Thermal management improvement in electric vehicles through design optimization of coolant distributor valves

Abstract

On battery electric vehicles a precise control of heat flows is required for passenger comfort and for both performance and safety of battery packs. This is typically achieved with a thermal management system which employs some type of liquid coolant to transfer heat. Coolant distributor valves are used to regulate coolant flows through the exchangers, for example to recover heat from hot sources, thus to increase vehicle energy efficiency. The development of this type of component is high-priced and the design is generally complex since several operating functions and manufacturing constraints should be satisfied. Despite this complexity and the positive impact such valves have on the thermal management of electric vehicles, a few works are currently available in the literature on design procedures for this component, where only a partial overview of the topic is provided and a comprehensive design methodology considering the effective operating conditions is still missing. In this work we construct a physical model of the valve for torque, internal leakage and pressure drop, and we build an optimization procedure to improve the global performance of the valve. We compare the obtained designs with a simpler approach that optimizes performance parameters independently and we show that designs which severely under-perform with respect to the uncontrolled performance parameters can be produced if an over-simplified design approach is followed. We then show with a global vehicle thermal model that the impact of valve design on global vehicle performance crucially depends on the thermal exchanges at vehicle level and, thus, on its operating conditions. In particular, the impact is considerable when mixing of cold and hot flows through the valve occurs. For a specific example vehicle evaluated in a type-3a cycle of the Worldwide Harmonized Light Vehicle Test Procedure, a valve determined with the proposed optimization procedure allows us to obtain in this condition an increase of about 1 km in the vehicle driving range with respect to a valve defined with the simpler approach.