CVT_Abhishek_Ghosh

7/31/2019 CVT_Abhishek_Ghosh

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CVTContinuously VariableTransmission

Presentation by

Abhishek Ghosh

Sixth Semester (2012)

Under the guidance of

G. C. Chell

Asstt. Professor

Deptt. Of Mechanical Engineering

Jalpaiguri Govt. Engineering College


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Transmission Basics 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 - from low to high - to make moreeffective use of the engine's torque as driving conditions change.

The gears can be engaged manually or automatically.


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Conventional GearboxGear 1 Able to accelerate well from complete stop

Able to climb

Top speed is limited

Gear 3 Very slow when acceleration from a complete stop

Cant climb

Top speed relatively high

A five-speed transmission applies one of five different gear ratios to the input shaft

to produce a different rpm value at the output shaft. Here are some typical gear

ratios with Engine at 3000 RPM:

Gear Ratio RPM1st 2.315:1 1,295

2nd 1.568:1 1,913

3rd 1.195:1 2,510

4th 1.000:1 3,000

5th 0.915:1 3,278


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Problems in Manual &

Automatic Transmission Speed Ratio limitations

with respect to optimum

power and efficiency

Fuel Economy, especially

while driving in bumper-

to-bumper traffic


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What is CVT

A Continuously Variable Transmission (CVT)is a transmission that can change steplessly

through an infinite number of effective gearratios between maximum and minimumvalues. This contrasts with other mechanicaltransmissions that offer a fixed number of gearratios. The flexibility of a CVT allows the

driving shaft to maintain a constant angularvelocity over a range of output velocities.


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Why CVTFeature Benefit

Constant, step less acceleration from a

complete stop to cruising speed

Eliminates shift shock makes for a smoother

ride

Works to keep the car in its optimum

power range regardless of how fast

the car is traveling

Improved fuel efficiency

Responds better to changing

conditions, such as changes in throttle

and speed

Eliminates gear hunting as a car decelerates,

especially going up a hill

Less power loss in a CVT than a typical

automatic transmission

Better acceleration

Better control of a gasoline engine's

speed range

Better control over emissions

Can incorporate automated versions

of mechanical clutches

Replace inefficient fluid torque converters


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A Timeline of CVT

innovation 1490 - Da Vinci sketches a stepless Continuously Variable Transmission

1886 - First Toroidal CVT patent filed

1935 -Adiel Dodge receives U.S. patent for Toroidal CVT

1939 - Fully Automatic Transmission based on planetary gear system introduced 1958 - DAF(Netherlands) produces a CVT in a car

1989 - Subaru Justy GL is the first US - sold production automobile to offer a CVT

2000 - Fiat& BMWoffer CVT in their models

2002 - Saturn Vue with a CVT debuts - first Saturn to offer CVT technology; GM

introduces CVT

2004 - Fordbegins offering CVT

2007 - Dodge Caliber, Jeep Compass and Jeep Patriot employ a CVT

2008 - Mitsubishi Lancermodel is available with CVT

2009 - SEAT Exeo is available with a CVT automatic transmission

2010 - the US Patent Office issued patent number 7,647,768 B1 for a series of hydraulic

Torque Converters that use hydraulic friction rather than mechanical friction as a CVT.


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Austin 18 (1934)

One of the earliest cars to use CVT


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Types of CVT Frictional

o Pulley-based or Metal Push Belt CVT

o Toroidal CVT

o Cone CVT

Hydrostatic CVT


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Metal Push Belt CVT Uses a pair of axially adjustable sets of

pulley halves called Variators

Both pulleys have one fixed and one

adjustable pulley halve

The transmission ratio is varied by

adjusting the spacing between thepulleys in line with the circumference of

the tapered pulley halves

A V-belt is used to transfers the

engine's power from one shaft to

another

The Variators are adjusted hydraulically

When one pulley is varied, the other

pulley must adapt itself inversely since

the length of the belt is fixed


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Metal Push Belt CVT:

Speed Ratios

Gear Ratio =

=


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Belt Design (Van Doorne Steel Belt) Almost all of todays belt driven CVTs

use this design invented by Dutch CVT

specialist Van Doorne.

Maximum torque it can withstand isaround 190hp.

Used in:

Honda Civic HX

Nissan Primera

Toyota Prius

Honda Insight

BMW Minicooper

Saturn Vue


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Simplified Mathematical Model

+ = -

+ = -

+ = -

In which Ie is the rotary inertia of engine; Is is the rotary inertia of the active pulley of CVT;

Iq is the rotary inertia of the passive pulley of CVT; Be, Bs and Bq represent the equivalent

damping coefficient of each axis respectively; i is the speed ratio of CVT and is the

transmission efficiency of CVT. Tr is the equivalent resistance torque of car weight and loadconverted to the output axis of CVT.


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Williams/Renault FW15C CVT

This prototype introduced in F1 racing in 1993. But FIA banned CVTs from

F1 in 1994 due to concerns that the best-funded teams would dominate if

they managed to create a viable F1 CVT transmission.


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CVT Power Transmission


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Audi Multitronic CVT

Uses a multi-plate clutch as the torque converter.

The electronics detect uphill and downhill gradients, and assist the

driver by compensating for the added load or boosting engine braking

torque accordingly.

Used in Audis 1.8L A4 and 3.0L A8.


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Metal Push Belt CVT in Action

Animated video of a Dodge CaliberCVT


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Toroidal CVT Uses rollers to transmit torque between

the input disc (which connects the

crankshaft) and output disc (which

connects the driveshaft).

A viscous fluid with high shear strength

properties is fundamental intransmitting 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.


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Toroidal CVT: Mechanism

Case I

Driving Shaft

(Top)

Faster

Driven Shaft

(Bottom)

Slower


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Case II

Driving Shaft

(Top)Equal Speed

Driven Shaft

(Bottom)


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Case III

Driving Shaft

(Top)

Slower

Driven Shaft

(Bottom)

Faster


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Cone CVT Made of one or more conical

bodies.

Function along their respective

generatrices.

Torque transmitted via friction

from a variable number ofcones to a central, barrel-

shaped hub

Only one contact point

between each cone and the

hub.


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Cone CVT in Action

Working video of a Cone CVT


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Hydrostatic CVT Uses variable-displacement

pumps to vary the fluid flow

into hydrostatic motors.

The rotational motion of the

engine operates a hydrostatic

pump on the driving side.

The pump converts

rotational motion into fluid

flow.

With a hydrostatic motor

located on the driven side,

the fluid flow is converted

back into rotational motion.

Used in: Lawn mover, garden

tractor, heavy equipment,

etc.


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MT vs. CVT The Continuously Variable Transmission

(CVT) proved 35% more efficient than the

Manual Transmission (MT).

With same car and engine, the CVT takes

only 75% of the time to accelerate to

100km/h, compared to the MT.

1991 FIAT UNO

Mass = 1250 kg

Torque = 101.2 N-m

@ 5700rpm

0 - 100 Km/h

CVT MT

8.8 sec 11.9 sec


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AT vs. CVTGear Efficiency Range

1 60 - 85%

2 60 - 90%

3 85 95%

4 90 95%5 85 94%

Power transmission efficiency of a typical five-

speed automatic:

Average efficiency of86%.

CVT Mechanism Efficiency Range

Rubber Belts 90 - 95%

Steel Belts 90 - 97%

Toroidal Traction 70 94%

Variable

Geometry

85 93%

Efficiency ranges for several CVT designs:

These CVTs each offer improved efficiency

over conventional automatic transmissions,

and their efficiency depends less on driving

habit than manual transmissions.


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CVT: The Good & the BadAdvantages Decreases engine fatigue

Allows for an 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% have been achieved)

Cheaper and lighter than Automatic

transmission

Smooth, responsive and quiet to drive

Newer CVTs have a manual option,

giving the driver more control, simulating

a MT

CPU can be configured to suit a wide

range of driving modes and styles

Disadvantages Limited torque capacity when compared

with manual transmissions

Larger and more costly than manual

transmissions

Slipping in the drive belt or pulleys (No

longer an issue due to new advances)

Rubber band effect (Solved)

Complacency by the automobile industry,

unwilling to discard billions of dollars in

development in MT & ATs


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The Future of CVT The internal combustion (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.

As CVT development continues, costs will be reduced further and

performance will continue to increase.

This cycle of improvement will ultimately give CVTs a solid foundation

in the worlds automotive infrastructure.


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References JOURNALS

o Dynamic Performance of a Metal V-belt CVT during Rapid Shift-Ratio Conditions for

Control Applications byRohan Bhate & Nilabh Srivastava

BOOKS

o

Clutch Turning Handbook byOlay Aaeno "No More Gears byFischetti Mark

o Popular Mechanics byMcCosh

LINKS

o http://en.wikipedia.org/wiki/Continuously_variable_transmission

o http://auto.howstuffworks.com/cvt.htmo http://www.sae.org/pdevent/WB1002

o http://cars.about.com/od/thingsyouneedtoknow/a/CVT.htm

o http://www.youtube.com/results?search_query=cvt

o http://cvt.com.sapo.pt/why/why_cvt.htm
http://en.wikipedia.org/wiki/Continuously_variable_transmissionhttp://auto.howstuffworks.com/cvt.htmhttp://cars.about.com/od/thingsyouneedtoknow/a/CVT.htmhttp://cars.about.com/od/thingsyouneedtoknow/a/CVT.htmhttp://www.youtube.com/results?search_query=cvthttp://cvt.com.sapo.pt/why/why_cvt.htmhttp://cvt.com.sapo.pt/why/why_cvt.htmhttp://www.youtube.com/results?search_query=cvthttp://www.youtube.com/results?search_query=cvthttp://cars.about.com/od/thingsyouneedtoknow/a/CVT.htmhttp://cars.about.com/od/thingsyouneedtoknow/a/CVT.htmhttp://cars.about.com/od/thingsyouneedtoknow/a/CVT.htmhttp://cars.about.com/od/thingsyouneedtoknow/a/CVT.htmhttp://cars.about.com/od/thingsyouneedtoknow/a/CVT.htmhttp://cars.about.com/od/thingsyouneedtoknow/a/CVT.htmhttp://auto.howstuffworks.com/cvt.htmhttp://en.wikipedia.org/wiki/Continuously_variable_transmission


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Thank You!

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CVT_Abhishek_Ghosh