With the rapid adoption of electric vehicles, including hybrid, extended-range, and pure electric types, the operational noise of powertrains has significantly decreased. This reduction has made abnormal noises from vibration-damping rubber components more prominent in China EV models. Through extensive research, we have developed a comprehensive methodology for analyzing and testing these abnormal noises. Our approach begins with collecting original signals under real-world driving conditions where noises occur, followed by analyzing the transmission paths. We then employ digital signal processing techniques, such as high-pass filtering, to replicate these conditions in laboratory settings. This allows us to reproduce the same abnormal noises observed in vehicles, accurately identify their root causes, and formulate effective solutions. Our study integrates theoretical analysis with empirical data, providing practical guidance for addressing abnormal noise issues in electric cars, particularly in the growing China EV market.
The study of abnormal noises has traditionally focused on vehicle-level and system-level aspects, such as chassis or powertrain systems. However, there remains a significant gap in component-level research, especially for vibration-damping rubber parts. This paper addresses this gap by examining the mechanisms and testing methods for abnormal noises in these components. We leverage vibration transmission path theory to dissect air-borne and structure-borne noise propagation in electric cars. For the six common types of abnormal noises—metal contact noise, stick-slip noise, stopper impact noise, decoupler membrane slap noise, cavitation noise, and resonance noise—we propose mitigation strategies, including low-friction coatings, optimized flow channel designs, and modal tuning. Our holistic solution encompasses rapid troubleshooting, bench validation, and vehicle evaluation, validated through a “material-structure-process”协同优化 strategy. This research aligns with international standards like ISO 10846-1–2008 and utilizes advanced sensors and digital signal processing, such as Fast Fourier Transform (FFT) analysis and high-pass filtering, to establish an efficient noise localization and evaluation framework. The findings support lightweight design and enhanced cabin quietness in electric cars, offering substantial engineering value for the China EV industry.
Mechanisms of Abnormal Noise Propagation in Vibration-Damping Rubber Components
Abnormal noises in vibration-damping rubber components, widely used across various vehicle systems, propagate through air-borne and structure-borne paths. Only frequencies within the 20–20,000 Hz range are audible to the human ear; infrasound below 20 Hz and ultrasound above 20,000 Hz remain imperceptible. Air-borne noise is often masked by environmental sounds like road and tire noise, making it difficult to detect inside electric cars. In contrast, structure-borne noise travels through rigid body components, such as chassis frames, and can amplify due to structural resonance, becoming more discernible in the cabin. For instance, in China EV models, vibrations from the powertrain may propagate via mounts to body rails or subframes, eventually reaching the steering wheel, floor, or seats. Similarly, road-induced vibrations follow paths from tires through suspension systems to the body, emphasizing the critical role of rubber components in noise isolation.
Vibration amplification occurs when the natural frequency of a structural component coincides with the excitation frequency, leading to resonance. The dynamic stiffness of rubber isolators plays a key role in vibration transmissibility. The transmissibility ratio \( T \) can be expressed as:
$$ T = \frac{1}{\sqrt{(1 – (f/f_n)^2)^2 + (2\zeta f/f_n)^2}} $$
where \( f \) is the excitation frequency, \( f_n \) is the natural frequency, and \( \zeta \) is the damping ratio. In electric cars, lower powertrain noise exacerbates the perception of such resonances, necessitating precise control of rubber properties.
Sound travels at different speeds through various media, with higher velocities in stiffer materials. This affects how quickly noises transmit through electric car structures. For example, structure-borne noises in China EV models can rapidly propagate via metal components to the cabin, as shown in Table 1.
| State | Medium | Transmission Speed (m/s) |
|---|---|---|
| Gas | Air (15°C) | 340 |
| Gas | Carbon Dioxide | 259 |
| Gas | Hydrogen | 1284 |
| Liquid | Water (Room Temperature) | 1500 |
| Liquid | Gasoline | 1100–1300 |
| Liquid | Alcohol | 1160 |
| Solid | Steel | 5000–6000 |
| Solid | Aluminum | 6420 |
| Solid | Glass | 4540–5640 |
| Solid | Wood | 3300–3600 |
| Solid | Nylon | 2600 |
| Solid | Rubber | 40–150 |
This table highlights that metals facilitate faster noise transmission, underscoring the importance of isolating rubber components in electric cars to prevent structure-borne issues in China EV applications.
Classification of Abnormal Noises and Mitigation Strategies
Based on industry experience and market feedback, we categorize abnormal noises in vibration-damping rubber components into six types, each with distinct mechanisms and preliminary diagnostic methods. For electric cars, these noises become more apparent due to lower background noise, and our strategies are tailored for China EV requirements.
First, metal contact noise arises from exposed metal skeletons in rubber parts colliding with adjacent components, producing high-frequency sounds. Second, stick-slip noise occurs during relative motion between rubber and other surfaces, such as soft coatings, where high friction causes sudden rebound and noise. Third, stopper impact noise results from rubber limiters hitting metal or other rubber parts, generating low-frequency vibrations. Fourth, decoupler membrane slap noise in hydraulic mounts happens when the membrane impacts flow channel plates under high-amplitude inputs. Fifth, cavitation noise is caused by vacuum bubble formation and collapse in hydraulic mounts during large displacements, often in high-temperature conditions. Sixth, resonance noise emerges when component natural frequencies align with excitation forces, amplified by insufficient damping.
We summarize the occurrence conditions and initial diagnostic methods in Table 2, which serves as a quick reference for engineers working on electric car noise issues in the China EV sector.
| Noise Type | Occurrence Conditions | Preliminary Diagnostic Method |
|---|---|---|
| Metal Contact Noise | Collision between uncoated metal parts (sharp sound) | Isolate contact areas with rubber |
| Stick-Slip Noise | Relative displacement under friction (high-frequency, low-amplitude) | Apply lubricants or reduce friction coefficient |
| Stopper Impact Noise | Rapid large-displacement rubber contact (low-frequency impact sound) | Fill gaps with soft materials like paper or cloth |
| Decoupler Membrane Slap Noise | Amplitude exceeding membrane-plate gap (slapping sound) | Optimize membrane stiffness or use non-floating structures |
| Cavitation Noise | High-temperature large displacement causing fluid negative pressure (cavitation sound) | Directly connect main and secondary liquid chambers bypassing channels |
| Resonance Noise | Coupling of system natural frequency and excitation frequency (structural sound) | Adjust rubber stiffness or damping properties |
To mitigate these noises, we propose targeted strategies. For metal contact noise, rubber coating or flexible material isolation reduces impact energy. Stick-slip noise is addressed with low-friction coatings like silicone grease or PTFE, and self-lubricating rubber formulations. Stopper impact noise can be minimized by adding features such as protrusions or grooves to limiters, or increasing rubber volume to lower stiffness. Decoupler membrane slap noise is controlled by reducing membrane hardness and optimizing structures with ribs or convex points; non-floating designs eliminate contact entirely. Cavitation noise is prevented through one-way valves in hydraulic mounts or inverted mounting to isolate forces. Resonance noise is managed by modal analysis to adjust stiffness or mass, shifting natural frequencies away from excitations. These approaches are particularly effective for hydraulic mounts, the most complex rubber dampers, and can be extended to other components in electric cars, enhancing China EV performance.
Testing Methodology for Hydraulic Mount Abnormal Noises
Hydraulic mounts are prone to abnormal noises under specific driving conditions in electric cars, such as low-speed travel on rough roads like cobblestone or washboard surfaces, or medium-speed traversal over large steps or speed bumps. These scenarios induce large displacements in the powertrain, exciting noises that transmit to the cabin. The trend toward high-performance, low-stiffness, and compact mounts in China EV models, combined with larger tires increasing road input, aggravates these issues. Our testing methodology enables precise reproduction and analysis of these noises.
First, we collect original signals from electric cars during noise-prone driving conditions. For example, data acquisition devices measure displacements and frequencies at mount active ends. In one case, we recorded amplitudes of ±1 mm at 10 Hz, which serve as input conditions for bench tests. This step is crucial for replicating real-world scenarios in China EV development.
Next, we conduct bench tests using servo-hydraulic actuators to apply displacements matching vehicle data or equivalent sinusoidal waves (e.g., ±1 mm or ±4 mm amplitudes). The test setup measures excitation displacement, load, and high-pass filtered (HPF) load, with optional acceleration or acoustic sensors. HPF processing isolates noise components above 100 Hz, excluding lower-frequency interferences like stopper impacts or stick-slip noises. The HPF load is analyzed to evaluate abnormal noises quantitatively.
We then perform frequency analysis using FFT to decompose HPF loads into spectral components. This identifies peak frequencies associated with specific noise mechanisms, such as 200–600 Hz for decoupler slap or higher ranges for cavitation. The relationship between noise frequencies and structural resonances helps assess compatibility with electric car bodies, including subframe resonances or secondary isolation effects. Thresholds for each frequency band are established based on empirical data from China EV applications.
For instance, in standard tests like PP2 (±1 mm amplitude) and PP8 (±4 mm amplitude), we set force limits of 10 N and 40 N, respectively, in the time domain. Exceeding these values indicates a high probability of noise. The force \( F \) can be modeled as:
$$ F = m \cdot a + c \cdot v + k \cdot x $$
where \( m \) is mass, \( a \) is acceleration, \( c \) is damping coefficient, \( v \) is velocity, \( k \) is stiffness, and \( x \) is displacement. In hydraulic mounts, additional terms account for fluid dynamics, such as pressure changes \( \Delta P \) in cavitation:
$$ \Delta P = \rho \cdot g \cdot h + \frac{1}{2} \rho \cdot v^2 $$
where \( \rho \) is fluid density, \( g \) is gravity, and \( h \) is height. This equation illustrates how vacuum formation leads to bubble collapse and noise in electric cars.
Case Studies on Hydraulic Mount Abnormal Noises
We present two case studies demonstrating our testing approach. In the first case, a hydraulic mount exhibited significant abnormal noises during bench tests. Under PP2 amplitude, the maximum HPF load reached 25 N, exceeding the 10 N threshold; under PP8, it peaked at 80 N, well above the 40 N limit. FFT analysis revealed prominent peaks in the 200–600 Hz range, characteristic of decoupler membrane slap noise. This alignment with theoretical predictions confirmed the noise mechanism.
In the second case, we modified the mount by replacing a floating decoupler with a non-floating design. Post-modification tests showed HPF loads reduced to 4–7 N for PP2 and 25–30 N for PP8, within acceptable limits. Vehicle evaluation confirmed noise elimination, validating the solution for China EV applications. Table 3 compares the results, highlighting the effectiveness of structural optimization.
| Decoupler Type | PP2 Amplitude Force (N) | PP8 Amplitude Force (N) | Vehicle Evaluation |
|---|---|---|---|
| Floating Decoupler | 12–25 | 45–80 | Abnormal Noise Present |
| Non-Floating Decoupler | 4–7 | 25–30 | No Abnormal Noise |
Based on these cases, we developed a standardized workflow for abnormal noise verification in vibration-damping components, as illustrated in Figure 1. The process starts with vehicle condition collection, proceeds to bench test reproduction, and concludes with data analysis and solution implementation. This flowchart ensures systematic handling of noise issues in electric cars, particularly for China EV manufacturers seeking to enhance cabin comfort.
Conclusion
The proliferation of electric cars, especially in the China EV market, has heightened the importance of addressing abnormal noises in vibration-damping rubber components. Reduced powertrain noise in pure electric modes makes these noises more perceptible, demanding rigorous analysis and testing. Our research provides actionable methodologies: during new electric car development, OEMs incorporate abnormal noise evaluations into NVH testing, requiring suppliers to pass bench tests before vehicle integration. For post-production issues, such as noises in 0 km or post-sale vehicles, our approach enables data collection under real conditions, bench reproduction, and root cause identification through spectral analysis. This facilitates targeted improvements, ensuring quieter and more reliable electric cars. By integrating theoretical insights with practical applications, we contribute to the advancement of China EV technologies, supporting global trends toward sustainable and high-comfort transportation.