As a key component of the transmission system in electric vehicles (EVs), the driveshaft is prone to various NVH (noise, vibration, and harshness) issues due to its operational conditions. During our research, we encountered a critical problem: the anti-wear gasket assembled between the driveshaft and hub bearing endface of an EV frequently fractured, leading to abnormal friction and NVH problems. This article details our approach to resolving this issue using Archard wear theory and engineering analysis tools, providing theoretical and practical insights for EV drivetrain design.
1. Introduction: The Challenge of Driveshaft Gasket Durability in EVs
Electric vehicles have witnessed rapid development, with increasing torque outputs and more frequent torque transitions placing stricter demands on drivetrain components. The driveshaft, responsible for power transmission and suspension motion compensation, operates under more severe conditions in EVs compared to traditional fuel vehicles—higher torque, faster instantaneous rate increases, and frequent torque conversions exacerbate wear and failure risks for associated parts .
Previously, a double-sided anti-friction agent-coated ring gasket was proposed to mitigate stick-slip friction between the driveshaft and hub bearing, effectively reducing 异响 (abnormal noise). However, in EV applications, this gasket showed premature fracture, prompting us to investigate its durability using Archard wear theory. Archard’s model, which describes wear as a function of pressure, sliding distance, and material properties, provided a theoretical foundation for our analysis .
2. Problem Statement: Fracture of Anti-Wear Gaskets in EV Drivetrains
During 整车耐久路试 (vehicle durability road testing) of an EV, we detected a “clicking” noise near the right hub during wheel start and braking. Inspection revealed that the anti-wear gasket between the driveshaft and hub bearing had fractured, with the hub bearing endface exhibiting roughness and sintering. The gasket’s surface coating had worn off, reigniting stick-slip friction and NVH issues .
The failed gasket was a 0.5mm-thick 65Mn steel ring with a 3mm contact width, coated with a domestic silicone-based high-temperature paint (Xinfulong). Analysis of the fracture showed:
- Brittle fracture characteristics with deformation, concentrated at the claw roots;
- Severe paint delamination and pitting in the central 3mm area, with sintering;
- Reduced thickness from 0.50mm at the edge to 0.40mm at the center, with inward concavity near the hub bearing .
Notably, this gasket had performed reliably in fuel vehicles, indicating that EV-specific operational conditions (e.g., higher torque and faster transitions) were key failure drivers .
3. Theoretical Analysis Based on Archard Wear Theory
3.1 Archard Wear Model and Its Application
The Archard sliding wear model describes the wear rate \(\dot{w}\) as:\(\dot{w} = \frac{K}{H} P^{m} V^{n}\) where K is the wear coefficient, H is material hardness, P is contact pressure, V is relative sliding velocity, and m and n are pressure and velocity exponents . For our case, the gasket experiences microscale reciprocating torsional friction, so we simplified the model to total wear W:\(W = \frac{K}{H} P S\) where S is the relative sliding distance. Key observations from this model:
- P is influenced by the locknut torque and contact area; reducing P via increased contact area is feasible without compromising safety;
- K depends on the coating quality and surface conditions, making coating improvement critical for durability .
3.2 CAE Analysis of Stress Concentration
Using Abaqus, we performed finite element analysis to identify stress hotspots. The results showed maximum tensile stress (717 MPa) at the gasket claws, approaching the tensile strength of 65Mn steel (≈735 MPa). As the gasket wore and thinned, its strength decreased, causing stress to exceed the material limit and leading to fracture .
4. Optimization Strategies for Anti-Wear Gaskets
4.1 Increasing Contact Area to Reduce Pressure
To lower contact pressure P, we proposed increasing the gasket’s contact width from 3mm to 5mm, expanding the contact area by 67%. This modification theoretically reduces P proportionally, as shown in the wear formula. Abaqus simulations confirmed that lower pressure decreases the wear coefficient K, further reducing wear rate .
4.2 Enhancing Coating Wear Resistance
The failed gasket’s coating (Xinfulong) showed poor durability, leading to metal-metal contact with a high friction coefficient (0.78). We replaced it with polytetrafluoroethylene (PTFE, Teflon), a material with an extremely low static friction coefficient (0.04) when in contact with steel. Combined with surface phosphating and sandblasting, PTFE forms a deep-adhesion coating that significantly reduces wear. Abaqus analysis showed that with PTFE, the gasket’s tensile stress dropped to 85 MPa, well below the material’s strength .
4.3 Thickening the Gasket to Improve Strength
Increasing the gasket thickness from 0.5mm to 1mm doubles its cross-sectional area, reducing tensile stress. CAE results indicated that even after coating wear, the stress decreases to 551 MPa, below the tensile strength of 65Mn. This measure enhances the gasket’s resistance to fracture during wear .
5. Experimental Validation of Optimization Strategies
5.1 Test Setup and Sample Combinations
We designed seven test samples with different combinations of the three optimization measures:
- Increased contact area (5mm width)
- PTFE coating with improved process
- Thickness increased to 1mm
Tests followed JB/T10189—2010, applying the maximum driveshaft torque at 1–4 Hz for 200,000 cycles. The results were evaluated for fracture, sintering, and coating integrity .
5.2 Results and Analysis
The table below summarizes the validation outcomes:
| Sample | Increased Contact Area | Improved Coating | Increased Thickness | Test Result |
|---|---|---|---|---|
| 1# | √ | – | – | Fracture |
| 2# | – | √ | – | Fracture |
| 3# | – | – | √ | Fracture |
| 4# | √ | √ | – | Good |
| 5# | √ | – | √ | Sintering |
| 6# | – | √ | √ | Good |
| 7# | √ | √ | √ | Good |
Key findings:
- Single measures (Samples 1–3) failed, highlighting the need for combined improvements;
- Samples 4, 6, and 7 (combining two or three measures) showed good performance, with no fracture or sintering;
- Sintering in Sample 5 indicated coating failure prior to fracture, confirming that coating durability is critical .
Based on these results and considering axial dimension constraints in the EV drivetrain, we implemented the combination of increased contact area and improved PTFE coating. This solution passed subsequent vehicle durability testing, resolving the gasket fracture issue .
6. Discussion: Engineering Implications for EV Drivetrains
Our study underscores the unique challenges of EV drivetrain components, where traditional solutions for fuel vehicles may not suffice. The higher torque and more dynamic loading in EVs necessitate materials and designs optimized for wear resistance and durability. The Archard theory proved invaluable in quantifying wear mechanisms, while CAE analysis enabled targeted design improvements .
The PTFE coating’s superior performance (friction coefficient 0.04 vs. 0.78 for steel-steel contact) demonstrates the importance of surface engineering in EV components. Additionally, the contact area expansion strategy offers a simple yet effective way to reduce pressure without major design overhauls, making it cost-effective for mass production .
7. Conclusion
In this research, we addressed the durability issue of anti-wear gaskets in EV driveshafts using Archard wear theory and engineering analysis. Key conclusions include:
- Increasing the gasket’s contact width reduces wear by lowering contact pressure, as described by the Archard model ;
- PTFE-based coatings with advanced processes significantly enhance wear resistance, reducing friction and stress ;
- Thickening the gasket improves its strength, though practical implementation may be constrained by dimensional requirements ;
- Combined optimization measures (contact area expansion and coating improvement) effectively solve the fracture problem, providing critical engineering experience for future EV models .
This work highlights the importance of integrating theoretical models with experimental validation in addressing EV component durability, paving the way for more reliable drivetrain designs in electric vehicles.