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mits motion to the timer is in the form of a tube T, revolved by spiral gears. An inclined slot is cut through the walls of this hollow driving member. A smaller shaft is carried inside of the hollow member, and a vertical slot is cut through this shaft in order to permit a pin to pass through it, said pin being actuated by a collar adapted to slide up and down on the outside of the hollow driving shaft. The pin passes through both the straight

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Fig. 39.—Parts of Delco 1914 System. A—Delco Timer, Coil and Con

denser Assembly. B—Construction of Delco Automatic Spark Advance. CDelco Voltage Regulator.

slot in the small shaft and the incline slot in the hollow driving member. If the collar holding the pin is moved it will change its angular relation with the small shaft which will advance the timing cam of the contact breaker. The collar is shifted by a spring loaded revolving ring R, which moves from the position shown in the drawing to a horizontal position as the speed increases. This ring is connected to the sliding collar and causes it to rise, advancing the spark as the engine speeds up or to fall, retarding the spark as the engine speed decreases. If desired, the spark timing may be controlled independently of the automatic advance mechanism by a spark lever connected to the corresponding member on the steering wheel. The voltage regulator, which will be described when discussing the generating function of the Delco instrument, is shown at Fig. 39, C.

Condenser.—The condenser consists of two long strips of folded tinfoil insulated from each other by paraffined or oiled paper, and connected as shown in Fig. 40. The condenser has the property of being able to hold a certain quantity of electrical energy, and like the storage battery, will discharge this energy if there is any circuit between its terminal. As the distributor contacts open the magnetism commences to die out of the iron core, this induces a voltage in both the primary and secondary windings of the coil. This induced voltage in the primary winding amounts to from 100 to 125 volts. This charges the condenser which immediately discharges itself through the primary winding of the coil in the reverse direction from which the ignition current originally flows. This discharge of the condenser causes the iron core of the coil to be quickly demagnetized and remagnetized in the reverse direction, with the result that the change of magnetism within the secondary winding is very rapid, thus producing a high voltage in the secondary winding which is necessary for ignition purposes. In addition to rapidly demagnetizing the coil the condenser prevents sparking at the breaker contacts—thus it is evident that the action of the condenser can very seriously affect the amount of the spark from the secondary winding and the amount of sparking obtained at the timer contacts.

Ignition Coil.—This is sometimes mounted on top of the motor generator and is what is generally known as the ignition transformer coil. In addition to being a plain transformer coil it has incorporated in it a condenser (which is necessary for all high tension ignition systems) and has included on the rear end an ignition resistance unit. The coil proper consists of a round core of a number of small iron wires. Wound around this and insulated from it is the primary winding. The circuit and arrangement of the different parts are shown in Fig. 41. The primary current is supplied through the combination switch and resistance on the coil, through the primary winding, to the distributor contacts. This is very plainly shown on the circuit diagram. It is the interrupting of this primary current by the timer contacts together with the action of the condenser which causes a rapid demagnetization of the iron core of the coil that induces the high tension current in the secondary winding. This secondary winding consists of sev

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Fig. 40.—Simplified Wiring Diagram Showing Action of Delco Ignition

System.

eral thousand turns of very fine copper wire, the different layers of which are well insulated from each other and from the primary winding, one end of which terminates at the high tension terminal about midway on top of the coil. It is from this terminal that the high tension current is conducted to the distributor where it is distributed to the proper cylinders by the rotor shown in Fig. 42.

Ignition Resistance Unit.—The ignition resistance unit which is shown in Fig. 41 is for the purpose of obtaining a more nearly uniform current through the primary winding of the ignition coil at the time the distributor contacts open. It consists of a number of turns of iron wire, the resistance of which is considerably more than the resistance of the primary winding of the ignition coil. If the ignition resistance unit was not in the circuit and the coil was so constructed as to give the proper spark at high speeds, the primary current at low speeds would be several times its normal value with serious results to the timer contacts. This is evident from the fact that the primary current is limited by the resistance

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Fig. 41.-Sectional View Showing Arrangement of Wiring in Delco

Ignition Coil.

of the coil and resistance unit by the impedence of the coil. (Impedence is the choking effect which opposes any alternating or pulsating current magnetizing the iron core.) The impedence increases as the speed of the pulsations increase. At low speeds the resistance of the unit increases, due to the slight increases of current heating the resistance wire.

The Circuit Breaker.—The circuit breaker is mounted on the combination switch as shown in Fig. 42. This is a protective device which takes the place of a fuse block and fuses. It prevents the discharging of the battery or damage to the switch or wiring

to the lamps, in the event of any of the wires leading to these becoming grounded. As long as the lamps are using the normal amount of current the circuit breaker is not affected. But in the event of any of the wires becoming grounded an abnormally heavy current is conducted through the circuit breaker, thus producing a strong magnetism which attracts the pole piece and opens the con.

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Fig. 42.-Delco Combination Switch with Ammeter and Circuit Breaker

Included.

tacts. This cuts off the flow of current which allows the contacts to close again and the operation is repeated, causing the circuit breaker to pass an intermittent current and give forth a vibrating sound. It requires 25 amperes to start the circuit breaker vibrating, but once vibrating a current of three to five amperes will cause it to continue to operate. In case the circuit breaker vibrates repeatedly, do not attempt to increase the tension of the spring, as

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