Under the microscope: low noise and vibration levels: One of the quietest estate vehicles

Sep 13, 2016
Stuttgart

In the interior, the new E-Class Estate is one of the quietest cars in its class – even though an estate is at a disadvantage by design compared to a saloon due to the large resonating body. Quiet running and low vibration make a significant contribution to the level of energising comfort, particularly on long journeys.

By implementing a raft of measures, the NVH experts at Mercedes-Benz have minimised annoying vibration and noise in the E-Class Estate. As on a cabriolet, struts strengthen the main floor and front end of the bodyshell. Thanks to these structural measures, the vehicle body is dynamically very rigid and transmits less noise due to structure-borne sound. Special insulation on the bodywork (including on the bulkhead, sidewalls and rear of the car), as well as sound absorbers under the rear seats and on the wheel arches, keep air-borne sound out of the vehicle interior.

The design of the chassis, axles and steering system reduces disturbances that can be caused by tyre noise on the road surface or the wheels being out-of-balance, for example. Engine and transmission mounts have also been optimised in terms of noise levels, and some model versions feature switchable engine mounts to ensure better decoupling of the excitations. Further special features on the Estate include the flexibly mounted striker for the tailgate, allowing it to move in a dynamically defined manner: air vibrations in the interior are absorbed dynamically and therefore not converted into noise.

Tracing disturbing noise: highly specialised processes

The development of noise-related comfort begins long before prototypes are available. Acoustics specialists apply a hybrid calculation method at an early stage. This involves working out the excitation data of the components and the transmission functions of bearings as well as the body in structure-borne and air-borne sound using a network model.

Special processes are then applied during subsequent fine tuning on the acoustics test benches to ensure a quiet and pleasant noise pattern in the interior. Such processes include the use of an "acoustic camera", which delivers high-resolution, three-dimensional mapping of the noises in the interior. The data are gathered using what are known as multi-arrays – the bundling of numerous microphones. Improvements can then be compared with the previous status.

The road testing at the end of the process serves as fine-tuning. Here the acoustic behaviour of the vehicle is checked under real-life conditions on all possible road surfaces (flat, rough). The aim is to ensure the quietest possible running on all surfaces.

Several aeroacoustic measures have been implemented. As on the E-Class Saloon, the exterior mirrors and A-pillars have been optimised in terms of aeroacoustics. The roof structure and the automatic tilting/sliding sunroof module have been aeroacoustically improved to reduce noise levels in these areas, too. In the case of the panoramic sliding sunroof, multiple wind-deflection measures (wind deflector, covers and seals with the appropriate geometry) ensure the same low level of noise as in the preceding model, despite the larger aperture. Further aeroacoustic measures: additionally sealed door handles, seals on the door joints and optimisations associated with the geometry of the sealing sections for the side windows. Improvements have also been made to the formed parts for the inside sealing rails so that these are connected to the window run channel without any gaps by positive locking.

The Acoustic Comfort package is available as an optional extra. A special acoustic film in the windscreen and side windows further reduces annoying noises and thus ensures low levels of background noise in the vehicle interior. To provide optimum heat insulation in the interior, the windscreen, side windows and rear windows are made of laminated safety glass with another layer of infrared-absorbing film. Surfaces in the interior like the armrests, steering wheel and seats get less hot from solar radiation as a result.

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