WO2001044655A2

WO2001044655A2 - Controllable ignition circuit

Info

Publication number: WO2001044655A2
Application number: PCT/AT2000/000346
Authority: WO
Inventors: Carl Maria Fleck
Original assignee: Fleck Carl M
Priority date: 1999-12-17
Filing date: 2000-12-18
Publication date: 2001-06-21
Also published as: DE50009885D1; EP1238195B1; EP1238195A2; WO2001044655A3; AU2126201A

Abstract

The invention relates to an ignition circuit for an externally-ignited internal combustion engine, especially a high-compression internal combustion engine, comprising an ignition coil (3) which is secondarily connected to a spark plug (4) and whose primary winding (L1) is series-connected to an electronic switch (T1, T2), this series connection being connected to a direct voltage source (U) whose control electrode is connected to a pulse generator (1) which supplies at least one control pulse for a predetermined ignition period. The invention provides that the ignition coil (3) is configured as a separate-winding transformer whose primary winding (L1) is connected in the shunt arm of a bridge circuit with an arm consisting of a series connection of two electronic switches (T1, T2) of the same type. A diode (D1, D2) is connected to each of the electronic switches (T1, T2) in antiparallel, respectively, and the pulse generator (1) subjects said electronic switches (T1, T2) to several pulses that are phase-shifted about 180°, respectively, during the predetermined ignition period. In this way, the invention achieves a considerable degree of ignition reliability.

Description

Controllable ignition circuit

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

In known ignition circuits of this type, an electronic switch is connected in parallel with the capacitor and is controlled by a single pulse from the pulse generator. When the electronic switch is switched on, there is a short circuit in the capacitor and thereby a rapid breakdown of the voltage across the capacitor, as a result of which there is a rapid increase in the current flow through the primary winding of the ignition coil designed as an economy transformer. This causes a single ignition voltage pulse on the secondary side of the ignition coil, which should be sufficient to ignite a spark between the two electrodes of a spark plug.

The breakdown voltage of the distance between the two electrodes of a spark plug increases with the pressure to which the gas mixture located between the electrodes is exposed. This results in high-compression spark-ignition internal combustion engines, e.g. with gas engines, significant problems. With such engines, misfiring occurs again and again unless extremely high ignition voltages are applied to the spark plugs. At such high ignition voltages, however, a correspondingly high energy is also stored in the ignition coil, which for the most part flows over the spark after each ignition of the spark gap of the spark plug.

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

However, if the ignition voltage is insufficient to produce a spark due to the pressure and / or the wear of the spark plug, the after the interruption flows electronic switch the stored energy in the capacitor. The next time the switch is turned on, this process is repeated, but there is practically no rise in the ignition voltage. If the ignition voltage is just due to the spark for igniting the given condition of the electrodes of the spark plug and the pressures provided in the combustion chamber of the internal combustion engine, irregular fluctuations occur due to the fluctuations in the pressure and the supply voltage, and thus an uneven run the internal combustion engine and thus to a significant loss in performance of the same.

For example, EP 0 070 572 discloses an ignition system in which the primary winding of the transformer is part of an LC resonant circuit, which in turn is connected in series with a transistor acting as a chopper or switch and a resistor. The transistor is driven with pulse trains with individual pulses modulated in their duration, so that the spark plugs are fed with ignition pulse trains with individual ignition pulses with modulated energy. However, if an ignition spark does not develop, a considerable amount of the energy stored on the secondary side of the transformer is lost for a subsequent ignition. Furthermore, the intended chopper is not suitable for the formation of firing sequences as are necessary for the formation of a plasma as described below.

In EP 0 942 519 AI, measures on the secondary side of a transformer of an ignition system are proposed, by means of which the use of diodes is avoided in the case of two rectifier transistors provided, which increases the efficiency of the ignition system. In particular, the secondary side of the transformer is designed in the form of two separate secondary turns. The primary winding of the transformer used for the ignition is located in the transverse branch of a half-bridge circuit, in which two switching elements are also provided. However, this version is not suitable for generating rapid firing sequences, in which the individual firing pulses follow one another within microseconds, with a variable pulse duty factor. In particular, there is no corresponding matching of the capacitances with the inductance of the ignition coil in connection with the frequency of the pulses delivered by the pulse generator for driving transistors. After all, this circuit is not suitable for generating high-voltage pulses because the FETs used on the secondary side are not compatible with high-voltage.

WO 98/19066 describes an ignition system in which the primary coil of a transformer is part of an oscillating circuit in which a capacitor and a discharge switch are arranged. The resonant circuit is excited in an externally controlled manner. The first ignition takes place by discharging a capacitor after closing a discharge switch. By excitation of the resonant circuit during the "jerking", enough energy is introduced to maintain the ignition spark for an arbitrarily long time. The ignition frequency is thus tied to the natural frequency of the resonant circuit and can therefore hardly be varied, in particular a circuit is not required in this embodiment suitable to generate successive ignition pulses very quickly.

In DE 40 09 145 AI, 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 the ignition, but on the other hand also 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, however, of phase-shifted pulse trains with a constant duty cycle. The aim of this invention is to replace the voltage converter, which has the task of converting the DC voltage originating from the on-board electrical system battery into the substantially higher DC charging voltage, so as to make the ignition system more compact and with a smaller number of components. However, the proposed circuit is not suitable for using the energy stored on the secondary side of the transformer for a subsequent ignition if the formation of an ignition spark should not take place.

The aim of the invention is to avoid these disadvantages and to propose an ignition circuit of the type mentioned at the outset which ensures reliable ignition even in the case of high-compression internal combustion engines and in which there is only a low current load on the electrodes of the spark plugs. In particular, the circuit should be suitable for supplying ignition pulses which bring about ionizations in the fuel mixture, even if no ignition initially occurs, and thus initiate plasma formation before the actual ignition occurs. The duty cycle of the firing order should be variable and the energy stored in the transformer should be returned to suitable storage capacitors if the firings have not taken place.

According to the invention, this is achieved in an ignition circuit of the type mentioned at the outset by the characterizing features of claim 1.

The proposed measures ensure that several ignition pulses can be generated during the intended ignition duration. This increases the likelihood of a successful ignition. The primary winding of the ignition coil is connected in the shunt arm of a bridge circuit consisting of a series connection of two identical electronic switches and a series connection of two capacitors, whereby to a diode is connected antiparallel to each of the electronic switches and a pulse generator applies a plurality of pulses, each phase-shifted by 180 °, to the electronic switches during the intended ignition duration. This also has the very significant advantage that, if there is no ignition spark between the electrodes, a large part of the energy in the circuit is stored in the circuit and is also available for the next ignition pulse. This also ensures that an ignition spark is formed during the intended ignition duration even under difficult ignition conditions.

With a suitable coordination of the capacities with the inductance of the ignition coil in connection with the frequency of the pulses supplied by the pulse generator, the capacitors can be charged via the supply voltage of the circuit if there is no sparking between the electrodes of the spark plug supplied by the ignition circuit during the first ignition pulse , This slow palpation of the field strength in the individual pulses leads to the preparation of the ignition spark, since the preliminary spark ("streamer") which forms with the first pulses leads to an increased formation of ions which are not broken down in the short pauses between the voltage pulses can.

As a result, the ignition circuit according to the invention, in contrast to the conventional ignition circuits in which only a single ignition pulse is generated during the intended ignition duration, results in a significantly higher level of ignition reliability even under very difficult ignition conditions, such as are the case with externally ignited high-compression engines.

Another advantage of the ignition circuit according to the invention lies in the fact that the ignition current, with the spark already ignited, between the electrodes of the spark plug can be controlled by changing the frequency and the width of the pulses driving the switches. This makes it possible to protect the electrodes of the spark plug to a very large extent, since a very considerable reduction in the ignition current is possible during the duration of the spark and the wear on the electrodes can be significantly reduced.

The large number of intermediate sparks generated during the ignition duration also results in a higher burning rate of the gas mixture in a cylinder of an internal combustion engine, which increases its efficiency. The number of intermediate sparks increases with increasing frequency of the pulses driving the switches.

Because of the large number of ignition sparks that are generated or are formed at a frequency between 100 kHz and 500 kHz during the duration of the ignition, a plasma cloud remains in the area of the electrodes of the spark plug, making it much easier to re-ignite a spark. This also enables a large opening angle directed towards the interior of the combustion chamber, e.g. 60 to 90 ° between the electrodes of the spark plug. With a large opening angle of the electrodes, a spark that burns between them is driven towards the interior of the combustion chamber due to the electromagnetic forces caused by the current flow, thereby facilitating ignition of the combustible mixture in the combustion chamber. In addition, larger electrode spacings can be provided than in conventional ignition circuits, since there is a considerably higher degree of ignition reliability due to the large number of ignition pulses that are generated during the intended ignition duration.

The proposed circuit also has the advantage that part of the energy stored in the ignition coil after the ignition of a spark between the electrodes of a spark plug into the capacitors flows back, which leads to a rapid decrease in the ignition current and thus the load on the electrodes of the spark plug. This also results in a correspondingly increased service life for the spark plug.

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

The features of claim 2 make it possible in a simple manner to increase the instantaneous supply voltage, the energy required for this being provided from the energy stored when the ignition has not occurred.

The features of claim 4 result in the advantage that the ignition spark is driven against the interior due to the electrodes that can be opened against the combustion chamber, and thereby better ignition of the mixture is achieved.

Due to the features of claim 5, it is possible to keep the load on the spark plug low and to reduce the ignition current by reducing the pulse duration of the pulses driving the switches of the bridge circuit after the ignition has taken place, thereby reducing the ignition current and thus the load on the electrodes of the spark plugs ,

The features of claim 6 also achieve a reduction in the ignition current after ignition.

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

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 circuit shown has a control part 1, which is essentially designed as a frequency divider, which at its two outputs II, III by 180 ° delivers phase-shifted signal trains. These signal trains result with respect to ground or a further connection 2, which is connected to a pole of the primary winding L1 of an ignition coil 3.

This pole of the primary winding L1 is also connected to a center connection of a series circuit formed from two electronic switches T1, T2, the control electrodes of which are connected to the outputs II and III of the control part 1.

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

A diode D1, D2 is connected antiparallel to each electronic switch T1, T2, preferably very rapidly switching diodes are provided.

A series connection of two capacitors C2, C3 is also connected in parallel with the series connection of the two electronic switches T1, T2, to the center connection of which the second pole of the primary winding L1 of the ignition coil 3, which is designed as a full transformer and is preferably provided with a ferrite core, is connected.

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

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

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

Furthermore, a sensor 6 for detecting the ignition current is provided, which is connected to a control circuit 5 connected is. This is supplied with a signal train VIII (Fig. 2), which enables the delivery of control pulses I to the control part 1 at a certain point in time and for a certain period of time. Furthermore, the control circuit 5 is loaded with a signal train IX. Within the time period for the delivery of control pulses I, this defines a time period after which the setpoint value for the ignition current is reduced.

Furthermore, it is also possible to apply a pulse train X to the control circuit 5, which reduces the setpoint value for the ignition current in accordance with a defined curve within the time period determined by the pulse train VIII.

In operation, a pulse train is applied to input I of control part 1 during a predetermined ignition duration, the pulse duty factor of which, as can be seen from FIG. 2, decreases over the ignition duration. It can also be provided to change the frequency of this pulse train over the ignition duration, in particular to reduce it over the ignition duration.

The pulse train I causes the pulse trains II, III (FIG. 2) at the outputs II, III of the control part 1, which are phase-shifted from each other by 180 ° and whose pulse duration and frequency depends on the pulse train I.

These pulse trains II, III effect a corresponding switching of the electronic switches T1, T2. If the switch T1 is switched through, there is a current flow via the primary coil L1 from point IV in the direction of point V of the ignition coil 3 and the capacitor C2 is discharged and the capacitor C3 is charged to the voltage of the voltage source U.

The voltage induced in the secondary coil L2 of the ignition coil 3 does not have to be sufficient to ignite a spark between the electrodes of the spark plug 4, as shown in diagram VI, which shows the ignition current through the spark plug 4.

After switching off the switch Tl and Switching on the switch T2 due to the pulse trains II, III leads to the formation of a current flow through the primary coil L1 of the ignition coil 3 in the opposite direction, ie from point V to point IV and to charging the capacitor C2 and discharging the capacitor C3. Due to the energy previously stored in the ignition coil, the capacitors C2, C3 may be charged beyond the voltage of the voltage source U. A prerequisite for this is an appropriate coordination of the frequency and the duty cycle of the pulse trains II and III as well as the capacitance of the capacitors C2, C3 and the inductance of the ignition coil 3.

This also increases the current flow through the primary coil L1 of the ignition coil 3 and thus the voltage induced in its secondary coil L2, which increases essentially with each switchover of the switches T1, T2 until the induced voltage is sufficient to provide a spark between the electrodes of the spark plug 4 trigger.

If a spark ignites between the electrodes of the spark plug 4, the ignition current that forms (diagram VII), which also flows through the secondary coil L2, has a corresponding reaction on the primary coil L1 of the ignition coil 3 and energy is returned to the circuit, as a result of which Ignition current, which loads the electrodes of the spark plug 4, drops.

Since the impingement of the switches T1, T2 with the pulse trains remains during the entire intended ignition duration, the capacitors are recharged during the entire intended ignition duration and thus, due to the associated current flows via the primary coil L1 of the ignition coil 3, to induce voltage peaks with alternating Polarity.

Since a plasma cloud remains in this area after the ignition of a spark between the electrodes of the spark plug 4, a relatively small voltage pulse is sufficient to to ignite a spark again, as can be seen from the diagrams VI, VII of FIG. 2.

By adjusting the frequency and the pulse duty factor of the pulse trains II, III accordingly, the ignition current that is formed can be rapidly reduced, thereby protecting the spark plug 4 and ensuring a long service life. For this purpose, the detection of the ignition current by the sensor 6 is used, the signal of which influences the pulse trains II, III output by the control circuit 5, the pulse width of the signal trains II, III being reduced in the event of an excessively high ignition current in order to reduce the ignition current.

Since not only an ignition pulse is triggered, as is the case with the conventional ignition devices, but a multiplicity of such pulses is also practically impossible in the case of high-compression spark-ignition internal combustion engines. In addition, the repeated ignition sparks cause a mixture to burn more rapidly in a combustion chamber of an internal combustion engine, as a result of which its efficiency increases.

Claims

PATENT CLAIMS

1. Ignition circuit for a spark-ignition internal combustion engine, in particular a high-compression internal combustion engine, with a secondary coil (3) connected to an ignition plug (4), the primary winding (L1) of which is connected in series with a capacitor (C2, C3) and this series circuit with a DC voltage source (U) is connected, an electronic switch (Tl, T2) being provided, the control electrode of which is connected to a pulse generator (1) which delivers at least one control pulse during an intended ignition duration, characterized in that the ignition coil (3) acts as a full transformer is formed, the primary winding (L1) of which is connected in the shunt branch consisting of a series connection of two identical electronic switches (Tl, T2) and a series connection of two capacitors (C2, C3), with the electronic switches (Tl, T2) each a diode (Dl, D2) is connected antiparallel and the pulse generator (1) w While the provided ignition period the electronic switches (Tl, T2) supplied with a plurality of phase-shifted by 180 ° pulses.

2. Ignition circuit according to claim 1, characterized in that the ignition coil (3) has a ferrite core.

3. Ignition circuit according to claim 1 and 2, characterized in that the setting of the capacitors (C2, C3) with respect to the inductance of the ignition coil (3) is such that the decaying magnetic field of the ignition coil (3), the voltage across the capacitors (C2, C3) by half to twice the operating voltage (U), preferably by the operating voltage (U).

4. Ignition circuit according to one of claims 1 to 3, characterized in that the electrodes of the spark plugs connected to the ignition coil (3) have an opening angle of 60 to 90 ° directed towards the interior of the combustion chamber.

5. Ignition circuit according to one of claims 1 to 4, characterized in that a sensor (6) is provided for detecting the ignition current, which is connected to a control circuit (5) which, depending on the ignition current, the pulse duration of the pulses of the pulse generator (1 ) decreased.

6. Ignition circuit according to one of claims 1 to 5, characterized in that a sensor (6) is provided for detecting the ignition current, which is connected to a control circuit (5) which controls the primary voltage at the bridge circuit as a function of the ignition current.

The patent attorney

Kliment