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BATTERY AND COIL IGNITION METHODS
How Compressed Gas May Be Ignited—Methods of Electric Ignition-Parts
of Simple Ignition System-Induction Coil Action-Timers and Distributors—Spark Plugs—Individual Coil System-Vibrator-Distributor Systems—Master Vibrator Systems—Non-Vibrator Distributor System-Low Tension Ignition-Double and Triple Ignition Systems—Battery Ignition System Troubles-Charging Storage Batteries—Care and Repair of Spark Plug Faults—Induction Coil—Timers—Wiring Troubles and Electro-static Effects—Timing Battery Ignition System.
How Compressed Gas May Be Ignited.—One of the most important auxiliary groups of the gasoline engine comprising the automobile power plant and one absolutely necessary to insure engine action is the ignition system or the method employed of kindling the compressed gas in the cylinder to produce an explosion and useful power. The ignition system has been fully as well developed as other parts of the automobile, and at the present time practically all ignition systems follow principles which have become standard through wide acceptance.
During the early stages of development of the automobile various methods of exploding the charge of combustible gas in the cylinder.were employed. On some of the earliest engines a flame burned close to the cylinder head and at the proper time for ignition, a slide or valve moved to provide an opening which permitted the flame to ignite the gas back of the piston. This system was practical only in the primitive form of gas engines in which the charge was not compressed before ignition. Later, when it was found desirable to compress the gas a certain degree before exploding it, an incandescent platinum tube in the combustion chamber, which was kept in a heated condition by a flame burning in it, exploded the gas. The naked flame was not suitable in this appli
cation because when the slide was opened to provide communication between the flame and the gas the compressed charge escaped from the cylinder with enough pressure to blow out the flame at times and thus cause irregular ignition. When the flame was housed in a platinum tube it was protected from the direct action of the gas, and as long as the tube was maintained at the proper point of incandescence regular ignition was obtained.
Some engineers utilized the property of gases firing themselves if compressed to a sufficient degree, while others depended upon the heat stored in the cylinder head to fire the highly compressed gas. None of these methods were practical in their application to motor car engines because they did not permit flexible engine action which is so desirable. At the present time, electrical ignition systems in which the compressed gas is exploded by the heating value of the minute electric arc or spark in the cylinder are standard, and the general practice seems to be toward the use of mechanical producers of electricity rather than chemical batteries used alone.
Methods of Electrical Ignition.—Two general forms of electrical ignition systems may be used, the most popular being that in which a current of electricity under high tension is made to leap a gap or air space between the points of the sparking plug screwed into the cylinder. The other form, which has been almost entirely abandoned in automobile practice, but which is still used to some extent on marine engines, is called the low-tension system because current of low voltage is used and the spark is produced by moving electrodes in the combustion chamber.
The essential elements of any electrical ignition system, either high or low tension, are: First, a simple and practical method of current production; second, suitable timing apparatus to cause the spark to occur at the right point in the cycle of engine action; third, suitable wiring and other apparatus to convey the current produced by the generator to the sparking member in the cylinder.
The various appliances necessary to secure prompt ignition of the compressed gases should be described in some detail because of the importance of the ignition system. It is patent that the scope of a work of this character does not permit one to go fully into the theory and principles of operation of all appliances which
may be used in connection with gasoline motor ignition, but at the same time it is important that the elementary principles be considered to some extent in order that the reader should have a proper
understanding of the very essential ignition apparatus. The first point considered has been the common methods of generating the electricity, then the appliances to utilize it and produce the required spark in the cylinder.
Essential Elements of Simple Ignition System.—The current obtained from the dry or storage battery or low-tension dynamo or magneto is not sufficiently powerful to leap the gap which exists between the points of the spark plug in the cylinder unless it is transformed to a current having a higher potential. The air gap between the points of the spark plug has a resistance which requires several thousand volts pressure to overcome, and as a battery will only deliver six to eight volts, it will be evident that, unless the current value is increased, it could not produce a spark between the plug electrodes.
The low voltage current is transformed to one of higher potential by means of a device known as the induction coil. The current from the battery is passed through the primary coil, which is composed of several layers of coarse wire wound around a core of soft iron wire to form an electro-magnet as shown at Fig. 25. Surrounding this primary coil is one composed of a large number of turns of finer conductor. When a current of electricity of low voltage passes through the primary coil, a current of very high electro-motive force is produced in the secondary winding. One end of each coil is grounded. The free end of the primary coil is coupled to the battery while that of the secondary coil is attached to the insulated terminal of the spark plug.
The arrangement of wiring at Fig. 25 is that employed in a typical transformer coil which is used to increase the voltage of the current sufficiently to cause it to overcome the resistance of the air gap at the spark plug and produce a spark which will ignite the gas. In the primary circuit are included a suitable timer for closing the circuit, a battery of chemical cells to supply the energizing current, and a vibrator or make-and-break mechanism on the coil. The secondary circuit includes the spark plug and the secondary winding of the coil.
When the primary circuit is closed by the cam of the timer making contact with the segment, the current from the battery flows through the primary coil of the transformer. This magnetizes the core which draws down the trembler blade, this in turn separating the platinum contact point of the vibrator and interrupting the current. As soon as the current is interrupted at the vibrator the core ceases to be a magnet and the trembler blade flies back and once again closes the circuit between the platinum points. Every time the circuit is made and broken at the vibrator an electrical impulse is induced in the secondary winding of the coil.
The vibrator may be adjusted so that it will make and break the circuit many times a minute and as a current of high potential is produced in the secondary winding with each impulse, a small spark will be produced between the points of the spark plug. The condenser is a device composed of layers of tin foil separated from each other by waxed or varnished paper insulation. It is utilized to absorb some of the excess current produced between the vibrator points, which causes sparking. This extra current is induced by the action of the primary coils of wire upon each other and by a reversed induction influence from the secondary coil.
If this current is not taken care of, it will impede the passage of the primary current and the sparks are apt to burn or pit the platinum contact points of the vibrator. When a condenser is provided the extra primary current is absorbed by the sheets of tin foil which become charged with electricity. When contact is made again the condenser discharges the current in the same direction as that flowing through the primary coil from the battery and the value of the latter is increased proportionately. There is less sparking between the vibrator points and a stronger current is induced in the secondary coil which in turn produces a more intense spark between the points of the spark plug.
A typical induction coil such as would be used for firing a onecylinder engine if used with a simple timer, or a multiple-cylinder engine if used in connection with a combined timer and distributor, is depicted in part section at Fig. 26. It will be observed that three terminal screws are provided on the box, one designed to be attached to the battery, the other two to the spark plug and ground, respectively. The terminal to which the battery wire is attached is coupled to the bridge member which carries the contact screw while