US 3313920 A
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Description (OCR text may contain errors)
P. GALLEZ HEATER PANEL Filed April 16, 1964 April 11, 1967 FIG! 7 4 mm AA \\\v /V//// O G II A 2 F above disadvantages and also to advantages whichwill be described hereinafter.
United States Patent 43,65 4 Claims. Cl. 219-522 This invention relates to a heater panel comprising at least one plate of an electrically insulating material, the surface of which has two distributing electrodes connected to an electrical power source, and an electrically conductive film extending between the electrodes.
Heater panels of this kind are generally constituted of a sheet of glass, one surface of which is covered with a thin film of metal or a conductive oxide, such as tin oxide. This film is used as a heater-resistance and is adapted to receive electrical power from an adequate source. To ensure that the electrical current is satisfactorily distributed over the entire panel surface, two electrodes of electrically conductive material are disposed in two marginal zones of the film. Each of these strips is connected to one terminal of the electrical power supply and forms a distributing electrode.
Heater panels of the above type maybe used as heating units for buildings. They can also be used as transparent elements, particularly for motor vehicle Windshields.
It has been found that the temperature of operation of.
such panels varies substantially from one zone of their surface to another. The temperature differences are due particularly to a lack of uniformity in the electrical resistance of the conductive filrn. Despite the care taken during manufacture, the layer of metal or metallic oxide has a lower electrical resistance in certain zones, which for example is caused by a local excess thickness. In these zones the current density is increased to the detriment of the adjacent zones and hence the temperature in such zones of greater current density is greater. Such local overheating is damaging to the conductive film and to the insulating sheet, which is also subject to damage.
It has also been found that there is frequently an irregular temperature distribution along the distributing electrodes because of variations in the contact resistance between the electrode and the conductive film. Contact breaks may take place at the hottest points. They have the effect of increasing the current density in the adjacent contact zones and hence causing new breaks thereat.
It is an object of the present invention to eliminate the provide a number of According to the invention, the conductive film is divided up into a plurality of strips, each of which is in electrical contact with each electrode.
- Although the strips receive electrical power from the same two electrodes, it will be seen that the current passing through each of them is determined by its own electrical characteristics. Since each strip is of a more uniform electrical resistance than the complete film, the current density is distributed therein more uniformly as well.
Advantageously, the strips forming the conductive film each have the same Width measured along a line perpendicular to the direction of flow of the electric current. Preferably, each electrode has a contact surface of the same area with each of the conductive film strips. The strips of the same width 'have the same electrical resistance if their length and their thickness are substantially the same which is most frequently the case. It is therefore advantageous to provide all the strips with contact surfaces of the same dimensions with the electrodes. Preferably, each strip of the conductive film has separate contact surfaces with each of the electrodes having areas which are in the same ratio as that of the total areas of the electrodes one to the other. This is particularly advantageous in the frequent cases in which the two electrodes are not of the same length, because the panel 'has an asymmetrical shape. This arrangement avoids an excessive current density at the contact between certain strips and an electrode.
In certain advantageous embodiments of a panel according to the invention, at least one of the strips of the conductive film has a local contraction. The contracted zone is thus given a higher operating temperature than that of the other parts of the panel. In fact in this zone there is a greater current density which evolves more heat. This local overheating has none of the disadvantages which were mentioned hereinfore, because it can be adjusted exactly both as regards position and strength. On the other hand, this embodiment is very advantageous when it is required to produce an intensive heat effect in one region of the panel. By way of example, the zone of a windshield situated in the path of vision of the driver is advantageously heated fairly strongly in order to eliminate more intensively any frost or mist tending to form there.
The accompanying drawings illustrate several embodiments of the invention and its advantages.
FIGURE 1 is an elevation of a windshield according to the invention.
FIGURE 2 is a section of the line IIII in FIGURE 1 to a larger scale.
FIGURE 3 is an elevation of another embodiment of a windshield according to the invention.
FIGURE 4 is a partial view of another form of windshield.
In the various figures like reference numerals denote like parts.
With reference to FIGURES 1 and 2, the windshield comprises a sheet of glass 1 covered with a thin transparent film '2 of an electrically conductive metal, such as, for example, copper. Distributing electrodes 3 and 4 are provided in marginal zones of the film 2. Said electrodes are, for example, in the form or an electrically conductive enamel. Leads 5, 6 are connected to an electrical power supply (not shown) and are soldered to respective electrodes. Another sheet of glass 7 is maintained on the film 2 and the electrodes 3 and 4 by a layer of transparent adhesive 8. I
According to the invention the film 2 is divided into strips, e.g., 9, 10 and 11. Each strip is in contact with the electrodes 3 and 4. The strips are formed by de positing the film 2 on the surface of the sheet 1, then applying the electrodes 3 and 4 thereon in the form of a conductive enamel, and finally by forming grooves, e.g., 12, 13 and 14, by scoring the film 2 with a pointed tool. The grooves 12, 13 and 14 extend through the entire thickness of the film 2 and isolate the film into the distinct strips 9, 10, 11 etc. The width of the grooves may be as small as desired, because the adjacent strips are substantially at the same electrical potential and are therefore effectively insulated by a fine groove.
In the arrangement illustrated, the strips 9, 10, 11 are of the same width. Each of these strips passes a current therethrough whose intensity is determined by the electric resistance of the strip and by the voltage of the supply. If unintentionally one of the strips, for example 11, has zone 15 of greater thickness (shown in chain dotted lines in FIGURE 1), it has a lower electrical resistance and therefore passes a current of slightly greater magnitude than the others. Since this current is distributed uniformly throughout the strip, the extra heat evolved is also spread over a large area. In contradistinction, in a continuous film, a zone such as 15 would 3 drain the current passing through adjacent zones of the film so that a considerable increase in the current density would be developed in zone 'resulting in a substantial increase intemperature. I In the windshield according to the invention the draining ofthe current is prevented by the grooves 13 and 14. Thus, random unpredictable heated zones caused by thickness variations will be localized by the individual strips according to the invention.
The' windshield shown in FIGURE 3 has the form of an irregular quadrilateral. -The electrodes 3 and 4 are disposed parallel to one another and are each located near one side of the quadrilateral. To form the strips 9, 10, 11, grooves are provided in the film 2 prior to the affixing of the electrodes 3 and 4 so that the grooves extend beneath the latter. i
The side zones16 and 17 of the film which are intended to receive the electrodes 3 and 4 are of different lengths. They are divided into as many zones of the same areae.g., 18' and 19 as there are strips 9,10, 11, i.e., five in the example illustrated. Each electrode 3 or 4 thereforehas contact surfaces of the same area with each stri-p 9, 10, 11 etc. Similarly, each strip, e.g. 9, is in contact with the electrodes 3 andv 4 at zones 18 and 19 whose areas are in the same ratio as that of the total areas of the side zone-s 16 and 17 of the electrodes 3 and 4 one to the other.
The windshield illustrated in FIGURE 4 comprises the same elements as the windshield shown in FIGURE 1. In addition, the transverse marginal zones 20 of the sheet 1 are covered 'by a layer of the same nature as that used for the film 2. A groove 21 completely separates the zones 20 from the film 2 and, on the one hand, from the adjacent strip 9 and, on the other hand, from the electrodes 3 and 4. This arrangement is advantageous in that the windshield is optically uniform. Moreover, since the zones 20 do not participate in conveying the electrical current, the heat evolved is concentrated in the film 2, i.e.-,in theportion of the windshield which is most frequently looked through.
The'strip 10 shown in FIGURE 4 has a contracted zone 22 formedby causing the grooves 12 and 13.t o converge towards one another in 'a central zone of the sheet 1. To this end, each of'the latter grooves com-' prises two portions 23, 23 which converge in'the con tracted zone "22. Despite the presence'of the latter, the electrical resistance of the strip 10'is" not very much different fromthat of the other strips'so that the current intensity flowing through it is substantially the same. On the other hand, in the contracted'zone '22 the current density and the electrical resistance are relatively high so that the heat evolved there is greater than in the other zones of the film 2. This arrangement is very advantageous in Windshields of motor vehicles, where. it
, enables mist and frost to be rapidly eliminated at certain selected locations, for example in front of the driver.
r The invention is not limited to the embodiments described hereinbefore. Variations and modifications are possible, more particularly by combining the features of the embodiments illustrated. The invention may also be applied to panels used for heating buildings,
What I claim is:
4 ,1. .A. heater panel comprising at least one electrically insulating glass sheet, an electrically conductive transparent film on said glass sheet, a single pair .of electrodes extendiig parallel to each other in contact with said film along the entire length of said film in marginal zones of said glass sheet, said electrodes being adapted for being connected to an electrical power source, said film having a plurality of grooves extending between the electrodes for isolating the film on either side of the grooves to define a plurality of isolated strips extending from one electrode to the other and in electrical contact therewith, said glass sheet being of quadrilateral outline and said grooves converging in one direction.
2'. Aheater panel as claimed in claim 1 grooves extend along straight lines.
3. A heater panel comprising at least one electrically insulating glass sheet, an electrically conductive transparent film on said glass sheet, a single pair of electrodes extending parallel to each other in contact with said film along the entire length of said film in marginal zonesof said glass sheet, said electrodes being adapted for being connected to an electrical power source, said film having a plurality of grooves extending between the electrodes for isolating the film on either side of the grooves to define a plurality of isolated strips extending from one electrode to the other and in electrical contact therewith, said electrodes having diiferent lengths and each strip wherein said of film being in contact with each of the electrodes along separate contact surfaces having areas which are in the same ratio as the ratio of the total areas of the electrodes one to the other.
4. A heater panel comprising at least one electrically insulating glass sheet, an electrically conductive transparent film on said glass sheet, a single pair of electrodes extending parallel to each other in contact with said film along the entire length of said film inmarginal zones of said glass sheet, said electrodes being adapted for being connected to an electrical power source, said film-having a plurality of grooves extending between the electrodes for isolating the film on either side of the grooves to Y define a plurality of isolated strips extending from one electrode to the other and in electrical contact therewith, said parallel electrodes having different lengths and said strips having the same width measured along any line parallel to the electrodes.
References Cited by the Examiner Schmidt 338-211 RICHARD M. WOOD, Primary Examiner.
Y. MAYEWSKY, Assist nt Examiner.