High voltage capacitor ignition

High-voltage capacitor ignition (electronics unit on the left, ignition transformer on the right)

The high-voltage capacitor ignition (HKZ), also called thyristor or English Capacitor Discharging Ignition (CDI) is designated in internal combustion engines a method of ignition , in which a capacitor charged by DC voltage and abruptly via the primary side of the ignition transformer is discharged. The high voltage generated on the secondary side is passed on to the spark plugs . In contrast to classic battery ignition with an ignition coil , high-voltage capacitor ignition stores the energy not in the ignition transformer but in the capacitor that gives it its name.

High-voltage capacitor ignition systems are used in special areas of application such as high-performance and motorsport engines and have largely been replaced in motor vehicles by fully electronic ignition systems (VEZ).

construction

Circuit principle of an HKZ, equivalent circuit diagram below

An HKZ basically consists of a DC voltage source U with a series resistor which charges the capacitor C via the primary side of the ignition transformer L1, as in the simplified circuit diagram opposite . The DC voltage U is in the range from 300 V to 500 V and is usually obtained via a DC voltage converter either from a battery , accumulator or an electrical generator driven by the internal combustion engine .

To trigger the thyristor Th is ignited via a control pulse from the control electronics (not shown), while the electrical energy stored in the capacitor C is suddenly discharged via the primary side of the ignition transformer L1 . The ratio of the number of turns of the ignition transformer to the number of turns n1 for L1 and n2 for L2 increases the voltage pulse by the factor of the voltage transformation ratio ü :

{\ displaystyle {\ ddot {u}} = {\ frac {n_ {2}} {n_ {1}}}}

Stepped up to the high voltage of up to a few 10 kV and fed via the ignition distributor to the respective spark plug to generate the ignition spark. At 3 kV / µs to 10 kV / µs, the rise time is around a factor of 10 higher than with inductive ignition coils, and the spark duration is in the range of 50 µs to 100 µs. After the ignition, the thyristor Th blocks again and the capacitor C is charged via the DC voltage source and series resistor for the next ignition.

In contrast to the inductive ignition coil with interrupter ignition, which also includes transistor ignition, the ignition transformer is not used for energy storage, but only for voltage transformation. The spark duration is dependent on the entire capacitance C ' and the leakage inductance Lσ formed by the resonance frequency, shown in the equivalent circuit diagram of the ignition circuit. The spark breakdown occurs after the first half-wave of the current has passed through the high-voltage circuit. With the HKZ, because of the short spark duration, the risk of insufficient ignition energy is higher than with interruption ignition.

Everding HKZ

Circuit principle of an Everding HKZ, equivalent circuit below

An extension that combines the advantages of high-voltage capacitor ignition with the considerably longer spark duration of the inductive ignition coil with interrupter ignition was developed by Helmut Everding in the 1960s .

As with the HKZ, with the Everding-HKZ, a capacitor C charged to a few hundred volts is discharged by the control pulse through the primary winding L1 of the ignition transformer by means of a thyristor . An additional DC voltage U _{Batt is applied} to the primary winding of the ignition coil for a predetermined period of time from approx. 1.0 ms to 1.2 ms, thus generating an additional and longer-lasting current flow through its coupling inductance M of the ignition transformer. This current forms the main part of the ignition spark, which is typical for the function. This allows the advantage of a rapid increase in the voltage of the HKZ to be combined with a relatively large ignition energy of 50 mJ , comparable to inductive interrupter ignitions .

Special

Legally, the English abbreviation for capacitor discharge ignition can lead to problems because the designation "CDI" is a registered trademark of Daimler AG .

literature

Hans-Hermann Braess, Ulrich Seiffert (Hrsg.): Vieweg manual automotive technology . Springer, 2013, ISBN 978-3-658-01691-3 .

Individual evidence

↑ Introduction to HKZ or CDI thyristor ignition technology. 2011, accessed August 10, 2015 .
^ H. Everding: Electronic ignition system for internal combustion engines. German patent 1965152 (1969)
↑ H. Everding: Electronic ignition system reduces harmful emissions. In: Electronics. Volume 1, 1976, pp. 61-64.
^ German Patent and Trademark Office, register number / file number 39733470.2

[mote1-1] Introduction to HKZ or CDI thyristor ignition technology. 2011, accessed August 10, 2015 .

[2] H. Everding: Electronic ignition system for internal combustion engines. German patent 1965152 (1969)

[3] H. Everding: Electronic ignition system reduces harmful emissions. In: Electronics. Volume 1, 1976, pp. 61-64.

[daimler_marke-4] German Patent and Trademark Office, register number / file number 39733470.2