Power Split CVT Modeling With Spool Valve Actuation

Abstract

New stringent emission regulations are requiring automotive engineers to develop vehicles featuring multiple energy sources and innovative drivetrain components. One such innovation is the continuously variable transmission (CVT) which offers a continuum of variable gear ratios for greater efficiency and elimination of unwanted jerks in comparison to fixed gear transmissions. The power split CVT configuration offers both fixed gearing and adjustable pulleys to satisfy the torque/speed demands. Spool valves regulate the hydraulic fluid to actuate the CVT’s primary and secondary sheaves for gear ratio manipulation based on the belt’s tension requirements. To fully support the evaluation of various powertrain configurations and control algorithms, a design tool must be developed which characterizes the complete powertrain system. In this paper, a power split CVT will be mathematically modeled and analyzed. Dynamic models will be introduced for the transmission, driveline, and chassis with attention focused on the CVT pulleys and hydraulics. Representative numerical results will be presented and discussed to quantify the performance of the power split CVT and sheave actuation for prescribed driving maneuvers.