control pulses 32 and 38, wherein the level "HIGH" is time-offset.

By applying the switching means 30 with the control signal 32, this is turned on during the duty cycle, so that the primary coil 28 of the first ignition coil 14 is energized. At the switch-off of the switching means 30 is formed in the collector of the switching means 30, a cut-off voltage (clamp voltage), which leads to the secondary coil 20 to induce a high voltage. This high voltage is applied across the resistor R ₁ to the electrode 18 and leads to the formation of a spark between the electrodes 18 and 22 of the spark plug 12. Exactly at this time, the switching means 36 is controlled by driving with the control signal 38, so that the primary coil 34th the second ignition coil 16 is energized. As a result, a positive turn-on voltage is induced in the secondary winding 24 of the second ignition coil 16, which adds to the negative burning voltage of the spark generated by the ignition coil 14. This will be the on the electrodes Increased 18 and 22 applied burning voltage. The high voltage supplied from the first ignition coil 14 is in the range of 800 V to 1200 V, while the positive on-voltage of the second ignition coil is in the range of 1200 V to 1700 V. Thus, the voltage applied to the electrodes 18 and 22 burning voltage is more than doubled by connecting the second switching means 36 and thus the second ignition coil 16. This increased ignition voltage increases the spark duration of the spark and the spark current, allowing higher energy to be transferred to the burning spark.

When the second ignition coil 16 is switched off, a burning voltage with the opposite polarity is produced analogously. If the ignition coil 14 is subsequently switched on in the manner of switching off the ignition coil 16 in an analogous manner, the positive starting voltage of the first ignition coil 14 is added to the burning voltage of the new ignition spark.

3 shows the course of the collector current of the switching means 30 (characteristic 40), the collector current of the switching means 36 (characteristic 42), the course of the ignition current (characteristic 44) on the spark plug 12 and the course of the clamping voltage of the switching means 30 (characteristic curve 46). shown.

It is clear from the characteristics that the high-voltage side of the ignition coil 14 and the high-voltage side of the ignition coil 16, which are connected when an ignition current is connected, in the primary winding 34 of the second ignition coil 16, a voltage is induced, which leads to a Stromkommutation on the primary side of the ignition coil 16. This Stromkommutation takes place with igniting the spark abruptly in the previously not energized - ie cold - primary winding 34. The characteristic curve of the characteristic 42 illustrates that at the shutdown time t _{2 of} the first switching means 30 ignites the spark and thus at the primary winding 34 of the ignition coil 16th flowing commutated current rises abruptly with a steep slope, then drops, then rise again. This temporary drop of the commutated at the primary side of the ignition coil 16 current is based on the heating of the primary winding 34. The characteristic 40 illustrates that at the shutdown time t _{2 of} the switching means 30, the charging current of the ignition coil 14 drops. It is clear that according to the characteristic curve 40, the charging current in the primary circuit of the ignition coil 14 slowly rises with a relatively flat loading ramp, while in the primary circuit of the ignition coil 16, the charging current - as explained - increases abruptly.

The ignition current at the spark plug 12 (characteristic 44) abruptly increases with switching off of the switching means 30 to a maximum value and drops over the burning time of the spark until the time t ₃ . At time t ₃ , the primary circuit of the ignition coil 16 is turned off, so that the fuel flow flows in the opposite direction and initially drops to a negative maximum value, and then rise again to zero. The course of the clamping voltage (characteristic curve 46) of the switching means 30 illustrates the Voltage jump at the switch-off time t ₂ , which leads to the ignition of the spark, and a voltage jump at time t ₃ .

In Figure 4, the characteristic curve 46 (clamp voltage U _CE ) of the switching means 30 is shown again. Furthermore, the course of the clamping voltage U _CE (characteristic curve 48) of the switching means 36 is shown. FIG. 5 shows the course of the clamping voltages U _{CE of} the switching means 30 or 36 from the time t ₃ . With reference to Figures 4 and 5 it is clear that according to characteristic curve 46 in Figure 4, the increase of the clamping voltage at time t ₂ during the ignition of the spark, subsequent reaction of the burning spark on the primary winding 28 and a voltage peak at time t ₃ , from the then the clamping voltage decays to the supply voltage. At time t ₃ , a coupling oscillation therefore occurs on the primary coil 28 of the ignition coil 14. The clamping voltage 48 of the switching element 36 drops from the supply voltage level to the saturation voltage level at time t ₂ . At time t ₃ , the clamping voltage of the switching means 36, as the characteristic curve 48 illustrates in Figure 5, increases abruptly and then sounds to the transformed burning voltage of the spark from. In FIG. 5, the voltage jump at time t ₃ at the clamp voltage of the switching means 30 is again shown in the characteristic curve 46. Here then also takes place a decay on the transformed burning voltage of the spark.

In the figures 6 and 7, the course of the turn-on voltage U _CE (characteristic 50), the course of the inrush current I _C (characteristic 52) of the switching means 30 and the course of the secondary voltage (characteristic curve 54) of the ignition coil 14 in a standard ignition system (Figure 6). and in the dual coil ignition system 10 according to the invention (FIG. 7). It is clear that in the double-coil ignition system 10, the turn-on voltage U _{CE has} the same course and the same stroke as in the known ignition system. To avoid so-called Einschaltfunken when switching the switching means 30 high-voltage diodes are used in the known ignition systems. In the double ignition system 10 according to the invention, the use of such high-voltage diodes is not possible by the coupling of the secondary sides of the two ignition coils 14 and 16. For this purpose, separate, not shown in the figures, known per se for reducing voltage circuits can be used.

FIG. 8 shows a modified circuit arrangement of the ignition system 10. The same parts as in Figure 1 are provided with the same reference numerals and not explained again.

The difference from the circuit variant shown in Figure 1 is that here the second switching means 36 is not actuated by a control signal 38 from the drive circuit, but the driving through the switching means 36 is dependent on the burning voltage of the spark of the spark plug 12.

For this purpose, the collector of the switching means 30 is connected via a resistor R ₃ to the cathode of a Zenerdi 60 ode. The anode of the Zener diode 60 is connected on the one hand to the base of a transistor 62 and on the other hand to a first terminal of a capacitor C whose further terminal is grounded. The emitter of the transistor 62 is also grounded, while the collector of the transistor 62 is connected to the base of another transistor 64 and a resistor R ₄ . An emitter of the transistor 64 is connected to the supply voltage U _BATT , while the collector of the transistor 64 is connected via a resistor R ₅ to the base of the switching means 36 (Zünddarlington). A breakdown voltage of the Zener diode 60 is, for example, 20 V.

By means of the circuit arrangement shown in FIG. 8, it is achieved that the transistor 62 is driven by the transformed firing voltage of the spark when it exceeds the breakdown voltage of the zener diode 60, in this case 20 V. The resistor R ₃ serves as a current limiting resistor. If the transistor 62 is turned on, this switches the transistor 64, which then connects the supply voltage U _BATT to the base of the switching means 36, so that this also controls. The capacitance C serves to attenuate the emitter-base path of the transistor 62 due to the fluctuating burning voltage applied to the base of the transistor 62.

FIG. 9 shows a circuit variant modified with respect to FIG. 8, in which the collector of the switching means 30 is connected to the cathode of a Zener diode 60 '. At the same time, the collector of the switching means 30 is connected to an emitter terminal of a transistor 66 whose collector is connected to the base of the transistor 62 via the resistor R ₃ . Further, the collector of the transistor 66 is connected via a resistor R ₆ to ground. The base of the transistor 66 is connected via a resistor R ₆ to the supply voltage U _BATT .

By the circuit _arrangement shown in Figure 9, the transistor 62 is then turned on when the transformed _{burning voltage} rises above the supply voltage U _BATT . The resistors R ₆ serve as high-resistance protective resistors for the transistor 62 when the switching means 30 are clamped. The zener diode 60 'has a breakdown voltage of, for example, 50 V, so that the maximum collector-emitter voltage of the transistor 66 is limited.

In the circuit variants shown in FIGS. 1, 8 and 9, it has been assumed that the spark plug 12 has two electrodes 18 and 22 insulated from each other and insulated from each other.

Claims (7)

1. Ignition system for an internal combustion engine, having an ignition device which requires a high voltage to ignite an ignition spark, characterized in that a secondary winding (20) of a first ignition coil (14) is connected to a first electrode (18) of a spark plug (12, 12'), and a secondary winding (24) of a second ignition coil (16) is connected to a second electrode (22) of the spark plug (12, 12'), in that primary windings (28, 34) of the first and second ignition coils (14, 16) can be connected to a supply voltage by a respective switching means (30, 36), and a drive circuit is provided which drives the ignition coils (14, 16) with a time delay.
2. Ignition system according to Claim 1, characterized in that the switching means (30, 36) are Darlington-pair transistors.
3. Ignition system according to either of the preceding claims, characterized in that control signals (32, 38) for the switching means (30, 36) are provided by an external drive circuit (engine controller).
4. Ignition system according to one of Claims 1 to 3, characterized in that the control signal (32) for the switching means (30) is provided by the external drive circuit, and the control signal (38) for the switching means (36) is provided as a function of an operating parameter of the ignition system (10).
5. Ignition system according to Claim 6, characterized in that the control signal (38) is provided when a predefinable arc voltage of the ignition spark of the spark plug (12, 12') is exceeded.
6. Ignition system according to either of Claims 4 and 5, characterized in that the predefinable arc voltage is determined by the breakdown voltage of a Zener diode (60).
7. Ignition system according to either of Claims 4 and 5, characterized in that the predefinable arc voltage is determined by the magnitude of a supply voltage (U_BATT).

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