Optimum Shifting of Hybrid and Battery Electric Powertrain Systems with Motors before and after a Transmission

This paper proposes an optimization-based transmission gear shifting strategy for electrified powertrains with a transmission. With the demand for reduced vehicle emissions, electrified propulsion systems have garnered significant attention due to their potential to improve vehicle efficiency and performance. An electrified propulsion system architecture of significance includes multiple electric motors and a transmission where some driveline actuators can transmit torque through changing gear ratios. If there is at least one electric motor arranged before the input of the transmission and at least one after the transmission output, a unique design opportunity arises to shift gears in the most energy efficient manner. An optimization-based gear shifting strategy is proposed where torque through the transmission is offloaded to the electric motor arranged after the transmission’s output, the transmission shifts gears with less torque transmitted through it, then the base optimization strategy is resumed after the gear shift. This optimization strategy improves energy efficiency by reducing clutch losses during the torque and speed phases of the gear shift.

The optimization solution for shifting gears in electrified powertrain systems with transmissions is described starting with an analysis of electrified powertrains that can implement this strategy. The optimization-based strategy is described in detail, showing the propulsion system maximizes energy efficiency considering a variety of operating conditions and gear shifting methods. Propulsion system efficiency is presented with an emphasis on electric motor power losses and clutch losses. Finally, a variance analysis is presented showing the impact of system parameters such as gear ratio spread on optimization.