US3047728A - Ignition system - Google Patents

Description

July 31, 1962 w. c. MARTIN 3,047,728

IGNITION SYSTEM FiledJune 22, 1959 Fmg. I. /4 ,0

mmf/vr 7'7 tZ/UUUUUU 'ME -r- United States arent O 3,047,728 IGNITION SYSTEM Walter C. Martin, Feasterville, Pa., assigner, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Delaware Filed June 22, 1959, Ser. No. 822,094 4 Claims. (Cl. 307-10) This invention relates to ignition systems and more particularly to improvements in -the conventional ignition system wherein energy is supplied to a transformer from a battery and is delivered as -a high voltage pulse to one of the engine spark plugs.

As is well understood, the conventional system employs a step-up transformer, usually in the form of an autotrans-former, having primary and secondary windings through which rthe high voltage pulses are derived. The primary circuit includes lthe battery, the breaker points (contacts), and vthe primary winding of said transformer, all connected in series. The breaker points are intermittently closed to supply energy from Ithe battery to said primary winding for Itransformation to said high voltage pulses which .are supplied through successively closed `contacts of the ldistributor to the spark plugs.

As is also well understood, each time the breaker points open Ithe self-inductance of the primary winding tends to maintain current how in the primary circuit, which tends to cause arcing 'across the breaker points. This would quickly destroy the points were it not for the fact that a condenser is connected lacross them. The continuing current charges the condenser which thus minimizes arcing across the breaker points. The condenser i-s 'therefore an essential element of the conventional system.

However, the combination of the primary winding and the condenser produces an undesired action. Since these elements inherently `constitute a resonant combination of inductance and capacitance, when the breaker points open a ringing action takes place, resulting in the production of decaying oscillations. These deleterious oscillations cause several undesired eifects. They partially defeat the purpose of the condenser as they produce a spill over voltage across the breaker points, and thus vtend to cause :arcing across the points and consequent shorter life yto the points. They also represent wasted energy ywhich is not delivered to -the spark plugs. They also make it difficult to. achieve precise accurate timing. These latter effects Atend to impair the performance of engine and may cause hard starting, engine roll, less pick-up, greater gasolene consumption, etc.

One object of this invention is to provide simple, inexpensive and highly ecient means for eectively squelching or suppressing the aforementioned deleterious oscillations.

Another object of the invention is to increase -the eciency of the conventional ignition system and thus improve the performance of the engine.

These objects are achieved by the provision in the primary circuit of means including a unilaterally-conductive device, preferably a semiconductor diode, for effectively suppressing the undesired oscila/tions when the primary circuit is opened. Thus in accordance with preferred forms of this invention, a semiconductor diode is connected in the primary circuit and is poled so as to be biased forwardly by the battery. Then when the breaker points open, the diode presents high impedance to reverse cur-rent how between the primary winding and the condenser. In the preferred embodiment of the invention, a variable resistance path is provided in shunt with the semiconductor diode and the two collaborate to achieve desired results as hereinafter described.

The invention may be fully understood from the folf 3,047,728 Patented July 31, 1962 lowing detailed description with reference to the accompanying drawing wherein- FIG. l is -a diagrammatic illustration of `an ignition system employing 4a unilaterally-conductive device, preferably in the form of a semiconductor diode, according to the present invention;

FIG. 2 shows the deleterious oscillations which take place in a conventional system and which this invention effectively squelches or suppresses;

FIG. 3 is :a diagrammatic illustration of an ignition system embodying another form of the present invention; and

FIG. 4 is a diagrammatic illustration of an ignition system embodying a preferred form of the invention.

Referring iirst to FIG. 1, the conventional ignition system comprises a battery 10', a manually-operable ignition switch y11, breaker points 12, a condenser 13 connected across the breaker points, and an autotransformer 14 whose primary winding comprises the turns below tap 15 1and Whose secondary winding comprises all of the turns between the upper end of the coil and ground. The secondary circuit extends to the distributor to supply high voltage pulses to the spark plugs as hereinbefore stated.

Disregarding for the time being the diode 16 which is provided by this invention, the operation of the conventional system is as follows. With the ignition switch 11 closed, when the breaker points l12 close current flows from the battery 10 through the primary winding of transformer 14, and energy is thus `stored in the magnetic held of the transformer. When the breaker points open, the magnetic field collapses and the stored energy is supplied in the form of a high voltage pulse to the distributor and thence to one of the spark plugs. It is desired, of course, 'that all of the stored energy be delivered to the spark plug to produce an intense spark, but this objective is partial-ly defeated by lthe 'aforementioned deleterious oscillations which represent wasted energy.

This may be 'seen more clearly with the aid of FIG. 2 whi-ch depicts the action in the primary circuit. The breaker points close at time t1 and the primary circuit 17' builds up until the breaker points open at time t2. While the breaker points are closed, energy is stored in the magnetic field of the transformer 14. When the breaker points open at time t2 the intention is that al1 of the stored energy `shall be delivered to one of the spark plugs. However, at that time the primary winding and the condenser 13 become effective as a resonant combination, and some of the stored energy is` transferred back and forth between the magnetic field of the transformer and the electrostatic field of the condenser, producing decaying oscillations as represented at 18. This not only tends to cause arcing at the breaker points but it also is a waste of energy which otherwise would be delivered to the spark plug. Consequently these undesired oscillations adversely affect the energy pulse delivered to the spark plug and cause the undesired effects hereinbefore mentioned.

In accordance with this invention, the diode 16 is provided in the primary circuit and is poled so as to be biased forwardly by the battery 10, When the breaker points are closed, the diode permits unimpeded ow of current in the primary circuit, and hence the diode does not interfere with the transfer of energy to the transformer. However, when the breaker points open the diode presents high impedance to reverse ow of current in the primary circuit, and it thus squelches or suppresses the undesired oscillations 118. Consequently substantially all of the energy stored in the magnetic field of the transformer is delivered to the spark plug in the form of a sharply-defined high voltage pulse.

With the diode included it has been found that it is 3 possible to adjust the ignition timing more accurately and the optimum adjustment advances the spark in relation to the optimum adjustment without the diode. With the diode included and with the advanced spark, the engine operates smoothly and more efficiently.

While yany diode may be used according to this invention, a semiconductor diode is preferred because it has less forward voltage drop than other forms of diodes.

It should be noted further that the semiconductor diode also serves as a fast-acting switch to relieve the breaker points and it thus helps to prevent arcing at the points. When the breaker points start to open, the semi-conductor diode quickly blocks the ilow of current, there being only a very slight delay due to storage. Because the diode is so fast acting in relation to the opening of the breaker points, it opens the circuit abruptly and thus helps to prevent arcing at the points.

The diode 16 may be a germanium diode but preferably it is a silicon diode. Preferably also the diode is of the welded junction type. It is characteristic of such a diode that if it fails it will not burn out but will maintain la closed circuit. Consequently if the diode should fail the system would operate in conventional manner.

Referring now to FIG. 3, the system there shown is identical with that of FIG. 1 except that a resistor 19 is shunted about the diode 16. In experimental use a resistor having a value of 100G ohms (l watt) has been used. When the breaker points are closed, the diode effectively short-circuits the resistor. When the breaker points open, the diode presents high impedance to reverse current ilow. While such current can flow through the resistor, the latter suppresses the undesired oscillations. It has been found that the resistor improves the shape of the pulse delivered to the spark plug. It is postulated that after the breaker points open and the condenser 13 charges to the voltage of the battery, the condenser discharges through the resistor at a rate determined by the R-C time constant of the resistor and the condenser, and

this improves the shape of the pulse delivered to the spark plug.

Referring now to` FIG. 4, there is shown a preferred form of the invention. In this instance a diode 20 is included in the primary circuit between the battery 10 and the lower end of transformer 14, and series-connected resistors 21 and 22 are provided in shunt with the diode. Resistor 21 is fixed and may have a value of 1000 ohms. Resistor 22 is variable and may have a value of l megohm. It has been found that with this arrangement the timing of the output pulse can be varied by varying resistor 22. It is postulated that this is due to the fact that variation of resistor 22 changes the R-C time constant.

In the arrangement of FIG. 4 the diode 20 is preferably a germanium diode which has been found to be entirely satisfactory in the location of FIG. 4, and of course the germanium diode is less expensive than the silicon diode.

Actual tests in automobiles have shown that this invention is highly effective to minimize wear of points,

4 to facilitate accurate timing and to provide easier starting, better engine performance, faster picloup, and less gasolene consumption.

In addition to the foregoing results, the squelching or suppressing of the undesired oscillations eliminates them as a source of radio interference. This incidental advantage is desirable, of couser, where an automobile is equipped with an auto radio.

An important additional advantage of this invention is that it does not require any special parts, such as a special coil, in the ignition system. Thus the invention may be applied to an existing system without modification or replacement of any of the parts thereof.

From the foregoing description it will be seen that this invention provides a simple, inexpensive and highly effective solution of the problem created by the undesired oscillations. While certain embodiments have been illustrated and described, it will be understood that the invention is not limited thereto but contemplates such modifications and further embodiments as may occur to those skilled in the art.

I claim:

1. In an ignition system, `step-up transformer means comprising a primary Winding and a secondary Winding, a secondary circuit including said secondary winding, a primary circuit including said primary Winding, a battery in said primary circuit, breaker points in said primary circuit, which points are recurrently closed and opened whereby energy is stored -in said transformer means when the breaker points are closed 4and is released to said secondary circuit when the breaker points open, a condenser connected across said breaker points to reduce arcing thereacross when the breaker points open, said primary winding and said condenser inherently constituting a resonant combination and tending to produce deleterious oscillations when the breaker points open, a unilaterallyconductive `device serially included in said primary circuit and arranged to permit free iiow of battery current in one direction but to prevent reverse current ow through said device, and a resistive path in shunt With said device, said resistive path permitting reverse current liow but having a resistance value effective to suppress said oscillations.

2. An ignition system according tol claim 1, wherein said resistive path comprises series connected xed and variable resistors.

3. An ignition system according to claim 1, wherein said unilaterally-conductive device is `a semiconductor diode.

4. An ignition system according to claim 2, wherein said diode is a germanium diode.

References Cited in the file of this patent UNITED STATES PATENTS 1,966,077 Nyman July 10, 1934 FOREIGN PATENTS 548,192 Great Britain Aug. 5, 1941

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