Abstract:
A ground-protecting screen for an exhaust duct of a motor vehicle comprises a metallic grid carrying a metallic fabric. Preferably the fabric faces towards the duct.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention. 
     The present invention relates to protective screens for exhaust systems for internal combustion engines. 
     2. Description of the Prior Art. 
     It sometimes happens that the gases passing through the exhaust duct of the internal combustion engine of a motor vehicle reach a very high temperature which can be of the order of 600°C. This is the case, in particular, of rotary engines at the exhaust of which a post-combustion device is provided to reduce the carbon monoxide content of the combustion gases whereby to prevent air pollution. 
     It has been proposed to protect the body of the vehicle by means of a refractory screen interposed between the body and the exhaust duct. If it is also desired to protect the ground, for example to prevent, if the vehicle is moving over grassy ground, the burning of the grass, this cannot be effected simply by interposing a refractory screen under the exhaust duct. Indeed, such a screen would then form with the body-protecting screen, a substantially closed sheath which would prevent the dissipation of heat by convection. Moreover, this screen would quickly be heated to a high temperature which, in turn, would cause the grass to burn. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a ground protection screen for the exhaust duct of the internal combustion engine of a motor vehicle, said screen comprising a metallic grid, and a metallic fabric, said fabric being located on the grid. 
     Further according to the present invention, there is provided in a motor vehicle a body, an exhaust system, said system comprising an exhaust duct, and a protective screen arranged between the exhaust duct and the ground, said screen comprising a first layer in the form of a metallic grid, and a second layer in the form of a metallic fabric. 
     Preferably, the metallic fabric has a geometrical transparency of between 55 and 70%, advantageously about 60%, and a gap width of between 0.9 and 1 mm, and preferably the metal grid is composed of expanded metal. 
     The screen may extend around the entire periphery of the exhaust duct, passing between the duct and a protective screen for the body of the vehicle. When the protective screen for the body is of a refractory material disposed between two metal support elements, the ground-protection screen forms the upper support element of the protection screen for the body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: 
     FIG. 1 is a vertical cross-section of an exhaust duct having a protective screen in accordance with the present invention; 
     FIG. 2 is a horizontal cross-section of the arrangement shown in FIG. 1; 
     FIG. 3 is a section taken on line III--III of FIG. 1; 
     FIG. 4 is a perspective view of part of the screen, the component parts of the screen shown separately; 
     FIG. 5 is a section taken on line V--V of FIG. 2; and 
     FIG. 6 is a section, similar to FIG. 3, of an alternative arrangement. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIGS. 1 and 2, an exhaust duct 1 extends under the body 2 of a vehicle, from a connection 3 leading from, and suitably supported in a conventional manner by physical attachment to an engine (not shown) mounted on the body 2, to an exhaust chamber 4; the chamber 4 is formed of two independent elements which are joined together by a length of ducting 1&#39;. 
     A protective screen 5 is disposed between the body 2 and the duct 1; this screen is made of an insulating material, for example alumina silicate, disposed between two aluminum support sheets. The screen 5 is inwardly curved and extends as far as a horizontal plane passing through the axis of the duct 1, the screen being fixed to the body by lugs 6. Behind the screen 5 is a screen 5&#39; which covers the elements of the exhaust chamber 4 and which is fixed by lugs 6&#39; to a rear axle frame 7 which is movable by a limited extent with respect to the body 2. 
     A curved screen 8 is located beneath the duct 1 so as to lie between the ground and the exhaust duct 1. As can be seen in FIG. 4, the screen 8 is in the form of a laminate comprising a layer 10 composed of a metallic grid to which is applied a layer 9 in the form of a metallic fabric 9, the fabric layer 9 facing towards the duct 1. In the embodiment shown the grid is made of expanded metal; the fabric 9 may, for example, be of No. 20 fabric which corresponds to seven meshes per centimeter, to a gap width of 0.9 to 1 mm, and to a geometrical transparency of 60%. 
     The screen 8 is fixed to the underside of the screen 5 as can be seen in FIG. 3, in any suitable conventional manner whereby contiguous flanges are held together by fastening means (not shown). Beneath the screen 5&#39;, in line with the portion of the duct which extends as far as the exhaust chamber 4, the screen 8 is fixed to a screen 8&#39; which is of the same construction and is disposed between the duct 1 and the screen 5&#39;. The screen 8&#39; is itself fixed to the duct 1 by a welded strap 11 and a bolt 12 (FIG. 1). 
     In a similar manner the ducting 1&#39; is surrounded by a screen 8 and a screen 8&#39; and maintained in spaced-apart relation by suitable conventional means such as brackets or straps (not shown). 
     In the embodiment shown in FIG. 6, the screen 5 is formed by an insulating material 13 disposed between two support elements. The lower support element, which is in contact with the duct 1 is formed of sheet metal 14, for example, of aluminum; the upper support element is constituted by the screen 8 which extends around the entire periphery of the duct. 
     In the ground-protection screen particularly described, the metallic fabric constitutes a semi-permeable screen. It does not stop the dissipation of heat by convection, but slows it down, and controls radiation; finally, it prevents grass from coming in contact with the duct and cannot set it on fire, since the fabric is at a temperature considerably lower than that of the duct. For its part, the metallic grid which, alone, would be inefficient because of the wide section of its gaps, strengthens the metallic fabric whose own strength would not enable it to withstand the stresses to which the screen may be subjected.