A new pass-by noise test method has been introduced, in which engine speeds and loads are reduced (compared to the old test method) to better reflect real world driving behavior. New noise limits apply from 1 July 2016, and tighten by up to 4dB by 2026. The new test method is recognized internationally, and it is anticipated that the limits will also be adopted in most territories around the world.
To achieve these tough new pass-by noise requirements, vehicle manufacturers need to address several important aspects of their products. Vehicle performance is critical to the test method, and is controlled by the full load engine torque curve, speed of response to accelerator pedal input, transmission type, overall gear ratios, tire rolling radius, and resistance due to friction and aerodynamic drag. Noise sources (exhaust, intake, powertrain, driveline, tires) and vehicle noise insulation are critical to the noise level radiated to the far-field.
A simulation method was developed that could account for all of these critical aspects and predict the pass-by noise test result. This simulation method is useful to explore and optimize a car at the early stage of product development when design decisions are easier and more cost-effective. Countermeasures suggested by the simulation were procured in hardware and tested. The expected benefits were achieved, signposting a route to achieve the pass-by noise requirements of 2026, and demonstrating that the simulation method was useful.