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STEPLESS SPEED DRIVES &CONTINUOUSLY VARIABLE TRANSMISSION (CVT)
INTRODUCTION
A continuously variable transmission (CVT) is a transmission that can change steplessly through an infinite number of effective gear ratios between maximum and minimum values.
This contrasts with other mechanical transmissions that offer a fixed number of gear ratios.
The flexibility of a CVT allows the driving shaft to maintain a constant angular velocity over a range of output velocities.
ADVANTAGES
This can provide better efficency than other transmissions by enabling the operation to run at its most efficient revolutions per minute (RPM) for a range of operating speeds.
Alternatively it can be used to maximize the performance of a machine by allowing the machine to turn at the RPM at which it produces peak power. This is typically higher than the RPM that achieves peak efficiency.
APPLICATIONS
Many small tractors for home and garden use have simple rubber belt CVTs
Combine harvesters have CVTs. This allows the operator to slow or accelerate as needed to accommodate variations in thickness of the crop.
Some drill presses and milling machines contain a pulley-based CVT where the output shaft has a pair of manually-adjustable conical pulley halves through which a wide drive belt from the motor loops.
TYPES OF STEPLESS DRIVES
Variable-diameter pulley (VDP) or Reeves drive
Toroidal or roller-based CVT (Extroid CVT )
Infinitely Variable Transmission (IVT)
Cone CVTs
Variable-diameter pulley (VDP) or Reeves drive
Toroidal or roller-based CVT (Extroid CVT)
Infinitely Variable Transmission (IVT)
IVT uses a set of epicyclic gears to achieve the required speed and torque range.
Then in the driven shaft is connected to a CVT to achieve a required speed.
In epicyclic gears, the planet gears are engaged or disengaged accordingly to achieve the required speeds
Cone CVTs
Uses 2 cones of equal diameter and lengths.
The cones are kept in opposite directions and a flat belt is used to connect them.
When high RPM is needed, the belt is moved to the larger end of the driver cone.
Then the belt automatically adjusts to the smaller end of driven cone