A robust basis is the ideal ingredient for a stiff bodyshell offering a high level of crash safety. It plays a decisive role in ensuring maximum noise-related comfort, outstanding vibration characteristics and hallmark Mercedes-Benz longevity.
In these terms, the E-Class Cabriolet had an ideal starting position, given that it is closely related to the E-Class Coupé – a two-door model which meets the very highest requirements when it comes to torsional stiffness and occupant protection.The same applies to the Cabriolet, which has one of the stiffest designs in its segment. The body’s static torsional stiffness can be seen as a reliable indicator of the excellent cumulative effect of the implemented measures. It has been increased by around 30 percent compared to the outgoing model.
To achieve this figure, the bodyshell of the E-Class Cabriolet received extra reinforcements compared to its Coupé sister model, the most important of which are as follows:
– The extremely robust A-pillar assembly consists of two high-strength steel tubes which are welded to the sheet-metal shells of the A-pillars. In the case of the E-Class Cabriolet, both tubes have an exceptionally robust Y-shape and stretch from the A-pillar intersection to the upper window frame.
– The plug-in B-pillars are extremely robustly connected as they engage in the side skirts, thus offering highly effective protection in the event of a crash. A shoe made from ultra-high-strength steel braces the inside of the B-pillar against the rear seat crossmember. The rear support against the rear panel runs in an arch-like shape to the rear seats.
– Reinforced side skirts and bulkhead platesin the doors protect the occupants in a lateral impact with a pole, for example. Likewise the reinforced shoulderline with its high-strength steel section enhances the exceptionally robust nature of the design.
– Ten bolts are used to attach the crossmember to the windscreen frame, making the crossmember significantly stiffer than its counterpart in the outgoing model.
– The floor assembly has been reinforced solidly at several points.
– The robust rear panel behind the rear seats further enhances the body’s lateral rigidity.
Roll-over protection: occupant protection zone comes through roof-drop test with flying colours
The roll-over protection consists of two robust bars, each with a diameter of 35 mm, which are housed in the rear head restraints in modules behind the rear seat backrests. A tilting cone sensor detects imminent danger to the occupants based on extreme skidding movements or acceleration caused by impact. If this sensor then sends a corresponding signal, pre-tensioned pressure springs are activated by pyrotechnic means, i.e. extremely quickly.
Consequently, both roll-over bars in the rear head restraints are extended. They reach their highest point and are locked automatically within a fraction of a second. In combination with the robust A-pillars, each of which is reinforced with two high-strength steel tubes, the steel bars provide highly effective roll-over protection. This effect is confirmed in the roof-drop test, an extremely tough in-house trial performed at Mercedes-Benz, in which the slightly tilted body is dropped onto the roof structure from a height of 50 centimetres, causing the vehicle to hit the ground with its full weight on one of the two A-pillars. According to the test specifications, the plastic deformation of the A-pillars is only allowed to be minimal.
Restraint systems: first Mercedes-Benz Cabriolet with headbags
With PRE-SAFE®, seven standard-fit airbags, belt tensioners and belt force limiters on all seats, as well as crash-responsive head restraints for the driver and front passenger, the new E-Class Cabriolet offers the most comprehensive array of safety features in this vehicle category. The range of airbags, which can deploy in thousandths of a second in an accident, comprises front and side airbags for the driver and front passenger, a kneebag for the driver and, for the first time in a Mercedes-Benz Cabriolet, headbags.
Whereas windowbags are used in cars with a conventional, fixed roof, mostly housed in the roof frame, the Mercedes-Benz safety specialists naturally had to employ a different airbag as well as choose a different installation position in the case of the E-Class Cabriolet. Here headbags are integrated into the door panelling in the beltline area. Covering a wide area – around 0.7 x 0.5 metres with a volume of 17 litres when deployed – the airbags provide extremely effective protection for occupants large and small in the event of a crash. The protection system comprising headbag, and thoraxbag optimises the level of protection afforded to individual parts of the body. Rear sidebags are available as an option.
Exemplary safety combined with maximum comfort is the best way to describe the restraint systems in the E-Class Cabriolet. When front passengers get into the car and close the doors, the seat belts are extended towards them by means of belt feeders – a Mercedes-Benz hallmark – making the belts extremely easy to put on. Once the rear passengers have taken their seats and belted up, the rear head restraints are raised from their recessed rest position to the driving position automatically. If only the front seats of the Cabriolet are occupied, there is always excellent rear visibility, while any rear passengers on board benefit from the protective effect of the head restraints in the event of a crash, providing they are wearing their seat belts.
What’s more, the geometry of the front seat belts has been optimised. The belt straps no longer run horizontally but, instead, are turned 35 degrees towards the occupants‘ shoulders. The advantage of this modification is that the wind pressure on the outside of the belt strap prevents annoying belt flapping when driving with the roof down. This dreaded „shoulder-knocking“ effect has been reduced substantially at speeds of up to 120 km/h.
Driver assistance systems: help in critical situations
Preventing traffic accidents is at the heart of Mercedes-Benz’s commitment to safety. This is why the engineers in Sindelfingen are dedicated to advancing the development of sophisticated assistance systems which warn and assist the driver in critical driving situations and can act autonomously if there is acute danger. ABS, ESP® and BAS (Brake Assist) were the first technologies of this kind; their positive effect has since been confirmed by an analysis conducted by the Mercedes Accident Research department based on anonymous data samples from the German Federal Statistical Office.
The new or modified driver assistance systems in the E-Class Cabriolet are based on state-of-the-art radar and sensor technology. They have been developed to help reduce the number of accidents caused by being too close to the vehicle in front, drowsiness and darkness.
Preventive protection measures: PRE-SAFE® now also includes AIRCAP®
In the new E-Class Cabriolet, occupant protection actually begins in the phase leading up to a possible accident thanks to the Mercedes-Benz PRE-SAFE® invention, which is specified as standard for the two-door model. In the event of critical driving situations with a high risk of an accident, the system activates protective measures as a precaution, allowing the seat belts and airbags to deploy with maximum effect in the event of any subsequent collision. This early accident detection is possible because PRE-SAFE® is an intelligent synergy of active and passive safety. It is linked to Brake Assist and the Electronic Stability Program (ESP®), for example, whose sensors can detect critical driving situations and send the relevant information to the electronic control units within a matter of milliseconds. PRE-SAFE® also uses these sensor data.
Anticipatory occupant protection can be activated in the event of emergency braking or critical lateral acceleration as well as when imminent danger is detected by the sensors of the assistance systems alone. The AIRCAP®automatic draught-stop is likewise integrated into the PRE-SAFE® system. If the system detects a risk of roll-over, AIRCAP®is retracted as a precaution.
Source: Daimler AG