Continuously variable transmissions (CVTs) have an infinitely
variable ratio, which allows the engine to operate more time in the
optimum range given an appropriate control of the engine valve
throttle opening (VTO) and transmission ratio. In contrast,
traditional automatic and manual transmissions have several fixed
transmission ratios forcing the engine to operate outside the
optimum range.
There are various types of CVTs but in this opinion a new
concept for a CVT using a belt with changing thickness is
described. If the thickness of belt is not negligible as compare to
radius of pulley, the neutral axis of rotation is taken as radius
of pulley plus half the thickness of belt. Therefore the effective
diameter of the pulley will change. If the belt is made up such
that its thickness decreases when stretched & increases when
compressed.
Consider that the smaller pulley is fixed and position of larger
pulley can be changed and Power is transmitted from smaller pulley
to larger pulley. If distance between pulleys is increased, the
thickness of belt decreases & vice-versa. Normally the
Transmission ratio (G) is given by
G = D/d, where d and D are diameters of smaller and larger
pulley respectively.
But due to considerable thickness't' of the belt
'G' changes to G = (D + t) / (d + t),
Now G will vary continuously as't' varies.
If the variation in transmission ratio is not sufficient then it
can be enlarged by increasing no. of belts in series. It can also
be increased using power split transmission.