This paper presents a new method to model the vehicle fuel consumption in the design of an eco-driving assistance system developed by IFSTTAR within the European Commission FP7 project eco-Driver. The ambition of the driver assistance system is to combine safety requirements and fuel consumption reduction by optimizing the vehicle speed and the gear management. The exact estimation of the vehicle fuel consumption plays a key role in the driver assistance system design. This paper extends the authors’ results about the vehicle fuel consumption model. The instantaneous fuel consumption rate is modelled as a piecewise polynomial of the instantaneous engine speed and the instantaneous engine torque. The real vehicle experiments show the good performances of this piecewise fuel consumption model.