A SEMINAR PRESENTATION ON

¥CONTINUOUSLY VARIABLE TRANSMISSION¥ (CVT)

Submitted fromPukhraj maliRoll no.:-12EELME035ME Engg. final year

Submitted toMr.Rahul ShrivastavHead of mechanical department

Today automobiles use either a conventional manual or automatic transmission with multiple planetary gear sets that use clutches to achieve discrete gear ratios .

The continuously variable transmission replaces discrete gear ratios with infinitely adjustable gearing through one of several basic CVT designs

A continuously variable transmission (CVT) is a transmission that can change seamlessly through an infinite number of effective gear ratios between maximum and minimum values

The flexibility of a CVT allows the input shaft to maintain a constant angular velocity.

Introduction of CVT

Overview of a CVT

Varies the transmission ratio continuously

Shifts automatically with an infinite number of ratios.

Seamless power delivery

Constantly changes its gear ratio to optimize engine efficiency

Allows the engine to rev almost immediately to deliver maximum torque

Basics of transmission

The job of the transmission is to change the speed ratio between the engine and the wheels of an automobile. The transmission uses a range of gears to make more effective use of the engine's torque as driving conditions change.

There are 3 type of transmission-1.Manual transmission2.Automatic transmission3.Semi automatic(CVT)

PROBLEMS WITH MANUAL & AUTOMATIC TRANSMISSION

The traffic condition has become annoying in our big cities so fuel consumption is very high

In such a case will automatic transmission make sense to the Indian customer.

But conventional automatics always consume slightly more fuel than manual transmission and the lack of sophisticated automatics.

Components of CVT

1. A variable –input driving pulley2. An output(driven) pulley3. A metal belt/rollers4. Sensors and microprocessors

Working principle

A pair of variable-diameter pulleys, each shaped like a pair of opposing cones, with a metal belt or chain running between them.

One pulley is connected to the engine (input shaft), the other to the drive wheels (output shaft)

As the pulley halves come closer together the belt is forced to ride higher on the pulley, effectively making the pulley's diameter larger.

Changing the diameter of the pulleys varies the transmission's ratio.

HOW CVT WORKS?

Types of CVT

Metal Push Belt CVT.Toroidal Drive CVT.Variable Diameter pulley Belt CVTHydrostatic CVT Magnetic CVT

Simulation of CVT

Push BeltThis belt transmits power between two conical pulleys, or sheaves, one fixed and one movable .

A sensor reads the engine output and then electronically increases or decreases the distance between pulleys, and thus the tension of the drive belt

Toroidal Traction Drive CVT:

Uses rollers to transmit torque between the input disc and output disc.A viscous fluid transmits torque between rollers and discs.

Rollers and discs never touch.

The angle of the rollers changes relative to shaft position resulting in a change in gear ratio.

The change in angle by a roller must be mirrored by the opposing roller.

Toroidal CVT

ADVANTAGES OF CVT Decreases engine fatigue “infinite” number of gear ratios, maintaining the engine in its optimum power range

More mechanically efficient than Automatic transmissions.

Greater fuel efficiency than both manual and automatic transmissions.(Fuel savings of more than 17%).

Smooth, responsive and quiet to drive

CVT Vs. Manual transmissionTheoretical comparison under “ideal” conditions

1991 FIAT UNOM=1250 KG,TORQUE=101.2 NM

0-100 KMPHMT-11.9 SEC /CVT-8.8 SEC

CVT proved 35% more efficient than the MT. With same car and engine, the CVT takes only 75% of the time to accelerate to 100km/h, compared to the MT.

DRAWBACKS Limited torque capacity when compared to manual transmissions.

Additional gear train required for reverse condition.

Larger and more costly than manual transmissions.

Unwillingness to discard billions of dollars in development in MT & AT’s.

USES OF CVT

Many small tractors for home and garden use have simple rubber belt CVTs. For example, the John Deere Gator line of small utility vehicles use a belt with a conical pulley system. They can deliver an abundance of power and can reach speeds of 30–32 mph (48–51 km/h), all without need for a clutch or shifting gears. Nearly all snowmobiles, old and new, and motor scooters use CVTs, typically the rubber belt/variable pulley variety.

In various ATV CVT is most widely used due to better fuel economy.

The IC engine is nearing both perfection and obsolescence; advancements in fuel economy and emissions have effectively stalled.

CVTs could potentially allow IC vehicles to meet the first wave of new fuel regulations

Costs will be reduced further and performance will continue to increase.

Ultimately it will give CVTs a solid foundation in the world’s automotive infrastructure.

Future of CVT

THANK YOU