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

Engine.

is provided and its adjustment is the same for all cylinders. As the one vibrator is depended on it will be kept in constant motion and less primary current will be needed to energize the primary windings.

A properly installed secondary distributor is the simplest method of obtaining synchronized ignition with battery and coil system. The use of a single coil greatly simplifies the system, especially on four and six cylinder engines where the multiple unit coil is large and occupies considerable room. The electrical wiring is simplified and the liability of trouble owing to short circuited wires, loose connections, etc., reduced because less w.re is needed

Q. What is the “master vibrator system”?

A. A master vibrator system is similar to the conventional multiple unit coil ignition method, the only exception being that a specially constructed vibrator is used for all four units of the coil. It is wired in circuit with the various coil units and operates regardless of which contact is made at the primary timer. With a master vibrator the advantage offered by the distributor system of only having one vibrator for any number of cylinders is obtained, but the wiring is not simplified and practically all the parts used in the conventional multiple unit coil system are used with the addition of the master vibrator. A master vibrator coil will consume more current than the regular multiple vibrator coil or a single. coil used with a distributor.

Q. Describe simple true high tension magneto system.

A. The essential parts of a high tension magneto ignition system. are outlined in diagram form at Fig. 95-A and it will be seen that. the wiring is very simple and not liable to give trouble. In this diagram the armature is shown in part section so that the various components and the methods of connecting them together can be readily ascertained. When the device is actually in use there are but five external wires. Four of those are heavily insulated and extend from the terminals on the magneto distributor to the spark plugs in the cylinder. The remaining wire is joined to the ground and can be interrupted when desired by a switch. Unlike a battery ignition system, the ground wire circuit is completed when it is.

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