Press Release
Chassis durability testing: Formula 1 on the test rig
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Gruelling endurance tests for all chassis components
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Test rig computer programmed with race-track and test-route data
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Underwater pressure test and temperature tests at 90 degrees Celsius
60 hours on the Hockenheimring: full throttle followed by braking followed by steering, over and over again. The wheels, wheel bearings and wheel hubs for newly developed Mercedes passenger cars must withstand this continuous pounding in order to get the go-ahead for series production.
This gruelling test of endurance – the chassis is subjected to lateral forces of up to 10,000 Newtons due to high acceleration when cornering and the components are heated up extremely quickly on account of the almost constant braking – is just one of many long-duration tests Mercedes performs on the chassis components. The new C-Class, due for launch in spring 2007, came through these tests several times during the course of its development.
For such extreme tests, the Mercedes engineers bring reality into the laboratory. The test rig computers are programmed with road characteristics and typical driving manoeuvres, enabling them to simulate the loads that occur when driving on a Formula 1 racing circuit such as the Hockenheimring or Nürburgring, for example. However, like body durability testing, chassis durability testing focuses primarily on the long-standing "Heide" torture-track endurance test which was developed by Mercedes engineers on the Lüneburg Heath roads during the fifties (see page 6).
This test – the world's toughest torture-track test – allows newly developed cars to be aged at a vastly accelerated rate: after just 2000 hours, the body and chassis have experienced the stresses and loads of an entire car lifetime.
For the torture-track endurance test on complete front and rear axle assemblies, the Mercedes-Benz Technology Centre in Sindelfingen has six servo-hydraulic test rigs which run day and night. Four installations are used to test the wheels, wheel bearings and wheel hubs under conditions akin to those experienced when driving around the Hockenheimring, while a further 150 test rigs are employed to rigorously check the chassis components – from the bearings to the rubber bellows, from the axle joints to the torsion-bar stabilisers.
Axle joints: thermal stress based on driving in heavy Tokyo traffic
Each test reflects the vast experience and know-how of the Mercedes engineers. They know exactly which factors cause the most stress to the chassis in real life. And they have adapted the test conditions precisely to mirror the everyday situations experienced by motorists all over the world.
As an example, they check the durability of the front and rear axle joints by performing a 100-hour pressure and movement test, during which the components are exposed to forces of up to 35,000 N and stretched to breaking point. As well as withstanding these high mechanical loads for long periods, the joints also have to resist high temperatures of up to 90 degrees Celsius – the level of thermal stress measured on the axle components whilst driving in city traffic in Tokyo, Japan. If the joints display any signs of play at the end of this wear test, the components are rejected.
Mercedes specialists are just as meticulous in their approach to testing the sealing bellows which protect the axle joints against dust, dirt and other environmental effects. To do this, they immerse the joint and sealing bellows in a glycol/water solution and move the components with varying angles of tilt up to 40,000 times in succession – 10,000 times at temperatures of minus 15 degrees Celsius alone.
Environmental simulation: three weeks of dirt and ice-cold water
Mercedes passenger cars also have to cope with other simulated everyday conditions during testing, such as a high-pressure water jet (80 bar) and the systematic spraying of the joints with ice-cold, dirty water and fine, hot sand dust over a period of three weeks. The most extensive test cycle in this environmental simulation lasts the full three weeks and includes over one million axle-joint load cycles in simulated driving on motorways, country roads, urban roads and torture tracks – far more than any Mercedes-Benz has to contend with during its long lifetime.
Hydro-bushings: 17,000 Newtons of load from all directions
The tests which Mercedes-Benz employs for the hydro-bushings on the front and rear axle are no less strenuous. Inside these rubber components is a viscous fluid which prevents the engine and wheel vibrations from being transferred to the body. In these tests, the high-tech components have to withstand temperature and environmental effects as well as forces of up to 17,000 Newtons, which act on the bushings from all directions.
Mercedes-Benz simulates these real-life conditions on axial test rigs – the only machines of their kind in the world. Here the hydraulically damped bushings are subjected to tests that simulate the wear and tear of an entire car lifetime.
In addition to this mechanical endurance test, the bushings and their elastomer fillings undergo a four-week temperature test at up to 70 degrees Celsius. Using thermographic cameras, the Mercedes engineers gain an insight into the inner workings of the bushings and can witness how the vibration-damping fluid reacts to this extreme heat.
