The fuel consumption of a vehicle is shown to be linearly proportional to (1) total vehicle work required to drive the cycle due to mass and acceleration, tire friction, and aerodynamic drag and (2) the powertrain (PT) mechanical losses, which are approximately proportional to the engine displaced volume per unit distance travelled (displacement time gearing). The fuel usage increases linearly with work and displacement over a wide range of applications, and the rate of increase is inversely proportional to the marginal efficiency of the engine. The theoretical basis for these predictions is reviewed. Examples from current applications are discussed, where a single PT is used across several vehicles. A full vehicle cycle simulation model also predicts a linear relationship between fuel consumption, vehicle work, and displacement time gearing and agrees well with the application data. When the fuel consumption of a PT is measured or predicted at a few distinct vehicle work levels for different gearings and engine displacements, the data can be used to develop a simple regression model which accurately captures the effects of weight, aerodynamic drag, tire rolling resistance, engine displacement, final drive ratio, and tire size changes. The number of detailed fuel consumption simulations required for PT application studies can therefore be greatly reduced.
