US3209739A - Ignition systems - Google Patents

Description

United States Patent O 3,209,739 IGNITION SYSTEMS Norman Alfred Jukes, Walsall, England, assiguor to Joseph Lucas (Industries) Limited, Birmingham, England Filed Oct. 21, 1963, Ser. No. 317,653 Claims priority, application Great Britain, Oct. 30, 1962, 40,948/ 62 1 Claim. (Cl. 123-148) This invention relates to ignition systems for internal combustion engines and has for its object to provide an ignition system in a convenient form.

An ignition system according to the invention comprises means for supplying a single spark to each of the engine spark plugs in turn when the speed of the engine is above a predetermined value, and for supplying a plurality of sparks to each plug in turn when the speed of the engine is below the predetermined value.

The accompanying drawing is a circuit diagram illustrating one example of the invention.

Referring to the drawing, there are provided first and second lines 4, for connection to a D.C. source so as to be of relatively positive and negative polarity in use respectively. There is further provided an ignition transformer 6, the primary winding 7 of which has one end connected to the line 4 and its other end connected to the line 5 through the collector and emitter of an n-p-n transistor 8. The secondary winding 9 of the ignition transformer 6 -is connected to a distributor through which it is connected in use to the spark plugs of the engine in turn.

The base of the transistor 8 is connected through a resist-or 11 to the line 5, and is further connected to the cathode of a diode 12 the anode of which is connected to the line 4 through a resistor 13. A point intermediate the diode 12 and resistor 13 is connected through the anode and cathode of a .second diode 14 to the collector of a transistor 15 having its emitter connected to the line 5. The collector of the transistor 15 is further connected to the first terminal through the anode and cathode of a diode 16 and a resistor 17 in series. Moreover the diode 16 is bridged by the primary winding 18 of a second transformer 19. The secondary winding 21 of the transformer 19 has one end connected to the base of the transistor 15 and its other end connected to the line 5 through the cathode and anode of a diode 22. The diode 22 is bridged by a capacitor 23 which is in turn bridged by a resistor 24 in series with a generator winding 25.

The generator winding 25 is associated with means driven by the engine for producing in the winding 25 pulses of substantially square wave form. These pulses commence at the instants at which a spark is to be applied .to a plug, and are of width equal to several degrees of rotation of the crank shaft of the engine.

In operation, before a signal appears in the generator winding 25, the transistor 15 is non-conductive, and current flows through the resistor 13 and diode 12 to the base of .the transistor 8 to render the latter conductive. Current flow through the base of the transistor 8 to the 3,209,739 Patented Oct. 5, 1965 ice winding 18 is prevented by the diode 14. Current How through the first transistor causes energy to be stored in the winding 7.

When a pulse appears in the generator winding 25, the capacitor 23 is charged and current iiows through the winding 21 to the base of the transistor 15 to render it conductive. The coupling pr-ovided by the transformer 19 provides feed-back to the transistor 15, so that it becomes fully conductive in a short time. When the transistor 15 is conducting, current previously flowing to the base of the transistor 8 is diverted through the transistor 15, and the transistor 8 becomes non-conductive. The resultant collapse of flux in the core of the ignition transformer 6 causes a spark to be applied .to a spark plug of the engine.

When the transistor 15 is fully conductive, there is no further feed-back through the transformer 19 so that the transistor 15 is rendered nonconductive. The transistor 3 now conducts once more to store energy in the winding 7. However, the transistor 15 is prevented from becom- .ing conductive again for a predetermined period of time during which the back generated in the winding 21 is conducted through the diode 22. The period of time is determined by the discharge time constant of the primary circuit of the transformer 19.

If, after the end of said predetermined period of time, the pulse applied :to tbe generator winding 25 is Still present, the cycle described above will be repeated and a further spark will be applied to the same plug. The Width of the pulses supplied by the generator winding is so chosen with respect to the time of operation of the block ing oscillator constituted by the transistor 15 and transformer 19 that above a predetermined engine speed only one spark will be applied to each plug. However, below the predetermined speed two or more sparks will be applied to each plug. It will be appreciated that this arrangement is particularly advantageous in facilitating starting of an engine.

Having thus described my invention what I claim as new and desire to secure by Letter-s Patent is An ignition system for an internal combustion engine comprising in eombinationa generator winding, means driven by the engine for producing in said winding pulses the widths of which vary with engine speed, a blocking oscillator operable by said pulses, and means for supplying a single spark to the engine each time the oscillator is operated, the arrangement being such that when the engine speed is below a predetermined value, each pulse will be sufficiently wide to operate the oscillator more than once so that more than one spark is applied to each plug of the engine.

References Cited by the Examiner UNITED STATES PATENTS 1,550,146 8/25 Brockway 123-179 2,527,211 10/50 Brinson 123-148 2,668,271 2/54 Harmon l23-148 3,028,524 4/ 62 Esprui 123-148 RICHARD B. WILKINSON, Primary Examiner.

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