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Cowboy Motorsports (CMS) is the quarter-scale tractor design team from Oklahoma State University. In our efforts to design a transmission for a 16 horsepower, four-wheel drive quarterscale tractor, we have created our own Infinitely Variable Transmission (IVT).

The objective of our design was to integrate the best combination of hydraulic and drive train components to produce an IVT transmission to replace our existing belt driven continuously variable transmission (CVT) in accordance with rule changes. The IVT, which is composed of a hydraulic pump and motor mounted in parallel with a planetary gearhead, was derived from a previous CMS design. It allows the tractor to shift gears continuously during a pull to accommodate the increasing force produced by the sled as well as varying track conditions. The shifting function is produced by controlling the speed and direction of rotation of the ring gear on the planetary gearhead.

Based on consultations with hydraulic engineers in industry as well as historic quarter scale pulling data, we were able to define the requirements of our system in terms of the necessary gear reduction, required output horsepower and torque, and overall system efficiency. By knowing the gear reduction of the final drive components and the planetary gearhead, we were then able to find the necessary hydraulic components to effectively control the planetary ring gear.

Based on dynamometer tests, the IVT was over 80% efficient, and this data was reinforced during pulls at the national competition. The transmission drove the tractor to a first place finish in the pulling competition and satisfied all of the design criteria.