THE IGNITION SYSTEM
The ignition system is the name applied to the batteries, coils, commutator and spark plug which, acting as a whole, produce an electric spark hot enough and at the right time to fire the charge in the cylinder. There are three ways in which an electric current may be obtained which have been found to be of practical use in automobile construction. First, by a dry battery; second, by a storage battery; and third, by magneto or dynamo. You can look up the construction of these things in any good book on electricity, so that I will not explain them further here. As the object of the whole system is to produce a sufficiently hot spark to fire the mixture at the right time, it is sometimes necessary to raise the pressure of the electric current. When either a dry battery or storage battery or a certain type of magneto is used, it is necessary to put it through what is known as an induction coil in order to raise the pressure so it will be high enough to jump across the two points in the cylinder.
An induction coil consists merely of a bundle of soft wires around which is wound two separate coils of wire. The first, known as the primary winding, is of coarse wire, and the second, known as the secondary winding, is of fine wire. When the current flowing through the primary coil is rapidly made and broken, another current of very high voltage is created in the secondary circuit.
Fig. 23—Wiring Diagram, showing electric circuit for one cylinder. The sketch is only diagrammatic—not a reproduction of any actual wiring system.
When the current starts to flow through the primary winding, the bundle of wires immediately becomes a magnet and attracts the vibrator. As soon as this occurs, however, the flow of the current is interrupted and the vibrator resumes its former position and the action is repeated. Thus you can see that the coil automatically makes and breaks its own circuit. The rapidity with which this is done may be changed at will by adjusting the vibrator screw.
Fig. 24—The Four-cylinder, Four-cycle Diagram, showing the order in which the various cylinders do their work.
Having thus obtained an electric current of sufficient strength to fire the mixture it is necessary to supply a device which will automatically open and close the electric circuit at the proper time. Such a device is called a commutator and consists of two parts; one a rotating part, actuated by the engine, which makes a metallic contact with one or more points on a stationary part, the points being so located that contact occurs at the proper time for igniting the charge in any particular cylinder.
Fig. 25—Four-cylinder Wiring Diagram.
In the four-cylinder wiring diagram ([Fig. 25]) various parts of an ignition system may be easily seen. The electric current is furnished either by a set of dry cells or by a storage battery. Four individual coils and a four point commutator are used. The commutator is driven by means of bevel gears from the engine itself. A single switch controls the whole circuit, it being provided with two points, making it possible for either battery to be used at will.
Fig. 26—Types of Spark Plugs.
Fig. 27—A Single Cylinder Commutator. Diagrammatic sketch.
Fig. 28—A Two-point Switch.
Fig. 29—A Four-cylinder Commutator.
Fig. 30—A Two-cylinder Commutator.