5) So
the development took a turn towards seeking an inspiration from what was
a very common sight - the bicycle brakes - conventional as well as 'caliper'
types - and thus disc brakes were born for Cars ! They have the following
advantages over Drum Brakes:
i) Being of 'exposed' construction, they permit higher
braking force application for the same area of friction material, as they
don't heat it up as much in an 'open' configuration as would be the case
with a 'closed/drum' construction.
ii) Further, by making the discs 'ventilated' type, still
higher braking/pad pressures can be used - without running the risk of 'fading'
the friction material. More so on ‘Ventilated Discs’ at the
end of this Article.
iii) Being free of the 'leading/trailing edge' limitations,
two units/on the same axle can reliably produce more or less identical braking
effort, thus overcoming the 'side drag' during emergency/high speed braking
- making them an ideal choice for deployment up front.
iv) It may be noted here that during braking, there is
a 'dynamic' shift in the weight of a Car from rear to front wheels and therefore,
by using suitable 'regulating valves' in the hydraulic system, upto 80%
0f the braking effort is diverted upfront and only the remaining/20% to
rear, so that the latter don't lock-up and the Car stops without any skidding.
6) However, inspite of the
above 'refinements', the possibility of one or more wheel/s locking during
hard braking could not be ruled out, particularly on wet/slippery surfaces
and while cornering - when the normal weight distribution between the 4-wheels
is upset any way. So the 'ABS' - Anti-lock Brake System - was born!
7) Such a System essentially
deploys computer controlled 'Sensors' on all wheels, which detect 'onset'
of a wheel lock - by constantly comparing it's/wheel rpm vs the road speed
of the car. The moment the 'ratio' exceeds a predetermined (1:1); the hydraulic
pressure to the particular wheel(s) is 'pulsated' by the controlling computer
- to prevent its locking and yet maintaining max braking effort.
8) In fact the ABS was first
developed for the Jet Aircrafts where the landing speeds/weights are high
and Runway lengths often wet and limited. It's been since perfected to the
extent that the Pilot can today touch down with the Brake Pedal 'fully home',
w/o fearing any skidding of the Aircraft, and bring it to a safe halt along
with other 'assisting' Systems - such as 'Air-Brakes' via the Wing-Flaps
and Reverse Thrust of the Jet Engines etc. Still higher landing speed A/Cs
deploy a 'Tail Parachute' also, as one may be aware.
Content
generated by S. K. Gupta. - 11/’02. |
