US3868938A

US3868938A - Transistor ignition system

Info

Publication number: US3868938A
Application number: US470675A
Authority: US
Inventors: Alan Neville Trass
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-02-11
Filing date: 1974-05-16
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04

Abstract

A transistor ignition system in which the timing of pulses delivered to an ignition coil is controlled by means of a disc rotatable between a light source and a photoelectric device the photoelectric device being connected to the ignition coil through a transistorized amplifier circuit in which the amplifier circuit is such as to produce an oscillatory voltage and thus a shower of sparks at the sparking plugs of the engine at least at low speeds. It is preferred that the oscillatory voltage is produced by a Darlington pair in the circuit.

Description

United States Patent [191 Trass 1 TRANSISTOR IGNITION SYSTEM [76] Inventor: Alan Neville Trass, 44 Moyran Pile-2232, Grays Point, New South Wales, Australia [22] Filed: May 16, 1974 [21] Appl. No.: 470,675

Related U.S. Application Data [63] Continuation-impart of Ser. No. 220,085, Jan. 24,

1972. abandoned.

[30] Foreign Application Priority Data Feb. 11, 1971 Great Britain 4460/71 Jan. 20. 1972 Australia 38106/72 [52] U.S. Cl 123/148 E, 315/209 T [51] Int. Cl. F02p 1/00 [58] Field of Search 123/148 E; 315/209 T [56] References Cited UNITED STATES PATENTS Ford 123/148 E 1 Mar. 4, 1975 10/1971 Gilbert 123/148 E 3,682,150 8/1972 Ford 123/148 E Primary Examiner-Manuel A. Antonakas Attorney, Agent,.or Firm wenderoth, Lind & Ponack [57] ABSTRACT A transistor ignition system in which the timing of pulses delivered to an ignition coil is controlled by means of a disc rotatable between a light source and a photoelectric device the photoelectric device being connected to the ignition coil through a transistorized amplifier circuit in which the amplifier circuit is such as to produce an oscillatory voltage and thus a shower of sparks at the sparking plugs of the engine at least at low speeds. It is preferred that the oscillatory voltage is produced by a Darlington pair in the circuit.

8 Claims, 8 Drawing Figures EATENTED 4 W5 SmLI 1 [ii 2 Zizz TO BASE 92 P'ATENTED 41975 SHEET 2 0f 2 FIG.30L

FIGJ

TRANSISTOR IGNITION SYSTEM This is a continuation-in-part of application Ser. No. 220,085, filed Jan. 24, I972, now abandoned.

The present invention relates to a transistor ignition system for an internal combustion engine of the kind (hereinafter referred to as the kind set forth") in which the timing of pulses delivered to an ignition coil is controlled by means of a disc rotatable between a light source and a photoelectric device the photoelectric device being connected to the ignition coil through a transistorized amplifier circuit.

The principal object of the invention is to provide an ignition system of the type referred to having a transistorized amplifier such that an oscillatory voltage is generated which causes the production of a shower of sparks at least during starting and low speed conditions. It has been found that the production of a shower of sparks on each occasion that a sparking plug is tired, rather than a single spark, tends to make for easier starting of the engine. It is also found that the engine requires less choke when cold and idles and runs more smoothly with a diminished tendency to stall. Provision may be made for the production of a shower of sparks at greater engine rpm should this be desired.

The invention may be constructed in preferred forms which provide additional advantages which are pointed out below in connection with preferred embodiments of the invention.

The invention consists in a transistor ignition system of the kind set forth wherein the transistorized amplifier circuit includes circuit means adapted and ar ranged to produce an oscillatory voltage at least under starting and low speed conditions whereby a shower of sparks is produced at each sparking plug on ignition. It is preferred that the said circuit means is constituted by a Darlington pair.

In order that the invention may be better understood and put into practice a preferred form thereof is hereinafter described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a circuit diagram of a transistorized amplifier for use in an ignition system for an internal combustion engine.

FIG. 2 shows an alternative circuit configuration for the left hand end of the circuit shown in FIG. 1 which is suitable for a system in which current flows in the ignition system when light is cut off from the photo transistor.

FIGS. 3 and 3a are a plan and elevation respectively showing a sensor and trigger plate assembly for use in connection with the invention.

FIGS. 4 and 4a are a plan and elevation respectively of a trigger plate having both dwell compensation and advance and retard mechanisms associated with it.

FIG. 5 is a plan view of a trigger plate for use with a light off-coil on sensor circuit.

FIG. 6 is a sectional view of the sensor unit.

In the circuit shown in FIG. 1 a stabilized voltage for the photo transistor Q1 is obtained via a dropping resistor R8 in series with a zener diode 21 across the supply. The voltage at the junction of R1 and R8 is preferably between 2.1 and 2.2 volts. This arrangement provides an extremely stable supply for the photo transistor as well as absorbing any induced spikes in the supply either from coil breakdown or other sources such as generators, fuel pumps, horns, or electric motors, all being effectively suppressed. This provides more than adequate radio suppression for the system. A dropping and limiting resistor R2 connects the supply to photo transistor Q1.

The light'source L is operated from the supply voltage available via dropping resistor Rl, to give maximum sensitivity to the photo transistor Q1. When light passes to the photo transistor Q1 its resistance will drop sharply to allow a voltage to be applied via base resistor R3 to the has of Darlington pair 02; 02 will therefore be switched on thus allowing the base of 03, via base limiting resistor O6, to be connected to earth through the collector and emitter of 02 plus emitter resistor R5. As Q3 is a PNP transistor this will cause it to be switched on allowing current flow to the ignition coil and capacitor C1 (if fitted). The magnetic flux builds up in the coil and the capacitor C1 commences charging. Interruption of the light beam causes the resistance of O1 to start to increase. At a critical point the voltage applied to the base of O2 is insufficient to hold it switched on. This also causes Q3 to be switched off thus preventing further current flowing to the coil and capacitor allowing the stored magnetic field to start to collapse. This is assisted by the capacitor and the resultant spark is generated for distribution to the appropriate cylinder. Zener diode Z2 protects transistor Q3 from excessive voltages which otherwise may be developed during coil breakdown.

The complete ignition system is, as shown, unshielded and utilizes unshielded cables. When the coil field collapses, the surges associated therewith act as positive feedback and actually drive Q2 back to a sufficient level whereby the transistor is again conductive. This allows current to flow once more to the ingition coil. Once the surge from the coil passes, the transistor Q2, and consequently Q3, again become nonconductive, since the amount of light impinging O1 is still decreasing. The coil field again collapses, producing further sparks, and the associated surges may once more drive the Darlington amplifier into conduction. This cycle is repeated although in a damped manner, since the light illuminating the photo-transistor is insufficient to maintain the transistor in its conductive state and due the system losses. This obviously occurs only at low frequency since the system response is limited. The following resistor values may be used: R2 3.9K; R3= 2.2K; R4 27K and R8 3.3K.

The function of the resistor R1 is to reduce the supply voltage so that the light source Lpreferably an incandescent lamp is operated at well below its rated voltage to lengthen its life and also to produce light of a frequency to which the photo transistor is most sensitive. In some circumstances it will be possible to choose a lamp the rated voltage of which is such that the use of R1 is unnecessary.

The circuit described above can be varied in operation to enable a spark to be generated when the sensor is switched on rather than off. This variation is shown in FIG. 2. The difference in operation is that the sensor photo transistor when energized shorts the available voltage to earth thus preventing Q2 from switching on. When it is de-energized the voltage being absorbed by R2 is now available to the base of 02 via R3. The resistance of R4 in each case is high compared with the base to emitter resistance of 02 so there is no effect on the operation of Q2 except to provide thermal stability to that transistor and a small amount of reverse bias to Q1. Note however, that R4 governs the rate of regener' cillation decreases due to the limited high frequency characteristics. This oscillation completely disappears at approximately idle rpm in the embodiment described.

If it is desired to extend the production of an oscillatory voltage, and thus a shower of sparks, to higher speeds this may be done by increasing the value of R4. R4 may be a variable resistor and a manual control provided for adjusting its value. The same result may be achieved by placing a resistor across Q1.

The circuit may be modified to provide for the use of light sensitive devices other than photo transistors and light sources other than incandescent bulbs.

An output suitable for operating a tachometor or electric fuel injection system is available from the terminal T at the junction of R6 and R7.

The presence of the capacitor C1 will depend on the type of ignition coil used, its normal value will lie between 0.2 and 0.5 ufds.

In order to interrupt the light source L periodically the arrangement shown in FIGS. 3 and 3a is used. A trigger plate 10 having in it slots 11 is arranged on the distributor shaft 12 thus taking the place of the normal make and break mechanism. The number and size of the slots 11 depends on the number of cylinders in the engine and its characteristics.

A sensor unit 13 shown in section in FIG. 6 mounted at one side of the plate 11 contains both the light source L in the form of an incandescent bulb and the photo transistor Q1. These are arranged so that a very narrow beam of light is directed onto the photo transistor and the apertures 16 through which the light shines are shaped to give maximum cut-off rate when the beam is interrupted during rotation of the plate 10, the apertures being preferably square or rectangular. The fact that the light source and the photo transistor are arranged in the same housing ensures that they remain accurately aligned and simplifies installation.

The effectiveness of the circuit shown in FIG. 1 at high speeds is enhanced by the provision on the trigger plate of an advance and retard mechanism and also a dwell compensator, the latter acting to increase the dwell angle with increasing engine speed. A suitable arrangement is indicated in FIGS. 4 and 4a in which an upper plate 15 and a lower plate 16 are provided with an appropriate number of slots for example four. The angular position of the upper plate 15 is controlled by a dwell compensator mechanism 17 and that of the lower plate 16 by an advance and retard mechanism 18. Details of these mechanisms may be conventional each consisting of a centrifugal device which acts to rotate the plate in relation to the shaft 12 to an extent depending on the rate of rotation of the shaft. The effect of movement ofthe plate 18 is to advance the spark as the speed of rotation increases. Rotation of the plate 17 controls the effective size of the slots in the plates and then the dwell angle. the arrangement being such that at idling speeds the width of the slots is a minimum, the

width increasing as engine speed increases. The dwell compensator or advance/retard mechanisms may be used individually as required in the installation.

For use with the modified circuit shown in FIG. 2 a plate 19 (FIG. 5) is used having projecting tongues 20 in place'of the slots 11. These tongues act to cut off the light at predetermined intervals to produce sparks at the sparking plugs of the ignition system.

The system described may be readily incorporated in existing vehicles by replacing the contact breaker points by the trigger plate and sensor assembly which can be readily constructed to fit within a standard distributor. The circuit described above may be incorporated in a suitable assembly with the necessary heat sink for Q3 and zener diode and mounted in a vehicle to which the system is to be applied.

What is claimed is:

1. A transistor ignition system, comprising:

means for controlling the timing of pulses delivered to an ignition coil; and

a transistor amplifier .circuit coupled between said controlling means-and said ignition coil and having positive feedback means coupled thereto for causing said amplifier circuit to produce an oscillatory voltage when the rate at which pulses are delivered to said ignition coil is relatively low and producing only single voltage pulses when said rate is relatively high, said positive feedback being provided by breakdown of the field of said coil, whereby a shower of sparks is produced at the spark plugs of the engine under starting and low speed conditions.

2. A transistorized ignition system as recited in claim 1 wherein said timing control means is comprised of a disc rotatable between a light source and a photoelectric device, the photoelectric device being connected to the ignition coil through said transistorized amplifier circuit, and wherein said transistorized amplifier circuit is comprised of means adapted to produce an oscillatory voltage under starting and low speed conditions whereby a shower of sparks is produced at each sparking plug on ignition.

3. A system as claimed in claim 2 wherein said means for producing an oscillatory voltage consists of a Bar lington pair connected to said photoelectric device, and said transistorized amplifier circuit further comprises an output transistor to which said Darlington pair is connected and which in turn is coupled to said ignition coil, said positive feedback being provided to the base of said Darlington pair.

4. A system as claimed in claim 2 wherein said photoelectric device is a photo transistor, and means coupled to said photo transistor for feeding said photo transistor with a stabilized voltage and comprising a dropping resistor copuled in series with said photo transistor and a Zener diode coupled in parallel across said photo transistor from between the dropping resistor and the photo transistor, whereby any spurious voltage spikes entering the system are suppressed.

5. A system as claimed in claim 2 further comprising a single casing having said light source and said photoelectric device mounted therein in fixed space relationship, said casing having space therethrough between the photoelectric device and the light source through which said disc is rotatable, said casing having a size and shape such that it can be mounted in a conventional distributor.

6. A system as claimed in claim 2 in which said photoelectric device is coupled to said amplifier circuit for causing a spark to be produced when said light from said source is blocked from reaching said photoelectric device.

7. A system as claimed in claim 2 wherein said disc has incorporated therewith means for advancing or retarding the delivery of the light to the photoelectric device in accordance with the speed of the engine and means for varying the dwell angle of the system in accordance with the speed of the engine.

8. A transistorized ignition system comprising a light source and a photoelectric device, a slotted disc rotatable between said light source and said photoelectric device for periodically allowing light to reach the photoelectric device between periods during which the light is blocked from reaching the photoelectric device, the rate of rotation being proportional to the speed of 6 the engine for which ignition is being supplied, an ignition coil, and a transistorized amplifier circuit coupled between said photoelectric device and said ignition coil, and comprising a high gain amplifier having an input coupled to said photoelectric device for receiving pulses from said photoelectric device in proportion to the speed of said disc, an output transistor to which the output of said high gain amplifier is coupled and having the output coupled to said ignition coil, and positive feedback circuit means coupled to said high gain amplifier for causing said amplifier to produce an oscillatory voltage when the rate at which light is periodically reaching said photoelectric device is relatively low and for producing only single voltage pulses when said rate is relatively high, whereby a shower of sparks is produced at the spark plugs of the engine under starting and low speed conditions.

Claims

1. A transistor ignition system, comprising: means for controlling the timing of pulses delivered to an ignition coil; and a transistor amplifier circuit coupled between said controlling means and said ignition coil and having positive feedback means coupled thereto for causing said amplifier circuit to produce an oscillatory voltage when the rate at which pulses are delivered to said ignition coil is relatively low and producing only single voltage pulses when said rate is relatively high, said positive feedback being provided by breakdown of the field of said coil, whereby a shower of sparks is produced at the spark plugs of the engine under starting and low speed conditions.

3. A system as claimed in claim 2 wherein said means for producing an oscillatory voltage consists of a Darlington pair connected to said photoelectric device, and said transistorized amplifier circuit further comprises an output transistor to which said Darlington pair is connected and which in turn is coupled to said ignition coil, said positive feedback being provided to the base of said Darlington pair.

8. A transistorized ignition system comprising a light source and a photoelectric device, a slotted disc rotatable between said light source and said photoelectric device for periodically allowing light to reach the photoelectric device between periods during which the light is blocked from reaching the photoelectric device, the rate of rotation being proportional to the speed of the engine for which Ignition is being supplied, an ignition coil, and a transistorized amplifier circuit coupled between said photoelectric device and said ignition coil, and comprising a high gain amplifier having an input coupled to said photoelectric device for receiving pulses from said photoelectric device in proportion to the speed of said disc, an output transistor to which the output of said high gain amplifier is coupled and having the output coupled to said ignition coil, and positive feedback circuit means coupled to said high gain amplifier for causing said amplifier to produce an oscillatory voltage when the rate at which light is periodically reaching said photoelectric device is relatively low and for producing only single voltage pulses when said rate is relatively high, whereby a shower of sparks is produced at the spark plugs of the engine under starting and low speed conditions.