EP0200010B1 - Ignition device - Google Patents

Abstract

An ignition system having a low voltage source serving as a starting point for producing of an ignition voltage at least one ignition spark gap via at least one ignition branch, said branch including a said ignition spark gap, a high voltage capacitor, a high voltage transformer for producing a voltage at the high voltage capacitor of at least the same order of magnitude as said ignition voltage, an auxiliary spark gap having a breakdown threshold, and timing control means for controlling voltage delivery timing to said branch; wherein said auxiliary spark gap is disposed at an output side of said high voltage transformer and said high voltage capacitor is coupled to said auxiliary spark gap in a manner causing the high voltage capacitor to discharge to said ignition spark gap when the breakdown threshold of the auxiliary spark gap is exceeded; wherein the high voltage transformer has minimum inductances and minimum impedances; wherein a medium voltage transformer for producing a voltage between the low voltage and the ignition voltage and a medium voltage storage capacitor that is chargeable by said medium voltage transformer are provided between the low voltage source and the high voltage transformer; and wherein a controllable element is provided in said branch at an input side of said high voltage transformer, said controllable element being controlled by the timing control means in a manner operable for separating and interconnecting said high voltage transformer and said medium voltage storage capacitor.

Description

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

When designing an ignition system, the basic goal is to achieve sparks with the highest possible ignitability. The aspect of high ignitability is gaining importance especially in connection with the lean burn engines that are currently being developed to save fuel, which use fuel-air mixtures (Lambda ≧ 1.4) that are unwilling to ignite and react very slowly, and with the use of exhaust gas catalytic converters that only misfire tolerated to a limited extent, because unburned fuel entering the catalytic converter can burn the catalytic converter.

When using a high-voltage storage capacitor and a spark gap in connection with the actual spark plug gap (DE-A-2 810 159), there is a possibility of high-energy spark that also saves the essential part of its energy, which is cheap, in the so-called spark head, i.e. in the breakthrough phase. However, with such an arrangement in the form of the storage capacitor, a capacitor of high capacitance must be charged to essentially the ignition voltage, which is the case with conventional transistor ignition systems because of their poor efficiency or also with high-voltage capacitor ignition systems with an efficiency that is good per se but low power with a reasonable load on the primary energy source (battery , Alternator) is practically not possible. This is mainly due to losses in the ignition coil and in the high-voltage distributor, through which the secondary side of the ignition coil is switched to the respective ignition branch.

Just like from DE-A-2 810 159, it is known from US-A-3 361 932 to discharge the ignition energy from a high-voltage storage capacitor via a spark gap into the ignition spark gap, which together with the spark gap is parallel to the high-voltage storage capacitor.

From GB-A-2 099 917 an ignition system according to the preamble of claim 1 is known. In this known ignition system, a medium-voltage storage capacitor is provided in the number of ignition strands and the high-voltage converter has inductors which allow the ignition energy stored in the high-voltage storage capacitor to be converted in a period of approximately 0.1 ms.

Against this background, it is an object of the invention to provide an ignition system which, without amplification or additional load on the primary energy source, is able to reliably deliver the required ignition voltage with a high-energy ignition spark.

This object is achieved according to the invention by an ignition system as characterized in claim 1.

The use of the low-inductance high-voltage converter in the multiplicity of ignition strands and the associated omission of a high-voltage ignition distributor makes a decisive contribution to ensuring that the energy is lossless and extremely quickly from the medium-voltage storage capacitor, to which the primary energy source works via the medium-voltage converter, into the high-voltage storage capacitor is reloaded. The capacity of the high-voltage storage capacitor can be chosen so high without loss of charging security that even after the spark gap has broken through, i.e. if storage capacity and spark plug capacity are in parallel, the voltage at the spark plug gap is still so high that it is suitable for all operating states Spark plug spark gap is sufficient. With a spark plug capacitance of approximately 20 pF, values of the order of 300 pF are typical for the high-voltage storage capacitor.

The spark gap represents a switch that suddenly changes to low resistance when the breakdown voltage is reached, with low inductance and low resistance of the entire ignition circuit, including the voltage converter generating the high voltage, ensuring that voltage rises on the spark gap of the order of 100 kV / µs can be achieved. As a result, the majority of the energy converted in the spark plug spark gap goes into the plasma structure and thus into the mixture to be ignited.

The low resistance and low inductance required for the individual ignition strands include the switching elements which switch the medium-voltage storage capacitor to the individual ignition strands. For this purpose, thyristors are preferably used, which can be easily opened at the correct time and which can be quickly blocked by themselves. A blocking oscillator is preferably provided for the medium-voltage converter on which the primary low-DC voltage source operates. It is short-circuit proof, relatively loss-free buildable, can be optimally adjusted in performance and has a sufficiently rapid voltage rise. The medium voltage storage capacitor to which the voltage converter operates is preferably charged to a voltage of the order of 700 V and has a capacitance of the order of magnitude of 1.5 µF. The high-voltage storage capacitor can thus be charged to voltage values of approximately 30 kV with a capacitance of the order of magnitude of 300 pF. Such a lossless transmission has proven to be impossible with conventional ignition coils with high inductance and with an ignition distribution on the high voltage side.

• Fig. 1 ein Blockschaltbild einer Zündanlage eines mehrzylindrigen Verbrennungsmotors,
• Fig. 2 das Schaltbild wesentlicher Teile der Fig. 1 im einzelnen, und
• Fig. 3 das Schaltbild auf der Sekundärseite des Hochspannungswandlers.

The invention is described in detail below with reference to the drawing. On this shows

• 1 is a block diagram of an ignition system of a multi-cylinder internal combustion engine,
• Fig. 2 shows the circuit diagram of essential parts of Fig. 1 in detail, and
• Fig. 3 shows the circuit diagram on the secondary side of the high voltage converter.

According to FIG. 1, starting from a voltage source in the form of an alternator 12 or a battery 11, a voltage converter 2 in the form of a blocking oscillator is acted upon by a voltage typical for these voltage sources, for example 12 V or less, via a disconnector in the form of a switch. The blocking oscillator 2 charges a medium-voltage energy store 1 in the form of a film capacitor of approximately 1.5 μF capacitance to a voltage of approximately 700 V. Behind this medium-voltage energy store 1, the circuit branches into parallel branches of the same structure, corresponding to the multiplicity of the units to be ignited, i.e. Spark plugs or cylinders. At the output of the medium-voltage energy store 1, controllable isolators, preferably fast thyristors, 3a, 3b, 3c, 3d, ... are parallel in the multiplicity of the ignition strings provided. Each such ignition circuit consists of a high-voltage converter 4x (x = a, b, c, ...) in the form of a low-inductance and ohmic, dielectric and magnetic, particularly low-loss transformer with a high coupling factor, a high-voltage energy store 5x in the form of a ceramic capacitor, for example one Capacity of the order of magnitude between 200 and 400 pF, a separating element 6x in the form of a spark gap filled with compressed gas and an energy store 7x with energy converter 8x in the form of the spark plug capacitance or the spark plug spark gap.

A preferred construction of an ignition line 4x to 8x is shown in FIG. 3. To the high voltage output of the High voltage storage capacitor 5x is connected to transformer 4x. In parallel is the series connection of spark gap 6x and spark plug capacity 7x with spark gap 8x. The spark plug capacitance is typically approx. 20 pF. In order for the voltage generated by the transformer 4x to actually drop substantially across the spark gap 6x before the spark gap 6x breaks down, the capacitance of this spark gap must be chosen to be small compared to the spark plug capacitance 7x, so it is preferably of the order of 2 pF. The storage capacitor 5x in turn must be so high with its capacitance that after switching through the spark gap, that is if the capacitance of the storage capacitor 5x and the spark plug capacitance 7x are in parallel, the total capacitance is still essentially determined by the capacitance of the storage capacitor 5x. This results in capacitance values for the storage capacitor of the order of 100 pF, ie 200 to 400 pF. It can thereby be achieved that the voltage across the spark plug gap 8x does not drop significantly below the voltage to which the storage capacitor 5x has been charged after the spark gap 6x has been switched through. The desired value for this voltage is of the order of 30 kV.

The generation of a voltage of the order of 30 kV on a capacitance of the order of a few hundred pF without additional load on the primary energy source, i.e. battery or alternator, is achieved by using the low-loss and low-inductance high-voltage transformers 4x in conjunction with dispensing with ignition distribution on the high-voltage side and their replacement by the isolators 3x on the low voltage side of the transformers 4x achieved in the multiplicity of these transformers.

Particularly suitable values for the high-voltage transformer are of the order of magnitude of 150 µH inductance, 350 m Ω resistance on the primary side in conjunction with 350 mH inductance, 180 Ω resistance on the secondary side. A ferrite core material ensures low core losses.

The low inductance of the high voltage transformer 4x leads to extremely rapid recharging processes from the medium-voltage storage capacitor into the high-voltage storage capacitor 5x that has just been connected, which, in conjunction with the rapid breakdown of the spark gap that is thereby promoted, provides 6x voltage increases of the order of magnitude 100 kV / µs on the spark plug spark gap. This favors the energy conversion in the spark gap 8x in the head of the spark, i.e. in the nanosecond range, and contributes to the fact that in the time available, there are only negligible amounts of energy due to possible shunts, such as those caused by sooting the insulator body of the spark plug can drain off.

The low inductance of the high-voltage transformer 4x makes its combination with the high-voltage storage capacitor 5x or the medium-voltage storage capacitor 1 very rapidly oscillating resonant circuits, so that the energy which is not converted in the nanosecond range can be returned to the medium-voltage storage capacitor. To make this possible, a diode can be provided antiparallel to the switching path of the thyristor 3x, which is already blocking at this time.

The requirements for the isolating element 3x located between the medium-voltage energy store 1 and the high-voltage converter 4x consist primarily in the fact that it can be controlled in a defined time, switches very quickly and is very low-resistance in the switched-through state in order to avoid losses here as well. These requirements are met to a particularly high degree by a fast thyristor, as is available today.

The separation elements 3x can be activated in any suitable manner. For example, a map computer that can be controlled via signal transmitters 10 (sensors), so that the ignition timing can be adjusted in accordance with engine requirements, load conditions, etc., can be used as the signal converter 9 that controls the isolating elements 3x. The signal converter 9 can also be a converted mechanical high-voltage ignition distributor without a high-voltage function, which contains the sensors for negative pressure adjustment, centrifugal force adjustment, cylinder detection, etc.

A blocking oscillator is preferred as medium-voltage converter 2 because it can be built with relatively little loss, can be optimally adapted in terms of performance, is short-circuit proof and offers a sufficiently rapid voltage rise in the millisecond range. In addition, it can be built small. By using the blocking oscillator principle, it is also possible to fully charge the medium-voltage energy store 1 with a pulse sequence of approximately 10 Hz, sufficient for engine starts, from a primary voltage of 3 V (extreme cold start).

In a further development of the principle described, it can be provided that a plurality of medium-voltage energy storage devices 1 act on each ignition train, with the provision of corresponding additional isolating elements 3x. This means that several high-energy sparks can be processed one after the other per ignition process and spark plug. Since the ignition system draws energy proportionally to the spark sequence of the battery or alternator, double sparks are possible up to half the maximum spark sequence, and triple sparks at a third of the maximum ignition sequence without a greater load on the battery or alternator than with the maximum spark sequence.

Multiple sparks which follow one another in time can also be implemented in such a way that the available energy of the medium-voltage energy store 1 is converted into tilting oscillations, in each case with the energy content of the high-voltage energy store 5x.

In order to ensure the low impedance of the ignition system, it is advisable to design the system to be compact and with short conduction paths. 1 shows several possible interfaces in the overall chain with the resultant possible combination of sub-components in certain structural units.

Figure 2 shows part of the circuit of Figure 1 in greater detail. The signal converter 9, for example a map computer, outputs its output control signals to the light-emitting diodes 20a, 20b, 20c, 20d, ... from optocouplers with which the power section is galvanically isolated from the control elements in order to suppress crosstalk from one ignition branch to the other. The phototransistors 21a, 21b, 21c, 21d, ... of the optocouplers give their signals to the control electrodes of the thyristors 3a, 3b, 3c, 3d, ..., which are in series with the primary windings of the high-voltage converters 4a, 4b, 4c, 4d , ... lie. At the series circuit consisting of the primary winding of the high-voltage transformer 4x and the thyristor 3x, in which a decoupling diode 22x is also present, the voltage of the medium-voltage capacitor 1 charged via the blocking oscillator 2 from the alternator or battery is at a voltage of the order of magnitude 1. As soon as the Thyristor, controlled by signal converter 9, switched through, current flows - because of the low inductance and low resistance of the high-voltage converter 4x and the speed of the thyristor 3x with short rise time and high peak currents. The high-voltage converter transforms the voltage on the primary side high and the high-voltage storage capacitor 5x, which is no longer shown in FIG. 2, is charged with high efficiency in the nanosecond range to the desired voltage of the order of magnitude of 30 kV.

If the energy that is not converted in the nanosecond range is to be fed back into the medium-voltage storage capacitor, the decoupling diodes 22x are omitted and diodes connected antiparallel to the thyristors are provided.

• a) Das Gemisch im Motor ist nur bedingt abmagerungsfähig, die ans Gas abgegebene Energie von 20 mJ ist nicht ausreichend für alle Betriebszustände. Die primärseitige Leistungsaufnahme betrug 96 W.
• b) Da beim Kaltstart bis 23 kV an der Zündkerze auftreten, wird zwar durch die Vorfunkenstrecke bis 20 kV abgesperrt, darüber steigt die Spannung an der Zündkerze aber mit normaler Geschwindigkeit von ca. 400 V/µs an. Bei leitfähigem Belag fließt oft zuviel Energie über den Isolatorfuß der Zündkerze ab, so daß es zu Zündaussetzern kommt.
• c) Zumindest bei kaltem, innen betautem mechanischen Verteiler kommt es hier zuHockspannungsüberschlägen bereits bei ca. 17 kV und damit zu Zündaussetzern.

The following experiment was carried out to prove the effectiveness of the described ignition advantage:
A six-cylinder engine was initially operated with a conventional transistor ignition with a mechanical high-voltage distributor, supplemented by spark plugs with 100 pF and spark gaps of 20 kV. The following shortcomings resulted:

• a) The mixture in the engine is only partially lean, the energy delivered to the gas of 20 mJ is not sufficient for all operating conditions. The primary power consumption was 96 W.
• b) Since up to 23 kV occur on the spark plug during a cold start, the spark gap cuts off up to 20 kV, but above this the voltage at the spark plug rises at a normal speed of approx. 400 V / µs. In the case of a conductive coating, too much energy often flows through the insulator base of the spark plug, so that misfiring occurs.
• c) At least in the case of a cold, internally defrosted mechanical distributor, high voltage flashovers occur already at approx. 17 kV and thus misfires.

The response voltage of the spark gaps was then increased to 27 kV and the capacitance of the storage capacitors increased to 330 pF.

With no commercially available, known ignition this combination could be made to switch through. Maintaining the design principle would have resulted in a power consumption of 360 W on the battery or alternator, which would not have been possible without reinforcing the battery or alternator. The ignition coil as an intermediate energy store has now been replaced by a capacitor with a capacitance of 1.5 µF to be charged to 700 V via a blocking oscillator, and this is reloaded into the 330 pF high-voltage storage capacitors using thyristors on the low-voltage side and low-loss and low-inductance transformers.

This made it possible to switch through the combination of 330 pF storage capacitor and 27 kV spark gap and at least 23 kV for each engine operating point to be offered on the spark plug as a needle pulse with a rise time of 100 kV / µs.

The application of the ignition system described is not limited to single and multi-cylinder reciprocating piston engines, but can also be used with rotary piston engines, gas turbines etc. with a wide variety of fuels diesel, gasoline, alcohol, ethanol, hydrogen, hydrogen gasoline, biogas, natural gas, propane etc. with more or less good mixture preparation, more or less emaciated.

The favorable use of energy in the ignition described makes it possible to use it with reduced ignition energy, for example, for additional heating systems for motor vehicles. Due to the high efficiency of the ignition system, solar cells or hand-operated dynamos are also conceivable as primary energy sources, as are high-performance batteries for short-term operation that generate a surge current of e.g. Bring 2 A.

Claims (6)

1. Ignition device for internal combustion engines having a plurality of ignition branches lying parallel to each other, in the case of which are provided a low-voltage source (11, 12), a medium-voltage transformer (4a, 4b, ... ) transforming the voltage of the low-voltage source (11, 12) to a medium voltage, a high-voltage transformer (4a, 4b, .... ) for each ignition branch, the high-voltage converter having a primary winding and a secondary winding, wherein a medium-voltage storage capacitor (1), which is connected to the medium voltage transformer, is discharged by means of a switching element (3a, 3b, ... ), which can be switched by means of a device for the timed triggering of the ignition line, via the primary winding of the high-voltage transformer, and ignition spark gaps (8a, 8b, ... ) connected to the secondary side of the high-voltage transformer (4a, 4b, ... ) are provided, characterised in that a common medium-voltage storage capacitor (1) is provided for all the ignition branches; in that each ignition spark gap (8a, 8b, ... ) has an auxiliary spark gap connected in series therewith; and in that there is connected to the secondary side of each high-voltage capacitor (4a, 4b, ...) a high-voltage storage capacitor (5a, 5b, ...) to which the series connection consisting of the auxiliary spark gap and the ignition spark gap is connected in parallel, wherein the high-voltage transformer (4a, 4b, ... ) has an inductance of at most 150 µH and an ohmic resistance of at most 350 m Ω on the primary side together with an inductance of at most 350 mH and an ohmic resistance of at most 180 Ω on the secondary side.
2. Ignition device according to claim 1, characterised in that a self-blocking oscillator is provided as the medium voltage transformer (2).
3. Ignition device according to claim 1 or 2, characterised in that thyristors are provided as the controllable switching elements (3a, 3b, ... ).
4. Ignition device according to claim 3, characterised in that there is provided, antiparallel to each thyristor (3a, 3b, ... ), a diode for feeding energy that has not been transformed in the nano-second range at the ignition spark gap back into the medium-voltage storage capacitor (1).
5. Ignition device according to claim 3, characterised in that the device for the timed triggering is electrically separated from the controllable switching elements (3a, 3b, ...) by means of optocouplers (20a, 21a; 20b, 21b, ...) for transmitting signals.
6. Ignition device according to anyone of the preceding claims, characterised in that a plurality of medium voltage transformers and a plurality of controllable switching elements are provided for each ignition branch, wherein the switching elements belonging to the same branch may be triggered in a time-delayed manner.

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