1977-02-01

Development of a Variable Speed Transmission for Light Tractors 770749

ABSTRACT

Traction drives date back to man's earliest attempts to transmit power. In the years following the turn of the last century many ideas for traction drive transmissions and applications were proposed. Many of these ideas were patented during this period but few became a commercial reality.

We took our first look at traction transmissions in 1961 and helped design a variable speed ball drive for automotive use. As with many traction drives, the drive was dropped because of limitations imposed by the lubricating fluid and the material used forthe drive elements.

Two major break-throughs in the past 15 years have drastically improved the capacity of traction transmissions. First, new traction fluids, developed by Monsanto and Sun Oil, improve traction by 150% over previous fluids used and increase capacity proportionally. These fluids are also excellent lubricants. Second, the use of modern bearing steels in traction drives give a 300% improvement in fatigue life. This allows higher loading on the drive elements, increasing basic transmission capacity.

Suddenly traction drive transmissions have become quiet, efficient competitors to hydraulic, electric and belt type variable speed drives.

We have developed a prototype traction transmission over the past three years. I will describe the chronological development of this variable-speed transmission from concept to final prototype design. This new transmission is a planetary traction drive coupled to a planetary gear set, yielding infinite ratio variations in forward and reverse directions.

From concept, our goal was a low cost, precision, variable speed transmission.

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