Internal combustion engine spark ignition apparatus producing an oscillating discharge current of a capacitor

Claim 3

Am apparatus for producing spark ignition of an internal combustion engine, comprising an ignition coil having primary and secondary windings, a capacitor connected in electrical circuit with the primary winding, voltage generating means for receiving a supply voltage and adapted to charge the capacitor to a voltage greater than said supply voltage, a thyristor connected in said circuit and arranged so that when fired to a conductive state the capacitor discharges in an oscillatory manner through the thyristor and the secondary winding, and control circuit means adapted to apply to the gate of the thyristor a firing signal to render the thyristor conductive for a period sufficient for a plurality of oscillations of the capacitor discharge current to pass through said primary winding, and means for inhibiting said voltage generating means from charging the capacitor during the discharge thereof produced by firing of the thyristor.

Claim 4

Am apparatus for producing spark ignition of an internal combustion engine, comprising an ignition coil having primary and secondary windings, a capacitor connected in electrical circuit with the primary winding, voltage generating means for receiving a supply voltage and adapted to charge the capacitor to a voltage greater than said supply voltage, a thyristor connected in said circuit and arranged so that when fired to a conductive state the capacitor discharges in an oscillatory manner through the thyristor and the secondary winding, and control circuit means adapted to apply to the gate of the thyristor a firing signal to render the thyristor conductive for a period sufficient for a plurality of oscillations of the capacitor discharge current to pass through said primary winding, and means for inhibiting said voltage generating means from charging the capacitor during the discharge thereof produced by firing of the thyristor.

Claim 5

An apparatus according to claim 2 wherein the voltage generating means comprises a transistor oscillator for producing an oscillating current from an input direct current, a step up transformer having a primary winding connected to receive said alternating current and having a secondary winding connected to a rectifier for producing a rectified direct current, said capacitor being connected to be charged by said rectified current.

Claim 6

An apparatus according to claim 3 wherein the frequency of oscillation of the transistor oscillator is an inverse function of the inductance presented by the primary coil of the transformer, and the secondary coil of the transformer is connected so that upon said firing of the thyristor the coil is shorted, the construction of the transformer being such that the mutual inductance of the primary and secondary coils reduces substantially upon said shorting of the secondary coil whereby to increase the frequency of oscillation of said transistor oscillator in such a manner as to decrease the electrical power transferred from said primary to said secondary coil, whereby to inhibit operation of the voltage generating means during said firing of the thyristor.

Claim 7

An apparatus according to claim 3 wherein said oscillator includes a bias current supply means adapted to supply to transistors of the oscillator a direct current to bias the transistors into operation, and means for preventing the supply of said bias current to the transistors in response to said firing of the thyristor whereby to inhibit operation of the oscillator during said firing of the thyristor.

Claim 8

An apparatus according to claim 4 or 5 wherein the transistor oscillator includes first and second complementary Darlington pairs of transistors each connected to a respective portion of said primary coil, a pick-up coil being connected to provide positive feedback from the primary coil to the translators.

Claim 9

An apparatus according to claim 6 including means defining a bias current supply path for said transistors, and a current by-pass path extending from said bias current supply path to the said circuit including said thyristor, the arrangement being such that upon firing of the thyristor, the bias current preferentially flows through the by-pass path rather than to the transistors whereby to inhibit operation of the oscillator during firing of the thyristor.

Claim 11

An apparatus according to claim 1 wherein said control circuit means includes an input for receiving electrical input pulses having a frequency indicative of engine speed and a phase indicative of the desired timing of spark ignition, and means responsive to said electrical pulses and arranged to generate firing pulses for the thyristor in such a manner that the duration of the firing pulses decreases with an increase in the frequency of the input pulses.

Claim 12

An apparatus as claimed in claim 1 installed on an internal combustion engine.