INTRODUCTION A continuously variable transmission(CVT) is a transmission that can changesteplessly through an infinite number ofeffective gear ratios between maximumand minimum values. This contrasts with other mechanicaltransmissions that offer a fixed number ofgear ratios. The flexibility of a CVT allows the drivingshaft to maintain a constant angularvelocity over a range of output velocities.3
ADVANTAGES This can provide better efficency than othertransmissions by enabling the operation torun at its most efficient revolutions perminute (RPM) for a range of operatingspeeds. Alternatively it can be used to maximize theperformance of a machine by allowing themachine to turn at the RPM at which itproduces peak power. This is typicallyhigher than the RPM that achieves peakefficiency.4
APPLICATIONS Many small tractors for home and gardenuse have simple rubber belt CVTs Combine harvesters have CVTs. Thisallows the operator to slow or accelerate asneeded to accommodate variations inthickness of the crop. Some drill presses and milling machinescontain a pulley-based CVT where theoutput shaft has a pair of manually-adjustable conical pulley halves throughwhich a wide drive belt from the motorloops.5
PRINCIPLES OF SELFALIGNINGinitial pressureproduced by theweight of a powerdisc is very small
Let P= initial friction force produced between disc and roller
STEPLESS REGULATIONCAN BE CARRIED OUT BY ELECTRICAL SYSTEM ELECTRONIC SYSTEM HYDRAULIC SYSTEM MECHANICAL FRICTION DRIVE ANDPRESSURE VARIATOR
ADVANTAGES OF STEPLESSREGULATION SYSTEM: No loss in speed Can arrange speed adjustment withoutstopping machine. It reduces time losses and very useful inautomatic tool Hydraulic drive avoids speed fluctuation
methods of Increasing range ofregulation1.BY USING MANYVARIATORSOnly beltdrive andgear driveis used
CHARACTERISTICS Here we donot use the full possibility of3 variators. Too many speeds can be repeated. The system is not very much usedbecause we donot get many number ofspeed.
2.COMBINATION OFVARIATORS WITH GEAR BOXES
CHARACTERISTICS Shaft 1st can have one constant speed. Shaft 2nd have a particular range of speeds. About shaft 3rd, three different speeds reducedby gear ratios corresponding to any point on2nd staff.>>DIFFICULTIESIf the initial range is big then the ratio cant beachieved as the gear box has its influence
3.VARIATORS WITHEPICYCLIC MECHANISM:
>DISADVANTAGES>complicated to manufacture.>can not be used in high speed.>low efficiency if high range is produced.>used only in feed drives.
ACKNOWLEDGEMENT:>Design of Machine Tools, Basu S.K., andPal D.K.>Machine tool Design and NumericalControl, Metha N.K.>GOOGLE SEARCH ENGINE