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Preamble:
The
‘dissertation’ that follows is the result of an innocuous
query posed to me some time back by an inquisitive mind – wanting
to know whether there was an ‘algorithm/relationship’ between
the ‘diferent speeds’ at which the inner and outer wheels
of a Car have to turn - when it goes over a curve ‘smoothly’.
My immediate reaction was that it is a subject good enough for a Ph.D.
in Automobile Engg.! But some more introspection alongwith the fundamentals
of it all – it didn’t turn out to be as frightening!!
It presupposes that most, if not all, Motorists know the principle of
‘Differential-Gears’ provided in a Car/4-wheeler for the very
purpose – to enable it take a turn ‘smoothly’.
Read on, if you were good enough at the 10+2 level Maths funda’s
and still like to pick your own brains……….
How does your car take a turn smoothly –
like the one below!
The
answer could be as simple as “… because I turn the Steering
Wheel”.
So what happens when you turn the Steering wheel? If you are thinking
that the front wheels then point in the direction you wanted them to -
you are not wrong. But there is more to it than what meets the eye.
Most of us are aware that when a 4-Wheeler/Car takes a turn, to enable
it go through it smoothly, its ‘outer’ wheels need to turn
faster than the ‘inner’ ones and this is facilitated by the
ubiquitous ‘Differential Gears’. These are visible in a Rear/4-
wheel Drive Car as a round/bulbous housing between the Rear/Front drive
wheels of a 2/4 Wheel Drive Car but not so on a Front Wheel Drive one
– as they are then accommodated in the Main Gear Box itself next
to the Engine.
 So let’s
start with the simple principle of Differential Gears. Look at the two
adjoining/concentric circles. The inner one represents the path of the
inner wheels and the outer one like wise - when a Car is on a turn. If
one were to compare the ‘circumferences’ of these two circles,
obviously the outer circle has a larger circumference. The difference
between the Radii of the two Circles is the ‘Track’ width
of a Car. Clearly, the inner wheel is ‘tracing’ the smaller
circle, and hence has to travel less ‘distance’ compared to
the outer wheel - which is tracing the outer/larger circle – BUT
in the same time ! Now, if these two wheels were to move at same speed/Rpm,
they will skid & screech but that is not what happens – thanks
to the Differential Gears!
Therefore, in other words, the Differential Gears ensure that both the
inner and outer wheels rotate at different rpm ‘as called for’
and yet get the power they need to maintain satisfactory ‘traction’
while going over a Curve.
So now we know why the inner wheel rotates at a lower rpm than the outer
one. |
