Mathematical Optimization of Gear Shift Schedules for Hybrid Electric Vehicle's Fuel Economy Improvement

Gear shift schedule for HEV transmission is very complex and significantly affects fuel economy (FE) and drivability. An inefficient shift schedule causes high mechanical losses in powertrain, less regenerative power, and degraded powertrain efficiency. In this paper, the approaches for mathematical optimization of HEV transmission gear shift schedules and application of driveability constrains are discussed. Moreover, during engine-off coast-down process, an energy based strategy of gear shift for maximizing regenerative power is also discussed. The mathematical optimization of gear shift schedules for maximizing FE is performed on a HEV, and characteristics of energy flow, gear shifts and powertrain performance are analyzed.