The igniter mechanism is simply a lever worked qe,:. by the camshaft which presses against the interrup ; tor lever with the movable electrode on it until the Spil latter makes contact with the fixed electrode and E: the circuit is then closed.
At the right instant the pressure on the movable electrode lever is released and a spring makes it snap back, thus wiping the fixed electrode and break ing the contact between them, and this makes a spark. An Otto igniter is shown at A and B in Fig. 25, and the mechanism working it is shown at A and B in Fig. 26.
Low Tension Magneto System.—A magneto elec tric machine, or just magneto for short, is a ma chine which generates electric alternating currents.
There are two kinds of low tension magnetos made, and these are used for generating currents for wipe spark igniters, as they are far less troublesome than the battery and spark-coil system. Named, these two types of low tension magnetos are (1) the rotat ing magneto and (2) the oscillating magneto.
The Low Tension Rotating Magneto.—A magneto of this kind is built up of two main parts and these are (1) the field magnet and (2) the armature.
The field magnet is merely a powerful, permanent horseshoe magnet, as shown at A in Fig. 27, and the armature is a cylinder of soft iron with grooves cut lengthwise in the opposite sides of it and having a shaft through it, as shown at B.
A single coil of fine insulated wire is wound in the grooves of the armature and the ends are con nected to brass collector rings, called sliprings, on the shaft, see B and C, but which are insulated from it and from each other. The shaft sets in a pair of bearings so that the armature can revolve freely be tween the poles of the magnet. A strip of copper, called a brush, presses on each one of the sliprings and a wire leads off from the fixed end of each one of the brushes, as at C. The magneto complete is shown at D.
If the armature is rapidly rotated low tension electric currents will be set up in the coil of wire on it by the magnet and these will flow to the sliprings, where they will be taken off by the brushes; if now the ends of the wires are connected together low tension, that is, low pressure, currents will flow through the circuit thus formed, but when it is used to produce sparks the wires are connected to the fixed and movable electrodes.
The Low Tension Oscillating Magneto.—The term oscillating magneto means that the armature oscil lates, that is, turns to and fro through a small arc instead of rotating continuously as in the magneto just described.
This rocking motion is accomplished by an arm that pushes the armature back a few degrees, when it is tripped by a lever and is then suddenly pulled around by a pair of powerful spiral springs. The whole scheme is shown at A and B in Fig. 28. This type of magneto is better than a rotating magneto only in that it is much easier to start the engine.
Jump Spark Igniters.—This type of ignition ap paratus is largely used on gas engines. There are two kinds of jump spark systems in vogue, and these are (1) the battery and jump spark coil system, and (2) the high tension magneto system.
The Jump Spark Coil System.—This is formed of (1) a dry, Edison-Lalande or a storage battery; (2) an induction coil, or jump spark coil as it is called; (3) a timer, and (4) a spark-plug.
The jump-spark coil is built up of two coils of wire, the first of which is of heavy insulated wire, called the primary coil, and this is wound on a soft iron core, while on the primary coil, but insulated from it, is wound a coil of fine wire called the sec ondary coil. An interruptor, generally called a vi brator, is worked by the core of the coil and this makes and breaks the primary circuit several hun dred times a minute. A diagram of the battery and jump spark coil system is shown at A in Fig. 29.
Now when a rapidly interrupted battery current flows through the primary coil it sets up high ten, skin currents in the secondary coil, and the pressure of these currents is high enough so that, if the ends of the secondary coil are separated a distance of % of an inch, a spark will jump between them.
If, now, the current from the battery was per mitted to flow through the spark coil all of the time it would spark continuously. To make it spark only when it is needed to explode a fuel charge a timer must be connected in circuit with the battery and the primary coil.