Abstract:
There is described a device for automatically preventing misting of the windscreen of a vehicle, wherein a number of sensors determine ambient conditions capable of misting the windscreen, and, upon such ambient conditions occurring, an electronic central control unit automatically activates the air-conditioning system of the vehicle to direct a stream of hot air onto the windscreen to raise its temperature and so prevent it from misting.

Description:
[0001]    The present invention relates to a device and method for automatically preventing misting of the windscreen of a vehicle.  
         BACKGROUND OF THE INVENTION  
         [0002]    As is known, of the numerous steps taken to improve driving safety, many are aimed at distracting the driver&#39;s attention from the road as little as possible, particularly as regards manual interaction with on-vehicle systems.  
           [0003]    Nevertheless, numerous sources of distraction still remain, foremost of which is undoubtedly demisting the windscreen.  
           [0004]    Demisting a vehicle windscreen, in fact, not only calls for turning on the air-conditioning system fan by hand, and possibly also orienting the air inlet ports manually to direct airflow onto the windscreen, but is also normally performed when the windscreen is already misted, so that it takes a fairly long time for full visibility through the windscreen to be restored.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the present invention to provide a device and method for automatically preventing misting of a vehicle windscreen.  
           [0006]    According to the present invention, there are provided a device and method for automatically preventing misting of a vehicle windscreen, as claimed in claims 1 and 9 respectively. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:  
         [0008]    [0008]FIG. 1 shows, schematically, a device for automatically preventing misting of a vehicle windscreen in accordance with the present invention;  
         [0009]    [0009]FIG. 2 shows an operational flow chart of the method for automatically preventing misting of a vehicle windscreen according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]    Number  1  in FIG. 1 indicates as a whole a device in accordance with the present invention for automatically preventing misting of the windscreen  2  of a vehicle  3 —in the example shown, a motor vehicle.  
         [0011]    Device  1  substantially comprises an internal-temperature sensor  4  supplying information relative to the temperature inside the passenger compartment  5  of vehicle  3 ; an external-temperature sensor  6  supplying information relative to the temperature outside vehicle  3 ; a relative humidity sensor  7  supplying information relative to the relative humidity inside passenger compartment  5  of vehicle  3 ; ad an electronic central control unit  8  connected to sensors  4 ,  6 ,  7 .  
         [0012]    More specifically, according to one aspect of the present invention, the internal-temperature sensor  4  used is conveniently a radiant mean temperature sensor, which is an optical sensor having a field of view whose angle depends on the optics with which it is equipped (e.g. α=30-60°), and comprising a thermocouple housed in a vacuum chamber and supplying information relative to the mean temperature radiating from the objects within its field of view. By adjusting the optics of the radiant mean temperature sensor, the field of view of the sensor can therefore be adapted to the conformation of passenger compartment  5  of vehicle  3  in which the sensor is housed.  
         [0013]    The internal-temperature sensor is conveniently located inside passenger compartment  5  of vehicle  3 , facing windscreen  2  of vehicle  3 , and preferably on the inner face of roof  8  of vehicle  3 , adjacent to the courtesy light (not shown).  
         [0014]    Relative humidity sensor  7  is also located inside passenger compartment  5  of vehicle  3 , facing windscreen  2  of vehicle  3 , and also preferably on the inner face of roof  8  of vehicle  3 , adjacent to the courtesy light.  
         [0015]    As an external-temperature sensor  6 , on the other hand, a temperature sensor already provided on vehicle  3  for other purposes is used, e.g. the air-conditioning system temperature sensor, which is normally located underneath the internal rearview mirror (not shown) of vehicle  3 , or the engine control system temperature sensor, which is normally located on the air intake conduit (not shown).  
         [0016]    Electronic central control unit  8  is connected to, and receives the electric signals generated by, internal-temperature sensor  4 , external-temperature sensor  6 , and relative humidity sensor  7 , and controls the air-conditioning system  9  of vehicle  3 —shown schematically in FIG. 1 by a fan—as a function of the electric signals to prevent misting of windscreen  2  of vehicle  3 , as described below with reference to the operational flow chart in FIG. 2.  
         [0017]    As shown in FIG. 2, electronic central control unit  8  first acquires the values of internal temperature Ti, external temperature Te, and relative humidity Ur supplied respectively by internal-temperature sensor  4 , external-temperature sensor  6 , and relative humidity sensor  7  (block  10 ).  
         [0018]    Electronic central control unit  8  then determines (block  20 ) the temperature Tv of the inner face of windscreen  2  of vehicle  3  as a function of internal temperature Ti and external temperature Te, according to the following equation:  
           C   v                 T   v            τ         =         α   1     ·     A   1     ·     (       T   1     -     T   v       )       -           a   e     ·   λ   ·     λ   pvb             a   e     ·     [         λ   pvb     ·     (       s   1     +     s   3       )       +     λ   ·     s   2         ]       +     λ   ·     λ   pvb           ·     A   1     ·     (       T   v     -     T   e       )                               
 
         [0019]    where:  
         [0020]    C v =windscreen heat capacity [J/K] 
         [0021]    T v =windscreen temperature [° C.] 
         [0022]    A 1 =windscreen area [m 2 ] 
         [0023]    T i =passenger compartment temperature [° C.] 
         [0024]    T e =external temperature [° C.] 
         [0025]    α 1 =internal convective heat exchange coefficient [W/(m 2 .K)] 
         [0026]    α e =external convective heat exchange coefficient [W/(m 2 .K)] 
         [0027]    s 1 =inner glass thickness [m] 
         [0028]    s 2 =pvb layer thickness [m] 
         [0029]    s 3 =outer glass thickness [m] 
         [0030]    λ=glass thermal conductivity [W(m.K)] 
         [0031]    λ pvb =pvb thermal conductivity [W(m.K)] 
         [0032]    Electronic central control unit  8  then determines the dew point temperature Tr inside passenger compartment  5  of vehicle  3 —that is, the temperature of the inner face of windscreen  2 , below which vapour inside passenger compartment  5  of vehicle  3  condenses on and mists windscreen  2 —as a function of internal temperature Ti and relative humidity UR inside passenger compartment  5  (block  30 ).  
         [0033]    More specifically, dew point temperature Tr is calculated as follows:  
         [0034]    first of all, the actual partial vapour pressure pw [Pa] at temperature Ti [° C.] and relative humidity UR [%] is calculated according to the equation:  
           pw= 6898.55*10{circumflex over ( )}( k 0+ k 1/( Ti* 1.8+491.72)+ k 2/( Ti* 1.8+491.72){circumflex over ( )}2)* UR/ 100  
         [0035]     where k0=6.21147, k1=−2886.373, k2=−337269.46;  
         [0036]    documented tables showing water vapour saturation pressure values as a function of temperature are then consulted, and, by interpolating the table values, dew point temperature Tr [° C.] is the temperature corresponding to the actual partial vapour pressure pw defined above and representing saturation pressure.  
         [0037]    At this point, electronic central control unit  8  compares the temperature Tv of the inner face of windscreen  2  with the dew point temperature Tr (block  40 ).  
         [0038]    As long as the temperature Tv of the inner face of windscreen  2  is higher than dew point temperature Tr (NO output of block  40 ), the physical conditions required to produce condensation on, and so begin misting, the inner face of windscreen  2  do not exist, so operation of electronic central control unit  8  starts again from block  10 .  
         [0039]    Conversely, when the temperature Tv of the inner face of windscreen  2  is below dew point temperature Tr (YES output of block  40 ), the physical conditions required to produce condensation on, and so begin misting, the inner face of windscreen  2  exist, so electronic central control unit  8  accordingly operates the air-conditioning system  9  of vehicle  3  to prevent windscreen  2  from misting (block  50 ).  
         [0040]    More specifically, intervention of electronic central control unit  8  to prevent windscreen  2  from misting substantially comprises activating the fan of air-conditioning system  9 ; heating the air intake from outside or inside vehicle  3  (normally using the heat radiated by the vehicle engine); and adjusting the air inlet ports to direct hot air onto the inner face of windscreen  2  to increase its temperature and so prevent it from misting.  
         [0041]    Once this is done, operation of electronic central control unit  8  starts again from block  10 .  
         [0042]    The advantages of the device according to the present invention will be clear from the foregoing description.  
         [0043]    In particular, the device according to the invention provides for predicting well in advance the physical conditions resulting in the formation of condensation on, and initial misting of, the inner face of the vehicle windscreen, and intervenes fully automatically to prevent the windscreen from misting. Tests conducted by the Applicant, in fact, show the algorithm described to be capable of predicting misting of the windscreen approximately three minutes in advance.  
         [0044]    As such, the driver of the vehicle is not required to operate the air-conditioning system to demist the windscreen, and visibility through the windscreen is at no time impaired.  
         [0045]    The device according to the invention also provides for predicting the physical conditions resulting in the formation of condensation on the inner face of the vehicle windscreen using a fairly small number of sensors—only two, in fact, seeing as how the external-temperature sensor used is one already installed on the vehicle for other purposes—thus enabling advantages in terms of cost, size, and location.  
         [0046]    By actually preventing misting of the windscreen, the device according to the invention is also more convenient energywise, as compared with conventional demisting, on account of the hysteresis associated with the change in state of the vapour.  
         [0047]    Clearly, changes may be made to the device as described and illustrated herein without, however, departing from the scope of the present invention as defined in the accompanying claims.  
         [0048]    For example, internal and external temperature may be determined otherwise than as described, e.g. indirectly from other physical quantities measured on the vehicle.  
         [0049]    The electronic central control unit may intervene differently to prevent misting of the windscreen, and the temperature of the inner face of the windscreen may be raised otherwise than as described.