Method of using feedforward compensation based on pressure feedback for controlling swash plate angle in a hydrostatic power unit of a continuously variable transmission
View Patent ↗A swash plate angle for a hydrostatic power unit of a continuously variable hydromechanical transmission is determined using a feedforward compensation term, to reduce reliance on closed loop control. The feedforward term is based on knowledge of the hydrostatic power unit determined as a function of knowledge of certain parameters, including, but not limited to, hydrostatic power unit pressure, swash plate angle, desired hydrostatic power unit ratio, and pump speed.
1. 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.
2. The method of claim 1 , wherein the pressure corresponds to an estimated pressure for the hydrostatic power unit, the estimated pressure being determined as a function of at least a calculated driveline torque for the transmission, and the pump speed.
3. The method of claim 1 , wherein the close-loop control term is determined by the processor-based controller implementing a PID control loop.
4. The method of claim 1 , wherein the desired hydrostatic reciprocal ratio is defined as a motor speed for the hydrostatic power unit divided by the pump speed.
5. 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 and an estimated 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.
6. The method of claim 5 , wherein the feedforward term is additionally determined as a function of a pump speed for the hydrostatic power unit.
7. The method of claim 5 , wherein the estimated pressure of the hydrostatic power unit is determined as a function of at least a calculated driveline torque value for the transmission, and a pump speed for the hydrostatic power unit.
8. The method of claim 5 , wherein the desired hydrostatic reciprocal ratio is defined as a motor speed for the hydrostatic power unit divided by a pump speed for the hydrostatic power unit.