CHAPTER XIIIGNITION SYSTEMS

The universal use of electricity as a means of igniting the fuel in gasoline motors, makes it necessary that the novice should know something of the fundamentals of the science.

Seeing the Effect of Electricity.—While it is impossible to see a current, there are certain mechanical devices which enables it to be seen by the effects produced on them. One of these devices is the armature which, if placed across the poles of a horseshoe magnet, will adhere to the magnet, by means of its magnetic pull.

Another exhibition is the spark caused by separating the contact point of a conductor through which a current is flowing, causing a spark.

Action of a Current.—The current flowing over a wire acts substantially the same as water flowing through a pipe, that is, the quantity is dependent on the size of the wire, just as in water where the diameter of the pipe determines the flow.

Amperes and Volts.—Water may flow sluggishlythrough a pipe, or be forced through with great violence. So with an electric current. Pressure, therefore, expresses the second similarity in the two mediums.

The quantity of flow in an electric current is calledamperesand the pressure is designated asvolts.

Conductivity.—All metals conduct a current with greater or less facility. Silver is the best conductor, followed by copper. German silver offers a great resistance, and many alloys offer greater or less opposition to the flow.

Resistance.—The length of a wire also serves to check the flow, and this may be overcome by enlarging the size of the wire, or by increasing the pressure, or voltage.

Generating Electricity.—A current may be generated by a dynamo, or by means of cells. The dynamo derives its motion from an engine, which turns, what is called, thearmaturepast a number of magnets, called thefield. The armature contains a series of wire wrappings, extending around from end to end, and the field is composed of metallic heads, each carrying a coil.

Magnetic Field.—When these coils have a current flowing through them the heads become magnetized, and have what is called amagnetic fieldsurrounding them and extending out some distance, and the armature coils pass through these magnetic fields.

As these wires cut the lines of force in the magnetic fields, a current is set up in the armature, and as the armature windings are connected up with the lead and the return wires which transmit the current, it will be seen that the strength, or pressure of the current depends on the speed of the armature movement.

Batteries.—The other method of generating a current is to use a jar ofelectrolyte, a liquid which may be either an acid or a salt solution. If certain metals which are opposite to each other, are placed in this solution, a chemical action takes place, which results in producing current, and this may be shown by connecting together the two metals by a wire outside of the jar.

Metallic Couples.—Within the jar the solution serves as the conductor between the two metals. Copper and zinc are two good metal couples, in which zinc is the positive, and copper the negative. As zinc is readily eaten away by the action of the electrolyte, carbon is used instead.

What Determines Voltage.—Each cell with the two metals, will furnish approximately two volts. It is immaterial whether the cell contains a pint or a gallon of liquid, or what the size of theplates may be. In any event the pressure will not be greater than two volts.

Controlling Amperage.—But the metal plates may be made very large, or have a great surface in each cell. The greater the surface the greater the amperage, so that while each cell has only two volts, it may have a very small amperage, or it may have two, five, ten, or even more amperes flowing therefrom.

Dry Batteries.—Instead of using cells with liquid in them, as the electrolyte, a dry cell is made which acts efficiently. This is usually made in the form of a zinc cup, within which is centrally held a carbon rod, and the space around the rod is filled with ground carbon and dioxide of manganese, and moistened with sal ammoniac.

Cell Construction.—The zinc cell and the carbon have upwardly-projecting posts to which the wires are attached, and when thus made the top of the cup is closed with pitch, or some suitable preparation to prevent evaporation and to retain the substances within, and the whole is then inclosed in a jacket, usually of pasteboard.

Usually these cells give one and a half volts, and are very durable. This is, of course, a very low voltage, and it is necessary, for this reason, to use at least a half dozen, to operate the coil used in an ignition system.

Connecting Up Cells.—If we have a number of cells they can be connected with each other so as to get an additional voltage as well as greater amperage. This statement must be understood in a definite way. Supposing we have six cells, each with an output of 1-1/2 volts, and an ampere flow of 25 in each. Multiplying 25 by 9 makes 225 watts.

Fig. 84. Series Wiring.

We may connect up the six cells in such a way that we can get

First: 9 volts, and 25 amperes, equal to 225 watts, or,

Second: 1-1/2 volts and 150 amperes, equal to 225 watts, or,

Third: 4-1/2 volts and 50 amperes, also equal to 225 watts.

In either case, you will see we have 225 watts. These three windings are designated asseries,parallel, and seriesmultiple.

The Series Connection.—The illustration, Fig. 84, shows the series winding. Here the positive wire B is connected with the carbon pole C, and the wire D, wired up with the zinc pole, E, the connections being made directly through each cell, to the outlet wire F. Now, as we have six cells, the combined voltage is 1-1/2 × 6 = 9 volts.

As, however, all the cells now act as one cell, the amperage is just the same as of one cell, namely, 25.

Fig. 85. Parallel Wiring.

The Parallel Connection.—Fig. 85 shows the parallel connection. Here all the carbon terminals A are connected together in series by a wire B, and all the zinc terminals C by a wire D. In this method the voltage of the battery is the same as that of a single cell, but the amperage is the same as that of a single cell multiplied by the number of cells, namely, 25 amperes × 6.

Series Multiple Connection.—The series multiple, Fig. 86, is so arranged as to form two distinct batteries, 1 and 2. Each battery is connected up in series, by means of the wires A, which join the carbon and zinc. In this way we have at one end a pair of carbon terminals which are joined by a wire B, and at the other end a pair of zinc terminals, joined by a wire C.

Fig. 86. Multiple Wiring.

If, now, these two wires B C are put into circuit with each other, as illustrated by the wires D, we shall have a form of battery which will have the voltage equal to the voltage of one cell multiplied by the cells in either battery 1 or 2. This is 1-1/2 volts × 3, equal to 4-1/2. The amperage, on the other hand, is found by that of one cell multiplied by the number of batteries. This is 25 amperes × 2, equal to 50.

This, if well understood, will enable the user,for instance, to strengthen a battery, where it is weak, by connecting it up in series multiple, instead of in parallel.

Naturally, the cells in the series should be of equal strength and should be frequently tested, to find where the weakness is. If the combined amperage is below the minimum, considering the time it has been in use, it is possible the cause is due to a weak cell, which takes from others, instead of giving. This should be replaced.

Storage Batteries.—The matter pertaining to these batteries is fully set forth in connection with Electric vehicles, in a subsequent chapter. Primary as well as storage batteries may be used for ignition purposes, the object being to obtain a form of battery which shall have a constant and reliable output, and give a reasonable service in point of time.

The Sparking Methods.—Automobiles are equipped with either thelowor thehightension system. Any circuit having a small voltage is termedlow tension, to distinguish it from ahigh tension, or high voltage.

When a current passes along a conductor, no visible effect is produced, unless the voltage should be too great for the carrying wire. In that case it will heat the conductor to redness and thus enablethe eye to see it. The heat is thus caused byresistance.

Air Resistance.—Air has resistance, the same as all other substances. It is, in fact an absolute non-conductor, so that with an ordinary current, such as is used for electric lighting, the separated ends of a conductor may be placed very close together and the current would not leap across.

Make and Break Spark.—On the other hand, even with the weakest current, if the two ends are brought into contact, and then separated, a spark will follow, due to the flow of the current which is interrupted at the breaking of the contact, and the effort of the current to keep on flowing through the wire.

This is called the low tension system, or themakeandbreakmethod of ignition, where the act of breaking the circuit produces the spark and ignites the charge.

The high tension system, on the other hand, depends on producing a current of sufficient pressure to be able to make the current leap across the small gap which is formed between the ends of the conductor.

The Spark Plug.—The mechanical device with the separated conductor ends, where the spark is produced, is called the spark plug, and must be locatedwithin the cylinder of the engine. The gap is between the separated ends of the conductor within the plug, is usually about one thirty-second of an inch.

How Produced.—The low tension may be produced either by a primary or a storage battery, or by a magneto designed for the purpose. This requires some consideration of the meaning and construction of a magneto.

Fig. 87. Dynamo Connection.Fig. 88. Magneto.

Fig. 87. Dynamo Connection.

Fig. 88. Magneto.

The Magneto.—This device is simply a dynamo, structurally, but it differs in this respect: What is called the field, or the cores around which the wires of the field are wound, are made of permanent magnets. The ordinary dynamo has merely soft iron, which is demagnetized as soon as the current ceases to flow in the field windings.

The permanent magnet cores are made of hardened steel, the same as is done with horse shoe magnets, and others of that class, whereby they are enabled to retain the magnetic charge. A dynamo must have its fields energized.

Difference Between Dynamo and Magneto.—Fig. 87 will give an idea of the difference between the two. In the dynamo the pole pieces A of the field have the ends of their windings B connected to the brushes C, and the circuit wires D for the electric lights are connected with the brushes.

On the other hand, the magneto with its field 1 of a permanent magnet, the armature 2 is in a permanent magnetic field, so that the current can be taken directly from the brushes 3 by the wires 4, as in Fig. 88.

Advantages of Magneto.—Owing to the permanent magnetized character of the field, it operates more satisfactory for ignition purposes on an automobile than a regular type of dynamo. The dynamo should be driven at a regular speed, whereas the magneto can be driven at any speed, as it is not self regulating, like the magneto. However, dynamos are used for the purpose, but in that case they are provided with mechanical means for giving them a regular motion.

Different Kinds of Magnetos.—There are two general types of magnetos; first those which haverotating armature; and second, those with stationary armatures and revolving inductors. Thehigh tensiontype is provided with a self-contained coil, or it may have a high tension coil separate from the magneto.

The low tension magneto has an armature of fairly thick wire, one end of the wire being grounded to the armature core and the other connected with a terminal which is insulated from the magneto. From these two points the current is distributed.

In the high tension magneto two coils are necessary, one called theprimary, and the other the secondary. The primary generates a low pressure current, and the secondary a high tension, and the spark is produced by the latter.

Igniters.—In the low tension system an igniter must be placed in the head of the engine cylinder which will mechanically make and break the circuit; but in the high tension device a spark plug is available, the points of which are stationary and in close contact with each other.

For the foregoing reasons, therefore, while the low tension is very simple so far as the wiring is concerned, the mechanical devices necessary to make and break, are somewhat difficult and complicated. The high tension wiring is much morecomplex, but it has the advantage that no mechanism is necessary in the engine except the spark plug.

High Tension Coils.—Before proceeding to an explanation of the systems referred to, we shall explain the action and operation of the high tension coils. These coils depend for their action on what is calledinductance. Suppose two wires lie side by side, but not touching each other, and a current of electricity is sent through one of these wires, which we will call the primary, the other, called the secondary, will take a current from the primary. If the wires are the same size, and of the same material, the current in the two wires will be of substantially the samepotentiality. By this is meant that they will have the same amperage and voltage.

Inductance.—But assuming that the primary wire is larger than the secondary, then the current carried by inductance across the space between the two wires will be changed in the secondary so that it has a larger voltage, but a correspondingly lower amperage. This is what high tension means.

The convenient way to arrange these wires parallel with each other, is to wind the two different size wires on the same core, in which thecoarse wire, which forms the primary, is first wound around the core, and on this is wound the fine wire.

Constructing a Coil.—Such a coil is shown in section in Fig. 89, in which the core A is a hard rubber or fiber tube, with disk ends B of the same material. The primary wire C is large in cross section, and carefully insulated. The opposite ends are brought out through the disk heads, and run to the generator, that is, the battery or dynamo. The fine wire D, which constitutes the secondary winding, is also of insulated wire, wrapped over the primary, and its ends are connected up with the sparking mechanism, as will be more fully explained hereinafter.

Fig. 89. Induction Coil.

A Simple High Tension Sparking System.—With such a coil, of proper size, and adapted to receive the required current, several things are necessary in order to produce a sparking effect.

Condenser.—One of these is a condenser, which, while a spark can be produced without it, is nevertheless an important element. The office of a condenser is to absorb a certain amount of current. It will be remembered that the drawing apart of the points in a conductor, produced a spark. Now in the secondary current, of the high tension system, is aninterrupter, a mechanism that makes and breaks the circuit continuously.

Interrupter.—Whenever the interrupter opens the circuit, the condenser absorbs the surging current produced by the break, so that it acts like a storage battery in the system.

Fig. 90. High Tension Circuit.

The interrupter may be made something like the mechanism of an electric bell, in which the current is interrupted as the clapper moves back and forth.

By referring to Fig. 90 a comprehensive idea may be obtained of a high tension system for igniting the compressed fuel in a gasoline engine.

Arrangement of a High Tension System.—Thedynamo A, or the battery, as the case may be, is connected up with the primary coil B, by means of the circuit wires C. The secondary coil D, which is, of course, wound around the primary B, in practice, has one of its terminals E extending to what we shall call the spark plug F.

The other terminal G, of the secondary coil, also extends to the spark plug F, there being, of course, a gap between the two ends of these wires in the spark plug.

Now, close up to the secondary, D, is a condenser H, the terminals of which are connected up with the two wires E G, and between the condenser and the spark plug F, is the interrupter I.

The High Tension Connections.—With this understanding of the action of the magneto, the accompanying sketch of a high tension system will be understood.

The magneto A, Fig. 91, has on its armature shaft B, two distributer rings C D, which form the terminals for the two wires E F, which run out from the armature winding. C is connected by metallic contact with this shaft, and D insulated therefrom. Also, alongside of the ring D, is the interrupter wheel G which engages the finger H, and thus interrupts the circuit.

Above the armature shaft, and parallel therewith, is a shaft I, turned at half the armatureshaft by means of the two gear wheels J K. On the end of this shaft is a finger J, revoluble therewith, and this engages successively with four contact plates K, each plate being connected with a spark plug in the engine, assuming, of course, that there are four cylinders in the engine.

Fig. 91. High Tension Connections.

The ring C has its contact finger connected by a wire L with one end of a primary coil M, while the other terminal has a wire N which goes to oneterminal of the interrupter G. The other outlet of the interrupter is connected up with the contact finger of the other collector ring D. This contact finger also has a wire connection P with one terminal of a condenser Q, the other end of the condenser being connected with the wire N, running from the primary coil M.

The Secondary Coil.—The secondary, or high tension coil R, has one end grounded, which means that it is connected up with the metal of the engine, and the other terminal is connected by a wire T, with the finger J on the distributer disk.

In operation, we will assume that the current leaves the armature over the wire E; it has two paths, one through ring D, wire O, and interrupter G, back to the other wire F of the armature; or, after passing the ring D it may pass over O, to the interrupter, then through wire N, primary coil M, and wire L, back to the armature.

Operation of System.—The revoluble disk of the interrupter G is so arranged that when the armature has the greatest current intensity it is opened by its turning movement, so that the current is compelled to take the last named course through the primary coil M, and at the same time a certain portion of the current is absorbed by the condenser Q.

This intense charge of the current in the primaryinduces a high tension current in the secondary coil R, and the result is that the current from the secondary goes through the wire T to the finger J, and from the finger J to the contact plate K, and to the particular spark plug which happens to be connected up by one of the wires U with that plate.

The Spark Gap.—The current in leaping over the gap made by the spark plug, goes through the engine metal to the other end of the secondary coil R, at the place indicated by S.

It should be understood that the coils M R are in a separate box, and usually placed in a convenient position in the machine.

The diagram illustrating the foregoing, is designed merely to show in a simple manner, how the different mechanical and electrical parts are connected up together.

Function of the Interrupter.—The interrupter G, while placed in the primary circuit, necessarily controls not only the primary, but also the secondary circuit. It should not be confounded with the distributer to which the wire T runs from the secondary coil.

The office of the interrupter is to break the primary circuit of the magneto at a time when a spark is required, and the duty of the distributer is to have its finger J in such a position at thatparticular time as to make the connection in the secondary circuit with the particular spark plug which requires a spark.

Vibratory Coils.—The secondary coil may be so constructed that it will give only a single spark at each impulse, or a plurality of them, and many argue that the latter is more efficient for that reason.

Fig. 92. Vibratory Coil.

The diagram, Fig. 92 will show how this type of secondary is made and operated. The induction coil has a core A of soft iron, and at one end is an armature B, mounted on the end of a spring finger C, this finger being attached to a binding post D.

The spring C holds the armature B normally out of contact with the end of the core A, and in contact with the end of an adjusting screw E which screws through a post F. The primary coil hasone of its ends connected up with the binding post D, by a wire G; and the other terminal of the primary, has a wire H which goes to the battery I, and from the battery to the post F, through wire J.

A condenser K is placed intermediate the two wires G J, by the connections L M. The wire H has a switch N in its line, as shown, and the secondary coil O is wound around the primary in the usual manner.

Operation of Vibratory Coil.—The operation is as follows: When the switch N is closed the current from the battery goes through the primary coil, wire G, spring finger C, and wire J back to the battery which originated the energy. The result of this current is to magnetize the core A, and thus draw the armature B away from the adjusting screw E, thereby breaking the primary circuit, which demagnetizes the core, and the spring finger returns and again establishes a circuit.

This action of the vibrating armature is exactly similar to the electric bell, but there is one important addition, and that is the condenser K which is added to the familiar mechanism, and the uses of which should be explained in connection with this apparatus.

Surging Movement of Current.—Whenevera primary current is broken, a surging effect takes place. When the break occurs the strength of the field or force in the armature winding rapidly decreases, and when the connection is again made this force rapidly increases. This objection of the current to constantly change its current strength, produces what is calledself inductance.

Timing Device.—The current in the secondary, which makes the spark, at the time the break occurs, depends for its strength on the rapidity with which the strength of the primary goes down, so that a timing device is used on a plain or ordinary coil to effect this.

Fig. 93. Contact Maker.

In the vibratory coil, however, the object is to make the break with exceeding rapidity so there will be a series of sparks, instead of only a single one at each break.

Contact Makers.—This device is designed to afford a means whereby a circuit is closed, and broken only at the time a spark is made. A type of this device is shown in Fig. 93.

It is simply a case A, usually attached to the gear box of an engine, which serves as the journal bearing for a shaft B, which enters at one side, and drives a cam C. Within the case is a spring finger D, attached to a binding post E, and the free end of the spring has an A-shaped contact point F which is designed to enter the V-shaped notch of the cam, as the latter turns.

To prevent the A-shaped projection from coming into contact with the cam when the V-shaped portion is opposite, an adjustable screw G is provided, which screws through a bushing of insulating material secured to the case.

Fig. 94. Contact Breaker.

The current is through the adjusting screw, spring finger D, and binding post E. By this construction the circuit is broken during the entire revolution of the cam, except when the notch in the cam appears at the A-shaped contact point.

The Contact Breaker.—Compare this with the contact breaker shown in Fig. 94. The case isalso provided to receive the end of a journal A, which rotates a cam. In this case the cam B has an A-shaped projection C. This projection comes into contact only momentarily with the anti-friction wheel D on one end of a lever E, which is pivoted midway between its ends to the case.

The free end of the lever is normally held out of contact with a terminal F, by means of a spring G. The terminal is insulated from the case. By this arrangement the circuit is closed at all times except during that short period when the point C is in contact with the wheel D.

Sparking Plugs.—Much of the difficulty of satisfactory running is due to the sparking plug which contains the small points, on which everything in the power system depends. The intense heat generated at that point by the secondary coil tends to destroy them, so that the points should be larger when used with a magneto, and they should be closer together than if used wholly with a battery.

Testing Plugs.—This is a simple matter, and in so-called engine troubles, this is generally the first thing considered. It should be unscrewed and laid on the cylinder so it is in metallic contact. The character of the spark exhibited, when the engine is cranked, will show whether or not the fault is due to the plug or to the electrical source.If no spark is obtained then the electrical system must be examined. Commence at the battery. When the engine is on the sparking point and the primary switch closed, the terminals of the suspected wires may be touched by a test wire and if a current then flows it will indicate a break at that point.

Short Circuiting Faults.—Ashort circuitis one where the path of the current is from the lead to the return wire at some point between the battery, or source of electrical energy, and the coil or other mechanism which is to be operated by the electricity.

When this occurs the first thing is to examine the conductors and ascertain whether the insulation is intact. Sometimes the insulation becomes worn or frayed, and it is not infrequent for the ends of the wire, where attached to the binding post to spread out, where the conductor is made up of a lot of small wires, and some of them touch the metal alongside of the binding post.

Short Circuiting of Secondary Wires.—The secondary wires often cause short circuiting by lying too close to the metal of the engine or case. Great care should be observed to use the best insulated wire, and to see that they are free from dangerous contact.

Stranded cables are better for all wiring purposes,as vibration will not affect the screws which hold them at the contacts. A solid wire will cause a constant jar, and affect all connections.

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