One fast lap after another on the high-speed oval in Nardò in southern Italy, winding uphill and downhill stretches on the Swabian Jura or stop-and-go traffic for hours on the Stuttgart Weinsteige - some Mercedes-Benz employees experience such punishing traffic situations day after day. And without ever leaving their workplaces in Untertürkheim, because they "drive a car without a car". Mercedes-Benz tests the drives of electric cars on eDrive test benches.
The electric drive of models in the fast-growing Mercedes-EQ family is being tested on a total of 13 test benches in Untertürkheim. Of these, seven are pure eATS test benches, where the power comes from a special direct current source, what is known as a battery simulation. On the six eDrive test benches, testing also includes the battery and the complete charging components of the vehicle. In addition, there are 13 test benches at the Nabern development site.
The test benches are connected to a monitoring room with computers. The most important measurement parameters for the test operation are visualised on one of the many monitoring screens. They tell the test bench driver in real time during the test whether everything is in order or whether a problem is imminent. Almost all year round, the testing operation runs around the clock. At weekends, there is an on-call service; automatic shutdowns are communicated to the staff members responsible via instant messages or push messages on their smartphones. Remote access to the automation, diagnostic and measuring computers is possible.
The trial program: a whole car lifetime is simulated
All electric drivetrains (eATS) for all series are tested on the test benches. Both in terms of function and efficiency as well as durability. On the test benches, the eATS are coupled to load machines via the drive shafts installed in the vehicle - just like the drivetrain with a combustion engine and transmission on conventional test benches. At each rotational speed, they simulate different stresses on the e-drive.
The testing programs depict high-speed and road endurance runs. For this purpose, the test benches are programmed with data from real routes, topography and corresponding load conditions, for example acceleration, staying on the gas, kickdown or recuperation. For example, Nardò, the Swabian Jura and the Stuttgart Weinsteige take place in the hall. And for security reasons (even before the coronavirus) without spectators.
With accelerated endurance runs, an entire car lifetime is simulated within a few months and with many megawatt hours of electricity. In this way, weak points can be detected in the shortest possible time and the drivelines optimised in good time before series production starts.
How long an eATS is tested on the test bench depends on the respective test program. The range extends from several weeks for testing individual functions to a whole year for an endurance run.