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A unified fuel consumption model

On Thursday, March 26 at 3:00 pm, Patrick Phlips of Ford Motor Company will present recent research by himself and a Ford team on how a power-based model can be used to characterize fuel consumption over a wide range of powertrain technologies and vehicle operating conditions.

Abstract

Previously fuel consumption on a drive cycle has been shown to be proportional to traction work, with an offset for powertrain losses. This model had different transfer functions for different drive cycles, performance levels, and applied powertrain technologies. Following Soltic it is shown that if fuel usage and traction work are both expressed in terms of cycle average power, a wide range of drive cycles collapse to a single transfer function, where cycle average traction power captures the drive cycle and the vehicle size. If this transfer function is then normalized by weight, i.e. by working in cycle average power/weight (P/W), a linear model is obtained where the offset is mainly a function of rated performance and applied technology. A final normalization by rated power/weight as the primary performance metric further collapses the data to express the cycle average fuel power/rated power ratio as a function of cycle average traction power/rated power ratio. This final transfer function is mainly a function of technology. It was used to estimate the effectiveness of technologies deployed by manufacturers to improve fuel consumption. Compared to the naturally aspirated PFI engines and six-speed automatic transmissions of a decade ago, three different combinations of downsized turbo or Atkinson engines, with either 8+ speed transmissions or CVTs achieve similar substantial improvements in efficiency. The useful work or power definition is expanded to include electrical power for customer functions, and power to drive the air conditioning, so that the model can be applied to ‘real world’ driving.