|
The Electrical
System
When
the automotive industry was in its infancy, it used electricity
only to ignite the fuel inside the engine. By the late 1920's, the
electric starter replaced the hand crank, electric headlights made
acetylene lamps obsolete and the braying of the electric horn drowned
out the squeak of the hand-squeezed air horn. Today, an automobile
requires an elaborate electrical system of circuits just to produce,
store, and distribute all the electricity it requires simply for
everyday operation.
The
first major component in the electrical system is the battery. The
battery is used to store power for starting, and for running auxiliary
devices such as clocks, radios and alarms when the engine is off.
The next major component is the starter motor, which is used to
start the engine. The third component is a charging device powered
by the engine, known as the alternator. It powers the electrical
system when the car is running, and restores the charge within the
battery. With these basic components, the car maintains its supply
of electricity. A device called the voltage regulator keeps the
power level stabilized, and the fuse box keeps minor problems from
becoming major ones.
Many
different auxiliary electrical devices are used in modern cars,
such as: radios, cellular phones, rear window defrosters and electric
door locks, as well as a vast array of motors powering everything
from the moon-roof on down.
Battery
The
car's initial source of electricity is a battery, whose most important
function is to start the engine. Once the engine is running, an
alternator takes over to supply the car's electrical needs and to
restore energy to the battery.
A
12-volt storage battery consists of layers of positively and negatively
charged lead plates that, together with their insulated separators,
make up each of six two-volt cells. The cells are filled with an
electricity-conducting liquid (electrolyte) that is usually two-thirds
distilled water and one-third sulfuric acid. Spaces between the
immersed plates provide the most exposure to the electrolyte. The
interaction of the plates and the electrolyte produces chemical
energy that becomes electricity when a circuit is formed between
the negative and positive battery terminals.
Starter
The
starter converts electricity to mechanical energy in two stages.
Turning on the ignition switch releases a small amount of power
from the battery to the solenoid above the starter. This creates
a magnetic field that pulls the solenoid plunger forward, forcing
the attached shift yoke to move the starter drive so that its pinion
gear meshes with the engine's crankshaft flywheel. When the plunger
completes its travels, it strikes a contact that permits a greater
amount of current to flow from the battery to the starter motor.
The motor then spins the drive and turns the meshed gears to provide
power to the crankshaft, which prepares each cylinder for ignition.
After the engine starts, the ignition key is released to break the
starting circuit. The solenoid's magnetic field collapses and the
return spring pulls the plunger back, automatically shutting off
the starter motor and disengaging the starter drive.
When
the starter is not in use, the drive unit is retracted so that its
pinion is disengaged from the flywheel. As soon as the starter is
activated, the forward movement of the solenoid plunger causes the
shift yoke to move the drive in the opposite direction and engage
the pinion and flywheel. The pinion is locked to its shaft by a
clutch that unlocks if the engine starts up and the flywheel begins
turning the pinion faster than its normal speed. By allowing the
pinion to spin freely for a moment, the clutch protects the motor
from damage until the drive is retracted.
Alternator
or Generator
The
alternating-current generator, or alternator, is the electrical
system's chief source of power while the engine is running. Its
shaft is driven by the same belt that spins the fan. It converts
mechanical energy into alternating-current electricity, which is
then channeled through diodes that alter it to direct current for
the electrical system and for recharging the battery.
Lighting
Circuit
The
automobile lighting circuit includes the wiring harness, all the
lights, and the various switches that control their use. The complete
circuit of the modern passenger car can be broken down into individual
circuits, each having one or more lights and switches. In each separate
circuit, the lights are connected in parallel, and the controlling
switch is in series between the group of lights and the fuse box.
The parking lights, are connected in parallel and controlled by
a single switch. In some installations, one switch controls the
connection to the fuse box, while a selector switch determines which
of two circuits is energized. The headlights, with their upper and
lower beams, are an example of this type of switch. Again, in some
cases, such as the courtesy lights, several switches may be connected
in parallel so that any switch may be used to turn on the lights.
Main
Lighting Switch
The
main lighting switch (sometimes called the headlight switch) is
the heart of the lighting system. It controls the headlights, parking
lights, side marker lights, taillights, license plate light, instrument
panel lights, and interior lights. Individual switches are provided
for special purpose lights such as directional signals, hazard warning
flashers, back up lights, and courtesy lights. The main lighting
switch may be of either the "push-pull" or "push-pull
with rotary contact" types. A typical switch will have three
positions: off, parking, and headlamps. Some switches also contain
a rheostat to control the brightness of the instrument panel lights.
The rheostat is operated by rotating the control knob, separating
it from the push-pull action of the main lighting switch.
When
the main lighting switch completes the circuit to the headlamps,
the low beam lights the way for city driving and for use when meeting
oncoming traffic on the highway. When the dimmer switch is actuated,
the single filament headlamps go "on," along with the
high beam of the two filament headlamps. The next actuation of the
dimmer switch returns the headlighting system to low beams only
on the two filament lamps. Some cars are equipped with an electronic
headlight dimming device, which automatically switches the headlights
from high beam to low in response to light from an approaching vehicle
or light from the taillight of a vehicle being overtaken. The dimmer
switch in the automatic headlamp dimming system is a special override
type. It is located in the steering column as part of a combination
dimmer, horn, and turn signal switch. The override action occurs
when a slight pull toward the driver on the switch lever provides
high beam headlights regardless of the amount of light on the sensor-amplifier.
For
some years there has been discussion about the advantages of a polarized
headlight system. Such a system comprises headlights which produce
polarized light in a particular plane. The windscreens of all cars
would be fitted with polarizing glass, which would be oriented so
that glare from an approaching vehicle would be essentially eliminated,
while the forward vision would still be kept at the present levels.
The advantages the system appear attractive, but the practical problems
of making the transition are very great, since it would not be practical
to convert all existing vehicles to this type of lighting. Also,
any benefits would only be marginal because glare itself is not
a frequent cause of accidents. However, many cars now have refracting
or colored glass to cut down on glare.
Due
to recent legislation, newer cars in Texas with the dimmer switch
mounted on the steering column will have to be refurbished with
standard floor-mounted dimmers. Too many Aggies are being found
in the ditch with their legs caught in the steering wheel.
Directional
Signal Switch
The
directional signal switch is installed just below the hub of the
steering wheel. A manually controlled lever projecting from the
switch permits the driver to signal the direction in which he wants
to turn. Moving the switch handle down will light the "turn
signal" lamps on the left front and left rear of the car, signaling
a left turn. Moving the switch upward will light the turn signal
lamps on the right (front and rear), signaling a right turn. With
the switch in a position to signal a turn, lights are alternately
turned "on" and "off" by a turn signal flasher.
Incorporated in the directional signal switch is a "lane change
switch mechanism." This feature provides the driver the opportunity
to signal a lane change by holding the turn lever against a detent,
then releasing it to cancel the signal immediately after the maneuver
is completed.
Stoplight
Switch
In
order to signal a stop, a brake pedal operated "stoplight switch"
is provided to operate the vehicle's stop lamps. In addition to
lighting the conventional rear lights, the switch also operates
the center high-mounted stop lamp, that became mandatory on later
models. Cruise control equipped vehicles may also utilize a vacuum
release valve. In this case, both the vacuum release valve and the
stoplight switch are actuated by movement of the brake pedal.
Horn
The
car horn on passenger cars provides the driver with a means of sounding
an audible warning signal. The horn electrical circuit generally
includes: battery, fuse or fusible link, horn relay, horn(s), steering
column wiring harness, horn switch, and body sheet metal. Often,
a cadmium plated screw is used to ground the horn to the body of
the vehicle. Horns usually are located in the forward part of the
engine compartment or in the front fender well. The horn switch
is built into the steering wheel or incorporated into the multi-functional
switch lever, which includes turn signal and dimmer switch.
Electricity
At Rest
The
ancient Greeks had a word for it. Records show that as early as
600 BC the attractive properties of amber were known. Thales of
Miletus (640-546 BC), one of the "seven wise men" of ancient
Greece, is credited with having observed the attraction of amber
for small fibrous materials and bits of straw. Amber was used by
these people, even as it is now, for ornamental purposes. Just as
the precious metals had their names of gold and silver, so amber
had its name: "electron." It was later shown that the
same effect can be obtained by rubbing a rod of glass or hard rubber
with a handkerchief. Many other nonmetallic materials are found
to have this property, which is known as "static electricity."
All
electrified materials behave either as glass or rubber. Glass has
a "positive" charge and hard rubber has a "negative"
charge. If you electrify two strips of hard rubber by rubbing them
with fur, they will repel each other. Two glass rods will behave
the same way. But, if you electrify a rod of rubber and suspend
it near an electrified rod of glass, they will attract each other.
One of the most important laws of electricity is "Bodies with
similar charges repel each other; bodies with opposite charges attract
each other." A positive charge is designated with a (+); a
negative charge by the sign (-).
Although
people have controlled electricity for many years, no one can explain
exactly what it is. Many different theories have been given as to
the nature of electricity through the years, but the modern one
is the "Electron theory." In short, the electron theory
proposes that all matter consists of tiny particles called molecules.
These molecules are made up of two or more smaller particles called
atoms. The atoms are then divided into smaller particles called
protons, neutrons, and electrons. These particles are all the same
in matter, whether in gas, liquid, or solid. The different properties
or characteristics of the matter take form according to the arrangement
and numbers of these particles which make up the atom. The proton
has a natural positive charge of electricity; the electron has a
negative charge; and the neutron has no charge at all, but just
adds weight to the matter.
Protons
and neutrons form the central core of the atoms about which the
electrons rotate. The electrons carry small negative charges of
electricity, which neutralize the positive charges of the protons.
The simplest atom of all is the hydrogen atom. It consists of one
positive proton and one negative electron. Other atoms, such as
those forming copper, iron, or silicon, are much more complicated.
Copper, for example, has 29 electrons circling about its nucleus
in four different orbits. While protons are much smaller than electrons
in size, they contain the bulk of the mass of every atom. One proton,
for example, weighs nearly two thousand times as much as an electron.
The electrons therefore are light particles or objects around a
small but relatively heavy nucleus.
It
is difficult to conceive the size of the atom. Research by physicists
has established that the mass on one electron is about .000,000,000,000,000,000,000,000,000,911
of a gram. If you assume that one proton in a hydrogen atom is the
size of a baseball in Kansas City, then the electron would have
an orbit which would reach from the Atlantic coast to the Pacific.
Along with the extremely small size of electrons and protons, they
are separated by relatively vast distances.
Conductors
and Insulators
Not
all substances are good conductors of electricity. As a general
rule, metals are good conductors whereas nonmetals are poor conductors.
The poorest of conductors are commonly called "insulators,"
or "nonconductors." Aluminum, copper, gold, iron, mercury,
nickel, platinum, and silver are examples of good conductors. Amber,
glass, mica, paper, porcelain, rubber, silk, and sulfur are all
nonconductors. The difference between a conductor and an insulator
is that in a conductor, there are free electrons, whereas in an
insulator, all of the electrons are tightly bound to their respective
atoms. In an uncharged body, there are an equal number of positive
and negative charges. In metals, a few of the electrons are free
to move from atom to atom, so that when a negatively charged rod
is brought to the end of the conductor, it repels nearby free electrons
in the conductor, causing them to move. They in turn repel free
electrons in front of them, giving rise to a flow of electrons all
along the conductor. There are a large number of substances that
are neither good conductors of electricity nor good insulators.
These substances are called "semi-conductors." In them,
electrons are capable of being moved only with some difficulty,
i.e., with considerable force.
Electricity
In Motion (Electrical Current)
When
an electric charge is at rest it is spoken of as "static electricity,"
but when it is in motion, it is referred to as an "electric
current." In most cases, an electric current is described as
a flow of electric charge along a conductor. To make an electron
current flow continuously along a wire, a continuous supply of electrons
must be available at one end and a continuous supply of positive
charges at the other. This is like the flow of water through a pipe:
to obtain a continuous flow, a continuous supply of water must be
provided at one end and an opening for its escape into some receptacle
at the other. The continuous supply of positive charge at the one
end of a wire offers a means of escape for the electrons. If this
is not provided, electrons will accumulate at the end of the wire
and the repulsion back along the wire will stop the current flow.
The
rate at which the free electrons drift from atom to atom determines
the amount of electrical current. In order to create a drift of
electrons through a circuit, it is necessary to have an electrical
pressure, or "voltage." Electric current, then, is the
flow of electrons. The more electrons in motion, the stronger the
current. In terms of automotive applications, the greater the concentration
of electrons at a battery or generator terminal, the higher the
pressure between the electrons. The greater this pressure (voltage)
is, the greater the flow of electrons.
In
modern electric car designs, the drive motors are often used as
the brakes also, allowing them to switch over into performing as
generators, which charge the batteries with the energy generated.
Electromagnetic
Principles
The
connection between electricity and magnetism was made by Oersted,
a Danish scientist, in 1820. He had frequently demonstrated the
nonexistence of a connection between electricity and magnetism.
His usual procedure was to place a current-carrying wire at right
angles to, and directly over, a compass needle to show that there
was no effect of one on the other. One occasion, at the end of his
lecture, he placed the wire parallel to the compass needle and saw
the needle move to one side. When he reversed the current in the
wire, the needle, to his amazement, deviated in the opposite direction.
Thus a great discovery concerning electromagnetism was made quite
by accident.
There
is no actual knowledge as to why some materials have magnetic properties
and others have not. The "electron theory" generally is
accepted as the best explanation of magnetism. It is also known
as the "domain theory."
According
to the theory, an electron moving in a fixed circular orbit around
the proton creates a magnetic field with the north pole on one side
of the orbit and a south pole on the other side. It is assumed that
the orbiting electron carries a negative charge of electricity,
which is the same as electrical current flowing through a conductor.
Current flow, then, is from negative to positive. When a number
of magnetized orbiting electrons exist in a material, they interact
with each other and form "domains," or groups of atoms
having the same magnetic polarity. However, these domains are scattered
in random patterns throughout and the material is, in effect, demagnetized.
Under the influence of a strong external magnetic field, domains
become aligned and the total material is magnetized. The strength
of its magnetic field depends on the number of domains that are
aligned. In magnetic substances, the domains align themselves in
parallel planes and in the same direction when placed in a magnetic
field. This arrangement of the electron-created magnets produces
a strong magnetic effect.
If
you stroke a piece of hardened steel with a magnet, the piece of
steel itself will become a magnet. (Steel railroad tracks laid in
a north-to-south direction become magnetized because they lie parallel
to the magnetic lines of the earth.) Much stronger magnets and magnetic
fields can be produced by electrical means. Placing a piece of steel
in any strong magnetic field will cause it to become magnetized.
A
magnetized field surrounds any conductor carrying an electrical
current. The discovery of that fact resulted in the development
of much of our electrical equipment. The "field of force"
is always at right angles to the conductor. Since the magnetic force
is the only force known to attract a compass needle, it is obvious
that a flow of electric current produces a magnetic field similar
to that produced by a permanent magnet. Not only is the field of
force at right angles to the conductor, but the field also forms
concentric circles about the conductor. When the current in the
conductor increases, the field of force is increased. Doubling the
current will double the strength of the field of force.
The
Left-Hand Rule (Magnetic Effect)
Oersted's
experiment has been interpreted to mean that "around every
wire carrying an electric current there is a magnetic field."
The direction of this field at every point, like that around a bar
magnet, can be mapped by means of a small compass or by iron filings.
If a wire is mounted vertically through a hole in a plate of glass
or other suitable nonconductor, and then iron filings are sprinkled
on the plate, there will be a lining-up of the filings parallel
to the magnetic field. The result shows that the magnetic lines
of force or "lines of induction" are concentric circles
whose planes are at right angles to the current.
The
"left-hand rule" used in electromagnetism can always be
relied upon to give the direction of the magnetic field due to an
electron current in a wire. Derived from experiment, the rule states:
"if the current-carrying wire were to be grasped in the left
hand, the thumb pointing in the direction of the electron current,
negative (-) to positive (+), the fingers will point in the direction
of the magnetic induction."
Magnetic
Properties of A Solenoid
Shortly
after Oersted discovered the magnetic effect of a current-carrying
wire, Ampere found that a loop or coil of wire (a single loop or
a coil of several turns of wire) acted as a magnet. A coil of wire
of this kind is sometimes referred as a "solenoid," or
as a "helix." The magnetic lines of force in a solenoid
are such that one side or end of the coil acts like a "N"
magnetic pole and the other side or end like a "S" magnetic
pole. At all points in the region around a coil of wire carrying
a current, the direction of the magnetic field, as shown by a compass,
can be predicted by the left-hand rule. Inside each loop or turn
of wire, the lines point in one direction, whereas outside they
point oppositely. Outside the coil, the lines go the same way they
do about a permanent bar magnet, whereas inside the coil they go
from "S" to "N". Not only does one coil of wire
act like a magnet, but two coils will demonstrate the repulsion
and attraction of like and unlike poles.
Electronics
(Solid State)
Electronics
refers to any electrical component, assembly, circuit, or system
that uses solid state devices. "Solid state" means that
these devices have no moving parts, other than electrons. Examples
of solid state devices include semiconductor diodes, transistors,
and silicon controlled rectifiers. These and many more have broad
application in automotive electronics.
Semiconductors
and Diodes
Semiconductors
are made from material somewhere between the ranges of conductors
and nonconductors. Semiconductors, basically, are designed to do
one of three things: (1) stop the flow of electrons, (2) start the
flow of electrons, or (3) control the amount of electron flow. A
semiconductor diode is a two-element solid state electronic device.
It contains what is termed a "P" type material connected
to a piece of "N" material. The union of the "P"
and "N" materials forms a PN junction with two connections.
The "anode" is connected to the P material; the "cathode"
is connected to the N material. A diode is, in effect, a one-way
valve. It will conduct current in one direction and remain non conductive
in the reverse direction. When current flows through the diode,
it is said to be "forward biased." When current flow is
blocked by the diode, it is "reverse biased." When a diode
is reverse biased, there is an extremely small current flow; actually,
the current flow is said to be "negligible." When the
P and N are fused together to form a diode, it can be placed in
a circuit. The P material is connected to the positive side of the
battery and the N material is connected to the negative side of
the battery. Connected in this manner, current will flow. If connected
in the reverse manner, current will not flow.
Transistors
and Resistors
A
transistor is a solid state device used to switch and/or amplify
the flow of electrons in a circuit. A typical automotive switching
application would be a transistorized ignition system in which the
transistor switches the primary system off and on. An amplifying
application could be in a stereo system where a radio signal needed
strengthening.
A
transistor is a three-element device made of two semiconductor materials.
The three elements are called "emitter," "base,"
and "collector." The outer two elements (collector and
emitter) are made of the same material; the other element (base)
is different. Each has a conductor attached. The materials used
are labeled for their properties: "P" for positive, meaning
a lack of electrons. It has "holes" ready to receive electrons.
"N" is for negative, which means the materials has a surplus
of electrons. The movement of a free electron from atom to atom
leaves a hole in the atom it left. This hole is quickly filled by
another free electron. As this movement is transmitted throughout
the conductor, an electric current is created from the negative
to the positive. At the same time, the "hole" has been
moved backward in the conductor as one free electron after another
takes its place in a sort of chain reaction. "Hole flow"
is from positive to negative. Current flow in a transistor, then,
may be either electron movement or hole flow, depending on the type
of material, and this determines the type of transistor it is as
well.
In
most 12 volt systems, a resistor is connected in series with the
primary circuit of the ignition coil. During the cranking period,
the resistor is cut out of the circuit so that full voltage is applied
to the coil. This insures a strong spark during cranking, and quicker
starting is provided. The starting circuit is designed so that as
long as the starter motor is in use, full battery voltage is applied
to the coil. When the starter is not cranking, the resistance wire
is cut into the circuit to reduce the voltage applied to the coil.
If the engine starts when the ignition switch is turned on, but
stops when the switch is released to the run position, it can indicate
that a resistor is bad and should be replaced.
At
no time should the resistor be bypassed out of the circuit, as that
would supply constant battery voltage and burn out the coil. The
resistor and resistor wires should always be checked when the breaker
points are burned, or when the ignition coil is bad.
|
