BMW i7 aims at "ultimate quiet performance". How to eliminate the noise peculiar to EV?

BMW i7

"Noisy" because EV is quiet

BMW is developing the i7, the flagship model of the EV family, to be released in 2022. This time, a part of the development program is released. We introduced a part of the thorough countermeasures to reduce the "noise" that is anxious because it is an EV as much as possible.

Generally, the image of "EV = quiet" is spreading, but it is rather difficult to take measures against noise because there is no noise derived from the internal combustion engine. NVH (Noise, Vibration, Harshness = Occurs when passing through irregularities such as seams, steps, and protrusions on paved roads, as other noise sources such as wind noise, road noise, inverter noise, and squeak noise of interior materials stand out. Impact noise and vibration) Performance requires even stricter measures.

To "achieve the highest comfort in BMW history"

The i7, the flagship model of BMW EV, is said to have improved NVH performance from all aspects such as aerodynamics, soundproofing materials, and vibration countermeasures in order to "realize the highest comfort in BMW history". At the GMW Group's R & D center (FIZ = Forschungs- und Innovations zentrum) in Munich, Germany, test engineers and development engineers conduct thorough experiments on noise sources and intrusion sources on a daily basis. At the same time, it also created a unique sound that alerts pedestrians to the approaching vehicle and the sound inside the vehicle. The electric drive unit has a specially designed mount for each model, and a new cover for the motor has also been developed. Official materials claim that it has achieved amazing quietness and low vibration by increasing the rigidity of the front end of the body and adopting tires with sound absorbing material inside.

Regarding the sound environment, we developed "BMW Iconic Sounds Electric" in collaboration with world-famous composer Hans Zimmer. The light and transparent sound fills the cabin with a futuristic mood in various situations such as when the ignition starts, when the door is open, and when driving.

Chassis dynamometer that can reproduce the traffic environment around the world

A state-of-the-art acoustic test facility designed to meet the performance requirements of electric mobility was installed in FIZ, an advanced research and development organization for the BMW Group's liver roasting. Here, any noise detected by a test driver in the real world can be reproduced. It is the engineer's job to take measures one by one for those "sources". The chassis dynamometer (which is of course a special quiet design in itself) is designed so that it can be replaced with a surface material that assumes the traffic environment around the world so that it can reproduce noise on various road surfaces and tire noise.

In addition, FIZ has test facilities that can reproduce various climates so that performance levels can be maintained even in extreme weather conditions. By making full use of air conditioners and ventilation systems, we have created an environment where we can simulate the weather in various regions of the world, from extremely cold regions to scorching regions.

Realistic reproduction of "everyday noise" such as truck passing sounds

In addition to measures against noise generated by the vehicle, the i7 also thoroughly dealt with noise entering from outside the vehicle. A thorough aerodynamic test was conducted in the wind tunnel experimental building. The shape of the handle, side mirrors, and underbody, which have been made into a flash surface, have been designed to minimize noise. Of course, the excellent aerodynamic performance is not only quiet, but also has a great effect on electricity costs.

A large number of speakers are installed in the simulator room that can reproduce various noises that occur in the real world, such as road construction and passing trucks. Here, the quietness of the cabin is verified by flowing various noises that are overflowing in the everyday world from all directions of the vehicle.

The sound absorbing material and sound insulating material were carefully selected based on the latest design concept, and the position and quantity were decided. The sound-absorbing material used for pillar trim, seats, roof liners, and rear-seat shelves is said to be one of the effective measures against noise outside the vehicle. Of course, the windows are also designed to prevent unpleasant noise, and the doors, sills, and wheel arches are also made of fleece material that suppresses road noise.

EMC testing equipment that is extremely important for modern products

EMC (electromagnetic compatibility = the ability of a product to operate normally even if it does not become an electromagnetic interference source and does not receive electromagnetic interference) is regarded as an extremely important product quality. Nowadays, test equipment for countermeasures is also indispensable. At the "EMC absorber hole" in the FIZ, it is possible to verify how the vehicle interacts with the outside world while exposing the prototype to a strong electromagnetic field.

Engineers are now able to analyze vehicle diagnostics sent in real time through fiber optics. EMC is an essential test requirement for modern cars in order for all features such as suspension control, drive assist mechanism, online data, navigation to phones, radios and TVs to work properly at all times.