EP1540994A2

EP1540994A2 - Heated glazing for a vehicle

Info

Publication number: EP1540994A2
Application number: EP03784186A
Authority: EP
Inventors: Dominique Glaverbel COSTER
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 2002-08-05
Filing date: 2003-08-04
Publication date: 2005-06-15
Also published as: AU2003266260A1; BE1015056A3; AU2003266260A8; WO2004016043A3; WO2004016043A2

Abstract

The invention relates to glazings that are part at least of the roof or top of vehicles. The inventive glazings have light transmission of less than 40 percent and are provided with heating means, such as thin wire conductors, screen printed wires, or thin conducting layers. Said heating means are sufficiently powerful to maintain the side of the glazing, which faces the passenger compartment, at a temperature that is about the same as the average temperature of the atmosphere in the passenger compartment.

Description

Heated glass for vehicle

The invention relates to glazing, which constitutes at least part of the roof or, roof, of vehicles.

Car manufacturers are directing their production towards vehicles which have an increasing surface area of glass walls. This trend, which first affected the windshields and rear windows of vehicles, was continued by the parts constituting the roof of these. Opening roofs were the first to benefit from this development. In this case, the glazing used had relatively limited dimensions.

The properties required at this stage of this evolution were essentially optical. The glass roof had to offer sufficient light transmission to produce the impression of “light opening”, but this same transmission had to remain within certain limits to keep the interior “private”.

Builders have more recently undertaken to develop models whose roof is mainly made up of glazing. These glazings are either in one piece or composed of several elements juxtaposed or not. Some of these glazings can be movable to release openings, others are fixed.

The increase in the glass parts of the roofs raises new problems. Among these, there is the question of their mechanical strength and the safety of these walls. This question arises all the more since the first achievements in this area called for tempered monolithic glazing.

To improve the mechanical resistance, it has been proposed to replace the toughened glazing with laminated glazing, of the type widely used for the composition of windshields, while however modifying the characteristics of light transmission. The windshields must indeed have, according to the standards in force, a transmission which is not less than 75 or 70% depending on the countries considered. Roofs, as shown, should have a much lower transmission. But ^the increase in glass surfaces, especially when the surfaces are not open, the problem of the passenger compartment heating particularly under the effect of solar radiation. The limitation of light transmission, however it is achieved, is automatically accompanied by a simultaneous limitation of energy transmission. However, specific measures are most often necessary to achieve a sufficient reduction in this energy transmission.

Other problems have also arisen which relate to the color of the transmitted radiation. For the approval of the occupants of the vehicle, it seems important that the passage of solar or artificial radiation through the glazing constituting the roof does not unpleasantly change the colors inside the passenger compartment, regardless of the qualities of transmission energetic and bright. Patent application EP 1 200 256 proposes in particular glazing units meeting this set of characteristics. In the previous developments, most of the efforts have focused on the selectivity of the transmission, in other words on the relationship between light transmission and energy transmission, the most interesting being to achieve the best possible selectivity. To improve this selectivity, two parameters have been systematically considered, the intrinsic selectivity of the glasses forming part of these glazings, in particular by an appropriate choice of compounds coloring these glasses, and the introduction into these glazings of dividers or of limiting, reflecting layers. or absorbing incident energy radiation.

Experience has shown that the presence of these roof glazing still poses comfort problems for passengers when the outside temperature is significantly lower than that of the passenger compartment. In this case, the presence of this surface, which is at least partially transparent to the radiation emanating from the passenger compartment, leads to the sensation which is sometimes described as "cold shoulder". Without the mechanism which leads to this inconvenience being perfectly identified, it is well known and becomes all the more troublesome the larger the area concerned. To avoid this inconvenience, the inventors propose to have on these glazings constituting at least part of the vehicle roof, means to ensure their heating. To avoid this unpleasant feeling, the heating of the glazing is preferably such that it leads the wall of the glazing facing the interior of the passenger compartment to a temperature close to that of the atmosphere of the passenger compartment or even slightly higher , so that the energetic radiation emitted by this wall towards the interior of the vehicle is of comparable size to that of the radiation which is emitted from the passenger compartment outside the vehicle.

In practice, the heating of the roof glazing is obtained electrically, by the Joule effect. The means used for heating these windows

10 roof, are more diverse than those implemented in particular for the heating of windshields, for the latter, in fact, the need not to significantly alter the field of vision of the driver or even that of passengers, limit the heating means in use, either of extremely thin wires, or of transparent conductive layers.

1.5 The transparent layers maintain perfect uniformity of transmission in the glazing, but their use can raise problems in terms of regulatory light transmission threshold. For the same applied voltage, the power delivered is higher the lower the electrical resistance of the layer. If the power must be relatively high, the resistance 0 must be low. The resistance of the layers depends, among other things, on their thickness. To have a low resistance, a solution therefore consists in increasing the thickness of the layer. Even if we speak of "transparent" layers, the conductive layers do not exhibit total transmission, and this is all the more reduced as the layer is thicker. 5 The heating of the side windows of vehicles, for similar reasons, is also subject to limitations, even if the light transmission may be slightly less than for the windshield, in particular as regards the side windows corresponding to the seats from the rear of the vehicle.

In the case of side glazing, the relatively limited dimensions 0 mean that the resistances usually remain in Umites for which, to obtain a sufficiently low resistance, the thickness of the layers does not pose of difficulty. For windshields obtaining a sufficiently low resistance is more difficult, particularly due to the constant increase in dimensions on the most recent models. For roofs, the dimensions are of the order of those of windshields or even greater. The characteristics of the heating elements used in roofs, fortunately, are not conditioned by light transmission requirements. The layers used, whatever their thickness, are not such that the light transmission is adversely affected. The difficulty in the case of roofs can, where appropriate, for thin heating layers, come from the usual limits of deposition techniques. For the constitution of the conductive layers of glazing for heated roofs, the usual techniques and materials for the formation of similar layers on glazing such as windshields can be used. It is also possible to use layers usually intended for building glazing. Common layers are especially metallic layers and particularly silver layers. It is also possible to use doped tin oxide type layers or any other conductive layer usually used on glazing.

Preferred layer stacks are for example those with a double layer of silver having a structure of the type: dielectric / argeni / dielectric / dielectric silver

The conductive metal layers are usually formed by vacuum deposition techniques. These layers are relatively fragile and, for this reason, preferably, are located on the faces of the glass sheets which are not exposed, in other words, they are preferably on the faces turned towards the interlayer of the laminate. If layers of this type are used on monolithic glazing, they are placed on your side facing the passenger compartment and, preferably, are protected by a dielectric layer resistant to abrasion.

Very fine filaments are another way of forming the heating elements of roofs. The practice of using these threads leads to introducing them into ύes laminated glazings, preferably in direct contact with one of the glass sheets and embedded in the polymer interlayer sheet. As for use in other glazing, these are wires, for example tungsten, of very small diameter, of the order of ten micrometers. The wires are spaced a few millimeters apart. Preferably they are wavy.

It goes without saying that the wires which can be integrated into the windshields can also be used in roof glazing without causing vision problems.

Other types of heating means are usually used on glazing such as rear glasses. These are networks of wires obtained by firing conductive paste enamels, applied by screen printing. These means have the advantage of having good mechanical strength. For this reason, the wires thus formed are often exposed on the face of the glazing facing the passenger compartment, without the interposition of additional protection. It is therefore a solution which can be advantageous in the case of monolithic glazing. In all cases, the wires formed from conductive enamels have the disadvantage of being much more apparent with respect to fine metal wires. The usual width of these screen-printed wires is usually of the order of 0.5 to 0.8 mm. These dimensions are acceptable on the rear glasses of vehicles. However, even for this use, the manufacturers want these wires to be as discreet as possible. Wires as thin as 0.3mm or less are now available.

For the roofs of motor vehicles the laminated glazings previously proposed, are in particular those which are the subject of publication WO 01/02167. These glazings have assemblies of glass which contain various coloring agents intended to favor, on the one hand, a lowering of the energy transmission TE, and, on the other hand, a control of the light transmission while retaining control over the color of the light transmitted in the passenger compartment. The energy transmission is kept as low as 15% or less and the light transmission for the examples given is less than 25%. Furthermore, it is provided in this patent that the glazing constituting the roof may also include thin layers on one or the other of the glass sheets, so as to better control the opto-energetic characteristics thereof. By way of example, the use of sunscreen layers, in particular based on metals such as silver, or on materials such as tin oxide doped with fluorine or antimony. These layers which make it possible to control the energy and light transmission in the passenger compartment, also offer the advantage of being able to serve as a heating layer for the glazing units considered insofar as they are also conductive. Answering the most delicate problems attached to these glazings, namely, on the one hand the control of the solar energy supply, and on the other hand the maintenance of comfort in winter, they therefore constitute particularly satisfactory solutions.

Analysis of the factors that determine thermal comfort in the passenger compartment when the outside temperature is significantly lower than in the passenger compartment, shows that the heat flux exchanged, whether by radiation, convection or conduction, is fundamental, and that this flow can be regulated by means of a roof which is electrically heated, whether the heating is carried out by means of fine wires or by means of thin conductive layers.

In practice, as a first approximation, it can be estimated that maintaining the glazing constituting the roof of the vehicle at a temperature close to that established in the passenger compartment by means of “air conditioning” or simple heating, makes it possible to eliminate the feeling of ^“ cold wall qe one can experience ^" eh the absence ^" of the control of this temperature.

In practice, efforts are made to ensure that the temperature of the internal face of the glazing is not more than 10 ° C. below the average temperature of the atmosphere in the passenger compartment, and preferably is not lower. over 5 ° C.

Various factors intervene which determine the temperature of the roof glazing, among these are mainly the difference existing between the temperature in the passenger compartment and the outside temperature, and also significantly the speed of movement of the vehicle which obviously increases the convection exchanges.

Other factors also come into play, such as exposure to solar radiation, which acts, through the greenhouse effect, independently of atmospheric temperature. To obtain permanent comfort, it is necessary to adapt the thermal contribution resulting from the heating of the glazing of the roof, to the variations of the conditions. of vehicle use. A simple mode of regulation consists in imposing a temperature on the internal face of the roof glazing, which is substantially equal to the average temperature in the passenger compartment. In this case, sensors determine the two temperatures. The received signals are then compared and are used by a circuit for controlling the power supply to the roof heating circuit until the temperature of the roof is brought back to a temperature closer to that of the passenger compartment. The regulation can be adjusted in a more elaborate way to take into account if necessary the sunshine. In this case, the sensors still determine the influence of solar radiation inside the vehicle, to establish the control instructions for the regulation of the roof heating.

It goes without saying that the power available for heating the roof must be sufficient to allow the regulation envisaged under all the usual conditions of use. The power depends not only on the heated surface, but also on the climatic conditions in which the use of the vehicle is located. Given the uses envisaged, in temperate climates, the power delivered is advantageously between 400 and 1500w / m ² .

The invention is described in more detail using examples of implementation of heated roofs.

The attached single figure illustrates the thermal behavior of various types of roofs, under various conditions of use.

A motor vehicle is equipped with a roof whose surface is approximately 1.2 m ² . To determine the influence of various kinds of roofs successively tested, the vehicle is placed in a chamber thermostated at a temperature of -18 ^C C. The blower associated with the enclosure makes it possible to recreate the conditions of movement of the vehicle. The conditions are set using a dynamometer inducing a rolling resistance corresponding to the chosen speed. The reported tests are carried out for conditions corresponding to speeds of 50km / h for the first 30 minutes, and 80km / h for the rest of the tests.

Under the conditions of the tests, the balance of the thermal flows from the interior of the vehicle to the exterior is measured, and vice versa. We consider under these conditions the differences existing in the balance of flows according to the nature of the roofs subjected to these tests.

Measurements are made successively for a metal roof lined with a fibrous facing (curve 1), a laminated glass roof made up of two glass sheets of 2.1 and 2.1 mm thick respectively, assembled using a 0.76mm thick poly-vinyl but ral (PVB) interlayer sheet (curve 2), and of the same roof consisting of laminated glazing additionally comprising a conductive heating layer delivering two constant powers (765 curve 3, and 920 curve 4). The conductive heating layer consists of a stack of layers such as: dielectric / dielectric argeni / argenVdielectric

This type of stacking is used in particular to form heated windshields. The comparison between the metal roof and the simple laminated glass roof clearly shows a difference which corresponds to a significantly higher loss in the case of glazing. This explains the feeling of cold felt by the occupants.

Conversely, the heated roof allows to find the same characteristics as for the metal roof for a power of 765w. For a delivered power of 920, taking into account the surface of the roof, the flux balance is even slightly higher for the heated glazing compared to the metal roof, for the simulated speed conditions. This power is therefore likely to maintain the same comfort conditions for even higher speeds.

Heating the roof glazing according to the invention therefore makes it possible, while retaining the glazing of roofs the properties which make them choose instead of traditional roofs, to avoid the thermal discomfort which was linked to the use of these roofs glazed.

A determination of the thermal comfort perceived by passengers is carried out in the cabin of the experimental vehicle. The determination is made according to the protocol of ISO standard 10551. These are subjective evaluations carried out on a diversified sample of individuals. The tests are carried out on the one hand with the vehicle equipped with non-heated roof glazing, on the other hand with the same vehicle equipped with the heated roof delivering a power of 765. The assessment is made for the stationary and moving vehicle.

There is a significant difference in the assessments made. The glazing heat, compared to non-heated glazing, has a positive difference varying from 0.5 to 2 points, depending on traffic conditions, on the comfort scale which is set from 0 to 9. The most noticeable difference is noted for the stationary vehicle. The "subjective" assessment therefore confirms the advantage conferred by the use of heated roof glazing according to the invention.

Claims

1. Roof glazing for motor vehicles with a light transmission of less than 40%, provided with heating elements of sufficient power to keep the side facing the passenger compartment at a temperature close to the average temperature of the atmosphere in the passenger compartment, whatever the outside temperature, and whatever the dimensions of the glazing.

2. Glazing according to claim 1 wherein the heating elements have sufficient power to be able to maintain the temperature of the face of the glazing facing the passenger compartment, at a temperature which does not deviate by more than 10 ° C from the temperature average cabin atmosphere. 3. Glazing according to claim 1 wherein the heating elements have sufficient power to maintain the temperature of the face of the glazing facing the passenger compartment, at a temperature which does not deviate by more than 5 ^α C from the temperature average cabin atmosphere.

4. Glazing according to one of the preceding claims comprising a circuit for regulating the power delivered by the heating elements as a function of the measurements made by temperature sensors arranged on the one hand on the internal face of the glazing, and on the other bet in the passenger compartment,

5. Glazing according to one of the preceding claims, consisting of an assembly of two glass sheets joined by means of an interlayer sheet of thermoplastic material, at least one of the glass sheets bearing on its face in contact with the interlayer , a set of thin layers including at least one conductive layer.

6. Glazing according to claim 5 in which the set of thin layers comprises at least one silver-based layer 7. Glazing according to claim 6 in which the set of thin layers comprises the sequence: dielectric / dielectric silver / silver diétectrique. S. Glazing according to one of one of claims 1 to 4 formed of a single sheet of tempered glass, which comprises on the face facing the passenger compartment a set of thin layers including at least one conductive layer.

9. Glazing according to one of claims 1 to 4, consisting of an assembly of two glass sheets joined by means of an interlayer sheet of thermoplastic material, in which the heating elements are fine conductive wires arranged at the interface between the interlayer sheet and one of the glass sheets. 10. Glazing according to one of claims 1 to 4, wherein the heating means are constituted by a network of wires obtained by cooking a conductive paste forming a conductive enamel after cooking.