Startup and Regeneration Problems in Hydromechanical Transmissions

Hydromechanical transmissions employing hydrostatic pumps and motors have high inherent efficiency if the ratio of power transmitted hydraulically to that transmitted mechanically is small. Where significant horsepower is to be transmitted over a wide range of torque multiplication, however, simple input-coupled and output-coupled transmissions require large hydraulic units, generate high gear loadings, and have reduced reverse torque at standstill. A transmission which is operated sequentially as output-coupled then input-coupled reduces hydraulic horsepower and gear loading. In a transmission with a pure hydrostatic start, reverse torque can be made equal to forward torque at standstill.