The new B-Class is the Mercedes-Benz among compact cars, offering a correspondingly high standard of passive safety. The body-in-white provides the basis here, both in terms of material – the proportion of high-strength and ultra-high-strength sheet steel stands at 67 percent – and with regard to its structural design.
Key features of the front-end structure are the systematic implementation of an available crash length of 435 millimetres, load distribution over several planes, the new bulkhead and floor concept and the integral support frame as a deformation element.
A total of three longitudinal member planes – consisting of the straight front longitudinal members, a second, upper plane attached to the front end consisting of extruded aluminium box sections and a third plane at the bottom in front of the integral support frame – allow impact energy to be reduced in a controlled manner.
The integral support frame provides the torque support for the transverse engine/transmission block and serves to attach the components for the front axle and steering. It consists of several steel plates, some in ultra-high-strength steel, and a hydroformed tube. In order to optimise its deformation properties, the integral support frame is connected via two aluminium struts leading forward to the aluminium radiator mount located under the front end. In the event of a frontal impact, forces can be discharged at an early juncture into the integral support frame via this third load path, in order to ensure the best possible energy dissipation.
A plastic crash wedge which is fitted at the rear of the front wheel arches helps to ensure that the wheels do not slide under the front doors in the event of a high-impact crash, irrespective of the turning angles. This means that it will be possible to open the doors, even after a serious accident.
The bulkhead also incorporates a special feature: So-called „skate runners“ in front of the two middle longitudinal members discharge forces into the floor. The continuous floor structure consists of a total of four straight longitudinal members. The tunnel roof reinforcements at front and rear combine with the tunnel to provide a further closed profile supporting the front end.
Controlled deformation: protection in side-on crashes
Rigid side structures and defined deformation management help to safeguard the survival space for occupants in the event of side impact. Elements here include the so-called „pole support“, a member fitted diagonally in the rear footwell between centre tunnel and floor side wall which is intended to prevent the floor from being torn open in the event of side impact with a tree.
High-strength steels are used in the upper area of the B-pillar, in order to minimise intrusion and to preserve the passenger cell in case of side impact. The lower area of the B-pillar is softer, in the interests of energy dissipation. The safety experts at Mercedes-Benz have christened the crack management system on the insides of the B-pillar „vampire teeth“. In a serious side-on crash, the seat belt retractor presses against the inner wall of the B-pillar. To prevent this from leading to a transverse crack which might affect structural integrity, small, tooth-like recesses define the crack direction.
On all seats: intelligent restraint systems
The B-Class protects its passengers with up to nine airbags. The standard complement comprises driver and front-passenger airbag, a kneebag for the driver, large thorax-pelvis-bags incorporated in the seat to protect the chest, stomach and pelvis area and windowbags. The windowbags extend over both rows of seats to the A-pillar triangle. They serve to protect the occupants‘ heads from hard contact in the event of side impact and can also help to keep limbs inside the vehicle in an accident. The driver and front passenger airbags operate in two stages, according to the expected severity of impact. The gas generator first of all fills the driver’s airbag with 60 and the front passenger’s airbag with 70 per cent gas. If a more severe impact is forecast, the second stage of the gas generator will additionally be activated after a delay and the airbags will be filled at a higher pressure level. Sidebags for the rear are optionally available.
The high safety expertise of the B-Class’s developers is reflected in a host of details. The deformable steering column yields by up to 100 millimetres when the driver exerts pressure on the airbag as a result of forward displacement in an accident, for example. The comfort features also reveal a fine touch: the driver’s airbag is connected to a vibration absorber in the steering wheel to reduce vibrations, for example.
The head restraints for driver and front passenger are new developments.
The onus in developing the new restraints was on further reducing the risk of whiplash injury. Key to effective whiplash prevention is the best possible adjustment of the distance from the rears of the occupants‘ heads. The restraint incorporates a button for this purpose on the left-hand side (as seen in the direction of travel). This release mechanism can be pressed to unlock the head restraint and increase the distance between head and head restraint. The button does not need to be pressed in order to reduce the distance. This enables single-handed operation in all adjustment positions.
Family-friendly: comprehensive precautionary measures in the rear
An exceptional feature in the compact class: belt tensioners and belt-force limiters also feature on the outer rear seats as standard. The roller mechanism incorporates a torsion bar which turns when the load on the bar exceeds a defined value. In this way it limits the belt force and reduces the strain on the occupants.
The B-Class’s family-friendly features also include Isofix child seat fasteners on the outer seats. Child seats can additionally be fixed to the vehicle by means of special anchorage points with top tethers.
Premiere in the compact class: preventive occupant protection system
The PRE-SAFE preventive occupant protection system which features in the B-Class is available for the first time in this vehicle category. This represents a further step in the ongoing democratisation of this innovation, which was premiered in the S-Class in 2002.
PRE-SAFE from Mercedes-Benz uses the time between detection of a potential accident situation and a possible collision to initiate preventive protection measures, thus reducing the loads exerted on the occupants in the event of a crash by up to 40 percent.
Core features of PRE-SAFE are reversible belt tensioning, the closing of side windows and sliding sunroof when critical lateral dynamics are detected and adjustment of the fully electric front passenger seat with memory function to an ideal position for maximum effectiveness of the restraint systems.
PRE-SAFE is activated when one of the following parameters is met: emergency braking, panic braking, pronounced over- or understeering, critical steering movements or heavy support by adaptive Brake Assist.
Source: Daimler AG