Steady State Speeds Load Determinations Using Electric Vehicle Power or Dynamometer Measurements on Conventional Vehicles

Track Road Load Derivations (RLDs) and subsequent load matching on test cell dynamometers has traditionally been conducted using vehicle coastdowns (CDs). Vehicle speed changes during these coastdowns are used to calculate the vehicle mechanical drag forces slowing vehicles when on the road. Track drag force, exerted on a vehicle, can also be quantified by holding a vehicle at a specific steady state speed and measuring the forces required to maintain that speed. This paper focuses on two methods to quantify speed dependent forces which a vehicle must work against when motoring. One method is the traditional coastdown method. The second reference method measures vehicle steady state speed forces necessary to propel the vehicle using both electric vehicle propulsion power flows and dynamometer measured forces. Track CDs require the vehicle to be placed in neutral. Hybrid Electric Vehicles (HEVs) do not necessarily have true neutral mechanical power transmission modes and some vehicles exhibit large variations from CD run to CD run. A steady state approach may prove a useful alternative road load determination method for electric vehicles which may otherwise need modification for the CD method.