ivt infinite variable transmission

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STUDY OF INFINITELY VARIABLE TRANSMISSION

1

A

SEMINAR REPORT

ON


PREPARED BY

U09ME611 MIHIR H. PATEL

GUIDED BY

Mr. VIKRAM P RATHOD

(ASST PROF. DEPARTMENT OF MECHANICAL ENGINEERING)

SARDAR VALLABHBHAI NATIONAL INSTITUTE OF TECHNOLOGY SURAT


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CERTIFICATE

This is to certify that the credit seminar report untitled STUDY OF

INFINI TELY VARIABLE TRANSMISSION SYSTEMS submitted by

Mr.MIHIR H PATELin partial fulfillment of the requirement for award of

the degree in B.TECH of Sardar Vallabhbhai National Institute OfTechnology, Surat is record of his own work carried out under mysupervision and guidance. The matter enclosed here is not been submittedelsewhere for award of any degree or diploma.

Mr. Vikram P Rathod

Assistant Professor,

MED, SVNIT

Surat

Jury 1 Jury 2


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Acknowledgement

I am deeply indebted to my guide Mr. Vikram Rathodfor

guiding me to successfully accomplish this credit seminar.

It was my privilege and pleasure to work under his

guidance. I am indeed grateful to him for providing helpful

suggestion from time to time. Due to his encouragement

and inspiration, I am able to present this preliminary

seminar.


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Table of Contents1. INTRODUCTION ....................................................................................................................................... 5

2. WHAT IS CVT ?........................................................................................................................................ 5

3. INFINITELY VARIABLETRANSMISSION................................................................................................... 6

3.1.KEY ELEMENTS OF IVT.6

3.2.WORKING FORMULA FOR PLANETARY GEAR SET7

4. VARIANTS OF IVT.................................................................................................................................... 8

4.1.ZERO-MAX DRIVE.8

4.2. TOROTRAK INFINITELY VARIABLE TRANSMISSION...9

4.3.

D DRIVE TECHNOLOGY . 104.4. HYBRID SYNERGY DRIVE ...11

4.5.TELAM CONSTANT GEAR MESH IVT13

5. BENEFITS OF IVT .................................................................................................................................... 15

6. DRAWBACKS OF IVT.............................................................................................................................. 16

7. APPLICATIONS OF IVT ....17

8. REFRENCES.18


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1..INTRODUCTION

Mechanical transmission devices allow energy and power to be transmitted through physical spaceand enable matching between differing characteristics of energy sources and loads. Similarly a

gearbox converts a small torque over a large angle to a large torque over a small angle.IVTis an acronym forInfinitely Variable Transmission. IVT falls under the category of ContinuouslyVariable Transmission(CVT). The IVT dates back to before the 1930s; the original design convertsrotary motion to oscillating motion and back to rotary motion using roller clutches. The stroke of theintermediate oscillations is adjustable, varying the output speed of the shaft. A specific type of CVTis the infinitely variable transmission (IVT), in which the range of ratios of output shaft speed toinput shaft speed includes a zero ratio that can be continuously approached from a defined "higher"ratio. A zero output speed (low gear) with a finite input speed implies an infinite input-to-outputspeed ratio, which can be continuously approached from a given finite input value with anIVT.Lowgears are a reference to low ratios of output speed to input speed. This low ratio is taken tothe extreme with IVTs, resulting in a "neutral", or non-driving "low" gear limit, in which the output

speed is zero. Unlike neutral in a normal automotive transmission, IVT output rotation may beprevented because the back driving (reverse IVT operation) ratio may be infinite, resulting inimpossibly high back driving torque. First let us understand what is a CVT?

2.WHAT IS CVT ?

CVT stands for Continuously Variable Transmission. CVT was originally conceptualized by FamousArtist Leonardo Da Vinci in the back 1490s1. Allowing an engine to operate within its high-

efficiency or high-power range maximizes fuel economy or performance, and in a geared manual orautomatic transmission this is best achieved by having a large number of gears. Transmissions with7-speeds and even 8-speeds are becoming available in passenger-car market, for example, tomaximize efficiency and/or performance over wide range of vehicle speeds. An alternative strategyto having a large number of discrete gears is to use a transmission that enables a continuously-variable transmission ratio.A continuously variable transmission or CVT can achieve an optimum matching between engine andload conditions without having to change gears through discrete steps. From standstill to vehicle

top speed, a CVT continuously transmits power from the engine to the wheels, even though theengine can be operating at a fixed speed. Use of a CVT allows an engine to run at optimum power orefficiency over a vehicles entire range of load conditions. This can improve economy, comfort,

emissions and durability. It also provides improved performance by avoiding gear changes, whichinterrupt the flow of energy from the engine to the wheels.A launch device such as a torque converter or clutch is typically required for CVTs, as the variable-speed element cannot typically generate torque at zero or very low wheel speeds. The basicdifference between CVT and conventional manual or automatic drive trains is number of effectivegear ratios. Virtually CVT has infinite number of effective gear ratios between zero and maximum.From an engineering point of view a variable transmission device is, conceptually, preferable to aconventional gearbox with its fixed gear ratios.

1Information source WIKIPEDIA


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3.INFINITELY VARIABLE TRANSMISSION

A specific type of CVT is the infinitely variable transmission (IVT), in which the range of ratios ofoutput shaft speed to input shaft speed includes a zero ratio that can be continuously approached

from a defined "higher" ratio. This low ratio is taken to the extreme with IVTs, resulting in a"neutral", or non-driving "low" gear limit, in which the output speed is zero. Unlike neutral in anormal automotive transmission, IVT output rotation may be prevented because the back driving(reverse IVT operation) ratio may be infinite, resulting in impossibly high back driving torque.

Most IVTs result from the combination of a CVT with a planetary gear system (which is also knownas an epicyclic gear system) which enforces an IVT output shaft rotation speed which is equal to thedifference between two other speeds within the IVT. This IVT configuration uses its CVT as acontinuously variable regulator (CVR) of the rotation speed of any one of the three rotators of the

planetary gear system (PGS). If two of the PGS rotator speeds are the input and output of the CVR,there is a setting of the CVR that results in the IVT output speed of zero. The maximum output/inputratio can be chosen from infinite practical possibilities through selection of additional input or output

gear, pulley or sprocket sizes without affecting the zero output or the continuity of the whole system.The IVT is always engaged, even during its zero output adjustment.

3.1. KEY ELEMENTS OF IVT:

The input gearset. The input gearset transmits the power from the engine to the planet gear inthe epicyclic gear train.

The variator. The variator is the means by which the IVT can deliver an infinite range ofratios. It affects the speed of rotation of the sun gear in the epicyclic and is responsible for thesmooth variation of ratios which the transmission produces.

Figure 1 Basic IVT Configuration

Epicyclic (planetary) gearset. The central gear (sun gear) is driven by the fixed engine rpm.The annulus gear is connected to the layshaft which decides the direction of output to wheels.While the planet gears form the output to the wheels.


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Controller: instead of using variator or splitting input power, another source of motion issupplied and the variation in its speed decides the output.

3.2. WORKING FORMULA OF PLANETARY GEAR SET i:

The planetary gear set

formula:

WP (DR + DS) = WR DR - WS

DS

(W: angular velocities; D:pitch circle diameters)

WP= output RPMWR= RPM of layshaftWS= input RPM = Win

What will be the IVT output speed?

What will be the IVT overall ratio?

Figure 2 Alternate Configuration of IVT

Figure 3 Planetary gear set with a CVR


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4.VARIANTS OF IVT

4.1. Zero-Max driveii

Zero-max drives are theconventional type of

IVTs that convertrotary motion toOscillatory and again

back to rotary. Externally, the Zero-

Max Drive consists of arugged, sealed castcase, an input shaft,output shaft and speed

control. Speed of the output

shaft is regulatedprecisely and easilythrough a control leverwhich includes aconvenient lockingmechanism or a screw control to hold speed at a desired setting. Models are available withoutput in clockwise or counterclockwise rotation to meet individual speed controlrequirements.

The general principle of operation of Zero- Max Drives gives infinitely adjustable speed by

changing the distance that four or more one- way clutches rotate the output shaft when theymove back and forth successively. The number of strokes per clutch per minute isdetermined by the input speed. Since one rotation of the input shaft causes each clutch tomove back and forth once, it is readily apparent that the input speed will determine thenumber of strokes or urgings the clutches give the output shaft per minute.

For example, with four clutches working in series and an input of 1800 RPM, the outputshaft is urged 7200 times per minute (1800 x 4) or 120 times per second (7200 60). If theinput speed is dropped to 900 RPM, the shaft is urged only 3600 times per minute and themaximum output speed will be cut in half.

Figure 4 Link Mechanism of Zero to Max Drive


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Looking at Figure 1, the input section, consisting of a shaft (A), eccentrics (B), andconnecting rods (C), converts rotary motion into linear motion. At the zero setting, themain links (D) pivot on points (H) and (J) without moving the clutches.

At any setting other than zero, the clutches (E) transfer the linear motion back into rotarymotion and drive the output shaft (F). A control link (G) swings through arc (K) when the

control lever is moved. At any point along arc (K) a different output speed is producedbecause the direction of throw of the connecting rod is altered from vertical (Figure 1 zeroRPM position) toward horizontal (Figure 2 maximum speed position), varying the length ofthe strokes the main links deliver to the overrunning clutches.

4.2. Torotrak Infinitely Variable Transmissioniii

The variator is the heart of the IVT and is the means by which the IVT can deliver aninfinite range of ratios. The Torotrak variator is termed full toroidal due to thegeometry of the discs. Inside the variator are two pairs of discs. The space betweeneach pair of discs forms a hollow doughnut shape or 'toroid'. Within each toroidalspace there are three rollers which transmit drive from the outer, engine driven, discs(shown in green) to the output discs (shown in yellow) located in the centre.

The variator is the heart of the IVT and is the means by which the IVT can deliver aninfinite range of ratios. The Torotrak variator is termed full toroidal due to the geometry

of the discs. Inside the variator are two pairs of discs. The space between each pair of discsforms a hollow doughnut shape or 'toroid'. Within each toroidal space there are three rollers

which transmit drive from the outer, engine driven, discs (shown in green) to the outputdiscs (shown in yellow) located in the centre.

Figure 6 Full Transmission System of Torotrak IVT

Figure 5 Roller arrangement of Torotrak IVT


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Each roller is attached to a hydraulic piston. The pressure in the pistons can be increasedor decreased to create a range of reaction torque within the variator.

In the Torotrak variator the rollers don't actually touch the discs; there is no metal-to-metalcontact. They are separated by special oil termed traction fluid. Rolling the edge of the

roller against the surface of the discs traps a microscopic oil film between them.

The variator is able to transmit power across the oil film. This is because the special longchain molecules used in traction fluid interlock with each other when the fluid iscompressed, becoming highly viscous (glassy) under pressure. This means that as pressureis exerted at the contact points between the rollers and the discs the oil resists the tendencyto slide and transmits the power effectively.

4.3. D Drive Technologyiv

D Drive is anInfinitely Variable Transmission system designed by Steve Durnin. Hereinstead of using Continuously Variable Transmission (CVT) as a Continuously VariableRegulator (CVR), an electric motor is used as CVR to regulate the speed of vehicle.

Ddriveuses one epicyclic gear set and one eccentric gear arrangement to vary the speed inboth forward and reverse direction.

Input is connected to eccentric gear(differential A) which in turn is connected to two shaftsthat are controlled by motors which then forward the power to epicyclic geararrangement(differential B) which differentiates the speed.

Now for example if upper shaft is rotating and lower shaft is stationary output is maximumforward, while if upper shaft is stationary then lower shaft speeds up giving maximumreverse, on contrary if both shafts are rotating at same speed in opposite direction then the isno output giving geared neutral. The motion here is self compensated in the epicyclic geararrangement.

In D drive technology output speed is the result of the variation in two control speeds and theactual speed of the main source(ICE).

Figure 7 d drive block diagram


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4.4. Hybrid Synergy Drivev

HSD replaces the gear box, alternator and starter motor with a pair of electrical motor-generators (MG), a computerized shunt system to control them, a mechanical power splitterthat acts as a second differential, and a battery pack that serves as an energy reservoir. Each

Motor-Generator (MG) can convert electricity to motion (mechanical power) or vice-versa.

The HSD works by shunting electrical power between the two motor generators and thebattery pack to even out the load on the gasoline engine. Since a power boost is available forperiods of acceleration, the gasoline engine can be sized to match only the average load onthe car, rather than its peak load: this saves fuel because smaller engines are more powerefficient.

The HYBRID SYNERGY DRIVE computer oversees operation of the entire system,determining which engine/MG should be running, or if both should be in use, or shutting offthe internal combustion engine when the electric motor is sufficient to provide the power asshown in figure 8.

Figure 8 Block Diagram of Hybrid Synergy Drive


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Red line= acceleration of a vehicle with IC petrol engine

Green line= acceleration of a combined HEV

Figure 10 Split Power mechanism in HSD

Figure 9 Acceleration characteristic for manual vs HSD


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4.5. TELAM CONSTANT GEAR MESH IVT

The Telam constant-gear-mesh infinitely variable transmission (IVT) from Tom Troester is aspecial type of continuously variable transmission (CVT).

In contrast to standard transmissions, which have only finite or step gear ratios producing

three, four, or five speeds, CVTs additionally have all ratios available between the gears. Thislets the engine run at its most efficient rpm while varying the vehicle speed.It has beenknown for decades in the automotive industry that a CVT increases fuel mileage. In fact,several are in use today. Allexcluding ones with supplemental motor planetary systemsare variations of the Van Doorne design.

The Van Doorne design is essentially a belt drive with two pulleys, each of which has avariable diameter. The simple belt drive relies on friction, which limits its use in automobilesas well as its ratio range. Refinements such as steel belts and push belts improved the drives

torque capacity, but it is still necessary to increase the normal force via the pulleys to furtherincrease torque capacity, which reduces efficiency.

Additionally, pending CAF standards to boost vehicle mpg are pushing automotivemanufacturers to develop six, seven, eight, and nine-speed transmissions. These are eitherdual-clutch transmissions (DCT) or conventional multistage planetary gear transmissionswith a torque converter. Both types are complex, heavy, and expensive to manufacture.

The scalable design is lightweight and efficient because it needs no high parasitic loadings to

increase the normal force. The Telam CVT has both forward and reverse rotation as well as ageared neutral inherent in the design, making it whats called an infinitely variabletransmission (IVT).

The design uses special cone gears in one planetary stage. The cone gears incorporate aninvolute gear geometry that provides constant gear meshing. The cones are planet gears,meaning they rotate about the input shaft and also about their own axis as in conventional

planetary gearing. The cone planet gears mesh with an adjustable internal ring gear ondifferent cone diameters, which varies the output ratio and direction of rotation.

To better understand the geared neutral and reverse rotation, consider a normal two-stageplanetary transmission. Like the Telam IVT, the output shaft receives two inputs. One comesfrom the input shaft/cone carrier rotation. The other comes from the gear cone rotation about

its axis, which spins in the opposite direction of the cone carrier/input shaft. When therotation of the cone gears about their axis, from one rotation of the input shaft/cone carrier,

Figure 11 Conical Planetary Gear Box in Telam IVT


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imparts one rotation of the output shaft, this is defined as geared neutral. Because the conesrotate in the opposite direction of the input shaft, the gear train yields a zero output-shaftrotation.

This feature also explains the integral reverse, which is just the adjustable internal ring gearmoving along the gear cone to a different diameter. Prototypes have demonstrated a forward

ratio range of over 18:1 and a reverse ratio range of over 5:1. This is equivalent to an 11-speed conventional automotive transmission. The Telam IVTs wide ratio range lets it interface to a flywheel battery for a simple practical

hybrid vehicle that could recover 70% of the braking energy of every-day type local driving. The flywheel hybrid vehicle consists of two lightweight Telam IVTs. The first IVT connects

to the engine and differential. The other IVT connects to the differential and flywheel battery. During normal driving with input from the accelerator pedal, the first IVT controls vehicle

speed by varying the IVT ratio while letting the engine run at optimum efficiency withlow emissions and low fuel consumption. During this time, the other IVT tracks thedifferential speed and adjusts the ratio to match the current flywheel battery rpm. In otherwords, the driver determines the acceleration rate and the IVT gets the feedback from the

accelerator pedal to use the energy from the flywheel battery. When the driver brakes, theother IVT controls vehicle deceleration by adjusting the IVT ratio to charge the flywheel

battery. Concurrently, the first IVT tracks the differential speed and adjusts the IVT ratio tomatch engine rpm.

Tracking engine rpms in this manner also allows recovering the normal engine brakingenergy down to zero vehicle speed or zero differential rpm. This is possible because bothTelam IVTs have a geared neutral. The Telam brake regenerative system is the primaryvehicle-brake system. Note that this is not possible with current hybrid-electric-brakingregenerative systems because they are severely limited by the charging rate of the battery, thedifficulty of generating electrical energy at low rpms, and the efficiency of the mechanical-electrical conversion process.

Also, the Telam IVT flywheel-battery system inherently functions as a start-stop device,which most experts say provides a 10 to 15% mpg increase in city driving. The softwareshuts downs the engine at zero vehicle speed or zero differential rpm. When the driverreleases the brake pedal and pushes the accelerator pedal, an IVT adjusts the IVT ratio tomatch the vehicle acceleration, which is determined by the stored energy from the flywheel

battery. The other IVT tracks the differential speed and adjusts the IVT to the engine startingrpm, which enables engine ignition and fuel. Control of the vehicles speed switches to the

first IVT when the engine is running and the accelerator produces a constant speed instead ofacceleration. This switch would happen sooner when the flywheel battery is depleted ofstored energy.

In addition to automobiles, Telam IVTs target applications presently using hydrostatictransmissions such as lawn tractors, skid-steering vehicles, and recreation vehicles. Other

applications might include wind generators, which could be controlled for 60 cycles atvarious blade speeds. Similarly, stationary generator engines under low loads could run atidle rpm while the generator runs at 60-cycle speed. This would save fuel at low electricalloads


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5.CONCLUSIONS

This is show the time period for which engine runs at optimum speed for a ManualTransmission and anInfinitely Variable Transmission.

Initially increase in speed is due to change of engine speed only then once engine reachesoptimum speed gear ratios change to give increase in velocity while engine constantly runs atoptimum speed.

Manual Transmission provides fixed gear ratios in forward direction while CVT provides

infinite ratios in forward direction, on contrary IVT gives infinite gear ratios in both forward& backward direction.

IVT is a positive drive system. As compared to conventional transmission systems that usefriction between belt and pulley or that between toroidal rollers for motion, IVT uses gearsthus no frictional and slip losses.

Because the IVT does not have discrete ratio steps, it can run the engine at optimumconditions at all times for fuel economy and emissions.

As planetary gear system is used in IVT, engine is in continuous contact with gear even atzero output thus eliminating wastage of fuel during shifting of gears as in manualtransmission.


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Also this mechanism eliminates sudden engagement of engine to gear assembly thus reducingwear & tear of gear

Due to the geared neutral feature of the IVT, the running engine can be directly connected tothe road wheels whilst the vehicle is stationary. There is no need for a separate starting device

such as an inefficient torque converter. IVT provides a better acceleration due to change of gear ratio rather than fixed ratio inManual Transmission.

IVT provides a quieter and smoother operation as compared to conventional drives. IVT has 50% lesser number of components than other transmission so reducing maintenance.

As shown above, d drive IVT gives the lowest fuel consumption for a given amount of run.

IVT uses 1/3 less amount of fuel during idling due to absence of torque converter or start-up

clutches.

Figure 12 Comparison of different drives by e3k


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6. DRAWBACKS OF IVT

IVTs constantly change their drive ratio, acting as the equivalent of an automatictransmission with thousands or millions of gears. Because the transmission changes are sosmooth, they lack the shift feel that accompanies the process of shifting through the four tosix gears on most automatic transmissions. Because of this, many drivers believe that theyfeel unnatural.

Considering Ddrive, it is not failsafe because if motors fail or locks then instead of stoppingit goes to maximum forward mode.

Life of Transmission system is decided by the precision of the alignment of gear assemblybecause a slight misalignment causes a large amount of stress on gear train which reduces theservice life of the system.

Though the name suggests infinite number of gear ratios, practically very high, but finitenumber of gear ratios are obtained.


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7. APPLICATIONS OF IVT

1. Torotrak Full toroidal variatorviis used in a concept car called PIXEL developed by TATA and

inspired from NANO. Figure on right side is cut away view of the transmission system

designed for PIXEL.

Figure 16 cutaway view of IVT used by JOHN DEERE

2. IVT has been used by JOHN DEERE in there earth movers and Farm movers. Figure on above

is the cutaway view of transmission system used by JOHN DEERE.

3. Figure on right is Eclipse Gearboxthat is used for wind turbine applications.

Figure 14 TATA Pixel concept car Figure 13 TOROTRAK IVT used in TATA Pixel

Figure 15 ECLIPSE GEARBOX for windmills


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Figure 17 TOYOTA PRIUS Hybrid using HSD

4. Another application of IVT is when used as power split drive as in Toyota Prius.

5. Torotrak is a UK-based spin-off of Rover/Leyland/BTG, who have taken up the mantle ofUK toroidal IVT development from Perbury.

6. Carraro of Italy have signed a license enabling them to develop the IVT for medium-sized

off-highway (agriculture and construction) and on-highway (bus and truck) applications.

7. Torotrak have also demonstrated the transmission in a 5.4L Ford Explorer SUV (SportsUtility Vehicle) and on FORD Mondeo showing successful results.


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8. REFERENCES

1. Zero-Max Adjustable speed drives,http://www.zero-max.com/adjustable-speed-drives-c-

21-l-en.html

2. Torotrac full toroidal Infinitely variable Transmission,http://www.torotrak.com/content/97/infinitely-variable-transmission-(ivt).aspx

3. Dr Ben McGarry,Report on ENGINEERING ASSESSMENT OF IVT CONCEPT, e3kA division of Gilmore Engineers Pty Ltd DBG:BM:208320,

http://infinitelyvariabletransmission.com.au/ivt/the-technology/

4. Terry Lestar,Solving the Gearbox Reliabilty Problem , LESTRAN ENGINEERING.

5. Case study of TOYOTA Prius Hybrid Synergy Drive, www.toyotacars.com

6. Gilmore, D.B., (1988) Fuel economy goals for future powertrain and engine options.International Journal of Vehicle Design, Vol. 9, no. 6, pp. 616-631. UK.

7. Bosch (2004)Bosch Automotive Handbook, 6th ed., Plochingen, Germany.

i

Case Study of TOYOTA Prius HSD,www.toyotacars.comiiZero-Max Adjustable speed drives,http://www.zero-max.com/adjustable-speed-drives-c-21-l-

en.htmliiiTorotrac full toroidal Infinitely variable Transmission,

http://www.torotrak.com/content/97/infinitely-variable-transmission-(ivt).aspxivDr Ben McGarry,Report on ENGINEERING ASSESSMENT OF IVT CONCEPT, e3k Adivision of Gilmore Engineers Pty Ltd DBG:BM:208320,

http://infinitelyvariabletransmission.com.au/ivt/the-technology/v Case study of TOYOTA Prius Hybrid Synergy Drive, www.toyotacars.com

viTorotrac full toroidal Infinitely variable Transmission,

http://www.torotrak.com/content/97/infinitely-variable-transmission-(ivt).aspx
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