Audi thermal management put to the test

Mr. Kröner, what does the thermal management of an Audi e-tron have to do?

In order to deliver an adequate performance even at more extreme temperatures, the vehicle’s high-voltage battery must, for example, be warmed or cooled. Thermal management ensures that this can work as well as possible in its ‘comfort range’.

This is like the performance of a smartphone battery which can be more limited at low temperatures than in the normal temperature range.

Thermal management makes a significant contribution when it comes to preventing temperature-related drops in the performance of the HV battery and other HV components. In everyday operation, short-term deviations from the comfortable temperature generally have little effect on system performance.

How do you determine whether the interconnections are working as desired?

Relevant tests on real vehicles are highly complex, expensive and time-consuming. That’s why here in Gaimersheim, together with our colleagues within Audi, we have developed a new testing bay, unique in the VW Group, that can present our test scenarios at a very early stage, regardless of the vehicle. This testing bay has been operational since 2020 and can realistically simulate virtually all driving conditions, significantly simplifying our work. With it we can recreate a wide variety of test scenarios that thermal management must cope with in order to validate the thermal management functions. The number of variations that we process with it is enormous. We are currently testing possible future configurations on the basis of around 120 project variants with an average of 100 test cases each. That’s why we also use the power of at least a dozen high-performance computers to carry out our measurements. It means we learn in real time whether our thermal management software works with the coolant and refrigerant circuits as designed or whether we need to optimize.

But this vehicle is virtual?

Not entirely. Everything that is important for thermal management, such as the control unit, coolant and refrigerant circuits as well as, for example, the air inlets of the air-conditioning system, are actually used in the correct position in a so-called ‘test trolley’. The real assembled parts therefore replace the real vehicle. We also create the necessary outside temperature, humidity or airflow on site. But we use the data from real routes to simulate the respective driving conditions. Yesterday morning, for example, we tested individual settings on the drive through Death Valley National Park and, in the afternoon, we took a virtual drive around the Nürburgring.

So, you use real values that were obtained in advance during drives at the corresponding locations to carry out virtual test runs on the behavior of the thermal management system?

That’s right. These are measured values for the drive itself, i.e., on the gradient, the curve radii, the average cornering speed on the racing line, possible accelerations and braking processes. We combine this information with our data on the microclimate locally as well as individual requirements for the air-conditioning system, for example, and for different loads.