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The braking system is the most important system in your car. If the
brakes fail, the result can be disastrous. The brakes are in essence
energy conversion devices, which convert the kinetic energy
(momentum) of your vehicle into thermal energy (heat).
When you step on the brakes, you command a stopping force ten times
as powerful as the force that puts the car in motion. The braking
system can exert as much as 1,000 pounds of hydraulic pressure on
each of the four brakes. In modern systems, the master cylinder is
separately power-assisted to activate the front and rear brakes. If
one set fails, the other can provide adequate braking power. Many
such safety systems within the braking system make modern brakes very
complex, but much safer than earlier braking systems.
High-performance disc brakes originally were developed for racing,
but are now used on many newer cars. On most cars, the front brakes
are of the disc type, and the ones in the rear are the drum type. The
parking brake is a cable operated system, which usually is attached
to the rear wheels.
In almost all braking systems, the brake pedal is connected to a
"master cylinder" by a push rod. The master cylinder is connected to
the brake cylinders ("slave cylinders") at each wheel by steel brake
lines and flexible rubber hoses. The entire hydraulic system is
filled with a special brake fluid, which is forced through the system
by the movement of the master cylinder pistons. The front disc brakes
use friction "pads" which are mounted in "calipers". The pads are
forced against machined surfaces of a rotating disc called the
"rotor". The rear brakes are usually of the "drum" type. In these,
the internal expanding brake "shoes" are forced against the inside
machined surface of a rotating drum.
In recent years, brakes have changed greatly in design. Disc brakes,
due to their lighter weight and better performance, are replacing
drum types on the rear wheels. Instead of linings which press
outwards against the inside of a drum, a disc attached to the axle is
gripped from either side by friction pads attached to the calipers.
The greatest advantage of disc brakes is that they are essentially
"fade" free. That is, repeated application does not result in
excessively high temperatures developing in the linings and drums,
lowering the stopping power of the brake. Commonplace on newer cars
are "anti-lock" brake systems, (ABS) which prevent the wheels from
completely stopping when the brakes are applied in a panic stop.
As impressive as these advances are, the basic process of converting
a vehicle's momentum into (wasted) heat has not changed since the
days of horse and buggy. To stop carriages, the driver would pull on
a lever which would rub on the wheel. But with the advent of
brake-charging electric vehicles, a new braking equation is opening
up the possibility of recapturing this lost energy, instead of warming
the air with it. In modern electric cars, when you step on the brake
the motor switches into "generator mode", and stores the car's
momentum as chemical energy in the battery, to be used when the light
turns green!
In 1923, a Packard was the first car in America with four-wheel
brakes. In 1927, four-wheel brakes were introduced in the Lincoln
production cars.
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