Abstract
Keywords - Stop-Start, Usage profile, durability, inhibitor
One of the main features of a micro hybrid vehicle is the automatic stop and restart of the engine to avoid engine idling when the vehicle is at rest (1). However, in real world usage stopping the engine may not always be desirable for reasons of safety, comfort or other factors. The actual number of stops to be expected from a vehicle over it's lifetime is of crucial interest when developing the durability targets for a micro hybrid system. In this research reported here, a methodology to analyse the frequency of automatic engine stop events in real world usage has been developed. This takes into account the situations where the automatic engine stop is rendered unavailable (or inhibited) by the system controller.
A statistical model has been constructed using a real world, real time, vehicle usage dataset measured for passenger cars and publicly available climate data combined with Monte Carlo analysis. This supports the prediction of occurrence of inhibitors during real world customer usage. The real world usage dataset, measured by an OEM in Europe, provided information regarding the vehicle speed profile, gear usage, engine warm up periods, ambient conditions as well as generic information about all the measured trips. Using the above mentioned sources, inhibiting conditions have been analysed individually, using simplified models where necessary. The simultaneous occurrence of inhibitors has been investigated and accounted for in the results.
Conclusions: The methodology developed in this study provides a useful tool which supports the calculation of durability requirements as well as the initial calibration for micro hybrid systems in vehicle applications. Parametric studies show the routes to further system optimization.