EP1238195B1 - Controllable ignition circuit - Google Patents

Description

The invention relates to an ignition circuit according to the Preamble of claim 1.

In known such ignition circuits is a electronic switch connected in parallel with the capacitor and is triggered by a single pulse of the pulse generator driven. When switching on the electronic switch it comes to a short circuit capacitor and thereby a rapid breakdown of the voltage across the capacitor, causing a rapid increase in the flow of current over the Primary winding of trained as Spartrafo ignition coil comes. This causes a single ignition voltage pulse at the Secondary side of the ignition coil, which ignites a spark between the two electrodes of a spark plug should.

The breakdown voltage of the line between the both electrodes of a spark plug increases with the pressure that the exposed between the electrodes located gas mixture is. This results in high-density spark-ignited Internal combustion engines, such as e.g. in gas engines, considerable Problems. With such engines, it always comes back to Misfiring, if not extremely high ignition voltages to the Spark plugs are placed. At such high ignition voltages is but also a correspondingly high energy in the ignition coil stored after each spark ignited the spark gap Spark plug for the most part flows over the spark.

However, this results in correspondingly high Ignition currents, which lead to rapid wear of the electrodes of the Lead the spark plug.

However, the ignition voltage is sufficient due to the pressure and / or the wear of the spark plug not for training of a spark, so flows after interrupting the electronic switch the stored energy in the Capacitor. The next time the switch is turned on This process is repeated, but it is practically too no increase in the ignition voltage. Is the ignition voltage just at the for a spark of a spark at each given state of the electrodes of the spark plug and the provided pressures in the combustion chamber of the internal combustion engine, so it comes because of the fluctuations of the pressure and the Supply voltage to an irregular ignition and thus too a restless running of the internal combustion engine and thus a significant loss of performance of the same.

For example, EP 0 070 572 discloses an ignition system at the primary winding of the transformer is part of an LC resonant circuit is, in turn, in series with a Chopper or switch acting transistor and a Resistor is switched. The transistor is doing with Pulse trains with modulated in their duration individual pulses controlled so that the spark plugs with Zündimpulsfolgen with fed in their energy modulated single ignition pulses become. However, if it does not lead to an education of a Zündfunkens should come with this structure on the Secondary side of the transformer stored energy for a subsequent ignition to a considerable extent lost. Furthermore, the intended chopper is not suitable for the formation of ignition sequences, as for training a plasma as described below are necessary. In EP 0 942 519 A1 measures are taken on the secondary side a transformer of a DC voltage source proposed by the two provided Rectifier transistors avoided the use of diodes which increases the efficiency of the voltage source. In particular, the secondary side of the transformer is in Form executed two separate secondary windings. The Primary winding of the transformer is thereby in the shunt branch of a half-bridge circuit, in addition also two switching elements are provided. This design is However, not suitable, rapid ignition sequences in which the individual ignition pulses within microseconds successive, with variable duty cycle to generate. In particular, there is no corresponding coordination of capacities with the inductance of the ignition coil in conjunction with the Frequency of the pulses delivered by the pulse generator Control of transistors provided. Finally suitable This circuit is not to high voltage pulses because the FETs used on the secondary side are not are high voltage compatible.

WO 98/19066 describes an ignition system in which the primary coil of a transformer is part of a resonant circuit in which a capacitor and a discharge switch are arranged. The resonant circuit is excited externally controlled. The first ignition is done by discharging a capacitor after closing a discharge switch. By excitation of the resonant circuit during the "return oscillation" enough energy is introduced to maintain the spark for any length of time. The ignition frequency is thus tied to the natural frequency of the resonant circuit and thus can hardly be varied, in particular, a circuit in this embodiment is not suitable to produce very rapidly successive ignition pulses.
In DE 40 09 145 A1, the primary winding of an ignition coil is used, on the one hand, to transform the ignition energy stored in a storage capacitor to the high value required for ignition, and, on the other hand, to transform the DC voltage supplied by a battery to the ignition energy to be stored in the capacitor , This is also realized by using switching transistors, which are controlled by phase-shifted pulse trains, but with a constant duty cycle. The aim of this invention is to replace the voltage converter, which has the task of converting the originating from the electrical system battery DC voltage in the much higher DC charging voltage, so as to equip the ignition more compact and with a smaller number of components. The proposed circuit is, however, not suitable for using the energy stored on the secondary side of the transformer for a subsequent ignition, if the formation of a spark should be omitted.

The aim of the invention is to overcome these disadvantages avoid and an ignition circuit of the type mentioned to propose, even at high compression Internal combustion engines ensure safe ignition and at it only leads to a low current load on the electrodes of the Spark plugs is coming. In particular, the circuit should be suitable to deliver ignition impulses in the fuel mixture, too if initially no ignition occurs, induce ionization and thus initiate plasma formation before it becomes the actual Ignition comes. The duty cycle of the firing order is intended variable and the energy stored in the transformer Failed ignitions in suitable storage capacitors traceable.

According to the invention this is in an ignition circuit of mentioned in the introduction by the characterizing features of Claim 1 reached.

The proposed measures ensure that several ignition pulses can be generated during the intended firing period. This increases the likelihood of a successful ignition.
The primary winding of the ignition coil is connected in the shunt branch of a series circuit of two similar electronic switches and a series circuit of two capacitors bridge circuit, wherein the electronic switches each have a diode is connected in anti-parallel and a pulse during the intended firing time, the electronic switch with several order each 180 ° out of phase pulses impinged. This also results in the very significant advantage that when ignoring a spark between the electrodes, a spark plug, the energy in the circuit is stored to a considerable extent and is also available for the next ignition pulse. This also ensures that it comes during the scheduled ignition duration even under difficult ignition conditions to form a spark.

With a corresponding coordination of capacities with the inductance of the ignition coil in conjunction with the Frequency of the pulse delivered by the pulse generator can be the Capacitors on the supply voltage of the circuit be charged when it at the first ignition pulse to none Sparking between the electrodes of the ignition circuit supplied spark plug comes. This slow key of the Field strength in the individual pulses leads to a Preparation of the spark, since already at the first impulses forming "streamer" into one cause increased formation of ions in the short breaks between the voltage pulses can not be reduced.

This results from the inventive Ignition circuit unlike the conventional Ignition circuits in which during the intended ignition duration only a single ignition pulse is generated, a significant higher ignition safety even with very difficult Ignition conditions, as they are in spark-ignited high-compression engines are given.

Another advantage of the invention Ignition circuit is in the fact that the ignition, at already ignited spark between the electrodes of the spark plug by changing the frequency and the width of the Switch driving pulses can be controlled. Thereby is a very extensive protection of the electrodes of the spark plug possible, since just during the burning time of the spark a very significant reduction of the ignition current is possible and As a result, the wear of the electrodes significantly reduced can be.

By the generated during the ignition duration variety Intermediate spark also results in a higher Burning rate of the gas mixture in a cylinder one Internal combustion engine, which increases their efficiency. The number of intermediate sparks increases with increasing Frequency of the pulses driving the switches.

Due to the large number of sparks that during the firing time with a frequency between 100 kHz and 500 kHz be generated or come to training, remains one Plasma cloud in the area of the electrodes of the spark plug, causing a re-ignition of a spark is much easier. This also allows a great, against the interior of the Combustion chamber directed opening angle of e.g. 60 to 90 ° between the electrodes of the spark plug. At a large opening angle of the electrodes will be between these burning spark against the interior of the combustion chamber due to the by the current flow caused electromagnetic forces driven and thereby igniting the combustible mixture relieved in the combustion chamber. In addition, larger ones can Electrode distances as in conventional ignition circuits be provided because just a much higher Zündsicherheit given due to the large number of ignition pulses is that generated during the intended ignition duration.

Due to the proposed circuit results also the advantage that part of the ignition coil stored energy after igniting a spark between the electrodes of a spark plug in the capacitors flows back, causing a rapid decrease of the Ignition current and thus the load of the electrodes Spark plug is coming. This also results in a corresponding increased service life for the spark plug.

To keep the losses low, it is advantageous to provide the features of claim 2.

Due to the features of claim 3, it is up easy way to increase the instantaneous supply voltage, where the necessary energy from the failed Ignition stored energy is provided.

Due to the features of claim 4, the results Advantage that the spark due to the against the Combustion chamber to be opened electrodes against its interior is driven and thereby a better ignition of the mixture is reached.

Due to the features of claim 5, it is possible keep the burden of the spark plug low and the ignition current by reducing the pulse duration of the switches of Bridge circuit driving pulses after ignition to reduce, whereby the ignition current and thus the burden of Electrodes of the spark plugs is reduced.

Due to the features of claim 6 will also a reduction of the ignition current after ignition reached.

Fig. 1 ein Schaltbild der erfindungsgemäßen Schaltung und

Fig. 2 Diagramme der Spannungsverläufe an verschiedenen Punkten der Schaltung nach Fig. 1.

The invention will now be explained in more detail with reference to the drawing. Showing:

Fig. 1 is a circuit diagram of the circuit according to the invention and

2 shows diagrams of the voltage profiles at different points of the circuit according to FIG. 1.

The illustrated circuit has a control part 1 on, which is designed essentially as a frequency divider, at its two exits II, III by 180 ° phase-shifted signal trains supplies. This results in this Signal trains with respect to ground or a further terminal 2, with one pole of the primary winding L1 of an ignition coil 3rd connected is.

This pole of the primary winding L1 is further with a central connection one of two electronic switches T1, T2 formed series connection, whose Control electrodes with outputs II and III of the control unit 1 are connected.

This series connection of the two electronic Switch T1, T2 is connected to ground GND and to a voltage source U connected, preferably a controllable voltage of 12 delivers up to 300V DC.

To each electronic switch T1, T2 is a Diode D1, D2 connected in anti-parallel, preferably very rapidly switching diodes are provided.

To the series connection of the two electronic Switch T1, T2 is further a series connection of two Capacitors C2, C3 connected in parallel, at whose Middle terminal of the second pole of the primary winding L1 as Fully transformer trained ignition coil 3 is connected, which is preferably provided with a ferrite core.

Furthermore, a storage capacitor C1 is provided, which is also connected to the voltage source U.

It follows, therefore, that the series circuits of electronic switch T1, T2, and the capacitors C2, C3 form two branches of a bridge circuit, in the transverse branch the primary coil L1 of the ignition coil 3 is connected.

One pole of the secondary coil L2 of the ignition coil 3 is over a resistor R1 to ground and the second pole to a Electrode of a spark plug 4 connected, the second electrode connected to ground.

Furthermore, a sensor 6 for detecting the Zündstromes provided with a control circuit. 5 connected is. This is with a signal train VIII (FIG. 2) supplied, the delivery of control pulses I to the control part 1 at a given time and for a given one Time allows. Furthermore, the control circuit 5 with a signal train IX acted upon. This puts within the Time period for the delivery of control pulses I a period of time fixed, after which the setpoint for the ignition current is reduced.

Furthermore, there is also the possibility of the To apply control circuit 5 with a pulse train X, the within the time specified by the pulse train VIII the setpoint for the ignition current according to a specified Curve reduced.

In operation, during a given ignition duration a pulse train is applied to the input I of the control part 1, its duty cycle, as can be seen from Fig. 2, over the ignition duration decreases. It can also be provided, the To change the frequency of this pulse train over the duration of the ignition, in particular to reduce the duration of ignition.

The pulse train I causes at the outputs II, III of the Control part 1, the pulse trains II, III (Fig. 2), the are mutually phase-shifted by 180 ° and their Pulse duration and frequency of pulse train I depends.

These pulse trains II, III cause a corresponding Switching through the electronic switches T1, T2. Will the Switch T1 is turned on, so there is a current flow via the primary coil L1 from point IV in the direction of point V of Ignition coil 3 and to a discharge of the capacitor C2 and a Charging the capacitor C3 to the voltage of the Voltage source U.

The case in the secondary coil L2 of the ignition coil. 3 Induced voltage must, like the diagram VI, the Ignition over the spark plug 4 shows not to ignite a Sparking between the electrodes of the spark plug 4 sufficient.

After switching off the switch T1 and Switching of the switch T2 due to the pulse trains II, III it comes to the formation of a current flow through the primary coil L1 of the ignition coil 3 in the opposite direction, i. from point V to Point IV and to charge the capacitor C2 and unload the Capacitor C3. Due to the in the ignition coil previously stored energy can thereby charge the Capacitors C2, C3 via the voltage of the voltage source U come out. Prerequisite for this is a corresponding Tuning the frequency and duty cycle of the Pulse trains II and III and the capacitance of the capacitors C2, C3 and the inductance of the ignition coil. 3

This also increases the flow of current over the Primary coil L1 of the ignition coil 3 and thus in their Secondary coil L2 induced voltage that essentially coincides with each switching of the switches T1, T2 increases until the induced voltage is sufficient to spark a between the To trigger electrodes of the spark plug 4.

Ignites a spark between the electrodes of the Spark plug 4, so causes the forming Zündstrom (Diagram VII), which also flows through the secondary coil L2, a corresponding reaction on the primary coil L1 of Ignition coil 3 and it will return energy to the circuit supplied, whereby the ignition current, the electrodes of the Spark plug 4 loaded, sinks.

Since the loading of the switches T1, T2 with the Pulse trains during the entire intended ignition duration it stays upright throughout the whole process Firing time to reload the capacitors and thus due the associated current flows through the primary coil L1 of the Ignition coil 3 for inducing voltage spikes with alternating Polarity.

Because after igniting a spark between the Electrodes of the spark plug 4 a plasma cloud in this area remains, a relatively small voltage pulse is sufficient to re-ignite a spark, as shown in Diagrams VI, VII of Fig. 2 can be seen.

By appropriate adaptation of the frequency and the Duty cycle of the pulse trains II, III may be the case forming Zündstrom rapidly reduced and thereby a Protection, or a long life of the spark plug 4 achieved become. This purpose is the detection of the ignition by the Sensor 6, wherein its signal through the control circuit. 5 impulses II, III influenced, with too high Ignition current, the pulse width of the signal trains II, III reduced is to reduce the ignition current.

Since not only an ignition pulse is triggered, like this in the conventional igniters is the case, but a variety of such pulses is also at high compression spark ignited internal combustion engines virtually a failure locked out. In addition, the repeated sparks cause a faster combustion of a mixture in a combustion chamber an internal combustion engine, whereby their efficiency increases.

Claims (6)

1. An ignition circuit for a spark-ignited internal combustion engine, especially a high-compression internal combustion engine, with an ignition coil (3) which is connected in a secondary manner with a spark plug (4) for producing high voltage and whose primary winding (L1) is connected with a capacitor (C2, C3) in series and said series connection is connected with a DC voltage source (U), with an electronic switch (T1, T2) being provided whose control electrode is connected with a pulse generator (1) which supplies at least one control pulse during a predetermined ignition period, characterized in that the ignition coil (3) is configured as a separate-winding transformer whose primary winding (L1) is switched in the shunt arm of a bridge circuit consisting of a series connection of two similar electronic switches (T1, T2) and a series connection which is switched parallel thereto and consists of two capacitors (C2, C3), with a diode (D1, D2) each being switched in an anti-parallel way relative to the electronic switches (T1, T2) and the pulse generator (1) subjects during the provided ignition period the electronic switches (T1, T2) with several pulses which are each phase-shifted by 180° and which have a changeable pulse duration and frequency.
2. An ignition circuit according to claim 1, characterized in that the ignition coil (3) has a ferrite core.
3. An ignition circuit according to claim 1 and 2, characterized in that the setting of the capacitors (C2, C3) occurs with respect to the inductivity of the ignition coil (3) in such a way that the degrading magnetic field of the ignition coil (3) displaces the voltage on the capacitors (C2, C3) by half up to double the operating voltage (U), preferably by the operating voltage (U).
4. An ignition circuit according to one of the claims 1 to 3, characterized in that the electrodes of the spark plugs connected to the ignition coil (3) have an aperture angle of 60 to 90° facing the interior of the combustion chamber.
5. An ignition circuit according to one of the claims 1 to 4, characterized in that a sensor (6) is provided for detecting the igniting current, which sensor is connected to a regulating circuit (5) which depending on the igniting current reduces the pulse duration of the pulses of the pulse generator (1).
6. An ignition circuit according to one of the claims 1 to 5, characterized in that a sensor (6) is provided for detecting the igniting current, which sensor is connected to a regulating circuit (5) which depending on the igniting current regulates the primary voltage on the bridge circuit.

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