US2955248A - Ignition system - Google Patents

Description

Oct. 4, 1960 a. H. SHORT 2,955,248

IGNITION SYSTEM Filed July 25, 1957 2 Sheets-Sheet 1 N0 wove INVENTOR. BROOKS 5/1027 ATTORNE' Y Oct. 4, 1960 B. H. SHORT 2,955,248

IGNITION SYSTEM Filed July 25, 1957 2 Sheets-Sheet 2 ATTORNEY value. Further, it will be IGNITION SYSTEM: Brooks H. Short, Anderson, Ind., assignor a; General Motors "Corporation, Detroit, Mich., a corporation of Delaware Filed tluly 25, 1951, Ser. No. 674,126

l6 Claims. c1. 323,58

'This invention relates to an ignition system for an inapplication is a continuation-in-part of plication Ser. No. 579,332, filedApril' 19, 1956.

In present-day ignition systems, the'current to the the ignition coil passes through a system of the coil. energy is equal to oules where L is the primary inductance of the coil in i henries and i is the current in the primary coil winding When the breaker points of the system separate, this stored energy is quickly released from the magnetic system and charges the capacities of secondary systems. The proportion of energy going to each system is determined by the relative capacities and inductances of each.

It is generally known that the value of the primary current when the contact points open decreases with engine speed, as can be determined by the relation =i( it my copending ap-' the primary and the I United States Pan-Bent- 15 ernal combustion engine and more particularly to an r an increase in either L or i will result in an increase in" the energy stored in the primary winding. An increase in L, however, will result in a decrease in current in the primarycircuit at high speed; The current in the present-day; ignition systems heretofore has been limited to a value that can be carried by the breaker points without deterioration when the engine is at low speeds. This current islimited to a maximum of about 4 /2 amperes' as it has been found that currents higher than this value would result in breaker point failures. s

When the circuit according to the present invention is employed, the current to the primary coil winding may reach the value of 8 to 10 amperes without damage to pass therethrough. Further, it is apparent that when a current of this magnitude is employed, the inductance of the primary circuit can be reduced to a muchlower value than is' used in' the present-day systems. This, of course, will improve the current at the break at high speeds.

It is also known that the coil output wave front shape is dependent to an extent on the total inductance and capacitance of the primary circuit, and that the wave trout becomes steeper as the total inductance or total capacitance of the primary circuit is reduced. A steep output wave front means that less, time will be required to raise the secondary voltage to plug tiring potential. Because of the short time, any energy loss due to fouled plugs is radicallyreduced, leaving the available energy for raising the plug to firing potential. This means that fouled spark plugs may be more readily fired. i

The above advantages are achieved by controlling the current flow in the primary winding of an ignition coil by a transistor to provide a simple, trouble-free'i-gnition system which will be reliable in its transistor when used in the ignition system possesses further advantages over devices heretofore used as it conducts at the voltage output of the storage battery and does not require a warm-up time. This latter characteristic of a transistor will make ignition available at the very instant the ignition key is turned on.

It should benoted that byusing a battery voltages that are used on present-dayinternal' combustion driven vehicles are suflicient to render the transistorconductive' or non-conductive at the proper times. This has a great advantage as the battery voltage need not he stepped up by the use of vibrator power packs and the like in order to operate the transistor. Moreover, the transistor need not be supplied with an energizing voltage for a cathode, or emitting element as the transistor does not employ such an element; In internal combustion driven conveyances, the electrical parts of an ignition system are road shock and the like, which electronic components such as vacuum tubes. The transistor is more reliable in operation as it can withstand the shock forces that are inherent in internal combustion driven vehicles.

It is therefore an object of'the present invention to control the'current flow in an ignition coil with atransistor, the conduction of which is controlled by a set of mechanically actuated breaker points.

A further object of the present invention is to use a transistor to .control the circuit to the primary winding of an ignition transformer.

Another object of the present invention is to control the current flow from. the battery to the primary windings of an ignition coil 'by a transistor that has its collector Patented Oct. 4, 1960 greater portion of the" transistor the normal subjected to vibration by is very harmful to many and emitter directly connected in circuit with the battery and coil winding and has its base in circuit with a pair of timer points which are mechanically actuated.

Still another object of this invention is to provide an ignition circuit wherein an ignition coil winding is connected to a transistor and wherein the transistor controls the current flow to the coil winding, thereja'eing a unidirectional current conducting element interposed between the transistor and coil winding to prevent current flow in a direction from the coil winding to the transistor.

A further object of this invention is to provide an ignition control circuit wherein the primary winding of an ignition coil is connected in series with a transistor across a direct current voltage supply and wherein a silicon diode is connected between the transistor and primary winding to prevent current flow from the primary winding to the transistor.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

Figure 1 is an electric circuit diagramof an ignition system employing a transistor for controlling the current flow to the primary winding of an ignition coil;

Figure 2 is a graphical representation showing the relationship between voltage and time in the secondary coil winding of an ignition coil when the ignition coil is connected in the circuit shown in Fig. 2;

Figure 3. is an improved electric circuit diagram of an ignition system made in accordance with this invention; and

Figure 4 is a graphical representation showing the relationship between time and voltage in the secondary coil winding of an ignition coil when the ignition coil is connected in the circuit shown in Fig. 2.

In the drawings the numeral 20 designates a storage battery which acts as a source of current for an ignition system of an internal combustion engine. The storage battery is of suflicient voltage to operate the electrical devices .used on an internal combustion driven vehicle. Thus, for automobile use, the battery preferably is of the standard 6 or 12-volt size. For larger internal combustion driven conveyances such as trucks or buses, the battery may he as large as 32 or 48 volts. switch 26 is used to' make and break the circuit to the ignition system, as will be hereinafter described. 1

The transistor 28 shown is of the well-known PNP type having a base 12, a collector c and an emitter e. The PNP transistor as used in the circuit shown is characterized by the fact that current in the order'of 8 to 10 amperes will flow from the emitter e to the collector 0 whenever the base I) is sufficiently negative with respect to the emitter e and the emitter with respect to the collector c. The transistor 28 further will not at any time pass current from the emitter to the collector when the voltage of the emitter is positive with respect to the collector by an amount up to 1,000 volts, if the base is not supplied with current. Another characteristic of the transistor shown is that the current flow between the emitter and collector is a function of the flow of current between the emitter and base which, in turn, is a function of the voltage difference between the emitter and base.

The emitter e of transistor tive lead 22. The collector connected through a junction 28 is connected to posic of the transistor 28 is 30 and the primary coil The ignition e is sufiiciently positive.

winding 32 of an ignition transformer 33 to the negative lead 24. A satisfactory ignition transformer may have a pr'mary to secondary turns ratio of 1 to 300. The secondary coil winding 34 supplies the ignition current and power through a distributor 35 to the spark plugs, diagrammatically shown at 36. The coil winding 34 has one end connected to the grounded side of the primary 4 coil winding 32 and the other end connected through the distributor 35 to the spark plugs 36 in the conventional manner.

The base b of transistor 28 is connected by a lead 37 through the breaker points 38 to the tap 40 on the resistance 42. The operation of the breaker points 38 and distributor 35 are so regulated that points 38 open at the optimum instant for engine firing, and the circuit through the distributor 35 to the spark plugs 36 is established simultaneously therewith. The resistor 42 preferably has a value of 16 ohms for a battery voltage of 12 volts and will have a proportionately higher value for higher battery voltages such as 32 or 48 volts. The resistance 42 is connected across leads 22 and 24, and a resistance 44 is connected across leads 22 and 37. The resistor 44 preferably has a value of 50 ohms for a battery voltage of 12 volts and is likewise made proportionately higher in resistance where the voltage is 32 volts or'48 volts. The condenser 46, which is connected between lead 22 and junction 30, minimizes voltage surges across the emitter and collector of transistor 28, and partially controls the wave front. be eliminated in some cases, where the inherent capacity of the transistor is sufiicient.

When the ignition switch 26 is initially closed, the circuit shown will be immediately energized. When the points 38 are open, the base b of transistor 28 will be at the same potential as the emitter e because of the resistance 44. The flow of current through resistance 42 will cause tap 40 to be negative relative to lead 22. Thus, when points 38 close, the base become negative relative to the emitter e. When the base b is negative relative to emitter e, the transistor 28 will immediately conduct and pass current to the primary coil winding to build up magnetic flux therein. This flux represents energy that is stored in the ignition coil.

When the breaker points '38 open, the emitter to the base circuit of transistor 28 is broken and the transistor. 28 immediately stops conducting current. In this connecti'on, as the collector current in a transistor is much greater than the base current will be flowing through the points 38 at the instant they open. This will assure practically an indefinite point life. When the current through the collector ceases, the'stored energy in the ignition coil will be released to cause the spark plugs to ignite, as is well known to those skilled in the art.

If des d, t e PNP type transistor may be replaced by an NPN type if the compone' ts of the circuit are properly reversed. Further, the variable resistance 42 may be a fixed resistance if the ohmic value selected is suflicient to provide the proper voltage drop between the base and emitter when the points are closed to provide sufiioient current to energize the primary coil winding.

Referring now to Fig. 3, an improved ignition control circuit is shown which employs a silicon diode. The same reference numerals that were used in Fig. l have been used in Fig. 3 to denote the identical component parts of the circuits. The circuit of Fig. 3 difiers from the circuit of Fig. 1 in that a silicon diode 48- is connected between the collector c and one side of the primary coil winding 32 of the ignition coil. The silicon diode has a rating of 10 amperes in a forward direction and has at least a 300-volt reverse voltage rating. The diode freely passes current in one direction and is connected in the ignition circuit so as to pass current from transistor 28 to the primary coil winding 32. The diode blocks flow of current in a reverse flow of current moving toward In order to 48, reference should be had to Figs. 2 and 4 of the drawings which show the curves of voltage across the secondoollectorc of transistor ary winding of the ignition coil versus time for the circuits I shown respectively in Figs. 1 and 3. By comparing the curves of Figs. 2 and 4, it can be seen that the second- This condenser can b of the transistor will direction and thus blocks anyunderstand the function of the silicon diode w an the transistor ary voltage transient with I e circuit of Fig. 3 is prolonged in time as compared with the secondary voltage that is produced with the circuit shown in Fig. 1. With the circuit of Fig. 3 that employs the silicon diode, a train of oscillations is set up whereas in the circuit of Fig. 1, the oscillation is cut short to a single pulse, which reduces the time that voltage is supplied tothe spark plugs.

If a comparison isrnade between the operation ofithe mice in secondaryvoltages produced By the bifcurts is readily apparent. Thus, in the circuits of Figs. 1 and 3, when transistor 28 is conducting, current passes from the battery 20, through transistor 218, and then through the primary winding 32 of ignition coil 33-. occurs when the breaker points 38 are closed, and the current through primary winding increases with the elapse of time, as is well known to those skilled in the art. When breaker points 38 open, the transistor 28 is rendered non-conductive to break the circuit between battery 20 and the primary winding 32. With the circuit broken, a voltage of self induction appears in the primary coil winding as aresult of the energy that was stored in the coil during the time the coil was connected with the battery. Since the primary coil is effectively connected directly across the condenser 46, the condenser is charged by this self-induced voltage to a polarity wherein the side of the condenser connected to primary co 32 is negative and the opposite side, positive. 180 electrical degrees later, this condenser polarity is reversed.

To this point in the operation of in Figs. 1 a once in operation of the two circuits. ing the charging of condenser 46, the condenser discharges and at this point in circuit operation the diode brings about a different operation for each circuit. In the circuit of Fig. 1 the condenser dischargm through the transistor in a direction reverse to the direction of current flow when the battery is supplying current to the coil. The reverse flow is due to the fact that collector c of transistor 28 is rendered positive with respect to the emitter e when the condenser is charged to a polarity wherein the bottom end of condenser 46 is positive. This reverse flow of current dissipates substantially all of the energy stored in the condenser in PR losses in the transistor and in the leads connecting the transistor and condenser. This dissipating of the energy stored inthe condenser accounts for the shortened time of secondary voltage which is illustrated in Fig. 2 and which is induced therein-by the variation of primary coil current.

, When the condenser 46 discharges in the circuit of Fig. 3, the diode 48 blocks reverse current through the transistor and the energy stored in the condenser is transferred to the primary coil 32 rather than being dissipated and associated leads, as is the case with 1. The condenser and primary coil thus the circuits shown Immediately followthan being dissipated, with the circuit of Fig. 3. It thus can be seen that the circuit of Fig. 3 produces a train of oscillations to provide a secondary voltage of longer duration as compared to the secondary voltage produced by the circuit of Fig. l. The circuit of Fig. 3 thus provides for improved sparking characteristics at spark plugs 36.

In summary, it should be noted that the use of a transistor in an by mechanically actuated breaker points. This is due to the fact that the transistor is aninherently elficient device, in-that the transistor has a very low voltage drop when conducting current and is capable of carrying high nd 3, the silicon diode 48 has made no diifercurrents. Moreover, the transistor does not consume filament power that must be supplied to vacuum tubes. The transistor thus is ideally suited for use in controlling the current to the primary coil of an ignition system from the efiiciency standpoint, and has other important advantages which have been described above.

Whilethe form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be-adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. An electrical ignition system comprising, a direct current volt-age source, an ignition coil having a primary winding and a secondary winding, means including a transistor connected in circuit with said primary winding and said voltage source for controlling the current flow in said primary winding from said source, and a unidirectional current conducting circuit element connected between said transistor and said primary winding for preventing the flow of current in a direction from said primary winding toward said transistor whereby energy stored in said primary winding is prevented from being dissipated in said transistor by current flow therethrough in one direction.

2. The system set forth in claim 1 wherein said unidirectional current conducting circuit element is a silicon diode.

3. An electrical ignition system comprising, a direct current voltage source, an ignition coil having a coil winding, a transistor having a base, emitter and collector, a biasing resistor connected across said voltage source, a circuitinterrupter, means connecting said transistor emitter to one side of said voltage source and to one side of said resistor, means connecting said interrupter between said transistor base and :an opposite side of said resistor, means connecting one side of said ignition coil to an opposite side of said voltage source, and a unidirectional current conducting element connected between the opposite side of said ignition coil and said transistor collector, said element being connected in the circuit in a direction to pass current from said collector to said coil and to block current in an opposite direction whereby energy stored in said coil winding is prevented from being dissipated in said transistor by current flow therethrough in said opposite direction.-

4. An electrical ignition system comprising, a voltage source,an ignition coil having a coil winding, a transistor connected in circuit with said voltage source and coil winding for controlling the flow of current to said coil winding, and means in circuit with said transistor and coil winding for preventing current flow in a direction from said coil winding toward said transistor whereby energy stored in said coil winding is prevented from being dissipated in said transistor by current flow therethrough in one direction.

5. An electrical ignition system comprising, a voltage source, a first power lead connected to a first side of said voltage source, a second power lead connected to the second side of said voltage source, a transistor, an ignition coil having a coil winding, means connecting said transistor and coil winding in series circuit relationship across said power leads, a biasing circuit for said transistor rendering said transistor conductive at certain times for passing current from said first lead to said sec ond lead through said transistor and coil winding, and means for preventing flow of current through said transistor in a direction toward said first lead whereby energy stored in said coil winding is prevented from being dissipated in said transistor by current flow therethrough in a direction toward said first lead.

6. An electrical ignition system comprising a direct current voltage source, an ignition coil having a primary winding, semi-conductor means connected in series with said voltage source and said primary winding for controlling the flow of current therebetween, a biasing circuit for said semi-conductor means for controlling the conduction thereofincluding a circuit interrupter, and a diode connected between said scan-conductor means and said primary winding in such a direction as to prevent flow of current in a direction from said primary winding toward said semi-conductor means whereby energy stored in saidprimary winding is prevented from being dissipated in said semi-conductor means by current flow there'- through in one direction.

References Cited in the file of this patent UNITED STATES PATENTS somerville Dec. 22,. 1942 Harris Dec. 16, 1952 Sherr' Dec. 28, 1954 Iinmel Nov. 1, 1955 Crosby Oct. 30, 1956 Well Sept. 17, 1957 'Houck -1 Apr. 28, 1959

Images