Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Agricultural Engineering


In recent years there has been a tremendous change taking place in the area of power transmission. The use of a hydrostatic transmission in place of the conventional gear-type transmission in power driven machines has increased substantially. The introduction by International Harvester Co. of a hydrostatic transmission into their fa.rm tractors has increased interest in this relatively new form of power transmission. The hydrostatic transmission was a logical next step over the increasing number of speeds offered in today’s farm tractor. A hydrostatic transmission allows the operator a choice of infinite speeds. This feature is especially important where the tractor is used for PTO work because of varying speed requirements with constant engine speed. The main disadvantage of a hydrostatic transmission is its lower efficiency of about 70 to 80 percent compared to about 90 percent for a standard gear-type transmission. At the present time not much published information exists on efficiencies of hydrostatic transmissions and the factors affecting efficiency such as load and speed. Because of this and their ever-increasing application it is necessary for technical students to become acquainted with their performance characteristics. Engineers who are considering the use of hydrostatic drives may also benefit from this study. Therefore, a hydrostatic transmission test stand was designed and built for · performance testing and demonstration. The increased use of the hydrostatic transmission in combines, windrowers, tractors; garden tractors, and construction equipment have added new interest in the area of power transmission. With the indication that the hydrostatic transmission will be used even more in the future, a better understanding of its characteristics is needed. The objectives of the study were: 1) Design and build a test stand for a small hydrostatic transmission (less than 15 HP); 2) Develop tests to evaluate the effect of input speed, pressure, temperature, and pump displacement on the efficiency of a small hydrostatic transmission; 3) Develop a laboratory exercise for use by technical students to become acquainted with the performance and characteristics of a hydrostatic transmission.

Library of Congress Subject Headings

Power transmission
Oil hydraulic machinery



Number of Pages



South Dakota State University