Bodywork and passive safety: Solid basis and comprehensive protective concept

Nov 28, 2018

The centrepiece of the body's safety concept is the highly rigid passenger compartment. Its great rigidity when subjected to accident-induced stress, e.g. in frontal, lateral or rear-end collisions and roll-overs, is above all due to the greater use of high-strength, ultra-high-strength and press-hardened sheet steel. Particularly effective protection is achieved by the interaction of the bodywork and modern restraint systems.

The strength of the entire side wall is increased by a floor assembly with high transverse rigidity. In the front footwells this is brought about by two inner and one outer reinforcing section between the inner shell of the front side members and the central tunnel. There is a continuous seat cross-member in the rear. These are augmented by seats with high transverse rigidity featuring tubular sections in the seat frame.

The upper area of the B-pillar is extremely rigid, with hot-formed ultra high-strength steel, while the lower area is slightly less rigid with deformable, ductile steel. This gives the B-pillars very good deformation kinematics. The steel doors have specific reinforcements. Additional protection is provided by impact elements in the side seat and B-pillar claddings.

The so-called Inertia door handles are the result of in-house accident research. These even more reliably prevent a door from opening during a side impact, as the door is locked in place at the handle when subjected to impact-induced forces.

Special measures for the structural safety of the vehicle's front section include the following:

  • the robust firewall cross-member of hot-formed, press-hardened steel between the two A-pillars
  • several parallel load paths for improved load distribution in a partial frontal collision (offset crash)
  • side members at the upper impact level connected to the A-pillars
  • effective load distribution from the front side members by means of specially reinforced A-pillars
  • a middle impact level with side members having specific crash kinematics
  • multi-layered floor structures for high energy absorption
  • an additional pedal floor cross-member to protect the footwell
  • continuous floor side members to improve energy transfer into the underbody structure, with a larger cross-section and material thickness than in the previous model
  • compatibility with other vehicles in the design of the front structure in the event of a frontal collision (protection of other road users).

The more compact drive units also play an important role. During a frontal collision, and acting together with the body structure, they allow more homogeneous deceleration and help to ensure the occupant protection for which Mercedes-Benz is well-known. Depending on impact severity, the engine and transmission are specifically displaced and disengaged from the new integral carrier.

Vehicles with a tailgate require a particularly well-conceived rear body structure to compensate for the large aperture of the body in the rear. For many years, e.g. in the E-Class Estate models, the structural concept of two peripheral sections has proved successful for Mercedes-Benz: the so-called C-ring at the level of the C-pillar and the D-ring around the tailgate aperture. Thanks to the geometry of the D-ring, it was possible to position the lower section of the C-ring completely below the rear floor while retaining the excellent rigidity of the previous model. This enlarged the load capacity and made a level load area possible.

The reduction of the severity of an accident is especially important in collisions with weaker road users such as pedestrians, since they do not have their own crumple zone. In addition to the active safety measures which help avoid accidents or mitigate the severity of accidents, protection measures were therefore also further developed. For example, in order to reduce the loads which arise in the event of a pedestrian's head impacting the bonnet of the vehicle, the design includes deformation space between the bonnet and the components beneath. This is two-fold: through the appropriate alignment and design of components such as control units and fluid containers in the engine compartment, and through the correspondingly flexible components that lie beneath it. The structure of the bumpers also acts flexibly in a collision.

Restraint systems: partnership with the safety bodyshell

The most important restraint system is the seat belt. Driver and front passenger are provided with three-point seat belts with pyrotechnic belt tensioners and belt force limitation. In combination with the PRE-SAFE® system (optional extra), the front seats are additionally equipped with electrically reversible belt reel tensioners. Both of the outer rear seats are fitted with a seat belt with reel tensioner and belt force limiter. The maximum belt tension level also takes into consideration smaller and lighter passengers. The centre belt is a standard three-point belt.

The new B-Class is equipped with driver and front passenger airbags, a driver's kneebag and windowbags as standard. The windowbags cover the first and second row of seats. In comparison to many of the competitors, these windowbags extend further forward to the A-pillar, thus offering particularly high protection potential. Thorax-pelvis side airbags are likewise standard in the front, and available as optional equipment for the rear.

Child safety: automatic deactivation of the front passenger airbag

A pressure sensor in the front passenger seat surface can detect whether the seat is unoccupied or whether an infant seat or other child seat is placed on the passenger seat. For a child seat facing backwards, the front passenger airbag is deactivated automatically, while for a child seat facing forwards it depends on the weight. Contrary to other systems that require the airbag to be deactivated with a key, this system reduces the risk of incorrect operation. A special transponder is not required. The system is standard or optional equipment depending on the market or region.

i-Size child seat attachments are used for i-Size child seats. This internationally standardised attachment system, the successor to Isofix, is provided for the outer rear seats as standard. This simplifies securing the child seat, and the fixed connection between the child seat and the vehicle can improve protection.