Grown interest in complex modern Hybrid Electric Vehicle (HEV) concepts has raised new challenges in the field of NVH. The switch between the Internal Combustion Engine (ICE) and the Electric Motor (EM) at low speeds produces undesirable vibrations and a sudden raise of noise levels that effects the sound quality and passenger comfort achieved by the close-to-silent electric powertrain operation. Starting the ICE in the most suitable driving situation to create a seamless transition between driving modes can be the key to minimize the NVH quality impact in driver and passenger’s perception in HEVs.
To integrate this important aspect in the early stages of the development and design phase, simulation technologies can be used to address the customer acceptance. By analyzing NVH measurements, the different noise components of the vehicle operation can be separated into ICE-related noise, EM-related noise and driving noise. To achieve highest system flexibility, these noise components can be synthesized, providing an integral NVH assessment tool that can be adapted to different driving conditions.
ICE and EM noise are simulated using additive synthesis of an underlying engine order preset, while the driving noise is recreated using variable filters whose parameters depend on both the specific vehicle and the driving situation.
This method delivers a very reliable and accurate estimation of the resulting sound quality. It can be used to produce a complete WLTP cycle that can be subjectively evaluated, judging optimal and critical sound behaviors that can be compared against other hybrid concepts.
By implementing the process and software presented here, OEMs can have a clear image of the NVH situation in their HEV project from an early stage, helping guide design decisions and reducing cost and time intensive evaluation loops in late development stages to a minimum.