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Safety: A reassuring feeling - Just one star is enough

Sep 2, 2011
In line with the Mercedes-Benz brand philosophy, the new M-Class represents the embodiment of the Mercedes-Benz holistic safety concept of Real Life Safety, which is derived primarily from what happens in a real accident situation. The extremely robust occupant compartment of the M-Class, together with the front and rear deformation zones, forms an effective basis for the occupant protection system. Both active safety and driver-fitness safety in the new M-Class are further improved by Assistance Systems, already primarily familiar from the S and E-Class.
As with all passenger car models from Mercedes-Benz, the philosophy behind the safety concept of the M-Class is broken down into four phases:
  • Safe driving: avoiding danger, warning and assisting the driver in good time
  • In the event of danger: anticipating and enabling preventive protective measures
  • In an accident: providing protection as needed
  • After an accident: avoiding even worse consequences and making rapid assistance possible
The high level of safety already achieved in the previous model has been increased even further. The many "invisible" Mercedes-Benz solutions in particular bring measurable benefits in real accident situations. To support new technologies or the evolution of existing systems, the engineers carried out numerous crash tests which went way beyond the tests normally specified, such as the roof-drop test for example, as well as various rollover tests. When it detects the need to do so, a rollover sensor system can activate side and window airbags, as well as belt tensioners. In total, as part of the M-Class development Mercedes-Benz tested 36 totally different loads under real test-conditions. This included comprehensive simulations for the digital prototype. Following this intensive development programme, the M-Class now has the potential to pass all international ratings with the best possible results.
The M-Class is also able to demonstrate the highest possible protection potential when it comes to more vulnerable road users such as pedestrians
or cyclists. In addition to yielding areas in the front section, folding exterior mirrors and smooth contours, the risk of injury caused by the vehicle has been reduced by adjusting the bonnet and increasing the distance to the components in the engine compartment. In addition, for the first time in the SUV segment, an active bonnet is fitted as standard equipment. It is able to reduce the acceleration forces of an impacting pedestrian or cyclist by intercepting them earlier.
"Electronic crumple zone"
As ever, the best accident is one which does not happen at all. The safety engineers at the Mercedes Technology Center are working intensively on this rather simple sounding statement, which in practice is actually a lot more difficult to implement. Both active safety and driver-fitness safety in the new M-Class are further improved by the numerous active and passive assistance systems:
  • ATTENTION ASSIST, warns the driver of drowsiness
  • Speed Limit Assist, displays road signs in the instrument cluster
  • Tyre pressure loss warning system
  • Intelligent Light System with specific lighting functions to match the relevant road and weather conditions
  • Night View Assist Plus with automatic person recognition
  • ADAPTIVE BRAKE with the functions Hill-Start Assist, priming, brake drying and hold function
  • Brake Assist (BAS) to support the driver in critical braking manoeuvres
  • Lane Keeping Assist warns the driver as soon as it detects that the driver has unintentionally left a recognised marked lane. In addition, Active Lane Keeping Assist can react with lane-correcting brake application
  • Blind Spot Assist warns the driver when vehicles are detected in the area of poor visibility, the so-called "blind spot". Additionally, Active Blind Spot Assist can counteract a possible collision by specific application of the brakes on one side of the vehicle, if the driver does not react to the warning.
  • Park Assist with PARKTRONIC, a system which can detect parking spaces and carry out the steering manoeuvres required for the parking process, simply leaving the driver to operate the brake and accelerator
  • Reversing camera, e.g. with "back-in" mode with dynamic guide lines for reversing into narrow parking bays or to aid with the coupling of trailers
  • Adaptive brake light warns vehicles behind in an emergency braking situation with flashing brake lights
Standard equipment forming part of the safety concept of the new M-Class includes the anticipatory safety system PRE-SAFE®, which combines active and passive safety synergies to reduce the loads exerted on the vehicle occupants in the event of an accident by up to 40 percent. Depending on the potential accident situation detected, the following reversible measures can be initiated for preventive occupant protection:
  • Driver and front passenger seat belts are tensioned
  • Windows are closed
  • Sliding sunroof is closed
  • Front passenger seat is adjusted (when fitted with Memory package)
Body: high energy absorption in the event of a front impact
The extremely robust occupant compartment of the M-Class, together with the front and rear deformation zones, forms an effective basis for the occupant protection system. The focus of the work here has been the tangible reduction of the loads exerted on the occupants. In the case of front impacts, the engineers were able to achieve more uniform deceleration, and therefore a lower peak load on the occupants. This was made possible by means of:
  • Design of the front axle carrier as a crash element, which is able to deform in a specific manner and in the case of an offset crash, for example, can divert the energy to the side of the vehicle opposite the side of impact
  • A novel aluminium gearbox crossmember mount with offset function: isolated against noise and vibration during normal operation, in the event of a crash this component is activated via hooks so that the centre tunnel can absorb additional energy in this area (diesel versions only)
  • Guide ramp on the brake booster, thus preventing unwanted block formation between the brake booster and the damper dome. The brake booster is also rotated to minimise possible brake pedal intrusion
  • A crash joint ensures that the mudguard is pushed away at the driver's door, and prevents the door from jamming after the impact. For the most part the doors can be opened without much effort
  • Ultra-high-strength steels in the A-pillar enhance the stability of the passenger compartment in both front impacts as well as in different rollover scenarios, primarily enabling doors to be opened easily after an offset crash
  • Projected sills create a direct load path to the front wheel. As a result, any possible forcing or intrusion of the wheels into the footwell can be avoided
  • Optimum energy conversion in the event of a front crash despite relatively short front-end length, thanks to enabling the load paths from the crashbox to the longitudinal body member, from the wheel to the sill, and due to the deformable subframe, which guides forces into the centre tunnel via the engine/transmission joint
  • The energy-absorbing steering column deforms up to 100 millimetres when subjected to external forces, thus freeing up additional deformation space for energy conversion. As a result, the loads on the driver can be reduced in the area of the head, neck and thorax
Side-impact protection thanks to intelligent bodyshell
Similar to the design of the front area of the new M-Class, the vehicle's intelligent bodyshell design also performs impressively in side-impact accident scenarios. The specific distribution of high rigidity and high deformability helps to ensure that the occupants benefit from favourable kinematics in the event of a side impact:
  • The lower part of the B-pillar, an important component in side impacts, is highly compressible, whereas its upper part is extremely rigid. As a result, intrusions and the speed of intrusions in the lower area are reduced, while in the upper area high-strength steels on the exterior sides of the pillar prevent it from buckling unfavourably in a side impact. In addition, this design solution increases the stability of the passenger compartment in the event of a rollover
  • The stiffening of the floor structure by means of a supporting element made of an ultra-high-strength material running across the entire width of the vehicle, and ultra-high-strength reinforcements in the driver's seat crossmember, help to reduce deformations, primarily in the event of a pole impact. As a result, the occupant survival space benefits from even better protection, and the thorax load on the occupants is reduced
  • The geometry and body connections of the pillars and the roof frame made of ultra-high-strength material have been optimised to provide the best possible crash safety
Brilliant finish: the rear assembly
The rear area of the M-Class also protects the sturdy passenger compartment in crash situations thanks to specific deformation work, therefore minimising the loads on the occupants. A special impact test conducted to check tank leakage gives an indication of the exceptional load capabilities of the rear part of the M-Class body. The test involved running a crash carriage into the rear of the M-Class at 80 km/h. The tank system survived this fatal impact without suffering any leaks.
To enhance rigidity, increase the energy absorption capability and improve deformation behaviour, the multi-piece rear longitudinal members feature a continuous closed cross-section with stepped plate thicknesses (tailored blanks). The spare wheel well forms an integrated part of the steel floor, and a steel flexible bumper bracket carries the rear bumper covering and is connected to the rear structure via two steel crashboxes.
Comprehensive restraint systems for occupant protection
The passive occupant protection systems, together with the "electronic crumple zone" and intelligent body design which have already been described, provide optimum protection potential, placing the M-Class at the top of its market segment. As part of this, a number of new deployment strategies are used. For example, the system can detect an impending rollover in the event of crash and if necessary deploy the head, side and window airbags, as well as the seat belt tensioners. Thanks to the new generously-sized side airbags and the window airbags with extended area of coverage, in the event of a crash the occupants can be more uniformly supported from the shoulder area down to the pelvic area, and thereby better protected. In side impacts too, the danger of injury is reduced thanks to extended coverage.
Additional protection potential is also provided for rear seat passengers with seat belt tensioners and force limiters on the outer seat positions. The integration of optional thorax bags in the tilt-adjustable folding seat backrests enables optimum airbag positioning for each backrest position. The components of the passive occupant protection systems include:
  • Two-stage adaptive airbags for the driver and front passenger
  • Kneebag for the driver
  • Sidebags for driver and front passenger (combined thorax/pelvis bags)
  • Sidebags in the rear row of seats as an option
  • Windowbags across both rows of seats from the A- to the C-pillar
  • 3-point seat belts on all five seats
  • Pyrotechnic reel tensioners and permanent belt force limiters as well as electrically reversible belt tensioners in the front, reel tensioners and single‑stage force limiters for the outer seats in the rear
  • ISOFIX child seat anchorage
  • Belt height adjustment for the driver and front passenger
  • Belt status display for rear-seat passengers in the instrument cluster
  • Automatic child seat recognition (optional) with deactivation of the front passenger airbag if a special Mercedes-Benz child seat is used
  • In a rear-end collision, a passive head restraint system developed specifically for this purpose can reduce the forces exerted on occupants
Occupant protection even after a crash
As part of the POST-SAFE® functions, the new M-Class can activate a variety of systems which can contribute towards avoiding post-accident risks. After a more serious crash, the hazard warning lights are automatically activated to warn surrounding traffic. At the same time, the doors are automatically unlocked so that the emergency services have the best possible unrestricted access to the passengers. And thanks to partial opening of the side windows, the interior is better ventilated after deployment of the restraint systems.
On detecting a collision, the central control unit switches off the fuel system to reduce the risk of a possible fire. After determining the cylinder positions, the engine management system opens the injection valves of those cylinders which are not under compression and discharges the high-pressure fuel area by direct evacuation of the remaining fuel in the combustion chamber. This reduces the risk of fuel escaping. To avoid fuel losses, all M-Class models are also fitted with cut-resistant fuel lines in all relevant locations. This also helps to reduce the risk of a possible fire breaking out.