NVH ANALYSIS Speed-Andrews. “If you imagine a broad spectrum of background uniform noise and suddenly there is a high-pitched tonal sound, such as a whistle, our brains instantly detect that because it stands out. As such, that’s what NVH departments focus on, mitigating any abnormal noise sources.” The shift to hybrid and electric vehicles over the last decade has introduced an array of these disturbing high-frequency abnormal noises – giving NVH engineers plenty to get stuck into. Hear and now There are three main sources of noise in a vehicle: wind, road and powertrain. “Wind noise and road noise remain largely the same for combustion and hybrid and electric vehicles, but the powertrain noise changes completely,” explains Dr Alexander Peiffer, head of the NVH battery-electric vehicles and active systems team at Audi. “Battery-electric vehicles change the focus of NVH as there is no internal combustion engine with its low-frequency order-based spectral characteristics, but an electric motor with high-frequency tonal components acting as structure and airborne sources. Hybrid vehicles increase the complexity further, which leads to greater development efforts.” Replacing an ICE with a battery, motor and inverter not only introduces new sources of high-frequency noise but also removes the low-frequency background noise of an engine that typically masks wind and road noise. It’s a familiar hurdle faced by acousticians who have been working to tackle the issue since the dawn of EVs. “This means areas that previously weren’t a problem now require attention,” highlights Jordan Craven, senior engineer at consultancy company Drive System Design (DSD) UK. “With the complex array of electronic, electromagnetic and mechanical subsystems in an electric powertrain, there are more subsystem interactions that we need to consider. For example, how the motors, transmission and inverters interact with each other to produce or propagate noise. This is becoming increasingly important as the drive for power density and efficiency is leading to greater integration, meaning subsystem interactions are stronger – and the criticality of understanding and optimizing the desired attribute set, especially NVH, is always increasing.” 24 MARCH 2024 www.AutomotiveTestingTechnologyInternational.com