Chapter VII: Ignition. Low Tension System

Electricity, that subtle force, which manifests itself in so many ways, is nevertheless beyond the power of man to see. The only way in which we know of its presence is by the results produced by its movements, because it can make itself known to our senses only by some form of motion.

The authorities regard light, heat and electricity as merely different forms of motion. The most that can be done with such a force is to learn the laws governing it.

Magnetism.--This is a form of electricity. In fact, it is one of the most universal manifestations, for without it electricity would be useless. When the first permanent magnet was found at Magnesia, it was not considered electricity. The sciences had not arrived at that point where they were able to classify it as belonging to lightning and other manifestations of that kind which we now know to be electricity.

The Armature.--But magnetism can no more be seen than electricity flowing through a wire. If a piece of metal has magnetism it will attract a piece of iron or steel placed in close proximity, and thus we are permitted to see the action.

The lightning in the upper atmosphere burns the gases in its path. This enables us to see, not the current, but its action,--the result produced by its power.

The electric current has many peculiar manifestations, the causes of some of them being known and utilized. In the use of this medium for igniting the fuel gas, many of the phases of electrical phenomena are brought into play, and it is necessary, therefore, to know something of the fundamentals of the science to enable us to apply it.

Characteristics of Electricity.--When a current passes along a wire, it does not describe a straight path, but it moves around the conductor in the form of circles. The current is not confined wholly to the wire itself, but it extends out a certain distance from it at all points.

Magnetic Field.--Every part of a wire which is carrying a current of electricity has, surrounding it, a magnetic field, of the same character, and to all intents and purposes, of the same nature as the magnetic field at the ends of a magnet.

Elasticity.--This current has also something akin to elasticity. That is, it surges to and fro, particularly when a current is interrupted in the circuit. At the instant of breaking a current in an electric light circuit there is a momentary flash which is much brighter than the normal light, which is due to the regular flow of the current.

This is due to the surging movement, or the elastic tension, in the current. Advantage is taken of this characteristic, in making a spark. This spark is produced at the instant that the ends of the wires are separated.

The Make and Break System.--No spark is caused by putting the two ends together, or by making the connection, but only by breaking it, hence it is termed the _make_ and _break_ method of ignition.

When the connection is broken the current tries to leap across the gap, and in doing so develops such an intense heat that the spark follows. As a result of the high temperature it is necessary to use such a material where the gap is formed that it will not be burned. For this purpose platinum, and other metals are now employed.

Voltage.--This plays an important part in ignition. Voltage is that quality which gives pressure or intensity to a current. It is the driving force, just as a head of water gives pressure to a stream of water.

High and Low Voltage.--A high tension current,--that is, one having a high voltage, will leap across a gap, whereas a low voltage must have an easy path. When the ends of a wire in a circuit are separated, air acts as a perfect insulator between them, and the slightest separation will prevent a low current from jumping across.

This is not the case with a high tension current, where it will leap across and produce the flash known as the _jump spark_.

Low Tension System.--Two distinct types of ignition have grown out of the voltage referred to, in which the _make_ and _break_ system uses the low tension, because of its simplicity in the electrical equipment.

Disadvantages of the Make and Break.--There is one serious drawback to the extended use of this system, and that is the necessity of using a moving part within the cylinder, to make and break the contact in the conductor, as it is obvious that this part of the mechanism must be placed within the compressed mixture in order to ignite it.

Amperes.--A current is also measured by amperes,--that is, the quantity flowing. A large conductor will take a greater quantity of current than a small one, just as in the case of water a large pipe will convey a greater amount of the liquid.

Resistance.--All conductors offer resistance to the flow of a current, and this is measured in _Ohms_. The best conductor is silver and the next best is copper, this latter material being used universally, owing to its comparative cheapness.

Iron is a relatively poor conductor. Resistance can be overcome to a certain extent, however, if a large conductor is used, but it is more economical to use a small conductor which has small resistance, like copper, than a heavy conductor, as iron, even though pound for pound the latter may be cheaper.

Direct Current.--There are two kinds of current, one which flows in one direction only, called the _Direct_. It is produced in a dynamo which has a pair of commutator brushes so arranged that as the armature turns and its wires move through the magnetic fields of a magnet, and have direction of the current alternate, these brushes will change the alternations so the current will travel over the working conductors in one direction only.

Primary and secondary batteries produce a direct current. These will be described in their appropriate places.

Alternating Current.--This is a natural current. All dynamos originally make this kind of current, but the commutator and brushes in the direct current machine change the output method only. The movement of this current is likened to a rapid to and fro motion, first flowing, for an instant, to one pole, and then back again, from which the term _alternating_ is derived.

While the sudden breaking in a circuit will produce a spark with either the direct or the alternating currents, the direct is usually employed for the make and break system, since batteries are used as the electrical source.

On the other hand the jump spark method employs the alternating current, because the high tension can be most effectively produced through the use of _induction coils_, which will be explained in connection with the jump spark method of ignition.

Generating Electricity.--There are two ways to produce a current for operating an ignition system, one by a primary battery, and the other by means of a magneto, a special type of dynamo, which will be fully explained in its proper place.

Primary Battery.--As we are now concerned with the make and break system, the battery type of generation, and method of wiring up the same, should first be explained.

Thus, in Fig. 34, a primary battery is shown, in which the zinc cell A has an upwardly-projecting wing B at one side, to which the conductor is attached; and within, centrally, is a carbon bar C. An electrolyte, which may be either acid or alkali, must be placed within the cell.

Making a Dry Cell.--The zinc is the negative, and the carbon the positive electrode. The best material for the electrolyte is crushed coke, which is carbon, and dioxide of manganese is used for this purpose, and the interstices are filled with a solution of sal-ammoniac.

The top of the cell is covered with asphaltum, so as to retain the moistened material and the liquid within the cell, and thus constituted, it is called a _dry cell_.

Energy in a Cell.--A battery is made up of a number of these cells. Each cell has a certain electric energy, usually from one and a half to one and three-quarter volts, and from twenty-five to forty amperes.

The amperage of a cell depends on its size, or rather by the area of the electrodes; but the voltage is a constant one, and is not increased by the change, formation, or size of the electrodes.

For this reason the cells are used in groups, forming, as stated, a battery, and to get efficient results, various methods of connecting them up are employed.

Wiring Methods.--As at least six cells are required to operate a coil, the following diagrams will show that number to illustrate the different types of connections.

Series Connection.--The six cells, Fig. 35, show the carbon electrodes A, of one cell, connected by means of a wire B with the zinc electrode wing C of the next cell, and so on, the cell at one end having a terminal wire D connected with the zinc, and the cell at the other end a wire E connected with the carbon electrode.

The current, therefore, flows directly through the six cells, and the pressure between the terminal wires D, E, is equal to the combined pressure of the six cells, namely, 1-1/2 × 6, which is equal to 9 volts. The amperage, however, is that of one cell, which, in these diagrams, will be assumed to be 25.

Parallel Connection.--Now examine Fig. 36. In this case the carbon electrodes A are all connected up in series, that is, one following the other in a direct line, by wires B, and the zinc electrodes C, are, in like manner, connected up in series with each other by wires D. The difference in potential at these terminals B, D, is the same as that of a single cell, namely, one and a half volt.

The amperage, on the other hand, is that of the six cells combined, or 150. This method of connecting the cells is also called _parallel_, since the two wires forming the connections are parallel with each other, and remembering this it may be better to so term it.

Multiple Connections.--This is also designated as _series multiple_ since the two sets of cells each have the connections made like the series method, Fig. 35. The particular difference being, that the zinc terminals of the two sets of cells are connected up with one terminal wire A, and the carbon terminals of the two sets are joined to a terminal B.

The result of this form of connection is to increase the voltage equal to that of one cell multiplied by the number of cells in one set, and the amperage is determined by that of one cell multiplied by the two sets.

Each set of cells in this arrangement is called a battery, and we will designate them as No. 1, and No. 2. Each battery, therefore, being connected in series, has a voltage equal to 4-1/2 volts, and the amperage 50, since there are two batteries.

Now the different arrangement of volts and amperes does not mean that the current strength is changed in the batteries or in the cells. If the pressure is increased the flow is lessened. If the current flow, or the quantity sent over the wires is increased, the voltage is comparatively less.

Watts.--This brings in another element that should be understood. If the current is multiplied by the amperes a factor is obtained, called _Watts_. Thus, as each cell has 1-1/2 volts and 25 amperes, their product is 37-1/2 watts.

To show that the same energy is present in each form of connection let us compare the watts derived from each:

Series connection: 9 volts × 25 amperes, equal 225 watts.

Parallel connection: 1-1/2 volts × 150 amperes, equal 225 watts.

Series Multiple connection: 4-1/2 volts × 50 amperes, equal 225 watts.

From the foregoing, it will be seen that the changes in the wiring did not affect the output, but it enables the user of the current to effect such changes that he may, for instance, in case a battery should be weak, or have but little voltage, so change connections as to temporarily increase it, although in doing so it is at the expense of the amperage, which is correspondingly decreased.

It would be well to study the foregoing comparative analysis of the three forms of connections, so far as the energy is concerned, because there is an impression that increasing the voltage, is adding to the power of a current. It does nothing but increase the pressure. There is not one particle of increase in the energy by so doing.

_Testing a Cell._--The cells should be frequently tested, to show what loss there is in the amperage. This is done by putting an ammeter in the circuit. If a meter of this kind is not handy, a good plan is to take off one of the wire connections, and snap the wire on the terminal, and the character of the spark will show what energy there is in the cell.

Testing With Instruments.--The method of testing with voltmeter and ammeter, is shown in Fig. 38. The voltmeter is placed in a short circuit between the two terminal wires, whereas the ammeter is placed in circuit with one of the wires. The reason for this is that the voltmeter registers the pressure, the power, or the difference of potential between the two sides of the cell, and the ammeter shows the quantity of current flowing over the wire.

In practice batteries are not used continuously for igniting. They are temporarily employed, principally for starting, because their continued use would quickly deplete them.

Simple Battery Make and Break System.--In order to show this method in its simplest form, examine Fig. 39, which diagrams the various parts belonging to the system.

We have illustrated it with two cylinders, portions of the heads being shown by the outlines A, A. B, B represent terminals which project into the cylinders, and are insulated from the engine heads. Through the sides of the engine heads are rock shafts C, the ends within the cylinder having fingers D which are adapted to engage with the inner ends of terminals B, B.

On the ends of the rock shafts outside of the cylinders, they are provided with levers E, E, one end of each being attached to a spring F, so that the tension of the spring will normally keep the upper end of the finger D in contact with the terminal B. The cut shows one finger engaging with B, and the other not in contact.

The other end of the lever E rests beneath a collar or shoulder G on a vertical rod H. The lower end of this rod engages with a cam I on a shaft J, and when the cam rotates the rod drops off the elevated part of the cam, and in doing so the shoulder G strikes the end of the lever E and causes the finger to rapidly break away from the terminal B, where the spark is produced.

To Advance the Spark.--For the purpose of advancing or retarding the spark, this rod has, near its lower end, a horizontally-movable bar K, which may be moved to and fro a limited distance by a lever L, this lever being the substitute in this sketch of the lever on the steering wheel of an automobile.

The spark is advanced or retarded by causing the lower end of the rod H to be moved to the left or to the right, so that it will drop off of the raised portion of the cam earlier or later.

The wiring up is a very simple matter. The battery M has one end connected up with one terminal of a switch N, while the other terminal of the switch has a wire connection with the terminal plugs B, B, in the cylinder heads.

The other end of the battery is connected with the metal of the engine, which may be indicated by the dotted line O which runs to the rock shaft C, and thus forms a complete circuit.

The operation is as follows: When the key P of the switch is moved over so that it contacts with the terminal N, the battery is thrown into the circuit, and the current then passes to the plug B of the first cylinder, as the finger D in that cylinder is in contact with that terminal, and it passes along the finger D, and rock-shaft C, to the metal of the engine, and passes thence to the battery, this course being indicated by the dotted line O.

At the same time, while cylinder No. 2 is also connected up with the battery, the shoulder of the rod H has drawn the finger D from its contact with the plug B, hence the current cannot pass in that direction.

As the cam I, of cylinder No. 1, turns in the direction of the arrow, the rod drops down and suddenly makes a break in the terminal of this cylinder, causing the ignition, to be followed by a like action in No. 2.

The Magneto in the Circuit.--To insure the life of the battery, so that it may be in service only during that period at the starting, when the magneto is not active, the latter is so placed in the circuit, that, at the starting, when, for instance, the automobile is being cranked, it is cut out by the switch on the dash board.

In Fig. 40, a simple two-pole switch is used. With the magneto it is necessary to have a three-point switch, R, and a plain coil S is placed between the switch and battery.

One side of the magneto T is connected by wire U with one of the points of the switch R, and the other side of the magneto is connected with the metal of the engine, which is indicated by the dotted line V.

In all other respects the mechanism is the same. The starting operation has been explained with reference to the preceding figure, and when the engine has picked up, and is properly started, the switch bar is thrown over so it contacts with the point connected up with the wire U leading to the magneto.

This, of course, cuts out the battery, and the engine is now running on the magneto alone. The object of the coil S is to oppose a rapid change of the current at the moment of the interruption. The coil induces a counter current the moment the break is made, and as the current continues to flow for a very short period after the break a spark of greater intensity is produced than if the circuit should be permitted to go from the battery to the sparker directly, as in the previous illustration.

The best spark is produced by quickly making the break between the points B, D, so that particular attention has been given to mechanism which will do this effectively.

Magneto Spark Plug.--One of the devices to obviate the difficulty of providing moving mechanism outside of the engine cylinder, is shown in Fig. 41. In this the coil A is connected with a terminal B at the head of the device and the other is connected to the plug C which screws into the cylinder head.

Within the core is a pivotally-mounted lever D, the upper end E of which is attracted by the tubular metallic core F, and the lower end having a contact point G, which is adapted to engage with a stationary point H.

The pivot I, on which the lever D is mounted, provides a means whereby the lever swings, and a spring J is so arranged that when the lower end of the lever is disengaged from the contact, the spring will return it to its normal position.

In its operation when a contact is formed by the timing device of the magneto, so as to give a spark, the circuit passes to the terminal B, coil A, and plug C, thus forming a complete circuit. This energizes the core A, pulling the upper end of the lever, and at the same time causes the lower end to disengage the two contacts G, H, which breaks the circuit and produces a spark.

The breaking of the circuit deënergizes the core, and the spring again draws the lever back to its normal position, ready for the next completion of the circuit by the timing device.

Such an arrangement is as simple as the spark plug usually employed in the use of the high tension system, although it is more expensive than the plug.