Frequent engine stop-start cycles in hybrid electric vehicles (HEVs) exacerbate noise, vibration, and harshness (NVH), degrading driving comfort-a challenge intensified by growing HEV market share. The initial crank angle (ICA) critically influences restart smoothness, yet traditional control systems relying on crankshaft sensors suffer from low-speed signal unreliability and increased complexity. This study proposes a position-sensor-free stop-position control strategy utilizing only the speed signal. By leveraging the deterministic relationship between speed extrema during the compression stroke and top dead center (TDC), real-time TDC detection and crank angle estimation are achieved. A C¹-continuous quadratic speed trajectory is designed to meet boundary conditions for final speed, acceleration and target position, integrating feedforward torque compensation and gain-scheduled PI feedback control. Vehicle tests demonstrate a positioning accuracy of 1.7Formula: see text, complete elimination of engine reversal, and recovery of 44.69 J of kinetic energy (6.25% of restart energy demand). By eliminating the need for dedicated crankshaft sensors, this approach simplifies control architecture, offering a cost-effective solution particularly beneficial for low-cylinder-count HEVs with pronounced speed fluctuations.
Yuan et al. (2026) studied this question.