Incorporating a Rotatable Valve Cam to Improve the Efficiency of a Hydraulic Motor in an Inline Hydro-Mechanical Transmission (i-HMT)

A hydro-mechanical transmission (HMT) transmits power both hydraulically and mechanically, allowing higher efficiencies than hydrostatic transmissions while maintaining continuously variable transmission ratios. Ordinary HMTs consist of a hydraulic pump/motor pair in parallel with a mechanical transmission, but their large sizes and high costs are major disadvantages. The Hondamatic inline HMT (iHMT) significantly reduces the size, cost, and complexity of an HMT through an inline design that eliminates gears. However, low power efficiency is the principal barrier to its more widespread use. A dominant loss is throttling due to fluid compressibility and non-optimal valve timing, especially in the hydraulic motor. In this paper a method of controlling the motor displacement is proposed, using a rotatable motor valve cam and check valves in conjunction with the Hondamatic's existing adjustable swashplate. The proposed modification implements near ideal pre-compression and decompression and is applicable for other swashplate type hydraulic motors. For the iHMT, power efficiency improvements of 4.8% to 14.4% at various operating conditions can be achieved.