What are the structural characteristics of the new energy vehicle system? What are the main challenges NVH faces?

Compared with traditional cars, new energy vehicles have added many new components in structure. Its power system, braking system and climate control system are very different. At the same time, the prominent road noise, wind noise and abnormal noise caused by the change of background noise are also different from those of traditional vehicles. NVH, a new energy vehicle, will be analyzed from the following aspects.

First, the body system and its NVH performance

With the energy crisis and the increasingly serious pollution caused by traditional fuel vehicles, replacing traditional fuel vehicles with new energy vehicles has become the future development trend of the automobile industry. At the same time, the development of NVH performance of new energy vehicles is also facing new challenges. In the body structure, the installation layout of cockpit, power transmission system and battery pack is different from that of traditional cars; In terms of quality, the quality of new energy vehicles has also been improved due to the addition of multiple battery lines. In terms of body materials, in order to reduce the weight of the body, the use of aluminum alloy, carbon fiber and other materials will also bring some challenges to NVH. In the aspect of acoustic packaging, the sound source of electric car compartment is reduced, and the acoustic balance needs to be redesigned; The battery is placed on the floor, and the floor is raised, which compresses the acoustic packaging space such as carpets.

Second, the chassis system and its NVH performance

With the increase of the body mass of electric vehicles, the rigidity of the chassis must be increased in the design. The increase of bushing stiffness has a great influence on NVH, which will cause roar; In addition, the ringing of wheel motor and wheel motor, or the ringing of wheel motor and chassis structure, will cause the coupling of structural sound and air sound; Kinetic energy recovery system and electric vacuum pump will also produce certain high-frequency howling and high-frequency noise. So when designing the chassis, we should consider its bearing capacity.

Third, the motor system and its non-NVH performance

The noise of motor system mainly includes three parts: electromagnetic noise, mechanical noise and cooling noise. Electromagnetic system includes the noise of the motor itself and the noise of the control system. The main sources of motor noise are radial electromagnetic force and tangential electromagnetic force, torque fluctuation, dynamic and static eccentricity and cogging noise; The noise of control system includes two parts: pulse width modulation noise and harmonic distortion. Bearing noise, dynamic unbalance noise and structural vibration noise are the main sources of mechanical noise. The liquid cooling system of new energy vehicles will also have some noise. Based on the electromagnetic force (density) and the verified motor structure model, the vibration and noise of the motor can be simulated, and the structural-acoustic-vibration coupling analysis can be carried out by using acoustic analysis tools to predict the radiation noise of the motor.

Four. Electronic control system and its NVH performance

The electronic control system of new energy vehicles is complex, energy and medium are integrated, and there are many working conditions and control variables, so it is difficult to coordinate and control. Especially when the driving mode is switched, the control system is complex, and it is difficult to control the performance balance, that is, to give consideration to power, reliability and comfort control. The NVH is poor under the conditions of low speed, high torque, and switching of driving modes. In terms of energy conversion, torque coordination and unloading torque will bring vibration and impact problems, noise problems caused by thermal management and cooling system, electric horn problems caused by braking energy recovery, and conflicts between NVH and dynamic performance and reliability.