DE4313901C2 - Method for generating ignition pulses and device for carrying out the method - Google Patents

Description

The invention relates to a method according to the preamble of the claim 1 and a capacitor ignition device for performing the method.

In igniters with a conventional method of sparking pulse Installation and with inductive ignition energy storage are relatively long-term (approx. 1.5 ms), trivially arranged in time (always one impulse for each Ignition timing), individual sparking pulses used. Such devices ensure reliable ignition down to the lower limit of the internal combustion engine Speed, but take a large power consumption and high reactance of the Ignition energy storage. The consequences of this are: Overheating, electrode erosion, soot formation, shunt sensitivity as well - because of the slowly rising pulse fronts - slow combustion process - Development with incomplete fuel combustion.

Ignition devices with the same pulse setup procedure, but with a more capacitive one Ignition energy storage (capacitor ignition), on the other hand, is tenfold Shortening of the front and pulse duration is typical, and therefore the above is missing. Disadvantage. However, this is the area of application for high-speed internal combustion engines limited because such a spark duration at low internal combustion engine The speed is too short for a reliable ignition (see e.g. car electronics, car electronics am Ottomotor / Bosch-Düsseldorf: VDI-Verlag, 1987, p. 130).

An improvement is due to the multi-flash system, i. H. Multi-spark ignition, reachable (e.g. H. de Boer. The car and its electrics - Stuttgart: Motorbuch- Verlag, 1990, p. 304, and DE 37 32 090 A1). Outside the low speed In areas, however, this pulse establishment process is superfluous and therefore always still associated with high power consumption and electrode erosion.

A further improvement can be achieved at any time in a certain operating state of the internal combustion engine, a packet of Ignition sparks, on the other hand only one in each operating state Ignition spark is caused, as in DE 26 16 693 A1 and DE 32 00 398 A1 is proposed. Electrodes are spared, the power consumption leaves  to; but here too the charging device of the ignition system must have a relative large nominal power (and related power consumption) that actually is only used in the low speed range - in multi-spark operation.

That being said, the main disadvantage of capacitor igniters remains despite of the improvements mentioned still up to date: occurs during this typical, extremely short spark duration (approx. 150 µs) an insufficient amount flammable fresh fuel-air mixture between the candle electrodes misfire occurs. Low speeds and lean gas mixtures increase the likelihood of such misfires even more.

The invention has for its object a method and a capacitor Ignition device to specify the scope of the short-term Sparks into the low engine speed range expand them in modern passenger cars with lean gas mixtures and moderate speeds to apply. In addition, the invention aims at further advantageous shortening of the spark duration not only the disadvantages mentioned eliminating conventional devices and maintaining benefits but also to reduce their production and material costs.

This object is achieved with the features specified in claim 1 and 5, respectively solved.

In known capacitor igniters, the high voltage rise time is although much shorter than with inductive coil ignition devices, it is always still 10-30 µs and remains unnoticed by developers, because the opinion prevails, only the spark duration is important for a safe ignition.

In reality, the rise time is very important.

Firstly, an electrical field already becomes available during the high voltage rise time built up between the electrodes. The free ones in the gas mixture Electrons are accelerated in this field and collide with gas molecules that thereby being ionized. A chain reaction occurs in the gas mixture, and that normally neutral mixture becomes conductive (see e.g. H. de Boer. The car and his electrics - Stuttgart: Motorbuch-Verlag, 1990, p. 290, center). This is causing a time-dependent energy dissipation or an energy loss. The increases Tension is also relatively slow, they are massive and therefore sluggish Ions enough time to move to the cathode under the influence of the field and there one  to form conductive cloud. The effective electrode distance and the him appropriate flashover voltage as well as for the initialization of the Inflammation, important flashover energy is thereby reduced disadvantageously.

Second, arcing occurs both in the electrical High voltage circuit as well as steamed in the burning gas mixture high-frequency vibrations (see e.g. H. de Boer. The car and its electrics - Stuttgart: Motorbuch-Verlag, 1990, p. 271, lines 9-11. from underneath). These contribute to accelerated propagation of combustion at (shock-vibration ignition) and are mainly from the high frequency losses and the impedance of the Ignition transformer dependent. If the transformer is only capable, only relative To produce slowly rising high-voltage impulses, that is Eddy current or hysteresis losses and impedance in the high frequency range are too large. The vibrations then go out quickly, the propagation of the combustion leaves disadvantageous, and rapid development of the combustion process with a complete Fuel combustion cannot be guaranteed.

Due to the restrictions of the high voltage rise time according to the invention Fronts of ignition pulses are the above. Significant losses too avoid. If this process condition is met, even the spark duration can Shortened by two to three times without loss of ignition reliability be, e.g. B. by the corresponding reduction in the ignition transformer Inductance or the storage capacitor capacity. This has another one favorable reduction in both rise time and power consumption Episode. Also the pulse or spark repetition frequency in multi-spark operation and accordingly the ignition reliability can be increased because z. B. the reduced ignition energy storage should absorb less energy at once and - with the same power consumption - more frequent charge-discharge cycles can be subjected. It is also insensitive to electrical shunts for the shorter sparks further improved (see e.g. Auto Electronics, Auto Electronics on Otto Engine / Bosch - Düsseldorf: VDI-Verlag, 1987, p. 131, lines 11-6 from below).

The method and the ignition device according to the invention ensure a safe Ignition in the low speed range by multi-spark ignition and close thereby the incomplete recharge of the ignition energy storage during the given multi-spark operation. The largest is always automatically Pulse repetition frequency ensured within the spark package, which is subject to full recharge is still possible. This results in a high one  Ignition intensity in the low speed range, where the flame reliability due to a typically lean or inhomogeneous gas mixture and one higher residual gas content is particularly topical.

Exceeding a speed setpoint above which a safe ignition already guaranteed by a conventional procedure with short-term single sparks can be determined. Multi-spark operation is in the speed range not necessary anymore; this is discontinued and against sparking operation, d. H. against the conventional sparking pulse setup, exchanged. This significantly reduces power consumption and Electrode erosion outside the low speed range. Furthermore, it will now possible to shorten the spark duration even further, because this alone Ignition supply difficulties in the low speed range are no longer restricted is (that speed range is the multi-spark operation with their Multiple reignitions available).

For the purpose of reducing the storage load time constant according to the invention by reducing the loader performance, the loader is the Ignition device with a charge control input that depends on Operating state of the ignition device or the internal combustion engine is to be actuated. Does the ignition device switch due to the detection of the internal combustion engine State (speed, temperature, etc.) in multi-spark operation, so the Power control input activated, the output power of the charging device takes to, and their output impedance as well as the charging time constant of this Output coupled storage capacitor sink.

Such an operation enables both those necessary for safe ignition To accommodate the number of pulses within the packet in multi-spark operation (by increasing performance), as well as the power consumption in single-spark operation noticeably reduce, since the necessary distance between neighboring pulses and the permissible loading time constant are much larger in the latter case. Multi-spark operation with its increase in performance is now mostly only at the start of the Internal combustion engine claimed. This is the long-term mean considerably lower the ignition device performance and the ignition transformer much more compact. Apart from that, the ignition device Overheating so far that a special heat sink on the device even not applicable.

The extension of the multi-spark package further developing the invention while lowering the  Engine speed in multi-spark operation has an advantageous effect on the Inflammability reliability because of an existing in the low speed range already mentioned typically lean inhomogeneous fuel mixture and a high Residual gas content requires an ever increasing ignition energy supply.

The complete sparking pulse list described above makes it possible to significantly reduce the spark duration, in many cases compared to the conventional installation procedure. You can see the rise time of the Spark voltage (front duration) easily through z. B. Reduction of Ignition energy storage capacity or the ignition transformer inductance further shorten without increasing the charging current. Through the present procedure the advantageous shortening of the pulse duration no longer poses a danger to the Reliability in the low speed range.

The invention is explained in more detail below using the drawing as an example.

A synchronous clock generator 1 (which can be, for example, an interrupter or a contactless transmitter) synchronizes the device work or the ignition process with predetermined ignition times in the internal combustion engine cycle. The task of a pulse shaper 2 is to suppress interference, including the contact bounce protection of the synchronous clock signal and, if necessary, its further preparation (adaptation).

A speed discriminator 8 monitors at its input the frequency of the output signal of the pulse shaper 2 (and thereby the engine speed) and generates a steady output signal when the speed preset value is exceeded. This sets a control device 4 through the operation selection input 4.2 in multi-spark operation. If the output signal of the speed discriminator 8 goes out, the control device is switched to single-spark operation.

In multi-spark operation, the control device 4 outputs its output pulse each time all three of its input signals ( 4.1, 4.2, 4.3 ) meet. The duration of the synchronous input signal 4.1 determines the duration of the multiple spark packet at the control device output. The return period of the key input signal 4.3 determines the pulse return period within the multiple spark package at the control device output. The ready signal output signal 3.1 (the push-button input signal 4.3 ) arises whenever the storage capacitor 5 at the charging current output 3.8 is fully charged and goes out each time the capacitor is discharged. The pulse return period within the packet at the output of the control device 4 is thus determined by a loading time constant.

During single-spark operation (the output signal of the speed discriminator 8 at the operational input 4.2 is extinguished), the control device 4 generates a single short-term pulse in each case to the output pulse front of the pulse shaper 2 regardless of the push-button input signal 4.3 . The same also applies to the first pulse of each packet in multi-spark operation, since the output of the pulse shaper 2 is firmly coupled to the synchronous input 4.1 .

The further work of the device is identical in both operating modes. Each output pulse of the control device 4 initiates a discharge 7 from which discharges the storage capacitor 5 through the primary winding of an ignition transformer 6, the latter thereby inducing a high voltage in the secondary winding, so that a spark sprayed.

A charging device 3 has a power control input 3.2 , which is connected to the output of the speed discriminator 8 . The output of the basic component, the voltage converter 3.3 , is connected to the charging current output 3.8 of the charging device 3 . The voltage converter 3.3 is encompassed by its own power control input with negative feedback by means of a voltage comparator 3.6 and an adder 3.7 . As a result, the charge of the storage capacitor 5 or the spark data remains stable in the wide range of the supply voltage and the engine speed. Apart from this, the output of the voltage comparator 3.6 is used for determining the complete storage capacitor charging and thus forms the readiness message output 3.1 . A reference voltage source 3.4 outputs a voltage specification value as a charging termination criterion. A reference power source 3.5 gives an initial value of the power of the voltage converter 3.3 . At the maximum speed in single-spark operation, this value is intended to ensure a charging time constant which is at least three times shorter than the minimum return period of the pulses or sparks in this operating mode, in order to ensure the complete recharging of the storage capacitor 5 between neighboring sparks. In multi-spark operation, the performance of the charging device 3 or the voltage converter 3.3 is to be increased compared to the single-spark operation. The second "+" input of the adder 3.7 , which takes care of this, forms the aforementioned power control input 3.2 of the charging device 3 .

In the control device 4 , a short-time pulse shaper 4.4 responds to the output pulse front of the pulse shaper 2 (ie at each ignition point) and generates a short-term pulse to trigger the discharge switch 7 . The multi-spark operation described above is realized by an AND logic stage 4.5 . The outputs of the short-term pulse shaper 4.4 and the AND logic stage 4.5 are connected to the output of the control device 4 by an OR logic stage 4.6 .

The significant reduction in the pulse duration, the power consumption and the average output power thanks to the present method makes it possible to manufacture the ignition transformer 6 from the new materials in a much more compact and inexpensive manner and thereby to shorten the high-voltage rise time significantly. In this case, those modern, high-quality materials are to be used (e.g. ferrite) that previously could not be considered here due to their low power transmission capacity.

Claims (6)

1. A method for generating ignition pulses in a capacitor ignition device for internal combustion engines, in which in each case by discharging a storage capacitor into an ignition transformer at each predetermined ignition time in a first operating state of the machine, only one ignition pulse and in a second operating state of the machine, a plurality of ignition pulses is generated and in which the storage capacitor is charged by a charging device, the output power of which is regulated, characterized in that the first operating state corresponds to an engine speed above a predetermined speed value and the second operating state corresponds to a speed below the predetermined value that in the second Operating state at each ignition point in addition to the single ignition pulse generated in the first operating state (single-spark operation) and further ignition pulses following this ignition pulse are generated in one package (multi-spark operation) In order to generate the further ignition pulses of the packet in multi-spark operation, the storage capacitor is always discharged when its charging voltage has reached a predetermined reference voltage value and that the output power of the charging device in multi-spark operation is regulated to a higher value. 2. The method according to claim 1, characterized in that the voltage rise the front of each ignition pulse is set so that the ignition voltage of the spark gap the charged spark plug is reached after 5 microseconds at the latest. 3. The method according to claim 1, characterized in that the charging time constant of the storage capacitor during the transition from the first to the second operating state the internal combustion engine is reduced. 4. The method according to claim 1, characterized in that the duration of the Ignition pulse packet in multi-spark operation reversed depending on the Engine speed is made. 5. capacitor ignition device for internal combustion engines for performing the method according to one of claims 1 to 4, characterized in that the control input of a with the primary winding of the ignition transformer ( 6 ) lying in series discharge switch ( 7 ) via an OR logic stage ( 4.6 ) with the output of a pulse generator ( 1 ) actuated by rotation of the crankshaft of the internal combustion engine and via the OR logic stage ( 4.6 ) and an AND logic stage ( 4.5 ) to the output of a voltage comparator ( 3.6 ), which has one input at that of the Charger output ( 3.2 ) to a storage capacitor ( 5 ) leading line and with its other input to a reference voltage source ( 3.4 ) that the AND logic stage ( 4.5 ) with its output at a logic input of the OR logic stage ( 4.6 ) and the logic inputs of the AND logic stage ( 4.5 ) each with the output of the voltage comparator ( 3.6 ), the pulse generator ( 1 ) and e of a speed discriminator ( 8 ) are connected, the latter consisting of a reference speed source ( 8.1 ) and a comparator ( 8.2 ), one input of which is at a reference speed source ( 8.1 ) and the other input of which is at the output of the pulse generator ( 1 ) , and that an adder ( 3.7 ) is provided, the output of which is at a power control input of the voltage converter ( 3.3 ) and whose non-inverting input is connected to the output of the speed discriminator ( 8 ), the further non-inverting input of which is connected to a reference voltage source ( 3.5 ) and their inverting input are connected to the output of the voltage comparator ( 3.6 ). 6. Ignition device according to claim 4, characterized in that the ignition transformer ( 6 ) has a core made of a material suitable for the high-frequency range, such as. B. has ferrite.