Properly sized under hood components in an electric vehicle is important for effective thermal cooling at different load conditions. Powertrain aggregate loop plays significant role in generating heat with heat sources like eMotor, inverter, variable frequency drivers, on board charger and so on. Radiator being the most critical part in electric vehicle which acts as a heat sink for these powertrain components. Radiator with the help of coolant removes heat generated by different components in powertrain loop. It becomes important to understand the heat generated by the powertrain components at different drive/load scenarios and decide on the correctly sized radiator and fan. Rightly sized radiator and fan combination helps to balance the tradeoff of precise thermal needs in eTruck to an oversized/undersized component.
Main objective of this study is to estimate heat loads from system model representing powertrain aggregate components to study the existing radiator capacity and propose the properly sized radiator and fan. Present work is carried out using both 3D and 1D commercial CFD software's STAR-CCM+ and GT-SUITE respectively. Air mass flow rates on the condenser and radiator for different vehicle speed and fan speed is calculated using STAR-CCM+ with the full vehicle model. Vehicle underhood parts are represented in COOL 3D software with given radiator, condenser and fan specifications by supplier. Powertrain loop with all the plumbing and components are modelled in GT-SUITE. All these models are integrated in GT-SUITE and calibrated with test data in terms of flow and thermal.
Gradeability and startability assessment and validation are carried out for realistic load scenarios using an integrated model. Radiator capacity and offsets in capacity requirements, along with the combination of fan size, are analyzed under different ambient conditions, heat loads, and vehicle speeds. This is done using a design of experiments approach to develop a speed derating matrix related to gradeability and startability. The studies are further extended to propose the optimum size of the radiator and fan, considering the worst-case heat load scenarios and vehicle speeds. Comprehensive radiator and fan sizing proposals, developed through an extended simulation framework, helped achieve optimum cooling and ensure no speed derating occurrences.