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NVH

(Noise, Vibration, Harshness)
A Completely New Level of Sound Control

In the past, being ‘quiet, vibrant-free’ was a virtue for a car. However, as people are redefining the meaning of a vehicle, being quiet is not always a good thing. Previously, the goal of Noise, Vibration, Harshness (NVH) development was to reduce vibration and noise, but it is now important not only to improve practical performance but also to stimulate driver sensitivity and to create a natural sound that best fits the vehicle; it is now an era in which customizing and emotional user experience are important aspects to a vehicle.
Hyundai Motor Group is developing NVH reduction from this perspective: developing a car that is Fun to Drive. 

FUTURESearching for the Right Sound

Advanced NVH reduction technologies with the IT technologies

The initial NVH performance development was focused primarily on quietness. Automakers have used a variety of noise-reducing parts, which sometimes harm fuel efficiency; also, they figured out that customers have different views when it comes to quietness. Therefore, the current development for NVH reduction is focused on the sound that suits each vehicle performance and what each driver wants.

In 2015, Hyundai Motor Group established control standards for noise and vibration caused by complex factors, combining dynamic handling with quiet road-noise, and improved the suspension and engine mount systems that affect quietness such as R&H, NVH, and power performance. The Group also developed technologies to improve the noise and vibration of high-power powertrain and introduced a system-level noise evaluation method. As a result, noise, shake, and volume linearity from the road surface were improved.

In 2016, the company focused on developing a driving sound system to develop dynamic sound quality for sports and high-performance cars; hence, the Active Sound Design (ASD), which produces indoor sound, Electronic Sound Generator (ESG), which allows users to feel the added vibration and sound, and Active Variable Exhaust System, which controls the sound of the exhaust. And to meet the enhanced external noise codes, the company improved the low-speed booming while increasing the sound at higher RPM. 

2017 was the year of vehicle optimization for power performance and R&H. In particular, vehicle performance optimization was achieved by reducing the center muffler and opening the exhaust valve to minimize exhaust back pressure affecting the vehicle’s power performance.

Hyundai Motor Group plans to implement NVH performance that reflects customer emotion while strengthening NVH technology in the future. The company is pushing for the development of indicators that can measure driving sounds from indoors and outside of sports and high-performance cars, and the company is also developing modular units for NVH performance that goes well with other performances in various criteria. In addition, the Group is planning to secure technologies that can respond to future environments such as combining IT technologies using the cloud system, developing NVH related to autonomous driving, and utilizing new materials

TECHNOLOGY Core Technologies of NVH

Between Sense and Sensibility

The most important part of NVH development would be still in the practical area; it is to provide a quiet, comfortable driving experience for passengers without any discomfort or shock. In order to develop NVH reduction, Hyundai Motor Group focused on creating a sense of quietness, acceleration harmonization, and sound unity of diesel. Then the company moved on to create NVH that goes well with R&H and power performance, while maintaining the existing level of quietness. 

The goal of NVH development is not only for quietness; it is to diversify the versions within the vehicle to broaden the choices for consumers. Hyundai Motor Group is developing NVH concept cars that have different characters in different sizes and even among the same-size models. Since sound is difficult to measure or evaluate, the company wishes to create an NVH ecosystem that focuses on the people who use the car and connects passengers to the car and car noise.

KEY TECH
1. Area of Practicality
Road Noise Reduced Through Soundwaves

RANC : Road-noise Active Noise Control

RANC System Structure

There are various kinds of noise coming from a driving car, such as engine noise from the powertrain, drag and wind noise from the vortex, or road noise. It’s not a big deal for a short trip, but continued exposure to noise can cause a massive amount of stress.

Hyundai Motor Group unveiled the world’s first RANC technology back in December 2019; using an Accelerometer, RANC calculates the vibration from the road to the car and the control computer analyzes road noise. Finding the optimal locations for the sensors is one of the most important factors to trace the sources of vibration. The technology actively reduces noise by emitting soundwaves inverted to incoming noise from roads, making a quiet cabin.

This problem was first approached through Passive noise control (PNC), where physical treatments such as using sound-absorbing tiles and dynamic dampers, or applying double-pane windows. However, this requires more parts attached, hence increased body weight and lower fuel efficiency.

As a result, Hyundai Motor Group started to develop the ANC (Active Noise Control) to be best suited for low frequencies (65~125 Hz). Besides, due to the limitations of noise measurement and analysis technology, the existing ANC for vehicles was only able to be utilized when noise was constant and the occurrence of the noise predictable. The current ANC technology has been most commonly used to counteract constant engine noise. Hyundai Motor Group’s RANC (Road-noise Active Noise Control), however, eliminates road noise, which has a lot of variables and travels way too fast to respond to.

The RANC system uses velocity sensors, amplifiers, microphones, along with Digital Signal processor (DSP), and acceleration sensors. Using an acceleration sensor, RANC calculates the vibration from the road to the car and the control computer analyzes road-noise, then sends the soundwave to the audio system. The microphone constantly monitors the road noise cancelation status and sends the information to the DSP.

Based on tests evaluating road surface, vehicle speed, and different seating positions, RANC was able to reduce in-cabin noise by 3dB. That 3dB level is roughly half the noise level as compared without RANC. And Hyundai Motor Group can potentially decrease the amount of unsprung weight in a vehicle, utilizing fewer sound-insulating parts and dampers as compared with before. The RANC system decreases low-frequency noise emitted especially by elevated viaducts or rough roads between 500~5,000Hz significantly. The automaker received a patent for its technology in the U.S. and Korea.

RANC is very significant because it has excellent noise reducing capabilities. Using conventional methods, in order to achieve as much noise reduction as RANC technology, the weight of the car would increase by a huge number. There is almost no powertrain noise from electric and fuel cell electric vehicles, so quelling road and wind noise becomes even more imperative. 

No More Tire Resonance

Hollow Sound-absorbing Wheels

As customers’ demand for a quieter car increases, the developmental direction of NVH reduction technology has been shifting. In the past, researchers only focused on preventing noise from entering the space, but now researchers are starting to spot the causes of noise and vibration and improve on it.

The hollow sound-absorbing wheel is a technology that reduces road noise, especially tire resonance. Tire resonance refers to noise in the 200Hz band generated by tire vibration while driving. The vibration of the tire side wall, which is caused by contact with the tire and the road surface, causes a resonance inside the tire to increase in amplitude, thereby generating noise. The resonance sound generated in this way is transmitted to the interior through the suspension and vehicle body through the tires and wheels. This tire resonance is one of the most annoying noises from the passenger’s perspective.

Effects of tire resonance
Hollow sound-absorbing wheels structure

The core of the hollow sound-absorbing wheel is the hollow structure inside the wheel. The hollow structure consists of a hollow chamber that acts as a sounding chamber and a sound-absorbing hole that looks like a small hole. When driving a vehicle, the hollow chamber and the sound-absorbing hole create an opposite sound wave of the tire resonance sound, and the opposite sound wave overlaps with the tire resonance sound to reduce noise. 

The hollow structure is made inside the wheel, unlike the technology of attaching a separate sound absorbing material or resonator, and has the advantage of being able to reduce the weight of the aluminum wheel.

The G80’s hollow sound-absorbing wheel reduces up to 5dB based on an 18-inch wheel, reducing about 44% of tire resonance noise. In addition, it is up to 4.9 kg (for one 20-inch wheel) lighter than regular wheels of the same design. This weight reduction effect also helps improve driving performance.

KEY TECH
2. Area of Sensibility
The Right Engine Sound

Active Sound Design (ASD)

Genesis GV80’s Interior Space with ASD technology

In the past, NVH development solely focused on reducing or eliminating the sound from a vehicle, but now it’s important to design the sound that suits the car. Under a certain level of quietness, making intense engine sound for high-performance cars, and heavy and luxurious sound for premium cars are more important.

Electric vehicles sometimes add sound for safety issues; this is because it is difficult for the drivers to feel accelerated due to lack of engine sound, or they are not used to the unfamiliar sound that had been always covered by loud engine noises. This requires the virtual engine sound or sophisticated noise reduction technology exclusively for electric vehicles.

ANC and ASD technology creates quiet yet dynamic sound

Creating good sound starts with reducing the amount of bad sound you don’t want to hear. ANC is a typical noise reduction technique that cancels out noise by releasing a soundwave that is opposite to external noise; this makes the technology practical. On the other hand, the one that corresponds to the customer emotion would be the Active Sound Design (ASD). It is to create a rich and dynamic engine sound by adding a new sound to the existing engine sound.

The engine sound equalizer technology applied to the Veloster offers three different engine sound choices (Refine, Dynamic, Extreme) depending on the driver’s preference. The engine tone can also be adjusted – low, medium, and high, and users even can change the sound response depending on the use of the accelerator pedal; the system allows the driver to customize the engine sound.

Connected but Separated in Taste

SSZ : Separated Sound Zone

Gentle classical music is heard in the car, while the children are listening to the latest pop songs using earphones – this would make the family look disconnected. The Separated Sound Zone (SSZ) technology, however, allows multiple sound fields, even between the limited seating arrangements within a car.

In 2018, Hyundai Motor Group announced the SSZ technology that optimizes speaker placements In the cabin of the vehicle, creating independent sound zones that do not interfere with one another.

SSZ Technology Concept

Cars have many speakers, and those in various locations can make the background music sound more vivid and richer in the cabin. However, it would also mean that each speaker can make a totally different sound so that each passenger can listen only to the sound coming out of the speakers right next to them.

And of course, this alone doesn’t mean they can listen to a completely different sound in each seat; the cabin is not that big of a place. The sound will get mixed up. More advanced technology is required to make this happen – including speaker arrangements, and the right algorithms to minimize the impact of reflective waves produced by each sound. It also requires to build a system to control the volume and phase of the sound from each speaker, so that the sound can be compartmentalized in each seat.

The SSZ control system allows acoustic compartmentalization within the cabin space, allowing passengers the freedom to (not) hear what they (don’t) want to hear. This technology is expected to become an increasingly useful audio feature in the future of autonomous vehicles.