Mercedes' new A-Class concept revolutionizes tiny car design
By Russell Williamson
MERCEDES new A-Class is more than just an evolution in small cars -- it is a revolution.
Not since the Mini has a car changed conventional engineering and design thinking in such a dramatic way.
At the heart of it is Mercedes' "sandwich concept", which has enabled the A-Class to break new ground in practicality, spaciousness and above all safety in such a small car.
Safety performance has always been a concern in small cars, given their light weight, short front end structures and limited crumple zones.
If a conventional small car is involved in a frontal crash, one of the major concerns is that the positioning of the engine and gearbox and their inability to absorb crash energy will result in the whole structure entering the passenger cell, causing significant injury to the occupants.
In order to deal with this problem, Mercedes developed the sandwich concept.
By using a raised floor -- about 200mm higher than a conventional car -- and positioning the engine and gearbox on an angle so that it is partly in front of and partly underneath the passenger cell, Mercedes have been able to ensure the A-Class offers the same occupant protection as its E-Class.
In a frontal crash in the A-Class, the engine can disengage from two of its eight fixing points and slide down and under the extremely solid front floor panel with minimum deformation of the foot well.
To ensure the safety of occupants in car-to-car crashes, the A-Class also utilizes a very strong ladder-frame chassis with straight stiff side and cross members beneath the floor, which reduces the impact of hitting a heavier larger car.
Both the stiff ladder frame and high sandwich floor also come into play in side impacts by minimizing intrusion and having the greatest load bearing structure -- the floor -- at the height of the side impact from a normal car.
Similarly, in a rear end crash, the strong side members which run the length of the car combined with the C-pillars, rear wheels and axle form a solid structure to stop any intrusion while the fuel tank is safely tucked away in front of the rear axle.
Despite the strength of the structure, Mercedes have managed to keep the weight down -- and subsequent fuel consumption low -- by using a mix of alternative materials where steel is not needed.
Aluminum, magnesium and plastic make up about 26 percent of the overall mass of the A-Class, representing weight savings of more than 30 percent compared to a conventional steel construction.
This also improves repairability with the plastic front quarter panels able to take 15 kmh impacts without sustaining any damage.
In addition to the safety advantages offered by the sandwich concept, it also has significant benefits in the practicality and spaciousness of the vehicle.
With the engine half under the floor, about 70 percent of the A-Class' total length of 3,575mm can be used for passenger and trunk space.
This large space -- 1,835mm from the driver's heel to the rear passenger's hip point -- is only 4mm short of the same space in the larger C-Class which is 900mm longer overall.
To make the most of this interior space, Mercedes has designed the seating system to be able to offer 36 different variations in the rear seat alone and the ability to remove all seats bar the driver's.
This provides for a luggage capacity that ranges from 390 liters with both the rear seat sections in place to 1,740 liters with all seats except the driver's removed.
The high floor and subsequent driving position combined with the large glass areas also improve all round visibility and make getting in and out of the car far easier than in a conventional small car.
With such an overhaul of traditional design and engineering concepts, that make the A-Class a viable vehicle for a very broad customer base, it will only be a matter of time before other carmakers copy and adapt the concepts.
For road users, this can only be a good thing, with safer, more practical and fuel efficient small cars transporting us into the 21st century.