Coolant Flow Control Strategies for Automotive Thermal Management Systems

The automotive thermal management system is responsible for maintaining engine and passenger compartment temperatures, which promote normal combustion events and passenger comfort. This system traditionally circulates a water ethylene glycol mixture through the engine block using a belt-driven water pump, wax pellet thermostat valve, radiator with electric fan, and heater core. Although vehicle cooling system performance has been reliable and acceptable for many decades, advances in mechatronics have permitted upgrades to powertrain and chassis components. In a similar spirit, the introduction of a variable speed electric water pump and servo-motor thermostat valve allows ECU-based thermal control. This paper examines the integration of an electric water pump and intelligent thermostat valve to satisfy the engine's basic cooling requirements, minimize combustion chamber fluctuations due to engine speed changes, and permit quick heating of a cold block. A controller architecture is introduced to regulate the operation of these two components. A series of mathematical models are presented to describe the dc servo-motor actuated thermostat valve, electric water pump, and thermal behavior of in-cylinder engine components. The multiple node resistor-capacitor engine model estimates the thermal behavior of the cylinder wall and cylinder head for use in the model-based control algorithm. Representative results are presented and discussed to investigate the performance of the proposed control strategy in regulating the thermal management system for various operating speeds.