Heatable laminated vehicle window with improved heat distribution

Abstract

A heatable laminated vehicle window for separating a vehicle interior from an outer surrounding area is presented. The vehicle window includes an outer pane bonded to an inner pane via a thermoplastic intermediate layer. An electrically heatable coating of the vehicle window is electrically connected to two busbars such that by applying a supply voltage across the two bus bars, a heating current that forms heating field flows between the two busbars. In one aspect, a metal element is arranged on or in the vehicle window such that heat is dissipated out of a region of the heating field that has elevated heat generation by means of thermal conduction of the metal element.

Claims

1. A heatable laminated vehicle window for separating a vehicle interior from an outer surrounding area, comprising: an outer pane and an inner pane that are bonded to one another via a thermoplastic intermediate layer; an electrically heatable coating that is electrically connected to at least two busbars provided for electrical connection to two poles of a voltage source, so that application of a supply voltage to the two poles causes a flow of a heating current to form a heating field between the at least two busbars; and at least one metal element that is arranged on or in the vehicle window, so that heat is dissipated out of a region of the heating field with elevated heat generation by means of thermal conduction of the at least one metal element.

2. The vehicle window according to claim 1, wherein the at least one metal element is a foil, a sheet, or a cast part.

3. The vehicle window according to claim 1, wherein a projection of the at least one metal element onto the electrically heatable coating corresponds to a region of the electrically heatable coating having a heating power that, locally, is at least 15% higher than an average heating power of the heating field.

4. The vehicle window according to claim 1, further comprising a locally limited region arranged between the busbars that is free of the heatable coating, wherein the at least one metal element is arranged next to a side of the locally limited region in a direction of the flow of the heating current.

5. The vehicle window according to claim 4, wherein the at least one metal element comprises two metal elements, each arranged on a respective side of the locally limited region in a direction of the flow of the heating current.

6. The vehicle window according to claim 1, wherein the at least one metal element overlaps a contact point between a busbar of the at least two busbars and a supply line connected thereto.

7. The vehicle window according to claim 1, wherein the at least one metal element is laminated into the vehicle window.

8. The vehicle window according to claim 7, wherein the at least one metal element is arranged on the heatable coating.

9. The vehicle window according to claim 8, wherein the at least one metal element has an electrical insulating coating.

10. The vehicle window according to claim 7, wherein the at least one metal element is separated from the heatable coating by material of the thermoplastic intermediate layer.

11. The vehicle window according to claim 1, wherein the at least one metal element is arranged on an interior-side surface of the inner pane.

12. The vehicle window according to claim 11, wherein the at least one metal element is a sheet or a cast part that is designed with cooling ribs.

13. The vehicle window according to claim 1, wherein the at least one metal element is arranged in a region of the vehicle window that is provided with an opaque masking print.

14. The vehicle window according to claim 1, wherein the heatable coating is arranged on a surface of the outer pane or the inner pane facing the thermoplastic intermediate layer.

15. The vehicle window according to claim 1, wherein the heatable coating is arranged on a carrier film within the intermediate layer.

16. The vehicle window according to claim 1, wherein a busbar of the at least two busbars is implemented as one of: a) fired printing paste, and b) a strip of an electrically conductive foil.

17. The vehicle window according to claim 16, wherein a) contains silver particles and glass frits, and wherein b) contains copper.

18. A method for producing a heatable laminated vehicle window for separating a vehicle interior from an outer surrounding area, the method comprising: preparing an outer pane, a thermoplastic intermediate layer, and an inner pane, wherein one of the outer pane, the inner pane, and the intermediate layer is provided with an electrically heatable coating; connecting the electrically heatable coating to at least two busbars provided for electrical connection to two poles of a voltage source so that by applying a supply voltage to the two poles, a heating current flows between the at least two busbars thereby forming a heating field between the at least two busbars; and bonding the outer pane and the inner pane to one another via the intermediate layer by lamination; wherein before or after lamination, at least one metal element is arranged on or in the vehicle window thereby dissipating heat out of a region of the heating field with elevated heat generation by means of thermal conduction of the at least one metal element.

19. A method for using of a vehicle window, comprising: providing a vehicle window according to claim 1; and using the vehicle window in means of transportation for travel on land, in the air, or on water.

20. The method of claim 19, wherein the means of transportation comprises motor vehicles and wherein the vehicle window is used as a windshield.

Description

(1) They depict:

(2) FIG. 1 a plan view of an embodiment of the vehicle window according to the invention,

(3) FIG. 2 a cross-section along A-A through the vehicle window of FIG. 1,

(4) FIG. 3 a cross-section along A-A through another embodiment of the vehicle window according to the invention,

(5) FIG. 4 a cross-section along A-A through another embodiment of the vehicle window according to the invention,

(6) FIG. 5 a plan view of another embodiment of the vehicle window according to the invention,

(7) FIG. 6 a flowchart of an embodiment of the method according to the invention, and

(8) FIG. 7 a flowchart of another embodiment of the method according to the invention.

(9) FIG. 1 and FIG. 2 depict in each case a detail of a vehicle window according to the invention. The vehicle window is the windshield of a passenger car and is implemented as composite glass composed of an outer pane 1 and an inner pane 2 that are bonded to one another via a thermoplastic intermediate layer 3. The outer pane 1 and the inner pane 2 are made of soda lime glass and have a thickness of, for example, 2.1 mm. The intermediate layer 3 is formed from a PVB film with a thickness of 0.76 mm.

(10) A heatable coating 4 is applied on the exterior-side surface III of the inner pane 2. The heatable coating 4 is, for example, a stack of a plurality of layers, which includes three conductive silver layers that are separated from one another by a plurality of dielectric layers. The heatable coating is transparent such that vision through the pane is not impaired to an extent that the pane would be made unsuitable as a windshield. Two busbars 5, 6 are applied on the heatable coating 4 for its electrical contacting. The busbars 5, 6 are implemented as approx. 5-mm-wide strips of a printed and fired screenprinting paste with silver particles and glass frits. The first busbar 5 is arranged along and in the vicinity of the upper edge O of the vehicle window; the second busbar 6, along and in the vicinity of the lower edge U. In the installed position of the windshield, the upper edge O points upward (roof edge) and the lower edge U points downward toward the ground (engine edge). The busbars 5, 6, for their part, are electrically contacted to supply lines 9, via which the connection of the busbars 5, 6 to the polls of an external voltage source is realised. The supply lines 9 are or contain a conductive copper foil, which is placed on and, optionally, soldered on a region of the busbars 5, 6. The second busbar 6 along the lower edge U is contacted by two such supply lines 9.

(11) By means of the busbars 5, 6, the current is introduced into the coating 4, not at points, but rather distributed over the width of the busbars 5, 6. The current flows through the coating 4 in the region between the busbars 5, 6, whereby this region is heated, and a heating field that covers the central vision area of the pane is formed. The vision area can thus be freed of ice or moisture as needed.

(12) The coating 4 is applied on the entire surface of surface III, with the exception of a peripheral edge region with a width of 10 mm and a communication window 8. The communication window 8 is arranged in the heating field between the busbars 5, 6 in the vicinity of the upper busbar 5 and is a coating-free region. The communication window ensures the transmission of electromagnetic radiation through the vehicle window, which would otherwise be reflected by the coating 4. Thus, for example, a sensor mounted on the inner pane 2 or radio data communication in the vehicle interior can function.

(13) The heating power of such a pane is not homogeneous over the entire heating field. Instead, there are typically regions with elevated heat generation and regions with lower heat generation. The regions with elevated heat generation (hot spots) can, in the worst case, result in burns if the window is touched by a person, or even in damage to the window. The objective of the present invention is consequently to prevent the regions of elevated heat generation and to improve the homogeneity of the heating power.

(14) A region with elevated heat generation develops in the vicinity of the contact points between the supply lines 9 and the busbars 5, 6. A disproportionately large share of the flow of electrical current into the coating 4 occurs, in fact, at these contact points.

(15) In order to dissipate the heat out of the regions of elevated heat generation, the vehicle window has metal elements 7. The metal elements 7 are implemented as approx. 50-m-thick copper foil and laminated into the vehicle window, wherein they are arranged on the interior-side surface II of the outer pane 1, i.e., between the outer pane 1 and the thermoplastic intermediate layer 3. Such a metal element is associated with each contact point between the lower busbar 6 and the supply lines 9, and is arranged overlapping with the contact point and extends from there a few centimeters in the direction of the center of the pane. The projection of the metal element 7 onto the coating 4 yields a a surface section that includes the region of elevated heat generation and also a region with contrastingly lower heat generation. The metal element 7 is thermoconductive. It heats up in the region of elevated heat generation and dissipates the heat into the regions of lower heat generation. The heat distribution is thus homogenised and a dangerous hot spot is avoided in the region of the supply lines 9. In the region of the contact point between the upper busbar 5 and its supply line 9, a metal element 7, which is not shown in the figure for reasons of clarity, can, of course, also be arranged.

(16) Other regions of elevated heat generation occur in relation to the communication window 8. Since the current must flow around the communication window 8 next to it side, the flow of current is concentrated adjacent to the side edges of the communication window 8, where hot spots form. Therefore, another metal element 7 is arranged next to the communication window on both sides in the direction of flow of the current. The metal elements 7 have a distance of a few millimeters from the communication window 8 and extend a few centimeters from the communication window 8. By means of the metal elements 7, the excess heat can thus be dissipated out of the vicinity of the communication window 8, whereby the hot spot is prevented.

(17) The metal elements and also the busbars 5, 6 are arranged in regions of the vehicle window that are provided with an opaque masking print 10. The masking print 10 is not shown in FIG. 1 for the sake of clarity. It runs along the pane edge with a width of approx. 10 cm, also around the communication window 8. The masking print 10 is applied on the surface II and the surface IV. The laminated-in metal elements 7 are concealed by it on both sides and are not perceived as disturbing by an observer.

(18) FIG. 3 depicts a section through an alternative embodiment of the vehicle window according to the invention. It differs from that described above in that the metal element 7 (copper foil) is arranged on the exterior-side surface III of the inner pane 2 and thus directly on the heatable coating 4. Since the uppermost layer of the coating 4 is a dielectric Si.sub.3N.sub.4 layer, the heating function of the coating 4 is not adversely affected, although the metal element 7 is electrically conductive. The metal element 7 can thus simply be placed on the coating 4 without special precautions. Optionally, the metal element 7 can also have an insulating coating, for example, a clear lacquer.

(19) FIG. 4 depicts a section through another embodiment of the vehicle window according to the invention. The metal element 7 is glued onto the interior-side surface IV of the inner pane 2. The metal element 7 is implemented as an aluminum-steel sheet with a thickness of approx. 7 mm. The thermoconductive action of the metal element 7 also acts through the inner pane 2 such that even this arrangement is effective. The metal element 7 can be a sheet mounted specifically for this purpose. However, even an already present component can be used as the metal element 7, in particular the mounting bracket of the sensor that is arranged behind the communication window 8 and whose functionality the communication window 8 ensures.

(20) FIG. 5 depicts a plan view of another embodiment of the vehicle window according to the invention. Here again, a metal element 7 is associated with the communication window 8 in order to avoid hot spots. In contrast to the embodiment of FIG. 1, the metal element 7 is not only arranged next to the communication window 8 but, rather, extends along the edge of the communication window 8 facing away from the nearest busbar 5 such that the communication window 8 is surrounded on three sides by the metal element 7. By means of this design, the excess heat that is generated next to the communication window 8 is conducted partially into the region below the communication window 8. This region is electrically shadowed by the communication window 8 such that, here, there is only little heat generation. The metal element 7 contributes substantially to the homogenization of the heat profile by specifically conducting heat out of the hot spot into a region in which improved heating action is required.

(21) FIG. 6 depicts a flowchart of an exemplary embodiment of the method according to the invention for producing a heatable laminated vehicle window in accordance with FIG. 2.

(22) FIG. 7 depicts a flowchart of another exemplary embodiment of the method according to the invention in accordance with FIG. 4.

EXAMPLES

(23) Different windshields with heatable coatings and a communication window 8 were investigated. After 12 minutes of heating action, thermography was recorded and the maximum temperature T.sub.max on the pane (hot spot) was determined. A pane without metal element 7 served as Reference System 1. In the examples according to the invention, the excess heat was dissipated out of the hot spot in the the vicinity of the communication window by different metal elements 7: a laminated-in foil made of aluminum, a laminated-in foil made of copper, and a so-called bracket (attachment device for attachment parts) made of cast iron glued onto Side IV. The measured values are summarised in Table 1, wherein T indicates the difference in the maximum temperature relative to the Reference System 1.

(24) TABLE-US-00001 TABLE 1 Metal Element 7 T.sub.max T 1 86.1 C. 2 Alu foil, laminated-in 76.6 C. 9.5 C. 3 Cu foil, laminated-in 63.0 C. 23.1 C. Cast-iron bracket 70.2 C. 15.9 C. on Side IV

(25) It is discernible from the table that all embodiments result in a significant lowering of the temperature on the hot spot. Critical maximum temperatures can be avoided and the heat distribution is homogenised. These are major advantages of the invention.

LIST OF REFERENCE CHARACTERS

(26) (1) outer pane (2) inner pane (3) thermoplastic intermediate layer (4) electrically conductive coating (5) busbar (6) busbar (7) metal element (8) coating-free region, communication window (9) supply line to busbar (10) opaque masking print (O) upper edge (U) lower edge I exterior-side surface of the outer pane II interior-side surface of the outer pane III exterior-side surface of the inner pane IV interior-side surface of the inner pane A-A section line