Design and Operation of a Rotatable Valve Cam to Improve the Efficiency of a Hydraulic Motor in an Inline Hydro-Mechanical Transmission

Abstract

Traditional Hydro-mechanical transmissions (HMTs) split transmitted power between hydraulic and mechanical channels, which allows them to maintain continuously variable transmission ratios while achieving higher efficiency than hydrostatic transmissions. The Hondamatic inline HMT (iHMT) reduces the size, cost, and complexity associated with traditional HMTs through an inline design that eliminates gears. However, previous work has demonstrated power efficiencies in the Hondamatic of $74-86\%$ over a range of operating conditions. In this thesis a simulation is used to model dynamics in the Hondamatic iHMT and to identify non-optimal pre-compression and decompression in the motor cylinders as a major cause of power loss. A rotatable cam for the motor cylinder valves and a strategy for its use in conjunction with an adjustable swashplate are invented and developed with the goal of improving efficiency over a wide range of operating conditions. A hydraulic test stand for the Hondamatic iHMT is built in order to evaluate the rotatable cam and associated strategy by comparing its performance to the baseline. Results of the performance testing are presented and average power efficiency improvements of $6.8\%$ and $9.8\%$ are demonstrated using two different cam profiles. Trends in actual and simulated performance using the baseline cam and rotatable cams are analyzed and used to draw conclusions. Advantages and shortcomings of the rotatable cam technology are discussed and recommendations for future work are presented.