Vehicle glazing with improved stiffness

A vehicle glazing with improved stiffness having a modified structure which comprises at least one stiffening portion, wherein each portion is a recessed portion and/or a raised portion, and wherein each portion has at least a portion of its contour being sharply curved.

FIELD OF THE INVENTION

The present disclosed invention relates to a vehicle glazing with improved stiffness, and more particularly to a thin vehicle glazing with modified structure to improve its stiffness.

BACKGROUND OF THE INVENTION

In response to the regulatory requirements for increased automotive fuel efficiency as well as the growing public awareness and demand for environmentally friendly products, automotive original equipment manufacturers, around the world, have been working to improve the efficiency of their vehicles.

One of the key elements of this strategy to improve efficiency has been the concept of light weighting. Often, more traditional, less expensive, conventional materials and processes are being replaced by innovative new materials and processes which while sometime being more expensive, still have higher utility than the materials and processes being replaced due to their lower weight and the corresponding increase in fuel efficiency. Sometimes, the new materials and processes bring with them added functionality as well in addition to their lighter weight. Vehicle glazing has been no exception.

By reducing the weight of the vehicle substantial improvements can be made in energy consumption. This is especially important for electric vehicles where the improvement directly translates into an increase in the range of the vehicle which is a key consumer concern.

The glazed area of vehicles has been steadily increasing and in the process displacing other heavier materials. The popular large glass panoramic roofs is just one example of this trend. A panoramic roof is a vehicle roof glazing which comprises a substantial area of the roof over at least a portion of both the front and rear seating areas of the vehicle. A panoramic roof may be comprised of multiple glazings and may be laminated or monolithic.

Reducing weight through the thickness in vehicle glazing is a clear trend in the automotive market. However, for some applications, such as roof windows, the thickness cannot be reduced due to stiffness issue. A thin vehicle glazing under pressure load deflects more than a thicker vehicle glazing with the same surface area and shape, especially at high speeds.

It would be advantageous to be able to produce a thinner glazing with improved stiffness.

SUMMARY OF THE INVENTION

Stiffness of a glazing is influenced by the geometry of the glazing as well as the materials of which it is comprised. On the material side, stiffness depends on the modulus of elasticity, also known as Young's Modulus, which is an intrinsic material property. On the geometry side, stiffness depends on size, shape and thickness, among others. Stiffness is proportional to the cube of the thickness.

In this sense, it is an object of the present invention to provide a thin vehicle glazing with modified structure to improve its stiffness.

This object can be attained by a vehicle glazing having a surface comprising at least one stiffening portion. Each portion of the at least one stiffening portion is selected from the group consisting of a recessed portion and a raised portion. Furthermore, each portion of the at least one stiffening portion is formed by bending a surface section, said bent section having at least a portion of its contour being sharply curved.

The present invention thus increases the stiffness of the glazing by making stiffening portions that modify the geometry of the glazing. Depending on the application type (e.g. movable or fixed), the glazing size (e.g. large or small) and the glazing type (e.g. curved/flat, monolithic/laminated) some parameters can be adjusted to improve stiffness. These parameters include, but are not limited to, stiffness portion(s) geometry (size and section), arrangement of the stiffness portion(s) over a glazing, thickness of layers in a laminated glazing and interlayer stiffness in a laminated glazing.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, there are shown preferred embodiments of the vehicle glazing according to the present invention.

FIG.1shows a curved vehicle glazing1having a surface2which comprises a stiffening portion3. The stiffening portion3is a recessed portion formed by bending a surface section4. In this embodiment the section4has a substantially rectangular shape with its contour5being sharply curved.FIGS.2-3show a cross sectional view A-A′ of the vehicle glazing1depicted inFIG.1, wherein the sharply curved contour6comprises a first bent portion7described by a first radius8followed by a second bent portion9described by a second radius10. This sharply curved contour6has a curved profile with a first direction and a second direction, both directions defined by the curvature with the first radius8and the curvature with the second radius10, respectively; so that the point at which the curved profile changes its direction is an inflection point11. The first radius8and the second radius10are less than or equal to about 150 mm, preferably less than or equal to about 50 mm, even more preferably less than or equal to 20 mm. It should be noted that both curvatures can have similar or different radiuses8,10.

The inflection point11is the point at which the sharply curved contour6becomes convex to concave or vice versa, as is shown inFIG.3. The present invention provides a vehicle glazing with complex curvatures having small or medium radiuses8,10. These curvatures are produced by using a bending technique such as press bending, gravity bending, laser-based bending or any other well-known technique. The selected technique (or combined techniques) depends on the size of radiuses. In addition, vacuum can be used to assist in the bending process.

FIG.4shows an exemplary embodiment wherein a vehicle glazing12having a recessed portion13comprises a laminated glazing with two glass layers14,15having a plastic interlayer16in between. Laminated glazing12is made by bonding two sheets of glass, the outer glass layer14and the inner glass layer15, wherein the inner glass layer15can be strengthened or annealed. The plastic interlayer16can be a plastic bonding layer comprised of a thin sheet of transparent plastic or thermo plastic interlayer.

Annealed glass is glass that has been slowly cooled from the bending temperature down through the glass transition range. This process relieves any stress left in the glass from the bending process. Annealed glass breaks into large shards with sharp edges. When laminated glazing breaks, the shards of broken glass are held together, much like the pieces of a jigsaw puzzle, by the plastic layer helping to maintain the structural integrity of the glass. A vehicle with a broken laminate12can still be operated. The plastic interlayer16also helps to prevent penetration by objects striking the laminate12from the exterior and in the event of a crash occupant retention is improved.

The plastic bonding interlayer16has the primary function of bonding the major faces of adjacent layers to each other. The material selected is typically a clear plastic. For automotive use, the most commonly used plastic bonding interlayer16is polyvinyl butyl (PVB). In addition to polyvinyl butyl, ionoplast polymers, ethylene vinyl acetate (EVA), cast in place (CIP) liquid resin and thermoplastic polyurethane (TPU) can also be used.

Plastic Interlayers are available with enhanced capabilities beyond bonding the glass layers together. The invention may include interlayers designed to dampen sound. Such interlayers are comprised whole or in part of a layer of plastic that is softer and more flexible than that normally used. The plastic interlayer may also be of a type which has solar attenuating properties. Standard thicknesses for automotive PVB interlayer are 0.38 mm and 0.76 mm.

In some preferred embodiments the laminated glazing12is asymmetric (glass layers having different thickness), wherein the ratio of thickness between outer layer14and inner layer15is ranging from about 1 to about 8 (e.g. 2.1 mm/0.7 mm). A preferred embodiment also comprises an asymmetric laminated glazing having a flexible plastic interlayer, such as a standard PVB, with a low shear modulus (e.g. about 0.5 MPa). In addition, in several embodiments the plastic interlayer15has a shear modulus from about 0.4 MPa to 500 MPa. It should be noted that, for a given laminated glazing thickness, an asymmetric laminated glazing is stiffer than the symmetric one.

In further preferred embodiment (not shown) a laminated glazing comprises at least one glass sheet and at least one plastic interlayer, wherein each glass sheet of said at least one glass sheet has a thickness from 0.5 mm to 5 mm. In addition, in several embodiments the laminated glazing has a height from 500 mm to 2000 mm, a width from 600 mm to 1500 mm and a bending depth less than 400 mm.

FIG.5shows a vehicle glazing17having a surface18which comprises two stiffening portions19. The stiffening portions19are recessed portions extending from edge20to edge21across a dimension of the surface18. In this embodiment each bent section has a substantially rectangular shape with at least a portion of its contour22,23being sharply curved, i.e. only two out of four sides of the rectangular section are sharply curved. Each portion is spaced apart from each other.

The vehicle glazing17is a movable roof window fixed on edges20,21, parallel to driving direction24, to a vehicle body. In this embodiment, the stiffening portions19are extended perpendicularly to said edges20,21.

FIG.6shows an embodiment wherein a vehicle glazing24having a surface25comprises one stiffening portion26. The bent section27has a circular shape with the whole contour sharply curved. The vehicle glazing24is a tempered monolithic glazing having a thickness from 2.5 mm to 5 mm.

FIG.7shows the vehicle glazing24depicted inFIG.6, wherein the bent section27has a sharply curved interior portion28. In several embodiments (not shown), the bent section of a stiffening portion has at least one sharply curved interior portion.

FIG.8shows the vehicle glazing17depicted inFIG.5, wherein an additional stiffening portion29is added. The bent section30has a circular shape as the vehicle glazing24ofFIG.6.

In all the embodiments, each portion of the at least one stiffening portion is selected from the group consisting of a recessed portion and a raised portion. In some embodiments, each portion of the at least one stiffening portion is further selected from the group consisting of a recessed portion followed by a raised portion and a raised portion followed by a recessed portion.FIG.9shows a front and top view of a flat vehicle glazing31which comprises a recessed portion32followed by a raised portion33. The raised portion33is an inverted recessed portion, i.e. a raised portion on one side corresponds to a recessed portion on the opposite side. The flat vehicle glazing31is a fixed roof (non-movable) fixed on four edges34,35,36,37to a vehicle body.

In some embodiments, the bent section of a stiffening portion has a geometric shape. The geometric shape can be selected from the group consisting of a circle (as inFIG.6), an oval (not shown), an ellipse (not shown), a polygon (as inFIG.5) and a polygon with rounded corners (as inFIG.1). In other embodiments (not shown), the bent section has a non-geometric shape, such as S-shape.

In some embodiments, the vehicle glazing comprises at least one glass sheet. The at least one glass sheet is selected from the group consisting of soda-lime, borosilicate and aluminosilicate. In addition, in several embodiments the vehicle glazing is selected from the group consisting of flat glazing, cylindrical glazing and spherical glazing.

It must be understood that this invention is not limited to the embodiments described and illustrated above. A person skilled in the art will understand that numerous variations and/or modifications can be carried out that do not depart from the spirit of the invention, which is only defined by the following claims.