Engine Optimization Concepts for CVT-Hybrid Systems to Obtain the Best Performance and Fuel Efficiency 2004-40-0056

The objective of the advanced transmission system concepts such as the Continuously Variable Transmission (CVT) and Hybrid Electric Drives is to improve fuel efficiency, lower emissions and reduce powertrain part count while not impacting cost. The control of the system, however, can greatly affect the final fuel consumption, performance and emissions for any of the possible configurations. This paper describes an engine control philosophy for a hybrid electric CVT powertrain concept with the fewest number of mechanical parts but with many modes of operation such as:

1. All electric operation 2. Regenerative braking to maintain the battery charge at a desired level. 3. Engine charge for maintaining the battery state of charge 4. Highway cruise efficiency. 5. Power enhancement by use of the electrical energy for passing and highway maneuvers. 6. Trailer towing and high load applications

The paper describes the optimization theory based upon the unique multidimensional characteristics of the CVT and illustrates the results of three alternative operating strategies with simulation and vehicle test data. The best of the tried control schemes is described and compared with the others. The reasons for the differences are described.