IGNITION 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 sluggishly through 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 called _amperes_ and the
pressure is designated as _volts_.
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, the _armature_ past a number of magnets,
called the _field_. 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 a _magnetic
field_ surrounding 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 of
_electrolyte_, 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 the plates 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.
[Illustration: 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 as _series_, _parallel_, and series _multiple_.
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.
[Illustration: 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.
[Illustration: 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 the _low_
or the _high_ tension system. Any circuit having a small voltage is
termed _low tension_, to distinguish it from a _high 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 enable the eye to
see it. The heat is thus caused by _resistance_.
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 the _make_ and _break_ method
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 located within 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.
[Illustration: Fig. 87. Dynamo Connection.]
[Illustration: 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 have rotating armature; and second, those with
stationary armatures and revolving inductors. The _high tension_ type
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 the
_primary_, 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 more complex, 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 called
_inductance_. 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 same _potentiality_. 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 the
coarse 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.
[Illustration: 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 an _interrupter_, 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.
[Illustration: 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.--The dynamo 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 armature shaft 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.
[Illustration: 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
one terminal 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 primary induces 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 that
particular 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.
[Illustration: 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 has one 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.--Whenever a 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 called _self 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.
[Illustration: 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.
[Illustration: 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 is also 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.--A _short circuit_ is 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.