Brakes are devices whose function it is to slow and stop and automobile.
They are mandatory for the safe operation of vehicles. When a car is in
motion, it has kinetic energy or energy derived from this motion. In
order for the car to slow down, this energy must be decreased. This is
accomplished by transforming it into another form. In the case of
brakes, this form is heat. In short, brakes transform the kinetic energy
of the car into heat energy, thus slowing its speed and, if enough energy
is transfered, bringing it to a stop.
Brakes have been refined and improved ever since their invention. The
increase in traveling speeds as well as the growing weights of cars have
made these improvements essential. The faster a car goes and the
heavier it is, the harder it is to stop. An effective braking system is
needed to accomplish this task. Today's cars often use a combination of
disc brakes and drum brakes. Disc brakes are usually located on the
front two wheels and drum brakes on the back two wheels. Detroit is
searching for even better engineered braking systems that will allow
automobiles to decelerate in a shorter distance, while still allowing
drivers to maintain control of their car.
Brakes operate by converting the kinetic energy (motion) of an automobile
into heat energy. How effectively this is achieved depends on the type
of braking system. There are two main types of brakes that have been
used in cars. These are disc brakes and drum brakes.
Disc brakes operate in a similiar fashion to that of a bicycle. It
involves pushing a block against a spinning wheel. This contact causes
friction, which changes kinetic energy into heat energy. Automobiles use
two of these blocks, one on each side of the wheel, which helps keep the
wheel more stable. When the brake pedal is pushed, the blocks (often
called brake shoes) push up against the wheel disc. The actual wheel is
attached to this disk and the two spin together. Therefore, when the
disc is slowed, the wheel also slows.
Drum brakes have their blocks located in the inside of a drum. Like the
disc in disc brakes, the drum in drum brakes are attached to the wheels.
When the brake pedal is pressed the curved brake shoes (blocks) are
pushed outward so that they make contact with the rotating drum. Just as
with disc brakes, this causes friction which turns kinetic energy into
heat energy, thus slowing the car.
Not only are their different types of brakes, but their are various
systems that operate these brakes. These include mechnical, hydraulic,
and power brake systems.
Mechanical brake systems are the most simple of the three. In a
mechanical system, when the brake pedal is pressed, it pulls on a line
that is connected directly to the brake shoe assembly, causing it to come
into contact with either the disc or drum. When the pedal is released,
the tension on the line is released, causing the brake shoe to release
its contact with the disc or drum. This type of system is the system
found on most bicycles.
Hydraulic brake systems involve a master brake cylinder and brake
cylinders at each of the wheels. When the brake pedal is pressed, it
moves a piston located in the master cylinder. This movement forces
brake fluid through tubes to each of the individual wheel cylinders. The
pistons in these cylinders are then moved, causing the brake shoes to
come into contact with either the disc or drum.
Power brake systems are basically the same as hydraulic brake systems
with one key difference. In power braking systems, the movement of the
piston in the master cylinder has a little help. During the intake
stroke of the engine, a vacuum is created. This vacuum is then used to
increase the pressure applied to the piston in the master cylinder.
Another development in brakes came with the invention of the anti-lock
brake system. This device helps drivers maintain control when braking in
wet or slippery conditions. How it does this is when the brake pedal is
pressed, a computer pumps the brake shoes in and out of contact with the
disc or drum many times per second. With normal brake systems, when the
brakes are applied in slippery conditions, the wheels lock up and the car
can easily lose control since it can not be steered as effectively. With
an anti-lock braking system the wheels never lock up so drivers can still
steer and therefore better maintain control of their cars.
All cars need a brake system, therefore it has been present in the
automobile since its invention. However, the technology of the
components and the design of the brake system have evolved throughout the
years.
In the early days of the automobile, drum brakes were the standard. Drum
brakes offered several advantages over other types of brakes. One of
these was that the drum could keep out water and dust, materials that
could damage disc brakes which were out in the open. The other, more
important advantage, was that drum brakes required drivers to apply less
pressure on the pedal as compared to disc brakes. This was especially
important in the days before hydraulic and power brake systems, both of
which decreased the amount of pedal pressure needed.
The next major advancement in brake technology came in 1918 with the
invention of four-wheel hydraulic brake systems by Malcolm Loughead. It
is interesting to note that Loughead was a member of the Lockheed family,
a company known better for producing airplanes. The hydraulic brake
system replaced the mechanical brake system that was in use at this
time. The mechanical system had numerous disadvantages. It made it
difficult to brake all the wheels evenly, often causing a loss of
control. In addition, it required drivers to exert tremendous amounts of
force on the brake pedal to slow the car. The hydraulic brake system
muliplied the force that was applied to the brake, lessening the amount
of force needed to be applied to the brake pedal by the driver. This
system was first used in the 1918 Duesenberg. It's advantages quickly
caught on and by 1929, four wheel hydraulic braking systems were standard
equipment on most higher priced cars. It took a few more years for
the feature to become common on lower price cars.
As the speed of automobiles and their weight increased, better braking
systems were required. The main problem with drum brakes is that the
heat is not efficiently disbursed. The heat that is produced inside the
drum does not escape easily since the drum prevents wind from drawing it
away. However, disc brakes were open to the passing wind. This allowed
the heat to be carried away which increased the efficiency of the brake.
It is interesting to note that disc brakes were first used in 1902.
However, their use was limited up until the 1950's since their efficiency
was not required and they required more pedal pressure to operate. The
reason for the higher pedal pressure is that disc brakes have no
self-servo effect or no self-energizing capacity that the drum brakes
have. The self-servo effect is caused by the forward motion of the car.
This forward motion helps pull the brake shoe into contact with the
drum. This helped lower the required pedal pressure. Now that their
efficiency was needed and the hydraulic brake system multiplied the force
applied to the brake pedal, disc brakes seemed to be the better
alternative. Chrysler was the first to widely introduce the disc brake
in its cars in the early 1950's. The system did not have much success.
It seemed that the brake pressure required of the driver was still a
little to great for the system to gain widespread consumer acceptance and
therefore it was dropped. It finally took the failing automaker
Studebaker to reintroduce the system in 1964. This time it saw much more
success and in a few years, disc brakes were common on most new cars.
One of the reasons that disc brakes were a success with the Studebaker
and not the Chrysler was due to the development of the power braking
system. Power brakes became common in the 1950's, after Chrysler had
developed and dropped its disc brake program. The system assisted the
movement of the piston in the master cylinder which meant that the driver
needed to apply less peddle pressure to get the same braking
effectiveness. Therefore, since ease of braking was no longer an issue,
the adoption of the more efficient disc brake became widespread.
Another development in braking systems came with anti-lock or anti-skid
braking. With conventional braking systems, when the brakes are applied
with enough pressure, the wheels will lock up. This results in a loss of
steering effectiveness which may cause a loss of control. With anti-lock
braking, the wheels do not lock up, allowing the driver to continue
steering. Anti-lock brakes are not a new technology. They had been used
in large aircraft since the 1950's and the British had used them in race
cars in the 1960's. The first automaker to use this technology in its
cars was Ford in 1969. It placed anti-lock brakes in the luxury
Thunderbird and COntinental Mark III. Today, anti-lock brakes are common
on many new cars.
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