US3800771A

US3800771A - Ignition systems

Info

Publication number: US3800771A
Application number: US00233623A
Authority: US
Inventors: R Mackie
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-03-10
Filing date: 1972-03-10
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02

Abstract

A capacitive discharge ignition system which does not use transistors and which transfers power from the vehicle battery to the discharge capacitor both inductively and capacitively thereby resulting in increased efficiency. The primary winding of a stepup transformer is connected in series with the vehicle battery and the distributor points and transfers energy to a discharge capacitor connected in the secondary circuit of the transformer when the points close. The discharge capacitor is also charged by energy from another capacitor in the secondary circuit which is charged during the previous points open period. The discharge capacitor is connected in parallel with the series combination of an SCR and the ignition coil of the vehicle and discharges through the ignition coil to provide spark energy when the SCR is turned on by the points opening. Reverse biasing of the gateemitter junction of the SCR begins shortly after turn on to prevent misfire and to facilitate turn off of SCR when the anode of the SCR becomes back-biased.

Description

United States Patent 1 Mackie v 111 3,300,771 1 Apr. 2, 1974 1 IGNITION SYSTEMS [76] Inventor: Ronald D. Mackie, Rt. 1, Box 776-P,

Pensacola, Fla. 32507 221 Filed: Mar. 10, 1972 y 21 Appl. No.: 233,623

Related US. Application Data [63] Continuation of Ser. No. 80326, Oct. 15, 1970,

Primary ExaminerLaurence M. Goodridge Assistant ExaminerRonald B. Cox

Attorney, Agent, or Firm-Browne, Beveridge, Degrandi & Kline [57] ABSTRAT A capacitive discharge ignition system which does not use transistors and which transfers power from the vehicle battery to the discharge capacitor both inductively and capacitively thereby resulting in increased efficiency. The primary winding of a step-up transformer is connected in series with the vehicle battery and the distributor points and transfers energy to a discharge capacitor connected in the secondary circuit of the transformer when the points close. The discharge capacitor is also charged by energy from another capacitor in the secondary circuit which is charged during the previous points open period. The discharge capacitor is connected in parallel with the series combination of an SCR and the ignition coil of Y the vehicle and discharges through the ignition coil to Claims, 1 DQ111515???" CR-G This application is a continuation of U. S. Pat. application Ser. No. 80,326 filed in the same of Ronald D. Mackie on Oct. 15, 1970, now abandoned.

The invention relates to an improved capacitive discharge ignition system for an automotive vehicle. While such discharge systems are known in the prior art, they are usually complicated electronic circuits including one or more switching transistors used to supply the discharge capacitor with energy from the battery of the vehicle. For instance, it is common in prior art discharge systems to utilize transistorized multivibrator or inverter circuits to supply the discharge capacitor with energy. Such circuits besides containing a number of components and therefore adding to the cost of the system, consume power, and therefore do not provide for the most efficient transmission of the energy of the vehicle battery to the discharge capacitor. Additionally, the transistors are heat-sensitive and require heat sinksto' effectively operate in the heated environment of the automotive engine.

7 The present invention eliminates the transistorized multivibrator or inverter circuitry by using the opening and closing of the distributor points to directly transfer energy to the discharge capacitor through a step-up transformer. Additionally, a second capacitor is charged during a portion of the cycle and adds to the energy transferred to the discharge capacitor by the 'step-up transformer thereby increasing the efficiency of power'transfer from the vehicle battery to the discharge capacitor. Further, a novel circuit is provided which results in improved biasing and triggering of the SCR.

lt is therefore an object of the invention to provide a capacitive discharge ignition system which contains a minimum of parts, is simple and inexpensive to fabricate, and provides improved performance for long periods of use. 1

It is a further object of the invention to provide a catively thereby increasing the efficiency of the system.

It is a further object of the invention to provide an improved method of triggering the SCR and of backbiasing the gate-emitter junction of the SCR when it is not being triggered.

It is a further object of the invention to provide an improved circuit in which voltage fluctuations at the anode of the SCR are reduced to prevent misfire of the SCR.

lt is a further object of the invention to provide direct chassis grounding of the SCR anode which results in simpler and cheaper mounting of the SCR, better transfer of heat from the SCR, and elimination of the possibility of a short occurring between an anode insulated from the chassis and the chassis.

It is a further object of the invention to provide for improved self-cleaning action of the distributor points.

It is a further object of the invention to provide a capacitive discharge ignition system which will work equally well with positive ground or negative ground engines.

The above objects are accomplished by providing a capacitive discharge ignition system in which the energy of the vehicle battery is directly transferred to the discharge capacitor by the opening and closing of the distributor points. The primary winding of a step-up transformer is connected in series with. the points and the vehicle battery, and the secondary winding of the transformer is connected to a circuit including the discharge capacitor. The discharge capacitor is charged when the points are closed by the energy at the secondary of the transformer and by energy stored in a capacitor in the secondary circuit during the previous points open period. The discharge capacitor is connected in parallel with the series combination of an SCR and the primary of the ignition coil and when the points open the gate-emitter junction of the SCR becomes forward biased to turn the SCR on thereby providing a current path for the charge stored on the discharge capacitor through the SCR and the ignition coil. Shortly after turn on the gate-emitter junction of the SCR becomes back biased by a novel circuit thus insuring that the SCR willbe turned ofi 'when the anode is back biased. The current energy which is not consumed by the spark or by the resistance of the ignition coil transfers back to the discharge capacitor within the opposite direction and when it reaches the maximum of the direction of current, reverses through the ignition coil thereby forward biasing a diode connected across the anode emitter junction of the SCR and reverse biasing the anode which in conjunction with the reverse bias of the emitter gate junction turns the SCR off until the points open again.

The invention will be better understood by referring to the FIGURE in connection with the following detailed description of a preferred embodiment of the invention.

Referring to the FIGURE, T1 is a standard step-up transformer, the secondary of which, in the preferred embodiment of the invention, is either center-tapped or wound in separate halves which are connected together at the center. T1 is wound so that if one end of the complete secondary is negative relative to the center tap the other end of the complete secondary will be positive relative to the center tap. 1n the preferred embodiment of the invention, a step-up ratio of 1:32 is used for the complete secondary embodiment. While a center tap secondary for T1 and a turns ratio of 1:32 are used in the preferred embodiment of the invention, it should be noted that other tap locations and turn ratios can be used to obtain the operating characteristics which will be described hereafter.

The primary winding of T1 is connected in series with the standard vehicle battery, the ignition switch, the standard ballast resistor, which may be approximately 3 ohms, and the distributor points. The capacitor connected across the distributor points is the standard points capacitor. The connections from the ballast resistor and the points to the primary winding of T1 should be made so that the end of the secondary winding of T1 connected to CR-l will be negative going with respect to the opposite end of the secondary when the current through the primary of T1 is interrupted by the points opening. As noted above, the present invention can be used with either a negative ground engine or a positive ground engine and assuming that the primary of T1 is wound so that the Pl terminal is negative going with respect to the P2 terminal when the current through the primary is interrupted by the points opening, in a negative ground engine the wire from the points should be attached to the P2 terminal and the wire from the ballast resistor should be attached to the Pl terminal while in a positive ground engine the connections should be reversed. In this way with either a negative or positive ground engine, current will flow through the primary of T1 in the same direction when the points are closed.

The primary winding of the ignition coil is also connected in a direction dependent on whether the engine is positively or negatively grounded. Proper connection to the ignition coil will insure that the spark voltage applied to the insulated electrode of the spark plug will be negative with respect to engine ground. In a negative ground installation the terminal P3 is connected to the minus terminal of the spark coil and P4 is connected to the plus terminal, while in a positive ground engine the connections are reversed.

The ignition coil is connected in series with the SCR and the series combination of the ignition coil and the SCR is connected in parallel with capacitor C1 which is the discharge capacitor of the invention. As in all capacitive-discharge ignition systems, a charge stored on a-discharge capacitor will discharge through a switch which is turned on periodically to supply a high voltage of short rise time duration to the ignition coil for firing a spark plug. In the present invention the SCR is the switch and the charge accumulated on discharge capacitor Cl discharges through the ignition coil when the SCR is triggered on by a forward bias signal applied to its gate-emitter junction.

It should be noted that the anode of the SCR is directly connected to ground. This connection permits direct and simplified mounting of the SCR to a metal ignition system enclosure which is directly connected to engine ground or chassis ground permitting more efficient heat transfer away from the anode and eliminating the chance that an insulated SCR anode has of shorting to the chassis or engine ground.

One of the features of the present invention is that energy from the vehicle battery is supplied to capacitor C1 not only through the inductive means of the transformer but also through capacitor C-2. C-2 in combination with the lower half of the T1 secondary and diodes CR-3 and CR-4, resistor R-l, capacitor C-3 and the emitter-gate junction of the SCR form a resonant circuit for transmitting inductive energy stored in the transformer T-l to capacitor C-2 as voltage energy.

The operation of the invention will now be described. As indicated above, transformer T-l is connected and wound so that when the points open, the end of the secondary winding connected to CR-l will be negative going with respect to the opposite end of the secondary. When the points are opened, therefore, one of the things which happens is that current travels from the bottom half of the secondary winding to capacitor C-2 thereby charging capacitor C-2. The size of capacitor C-2 is chosen with respect to the engine RPMs and the other components in the circuit so that it is fully charged and has already begun to discharge by the time that the points close. When the points close therefore C-2 will be somewhere in the process of transferring energy to discharge capacitor C4 through the entire secondary winding of transformer T-l.

Due to the step-up ratio of transformer T1, as the points close a highvoltage is placed in series aiding with discharging capacitor C2 across discharge capacitor C-l. If a 1:32 step-up ratio and a 3-ohm ballast resistor are used, then an apparent voltage source of approximately 384 volts having an internal resistance of approximately 3072 ohms will be effectively placed in series with capacitor C2 when'the points close. Then capacitor C-l is charged to a maximum voltage from the energy in the secondary of the transformer combined with the energy transferred to capacitor C2 during the previous points open period. After most, if not all, of the stored energy on capacitor C-2 has been used to charge capacitor C1, diode CR-2 which is connected across capacitor C-2, prevents any remaining charging current through C-l from reverse charging C-2.

After discharge capacitor C-l is charged to its maximum voltage, the points open'and O2 is charged as described above.

The charging of capacitor C-2 through resistor R-l causes current to flow through R4 in the forward bias direction of diode CR4 and causes a voltage across resistor R-l which is effective to forward bias the gateemitter junction of the SCR thereby turning the SCR on a short time after the points open. Diode CR-4 equalizes the variable resistance emitter-gate junction of the SCR and insures that there will be adequate current flow through the emitter-gate junction as the points open to positively fire the SCR. The turned-on SCR is an effective closed switch and along with the ignition coil forms a low resistance path across discharge capacitor C-l. The stored charge on capacitor C-l immediately discharges through the ignition coil in a direction from terminal P-3 to terminal P-4 and through the SCR. Due to the extremely rapid rise of voltage across the primary of the ignition coil the time during which the voltage rises to the sparking potential of the spark plug is extremely short and herein lies the great advantage of the capacitor discharge ignition system over the conventional points ballast ignition system. The extremely short rise time in which the large voltage of C-1 is impressed across the primary of the spark coil can mean the difference between firing and not firing the spark plug.

After tum-on the SCR cannot be turned off merely by reverse biasing the gate-emitter junction but rather both the gate-emitter junction and the anode must be back biased to efiect turn off. One of the novel features of the invention is the provision of means which begins to back bias .the gate-emitter junction of the SCR immediately following turn-on so as to prevent misfire and so that the SCR can be turned off as soon as the anode is back biased and this means will now be described.

When the points open and as the current increases through resistor R-l to forward bias the gate-emitter junction of the SCR, capacitor C-3 is charged. The current increases through resistor R-l to the point where it equals the charging current through the capacitor C-2. After this point the current begins to decrease through resistor R-l until capacitor C-2 reaches full charge and when capacitor C-2 does reach full charge the voltage across resistor R-l will be zero. While the current through resistor R-l is decreasing, capacitor C-3 discharges through diode CR-S, thereby backbiasing the SCR. When capacitor C2 completes charging as described above, it begins to transfer energy to capacitor C-l through the secondary of the transformer and through diode CR-S thereby maintaining the back biasing of the gate-emitter junction until the points close again when back biasing is continued until either the completion of the charging of capacitor C-l or until the points open which might occur before the completion of charging of capacitor C-l at higher engine speeds. Thus it is seen that according to the novel circuit arrangement of the invention, the back biasing of the SCR begins to take place shortly after turn-on and continues right through until the charging of capacitor C-l is completed or until the points open again.

After the SCR is turned on, current builds up to a peak in the primary of the spark coil about the time that the voltage on discharge capacitor C-l has dropped to zero. Whatever current energy is not consumed either by the spark itself or by the resistance of the spark coil windings begins to transfer back to capacitor C-l as voltage energy which is opposite in polarity to the voltage energy which was originally stored on capacitor C-l from the battery. When the voltage on capacitor C-l reaches a maximum in the opposite direction current reverses through the primary of the spark coil forward biasing and flowing through diode CR-6 and thereby reverse biasing the anode of the SCR which in conjunction with the reverse biasing of the gate-emitter junction previously described turns the SCR off until the next opening of the points.

Current flow continues through diode CR-6 until most of the current energy remaining in the spark coil is returned to capacitor C-l with thesame voltage polarity as the voltage energy which will be added to capacitor C-l from the battery. This energy returned to C-1 from the spark coil combines with the energy added to C-1 from the battery when the points close again and from capacitor C-2. The energy in the spark coil not returned to capacitor C-l oscillates until damped bycoil resistance. These oscillations which cause voltage fluctuations at the anode of the SCR are normally too weak by themselves to cause SCR misfire and are allowed to die out before being added to the voltage fluctuations caused by the charging of capacitor G1 with energy from the battery.'The fact that energy not used in firing a spark plug is restored to C-1' for release the next time the points open allows the practice of bypassing the ballast resistor to be dispensed with.

One of the novel features of the invention is the connection of the discharge capacitor in parallel with the series combination of the ignition coil and the SCR. This location of discharge capacitor C1 prevents charging currents to 01 via CR-l from passing through the primary of the spark coil which if allowed to happen could cause voltage fluctuations at the anode of the SCR sufficient to cause misflre.

Another advantage of the invention is that the circuit provides for self-cleaning of the distributor points by allowing adequate current to flow through the points while simultaneously reducing the inductive effect which tends to cause arcing in a conventional ignition system. This inductive efiect is reduced by the reflection of a substantial capacitance in parallel with the primary of the transformer each time the points open. The tendency of the primary inductance of the transformer to hold an arc across the points is reduced to the extent that the invention can operate with the standard points capacitor completely removed.

Typical values for the components of the invention are listed below:

T-l 4 M.h. primary 4 a. D C, 1:32 turns ratio C-1 1 MFd, 600vDC G2 0.25 MFd 1000vDC C-3 0.01 MFd 200vDC R-l 47 ohms, 1 watt The above values are illustrative only and should not be construed to be limiting. They have been found to work satisfactorily at typical engine speeds, up to those speeds at which a complete cycle from points opening to points opening would be about 2000 microseconds. The SCR can be a General Electric type GEX-l6 or equivalent and all diodes are standard semiconductive diodes such as silicon diodes. The capacitor C-2 is sized to provide adequate trigger current for the SCR, to provide for rapid transfer of energy from the primary winding of T-l to C-2 and to insure that most, if not all, of the energy stored on O2 is transferred to G1.

There has thus been described above a capacitive discharge ignition system which does not use transistors and which operates efficiently.

While I have disclosed and described the preferred embodiment of my invention, I wish it understood that I do not intend to be restricted solely thereto, but that I do intend to include all embodiments thereof which would be apparent to one skilled in the art and which come within the spirit and scope of my invention.

1 claim:

l. A capacitive discharge ignition system which transfers energy from the battery of a vehicle to a discharge capacitor without the use of switching transistors, comprising: 1

a step-up transformer having a primary winding and a secondary winding, said primary winding being connected in series with said vehicle battery and the distributor points of said vehicle, a discharge capacitor, a silicon controlled rectifier and an ignition coil being connected in circuit relationship with each other and with the secondary winding of said transformer, means for applying the voltage across said secondary winding of said transformer. to said discharge capacitor when said points close to charge said discharge capacitor without the use of switching transistors, means for discharging said discharge capacitor through said silicon controlled rectifier and said ignition coil when said points open to provide an ignition spark, and means for aiding said transformer in charging said discharge capacitor, said means for aiding including a storage capacitor and means for charging said storage capacitor when said points open.

2. The system of claim 1 wherein said discharge capacitor is connected in parallel with the series combination of said silicon controlled rectifer and said ignicapacitor to discharge through said silicon controlled rectifier and said ignition coil.

4. The system of claim 3 further comprising means for back-biasing said gate-emitter junction of said silicon controlled rectifier shortly after turn-on so that said silicon controlled rectifier will be turned off when its anode becomes back biased.

5. The system of claim 4 wherein said means for triggering said gate-emitter junction of said silicon controlled rectifier includes a resistor connected in the secondary circuit of said transformer and the gate-emitter circuit of said silicon controlled rectifier, said resistor being supplied with current when said points open to impress a forward bias voltage across said gate-emitter junction.

6. The system of claim 5 wherein said means for back-biasing comprises the series combination of a capacitor and diode connected in said gate-emitter circuit and in parallel with said resistor, said capacitor being charged by the current flowing through said resistor, and being discharged through said diode to back bias said gate-emitter junction.

7. The system of claim 6 further comprising a diode connected across the anode-emitter junction of said silicon controlled rectifier in a direction opposite to the direction of the anode-emitter junction for turning said silicon controlled rectifier off.

8. The system of claim 6 wherein the anode of said silicon controlled rectifier is directly connected to ground.

9. The system of claim 8 wherein a capacitance proportional to the capacitance of said storage capacitor is effectively placed in parallel with said primary winding of said transformer each time said points open thereby compensating for the inductive effect of the primary winding of said transformer and permitting said points to be cleaned by current passing through them.

10. A capacitive discharge system for connection in a secondary winding, said primary winding being adapted for series connection with said vehicle battery and said distributor points, a discharge capacitor and a silicon controlled rectifier in circuit connection with each other and with the secondary winding of said transformer, means for charging said discharge capacitor from the secondary winding of said transformer when current increases through said primary winding of said transformer and means for discharging said discharge capacitor through said silicon controlled rectifier when current decreases through said primary winding of said transformer, a storage capacitor connected in series with the secondary winding of said transformer, means for charging said storage capacitor when the current in the primary winding of said transformer decreases and means for discharging said storage capacitor to aid in charging said capacitor, whereby when said primary winding is connected in series with said vehicle battery and said points, and said ignition coil is connected in series with said silicon controlled rectifier, said discharge capacitor is charged when said points close and is discharged through said ignition coil to provide an ignition spark when said points open.

11. The system of Claim 10 wherein said discharge capacitor is connected in parallel with said silicon controlled rectifier and said means for discharging said discharge capacitor comprises means for triggering the gate-emitter junction of said silicon controlled rectifier with a forward bias signal to turn said silicon controlled rectifier on, whereby when said ignition coil of said vehicle is connected in series with said silicon controlled rectifier said discharge capacitor will discharge through said ignition coil, means for back biasing the gate emitter junction of said silicon controlled rectifier shortly after turn-on so that said silicon controlled rectifier will be turned off when its anode becomes back biased, said means for back-biasing the gate-emitter junction comprising the series combination of a capacitor and a diode connected in the gate-emitter circuit.

Claims

1. A capacitive discharge ignition system which transfers energy from the battery of a vehicle to a discharge capacitor without the use of switching transistors, comprising: a step-up transformer having a primary winding and a secondary winding, said primary winding being connected in series with said vehicle battery and the distributor points of said vehicle, a discharge capacitor, a silicon controlled rectifier and an ignition coil being connected in circuit relationship with each other and with the secondary winding of said transformer, means for applying the voltage across said secondary winding of said transformer to said discharge capacitor when said points close to charge said discharge capacitor without the use of switching transistors, means for discharging said discharge capacitor through said silicon controlled rectifier and said ignition coil when said points open to provide an ignition spark, and means for aiding said transformer in charging said discharge capacitor, said means for aiding including a storage capacitor and means for charging said storage capacitor when said points open.

2. The system of claim 1 wherein said discharge capacitor is connected in parallel with the series combination of said silicon controlled rectifer and said ignition coil.

3. The system of claim 2 wherein said means for discharging said discharge capacitor comprises means for triggering the gate-emitter junction of said silicon controlled rectifier with a forward bias signal to turn said silicon controlled rectifier on and cause said discharge capacitor to discharge through said silicon controlled rectifier and said ignition coil.

10. A capacitive discharge system for connection in a vehicle having a battery, a distributor with points and an ignition coil, comprising: a step-up transformer having a primary winding and a secondary winding, said primary winding being adapted for series connection with said vehicle battery and said distributor points, a discharge capacitor and a silicon controlled rectifier in circuit connection with each other and with the secondary winding of said transformer, means for charging said discharge capacitor from the secondary winding of said transformer when current increases through said primary winding of said transformer and means for discharging said discharge capacitor through said silicon controlled rectifier when current decreases through said primary winding of said transformer, a storage capacitor connected in series with the secondary winding of said transformer, means for charging said storage capacitor when the current in the primary winding of said transformer decreases and means for discharging said storage capacitor to aid in charging said capacitor, whereby when said primary winding is connected in series with said vehicle battery and said points, and said ignition coil is connected in series with said silicon controlled rectifier, said discharge capacitor is charged when said points close and is discharged through said ignition coil to provide an ignition spark when said points open.

11. The system of Claim 10 wherein said discharge capacitor is connected in parallel with said silicon controlled rectifier and said means for discharging said discharge capacitor comprises means for triggering the gate-emitter junction of said silicon controlled rectifier with a forward bias signal to turn said silicon controlled rectifier on, whereby when said ignition coil of said vehicle is connected in series with said silicon controlled rectifier said discharge capacitor will discharge through said ignition coil, means for back biasing the gate-emitter junction of said silicon controlled rectifier shortly after turn-on so that said silicon controlled rectifier will be turned off when its anode becomes back biased, said means for back-biasing the gate-emitter junction comprising the series combination of a capacitor and a diode connected in the gate-emitter circuit.