Browse Publications Technical Papers 2004-40-0026
2004-08-23

CVT Using a Belt with Changing Thickness 2004-40-0026

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.

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