Optimizing Thermal Management in Electrified Vehicles

This requirement applies equally to hybrid electric vehicles (HEVs), battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs). How can the development of efficient thermal management systems be supported with a holistic development approach in order to design energy management systems in a targeted manner? Luis Vincent Fiore, M. Sc., Research Associate, Institute for Internal Combustion Engines and Vehicle Drives (VKM) at TU Darmstadt, will be speaking on this topic at the 24th International VDI Congress Dritev.
 

From the Road to the Test Bench

The institute, which has always been broadly positioned in the field of vehicle drive technology, has identified the area of thermal management as a key focus for the future, says Luis Fiore: “We are dealing with a high level of system complexity in both electrified drives and fuel cell drives. This also increases the importance of thermal management.” In order to do justice to the complexity and specific requirements during the development process, the institute wants to use the ThermoLab as a hardware-in-the-loop (HiL) test bench to transfer tests from the road to the test bench at an early stage.
 

Early Validation in the Development Process

The reason: The temperature sensitivity of drivetrain components requires the early development and validation of thermal operating strategies in order to ensure high efficiency and minimize ageing effects. Optimum thermal conditioning of drivetrain components can be achieved through situation-specific, bidirectional heat transfer between components. For the testing and development of thermal operating strategies, all components and the thermal boundary conditions must be transferred to a HiL-capable, thermohydraulic test bench such as the VKM ThermoLab test bench. Components that are not yet available as hardware must be emulated.
 

Less Effort – More Precise Results

To map the different requirements and battery behavior in a prototype vehicle, the Darmstadt-based institute has developed model-based emulation. With this approach, the Darmstadt scientists want to keep the effort for the early development process as low as possible and at the same time improve the quality of the development results. The results, in turn, are used to draw conclusions about the entire energy management system at an early stage.

“It is essential for the progress of the overall project to secure the development results for thermal management at a very early stage. We are convinced that ThermoLab can make a significant contribution to this,” continues Luis Fiore. The methodology is equally applicable to the various phases in the development cycle – for example, from the design of a cooling circuit to the effective control behavior at different temperatures and, thirdly, to the systemic level: How is the cooling circuit fundamentally designed, how should it be dimensioned and designed? Which coolant pump is required, how should it be dimensioned, what thermodynamic boundary conditions and interactions are to be expected in the system? These and other questions should be clarified as early as possible in the development process.
 

Reduce Validation Effort

The scientists associate a central expectation with their holistic methodological approach: “Due to the combination of simulation and testing, there is significantly less effort required for validation when the prototype of the vehicle is built. In this case, the system only needs to be calibrated again to reconfirm the previous assumptions – this significantly reduces time and effort in the development process,” continues Luis Fiore.

In addition to the efficiency gain, it is also possible to test different concepts and system variations in a much shorter time and thus identify the most suitable solution. For example, emulators can be scaled in such a way that they can thermohydraulically reproduce different batteries on the ThermoLab. Conversely, the development process can be designed more specifically for the desired range X, for example. This makes it possible to optimally dimension batteries – with all the associated benefits from lower costs to an optimized CO2 footprint.

Thermal management for fuel cell vehicles is even more challenging, as the heat is mainly dissipated via the cooling system due to the low exhaust gas temperatures and the thermal management has an operationally relevant monitoring function to ensure cold start capability. This makes it all the more important to ensure the appropriate dimensioning of the cooling components at an early stage of development.
 

Continuous Data Synchronization

Luis Fiore goes on: “At Dritev, we will show how we developed a highly efficient thermal management system for a prototype vehicle using our development methodology at ThermoLab.” Real-time co-simulation is used to continuously compare the simulation with the hardware components on the test bench. “The holistic approach – by linking simulation and testing and the simulation-supported thermal-hydraulic emulation of drive components on the real test bench setup – means an enormous gain in speed, from which future series development projects could benefit.”