Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
10461Zl
This invention relates to clear vision windshields and
to methods and means for keeping windows exposed to weather clear.
As the invention is of particular use in keeping the windows of
automobiles clear of condensed mist and steam on the inside it
will ble described in that application.
At present there are known electrically heated wind-
shields and other windows in whLch electrical heating means sup-
plied by a power source, e.g. the car battery, is mounted on or
in the window, and by heating it frees the inside from condensed
mist and steam and the outside from snow and sleet. Such heat-
ing means are constructed so that the operator can turn them on
and off as needed. The drain on the battery continues until the
operator thinks to turn it off and, also, long after it has cleared
the window of frost and steam. This unavoidable excess drain
on the battery is undesirable from all points of view, as the
quantity of energy available is reIatively small and such exces-
sive drain can have deleterious effects on the battery.
It is an object of this invention to reduce the amount
of energy consumed by such windows. It is another object to take
control out of the hands of the operator and substitute an
automatically operating system or a system which needs only an
initial impulse by the operator to operate automatically. Another
object is to reduce the consumption of energy without reducing
the effectiveness of the window heater.
The objects of the invention are accomplished, generally
speaking~ by using the aqueous deposit on the windshield to start
and stop the heating current. Thus, when the deposit of ice,
sleet, or snow forms on the outside of the windshield, or when a
condensate forms on the inside, the deposit itself initiates the
flow of current and its disappearance ends the flow until a new
deposit forms.
In this new system the current does not flow unless
it is really necessary and the overall consumption of energy
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is greatly reduced, which makes it possible to increase the speci-
fic intensity of the heating to reduce the deposit more quickly
without increasing the overall consumption, or to increase the
area of surface being heated with equal advantage.
In theory one should select, as the criterion for the
contro] apparatus, the nature and amount of deposit to be remoYed
from the window by heating, whether ice, frost, snow, sleet, or
condensate, and should use electrodes appropriate to the condi-
tions to be encountered. In vehicles one function is to keep
the window free of condensate, and for that purpose it suffies
to have the heating unit activated by the condensate itself, which
forms on the inner surface. The activating command is issued
eIectrically, sensitive electrodes mounted on the window, are ~-
electrically connected by the deposit, current flows, and the
flowing current causes to connect the heater to the poles of the ~-~
battery. In the preferred form, the current initiated by the
deposit flows to an amplifier which issues and amplified current
which activates a re~ay to close a switch which throws the full
current of the battery into the heater. When the deposit dis-
appears the initiating current is cut off, the relay ceases to
function, and the battery is cut off from the heater. The ampli-
fier is mounted in any convenient spot in the electrical system ;
of the car and may be of any appropriate type, the one in the
drawing being a four-stage booster of efficient design for this -
purpose.
In one form of the invention the sensor takes the form
of an aqueous switch composed of two electrodes or contacts
mounted side by side and close together on the surface of the
glass. When the glass is dry no current flows but as soon as
the deposit of condensate forms between the electrodes current
passes. Such eIectrodes may advantageously take the form of two
combs with intercalated teeth which are close together without
touching.
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The invention i8 particularly advantageous in combin-
ation with windows upon which heating circuits have been printed
and baked. The lines and electrodes of the sensor circuit can be
applied in the ~ame way o~ the same materials.
The above and further ob~ects and novel features of the
pre~ent invention will more fully appear from the following
detailed description when the same i8 read ln connection with the
accompanying drawings. It is to be expre~61y understood, however,
that the drawings are ~or the purpose of illustration only and
are not intended as a definition of the limits of the in~ention.
In the drawings, wherein like reference characters refer
to like parts throughout the several views,
FIG. 1 18 a diagrammatic view of a window with the
heating and sensor units applied to its face,
FIG ~ is a full scale view of a preferred form of
sensor;
FIG. 3 is a ~chematic wirlng diagram for the preferred
~orm of the invention3 and
FIG. 4 iB a schematic diagram in typical electrical
symbols o~ an amplifying circuit.
In FIG. 1 the window, 1, which could be the backlight
of an automobile has on its inner face the bus bands or terminals
2,3 connected by the heatiDg lines 4, the whole forming a heating
grid deposited by printing, for example made of a known type of
low melting frit mixed with silver, which is readily applied,
for example by the silk screen techni~ue. Such conductors are
applied to the surface of the glasæ and baked on, advantageously
during a thermal treatment such as precedes the bending or
tempering of the glass. Below the heating grid and parallel to
the lines 4 are disposed similarly constituted lines 5, 6 having
overlapped ends 5~, 6~ which are spaced slightly apart and
constitute electrodes capable of interconnection by any aqueous
deposit which touches them both Line 6 is connected to bus
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band 3, and through it to one pole of the car battery, and line 5
is connected to a contact 8, separate from bus band 2. The con-
tact 8 i5 connected to the other pole of the car battery through -~
the windings of a relay ll(best seen in Fig. 3) which activates
a switch 12, normally biased to inoperative position, in a line
connecting the battery to bus band 2. Thus, when an aqueous
deposit such as condensed moisture from the air covers the gap
between the electrodes the current of the battery is turned into
the heating unit, and when the heating unit has dissipated the
deposit the current no longer flows through the heater as the
current no longer passes from 5' to 6', the relay being deacti-
vated and the spring-biased switch springing to open position,
breaking the line between the battery and the heater.
The sensor should be placed in a place on the window
rather close to the heater so that the heater will aid in clear-
ing the gap. The system will normally be placed on the inside
of the car window, which has the advantage of deYeIoping the
heat first on the face of the glass which~must be kept free from
condensate. In that arrangement the sensor is controlled by the
condensate alone, but in other cases the sensor may be placed
outside while the heater remains inside so as to be activated ~ -
during rain, snow, or sleet; or sensors may be connected in par-
allel, one outside and one inside so that activation is either
by aqueous condensation inside or aqueous deposit outside. In
systems, wherein thé heating means is embedded between the outer
and inner layers of a laminated windshield, the sensors can be
placed either on the inside or the outside face of the windshield,
or both. Printed and baked lines are equally useful in cases
wherein the heater is an interlayer in a laminated windshield
or is embedded in the interlayer of such a laminate.
It is to be noted that this invention is equally appli-
cable to walls which are not transparent but which must be kept
clear of steam, mist and deposits dissipable by heat.
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In Fig. 2 is shown at 7 a preferred form of sensor.
The conductors 5 and 6 are attached to relatively wide transverse
conductors or bus bands 5a and 6a, from which extend a series of
finer interlineated conductors, Sb and 6b in straight lines which -~ ~
do not touch. In one case the space separating conductive lines ~ -
5b and 6b was on the order of 0.2mm. the spacing from the center
of one line to the center of the adjacent line being adjacent
line being shown as 1 mm. on the drawing. In other cases the
spacing may well be different to conform to different conditions
and different sources of power. In the particular case illust-
rated as soon as a deposit of condensate sufficient to obscure
vision is deposited on the glass of the sensor or aqueous switch,
the electrical lmpedance decreases enough under the influence of
the humidity at the sensor to permit a current to flow from con-
ductors 5 to 6 closing the reIay switch controlling the heater.
It can be helpful to roughen the sur~ace of the glass to which
the sensor is applied, for instance by a sand blast, to make it
more hydrophilic. Other means may also be adopted to make the
sensor more hydrophilic and hence more responsive,
In Fig. 3 is shown a complete system for a car window.
The plus side of the battery is connected to a manual switch 13
which is used by the operator to actiYate the system, which
thereafter is controlled by sensor 7. The plus line is thus
connected to relay switch 11-12, the blade of which is spring
blased to open position and closed by reIay coil 11. The reIay
coil is connected to the plus-and minus poles of the battery
through an amplifier 10 and the sensor 7. When the lines of the
sensor are bridged by an aq~eous deposit, current flows through
the relay coil and closes switch 12; the battery current then ~-
acti~ates the heater 2, 4, 3 and heating continues until the
surface of the sensor is dried by heat, whereupon the current
ceases to flow through the relay, the switch 12 springs to open
position, and the system becomes inoperative until the sensor
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10461Z~
is again activated.
In Fig. 4 is schematically presented an amplifier of
four stages between the sensor and the relay. The various in-
struments in the amplifier are indicated by standard symbols
which will be comprehensible to persons familiar with booster
circuits and electrical symbology. It is to be understood that ~;
this amplifier is representative of a number of useful types.
The amplifier of the drawing is constructed so that
for a current of abbut 20 to 30 microamperes in conductor S the
relay 11 is excited to close the switch blade 12. When the elec-
trical resistance between the electrodes of sensor 7 attains a -~
Yalue of about 6 x 105 ohms as the deposit is evaporated by heat, ~; ;
the relay is cut off and the switch 12 opens. The reIay in this ~ -
case is constructed to operate again when the resistance in the
sensor drops to about 5 x 104 ohms. The whole system is cut
off by opening switch 13.
The advantages of the system are many. It can;be
constructed to accommodate any source of power and to any degree
of sensitivity. The width of the gap in the sensor will affect
sensitivity, which can also be affected by making the sensor
surface more or less hydrophilic. It will respond to any aqueous
deposit.
As many apparently widely different embodiments of
the present invention may be made withbut departing from the
spirit and scope thereof, it is to be understood that the
invention is not limited to the specific embodiments. What is
claimed is:
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