Electric heating device, particularly for a heating or air-conditioning unit in a vehicle

Abstract

Electric heating device comprising an electric radiator ( 10 ) for heating the air passing through it, said radiator comprising a casing ( 12 ), at least one resistive element mounted in the casing and constituted by at least one zigzag metal strip ( 22 ) which is disposed so as to be directly exposed to the air passing through the casing, and a circuit ( 30 ) for controlling the electrical supply of the resistive element or elements connected to a power supply. The electric radiator ( 10 ) comprises a set of individual heating modules ( 20 ) disposed parallel to one another in the casing ( 12 ) and so as to be directly exposed to the air passing through the casing, each heating module ( 20 ) comprising a pleated or corrugated metal strip ( 22 ) and an electronic switch controlled by the control circuit ( 30 ) intended to selectively inhibit the electrical supply of the metal strip ( 22 ).

1 . Electric heating device comprising an electric radiator ( 10 ) for heating the air passing through it, said radiator comprising a casing ( 12 ), at least one resistive element mounted in the casing and constituted by at least one zigzag metal strip ( 22 ) which is disposed so as to be directly exposed to the air passing through the casing, and a circuit ( 30 ) for controlling the electrical supply of the resistive element or elements connected to a power supply, 
 characterised in that the electric radiator ( 10 ) comprises a set of individual heating modules ( 20 ) disposed parallel to one another in the casing ( 12 ) and so as to be directly exposed to the air passing through the casing, each heating module ( 20 ) comprising a pleated or corrugated metal strip ( 22 ) and an electronic switch ( 25 ) controlled by the control circuit ( 30 ) intended to selectively inhibit the electrical supply of the metal strip ( 22 ).    
   
   
       2 . Device according to  claim 1 , characterised in that each heating module ( 20 ) also comprises an electrically insulating support ( 40 ) comprising a moulded rail ( 45 ) intended to accommodate and hold in position said metal strip ( 22 ).  
   
   
       3 . Device according to  claim 2 , characterised in that the moulded rail ( 45 ) has flanges ( 45   a ,  45   b ) between which the tops of the corrugations are held laterally and separations ( 46 ) for maintaining a certain regularity of the pitch of the corrugated or pleated metal strip ( 22 ).  
   
   
       4 . Device according to any one of  claims 1  to  3 , characterised in that the heating module ( 20 ) comprises at least one thermal and electrical protection element, directly exposed to the air passing through the heating module and in series with the metal strip ( 22 ).  
   
   
       5 . Device according to  claim 4 , characterised in that the protection element comprises at least one hot-melt link ( 58 ) in series with a metal strip ( 22 ).  
   
   
       6 . Device according to  claim 4 , characterised in that the protection element comprises a spring blade ( 57 ) and a hot-melt link ( 58 ) formed by a brazed joint between one end of the metal strip ( 22 ) and one end of the spring blade ( 57 ), the other end of the spring blade being immovably attached to the support ( 40 ) and electrically connected to a terminal  56 .  
   
   
       7 . Device according to either one of claims  5  and  6 , characterised in that the brazed joint of the hot-melt link ( 58 ) has a melting point matching an upper temperature limit.  
   
   
       8 . Device according to  claim 7 , characterised in that the brazed joint of the hot-melt link ( 58 ) is formed by a eutectic solder joint.  
   
   
       9 . Device according to  claim 6 , characterised in that the spring blade ( 57 ) is directly exposed to the air passing through the heating module ( 20 ) and openings in the form of louvres are formed in the spring blade ( 57 ).  
   
   
       10 . Device according to any one of  claims 6  to  9 , characterised in that the spring blade ( 57 ) has a cross-section smaller than or equal to that of the metal strip ( 22 ).  
   
   
       11 . Device according to any one of  claims 6  to  10 , characterised in that the spring blade ( 57 ) has a resistivity greater than or equal to that of the metal strip ( 22 ).  
   
   
       12 . Device according to any one of  claims 1  to  11 , characterised in that a metal connection support ( 50 ) connected to the electrical power supply is integrated into the insulating support ( 40 ) allowing the electrical supply of the metal strip ( 22 ).  
   
   
       13 . Device according to any one of  claims 1  to  12 , characterised in that the electronic switch ( 25 ) is integrated onto the metal connection support ( 50 ) through tracks formed by said support.  
   
   
       14 . Device according to either one of claims  12  and  13 , characterised in that flanges ( 52 ) are formed in the metal connection support ( 50 ) facilitating the heat dissipation of the electronic switch ( 25 ) by the air passing through the heating module ( 20 ).  
   
   
       15 . Device according to any one of  claims 6  to  14 , characterised in that the end of the spring blade ( 57 ) immovably attached to the insulating support ( 40 ) is soldered permanently to the connection terminal ( 56 ) electrically independent of the metal connection support ( 50 ) thus allowing electrical connection of the strip or of the spring blade to an external terminal or busbar ( 35 ).  
   
   
       16 . Device according to any one of  claims 1  to  15 , characterised in that each heating module ( 20 ) also comprises at least one protection mechanism of reversible or resettable type ( 61 ) connected directly or indirectly to the metal strip ( 22 ) preventing excessive heating.  
   
   
       17 . Device according to  claim 16 , characterised in that the reversible protection mechanism ( 61 ) is a thermal sensor or detector delivering information to the control circuit ( 30 ), matching the temperature of the metal strip ( 22 ) or of the spring blade ( 57 ) in order that the control circuit ( 30 ) disconnects the electrical supply in the case of excessive heating.  
   
   
       18 . Device according to  claim 17 , characterised in that the thermal sensor or detector is connected thermally to the spring blade ( 57 ).  
   
   
       19 . Device according to either one of claims  17  and  18 , characterised in that the thermal sensor or detector comprises an element chosen from amongst an NTC resistor, a PTC resistor, a bimetallic strip and a PTC effect polymer switch.  
   
   
       20 . Device according to any one of  claims 6  to  18 , characterised in that moreover the spring blade ( 57 ) has a PTC effect thus providing the function of a thermal sensor.  
   
   
       21 . Device according to any one of  claims 1  to  20 , characterised in that each heating module ( 20 ) has a heating power of between 0 and 500 W and preferably between 300 W and 400 W.  
   
   
       22 . Device according to any one of  claims 1  to  21 , characterised in that the casing ( 12 ) comprises a set of cells ( 14 ) intended to accommodate and hold in place each heating module ( 20 ).  
   
   
       23 . Device according to  claim 22 , characterised in that the casing ( 12 ) receives a cover ( 39 ).  
   
   
       24 . Device according to any one of  claims 1  to  23 , characterised in that the control circuit ( 30 ) comprises means of varying the power supplied by the radiator by modulating the supply voltage delivered to each heating module ( 20 ).  
   
   
       25 . Device according to  claim 24 , characterised in that the control circuit ( 30 ) comprises means of varying the supplied power by pulse width modulation.  
   
   
       26 . Device according to any one of  claims 1  to  25 , characterised in that the different heating modules ( 20 ) comprise metal strips ( 22 ) having substantially identical resistances.  
   
   
       27 . Device according to any one of  claims 1  to  26 , characterised in that each metal strip ( 22 ) of each heating module ( 20 ) has a corrugation period with a length of between 1.8 mm and 6 mm.  
   
   
       28 . Device according to any one of  claims 1  to  27 , characterised in that each metal strip ( 22 ) of each heating module has a peak-to-peak amplitude between corrugation tops of between 5 mm and 20 mm.  
   
   
       29 . Device according to any one of  claims 1  to  28 , characterised in that each metal strip ( 22 ) of each heating module has a width of between 5 mm and 20 mm.  
   
   
       30 . Device according to any one of  claims 1  to  29 , characterised in that each metal strip ( 22 ) of each heating module has a thickness of between 50 μm and 250 μm and preferably between 80 μm and 180 μm.  
   
   
       31 . Device according to any one of  claims 1  to  30 , characterised in that each metal strip ( 22 ) of each heating module is made of a material chosen from amongst an iron-based alloy and a copper-based alloy.  
   
   
       32 . Device according to  claim 31 , characterised in that the copper-based alloy is an alloy chosen from amongst CuNi30, CuNi45 and CuNi18Zn20.  
   
   
       33 . Device according to  claim 31 , characterised in that the material is an alloy having a positive temperature coefficient resistance effect.  
   
   
       34 . Device according to any one of  claims 1  to  33 , characterised in that openings in the form of louvres ( 26 ) are formed in each strip ( 22 ).  
   
   
       35 . Device according to  claim 34 , characterised in that the louvres ( 26 ) comprise fins ( 26   a ) which form an angle of between 200 and 350 with respect to the plane of the strip ( 22 ).  
   
   
       36 . Device according to any one of  claims 1  to  35 , characterised in that each strip ( 22 ) is provided with an electrically insulating and/or corrosion protection covering.  
   
   
       37 . Device according to any one of  claims 1  to  35 , characterised in that each metal strip ( 22 ) has a profile chosen from amongst a sinusoidal profile, a triangular profile, a rectangular profile and a trapezoidal profile.  
   
   
       38 . Device according to any one of  claims 1  to  37 , also comprising an air flow generator ( 7 ), characterised in that the electronic switches ( 25 ) driven by the control circuit ( 30 ) inhibit the electrical supply of the heating modules ( 20 ) when the air flow rate passing through the radiator ( 10 ) is below a minimum value, in order to provide protection against excessive heating.  
   
   
       39 . Device according to  claim 38 , in which the air flow generator ( 7 ) comprises a fan ( 3 ), characterised in that means are provided for supplying the control circuit ( 30 ) with a signal representing the speed of rotation of the fan in order to inhibit the electrical supply of the heating modules when the speed of rotation of the fan is below a predetermined threshold.  
   
   
       40 . Heating or air-conditioning apparatus for a motor vehicle, characterised in that it comprises a heating device according to any one of  claims 1  to  39 .  
   
   
       41 . Apparatus according to  claim 40 , characterised in that it comprises an electric radiator disposed downstream of a liquid heat exchanger in an air circulation channel.  
   
   
       42 . Apparatus according to either one of claims  40  and  41 , characterised in that the electric radiator is disposed in proximity to an air outlet aperture.