Under the microscope: endurance testing - A vehicle lifespan at time lapse speed

Feb 10, 2014
Apart from purely road-based endurance tests, endurance testing of the new GLA-Class involved additional trials with stresses related to all-wheel-drive operations off paved roads. During the nine months of endurance testing, an entire vehicle lifespan from customer perspective is simulated at time lapse speed. In all, 24 GLA models completed this marathon and other endurance tests, racking up a total of 1.8 million kilometres in the process.
Like the GLK-Class before it, which was renowned for its robustness, the GLA‑Class successfully was put through a special endurance test: the Track&Field endurance test. This test, covering some 80,000 kilometres, is based on the road endurance tests and is supplemented with a number of special sections far off paved roads, a sprint programme at the Nürburgring Nordschleife and intensive trials in an Alpine environment. Following positive experiences with the GLA and GLK the Track&Field endurance test will be the final examination for all compact Mercedes-Benz SUVs.
Compared to the ML, GL and G-Class models, which fulfil the requirements for the most extreme off-road applications, the Track&Field endurance test represents the performance profile that customers expect from a compact SUV: the main area of usage is on the road, however there are considerable expectations of the skills off the beaten track. For this reason the track & field endurance test was elaborated, exactly mirroring the performance spectrum of a compact SUV based on the use profile of the customers. But this does not mean the GLK and GLA are softies fit solely for boulevards: the demands made by the track & field endurance test are very harsh, as demonstrated for example by the off-road endurance runs conducted on a tank crew training ground.
During this nine-month GLA marathon the focus of the tests is on the durability and reliable operation of the new 4MATIC all-wheel drivetrain, the suspension and the comfort, control and assistance systems. In addition, the track & field test ensures the strength and durability of the entire structure of the SUV body structure.
Documentation: collection of comprehensive data provides insights and enables projections
Simulating the entire lifespan of a vehicle within nine months requires a defined load scenario which the testing engineers realise with different "load collectives". The track & field endurance test includes extensive drives on country roads, motorways or in inner-city stop-and-go traffic – disciplines familiar from the conventional road endurance testing programme covering 150,000 kilometres. In part, these stretches are covered by the GLA test vehicles towing a trailer with the maximum allowable towing capacity; this is intended to further intensify the structural loads on the body. But the distance of 1.8 million kilometres covered by the 24 GLA long-distance runners only partially reflects the scope of the test disciplines. In the track & field endurance test the test drivers also check all the controls and operating devices according to an exactly defined procedure.
Always on board with the test driver: the computer to record all the data. It continuously records 190 different measured variables for the standard-fit monitoring and control systems and some 50 variables for additionally installed sensors. To safeguard and evaluate the data they are transmitted to the Mercedes-Benz Technology Center (MTC). Subjective impressions of the experienced drivers help to further enhance production maturity.
All information is managed with Daimler's own development tool FINAS (Vehicle Information and Administration System). Here the complete vita of the GLA prototypes with all measured data and vehicle-specific information such as stage of development, equipment, chassis, tyres or engine are saved, and pending or performed service or repair work is entered.
Aggravated conditions: Nürburgring, Alps, tank practice grounds
One kilometre at racing pace on the Nürburgring North Loop is equivalent to the load experienced during 20 kilometres in the real life of an automobile. The GLA has to complete 240 laps or about 5000 kilometres in the test. This adds up to the equivalent of 100,000 "workaday" kilometres. The endurance tests in an Alpine environment are similarly demanding. One stretch in the Italian Alps covers a distance of 154 kilometres, includes nine Alpine passes and winds through 450 bends. The vehicles have to cover differences in elevation of 4300 metres, and the total test distance after 20 laps on this surface is 3080 kilometres. The numerous winding bends impose a particular strain on both the chassis and the 4MATIC drivetrain as the vehicle accelerates out of the bends, and ensure that the dynamic handling control systems have their work cut out.
In view of its lineage, Mercedes-Benz requires that the new compact SUV also prove its mettle off surfaced roads. After all, in deference to the G-Class – the grandfather of all SUVs and cross-country vehicles with the star – only those vehicles that also meet certain minimum requirements off-road may carry a "G" in their name. To ensure this, the track & field endurance test includes a run that very freely construes the term "primitive road" – the so-called tank ring road of a military training area of the German Armed Forces in southern Germany. Where 62-tonne tracked monsters normally tear up the terrain, the GLA had to complete 1000 kilometres and thereby prove that it is capable of withstanding even such adverse conditions on a sustained basis.
The sequence of tests plays an important role in the track & field endurance test. Here, too, the track & field endurance test is aligned with the real-life demands on an SUV owned by the customer. The individual on- and off-road disciplines are broken down into test cycles which are completed in varied patterns according to a defined distribution. For instance, a drive over country roads can be followed by an off-road excursion, or a city drive can be followed by a long stretch of motorway, just like in real life.
To cover various load scenarios for a customer-owned vehicle, in addition a number of disciplines involve different loads. For this purpose, either steel bars are firmly screwed to the vehicle floor in the rear, or the test drivers are accompanied by "water boys": water-filled plastic torsos weighing 82 kilograms, strapped to the seats with standard seat belts.
Finale: complete disassembly and detailed evaluation
After completing track & field endurance testing the GLA models are disassembled and their individual components are spread out like an automotive puzzle. Behind closed doors the specialist departments the development and test engineers subsequently evaluate all vehicle components, focussing on those areas where any anomalies have been observed during the endurance tests. If no further nonconformances are found in these sections, their fitness for series production can be certified.
However, if further problems or previously undiscovered problems arise, the engineers become active again until they find a perfect solution. If in doubt, GLA endurance test subjects are sent on their rounds again and the tests on devices such as the body testing facility or the road simulation test rig are intensified. After the closed-door meetings over the disassembled GLA, further assessments follow: in the appropriate development units the engine, transmission and 4MATIC drivetrain then are completely disassembled, measured and scrutinised.
Track & field endurance test: one of many
The track & field endurance test rounds off the extensive endurance testing programme carried out worldwide by Mercedes-Benz. This endurance testing programme differs fundamentally from the development and tuning runs performed on new models; these are done additionally. Whereas on these runs the characteristics laid down in the specifications book are verified, programmes like the track & field endurance test verify the reliability and durability of new models.
Other endurance tests:
  • World endurance test: 50,000 km worldwide in extreme climatic and topographic conditions
  • Trailer endurance test: 25,000 km with a special loaded trailer
  • Rough road endurance test: 2000 km over extremely rough roads ("Heide" endurance test)
  • Corrosion endurance test: 12-week testing in climate and corrosion chambers and on real-life routes
  • Function tests: Checking of control systems and dynamic handling control systems on load-specific routes
  • Hockenheim endurance test: 6000 km on the Grand Prix circuit at racing speed
  • Full-load endurance tests over 30,000 or 50,000 km on cordoned-off high-speed tracks such as Nardo (southern Italy) or the Mercedes-Benz testing grounds in Papenburg, northern Germany