As electric vehicles (EVs) continue to gain popularity worldwide, particularly in the context of China EV battery technology, the demand for quieter and more refined driving experiences has become a key focus. One often overlooked aspect is the noise generated by high-voltage relays within the EV power battery packs during power-on and power-off sequences. These relays, essential for controlling high-voltage circuits, can produce significant transient noise that may affect user comfort. In this article, I explore the sources of this noise, its propagation mechanisms, and various optimization strategies based on experimental data. Through rigorous testing in semi-anechoic chambers, I evaluate methods such as using horizontal relays, incorporating vibration damping pads, applying sound-absorbing materials, and enhancing structural modals. The goal is to provide actionable insights for improving the acoustic performance of EV power battery systems, ultimately contributing to the advancement of China EV battery designs.
High-voltage relays in EV power battery packs serve as critical components for managing electrical flow, but their operation involves mechanical impacts that generate noise. This noise primarily stems from the collision of moving contacts with stationary contacts and the impact of moving iron cores against yoke plates during relay engagement and disengagement. In a typical China EV battery setup, these relays are housed within the Battery Distribution Unit (BDU), which is mounted on the battery pack’s metal substrate. The enclosed nature of battery packs, often designed to meet IP67 protection standards, means that noise propagation is dominated by structural paths rather than airborne transmission. My investigations reveal that structural vibrations through mounting bolts and enclosures play a major role, emphasizing the need for targeted optimizations in EV power battery systems.
To understand the noise propagation, consider the two primary paths: airborne and structural. Airborne transmission involves sound waves traveling through the air inside the battery pack, partially reflecting off or penetrating the BDU plastic外壳, while structural transmission occurs through solid components like bolts and enclosures. Experimental data show that when bolts are removed, noise levels can drop by up to 11 dB(A), highlighting the significance of structural damping. This aligns with general acoustic principles where the sound pressure level (SPL) is given by $$L_p = 10 \log_{10} \left( \frac{p^2}{p_0^2} \right)$$ where \( p \) is the measured sound pressure and \( p_0 \) is the reference pressure (typically 20 μPa). For EV power battery applications, reducing structural vibrations is crucial, as it directly impacts the overall noise, vibration, and harshness (NVH) performance of China EV battery systems.
One effective approach to noise reduction is optimizing the noise source itself. High-voltage relays come in two main types: vertical and horizontal. Horizontal relays, where the actuation mechanism operates laterally, tend to produce less noise because the moving iron core does not exert gravitational force on the yoke plate, reducing impact energy. In my tests on China EV battery prototypes, switching from vertical to horizontal relays resulted in noise reductions of 2 to 6 dB(A). This can be modeled using the kinetic energy equation $$E_k = \frac{1}{2} m v^2$$ where \( m \) is the mass of the moving part and \( v \) is its velocity upon impact. By minimizing \( v \) through design adjustments, the resultant noise is lowered, benefiting EV power battery reliability and user experience.
Another key strategy involves the use of rubber vibration damping pads to mitigate structural noise transmission. These pads, typically made of materials with high damping coefficients, absorb vibrational energy and reduce the transfer of forces through mounting points. For instance, in a hybrid EV power battery pack, initial tests with standard rubber pads (70 HB hardness) showed noise reductions of 1 to 3 dB(A) and loudness decreases of 1 to 3 sone. Loudness, measured in sone, relates to human perception and can be approximated by $$N = 2^{(L_N – 40)/10}$$ where \( L_N \) is the phon level. To enhance this, I developed an optimized damping pad design with dual studs separated by rubber, which further reduced noise by 1 to 5 dB(A) and loudness by 3 to 7 sone. This improvement is critical for advancing China EV battery NVH standards, as it addresses the core issue of bolt-induced structural transmission.
| Optimization Method | Noise Reduction (dB(A)) | Loudness Reduction (sone) | Key Features |
|---|---|---|---|
| Horizontal Relay | 2–6 | N/A | Reduces impact force through lateral actuation |
| Standard Rubber Damping Pad | 1–3 | 1–3 | 70 HB hardness, with steel bushing |
| Optimized Damping Pad | 1–5 | 3–7 | Dual-stud design with rubber isolation |
| Sound-Absorbing Cotton Wrap | 1–5 | 1–3 | External application for airborne noise |
| Structural Modal Optimization | 7–10 | ~15 (50% reduction) | Enhanced BDU and battery pack stiffness |
In addition to source and damping optimizations, I explored the use of sound-absorbing materials like acoustic cotton wraps. However, this method showed limited effectiveness, with noise reductions of only 1 to 5 dB(A) and loudness decreases of 1 to 3 sone. Moreover, practical constraints such as thermal management and fire safety in China EV battery packs make this approach less viable. Instead, focusing on structural enhancements proved more rewarding. By optimizing the battery pack’s modal properties, particularly the natural frequencies of the BDU外壳 and upper cover, I achieved significant noise reductions of 7 to 10 dB(A) and a 50% drop in loudness (approximately 15 sone). This involves ensuring that the structural natural frequencies do not coincide with the excitation frequencies from relay impacts, which can be analyzed using the modal frequency equation $$f_n = \frac{1}{2\pi} \sqrt{\frac{k}{m}}$$ where \( k \) is the stiffness and \( m \) is the mass. For EV power battery designs, using aluminum structures instead of steel can improve damping and reduce noise persistence, as aluminum has a lower Young’s modulus and higher damping coefficient.
To validate these optimizations, I conducted experiments in a semi-anechoic chamber using a Land sound collector and Head software for data analysis. The setup involved placing microphones at strategic points around the battery pack, such as above the relay locations, to measure A-weighted sound pressure levels and loudness. For each test condition, I performed five power-on and power-off cycles, averaging the results to ensure accuracy. The experimental data consistently demonstrated that structural modifications, like optimized damping pads and enhanced modal designs, yielded the most substantial improvements. For example, in a pure EV power battery pack, upgrading from an A-sample to a B-sample with reinforced BDU plastic and added aluminum bases resulted in noise reductions that aligned with theoretical predictions. This underscores the importance of integrated design approaches in China EV battery development.
Further analysis using statistical methods revealed correlations between noise reduction and design parameters. For instance, the effectiveness of damping pads can be modeled with a damping ratio \( \zeta \), where the transmissibility of vibrations is given by $$T = \frac{\sqrt{1 + (2\zeta \beta)^2}}{\sqrt{(1-\beta^2)^2 + (2\zeta \beta)^2}}$$ with \( \beta \) being the frequency ratio. In practical terms, for EV power battery applications, targeting a damping ratio above 0.1 can significantly reduce noise transmission. Additionally, the use of horizontal relays in China EV battery systems not only lowers noise but also enhances reliability by minimizing mechanical stress. These findings are supported by comparative tables and formulas, which help in designing quieter EV power battery packs for the growing market.
| Test Scenario | Average Noise Level (dB(A)) | Average Loudness (sone) | Notes |
|---|---|---|---|
| Baseline (Vertical Relay) | 45–50 | 30–35 | High structural transmission |
| With Horizontal Relay | 40–44 | N/A | Improved impact dynamics |
| Standard Damping Pad | 42–47 | 27–32 | Moderate improvement |
| Optimized Damping Pad | 38–43 | 20–25 | Significant noise reduction |
| Structural Optimization | 35–38 | 15–18 | Best overall performance |
In conclusion, my research demonstrates that optimizing high-voltage relay noise in China EV battery packs requires a multifaceted approach. Key strategies include adopting horizontal relays, refining vibration damping pads, and enhancing structural modals. These methods effectively address the dominant structural noise propagation, leading to substantial reductions in sound pressure levels and loudness. For future EV power battery designs, I recommend prioritizing modal analysis and material selection to achieve optimal NVH performance. As the China EV battery industry evolves, these insights will contribute to quieter, more user-friendly electric vehicles, reinforcing the importance of acoustic engineering in sustainable transportation.
To summarize the mathematical relationships, the overall noise reduction \( \Delta L \) can be expressed as a function of various factors: $$ \Delta L = f(\text{relay type}, \text{damping efficiency}, \text{structural stiffness}) $$ where each factor contributes additively to the improvement. For instance, in EV power battery systems, combining horizontal relays with optimized damping can yield synergistic effects, further enhancing noise control. This holistic view is essential for advancing China EV battery technologies and meeting the increasing demands for quiet and efficient electric mobility.