Ratio-Metric Hesitation Fuel Detection and Compensation in Power Split Hybrid Electric Vehicles

Power Split Hybrids are unique when compared to conventional powertrains from the perspective that the engine speed is directly controlled by the motor/generator at all times. Therefore, traditional methods of detecting variations in fuel volatility do not apply for Power Split Hybrid based configurations. In their place, the Ratio-metric Fuel Compensation (RFC) method has been developed for Power Split Hybrid generator configurations to detect and compensate for engine hesitations within milliseconds of the first injection event. Furthermore, test results have shown that in the presence of low volatility fuel, RFC provides robust starts at the ideal lean air fuel ratio required for PZEV emissions compliance. Through real-time engine torque measurements by the HEV generator the RFC event-based computer algorithm was able to recognize that the combustion lean limit had been reached, thereby triggering the precise amount of fuel compensation required to maintain the actual air/fuel ratio at the commanded air/fuel ratio target of 1.10, a value consistent with complete fuel combustion.