More specifically, the present invention relates to a controlled-deformation panel which is particularly suitable for producing high-performance vehicle body parts, to which the following description refers purely by way of example.

BACKGROUND ART As is known, most currently produced high- performance cars feature a number of external aerodynamic negative-lift appendixes, commonly known as"stabilizers" or"spoilers", appropriately arranged on the vehicle body to increase vertical load on the moving vehicle and so improve road-holding and traction.

Such spoilers, however, have the major drawback of impairing the overall aerodynamic efficiency of the vehicle by greatly increasing the power required to bring the vehicle up to and maintain any given speed, i. e. of increasing drag.

By way of a solution to the problem, some car manufacturers have equipped certain models with movable spoilers capable of assuming, on command, a rest or minimum-angle position impairing the aerodynamic efficiency of the vehicle as little as possible, or an extracted maximum-angle position to increase the vertical load on the moving vehicle and so improve road-holding and traction.

Movable spoilers obviously call for a number of electric and/or pneumatic actuators to move them between the rest or minimum-angle and the extracted or maximum- angle positions; and an electronic central control unit to coordinate operation of the electric and/or pneumatic actuators so as to adjust the aerodynamic configuration of the vehicle without producing a sharp change in the attitude, and so endangering the stability, of the vehicle.

To improve overall aerodynamic efficiency, in recent years, prototype high-performance vehicles have been designed in which the increase in vertical load depends, not on spoilers, but on a number of body plates capable, on command, of changing shape to alter the aerodynamic profile of the vehicle, i. e. the shape of the body, to increase the negative lift of the vehicle when necessary, i. e. generate a vertical load which presses the vehicle down onto the road.

Unfortunately, currently used panels are so expensive to produce as to virtually rule out any

possibility of normal mass production.

DISCLOSURE OF INVENTION It is an object of the present invention to provide controlled-deformatiqn body panels of acceptable production cost.

According to the present invention, there is provided a controlled-deformation panel, characterized by comprising a sheet of elastically deformable material, and a bundle of tension wires inserted at least partly inside the sheet, close to one of the two lateral surfaces of the sheet; the tension wires being anchored at the ends to the body of the sheet; and the panel also comprising wire-tensioning means for selectively exerting mechanical pull on the tension wires to produce controlled deformation of the body of the sheet.

BRIEF DESCRIPTION OF THE DRAWINGS A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a view in perspective, with parts in section and parts removed for clarity, of a controlled- deformation panel in accordance with the teachings of the present invention; Figure 2 shows a view in perspective, with parts in section and parts removed for clarity, of a variation of the controlled-deformation panel in Figure 1; Figure 3 shows a section of a component part of the controlled-deformation panel in Figure 2;

Figure 4 shows a view in perspective of a vehicle featuring a number of controlled-deformation body panels as shown in the above Figures.

BEST MODE FOR CARRYING OUT THE INVENTION With reference to Figures 1 and 4, number 1 indicates as a whole a controlled-deformation panel, which may be used to advantage for producing body parts of a vehicle 2, to alter, on command, the aerodynamic profile, i. e. the body shape, and so control negative lift of, the vehicle.

For example, with reference to Figure 4, controlled- deformation panel 1 may be used to advantage for producing the hood, luggage compartment lid, and/or the flat-underbody channels of a vehicle 2.

With reference to Figure 1, panel 1 comprises a sheet 3 of elastically deformable material, e. g. a plastic material with or without reinforcing fibers; and a bundle of tension wires 4 inserted inside sheet 3, close to one of the two lateral surfaces of sheet 3.

Tension wires 4 are anchored at both ends 4a to the body of sheet 3; and panel 1 also comprises wire-tensioning means for selectively exerting mechanical pull on tension wires 4 to produce controlled deformation of the body of sheet 3.

More specifically, the tensioning means of panel 1 reduce tension wires 4, on command, to a predetermined total length to produce controlled deformation of the body of sheet 3.

The type of deformation imposed on sheet 3 obviously depends on the spatial distribution of tension wires 4 inside the body of sheet 3.

In the example shown, sheet 3 is flat and rectangular, and comprises a central supporting core 3a of Nomex (i. e. a sheet of honeycomb aluminium of given thickness); and two cover sheets 3b of composite material (e. g. glass fiber or carbon fiber embedded in an epoxy resin matrix) covering central core 3a on opposite sides.

Sheet 3 may obviously also be defined by a one-piece sheet of composite material of given thickness.

In the example shown, tension wires 4 are housed and slide inside tubular sheaths 5 embedded in one of the two cover sheets 3b, are parallel to the two minor lateral edges of sheet 3, and are anchored to the body of sheet 3, at the major lateral edges of sheet 3, so that contraction, i. e. a reduction in the total length, of the wires causes the body of sheet 3 to curve into a semicylindrical shell.

With reference to Figure 1, in a first embodiment of panel 1, tension wires 4 are defined by wires made, along at least a portion of their length, of shape-memory metal material (e. g. a titanium-nickel, copper-zinc-aluminium, or copper-aluminium-nickel alloy), and able to assume a predetermined length Lo at a temperature equal to or greater than a predetermined temperature To.

Shape-memory materials are metal materials capable of recovering a set macroscopic shape simply as a result

of a change in temperature or applied stress, and of effecting a solid-state phase transformation in which the start and end phases are both solid structures differing only as regards the crystallographic arrangement.

Such a solid-state phase transformation is commonly known as"thermoplastic martensitic transformation", and the temperature at which it occurs as"transition temperature".

More specifically, shape-memory materials are capable of assuming two different crystallographic configurations, depending on temperature : a first, commonly known as the martensitic phase, is typical of low temperatures and characterized by a high degree of deformability and a low yield point; a second, commonly known as the austenitic phase, is typical of high temperatures and characterized by a high degree of structural rigidity combined with a tendency to assume a predetermined macroscopic shape stored in the material itself by appropriate heat treatment.

In a first embodiment of panel 1, each tension wire 4 is defined by a wire made entirely of shape-memory metal material appropriately heat treated to assume, in the austenitic phase, a macroscopic shape in which the total length of the wire equals length Lo When brought to a temperature equal to or greater than the"transition temperature", i. e. to a temperature equal to or greater than temperature To, tensions wires 4 therefore all tend to assume the set length Los thus

deforming the body of sheet 3. More specifically, since length Lo is less than the width d of sheet 3 at rest, when the temperature of tension wires 4 is equal to or greater than temperature To, the body of sheet 3 tends to deform elastically and curve to bring the major lateral edges of sheet 3 closer together.

Conversely, in the martensitic phase, i. e. below temperature To, the shape-memory metal material of which tension wires 4 are made has such a low yield point as to be less than the springback force which tends to restore sheet 3 to its original flat shape, so that tension wires 4 extend to a total length greater than length Lo, and sheet 3 again assumes its natural, i. e. flat, shape.

Tension wires 4 made at least partly of shape-memory metal material therefore also act as linear actuators capable, on command, of reducing the total length of tension wires 4 to length Lo to produce controlled deformation of the body of sheet 3.

To contract tension wires 4, panel 1 has a wire- heating device 8, which, on command, heats tension wires 4, or the portions of tension wires 4 made of shape- memory metal material, to a temperature equal to or greater than the"transition temperature", i. e. to temperature To, so as to bring about the solid-state transformation phase typical of above cited shape-memory <BR> <BR> metal materials (i. e. "thermoplastic martensitic transformation").

In the example shown, wire-heating device 8

comprises a number of electric resistors 9 arranged along tension wires 4; and an electronic central control unit 10, which, on command, feeds a given, not necessarily constant, electric current through the electric resistors to Joule-effect heat tension wires 4. Electric resistors 9 may be defined either by tension wires 4 themselves, which, being made of metal alloy, are electrically conductive, or by a number of wires made of electrically conductive material and coiled about tension wires 4.

In short, in the first embodiment of panel 1, the wire-tensioning means comprise tension wires 4, or the portions of tension wires 4 made of shape-memory metal material; and wire-heating device 8.

With reference to Figures 2 and 3, in a second embodiment of panel 1, tension wires 4 are made entirely of steel, carbon fiber, or other high-strength material; and the wire-tensioning means comprise a number of linear actuators 11, each located along a respective tension wire 4 of panel 1, and for reducing, on command, the total length of respective tension wire 4 to length Lo to produce controlled deformation of the body of sheet 3.

In the example shown, each linear actuator 11 is located at one of the two ends 4a of respective tension wire 4, connects end 4a to the body of sheet 3 (the other end 4a of tension wire 4 is anchored to the body of sheet 3), and comprises: a hollow cartridge 12 anchored to the body of sheet 3 and coaxial with end 4a of tension wire 4; a piston 13 mounted to slide axially inside hollow

cartridge 12; and two precompressed helical springs aligned with each other and housed inside hollow cartridge 12, on opposite sides of piston 13.

The two precompressed helical springs, hereinafter indicated 14 and 15, act on piston 13 in opposition to each other to keep piston 13 in a position of equilibrium depending on the coefficient of elasticity of helical springs 14 and 15.

End 4a of tension wire 4 is fitted to slide through the shell of hollow cartridge 12, and is fixed to the body of piston 13; and one of helical springs 14,15-in the example shown, helical spring 14-is made of shape- memory metal material appropriately heat treated so that the body of the spring has a predetermined axial length Ho in the austenitic phase.

When brought to a temperature equal to or greater than the"transition temperature", i. e. to a temperature equal to or greater than temperature To, helical spring 14 therefore tends to assume axial length Ho, thus forcing piston 13 to assume, inside hollow cartridge 12, a new position of equilibrium in which the total length of the whole defined by tension wire 4 and relative linear actuator 11 equals the length Lo required to produce predetermined controlled deformation of the body of sheet 3.

The axial travel of piston 13 from the position of equilibrium corresponding to helical spring 14 in the martensitic phase to the equilibrium position

corresponding to helical spring 14 in the austenitic phase obviously determines the amount by which the total length of tension wires 4 is reduced.

As in the first embodiment, the wire-tensioning means in the second embodiment of panel 1 also comprise a device for controlling the linear actuators 17, and which, on command, brings spring 14 to a temperature equal to or greater than the"transition temperature", i. e. to temperature To, to bring about the solid-state phase transformation typical of shape-memory metal materials (i. e."thermoplastic martensitic transformation").

Like wire-heating device 8, device controlling the linear actuators 17 comprises, in the example shown, a number of electric resistors 18 distributed along the body of helical spring 14; and an electronic central control unit 19, which, on command, feeds a given, not necessarily constant, electric current through electric resistors 18 to Joule-effect heat the body of spring 14.

In this case, too, electric resistors 18 may be defined either by the body of helical spring 14, which, being made of metal alloy, is also electrically conductive, or by a number of wires made of electrically conductive material and coiled about the body of helical spring 14.

Operation of controlled-deformation panel 1 is easily deducible from the foregoing description with no further explanation required.

The advantages of controlled-deformation panel 1 as described and illustrated herein are obvious: production cost is compatible with normal mass production, so that mass produced vehicles can also benefit from all the advantages, in terms of aerodynamic efficiency, derived from a vehicle body with no external spoilers, which increase drag, fuel consumption, and pollution.

Another advantage of controlled-deformation panel 1 lies in it being extremely straightforward structurally, and therefore highly reliable.

Clearly, changes may be made to controlled- deformation panel 1 as described and illustrated herein without, however, departing from the scope of the present invention.

For example, as opposed to being substantially flat, sheet 3 may be curved ; in which case, tension wires 4 may be used to accentuate or reduce the curvature of sheet 3 on command.

In a further embodiment of panel 1, sheet 3 may comprise a number of reinforcing ribs projecting from one of the two faces of sheet 3, perpendicularly to the bundle of tension wires 4; and the tubular sheaths 5 housing tension wires 4 are fitted successively through all the reinforcing ribs, so that sheath portions embedded inside the reinforcing ribs alternate with sheath portions outside sheet 3.