FR2698166A1 - Vehicle window surface temp. measuring process - using colour after heating of liquid crystal film on surface of vehicle window glass - Google Patents

Abstract

A vehicle window (2) is electrically heated by an array of resistance wires (3). The surface of the window is covered by a film of liquid crystal (1) which adheres to the window by an electrostatic effect. The liquid crystal film assumes colours corresp. to applied temperature. In operation, successive observations of the colours taken on by the liquid crystal film are made over a period representative of the deicing time. These observations are compared to previous calibrations and enable the deicing times for particular zones (Z1, Z2, Z3) to be determined. USE/ADVANTAGE - Measuring temp. of resistance heating window of vehicle. Liquid crystal film enables temp. to be measured at various points of vehicle window in very simple manner.

Description

METHOD FOR MEASURING THE SURFACE TEMPERATURE
OF A GLASS, PARTICULARLY WITH HEATING RESISTANCE.

OF A MOTOR VEHICLE.

The invention relates to a method for measuring the temperature on the surface of a window pane, in particular with heating resistance, of a motor vehicle.

The invention relates more particularly to a temperature measurement method which applies a liquid crystal film, the color changes of which correspond to changes in temperature.

The publication FR-2 247 927 describes a method for controlling a heating resistor in which a polarized scanning probe changes potential upon encountering a cut in the heating resistor and provides information on the presence of a fault.

This method does not, however, allow a temperature measurement.

The subject of the invention is a method of measuring the temperature on the surface of a window pane, in particular with heating resistance, which is very easy to use by depositing a liquid crystal film adhering to the window pane.

The subject of the invention is also a measurement of the temperature at various points of the window allowing observation and analysis of the variations in the temperature of said window.

According to the invention, the method consists in adhering a liquid crystal film to the glass, heating said glass and comparing the colors of the film with standard colors representative of the temperature.

The process thus carried out makes it possible, for example, to display at room temperature the distribution of the heating zones of the pane in very cold weather from a rise in temperature in correspondence with a change in color of the liquid crystals.

Other characteristics and advantages of the invention will appear on reading the description of an example of implementation of the method for a heating glass, with reference to the appended drawing in which: - Figure 1 is a schematic representation of a heating resistance glass on which the temperature measuring device is mounted.

A liquid crystal film 1 is placed on the surface of a pane 2 with a heating resistor 3 before the supply of said resistor 3.

The film 1 adheres to the window 2 by an electrostatic effect.

The liquid crystal film I, as described by way of example in publication US Pat. No. 3,782,119, consists of assemblies of encapsulated liquid crystals of different size and composition dispersed in a film-forming binder.

The composition of a given layer of encapsulated liquid crystals corresponds to a determined temperature and becomes colored when this temperature is reached.

It is thus possible to carry out a calibration of the colors reflected by the liquid crystals in correspondence with the desired operating temperatures of the window 2.

When the resistor 3 is supplied, the film 1 changes color as soon as one of the previously determined temperatures is reached.

The colors of film 1 obtained and compared to standard colors indicate the temperature at any point on the surface of the window 2 covered by the film 1.

The method according to the invention makes it possible to determine the defrosting time of zones Z1, Z2, Z3 of the window 2 following successive observations during a determined period.

Without departing from the scope of the invention and thanks to the flexibility of the film 1, the measurement method can also be implemented for checking a headlight or rear-view mirror.

Claims (2)

CLAIM 1) Method for measuring the temperature on the surface of a window (2), in particular with a heating resistance (3), of a motor vehicle which consists in adhering a film (1) with liquid crystals to the window (2), heating said window (2) and comparing the colors of the film (1) with standard colors representative of the temperature. 2) Method according to claim 1, characterized in that one makes successive observations of temperature variation of the film (1) during a determined period representative of the defrosting time of the window (2).