BRAKES,SUSPENSION
The Brake System (An Overview)
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.
The Steering/Suspension System (Overview)
"Suspension," when discussing cars, refers to the use of front and
rear springs to suspend a vehicle's "sprung" weight. The springs used
on today's cars and trucks are constructed in a variety of types,
shapes, sizes, rates, and capacities. Types include leaf springs,
coil springs, air springs, and torsion bars. These are used in sets
of four for each vehicle, or they may be paired off in various
combinations and are attached by several different mounting
techniques. The suspension system also includes shocks and/or struts,
and sway bars.
Back in the earliest days of automobile development, when most of the
car's weight (including the engine) was on the rear axle, steering
was a simple matter of turning a tiller that pivoted the entire front
axle. When the engine was moved to the front of the car, complex
steering systems had to evolve. The modern automobile has come a long
way since the days when "being self-propelled" was enough to satisfy
the car owner. Improvements in suspension and steering, increased
strength and durability of components, and advances in tire design
and construction have made large contributions to riding comfort and
to safe driving.
. Two of the most common steering mechanisms are the "rack and pinion"
and the standard (or recirculating-ball) systems, that can be either
manual or assisted by power. The rack and pinion was designed for
sports cars and requires too much driver muscle at low speeds to be
very useful in larger, heavier cars. However, power steering makes a
heavy car respond easily to the steering wheel, whether at highway
speeds or inching into a narrow parking place, and it is normal
equipment for large automobiles.
The suspension system has two basic functions, to keep the car's
wheels in firm contact with the road and to provide a comfortable
ride for the passengers. A lot of the system's work is done by the
springs. Under normal conditions, the springs support the body of the
car evenly by compressing and rebounding with every up-and-down
movement. This up-and-down movement, however, causes bouncing and
swaying after each bump and is very uncomfortable to the passenger.
These undesirable effects are reduced by the shock absorbers.