Variable and Fixed Airflow for Vehicle Cooling

This paper describes rationale for determining the apportionment of variable or ‘shuttered’ airflow and non-variable or static airflow through openings in the front of a vehicle as needed for vehicle cooling. Variable airflow can be achieved by means of a shutter system, which throttles airflow through the front end and into the Condenser, Radiator, and Fan Module, (CRFM). Shutters originated early in the history of the auto industry and acted as a thermostat [1]. They controlled airflow as opposed to coolant flow through the radiator. Two benefits that are realized today are aerodynamic and thermal gains, achieved by restricting unneeded cooling airflow. Other benefits exist and justify the use of shutters; however, there are also difficulties in both execution and practical use. This paper will focus on optimizing system performance and execution in terms of the two benefits of reduced aerodynamic drag and reduced mechanical drag through thermal control. For a device(s) to receive credit for improved drag and fuel economy, performance in the EPA Coast Down test must be improved. If the device(s) are open in the Coast Down test, then the benefit will not be reflected in the fuel economy label. If the device(s) are over-utilized to exploit possible gains on the Coast Down, then the resulting label value will be better than the real world gain. In other words, to have an optimized system, the measured fuel economy value must be derived in a manner consistent with typical consumer use. To that end, this paper will explore the determination of, as well as the difference between every day use and severe use, and how to best provide the consumer the means of using only the fuel required to cool the vehicle, given the operating conditions.