1. Introduction
With the rapid development of new energy vehicles, the demand for vehicle performance in various aspects is increasing. Among them, the issue of noise, vibration, and harshness (NVH) has become a key factor affecting the comfort and quality of vehicles. In particular, the gear order noise of the transmission, which was previously masked by the engine noise in traditional vehicles, has become more prominent in new energy vehicles. This not only affects the driving experience of passengers but also poses challenges to the design and development of vehicle transmissions.
The traditional approach to dealing with transmission gear order noise often involves post-optimization during the development process. However, this method usually requires a large amount of time and resources, and may not be able to achieve satisfactory results if the initial design is not proper. Therefore, it is necessary to explore a more efficient and effective design method from the very beginning of the design process.
This article presents a DNA design method for gear order noise of new energy passenger vehicle transmissions. This method emphasizes considering various factors related to gear order noise from the concept design stage, aiming to improve the success rate of the first design, shorten the development cycle, and reduce verification resources.
2. Concept Design Stage
2.1 Gear Order Noise “DNA” Design Concept
The gear order noise “DNA” design is a method that defines indicators related to the performance of the transmission system from the initial design stage. It comprehensively considers various requirements from performance to reliability, from processing to cost, and from cycle to platformization.
2.2 Decision Matrix for Design Selection
To meet the various requirements mentioned above, a decision matrix is used as a tool for decision-making. The decision matrix assigns different weights to factors such as benchmarking applications, performance, weight, reliability, process, platformization, cost, and cycle. The scores of different schemes are evaluated based on their performance in these aspects, and the final weighted total score of each scheme is calculated by multiplying the weight and the score. This helps in comparing and selecting the optimal design scheme.
| Indicator | Scheme 1 (Baseline) Scheme 2 | ||
|---|---|---|---|
| Weight | Description | Score | |
| Benchmarking Application | 5 | 5 | |
| Performance | 8 | 5 | |
| Weight | 5 | 5 | |
| Reliability | 8 | 5 | |
| Associated Change | 8 | 5 | |
| Process | 5 | 5 | |
| Platformization | 5 | 5 | |
| Cost | 8 | 5 | |
| Cycle | 5 | 5 | |
| Total Score | 285 |
2.3 Sources of Gear Order Noise
The generation of gear order noise mainly stems from the impact during gear tooth meshing. The vibration generated by the impact is transmitted from the tooth surface to the tooth body, then to the shaft, and finally to the transmission housing through the bearings on the shaft, causing the vibration of the housing surface and resulting in the audible gear order noise.
2.4 Optimization of Meshing Times
- Reducing Gear Rotational Speed and Selecting Appropriate Number of Teeth: The high rotational speed of gears and a large number of meshing times per second can lead to high-frequency noise. In the case of the first-stage gear connected to the motor, although its rotational speed is high (up to 16,000 r/min), when selecting the number of teeth, a relatively lower number should be chosen while avoiding root cutting (less than 17 teeth). In a multi-stage transmission, the gear ratio of each stage is also crucial. In addition to considering the meshing order of each stage, it is necessary to avoid the slot and pole orders of the motor. There should be a certain order deviation (greater than 7% or higher) between the first-order and its multiple orders of different components to prevent resonance caused by the same vibration source at the same frequency during meshing.
- Example of Meshing Order Deviation: For example, in a certain transmission, the P3 shaft gear directly connected to the motor has 26 teeth, with a main order of 26. It needs to be checked against the 8th order and its multiple orders of the motor. According to current experience, a deviation requirement of greater than 7% should be met within 5 times the order, and after 5 times the order, due to the decrease in energy, it may not need to be emphasized as much.
2.5 Reduction of Meshing Impact Energy
- Maintaining Appropriate Working Clearance: In addition to optimizing the meshing times, it is necessary to reduce the impact energy during meshing to decrease the vibration amplitude. This requires reserving a certain working side clearance to allow lubricating oil to enter and accommodate part processing and assembly errors. Based on contact dynamics theory, a gear meshing contact impact model can be established. When the gear is not in meshing contact, the active tooth surface accelerates, and the impact energy can be approximately calculated as . When the torque is constant, the impact size E is related to the acceleration time . Therefore, to reduce the impact energy, the tooth side clearance can be reduced to shorten , and the rotational inertia of the driven gear can be reduced to lower the relative velocity v.
- Importance of Contact Ratio: Another design indicator for gears is the contact ratio. An increase in the contact ratio can reduce impact. However, when designing, attention should be paid not only to the distribution relationship between the normal contact ratio and the axial contact ratio , but also to the risk of brittle fracture of the tooth top width after heat treatment when excessively pursuing a high normal contact ratio .
2.6 Superior Support and Positioning Structure
- Axial Positioning: The axial positioning of gears requires a scheme that reduces axial movement to avoid fluctuations in the axial tooth side clearance. At the same time, sufficient meshing allowance should be reserved to ensure the meshing overlap after gear movement and installation, usually ensuring that the unilateral allowance is ≥1.5 mm. In the detailed design stage, it is necessary to check whether this meshing allowance meets the requirements through a dimension chain.
- Radial Positioning: For radial positioning, a scheme with the highest coaxiality should be selected to ensure the stability of the normal tooth side clearance and contact ratio during gear meshing, that is, to ensure the center distance during gear meshing.
- Selection of Support Structure: In addition, a structure with high support stiffness should be selected, and the bearing matching should be optimized to reduce the deformation of the support shaft and narrow the meshing angle between the shaft and the gear. For example, when using a cantilever structure, the length of the cantilever should be shortened as much as possible to optimize the support stiffness of the gear. High-strength materials should be used, and corresponding heat treatment requirements should be set.
2.7 High-Precision Processing Technology
- Error Sources in Gear Processing: During gear processing, errors may occur in the shape of each tooth, the shape between teeth, and the tooth side clearance on the circumference due to the continuous processing method (such as roll/shaver – heat treatment – grind/finish). These errors can affect the tooth side clearance and ultimately cause fluctuations in the impact energy. Although internal gear rings can be processed with all teeth in one go through broaching, heat treatment is still required, and due to the difficulty of post-heat treatment processing, errors may also exist.
- Consideration for Processing Technology: With the development of high-speed motors, the accuracy requirements for input gear pairs are increasing. Therefore, when designing, the processability of part processing should be considered, the clamping and positioning accuracy should be improved, and the shape of the part should be regulated to reduce heat treatment deformation, which is beneficial for both processing and reducing processing errors.
2.8 Concept Design Summary
In the concept design stage, if the “DNA” design of gears is not good, many macroscopic optimizations in the detailed design stage may not be carried out smoothly or the optimization effect may be limited. Therefore, in addition to ensuring basic strength, the above aspects also need to be considered.
3. Detailed Design Stage
3.1 Macroscopic Optimization of Order Noise
- Confirmation of Meshing Dislocation: At the macroscopic level, it is necessary to confirm the meshing dislocation amount of gears, which is the deviation between the actual meshing position and the ideal meshing position of a pair of meshing gear pairs. A lower value indicates better meshing conditions. The meshing dislocation amount is affected by factors such as the thickness of the gear rim and web. If the thickness is too thin, larger deformation will occur under the action of gear force, increasing the dislocation amount. The deflection of the shaft and the clearance and limit of the bearing also affect the meshing dislocation amount. For example, using a long cantilever structure when the gear is far from the support point on the shaft will increase the shaft deformation and thus the dislocation amount.
- Limitations of Macroscopic Optimization: Although macroscopic optimization can reduce the meshing dislocation amount, it cannot completely eliminate its influence. Deformation will only be reduced but not completely disappear, so further optimization at the microscopic level is required.
3.2 Microscopic Optimization of Order Noise
- Confirmation of Transmission Error and Contact Spot Simulation: At the microscopic level, it is necessary to confirm the transmission error of gears and conduct contact spot simulation. By importing the stiffness of components, the support stiffness of the bearing seat can be made close to the actual situation, improving the simulation accuracy. Gear modification can be used to optimize gear contact, such as adding normal and axial bulges and making fine adjustments in the direction of the pressure angle or spiral angle. When setting the modification parameters, it is necessary to ensure that the left and right tooth surfaces, the actual contact tooth surface, the tooth surface specified in the drawing, and the tooth surface processed and detected are the same to avoid deviations when the design is implemented.
- Simulation of Different Torque Conditions: By setting different torque conditions (such as 30%, 60%, and 90% torque) to simulate vehicle forward movement, towing, energy recovery, and reverse movement, the peak-to-peak transmission error (PPTE) under different conditions and the contact spots can be obtained. Through the design of experiment (DOE) method, with the gear modification parameters as factors, the tolerance deviation and median as levels, and the transmission error as the response value, a full-factor design of the modification parameters can be carried out. The effect diagrams of each modification under different conditions can be obtained through effect analysis, which can help to confirm the median and tolerance band range of the design value and obtain the modification tendency of parts, enhancing the robustness of the design.
4. Design Verification
4.1 Testing Methods and Contents
- Durability Test: Through sample production and prototype building, various tests are carried out. After the durability test, the gear is detected using a gear measuring machine to observe the meshing situation on the tooth shape and tooth direction. The measurement results show that there is no meshing depression due to uneven load, and the tooth surface contact state is good, close to that of a new part.
- Order Noise Test: The order noise test is carried out to obtain the waterfall plot and slice information of the test. On the bench and in the whole vehicle, no obvious gear order lines are found, and the order slices are about 30 dB lower than the total sound pressure level, indicating good performance.
- Gear Meshing Spot Test: The gear meshing spot test is carried out according to the simulated load. The obtained spots are compared with the simulated contact shape, and no uneven load phenomenon is observed, which is basically consistent with the simulation results.
4.2 Significance of Design Verification
The design verification process helps to confirm the design, correct the model, and improve the simulation accuracy. It ensures that the designed product meets the requirements and has good performance.
5. Summary
The DNA design method for gear order noise of new energy passenger vehicle transmissions presented in this article has many advantages. In the concept design stage, the input and boundaries are confirmed, and the design and performance index requirements are defined. In the detailed design stage, the design is refined and optimized, and the robustness is enhanced through DOE analysis. In the design verification stage, the design is confirmed through testing. This method can improve the reliability and success rate of product development, shorten the development cycle, and reduce development costs. It provides a new design idea and method for the transmission manufacturers in the new energy vehicle industry, which is of great significance for improving the NVH performance of vehicle transmissions and enhancing the overall quality of vehicles.
6. The Importance of Gear Order Noise Control in New Energy Vehicles
6.1 Impact on Driving Experience
In new energy vehicles, the absence of engine noise makes the transmission gear order noise more noticeable. Uncontrolled gear order noise can cause discomfort to passengers, affecting their perception of the vehicle’s quietness and smoothness. A quiet and comfortable driving environment is crucial for enhancing the driving experience, especially during long trips or in urban driving conditions where noise pollution is a concern.
6.2 Market Competitiveness
As the new energy vehicle market becomes increasingly competitive, vehicle manufacturers are constantly striving to improve the overall quality and performance of their products. NVH performance, including gear order noise control, has become an important factor in differentiating vehicles. A vehicle with better noise control is more likely to attract customers and gain a competitive edge in the market.
7. Comparison with Traditional Design Methods
7.1 Post-Optimization in Traditional Design
Traditional design methods often focus on post-optimization during the development process. After the initial design of the transmission is completed, problems related to gear order noise are identified and addressed through various optimization techniques. This approach may involve making adjustments to the gear geometry, changing the material properties, or modifying the manufacturing process.
7.2 Drawbacks of Traditional Methods
However, the traditional post-optimization approach has several drawbacks. Firstly, it requires a significant amount of time and resources, as multiple iterations of design and testing may be necessary to achieve satisfactory noise reduction. Secondly, if the initial design has fundamental flaws, it may be difficult to achieve optimal noise control through post-optimization alone. This can lead to suboptimal performance and increased development costs.
7.3 Advantages of the DNA Design Method
In contrast, the DNA design method presented in this article addresses gear order noise from the very beginning of the design process. By considering noise-related factors during the concept design stage, potential problems can be identified and resolved early on. This approach not only saves time and resources but also improves the likelihood of achieving excellent noise control in the final product.
8. Future Trends and Challenges
8.1 Technological Advancements
With the continuous development of technology, there are several trends that will impact the design and control of gear order noise in new energy vehicles. For example, the increasing use of advanced materials with better mechanical properties and noise absorption characteristics can help to reduce gear noise. Additionally, the development of more sophisticated simulation and analysis tools will enable designers to better predict and optimize gear order noise during the design process.
8.2 Challenges in Meeting Stringent Requirements
Despite these technological advancements, there are still challenges to be faced. As regulations and customer expectations regarding vehicle NVH performance become more stringent, meeting these requirements will require continuous innovation and improvement. Designers will need to balance the trade-offs between noise control, performance, cost, and manufacturability to develop transmissions that meet all these criteria.
8.3 Integration with Overall Vehicle Design
Another challenge is the integration of gear order noise control with the overall vehicle design. The transmission is just one component of the vehicle, and its performance is affected by other systems such as the motor, the chassis, and the body structure. Achieving optimal noise control requires a holistic approach that takes into account the interaction between different vehicle components.
9. Case Studies
9.1 Successful Application of the DNA Design Method
Several vehicle manufacturers have successfully applied the DNA design method to their new energy vehicle transmissions. For example, Company X implemented this method in the design of a new electric vehicle transmission. By following the DNA design principles, they were able to achieve significant reduction in gear order noise compared to their previous designs. The transmission exhibited excellent NVH performance, resulting in improved customer satisfaction and a competitive advantage in the market.
9.2 Lessons Learned from Case Studies
From these case studies, several lessons can be learned. Firstly, the importance of early consideration of gear order noise in the design process cannot be overstated. Secondly, a comprehensive approach that takes into account all aspects of the transmission design, from concept to verification, is essential for achieving optimal noise control. Finally, continuous monitoring and improvement of the design based on test results are necessary to ensure long-term success.
10. Conclusion
In conclusion, the DNA design method for gear order noise of new energy passenger vehicle transmissions offers a promising approach to improving the NVH performance of vehicles. By addressing noise-related issues from the concept design stage, this method can save time and resources, improve the success rate of product development, and enhance the overall quality of vehicles. As the new energy vehicle market continues to grow and evolve, the importance of gear order noise control will only increase. Manufacturers should embrace this innovative design method and continue to explore ways to further optimize gear order noise control in their future products. This will not only benefit the driving experience of customers but also contribute to the competitiveness of their vehicles in the market.