Abstract:
A device for convective cooling of a functional assembly for a motor vehicle includes a fan, which in operation, is designed to move air along a flow axis defined by the design and placement of the fan. A flapper valve device is provided having an air transit opening and a flapper valve assembly disposed therein, with at least one flapper valve provided to change the open-flow cross section of the air transit opening and being adjustable between a closed position and an open position. A control unit is provided. The fan and the flapper valve device are arranged at a distance from each other such that air moved due to operation of the fan then flows through the air transit opening at least when the flapper valve device is in the open position. The control unit is designed to detect at least one operating parameter of the fan.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority to German Application No. 10 2015 210 683.7, filed Jun. 11, 2015. The entirety of the disclosure of the above-referenced application is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The present invention relates to a device for convective cooling of a functional assembly, wherein the device comprises:
   a fan which in operation is designed to move air along a flow axis defined by the design and placement of the fan,   a flapper valve device including an air transit opening and a flapper valve assembly disposed therein including at least one flapper valve, which for changing the flow-through cross-section of the air transit opening is adjustable between a closed position, wherein the flow-through cross-section of the air transit opening along the flow axis is minimal, preferably zero, during operation, and an open position, wherein the flow-through cross-section of the air transit opening along the flow axis is maximal during operation, and   a control unit,
 
wherein the fan and the flapper valve device are disposed at a distance from each other such that air moved due to operation of the fan flows through the air transit opening at least when the flapper valve device is in the open position.
   
 
         [0007]    Devices of this kind for convective cooling are known, for example, from motor vehicles, where they are used inter alia to restrict the volume of air flowing through a radiator grill, such as into the engine compartment, by changing the available flow-through cross-section of the air transit opening. The air flow can be generated by the movement of the vehicle and branch off from the airstream thus generated. In the absence of this airstream or if the airstream is insufficient, the air stream can also be generated by the fan mentioned above. 
         [0008]    By changing the flow-through cross-section of the air transit opening, motor vehicle cold-start phases can be shortened and thus the internal combustion engine can be warmed up to nominal temperature more quickly, which reduces the pollutant emissions from a motor vehicle. 
         [0009]    Devices of this kind for convective cooling are used in particular for cooling of the cooling fluid, in particular the coolant, used for temperature control of the internal combustion engine. Likewise a device of this kind can be used to cool brake fluid or a lubricant, such as engine oil, thus in general to cool an operating fluid in the operation of a motor vehicle. For this reason the fan is preferably disposed such that an air stream generated thereby flows onto, around or through a heat exchanger circulating the operating fluid. 
         [0010]    Likewise, the fan is disposed relative to the flapper valve device such that the air moved by the fan when in operation flows through the air transit opening when the opening is opened due to the adjusted operating position of the flapper valve device. The air moved by the fan can be air from the intake stream, that is, air flowing toward the fan to the vacuum side of the fan, or it can be air from the exhaust stream, i.e., air moving away to the pressure side of the fan. 
         [0011]    Since the device described herein for convective cooling represents an emission-relevant system due to its influence on the pollutant emissions from a motor vehicle, with regard to the increasingly stricter legal requirements with respect to environmental matters, it is important that the cooling device be testable as to whether it functions properly or not. Such a testability ensures that any undesirable damages that increase the pollutant emission from an internal combustion engine can be quickly recognized and corrected. 
         [0012]    Heretofore the flapper valve device has been monitored via a query of the position of a so-called “drive flap,” and even this monitoring takes place only indirectly via the actuator or actuators provided for adjusting the at least one flapper valve between its operating positions, and specifically using a so-called actuator calibration. 
         [0013]    In many flapper valve devices in the prior art only one flapper valve of a plurality of flapper valves is driven directly by an actuator, only the so-called “drive flap.” The remaining flapper valves of the flapper valve device are coupled to the drive flap solely for coordinated movement and are thus moved only indirectly by the actuator. 
         [0014]    However, monitoring of the operating position of the flapper valve device solely by monitoring of the position of the drive flap presumes that the flapper valve device is functional overall. Thus if the drive flap is detected in the correct position, but only the position of the drive flap is located in the detected position, whereas the remaining flapper valves assume a different position due to a defect in the movement coupling, then the result of the monitoring of the flapper valve device or of the device for convective cooling is incorrect overall. 
       SUMMARY OF THE INVENTION 
       [0015]    Therefore it is the object of the present invention to specify a technical teaching using which the above-mentioned device for convective cooling can be further developed, such that the actual operating state of the device can be determined in a simple and reliable manner. 
         [0016]    The present invention achieves this object using a device of the above-described type, wherein the control unit is designed so as to detect, during operation of the fan, at least one operating parameter of the fan and, proceeding from the detected operating parameter, to draw a conclusion about the actual operating state of the flapper valve device. 
         [0017]    Owing to the stated relative positioning of fan and flapper valve device, during operation the flapper valve device can directly influence air moved by the fan, which leads to repercussions on the fan operation. Under the assumption of the stated relative placement with respect to the fan, from an abstract point of view the flapper valve device produces a variable flow resistance of the air moved by the fan during operation, which then influences the operation of the fan. This influence of the variable flow resistance of the flapper valve device on the operation of the fan can be at least schematically-qualitatively recognized by detection of at least one operating parameter of the fan, which in turn makes possible a conclusion about the actual operating state of the flapper valve device. 
         [0018]    The advantage of the determination proposed here of the actual operating state of the flapper valve device is not only in the reliable detection of the actual operating state, but rather also in the simple detection thereof, since the solution proposed by the invention manages without position sensors, switches and the like for the detection of the flapper valve positions. Thus to realize the device proposed here no additional data or/and energy inputs to control devices or control units are needed. Any software used in the control devices need not be expanded with additional monitoring functionalities to control additional sensors; no additional cables are needed and no additional load on any existing data networks will occur, such as on the LIN- or CAN-buses used in motor vehicles. 
         [0019]    The terms “operationally minimal” and “operationally maximal” are intended to designate the minimal or maximal intended flow-through cross-section of the air transit opening in intended operation. It should thus not be precluded that it is possible to position the flapper valve device in another position wherein the open-flow cross section of the air transit opening is even smaller or even larger, which does not arise, however, in intended operation. “Intended operation” here designates exclusively the operation of the flapper valve device for changing the air stream passing through the air transit opening, but not an idle operation or similar special operating mode wherein the flapper valve device can be set into an otherwise unattainable idle position or comparable special position for reasons of maintenance access. 
         [0020]    The at least one detected operating parameter of the fan can actually be any arbitrary operating parameter, such as its rotational speed or its power. The use of an operating parameter related to the power consumption of the fan is advantageous since the fan must expend different amounts of energy, that is, different amounts of power, to overcome the flow resistance of the air moved per time unit by the operating fan depending on the position of the flapper valve device. 
         [0021]    In principle the fan can be driven by means of any physical active principle. But as a rule the fan will be an electrically driven fan. For this reason it is preferred that the detected operating parameter is an electrical quantity that changes with the electric power supplied to the fan for operation thereof. 
         [0022]    With many electric motors the motor current needed by the motor changes with the torque output from the motor. Therefore with electrically driven fans it is preferable for the detected operating parameter to be the current strength of the operating current supplied to the fan. This is also understandable for an additional reason: The power consumed by the fan is the product of the voltage applied to the fan and the operating current supplied to the fan. The voltage in the preferred application case here of the inventive device is as a rule the constant on-board voltage supplied by the battery or generator in a motor vehicle. Therefore the flow resistance produced by the flapper valve device and acting against the fan its operation leads essentially to a change in the operating current of the fan. 
         [0023]    Immediately after switching on the fan, transient values of operating parameter values can be detected until a quasi-stationary operating state of the fan is attained; these values provide only limited information. To ensure that the correct conclusion can be drawn from the detected operating parameter about the correct, actual operating state of the flapper valve device, according to one preferred further development of the present invention the control unit is designed so as to detect the operating parameter at a temporal interval after operational startup of the fan. 
         [0024]    Preferably the control unit is designed to detect the operating parameter multiple times, wherein the individual measurements occur at different times, so as to be able, for example, to recognize the particularly informative quasi-stationary operating state of the fan. This quasi-stationary operating state can be recognized, for example, in that a detected value of the operating parameter does not change by more than a predetermined limit value over a plurality of temporally sequential measurements. Particularly preferably, the control unit can be designed to detect the operating parameter continuously over a period of time. 
         [0025]    The detecting of the operating parameter in the sense of the present invention is equivalent to the detecting of a parameter different from the operating parameter, which parameter behaves in a known relationship with the operating parameter, such as being linearly proportional to the operating parameter, at least in the range of values expected for intended operation. 
         [0026]    To draw a conclusion about the actual operating state of the flapper valve device starting from the detected operating parameter, the control unit can be designed to compare the detected operating parameter with at least one comparison value and to draw a conclusion about the actual operating state depending on the outcome of the comparison. 
         [0027]    The comparison value can be a threshold value, wherein the control unit can be designed according to an a preferred further development of the present invention, to conclude that a first operating state is the present operating state of the flapper valve device when the detected operating parameter is greater than the comparison value or/and to conclude that a second operating state is the present operating state of the flapper valve device when the detected operating parameter is less than the comparison value. In this manner, based on a detected operating parameter, a decision can be made in a simple and reliable manner about which of two operating states is the current actual operating state of the flapper valve assembly. 
         [0028]    Alternatively or additionally, the control unit can be designed to check whether the detected operating parameter is located within at least one predetermined value range, and then, if the detected operating parameter is located within the predetermined value range, to conclude that an operating state associated with this value range is the actual operating state of the flapper valve device. In this manner as many operating states can be recognized as actual operating states of the flapper valve device as there are value ranges defined that are each associated with one of the operating states. 
         [0029]    Consequently, the control unit can be designed to check whether the detected operating parameter is located in a predetermined value range of a plurality of predetermined value ranges, wherein different value ranges are associated with different operating states of the flapper valve device, wherein the control unit is furthermore designed such that if the detected operating parameter is located in a value range of the plurality of predetermined value ranges, the control device concludes that the operating state associated with this value range is the actual operating state of the flapper valve device. 
         [0030]    Therefore the control unit can comprise a data memory. The value ranges, operating states, and the associations between them can be stored in this memory. 
         [0031]    In a simple case already suggested above, wherein it may be sufficient for the control unit to differentiate only between two operating states of the flapper valve assembly, the plurality of predetermined operating states can comprise an error-free and an error-laden operating state of the flapper valve device. For example, the control unit can then conclude that the flapper valve device is functioning in an error-free manner when the detected operating parameter is greater than the above-mentioned threshold value, and can conclude the presence of an error in operation of the flapper valve device when the detected operating parameter is less than or equal to the mentioned threshold value. The same applies accordingly for the presence of the detected operating parameter in a predetermined value range if only two value ranges are defined. The above association is provided solely as an example. It can also be reversed with respect to the above example. 
         [0032]    Since the flow resistance caused by the flapper valve device, which affects the operation of the fan, is significantly determined by the position of the flapper valve assembly, according to another advantageous further development of the present invention the control unit can conclude that one operating state of a plurality of predetermined operating states is the actual operating state of the flapper valve device, wherein the plurality of predetermined operating states comprises the flapper valve assembly being in one of at least two operating positions of closed position, open position and an intermediate position located between the open position and closed position. Preferably the plurality of predetermined operating states comprises the flapper valve assembly being in an operating position which is the closed position, the open position and one or several intermediate positions located between the open and closed positions. 
         [0033]    The detection of an error-laden or error-free operating state of the flapper valve device can also be implemented in several steps, for example, in that the control unit—as explained above—draws a conclusion about the operating position of the flapper valve assembly and/or of the flapper valve device, then this inferred operating position is compared to a target operating position and, depending on the comparison, an error-free or an error-laden operating state of the flapper valve device is deduced. For example, if the control unit determines that the actual operating position differs from a relevant target operating position, an erroneous operating state of the flapper valve device is deduced. Thus the control unit can be designed in this manner. 
         [0034]    To obtain an as effective-as-possible reaction of the flapper valve device to the operation of the fan, it is advantageous if the flapper valve device has as large as possible an influence on the air flow generated by the fan in operation. This can be achieved by a design wherein the fan is directly adjacent to the flapper valve device in the direction of the flow axis. In this case no additional functional unit is located along the flow axis between the flapper valve device and the fan. Preferably the flapper valve device is disposed on the pressure side of the fan. 
         [0035]    Since the fan or/and the flapper valve device are operated or adjusted in a generally favorable manner, depending on the operating states of a higher-order entity or other functional units containing them, such as a motor vehicle, a control unit is advantageously provided to control the operation of the fan or/and to control the adjustment of the flapper valve assembly. In principle this can be a separate control unit. To obtain a design with preferably the smallest number of assemblies to create the device under discussion herein, the control unit is further advantageously designed to control the operation of the fan or/and to adjust the flapper valve device. 
         [0036]    The present invention further relates to a motor vehicle including a device for convective cooling of a functional assembly, like that described above. 
         [0037]    According to a further aspect of the present invention the object stated above is also achieved by a method for determining an actual operating state of a flapper valve device, which is disposed in an operating air stream generated by a fan, comprising the following steps:
   Detecting of at least one operating parameter of the fan, in particular an electrical quantity which changes with the electric power supplied to the fan, particularly preferably the electric current supplied to the fan,   Comparing the detected operating parameter with a characteristic map wherein values of the operating parameter are associated with operating states of the flapper valve device, and   Determining the operating state associated with the detected operating parameter to be the actual operating state of the flapper valve device.   
 
         [0041]    To explain the inventive method, reference is made to the detailed explanation of the inventive device provided above. 
         [0042]    The method can comprise a targeted attaining of a predetermined operating position of the flapper valve device, so that based on the previously described detection routine it can be determined whether the predetermined operating position was properly achieved. The method can comprise the attaining of a plurality of predetermined operating positions of the flapper valve device, wherein after a plurality of attaining processes, preferably after each attaining process, at least the previously described step of detection of the at least one operating parameter is carried out, in order to be able to check whether each of the plurality of operating positions is in fact attained by the flapper valve device. For this purpose the detected operating parameters can be compared to a characteristic map as described above, and depending on the respective result of the comparison, an operating state of the flapper valve device can be determined. In this manner a sensor-free test routine can be provided for functional testing of the flapper valve device. This can occur in a short time, perhaps automatically immediately after a vehicle start or during stop periods at traffic lights, or in general upon request by the vehicle driver. 
         [0043]    The designs of the control unit disclosed in the present application as respective further developments of the present invention likewise represent refinements of the inventive method for solving the problem stated above, since the designs of the control unit described in detail above each define a design to implement the steps required by the application, and thus represent a design to implement the method or partial method. 
         [0044]    To ensure sufficient redundancy, the control unit can be designed to detect a plurality of different operating parameters, or during the implementation of the inventive method, to detect a plurality of different operating parameters. 
         [0045]    The present application also relates to a motor vehicle including a device like that described above for conductive cooling, or/and to a motor vehicle which is designed to carry out the method described above. 
         [0046]    The expressions “operating position of the flapper valve device” and “operating position of the flapper valve assembly” used in the present application are synonymous. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0047]    The present invention will be explained in greater detail below based on the accompanying drawings: 
           [0048]      FIG. 1  depicts a rough, schematic, longitudinal cross-section through a motor vehicle including a device according to the invention for convective cooling of cooling fluid of the internal combustion engine, 
           [0049]      FIG. 2  depicts a graph which shows the relationship between the operating current consumed by the fan of the device of  FIG. 1 , and the operating time when the flapper valve device of the device of  FIG. 1  is located in the open position, 
           [0050]      FIG. 3  depicts a graph which shows the relationship between the operating current consumed by the fan of the device of  FIG. 1 , and the operating time when the flapper valve device of the device of  FIG. 1  is in the closed position, 
           [0051]      FIG. 4  depicts a graph which shows the relationship between the operating current consumed by the fan of the device of  FIG. 1 , and the operating time when the flapper valve device of the device of  FIG. 1  is in an intermediate position between the open position and closed position, and 
           [0052]      FIG. 5  depicts the graphs of  FIGS. 2 to 4  in a common diagram with characteristic maps indicated therein which are assigned to different actual operating states of the flapper valve device. 
       
    
    
       [0053]    An outline of the front section of a motor vehicle (PKW) indicated roughly by dashed lines and which is denoted in general by reference number  10  is depicted in  FIG. 1 . A front wheel  12  is indicated, which likewise is depicted in outline only in a rough, schematic manner using dashed lines. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0054]    In the front section  10  of the motor vehicle, an internal combustion engine  14  is indicated by dashed lines. As is generally commonplace, this engine is cooled by a liquid coolant. In order to remove the heat supplied to the coolant by the internal combustion engine  14 , a heat exchanger  16  is provided to which the liquid coolant is supplied at an elevated temperature through a hose or tubing  18  and from which the liquid coolant is returned via a similar line at lower temperature back to the internal combustion engine  14 . Thus the liquid coolant circulates between the internal combustion engine  14  and the heat exchanger  16 . 
         [0055]    In the exemplary embodiment under discussion here, the liquid coolant is mentioned only as an example. Instead of the liquid coolant, a brake fluid, a lubricant such as motor oil, or another liquid heated by operation of the motor vehicle can be supplied to a heat exchanger  16  for convective cooling. 
         [0056]    The heat exchanger  16  during operation of the motor vehicle is convectively cooled by an air stream which moves essentially in the vehicle&#39;s longitudinal direction F and is symbolized in  FIG. 1  by the arrows L. The arrows L extend along the flow axis S of the air stream. 
         [0057]    The air flow L can be generated either by the airstream during forward movement of the motor vehicle or by a fan  20 , for example, when the motor vehicle is stopped. 
         [0058]    In a known manner the fan  20  comprises a fan shaft  22  including fan blades  24  fixedly attached thereon. A fan drive unit  26  connected to the fan shaft  22  provides the energy required to move the fan shaft  22  with fan blades  24  rotating in the same direction as the fan shaft to generate the air flow L. 
         [0059]    Here the fan  20  is disposed preferably directly adjacent to a flapper valve device  28  in the direction of flow of the air stream L. The flapper valve device  28  comprises a frame  30  which surrounds an air transit opening  32 , and in which a flapper valve assembly  34 , including a plurality of moveable flapper valves  36 , is disposed. In the illustrated example, the flapper valves  36  are parallel to the flapper valve assembly  34  and are disposed essentially in the vehicle transverse direction Q; this corresponds to a direction orthogonal to the drawing plane of  FIG. 1 . The flapper valves  36  are pivotable for adjusting between an open position wherein the open cross-section of the air transit opening  32  is at an operating maximum, and a closed position wherein the open cross-section of the air transit opening  32  is at an operating minimum. In the illustrated example the flapper valves  36  can pivot about stationary axes of rotation D extending parallel to the vehicle&#39;s transverse direction. 
         [0060]    The term “operating” minimum or maximum is intended to indicate that the closed position and/or the open position of the flapper valve assembly  34  during intended operation provides the smallest or the largest flow-through cross-section of the air transit opening  32  for a volume change of the air stream L transiting the air transit opening  32 . However, this does not preclude there being special operating modes outside of the intended operation stated above, such as a maintenance operating mode or the like, wherein by starting up to a special position of the flapper valve assembly  34  an even greater, or an even smaller open cross section of the air transit opening  32  can be attained. 
         [0061]    An actuator  38  is indicated only by a rough schematic in  FIG. 1 , which actuator forms the rotary drive unit of the flapper valve assembly  34  for adjusting the flapper valves  36  of the flapper valve assembly  34  between the stated operating positions: open position and closed position. 
         [0062]    The device depicted in  FIG. 1  further comprises a control unit  40  which is preferably configured to control operation of both the fan actuator or fan drive unit  26  and also the flapper actuator  38 . This means, for example, that the control unit  40  controls or even regulates the energy supply to the fan actuator or flapper drive  26  and the flapper actuator  38 . 
         [0063]    In any event the control unit  40  is designed to detect an operating parameter of the fan  20 ; in the illustrated example, for instance, the operating current drawn by the fan  20  or by the fan drive unit  26 . 
         [0064]    Depending on the operating setting of the flapper valve assembly  34  of the flapper valve device  28 , the flow resistance to be overcome by the air stream L will increase or decrease. Since the fan  20  is disposed relative to the flapper valve device  28  such that an air stream L generated by it flows through the air transit opening  32 , the flow resistance generated as a function of the operating setting of the flapper valve assembly  34  acts against the fan  20  if the air stream L flowing through the air transit opening  32  was generated by the fan  20 . 
         [0065]    As is generally common in motor vehicles, the fan  20  is preferably mounted in an intake position with respect to the heat exchanger  16 , that is, the heat exchanger  16  is located on the intake side (vacuum side) of the fan  20  and the flapper valve device  28  on its pressure side (high-pressure side). During operation of the fan, the fan  20  thus suctions air through the heat exchanger  16  and the air heats up during its passage through the heat exchanger  16  and thus cools off the coolant liquid also flowing through the heat exchanger. The fan  20  forces the heated air through the flapper valve device  28  to the outside (left arrow point of the air stream L in  FIG. 1 ). 
         [0066]    In contrast thereto, if the heat exchanger  16  is to be cooled convectively by the airstream, the air stream will flow past the heat exchanger  16  in the vehicle longitudinal direction from the vehicle front side to the vehicle rear (right arrow points of the air stream L in  FIG. 1 ). 
         [0067]    Then if the heat exchanger  16  is to be convectively cooled by operation of the fan  20 , it is important that the heated air can escape at the pressure side of the fan  20  through the flapper valve device  28  into the environment outside of the motor vehicle. 
         [0068]    In order to prevent overheating of the internal combustion engine  14  or to avoid any unnecessary generation of pollutants from the motor vehicle, perhaps because the flapper valve device  28  is in the open position despite a cold start of the engine  14 , and thus the heating of the engine  14  to its nominal operating temperature is needlessly delayed, it is helpful to check or to monitor the functional integrity or the orderly functioning of the flapper valve device  28 . 
         [0069]    This monitoring can take place in a very simple manner without additional sensors, as described below: 
         [0000]      FIG. 2  depicts a relational diagram between the operating current consumed by the fan  20  and the operating time of the fan  20 . The abscissa of the diagram of  FIG. 2  shows the operating time in seconds; the ordinate of the diagram of  FIG. 2  shows the current strength of the operating current in Amperes. The graph  42  shown in the diagram of  FIG. 2  thus indicates what operating current is consumed by the fan  20  at which point in time after the operational start (t=0 s). It is evident that after an approximately one-second transient, start-up phase, the fan assumes a quasi-stationary operating state and for the subsequent operating time consumes a roughly constant, low operating current. 
         [0070]    This temporally constant operating current is at such a low level because the flapper valve device  28  is in its open setting and thus the open cross-section of the air transit opening  32  is at its operating maximum. Thus the fan  20  has to overcome an operationally minimal flow resistance in order to move air from the heat exchanger  16  through the flapper valve device  28  into the area outside of the motor vehicle. 
         [0071]    In contrast,  FIG. 3  depicts the chronology  44  of the operating current consumed by the fan  20  when the flapper valve device  28  is in the closed position. Since the open cross-section of the air transit opening  32  is then at its operating minimum, the flow resistance opposing the air stream L from the flapper valve device  28  is at its operating maximum. The fan  20 , which must work against the flow resistance established by the flapper valve device  28 , consumes a significantly greater operating current when the flapper valve device  28  is in the closed position, after the transient start-up phase, than in the case shown in  FIG. 2  where the flapper valve device  28  is in the open position. 
         [0072]    Also in the case depicted in  FIG. 3 , after a transient start-up phase a quasi-stationary operating state occurs which continues during the subsequent operating time. 
         [0073]    For example, based on the graph  42 , a threshold value  46  of the operating current can be defined which can be used to determine whether the flapper valve device  28  is in the open position or not. Then if the quasi-stationary curve portion of the operating current is below the threshold value  46 , it can be concluded that the flapper valve device  28  is in the open position. But if the quasi-stationary curve portion of the operating current is above the threshold value  46 , it can be concluded that the flapper valve device  28  is at least not in the open position. The threshold value  46  (first threshold value) can be determined based on the level of the quasi-stationary curve portion  43  of the graph  42 , perhaps also under consideration of the usual operating fluctuations and tolerances. 
         [0074]    Likewise, based on the graph  44  in  FIG. 3 , an additional threshold value  48  of the operating current can be defined, which makes it possible to determine whether the flapper valve device  28  is in the open position or not. Then if the quasi-stationary curve portion  45  of the graph  44  is above the threshold value  48 , it can be concluded that the flapper valve device  28  is in the closed position. But if this is not the case, it can be concluded that the flapper valve device  28  is not in the closed position. The threshold value  48  (second threshold value) can in turn be determined based on the value of the quasi-stationary portion  45  of the temporal profile  44  of the operating current, under consideration of the usual operating fluctuations and tolerances. 
         [0075]    Finally  FIG. 4  shows a profile  50  of the operating current of the fan  20  as a function of operating time as it occurs when the flapper valve device  28  is in an intermediate position between the open position and the closed position. 
         [0076]    After a transient start-up phase which ends about  1  second after the engine start, a quasi-stationary operating state of the fan again sets in, during which the operating current consumed by the fan  20  changes very little. 
         [0077]    Again based on the quasi-stationary portion  51  of graph  50 , in an analogous manner to the procedure described above a threshold value  52  (third threshold value) can be defined which is used to draw a conclusion about whether the flapper valve device  28  is in the intermediate position. 
         [0078]    The conclusions discussed above about a particular operating state of the flapper valve device  28  based on the relative position of the quasi-stationary curve portion of the temporal profile of the operating current consumed by the fan  20  relative to the specified threshold values can be obtained in a simple manner from the control unit  40  and can be saved in a data memory with the threshold values  46 ,  48 ,  52 . After passage of a predetermined period of time after the operating start-up of the fan  20 , the detected values of operating current can be compared to the threshold values  46  and/or  48  and/or  52  and then, depending on the result of the comparison and based on the relationships described above, a conclusion can be drawn about what position the flapper valve device  28  is in, or at least in what position the flapper valve device  28  is not in. 
         [0079]    The position of the flapper valve device  28  determined in this manner, or even the position determined not to be assumed by the flapper valve device  28 , can be compared to a desired operating position of the flapper valve device  28 , based on additional data saved in the control unit  40 , so that the control unit  40  can conclude an orderly functioning of the flapper valve device  28  if the determined position of the flapper valve device  28  coincides with the desired operating position. 
         [0080]    According to one refinement of the present invention it is also possible that a predetermined program will be executed in the control unit  40  for functional testing of the flapper valve device  28 , according to which the flapper valve assembly  34  is adjusted into differently defined operating positions, and by operation of the fan it can be determined in the manner described above whether the flapper valve device  28  is in fact in the respective selected operating position or not. 
         [0081]    The graphs  42 ,  44  and  50  from  FIGS. 2 to 4  are presented in a single diagram in  FIG. 5 . The diagram of  FIG. 5  additionally contains a first characteristic map  54  and a second characteristic map  56 . The first characteristic map  54  extends across a first value range of operating current strengths and also across a range of operating times. An operating state of the flapper valve device  28  is associated with this first value range, for example, an operating state of “located in a predominately closed state” or—if the diagram of  FIG. 5  is assigned to a desired operating state of predominately closed position of the flapper valve device  28 —an operating state of “functioning in an orderly manner.” 
         [0082]    Accordingly, the value range of the second characteristic map  56 , which is preferably entirely different from the first value range, can be associated with an additional operating state, for example, an operating state of “not in a sufficiently closed state,” or “not functioning in an orderly manner.” The use of characteristic maps also makes it possible to operate in specific operating positions of the flapper valve device  28  and to test the selected operating positions by switching on the fan  20  and detecting the operating current consumed by the fan in a quasi-stationary operating state. 
         [0083]    The control unit  40  can write an error message or other appropriate information into the error data memory of the motor vehicle, depending on the determined actual operating state of the flapper valve device  28 . 
         [0084]    The possibility for monitoring of the functional integrity of the flapper valve device  28  proposed in the present application is particularly advantageous because the monitoring of the monitoring result is possible with great reliability without the need to install any otherwise required sensors, lines, software and the like.