Regulated Ignition Amplifier Circuit

Abstract

Regulated ignition amplifier circuit wherein a transistor switch is controlled to build up a regulated constant current through an ignition coil primary winding and then opened to cause an increase in the voltage of both the primary and the secondary windings. A capacitor is charged during closure of the transistor switch from the rectified voltage developed by an oscillator, the oscillator being controlled through regulating circuitry from the voltage across the capacitor to charge the capacitor to a substantially constant voltage. In response to the increase in voltage of the primary winding, the capacitor is discharged through the primary winding by means of a silicon controlled rectifier and a disabling circuit responds to discharge current to disable the oscillator through the regulating circuitry to permit the rectifier to revert to a non-conductive state.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is related to my copending application Ser. No. 330917, filed Feb. 9, 1973 and entitled IGNITION AMPLIFIER CIRCUIT.

This invention relates to a regulated ignition amplifier circuit and more particularly to a circuit which generates an ignition pulse having a sharp rise time and a long duration and which is regulated to obtain optimum operation irrespective of wide variations in operation conditions.

BACKGROUND OF THE PRIOR ART

Prior art ignition systems have generally been either of a current interruption type in which current through an ignition coil primary winding is interrupted to collapse the magnetic field thereof and to generate a high voltage in the ignition coil secondary winding or of a capacitor discharge type in which a capacitor is discharged through the primary winding. Such systems have not been entirely satisfactory in that it has not been possible to obtain firing of wetted or fouled plugs and also at the same time minimum exhaust emissions. Prior systems have also been subject to wide variations in response to changes in operating conditions such as engine speed, battery voltage and the like. Regulating circuits proposed for minimizing such variations, by regulating the time of charge of a capacitor or the time of build-up of current through the ignition coil primary winding, have been relatively complicated and not always reliable in operation.

BRIEF SUMMARY OF THE INVENTION

According to an important feature of the invention, a circuit is provided including charging means for applying a charging voltage to capacitor means and discharge means for discharging the capacitor through an ignition coil primary winding to generate a high voltage wave form in the ignition coil secondary winding for ignition, with regulating means being provided responsive to the voltage applied to the capacitor means for controlling the charging means to charge the capacitor means to a substantially constant regulated voltage prior to discharge. With this arrangement, the energy of the high voltage ignition wave form is substantially constant, to insure firing of a fuel-air mixture under a wide range of operating conditions.

According to another important feature, disabling means are provided for disabling the charging means during discharge of the capacitor means, to avoid loading down of the charging means and dissipation of energy, and allowing the efficient application of the charge voltage after the capacitor means is discharged through the primary winding means. This feature is particularly desirable with a circuit in which the discharge means includes a silicon controlled rectifier, and insuring that the rectifier will revert to a non-conductive state prior to application of the charging voltage.

A further feature is in the use of common circuitry for both the regulating of the capacitor voltage and the disabling of the charging means, simplifying the circuit and minimizing the number of required components.

In accordance with a specific feature, the charging means includes oscillator means for connection to a DC source such as the battery of an automobile in which the ignition system is used, the oscillator means being operative to generate a high AC voltage which is rectified to produce a capacitor charging voltage and the regulating means includes transistor means for controlling the oscillator means in accordance with the voltage across the capacitor means. Preferably, the oscillator means is such that a regulated substantially constant voltage is developed with a DC supply voltage varied from a minimum value to a maximum value on the order of twice the minimum value.

According to another important feature, current through the ignition coil primary winding is built up to a value which is regulated through a transistor circuit to be substantially constant, the current being abruptly cut off to allow collapse of the magnetic field of the coil and to develop an increasing voltage in the ignition coil secondary winding of uniform nature, energy of the magnetic field being substantially constant before the collapse. Preferably, this arrangement is used in combination with the discharge of capacitance means charged to a regulated voltage with the capacitor discharge taking place shortly after the start of the increase in voltage developed after the current is cut off. The capacitor discharge produces a short duration pulse, having a sharp rise time, followed by a continuation of the inductive discharge of prolonged duration. My aforesaid related application more fully describes the advantages of combining a sharp rise time with a prolonged duration. With the combination of this invention, such an operation is obtained and through the combination of the voltage and current regulating means, the ignition wave form is substantially constant and independent of variations in supply voltage and other operation conditions.

This invention contemplates other objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE is a circuit diagram of a regulated ignition amplifier circuit according to the invention, shown connected to an ignition coil and points of an ignition system.

DESCRIPTION OF A PREFERRED EMBODIMENT

Reference numeral 10 geneally designates a regulated ignition amplifier circuit constructed in accordance with the principles of this invention. The circuit 10 is shown connected to terminals 11, 12 and 13 of a conventional ignition coil 14 including a primary winding 15 connected between terminals 11 and 12 and a secondary winding 16 connected between terminals 11 and 13. Circuit 10 is also connected to a ground terminal 18 which through a common ground is connected to the negative terminal of a battery 19 having a positive terminal connected through a switch 20 to the terminal 11. In the illustrated arrangement, a breaker point contact 21 is grounded and a second contact 22, connected to the circuit 10, is operated by a cam 23 which is ganged to a rotating arm 24 of a conventional distributor 25. Arm 24 is connected to terminal 13 of the ignition coil 14 and is sequentially engaged with contacts connected to spark plugs, the connection of one contact 26 to a spark plug 27 being shown.

In operation, with the switch 20 closed and with the engine rotating, points 21 and 22 are closed for a substantial length of time prior to the beginning of each power stroke of the engine and are opened at the beginning of each power stroke at which time a high voltage wave form is developed at terminal 13 and is applied through the distributor 25 to the proper spark plug. The circuit 10 operates to develop a high voltage wave form which has a very sharp rise time and a prolonged duration, effective to fire wetted plugs or plugs fouled by carbon deposits and is also effective to insure complete burning of fuel to minimize emissions.

The circuit 10 comprises a transistor 30 having an emitter connected through a resistor 31 to the ground terminal 18 and a collector connected to the ignition coil terminal 12. The base of transistor 30 is connected through a pair of diodes 32 and a parallel resistor 33 to ground and is also connected to the emitter of a transistor 34 having a collector connected through a resistor 35 to the terminal 11. The base of transistor 34 is connected through a capacitor 36 and a parallel resistor 37 to the terminal 11, and also to the collector of a transistor 38 having a grounded emitter and having a base connected to the contact 22 and also through a resistor 39 to the line 11.

In operation, with contacts 21 and 22 engaged, the base of transistor 38 is grounded and transistor 38 is non-conductive, a high voltage being developed at the collector thereof to drive the transistor 34 into conduction, transistor 34 being operative as an emitter-follower to drive transistor 30 into conduction. In accordance with an important feature, the current through the transistor 30 is limited to a substantially constant value by the operation of the diodes 32, in conjunction with resistor 31 to limit the drive of the transistor 30, and the current through the primary winding 15 is built up to a value which is substantially constant and independent of wide variations in supply voltage.

During the closure of contacts 21 and 22 and the build-up of current through the primary winding 15, a capacitor 40 is charged from a charging circuit 41 with a polarity as indicated in the drawing, the charging circuit 41 being controlled from a regulator circuit 42 in accordance with the invention, operative to automatically regulate the voltage to which capacitor 40 is charged. When contacts 21 and 22 open, base-emitter current is supplied to the transistor 38 through the resistor 39 and transistor 38 conducts heavily to cut off transistor 34 which cuts off transistor 30. The voltage at terminal 12 then starts to increase in a positive direction and after it increases to a certain value, capacitor 40 is discharged through the primary winding 15, by means of a silicon controlled rectifier 44 having an anode connected through a primary winding 45 of a controlled transformer 46 to a circuit point 47 which is connected through the capacitor 40 to the terminal 11 and having a cathode connected through a diode 48 to the terminal 12. The current from discharge of capacitor 40 produces a high voltage short duration pulse and a sharp rise time for firing of wetted or fouled plugs.

Control transformer 46 applies a control signal to the regulator circuit 42 to disable the charging circuit 41 during discharge of the capacitor 40 in accordance with an important feature of the invention and as hereinafter described.

Silicon controlled rectifier 44 is triggered in response to the increasing voltage at terminal 12 developed when the transistor 30 is cut off. In particular, the gate of the rectifier 44 is connected through a resistor 49 to the cathode thereof and through a resistor 50 to the terminal 12 with a capacitor 52 being connected between the cathode of rectifier 44 and ground. When transistor 30 is cut off, the resulting collapse of the magnetic field in the coil 14 causes the voltage at terminal 12 to go positive and producing current flow through the resistors 49 and 50, charging capacitor 52 with the diode 48 being blocked at this time. When the voltage across resistor 49 reaches a certain value, for example, from 0.6 to 1.0 volts, and with the anode of the rectifier 44 being positive relative to the cathode thereof, the rectifier 44 is rendered conductive to discharge capacitor 40 through diode 48 and the primary winding 15.

It is here noted that a diode 54 may be provided having an anode connected to ground and a cathode connected to terminal 12 for the purpose of preventing terminal 12 from going substantially negative relative to ground and thus preventing the development of a highly positive voltage at terminal 13.

The charging circuit 41 comprises an oscillator including a pair of alternating conductive transistors 55 and 56 having emitters connected together and to ground and having collectors connected to opposite ends of a primary winding 57 of a transformer 58, a center tap of winding 57 being connected to terminal 11. The bases of the transistors 55 and 56 are connected through resistors 59 and 60 to ground and through diodes 61 and 62 to opposite ends of a feedback winding 63 of the transformer 58, a center tap of the feedback winding 63 being connectable through the regulator circuit 42 to the terminal 11 to cause oscillatory action with transistors being alternately conductive.

The transformer 58 has a secondary winding 64, having a much larger number of turns than the primary winding 57, end terminals of the secondary winding 64 being connected through diodes 65 and 66 to ground and through diodes 67 and 68 to a circuit point 69 connected through a current-limiting resistor 70 to the circuit point 47. Diodes 65-68 are so poled as to operate as a bridge rectifier to develop a full wave rectified voltage at circuit point 69 for charging the capacitor 40 through the current limiting resistor 70.

The regulator circuit 42 comprises a transistor 72 having an emitter connected to terminal 11 and a collector connected through a resistor 73 to the center tap of the feed back winding 63. The base of the transistor 72 is connected through a resistor 74 to the terminal 11 through a resistor 75 to the collector of a transistor 76 the emitter of which is grounded. The base of the transistor 76 is connected to the collector of a transistor 77 and through the parallel combination of a resistor 78 and a capacitor 79 to a circuit point 80 which is connected through an inductor 81 to terminal 11 and through a resistor 82 to the collector of a transistor 83. The emitter of transistor 77 is grounded while the base thereof is connected to the emitter of transistor 83 and through a resistor 84 to ground. the base of transistor 83 is connected through a resistor 85 to ground and through resistors 86-89 to the circuit point 47.

In operation, when the potential at the circuit point 47 is low, conduction through the transistor 83 is low and conduction through the transistor 77 is low so that the potential of the collector thereof is high, driving the transistor 76 to conduct heavily. Transistor 76 drives the transistor 72 which drives the oscillator transistors 55 and 56 to produce a high rectified voltage at the output circuit point 69 to rapidly charge the capacitor 40 through the current-limiting resistor 70. As the charge of the capacitor 40 increases, the voltage at the base of transistor 83 increases and the conduction of transistors 83 and 77 is increased, reducing the drive of transistor 76, transistor 72 and the oscillator transistors 55 and 56, reducing the magnitude of the rectified voltage at the output circuit point 69. Ultimately, a condition is reached in which capacitor 40 is charged to a certain substantially constant regulated voltage and operation of the oscillator is continued only to the extent necessary to maintain the capacitor 40 charged to that voltage.

As mentioned above, the control transformer 46 applies a control signal to the regulating circuit 42 to disable the charging circuit 41 during discharge of the capacitor 40. In particular, control transformer 46 has a secondary winding 91 one terminal of which is connected to ground and the other terminal of which is connected through a diode 92 to a circuit point 93 connected through a capacitor 94 to ground and through a resistor 95 and a diode 96 to the base of the transistor 83. Transformer 46 is preferably specially designed in a manner such that the primary 45 always appears inductive no matter what impedance is in the secondary.

When the discharge current of capacitor 40 flows through the primary winding 45, a voltage is developed across secondary winding 91 which charges capacitor 94 through diode 92, the voltage from capacitor 94 being applied through resistor 95 and diode 96 to the base of transistor 83 causing transistor 83 and transistor 77 to conduct, cutting off transistors 76 and 72 and the oscillator transistors 55 and 56. When discharge of the capacitor 40 is completed, capacitor 94 continues to supply current to the base of transistor 83 for a certain time interval, the capacitor being discharged through resistor 95, diode 96, resistor 85 and the base-emitter junction of transistor 83. During the time interval of continued conduction of transistor 83, the silicon controlled rectifier 44 reverts to a non-conductive state and at the end of the time interval, the regulator circuit operates as above described, so controlling the charging circuit 41 to charge the capacitor 40 to a substantially constant voltage prior to the next discharge thereof.

Thus a short-duration high voltage pulse is developed at the terminal 13 followed by a prolonged voltage, both being of substantially constant amplitude by virtue of regulation of current through the transistor 30 and the regulation of the charge voltage of the capacitor. By way of example, and not by way of limitation, in a system using a 12 volt battery, the current and voltage may be maintained constant with a supply voltage increased up to 16 volts, as during operation of a generator, or decreased down to eight volts or less, as during cold weather starting conditions.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.

Claims

What is claimed is:

1. In a circuit for energizing an ignition coil including inductively coupled primary and secondary winding means, capacitor means, and control means coupled in circuit with said capacitor means and said primary winding means, said control means comprising charging means for applying a voltage to said capacitor means for charging said capacitor means, discharge means for discharging said capacitor means through said primary winding means to generate a high voltage wave form in said secondary winding means for ignition, disabling means for disabling said charging means during discharge of said capacitor means through said primary winding means, said disabling means including means responsive to discharge current of said capacitor means to develop a control signal, and control means responsive to said control signal to disable said charging means, said disabling means including a control transformer having primary and secondary windings, said primary winding of said control transformer being coupled in series between said capacitor means and said primary winding means to develop said control signal in said secondary winding thereof in response to discharge current of said capacitor means through said primary winding thereof.

2. In a circuit as defined in claim 1, said discharge means including silicon controlled rectifier means rendered conductive for discharging said capacitor means through said primary winding means, said disabling means being effective to prevent said charging means from maintaining current through said silicon controlled rectifier means and to allow said silicon controlled rectifier means to revert to a non-conductive state after substantially complete discharge of said capacitor means.

3. In a circuit as defined in claim 1, said control means being operative to disable said charging means for a predetermined time interval after termination of flow of said discharge current.

4. In a circuit as defined in claim 1, regulator means responsive to the voltage applied from said charging means to said capacitor means and arranged for controlling said charging means to charge said capacitor means to a substantially constant regulated voltage prior to discharge by said discharge means, said disabling means being operative through said regulator means in controlling disabling of said charging means.

5. In a circuit as defined in claim 4, said charging means comprising oscillator means for connection to a DC source to develop a high AC voltage and rectifier means for rectifying said high AC voltage to develop a high rectified voltage for charging said capacitor means, said regulator means comprising transistor means controlling operation of said oscillator means, and means controlling said transistor means in response to the voltage across said capacitor means.

6. In a circuit as defined in claim 1, current control means for building up current through said primary winding means and then cutting off said current to develop a short duration high voltage pulse in said secondary winding means immediately prior to operation of said discharge means.

7. In a circuit as defined in claim 6, said current control means including transistor means in series with said primary winding means, and means for regulating current through said transistor means to cause a build-up of current through said primary winding means to a substantially constant value prior to cutting off of said current.