Sources of NVH in Electric Vehicles
NVH performance is one of the most important performance indicators of automobiles and directly determines the user-perceived quality. Improving the comfort of products can ensure excellent market competitiveness.
Compared with traditional fuel vehicles, electric vehicles are quieter. The working principle of the internal combustion engine is that the explosion caused by the combustion of fuel in the cylinder drives the piston to move, thereby driving the car forward. Electric vehicles drive the vehicle by converting electrical energy into mechanical energy. There is no internal combustion process when the motor is running, so the noise is lower. This is especially obvious when driving at low speeds. Electric vehicles can provide a smooth driving experience and give people a comfortable and quiet feeling.
However, NVH will also face new problems during the design of electric vehicles :
Modal planning problem : A car is a complex system with interrelated components. It is necessary to adopt vehicle modal planning to avoid NVH problems or solve existing NVH problems. If the problem frequency is low, it is mainly achieved through modal planning. If the problem frequency is high, it is mainly achieved through acoustic packaging. Simply put, it is to avoid resonance through modal separation. The modal planning table can be used to guide the overall NVH design of the car, so the modal planning table is very important.
Motor noise : The noise of the drive motor is mainly divided into aerodynamic noise, electromagnetic noise and mechanical noise. Among them, aerodynamic noise is the main noise when running at high speed, and electromagnetic noise is the main noise when running at medium and low speed.
Gear noise : Gear transmission noise, the noise radiated by the vibration of the gear body caused by the mutual collision or friction of the meshing gear pairs or gear sets during transmission. In the gear system, according to different mechanisms, the noise can be divided into acceleration noise and self-ringing noise. On the one hand, when the gear teeth are meshing, the impact causes the gear to produce a large acceleration and cause disturbances in the surrounding medium. The sound radiation generated by this disturbance is called the acceleration noise of the gear. On the other hand, under the action of the dynamic meshing force of the gears, the various components of the system will vibrate, and the sound radiation generated by these vibrations is called self-ringing noise.
Road noise and tire noise : The excitation source of road noise comes from the road surface. The unevenness of the road surface will produce periodic or random excitations, which are transmitted to the car body through the tires and suspension system.
Wind noise : Wind noise is a kind of aerodynamic noise with broadband characteristics. When a vehicle is traveling at high speed, there is intense friction between the vehicle and the air, forming a boundary layer on the vehicle surface, especially at some locations with structural mutations, such as wipers, antennas, rearview mirrors, etc. Airflow separation occurs at the boundary layer, forming vortices and turbulence. The turbulent airflow interacts with each other, generating pressure changes, which act on the vehicle body, causing body vibration and generating radiated noise.
Active noise control : The warning sound outside the vehicle. When an electric vehicle is at a low speed, it is very quiet, making it difficult for pedestrians to detect the approach of the vehicle. Research on low-speed warning sounds is needed.
The main noise sources of electric vehicles
1. Powertrain system
The main vibration source of the powertrain is the drive motor, and the excitation form is motor torsion and sway. The vibration of the drive motor is caused by factors such as electromagnetic force, rotor mechanical imbalance, and aerodynamics. It is mainly divided into three categories: electromagnetic vibration generated by the stator, rotor unbalance vibration, and vibration generated by the bearing. For an ideal motor, the main vibration source is the electromagnetic force of the motor. The vibration force generated by the electromagnetic force includes radial force and tangential force. The radial force of the electromagnetic force is mainly considered, which will cause unbalanced vibration of the rotor.
2. Transmission system
Electric vehicles have no clutch or shift cable, and the power is transmitted directly through the reducer. The gear teeth will deform during force operation. In addition, the errors in gear manufacturing and installation will cause collisions and impacts when the gears are engaged and disengaged. Therefore, reducer howling excitation is prone to occur.
3. Chassis system
Electric vehicles mostly use low rolling resistance tires. Due to changes in mass distribution, the axle load distribution and suspension hardness of the vehicle suspension are adjusted accordingly. Therefore, the attenuation ability of road excitation is poor and the contribution of road noise increases.
4. Accessory noise
Electric vehicles do not have internal combustion engines, so the noise excitation of electrical appliances such as electric vacuum pumps, water pumps, electric compressors, cooling fans and HVAC assemblies is more likely to be prominent. In particular, when the power battery is cooled by air conditioning, the power battery evaporator fan will also generate noise during operation.
Sourceļ¼https://blog.csdn.net/moyunzhiyin/article/details/137039841
