Abstract
The transmission efficiency of a multi-range hydro-mechanical continuously variable transmission (HMCVT) is researched, which considered the factors of the power cycle and the efficiency variation of hydraulic units with their input power and speed. An efficiency algorithm of the closed pump-motor system is given, which is relative to the speed, pressure and displacement of hydraulic units. Efficiency formulas of typical structures of HMCVT are derived by meshing power method. The efficiency of a multi-range HMCVT is calculated. The calculated efficiency is consistency with the measured efficiency. The result shows that the average efficiency of HMCVT is reasonably higher than the peak efficiency of pure hydraulic transmission, although the efficiency varies obviously with the transmission ratio, the input power or torque. When the output torque of engine is smaller, the efficiency of HMCVT is lower. However, the speed change of engine has a less influence on the efficiency of HMCVT.
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