Under
the bonnet
Automobile
technology has progressed by leaps and bounds. Nevertheless, the basic
principles of fluid power still govern the industry, says Kaushik Karforma
Amid
cheers and boos from a crowd of people, the man gets behind the wheels
of an ordinary-looking car, keys in a few commands in the laptop; the
on-board computer sends the instructions to the engine; the engine makes
the adjustments, and presto! The car races down the dark, empty streets,
its exhaust belching out a long spurt of flame.
Besides
communicating the thrill of drag racing, this scene from the 2001 summer
hit The Fast and the Furious manages to convey some messages about the
basics of automobile propulsion and the principles of fluid power, albeit
to an informed audience.
But
we’re getting ahead of ourselves. Let’s start from the basics.
Engines
are the mainstay in an automobile. They incorporate both hydraulics
and pneumatics in their operations. To start with, let’s see how the
internal combustion engine works. The basic principle behind any internal
combustion engine is this: if a tiny amount of energy is squeezed into
a small space and ignited, an incredible amount of energy is released
in the form of expanding gas that is used to propel an object. In an
automobile engine, a cycle is created that sets off explosions like
this, hundreds of times per minute; the energy generated is harnessed
to propel the car.
The
explosions are set off by means of the four-stroke combustion cycle.
This cycle comprises four basic elements: piston, crankshaft, connecting
rod and spark plug. However, automobile technology has moved light-years
since. Cars now incorporate turbo-chargers for speed. Various automakers
have developed substantial intellectual property through several years
of intensive research and development. BMW turbo-chargers, for instance,
make use of the engine’s exhaust fumes, a form of energy that would
normally be useless. The turbo-charger consists of a turbine and a compressor
that are connected by a common shaft. Incoming air is concentrated in
the compressor and the intercooler reduces its temperature. This ensures
that engine performance is increased and emissions are reduced.
One
of the most important elements in an automobile is the brake system.
The brakes function on the principles of hydraulics. The basic idea
behind any hydraulic system is this: force applied at one point is transmitted
to another point by means of an incompressible fluid, usually some oil.
Most brake systems also manage to multiply the force applied by means
of a master cylinder and several slave cylinders. Moreover, since oil
is incompressible, the shape and length of the pipes do not matter.
When
the brake is pedalled, a rod connected to the pedal exerts pressure
on a piston which forces brake-fluid from the brake fluid reservoir
into the master brake cylinder. The brake pedal pressure is transmitted
and amplified, from the master cylinder, via brake lines to calipers
or wheel cylinders which force grouped pairs of brake pads into contact
with either the brake rotors or drums which brings the vehicle to a
safe stop.
Friction
is created when the brake pads or shoes press against the rotors or
drums. This friction is what causes the car to stop when brakes are
applied. The heat that builds up in drums and rotors (in certain cases
the surface temperatures of which can exceed 1,333oF ) also causes the
brake fluid to heat up.
One
of the earlier variants of the brake, called drum brakes, when used
repeatedly, had a tendency to “fade” (when the heat built up from stopping
distorts or glazes the drum and no longer allows the pads to provide
friction against the drum), leading to a temporary loss of braking power.
Disc brakes, the solution to this problem, were discovered in the 1950s.
Since then, brake technology has come a long way. These days, cars usually
sport anti-lock automatic brake systems. These brakes have sensors that
can tell when the brakes are on the verge of locking; then automatically
pump the brakes fluid (up to 20 times a second) when the vehicle’s driver
“stands” on the brake pedal, thus helping to prevent the vehicle from
skidding. And the way things seem to be moving, hydraulic brake fluids
seem to be on their way out – Delphi’s “brake-by-wire” technology does
away with brake fluids.
Another
type of brakes use pneumatic technology, as opposed to hydraulic technology.
These power brakes, as they are known, are in principle the same as
the hydraulic system except that the piston of the master cylinder is
operated by a vacuum piston and cylinder, instead of by the pressure
exerted on the brake pedal.
Today,
automobiles are becoming more and more lifestyle-oriented. People no
longer want to go just from Place A to Place B; they want to go there
in style and comfort. One of the ways of ensuring a comfortable ride
is to have a good suspension system. At the heart of a good suspension
system lies smoothness. The fact that a person could be driving at the
speed of 140 mph and be lulled into believing that he is driving at
the speed of 30, is the result of a good suspension system. It is the
suspension system that gives the driver that feel of gliding over concrete.
Suspension
systems technology has progressed a lot since the Graygood hydraulic
shock made in 1906. Today, a suspension system that is a combination
of hydraulic fluid and air has been developed in which the elastic medium
is a sealed-in, fixed mass of air, and no air compressor is required.
The hydraulic portion of each spring is a.....
....CONTD
