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.
[Illustration: _Fig. 34. Dry 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.
[Illustration: _Fig. 35. Series Connection._]
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.
[Illustration: _Fig. 36. Multiple, or Parallel Connection._]
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.
[Illustration: _Fig. 37. Series-Multiple Connection._]
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.
[Illustration: _Fig. 38. Circuit Testing._]
_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.
[Illustration: _Fig. 39. Make and Break, with Battery._]
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.
[Illustration: Fig. 40. Make and Break, with Magneto.]
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.
[Illustration: _Fig. 41. Magneto Spark Plug._]
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.