Internal combustion engine cooling strategies: Theory and test

Advanced automotive thermal management systems integrate electro-mechanical components for improved fluid flow and thermodynamic control action. Progressively, the design of ground vehicle heating and cooling management systems require analytical and empirical models to establish a basis for real time control algorithms. One of the key elements in this computer controlled system is the smart thermostat valve which replaces the traditional wax-based unit. The thermostat regulates the coolant flow through the radiator and/or engine bypass to control the heat exchange between the radiator's coolant fluid and the ambient air. The electric water pump improves upon this concept by prescribing the coolant flow rate based on the engine's overall operation and the driver commands rather than solely on the crankshaft speed. The traditional radiator fan is belt driven and equipped with a clutch to limit parasitic loads during operating conditions that provide sufficient radiator heat rejection. A DC motor-driven radiator fan offers improved control over the air flow rate to better regulate radiator heat rejection while reducing power consumption. Ideally, the thermal management system will accept multiple engine sensor feedback including, but not limited to, the engine cylinder temperature, oil temperature, coolant temperature, engine block temperature, engine load, and throttle angle. To achieve this concept, these electrically driven system components must be mathematically described, computer controlled, and configured on an internal combustion engine.; A unique experimental platform has been developed featuring a 4.6L V8 engine, with extensive block-embedded thermocouples, attached to a water-brake dynamometer. Three physical cooling system configurations were tested for prescribed engine temperature tracking and power consumption: an electrically driven fan in combination with a wax-based thermostat and a crank shaft driven cooling pump (Tests 1 & 2); a servo-motor driven radiator fan and smart thermostat valve in combination with the engine driven cooling pump (Tests 3 & 4); and an electrically driven radiator fan, smart thermostat valve, and servo-motor coolant pump (Tests 5 & 6). These cooling system configurations facilitated the testing of three different controller concepts based on factory emulation, classical control, and thermodynamic optimization. Each cooling system is evaluated with a test profile encompassing steady state and transient engine operation by including step changes in the engine speed, engine load, and air speed. Data acquisition and control activities were supported by a dSPACE DS1104 hardware board which managed the real-time interface between the Control Desk software and the physical system.; The experiments demonstrated that steady state coolant temperature regulation was improved with computer control of the radiator fan, thermostat valve, and coolant pump (Tests 5 & 6) which is noted by accurately tracking the set point temperature within +/-0.5°C. Most importantly this system (Test 5 & 6) was able to meet the cooling needs with 60W power consumption. A reduction of 478W parasitic energy use in situations where vehicle ram-air provided a sufficient heat rejection rate when compared to the factory emulation power use of 538W(Test 1). However, with this increased level of control, the system revealed temperature variations of +/-3.0°C in Test 3 versus +/-0.1°C in Test 1 during transient response to ram-air. Overall, computer control of the automotive cooling system enhances temperature tracking ability and reduces the parasitic loading.