CA1079337A

CA1079337A - Heated window with a moisture sensor having a high impendance

Info

Publication number: CA1079337A
Application number: CA253,892A
Authority: CA
Inventors: Sergio Roselli
Original assignee: Saint Gobain Industries SA
Current assignee: Saint Gobain Industries SA
Priority date: 1975-06-02
Filing date: 1976-06-02
Publication date: 1980-06-10
Also published as: DD124373A5; ATA396776A; FI761533A; CH611097A5; BE842460A; NL7605833A; PT65155A; DK240876A; AU1450476A; AT376863B; CS214661B2; FR2313239A1; AU497166B2; NO761851L; PT65155B; DE2622932A1; IT1068114B; NO148807C; ES448437A1; NO148807B

Abstract

HEATED WINDOW WITH A MOISTURE
SENSOR HAVING A HIGH IMPEDANCE

Abstract of the Disclosure A window has a heating grid and a moisture sensor formed thereon for connection to a detector which automatically controls the heating. The sensor has an output terminal and another terminal connected to a heating conductor, the sensor being positioned outwardly of the heating grid with the area of the sensor including the output terminal lying in the heating zone.
Advantageously the outer limit of the sensor is closely adjacent the outer limit of the heating zone. The output terminal is positioned between the outward limit of the sensor electrodes and the boundary heating conductor. A shield electrode connected to the heating conductor may be provided. The sensor may be located between a pair of heating conductors adjacent a heating grid collector with one electrode connected to the conductors.
For deep windows, the sensor may be located in an offset branched section of a boundary heating conductor.

Description

~ 93,,~7 1 ¦ The present invention relates to a window equipped wi-th a

2 ¦ printed heating network or grid which is controlled by means of a

3 ¦ moisture cletector designed to detect the presence of a deposit ¦ capable of obscuring visibility.
5 ¦ Windows of this type are known. They comprise one or more 6 ¦ sensors which are located at a distance from the heating network 7 ¦ or grid corresponding to the limit of the region cleared by the 81 latter and which are connected to a control circuit so as to 9¦ trigger the heating system when this region is cloude~ over but 10¦ to interrupt it as soon as the region has been cleared. ~ccord-11¦ in~ to the method currently considered the most satisfactory, the 12¦ sensor is produced by the silk screen technique at the same time 13¦ as the heating network and its electrodes are reinforced and then 1~¦ protected in the same way by means of a deposit of copper and 15¦ nickel. These sensors general~y consist of two electrodes in the 16¦ form of interdi~itated combs defining an active zone dis-17¦ posed astride the border of the heated region and the teeth of ~81 which are preferably vertical.
'9¦ The two combs can each be connected to a free terminal, 20¦ but it is preferable~ both to reduce the cost and also to reduce 21¦ the size of the detector t to connect one of the electrodes 22¦ directly to ground by one of the collectors of the heating - 23¦ network or, alternatively, to connect this electrode as close as ¦
2~1 possible to one o~ the printed resistive bands or conductors con-251 stituting this-network; this being achieved at the cost of 26¦ certain precautlons involved in the design of the electronic 271 control circuits used therewith. This solution is especially 1 2~ suitable when two separate sensors are used or whenl for example, ; the sensor is placed on the axis of the window at the upper part of t~e region to be cleared. In this latter case, the lowerpart . . , , . ~
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~ 3~7 1 ¦of the electrodes is located in the im~ediate ~icinity of the 2 ¦upper resistive band or conductor which is advantageously used 3 ¦ as the terminal for one of the combs. The effective heating ¦ range of this resistive band covers a width of 15 to 20 milli-51 meters on either side and the upper part of the sensor i5 located 61 approximately 20 or 25 millimeters from the resistive band.
71 A~though the electrodes are minimaily soluble, it is 81 preferable to carry out detection by means of an alternating 9¦ signal and to DC isolate each sensor by mean~ of a capacitance 10¦ mounted in series with each free terminal so as to eliminate 11 continuous voltages produced between the detection circuit and 12 the heating network as these voltages are capable of causing 13 troublesome polarization and sometimes chemical damage. Even 14 with alternating current, the presence of moisture is detected through the variation in the resistance of the sensor. It is 16 important to select a very high detection threshold, for example, 17 between 10 and 10 ohms. It has been found that this not only 1~ increases the stability of operation but it also saves energy 19 owing to more rapid detection of a rnoisture deposit. I
However, the proposed solutions have still not been completely 21 ¦ satisfactory. After a specific period of operation the heating 22 ¦ system may remain energized even after the visibility zone has 23 ¦ been cleared. This phenomenon, which occurs mainly during humid 24l - weather when there are a number of occupants in the vehicle, 251 can be a~tributed to the progressive formation of a wide layer 26¦ of moisture :in the unheated region. This conducting layer is 27 capable of forming, at least in certain types of vehicles, 2~ a bridge between the periphery of the sensor, various points on 29 the heating network itself and finally ~he framework of the 30 window. }t t:hus produces short circuit resistances, the value of ;

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which cannot exceed 10~ ohms, and as a result, operatlon is blocked if the regulating threshold selected i5 higher. In any event continuous annoying or even harmful components are again produced.
The object of the present invention is to obviate this type of difficulty. It is proposed to avoid any kind of conducting bridge between the free terminal of the senso~
and other points such as the edge of the window. Accordingly, it is proposed to situa~e the entirety of each sensor, including its electrodes and supply terminals, withln the outer limit of effectiveness oE the heating conductors. This being the case, even in the presence of a realtively large deposit, the sensor is rapidly surrounded by a non-conductive zone which eliminates any leakage 90 that the heating action is stopped as soon as the window is sufficiently cleared of moisture in the visibility range. Disturbing currents are also eliminated.
Thus, the invention relates to a heated ~indow having a heating grid formed of a plurality oE resistive heating conductors and a moisture ~ensor formed on the wlndow for connection to a moisture detector for automatically .
~ controlling the energizatlon of the heating grid. The sen~or .
has a first electrode connected to an output terminal and a second electrode connect~ed to a heating conducto~ of the .
heating grid. The area of the sensor including the output terminal ~ i9 disposed within the heating zone of the - heating grid. The output terminal i~ positioned closer ~o ; the center of the heating zone than the edge of the area of the sensor furthest from the center of the heating zone.
- Accordingly, it is no longer necessary to select a high threshold which triggers the hea~ing system even be~

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a visible deposit appears on the active zone formed by the comb in order to insure that, when condensation is small, the limit of the visibility zone, while closing in, will still remain outside of this active zone.
According to an advantageous feature of the invention, the limit oE the active zone of the sensor which is disposed furthest away from the heating conductors is located in the immediate proximity of the corresponding outer edge of the sensor and also in the immediate proximity of the outer limit of the heating zone. It is thus possible to avoid reducing the size of the visibility zone to an excessive degree.
In the first embodiment, the sensor is placed along the . ~ "
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~ 337 l ¦ upper band or conductor of the he~ting nc-twork or grid, and the 2 ¦ distance between the latter and the edge of the window is 3 ¦ sufficiently small to permit connection of the connection cable.

4 ¦ The principle of this embodiment consists in reducing the height

5 ¦ of the sensor while avoiding increasing its width such that the

6 ¦ comb system including its comlection terminal is located entirely 71 within the effective zone of influence of the resistive heating 81 conductor. During the initial heating stage, there is a 9¦ parasitic current inside the sensor which does not constitute lO¦ an actual disadvantage because it is transitory.
ll¦ In a second embodiment isolation of the sensor is ensured 12¦ b~ a protective element connected at a potential very close to 13¦ that of the connection to ~the heating network and which encloses l~¦ the electode connected to the free terminal. The protective 15¦ element will preferably be sufficiently close to the latter ]~ electrode to constitute a part of the second electode. Similar 17¦ isolation can be obtained by positioning the sensor between two 1 8 ¦ conductors of the heating network at a suitabl~ selected position '~ within the heated zone. This solution eliminates continuous 20¦ components from the start.
21¦ An especially important variant consists in producing an 22¦ auxiliary heating zone outside and adjacent the visibility zone 231 per se, in the vicinity of the edge of the window. The sensor 241 is placed inside this auxiliary heating zone, preferably between 251 two branched heating wires, the section and spacing of which are 26¦ such that the heating conditions repxoduce in an optimum manner 271 the conditions prevailing inside the visibility zone. It is 28¦ possible to use a plurality of sensors, but it is sufficient 291 a;nd preferable to provide only a single sensor and in this case 30~ to place it at the upper part of the window. Many vehicles now _ 4 _ ~ I .
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~ 337 1 possess very deep rear windows. The resistlve ~ands forming the 2 upper and lower bounclaries of the heating network are therefore 3 located fairly far away from the corresponding edges of the 4 window as it would be difficult to clear the entire surface of the window without consuming excessive electricity. In such a case, it is not advisable to make a connection to the free

7 terminal of the sensor by means of a printed wire crossing the

8 moist zone or to locate it at a considerable distance from the

9 edge of the window as it woulcl otherwise be necessary to supply the detector by means of a correspondingly long cable. This cable 11 would be very conspicuous, and detrimental bo-th in terms of 12 visibility and vulnerability~ This variant is especially adapted !
13 to such situations.
]~ It is possible to construct the upper edge of the sensor as a channel or gutter in a manner known per se. Then droplets 1~ formed by condensation can flow a~ay from the active zone between 17 the electrodes. It is even more desirable to protect the active 1~ zone by means of an independent channel.
,9 Various embodiments of the invention, provided by way of example onl~, will be described hereinafter with reference to 21 the accompanying drawings in which:
22 FIG. 1 shows a shallow rear heated window equipped with a 23 moisture or humidity sensor;
24 FIG. 2 is a detailed view of a sensor according to the invention designed for use in the window of FIG. l;

26 FIGS. 3 and 4 show two advantageous variants of the 27 prèceding sensor;

28 FIG. 5 is a de~ailed view of a sensor placed between two 29 resistive bands of the heating grid;
FIG~ 6 shows a very deep rear window equipped with a sensor _ ~ _ , .
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~17g337 1 ¦ according to the invention; and 2 ¦ FIG. 7 shows a sensor designed for use on the window of 3 1 FIG. 6.
¦ In all the sensors shown in these figures, a portion of at 5 ¦ least one of the resistive heating bands or conductors serves as 61 the connection to one electrode or comb of the sensor. This 71 feature is not absolutely essential but it is advantageous as 81 it enables the height of the sen.sor to be reduced. It also 9¦ improves operation during very cold weather by eliminating the

10¦ possibility of ice formation.

11 The rear heating window 1, according to FIG. 1, is e~uipped

12 with a network or grid 2 of horizontal printed resistive heating

13 conductors connected between two common bus conduckors or

14 collectors 3 and 3'. This network is preferably formed by means of an electro-conducting frit deposited by the silk screen 1~ ~echnique and then incorporated in the glass by flring, and 17 subse~uently reinforced and protected by electoplating. The ~8 grid covers the major part of the window 1 and the outer or '9 boundary resistive bands 4, 4' are located at a fairly short 20¦ distance from the corresponding edges 5, 5' of the window 1.
; 21¦ When the heating grid is switched on, the cleared zones surround-22¦ ing each resistive conductor progressively grow closer together 231 and the region which the grid is capable of clearing stops along 241 two lines A, A'. The distance between the lines A, A' and the 1~¦ upper and lower heating conductors 4~ 4' can reach about 20 to 26¦ 25 millimeters depending on the atmospheric condltions. In ¦ fact, lf the system comprises automatic control means and the 28¦ detector consists, for example, of a moisture or humidity sensor ~1291 disposed at 6~on the axis of symmetry of the window above the 30¦ upper heating conductor, the heating system ceases to operate ~: 1 ~

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. ! . ' . . ' . ~ , ~ 337 1 ¦ sliglltly earlier. Such cessation occurs when the upper limit of 2 ¦ the cleared zone (which progresses upwards ~rom the upper heating 3 ¦ conductor 4 during operation of the heating system~ has ~¦ sufficiently cleared the active zone formed by the electrodes 51 of the sensor, reaching, for e~ample, two lines B, B' whose 61 location depends on the form of the sensor and the regulation of 7¦ the detector~
81 The detector can include further moisture sensors located, 9 for example, at 6' beneath the lower heatiny conductor, at 7 along the collector or bus connected to ground, or at 7' alony 11 the collector supplied by the positive terminal of the battery.
12 A control circuit 8, which is supplied by the battery, is con-13 nected by means of a capacitor 9 to the free 14 terminal 10 of the sensor so that the signal from the detector

15¦ opens or closes the control contact s of the heating grid by 1~ ¦means of a relay S as a function of the ah~ence or presence of 17 moisture on the inner face of the window where the sensor or ~8 sensors are located.
19 FIG. 2 shows the inner structure of a sensor according to the invention which is utilizable at position 6 of FIG. 1. This 21 sensor, which is approximately 15 millimeters in heiyht, com~
22 prises two electrodes 11 and 12 consisting of interdigitated 23 combs. The vertical teeth of comb 12 are connected directly 24 to the heating conductor 4. The vertical teeth of comb 11 are connected by an upper collector conductor 13 (~orminy the back 2~ of the comb~, to a conducting surface 14 used to secure the 27 connection terminal 10. The surface 14 is situated beneath the 28 co~b back l3 such that the part 15 of the active zone furthest 29 away from t~le heating conductor 4 is only se~arated from the outer 30 edge of the sensor furthest away from this heating conductor by _ 7 _ .
-~ 337' 1 the thickness of 13, i.e., by some tenths of millimeters. As a 2 result, the limit of the clouded reg.ion formed by the line B is 3 located at approximately 1 mm from the sensor, such tha-t a 4 zone 15', having a greater resistance than the internal resis-tance of the sensor, is produced between the latter and the 6 ground constituted by the bodywork of the vehicle along the 7 upper edge 5, before heating is ceased.
The sensor also includes a secondary conducting surface 16 9 connected to the heating conductor ~ which is intended to facilitate electroplating. An electroplating electrode connected 11 to the suxface 14 of the upper comb will also be brought into 12 contact with the surface 16, thereby enabling the metal deposit 13 on the teeth of the lower comb to be reinforced. If this pre-lg caution were not ta]cen, the density of the electroplating current would tend to be reduced in the corresponding zone owing to the lG relativel~ large surface area of the printed networ]; at the t 17 location of the sensor and owing to the voltage gap between its I :
~8 two combs.
19 In the embodiment represented in FIG. 3, the design of the sensor is similar, but the two conducting surfaces 1~ and 16 ~1 are disposed one above the other. This enables the width o the 22 sensor to be reduced without excessivély increasing its height.
23 In addition the electrode 11, connected to the free terminal 10, 24 is enclosed by a conductor 17 connecte~ . to heating conductor 4 and hence forming part of electrode 12. Conductor 17 constitutes .
26 a shield which isolates the electrode 11 from the ground con-27 stituted by the bodywork along the edge of the window. As the 28 electrode 11 is itself DC isolated by the capaci-tor 9 (FIG. 1), 29 there can be no appreciable continuous voltage between the sensor electrodes. The external leakage currenk is not disturbing on _ 8 _ .
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~ 33~

1 tlle whole and fur-thermore remains weak if the sensitivity of 2 the sensor is suitably adjusted, as the limit of the visibility 3 ~one is again moved back beyond the outer edge. The conductor 17 4 also guards against any possible drops of condensate flowing into the active zone 15, but it is advantageous to provide a 6 channel or gutter 18 thereabo~e which can extend into the moist 7 region without any disadvantage. The teeth 11 of the comb 8 electrode are terminated with:in a few millimeters of the heatiny 9 conductor 4, with the exception of the two outer teeth which descend to within a few tenths of a millimeter.
11 The sensor shown in FIG~ 4 is also similar, but the comb 11 12 with the terminal 10 is inverted. The collector 13 thus runs 13 along the resistive heating conductor ~ at some tenths of a 1~ millimeter therefrom. ~he other comb is also inverted, with the back thereof connected to heating conductor 4 and the back ]6 and outer teeth forming a shield around comb 11.
17 FI~. 5 shows the inner structure of a sensor laterally ~8 disposed between two heating conductors, for example at 7' '9 (FIG. 1) on one o~ the sides of the window. The comb formed 20 by the electrode 12, connected to the heating grid,is double, 21 and comprises two sets of vertical teeth,one set being connected 22 to the upper heating conductor 19 and the other to the lower 23 heating conductor 20. The complementary electrode lI has teeth Z4 connected by a median collector 13 to a conducting surface 14 25 on which the connection terminal 10 is affixed. An auxiliary 26 conducting sur~ace is formed by the bus or collector 3'of the 27 heating network. The heating action ceases when the cleared zone 28 reaches a line corresponding substantially to the line C. The 29 sensor is then entirel~ situated in a dry zone and is also 30 surrounded on three sides by conductoxs situated at the potential _ 9j : . ' '. : : . ~

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1 ¦ of the electrode 12. It is possible, but not especially 2 ¦ advantageous, to provide the sensor with a shield conductor 17 3 ¦ on its fourth side.
¦ FIG. 6 shows a deep rear window 21, the upper heating con-5 ¦ ductor 22 of which is located at a considerable distance from the 6 ¦ upper edge 25. This distance can be as great as 200 mm and more.
- 71 According to the invention, the median part 23 of the heating 81 conductor 22 is nevertheless situated close to the upper edge 25 ¦ of the window in the central zone, over a distance of up to lO¦ approximately 10 cm., and it is divided in its middle part into 11¦ two branches 23a, 23b, thus producing a secondary visibility 12¦ zone 27 in which the moisture sensor is situated. The sensor 13¦ is represented in FIG. 7 and has a form similar to that of FIG. 5.
1~1 The two branches 23a, 23b are connected in parallel by two 15~ auxiliary surfaces 26r 26'. They have a rounded shape which, lG wlth the upper branch of the sensor, facilitates the flow of 17 ¦ water over the sides outside of the active zone 28. Respective ~8 ¦ sets of teeth of one electrode are connected to respective 19¦ branches 23a and 23b. The teeth of the other electrode are 20 ¦connected to a conducting surface 24 to which is attached the 21 ¦ connection terminal 30.
22 ¦ The diversion of water referred ~o in the foregoing, as by 231 channels or gutters, is due to the fact that the printed con-2~1 ductors are raised in relief from the surface of the window.
251 As will be noted, in the illustrated embodiments the output 26 terminal is positioned between the heating conductor to which one electrode~of the sensor is connected and the outward limit 28 of the electrodes of:~the sensor, or between two heating conductors 29 Thus, with th~e sensor positioned within the heating zone of the 30 heating grld, and advantageously with the outer limit of the : . .

~L~7~3337 1 ¦ sensor closely adjacent the outer limit of the heatiny ~one, the 2 ¦ terminal area is cleared of moisture as soon as the active area 3 ¦ of the sensor so that leakage paths which could prolong the ¦ energization of the heating grid after the desired area of the ~¦ window has be n cleared are avoided.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A heated window having a heating grid formed of a plurality of resistive heating conductors and a moisture sensor formed on the window for connection to a moisture detector for automatically controlling the energization of the heating grid, said sensor having a first electrode connected to an output terminal and a second electrode connected to a heating conductor of the heating grid, the area of the sensor including said output terminal being disposed within the heating zone of the heating grid and said output terminal being positioned closer to the center of the heating zone than the edge of the area of said sensor farthest from the center of the heating zone.

2. A heated window according to claim 1 in which said sensor is positioned outwardly of the heating grid and said second electrode is connected to a boundary heater conductor of the heating grid.

3. A heated window according to claim 2 in which the outer limit of said area of the sensor is closely adjacent the outer limit of said heating zone.

4. A heated window according to claim 2 in which said output terminal is positioned between the outward limit of the electrodes of said sensor and said boundary heating conductor.

5. A heated window according to claim 4 in which said plurality of resistive heating conductors are disposed in a substantially horizontal relationship and in which said sensor is positioned along and above the uppermost heating conductor intermediate the ends of the heating conductor.

6. A heated window according to claim 5 in which said second electrode is connected to said uppermost heating conductor, and including a shield electrode adjacent and outside the sides and top of said first electrode and connected to said heating conductor.

7. A heated window according to claim 1 further characterized by said resistive conductors extending in spaced parallel relationship between common collectors, said sensor being positioned adjacent one of said collectors between a pair of adjacent heating conductors, said sensor having a first electrode connected to an output terminal and a second electrode connected to said pair of adjacent heating conductors at points adjacent said one collector.

8. A heated window according to claim 7 in which said second electrode includes a conductor positioned outside said first electrode on the side thereof away from said one collector.

9. A heated window according to claim 1 further characterized by a boundary heating conductor of the heating grid having an intermediate branched section with two spaced branches connected in parallel, said sensor being positioned between said spaced branches and having a first electrode connected to an output terminal and a second electrode connected to said spaced branches.

10. A heated window according to claim 9 in which said intermediate branched section is offset outwardly with respect to the remainder of said boundary heating conductor.