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wire to produce a hot energetic spark a current of sufficient intensity may be produced directly from the mechanical generator without the use of a "kick-coil” such as necessary with a battery.

Q. Must magneto be timed?

A. The armature of the magneto must be timed with a certain definite relation to the crankshaft of the motor because the igniter points separate in the combustion chamber only when the magneto armature has attained that portion of a revolution where the current generation in the armature winding is at its maximum value. This means that the magneto must be driven by positive means from the engine crankshaft, and on a four cylinder engine the magneto armature runs at crankshaft speed just as in the high tension forms.

Q. What are the advantages of this system?

A. It is claimed that the low tension system of ignition is not affected by water as is the high tension form with exposed spark plugs and that it will produce a hotter spark than will the high tension system. It is widely used in marine and stationary installations but is seldom employed at the present time on motors intended as automobile power plants.

LESSON ELEVEN

HIGH TENSION IGNITION SYSTEMS

Q. How many types of high tension ignition systems are used?

A. Two main forms of high tension systems are used, those in which the current is generated by a magneto and the others which use chemical current producers to generate the electrical energy which must be intensified by means of transformer coil before it can be directed to the plugs.

Q. Describe action of simple induction coil, timer, and battery system for single cylinder engines.

A. The arrangement of the parts of a simple, high tension ignition system has been previously considered and is clearly outlined at Fig. 77-A. The current is supplied by means of a storage battery or a six cell dry battery, as desired. The positive terminal of the dry battery group and that of the storage battery are joined together and are connected with the ground which may be any point on the metal frame of the engine. The wire from the zinc terminal of the dry battery group goes to one side of a two point switch while the negative terminal of the storage battery is connected to the other side of the switch. Either the dry or storage battery may be brought in circuit with the induction coil and timer by moving the switch lever to one side or the other.

The timer is a simple form having one insulated contact segment which is connected to one of the primary terminals of the coil. The other primary terminal of the coil is connected to the switch lever while the secondary coil terminal is connected to the insulated terminal of the spark plug by means of a well insulated high tension cable. As the crankshaft of the engine revolves, it turns the revolving contact member of the timer and when the piston reaches the proper position in the combustion chamber the roll on the revolving timer member makes a contact with the insulated segment carried by the timer case. Assuming that the switch lever is on the storage battery contact button, the current will flow from the positive terminal of the storage battery to the ground on the engine base and from thence through the medium of the metal parts of the engine to the revolving timer brush, which is in metallic contact with the engine camshaft, and which, therefore, transmits the current through the insulated segment to the primary terminal of the spark coil, because of the connection or wire joining these two parts.

When the current passes through the primary winding of the coil it produces a secondary current in the high tension winding as has been previously explained and passes out of the coil box through the primary terminal which is joined to the switch lever and from that point back to the storage battery through the switch lever and the wire connecting the battery with the switch. As long as the engine revolves a contact will be established at the timer every two revolutions of the crankshaft and a current will flow from the batteries through the primary winding of the coil and back again to the battery. Each time a primary circuit is established at the timer a spark will be produced at the spark plug points and the gas compressed in the combustion chamber by piston will be exploded.

Q. Outline action of induction coil, timer, and battery system for four cylinder engine.

A. The action of the four cylinder ignition system outlined at Fig. 100 is exactly the same as that previously described. Instead of a single unit coil a spark coil assembly having four units, one for each cylinder, is employed and a timer is used that has four insulated contact segments, one for each cylinder of the engine. As the timer contact revolves it makes an electrical connection with the various insulated segments in turn so that the various primary windings are energized when a spark is desired in the cylinder that is to be fired, depending upon the firing order. In the group shown at Fig. 100, a spark takes place first in cylinder No. 1, then in cylinder No. 2, followed by a spark in cylinder No. 4 and lastly one in cylinder No. 3.

Q. Describe action of distributor system.

A. It is not necessary to use a separate unit for each cylinder to be fired as single induction coil may be used for any number of cylinders, if a combined primary timer and secondary distributor is employed. A distributor system for a six cylinder engine is clearly shown at Fig. 104. The batteries are connected to the switch which is mounted on the face of the spark coil in the customary manner and the connection between the switch lever and the primary winding is made in the regular way, only that the wire does not show because the connect on is made inside of the coil box. The primary timer is just the same as the form used in all battery ignition systems except that the six insulated primary contact segments are joined together by a metal band outside of the body and a single wire leads from these to the primary terminal at the top of the coil, which is exactly the same type as used on a single cylinder engine.

The secondary terminal of the coil is connected to the rotating distributing brush carried at the upper portion of the distributor. This secondary brush establishes contact with the various terminals, which are joined to the spark plugs in the cylinders. The wires are arranged in such a manner that the spark plugs are brought into action progressively as the firing order dictates. The primary timer portion establishes six contacts every revolution and all of these energize the one primary winding. The distributor brush is depended on to do the timing and to convey the high tension current from the spark coil to the plug where the spark is to occur.

Q. What are the advantages of the distributor system?

A. When a separate induction coil unit is used for each cylinder it is difficult to adjust the vibrators on all of the coil units so that they will be exactly the same in adjustment and it is possible for one or more of the vibrators to lag behind the others, i. e. they will not start to vibrate as quickly as those which may differ in adjustment and as a result the spark does not occur at absolutely the same time relative to the piston position in all the cylinders. When a single coil is used on a multiple cylinder engine but one vibrator

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Fig. 104.-Typical High Tension Battery Ignition System With Secondary Distributor for Six-Cylinder

Engine.

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