A Linear Quadratic Integral Approach to the Profiling of Engine Speed for Synchronization

During driving conditions, when it is needed to transition from Electric Vehicle (EV) to Hybrid Vehicle operation, synchronization of the engine with the shaft and transmission is essential to enable clutch engagement and, subsequently, providing engine power to the wheels. Challenges arise when the engine must generate power to move itself and cannot rely on electric motors for precision. Cost-effective hybrid vehicle propulsion architectures which utilize small 12V belt-starter generators (BSGs) to initiate engine activation are inherently affected. In these situations, a speed profile that balance rapid response and control effort while considering system limitations to mitigate undesirable overshoots and delays, is required. This paper presents a Linear Quadratic Integral (LQI) approach to formulate a speed reference profile that ensures optimal engine behavior. The proposed strategy is seamlessly integrated as an open-loop feedforward controller into a powertrain torque control supervisor. System constraints are evaluated downstream the LQI where the electric authority is considered, and the target is achieved by jointly actuate electric machine and the engine. A low-level engine control is tasked to command the actuators to meet such profile. Through the utilization of case studies, including scenarios involving engine activation during EV mode, the paper highlights the effectiveness of the proposed strategy.