Abstract:
A sheath for protecting a hose, particularly a fuel conduit, against shocks consists of a knitted tubular structure ( 10 ) with two faces, a first face ( 11 ) being made in the form of jersey and a second face ( 12 ) being made in the form of cotton fleece.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a sheath for protection of a pipe against impacts, in particular for fuel pipes. 
   The present invention applies generally to the protection of pipes for circulating fuel in automobile vehicles. 
   Fuel pipes are generally made of plastic and are fragile with regard to impacts. In particular, in the event of an accident to the vehicle, a part hitting a plastic fuel pipe risks piercing the pipe, thereby causing a fire due to the leakage of fuel. 
   In order to damp impacts on a fuel pipe, there exist rubber sleeves intended to cover the pipe. However, such rubber sleeves are difficult to slide over the plastic pipes. 
   There also exist plastic ducts conformed specifically to the shape of the fuel pipes to be protected. Such ducts are costly to fabricate, however, and must be specific to each application. 
   An object of the present invention is to propose a new impact protection sheath that removes the drawbacks cited above. 
   SUMMARY OF THE INVENTION 
   To this end, the present invention is directed to a sheath for protection of a pipe against impacts, in particular for fuel pipes, consisting of a tubular knitted structure with two faces, a jersey-knit first face and a molleton second face. 
   Thus a flexible tubular knitted structure that is simple to fabricate and to fit over fuel pipes of different diameters is provided. The tubular knitted structure adapts to different conformations of fuel pipes and may be positioned easily. 
   The jersey-knit face retains the knitted structure and provides mechanical strength and shear resistance in the protection sheath. 
   The molleton second face ensures damping of impacts thanks to the expanded structure of this second face. 
   In practice, the first face constitutes an external face of the protection sheath and the second face constitutes an internal face intended to come into contact with the pipe. 
   According to an advantageous feature of the invention, the second face consists of multifilaments with a linear density greater than or equal to 1 200 decitex and preferably greater than 2 000 decitex. 
   The use of a heavy yarn to produce the molleton face of the sheath ensures very good damping of impacts and prevents piercing of the fuel pipe covered in this way by the impact protection sheath. 
   To improve further the expanded structure of the molleton face, this second face consists of textured polymer multifilaments. 
   This impact protection sheath is preferably produced by circular knitting, thus enabling an economical textile process to be used for the production of the impact protection sheath conforming to the invention. 
   Other features and advantages of the invention will become further apparent in the course of the following description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the appended drawings, provided by way of nonlimiting example: 
       FIG. 1  is a perspective view of an impact protection sheath conforming to one embodiment of the invention; 
       FIG. 2  is a view of the impact protection sheath from  FIG. 1  in partial section; and 
       FIGS. 3 to 5  are diagrams showing different types of knitted structure used to constitute an impact protection sheath conforming to one embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A sheath conforming to the invention for protection of a pipe against impacts will be described first with reference to  FIGS. 1 and 2 . 
   This impact protection sheath is intended to protect plastic pipes, and especially to protect fuel pipes used in automobile vehicles to prevent piercing of the pipe and leakage of fuel, in particular in the event of an accident to the automobile vehicle. 
   As clearly shown in  FIG. 1 , the impact protection sheath  10  consists of a tubular knitted structure with two faces, a jersey-knit first face  11  and a molleton second face  12 . 
   This type of knitted sheath can be produced by a circular knitting process enabling a closed tubular sheath with two faces to be knitted directly using the molleton technique. 
   In this embodiment, the jersey-knit first face  11  constitutes the external face of the protection sheath  10  and the second face  12  constitutes the internal face, intended to come into contact with the fuel pipe when the protection sheath is slid over such a pipe. 
   In this embodiment, the jersey-knit first face  11  and the molleton second face  12  are produced using a yarn of the same kind, for example polymer multifilaments, such as polyester or polyamide multifilaments. 
   Of course, different yarns could be used to produce the external face  11  and the internal face  12 . 
   In particular, the jersey-knit first face  11  could be produced entirely from a monofilament or by combining a monofilament and multifilaments of types different from those used to achieve the expansion of the molleton second face  12 . 
   The multifilaments used for the second face  12  are preferably sufficiently heavy to enable a thick internal face  12  capable of damping impacts to be obtained. 
   For example, the multifilaments used have a linear density greater than 2 000 decitex (2 000 g per 10 000 m of yarn). 
   Of course, other types of multifilaments may be used, provided that they have sufficient linear density, preferably greater than 1 200 decitex, or even 1 500 decitex. 
   Moreover, textured polymer multifilaments are preferably used to ensure expansion of the molleton second face  12 . 
   In the conventional way, textured multifilaments may be used in accordance with the false twist (FT) process or the fixed false twist (FFT) process. 
   Of course, other texturizing processes could be used for the multifilaments employed in the impact protection sheath conforming to the present invention. 
   Thanks to circular knitting using a molleton technique, the second face of the protection sheath  10  consists of multifilament floats  12   a.    
   The length of the floats  12   a  corresponds to a length of the tubular knitted structure from 3 to 10 needles, and preferably from 4 to 6 needles. 
     FIG. 3  shows by way of example the production of a float in a knitted structure. 
   In this diagram, the length of the float  12   a  is equal to three needles, corresponding to three stitches of the jersey-knit first face. 
   The number of floats  12   a  in a cross section of the tubular knitted structure is preferably from three to six. 
   In the embodiment shown in  FIG. 1 , the number of floats  12   a  in the cross section is equal to four. 
   As shown clearly in  FIGS. 1 and 2 , in this embodiment the floats  12   a  are woven into longitudinally aligned stitches of the jersey-knit first face  11 , i.e. interwoven with the same warp filament. 
     FIG. 4  shows an example of knitting for producing a molleton with floats  12   a  interlaced regularly with the jersey-knit structure  11 . 
   Of course, other types of knitting enabling a molleton technique to be employed may be used, and in particular, as shown in  FIG. 5 , a knitting technique in which the interlacing of the molleton filament is offset by one needle in each row (this technique is known as diamond molleton). The floats are then woven in a diamond configuration, the interlacing of the molleton filament being offset by one warp filament in each row. 
   Thanks to the molleton knitted structure, the filament constituting the internal face  12  of the sheath  10  is fixed to the external face  11 , but not interlaced, so that the fibers may expand freely and thereby produce a heavy and thick layer for damping impacts on the sheath  10 . 
   The molleton face provides sufficient damping with regard to impact. The Applicant has thus noted that the presence of such an impact protection sheath on a plastic pipe doubles the intrinsic impact resistance of this plastic pipe. 
   Moreover, the jersey-knit external structure retains the sheath and provides overall mechanical strength, in particular with regard to abrasion. 
   It will be noted in particular that for automotive applications such a sheath may be impregnated with a fire treatment product to improve the fire resistance of the sheath. 
   There is obtained in this way a textile sheath that is simple to fabricate by a circular knitting process and simple to fit to a fuel pipe, as much in terms of diameter as in terms of length. 
   In particular, the diameter of such an impact protection sheath  10  may be from five to twelve millimeters and preferably equal to eight or ten millimeters. 
   In order to stabilize the diameter of the impact protection sheath after it is knitted, it is possible to apply heat treatment to the protection sheath. Heating the sheath causes slight shrinkage of the polymer used in the knitted structure, to stabilize the diameter of the protection sheath  10 . 
   In practice, fitting such a sheath is simple. Thanks to its flexible structure, it may be threaded onto a fuel pipe and positioned at any location, espousing perfectly the curves of the pipe. 
   It may preferably be cut to the required length by hot cutting. Hot cutting cauterizes the end of the protection sheath and thus avoids all risk of pollution by dust or filament debris during fitting.