As a key component in the transmission system of automobiles, the drive shaft is prone to various NVH (Noise, Vibration, and Harshness) issues during operation. In electric vehicles, the drive shaft’s working conditions have become more demanding due to higher torque outputs, rapid torque changes, and frequent torque reversals. This exacerbates problems such as stick-slip friction between the drive shaft and hub bearing interfaces, leading to abnormal noises during startup and braking. A common solution involves using a ring gasket coated with anti-friction agents on both sides, which effectively mitigates stick-slip induced noise by altering the friction characteristics. However, in electric vehicles, these gaskets often experience premature failure, including fracture and wear, resulting in renewed NVH issues. This paper addresses the durability problem of anti-wear gaskets in electric vehicle drive shafts by applying Archard wear theory and employing engineering analysis tools like Abaqus. Multiple improvement strategies are proposed, combined, and validated to resolve gasket fracture issues, providing a theoretical foundation and practical insights for future electric vehicle development.
The drive shaft, comprising outer and inner constant velocity joints, shafts, and dust covers, transmits power while accommodating suspension movements. In many electric vehicles, the drive shaft connects to the hub bearing via splined structures secured by lock nuts. Gaps and elastic deformations in the splines under high torque can cause relative motion at the contact surfaces, triggering stick-slip friction and noise. While solutions like anti-wear gaskets have proven effective in traditional internal combustion engine vehicles, the unique demands of electric vehicles—such as instantaneous torque application and lower background noise—highlight durability shortcomings. In China EV markets, where electric vehicle adoption is rapidly growing, ensuring component reliability is critical for customer satisfaction and brand reputation.
In one case, an electric vehicle undergoing endurance testing exhibited a “clicking” noise during wheel startup and braking. Investigation revealed that the anti-wear gasket between the drive shaft and hub bearing had fractured, and the hub bearing surface showed signs of roughness and sintering. The gasket, made of 65 Mn steel with a thickness of 0.5 mm and a contact width of 3 mm, was coated with a friction-reducing agent (e.g., Xinfuron, an organic silicon-based high-temperature coating). Fracture analysis indicated brittle failure at the claw roots, severe coating wear over a 3 mm central area, and thickness reduction to 0.40 mm due to wear. This failure not only caused NVH problems but also risked safety in electric vehicle operations. The transition to electric vehicle architectures in China EV manufacturing necessitates robust solutions to such wear-related issues.
The wear mechanism of anti-wear gaskets involves sequential stages: initial coating wear, increased friction coefficient, base material wear, and eventual fracture when tensile stresses exceed material strength. To analyze this, Archard’s wear theory provides a foundational model. The wear rate at a contact point can be expressed as:
$$ \dot{w} = K \frac{P^m V^n}{H} $$
where \( \dot{w} \) is the wear rate, \( K \) is the wear coefficient, \( H \) is the material hardness, \( P \) is the contact pressure, \( V \) is the relative sliding velocity, and \( m \) and \( n \) are exponents for pressure and velocity, respectively. For simplification in reciprocating torsional friction scenarios common in drive shafts, the total wear volume \( W \) can be approximated as:
$$ W = K \frac{P S}{H} $$
Here, \( S \) represents the relative slip distance, constrained by the spline geometry of the drive shaft. The wear coefficient \( K \) varies widely—by over 1000 times—depending on surface conditions and lubrication. In electric vehicle applications, factors like higher torque and frequent cycling amplify wear, making accurate prediction challenging. Material hardness \( H \) is fixed for a given gasket material, while contact pressure \( P \) depends on the lock nut torque and contact area. Reducing \( P \) by increasing the contact area is a viable strategy, as is enhancing coating durability to improve \( K \).
Based on Archard’s model, several optimization measures were identified to enhance gasket durability in electric vehicles. First, increasing the contact area between the gasket and hub bearing surface reduces contact pressure \( P \). Originally, the gasket had a 3 mm wide annular contact; expanding this to 5 mm increases the area by 67%, significantly lowering \( P \). According to the wear equation, this directly reduces wear volume \( W \). Additionally, lower pressure may positively influence the wear coefficient \( K \), further diminishing wear rates. Finite element analysis (FEA) using Abaqus confirmed that stress concentrations, particularly at claw roots, contribute to fracture. For instance, in the original design, maximum tensile stresses reached 717 MPa under high-friction conditions, nearing the tensile strength of 65 Mn steel (approximately 800 MPa). Increasing the contact width redistributes stresses, as shown in Table 1, which summarizes key parameters.
| Parameter | Original Design | Improved Design |
|---|---|---|
| Contact Width (mm) | 3 | 5 |
| Contact Area Increase | Baseline | 67% |
| Max Tensile Stress (MPa) | 717 | Reduced (FEA results) |
| Wear Volume (Relative) | High | Lower |
Second, improving the coating’s wear resistance is crucial. The original coating, such as Xinfuron, although effective in reducing friction, wore off quickly under electric vehicle conditions, leading to metal-to-metal contact with a friction coefficient as high as 0.78. Alternative coatings like polytetrafluoroethylene (PTFE, or Teflon) offer superior durability. PTFE has an extremely low friction coefficient—static friction of 0.04 and dynamic friction of 0.02—which not only mitigates stick-slip noise but also reduces the wear coefficient \( K \). Coating processes like phosphating or sandblasting enhance adhesion, prolonging service life. Abaqus simulations under low-friction conditions (e.g., with PTFE) showed tensile stresses dropping to around 85 MPa, well below the material’s strength limit, preventing fracture. This is particularly beneficial for China EV models, where long-term reliability is a priority.
Third, increasing gasket thickness from 0.5 mm to 1.0 mm boosts cross-sectional area, reducing tensile stresses. Even if the coating wears off, FEA indicated that stresses could decrease to 551 MPa, below the material’s tensile strength, thus delaying fracture. However, thickness changes may impact axial dimensions in the drive assembly, requiring careful integration in electric vehicle designs.
To validate these measures, seven sample combinations were tested under accelerated conditions based on the JB/T 10189-2010 standard for torsional fatigue strength. The test involved applying the maximum torque of the electric vehicle drive shaft at frequencies of 1–4 Hz for 200,000 cycles. Failure was defined as fracture, sintering, or coating loss that could lead to NVH issues. Table 2 summarizes the combinations and results.
| Sample | Increased Contact Area | Improved Coating | Increased Thickness | Test Result |
|---|---|---|---|---|
| 1# | Yes | No | No | Fracture |
| 2# | No | Yes | No | Fracture |
| 3# | No | No | Yes | Fracture |
| 4# | Yes | Yes | No | Good |
| 5# | Yes | No | Yes | Sintering |
| 6# | No | Yes | Yes | Good |
| 7# | Yes | Yes | Yes | Good |
Results showed that single-factor improvements (Samples 1–3) were insufficient, as all led to fracture or sintering. For instance, Sample 1, with only increased contact area, still fractured due to coating wear. Sample 2, with coating improvement alone, could not withstand high stresses. Sample 3, with thickness increase, experienced sintering, indicating coating failure. In contrast, combined measures (Samples 4, 6, and 7) performed well, with no coating loss or fracture. Sample 4, combining increased contact area and improved coating, passed the test and was subsequently validated in full vehicle endurance tests for electric vehicles. This combination was adopted for implementation, as it avoided dimensional changes associated with thickness increases, which are critical in tight electric vehicle packaging.
The optimization process underscores the importance of a holistic approach. For electric vehicle drive shafts, the wear equation can be extended to account for operational specifics. For example, the relative slip \( S \) depends on spline design and torque fluctuations common in electric vehicle regenerative braking. The modified wear volume formula for electric vehicle applications is:
$$ W_{EV} = K_{EV} \frac{P S_{EV}}{H} $$
where \( K_{EV} \) and \( S_{EV} \) are tailored for electric vehicle conditions, such as higher cycle rates. Additionally, material selection plays a role; for instance, using harder materials or composites could further enhance \( H \). In China EV development, cost-effectiveness is also considered, making solutions like PTFE coatings and area increases more feasible than material changes.
In summary, addressing anti-wear gasket durability in electric vehicle drive shafts requires a multi-faceted strategy rooted in Archard wear theory. Increasing the contact area reduces contact pressure and wear, while advanced coatings like PTFE lower friction coefficients and wear rates. Thickness increases provide mechanical strength but must be balanced with design constraints. Validation through combined measures ensures robustness, as demonstrated in testing. This approach not only resolves immediate fracture issues but also contributes to the broader goal of improving NVH performance in electric vehicles. For the rapidly expanding China EV market, these insights offer a scalable framework for enhancing component longevity and customer satisfaction. Future work could explore dynamic modeling of wear in electric vehicle drive systems under real-world conditions, further refining these strategies for next-generation electric vehicle platforms.