Abstract:
A protective sleeve for covering elongated substrates is disclosed. The sleeve is knitted from a combination of first and second filamentary members having different properties from one another. The filamentary members are plated so that the filamentary members having properties compatible with the substrate are positioned predominantly on the inner surface of the sleeve facing and engaging the substrate. Filament properties include heat resistance, high-tensile strength, resistance to abrasion, chemical attack and damping capability. Ribs are integrally knitted lengthwise along the sleeve to form insulating air pockets. The ends of the sleeve are finished with welts to prevent unraveling.

Description:
RELATED APPLICATION  
       [0001]    This application is based on and claims priority to U.S. Provisional Patent Application No. 60/284,027, filed Apr. 16, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to sleeving for covering and protecting elongated substrates, the sleeving having different surfaces with different properties compatible with the substrate and the environment of the sleeve.  
         BACKGROUND OF THE INVENTION  
         [0003]    Protective sleeving for covering elongated substrates must often perform several functions and have multiple different properties and characteristics which allow such functions to be performed effectively and efficiently. For example, it may be desired to provide a durable, protective sleeve for covering a glass substrate such as an automobile windshield, allowing it to be safely transported and handled prior to installation. The inner surface of such a sleeve should be compatible with the substrate in some meaningful way. For example, the inner surface should not scratch or adhere to the glass and should allow the substrate to be removed easily. Such properties are not necessary for the outer surface of the sleeve however, but other properties, such as durability, tensile strength, resistance to moisture or abrasion resistance may be desired for the outer surface.  
           [0004]    In another example, protective sleeve may be needed to perform an insulating function for an elongated substrate such as conduit used in automobile exhaust gas recirculation systems. Pollution emitted from internal combustion engines may be reduced by exhaust gas recirculation (EGR), wherein a small amount of exhaust gas is mixed with the air-fuel charge entering the cylinder. The presence of exhaust gas mixed with the fuel-air charge tends to retard the combustion of the fuel during the power stroke, absorbs heat and thereby reduces the amount of oxides of nitrogen formed during the combustion process.  
           [0005]    EGR systems require that conduit be routed through the engine compartment in order to conduct the exhaust gas from the exhaust manifold back to the intake manifold. The exhaust gases from the exhaust manifold are very hot, typically on the order of 1000° F. Thus, the conduit carrying these gases will tend to be hot also, and this can cause problems within the engine compartment. Unless somehow insulated, the hot conduit radiates heat which tends to blister adjacent painted surfaces, melt nearby plastic and rubber components and also presents a serious burn hazard to technicians working on the engine.  
           [0006]    Insulative coverings for EGR conduit often require sophisticated coatings on their inner surfaces to protect them against the high operating temperatures of the EGR systems. In addition to high temperatures, the coverings are also subjected to a harsh vibrational environment and must endure hundreds of thousands of vibrational cycles without cracking, splitting or coming loose from the conduit. Furthermore, the conduit conventionally has flanged ends for connecting to the various manifolds and the EGR valve, the flanged ends also being hot but being difficult to accommodate by a wrapped insulating sleeve for example. EGR conduit tends to be any shape but straight and may be bifurcated as well, thus, presenting further challenges to the application of insulation in a convenient, cost-effective manner.  
           [0007]    There is clearly a need for an insulative sleeve which is readily adaptable to various complicated shapes and which can provide desirable properties compatible with the substrate as well as with other requirements needed to withstand the expected environment for the sleeve.  
         SUMMARY AND OBJECTS OF THE INVENTION  
         [0008]    The invention concerns a sleeve for covering an elongated substrate. The sleeve comprises an inner surface positionable to face and surround the substrate and an outer surface positionable to face away from the substrate. The sleeve is formed from a plurality of first filamentary members interlaced with a plurality of second filamentary members. The first filamentary members have properties compatible with the substrate and are positioned predominantly on the inner surface of the sleeve for engaging the substrate. The second filamentary member have properties different from the first filamentary members and are positioned substantially on the outer surface of the sleeve.  
           [0009]    For example, if the substrate comprises an elongated heat source such as an EGR conduit which is to be insulated, the sleeve is formed from a plurality of heat-resistant first filamentary members interlaced with a plurality of second filamentary members. The heat-resistant first filamentary members are positioned predominantly on the inner surface for engaging the heat source, and the second filamentary members are positioned substantially on the outer surface remote from the heat source. The second filamentary members are chosen to have properties different from the first filamentary members, such as abrasion resistance, or vibration damping.  
           [0010]    Preferably, the first and second filamentary members are interlaced by knitting. This gives the sleeve the ability to stretch and conform to any shape of substrate or conduit, as well as any connecting flange or fitting. Knitting also allows the first filamentary members to be plated with the second filamentary members to conveniently position the first filamentary members predominantly on the inner surface during the manufacture of the sleeve.  
           [0011]    The sleeve may be formed as a single or a double knit. For the double knit sleeve, the first and second filamentary members are knitted on separate needles to form a first knitted layer and a second knitted layer surrounded by the first knitted layer. The first knitted layer forms the inner surface and is predominantly formed of the heat-resistant first filamentary members. The layers may be knitted in the manner of a rib knit and the ends of the sleeve are finished off in knitted welts to prevent unraveling without the need for separate finishing steps such as sewing.  
           [0012]    Sleeves according to the invention may be single tubes or may be bifurcated with multiple branch sections interknitted to accommodate bifurcated substrates.  
           [0013]    The invention also includes a method of manufacturing a sleeve for covering an elongated substrate. The method comprises the steps of:  
           [0014]    (A) interlacing a plurality of first filamentary members, having properties compatible with the substrate, with a plurality of second filamentary members, having properties different from the first filamentary members, to form an inner surface of the sleeve positionable to face and surround the elongated substrate, and an outer surface positionable to face away therefrom; and  
           [0015]    (B) positioning the first filamentary members predominantly on the inner surface.  
           [0016]    Preferably, the interlacing step comprises knitting the first and second filamentary members, and the positioning step comprises plating the first filamentary members with the second filamentary members to achieve the desired location of the first filamentary members on the inside surface of the sleeve.  
           [0017]    It is an object of the invention to provide a sleeve for covering a substrate, the sleeve having an inside surface predominantly formed of filamentary members which have properties compatible with the substrate.  
           [0018]    It is a further object of the invention to provide a sleeve for covering a substrate, the sleeve having an outside surface predominantly formed of filamentary members which have properties different from the properties of the filamentary members forming the inside surface of the sleeve.  
           [0019]    It is also an object of the invention to provide a heat-resistant sleeve for insulating substrates such as EGR conduits, which form elongated heat sources.  
           [0020]    It is another object of the invention to provide a heat-resistant sleeve comprised of interlaced filamentary members.  
           [0021]    It is again another object of the invention to provide a heat-resistant sleeve which can withstand sustained vibration environments.  
           [0022]    It is yet another object of the invention to provide a heat-resistant sleeve which is flexible and stretchable and able to conform closely to the shape of the heat source.  
           [0023]    It is still another object of the invention to provide a heat-resistant sleeve which can be manufactured to have more or less bulk as required for a particular application.  
           [0024]    These and other objects and advantages of the invention will be apparent upon consideration of the following drawings and detailed description of the preferred embodiments. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is a side view, partially cut away, of a heat-resistant sleeve according to the invention;  
         [0026]    [0026]FIG. 2 is a side view, also partially cut away, of a bifurcated heat-resistant sleeve according to the invention;  
         [0027]    [0027]FIG. 3 is a detailed view of a single knit plated stitch used to form sleeves according to the invention;  
         [0028]    [0028]FIG. 4 is a detailed view of a double knit plated stitch used to form sleeves according to the invention; and  
         [0029]    [0029]FIG. 5 is a partially cut-away perspective view of another embodiment of a protective sleeve according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    [0030]FIG. 1 shows a sleeve  10  according to the invention suitable for insulating elongated heat sources, such as an EGR conduit  12  on an internal combustion engine. Sleeve  10  has an inner surface  14  positioned to face the conduit  12  and an outer surface  16  which faces away from the conduit or other heat source. Sleeve  10  is preferably knitted from at least two different types of filamentary members  18  and  20  as shown in FIGS. 3 and 4 and described in detail below.  
         [0031]    A plurality of ribs  22  and  24  may be knitted on the outer surface  16  and/or on the inner surface  14  of the sleeve  10 . When knitted on the outer surface, the ribs  22  act as bumpers to protect the EGR conduit and cushion it from impact damage. Ribs  24 , placed on the inner surface  14 , provide added insulation by forming a series of longitudinal air pockets  26  between the sleeve  10  and the EGR conduit  12 . The ribs  24  also reduce the contact area between the conduit and the sleeve, thus providing additional insulation against conductive heat transfer. The ribs  22  and  24  are integrally formed in the sleeve by a rib knit stitch as is well known in the art. The ends of sleeve  10  are finished by integrally knitting welts  28  to prevent unraveling of the sleeve.  
         [0032]    [0032]FIG. 2 shows an example of a bifurcated sleeve  30  according to the invention. Bifurcated sleeve  30  is similar to the single sleeve  10  in that it is knitted from at least two different types of filamentary members, has an inner surface  14  and an outer surface  16 , may have integrally knitted internal and/or external ribs  24  and  22  and ends finished with welts  28 . Sleeve  30  is bifurcated into two separate sleeve portions  32  and  34  which separate at a bifurcation point  36 . Sleeve segments  32  and  34  are preferably integrally knitted as part of sleeve  30  by varying the size and density of the stitches in the region of the bifurcation to effect the separation of the sleeve segments as is known in the art.  
         [0033]    Sleeves such as  10  and  30  according to the invention are preferably knitted because knitting provides several distinct advantages over other forms of interlacing filamentary members such as weaving and braiding, as well as over non-woven coverings such as felts or homogeneous coverings of extruded or molded plastics. Knitted structures have great flexibility and can expand or contract as needed to readily conform to complex curves without kinking as may be required to follow a tortuous EGR conduit snaking through an engine compartment from exhaust to intake manifold. Knitted structures have great elasticity and resilience which allows them to be stretched over tubing of various diameters and hug the outer surface of the conduit in a form fitting manner, automatically adjusting to changes in shape at any section along the conduit. This allows the sleeve to accommodate flanges, valves or other irregular features of the EGR system without the need to customize the sleeve for a particular shape. Knitted structures are also able to withstand harsh vibration without fear of fatigue failure. Furthermore, knitted items may be produced rapidly and relatively inexpensively on modern, programable high-speed knitting machines.  
         [0034]    Sleeves such as  10  and  30  are preferably knitted using at least two different filamentary members  18  and  20  as shown in FIGS. 3 and 4. FIG. 3 shows a single knit configuration and FIG. 4 illustrates a double knit. There are various advantages to both single and double knits as described below. Regardless of the knit used, filamentary member  18  is plated with filamentary member  20  in the knit structure. Plating in the single knit design of FIG. 3 is achieved by knitting both filamentary members on the same needle and forcing one filamentary member  18  to the tip of the needle and the other filamentary member  20  to the back of the needle by means of a feed mechanism mounted on the knitting machine. This results in loops  38  of filamentary members  18  being positioned predominantly on one face  40  of the knit structure while the other filamentary member  20  forms loops  42  and is positioned predominantly on the opposite face  44  of the knit structure. Thus, with the single knit, a single fabric layer may be formed having opposite faces  40  and  44  with different physical characteristics depending upon the characteristics of the filamentary members  18  and  20  chosen for the knit.  
         [0035]    In the example of a sleeve for the EGR conduit, filamentary member  18  is made of materials such as silica, glass, ceramic, stainless steel or bi-component DREF yarns where both components of the yarn are resistant to high temperatures. An example of a suitable DREF yarn would have a glass fiber core with a silica fiber covering. Prototype sleeves according to the invention have been fabricated using commercially available DREF yarns having a glass fiber core with a para-aramid fiber covering that has a relatively high elastic modulus and tensile strength with excellent heat and chemical resistance. Thermal decomposition of this yarn begins at about 932° F. The yarn maintains more than half of its room temperature strength at temperatures as high as 482° F. Ignition temperature of the yarn is about 1202° F. which can withstand relatively high temperatures.  
         [0036]    During knitting, loops  38  of the filamentary members  18  are arranged predominantly on the inner surface  14  of sleeve  10  or  30 . Thus, the filamentary member better able to withstand high temperature is arranged adjacent to the heat source surrounded by the sleeve. The filamentary members  20  which form loops  42  are arranged predominantly on the outer surface  16 . The outer surface filamentary members  20  may be chosen from among materials such as aramids, various nylon formulations, polyester, polypropylene, as well as other materials such as stainless steel, nitinol, elgiloy or other materials having high tensile strength, fatigue strength, relatively great resistance to abrasion or impact damage or noise damping qualities in order to provide protection to the sleeve and conduit against a harsh environment such as the engine compartment of an automobile. Bi-component yarns, especially DREF yarns, are also feasible. For the example sleeve for EGR conduit, a preferred material for the filamentary members  20  is oxidized pan fiber (OPF). OPF is a modified acrylic fiber heated at low temperature (less than 300° C.) in an oxygen atmosphere to produce a highly thermally resistant, infusable fiber with a well oriented polymer structure having a carbon content of about 60%. OPF combines high strength characteristics with excellent heat resistance and insulating properties appropriate for a high temperature application such as sleeving for an EGR conduit.  
         [0037]    The single knit design allows multiple characteristics to be present in a single layer sleeve, thus, reducing bulk and weight of the sleeve and allowing it to be used on conduits of relatively small diameter or over curves having relatively small bend radii.  
         [0038]    In the double knit design illustrated in FIG. 4, the filamentary members  18  and  20  are plated by knitting the different filamentary members on separate needles. This yields two separate interknitted layers of material,  46  and  48 . On layer  46 , loops  38  of filamentary member  18  predominate, whereas on layer  48 , loops  42  of filamentary member  20  predominate. Thus, each layer has distinct properties associated with the characteristics of the particular filamentary member forming the predominating loops.  
         [0039]    For the double knit EGR sleeve, layer  46  may be arranged as an inner layer comprising inner surface  14 , and layer  48  is then arranged as an outer layer comprising outer surface  16 . Inner layer  46  is preferably formed of loops  38  of filamentary member  18 , made from heat-resistant materials such as silica, glass, ceramic, stainless steel or bi-component DREF yarns where both components of the yarn are resistant to high temperatures. Outer layer  48  may be formed of loops  42  of filamentary member  20  formed of material having high tensile strength such as aramid fiber. The two layer design of the double knit, although heavier and bulkier than the single knit, can provide better isolation between the interior and exterior of the sleeve since there are two distinct layers which cover the entire surface of the heat source.  
         [0040]    The operational temperature of the EGR conduit will often determine the choice of material for filamentary member  18 . Silica yarn or filament provides protection against temperatures as high as 1832° F. Glass fibers also provide significant thermal protection on the order of 1022° F. Specially fabricated nylon fibers, sold under the commercial brand name “Nomex”, are useful for temperatures of 572° F. or lower.  
         [0041]    [0041]FIG. 5 shows another example of a knitted sleeve  50  according to the invention. Sleeve  50  is a cover for automotive glass products such as a windshield  52  and is used to protect the windshield during transport and handling prior to installation. The inner surface  54  of sleeve  50  should be compatible with the glass windshield  52  in that the sleeve should not scratch or adhere to the glass. The outer surface  56  need not have these properties, but it may be advantageous to impart other properties to the sleeve such as durability, tensile strength and resistance to abrasion so that the windshield will be effectively protected and the sleeve  50  will be reusable.  
         [0042]    A sleeve such as  50  can be knitted according to the invention using low-friction, non-stick filamentary members  58  made, for example, from polytetrafluoroethylene, the filamentary members  58  being positioned predominantly on the inner surface  54  of the sleeve  50 . Such filamentary members are compatible with the glass substrate in that they will not scratch the glass or adhere to it. To provide durability to the sleeve  50 , the filamentary members  58  are knitted with durable, high-strength filaments  60  made from multifilament aramid fibers, for example. This imparts durability and abrasion resistance to the sleeve  50 . Knitting the sleeve allows the filamentary members  58  and  60  to be plated so that filamentary members  58  are predominantly positioned on the inner surface  54  of the sleeve and the filamentary members  60  are predominantly on the outer surface  56  of the sleeve.  
         [0043]    The knit design, whether single or double knit, allows the sleeve to have greater bulk where necessary, to compensate for higher temperatures or higher mechanical or thermally induced stresses. The bulk of the knit design is increased by overfeeding one or the other of filamentary members  18  or  20  as necessary to form extended loops analogous to the knap found in terry cloth.  
         [0044]    Production of the sleeve according to the invention is preferably by means of a double cylinder knitting machine with multiple feeds and having electronic control for forming ribs and end welts. A non-reciprocating machine could be used since, unlike hosiery, no heel or toe need be formed.  
         [0045]    Knitted protective sleeving formed of filamentary members having different properties according to the invention provides a covering which is readily adaptable to almost any shape or configuration and places the filamentary member chosen for its specific properties where it will be most effective, thus, affording the most economical and efficient use of material.