Feasibility of free ball traction drive (a continuously variable transmission) in automotive applications

FREE BALL TRACTION DRIVE SUMMARYThe primary function of transmission is to transmit mechanical power from power source to some form of useful output device .since the invention of the internal combustion engine, it has been the goal of transmission designers to develop more efficient methods of coupling the output of an engine to a load while allowing the engine to operate in its most efficient or highest power range. Conventional transmissions allow for the selection of discrete gear ratios, thus limiting the engine to providing maximum power or efficiency for limited ranges of output speed. A continuously variable transmission (cvt) is a type of transmission, however that allows an infinitely variable ratio change within a finite range ,thereby allowing the engine to continuously operate in its most efficient or highest performance range Continuously variable transmission have been use for many years. Near the beginning of the twentieth century, Cars like Sturtevant,cartecar,and labert featured friction dependent CVTs(puttre 1991).these friction drive CVTs were common in automotive use until engines capable of producing higher torques became common and necessitated them move to geared, fixed ratio transmissions capable of high torque transfer and having wear characteristics than friction dependent CVTs.Only in the past. Few years, with the advent of advanced materials and technology, have friction dependent CVTs returned to commercial application in the automotive industry. To provide a foundation and motivation for the research presented, the report presents a definition of continuously variable transmission. For background purposes, a review of the current literature on CVTs was included. The families in which various embodiments can be classified are presented, along with a description of the operating principles in each family. A new family of embodiments of the positive engagement classification is also presented, along with principles governing new classification. The research focused most heavily on embodiments in the final classification. It included design, development and testing of free ball traction drive as shown in the picture.Construction & workingThe major components of free ball traction drive are steel ball (1) positioned between two axially displaced hollow cones (2&3) and acts as a power transmission element.When the load is applied the transmission ball is pulled in triangle formed by two hollow cone disks by an amount equal to the elastic deformation of the parts under load. Thus the contact pressure is directly proportional to the output torque. Clockwise or counterclockwise rotation is permissible. The output speed of drive is infinitely variable and is achieved by adjusting the position of the steel ball by rotating the speed setting spindle knob (4).speed setting is permissible both at rest and in motion. In the upper adjustment position ratio of 3:1 reduction is created between input and output shaft. In the lower adjustment position the ratio is 1:3 increaser. The total speed range covered is 9:1.for speed range of 6:1, higher input horse power is possible since the output horse power is determined by lower output speed. The drive maybe used in any mounting position and can be made hermetically sealed. Power must be transmitted through the unit only in the direction shown by the arrow on the outer housing.Fig. Free ball traction drive

Operating features1. The drive is a constant horse power device but can be used as a constant torque at maximum output speed over the entire adjustment range.2. Standard speed ratios are 6:1 or 9:13. The output speeds can be upto 5400 rpm4. The drive is 85% efficient5. Speed accuracy is +/-1% of the output speed at constant load.The thesis further included design -: 1) system design and 2) mechanical design, cost analysis, observations and testing, advantages and disadvantages and applications of the drive.Experimental findings of advantages in regards automobiles:Cvts can compensate for changing vehicle speeds allowing the engine speed to remain at its level of peak power and efficiency. This improves fuel economy and reduce exhaust emissions.There are 25% fewer moving parts in transmission 20% fuel economy compared to past transmission technologies.Experimental findings of drawback in automobile operations: Become jerky at low speedsAlso, other drawbacks to overcome are Intricate parts with high material cost e.g., silicon nitride, silicon carbideDrive looks at situations, better suited for amusement vehicles.CVT is new technology so there are limited people that understand the operations with in a cvt.ConclusionFor variable speeds gearboxes are used in machine tool, but gears are having some disadvantages like high manufacturing cost, gear shifting difficulty, noisy meshing of teeth, large space requirement and are prone to backlash.On the other hand ball traction drive overcomes drawbacks of gearbox. It is smooth (step less) drive giving wide range speed variations with minimum control for speed changing.Due to these characteristics and with proper funding for research it is possible to create a fbtd satisfy automobile needs.

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