US3710131A

US3710131A - Transistorized ignition systems

Info

Publication number: US3710131A
Application number: US00212196A
Authority: US
Inventors: E Ford
Original assignee: Lumenition Ltd
Current assignee: Lumenition Ltd
Priority date: 1971-01-08
Filing date: 1971-12-27
Publication date: 1973-01-09
Anticipated expiration: 1990-01-09
Also published as: IT948142B; SE386716B; ES399119A1; AU3747071A; DE2200704B2; JPS5347856B1; DE2200704A1; CA932382A; AU453491B2; FR2131323A5

Abstract

A transistorized ignition system for switching the primary winding of an ignition coil of an internal combustion engine having the following improvements over the system disclosed in U.S. Pat. No. 3,605,712: A. PROTECTION OF THE POWER TRANSISTOR AGAINST POSITIVE GOING TRANSIENTS BY MEANS OF A ZENER DIODE; B. PROTECTION OF THE POWER TRANSISTOR AGAINST NEGATIVE GOING TRANSIENTS BY MEANS OF A DIODE; C. CLEAN SWITCHING OF THE PHOTO-TRANSISTOR CONSTITUTING THE INFRA-RED DETECTION DEVICE BY MEANS OF A DIODE CONNECTED THEREACROSS; D. A LENSING SYSTEM FOR THE INFRA-RED LAMP AND PHOTO-TRANSISTOR TO ENSURE THAT THE RADIATION BEAMS FROM THE LAMP TO THE PHOTOTRANSISTOR ALL CONVERGE AT A POINT IN THE PLANE OF THE ROTATING CHOPPER DISC; AND E. SLOW DOWN OF THE RATE OF SWITCHING OF THE POWER TRANSISTOR BY MEANS OF AN IRON CORED INDUCTOR BETWEEN THE OUTPUT OF THE TRIGGER AND THE BASE ELECTRODE OF THE POWER TRANSISTOR.

Description

United States Patent (191 Ford 1 Jan. 9, 1973 [S4] TRANSISTORIZED IGNITION Primary Examiner-Robert K. Schaefer SYSTEMS Assistant Examiner-William J. Smith [75] Inventor: Eric Harold Ford, London, England Attorney-Roberts Larson et [73] Assignee: Lumenition Limited, London, En- [57] ABSTRACT gland A transistorized ignition s stem for switchin the riy 8 P [22] Filed: Dec. 27, 1971 mary winding of an ignition coil of an internal combustion engine having the following improvements [21] Appl' 2l2l96 over the system disclosed in US. Pat. No. 3,605,712:

a. protection of the power transistor against positive [30] Foreign Application Priority Data going transients by means of a zener diode;

. b. protection of the power transistor against negajan. (oireatl grtta n five g g transients y means of a diode; 1971 i 4 71 c. clean switching of the photo-transistor constitutmam ing the infra-red detection device by means of a v diode connected thereacross; [2%] (3| ..307/l0 R, 120]; d a lensing System for the finned lamp and photo d :3 transistor to ensure that the radiation beams from 1 l9 0 "fig/148 E 6 the lamp to the photo-transistor all converge at a point in the plane of the rotating chopper disc; and [56] References Cited e. slow down of the rate of switching of the power UNITED STATES PATENTS transistor by means of an iron cored inductor between the output of the trigger and the base Ford E X electrode of the power transiston 3,646,926 3/l972 Plume ..123/l48 E 7 Claims, 10 Drawing Figures PAIENTEDIIII 9mm 3.710.131

SHEET 4 UF 5 I I I 5 TIME T (I) Kn TIME 0 A TIME TIME TRANSISTORIZED IGNITION SYSTEMS The present invention relates to a number of improvements in the solid state transistorized ignition system disclosed in U.S. Pat. No. 1,219,833.

This prior patent discloses a device for providing rapid switching of the primary circuit of an ignition coil of an internal combustion engine to thereby induce a desired voltage in the secondary circuit. This device essentially includes a photo-transistor sensitive to infrared radiation which will switch on or conduct when exposed to the radiation and switch off when the radiation is cut off; a gallium arsenide lamp emitting infrared radiation; an element which is opaque to infra-red radiation positioned between the lamp and the phototransistor, the opaque element having as many equispaced apertures therein as there are cylinders in the engine, and being moved in timed relation to the engine revolutions; a transistorized amplifier having a plurality of stages connected in cascade to the output of the photo-transistor, the stages being arranged to switch in inverse relation to one another; and a power transistor connected to the output of the amplifier and switched in inverse relation to the last stage thereof, the power transistorbeing connected in circuit relationship with the ignition coil such that each time a beam of infra-red radiation is cut off from the photo-transistor the transistorized amplifier causes rapid switching of the primary circuit to produce the desired voltage in the secondary circuit.

The improvements to which the present invention relates are as follows:

I. protection of the power transistor against transient voltages in the primary circuit on switch off;

2. prevention of dirt on the covers of the infra-red lamp and photo-transistor from affecting the accurate timing;

3. ensuring clean switching of photo-transistor to prevent oscillation thereof.

With respect to the first of these improvements, it is normal practice to protect a power transistor used for switching an inductive circuit against high induced voltage by means of either a zener diode or a condenser connected across the collector and emitter electrodes of the transistor.

The disadvantage of using the zener diode across the collector and emitter electrodes is that it must withstand the voltage and current from the inductive load when switching takes place. This means using a high power zener diode which is very expensive. The disadvantage of using the condenser across the collector and emitter electrodes is that it stores energy and returns it to the circuit. This can result in both oscillation or possible damage to the transistor. Also the condenser must be high rated.

With respect to the second of these improvements, the rays of infra-red radiation emitted by the gallium arsenide infra-red source are substantially parallel and form a beam whose width is constant between the infrared source and the photo-transistor. Normally, the fact that there is a material width" to this beam is irrelevant for normal operation of the device.

However, the presence of dirt or other obscuring matter on either the lens system of the gallium arsenide source or the photo-transistor can cause a change in the accurate timing of the device if this dirt tends to obscure one particular area of the lens more than another. Also, the deposition of dirt evenly over the lens system will cause the switching to take place earlier. Thus, in the event of the gallium arsenide source becoming fouled by dirt or oil in one particular area, the timing of the ignition could be altered which would affect the running of the internal combustion engine particularly at high engine speeds.

With respect to the third of these improvements, one of the problems encountered in fast switching transistorized circuits is that due to the inter-electrode capacitance of the photo-transistor. It has been found that the photo-transistor may make one or more attempts to switch before switching actually occurs. This can be particularly disadvantageous at high speed since under very adverse conditions the timing could go awry.

According to the present invention there is provided a transistorized ignition system for switching the primary winding of an ignition coil of an internal combustion engine, including infra-red operated pulse generating means consisting of an infra-red lamp, a phototransistor detector and a bladed chopper disc driven in synchronism with the engine revolutions to thereby in terrupt the infra-red beam from the lamp in timed relation therewith; means for ensuring that the phototransistor produces cleanly switched square wave pulses without a trace of oscillation; lensing means associated with the lamp and photo-transistor for ensuring that the infra-red radiation beams all converge at a point in the plane of the rotation chopper disc; a transistorized trigger circuit having a plurality of transistors arranged in cascade to be triggered in inverse relation to one another from the output of the photo-transistor; a transistorized power stage arranged to switch in inverse relation to the last stage of the trigger circuit, said power stage being in series with the primary winding of the ignition coil; means for slowing down the fast switch off of the power stage; and means for protecting the power stage against induced positive and negative going transients at the instant of switch off.

The means for ensuring that the photo-transistor produces cleanly switched square-wave pulses may be a diode connected across the emitter and collector electrodes thereof.

The means for protecting the power stage against induced positive going transients may be a zener diode and resistor connected in series between the collector and base electrodes of a transistor in the power stage.

The means for protecting the power stage against induced negative going transients may be a diode connected across the collector and emitter electrodes of the last transistor in the power stage.

The lensing means may include a first housing for the infra-red lamp, a second housing for the phototransistor, a plano-convex lens secured to said first housing and a piano-convex lens secured to said second housing, whereby the beams of infra-red radiation all converge at a point substantially midway between the two lenses.

The present invention will now be described in greater detail by way of example with reference to the accompanying drawings, wherein:

FIG. 1A is a plan view of a distributor body for a Ford V8 engine with rotor arm removed;

FIG. 1B is a part sectional elevation taken on the line [-1 of FIG. 1A;

FIG. 2 is a circuit diagram showing one preferred form of trigger and protective devices suitable for use in a Ford V8 engine;

FIG. 3 is a part circuit diagram in which a darlington pair is substituted for the power transistor, for use with an engine having a large number of cylinders;

FIG. 4 shows a series of graphs which explain the voltage and current waveforms in the ignition coil before and after the addition of the zener diode and iron cored inductor to the circuit shown in FIG. 2;

FIG. 5 shows a detailed diagrammatic arrangement of one preferred form of a solid state infra-red system for use with the ignition system;

FIGS. 6A and 6B are oscilloscope traces of the spark voltage with partially fouled plugs of a conventional contact breaker system and the ignition system of the present invention; and

FIGS. 7A and 7B are graphs showing the performance of the ignition system of the present invention as compared with a conventional contact breaker system.

Referring to FIGS. 1A and 13, a distributor body 20 of known type has a large diameter cylindrical portion 22 which is concentric with a shaft 24. The shaft 24 has near its upper end 26 a cam 28 consisting of eight lobes joined by faces of large-radius curvature. The shaft is driven from its lower end 30 by an engine (not shown) to whose speed the speed of the shaft 24 is therefore proportional. The cam 28 is pivotably displaceable relative to the lower end 30 of the shaft 24 by a small amount, depending on the speed of rotation of the shaft 24. The displacement is achieved by means of a centrifugal advance mechanism (not shown).

The upper end 26 of the shaft 24 is hollow and is provided with a locating slot 32. A rotor arm (not shown) fits over the upper end 26 of the shaft and a lug integrally formed with the arm engages with the slot 32 to rotationally locate the rotor arm.

The large diameter cylindrical portion 22 contains at its base a base plate 34, which is rigidly secured thereto by two screws 36.

A second plate 38 is pivotably attached to the base plate 34 by means of a pin 40, two plain washers 42, a spring washer (not shown) between the two plain washers 42, and a circlip 44. The circlip 44, the washers 42 and spring washer (not shown) are concentric with the pin 40. The spring washer (not shown) exerts a vertical force between the two plain washers 42 to prevent vibration of the plate 38, because the circlip 44, fitting in a groove (not shown) in the pin 40, transmits this force to the pin 40. The plate 38 is rotationally displaceable about the pin 40 and therefore eccentrically to the shaft 24, on operation of a vacuum advance/retard mechanism 46 of known type. The mechanism 46 is connected to the second plate 38 by a push rod 48, which is of circular cross-section but has a flattened end portion 50 having a hole through which a pin 52, connected to the second plate 38, passes. The second plate 38 is electrically connected to the base plate 34 by a flexible copper-braid wire 54.

On the second plate 38 is mounted, by means of two screws 56, a lens unit 58. The lens unit 58 includes a steel body 60 with two extensions 62 through which the screws 56 pass and two extensions 64, one vertically above the other, which carry a gallium arsenide lamp 1 for emitting infra-red radiation and an infra-red detector in the form of a photo-transistor 2.

Over the cam 28 is clipped a chopper disc 3 made of spring steel plate. The chopper disc 3 has a central hole with four mutually perpendicular inwardly projecting locating lugs 68 which abut the top shoulder of the cam 28. At 45 to each of the lugs 68 are downwardly extending curved grips 70 which hold against four of the cam faces. The outer periphery of the chopper disc 3 has eight equi-spaced radial blades 72, each of which is reinforced by a radial rib 74 which joins a circular strengthening rib 76 formed in the chopper disc 3.

When the shaft 24 revolves, each of the blades 72 of the chopper disc 3 passes in turn between the lamp 1 and the photo-transistor 2 of the lens unit 58 and thus interrupts the infra-red beam. The interruption serves to produce a spark by electrical means to be described later. The spark occurs at a predetermined position of shaft rotation, but this position is alterable by means of the vacuum advance/retard mechanism 46, as well as by the centrifugal advance mechanism (not shown) mentioned above. When the vacuum mechanism 46 operates, the push rod 48 moves horizontally and pivots the second plate 38 about the pin 40. Thus the lens unit 58 is moved to a new position relative'to the distributor body 20, and the timing of the spark is thus altered.

Three wires 78 associated with the lens unit 58 emerge from the cylindrical portion 22 of the distributor body 20 through a rubber grommet 80, these wires being the common supply wires to the lamp 1 and photo-transistor 2 and also the output from the phototransistor 2.

Referring now to FIG. 2, the complete ignition circuit is shown in full. It includes firstly an infra-red solid state pulse generation means consisting of the gallium arsenide lamp 1, the photo-transistor 2 and chopper disc 3; secondly a trigger circuit consisting of three N- P-N silicon transistors T1, T2 and T3 arranged as a cascaded current switching amplifier; and thirdly a power stage consisting of a power transistor whose emitter-collector circuit is in series with the primary winding of an ignition coil 4.

In the infra-red solid state generating means part of the circuit, resistors R5 and R6 are connected in series with the gallium arsenide lamp 1 and photo-transistor 2 respectively. A zener diode Z2 is connected in parallel with both these circuits in order to stabilize the voltage thereacross. A resistor R4 connects the whole of this part of the parallel circuit to the battery voltage of +1 2 volts. A low leak diode D4 is connected across the emitter and collector electrodes of the photo-transistor 2. The diode D4 has the effect of reducing the interelectrode capacitance between these two electrodes and thus enables the phototransistor to switch cleanly when it receives the infra-red radiation from the gallium arsenide lamp 1.

The transistors T1 to T3 which form the fast inverse switching trigger have their emitter electrodes earthed whilst their collector electrodes are connected to the 12 volt battery voltage through respective resistors R1, R2 and R3. A resistor R7 is connected between the base electrode of the first transistor T1 and the collector electrode of the transistor T2, this resistor assisting in the fast switching of the trigger.

Between the collector electrode of the third transistor T3 and the base electrode of the power transistor P there is a series circuit consisting of a diode D1 and an iron cored inductor L. A zener diode Z1 and resistor R9 in series are connected across the collector and base electrodes of the power transistor P to protect it against positive going transients as will be explained later on. A diodeDZ is connected across the emitter and collector electrodes of the power transistor P in order to protect it against negative going transients. The base electrode of the power transistor is connected to earth via a parallel circuit consisting of a diode D3 and a resistor R8.

The collector-emitter circuit of the power transistor P is in series with the primary winding of the ignition coil 4, the power transistor controlling the operation of the coil by switching in inverse relation to the state of the transistor T3. One end of the secondary winding of the coil 4 is earther whilst the other end is connected to a distributor 5 and thence to the individual eight plugs 6 of the engine.

The state of the transistors at any given instant may be conveniently summarized by the following table:

OFF

In certain applications and in particular where the internal combustion engine has a large number of cylinders, for example more than eight, it is desirable to replace the single power transistor by two power transistors arranged as a darlington pair. FIG. 3 shows such an arrangement where two power transistors P1 and P2 have their collector electrodes commoned and the emitter electrode of the transistor P1 is connected to the base electrode of the transistor P2. The zener diode Z1 in series with the resistor R9 is connected between the commoned collector electrodes of the two power transistors and the base electrode of the power transistor P1. The protective diode D2 is connected between the commoned collector electrodes and the emitter electrode of the power transistor P2. The other components of the circuit are otherwise the same as in the embodiment of FIG. 2 except that a resistor R10 connects the junction between the emitter electrode of the transistor P1 and the base electrode of the transistor P2 to earth.

The operation of the trigger circuit comprising the transistors T1 to T3 is such that every on" transistor is fully saturated and every off transistor is fully off, i.e. no base current flows. The on" transistors thus act as short-circuit paths for any transients which may be generated due to the fast switching of the primary winding of the ignition coil 4, and since there is at least always one transistor in the chain on" at any one time, the circuit is fully transient proof and there is no danger of any of the off transistors being broken down.

The power transistor P or the darlington pair P1-P2 is fully protected by means of the zener diode Z1 and the diode D2. The zener diode Z1 is arranged to conduct above a certain voltage level so that if there are any positive going transients induced in the circuit when the power transistor or darlington pair has switched off, these break down the zener diode Z1 which conducts them through the resistor R9 to the base electrode of the power transistor P or P1. The power transistor P or darlington pair P-P2 is thus caused to turn on in a controlled manner for the dura tion of these transients so that there is no danger of the power transistor or darlington pair being broken down in the event of high voltage surges taking place. Negative going transients which occur when the power transistor P or darlington pair P1-P2 is turned off are taken care of by the diode D2 which conducts these thus preventing any break down thereof. The purpose of the diode D1 is to prevent the voltage passed by the zener diode Z1 from flowing to earth via the transistor T3.

The switching action of the circuit shown in FIG. 2 without the provision of the inductor L between the collector electrode of the transistor T3 and the base electrode of the power transistor P is so fast that the action produces excessive transients and radio interference. The purpose of the inductor L is to thus slow down the switching action of the power transistor P, this action being shown in the various graphs of FIG. 4 which also shows the protective effect of the zener diode Z1.

The origin on the time axis (abscissa) is the point at which the power transistor P turns off to cause the magnetic collapse of the field in the primary winding of the coil 4, and thus induce a high voltage in the secondary winding for the spark. Curve (a) thus shows the secondary voltage induced in the coil which has a very rapid rise time. In the case where the circuit does not include the inductor L nor the zener diode, the primary current in the coil is shown in curve (b), and it will be seen that this has a very fast turn off time of the order of 17 ,u. secs. The induced primary voltage due to the rapid turn off is shown in curve (0). A very high positive spike occurs in this induced voltage a few p. seconds after turn off. The following transients are less potent but the first positive going one is very dangerous.

Curves (d) and (e) show the induced primary voltage and current with the addition of the inductor L and the zener diode Z1. The zener diode effectively clips the positive going transient in the primary voltage and conducts above a certain level, for example 200 volts. The negative going peaks of the induced primary voltage are effectively clipped by the diode D2 which conducts when the induced voltage swings negative. The inductor L slows down the turn off time from l7 to 40 t sees. as is evident from curve (e). The voltage curve for the voltage induced in the secondary winding is virtually unaffected by the provision of the zener diode Z1 and the inductor L7 The use of a zener diode for protecting a power transistor against break down due to transients and voltage surges has the advantage that it is extremely cheap compared with conventional methods since only a low power and therefore inexpensive zener diode is necessary. Moreover negative transients are taken care of by the provision of the diode connected across the emitter-collector electrodes of the power transistor.

Not only is the power transistor fully protected against break down, but its switching time is slightly slowed down by the provision of the iron cored inductor. The same switching action is achieved with the two power transistors P1 and P2 arranged as a darlington pair.

Referring now to FIG. 5, the layout of the infra-red lensing system is shown in much greater detail. The infra-red gallium arsenide lamp 1 is housed in a metal housing 12 which is shaped in the form of a square C. The housing also holds a plano-convex lens 13. The photo-transistor 2 is housed in a similar shaped housing 14 which also holds a lano-convex lens 16. It will be seen from the drawing that any ray of infra-red radiation emitted from the lamp 1 after passing through the planoconvex lens 13 is brought to a focus at a point 17 and then diverges again before being brought to a focus on the photo-transistor 2 after passing through the plane-convex lens 16. The chopper disc 3 is thus arranged so that the blades 72 will cut the infra-red radiation from the gallium arsenide lamp 1 at the point 17. As can be seen from FIG. 1A, the disc 3 has eight equispaced blades 72, so that when the disc 3 is rotated, the blades 72 alternately block the infra-red radiation from reaching the photo-transistor 2. Since the blades 72 cut the rays of infra-red at their convergent point, in the event of an area of the lens 13 of the gallium arsenide lamp 1 becoming obscured with dirt or oil, this does not affect the exact time at which the radiation is cut off from the photo-transistor 2.

Instead of using a plano-convex lens system as illustrated a double convex system may be installed in the housings l2 and 14.

Referring now to FIGS. 6A and 6B, which show two oscilloscope traces of the spark voltage, it will be readily appreciated that under the conditions of partially fouled plugs, the conventional contact system performs very poorly indeed, there being about a 3 percent inherent random misfire as a result. On the other hand due to the superior design of the ignition system according to the present invention there is absolutely no misfire with partially fouled plugs as shown in FIG. 6B.

The superior performance of the ignition system according to the present invention is also evident from the graph of FIG. 7A where secondary voltage in KV is plotted to a base of engine revolutions per minute X 1000. Curve (f) shows the conventional contact breaker system which has a maximum secondary voltage of 24 KV at slow engine speeds, but which falls off relatively rapidly so that by 6500 RPM the secondary voltage is only of the order of 14 KV. On the other hand the ignition system according to the present invention as shown by curve (g) has a substantially constant secondary voltage of 30 KV between and 5000 RPM. For speeds higher than 5000 RPM, the secondary voltage does decrease slightly, but even at 10,000 RPM it is still as high as 25 KV.

Finally curve (h) in the graph of FIG. 7B shows how the secondary voltage decreases with battery volts below the nominal 12 volts level. Even if the battery voltage is as low as 6 volts, a secondary voltage of 15 KV can be achieved. Provided there is sufficient power in the battery to turn the engine over, the ignition system will fire the engine.

What I claim and desire to secure by Letters Patent l. A transistorized ignition system for switching the primary winding of an ignition coil of an internal combustion engine, including infra-red operated pulse generating means consisting of an infra-red lamp, a

photo-transistor detector and a bladed cho p er disc driven in synchromsm with the engine revo utions to thereby interrupt the infra-red beam from the lamp in timed relation therewith; means for ensuring that the photo-transistor produces cleanly switched square wave pulses without a trace of oscillation; lensing means associated with the lamp and photo-transistor for ensuring that the infra-red radiation beams all converge at a point in the plane of the rotating chopper disc; a transistorized trigger circuit having a plurality of transistors arranged in cascade to be triggered in inverse relation to one another from the output of the photo-transistor; a transistorized power stage arranged to switch in inverse relation to the last stage of the trigger circuit, said power stage being in series with the primary winding of the ignition coil; means for slowing down the fast switch off of the power stage; and means for protecting the power stage against induced positive and negative going transients at the instant of switch off.

2. A transistorized ignition system according to claim 1, wherein the means for ensuring that the photo-- transistor produces cleanly switched square-wave pulses is a diode connected across the emitter and collector electrodes thereof.

3. A transistorized ignition system according to claim 1, wherein the means for protecting the power stage against induced positive going transients is a zener diode and resistor connected in series between the collector and base electrodes of a transistor in the power stage.

4. A transistorized ignition system according to claim 1, wherein the means for protecting the power stage against induced negative going transients is a diode connected across the collector and emitter electrodes of the last transistor in the power stage.

5. A transistorized ignition system according to claim 1, wherein the means for slowing down the fast switch off of the power stage is an iron cored inductor and diode connected in series between the collector electrode of the last stage of the trigger circuit and the base electrode of the first transistor of the power stage.

6. A transistorized ignition system according to claim 1, wherein the lensing means includes a first housing for the infra-red lamp, a second housing for the phototransistor, a plano-convex lens secured to said first housing and a plane-convex lens secured to said second housing, whereby the beams of infra-red radiation all converge at a point substantially midway between the two lenses.

7. A transistorized ignition system according to claim 1, wherein said power stage consists of a darlington pair having their collector electrode commoned together.

Claims

1. A transistorized ignition system for switching the primary winding of an ignition coil of an internal combustion engine, including infra-red operated pulse generating means consisting of an infra-red lamp, a photo-transistor detector and a bladed chopper disc driven in synchronism with the engine revolutions to thereby interrupt the infra-red beam from the lamp in timed relation therewith; means for ensuring that the photo-transistor produces cleanly switched square wave pulses without a trace of oscillation; lensing means associated with the lamp and phototransistor for ensuring that the infra-red radiation beams all converge at a point in the plane of the rotating chopper disc; a transistorized trigger circuit having a plurality of transistors arranged in cascade to be triggered in inverse relation to one another from the output of the photo-transistor; a transistorized power stage arranged to switch in inverse relation to the last stage of the trigger circuit, said power stage being in series with the primary winding of the ignition coil; means for slowing down the fast switch off of the power stage; and means for protecting the power stage against induced positive and negative going transients at the instant of switch off.

2. A transistorized ignition system according to claim 1, wherein the means for ensuring that the photo-transistor produces cleanly switched square-wave pulses is a diode connected across the emitter and collector electrodes thereof.

6. A transistorized ignition system according to claim 1, wherein the lensing means includes a first housing for the infra-red lamp, a second housing for the photo-transistor, a plano-convex lens secured to said first housing and a plano-convex lens secured to said second housing, whereby the beams of infra-red radiation all converge at a point substantially midway between the two lenses.