CONTENTS

1. Introduction2. Continuously Variable Transmission (CVT)3. Conversion of a CVT into an IVT4. Infinitely Variable Transmission6. Conclusion7. References

1. INTRODUCTION

After more than a century of research and development, the gear transmission is nearing both perfection and obsolescence: engineers continue to explore the outer limits of efficiency and performance. Attempts have been made to overcome these limitations through replacing the sources of friction with mechanisms to duplicate their functions. This leads to the development of PIV. PIV is an infinitely variable transmission which is a sub category of continuously variable transmission, which has got many industrial applications especially in Textile Industries, Packaging & Corrugating Industries, Food Processing Industries, Rubber Machinery, Rotary Printing Machinery, and Chemical & Pharmaceuticals. It is a step less speed control. It is mainly a chain drive. It contains sprockets which are two pairs of wheels. It is mounted on splined shafts which are radically grooved and cone shaped. Chains are such that chain links contain self-tooth-forming hardened steel slats.

2. CONTINUOUSLY VARIABLE TRANSMISSION (CVT)

After more than a century of research and development, the internal combustion (IC) engine is nearing both perfection and obsolescence: engineers continue to explore the outer limits of IC efficiency and performance, but advancements in fuel economy and emissions have effectively stalled. While many IC vehicles meet Low Emissions Vehicle standards, these will give way to new, stricter government regulations in the very near future. With limited room for improvement, automobile manufacturers have begun full-scale development of alternative power vehicles. Still, manufacturers are loath to scrap a century of development and billions or possibly even trillions of dollars in IC infrastructure, especially for technologies with no history of commercial success. Thus, the ideal interim solution is to further optimize the overall efficiency of IC vehicles.

One potential solution to this fuel economy dilemma is the continuously variable transmission (CVT), an old idea that has only recently become a bastion of hope to automakers. CVTs could potentially allow IC vehicles to meet the first wave of new fuel regulations while development of hybrid electric and fuel cell vehicles continues. Rather than selecting one of four or five gears, a CVT constantly changes its gear ratio to optimize engine efficiency with a perfectly smooth torque-speed curve. This improves both gas mileage and acceleration compared to traditional transmissions.

The fundamental theory behind CVTs has undeniable potential, but lax fuel regulations and booming sales in recent years have given manufacturers a sense of complacency: if consumers are buying millions of cars with conventional transmissions, why spend billions to develop and manufacture CVTs?

Although CVTs have been used in automobiles for decades, limited torque capabilities and questionable reliability have inhibited their growth. Today, however, ongoing CVT research has led to ever-more robust transmissions, and thus ever-more-diverse automotive applications. As CVT development continues, manufacturing costs will be further reduced and performance will

continue to increase, which will in turn increase the demand for further development. This cycle of improvement will ultimately give CVTs a solid foundation in the world’s automotive infrastructure.

2.1 Background and History

To say that the continuously variable transmission (CVT) is nothing new would be a gross understatement: Leonardo da Vinci sketched his idea for CVT in 1490. In automotive applications, CVTs have been around nearly as long as cars themselves, and certainly as long as conventional automatics. General Motors actually developed a fully toroidal CVT in the early 1930s and conducted extensive testing before eventually deciding to implement a conventional, stepped-gear automatic due to cost concerns. General Motors Research worked on CVTs again in the 1960s, but none ever saw production . British manufacturer Austin used a CVT for several years in one of its smaller cars, but “it was dropped due to its high cost, poor reliability, and inadequate torque transmission” . Many early CVTs used a simple rubber band and cone system, like the one developed by Dutch firm Daf in 1958.

However, the CVT could only handle a 0.6 L engine, and problems with noise and rough starts hurt its reputation. Uninspired by these early failures, automakers have largely avoided CVTs until very recently, especially in the United States.

2.2 CVT Theory and Design

Today’s automobiles almost exclusively use either a conventional manual or automatic transmission with “multiple planetary gear sets that use integral clutches and bands to achieve discrete gear ratios” . A typical automatic uses four or five such gears, while a manual normally employs five or six. The continuously variable transmission replaces discrete gear ratios with infinitely adjustable gearing through one of several basic CVT designs.

Push Belt

This most common type of CVT uses segmented steel blocks stacked on a steel ribbon, as shown in Figure (1). This belt transmits power between two conical pulleys, or sheaves, one fixed and one movable . With a belt drive:

In essence, a sensor reads the engine output and then electronically increases or decreases the distance between pulleys, and thus the tension of the drive belt. The continuously changing distance between the pulleys—their ratio to one another—is analogous to shifting gears. Push-belt CVTs were first developed decades ago, but new advances in belt design have recently drawn the attention of automakers worldwide.

Toroidal Traction-Drive

These transmissions use the high shear strength of viscous fluids to transmit torque between an input torus and an output torus. As the movable torus slides linearly, the angle of a roller changes relative to shaft position, as seen in Figure (2). This results in a change in gear ratio.

Variable Diameter Elastomer Belt

This type of CVT, as represented in Figure (2), uses a flat, flexible belt mounted on movable supports. These supports can change radius and thus gear ratio. However, the supports separate at high gear ratios to form a discontinuous gear path, as seen in Figure (3). This can lead to the problems with creep and slip that have plagued CVTs for years .

This inherent flaw has directed research and development toward push belt CVTs.

2.3 Inherent Advantages & Benefits

Certainly, the clunk of a shifting transmission is familiar to all drivers. By contrast, a continuously variable transmission is perfectly smooth—it naturally changes “gears” discreetly and minutely such that the driver or passenger feels only steady acceleration. In theory, a CVT would cause less engine fatigue and would be a more reliable transmission, as the harshness of shifts and discrete gears force the engine to run at a less-than-optimal speed.

Moreover, CVTs offer improved efficiency and performance. Table (1) below shows the power transmission efficiency of a typical five-speed automatic, i.e. the percentage of engine power translated through the transmission. This yields an average efficiency of 86%, compared to a typical manual transmission with 97% efficiency. By comparison, Table (2) below gives 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. Moreover:

Because the CVT allows an engine to run at this most efficient point virtually independent of vehicle speed, a CVT equipped vehicle yields fuel economy benefits when compared to a conventional transmission. Testing by ZF Getriebe GmbH several years ago found that “the CVT uses at least 10% less fuel than a 4- speed automatic transmission” for U.S. Environmental Protection Agency city and highway cycles.

Moreover, the CVT was more than one second faster in 0-60 mph acceleration tests . The potential for fuel efficiency gains can also be seen in the CVT currently used in Honda’s Civic. A Civic with a traditional automatic averages 28/35 miles per gallon (mpg) city/highway, while the same car with a CVT gets 34/38 mpg city/highway. Honda has used continuously variable transmissions in the Civic for several years, but these are 1.6 liter cars with limited torque capabilities. Ongoing research and development will inevitably expand the applicability of CVTs to a much broader range of engines and automobiles.

CVTs can compensate for changing vehicle speeds, allowing the engine speed to remain at its level of peak efficiency. This improves fuel economy and by effect, exhausts emissions. CVTs operate smoothly since there are no gear changes which cause sudden jerks. Very few problems have been reported with the CVT transmission, lowering cost of ownership. There are 25% fewer moving parts to a CVT transmission It is also cheaper to repair. The fluids do not have to be changed as often as automatic transmission Disadvantages Many early CVT driven cars had disappointing performance. The original Ford Fiesta 1.1 CTX, for example, used 8.2 percent more gasoline than the manual transmission version in city driving. CVTs operate smoothly. This can give a perception of low power, because many drivers expect a jerk when they begin to move the vehicle. The expected jerk of a non-CVT can be emulated by CVT control software though, eliminating this marketing problem.

Since the CVT keeps the engine turning at constant RPM over a wide range of vehicle speeds, pressing on the accelerator pedal will make the car move faster but doesn't change the sound coming from the engine as much as a conventional automatic transmission gear-shift. This confuses some drivers and, again, leads to an impression of a lack of power.

CVT torque handling capability is limited by the strength of their transmission medium (usually a belt or chain), and by their ability to withstand friction wear between torque source and transmission medium for friction-driven CVTs. CVTs in production prior to 2005 are predominantly belt or chain driven and therefore typically limited to low powered cars and other light duty applications. Units using advanced lubricants, however, have been proven to support any amount

of torque in production vehicles, including that used for buses, heavy trucks, and earth moving equipment.

Because automotive CVTs are automatic, they are stigmatized in some regions; while automatic transmissions are common in the Americas, places such as southern Europe do not generally accept automatic transmissions of any kind. Japan with its generally smaller cars and stop-and-go traffic, has proven a much better market for CVT driven cars.

2.4 Applications

Tractors just as cars have the need for a flexible system to convey power from their engine to their wheels. The C.V.T. will provide just this and at high fuel savings with low atmospheric pollution.

Golf Carts stand to benefit from the C.V.T. as well in the way electric cars do. that is: Large range of speeds, longer driving range between charges, Fewer batteries, lower maintenance cost, less weight.

Motorized Wheelchairs. Battery run, speed controlled by a rheostat. Going up a ramp slowly causes a drop in power (when it's most needed). C.V.T. is a form of transmission, lower speed means MORE POWER.

Bicycles. Ever try to shift gears while pedaling uphill? Good news; the KINESIS C.V.T. will automatically select the appropriate for the situation "gear" ratio. No hassle, no trouble. End of story.

Power tools and household appliances, that vary from bench top drills to wash machines and blenders need to depart from the centuries old belt and pulley configuration for smoother operation and more reliability.

Industrial Equipment and production machinery often use either gears or cumbersome belt and pulley configurations. C.V.T. can do away with all that and additionally give them infinite ratios.

Mini machines Small devices that need to operate in a wide range of speeds, as the need arises. Our unique design allows the production of an inexpensive miniature C.V.T. to enable them do just those.

2.5 Challenges & Limitations

CVT development has progressed slowly for a variety of reasons, but much of the delay in development can be attributed to a lack of demand: conventional manual and automatic

transmissions have long offered sufficient performance and fuel economy. Thus, problems encountered in CVT development usually stopped said progress. “Designers have … unsuccessfully tried to develop [a CVT] that can match the torque capacity, efficiency, size, weight, and manufacturing cost of step-ratio transmissions”. One of the major complaints with previous CVTs has been slippage in the drive belt or rollers.

This is caused by the lack of discrete gear teeth, which form a rigid mechanical connection between to gears; friction drives are inherently prone to slip, especially at high torque. With early CVTs of the 1950s and 1960s, engines equipped with CVTs would run at excessively high RPM trying to “catch up” to the slipping belt. This would occur any time the vehicle was accelerated from a stop at peak torque: “For compressive belts, in the process of transmitting torque, micro slip occurs between the elements and the pulleys. This micro slip tends to increase sharply once the transmitted torque exceeds a certain value …”

For many years, the simple solution to this problem has been to use CVTs only in cars with relatively low-torque engines. Another solution is to employ a torque converter (such as those used in conventional automatics), but this reduces the CVT’s efficiency.

Perhaps more than anything else, CVT development has been hindered by cost. Low volume and a lack of infrastructure have driven up manufacturing costs, which inevitably yield higher transmission prices. With increased development, most of these problems can be addressed simply by improvements in manufacturing techniques and materials processing. For example, Nissan’s Extroid “is derived from a century-old concept, perfected by modern technology, metallurgy, chemistry, electronics, engineering, and precision manufacturing”.

In addition, CVT control must be addressed. Even if a CVT can operate at the optimal gear ratio at any speed, how does it “know” what ratio to select? Manual transmissions have manual controls, where the driver shifts when he or she so desires; automatic transmissions have relatively simple shifting algorithms to accommodate between three and five gears. However, CVTs require far more complex algorithms to accommodate an infinite division of speeds and gear ratios.

2.6 CVT Varieties

Several other types of CVTs have been developed over the course of automotive history, but these have become less prominent than push belt and toroidal CVTs. A mutating traction drive uses a pivoting, conical shaft to change “gears” in a CVT. As the cones change angle, the inlet radius decreases while the outlet radius increases, or vice versa, resulting in an infinitely variable gear ratio. A variable geometry CVT uses adjustable planetary gear-sets to change gear ratios, but this is more akin to a flexible traditional transmission than a conventional CVT.

2.7 Existing CVT Designs

• Ratcheting • Hydrostatic • Toroidal • V-Belt & Pulley • Infinitely Variable Transmission (IVT)

3. CONVERSION OF A CVT INTO AN IVT

CVTs only provide positive ratios. Therefore, a reverse gear and a clutch (or a torque converter) is necessary. IVTs (Infinitely Variable Transmissions) provide a full range of ratio from reverse, through stationary, and from extremely low speeds, up to high overdrive. The engine is permanently connected to wheels. Clutch and reverse gear are not required.

- Fig 4

A planetary gear set (epicyclic) can be used to convert a CVT into a IVT by power split.The planetary gear set "subtracts some RPMs" from the CVT output. Thus, the overall ratio spread can be freely customized.

The planetary gear set formula:

WP × (DR + DS) = WR × DR - WS × DS

(W: angular velocities; D: primitive diameters)

.

Fig 5 CVT with planetary gear set

Fig 6 CVT with epicyclic gear set

3.1 Determination of IVT speed:

(Win = engine speed ; Rcvt = CVT ratio)

What will be the IVT overall ratio?

(Ratios are input speed/output speed )

3.2 Six combinations of a CVT and a planetary gear set:

IVT is a combination of CVT with an epicyclic gear system (power split).The different combinations of a CVT and a planetary gear set are as shown below. The input can be given to planets, sun gear or to ring gear and the out put can also be taken from these three gears. The input and and the output can be interchanged so that we can get six different combination for an effective IVT.

Fig 7 Different combination of CVT and planetary gear set.

4. INFINITELY VARIABLE TRANSMISSION (IVT) A specific type of CVT is the infinitely variable transmission (IVT), in which the range of ratios of output shaft speed to input shaft speed includes a zero ratio that can be continuously approached from a defined "higher" ratio. A zero output speed with a finite input speed implies an infinite input-to-output speed ratio, which can be continuously approached from a given finite input value with an IVT. Low gears are a reference to low ratios of output speed to input speed. This 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,

although, unlike neutral in a normal automotive transmission, the output torque may be non-zero: the output shaft is rigidly fixed at zero speed rather than being freely rotating.

Most IVTs result from the combination of a CVT with an epicyclic gear system (which is also known as a planetary gear system) which enforces an output shaft rotation speed which is equal to the difference between two other speeds. If these two other speeds are the input and output of a CVT, there can be a setting of the CVT that results in an output speed of zero. The maximum output/input ratio 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.

IVTs can in some implementations offer better efficiency when compared to other CVTs as in the preferred range of operation because most of the power flows through the planetary gear system and not the controlling CVT. Torque transmission capability can also be increased. There's also possibility to stage power splits for further increase in efficiency, torque transmission capability and better maintenance of efficiency of a wide gear ratio range.

An example of a true IVT is the Hydristor because the front unit connected to the engine can displace from zero to 27 cubic inches per revolution forward and zero to -10 cubic inches per revolution reverse. The rear unit is capable of zero to 75 cubic inches per revolution.

The IVT moves away from the constraints of stepped ratio automatic transmissions and unlike Continuously Variable Transmissions there is no torque limitation. The ratio range is provided not by a system of gears, as found in a conventional automatic transmission, but by a variator which consists of a set of discs and rollers.

The IVT technology allows control of the complete power train enabling optimisation of the efficiency of the engine. In conventional transmissions the engine and transmission are controlled separately.

The IVT is torque controlled rather than ratio controlled. The software determines the torque required at the road wheels and then requests torque from the transmission rather than setting a specific ratio. The engine can then be used to deliver the power at its most efficient operating point. In conventional automatics where the gear ratios are fixed the engine only runs at its most efficient operating points for short periods of time.

This optimisation of the entire power train brings about a fuel economy benefit in three ways:

Due to the geared neutral feature of the IVT the engine can be directly connected to the road wheels whilst the vehicle is stationary. There is no need for a separate starting device such as an inefficient torque converter.

Due to its wide ratio spread the IVT provides the ability for the engine to run at a high overdrive of 74mph/1000rpm.

Because the IVT does not have discrete ratio steps it can run the engine at optimum conditions for fuel economy and emissions.

Fig 8 An IVT Machine

An IVT machine includes an input shaft, a drive wheel on the input shaft, an output shaft, a ratio changing device which is mounted on the output shaft, an endless belt which passes over the drive wheel and in an open loop on the ratio changing device, control elements for enlarging and reducing the belt loop dimension about the output shaft axis, belt guide elements providing a throat through which the belt enters and leaves its loop on the ratio changing device, and a drive arrangement on the ratio changing device for the transmission of drive power to the output shaft and is engaged with the belt in a portion of its loop on the device and engageable with the belt on both sides of the throat in its transition across the throat during rotation of the ratio changing device.

4.1 Advantage:

Fixed Ratio

CVT

Input

Planetary Gear

Output

1. Improved Transmission Ratios 2. Zero TR without zero input 3. Negative TR for reverse 4. Wider range of + TR values

4.2 Components:1. V-Belt and Pulley CVT 2. Planetary Gear Train 3. Fixed Ratio Mechanism

Input Power is Split through CVT to Fixed Ratio Mechanism and Planetary Gear

4.3 Problems with current IVT Design:

Internally less efficient than manual and automatic transmissions Friction driven components for variable control

High Losses High Stresses Low Durability High Maintenance

4.4 Proposed Design Qualities:

Use high internally efficient components to achieve transmission ratios Have two separate power inputs Have both positive and negative (reverse) transmission ratios without large change in

variable controller speed Eliminate friction driven components