continuously variable cvt
Post on 07-Apr-2018
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Continuously Variable
Transmission(CVT)
ED08B006
ED08B014
ED08B022
ED08B030
ROHAN
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Problems in manual & automatic
transmission There are a limited number of gear ratios .So the
transmission wont be smooth due to sudden gearchanges.
Maintaining the engine in its optimum power range would
be difficult due to limited number of gear changesthereby reducing gas mileage and fuel consumption.
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CVT
A continuously variable transmission (CVT) isa transmission that can change steplessly through aninfinite number of effective gear ratios betweenmaximum and minimum values.
The flexibility of a CVT allows the driving shaft tomaintain a constant angular velocity over a range ofoutput velocities , thereby providing better fuel
economy.
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History
1490 - Leonardo da Vinci sketches a steplesscontinuously variable transmission
1886 - first toroidal CVT patent filed
1935 - Adiel Dodge receives U.S. patent for toroidal CVT
1939 - fully automatic transmission based on planetarygear system introduced
1958 - Daf (of Netherlands) produces a car with CVT
1989 - Subaru Justy GL becomes the first U.S.-soldproduction automobile to offer a CVT
2002 - Saturn Vue with a CVT launched in the market,first Saturn to offer CVT technology
2004 - Ford begins offering a CVT
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CVT Designs
Pulley based CVT
Toroidal CVT
Hydrostatic CVT
Infinitely Variable Transmission (IVT)
Ratcheting CVT
Variable toothed wheel transmission
Cone CVTs
Radial roller CVT
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In this most common CVT system, there are two V-belt
pulleys that are split perpendicular to their axes of rotation,
with a V-belt running between them.
The gear ratio is changed by moving the two sections of one
pulley closer together and the two sections of the other pulley
farther apart.
Due to the V-shaped cross section of the belt, this causes the
belt to ride higher on one pulley and lower on the other.
Pulley based CVT
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Pulley based CVT
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Toroidal CVT
Toroidal CVTs are made up of discs and rollers thattransmit power between the discs.
The discs can be pictured as two almost conical parts,point to point, with the sides dished such that the twoparts could fill the central hole of a torus.
One disc is the input, and the other is the output.
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Toroidal CVT
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Hydrostatic CVTs
Hydrostatic transmissions use a variabledisplacement pump and a hydraulic motor.All power is transmitted by hydraulic fluid.
These types can generally transmit more
torque. They have the advantage that the hydraulic
motor can be mounted directly to the wheelhub, allowing a more flexible suspensionsystem and eliminating efficiency lossesfrom friction in the drive shaftand differential components.
This type of transmission is relatively easyto use because all forward and reversespeeds can be accessed using a singlelever.
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Hydrostatic CVTs
The rotational motion of the engine operates a hydrostatic pump onthe driving side.
The pump converts rotational motion into fluid flow.
Then, with a hydrostatic motor located on the driven side, the fluid
flow is converted back into rotational motion. At a low speed, power is transmitted hydraulically, and at a high
speed, power is transmitted mechanically. Between these extremes,the transmission uses both hydraulic and mechanical means totransfer power.
Hydromechanical transmissions are ideal for heavy-dutyapplications, which is why they are common in agricultural tractorsand all-terrain vehicles.
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CVT Control
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Benefits of CVT
Provide engine torque in optimum condition (road loads /drive shaft torque)
No shift clonk
Transmission ratio can be adjusted continuously
Improved fuel efficiency
Better acceleration
Eliminates gear hunting especially when going up a hill
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VELOCITY vs ENGINE SPEED
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Disadvantages of CVT
CVT torque-handling capability is limited by the strengthof their transmission medium (usually a belt or chain),and by their ability to withstand friction wear betweentorque source and transmission medium (in friction-driven CVTs).
Some CVTs transmit torque in only one direction,rendering them useless for regenerative or engine-assisted vehicle braking; all braking would need to beprovided by disc brakes, or similar dissipative systems.
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Thank You
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