Road Load Simulation Testing for Improved Assessment of Powertrain Noise and Vibration 2011-01-0924

This paper describes the development of an improved method for Noise and Vibration (N&V) chassis dynamometer testing using Road Load Simulation (RLS). Powertrain-induced noise and vibration testing on a chassis dynamometer has commonly been conducted using fixed loads or simplistic load versus speed approximations. Simple speed control and load control dyno test conditions are largely sufficient to provide representative noise and vibration performance assessment when the powertrain and its controls are insensitive to differences between the actual road load and the dyno load. With the recent growth of advanced engine control systems and hybrid powertrains, more representative road load simulation is required to ensure proper operation of the increasingly sophisticated and diverse powertrain and chassis control systems. Proper exercise of these control systems often determines the quality of the noise and vibration data. An example of this is provided for a full pedal acceleration test to measure interior sound pressure level. Noise data are acquired using a simple steady state speed control dyno test, and RLS real time run-up test. Sound pressure variation trends in the data from each test method are examined and the major source of variation is attributed to thermally-induced engine spark control changes caused by extended test duration under full engine load. Data from the RLS test method show greatly reduced run-to-run variation, when the number of consecutive test runs is limited to prevent thermally-induced spark retard. These results show that the improved RLS full pedal acceleration test more accurately represents the on-road performance, and results in a more robust powertrain noise assessment on the chassis dyno. Although the results presented include primarily sound pressure measurements, the advantages of the RLS dyno test method are also applicable to powertrain-induced vibration measurements.