GB2054329A

GB2054329A - Heatable mirror

Info

Publication number: GB2054329A
Application number: GB8022322A
Authority: GB
Original assignee: NKF Groep BV
Current assignee: NKF Groep BV
Priority date: 1979-07-11
Filing date: 1980-07-08
Publication date: 1981-02-11
Also published as: FR2460806A1; IE801414L; FR2460806B1; GB2054329B; DE2927954A1; DE2927954C2; IE49852B1

Abstract

In a heatable mirror, a PTC- resistor 12 is arranged as a heating and control element in the interior of the mirror housing 2, the resistor applying its heat indirectly to the back 6 of the mirror glass 4 via a heat-conductive member 7. The mirror may be exposed to the weather, as is the case for an outside rear view mirror of a motor vehicle. <IMAGE>

Description

SPECIFICATION Heatable mirror The invention relates to a heatable mirror, such as a rear view mirror for motor vehicles, whose mirror glass is heated by a heating element with controllable heat capacity.

It is known to heat mirrors which are exposed to the weather, for example outside rear view mirrors of motor vehicles, electrically to prevent or eliminate fogging, wetting, coating with ice, etc.

Various heating elements have already been proposed for this purpose. The heating element may be provided in, for example, the form of a layer of a conductive synthetic material, a conductive paste and such-like, deposited on the back of the mirror glass by means of printing, spraying or painting, as in the published German Patent Application DE-OS 27 1 9 1 74. It has already been proposed to use an incandescent bulb or such-like, arranged in the housing of the mirror and which applies its heat through an air gap, provided for that purpose, to the mirror glass, as in published German Patent Application DE-OS 27 24 018.

No control of the heat has been provided in the two above-mentioned cases. This may result in that the heating element cannot deliver a sufficient quantity of heat at very low temperatures or that the heating element and/or the mirror is damaged at high temperatures. To avoid these disadvantages it has already been proposed to glue a strip of heating foil onto the surface te be heated and to arrange a thermostat in the immediate vicinity of the surface to be heated, as in published German Patent Application DE-OS 26 45 231. In such an arrangement, the thermostat adjusts the thermal capacity of the heating element between a minimum and a maximum temperature.However, this requires two electric elements, namely the heating foil and the thermostat; both elements must be connected to the mirror glass in such a way that an adequate heat conduction is ensured and both elements must also be connected electrically to the current supply. The floor heating control which is disclosed in the published utility model DE-GM 75 35 771 has a similar construction. Finally, it has already been proposed for use for a heating plate the arrangement of several PTC-conductors in the form of rectangular rods as the heating resistors, as in published German Patent Application DE-AS 12 86 242.

It is an object of the invention to provide a heatable mirror with little cost and effort and having an arrangement which ensures a controlled heat production and discharge for a long period of time.

According to the invention, there is provided a heatable mirror, such as a rear view mirror for motor vehicles, whose mirror glass is heated by a heating element with controllable heat capacity, characterized in that the heating element comprises at least one PTCresistor which is arranged in an indirect heat contact with the mirror glass by means of an intermediate heat-conducting member.

According to the invention there is also provided a heatable mirror such as a rear view mirror for motor vehicles, whose glass is heated by a heating element with controlled heat capacity, characterized in that the heating element is a PTC-resistance body, which is in an indirect heat contact with the mirror glass.

To ensure a suitable heat distribution over the mirror area, which is particularly required for large mirrors, for example for trucks, a heat distribution plate may be arranged between the back of the mirror glass and the PTC-resistor which in a primary contact area is connected in a heat-conducting manner to the PTC-resistor. To improve the heat distribution, the primary contact area of the heat distribution plate extends approximately parallel to the mirror glass and connected via at least one connecting strip to at least a secondary contact area, which also extends approximately parallel to the mirror glass and is connected in a heat-conducting manner to the mirror glass. For rectangular mirrors in particular, the heat distribution plate may be in the form of a gutter by means of a corresponding arrangement of the contact areas and connecting strips.In a corresponding manner, the heat distribution plate may be in the form of a dish for a round mirror by means of a corresponding arrangement of the contact areas and connecting strips. For larger mirror surfaces, for example, for traffic mirrors of a large surface area, several PTC-resistors may be used. In these cases the heat distribution plate may either have several gutter-shaped or dish-shaped recesses, or several heat distribution plates, it being possible that two or more PTC resistors are arranged on one heat distribution plate. The PTC-resistor may be soldered on the heat distribution plate and the heat distribution plate may be glued to the mirror glass.

The invention ensures a suitable controlled heat generation and distribution for a long period of time, namely during the service life of the mirror. The invention can be realised without a great deal of technical effort and with little cost. It is limited to only a few electrical contact areas, which are possible sources of faults, and does not require electromechanical controls which are subject to wear. Various embodiments are possible and the invention can be easily adapted to the most diverse requirements.

An embodiment of the invention will now be described in detail with reference to the accompanying drawings, of which: Figure 1is a cross-sectional view, on the line I-I of Fig. 2, of a rear view mirror according to the invention, intended for a motor vehicle, and Figure 2 is a view in the direction indicated by means of arrow S in Fig. 1 of the back of the mirror glass, the housing which contains the mechanical and electrical connections having been omitted.

Mirror 1 has a housing 2 made of a suitable material, for example plastics material or sheet metal. Housing 2 is dish-shaped and is provided with an inwardly-directed lip 3. The housing 2 holds a mirror glass 4 by means of a peripheral seal 5, consisting of rubber or such-like, located between the mirror glass 4 and the lip 3.

A heat distribution plate 7 made of metal is glued to the back 6 of the mirror glass 4. By means of a punching-bending operation this plate is given the form of a gutter so that a central, primary contact area 8, two connection strips 9 and 9a connected thereto and two secondary contact areas 10 and 1 0a are produced on the back 6 of the mirror. The areas 8, 10 and 1 0a extend parallel to the mirror glass 4, while the connecting strips 9 and 9a extend at an angle of approximately 45 to the mirror glass 4. A disc-shaped PTC resistor body 1 2 is soldered, by soldered connection 13, to the side 11 of the heat distribution plate 7 which faces away from the mirror glass 4.Current is applied via an electric conductor 14, to which the PTC resistor 1 2 is connected by means of a soldered connection 1 5. The conductor 14 is connected to the current source, not shown, of the motor vehicle, preferably via the ignition switch of the vehicle. The second electrical connection to the PTC resistor 1 2 is made by means of the soldered connection 16, from which a conductor 1 7 leads to a soldered or clamped connection 18 on a contact washer 1 9. The contact washer 1 9 is clamped between the housing 2 and the head of a hollow threaded bolt 20 which extends through a hole 21 in the housing 2. The mirror 1 is secured to the vehicle body by means of thebolt 20.The conductor 14 is passed through the bore of the hollow bolt 20 to the current supply of the vehicle, while the conductor 1 7 is electrically connected to chassis of the vehicle via the bolt 20 and the washer 19.

The cavity inside the housing 2 may be filled with a thermally-insulating material. Alternatively or additionally, the material of the housing itself may be made of a thermally-insulating material, or the material of the housing may be internally coated with such a material.

The mirror heating system functions as follows. When the vehicle is started by means of the ignition switch, the mirror heating is switched on simultaneously. The PTC-resistor 1 2 consumes approximately 25 W until it reaches a temperature of approximately 1 0O'C, the temperature at the back of the mirror then being approximately 50"C. Then the heating automatically switches to a lower power consumption of approximately 5 W.

This range may be denoted the stand-by range. Rain, frost, fog and such-like produce a decrease in temperature as they withdraw energy due to evaporation, which cools PTCresistor 1 2 and causes it to switch back to its higher power consumption. The electric heating energy then supplied causes the mirror to clear again within a short period of time. In motor vehicles a PTC-resistance element may be used which has a resistance in the range from approximately 3 to 6 Ohm at temperatures below about 100"C and a resistance of about 100 Ohm at temperatures and at high temperatures a high-resistance above approximately 100 Ohm.

Although the above-described embodiment relates to a heatable mirror having a single PTC-resistor and a single heat distribution plate, other embodiments may of course include a plurality of such PTC-resistors mounted on one or more said heat distribution plates-the number of each largely depending on the area of the mirror concerned.

Claims

1. A heatable mirror, such as a rear view mirror for motor vehicles, whose mirror glass is heated by a heating element with controllable heat capacity, characterized in that the heating element comprises at least one PTCresistor which is arranged in an indirect heat contact with the mirror glass by means of an intermediate heat-conducting member.

2. A mirror as claimed in Claim 1, characterized in that the said member is a heat distribution plate arranged between the back of the mirror glass and the PTC-resistor, a first portion of which plate is connected in a heatconducting manner to the PTC-resistor, and one or more further portions of which are connected to the back of the mirror glass in a heat-conducting manner.

3. A mirror as claimed in Claim 2, characterized in that the said first and further portions extend substantially parallel to the mirror glass and the first portion is spaced from the back of the mirror glass.

4. A heatable mirror such as a rear view mirror for motor vehicles, whose glass is heated by a heating element with controlled heat capacity, characterized in that the heating element is a PTC-resistance body, which is in an indirect heat contact with the mirror glass.

5. A mirror as claimed in Claim 4, characterized in that a heat distribution plate, which is connected in a primary contact area in a proper heat-conducting manner to the PTC resistor is arranged between the back of the mirror glass and a flat PTC-resistor.

6. A mirror as claimed in Claim 5, charac terized in that the primary contact area of the heat distributing plate extends approximately in parallel with the mirror glass and is connected by means of at least one connecting strip to at least one secondary contact area which also extends approximately in parallel with the mirror glass and is connected to the mirror glass in a heat-conducting manner.

7. A mirror as claimed in Claim 6, characterized in that the heat distribution plate is gutter-shaped by means of a corresponding arrangement of the contact areas and connecting strips.

8. A mirror as claimed in Claim 6, characterized in that the heat distribution plate is dish-shaped by means of a corresponding arrangement of the contact areas and connecting strips, respectively.

9. A mirror as claimed in any of the Claims 4 to 8, characterized in that two or more PTC resistors are provided.

10. A mirror as claimed in any of the Claims 6 to 9, characterized in that two or more heat distribution plates are provided.

11. A mirror as claimed in the Claim 9 as dependent upon Claim 7, characterized in that each heat distribution plate forms two or more gutters.

1 2. A mirror as claimed in the Claim 9 as dependent upon Claim 8, characterized in that each heat distribution plate has two or more dish-shaped recesses.

1 3. A mirror as claimed in any of the Claims 2 to 12, characterized in that the PTCresistor is soldered to the heat distribution plate and that the heat distribution plate is glued to the mirror glass.

14. A heatable mirror substantially as herein described with reference to the accompanying drawings.