Electrical
System
 The
electrical system of the automobile was, at first limited to the
ignition equipment. However, electric lights and horns began to replace
the kerosene and acetylene lights and the bulb horns with the advent of
the electric starter on a 1912 model. Electrification was rapid and
complete, and, by 1930, six-volt systems were standard everywhere. The
electrical system consists of a storage battery, generator, starting
(cranking) motor, lighting system, ignition system, and various
accessories and controls.
It was difficult to meet high ignition voltage requirements with the
increased engine speeds and higher cylinder pressures of the post-World
War II cars. The larger engines required higher cranking torque.
Additional electrically operated features, such as radios, window
regulators, and multispeed windshield wipers, also added to system
requirements. 12-volt systems generally replaced the 6-volt systems in
1956 production to meet these needs.
The ignition system consists of the spark plugs, coil, distributor, and
battery, and provides the spark to ignite the air-fuel mixture in the
cylinders of the engine. In order to jump the gap between the electrodes
of the spark plugs, the 12-volt potential of the electrical system must
be stepped up to about 20,000 volts. This happens with the aid of a
circuit that starts with the battery, one side of which is grounded on
the chasis and leads through the ignition switch to the primary winding
of the ignition coil and back to the ground through an interrupter
switch. A high voltage id induced across the secondary of the coil by
interrupting the primary circuit. The high-voltage secondary terminal of
the coil leads to a distributor that acts as a rotary switch,
alternately connecting the coil to each of the wires leading to the
spark plugs.
It was in the 1970s that solid-state or transistorized ignition systems
were introduced. Increased durability by eliminating the frictional
contacts between breaker points and distributor cams was provided by
these distributor systems. A revolving magnetic pulse generator in which
alternating-current pulses trigger the high voltage needed for ignition
by means of an amplifier electronic circuit replaced the breakerpoint.
Changes in engine ignition timing are made by vacuum or electronic
control unit (microprocessor) connections to the distributor.
The generator is the basic source of energy for the various electrical
devices of the automobile. An alternator that is belt-driven from the
engine crankshaft is also used at times. The design is usually an
alternating-current type with built-in rectifiers and a voltage
regulator to match the generator output to the electric load and also to
the charging requirements of the battery, regardless of engine speed.
To store excess output of the generator, a lead-acid battery is used
which serves as a reservoir. Energy for the starting motor is thus made
available along with power for operating other electric devices when the
engine is not running or when the generator speed is not sufficiently
high to carry the load.
The starting motor then drives a small spur gear, which is so arranged
that it automatically moves into mesh with gear teeth on the rim of the
flywheel as the starting-motor armature begins to turn. As soon as the
engine starts, the gear is disengaged, which prevents the starting motor
from getting damaged due to overspeeding. The starting motor is designed
for high current consumption and delivers considerable power for its
size for a limited time.
Headlights
Night driving has long been dangerous due to the glare of headlights
that blind drivers approaching from the opposite direction. Therefore,
headlights that satisfactorily illuminate the highway ahead of the
automobile for night driving without temporarily blinding approaching
drivers have long been sought. To correct this problem resistance-type
dimming circuits, which decreased the brightness of the headlights when
meeting another car, were first introduced. This gave way to mechanical
tilting reflectors and later to double-filament bulbs with a high and a
low beam, called sealed-beam units.
There was only one filament at the focal point of the reflector in the
double-filament headlight unit of necessity. Greater illumination
required for high-speed driving with the high beam, consequently, the
lower beam filament was placed off center, with a resulting decrease in
lighting effectiveness. From the 1950s, manufacturers equipped their
models with four headlights to improve illumination.
In some cars, dimming is automatically achieved. This happens by means
of a photocell-controlled switch in the lamp circuit that is triggered
by the lights of an oncoming car. Larger double-filament lamps and
halogen-filled lamp bulbs with improved photometrics permitted a return
to two-headlight systems on some cars. At many places the law limits the
total intensity of forward lighting systems to 75,000 candlepower
(800,000 lux).
In most new automobiles, lowering front hood heights for improved
aerodynamic drag and driver visibility reduces the vertical height
available for headlights. Due to this, lower-profile rectangular
sealed-beam units and higher-intensity bulbs, in conjunction with
partial parabolic reflectors with reduced vertical axis, were adopted in
the 1970s. In some cases, models featured full-size concealed headlights
that were not visible until turned on. An electric motor linkage was
used to rotate the lamp housing or a housing cover into proper position
to supply lighting. Aerodynamic benefits were provided by this system
only when the headlights were concealed.
In the 1960s, signal lamps and other special-purpose lights were
increased in usage. Amber-colored front and red rear signal lights are
flashed as a turn indication; all these lights are flashed
simultaneously in the "flasher" system for use when a car is
parked along a roadway or is traveling at a low speed on a high-speed
highway. The law requires that marker lights that are visible from the
front, side, and rear be also present. Red-colored rear signals are used
to denote braking, and, on some models, cornering lamps to provide extra
illumination in the direction of an intended turn are available. These
are actuated in conjunction with the turn signals. To provide
illumination to the rear when backing up, backup lights are required.
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