Techniques of Measurement, Variations and Effects of Vehicle Friction Losses on Electric Dynamometers

Techniques were developed with the electric dynamometers to:

1. 1.
   Measure vehicle driveline and tire losses on the emission rolls; and
2. 2.
   Establish the windage and friction settings required to match the dynamometer load to the actual road load or other desired load conditions.

Vehicle driveline and tire losses were measured on 33 similar front wheel drive vehicles equipped with the same tire size. The total losses averaged 6.2 HP at 50 MPH and ranged from 4.8 to 8.4 with a standard deviation of .75 HP. With the standard dynamometer load used for the FTP test with that vehicle, the ± .75 HP represents a 11% change in load and about a 5% effect on fuel economy. The difference between the maximum and minimum driveline and tire losses measured would result in a 27% change in load and an approximate 11% change in fuel economy. Tires accounted for the largest percentage of the total losses while the brake systems caused the greatest variations.

Measurement of the vehicle losses and the ability to match the dynamometer to a desired load would allow testing all vehicles in a given program at the same load conditions. This would eliminate the effect of variations in losses when comparing the merits of various development designs and calibrations.