Mild Regenerative Braking to Enhance Fuel Economy via Lowered Engine Load Due to Alternator 2008-01-2560

Brake energy recovery is one of the key components in today's hybrid vehicles that allows for increased fuel economy. Typically, major engineering changes are required in the drivetrain to achieve these gains. The objective of this paper is to present a concept of capturing brake energy in a mild hybrid approach without any major modifications to the drivetrain or other vehicular systems. With fuel costs rising, the additional component cost incurred in the presented concept may be recovered quickly. In today's vehicles, alternators supply the electrical power for the engine and vehicle accessories whenever the engine is running. As vehicle electrical demands increase, this load is an ever-increasing part of the engine's output, negatively impacting fuel economy. By using a regenerative device (alternator) on the drive shaft (or any other part of the power train), electrical energy can be captured during braking. This strategy reduces the duty cycle of the engine-mounted alternator and the resultant negative fuel economy impact. A mathematical model of the vehicle, using the RAPTOR™ vehicle simulation tool, was used to quantify alternator load and impact of the brake energy recovery on alternator duty cycle. Simulation results are presented to quantify the fuel economy benefits for a representative vehicle.