DUAL IGNITION SYSTEMS
It has been the custom to equip jump-spark engines with two complete systems of ignition, one operated by a magneto and the other by coil and battery. Each system has its own spark plugs, timing device, wiring, etc., the two being connected only at the switch. Many of these duplicate parts have been eliminated by the introduction of dual ignition systems, and the mechanism is correspondingly simplified. The Bosch dual system is a good example of the principles involved, and a diagram of the connections is shown on Fig. 16. The magneto used is of the usual two-spark type, except that the secondary current, instead of being led from the collecting ring direct to the distributer, is taken to the switch that is located in the coil box on the dash. In addition to the regulation interrupter illustrated on Fig. 11, the magneto is provided with a second interrupter or circuit breaker that controls the flow of the battery current, and takes the place of a timer. While the magneto interrupter revolves with the armature, and is operated by stationary cams, the battery circuit breaker is stationary, and is operated by a two-nose cam that revolves with the armature shaft. The stationary and revolving cams are so set that the interrupter and circuit breaker break their circuits at the same instant.
Fig. 16.—Bosch Jump-Spark Dual System.
The coil is contained in a brass case on the dash, and in design and construction is a duplicate of the magneto armature. Attached to the coil is a handle that projects through a slot in the case, by means of which the coil may be turned partly around in the case. The terminals of the coil windings are attached to metal knobs located on the under side of a fiber plate that forms the bottom of the coil, and turning the coil by the handle moves these knobs in and out of contact with corresponding knobs on the bottom of the case. These knobs form the switch that cuts off all current, or permits the engine to be run on magneto or battery. When the switch is in such a position that the magneto produces secondary current, this flows from terminal 3 of the magneto to terminal 3 of the switch; thence by the switch connection to terminal 4 and to the secondary distributer. When the battery is switched in, the magneto primary is grounded, and secondary current from the coil flows over wire 4 to the secondary distributer.
By pressing a button on top of the coil case, a vibrator is cut into the circuit to permit starting the engine on the spark. When the engine starts the button is released, and ignition is produced by the single spark that results from the demagnetizing of the core that follows the breaking of the battery circuit by the circuit breaker. Throwing the switch breaks the battery circuit and cuts in the magneto.