Passive safety: Safety comes from experience

Nov 4, 2014
Daimler's 75 years of safety expertise[1] and smart's 21 years of expertise in building small cars[2] have gone into the safety concept of the new smart generation. The basic idea embodied so successfully by the preceding models has been retained. Like a nut, the interior is protected from harm by a rigid shell: the tridion cell. The Mercedes-Benz engineers put a special focus on “real-life safety" for the new smart models, for example in collisions with considerably larger vehicles.
In view of the more stringent safety requirements and expansion to the new smart forfour, the bodyshell of the new 453 model series and the tridion safety cell have undergone further development. A high proportion of ultra-high strength hot-formed steels and maximum-strength multiphase steel is now used. These are used in the sidewall and in particular in the substructure. Every element of the bodyshell has been developed to match the stress requirements in terms of geometry, material thickness, joining method and material quality.
In order to assure the structures of a high level of deformation and energy absorption capacity in frontal collisions, the new smart generation has been provided with the largest possible crumple zones and attention has been devoted to ensuring an effective flow of the accruing forces. In a severe frontal collision, the rear structure also helps to absorb the energy acting on the vehicle, for example. The forces are channelled evenly into the extremely robust passenger cell, which is designed as a safety cage. Particularly extensive work went into adapting the new front axle carrier to crash requirements.
The highly robust tridion passenger cell is able to prevent major deformation even in very severe collisions, thus helping to protect the occupants' space. The fuel tank is located safely outside the deformation zone in front of the rear axle. In conjunction with the restraint systems, the smart developers therefore expect four stars in the NCAP rating.
Amassed know-how: development in line with Mercedes-Benz standards
The Mercedes-Benz safety engineers were involved in the cooperation project with Renault throughout all phases of the development process and were able to contribute their amassed know-how. In the area of computer simulation, for example, it was possible to calculate in detail the behaviour of individual weld spots or the newly introduced bonding methods, such as MIG soldering.
The number of assessed collision cases far exceeded the mandatory scope, both in the simulations and in real crash testing. The new smart fortwo underwent the same development programme as the new Mercedes-Benz C-Class, for example. As the new smart fortwo has been developed for the global market, the number of crash tests was around four times what is required for vehicles designed primarily for the European market.
In keeping with the Mercedes-Benz “real-life safety" philosophy, the focus in car-to-car tests was on compatibility with substantially larger and heavier vehicles. For example, the new smart fortwo was required to demonstrate its capabilities in frontal collisions with the S- and C-Class (see next section for details).
Restraint systems: interaction of all components:
The way in which all components (body, seat belts, airbags and sensor system) interact is crucial to effective protection. The forward displacement space for the occupants is designed to be sufficient to provide them with an adequate deceleration distance to minimise accident-induced physical stress in the event of a collision. In addition, as is usual in Mercedes-Benz vehicles, a telescoping steering column was integrated for the driver. In the event of a crash it provides additional forward travel of approx. 100 mm and absorbs additional energy with its defined behaviour when force is applied. In the design of the interior trim and the cockpit in particular a focus was deliberately placed on roundness and yielding materials. This can also help to prevent injuries.
Driver and front passenger are each provided with a 3-point seat belt with belt force limiter and pyrotechnic belt tensioner as standard. The rear seats in the smart forfour each have a three-point seat belt with pyrotechnic belt tensioner and belt force limiter – features which other manufacturers do not necessarily provide, even in higher classes of vehicle. A rear belt status indicator in the overhead control panel comes as standard.
The ISOFIX fastening system with TopTether attachment features as standard on the passenger seat of the fortwo and the rear seats of the forfour, providing a simple means of attaching child seats rigidly to the vehicle. The child seats themselves come from the Mercedes-Benz range.
The headrests for driver and passenger are integrated in the backrests and cannot be adjusted. They reduce the risk of injuries to the cervical vertebrae in a rear-end collision.
Driver and passenger airbag, kneebag and head/thorax bags as standard
The smart models come with driver airbag, driver kneebag and passenger airbag as standard. The kneebag has a positive influence on occupant kinematics in a frontal collision, thus offering the driver additional protection in many frontal collision scenarios. The principle of the telescoping steering column has been adopted 1:1 from the Mercedes-Benz range.
The standard-fit sidebags (head-thorax bags) are accommodated in the driver and front passenger seat backrests and provide side cover for the respective occupants' head and chest. The sidebags incorporate two chambers to enable due adaptation to different sizes of head/upper body. When inflated in side-on collisions they are able to lower the degree of stress to which the chest area is exposed and reduce the risk of the head colliding directly with the side window or other objects likely to cause injuries, such as a pylon, a tree or parts of a colliding vehicle. The occupants' pelvic areas are additionally protected by deformation elements installed at appropriate points in the door panels.
The smart fortwo and forfour are equipped with an electronic control unit that triggers the respective restraint systems depending on the predicted impact severity. For better recognition of a side impact the central crash sensor is supported by satellite sensors in the area of the B-pillar base and pressure sensors in the front doors. Side airbags and belt tensioners are activated on the side sustaining the impact when the central electronic controller detects a side crash of a certain severity.
Pedestrian protection: clear improvements
The design of the front has been optimised for pedestrian protection as far as possible in view of the extremely short length of the front section. For example, in order to reduce the loads which arise in the event of a pedestrian impact on the front bonnet of the vehicle, the deformation space between the front bonnet and the components beneath it has been optimised. The deformation characteristics of the front bonnet were specifically developed to meet these demands. A good, large impact area was realised in the design of the front of the vehicle. The constructive design of the front bumper leads to reduced loads in the event of pedestrian leg impact.
After an accident: rescue assistance
To facilitate effective help, both smart versions have sturdy grab handles that are able to transfer great force when the doors are opened – a feature not taken for granted in this segment. Depending on the severity of the impact and the type of accident the following functions can additionally be performed: unlocking of the doors, shutdown of the engine and fuel pump and activation of the hazard warning lights.
[1] The systematic development of safety measures started in 1939 when Béla Barényi joined Daimler; on 23 January 1951 the patent for the safety cell was granted
[2] Development of the first smart generation started in 1993
The new smart fortwo 2014: Preparation for the car to car crash. smart fortwo vs. S-Class
The new smart fortwo 2014: Preparation for the car to car crash. smart fortwo vs. S-Class
The new smart fortwo 2014: Preparation for the car to car crash. smart fortwo vs. S-Class
The new smart fortwo 2014: Preparation for the car to car crash. smart fortwo vs. S-Class