Experimental Validation of Stop & Start Sailing Strategy for Real-world Driving Cycles

Nowadays OEMs are facing the challenge of producing vehicles that meet future fuel economy and emissions requirements at an affordable price to satisfy the desired customer value. Stop and start system has been favourably accepted by OEMs lately, as it offers significant fuel economy improvements at minimal cost. S&S system removes the engine’s drag torque, when no traction is required, preventing from burning extra fuel. According to upcoming homologation cycles and due to more stringent CAFE targets, S&S should be further improved, by operating it even with vehicle in motion. This new operating mode is known as Sailing: it decouples the engine from the driveline during coasting, extending the distance covered by the vehicle, and shutting the engine off. The automation of transmissions paves the way to the introduction of this feature. In order to assess the benefits of the sailing feature over real-driving conditions, an innovative control strategy has been developed and assessed. The paper evaluates, through an experimental test campaign on a C-segment vehicle powered by mid-sized EU6 diesel engine, the fuel economy potential and the impact on diesel emissions of S&S Sailing over real-world driving cycles, i.e. WLTP and Real Drive Emission. A “Design for Six Sigma” approach has been used to identify the optimal trade-off between frequency and duration of sailing events. The data collected over the new WLTP cycle highlight significant fuel economy benefits without any significant engine emission drawbacks.