Body testing facility: the M-Class on the road simulator

A totally dependable body and chassis systems that can cope with high levels of strain under even the most demanding conditions over hundreds of thousands of kilometres are particularly indispensable in an SUV such as the Mercedes-Benz M-Class, with its broad on-road and off-road performance spectrum. Besides practical tests with the prototypes, the engineers also subject the M-Class body to an exhaustive test of durability during the development phase that ranks amongst the toughest examinations in the world for body and chassis. Lasting several weeks, the load cycle covers a total of 3000 kilometres, which corresponds to an average of 300,000 kilometres of routine driving. This is because every kilometre driven on one of the state-of-the-art test rigs is 100 times more gruelling than in everyday driving. SUVs which come through this endurance test unscathed will be able to withstand the strain of a tough day's driving on and off the road in the Mercedes-Benz M-Class.

The test programme comprises various "load spectra", which the engineers refer to as virtual test tracks. The individual courses are not dreamt up by the team of testers, however. Instead, real routes were digitised, including the "Heide" test with its tortuous pothole and cobblestone sections, special off-road torsion drives with maximum torsion levels, and corrugated tracks in Africa with high-frequency excitation. Computers orchestrate the sophisticated test rigs on the basis of this data. The rigs' servo-hydraulic cylinders mercilessly knock, jerk, shake and twist the bodies, just like on a real test drive. In all, 26 actuating cylinders arranged vertically and horizontally are responsible for stimulating the body on the test rig. A hydraulic system generates a pressure of 210 bar and pumps as much as 2000 litres of oil into the cylinders every minute. This enables the formidable forces of up to 20,000 Newtons to be produced, which shake the car thoroughly in quick succession at the computer's command.

To allow them to detect any damage early, the Mercedes engineers halt the test rigs after around 100 kilometres each time, or when one of the 150 or so sensors that permanently monitor the vehicle emits a signal to automatically shut down the facility. The body is then inspected meticulously for the tiniest sign of damage. The experts are highly experienced, so they know exactly where the critical points are and what they should look out for. Apart from the weld points and bonded connections, the panels along the force transmission paths between the chassis and body are also carefully scrutinised, as these areas have to withstand very high forces in an SUV when negotiating rough roads or torsion sections. The candidate is deemed to have passed the endurance test if its body shows zero signs of damage. Even the finest of cracks, which can only be spotted with the aid of special fluorescent colours and under ultraviolet light, are unacceptable.

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