The road to series production: simulation, test rigs, road testing
- Initially there are electronic simulations and virtual crash tests, aerodynamic studies and suspension tests
- Extensive tests include winter testing in northern Sweden, summer testing in Spain and endurance testing
- In addition there are special tests for the electric drive, fuel cell and interplay between all the drive components
Intensive functional and fatigue testing of individual components and later also of the complete test vehicles on a host of test rigs speed up the development process. The Fuel Cell Centre of Competence in Kirchheim-Nabern east of Stuttgart plays a crucial role in the GLC F-CELL.
The test facilities in Nabern include five climatic chambers allowing temperatures of -40°C to +85°C. Some test rigs have an inclination feature which allows the drive unit to be inclined along both axes, and also diagonally, by 19 degrees. This, for example, verifies the absolute cold-starting ability of the fuel cell system.
Other climatic test benches perform different driving cycles plus consumption measurements under a wide variety of climatic conditions. The system software is also developed on the test rigs. Some systems have covered around three million kilometres in this way, without ever having been on a road. The development work was concluded with a six-month endurance test absolved at an average speed of 85 km/h despite numerous urban traffic phases including start/stop.
Driving resistances are simulated on the test rigs with the help of generators. The electric power generated by the fuel cell, a total of around 400 MWh to date, is fed into the plant's power network. Every year the fuel cell experts use around 70 tonnes of hydrogen for their development tests. The only "exhaust gas" emitted is water vapour.
The Vehicle Safety Technology Center (TFS), which opened in November 2016 as the world's most modern crash test centre, offers entirely new possibilities for testing vehicles with alternative powertrains, vehicle-to-vehicle tests or for the design of assistance systems and PRE-SAFE®. The GLC F-CELL received its aerodynamic finishing touches in the wind tunnels in the Mercedes-Benz Technology Center Sindelfingen: Even the most extreme weather events can be moved indoors here. Temperatures ranging from minus 40 to plus 60 degrees Celsius, hurricanes with wind speeds of up to 265 km/h, tropical downpours and heavy snowstorms are all part of the standard repertoire available to the test engineers.
After the first prototypes were roadworthy, the summer and winter road testing of the GLC F-CELL began. The vehicles were driven on the proving grounds in Spain (IDIADA near Barcelona), Sweden (Arjeplog) and Germany (Boxberg), among others. The road tests also took the test teams to the Sierra Nevada (Spain) and the low mountain ranges of the Schwäbische Alb and the Black Forest in Germany. The test programme comprised more than 500 individual tests, which in addition to the standard test regimen for all vehicles also included special tests for the electric powertrain, the fuel cell, and the interplay of all powertrain components. The special endurance tests also include the so-called taxi-test, which represents urban driving with frequent idle times, and the high-mileage driver cycle where the focus is on high daily mileages.
Hot on ice: final winter trials of the F-CELL pre-series models
The company has been testing each new model under extreme conditions near the Arctic Circle for decades – in icy temperatures down to minus 35 degrees Celsius, on snow-covered roads and on sheer ice on frozen lakes. To this end, Mercedes-Benz has set up a test centre in the small northern Swedish town of Arjeplog in Lapland. In addition to the road testing in the far north, tests take place on specially set-up testing tracks here. Demanding hill climbs with gradients of up to 20 percent, test tracks with varying coefficients of friction, handling courses, and skid pads on the almost sheer ice of the frozen lake pose the stiffest of challenges for the powertrain and control systems.
New challenges for an electric vehicle include the output of the electric motor during cold starting and with a cold battery, the cold-starting properties of a fuel cell (stack), the vehicle's range under the customer's normal operating conditions, handling of charging cables and filling nozzles, pre-entry climate control, and the operating strategy complete with recuperation. Added to this is the specific configuration of the vehicle dynamics and the ESP® system.
In addition to the interaction between the fuel cell and the high-voltage battery, other points of interest in the GLC F-CELL are, for example, how well the carbon-fibre enclosed hydrogen tanks perform, and how reliably the valves operate in the cold.