The Environmental Protection Agency has recently purchased electric dynamometers for use in emission and fuel economy testing of light duty vehicles. These dynamometers are equipped with a single large diameter roll (1.219 meter, 48 inch) and electric inertia/road load simulation capability. The dynamometers are required to pass a series of robust performance requirements. The evaluation of the system performance was based on data acquisition and analysis completely independent of the dynamometer's operational and analysis software. An independent test system was used for verification of the dynamometer's operational features, control, and error reporting software. Testing was performed following the dynamometer installation at the EPA National Vehicle Fuel and Emission Laboratory (NVFEL). EPA performed evaluation tests, analyzed the data, and graphically displayed the results using commercially available microcomputer hardware and programs.
EPA designed the test data acquisition system and assembled the components. The data acquisition system specifications, final component build-up documentation, overall capabilities, and various methods of numerical or statistical analysis are presented.
The testing program consisted of accelerations, coastdowns, steady speeds, and the Federal Test Procedure Bag 1 driving schedules. The simulation settings for two different load curves were used on inertia weight settings which range from 907 kilograms to 2495 kilograms (2000 pounds to 5500 pounds). The tests were performed with and without a vehicle. The parameters which were monitored included time, dynamometer speed, acceleration rates, load cell output, dynamometer control demand signal, vehicle wheel speed, vehicle wheel torque, and motor amperage. The data was sampled at 20 and 500 hertz rates with 16-bit resolution. The criteria examined consisted of accuracy, repeatability, and response requirements. This program objectively quantifies the dynamometer performance characteristics in these tests.