Abstract

With the vigorous development of the new energy vehicle industry, the drive motor, as a core component, directly determines the overall quality of the vehicle. Among them, the problem of bearing noise has become increasingly prominent, seriously affecting the driving comfort and noise reduction performance of the vehicle. This paper deeply analyzes the generation mechanism of bearing noise in the drive motors of new energy vehicles, expounds the root causes of noise from multiple aspects such as electromagnetic, mechanical, and lubrication factors, and proposes a series of targeted improvement measures. The aim is to provide theoretical support and practical guidance for improving the noise reduction level and reliability of the drive motors of new energy vehicles.

Keywords

New Energy Vehicles; Drive Motor; Bearing Noise; Improvement Measures

1. Introduction

New energy vehicles, with their advantages of environmental protection and energy conservation, are gradually becoming the mainstream development trend of the global automotive industry. The drive motor, as the "heart" of new energy vehicles, is crucial for its stable operation and quiet performance. The bearing, as a key component of the drive motor, plays an important role in supporting the rotor and ensuring the rotation accuracy. However, in actual operation, bearing noise often becomes a major problem affecting the driving experience of new energy vehicles. Excessive bearing noise not only reduces the quietness inside the vehicle but may also indicate potential faults in the bearing, affecting the reliability and service life of the drive motor and even the entire vehicle. Therefore, it is of great practical significance to deeply study the causes of bearing noise in the drive motors of new energy vehicles and explore effective improvement measures.

2. Classification and Generation Mechanism of Bearing Noise in Drive Motors of New Energy Vehicles

2.1 Electromagnetic Noise

In the drive motors of new energy vehicles, electromagnetic noise is one of the more complex and influential noise sources. When the motor is powered on and running, the magnetic fields between the stator and the rotor interact to generate electromagnetic forces. On the one hand, these electromagnetic forces are used to drive the rotation of the motor rotor, and on the other hand, they will cause the vibration of the motor structure, thereby generating noise. Its generation mechanism mainly includes the following aspects:

Unbalanced Magnetic Pull: During the operation of the motor, due to factors such as uneven air gaps and asymmetric magnetic circuits, the magnetic pull between the stator and the rotor will be unbalanced. This unbalanced magnetic pull will cause the stator to vibrate periodically, and the noise will be radiated into the surrounding air through the casing. For example, when the motor rotor is eccentric, the size of the air gap will change, resulting in uneven magnetic conductance, thus generating an unbalanced magnetic pull and causing electromagnetic noise.

Cogging Torque: Cogging torque is a unique electromagnetic phenomenon in permanent magnet synchronous motors. Due to the presence of stator teeth and slots, the air gap magnetic conductance changes periodically, resulting in the generation of cogging torque during the operation of the motor. The fluctuation of the cogging torque will cause the vibration and noise of the motor, especially when the motor is running at a low speed, this influence is more obvious. By adopting design methods such as fractional slot windings, stator skewing, or rotor skewing, the cogging torque can be effectively reduced, and the electromagnetic noise can be decreased.

Harmonic Magnetic Field: The power supply of the motor often contains harmonic components, and these harmonics will generate a harmonic magnetic field inside the motor. The harmonic magnetic field interacts with the fundamental magnetic field to generate additional electromagnetic forces, causing the vibration and noise of the motor. In addition, the design parameters of the motor itself, such as the number of winding turns and the air gap length, will also affect the distribution of the harmonic magnetic field, and thus have an impact on the electromagnetic noise.

2.2 Mechanical Noise

Mechanical noise is another important part of the bearing noise in the drive motors of new energy vehicles, mainly caused by the mechanical structure and operating status of the bearing itself.

Bearing Wear: After long-term operation or under harsh working conditions, components such as the rolling elements, raceways, and cages of the bearing will experience wear. When the wear between the rolling elements and the raceways reaches a certain extent, it will lead to an uneven contact surface, generating impacts and vibrations during operation, and thus causing noise. For example, in an environment with high temperature, high humidity, or a lot of dust, the wear rate of the bearing will accelerate, and the noise problem will be more prominent.

Improper Bearing Clearance: Bearing clearance refers to the amount of movement of one ring relative to another ring in different directions when the bearing is not installed and is not subject to external forces. If the clearance is too large, the bearing will shake greatly during operation, resulting in increased impacts between the rolling elements and the raceways, generating noise; if the clearance is too small, it will increase the friction resistance of the bearing, cause the bearing to heat up, and may even lead to the bearing getting stuck, also generating abnormal noise. Therefore, it is crucial to reasonably select and adjust the bearing clearance to reduce mechanical noise.

Rotor Unbalance: The rotor is the rotating component of the drive motor. If there is an uneven mass distribution during the manufacturing or assembly process of the rotor, it will lead to rotor unbalance. When the motor rotates at a high speed, the unbalanced rotor will generate a centrifugal force, causing the bearing to bear additional loads, thus triggering vibrations and noise. In order to reduce the impact of rotor unbalance, it is usually necessary to conduct dynamic balance tests and corrections on the rotor.

2.3 Lubrication Noise

Lubrication plays a crucial role in the normal operation of the bearing, and poor lubrication will also cause the bearing to generate noise.

Poor Performance of Lubricating Grease: The performance indicators of lubricating grease, such as viscosity, consistency, and oxidation resistance, directly affect its lubrication effect. If the viscosity of the lubricating grease is too low, it cannot form a thick enough oil film between the rolling elements and the raceways, resulting in direct metal contact and generating friction noise; if the viscosity is too high, it will increase the stirring resistance, cause the lubricating grease to heat up, and also generate noise. In addition, if the oxidation resistance of the lubricating grease is poor, it is easy to deteriorate during long-term use and lose its lubricating function, which will also lead to an increase in bearing noise.

Improper Filling Amount of Lubricating Grease: Both excessive and insufficient filling amounts of lubricating grease will affect the operating performance of the bearing. If the filling amount is too much, the bearing will be subject to greater resistance during operation, generating a stirring sound and a heating phenomenon, and thus increasing the noise; if the filling amount is too little, it cannot provide sufficient lubrication, resulting in increased wear between the rolling elements and the raceways, generating noise. Generally speaking, the filling amount of lubricating grease for the bearing should be reasonably selected according to factors such as the type, size, and working conditions of the bearing, usually accounting for 1/3 - 2/3 of the internal space of the bearing.

3. Influencing Factors of Bearing Noise in Drive Motors of New Energy Vehicles

3.1 Motor Design Factors

Pole-Slot Combination: The combination mode of the number of poles and slots of the motor will affect the distribution of the air gap magnetic field and the magnitude of the electromagnetic force, and thus have an impact on the bearing noise. An unreasonable pole-slot combination may cause the frequency of the electromagnetic force wave to be close to the natural frequency of the bearing or the motor structure, triggering resonance and increasing the noise.

Air Gap Length: The air gap length has an important impact on the electromagnetic performance and bearing noise of the motor. If the air gap is too small, the electromagnetic force will increase, increasing the load on the bearing, and at the same time, it is easy to cause friction between the stator and the rotor, generating noise; if the air gap is too large, it will reduce the efficiency of the motor, and may also make the magnetic field distribution uneven, causing electromagnetic noise. Therefore, in the motor design, it is necessary to comprehensively consider the electromagnetic performance and noise requirements and reasonably determine the air gap length.

3.2 Bearing Selection and Installation Factors

Bearing Type: Different types of bearings have different structural characteristics and performance advantages, and their noise levels also vary. For example, deep groove ball bearings are suitable for high-speed and light-load applications and have relatively low noise; while tapered roller bearings can bear large radial and axial loads, but they may generate relatively high noise during operation. When selecting the bearing type, it is necessary to comprehensively consider the specific working conditions and noise requirements of the drive motor.

Bearing Precision: The precision grade of the bearing directly affects its rotation accuracy and running stability. High-precision bearings can reduce the vibrations and impacts between the rolling elements and the raceways, and lower the noise. Therefore, in the drive motors of new energy vehicles, bearings with a relatively high precision grade are usually selected to meet the requirements for quiet performance.

Installation Quality: The installation quality of the bearing also has a significant impact on its noise level. During the installation process, if the installation position of the bearing is inaccurate, or the fit is too loose or too tight, it will cause the bearing to bear additional stress during operation, generating vibrations and noise. In addition, damages such as bumps and scratches during the installation process may also affect the normal operation of the bearing and increase the noise.

3.3 Operating Condition Factors

Rotational Speed: As the rotational speed of the motor increases, the relative movement speed between the rolling elements and the raceways of the bearing accelerates, and the friction and impact will also increase accordingly, resulting in an increase in noise. Especially when running at a high speed, aerodynamic noise will also become one of the main noise sources.

Load: The magnitude and nature of the load borne by the bearing have an important impact on the noise. When the load is too large, the contact stress between the rolling elements and the raceways of the bearing increases, the wear accelerates, and the noise will also increase accordingly. In addition, impact loads and alternating loads will also cause fatigue damage to the bearing, further deteriorating the noise problem.

Temperature: Temperature has a significant impact on the lubrication performance and material properties of the bearing. In a high-temperature environment, the viscosity of the lubricating grease will decrease, and it is easy to flow away, resulting in poor lubrication and generating noise; at the same time, high temperature will also reduce the hardness of the bearing material, increasing the risk of wear. In a low-temperature environment, the fluidity of the lubricating grease deteriorates, which will also affect its lubrication effect and generate noise.

4. Improvement Measures for Bearing Noise in Drive Motors of New Energy Vehicles

4.1 Optimize Motor Electromagnetic Design

Reasonably Select the Pole-Slot Combination: Through theoretical analysis and simulation calculations, select an appropriate combination of the number of poles and slots to make the air gap magnetic field distribution more uniform, reduce the generation of electromagnetic force waves, and thus lower the electromagnetic noise. For example, the adoption of a fractional slot winding design can effectively reduce the cogging torque and electromagnetic force fluctuations, and reduce the vibration and noise of the motor.

Optimize the Air Gap Magnetic Field: By improving the magnetic circuit design of the motor, such as using high-performance permanent magnet materials, optimizing the shape and arrangement of the permanent magnets, etc., the air gap magnetic field can be made more uniform, reducing the influence of unbalanced magnetic pull and harmonic magnetic fields, and lowering the electromagnetic noise. In addition, the amplitude of the electromagnetic force can be reduced by increasing the air gap length, but it should be noted that the increase in the air gap length will have a certain impact on the efficiency of the motor, and a trade-off needs to be made between the two.

Adopt Electromagnetic Shielding Technology: Set an electromagnetic shielding layer between the stator and the rotor of the motor, which can effectively reduce the leakage and mutual interference of the electromagnetic field and reduce the propagation of electromagnetic noise. The electromagnetic shielding layer can be made of high magnetic permeability materials, such as soft magnetic alloys, etc. Through reasonable structural design and installation methods, the shielding effect can be improved.

4.2 Improve Bearing Selection and Installation

Select Low-Noise Bearings: According to the working conditions and noise requirements of the drive motor, select bearings with low-noise characteristics. For example, some bearings specially designed for the drive motors of electric vehicles adopt special structural designs and manufacturing processes, which can effectively reduce noise. At the same time, when selecting bearings, factors such as the bearing capacity, rotational speed performance, and lubrication method of the bearing should also be considered to ensure that the bearing can operate stably under various working conditions.

Improve the Bearing Installation Precision: Formulate strict bearing installation process specifications to ensure that the installation position of the bearing is accurate and the fit is appropriate. During the installation process, use special installation tools and equipment to avoid damaging the bearing. In addition, high-precision machining can be carried out on components such as the bearing housing and the motor end cover to improve their installation precision and reduce the bearing noise caused by installation errors.

Adopt Bearing Preloading Technology: Appropriate preloading of the bearing can eliminate the bearing clearance, improve the rigidity and rotation accuracy of the bearing, reduce the vibrations and impacts between the rolling elements and the raceways, and thus lower the noise. The magnitude of the preloading force should be reasonably selected according to factors such as the type, size, and working conditions of the bearing. Excessive preloading force will increase the friction and heating of the bearing, which is not conducive to reducing noise instead.

4.3 Optimize the Lubrication System

Select Appropriate Lubricating Grease: According to the working temperature, rotational speed, load, and other working conditions of the drive motor, select lubricating grease with appropriate performance. For example, in a high-temperature environment, lubricating grease with good high-temperature resistance and oxidation resistance should be selected; when running at a high speed, lubricating grease with low viscosity and strong shear resistance should be selected. At the same time, attention should also be paid to the compatibility of the lubricating grease to avoid a decrease in performance due to mixing with other lubricants.

Control the Filling Amount of Lubricating Grease: Reasonably control the filling amount of the lubricating grease according to the recommendations of the bearing manufacturer. In actual operation, the filling amount of the lubricating grease can be accurately determined by methods such as the weighing method or the volume method. In addition, after the bearing has been running for a period of time, the consumption of the lubricating grease can be checked, and an appropriate amount of lubricating grease can be added in a timely manner to ensure that the bearing is always in a good lubrication state.

Improve the Lubrication Method: In addition to the traditional lubricating grease lubrication method, other advanced lubrication methods can also be considered, such as mist lubrication and oil-air lubrication. These lubrication methods can more accurately control the supply amount and distribution of the lubricant, improve the lubrication effect, and at the same time reduce the noise generated by the lubrication system. For example, mist lubrication can atomize the lubricating oil into tiny particles and evenly deliver it to all parts of the bearing, achieving efficient lubrication without obvious stirring noise.

4.4 Other Improvement Measures

Add Damping and Sound Insulation Measures: Add damping materials, such as damping rubber and damping coatings, to the casing, end cover, and other parts of the motor, which can effectively suppress the structural vibration and reduce the radiation of noise. At the same time, set up a sound insulation cover or sound insulation barrier around the motor, and use sound-absorbing materials, such as sound-absorbing cotton and foam plastic, to absorb and reflect the noise, reducing the propagation of noise to the surrounding environment.

Optimize the Cooling System: Reasonably design the cooling system of the motor to ensure the smooth flow of cooling air, avoid the generation of vortices and turbulent flows, and reduce the aerodynamic noise. The performance of the cooling fan can be optimized by improving parameters such as the blade shape, number, and angle of the cooling fan, reducing the noise generated during the operation of the fan. In addition, the liquid cooling method can be used instead of the air cooling method to reduce the noise generated by the cooling system.

Strengthen the Dynamic and Static Balance of the Motor: During the manufacturing process of the motor, conduct strict dynamic and static balance tests on the rotor to ensure that the mass distribution of the rotor is uniform and reduce the vibrations and noise caused by rotor unbalance. For motors running at a high speed, the requirement for dynamic balance precision is higher, and high-precision dynamic balance equipment and processes need to be used for correction.

5. Conclusion

The problem of bearing noise in the drive motors of new energy vehicles is a complex systematic problem, involving multiple aspects such as the electromagnetic design of the motor, bearing selection and installation, the lubrication system, and the operating conditions. By deeply analyzing the generation mechanism and influencing factors of the noise and taking targeted improvement measures, such as optimizing the motor electromagnetic design, improving bearing selection and installation, optimizing the lubrication system, and adding damping and sound insulation measures, the bearing noise can be effectively reduced, and the noise reduction performance and reliability of the drive motors of new energy vehicles can be improved. With the continuous development of new energy vehicle technology and the increasing requirements of consumers for driving comfort, the control of bearing noise in drive motors will become an important topic that needs continuous attention and research in the development of the new energy vehicle industry. In the future, it is necessary to further strengthen the research and innovation of related technologies, continuously explore more effective noise control methods and technical means, and provide more solid technical support for the development of new energy vehicles.