US3515937A

US3515937A - Spark ignition apparatus

Info

Publication number: US3515937A
Application number: US773568A
Authority: US
Inventors: Keith Douglas Collins
Original assignee: Rotax Ltd
Current assignee: Lucas Support Services Ltd
Priority date: 1967-11-21
Filing date: 1968-11-05
Publication date: 1970-06-02
Anticipated expiration: 1987-06-02
Also published as: DE1808737A1; FR1592656A; GB1239756A

Description

June 2 1970 K. coLLjN -3, 5 ,5 ,93 7

SPARK IGNITION APPARATUS:

Filed Nov. 5, 1968 INVEN OR.

M94 M W BY/M V ATTORNEYJ US. Cl. 315209 7 Claims ABSTRACT OF THE DISCLOSURE A spark ignition apparatus for supplyinghigh voltage pulses to an ignition plug and comprising capacitors, a pair of rectifiers, through which said capacitors are charged respectively, a pair of transformers for supplying alternating current to the rectifiers, a resistor through which the primary windings of the transformers can be connected to a source of AC. supply, means for connecting said first capacitor to a pair of output terminals, triggerable means for connecting said second capacitor to said terminals and means for supplying a triggering pulse to said triggerable means at a predetermined time after capacitor has been connected to said output terminals.

This invention relates to spark ignition apparatus for supplying high voltage pulses to an ignition plug and has for its object to provide such apparatus in a form in which a first voltage pulse is applied to the plug to condition same and then a second voltage pulse is applied to the plug to produce a discharge.

According to the invention spark ignition apparatus of the kind specified comprises in combination, first and second capacitors, a pair of rectifier means through which said capacitors are charged respectively, a pair of transformers for supplying electric current to the rectifier means respectively, a resistor through which the primary windings of said transformers can be connected to a source of AC. supply, means for connecting said first capacitor to a pair of output terminals so that the capacitor can be discharged through an ignition plug connected across said terminals when the voltage across said first capacitor attains a predetermined value, triggerable means for connecting said second capacitor to said pair of output terminals, and means for supplying a triggering pulse to said triggerable means at a predetermined time after said first said capacitor has been connected to said output terminals.

One example of a spark ignition apparatus in accordance with the invention will now be described with reference to the accompanying circuit diagram. Referring to this diagram there is provided a pair of supply terminals for connection to a source of AC. supply 10. One of the supply terminals is connected to one end of the primary winding of a transformer T1 the other end of which is connected to one end of the primary winding of a further transformer T2. The other end of the primary winding of transformer T2 is connected to a fixed contact of a selector switch S1a the wiper of which is connected to the aforesaid one supply terminal. The other supply terminal is connected to the wiper of a further selector switch Slb the wipers of the two selector switches being ganged together. The selector switches are provided with three sets of fixed contacts and the outermost pair of contacts of switch Slb are bridged by a resistor R1. The fixed contact of selector switch Slb corresponding to the fixed contact of selector switch Sla which is connected to the primary winding of transformer T2, is connected by way of resistor R2 to a point intermediate the primary windings of the transformers. Furthermore, a further Patent O Patented June 2, 1970 transformer T3 is provided and one end of the primary winding thereof is connected to a point intermediate resistors R1 and R2 and the other end of the primary winding is connected to the end of the primary winding of transformer T2 which is connected to selector switch Sla.

The secondary windings of the transformers T1 and T2 are connected to full wave rectifier combinations D1D4, DS-D8, respectively and the negative output terminals of the two rectifier combinations are connected to an earth line referenced 11 by way of resistors R14 and R15 respectively. The positive output terminal of the rectifier combination D1-D4 is connected to one side of a capacitor C1 and the other side of the capacitor is connected to the earth line 11. In parallel with this capacitor is a resistor R3. The positive terminal of the rectifier combination Dl-D4 is also connected to one electrode of a spark discharge tube V1 and the other electrode of this tube is connected to an output terminal 12 between which and a further output terminal 13 connected to the earth line 11, is an ignition plug P1. 'In parallel with this plug is a resistor R13. A similar circuit is connected to the positive output terminal of the rectifier combination D5-D8 and in this case the capacitor resistor and discharge tube are referenced C2, R4 and V2 respectively.

The secondary winding of transformer T3 has one end thereof connected to the anode of a diode rectifier D9, the cathode of which is connected to one end of a resistor R5 having its other end connected to one terminal of a capacitor C3. The other terminal of the capacitor is con nected to the other end of the secondary winding of the transformer T3. A point intermediate the resistor R5 and the capacitor C3 is connected to one end of a resistor R11 the other end of which is connected to one end of the primary winding of a further transformer T4. The other end of the primary winding of this transformer is connected to the anode of a thyristor SCRZ the cathode of which is connected to a return line 14 which is con nected to the secondary winding of the transformer T3. The primary winding of the transformer T4 is bridged by a diode rectifier D11. One end of the secondary winding of the transformer T4 is connected to the output terminal 12 whilst the other end is connected by way of a resistor R12 to a trigger electrode of the discharge tube V2. The trigger electrode is conveniently defined by a metallic band encircling the tube but insulated from the electrodes thereof.

Connected to a point intermediate the resistors R5 and R11 is the anode of a thyristor SCR1 and the cathode of this thyristor is connected by way of a resistor R6 and a capacitor C4 in series to the return line 14. The cathode of the thyristor SCR1 is also connected to the return line 14 by way of resistors R7 and R8 in series and a point intermediate the resistors R7 and R8 is connected to the return line 14 by way of a capacitor C5. A point intermediate the resistor R6 and the capacitor C4 is connected to the anode of a diode rectifier D10 the cathode of which is connected to the emitter terminal of a p-n-p type transistor TR1. The base of this transistor is connected to a point intermediate the resistors R7 and R8 and this point is also connected to the collector terminal of an n-p-n type transistor TR2. The base of the transistor TR2 is connected to the collector terminal of the transistor TRl whilst the emitter thereof is connected to the return line 14 by way of resistors R9 and R10 in series. The point intermediate these resistors is connected to the trigger electrode of the thyristor SCRZ. The trigger electrode of the thyristor SCR1 is connected to one end of the secondary winding of a current transformer CT1 the other end of which is connected to the cathode of the thyristor.

The operation of the apparatus will now be described assuming first of all that the selector switches are in the po'sition'in which they are indicated in the accompanying drawings. In this position only the primary winding of transformer T1 is connected to the source of supply and this by way of resistors R1 and R2 in series. With the terminals 10 connected to the source of supply capacitor C1 is gradually charged until it attains a voltage sufficient to cause breakdown of the discharge tube V1 and when this occurs the Capacitor is discharged through the sparking plug represented by P1 and conveniently this plug is of the surface discharge type. As soon as the capacitor C1 is discharged the discharge tube V1 ceases to conduct and the capacitor is recharged so that a further spark occurs after a predetermined time which is generally controlled by the values of the resistors R1 and R2 in the primary circuit of the transformer.

When the selector switches are switched to their alternative positions the primary winding of transformer T3 is directly connected across the supply terminal 10 whilst the primary winding of the transformers T1 and T2 are connected in parallel with each other and in series with the supply terminals by way of resistor R2. Charging and discharging of capacitor C1 takes place as described above under the control of the discharge tube V1. Whilst capacitor C1 is being charged capacitor C2 is similarly charged and by virtue of the resistor R2 the voltages across the two capacitors is substantially equal this is of course assuming that the tranformers T1 and T2 have the same turns ratio. Capacitor C2 does not however discharge automatically by way of discharge tube V2 since the latter requires a triggering pulse to be supplied thereto before conduction occurs. However, when the triggering pulse is supplied capacitor C2 is discharged through the spark plug and it is arranged that this discharge occurs at a predetermined time after the discharge of capacitor C1.

In order to supply the triggering pulse to the discharge tube V2 the circuit associated with transformer T3 is provided. When the primary winding of the transformer T3 is connected to the supply terminals 10 capacitor C3 is charged to a predetermined value but thyristors SCR1 and SCR2 are in their non-conducting state so that there is no flow of current in the primary of transformer T4. However, when capacitor C1 is discharged a voltage pulse appears at the secondary winding of the current transformer CT1 and this causes conduction of thyristor SCR1. Resistors R7 and R8 act to maintain current flow through the thyristor SCR1 so that it does not switch off as soon as the triggering pulse disappears. With thyristor SCR1 conducting C4 gradually charges by way of resistor R6 and at a predetermined voltage which is set by the values of the resistors R7 and R8, transistors TR1 and TR2 are rendered conductive and a voltage pulse is applied to the thyristor SCR2. As soon as thyristor SCR2 conducts capacitor C3 is discharged through the primary winding of transformer T4 and a high voltage pulse appears at the secondary winding thereof. This pulse is applied to the trigger electrode of the discharge tube V2 and causes conduction thereof to effect discharge of capacitor C2 through the spark plug.

By careful choice of the values of resistor R6 and capacitor C4 any predetermined time delay can be obtained. It is desirable that the delay should be less than one millisecond and in a practical circuit a nominal delay of 900 microseconds has been obtained with a stability better than 2.5%.

Diode D10 in the circuit associated with transformer T3 is provided to limit the reverse base emitter voltage which can be applied to the transistor TR1, and diode D11 connected across the primary winding of transformer T4 suppresses the reverse voltage which can appear across this primary winding as the flux in the core collapses. In this manner thyristor SCR2 is protected. Capacitor C acts to isolate the transistors TR1 and TR2 from the transient which is injected into the circuit by the current transformer and in this way premature triggering of the transistor combination'is preventedl I Resistor R13 which is connected across the

output terminal

12 and 13 acts to limit the voltage which can be attained across capacitor C1 and C2 in the event that the spark plug is removed and resistors R3 and R4 act to discharge capacitors C1 and C2 respectively when the apparatus is disconnected from the source of supply.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is: s 1. A spark ignition apparatus for supplying a first voltage pulse to an ignition plug and a second voltage pulse to the same plug and comprising in combination, first and second capacitors, one plate of each of said capacitors being connected to a common output terminal for connection to one terminal of theignition plug, a pair of rectifier means through 'which said capacitors are charged respectively, a pair of transformers for supplying alternating electric current to the rectifier means respectively, a resistor through which the primary windings of said transformers can be connected to a source of AC. supply, means for connecting the other plate of said first capacitor to a second output terminal for connection to the other terminal of the ignitionplug, so that the first capacitor can be discharged through the ignition plug when the voltage across said first capacitor attains a predetermined value, triggerable means for connecting the other plate of said second capacitor to said second output terminal, and means for supplying a triggering pulse to said triggerable means at a predetermined time after said first capacitor has been connected to said second output terminal.

2. A spark ignition apparatus as claimed in claim 1 including third rectifier means and a third transformer for supplying current thereto, said third transformer and said third rectifier means forming a source of DC. supply for said triggerable means.

13. A spark ignition apparatus as claimed in claim 2 in which said triggerable means includes a third capacitor, a thyristor through which said third capacitor is charged from said D.C. supply, means for supplying a firing pulse to said thyristor when the first capacitor is discharged, and means operable when the voltage across said third capacitor attains a predetermined value to supply a triggering pulse to said triggerable means.

4. A spark ignition apparatus as claimed in claim 3 in which the means operable to supply a triggering pulse to the triggerable means comprises a fourth capacitor arranged to be charged from said source of DC. supply a third transformer having its primary winding connected in series with said fourth capacitor and a second thyristor, the transformer having its secondary winding connected to said triggerable means, and a voltage sensing circuit responsive to the voltage developed across said third capacitor, said voltage sensing circuit being arranged to supply a firing pulse to said second thyristor when the voltage across said third capacitor attains a predetermined value, the second thyristor effecting the discharge of said fourth capacitor through the primary winding of the third transformer thereby causing a voltage to be induced in the secondary winding thereof.

5. A spark ignition apparatus as claimed in claim 4 in which said third capacitor is charged from the terminals of the fourth capacitor so that discharge of the fourth capacitor renders both of said thyristors nonconductive.

6. A spark apparatus as claimed in claim'5 in" which the means for supplying a firing pulse to said first thyristor comprises a current transformer through the primary of which passes the current flowing to the output terminals from the first capacitori 7. A spark ignition apparatus as claimed in claim 6 in which said triggerable means and said means for connecting the first capacitor to the pair of output terminals comprises a pair of spark discharge tubes, the

tube which constitutes the triggerable means being pro- JOHN W. HUCKERT, Primary Examiner vided with a trigger electrode A. I. JAMES, Assistant Examiner References Cited UNITED STATES PATENTS US. 01. X.R.

3,028,524 4/1962 0 315214 3,127,540 3/1964 Collins 315-180 3,202,874 8/ 1965 Bardocz 315232 3,418,990 12/1968 Lindell 123-148