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CONTINUOUSLY VARIABLE TRANSMISSION
A Seminar Report
Submitted by
VARGHESE JOY
MECHANICAL ENGINEERING DIVISIONSCHOOL OF ENGINEERING
COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGYCochin 682 022
SEPTEMBER 2006
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MECHANICAL ENGINEERING DIVISIONSCHOOL OF ENGINEERING
COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGYCochin 682 022
CERTIFICATE
This is to certify that the Seminar Report entitled CONTINUOUSLY VARIABLE
TRANSMISSION submitted by Mr. VARGHESE JOY of the Mechanical Engineering
Division towards the partial fulfillment of the requirements for the VII Semester of the B.
Tech Degree course in Mechanical Engineering of Cochin University of Science and
Technology, is a bonafide record of the seminar talk presented by him/her on
Seminar Coordinator Seminar Supervisor
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ACKNOWLEDGEMENT
I express my deep gratitude to almighty, the supreme guide, for bestowing his
blessings up on me in my entire endeavor.
I would to like to express my sincere thanks to Dr. P.S Sreejith Head of
Department of Mechanical engineering for all his assistance
I wish to express my deep sense of gratitude to Lecturer Mr. Gireesh Kumaran
Thampi. Department of Mechanical Engineering who guided me through out the seminar.
His overall direction and guidance has been responsible for the successful completion of
the seminar.
I would also like to thank Lecturer Mr. Ajith Kumar for his valuable suggestions.
Finally, I would like to thank all the faculty members of the department of
mechanical engineering and my friends for their constant support and encouragement.
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ABSTRACT
Continuously Variable Transmissions (CVT) offer a continuum of gear ratios
between desired limits. This allows the engine to operate more time in the optimum range
given an appropriate control of the engine valve throttle opening (VTO) and transmission
ratio. In contrast, traditional automatic and manual transmissions have several fixed
transmission ratios forcing the engine to operate outside the optimum range. The present
research focuses on developing models to understand the micro slip behavior and to define
an operating regime of a metal pushing V-belt CVT. Slip is modeled on the basis of gap
redistribution between the elements. Studies were conducted to observe the influence of
loading conditions (i.e. axial forces and torques) on the slip behavior and torque
transmitting ability of the CVT. The model also investigates the range of axial forces
needed to initiate the transmission and to successfully meet the load requirements. The
mathematical model and the results corresponding to different loading scenarios are
discussed. CVT (Continuously Variable Transmission) is a system that makes it possible to
vary progressively the transmission ratio and it allows engine to run at its optimum speed.
In this paper a CVT using a belt with changing thickness is described. Developments in
clamping force control for the push belt Continuously Variable Transmission (CVT) aim at
increased efficiency in combination with improved robustness. Current control strategies
attempt to prevent macro slip between elements and pulleys at all times for maximum
robustness. CVT efficiency increases which will lead to an improvement in fuel
consumption up to 5%.
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CONTENTS
1. Introduction
2. History
3. Why there is a need for transmission?
4. Continuously Variable Transmission
5. Why we use a CVT?
6. How does CVT Work?
7. Belt design
8. Types of CVT
9. Advantage and drawbacks
10. Implementation- Example
11. Conclusion
12. Reference
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1. INTRODUCTION
The overwhelming majority of transmissions in road going vehicles are either
manual or conventional automatic in design. These transmissions use meshing gears that
give discrete ratio steps between engine and the vehicle speed .However, alternative
designs exist that can transmit power and simultaneously give a step less change of ratio; in
other words a Continuously Variable Transmissions. Continuously Variable Transmissions
are a type of automatic transmission that provides an uninterrupted range of speed ratios,
unlike a normal transmission that provides only a few discrete ratios.
Continuously variable transmissions (CVT) offer a continuum of gear ratios
between desired limits. The present research focuses on developing models to understand
the micro slip behavior and to define an operating regime of a metal pushing V-belt CVT.
Slip is modeled on the basis of gap redistribution between the elements. Studies were
conducted to observe the influence of loading conditions (i.e. axial forces and torques) on
the slip behavior and torque transmitting ability of the CVT. The model also investigates
the range of axial forces needed to initiate the transmission and to successfully meet the
load requirements. CVT is an emerging automotive transmission technology that offers a
continuum of gear ratios between high and low extremes. Today, Continuously Variable
Transmissions have lured a great deal of automotive manufacturers and customers. Several
car companies like Honda, Toyota, Ford, Nissan, etc., have been doing intensive research to
exploit the advantages of a CVT. The chief advantage of a CVT is its ability to offer an
infinite range of gear ratios with fewer moving parts, and consequently this influences
engine efficiency, fuel economy, and cost.
Continuously Variable Transmissions (CVTs) have developed notably indifferent
applications over the past years. This is especially true in the automobile field because of
advantages in terms of car handling and efficiency on urban roads. The advantages of a
Continuously Variable Transmission are in terms of its power and efficiency. A
Continuously Variable Transmission is different from the conventional automatic
transmission unit.
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2. HISTORY
The CVT (Continuously Variable Transmission) design was developed by inventor
Dr Jan Naude as a result of a long felt need for an all gear non-traction fluid, non-hydraulic,
continuously variable gearbox/transmission. CVTs were first patented in Europe in the
19th century, but are just now coming into their own in a big way in the American market
place. The CVT results in a more efficient and versatile drive train in comparison to
conventional drive trains and has been designed as an alternative to existing gearboxes,
providing greater efficiency for equivalent cost. The formation of the company is the
culmination of negotiations between partners Dr Jan Naude and Marinus van den Ende and
Barloworld Equipment. This Barloworld Equipment Smart PartnershipTM, Varibox CVT
(Pty) Ltd trading as Barloworld CVT Technologies was created to expand and bring to the
market the innovative inventions of Dr Jan Naude.
According to TOROTRAK, the first patent for a toroidal CVT was filed at the end
of the century was designed and built by Dutch Hub van Doorne, co-founder of DAF, in the
late 1950s, specifically to produce an automatic transmission for a small, affordable car.
The first DAF car using van Doorne's CVT was produced in 1958. Van Doorne's patents
were later sold to Volvo along with DAF's car business
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3. WHY THERE IS A NEED FOR TRANSMISSION?
According to some engineers, the transmission is a large, expensive bracket to stop
the engine dragging on the road. In reality transmissions are much more interesting than the
other, less significant, parts of the power train. Essentially, the transmission takes the power
from the engine to the wheels, in doing so actually makes the vehicle usable. The functions
that enable this include:
Allow the vehicle to start from rest, with the engine running continuously.
Let the vehicle stop by disconnecting the drive when appropriate.
Enable the vehicle to start at varied rates, under a controlled manner.
Vary the speed ratio between the engine and wheels.
Allow this ratio to change when required.
Transmit the drive torque to the required wheels.
The transmission needs to perform all of the above functions and others\refined manner.
The structural aspects of the transmission, predominantly the casting, often contribute
significantly to the structure of the power train and the vehicle as a whole. This is important
when it comes to engineering for the lowest noise and vibration. The stiffness of the power
train assembly itself is important in determining the magnitude and frequency of the
vibrations at the source (the engine). This stiffness (and indeed the strength) can also be
important to the integrity of the vehicle in a crash. Particularly with front wheel drive
vehicles, the way in which the body collapses on impact has to be engineered very
carefully, and the presence of a large rigid lump such as the power train has a critical
influence on the way this occurs. The size, shape and orientation of the unit also affect the
intrusion into the passenger space after an impact.
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4. CONTINUOUSLY VARIABLE TRANSMISSIONS (CVT)
Continuously variable transmissions (CVTs) have an infinitely variable ratio,
which allows the engine to operate more time in the optimum range given an appropriate
control of the engine valve throttle opening (VTO) and transmission ratio .In contrast,
traditional automatic and manual transmissions have several fixed transmission ratios
forcing the engine to operate outside the optimum range With growing interest in
improving the fuel economy in the moving vehicles continuously variable transmission s
has attracted a great deal of interest. This type of transmission provide continuously
variable reduction ratio that enables the engine to operate under the most economical
conditions over a wide range of vehicle speed.
Two representative type of continuously variable transmission are Van Doorne belt
system and Perbury (Trotrak) system. Van Doorne system, it was installed in since 1955.
It has pair of conically faced pulleys, as shown in figure. The effective radius of the pulley,
and hence the reduction ratio, can be varied by adjusting distance between the two sides of
the pulley. on the original system the reduction ratio can be controlled by mechanical
means through centrifugal weight on the driving pulley and engine vacuum actuator .more
recently microprocessor based control system has-been developed .this type continuously
variable trans mission can achieve a reduction ratio, ranging from 4 to 6 . The
mechanical efficiency of the transmission varies from load and speed. The variation in
efficiency with input torque and speed at a reduction ratio 1 for a system designed for a
light weight passenger car. To improve the efficiency with reduce noise and wear, a
segmented steel belt or a push belt system has been developed. it comprises a set of belt
element about 2 mm thick , with slots on each side to fit two high tensile steel bands which
hold them together .unlike the conventional v-belt ,it transmit power by the compressive
force between the belt elements ,instead of tension . The Van Doorne system is most
suitable for low power applications, mainly in front wheel drive vehicles and has been used
in small size passenger cars and snow mobiles.
The continuously variable transmission (CVT) has been around as long as the
automobile. Engineers have always recognized its theoretical advantage over the multi ratio
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gearbox. A CVT enables the engine to run at its most fuel-efficient or most power-efficient
speed while driving the vehicle at any speed desired.
With a CVT engine speed and vehicle speed are no longer connected by a series of
discrete ratios. Instead, they can function independently across a wide and step less band
according to engine characteristics and performance requirements. The advantages of this
infinite ratio selectivity are enormous. Most obvious in the IC engine application is that the
engine can be loaded into its most fuel-efficient region at cruising speeds, then allowed to
accelerate into its region of greatest output when peak power is needed, regardless of
vehicle speed. Practical problems have consistently plagued the design. hut the CVT is now
coming of age.
Fig No.1
Continuously Variable Transmissions (CVT)
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Fig No.2
Van Doorne belt system
The Perbury System is shown in fig. the key component of the system is variator,
which consists of three disks .with the outer pair connected to the input shafts and the inner
one is connected to the output shaft .the inner surface of the disk are of the toroidal shape
.
Fig No.3
Perbury (Trotrak) systems
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Continuously Variable Transmissions (CVT) is typically composed of two
hydraulically actuated variable radii pulleys and a metal pushing belt (see Figure 1). CVTs
offer a continuum of infinitely variable gear ratios by changing the location of pulleys
heaves. As a result, CVTs have the potential to increase the overall vehicle efficiency and
reduce the jerk usually associated with manual and automatic transmissions. Although
many criteria characterize performance, the focus is on fuel consumption and vehicle
longitudinal dynamics (jerk) during vehicle acceleration One shortcoming however, is their
difficulty in transmitting high torque at low operating speeds, which so far has limited their
use to small vehicles. Alternatively, power-split CVTs (PSCVTs) offer both fixed gears and
adjustable pulleys and are able to extend the torque transmission capability significantly. A
CVT relies on a flexible metal belt and pulleys to constantly shift gear ratios, boosting fuel
economy as much as 10 percent. They are also smaller, lighter, cheaper and easier to build
and install than traditional stick-shift or automatic transmissions. For all these reasons,
CVTs are starting to get a lot of attention from car-makers worldwide, as they continuously
look for ways to help their cars and trucks get better mileage, and be lighter, less expensive
to build and easier to repair.
Fig No.4
Cross Section Of CVT Pulley
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5. WHY USE A CVT?
Traditional transmissions use gears, friction plates and hydraulic fluid to transfer
power from an engine to a drive shaft. Continuously variable transmissions use a simple
belt and pulley system, creating a "continuously variable" gear ratio that is more fuel-
efficient CVT technology replaces the gears and friction plates in traditional transmissions
with a belt and pulley system to transfer the power smoothly from a motor to the wheels.
The pulleys inside a CVT are typically cone-shaped, and the belt that runs between
them slides between the narrow and wide ends of each pulley. That creates a "continuously
variable" gear ratio to transfer power from the engine to the wheels.
A CVT is an ideal power transmission device for a snowmobile for one main reason
it allows power from the engine to be transmitted continuously to the ground. In contrast, a
standard gear-box transmission takes time to shift gears, time in which the engine and
wheels are disconnected, and results in a loss of momentum. Because of the terrain that
snowmobiles often encounter (snow, and specifically unbroken snow), it is not practical to
experience a loss of momentum while operating a snowmobile. The time spent in changing
gears would allow the high drag properties of deep snow to overcome most of the vehicles
momentum. By using a CVT, snowmobiles overcome this dilemma and deliver
uninterrupted engine power to the ground. Furthermore, the two and four-stoke engines
common to snowmobiles have a smaller range of deliverable power than those used in
geared transmissions, so use of a CVT allows for the engine to operate at a constant speed,
namely that speed which produces the maximum power.
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6. HOW DOES A CVT WORK?
Although there are different variations on the CVT theme, most passenger cars use a
similar setup. Essentially, a CVT transmission operates by varying the working diameters
of the two main pulleys in the transmission. The pulleys have V-shaped grooves in which
the connecting belt rides. One side of the pulley is fixed; the other side is moveable,
actuated by a hydraulic cylinder. When actuated, the cylinder can increase or reduce the
amount of space between the two sides of the pulley. This allows the belt to ride lower or
higher along the walls of the pulley, depending on driving conditions, thereby changing the
gear ratio. If you think about it, the action is similar to the way a mountain bike shifts gears,
by "derailing" the chain from one sprocket to the next except that, in the case of CVT,
this action is infinitely variable, with no "steps" between.
The "stepless" nature of its design is CVT's biggest draw for automotive engineers. Because
of this, a CVT can work to keep the engine in its optimum power range, thereby increasing
efficiency and gas mileage. A CVT can convert every point on the engine's operating curve
to a corresponding point on its own operating curve
With these advantages, it's easy to understand why manufacturers of high-mileage vehicles
often incorporate CVT technology into their drive trains. Look for more CVTs in the
coming years as the battle for improved gas mileage accelerates and technological advances
further widen their functionality.
A CVT operates on dynamic principles which are based on three main mechanical
components flyweights or cams, springs, and ramps. Essentially, these three component-
types work in conjunction to transmit engine power and torque to the ground, while
maintaining a constant engine speed. There are certain mechanical feedback systems,
created by the CVT components, which govern how the transmission behaves, and
ultimately how the snowmobile performs. The A+CVT developed by Larry Anderson uses
flexible sprocket bars along the pulley shafts to create a more efficient and durable positive
drive system rather than the typical friction drive of a belt system.
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Fig No.5
Continuously Variable Transmissions (CVT) Unit
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Fig No.6
CVT Unit Incorporated In The Vehicle
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7. BELT DESIGN
7.1 Push Belt Loading During Variator Operation
The heart of a CVT system is the variator, i.e. the push-belt/pulley system illustrated
in Figure 1. In the variator, torque or power is transmitted from the primary to the
secondary pulley via friction between the push-belt elements and the pulley sheaves
.Stepless shifting between the extreme LOW (under drive) and OD (overdrive) ratios is
achieved by varying the pulley clamping forces and thereby changing the axial position of
the moveable pulley sheaves, modifying the effective running radius. An example of a Van
Doorne push-belt is shown in Figure 2.
During operation of the variator, the push-belt and pulleys undergo cyclic (fatigue)
loading. Stress levels in the push-belt elements and pulleys are determined by the applied
pulley clamping forces, rotational speeds, and torque levels. Experience has shown that
fatigue loading of the elements and pulleys is less critical in practice than ring fatigue
loading. The push-belt rings are mainly subjected to bending and tensile stresses, although
in a rather complex manner. In general, the bending stresses are determined by the applied
running radii (transmission ratio) and the ring thickness. The tensile stresses are mainly
determined by the applied pulley clamping forces, rotational speeds, and torque.
Fig No.7
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Fig No.8
Example Of A Variator And Its Working Principle
Fig No.9
Push Belt Loading And Doorne Push Belt
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7.2 CVT Using A Belt With Changing Thickness
Continuously variable transmissions (CVTs) have an infinitely variable ratio, which
allows the engine to operate more time in the optimum range given an appropriate control
of the engine valve throttle opening (VTO) and transmission ratio. In contrast, traditional
automatic and manual transmissions have several fixed transmission ratios forcing the
engine to operate outside the optimum range. There are various types of CVTs but in this
opinion a new concept for a CVT using a belt with changing thickness is described. If the
thickness of belt is not negligible as compare to radius of pulley, the neutral axis of rotation
is taken as radius of pulley plus half the thickness of belt. Therefore the effective diameter
of the pulley will change. If the belt is made up such that its thickness decreases when
stretched & increases when compressed .Consider that the smaller pulley is fixed and
position of larger pulley can be changed and Power is transmitted from smaller pulley to
larger pulley. If distance between pulleys is increased, the thickness of belt decreases &
vice-versa. Normally the Transmission ratio (G) is given by
G = D/d,
Where d and D are diameters of smaller and larger pulley respectively.
But due to considerable thicknesst of the belt G changes to
G = (D + t) / (d + t),
Now G will vary continuously ast varies. If the variation in transmission ratio is
not sufficient then it can be enlarged by increasing no. of belts in series. It can also be
increased using power split transmission.
Most commonly used another type of transmission is chain type. It is described
below the new A+CVT Steel Block Chain was designed specifically for use with the dual-
cone A+CVT. This chain consists of steel block links connected with steel pins and side
plate links. Each block link has a drive lug protruding from the inner side, which meshes
with the floating sprocket bars. The drive lug is designed so that there is a single vertical
line of contact with the floating sprocket bars. This allows for a single speed ratio at each
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point. This would be impossible with a belt, since a belt has multiple speed ratios across its
width, and a CVT cannot function with multiple speed ratios simultaneously. A U.S. Patent
for the A+CVT Chain has been applied for.
The original A+CVT used a beaded chain for demonstration purposes. The new
A+CVT Steel Block Chain was developed in response to concerns expressed by some
engineers that a beaded chain would be too weak for heavy-duty applications. We remain
convinced that a beaded chain of sufficient quality and strength could be developed for use
with the A+CVT. However, our attention has shifted to the new A+CVT Steel Block Chain,
as it can be scaled to meet any torque requirements more easily
CVT stands for continuously variable transmission. This type of transmission
allows for a change in ratios without stopping or disengaging the gears. Most CVT's are
friction drive, with some means of varying the relative diameters of the driving components
while driving. These friction drive transmissions are simple, but can only transmit a limited
amount of torque before the wheels start slipping. There are some CVT's that use gears and
cranks that offer positive drive without a chance for slippage, but these are much more
complicated. My Lego CVT is a friction drive assembly, and it is really just a quick concept
that wouldn't be very practical in real applications.
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8. TYPES OF CVT
8.1 Pulley Based CVT
Fig No.10
Pulley Based CVT
This type of CVT uses pulleys pulley is a wheel with a groove along its edge, for holding a
rope or cable. Pulleys are usually used in sets designed to reduce the amount of force
needed to lift a load. However, the same amount of work is necessary for the load to reach
the same height as it would without the pulleys. The magnitude of the force is reduced, but
it must act through a longer distance. Pulleys are usually considered one of the simple
machines. A chain Roller chain or bush roller chain is the type of chain most commonly
used for transmission of mechanical power on bicycles, motorcycles, and in industrial and
agricultural machinery. It is simple, reliable, and efficient (as much as 98% efficient under
ideal conditions), but requires more attention to maintenance than may be desired by
potential owners; therefore there has been of late a tendency towards the use of other modes
of other modes of power transmission such as the cog belt.
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8.2 Roller-Based CVT
Consider two almost-conical parts, point to point, with the sides dished in such that
the two parts could fill the central hole of a torus is a doughnut-shaped surface of revolution
generated by revolving a circle about an axis coplanar with the circle. The sphere is a
special case of the torus obtained when the axis of rotation is a diameter of the circle.
If the axis of rotation does not intersect the circle, the torus has a hole in the middle
and resembles a ring doughnut, a hula hoop and an inflated tire (U.K. tyre). The other case,
when the axis of rotation is a chord of the circle, produces a sort of squashed sphere
resembling a round cushion. Torus was the Latin word for a cushion of this shape. One part
is the input, and the other part is the output (they do not quite touch). Power is transferred
from one side to the other by one or more rollers. When the roller's axis is perpendicular to
the axis of the almost-conical parts, it contacts the almost-conical parts at same-diameter
locations and thus gives a 1:1 gear ratio. The roller can be moved along the axis of the
almost-conical parts, changing angle as needed to maintain contact. This will cause the
roller to contact the almost-conical parts at varying and distinct diameters, giving a gear
ratio of something other than 1:1.
8.3 Hydrostatic CVT
Some continuously variable transmissions instead use a variable displacement pump
variable displacement pump is a device that converts mechanical energy to hydraulic (fluid)
energy. Some of these devices can also be reversible, meaning that they can act as a
hydraulic motor and generate mechanical energy from fluid energy. The displacement can
be adjusted to increase or decrease the amount of fluid pumped and a hydraulic motor to
transmit power. These types can generally transmit more torque, but they are very
expensive to buy and maintain. However, they have the advantage that the hydraulic motor
can be mounted directly to the wheel hub, allowing a more flexible suspension system and
eliminating efficiency losses from friction in the drive shaft and differential components.
This type of transmission has been effectively applied to expensive versions of light duty
ridden lawn mower
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8.4 Intermeshing Cones
The basic principle here is that two cones are fashioned such that they can slide in
and out of one another, effectively creating a v-shaped pulley that varies in size as the
cones are moved in and out of one another. Anderson's idea is a modification of the dual-
cone CVT. It uses floating sprocket bars along the length of each cone to engage a chain.
This creates a more durable, positive drive system instead of using simple friction to move
a belt up and down the cones. Belt-driven CVTs are friction dependent - and that result in
power loss and a less efficient system, he said.
"There's not much more auto companies can do (to improve fuel efficiency) by
shaving weight and using plastic in bumpers and fenders," Anderson said. "The
transmission is one place where they can go to improve fuel efficiency
8.5 Toroidal
The toroidal transmission consists of two sets of planetary type, steerable rollers
housed between an inner and outer toroidal-shaped disc, one driving and the other driven.
By tilting the steerable rollers, the relative diameters of engagement of the input and output
toroidal discs can be varied to achieve a desired speed ratio. Very high contact pressures
exist at the point of contact between the steerable rollers and the toroidal discs. Torque is
transferred at the point of contact under a high shear stiffness traction fluid placed under
extremely high pressures, causing the fluid to become glass-like. In this mode, its behavior
is described as elastrohydrodynamic. With the fluid operating in the elastrohydrodynamic
region, metal to metal contact between the rollers and toroidal discs is prevented.
Fig No.11
Toroidal
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The toroidal CVT transfers torque with the help of a traction fluid, which becomes
glass-like under extremely high pressures. This configuration handles extremely high
torques at high efficiencies. SWRI engineers use computer models to model CVTs and
other transmissions to determine optimal sizing, estimate expected performance levels, and
evaluate many different options in a timely manner before beginning hardware fabrication -
all of which reduce overall development time and costs.
8.6 Super Simple
Anderson's idea is a modification of the dual-cone CVT. It uses floating sprocket
bars along the length of each cone to engage a chain. This creates a more durable, positive
drive system instead of using simple friction to move a belt up and down the cones. Belt-
driven CVTs are friction dependent and that result in power loss and a less efficient system,
he said. "There's not much more auto companies can do (to improve fuel efficiency) by
shaving weight and using plastic in bumpers and fenders," Anderson said. "The
transmission is one place where they can go to improve fuel efficiency.
Fig No.12
Anderson's Dual-Cone CVT
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9. ADVANTAGES AND DRAWBACKS
CVTs have much smoother operation than hydraulic automatic transmissions
automatic transmission is an automobile gearbox that can change gear ratios automatically
as the car or truck moves, thus freeing the driver from having to shift gears manually. The
frictional force is a function of the force pressing the surfaces together and the coefficient
of friction between the materials. In particular: and strength tensile strength of a material is
the maximum amount of tensile stress that it can be subjected to before it breaks. This is an
important concept in engineering, especially in the fields of material science, mechanical
engineering and structural engineering.CVTs can smoothly compensate for changing
vehicle speeds, allowing the engine speed to remain at its level of peak efficiency. This
improves both fuel economy and exhaust.CVT's design advantages lie not only in its
efficiency but its simplicity .It consists of very few components. A continuously variable
transmission typically includes the following major component groups:
A high-power/density rubber belt
A hydraulically operated driving pulley
A mechanical torque-sensing driving pulley
Microprocessors and sensors
Because of this simplicity in design, CVT offers some advantages over traditional
transmissions, although it also has certain Drawbacks. For instance, its belt-driven
orientation limits its application; until recently, cars with engines larger than 1.2 liters were
considered incompatible with CVT. More and more, however, CVTs are becoming
available that can handle more powerful engines, such as the V6 power plants found in
some Nissan and Audi vehicles. CVTs offer a continuum of infinitely variable gear ratios
by changing the location of pulleys heaves. As a result, CVTs have the potential to increase
the overall vehicle efficiency and reduce the jerk usually associated with manual and
automatic transmissions. One shortcoming, however, is their difficulty in transmitting high
torque at low operating speeds, which so far has limited their use to small vehicles. Other
disadvantages include its larger size and weight. Still, in the right situation, CVT's
advantages outweigh its disadvantages. Less complexity and moving parts theoretically
mean fewer things to go wrong and maintain.
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Fig No.13
Modified CVT Efficiency Map
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10. EXAMPLES- IMPLEMENTATION
Many small tractors for home and garden use have simple CVTs, as do most
snowmobiles. Almost all motor scooters today are equipped with CVT.
Adaptable for
1. Automobile 2.Trucks 3 Military vehicles 4. Heavy construction equipments 5.
Bicycle 5. Motor cycles 6. Industrial machinery 7.Any type of motor
Possibly the largest vehicle currently sold with a CVT is the Nissan Murano, a mid-
size sport utility vehicle with a 3.5L V6 engine. The CVT is also available for Audi, Fiat,
Honda, Mercedes-Benz and Mini Cooper cars.
Some combines have CVT. The machinery of a combine is adjusted to operate best
at a particular engine speed. The CVT allows the forward speed of the combine to be
adjusted independently of the machine speed. This allows the operator to slow down and
speed up as needed to accommodate variations in thickness of the crop.
Automobiles Equipped With CVT
Audi A4 2.0/1.8T/2.4/3.0/2.5 TDI
Audi A6 2.0/1.8T/2.4/3.0/2.5 TDI
Fiat Punto 1.2
Ford Escape Hybrid 2.3 4cyl
Ford Focus C-MAX 1.6 TDCi 110ps
Honda Civic Hybrid 1.3 4cyl
Honda HR-V 1.6
Honda Insight 1.0 3cyl
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11. CONCLUSION
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12. REFERENCES
1. M J Nunney, Light and Heavy Vehicle Technology, Elsevier Publishers
2. W D Erickson, Belt Selection and Application for Engineers, Marcel Dekker Publishers
3. Heinz Heisler, Advanced Vehicle Technology, Elsevier Publishers
5. William B Ribbens, Understanding Automotive Electronics
6. Belt Slip-A Unified Approach by Gerbert.G, ASME Journal of Mechanical Design, Voll.118, No.3
7. www. howstuffs works.com
8. http://www.lib.ucdavis.edu/dept/pse/resources/CVT04/
9. www.theaudimultitronic CVT
