Modern Approaches to Electric Vehicle Noise and Vibration
Often what comes to mind when discussing electric vehicles are range, charging infrastructure, fast charging, battery costs, etc. Often overlooked are the electric vehicle’s noice and vibration characteristics and how they align with consumer expectations.
One of the most interesting aspects of electric vehicles is the absence of the internal-combustion-engine noise, which often masks other types of noises such as wind, road, and vehicle accessories. Wind and road noise can be very incessant; it is heard throughout the entire duration of the trip. For very long, high-speed vehicle travel, road and wind noise commonly cause driver fatigue and have an overall negative effect on the passenger experience.
“If you are a performance car guy, you may want to hear the engine—but nobody buys a car and wants to hear the road noise,” said Andrea Frey, senior NVH project engineer at Autoneum North America Inc. in Novi, Mich.
Vehicle accessory noise from sources such as HVAC systems, power steering, and switching mechanisms also becomes more prominent. Because these noises are typically masked by the internal combustion engine, operators will often perceive this sound as something being mechanically wrong with the car—often resulting in many trips to the dealership or local mechanic.
Electric motors offer some unique challenges with respect to vehicle noise. The motors themselves are quiet, but the sound quality coming from them can be very high-pitch and tonal. Many consumers often report a “whining” noise with electric motors.
Vehicle designers and NVH experts are looking at a variety of solutions—systems design, material sound packaging, active noise control, etc.—to address these noise concerns. Design engineers have been addressing electric motor whine by controlling the motor to create complementary low-order tone, said Sumanth Dadam, software engineer and powertrain Calibration Controls NVH at Ford Motor Company in Dearborn, Mich. The motor is controlled to generate random dithering noise to raise masking noise floor. It also reduces the tone-to-noise ratio around tonal targets, combining complementary injection at low frequency and dithering at high frequency.
Materials engineers have also developed many products designed to suppress the unique unwanted noise from electric vehicles. “The big challenge is learning how to apply sound package in a different way now that there are different noise sources that we perceive differently,” explained Autoneum’s Frey. Additionally, there are material considerations regarding durability, water absorption, lightweighting, and thermal requirements.
“In Europe, there are more stringent pass-by noise regulations, which for us translates to very high acoustic requirements at a material level for underbody panels,” Frey added. “It’s important to make something that meets those acoustic requirements while also taking into account aerodynamic, water absorption, and stone impingement considerations. Generally, things that absorb sound really well also absorb water really well.”
To address this underbody challenge, Autoneum developed its Ultra-Silent material package, a polyethylene terephthalate (PET)- based, glass-free mono-material. According to the company, the material is water-resistant and heat-resistant while reducing vehicle noise by up to two decibels. Ultra-Silent is particularly well suited for electric vehicles to reduce underbody panel weight while reducing tire noise and absorbing mid-high frequency noise emitted by the accessories.
Some electric vehicle applications require sound packages that are also both lightweight and act as a thermal barrier. Autoneum has adapted its textile interior technology to create Hybrid-Acoustics PET material that can be molded to encapsulate an electric motor to provide both sound absorption and thermal insulation. The material is designed to be 40% lighter than other insulators, flameproof, and temperature resistant up to 180°C.
A sound strategy
The solution is not always to remove noise, according to Gary Newton, vehicle dynamics and NVH simulator solutions sales at VI-grade in Canton, Mich. “For years,” he said, “we’ve been trying to bleed noise out of the vehicle, and now we are trying to put the ‘right’ noise back into the vehicle. On top of that, companies are looking at how to create the best sound experience for their brand. People want to feel a certain way in the vehicle, so how can we create that ‘feel.’” These are the arts of sound enhancement, sound design, and active noise control.
Vehicle designers and NVH experts have been studying very closely the types of experiences consumers desire with their vehicles, whether it be performance-related or comfort. “People want a positive user experience, and the sound of a vehicle that is not only pleasing to them, but also that fits the vehicle,” Newton said. “Consumers also want a smooth and comfortable ride.”
Sound design and strategies start early in the vehicle development process and can entail months of design, testing, and validation. The process can often be very expensive and greatly impact an automaker’s time to market. As a result, the industry has moved more toward using simulation as a tool for speeding design iterations, testing, and validation. Simulator technology has advanced significantly over the past 20 years and has even enabled developers to model the acoustic experience.
VI-grade’s NVH driving simulators enable vehicle design and development engineers to experience and understand the NVH characteristics of a vehicle by reproducing sound and vibration from electric motor, road, and wind noise contributions. This leads to fast and confident NVH decisions.
“Today, on a simulator, you can experience both your electric vehicle’s NVH and vehicle dynamics performance targets without a prototype. There is real power being able to subjectively link those together to accelerate critical decision making without the harsh consequences of doing them both independently,” Newton added.
Take part in further discussions on sound design and noise mitigation for electric vehicles at the upcoming SAE Noise and Vibration Conference & Exhibition , a hybrid event taking place digitally and in-person in Grand Rapids, Michigan, September 7-10, 2021. Visit the Noise and Vibration Conference registration page for more information and to register.
This article was written for Update by Frank Bokulich , Manager of Events at SAE and Content Developer for the Noise and Vibration Conference.