With the widespread adoption of electric vehicles, the internal combustion engine has been replaced by electric motors, eliminating engine noise during low-speed operation. However, at higher speeds, road and tire noise become the dominant sources of interior noise in electric SUVs. As living standards improve and the automotive industry advances, consumer demands for vehicle comfort have intensified. Noise, Vibration, and Harshness (NVH) performance, being highly perceptible, has emerged as a critical indicator of overall comfort. Road noise response is present across all driving conditions, making its control and optimization essential. Since it cannot be entirely eliminated, the design focus shifts toward enhancing road noise quality and reducing sound pressure levels to achieve superior acoustic performance.
In this study, I address road noise control through a practical case involving an electric SUV. By analyzing the mechanisms of road noise generation and optimizing tire characteristics and suspension bushing stiffness, I achieved a reduction of 2.8 dB in rear passenger noise under rough road conditions at 60 km/h. This approach provides valuable insights and methodologies for mitigating noise issues in electric SUVs.
The primary objective in optimizing road noise for electric SUVs is to identify its sources and implement targeted design improvements. In a controlled experimental setting, a five-seater electric SUV exhibited excessive interior noise and prominent tire cavity resonance when driven at 60 km/h on rough surfaces, significantly compromising ride quality. Initial assessments pointed to road noise as the key issue.
To pinpoint the root cause, I utilized the LMS Test.lab system to measure noise levels at the front passenger’s right ear (FFR) and the rear passenger’s left ear (RRL). Under rough road conditions at 60 km/h, the results indicated that the RRL sound pressure level was 3.1 dB(A) higher than that of comparable electric SUVs, confirming the need for optimization.
Road noise propagates through two main paths: airborne and structure-borne transmission. Airborne noise originates from tire radiation and is attenuated by the vehicle’s acoustic packaging before entering the cabin. Structure-borne noise results from tire vibrations transmitted through the wheel rim, suspension system, and body structure. The combined effect forms the overall road noise experienced in electric SUVs.
Tires are the primary source of road noise in electric SUVs, and their NVH performance directly influences interior acoustics. Key uniformity parameters affecting tire vibrations include:
| Uniformity Parameter | Description |
|---|---|
| RFV (Radial Force Variation) | Maximum variation in radial force per tire revolution under load. |
| RFV1H (First Harmonic of RFV) | Fundamental harmonic component of radial force variation. |
| LFV (Lateral Force Variation) | Maximum variation in lateral force per tire revolution. |
| CON (Conicity Force) | Lateral force offset independent of tire rotation direction. |
| RRO (Radial Run-Out) | Difference between maximum and minimum tire radius. |
| LRO (Lateral Run-Out) | Difference in lateral dimensions relative to the tire’s central plane. |
The suspension system further attenuates road-induced vibrations. I modeled the suspension as a mass-spring-damper system, where the chassis bushing acts as an isolator. The equation of motion is given by:
$$ m\ddot{x} + c\dot{x} + kx = f(t) $$
where \( m \) is the mass, \( c \) is the damping coefficient, \( k \) is the stiffness, and \( f(t) \) is the excitation force. The isolation efficiency depends on the frequency ratio \( \frac{f}{f_n} \), where \( f_n \) is the natural frequency. Effective isolation occurs when the frequency ratio exceeds \( \sqrt{2} \). The relationship between frequency ratio and isolation efficiency is summarized below:
| Frequency Ratio | Isolation Efficiency (%) | Human Perception |
|---|---|---|
| 1 | Resonance | Damaging |
| 1.414 | 0 | No Effect |
| 1.5 | 20 | Not Noticeable |
| 2 | 66.7 | Acceptable |
| 2.5 | 81.1 | Good |
| 3 | 87.5 | Excellent |
For bushings, the isolation ratio \( \eta \) is proportional to the ratio of Input Point Inertance (IPI) to bushing stiffness \( k \):
$$ \eta \propto \frac{\text{IPI}}{k} $$
Optimal isolation is achieved when \( \frac{\text{IPI}}{k} \geq 5 \). Critical bushings for road noise control in electric SUVs include the rear trailing arm bushing, rear shock absorber upper bushing, front shock absorber upper bushing, and front control arm bushing.
To optimize the suspension system, I first reduced the front control arm bushing stiffness from 920 N/mm to 644 N/mm. While this had minimal impact on RRL sound pressure at 60 km/h, it improved FFR noise by approximately 1 dB(A) at 40 km/h. Subsequently, I lowered the rear trailing arm bushing stiffness from 1196 N/mm to 838 N/mm, resulting in a 0.3 dB(A) reduction in RRL noise at 60 km/h.
A significant improvement came from replacing the rigid subframe connection with a bushing-isolated subframe. This modification reduced RRL noise by 2 dB(A) at 60 km/h on rough roads and subjectively diminished pattern noise and tire cavity resonance, enhancing the acoustic comfort of the electric SUV.
Tire optimization focused on improving uniformity parameters. The table below compares original and optimized tire uniformity values:
| Uniformity Parameter | Original State (Avg.) | Optimized State (Avg.) |
|---|---|---|
| RFV (kgf) | 6.5 | 5.56 |
| RFV1H (kgf) | 4.32 | 3.79 |
| LFV (kgf) | 5.33 | 4.75 |
| CON (kgf) | N/A | N/A |
| RRO (mm) | N/A | N/A |
| LRO (mm) | N/A | N/A |
Implementing these tire changes yielded a 0.5 dB(A) reduction in RRL noise at 60 km/h. The combined optimizations—tire uniformity improvement, bushing stiffness reductions, and subframe isolation—collectively lowered road noise by 2.8 dB(A), bringing the electric SUV’s performance in line with competitive models.
In conclusion, road noise in electric SUVs is a complex NVH challenge requiring a multifaceted approach. Through tire optimization, suspension bushing adjustments, and subframe isolation, I successfully reduced rough road noise at 60 km/h by 2.8 dB(A) and improved tire cavity noise, demonstrating effective strategies for enhancing acoustic comfort in electric SUVs. The integration of these solutions underscores the importance of holistic design in achieving superior NVH performance for electric SUVs.
The optimization process for electric SUVs involved detailed analysis of excitation sources and transmission paths. By focusing on tire and suspension components, I developed a robust methodology for road noise control. Future work could explore active noise control systems to further enhance the quietness of electric SUVs, leveraging their unique acoustic characteristics. The success of this study highlights the potential for continuous improvement in electric SUV NVH performance through iterative testing and design refinement.
Electric SUVs represent a growing segment in the automotive market, and their noise characteristics differ significantly from conventional vehicles. The absence of engine noise amplifies the perceived levels of road and wind noise, making effective control strategies essential. In this context, the optimization of tire and suspension systems plays a pivotal role in defining the acoustic identity of electric SUVs. The methodologies applied here can be adapted to various electric SUV models, providing a scalable solution for noise reduction.
Moreover, the use of advanced testing equipment like LMS Test.lab enables precise identification of noise sources, facilitating targeted interventions. The relationship between bushing stiffness and isolation efficiency, as derived from vibrational analysis, offers a quantitative basis for design decisions in electric SUVs. By maintaining a frequency ratio above 2, designers can ensure adequate vibration isolation, contributing to a quieter cabin environment.
The tire optimization process also revealed the importance of harmonic components in road noise. Reducing RFV1H and LFV values directly impacted the perceived noise quality, emphasizing the need for high-precision manufacturing in tire production for electric SUVs. As the industry moves toward stricter noise regulations, such detailed attention to component-level parameters will become increasingly critical.
In summary, the comprehensive approach to road noise control in electric SUVs—encompassing source identification, path analysis, and component optimization—yielded significant improvements in acoustic comfort. The integration of experimental data with theoretical models provided a solid foundation for decision-making, ensuring that the solutions were both effective and efficient. This work contributes to the broader goal of enhancing the user experience in electric SUVs, making them not only environmentally friendly but also exceptionally comfortable and quiet.