Little Bit About Automotive Brake Systems...
cars we know today have been refined tremendously over
the years. We have gone from the early days of steam-powered, self-propelled
vehicles to the gasoline and/or "hybrid" engines of modern vehicles. Over this time,
cars have become ever more reliable and dependable - so much so
that most people have forgotten to appreciate the technology
behind their driving wheels - out of sight, out of
mind so to speak. The same thing applies to the brake system that
our lives depend on every moment we are on the road.
Most people's knowledge of brake system is limited to the
single brake pedal that they step on to slow
down or stop their cars.
information that follows provides some information into what
happens when you step on the brake pedal in your car.
you ever wondered how, with relatively little energy, your foot can bring a car
weighing more than 1 ton roaring down the highway at 110-km/hr (a law
abiding Malaysian driver on the PLUS highway!) to a screeching stop? The answer
is through the physics principle of Leverage (mechanical advantage)
and Pascal's Law (hydraulic force multiplication).
Pascal's Law states that "a change in the pressure
of an enclosed incompressible fluid is conveyed undiminished
to every part of the fluid and to the surfaces of its
container." Simply put, the principles above allow a cleverly designed brake fluid
circuit (to transmit brake fluid through brake hoses and pistons, to convert a 10-kg force stepping the brake pedal down 3-cm, into
a whopping 1,000-kg force or more acting on the brake disc at the wheels! Of course,
the catch is the brake piston can only extend a few
1. Leverage and Pascal's Law on Brake System
2. Typical Non-ABS Brake System
A typical brake system consists of:
Pedal - uses leverage to transfer the multiplied
effort from the driver's foot to the master cylinder.
Cylinder - located under the hood connected directly
to the brake pedal, acts as a holding tank for brake
fluid until it is needed. When the brake pedal is
depressed, the master cylinder forces fluid to each
of the vehicle's wheels.
Brake Lines and Flexible Brake Hoses - connects
the master cylinder to the wheel or slave cylinder
located at each wheel.
Fluid - to transmit pressure and motion in the
brake system. Due to the intense heat generated by
components of the brake system, brake fluid must
have a high boiling point. Brake fluid must also have a
low freezing (melting) point to ensure proper operation
at any low temperatures that the vehicle
may encounter. 2 types of brake fluids are available,
namely glycol based (DOT-3 and 4) and silicone based
(DOT-5); rated by the Department of Transportation (DOT),
USA based on their respective boiling points.
Booster - available in the power-assisted brake
system that uses the engine's energy to add pressure
to the master cylinder.
Brake - uses a clamping action to produce friction
between the brake disc and the brake pads mounted
in the caliper attached to the suspension members.
When the brake pedal is pushed, brake fluid from the
master cylinder compresses the brake pads against
the brake discs. The friction between the stationary
brake pads and the revolving brake disc causes the
brake discs and wheel to slow and stop. Disc brakes
work using much the same basic principle as the brakes
on a bicycle; as the caliper pinches the wheel with
pads on both sides, it slows the bicycle.
Brake - brake drum is a heavy flat-topped cylinder,
which is sandwiched between the wheel rim and the
wheel hub. The inside surface of the drum is acted
upon by the linings of the brake shoes. When the brake
pedal is pushed, pressure from the master cylinder
causes the wheel cylinder to push the brake shoes
against the brake drums which are attached to the
vehicle's wheels. The friction between the stationary
shoes and the revolving drums causes the drums to
slow and stop the wheels.
3. Disc Brake Assembly
3. Drum Brake Assembly
In summary, a brake system is essentially an energy conversion device that
converts kinetic energy (car in motion possessing momentum)
to potential energy (car stopping) by dissipating
heat and noise to the surrounding air. The friction surfaces
of the brake pads on a disc brake, or the brake shoes
on a drum brake convert the forward motion of the vehicle
into heat. Heat is what causes the friction surfaces (linings)
of the pads and shoes to eventually wear out and require
replacement. When it is time to replace brake pads or brake shoes,
there will generally be an audible squealing noise during braking.
mentioned earlier, brake systems are often neglected by
most drivers. In actuality, we should pay the most attention to
our brake systems as our safety on the road very much depends on the
proper functioning of the brake system. At a minimum, the
brake system should be inspected by a qualified mechanic
once a year for pad or lining wear (to check if replacement pads or linings are necessary),
brake fluid leakage, brake disc thickness variation, broken seals and other wear