US3399658A - Spark ignition system - Google Patents

Description

Se t. 3, 1968 G 3,399,658

SPARK IGNITION SYSTEM F'iled April 26, 1966 IIJ wm T1U/ U BH E ml D FLU DISTRIBUTO 3,399658 SPARK IGNITION SYSTEM Brian Gilbert, Sutton Coldtield, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England, a British company Filed Apr. 26, 1966, Ser. No. 545,405 Claims priority, application Great Britain, May 5, 1965, 18,904/65 3 Claims. (Cl. 123148) ABSTRACT OF THE DISCLOSURE In a spark ignition system, current flow in a winding is interrupted by a semi-conductor switch, and the energy available as a result of the interruption is used to produce a spark. A feedback transformer is used to turn the switch oi rapidly, and in addition, a capacitor is provied which maintains the current flow in the winding until the switch is fully olf.

This invention relates to spark ignition systems for internal combustion engines.

A spark ignition system according to the invention comprises in combination a switch which can be turned on and off by signals applied to a control electrode forming part of the switch, means for applying signals to said control electrode to turn the switch on and ofl and thereby produce the required sparks, a transformer having a primary winding in series with said switch, and a secondary winding coupled to said triggering electrode, said transformer increasing the drive to said triggering electrode when the switch is turned off and so reducing the time taken to turn the said switch otf, and a capacitor connected in circuit with said switch in such a position that when the switch starts to turn otf current flowing through the switch is diverted through the capactor untl the capacitor is charged, the position of said capacitor being such that it does not dissipate energy stored in said primary winding.

In the accompanying drawings, FIGURES 1 and 2 are circuit diagrams illustrating two examples of the invention.

Referring to FIG.URE 1, there are providedterminals 11, 12 which in use are connected to the battery of a vehicle so as to be positive and negative, Conveniently, the positive terminal is earthed as indicated. Connected in series between theterminals 11, 12 is an engine-driveninterrupter 13, aresistor 14, and aninductor 15. Theinterrupter 13 is bridged by acapacitor 16, and a point intermediate theresistor 14 andinductor 15 is connected to theterminal 12 through parallel paths containing respectively a capacitor 17 and a resistor 18, and is also connected through the secondary winding 19 of a transformer 21 to the gate of a gate controlled switch 22. The winding 19 is bridged by aresistor 23.

The switch 22 is a device havng properties similar to a controlled rectifier, plus the additional property that it can be switched oif by a negative signal between its gate and cathode. The device 22 has its cathode con nected to theterminal 12, and its anode connectedto the terminal 11 through a series circuit including theprimary winding 20 of the transformer 21, theprimary winding 24 of an ignition transformer 25, and aresistor 26. The winding 20 and switch 22 are bridged by acapacitor 27, and thesecondary winding 28 of the transformer 25 is con nected through adistributor 29 to theplugs 30 of the engine in turn.

In operation, when theinterrupter 13 closes, current flows through theinterrupter 13, theresistor 14, the winding 19 andresistor 23 in parallel, and the gate and cathode of the switch 22 to turn the switch 22 on. Curnited States Patent C) rent can flow through the switch 22, the winding 20, the winding 24 and theresistor 26. At the same time, current flowing through theresistor 14 flows through theinductor 15, so that energy is being stored in theinductor 15 and thewindings 20 and 24. When theinterrupter 13 opens, the energy stored in theinductor 15 causes the gate of the switch 22 to become negative with respect to the cathode of the switch 22 and after a short delay due to the charge storage efiect of the switch 22, the switch 22 starts to turn 0. As the switch 22 starts to turn ot, current flowing in the winding 20 decreases, but the current flowing in the winding 24 does not decrease immediately because of the presence of thecapactor 27. However, the falling current in the winding 20 causes energy to be fed back to the gate of the switch 22 by way of the winding 19, and this additional energy assists in turning oi the switch 22. Thus, the switch 22 turns o rapidly, and the rapid fall in current in the winding 24 produces a spark at the appropriate plug. It should be noted that the point intermediate theresistor 14 andinductor 15 is driven negative by theinductor 15, but is driven positive by the transformer 21. Thus, large changes of voltage do not occur at this point, which is of considerable assistance where theinterrupter 13 is of limited voltage rating. It will be appreciated that theinterrupter 13 could be replaced by many other forms of engine-driven switch which need not be mechanical.

The purpose of theresistors 18, 23 is to minimize or prevent oscillations in the circuit including the gate of the switch 22. Thecapacitors 16, 17 limit the rate of rise of voltage across thenterrupter 13, thereby minimising arcing. Thecapacitor 27 in addition to its function already described, limits the voltage across the switch 22 to an acceptable value.

It should be noted that with thecapacitor 27 connected as shown, fall of current in thewinding 24 is delayed when the switch 22 starts to turn ofr without dissipation of the energy stored in the winding 20. The same eect can be achieved by having one side of thecapacitor 27 connected to a point intermediate thewindings 20, 24 and its other end connected to the terminal 11 either directly or through theresistor 26. However, thecapacitor 27 must not be connected directly across the anode and cathode of the switch 22, otherwise it dissipates energy stored in the winding 20. In a modification, a resistor is connected in series with thecapacitor 27 in order to protect the switch 22 in the event of it being switched on accidentally whilst thecapacitor 27 is charged to a high voltage. In another modification, theinductor 15 is not coupled to the gate circuit as indicated, but forms the primary winding of a transformer the secondary winding of which is coupled to the gate circuit in the same way as theinductor 15. This modification is particularly useful in negative earth systems.

Tuming now to the exarnple shown in FIGURE 2, the connections between thesupply terminals 11, 12 and the gate of the switch 22 are the same as those shown in FIGURE 1, and are designated by the same reference numerals. Moreover, the cathode of the switch 22 is con nected to theterminal 12, and the anode of the switch 22 is connected to one end of the winding 20 as before. However, the other end of thewinding 20 is connected to the terminal 11 through a diode 31, an inductor 32 and a resistor 33 in series. A point intermediate the winding 20 in FIGURE 1. However, the way in which the sparlgs are produced is somewh'at different, In order to understand the operation, assume that thecapacitor 34 is charged and the switch 22 is turned off. At the instant when the switch 22 is turned on, the capacitor 34 discharges through the winding 24 and the switch 22 and winding 20 to produce the required spark. At the same time, current flo'ws through the series circuit ncluding resistof33, inductor 32, diode 31, winding 20 and switch 22, so that energy is stored in inductor 32. When the switch 22 is turned ofi, the energy stored in inductor 32 is transferred to the capacitor 34, the winding 24 being bridged by the diode 35 while the capacitor 34 is being charged. The cycle is then rpeated to produce the next spark. It will be appre- Ciated that the transformer 21 assists in turning the switch 22 oif as in FIGURE 1, andthat the capacitor 34 is charged to a voltage considerably in excess of the battery voltage. The capacitor 34 aiso perforrns the function of thecapacitor 27 in FIGURE 1, in that it maintains current flow in the winding 32 until the switch 22 is fully off, whereupon the stored energy is transferred to capacitor In both FIGURE 1 and FIGURE 2, the transformer 21 assists in turning on the switch 22 rapidly as well as switching it oi. In FIGURE 1 this effect is not important, but it is of assistance in FIGURE 2, because the spark is produced when the switch 22 is turned on. Althoughin FIGURE 2 the spark is not produced when the switch 22 is turned oif, it is still of importance that the switch 22 should be turned off rapidly, so that maximum energy is transferred from the inductor 32 to the capacitor 34, with a minimum of dissipation in switch 22.

In both examples, the switch 22 could be replaced by other forms of switch the conduction of which can be contro1ied by signals applied to a control eiectrode. For example, the switch 22 could be replaced by a transistor. A transistor does not of course require a bias to turn it oif, it being only necessary to remove the bias which turns the transistor on. However, for rapid switching, it is preferable not to rely merely on removai of a bias from the base of a transistor, but to provide a definite signal to bias the transistor to nonconduction. The circuit components would of course be chosen to provide a bias to the transistor as long as the transistor is required to conduet.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. 1 spa rlg ignition system for an internal cornbustion engine, comprising in combination a D.C. source, a series circuit connected across said D.C. source and including a storage winding, the prirnary winding of a feedback transformer and a semi-conductor switch which can be turned on and otf by.signais applied to a controi elec trede forming part of the switch, means operable in timed relationshipto the engine for applying signals to said control electrode to turn said switch on and to turn said switch off,a secondry winding on said feedback transforrner, mens coupling said secondary winding to said control electrode whereby said feedback transformer assists rapid turn-oi of said switch, a capacitor, means coupling said capacitor in the circuit whereby said capacitor maintains current flow in said storage winding when said switch starts to turn otf untilsaidswitch is fnlly off, said capacitor having no effect on said feedback transformer but ensuring that current flow in said storage winding is interrupted rapidly, and meansutilising the energy available when the current flow in said storage winding is interrupted to produce sparks at the p1ugs of the engine in turn in timed relationship to the engine.

2. A system as ciaimed in claim 1 including an ignition transformer having a secondry winding coupled to said piugs in turn through a distributor and a primary winding constituted by said storage winding, each spark being produced when the switch is fully turned off.

3. A system asc1airned in claim 1 including a diode in said series circuit positioned between said storage winding and said prirnary winding, said capacitor being connected across the series circuit of said primary winding and said switch in series with the primary winding of an ignition transformer the secondary winding of which is connected to the plugs of the engine in turn through a distributor, the energy storcd in the storage inductor being transferred to the capacitor when said switch is fully ofi and being retained by said diode, and each spark being produced by discharge of the capacitor when said switch is turned on.

References Cited UNITED STATES PATENTS 7/ 1966 Stuermer. 1/1967 Quinn.

RALPH BLAKESLEE, Prmary Examiner.

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