Variable Shift Schedule Control for Integrated Starter Generator Equipped Hybrid Vehicles

In this study, conducted during 42V product development by Visteon, a Variable Shift Schedule¹ (VSS) control strategy was designed and tested on a vehicle equipped with an Integrated Starter Generator (ISG) and a step ratio automatic transmission. The strategy incorporates two ratio change points (a high point and a low point) for a given vehicle speed and driver demand torque (measured by throttle position). By evaluating battery state of charge (SOC) and torque boost available from the electric drive system, the strategy can interpolate the earliest point for a change in ratio. It can also choose to “lock” the torque converter elements within the automatic transmission (AT) while continuing to provide consistent vehicle performance. The result is the ability to operate the internal combustion (IC) engine in a range of greater efficiency during the up-shift sequence. In addition the automatic transmission is able to remain in higher ratio ranges for extended durations. This effectively creates a vehicle that operates at levels of greater fuel efficiency and lower emissions. Computer Aided Engineering (CAE) modeling experiments are carried out to prove the validity of the proposed transmission control strategy and support the claims.