Fig. 59. Breaker—Slip Ring—Distributor
A cam on the armature shaft comes into contact with the arm on which the second point is located, forcing it from the stationary point, thus breaking the low tension current which returns to the secondary coil, the magnetizing and demagnetizing caused by the break in the low tension current, and sets up a rapid alternating current. One end of the secondary is led to a collector ring on the front of the magneto. [Fig. 59A] shows the collector ring. A carbon brush collects the current from the ring and conducts it to the distributor’s centrally located arm. [Fig. 59B] shows the distributor. The centrally located arm is timed to deliver the current, or comes into contact with one of the segments or brushes and allows the current to flow from the segment to the gap at the spark plug, where it jumps the gaps and ignites the gas in the cylinders at the proper time. Then it returns through the ground (the engine and the frame) to the magneto, where it passes back into the secondary coil, passing through an insulated condenser consisting of small plates of steel insulated from one another. This regulates the flowage of the returning current, by reducing it through resistance, and prevents the armature from heating.
A safety spark gap is provided on some magnetos which causes the spark to jump and lose some of its force through resistance when the plugs become shorted. This also restricts the current and greatly aids the condenser in performing its purpose.
CHAPTER XVI
BOSCH HIGH TENSION MAGNETO
Operation, Adjustment and Care
Like all other types of high tension magnetos, the Bosch Type ZR. Ed. 16 explained in this chapter, generates its own current and is usually employed as sole ignition on an engine.
The timer and distributor are integral; and the rotation of the armature, between the poles of strong permanent field magnets, sets up or induces a current in the armature primary circuit, which is farther augmented at every one hundred and eighty degrees of revolution of the armature shaft, by the abrupt interruption of the primary circuit by means of the magneto interruptor. At the opening of the primary circuit the resulting discharge of current from this circuit induces a current of high voltage in the armature secondary circuit. The high tension current thus created is collected by a slip ring on the armature and passes to the slip ring brush then to the various magneto distributor terminals each of which is connected to a spark plug in its respective cylinder.
The operation of the instrument will be more clearly understood from a study of the complete circuits, primary and secondary, which follows.
The Primary or Low Tension Circuit.—The beginning of the armature primary circuit is in metallic contact with the armature core, and the end of the primary circuit is connected by means of the interruptor fastening screw to the insulated contact block supporting the long platinum contact on the magneto interruptor. The interruptor lever carrying a short platinum contact, shown in [Fig. 60] at C is mounted on the interruptor disc, which in turn, is connected to the armature core. The primary circuit is completed whenever the two platinum contacts of the interruptor are brought together, and separated whenever these contacts are separated.
From the latter point the high tension current passes to the distributor brush ([shown] at D) which is held in a brush holder on the distributor gear, and consequently rotates with the distributor gear. Metal segments are imbedded in the distributor plate and as the distributor brush rotates it makes successive contacts with the segments, passing the current onto the spark plug gaps through the high tension cables which are attached to the segment terminal posts.