Ignition system for internal combustion engines

Details Ignition system for internal combustion engines Ignition system for internal combustion engines

1994-06-02

1995-08-29

Wieder, Kenneth A.

Electricity: measuring and testing

Internal-combustion engine ignition system or device

Coil

324378, 324380, 123644, 315209T, F02P 1700

Patent

active

054463858

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

German Published Patent Application 23 39 896 shows a circuit including an element having a specific breakdown voltage coupled to the control electrode of the switching transistor in the primary circuit between the primary winding and the contact-break distance of the ignition transistor. If the voltage exceeds a permissible value when the contact-break distance of the ignition transistor makes the transition to the nonconducting state, then the voltage at the element having a specific breakdown voltage breaks through, and a control current begins to flow across the control path of the ignition transistor, which control current again makes the emitter-collector path of the ignition transistor somewhat permeable to current. As a result, the voltage at the contact-break distance of the ignition transistor drops again, and, in fact, continues to drop until the voltage at the switching element having a specific breakdown voltage falls below this breakdown voltage. This configuration comprising the element having a fixed breakdown voltage (Zener diode) cannot ensure overvoltage protection for all operating ranges. For example, if one designs the ignition system and, thus, the element having a specific breakdown voltage, so as to allow an adequate secondary voltage to still be provided for all operating states, given a large secondary load, then larger values can occur on the parts energized with high voltage, given a low secondary load. Such an overloading can lead to their destruction, when, for example, a spark plug connector drops out and a breakdown occurs across the high-voltage insulation.
As such, conventional systems work with a fixed primary Zener-type characteristic as a voltage bracketing of the ignition transistor and, thus, do not provide a satisfactory compromise between a sufficient secondary voltage supply and high-voltage strength of the parts that are energized with high voltage.


SUMMARY OF THE INVENTION

In accordance with the present invention, an ignition system for an internal combustion engine includes an ignition coil and an ignition output stage in the primary circuit of the ignition coil. Current through the primary circuit, and as a result a voltage at the secondary winding at the ignition spark, is dependent upon a bracketing voltage of a bracketed circuit arrangement. The bracketing voltage is dependent upon a primary voltage and an output of an evaluation unit which are coupled to the bracketing circuit arrangement. The evaluation unit monitors the primary voltage to determine whether the ignition coil has a high secondary load or a low secondary load. The evaluation circuit then induces a high bracketing voltage on the bracket circuit arrangement if it determines that there is a high secondary load and induces a low bracketing voltage on the bracket circuit arrangement if it determines that there is a low secondary load.
It is particularly advantageous that an optimal voltage value is made available in each case for an ignition spark by evaluating the rise time of the primary voltage. Furthermore, it is especially advantageous that the voltage reached in the primary winding after expiration of a specifiable time is able to be evaluated as a measure for the secondary load. Thus, one can react immediately to altered operational conditions.
Finally, the advantage of detecting the load acting on the secondary side is that this provides an indication of the available ignition voltage supply. Thus, for example, the rise time of the primary voltage or the attainment of a predetermined primary voltage value within a specifiable time can be evaluated as a measure for the ignition-voltage supply. Another advantage of this primary-side acquisition of the ignition-voltage supply on the secondary side of the ignition coil is that it can be drawn upon during normal operation of the engine for diagnostic evaluation, to recognize possible errors in the ignition system. Thus, a flat rise in the secondary voltage is an indication that a spark plug connector is exhibit

REFERENCES:
patent: 3749974 (1973-07-01), Kissel
patent: 4077379 (1978-03-01), Jundt et al.
patent: 4285323 (1981-08-01), Sugiura et al.
patent: 4413192 (1983-11-01), Niemetz
patent: 4912373 (1990-03-01), Moreau
patent: 4913123 (1990-04-01), DeBiasi et al.
patent: 5043633 (1991-08-01), Perkins
2244 Research Disclosure (1988) Aug., No. 292, New York, N.Y., USA.

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