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
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
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.
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 conguide 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 conguide with the turn signals. To provide
illumination to the rear when backing up, backup lights are required.