GB2303465A

GB2303465A - Mirror electrically heated through its reflective layer

Info

Publication number: GB2303465A
Application number: GB9514805A
Authority: GB
Inventors: Eric Arthur Branson; Teresa Mary Gray
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1995-07-19
Filing date: 1995-07-19
Publication date: 1997-02-19
Also published as: GB9514805D0

Description

A Mirror Assembly The present invention relates to heated mirror assemblies, such as those used for vehicle door mirrors.

Generally heated mirrors comprise a layer of metal, such as silver or chrome, on glass, with a heating element behind the glass. These mirrors are heavy and use a large amount of electrical power to heat up sufficiently to demist or defrost.

The present invention provides a mirror assembly comprising an electrically non-conductive support member with a layer of reflective, electrically conductive material thereon forming the reflective surface of the mirror, and electrical contacts for passing electrical current through the layer of reflective material to heat said layer.

Preferably the layer of reflective material is provided on the front surface of the support member. This means that the support member does not need to be heated up to demist or defrost the mirror. In this case the support member is preferably made of material which is a poor heat conductor, such as plastics, although other materials such as glass could also be used.

Alternatively the reflective material can be provided on the rear surface of the support member, which may then advantageously be made of glass to provide good optical characteristics.

The layer of conductive material is preferably applied to the support member by electro-coating. This enables the layer to be made thin enough for the electrical resistance to be high enough to provide sufficient heating. Preferably the layer is aluminium which has a suitably high resistivity.

Preferably said reflective layer comprises one or more bands, the length of which is greater than the length of the mirror. This means that the resistance of the layer is increased which increases the heating provided for a give voltage supply.

Preferably said layer comprises a single band forming substantially the whole of the reflective surface and having one of the electrical contacts at each end.

A preferred embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings of which: Figure 1 shows a mirror assembly according to the present invention, and Figure 2 is a section through the mirror assembly of Figure 1.

A vehicle door mirror assembly comprises a plastics support layer 10 which has a flat front surface 12 onto which a layer 14 of aluminium 10 zm thick has been applied by electroplating. A series of parallel lines 15 are scribed through the aluminium layer 14 so that the layer is divided into a single long strip 16 which follows a labyrinthine path across the support member 10. Electrical contacts 18, 19 are connected to each end of the strip so that an electrical current from the vehicle battery 20 can be supplied to the strip 16 through a switch 21. A layer 22 of transparent plastics material is applied over the aluminium layer 12 to protect it from water and scratching.

In a specific example, if the mirror is lOOmm by 150mm and the lOym aluminium layer is divided into a strip lmm wide, the amount of heating power provided from a 12V vehicle battery would be about 3.4W. This could heat a 10m layer of water covering the mirror by 200C in about 4 seconds, and thaw the same amount of ice in about 15 seconds.

The use of plastics for the support member provides good electrical insulation for the aluminium layer, and also benefits from being a poor conductor of heat. This means that the heat produced is almost all used for demisting or defrosting the mirror and is not used up in heating the support member. The protective layer is made very thin, and of a material of low heat capacitance, so that it will not need much heat to raise its temperature to demist or defrost the mirror.

In some circumstances it may be preferred to use glass for either one or both of the support layer and the protective layer of the mirror. This is because glass can generally provide a better surface quality. This could be done by a substitution of glass for plastic in the embodiment described above. Alternatively the metal layer can be applied to the back of a layer of glass which can then act as the support member and the protective layer.

The glass can then be attached to a mounting member such as a plastics layer by means of adhesive or other suitable means. If the mirror is curved, for example being convex so as to provide a wide range of vision, the plastics layer can be shaped to the same shape as the glass. This arrangement has the advantage that the optical quality of the mirror is the same as conventional glass mirrors, but the glass layer can be made very thin so the thermal capacity of the assembly is very low.

Claims

1. A mirror assembly comprising an electrically non conductive support member with a layer of reflective, electrically conductive material thereon forming the reflective surface of the mirror, and electrical contacts for passing electrical current through the layer of reflective material to heat said layer.

2. An assembly according to claim 1 wherein said layer is applied to the support member by electro-coating.

3. An assembly according to claim 1 or claim 2 wherein the electrically conductive material is aluminium.

4. An assembly according to any foregoing claim wherein the electrically conductive material is applied to the front surface of the support member so that the top surface of the layer forms the reflective surface of the mirror.

5. An assembly according to claim 4 further comprising a transparent protective layer covering the layer of reflective material.

6. An assembly according to any one of claims 1 to 3 wherein the electrically conductive material is applied to the rear surface of the support member.

7. An assembly according to claim 6 wherein the support member is made of glass.

8. An assembly according to any foregoing claim wherein said layer comprises one or more bands, the length of which is greater than the length of the mirror.

9. An assembly according to claim 8 wherein said layer comprises a single band having one of the electrical contacts at each end.

l0.An assembly according to claim 8 or claim 9 wherein the band or bands are formed by removing lines of said conductive material from the support member.

ll.A mirror assembly substantially as hereinbefore described with reference to the accompanying drawings.