Ultracapacitor Enabled Gatekeeper Energy Management Strategy for Single Mode eCVT Hybrid Vehicle Propulsion

Power split electronic continuously variable transmissions (eCVT´s) have evolved rapidly since the introduction of the Toyota Prius concept sedan at the 1995 Tokyo auto show. Exhibiting smooth and seamless speed transitions by virtue of its lack of clutch or step ratio gear change transmission, the eCVT has found remarkable acceptance in the marketplace in both economy and performance optimized hybrids. Performance places increased demands on the vehicle energy storage system (ESS) in the form of higher power cycling and thermal dissipation. Energy management strategies (EMS) have become very prominent in the need to manage the multiple power sources via efficiency optimizing control of engine output, floating bus voltage level on the generator and motor, electronically controlled brakes, and converter buffering of the traction battery. This investigation proposes a novel gatekeeper EMS that relies on the ultracapacitor as the power cache focal point for all ESS energy transactions. It is found that controlled power circulation to replenish the battery significantly reduces battery cycling and provides state of charge (SOC) control that facilitates battery size reduction