Method of using feedforward compensation based on pressure feedback for controlling swash plate angle in a hydrostatic power unit of a continuously variable transmission

A method for automatically controlling an angle of a swash plate of a hydrostatic power unit of a continuously variable hydro-mechanical transmission, the method comprising:

• determining, with a processor-based controller, a desired hydrostatic reciprocal ratio of the hydrostatic drive unit based on a desired transmission reciprocal ratio for the transmission;
• determining, with the processor-based controller, a feedforward control term based on the desired hydrostatic reciprocal ratio of the hydrostatic power unit, a pump speed for the hydrostatic power unit, and a pressure for the hydrostatic power unit;
• determining, with the processor-based controller, a closed-loop control term based on an error calculated as a function of the desired hydrostatic reciprocal ratio;
• calculating, with the processor-based controller, a swash plate command based on the feedforward control term and the closed-loop control term;
• and
• transmitting, with the processor-based controller, the swash plate command for adjusting the angle of the swash plate.