Flagship EV undergoes environmental testing

| Environmental Testing

EMC test hall has capacity for full vehicle electro-magnetic compatibility testing

The BMW i7 electric vehicle has endured acoustic, vibration and climatic testing to meet the expectations of the EV market

Optimised noise insulation, aero-acoustics and vibration comfort. These are some of the challenges that have been facing BMW engineers in developing their electric vehicle range. Whilst all three of these factors have always been important to consumers, the sources, transmission and mitigation of noise and vibration have changed substantially with vehicle electrification. The acoustic and vibration signature of an electric vehicle is entirely different from that of vehicles with conventional or legacy powertrains.

To meet the demanding market requirement for top-of-the-range automotive products, the developers of the new BMW i7 have put the car through a diverse range of tests in the company’s own laboratories and test benches. The environmental test facilities at BMW have been equipped and configured to provide development and test engineers with the ability to perform all the testing programmes that are required, including acoustic, vibration, climatic and electromagnetic compatibility testing.

BMW i7

The BMW i7 is an electric vehicle with a combined power consumption of 22.5 – 19.5 kWh/100 km according to WLTP and CO2 emissions of 0 g/km, based on tests performed so far. It is being developed with the aim of combining the latest in automotive power train technology with the level of comfort required in the market. One key factor in this respect is the acoustic properties.

The level of well-being in the interior of a purely electrically powered luxury saloon car is largely determined by the degree to which disturbing noises can be kept away from the occupants. There are a variety of potential noise sources to be taken into account here, so near-production prototypes of the BMW i7 – and indeed all other model variants of the future BMW 7 Series – undergo an extensive programme as part of their acoustic testing.

BMW Laboratory

At the extensive and modern facilities in the Research and Innovation Centre (FIZ) in Munich, test and development engineers are able to check the full range of the vehicle’s sound emissions and propogation to make assessments of its noise, vibration and harshness (NVH) characteristics. Motor and rolling noise are analysed in detail, as are the aero-acoustics and vibration levels, in order to fully determine its acoustic properties and NVH characteristics. This also includes precise alignment of acoustic pedestrian protection and the motor sound emitted in the interior of the BMW i7 – the latter having been developed as part of BMW IconicSounds Electric, a collaborative venture between the BMW Group and Hollywood film music composer Hans Zimmer so that the driver has a choice of characteristic silence or BMW IconicSounds Electric.

The acoustic test benches at the new branch of the BMW Group’s Research and Innovation Centre FIZ North are specially designed to meet the requirements of electro-mobility and enable all driving situations to be simulated realistically. Any irritating noises registered by development engineers during test drives on the road can be recreated and selectively eliminated. Roller dynamometers with a unique quiescent level and interchangeable surface coverings enable the measurement and validation of drive acoustics and tyre noise on all road surfaces that are relevant to day-to-day traffic anywhere in the world.

The standards that the engineers aspire to for the BMW i7 apply to acoustic comfort as well as other aspects of quality. Therefore, a lot of importance was attached to noiseless power delivery of the electric motor. Contributing factors here include acoustic optimisation of the electric drive units, a model-specific mount concept and a newly developed noise encapsulation for the electric motors. Taken together, these measures enable the BMW i7 to achieve effective acoustic decoupling across a wide frequency range, thereby ensuring maximum acoustic comfort in the interior in all driving situations. As a result, the driver of the purely electrically powered car always has the choice of enjoying either the characteristic silence of the motor or the emotionally powerful BMW IconicSounds Electric sound system.

Increased body rigidity at the front end and tyres with a foam absorber on the inside for integrated noise insulation likewise help raise the acoustic and vibration comfort.

Climatic and wind tunnel testing

In order to be able to test the effectiveness of all measures under extreme climatic conditions too, the development engineers at FIZ North use an acoustic climatic test chamber specifically designed for this purpose. There, all globally relevant conditions can be simulated and a wide variety of noise sources can be analysed and optimised such as the acoustics of the air conditioning and ventilation system throughout the entire vehicle – in particular at very low or very high temperatures.

In the same way as the motor and tyre rolling acoustics, ambient noise can also be selectively reduced. For this purpose, the aero-acoustics of the BMW i7 are perfected in the acoustic wind tunnel. Clear-cut body surfaces, flush-integrated door handles, aerodynamically optimised exterior mirrors and an almost completely closed underbody not only contribute to the low air resistance of the car but also help create its excellent acoustics.

External noise simulation

In addition to the noise and vibrations emanating from the vehicle itself, it is also the noise sources from the outside that can impair the experience of comfort while driving. The new acoustic simulator at FIZ North enables the noise emitted in day-to-day traffic to be simulated under laboratory conditions – this includes the sounds made at road construction sites and by passing trucks, for example. Numerous loudspeakers are used to project these sounds onto the vehicle prototypes from all directions to test the effectiveness of the interior noise insulation.

Highly effective and also weight-optimised sound insulation is enabled by the use of innovative materials developed in conjunction with acoustic lightweight construction. One of the ways in which outstanding shielding of external and intrinsic noise is achieved is by means of sound absorbers incorporated in the pillar trim, seats, roof liner and rear shelf. Together with the comfort glazing, which prevents unwelcome noise from entering through the window panels, this adds to the overall acoustic performance of the vehicle. There are also fleece elements in the doors and on the sill and wheel arch trim which reduce rolling noise.

Electro-Magnetic Compatibility

With their detailed analyses and precise optimisation, the development and test engineers seek to ensure that the new BMW i7 offers what they believe to be the best environmental testing performance in the industry. This includes an analysis of electromagnetic compatibility (EMC). In the EMC absorber hall at the FIZ facility, prototypes of the car are exposed to powerful electromagnetic fields to test the susceptibility of their electrical systems to interference and see how they interact with the environment.

EMC performance is an essential criteria not only for comfort and usability of the product, but also for certification against international standards for the markets into which the vehicle will be sold. To achieve this, the test engineers are able to analyse the diagnostic results transmitted from the vehicle in real time via fibre optic cables and build a comprehensive picture of the radio frequency environment of the car so this can be mapped against different criteria – both the company’s own requirements and those of the standard bodies. The test programme in the EMC absorber hall enables comprehensive protection of the entire vehicle, ensuring absolutely reliable functioning of the suspension control and assistance systems and interference-free reception of online data, telephone, radio, TV and navigation signals.

Jonathan Newell
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