| 9)
Coming
now to Plain vs Ventilated Disc Brakes, Plain ones deploy 'Solid’
Discs, and are generally used on lighter/slower moving Cars such as most
in our A/B gr. On the otherhand, 'Ventilated Discs' are used in heavier
and faster moving C/gr Cars. Their other features are:
i) Ventilated Discs employ a very simple principle of
a 'Turbine/Pump' Rotor, in the sense that there are two parallel and flat
discs - one for each pad - and in between them, a set of 'centrifugal/turbine'
Blades is 'sandwiched'.
ii) With the above construction, when such a 'composite-disc'
rotates, it draws in ‘ambient’ air from its hub-side openings
of the Wheel Rim and 'throws' it out from its periphery - just like a
Centrifugal Air/Water Pump.
iii) This so generated constant flow of air through such
a set-up keeps them cool when brakes are applied - thus preventing overheating
of the entire System - including burnout/fading of the brake pads. It
can easily be visualised that faster the Vehicle road speed, higher will
be the Ventilated Disc rpm and therefore, higher the cooling!
10) Coming now as to why
they are 'usually' (Not Always) upfront, there are a few practical reasons
- such as:
i) Apple to apple, Disc Brake Assys are more expensive
than Drum Brakes'.
ii) Equal Braking effect on 2-Drum Brakes on the same
axle, so necessary for a straight-line stop, is difficult to achieve with
reliability and consistency over a period of time. Disc Brakes have no
such limitation.
iii) During Braking, there is a 'Dynamic Shift' of the
Car's weight upfront as discussed above. Thus the choice for the major
'Pall bearer/front axle’ Brakes falls on Disc Brakes.
iv) Since Every Car must have a 'Parking/Hand Brake',
which has to be Mechanically/Cable Operated, unlike the main Hydraulic
ones, the relevant Hand Brake mechanism can be easily built into a Drum
Brake System - whereas, it's practically impossible to do so on a Disc
Brake Assy.
v) While at it, it may be interesting to know that high
speed/high performance Cars which have Disc Brakes at the rear also, have
separate/tandem Drums on the same hub - exclusively for PB/HB purposes!
Content
generated by S. K. Gupta. - 11/’02. |
