Tousignant, T., Govindswamy, K., Eisele, G., Steffens, C. et al., "Optimization of Electric Vehicle Exterior Noise for Pedestrian Safety and Sound Quality," SAE Technical Paper 2017-01-1889, 2017.
The automotive industry continues to develop new powertrain and vehicle technologies aimed at reducing overall vehicle-level fuel consumption. Specifically, the use of electrified propulsion systems is expected to play an increasingly important role in helping OEM’s meet fleet CO2 reduction targets for 2025 and beyond. Electric and hybrid electric vehicles do not typically utilize IC engines for low-speed operation. Under these low-speed operating conditions, the vehicles are much quieter than conventional IC engine-powered vehicles, making their approach difficult to detect by pedestrians. To mitigate this safety concern, many manufacturers have synthesized noise (using exterior speakers) to increase detection distance. Further, the US National Highway Traffic Safety Administration (NHTSA) has provided recommendations pursuant to the Pedestrian Safety Enhancement Act (PSEA) of 2010 for such exterior noise signatures to ensure detectability. This has created potential challenges for automakers to meet the anticipated regulatory requirements while maintaining a high level of sound quality for both exterior and interior noise.In development of exterior noise signals, the goal is to achieve the required levels and transient pitch requirements, while ensuring the noise is both pleasant from outside of the vehicle and non-intrusive to the vehicle interior cabin. This paper discusses the use of a systematic approach, using exterior and interior noise simulations to optimize system sound design. Utilizing an exterior transfer path approach between potential speaker locations, this approach evaluates the sensitivity of variables such as speaker location, noise source routing, exterior noise transfer functions, and sound source design to achieve the required levels and directivity while minimizing overall exterior noise intrusion. At the same time, transfer path analysis to the vehicle interior is utilized to assess the influence of exterior noise sources on vehicle interior sound quality.