Ignition system power converter and controller

• US 5,558,071 A
• Filed: 02/24/1995
• Issued: 09/24/1996
• Est. Priority Date: 03/07/1994
• Status: Expired due to Fees

• Current Assignee: Combustion Electromagnetics Incorporated
• Original Assignee: Combustion Electromagnetics Incorporated
• Inventors: Ward, Michael A. V., Hill, Winfield, Pennell, Arthur J.
• Primary Examiner(s): WOLFE JR, WILLIS RAY
• Application Number:
  US08/396,194
• Time in Patent Office: 578 Days
• Field of Search: 123/598, 123/606, 123/620, 123/634, 123/637, 363/15, 363/16, 363/18, 363/22
• US Class Current: 123/598
• CPC Class Codes: F02P 3/02 having inductive energy storage, e.g. arrangements of induction coils ignition coils structurally combined with sparking plugs F02P13/00; constructional details of ignition coils H01F38/12
• CPC Class Codes: F02P 3/0892 using digital techniques
• CPC Class Codes: F02P 9/002 Control of spark intensity, intensifying, lengthening, suppression by means of current control in the storage devices F02P3/05, F02P3/09, during starting F02P15/12
• CPC Class Codes: F02P 9/007 by supplementary electrical discharge in the pre-ionised electrode interspace of the sparking plug, e.g. plasma jet ignition
• CPC Class Codes: H01F 38/12 Ignition, e.g. for IC engines

Abstract

A high efficiency high power DC to DC power converter and controller system for a CD ignition system with a simple converter controller (8) for controlling a power switch (2) of a transformer (1) operated as a flyback which includes a lossless snubber (6) and simple current sensor (8a) for sensing and controlling the power converter current, and further including ignition trigger conditioner (9) and phase conditioner (10) for operating a trigger output circuit (11) based on an octal counter (67) for triggering ignition coil circuits of a preferred distributorless ignition circuit of the hybrid ignition system type.

Claims

1. A DC to DC voltage step-up power converter including energy storage and voltage step-up inductive means and a main power switch means SE for controlling current in said inductive means to raise a low input voltage power supply means to a high output voltage Vc, the power converter including a converter controller comprising controlled oscillator means for turning said switch SE on and off for durations Ton and Toff respectively, the oscillator means including a summing time measuring device which achieves a high measure level HIGH in time Ton and a low subtracting time measuring device which achieves a low measure level LOW in time Toff, the summing occurring until the level HIGH is obtained whereupon the subtracting begins until the level LOW is obtained whereupon the summing begins, and so on, said summing device sensing said high output voltage load at voltage Vc and summing with a rate factor A+ and summing in inverse proportion to the voltage Vc to define the off-time Toff which decreases with increased voltage Vc, and said subtracting device subtracting at a rate A- to define the on-time Ton.

2. An automotive ignition system of the capacitive discharge, CD, type with at least one CD capacitor and at least one coil Ti with switches SSi, and a flyback type voltage step-up power converter and controller for charging said capacitors, said power converter comprising a transformer and power switch SE and low ESR filter capacitors connected to a battery for supplying current to the primary winding of said transformer, and further comprising a current sensing circuit comprised of sensor resistors connected between the low voltage end of the transformer secondary winding and ground and an NPN sensor transistor with its base connected to ground, its emitter connected to the other end of said sensing resistors, and its collector providing a sensing actuating point to control the peak power converter peak current Ipk through feedback to a converter controller driver circuit which turns said power switch SE on and off to charge said CD capacitors.

3. The ignition system as defined in claim 2 wherein said power converter includes snubber means connected between the battery and the drain of said FET switch which is of the N-type, said snubber including snubber capacitor and diode and energy handling components.

4. The ignition system as defined in claim 3 wherein said energy handling components comprises a power resistor of order of magnitude of 1000 ohms.

5. The ignition system as defined in claim 2 wherein said energy handling components comprise an energy storage inductor, a voltage control zener diode, and a diode connected with its anode to ground and its cathode to one end of said inductor, wherein excess energy following switch SE opening is stored in said inductor and delivered back to the battery.

6. The ignition system as defined in claim 5 wherein said energy handling components include an FET switch and control resistors.

7. The ignition system as defined in claim 2 wherein said ignition is of the hybrid dual discharge type including low frequency capacitor C0, high frequency capacitor C1, one or more inductor and diode means, one or more ignition coils Ti with dual switches Si/SDi, where Si is an SCR, and SDi is an SCR for a distributorless ignition and a diode for a distributor ignition.

8. The ignition system as defined in claim 7 wherein inductor means includes at least one inductor Le0 with a series diode connected between said two capacitors, and wherein switch Si is connected with its anode to the low voltage end of the primary winding of said coil Ti and its cathode to ground, and wherein switch SDi has its anode connected to the anode of Si and its cathode to the intersection of said inductor Le0 and capacitor C0, and wherein for a distributorless ignition trigger of said switch SDi has the cathode of a high voltage Vc connected to it and the anode connected to the trigger of switch Si, with trigger signal applied to triggers on ignition firing.

9. The ignition system as defined in claim 7 wherein said capacitors are in the range of values of 1 to 10 microfarads charged to a voltage approximately 360 volts by said power converter and wherein C1 is less than C0.

10. A DC to DC voltage step-up power converter including energy storage and voltage step-up inductive means and a main power switch means SE for controlling current in said inductive means to raise a low input voltage power supply means to a high output voltage Vc, the power converter including a converter controller comprising controlled oscillator means for turning said switch SE on and off for durations Ton and Toff respectively, the oscillator means including a timing capacitor Ct which is charged up to a high threshold voltage Vhth and discharged through a discharge point to a low threshold voltage Vlth to define the two periods Toff and Ton, capacitor Ct being charged through a resistor Rc connected at one end to said discharge point and at the other end to said high output voltage load at voltage Vc to define the off-time Toff which decreases with increased voltage Vc, and timing capacitor Ct discharging through a resistor Rb connected between capacitor Ct and the discharge point to define the on-time Ton, and wherein a diode is placed across resistor Rb for by-passing resistor Rb during charging of timing capacitor Ct through resistor Rc.

11. The power converter as defined in claim 10 wherein said controlled oscillator is built from a 555 timer.

12. The power converter as defined in claim 10 wherein a voltage limiting zener diode is connected to the discharge point with its anode to ground which provides over-voltage protection and a high input power supply voltage shut-off.

13. The power converter as defined in claim 12 wherein the anode of said zener diode is connected to the base of an NPN transistor whose emitter is grounded and whose collector is connected to the timing capacitor Ct to discharge and hold the timing capacitor low whenever the voltage at said discharge point exceeds the zener voltage.

14. The power converter as defined in claim 13 wherein said input power supply is an automotive 12 volt battery and said zener diode has a zener voltage of at least 9.1 volts for power converter shut-off at battery voltages above 18 volts.

15. The power converter as defined in claim 10 wherein said controlled oscillator means comprises a comparator constructed and arranged to operate as an oscillator.

16. The combination as defined in claim 15 wherein said timing capacitor Ct is connected to the inverting input of said comparator to provide a high comparator output during capacitor Ct charging, designating time Toff, and a low comparator output during discharging designating time Ton, wherein the output of said oscillator is connected to a voltage inverting circuit to produce a positive drive signal during time Ton and a low signal during time Toff.

17. The power converter and controller as defined in claim 16 wherein output of said inverting circuit is applied to the bases of complementary NPN and PNP transistors with interconnected bases and emitters and with collectors to Vcc and ground respectively, the emitters in turn providing the turn-on and turn-off drive for said power switch SE through a small resistor shunted with a fast diode for fast turn-off of the switch, said resistor connected between said emitters and the gate of said switch SE which is an FET.

18. The power converter and controller as defined in claim 10 in combination with an ignition controller means for use in an IC engine capacitive discharge, CD, ignition system with one or more CD capacitor means connected to the power converter high voltage output for being charged by the power converter to the high voltage Vc, said ignition controller means constructed and arranged to receive a generic ignition trigger signal comprised of a voltage pulse or points closure and converts that signal to a well defined sharp short duration pulse which is applied to the base of a transistor to produce a variable gate trigger Tg of duration from a fraction of a millisecond, msec, to several milliseconds, which turns-on ignition firing switch means for a time Tg whose duration changes inversely with engine speed of said engine.

19. The combination as defined in claim 18 wherein the output of said trigger comparator is normally high through connection to filtered power supply voltage Vcc through pull-up resistors, which changes to a low state G0 during the gate time Tg, said low triggered state G0 driving an inversion circuit based on a PNP transistor whose emitter is connected to Vcc and whose collector produces the inversion gate signal G which is applied, in turn, to the bases of complementary NPN and PNP transistors with interconnected bases and emitters and with collectors to Vcc and ground respectively, the emitters in turn providing the turn-on and turn-off drive for ignition coil switches SSi.

20. The combination as defined in claim 18 wherein said variable gate Tg is produced by means of a trigger comparator whose inputs, have impressed on them, immediately following the trigger signal, a rising voltage waveform of voltage Vrise and a decaying voltage waveform of voltage Vdec, where Vrise<

Vdec, such that the intersection Vrise=Vdec defines the gate trigger duration Tg, and wherein said rising voltage waveform, following intersection and flipping of the comparator output, becomes changed to a decaying voltage waveform Vrd with a longer time constant to define an initial voltage threshold Vri for the initially rising voltage waveform Vrise, where Vri increases with engine speed to reduce gate time Tg with engine speed.

21. The combination as defined in claim 20 wherein the trigger input circuit includes an in-series diode with a point bounce resistor of large resistance across it, a differentiating capacitor, and a voltage divider to the base of said transistor which is an NPN gate producing transistor switch Sdec with collector to a reference voltage Vref and with emitter connected to a timing capacitor Csig shunted by a timing resistor Rsig which define the decaying voltage waveform Vdec which takes on an initial value close to Vref essentially without delay upon switch Sdec turn-on by immediate charging of capacitor Csig, which starts to decay with voltage Vdec on switch Sdec turn-off at the end of said short duration pulse of time much less than gate period Tg, said voltage Vdec being impressed on the inverting input of said trigger comparator through a delay circuit, and wherein a second NPN transistor switch Srise with collector connected to the voltage Vref through a second timing resistor Rrise whose emitter is connected to a second timing capacitor Crd comprises the circuit producing the second voltage rise and decay waveforms Vrise and Vrd by charging up capacitor Crd gradually through resistor Rrise when switch Srise is turned on and discharging it when switch Srise is turned off, with the voltage rise Vrise occurring during the gate time Tg and the decay voltage Vrd after the time Tg, to apply the voltage Vrise to the non-inverting input of the trigger comparator which switches its state when Vrise reaches Vdec, i.e. Vrise=Vdec, turning off switch Srise and allowing capacitor Crd to discharge with voltage waveform Vrd through a capacitor Crd shunt resistor Rsh, greater than Rrise, with a longer time constant than the time constant of the waveform Vrise, and wherein the level to which the voltage Vrd decays Vri is proportional to the engine speed thus putting an initial voltage off-set Vri on Vrise which allows Vrise to reach the level of Vdec more rapidly after trigerring on and off of switch Sdec by said short duration pulse to produce said shorter gate trigger duration Tg with engine speed.

22. The combination as defined in claim 18 wherein the power converter operation is turned off during ignition firing by the output trigger Tg driving a transistor switch which pulls the timing capacitor Ct close to ground.

23. The combination as defined in claim 22 wherein a start-up circuit is provided for restarting the power converter which includes the electrical power source supply of voltage Vcc feeding the power converter and a resistor of order of magnitude of 100 ohms connected between said supply voltage Vcc and the output load capacitor of the power converter through an isolation diode, as well as one or more resistors in the tens to hundreds kohm resistor range connected to the supply voltage Vcc and/or to a lower regulated voltage Vref of said supply for helping provide a limited charge to timing capacitor Ct to speed up its restart without charging the timing capacitor to a level to turn the power converter on when the ignition primary circuit is in an operating mode or in a latched, low voltage, mode.

24. The combination as defined in claim 18 wherein said ignition controller includes a phase conditioner circuit for obtaining ignition firing phasing information and applying it to a counter with output able to drive multiple switches SSi of ignition coils Ti of a distributorless ignition system for a multi-cylinder engine and having said counter properly phase the ignition firing signals which are delivered to said switches SSi.

25. The combination as defined in claim 24 wherein said phase input circuit comprises a phase comparator whose inverting input is connected to a reference voltage Vref through as voltage divider producing a voltage Vinv about half of Vref and whose non-inverting input is connected to Vcc through a voltage divider comprised of a high value first divider resistor connected to the non-inverting input which places a low voltage there of about one volt producing a normally low phase output signal, the comparator having three phase input connections to it:

1) a positive input PHASE+ comprising a resistor connected to the non-inverting input to which is applied a positive voltage signal of value greater than Vinv;

2) a closure input PHASE0 comprising a resistor much smaller than said first divider resistor shunting said first divider resistor when its other end PHASE0 is connected to the PHASE+ input and produces a voltage greater than Vinv;

3) a negative input PHASE- comprising a PNP transistor with grounded base and collector connected to the comparator'"'"'s inverting input and whose emitter is connected to a voltage node divider point of one resistor connected to Vcc and the other to the input PHASE- such that when the input goes sufficiently negative the transistor base-emitter junction becomes forward biased and the collector, and hence inverting input, is pulled within a few tenths of a volt below ground and held there by a schottky diode, shunted by a capacitor and resistor, whose anode is grounded and cathode is connected to the inverting input.

26. The combination as defined in claim 24 wherein the clock input CLK of the counter is connected to Vcc, the phase output positive signal of said phase conditioner circuit is applied to the reset input, RST, of the counter, and the trigger output low signal G0 of the trigger circuit, which is delayed relative to the phase signal, is applied to the enable, ENA, input of the counter, which causes the counter outputs to sequence starting with the first output which begins the sequencing when the phase signal is received.

27. The power converter as defined in claim 10 wherein said power converter is a flyback converter with said inductive means comprising a step-up transformer including a primary and secondary winding wound concentrically on a magnetic core to provide a low leakage inductance and said switch means SE turning on and off current in the primary winding.

28. The power converter as defined in claim 27 wherein magnetic core of said transformer comprises an ETD E-type ferrite core with an air gap.

29. The power converter as defined in claim 28 wherein snubber switch Sn is not used and the zener itself takes the place of the snubber switch, permitting current flow and energy build-up in snubber inductor Lsn when the snubber capacitor voltage exceeds the zener voltage with said energy being delivered to said input power supply when the zener ceases to conduct as a result of the snubber capacitor voltage drop.

30. The power converter as defined in claim 27 wherein said converter controller includes an active low loss snubber for limiting the peak voltage on switch SE turn-off comprised of a snubber capacitor Csn and series diode, an energy storage inductor Lsn of inductance about 50 uH, a snubber switch Sn connected between said capacitor Csn and inductor Lsn, a diode with anode to ground for providing a path for energy stored in said inductor to be delivered to the converter power supply when said switch Sn opens, and a snubber zener diode Zsn for sensing and controlling the voltage on said snubber capacitor for turning it on and off when the capacitor voltage exceeds or drops below a prescribed value Vsn, and wherein energy stored in said inductor Lsn is delivered before or at the end of the off-time T-off of said controlled oscillator means.

31. The power converter as defined in claim 30 wherein said input power supply is an automotive 12 volt battery and said output voltage Vc is approximately 360 volts and said snubber capacitor is of capacitance Csn of about 0.1 microfarads (uF) and said snubber zener is of zener voltage approximately 24 volts.

32. The power converter as defined in claim 27 wherein said flyback converter controller includes a transformer secondary winding current sensor circuit comprised of a sensor resistor Rsense and an NPN transistor, where Rsense is between a fraction of an ohm and a few ohms and is placed between the end point of the transformer secondary winding and ground and the transistor is placed with its base and emitter across the sensor resistor with its base at ground, its emitter at said secondary winding end point, and its collector is connected to the discharge point, such that following said main switch SE opening and transformer secondary winding current rise above a threshold current Ith the emitter-base junction becomes forward biased at 0.62 volts and the sensor transistor is actuated, i.e. turned on, diverting off-time charging current to capacitor Ct to increase the off-time Toff by an amount proportional to the current overshoot above the threshold current Ith and establish a peak set current level in the transformer and switch SE and protect them from over-current.

33. The power converter as defined in claim 32 wherein a temperature compensating thermistor of negative temperature coefficient, NTC, and an small resistor of zero to a few ohms in series with the thermistor are placed across said sensor resistor to compensate for the change in base-emitter voltage Vbe of said sensor transistor over a temperature range.

34. The power converter as defined in claim 32 wherein the circuit design off-time Toff determined by the resistor Rc is shorter than that required to fully discharge the current in the secondary transformer winding resulting in peak current Ipk build-up which actuates the sensor transistor to increase the off-time and set a steady DC current level Idc and a defined peak current Ipk.

35. The power converter as defined in claim 34 wherein said DC current level is about 10 amps, said peak current Ipk is about 20 amps, and said change in current level Iac is about 10 amps, and said frequency at which the oscillating part of the power converter current Iac ramps up and down between about 10 to 20 amps is about 60 kHz.

36. The power converter as defined in claim 35 wherein the high voltage diode placed at the output of said transformer is an ultra fast diode.

37. The power converter as defined in claim 27 wherein the secondary winding is wound as a single layer of magnet wire around the center post of the magnetic core of said transformer and the primary winding is wound as a single layer on top of said secondary winding to provide lowest leakage inductance.

38. The power converter as defined in claim 37 wherein the primary winding turns Np is approximately 7 turns and the turns ratio N of secondary turns Ns to primary turns, N=Ns/Np, is approximately 12.

39. The power converter as defined in claim 38 wherein the core is a gapped core to provide approximately 12 microhenries (uH) of primary inductance Lp for said approximately 7 primary wire turns.

40. The power converter as defined in claim 39 wherein said input power supply is an automotive 12 volt battery and said output voltage Vc is approximately 360 volts and said switch SE is a 60 volt high efficiency FET switch.