Next-Generation Low-Voltage Power Nets Impacts of Advanced Stop/Start and Sailing Functionalities 2017-01-0896
The range of tasks in automotive electrical system development has clearly grown and now includes goals such as achieving efficiency requirements and complying with continuously reducing CO2 limits. Improvements in the vehicle electrical system, hereinafter referred to as the power net, are mandatory to face the challenges of increasing electrical energy consumption, new comfort and assistance functions, and further electrification. Novel power net topologies with dual batteries and dual voltages promise a significant increase in efficiency with moderate technological and financial effort. Depending on the vehicle segment, either an extension of established 12 V micro-hybrid technologies or 48 V mild hybridization is possible.
Both technologies have the potential to reduce fuel consumption by implementing advanced stop/start and sailing functionalities. Additional engine-stop phases and even reduced driving resistance have positive impacts on the fuel consumption but lead to higher load on the electrical system and an energy deficit by reducing the recuperation and charging phases. Therefore, power net architecture and electrical energy management play an essential role with regard to safety and efficiency issues.
The first step of this study is an examination of stop/start and sailing functionalities by analyzing extensive real-world driving measurements of a C-segment vehicle. The sailing function decouples the engine in situations without driver torque request with the engine remaining idle. Fuel and electrical energy consumption are analyzed in detail on defined test routes with varying electrical load.
Secondly, simulations are carried out to evaluate the impacts of advanced sailing functionalities. A vehicle simulation is coupled to a dedicated power net simulation and calibrated to the real-world driving measurements. An engine off sailing algorithm is implemented, and the effects on fuel consumption and electrical energy balance are evaluated under varying boundary conditions. These analyses are conducted in several dual-battery and dual-voltage architectures. Starting from those results, the requirements for prospective automotive power nets can be derived to give an outlook for further opportunities and optimization potential.