New Mercedes C Class: The Testing

Press Release

Body durability testing: An entire car lifetime in just four weeks

• One of the world's toughest tests for car bodies and chassis units

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  Stresses and loads equivalent to 300,000 km of everyday driving

• Endurance testing based on torture-track tests on Lüneburg Heath

• C-Class completes extreme series of tests on test rigs and test tracks

The body shakes and shudders to an almost unbelievable extent. Tremendous forces are applied to strike and pull the axles, causing the car to shift abruptly by varying degrees without any respite whatsoever.

There is method behind all that happens on this test rig at the Mercedes Benz Technology Centre. This is one of the world's toughest tests for cars – a standard programme for every newly developed Mercedes-Benz, designed to ensure the long-term reliability for which the brand is renowned. Cars which pass this test and successfully withstand all the shocks and vibrations have experienced an entire car lifetime – and an extremely strenuous one at that – in just a matter of weeks.

This is because every kilometre completed on one of the state-of-the-art installations is 150 times more intensive than normal driving on the road. The test runs for a total of 2000 kilometres. In terms of the stresses and loads exerted on the car, this is equivalent to a Mercedes customer driving for 300,000 kilometres. Vehicle components which come through this test of endurance unscathed are therefore more than capable of withstanding the rigours of everyday driving.

The new C-Class, due for launch in spring 2007, passed this stern examination three times: once as a hand-built prototype in order to pinpoint any problem areas at an early stage, once as a pre-production vehicle manufactured using the series-production tools and, finally, once more as a factory-produced car.

History is a great teacher: testing based on the Lüneburg Heath roads

The relentless rig test has a (surprisingly harmless) name: it is called the "Heide" endurance test (from the German word meaning "Heath") and, although it sounds like an exercise in country pursuits, actually refers to the history of the test programme which began on Lüneburg Heath.

Here country outings in the car were a unique experience in the fifties. Not least because anyone venturing off the beaten track between Uelzen, Soltau and Lüneburg to get a close-up view of the idyllic surroundings subjected both themselves and their cars to the sternest of tests. Tarmac roads were something of a rarity. Instead vehicles had to labour over dirt tracks beset with potholes and bumps or struggle over large cobblestones which had an equally unsettling effect on both the body and the chassis.

Reports about the state of these heath roads circulated quickly. Inevitably the Mercedes-Benz engineers in Stuttgart – always on the look-out for suitable routes to test new models – got wind of this. During a reconnaissance mission in northern Germany, they found precisely what they were looking for: the Lüneburg Heath roads provided tough and, therefore, ideal conditions for car tests.

This is how the "Heide" test became an integral part of the Mercedes test programme. Engineers and test drivers regularly met up in the small town of Bispingen to embark upon the test drives on the heath's unsurfaced roads and dirt tracks. It was not long before they realised that this test was so punishing on the car body and chassis that, within a matter of weeks, the cars had experienced the stresses and loads of an entire vehicle lifetime.

The roads of Lüneburg Heath are now in a much better state and have had the benefit of tarmac for many years. But Mercedes-Benz still performs the "Heide" test, albeit in simulated guise on test rigs and at proving grounds. Before the tarmac arrived, the test specialists managed to copy the bumpy surfaces of the original heath roads using plaster casts. They were therefore able to reproduce the roads on in-house torture-test tracks which were set up on the periphery of the proving ground in Stuttgart-Untertürkheim and in Sindelfingen.

Later the development team succeeded in digitising the "load spectrum" and feeding the sophisticated test rig computers with data describing the high forces and torques which occur when negotiating the torture-track route. The test rigs' servo-hydraulic cylinders strike, pull, shake and bend the car bodies just as relentlessly as a drive on Lüneburg Heath did around 50 years ago.

Pure stress: forces of up to 20,000 Newtons

The 2000-kilometre stretch on the test rig lasts four to five weeks and simulates driving on various route profiles at speeds of just 25 and 60 km/h. This is all that is required to reproduce the extreme stresses and loads exerted on the car body by the bumpy roads. A total of 26 vertically and horizontally arranged servo cylinders pound the car body mercilessly. A hydraulic system pumps up to 2000 litres of oil per minute into the cylinders, generating a staggering 210 bar of pressure. This is how the immense forces of up to 20,000 Newtons, which are applied in quick succession by computer control and shake the car to its core, are achieved.

The cars which take part in the torture-track endurance test are always full-specification models with the heaviest engine and the largest wheel/tyre combination possible. also, additional weights are applied at the front and rear axles.

To detect any damage at an early stage, the Mercedes engineers stop the test rig every 100 kilometres or so or if one of the approximately 150 sensors which permanently monitor the vehicle gives the signal to automatically shut down the test rig. The car body is then meticulously checked for damage. On account of their vast experience, the Sindelfingen specialists know exactly where the critical points are located and what to look out for. Whether it be the weld points, the bonded connections or the panels on the force-application paths between the body and the chassis, every aspect is subjected to the closest scrutiny, since these are the areas which have to withstand extremely high forces in torture-track endurance tests such as the "Heide" test. Other car body components that have to endure high loads include the integral support frame to which the front axle, steering and engine are fastened.

In addition, the Mercedes engineers scrupulously test and improve these and other problem zones in a separate components laboratory. Here, individual components – such as shock absorber towers, torsion bar bearings and pedal recesses – and body sections for new models have to pass durability tests. Many of these non-stop test programmes are also based on field data gathered over a period of around 50 years, stretching back to the time when tests were still conducted on Lüneburg Heath.

Body engineering: conflict of aims between durability and lightweight design

The vehicle only passes the endurance test if the body shows no signs of damage whatsoever. Even hairline cracks which can only be seen using special fluorescent fluids or under ultraviolet light are unacceptable.

Theoretically speaking, it would be easy to meet these high Mercedes standards: simply by using a vast amount of material. The car bodies would then be so robust that even the "Heide" test would seem like a stroll in the park. But automotive development is all about solving conflicts of aims. And this certainly applies in the case of body engineering. Here it is not just about ensuring excellent durability and longevity. A host of other, sometimes contradictory requirements also have to be fulfilled. By way of example, the body has to act as a sturdy backbone for the chassis as well as ensuring precise handling qualities and preventing annoying vibrations. Furthermore, the body has to be lightweight and aerodynamic in order to boost fuel economy. Plus it has to meet the most stringent of safety standards and be easy to repair.

The torture-track endurance test is one of the best ways of meeting all of these requirements. The test results, always achieved under the same conditions, show the engineers at a very early stage whether the concept will work, at what point damage occurs and which parts of the body are made using excessive or insufficient material.