US3868937A

US3868937A - Ignition system with improved triggering circuit

Info

Publication number: US3868937A
Application number: US316735A
Authority: US
Inventors: Richard Zechlin; Robert M Henderson
Original assignee: Colt Industries Operating Corp
Current assignee: Colt Industries Operating Corp
Priority date: 1972-12-20
Filing date: 1972-12-20
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04

Abstract

An ignition system is disclosed having improved triggering means for triggering and firing associated spark plugs with better accuracy and reliability.

Description

United States Patent Zechlin et al. Mar. 4, 1975 IGNITION SYSTEM WITH IMPROVED TRIGGERING CIRCUIT [56] References Cited [75] Inventors: Richard Zechlin, Beloit; Robert M. UNITED TATES PATENTS Henderson, William Bay, both of 3,331,362 7/1967 Mitchell 123/148 0C Wis. 3,692,009 9/1972 Issier 123/148 OC 3,741,183 61973 S 123148 0 [73] Assignee: Colt Industries Operating Corp. wrm C g g ig g Morse Primary Eraminew-Manuel A. Antonakas ew or Assistant Examiner-Ronald B. Cox [22] Filed: Dec. 20, 1972 Attorney, Agent, or Firm-Leo J. Aubel [2]] Appl. No.: 316,735 ABSTRACT An ignition system is disclosed having improved trig- [52] E' 'C I 123/148 gering means for triggering and firing associated spark gz' MC I plugs with better accuracy and reliability. 1 23/148 1 7 Claims, 2 Drawing Figures IGNITION SYSTEM WITH IMPROVED TRIGGERING CIRCUIT BACKGROUND or THE lNVENTlON Breakerless ignition systems are well known in the prior art. With the advent of improved semi-conductor components and reliable semi-conductor circuits, breakerless ignition systems have enjoyed considerable commercial acceptance as ignition systems for combustion engines.

Prior art breakerless ignition systems generally work relatively satisfactory; however, it is an object of the present invention to provide an ignition system which is improved over the prior art in its accuracy of firing; and, to provide a triggering system having improved reliability. Further, the present system provides features for more precisely and accurately controlling the advance and timing of the ignition to thereby provide a more efficient operation of the associated engine for each operating condition.

The foregoing features and advantages of the invention will be apparent from the following more particular description of the invention. The accompanying drawings listed hereinbelow are useful in explaining the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram ofthe inventive system; FIG. 2 are waveforms useful in explaining the opera tion of the system.

DESCRIPTION OF THE INVENTION Refer now to FIG. 1 which shows an embodiment of the ignition system 11 according to the invention. A suitable source of excitation is indicated by magnet rotor M which energizes winding assembly W1 having a firstwinding 13 and a second winding 15. The first winding 13 is connected across fullwave diode rectifier 17 to provide a rectified DC (direct current) voltage through conductive leads 19 and 21 to the remaining portion of the circuit. A zener diode 23 is connected across the output of the rectifier 17 to provide a voltage limiting function for the circuit of FIG. 1. Lead 21 is connected through a resistor 25 to a common or reference lead 27. A storage capacitor 29 is connected from lead 19 to the common lead 27. A resistor 31 has one terminal connected to lead 19 and the other terminal connected to the collector electrode c of an NPN transistor 33 which has its emitter 2 connected to common lead 27, and its base b connected as will be explained.

An AC coupling capacitor 35 has one terminal connected to lead 19 and the other terminal connected through a zener doide 37 to the common lead 27. The junction of resistor 31 and the collector c of transistor 33 is connected to the junction of capacitor 35 and zener diode 37 by lead 39.

An AC bias source indicated as the second,winding connects across a second fullwave diode rectifier 43 to provide a control bias voltage. One output terminal of rectifier 43 is connected to common lead 27, and the other output terminal of rectifier 43 is connected through a resistor 45 to a control bias lead 47.

A resistor 49 has one terminal connected to lead 47 and its other terminal connected to the anode of a diode 51. The cathode of diode 51 is connected to the junction of rectifier 17 and resistor 25. A bias capacitor 53 is connected from lead 47 to common lead 27.

Referring back to transistor 33, its base b, is connected through a resistor 55 to the control bias lead 47. The base b of transistor 33 is also connected through a resistor 57 and a diode 59 to the cathode of silicon control rectifiers 61 and 63. It will be appreciated that in the system as indicated, the engine has six cylinders, therefore there are six ignition coils; however, only two ignition coils (coils numbered one and six) and their associated circuits are shown in the drawing since the intervening ignition circuits for each of the other cylinders are identical to those for the cylinders shown. Note that the invention is not limited to use for any particular number of cylinders.

A capacitor 65 has one terminal connected to the junction of resistor 57 and the cathode of diode 59 and its other terminal connected to the common lead 27. A resistor 62 has one terminal connected to the junction of the anode of diode 59 and the cathode of SCR 61, as well as to the cathode of SCR 63 associated with the sixth ignition coil. The other terminal of resistor 62 is connected to the common lead 27. A capacitor 69 is connected in parallel with resistor 62.

For purposes of this description SCRs 61 and 63 are referred to as power SCRs.

Refer now to the circuit of SCR 6] and, as mentioned, the circuit of SCR 63 is identical thereto. The anode of SCR 61 is connected to the primary winding of its respective ignition coil or transformer 73. The other terminal of winding 71 is connected to ground lead 19. The secondary output winding 75 of ignition coil 73 is connected to provide a spark across the assoeiated spark plug SP1.

The control electrode or gate 3 of a trigger pilot SCR 79 is connected to the junction of adjustable resistor 77 and pulser coil 81. The other terminal of resistor 77 is connected to control lead 47 and the other terminal of pulser coil 81 is connected to common lead 27. The cathode c of SCR 79 is connected to the gate g of SCR 61 and through resistor 70 to common lead 27. The anode a of SCR 79 is connected to lead 39 and thus to thejunction of capacitor 35, zener diode 37, resistor 31 and the collector c of transistor 33. Note that SCR 83 (for the sixth ignition circuit) corresponds to SCR 79.

A suitable pulser assembly comprising a rotatable trigger wheel 91 having one or more projections 93 on its periphery is driven in synchronism with the rotor of the magneto by means of a suitable shaft, not shown. As each projection 93 passes the trigger coil 81, a discharge is initiated in the respective spark plug SP1. Coil 82 for the sixth ignition circuit corresponds to coil 81.

Initially, assume capacitor 29 charges to the voltage developed across fullwave rectifier 17 as indicated at 88 in FIG. 2 (a). Note that since capacitor 35 and zener diode 37 are connected in series with each other across capacitor 29, capacitor 35 charges to the voltage level of capacitor 29 less the voltage drop across the zener diode as at 90 in FIG. 2(1').

As pulser 91 is rotated, it causes pulser coil 81 to be energized, see waveform FIG. 2 (g). When the voltage on pulser coil increases to point 92, the voltage is effective at gate g of SCR 79 to bias SCR 79 to be in a conductive mode. The voltage on the anode of SCR 79 will drop as shown in FIG. 2 (/1). With SCR 79 turned ON. the lower terminal of capacitor 35 will be connected through lead 39 and the anode to cathode circuit of SCR 79 to the common lead 27. Thus, the lower terminal of capacitor 35 is pulled down to the reference voltage level on common lead 27. I

Since, as noted above, capacitor 35 is charged to a voltage level less than the voltage on capacitor 29, capacitor 35 will instantaneously charge as at point 94, on FIG. 2(1'), to the voltage level of capacitor 29.

The aforementioned will cause capacitor 29 to discharge through a path which may be traced from the upper plate of capacitor 29 through coupling capacitor 35, the anode to cathode circuit of SCR 79, and the gate to cathode circuit of SCR 61 and resistor 67 and capacitor 69 to the lower plate of capacitor 29, thereby turning thepower SCR 61 ON.

With power SCR 61 conducting, a current path for capacitor 35 may be traced upwardly from reference lead 27 through zener diode 37, capacitor 35 through winding 71, through the anode to cathode circuit of SCR 61, and capacitor 69 back to reference lead 27. Capacitor 29 will complete discharging through an electrical path traceable from the upper terminal of ca pacitor 29, the winding 71, the anode-to-cathode circuit of SCR 61, and coupling capacitor 69 to the lower terminal of capacitor 29. The foregoing will, of course, energize winding 75 and fire the spark plug SP1.

The windings 71 and 75 of transformer 73 form an oscillatory LC circuit with capacitor 29. This oscillatory LC circuit develops a negative voltage on the upper terminal of resistor 25. Accordingly, a current is caused to flow from the lower terminal of capacitor 29 through capacitor 53, lead 47, resistor 49, diode 51 to the upper terminal of resistor 25; lead 21, zener diode 23 in parallel with diode rectifier 19 and lead 19 to the upper terminal of capacitor 29. When this occurs, the negative voltage on lead 47 is increased thereby increasing the control bias applied through resistor 77 to the gate of SCR 71. This provides a negative current for the pilot SCR 79 causing it to turn off, as at 98, FIG. 2(11).

The current through SCR 61 also develops a bias voltage, as at 97 in FIG. 2(0), in the circuit comprised of capacitor 69 and resistor 67. This bias referred to herein as power bias is used to provide a negative gate voltage to the power SCRs. This voltage also charges capacitor 65 through diode 59. The voltage on capacitor 65 as at 100 FlG. 2(d), causes current to flow through resistor 57 to thereby turn transistor 33 as at 101 FIG. 2(e). When transistor 33 is turned ON, capacitor 35 is effectively connected directly in parallel with capacitor 29.

The time constant of capacitor 65, and resistors 57 and 55 is such that transistor 33 is held conductive for a period of time longer than that required for the voltage on the pulser coil to become increasingly positive to overcome the effect of the increased control bias, FIG. 2(f). When transistor 33 is ON, a current path may then be traced from the source; i.e. from the upper terminal of rectifier 17 through capacitor 35 and the collector to emitter of transistor 33 and resistor 25 to the lower terminal of rectifier 17. When transistor 33 turns OFF or becomes non-conductive as at 102 FIG. 2(a). the pilot SCR 79 will have again become conductive so that capacitor 35 is still effectively connected directly in parallel with capacitor 29.

When the pilot SCR 79 turns OFF because of the pulser going negative by passing the timing pin, the system returns to its initial condition. The power bias thus compensates for the control bias to properly control the triggering operation.

The advance of the system is controlled by the amount of direct current control bias provided to the pulser coil as by the adjustable resistor 77. One such resistor being connected to each of the ignition circuits 'of each cylinder.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

.1. An ignition system for generating ignition pulses for the spark plugs of an associated engine comprising, in combination, a storage capacitor, means for charging said capacitor to a predetermined level, an ignition transformer winding connected to said storage capacitor, a coupling capacitor circuit connected to be charged in parallel with said storage capacitor, a circuit for selectively discharging said storage capacitor including first and second solid state selectivity conductive devices, triggering means including rotatable means driven by the associated engine for developing cyclic triggering pulses and for imposing said pulses to trigger said first device to conduction, said first device connected in a series circuit including said coupling capacitor, said second device connected in a series circuit including said storage capacitor and said winding, and the first device being connected to control the initiation of conduction of said second device whereby when said triggering means triggers said first device to conduction, said storage capacitor initially discharges through said coupling capacitor and said first device. thereby first causing said first device to become conductive and initiate conduction of said second device and enabling said storage capacitor to provide its principal discharge through said second device and said winding to thereby initiate an ignition pulse.

2. An ignition system as in claim 1 wherein said first and second solid state devices comprise respectively first and second silicon control rectifiers (SCRs), each having an anode, a cathode and a gate electrode, said triggering means imposing said pulses on the gate of said first SCR to trigger said first SCR to conduction, the coupling capacitor connecting the anodes of said SCRs to said storage capacitor, the cathode of said first SCR being connected to the gate of said second SCR, whereby when said triggering means triggers said first SCR to conduction, said storage capacitor discharges through said coupling capacitor thereby first causing said first SCR to become conductive and then causing said second SCR to become conductive and enabling said storage capacitor to discharge through said winding to thereby initiate an ignition pulse.

3. An ignition system as in claim 1 wherein a zener diode is connected in series with said coupling capacitor and said coupling capacitor and said zener diode are connected in parallel with the storage capacitor whereby said coupling capacitor is charged to a level less than the charge on said storage capacitor, whereby when said first SCR is biased to conduct said coupling capacitor charges to the level of said storage capacitor. and said storage capacitor discharges through said coupling capacitor and said first SCR to cause said first SCR to conduct.

4. An ignition system as in claim 1 wherein said coupling capacitor is connected in parallel with said winding and the LC circuit formed by said capacitor and said winding is in the discharge path of said storage capacitor.

5. An ignition system as in claim 1 further including control bias means comprising capacitance and resistance means connected to-said storage capacitor and to the gate electrode of said first SCR, said storage capacitor and said winding effectively providing an oscillatory LC circuit whereby a negative voltage is developed through said inductance and impedance elements which is coupled to said first SCR to turn said SCR storage capacitor.

Claims

1. An ignition system for generating ignition pulses for the spark plugs of an associated engine comprising, in combination, a storage capacitor, means for charging said capacitor to a predetermined level, an ignition transformer winding connected to said storage capacitor, a coupling capacitor circuit connected to be charGed in parallel with said storage capacitor, a circuit for selectively discharging said storage capacitor including first and second solid state selectivity conductive devices, triggering means including rotatable means driven by the associated engine for developing cyclic triggering pulses and for imposing said pulses to trigger said first device to conduction, said first device connected in a series circuit including said coupling capacitor, said second device connected in a series circuit including said storage capacitor and said winding, and the first device being connected to control the initiation of conduction of said second device whereby when said triggering means triggers said first device to conduction, said storage capacitor initially discharges through said coupling capacitor and said first device, thereby first causing said first device to become conductive and initiate conduction of said second device and enabling said storage capacitor to provide its principal discharge through said second device and said winding to thereby initiate an ignition pulse.

2. An ignition system as in claim 1 wherein said first and second solid state devices comprise respectively first and second silicon control rectifiers (SCR''s), each having an anode, a cathode and a gate electrode, said triggering means imposing said pulses on the gate of said first SCR to trigger said first SCR to conduction, the coupling capacitor connecting the anodes of said SCRs to said storage capacitor, the cathode of said first SCR being connected to the gate of said second SCR, whereby when said triggering means triggers said first SCR to conduction, said storage capacitor discharges through said coupling capacitor thereby first causing said first SCR to become conductive and then causing said second SCR to become conductive and enabling said storage capacitor to discharge through said winding to thereby initiate an ignition pulse.

3. An ignition system as in claim 1 wherein a zener diode is connected in series with said coupling capacitor and said coupling capacitor and said zener diode are connected in parallel with the storage capacitor whereby said coupling capacitor is charged to a level less than the charge on said storage capacitor, whereby when said first SCR is biased to conduct said coupling capacitor charges to the level of said storage capacitor, and said storage capacitor discharges through said coupling capacitor and said first SCR to cause said first SCR to conduct.

5. An ignition system as in claim 1 further including control bias means comprising capacitance and resistance means connected to said storage capacitor and to the gate electrode of said first SCR, said storage capacitor and said winding effectively providing an oscillatory LC circuit whereby a negative voltage is developed through said inductance and impedance elements which is coupled to said first SCR to turn said SCR OFF.

6. An ignition system as in claim 1 further including capacitance and resistance bias means connected to be effective on the gat electrode of the second SCR to provide a negative gate voltage thereto to turn said second SCR OFF.

7. An ignition system as in claim 5 further including a transistor connected in series with said coupling capacitor, said capacitance and resistance bias controlling conduction of said transistor to thereby effectively connect the coupling capacitor in parallel with said storage capacitor.