US3390668A

US3390668A - Electronic ignition system

Info

Publication number: US3390668A
Application number: US542410A
Authority: US
Inventors: Arthur G Hufton
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1966-04-13
Filing date: 1966-04-13
Publication date: 1968-07-02
Anticipated expiration: 1985-07-02

Description

July 2, 1968 A. G. HUFTON 3,390,668

ELECTRONIC IGNITION SYSTEM Filed April l3, 1966 FIG. 1

l6 7 TO u CENTER POST l8 0F DIST.

FIG. 2

4 I36 25 32 f as F I 3 Inventor b B ARTHUR G. HUFTON C C m May/flaw ATTYS.

United States Patent 3,390,668 ELECTRONIC IGNITION SYSTEM Arthur G. Hutton, Elk Grove Village, Ill., assignor to Motorola, Inc., Franklin Park, Ill., a corporation of Illinois Filed Apr. 13, 1966, Ser. No. 542,410 12 Claims. (Cl. 123-148) ABSTRACT OF THE DISCLOSURE Ignition system including a magnetic pickup operable from distributor breaker cam with high impedance winding and lower impedance winding. The high impedance winding provides pulses to a first transistor which actuate a second transistor which controls a damped oscillator providing an ignition firing pulse. A capacitor is connected to the first transistor and charges from the pulses to bias off the transistor when the pulses reach a given frequency. Pulses from the low impedance winding are coupled to the second transistor and act to trigger the same above the given frequency.

This invention relates to ignition systems for internal combustion engines, and more particularly to ignition systems wherein timing pulses are produced by a magnetic device synchronized with the engine.

Ignition systems for internal combustion engines must produce high energy voltage pulses for igniting the fuel in the cylinders of the engine. These high voltage ignition pulses may be produced by the interruption of current flowing in an ignition coil or may be produced by a rapid discharge of current through the ignition coil from an energy storage device such as a capacitor. In either case, the ignition pulses must be synchronized in some manner with the operation of the internal combustion engine.

Ignition systems using magnetic pickup devices have been provided which do not require the mechanical cam actuated breaker contacts. Such a system is described and claimed in Patent No. 3,203,412, issued Aug. 31, 1965, to Oleh M. Kuritza and Edward V. Havel, and assigned to the assignee of the present invention. In such an ignition system, a transistor circuit interrupts the coil current in response to timing pulses supplied to the transistor circuit from the magnetic pickup device. The magnetic pickup device can also be used to supply timing pulses to control the discharge or firing of a capacitor in a capacitor discharge type ignition system. In the latter case, the timing pulses produced by the pickup device may be used to operate a transistor circuit which produces firing pulses to trigger the capacitor firing.

In a capacitor discharge system actuated by a magnetic pickup device it may be difiicult to obtain timing pulses of sufficiently high voltage to cause the transistor circuit to produce large enough firing pulses when the magnetic pickup device is operating at low speeds. Further, magnetic pickup devices have been found unsatisfactory for incorporation in existing ignition systems as they require relatively extensive modification of the distributor which includes a cam for operating mechanical breaker points. This makes ignition systems using magnetic pickup devices relatively expensive and impractical for installation in existing systems using cam operated mechanical breaker contacts to convert such systems to contactless systems.

An object of the invention is to provide an improved magnetic pickup device for use in an ignition system, which can be easily incorporated in the housing of a distributor as currently used on automobile ignition systems.

Another object of the invention is to provide an ignition system utilizing a magnetic pickup device and a tran- "ice sistor circuit wherein voltage pulses of a relatively high value are produced during low speed operation of the pickup device.

A feature of the invention is the provision, in a distributor, of a magnetic pickup device having a magnetic core with one pole end thereof disposed adjacent the periphery of the cam and with a permanent magnet and a coil coupled to the core so that a voltage is developed in the coil as the cam rotates. The opposite pole of the core is disposed such that an air return flux path exists between the opposite pole and the cam.

Another feature of the invention is the provision of a firing circuit connecting a magnetic pickup device to an ignition circuit, which firing circuit operates as a damped oscillator to produce a single firing pulse for the firing circuit in response to each timing pulse supplied thereto from the pickup device.

Still another feature of the invention is the provision of an ignition system for an engine having a pulse with a high impedance coil and a low impedance coil, and a transistor circuit having a first stage triggered by the high impedance coil to in turn trigger a second stage, with the first stage being rendered inoperative by pulses having a fast repetition rate resulting from high speed operation of the engine and pulses from the low impedance coil acting to trigger the second stage for such operation.

In the drawings:

FIG. 1 is a circuit diagram of the ignition circuit of the invention;

FIG. 2 is a section view through the distributor showing the breaker cam and pickup device along the lines 22 of FIG. 1; and

FIG. 3 is a chart illustrating the operation of the circuit of FIG. 1.

In accordance with the invention, an ignition system for an internal combustion engine includes a magnetic pickup device operable in synchronism with the internal combustion engine to produce timing pulses. The magnetic pickup device may be mounted in a distributor having a polygonal breaker cam rotatable in synchronism with the engine, and includes an elongated core having a pole disposed adjacent the periphery of the cam. A permanent magnet is coupled to the core and a pair of windings are provided thereon to produce pulses as the cam rotates. The first winding has a high impedance which operates during starting, and the second winding applies pulses to a second point in the firing circuit after the engine is operating. The stage of the firing circuit coupled to the first coil is automatically disabled when the firing pulses reach a predetermined speed. A damped oscillator provides a single firing pulse in response to each timing pulse applied through the coupling circuit from the pickup device.

Referring now more particularly to the drawing, FIG. 1 shows the invention used in connection with an ignition system of the capacitor discharge type. An ignition capacitor 11 is charged through DC to DC converter 12 and diode 13 to a very high voltage. When the semiconductor controlled rectifier 14 is triggered on by means of a pulse applied to the gate thereof, the capacitor 11 discharges through the primary portion of high voltage ignition transformer or coil 15. This produces a very high voltage in the secondary of ignition coil 15, which is applied to the center post 18 of the distributor (FIG. 2). This is coupled by the rotary contact 19 of the distributor to the spaced contacts 20 which are in turn connected to the spark producing devices of the cylinders of the engine for igniting the fuel in the cylinders. A diode 16 is connected in reverse polarity across rectifier 14 to damp reverse voltage transients produced in the coil 15.

Semiconductor controlled rectifier 14 is triggered by pulses produced in synchronism with the operation of the internal combustion engine. These pulses are derived from rotation of the breaker cam 25, which may be the existing breaker cam in a distributor. A magnetic structure is positioned adjacent to the cam 25, and is mounted on a plate 30 to be secured in place of the plate which supports the breaker points in a known distributor. A laminated magnetic structure 31 including two angularly spaced arms, has an end 32 positioned to be closely adjacent to the points a of the cam 25.

Coils

33 and 34 are positioned on the magnetic structure 31, and permanent magnets 35 and 36 are also positioned thereon. As the cam 25 rotates and the points 25a thereof pass the end 32 of the magnetic structure 31, the flux through

coils

33 and 34 will increase. As the flats between the points come adjacent the end 32 of the magnetic structure 31, the flux through the coils will decrease. Since the return path between the cam 25 and the magnetic structure 31 has a large air gap, the variation in flux will not have sharp transitions. The coil 33 has a large number of turns, such as 1200 turns, and a relatively high impedance, and therefore develops a relatively large voltage from the change in flux. The coil 34 has about half as many turns, such as 600 turns, and produces a smaller voltage from a given change in flux. The

coils

33 and 34 are wound in opposite phase for a reason to be explained. Curve a of FIG. 3 shows the voltage developed in coil 33 and curve b shows the waveform of the voltage developed in the coil 34. The frequency and amplitude of the voltage waves depends upon the speed of the cam 25, and curves a and b merely show the opposite phase relationship of the two voltages.

The magnetic structure is shown in FIG. 2 in the distributor housing which includes a base 71 and a cap 72. A distributor shaft 73 extends upwardly into the housing and drives the drive plate 75. Drive plate 75 is connected through the usual spring biased fiyweights 77 and drive pins 78 to a centrifugal advance plate 79. Advance plate 79 drives the rotar shaft 81 upon which the rotor 83 is mounted. Rotor 83 carries the moving contact of the distributor and the fixed contacts of the distributor extend downwardly in the interior of cap 72 as is well known in the art. Rotor shaft 81 carries the cam 25 which is of the type used to operate mechanical breaker points. The periphery of the cam generally comprises a plurality of substantially planar surfaces which intersect in lines extending parallel with the axis of rotation of the cam. As may be seen from FIG. 1, this forms a plurality of points 25a on the cam.

The magnetic pickup device includes a single pole piece 31 which corresponds substantially with the height of the distributor cam 25. The pole piece 31 is secured by the non-magnetic spacer 86 to plate which is mounted on the vacuum advance plate 88 of the distributor. Permanent magnet 36 is shown in engagement with the pole piece 31 adjacent the end 32 thereof. A second magnet is shown in FIG. 1, and the two magnets have identical poles adjacent the pole piece 31, and have their opposite poles disposed such that an air return path exists between these poles and the cam 25. The whole face of each of the magnets 35 and 36 is embraced by the pole piece without any narrowing between the magnet and the gap formed between the pole end 32 and the cam 25 which would decrease the value of the reluctance in the flux path.

The circuit of FIG. 1 includes a voltage divider extending from the positive potential terminal 40 through resistor 41 and

diodes

42, 43, 44 and 45. The potential applied to the base of transistor 46 from the voltage divider through resistor 47 provides a small positive bias therefore which is not enough to render transistor 46 conducting. This positive bias is determined by the voltage drop across diode 48 and the coil 33 which has one terminal connected to ground. The emitter of transistor 46 is connected to ground, and the collector is connected through resistor 49 to the junction between diodes 43 and 44 and provides a positive potential determined by the voltage divider. When the cam 25 starts to rotate as the engine is started, the positive half cycles of the voltage developed in coil 33 render transistor 46 conducting. This is indicated by point c on curve a in FIG. 10.

When transistor 46 conducts, the voltage at the collector electrode drops, and this is applied through the diode 50 and resistor 51 in parallel with capacitor 52 to the base of transistor 54. Transistor 54 is normally held conducting by the potential applied to its base electrode through resistor 53. When transistor 46 conducts, the voltage applied to the base of transistor 54 drops and this transistor is cut off. When transistor 54 is out 01f, the voltage at its collector rises to the supply voltage, be cause of the connection through resistor 55.

The collector of transistor 54 is connected to the base of transistor 56 to render the same conducting. When transistor 54 conducts, the base of transistor 56 is held at ground so that this transistor is normally oil. When transistor 54 is cut off, the increased voltage applied from the collector thereof to the base of transistor 56 renders the latter conducting. Transistor 56 is connected in a regenerative circuit with transistor 58 through common emitter resistor 57, and acts to cut off this transistor.

The base of transistor 58 is connected through resistor 59 and resistor 41 to the positive potential point 40, and the collector is connected thereto through resistor 60 and the primary Winding 27 of transformer 26. Transistor 58 is normally biased on by the potential so applied. Resistor 63 is connected between the base and collector electrodes of transistor 58 and establishes the base potential when transistor 58 conducts. Transformer 26 has a secondary winding 28 connected to the semi-conductor controlled rectifier 14. A diode 29 is connected across the primary winding 27 to damp out transients. When transistor 56 conducts, resistor 59 is connected through the parallel circuit including resistor 61 and capacitor 62, the emitter to collector path of transistor 56, and resistor 57 to ground. This drops the potential at the base of transistor 58 so that this transistor starts to turn off, and the regenerative action through emitter resistor 57 cuts off transistor 58 very rapidly. This causes a sharp pulse to be developed in the primary winding 27 of transformer 26. The Zener diode 64 protects the transistor 58 from breakdown due to high reverse transient voltages which may be developed in the primary winding 27 of transformer 26.

During starting, the voltage change in coil 33 resulting from the change in flux therethrough is applied to turn on transistor 46, which is biased to be rendered conducting by a very small voltage change. As the engine starts and begins to turn over faster, the voltage changes will increase in amplitude. The negative half cycles from coil 33 are conducted through diode 48 to capacitor 65. These voltage pulses charge capacitor 65 so that after a period of time a voltage is built up thereacross which holds transistor 46 cut off. Accordingly, the transistor 46 operates only during starting of the system.

As the engine speed increases, the voltage pulses produced in the coil 34 increase to a level so that the pulses applied through resistor 51 and capacitor 52 act to cut off the transistor 54. This is represented by point d in FIG. 2. At low speeds, the pulses from coil 34 are of insufiicient amplitude to provide this triggering action, and the pulses in coil 33 trigger transistor 46 to provide pulses of adequate amplitude to cut off transistor 54. The system automatically switches from coil 33 to coil 34 as th engine speed increases.

Since the system is highly sensitive particularly during starting, there is a possibility that the system might be triggered accidentally by the mechanical vibrations resulting from the engine starter, or by vibrations produced by slamming the door of the vehicle. Resistor 66 and capacitor 67 connected between the base and collector of transistor 46 form a high pass filter to short out high frequency extraneous signals.

The circuit described provides accurate triggering of the automobile ignition system at all engine speeds, with timing information at least equally as good as conventional mechanical breaker points. Triggering is readily obtained at battery voltages from 6 volts to in excess of 16 volts, and at temperatures between approximately 40 F. and 300 F. It may therefore be seen that the invention provides an improved ignition system for an internal combustion engine and an improved magnetic pickup device for use therewith.

I claim:

1. In an ignition system for an internal combustion engine which includes an ignition coil and a switching device for applying current to the ignition coil for producing high voltage pulses, the combination including, a magnetic pickup device operable in synchronism with the internal combustion engine and having first and second pickup windings in which timing pulses are developed in response to operation of the engine, and semiconductor circuit means for connection to the switching means for producing pulses for actuating the same, said circuit means including first and second portions coupled to said first and second windings respectively and responsive to timing pulses applied therefrom, said first portion being coupled to said second portion and actuating the same to produce switching pulses for starting the engine, said first portion including means acting to disable the same in response to timing pulses of a predetermined frequency produced as the speed of the engine reaches a given value, said second portion being responsive to pulses from said second winding produced at engine speeds above said given value for producing switching pulses for operation of the engine.

2. An ignition system in accordance with claim 1 wherein said first portion includes a transistor having a base electrode, means applying a potential to said base electrode for holding said transistor non-conductive, and diode means connecting said first winding to said base electrode for applying voltage pulses thereto for rendering said transistor conductive.

3. An ignition system in accordance with claim 2 including a capacitor connected between said base electrode and a reference potential, said capacitor being charged by pulses applied to said base electrode by said first winding to cut off said transistor when the speed of the engine reaches the given value.

4. The combination of claim 1 wherein said first winding has a higher impedance and produces timing pulses of larger amplitude than said second winding.

5. The combination of claim 1 wherein said semiconductor circuit means includes damped oscillator means coupled to said second portion and providing a single firing pulse in response to each pulse applied thereto by said second portion.

6. The combination of claim 1 wherein said first portion includes a transistor which is rendered conducting by said pulses from said first winding, and said second portion includes a second transistor which is rendered nonconductive by pulses applied thereto by said first portion until said first portion is disabled, with said second winding applying pulses to said second transistor to render the same non-conductive as the speed of the engine approaches said given value.

7. The combination of claim 6 further including oscillator means having third and fourth transistors, with said third transistor being normally non-conductive and said fourth transistor being normally conductive, and means connecting said second transistor to said third transistor to render said third transistor conductive when said second transistor is cut off.

8. The combination of claim 1 wherein said magnetic pickup device is adapted for use with an internal combustion engine having a polygonal breaker cam, wherein said magnetic pickup device has a magnetic core extending through said first and second windings and having a portion positioned adjacent the breaker cam, and permanent magnet means engaging said core for providing a field through said windings.

9. The combination of claim 8 wherein said permanent magnet means includes first and second permanent magnets having like magnetic poles engaging said magnetic core, and providing flux in a path including said magnetic core, the breaker cam, the air gap between the breaker cam and said core, and the air return path from the breaker cam to said magnetic pickup device.

10. The combination of claim 1 wherein said magnetic pickup device is adapted for use with an internal combustion engine having a distributor including a housing and a polygonal breaker cam therein, and wherein said magnetic pickup device has a magnetic core with first and second angularly positioned portions, with said first portion of said core extending through said first and second windings and said second portion of said core having an end positioned adjacent the breaker cam, and permanent magnet means engaging said core for providing a field through said winding, said pickup device being shaped to fit within the housing of the distributor.

11. The combination of claim 10 wherein said permanent magnet means includes first and second permanent magnets having like magnetic poles engaging said core.

.12. The combination of claim 11 wherein said first and second windings have a common terminal connected to a reference potential and are positioned on said core between said first and second permanent magnets, and said like magnetic poles of said magnets engage the same side of said core.

References Cited UNITED STATES PATENTS 3,139,876 7/1964 Jukes. 3,196,313 7/1965 Quinn. 3,314,407 4/ 1967 Schneider. 3,324,841 6/1967 Kebbon et a1 123-149 LAURENCE M. GOODRIDGE, Primary Examiner.