Abstract
Thermal management has become a fundamental function to improve the energy-efficiency in electric vehicles, since a precise control of heat flows is necessary for both safety and performance of battery packs and, also, for passenger comfort. For this type of vehicles, the design of thermal-management components has become fairly complex due to the introduction of new electrical devices, which have contributed to redefine the functionality of the existing parts and to revolutionize the layout of systems. This Industrial PhD thesis aims to develop design tools for the development of thermal-management components able to improve the energy-efficiency of battery-electric vehicle platforms. The work has been performed in collaboration with the industry-partner Röchling Automotive, specialized in designing and manufacturing plastic solutions for the automotive sector. Three targets have been defined for this project: 1. to analyze systems and components involved in the thermal management of market-representative vehicle architectures, emphasizing the main modifications in electric vehicles with respect to conventional platforms, 2. to construct a global vehicle thermal model for a typical battery-electric vehicle platform, through which defining design methodologies for thermal-management components that consider the vehicle energy-performance, 3. to produce design procedures for coolant distributor valves of thermal-management systems which take into account both performance and design parameters as well as the integration in the vehicle layout. Chapter 2 provides a brief description of the ongoing electrification process in the automotive sector, and illustrates the state-of-art of thermal management with literature and vehicle tear-down data. Chapter 3 presents a full-vehicle thermal model which computes heat and energy flows for a representative battery-electric vehicle. Coolant circuit and the interconnected systems are modeled with data from vehicle tear-down analysis. Control strategies are implemented to regulate heat and energy flows based on thermal state of sub-systems such as battery pack and passenger cabin. An application example of the vehicle is described, where heat and energy flows are evaluated in various environmental temperature conditions. Chapter 4 describes parametrized performance models for coolant distributor valves and other interesting thermal-management components such as heat exchangers and controllable flaps which regulate airflow through the radiator, so known as active grill shutters. For valves, a block model is used to compute the main fluid dynamic parameters. In particular, a specific rotating valve topology is considered, where internal leakage and pressure drop have a significant impact on design constraints. The constructed parametrized models are coupled to the full-vehicle thermal model in order to perform parametric investigation aimed to evaluate the impact of component design on the vehicle energy-performance. One of the main outcomes concerns the development of a methodology which selects realistic design targets for coolant distributor valves preserving the vehicle energy-efficiency. Chapter 5 is concerned with the definition of a design methodology for coolant distributor valves based on a parametrized model of the main physical processes. The methodology is demonstrated on a specific design of rotating valve, where the main performance parameters - such as torque, internal leakage and pressure drop - are coupled. Accordingly, an optimization procedure is presented which minimizes a global performance index of the valve. The resulting design configuration is assessed in the global vehicle thermal model.