The invention relates generally to shrouds for motor vehicle cooling fans and more particularly to a shroud for a motor vehicle engine cooling fan which utilizes a Coanda surface to provide air flow through the annulus between the fan blade tips and the shroud and includes an integral air supply.
As motor vehicle engine compartment designs continue to evolve in response to increasing demands of vehicle and engine efficiency, operating temperatures continue to increase while the engine compartment's frontal area and natural air flow continue to reduce. All of these considerations conspire to increase underhood operating temperatures.
Nonetheless, a vehicle traveling at highway speeds at elevated ambient temperatures presents no significant engine cooling problems. Likewise, a vehicle stopped in traffic in moderate ambient temperatures presents no significant cooling problems. The combination, however, of high ambient temperatures and operation in congested, slow moving traffic wherein air heated by one vehicle is ingested by an adjacent vehicle and heated further represents an acknowledged severe engine operating condition. A second severe operating condition known as "hot soak" occurs when the engine has been subjected to heavy load by, for example, pulling a trailer uphill and the vehicle then stops. Operation under these conditions demands operation of and dependence upon the engine driven cooling fan. Operation in these conditions also demands the highest possible efficiency from the fan in order to achieve maximum cooling and safe engine operating conditions.
Such fan efficiency is achieved by well-known and recognized parameters such as the number of fan blades and their configuration as well as a properly designed radiator/fan shroud which maximizes radiator air flow and heat transfer while minimizing leakage and back flow around the fan.
In this regard, a problem inherent in motor vehicle design typically interferes with the attainment of high fan efficiencies. This problem results from the mounting of the radiator and fan shroud to the vehicle body whereas the fan is mounted upon the engine which is, in turn, secured to the vehicle body or frame through a plurality of engine mounts. These engine mounts are typically resilient and allow controlled motion of the engine and associated drive train components relative to the body or frame in response to engine reaction torque and vehicle acceleration and deceleration. While the spacing of the fan tips from the shroud can vary depending upon the fan and shroud location relative to the engine mount, the stiffness of the engine mounts and other variables, it has been found that spacing on the order of one-half inch (12.7 mm) to one inch (25.4 mm) or more is necessary to ensure that given the greatest excursion of the engine and fan relative to the shroud and vehicle body, the fan does not contact the shroud.
Unfortunately, the introduction of an annular space of this size has a significant deleterious effect on fan efficiency. Fan efficiencies in such configurations have been determined to be on the order of sixteen percent. Viewed not only from the perspective of fan efficiency but also from the perspectives of achieving necessary engine cooling with a given fan size and overall engine efficiency and fuel consumption, this is not a desirable figure. Accordingly, it is apparent that improvements in the configuration of motor vehicle cooling fans which provide improved fan efficiency and thus motor vehicle cooling are desirable.