The job of the transmission isto change the speed ratiobetween the engine and thewheels of an automobile. The transmission uses a rangeof gears -- from low to high -- tomake more effective use of theengines torque as drivingconditions change. The gearscan be engaged manually orautomatically.
An automatic transmissionis an automobile gearboxthat can change gearratios automatically as thevehicle moves, freeing thedriver from having to shiftgears manually.
• This unique transmission does not have several set of gears like mosttransmissions, but rather have an infinite number of gear ratios.• CVT does not strictly require the presence of a clutch, allowing thedismissal thereof.• Seamless acceleration with a “direct” drive feel for enhanced drivingpleasure.• With fewer moving parts, CVT is simpler than Automatic Transmissionin principle.• CVT is emerging as a keystone technology that enables other
o 1490 - Da Vinci sketches a stepless continuously variabletransmissiono 1886 - First Toroidal CVT patent filedo 1935 - Adiel Dodge receives U.S. patent for Toroidal CVTo 1939 - Fully Automatic Transmission based on Planetary gearsystem introducedo 1958 - Daf (of The Netherlands) produces a CVT in a caro 1989 - Subaru Justy GL is the first U.S.-sold productionautomobile to offer a CVTo 2002 - Saturn Vue with a CVT debuts; first Saturn to offer CVTtechnologyo 2004 - Ford begins offering a CVT
o Provide engine torque in optimum condition (roadloads / drive shaft torque)o No shift clonko Transmission ratio can be adjusted continuouslyo Improved fuel efficiencyo Better accelerationo Eliminates gear hunting especially when going upa hill
Audi A4, a5, A6, A7 Fiat Punto, Ford Fiesta Honda City, Jazz Mercedes Benz A & B Class Nissan Micra Suzuki SX4 Toyota Prius
Toroidal CVTs Hydrostatic CVTsPulley Based CVTs
The variable-diameter pulleysare the heart of a CVT. Eachpulley is made of two 20-degreecones facing each other. A beltrides in the groove between thetwo cones. V-belts are preferred if the belt ismade of rubber. V-belts get theirname from the fact that the beltsbear a V-shaped cross section,which increases the frictionalgrip of the belt.
Driver GearPrimary PulleyDriver and DrivenShaftSecondary PulleyV - belt
o Driving gear, as in the name it issituated at the driving side of thepulley based continuous variabletransmission system. The drivinggear is the most complex parts ofpulley based continuous variabletransmission system. It comprisesof many types gears system andclutch.o It comprises of planetary gears,annular gear, sun gear, and twodifferent sets of clutch system –Forward gear clutches andReverse gear clutches.
The primary pulley is situated atthe driving side of the pulley basedcontinuous variable transmissionsystem. It supports the drivinggear and belt from maintaining itsposition at different situations.
The driving and driven shaft are the base of pulley basedcontinuous variable transmission system. The driving and driven shaft are at the driving and driven side ofthe pulley based continuous variable transmission system.
There are two secondary pulleyin the pulley based continuousvariable transmission system.Both the secondary pulleys aresituated at the driven end of thepulley based continuousvariable transmission system. Itis at both situated on the drivenshaft facing opposite to eachother.
The common characteristic ofthe V-belt drives is the use ofa drive and driven sheave,each with variable diameters.The effective diameter of thesheave is adjusted by varyingthe distance between the twohalves of the sheave .
If we compare continuousvariable transmission systemwith a 6-speed manualgearbox then we can say thesemi-intermediate gear ratio issomewhat similar to 2nd gearof the 6-speed manualgearbox. At this stage the radius of thebelt is somewhat 40-60position, 40 at driving end and60 at driven end.
At this stage the radius of the beltis somewhat 50-50 position, 50 atdriving end and 50 at driven end. At this stage the distancebetween the driving gear and theprimary pulley at the driving endand the distance between the twosecondary pulleys at the drivenbecomes equal. The belt radius is equal at bothend.
If we compare continuousvariable transmission system witha 6-speed manual gearbox thenwe can say the semi-high gearratio is somewhat similar to 4thgear of the 6-speed manualgearbox. This stage just opposite to thesemi-intermediate stage.
This stage just opposite to thefirst stage i.e., at low gear. If we compare continuousvariable transmission system witha 6-speed manual gearbox thenwe can say the high gear ratio issomewhat similar to 5th gear ofthe 6-speed manual gearbox.
The main advantage of CVTs isthat they allow an engine to runat its ideal RPM regardless ofthe speed of the vehicle. Thisimproves fuel economy and byeffect, exhaust emissions. CVT equipped vehiclesconsumes 10% less fuel whencompared with the automatictransmissions.(from Nissan motor’s journal)
Wider gear ratio range. In CVT, the gear ratio range from low to high gear is expanded,attaining a top-of-class ﬁnal gear reduction ratio of about 6. The extended low end of the range to improve acceleration,and the high end to improve fuel economy. Flexibly tunable to match engine characteristics, therebyenabling optimization of the balance between combustionefﬁciency and acceleration.
There are 25% fewer moving parts to a CVT transmission. Less power loss in a CVT than a typical automatictransmission. Responds better to changing conditions, such as changes inthrottle and speed.
Many small tractors for home and garden use simple rubberbelt CVTs. All snowmobiles, old and new, and motor scooters use CVTs. Some combine harvesters have CVTs. CVTs have been used in aircraft electrical power generatingsystems and in Formula race cars. Some drill presses and milling machines contain a pulley-basedCVT.
Much Of The Existing Literature Is Quick To Admit That TheAutomotive Industry Lacks A Broad Knowledge Base RegardingCvts. Whereas Conventional Transmissions Have BeenContinuously Refined And Improved Since The Very Start Of The20th Century, CVT Development Is Only Just Beginning. AsInfrastructure Is Built Up Along With Said Knowledge Base, CvtsWill Become Ever-more Prominent In The Automotive Landscape.Even Today’s Cvts, Which Represent First-generation Designs AtBest, Outperform Conventional Transmissions. Automakers WhoFail To Develop Cvts Now, While The Field Is Still In Its Infancy,Risk Being Left Behind As CVT Development And ImplementationContinues Its Exponential Growth. Moreover, Cvts Are Do Not FallExclusively In The Realm Of IC Engines.
CVT is the most superior technology for power transmission. And it would be the widely acceptable technology throughoutthe world.
Prepared By –ANDALIB SHADANDEBJIT PALSIDDHARTHA SAHASUBHASISH BHADRASUMIT KUMARCHOUDHARYWARIS AHMED