High-voltage switch

Internal-combustion engines – High tension ignition system – Power supply – ignition coil primary – and interrupter element...

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Details

F02P 312

Patent

active

050443496

DESCRIPTION:

BRIEF SUMMARY
PRIOR ART

The invention is directed to a voltage controlled electronic high-voltage switch, particularly for ignition systems of internal combustion engines, which at a given voltage level is triggered into the conductive state.
It is known that spark plugs in internal combustion engines become carbon-fouled particularly during cold starting. Carbon fouling also occurs if spark plugs with an excessive heat value are used in an internal combustion engine. The layer of soot on a spark plug leads to a shunt which causes an energy discharge during the rise in the ignition voltage at the spark plug. Accordingly, the ignition voltage is often not achieved, so that misfiring occurs.
Booster or series connected spark gaps in the ignition systems which comprise electrodes fused into a glass bulb and provide for a spark at a predetermined voltage serve to solve this problem. But a disadvantage of these booster gaps consists in that the ignition voltage of the booster gap changes from one spark to another and during the life of the booster gaps. This is due to the erosion of the electrodes and to the fact that the gas surrounding the electrodes changes over time.


SUMMARY OF THE INVENTION

The high voltage switch according to the invention is assembled of a cascade of thyristors or silicon controlled rectifiers each having its gate connected to its cathode to act as a breakdown diode. The gate-cathode connection is provided within the chip of each thyristor.
In contrast to the prior art, the high-voltage switch according to the invention has the advantage that the ignition voltage can be preselected in a very accurate manner and in that the influence of shunts on the spark plug are practically eliminated. Due to the voltage-controlled, electronic high-voltage switching cascade, the ignition voltage is only applied to the spark plug after a selectable, high voltage of e.g. 20 kV. Accordingly, shunts cannot take effect during the rise in the ignition voltage. Also, spark plugs with excessive heat values fire readily even during cold starting.
The use of break-down or state-changing diode cascades as high-voltage switching elements is particularly advantageous. Ten to fifty of these diodes can be stacked one on top of the other, e.g. integrated in the connector of a spark plug, depending on the dielectric strength in individual state-changing diodes and depending on the desired ignition voltage. At a blocking voltage of 1 kV per diode and an ignition voltage of 20 kV, twenty of these components can consequently be connected in series.
An embodiment example of the invention is explained in more detail in the following description with the aid of the drawing


BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a basic wiring diagram of an ignition system including the high-voltage switches according to the invention; and
FIG. 2 shows the voltage curve at the spark plug and at the secondary winding of an ignition coil of the ignition system according to FIG. 1.


DESCRIPTION OF THE PREFERRED EMBODIMENTS

The high-voltage switch is generally usable in connection with high-voltage consumers. The use of the high-voltage switch according to the invention in an ignition system of a motor vehicle is described in the following by way of example.
FIG. 1 shows an ignition coil 1 whose primary winding 2 is connected via a control transistor 3 to a voltage supply U.sub.B, e.g. the battery of a motor vehicle, not shown. The control transistor 3 is driven in a known manner by a non-illustrated control device via a control terminal 4.
The secondary winding 5 of the ignition coil 1 is connected with a distributor 6 which drives the individual high-voltage consumers, in this instance the spark plugs 7 of a motor vehicle. A voltage-controlled, electronic high-voltage switching unit which is preferably constructed as a state-changing or break-down diode cascade 8 is arranged immediately prior to the individual spark plugs, only one of which is shown here for the sake of simplicity.
The state-changing diodes are two-pole silicon controlled rec

REFERENCES:
patent: 4138710 (1979-02-01), Tsukuru
patent: 4411247 (1983-10-01), Kunita et al.
patent: 4463744 (1984-08-01), Tanaka et al.
patent: 4653460 (1987-03-01), Ooyabu et al.

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