In the present article it is investigated why active grille shutters (AGS) can
have very different aerodynamic characteristics, ranging from progressive to
strongly degressive, and which factors influence them. For this purpose, the
authority concept known from the field of heating, ventilation, and
air-conditioning (HVAC) is referred to. According to this theory, the control
characteristics of dampers depend primarily on the ratio of the pressure losses
at the fully open damper to the pressure losses of the rest of the system. The
adaptation of the concept to the automotive field shows that, in addition to the
pressure losses, the geometry of the cooling air ducting plays a decisive role
in motor vehicles. The effect of driving speed and fan operation on the
characteristic curves is also being investigated. In addition, authority theory
can also be used to derive the conditions under which the opening characteristic
curve of an AGS provides a good prediction of the real characteristic curve. And
finally, the authority theory offers the possibility of predicting the AGS
characteristics in detail. To this end, a concept is being developed that draws
on suitable inherent reference characteristics of control dampers from the HVAC
sector. The practical application of the concept will be demonstrated using
various examples of AGS from real vehicles. The comparison of the predicted
characteristic curves with the measured data shows good agreement, with
characteristic curve details also being reproduced. A prerequisite, however, is
the knowledge of the pressure losses of the AGS in the fully open state as well
as the pressure losses of the remaining cooling air duct. For this purpose, a
method is shown, which can be used to estimate the relevant pressure losses.
Overall, this provides a new calculation method that can be used to estimate the
aerodynamic characteristics of AGS in the early development phase of motor
vehicles.