Analyzing uncertainty in evaluation of vehicle fuel economy using FTP-75

Fuel economy is one of the major issues in the development of automobiles, along with performance and drivability. During a fuel economy test, the driver should follow the target schedule as closely as possible. However, it is impossible even for a skillful driver to completely follow the prescribed speed pattern; therefore, a speed tolerance, the extent to which violation of the prescribed speed pattern is permitted, is approved by the administrator of the test and has been used during fuel economy certification tests. Consequently, there is a difference in speed every time that a fuel economy certification test is conducted and therefore there is also a deviation in the certified fuel economy. Nevertheless, no research has been carried out into the deviation of fuel economy according to the observance of the target schedule by a driver. In this respect, this research aims to investigate the deviation of fuel economy which may take place during a fuel economy certification test. Fuel economy deviation is examined in three cases: driving at the highest or lowest speed in the defined range of speed tolerance, driving with the maximum or minimum tolerated acceleration, and driving with periodic variation from the prescribed speed. The periodic variation effects to the fuel economy deteriorated by more than 8%.