ivt infinite variable transmission

STUDY OF INFINITELY VARIABLE TRANSMISSION

A SEMINAR REPORT ON

“STUDY OF INFINITELY VARIABLE TRANSMISSION”

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 INFINITELY VARIABLE TRANSMISSION SYSTEMS” submitted by Mr. MIHIR H PATEL in partial fulfillment of the requirement for award of the degree in B.TECH of Sardar Vallabhbhai National Institute Of Technology, Surat is record of his own work carried out under my supervision and guidance. The matter enclosed here is not been submitted elsewhere 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 Rathod for 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 Contents 1. INTRODUCTION ....................................................................................................................................... 5 2. WHAT IS CVT ? ........................................................................................................................................ 5 3. INFINITELY VARIABLE TRANSMISSION ................................................................................................... 6 3.1. KEY ELEMENTS OF IVT……………………………………………………………………………………………………………………….6 3.2. WORKING FORMULA FOR PLANETARY GEAR SET………………………………………………………………………………7 4. VARIANTS OF IVT .................................................................................................................................... 8 4.1. ZERO-MAX DRIVE……………………………………………………………………………………………………………………………….8 4.2. TOROTRAK INFINITELY VARIABLE TRANSMISSION…………….……………………………………………………………..9 4.3. D DRIVE TECHNOLOGY . ………………………………………………………………………………………………………………10 4.4. HYBRID SYNERGY DRIVE ...……………………………………………………………………………………………………………11 4.5. TELAM CONSTANT GEAR MESH IVT…………………………………………………………………………………………………13 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 space and 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. IVT is an acronym for Infinitely Variable Transmission. IVT falls under the category of Continuously Variable Transmission (CVT). The IVT dates back to before the 1930s; the original design converts rotary motion to oscillating motion and back to rotary motion using roller clutches. The stroke of the intermediate oscillations is adjustable, varying the output speed of the shaft. 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 (low gear) 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 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 a normal 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. First let us understand what is a CVT?

2. WHAT IS CVT ?

CVT stands for Continuously Variable Transmission. CVT was originally conceptualized by Famous Artist Leonardo Da Vinci in the back 1490‟s1. Allowing an engine to operate within its highefficiency or high-power range maximizes fuel economy or performance, and in a geared manual or automatic transmission this is best achieved by having a large number of gears. Transmissions with 7-speeds and even 8-speeds are becoming available in passenger-car market, for example, to maximize efficiency and/or performance over wide range of vehicle speeds. An alternative strategy to having a large number of discrete gears is to use a transmission that enables a continuouslyvariable transmission ratio. A continuously variable transmission or CVT can achieve an optimum matching between engine and load 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 the engine can be operating at a fixed speed. Use of a CVT allows an engine to run at optimum power or efficiency over a vehicle‟s entire range of load conditions. This can improve economy, comfort, emissions and durability. It also provides improved performance by avoiding gear changes, which interrupt 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 variablespeed element cannot typically generate torque at zero or very low wheel speeds. The basic difference between CVT and conventional manual or automatic drive trains is number of effective gear 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 a conventional gearbox with its fixed gear ratios.

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Information 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 of output 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 a normal 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 known as an epicyclic gear system) which enforces an IVT output shaft rotation speed which is equal to the difference between two other speeds within the IVT. This IVT configuration uses its CVT as a continuously 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/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.

3.1.

KEY ELEMENTS OF IVT:



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



The variator. The variator is the means by which the IVT can deliver an infinite range of ratios. It affects the speed of rotation of the sun gear in the epicyclic and is responsible for the smooth 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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STUDY OF INFINITELY VARIABLE TRANSMISSION  Controller: instead of using variator or splitting input power, another source of motion is supplied and the variation in its speed decides the output.

Figure 2 Alternate Configuration of IVT

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 RPM WR= RPM of layshaft WS= input RPM = Win

Figure 3 Planetary gear set with a CVR

What will be the IVT output speed?

What will be the IVT overall ratio?

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4. VARIANTS OF IVT 4.1. Zero-Max driveii  Zero-max drives are the conventional type of IVTs that convert rotary motion to Oscillatory and again back to rotary.  Externally, the ZeroMax Drive consists of a rugged, sealed cast case, an input shaft, output shaft and speed control.  Speed of the output shaft is regulated precisely and easily through a control lever which includes a convenient locking mechanism or a screw control to hold speed at a desired setting. Models are available with output in clockwise or counterclockwise rotation to meet individual speed control requirements.  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 they move back and forth successively. The number of strokes per clutch per minute is determined by the input speed. Since one rotation of the input shaft causes each clutch to move back and forth once, it is readily apparent that the input speed will determine the number 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 output shaft is urged 7200 times per minute (1800 x 4) or 120 times per second (7200 ÷ 60). If the input speed is dropped to 900 RPM, the shaft is urged only 3600 times per minute and the maximum output speed will be cut in half.

Figure 4 Link Mechanism of Zero to Max Drive

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STUDY OF INFINITELY VARIABLE TRANSMISSION  Looking at Figure 1, the input section, consisting of a shaft (A), eccentrics (B), and connecting rods (C), converts rotary motion into linear motion. At the zero setting, the main 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 rotary motion 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 produced because the direction of throw of the connecting rod is altered from vertical (Figure 1 zero RPM position) toward horizontal (Figure 2 maximum speed position), varying the length of the 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 an infinite 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 discs forms 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 output discs (shown in yellow) located in the centre.

Figure 5 Roller arrangement of Torotrak IVT Figure 6 Full Transmission System of Torotrak IVT

 The variator is the heart of the IVT and is the means by which the IVT can deliver an infinite 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 discs forms 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 output discs (shown in yellow) located in the centre. 9

STUDY OF INFINITELY VARIABLE TRANSMISSION  Each roller is attached to a hydraulic piston. The pressure in the pistons can be increased or 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-metal contact. 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 long chain molecules used in traction fluid interlock with each other when the fluid is compressed, becoming highly viscous (glassy) under pressure. This means that as pressure is exerted at the contact points between the rollers and the discs the oil resists the tendency to slide and transmits the power effectively. 4.3.

D Drive Technologyiv

Figure 7 d drive block diagram

 D Drive is an Infinitely Variable Transmission system designed by Steve Durnin. Here instead of using Continuously Variable Transmission (CVT) as a Continuously Variable Regulator (CVR), an electric motor is used as CVR to regulate the speed of vehicle.  D‟drive uses one epicyclic gear set and one eccentric gear arrangement to vary the speed in both forward and reverse direction.  Input is connected to eccentric gear(differential A) which in turn is connected to two shafts that are controlled by motors which then forward the power to epicyclic gear arrangement(differential B) which differentiates the speed.  Now for example if upper shaft is rotating and lower shaft is stationary output is maximum forward, while if upper shaft is stationary then lower shaft speeds up giving maximum reverse, on contrary if both shafts are rotating at same speed in opposite direction then the is no output giving geared neutral. The motion here is self compensated in the epicyclic gear arrangement.  In D drive technology output speed is the result of the variation in two control speeds and the actual speed of the main source(ICE).

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STUDY OF INFINITELY VARIABLE TRANSMISSION 4.4.

Hybrid Synergy Drivev

 HSD replaces the gear box, alternator and starter motor with a pair of electrical motorgenerators (MG), a computerized shunt system to control them, a mechanical power splitter that 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.

Figure 8 Block Diagram of Hybrid Synergy Drive

 The HSD works by shunting electrical power between the two motor generators and the battery pack to even out the load on the gasoline engine. Since a power boost is available for periods of acceleration, the gasoline engine can be sized to match only the average load on the car, rather than its peak load: this saves fuel because smaller engines are more power efficient.  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 off the internal combustion engine when the electric motor is sufficient to provide the power as shown in figure 8.

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Figure 9 Acceleration characteristic for manual vs HSD

Red line = acceleration of a vehicle with IC petrol engine Green line = acceleration of a combined HEV

Figure 10 Split Power mechanism in HSD

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STUDY OF INFINITELY VARIABLE TRANSMISSION 4.5.

TELAM CONSTANT GEAR MESH IVT

 The Telam constant-gear-mesh infinitely variable transmission (IVT) from Tom Troester is a special 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. This lets the engine run at its most efficient rpm while varying the vehicle speed.It has been known for decades in the automotive industry that a CVT increases fuel mileage. In fact, several are in use today. All — excluding ones with supplemental motor planetary systems — are variations of the Van Doorne design.  The Van Doorne design is essentially a belt drive with two pulleys, each of which has a variable diameter. The simple belt drive relies on friction, which limits its use in automobiles as 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 further increase torque capacity, which reduces efficiency.  Additionally, pending CAFÉ standards to boost vehicle mpg are pushing automotive manufacturers to develop six, seven, eight, and nine-speed transmissions. These are either dual-clutch transmissions (DCT) or conventional multistage planetary gear transmissions with a torque converter. Both types are complex, heavy, and expensive to manufacture.

Figure 11 Conical Planetary Gear Box in Telam IVT

 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 a geared neutral inherent in the design, making it what‟s called an infinitely variable transmission (IVT).  The design uses special cone gears in one planetary stage. The cone gears incorporate an involute 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 on different cone diameters, which varies the output ratio and direction of rotation.  To better understand the geared neutral and reverse rotation, consider a normal two-stage planetary transmission. Like the Telam IVT, the output shaft receives two inputs. One comes from 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 the rotation of the cone gears about their axis, from one rotation of the input shaft/cone carrier, 13




  







imparts one rotation of the output shaft, this is defined as geared neutral. Because the cones rotate in the opposite direction of the input shaft, the gear train yields a zero output-shaft rotation. This feature also explains the integral reverse, which is just the adjustable internal ring gear moving 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 11speed conventional automotive transmission. The Telam IVT‟s 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 with low emissions and low fuel consumption. During this time, the other IVT tracks the differential speed and adjusts the ratio to match the current flywheel battery rpm. In other words, 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, the other 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 to match engine rpm. Tracking engine rpms in this manner also allows recovering the normal engine braking energy down to zero vehicle speed or zero differential rpm. This is possible because both Telam IVTs have a geared neutral. The Telam brake regenerative system is the primary vehicle-brake system. Note that this is not possible with current hybrid-electric-braking regenerative systems because they are severely limited by the charging rate of the battery, the difficulty of generating electrical energy at low rpms, and the efficiency of the mechanicalelectrical 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 software shuts downs the engine at zero vehicle speed or zero differential rpm. When the driver releases the brake pedal and pushes the accelerator pedal, an IVT adjusts the IVT ratio to match 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 starting rpm, which enables engine ignition and fuel. Control of the vehicle‟s speed switches to the first IVT when the engine is running and the accelerator produces a constant speed instead of acceleration. This switch would happen sooner when the flywheel battery is depleted of stored energy. In addition to automobiles, Telam IVTs target applications presently using hydrostatic transmissions such as lawn tractors, skid-steering vehicles, and recreation vehicles. Other applications might include wind generators, which could be controlled for 60 cycles at various blade speeds. Similarly, stationary generator engines under low loads could run at idle rpm while the generator runs at 60-cycle speed. This would save fuel at low electrical loads

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5. CONCLUSIONS

 This is show the time period for which engine runs at optimum speed for a Manual Transmission and an Infinitely Variable Transmission.  Initially increase in speed is due to change of engine speed only then once engine reaches optimum speed gear ratios change to give increase in velocity while engine constantly runs at optimum 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 use friction between belt and pulley or that between toroidal rollers for motion, IVT uses gears thus no frictional and slip losses.  Because the IVT does not have discrete ratio steps, it can run the engine at optimum conditions at all times for fuel economy and emissions.  As planetary gear system is used in IVT, engine is in continuous contact with gear even at zero output thus eliminating wastage of fuel during shifting of gears as in manual transmission.

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STUDY OF INFINITELY VARIABLE TRANSMISSION  Also this mechanism eliminates sudden engagement of engine to gear assembly thus reducing wear & tear of gear  Due to the geared neutral feature of the IVT, the running 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.  IVT provides a better acceleration due to change of gear ratio rather than fixed ratio in Manual 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.

Figure 12 Comparison of different drives by e3k

 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.

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6. DRAWBACKS OF IVT  IVTs constantly change their drive ratio, acting as the equivalent of an automatic transmission with thousands or millions of gears. Because the transmission changes are so smooth, they lack the shift feel that accompanies the process of shifting through the four to six gears on most automatic transmissions. Because of this, many drivers believe that they feel unnatural.  Considering D‟drive, it is not failsafe because if motors fail or locks then instead of stopping it goes to maximum forward mode.  Life of Transmission system is decided by the precision of the alignment of gear assembly because a slight misalignment causes a large amount of stress on gear train which reduces the service life of the system.  Though the name suggests infinite number of gear ratios, practically very high, but finite number of gear ratios are obtained.

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7. APPLICATIONS OF IVT

Figure 14 TATA Pixel concept car

Figure 13 TOROTRAK IVT used in TATA Pixel

1. Torotrak Full toroidal variatorvi is 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 Figure 15 ECLIPSE GEARBOX for windmills

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 Gearbox that is used for wind turbine applications.

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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 of UK 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 (Sports Utility 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-c21-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, e3k A 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.com Zero-Max Adjustable speed drives, http://www.zero-max.com/adjustable-speed-drives-c-21-len.html iii Torotrac full toroidal Infinitely variable Transmission, http://www.torotrak.com/content/97/infinitely-variable-transmission-(ivt).aspx iv Dr Ben McGarry, Report on ENGINEERING ASSESSMENT OF IVT CONCEPT, e3k A division 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 vi Torotrac full toroidal Infinitely variable Transmission, http://www.torotrak.com/content/97/infinitely-variable-transmission-(ivt).aspx ii

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ivt infinite variable transmission

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