As a key component in the transmission system of modern vehicles, the drive shaft plays a critical role in power transfer while accommodating suspension movements and maintaining constant velocity. In the context of electric car development, particularly in the rapidly expanding China EV market, drive shafts face unique challenges due to higher torque outputs, faster torque rise rates, and frequent torque reversals. These conditions exacerbate NVH (Noise, Vibration, and Harshness) issues, such as stick-slip induced noises during startup and braking. A common solution involves using a ring-shaped gasket coated with anti-friction agents on both sides, inserted between the drive shaft and hub bearing end faces to mitigate friction-induced sounds. However, in electric car applications, these gaskets often suffer from premature fracture, leading to renewed NVH problems. This article, based on my engineering experience, explores the durability issues of anti-wear gaskets in electric car drive shafts using Archard wear theory, supported by ABAQUS simulations, and proposes effective solutions validated through rigorous testing.
The drive shaft assembly in an electric car typically consists of outer and inner constant velocity joints, a shaft, and protective boots, all designed to transmit power efficiently. In many China EV models, the connection between the drive shaft and hub bearing relies on axial splines secured by a lock nut. Due to inherent spline clearances and elastic deformations under high torque, relative motion can occur at the contact surfaces, triggering stick-slip phenomena and associated noises. To address this, a dual-sided anti-friction gasket was introduced, which alters the friction characteristics and effectively suppresses stick-slip incidents in conventional vehicles. However, in electric car environments, where operational demands are more severe, these gaskets frequently experience fractures, as observed in durability tests. For instance, during road testing of a specific China EV model, audible “clicking” sounds were detected during wheel acceleration and deceleration, traced back to gasket failure and surface damage on the hub bearing. Post-failure analysis revealed brittle fractures at the gasket’s claw roots, severe coating wear, and localized thinning, indicating inadequate durability under electric car conditions.
To understand the root cause, I applied Archard wear theory, which provides a fundamental framework for analyzing sliding wear. The Archard model expresses the wear rate at a contact point 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, and $V$ is the relative sliding velocity. The exponents $m$ and $n$ account for pressure and velocity dependencies, but in the context of electric car drive shafts, where the motion involves microscopic reciprocating torsion, the model can be simplified for specific工况 assessment. The total wear volume $W$ over a sliding distance $S$ is given by:
$$ W = K \frac{P S}{H} $$
In electric car applications, the wear coefficient $K$ varies significantly based on surface conditions, lubrication, and material pairs, with values ranging over orders of magnitude for metal-on-metal contacts. Material hardness $H$ is tied to the gasket base material, such as 65 Mn steel, but short-term variations are minimal. Contact pressure $P$ is influenced by the lock nut torque and the contact area between the gasket and hub bearing. Given that reducing lock nut torque is not advisable for safety reasons, optimizing the contact area becomes crucial. From Equation (2), it is evident that increasing the contact area reduces $P$, thereby decreasing wear. Additionally, enhancing the coating quality can improve the wear coefficient $K$, as coatings with lower friction coefficients and better durability reduce the overall wear rate. For electric car drive shafts, where torque fluctuations are more pronounced, these factors are critical to preventing gasket failure.
Based on this analysis, I proposed several optimization measures to improve gasket durability in China EV models. First, increasing the contact width of the gasket and hub bearing end face from 3 mm to 5 mm expands the contact area by approximately 67%, which directly reduces contact pressure $P$. According to Equation (2), this should lead to a substantial decrease in wear volume. Moreover, lower pressure can positively affect the wear coefficient $K$, further mitigating wear. Second, improving the coating耐磨性 is essential. The original coating, a water-based organic silicone material, showed poor durability under electric car conditions, leading to rapid wear and metal-to-metal contact. Replacing it with polytetrafluoroethylene (PTFE), commonly known as Teflon, offers superior耐磨性 due to its low friction coefficient and excellent thermal stability. For instance, the static friction coefficient for steel-PTFE contacts is as low as 0.04, compared to 0.78 for rough high-carbon steel pairs, which significantly reduces the wear coefficient $K$ and delays coating failure. Third, increasing the gasket thickness from 0.5 mm to 1 mm enhances its cross-sectional area, reducing tensile stresses under load. Using ABAQUS simulations, I analyzed the stress distribution: for a worn gasket with a high friction coefficient, the maximum tensile stress reached 717 MPa,接近 the tensile strength of 65 Mn steel, but with increased thickness, this stress dropped to 551 MPa, below the material’s limit, thereby reducing fracture risk.
To validate these measures, I conducted bench tests based on JB/T 10189-2010 standards for torsion fatigue strength, applying the maximum torque of the electric car drive shaft at 1–4 Hz for 200,000 cycles. Different combinations of the proposed measures were tested, as summarized in Table 1. The results showed that single-factor improvements, such as only increasing contact area or coating quality, were insufficient to prevent fracture or sintering. However, combinations involving multiple measures, like enhanced contact area with improved coating, yielded good results, with no coating failure or fractures. This underscores the importance of integrated solutions for electric car applications.
| 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 |
The test outcomes highlight that while individual improvements offer some benefits, their synergy is essential for robust performance in electric car drive shafts. For example, Sample 4, which combined increased contact area with improved coating, passed the test without issues, whereas Sample 5, with area increase and thickness boost, showed sintering, indicating coating failure. In practical terms, for the China EV model under study, the combination of enlarged contact area and advanced coating was adopted, successfully resolving the gasket fracture problem in subsequent road tests. This approach not only enhances durability but also aligns with the cost and timeline constraints of electric car development.
In conclusion, the application of Archard wear theory, combined with engineering simulations, provides a systematic method to address anti-wear gasket durability in electric car drive shafts. Key insights include: increasing the contact area reduces pressure and wear; employing high-performance coatings like PTFE lowers the wear coefficient; and enhancing gasket thickness mitigates tensile stresses. The validation through combined measures demonstrates that holistic solutions are necessary for the demanding conditions of China EV markets. This research contributes valuable theoretical foundations and practical experience for future electric car models, ensuring reliable NVH performance and supporting the growth of sustainable transportation. As the electric car industry evolves, continued refinement of these strategies will be vital for overcoming similar challenges in drive system components.