GB2270555A - Heat shields - Google Patents

Abstract

A heat shield (10; 30) comprises a first metal sheet (12; 32) which is substantially smooth and provides a substantially continuous heat-reflecting surface (13; 33) and a second metal sheet (14; 34) which is formed substantially in its entirety into parallel corrugations (15). The second sheet (14; 34) engages an opposite surface of the first sheet (12; 32) along crests (16) of the corrugations (15) and is secured thereto by metal fastening means (20) at points spaced along some only of said crests (16). <IMAGE>

Description

HEAT SHIELDS This invention is concerned with heat shields, e.g.

for use in vehicles.

Many vehicles contain significant sources of heat from which it is necessary to shield equipment or cargo which may be damaged by exposure to excessive heat, or passengers who may be rendered uncomfortable. For example, electrical or electronic components housed in an engine compartment may require to be shielded from heat generated by the engine, or passengers may require to be shielded from heat generated by an exhaust system.

Heat shields for use in vehicles must combine good resistance to heat transfer with the ability to withstand the temperatures to which they are subjected. It is also essential that heat shields have acceptable acoustic properties, i.e. they must not generate significant levels of noise as the vehicle operates. Other desirable properties are lightness, cheapness and suitability for recycling, i.e. they should be made of readily re-usable materials, preferably a single material.

Many heat shields which are in use or have been proposed have a heat-reflecting surface intended to reflect radiant heat back towards the heat source. Generally, such surfaces are provided by metal sheets or foils which can withstand the temperatures experienced and are good reflectors of infra-red radiation. Aluminium or an alloy thereof can be used as it is a particularly good reflector of infra-red radiation and is lighter than, for example, steel. However, as metals are good conductors of heat and not all the heat radiated from the source is reflected, such heat shields require to be provided with some means for reducing heat conduction therethrough. For example, layers of a good heat insulating material can be added, e.g. mineral wool, but this material may be expensive, increases the weight of the heat shield, and reduces its suitability for re-cycling.Insulation may, alternatively, be provided by air spaces enclosed or partially enclosed between layers of metal foil which is embossed, crumpled or corrugated. Such foil layers are, however, flimsy necessitating a complex structure to hold the foil in position and protect it from damage.

It is an object of the present invention to provide a heat shield having a simple construction and which is suitable for re-cycling.

The invention provides a heat shield comprising a first metal sheet which is substantially smooth and provides a substantially continuous heat-reflecting surface, a second metal sheet which is formed substantially in its entirety into parallel corrugations, the second metal sheet engaging an opposite surface of the first metal sheet along crests of the corrugations of the second sheet, and metal fastening means securing the second metal sheet to the first metal sheet at points spaced along some only of said crests.

By the term "substantially smooth" when applied to a metal sheet, we mean that the sheet is not perforated, embossed, corrugated or crumpled to any significant extent although it may be bent to give the heat shield a threedimensional shape, e.g. to surround or partially surround the heat source.

In a heat shield according to the invention, the heatreflecting surface of the first smooth metal sheet reflects a substantial amount of the incoming infra-red radiation back towards the source thereof. The air spaces created by the corrugations have an insulating effect and also, in some cases, allow heat to be removed by air forced along the air spaces, or air may be caused to flow along the spaces by convention. Where the crests occur, there are no air spaces but heat conduction is reduced by the resistance to heat flow caused by interfaces between the sheets.

Furthermore, oxide films formed on the surfaces will increase the insulating effect. The heat shield can withstand the temperatures involved and is of all metal construction so that it is suitable for re-cycling. The suitability for re-cycling can be increased if the sheets and the fastening means are all made of the same metal, thereby also reducing the possibility of corrosion due to electrolytic effects. The heat shield is also of simple construction having only two major components that are not flimsy. The heat shield is also acceptable acoustically especially as the sheets can flex between the crests where the fastening means secures the sheets together.

In order to increase the insulating effect, the heat shield may also comprise a third metal sheet which engages the second sheet along the troughs of said corrugations on the opposite side of the second sheet to that which engages the first sheet. The third sheet encloses further air spaces. The third sheet may be substantially smooth and the heat shield comprises further fastening means securing the third sheet to the second sheet at points spaced along some only of said troughs. In this case, said first and third sheets may have edge portions extending beyond said second sheet, said edge portions being joined together, e.g. by one being turned over the other.

Instead of being substantially smooth, the third sheet may be formed substantially in its entirety into corrugations whose crests engage said troughs. This creates further air spaces. The third sheet may be provided by a folded over continuation of said second sheet. The heat shield may also comprise a fourth metal sheet which engages the third sheet along troughs of said corrugations on the opposite side of the third sheet to that which engages the second sheet. The fourth sheet may be substantially smooth and may have edge portions secured to edge portions of the first sheet.

The metal of at least one of said sheets may be in the form of a mat of metallic fibres or may be reinforced with metallic fibres which may be in the form of a mat. This enables the sound damping properties of fibres to be utilised.

The sheets may be made of aluminium or aluminium alloy as they are particularly good reflectors of infra-red radiation.

The fastening means may comprise spot welds.

There now follow detailed descriptions, to be read with reference to the accompanying drawings, of three heat shields which are illustrative of the invention.

In the drawings: Figure 1 is a perspective view of the first illustrative heat shield; Figure 2 is an end view of the first illustrative heat shield; Figure 3 is an end view of the second illustrative heat shield; and Figure 4 is an end view of the third illustrative heat shield.

The first illustrative heat shield 10 is generally planar except for a channel 11 formed therein which is intended to fit around an exhaust pipe (not shown) of a vehicle.

The heat shield 10 comprises a first metal sheet 12 made of aluminium alloy. The sheet 12 is continuous across the width and length of the shield 10 and is substantially smooth, i.e. it has no corrugations or embossments and only sufficient bends to enable it to skirt the channel 11. A surface 13 of the sheet 12 provides a substantially continuous heat-reflecting surface which bounds the channel 11.

The heat shield 10 also comprises a second metal sheet 14 made of the same aluminium alloy as the sheet 12. The second sheet 14 is formed substantially in its entirety into parallel corrugations 15 which extend parallel to the channel 11. These corrugations 15 are generally sinusoidal in end view and have crests 16 which engage on an opposite surface 17 of the first sheet 12 to the surface 13 thereof.

Thus, the second sheet 14 engages the first sheet 12 along the crests 16 and the corrugations 15, in combination with the surface 17, enclose air channels 18 extending parallel to the channel 11. The air channels 18 are open at the ends thereof.

In modifications of the first illustrative heat shield 10, the second sheet 14 may be continuous across the width and length of the shield, but, in the shield 10, the second sheet 14 is divided into three sections 14a, 14b and 14c.

The sections 14a and 14c are generally planar, except for the corrugations 15 and engage planar portions of the sheet 12 on opposite sides of the channel 11. The other section 14b engages the bottom of the channel 11 and is shaped to conform to the shape of the sheet 12 in this region. The sheet 14 is divided into the sections 14a, 14b and 14c to avoid complex bending of the sheet 14 at the convex bends 19 in the sheet 12 along the sides of the channel 11.

The first illustrative heat shield 10 also comprises metal fastening means securing the sections 14a, 14b and 14c of the second sheet 14 to the first sheet 12. This fastening means is provided by spot welds 20 (represented by dots in Figure 1) which are located at points spaced along some only of the crests 16. Securing the sheets together only at points spaced along some only of the crests 16 enables the sheets 12 and 14 to flex relative to one another between these crests which is beneficial acoustically.

The first illustrative heat shield 10 provides air spaces in the channels 18 which have an insulating effect.

Heat can also be removed by air passing along the channels 18 due to a vehicle's motion, to convection effects, or to forced air blowing. The shield 10 is acceptable acoustically and, as it is made entirely of one metal, is suitable for re-cycling.

The second illustrative heat shield 30 shown in Figure 3 comprises a first metal sheet 32 (providing a continuous heat-reflecting surface 33) and a second metal sheet 34 which is corrugated. The sheets 32 and 34 are similar to the sheets 12 and 14 described above and are secured together by similar spot welds along some of the crests of the corrugations. The heat shield 30 differs from the first illustrative heat shield 10 in that it also comprises a third metal sheet 36 which engages the second sheet 34 along troughs 38 of the corrugations thereof on the opposite side of sheet 34 to that which engages the first sheet 32.

The third sheet 36 is substantially smooth and the shield 30 comprises further spot welds (not shown) securing the sheet 36 to the sheet 34 at points spaced along some only of the troughs 38. The first and third sheets 32 and 36 have edge portions 32a and 36a which extend beyond the second sheet 34 at the sides (but not the ends) of the shield 30. These edge portions 32a and 36a are secured together by the edge portions 36a being turned over the edge portion 32a.

The second illustrative heat shield 30 encloses channels 38 between the sheets 32 and 34 and additional channels 40 between the sheets 34 and 36. These channels 38 and 40 provide insulation and allow air to pass through the shield 30 to remove heat therefrom.

Figure 3 shows the third illustrative heat shield 50 which comprises four metal sheets 52, 54, 56 and 58 which are all made of the same aluminium alloy. The first metal sheet 52 is substantially smooth and provides a continuous heat-reflecting surface 53. The second sheet 54 is formed substantially in its entirety into corrugations and engages an opposite surface 55 of the sheet 52 along crests of the corrugations. Spot welds (not shown) provide metal fastening means securing the sheet 54 to the sheet 52 at points spaced along some only of said crests. The third sheet 56 is formed substantially in its entirety into corrugations whose crests engage the troughs of the corrugations of the sheet 54. The third sheet 56 is provided by a continuation of the sheet 54 which is folded over at 57 through 1800. The fourth sheet 58 engages the third sheet 56 along troughs of the corrugations thereof on the opposite side of the third sheet 56 to that which engages the second sheet 54. The fourth sheet 58 is spot welded to the third sheet 56 at points spaced along the troughs of the third sheet 56.

The first sheet 52 and the fourth sheet 58 have edge portions 52a and 58a which extend beyond the second sheet 54 and the third sheet 56 widthwise of the shield 50. The edge portions 52a and 58a are secured together by turning the edge portion 58a over the edge portion 52a.

The third illustrative heat shield 50 encloses channels for air between the sheets 52 and 54, between the sheet 54 and 56, and between the sheets 56 and 58.

Claims (14)

1 A heat shield comprising a first metal sheet which is substantially smooth and provides a substantially continuous heat-reflecting surface, a second metal sheet which is formed substantially in its entirety into parallel corrugations, the second metal sheet engaging an opposite surface of the first metal sheet along crests of the corrugations of the second sheet, and metal fastening means securing the second metal sheet to the first metal sheet at points spaced along some only of said crests.

2 A heat shield according to Claim 1, wherein the heat shield also comprises a third metal sheet which engages the second sheet along troughs of said corrugations on the opposite side of the second sheet to that which engages the first sheet.

3 A heat shield according to Claim 2, wherein said third sheet is substantially smooth and the heat shield also comprises further metal fastening means securing the third sheet to the second sheet at points spaced along some only of said troughs.

4 A heat shield according to Claim 3, wherein said first and third sheets have edge portions extending beyond said second sheet, said edge portions being secured together.

5 A heat shield according to Claim 4, wherein said edge portions are secured together by one being turned over the other.

6 A heat shield according to Claim 2, wherein said third sheet is formed substantially in its entirety into corrugations where crests engage said troughs.

7 A heat shield according to Claim 6, wherein said third sheet is provided by a folded over continuation of said second sheet.

8 A heat shield according to either one of Claims 6 and 7, wherein the shield also comprises a fourth metal sheet which engages the third sheet along troughs of said corrugations on the opposite side of the third sheet to that which engages the second sheet.

9 A heat shield according to Claim 8, wherein said first and fourth sheets have edge portions extending beyond said second and third sheets, said edge portions being secured together.

10 A heat shield according to any one of Claims 1 to 9, wherein at least one of said sheets is in the form of a mat of metallic fibres.

11 A heat shield according to any one of Claims 1 to 9, wherein the metal of at least one of said sheets is reinforced with metallic fibres.

12 A heat shield according to any one of Claims 1 to 11, wherein the sheets are made of aluminium or aluminium alloy.

13 A heat shield according to any one of Claims 1 to 12, wherein the metal fastening means comprises spot welds.

14 A heat shield substantially as hereinbefore described with reference to and as shown in Figures 1 and 2, or Figure 3, or Figure 4 of the accompanying drawings.