On May 9, 2024, the seminar on key technologies for bearing electrical corrosion of 800V drive motor systems, hosted by the Electric Vehicle Industry Technology Innovation Strategic Alliance and undertaken by C&U Co., Ltd., was successfully held in Wuhu, Anhui Province. The conference invited more than 80 industry experts from universities, scientific research institutes, vehicle enterprises, motor companies, materials and parts enterprises to focus on the problem of bearing electrical corrosion of drive motor systems, and conducted in-depth discussions on the mechanism of bearing electrical corrosion, bearing anti-electric corrosion technical route and development trend, shaft current and shaft voltage testing and evaluation methods. The meeting was presided over by Zhao Qian, deputy chief researcher of the Electrification Center of the Society of Automotive Engineers of China, and Qu Jingyao, director of the Industrial Technology Research Department of the Electrification Center, and He Peng, general manager of sales of C&U Co., Ltd., delivered speeches for the meeting.
Group photo of the meeting
In the guest speech session, Xu Xiaoyang, bearing chief engineer of SAIC Jieneng Electric Drive Business Department, Guo Changjian, chief engineer of C&U Co., Ltd., Yang Xiongjie, R&D manager of Mante (Guangzhou) Magnetic Device Co., Ltd. (Magnetec-China), Wu Weiwei, manager of product management department of Hecheng New Material Technology (Shanghai) Co., Ltd., Jing Yunyong, development manager of Wuxi Star Drive Technology Co., Ltd., and Du Bochao, associate professor of Harbin Institute of Technology, gave speeches and sharing. In addition, Harbin Institute of Technology, Harbin Institute of Technology, Beijing Jiaotong University, Major, Institute of Electrical Engineering of the Chinese Academy of Sciences, China Automotive Center, China Automotive Research Institute and other universities and scientific research institutions, FAW, Dongfeng, SAIC, GAC Aion, Chery New Energy, JAC Yttrium, BYD, Weilai, Xiaopeng, Li and other vehicle enterprises, Magna, Bosch, BorgWarner, UMC, Chongqing Tsingshan, Hainachuan, SAIC Transmission, Huayu, CRRC Times, Echotech, Wuxi Xingxi, Honeycomb Yichuang, JEE and other motor and electronic control enterprises, Hongda, Mante, Yunlu, Hecheng, Sinopec lubricants and other materials and parts companies participated in the follow-up discussion.
1
The risk of electrical corrosion in 800V electric drive system has surged, and the development trend of anti-electric corrosion technology is a combination of "blocking, conduction, and reduction".
The 800V electric drive system presents the characteristics of high voltage, high power, high frequency and high speed. Higher voltage stages raise shaft voltages, higher motor power surges induced energy, higher switching frequencies mean more breakdowns, and higher speeds lead to higher operating temperatures and lower oil viscosity making bearing films more prone to breakdown. As a result, the risk of electrical corrosion in 800V electric drive systems has increased dramatically, and special attention must be paid to the risk of electrical corrosion of the bearings on the gearbox side.
The solution strategy of electrical corrosion includes source treatment and path treatment, and a variety of measures can be reasonably matched according to the degree of electrical corrosion risk. The source treatment technology includes the electromagnetic balance design of the motor, the optimization of the output waveform of the inverter and the optimization of the inverter control strategy, among which the AC magnetic ring is more and more widely used and can be used as one of the auxiliary means of anti-electric corrosion technology, but the forward design of the source treatment is very difficult, and the design balance point needs to be considered from the overall system situation. Among the insulation blocking technology, ceramic ball bearings are the most mature and reliable, but the cost is high; Insulated plastic-covered/coated bearings have high requirements for contact interfaces, which have yet to be verified by the market; Insulated shafts have not been promoted in the automotive industry; The insulated bearing chamber has yet to be verified, and various new insulation schemes are constantly emerging, and the cost is constantly decreasing.
In the bypass grounding technology, the conductive ring is suitable for both dry and wet cavities, with excellent conductivity but high cost; The conductive carbon brush has many wear particles and short durability life; The conductivity of conductive non-woven fabrics/conductive rubber in wet cavities is significantly reduced, and the durability effect must be paid attention to; The integrated conductive oil seal saves axial space, but is only suitable for dry cavities; The integrated conductive bearing can also save axial space, and there are various grounding schemes, which need to be selected reasonably and low-cost according to the application environment and the degree of electrical corrosion risk.
Xu Xiaoyang, the bearing chief engineer of SAIC Jieneng Electric Drive Business Department
2
At present, there are still problems in the cost, reliability, installation space and other aspects of magnetic rings, insulated bearings and conductive rings, and there is no cost-effective single anti-bearing electrical corrosion scheme
Nanocrystalline magnetic rings can be referred to as "inductive absorbers" that reduce shaft voltage and shaft current while improving EMC performance. The magnetic permeability and Hc value of nanocrystalline alloys are close to those of crystalline high permalloy and cobalt-based amorphous, and the saturated magnetic inductance Bs is comparable to that of medium nickel permalloy, and the high-frequency loss under high magnetic inductance is much lower than that of iron-based amorphous and silicon steel, and has better corrosion resistance and magnetic stability. The nanocrystalline magnetic ring uses the principle of electromagnetic induction to absorb high-frequency interference signals in the circuit and convert them into heat energy dissipation. MIND has had specific applications in paper mills, steel mills, electric vehicles, etc., and has not had any problems with electrical corrosion of bearings for many years.
R&D Manager of Mante (Guangzhou) Magnetic Devices Co., Ltd. Yang Xiongjie
Ceramic ball bearings, ceramic insulated bearings, and resin insulated bearings belong to the insulation blocking scheme, and the cost still has room for further reduction. The resistivity of ceramic balls is as high as 1018Ωmm2/m, and the density is less than half of that of bearing steel, but the crushing load is small and the toughness is poor, so ceramic ball bearings are suitable for high-speed rotation and stable insulation performance, but they are not impact-resistant and the price is high, and the powder is basically dependent on imports; The dimensions of ceramic/resin insulated layer bearings are the same as those of conventional products, which are suitable for high-speed movement and have stable insulation performance, but the process of ceramic insulated layer bearings is complex and the price is high. The conductive grease bearing is made of special conductive grease, which is suitable for high-speed rotation, but not suitable for 800V high-voltage scenarios.
Guo Changjian, Chief Engineer of C&U Co., Ltd
To solve the problem of electrical corrosion of bearings, it is necessary to clarify and eliminate three common cognitive misunderstandings, and adopt reasonable application measures. First, it is necessary to judge whether it is a discharge waveform or a non-discharge waveform by the shaft voltage waveform, not that the lower the measured shaft voltage, the better; Second, the motor is not at ease when it adopts insulated bearings, and the bearing part of the reducer end will cause electrical corrosion after becoming the unloading path of the shaft voltage; Thirdly, the conductive ring is not installed at either shaft end, and the shaft voltage at one end of the conductive ring will drop greatly, but the other end will drop less.
Wu Weiwei, Manager of Product Management Department of Hecheng New Material Technology (Shanghai) Co., Ltd
3
Shaft voltage/shaft current and bearing electrocorrosion testing and evaluation method group standards need to be formulated urgently to continue to solve the pain points for the industry.
At present, there is no unified standard for shaft voltage and shaft current testing in the industry, and Wuxi Xingdrive and Harbin Institute of Technology have led two group standards respectively. Wuxi Stardrive has joined forces with more than 30 units to carry out the compilation of the group standard of "Shaft Voltage Test Method for Drive Motor System", which was established in September 2023, covering the requirements of test instruments and equipment, the transformation of the bearing voltage test prototype, the transformation of the bearing current test prototype, the construction of the test bench, the definition of working conditions and the analysis of the results, etc., which is currently in the revision stage after submitting for review.
Jing Yunyong, development manager of Wuxi Star Drive Technology Co., Ltd
Harbin Institute of Technology, together with nearly 20 units, has carried out the compilation of the standard of "Electrocorrative Test and Evaluation Methods for Electric Vehicle Drive Motor Bearings", which was established in January 2024 and describes the electrical corrosion test and evaluation methods of electric vehicle drive motor bearings, including test conditions, operation specifications and evaluation methods, etc., which is suitable for the electrical corrosion test and evaluation of electric vehicle drive motor bearings driven by voltage source motor controllers.
Du Bochao, associate professor of Harbin Institute of Technology
At the end of the meeting, Qu Jingyao, Director of the Industrial Research Department of the Electrification Center of the Society of Automotive Engineers of China, summarized the meeting. High voltage and high speed are still the long-term development direction of electric drive systems, especially considering the subsequent demand for megawatt charging, and the voltage platform is expected to be further improved. Bearing is an important link to ensure safety and reliability after high pressure, and it is also a key technical product for various performance indicators such as NVH, efficiency and reliability of electric drive assembly system. With the development of the new energy vehicle industry, the domestic precision transmission parts technology industry chain continues to rise and mature, and in the future, with the deepening of electrification and intelligent integration, it will surely bring new development of precision transmission technology. Subsequently, the Society of Automotive Engineers of China will continue to carry out work in the field of electric drive system in the field of common technological innovation, standard development, hot topic discussion, etc., and hope to get industry support.
Source: Electric Vehicle Alliance