Fuel Consumption Test Method for 4WD HEVs – On a Necessity of Double Axis Chassis Dynamometer Test –

Concerns regarding global climate change have caused the transportation sector to look for alternatives to petroleum as a fuel for vehicles of all types. Hybrid electric vehicles (HEVs) have been recognized as being particularly efficient for urban traffic use. In the last few years, Four wheel drive (4WD) transmissions have been developed for heavy passenger vehicles. As these vehicles become more popular, there is a need for accurate fuel consumptions test methods. Clearly the most accurate fuel consumption measurements would be obtained by using dual axis dynamometers, but these systems are not always available. Single axis dynamometers are commonly used for evaluating fuel consumption, but these are inadequate for 4WD vehicles without adjustments to account for the uncertainty that will result from disabling one of the drive axles.This paper describes a method for extrapolating fuel consumption results from single axle chassis dynamometer testing to estimate the fuel consumption of 4WD vehicles. A simple method is proposed that will allow reasonable estimates of fuel consumption for 4WD vehicles to be made from single axle dynamometer testing.This paper also describes methods to reduce the uncertainty in 4WD chassis dynamometer testing by paying particular attention to road load, tire conditions and restraint characteristics.