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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