FR3006143A1 - HEATING DEVICE SUITABLE FOR SINKING A CONDUIT OF TRANSPORT OF A FLUID - Google Patents

Abstract

The invention relates to a heating device adapted to the cladding of a conduit for conveying a fluid, comprising a first conductor (1) filamentary electrical, a second conductor (2) electrical filiform, and a resistive wire (3) crossing multiple times said first conductor (1) and said second conductor (2) so as to form between said first and second conductors (1, 2) several resistive links (31, 32), an electrical contact being established at each cross between the wire resistive (3) and one of said first and second conductors (1, 2). The invention also relates to an assembly comprising a fluid transport conduit of a motor vehicle and such a heating device.

Description

The present invention relates to a heating device adapted to the sheathing of a conduit for transporting a fluid. It relates to the field of heating ducts intended for the transport of fluids, in particular using electrical devices. Such heating may be intended to prevent the freezing of liquids transported, thaw, or elevate temperature.

The invention finds its preferential applications in the field of transport, especially in motor vehicles. In many applications, it is necessary or advantageous to have a means adapted to heat a fluid flowing in a conduit. Typically, in the automotive industry, there are three examples of functions for which this need exists: the heating of a gearbox for the selective catalytic reduction of the nitrogen oxide contained in the exhaust gas, the heating of the liquid of windscreen washer before spraying, and heating the crankcase gases of an engine before their reintroduction to the engine intake.

Combustion engines, including engines fitted to motor vehicles, are subject to increasingly stringent standards for the gaseous pollutants they emit. The regulated pollutants are carbon monoxide (CO), unburnt hydrocarbons (HC), particulates, and nitrogen oxides (N0x). Various devices are known for the treatment of the exhaust gases of combustion engines, so as to greatly reduce the pollutants regulated at the exit of the engine exhaust line. One of the known devices for treating nitrogen oxides is known as the "SCR" catalyst (English acronym for "Selective Catalytic Reduction" which can be translated as "Selective Catalytic Reduction"). An SCR device thus comprises a catalyst for reducing the nitrogen oxides, using a reducing agent that must be introduced into the exhaust gas before they reach the catalyst. The reducing agent may in particular be ammonia, obtained by decomposition of a urea solution, for example a 32.5% urea solution which is distributed commercially. The term "reducing agent" will be used hereinafter indifferently to denote the reducing agent or the precursor of such a stored agent and introduced into the exhaust gas, or a solution of such an agent or its precursor. This technology allows efficient treatment of nitrogen oxides. Nevertheless, one of the disadvantages of this technology lies in the fact that the reducer is likely to freeze at low temperature, for example at -11 ° C for a 32.5% urea solution. It is therefore important, to ensure the reliability and efficiency of this system, to be able to ensure that the reducer does not freeze, especially in the conduit, also called pipe, in which it is transported from its storage tank to its point of introduction into the exhaust. A duct heating device is therefore required.

The windshield washer devices of motor vehicles comprise a reservoir containing a liquid suitable for washing the windows and conduits for spraying the liquid onto a glass surface of the vehicle, such as the windshield, the rear window, or the headlights. . In order not to freeze, the liquid contains an antifreeze. However, at very low temperatures, it can have a high viscosity, harmful to a good cleaning of windows. It is therefore known that heating the liquid using a suitable device, for example at its transport conduit, avoids this disadvantage. In a combustion engine, the gases passing from the combustion chamber to the casing are recycled in a known manner to the intake of the engine. This function is generally designated by the English phrase "blow-by". The crankcase gases are loaded with vaporized fuel as well as with oil, which oil will be recovered as much as possible by a de-oiling device before reintroduction of the gases at the intake of the engine. In very cold conditions, condensates can form in the ducts carrying these gases, which can cause the formation of amalgam likely to clog the ducts. An increase in the pressure in the crankcase can then occur, this increase in pressure may cause engine failure. There is therefore a need for heating fluids transported in a conduit, in the automotive field. A similar need exists in many other fields, for example rail transport, chemicals or petrochemicals. Document FR2924786 discloses a heating device for a SCR gear pipe, in which a resistive wire is disposed inside the pipe. Such a device is however complex to implement, insofar as the ends of the resistive wire must emerge from the pipe to allow its power supply, which can cause sealing problems. In addition, it is necessary to provide an electrical circuit having a terminal at each end of the resistive wire, these ends 15 being geometrically spaced apart from each other. Finally, this device is not suitable to be installed as a retrofit on an existing pipe. The invention aims to provide a heating device for heating a fluid transport conduit, solving one or more of the aforementioned drawbacks of known devices. The invention therefore relates to a heating device adapted to the sheathing of a conduit for conveying a fluid, comprising a first filamentary electric conductor, a second filamentary electrical conductor, and a resistive wire crossing several times said first conductor and said second conductor so as to form between said first and second conductors 25 a plurality of resistive links, an electrical contact being established at each crossing between the resistive wire and one of said first and second conductors. The resistive links thus created behave from an electrical point of view as a set of resistors in parallel. By imposing an electrical voltage (potential difference) between the first conductor and the second conductor, heat generation will occur by Joule effect at each of the resistive links. It is thus not necessary to provide additional electrical connection to close the electrical circuit. The distribution of the resistive links along the conductors makes it possible to modulate the linear distribution of the heat generated. Preferably, the first conductor and the second conductor have a substantially constant relative spacing. The relative spacing between the first conductor and the second conductor is understood as the shortest straight line distance between the first and second conductors. A constant relative spacing allows the easy creation of resistive links of the same length, having the same resistance, and each generating the same heat energy.

Preferably, the resistive links are regularly spaced along the conductors. It is thus possible to obtain a substantially homogeneous distribution of the heat produced along the heating device, by arranging bonds of the same resistance regularly along the device. Preferably, the conductors and the resistive wire are devoid of electrical insulating sheathing. This ensures electrical contact between them when mechanical contact is established. The resistive wire and / or the conductors may be of the monofilament type, or of the multi-filament type. According to a first embodiment of the invention, the conductors and the resistive wire are fixed, for example bonded, on a flexible support adapted to the cladding of a conduit. A support adapted to the cladding of a duct may be a support that is sufficiently flexible to be wound around said duct, or a support having a tubular shape. According to a second preferred embodiment of the invention, the conductors and the resistive wire are included in the invention. constitution of an interlaced structure. According to a first variant of this second preferred embodiment, the interlaced structure can be woven and comprise warp son and weft son. The first and second conductors may be intertwined along warp threads or may constitute warp threads. The resistive wire may be interwoven along weft wires or may constitute weft wires. The interlaced structure can also be knitted.

The device may have a substantially tubular shape obtained by thermoforming. For this, a semi-finished product can be manufactured flat, then shaped by thermoforming so as to tend to wind on itself in the absence of constraints. Thus, it is possible to obtain a sheath that can be placed around the duct to be heated without having to introduce it through one end of the duct. According to a second variant of the second embodiment, the structure is braided in tubular form, the first and second conductors being intertwined so as to form two helices of the same orientation, the resistive wire being intertwined so as to form a helix of opposite orientation . The device may comprise a plurality of resistive wires forming a plurality of helices of the same orientation. Preferably, independently of the embodiment, the heating device may comprise a surface coating electrically insulating the conductors and the resistive wire of the external environment. The invention also relates to an assembly comprising a fluid transport duct of a motor vehicle, and a device as defined above that encases said duct, the latter being chosen from: a duct of a washer fluid circuit , a conduit of a recirculation circuit at the inlet of the crankcase gases, or a transport duct of a liquid reductant for the catalytic reduction of the nitrogen oxides. Other features and advantages of the invention will become apparent in the description below. In the accompanying drawings, given by way of non-limiting examples: FIG. 1 shows, in a schematic three-dimensional view, a device according to one embodiment of the invention; - Figure 2 shows, in a schematic view, a device according to one embodiment of the invention in a variant with a woven structure; - Figure 3a shows, in a schematic three-dimensional view, a device according to one embodiment of the invention. - Figure 3b shows, in a schematic three-dimensional view, an assembly comprising a heating device sheathing a pipe to be heated and said conduit. - Figure 4 shows, in a schematic three-dimensional view, a device according to one embodiment of the invention, in a variant with a braided structure. - Figure 5 schematically shows an example of regulation of the voltage applicable to a heating device according to the invention; According to a first embodiment shown in FIG. 1 according to a schematic view, a heating device comprises a first filiform electric conductor 1 and a second filiform electric conductor 2. The term conductor means an element having sufficient electrical conductivity to constitute, in the context of a device according to the invention, substantially an electrical equipotential. Such a conductor may in particular consist of a copper or aluminum wire, or a copper or aluminum alloy, for example a copper-magnesium or aluminum-magnesium alloy. The yarn may be of the monofilament type, that is to say having a single strand or filament, or of the multi-filament type, that is to say having several strands or filaments. In the embodiment shown here, the two conductors are substantially parallel, and therefore remain substantially equidistant from each other over all or part of their length. In the invention, a resistive wire 3 crosses several times the first conductor 1 and the second conductor 2, thus creating resistive connections 25 between the conductors. In the example shown here, the resistive son 3 successively crosses twice the first conductor, then twice the second conductor, and so on. The resistive wire 3 is so named, in that it has a low electrical conductivity, so as to undergo a joule effect heating when a suitable potential difference is established between the first conductor 1 and the second conductor 2. resistive wire may in particular be made resistive may in particular be made of stainless steel or resistive alloys such as constantan (copper-nickel), manganins (copper-nickel-manganese) or nickel-chromium alloys. It may be of the mono-filament type, or of the multifilament type. It may for example have an electrical resistance of the order of 14 Ohms per linear meter, in the context of an application of the device to the heating of a conduit of a motor vehicle. Typically, a copper-nickel alloy wire with a section of 0.35 mm 2 has a resistance of the order of 1.5 Ohm per linear meter. A stainless steel wire may typically have a resistance of 2 to 30 ohms per linear meter, or any other value by adjusting the wire section to obtain the desired value. The resistivity of the resistive wire is obviously adapted according to the heat energy to be produced, depending on the application in question and the available electrical power. At each crossing between the resistive wire 3 and one or the other of the conductors (1, 2), an electrical contact is established. Typically, in a variant of the invention in which the conductors 1, 2 and the resistive wire 3 consist of bare son, that is to say not having external insulation, a good mechanical contact is sufficient to establish a satisfactory electrical contact. The use of a multi-filament type wire to constitute the conductors 1, 2, and / or the resistive wire 3, allows easy implementation, a multi-filament yarn having greater flexibility compared to a monofilament yarn same section. The use of a multi-filament type wire to constitute the conductors 1, 2, and / or the resistive wire 3 also makes it possible to obtain a contact surface at the level of the crossings between the resistive wire 3 and one conduct 1, 2 greater than the contact surface obtained with monofilament son. Thus, the resistive wire 3 makes it possible to constitute a set of resistive links 31, 32, between the first conductor 1 and the second conductor 2. According to the embodiment represented here, the first and second conductors 1, 2 are equidistant from one another. on the other, over their entire length including crossings with the resistive wire 3. Their relative spacing e is constant. Each resistive link 31, 32 will allow the generation of the same heat energy. The resistive links being preferentially distributed equidistantly along the conductors, the device thus obtained has a homogeneous heating over the entire heating length of the device. The heat energy generated per linear meter of the conductors or the device is therefore substantially constant over the entire heating length of the device. This feature is particularly advantageous for applications in which the heating temperature must be controlled, to be sufficient without being excessive at any point of heating. Typically, the heating of a SCR reductant line must be sufficient to prevent any freezing of the reducer, and this all along the pipe, without overheating the reducer at the risk of losing its physicochemical properties or channeling at the reducer. risk of damaging it. According to the embodiment of the invention presented in FIG. 1, the conductors 1, 2, as well as the resistive wire 3 are fixed, for example by gluing, on a support 4. The support 4 can be flexible in order to be able to be conformed to a pipe to be heated. It may be constituted, for example, a plastic film or felt. It can be sticker. The assembly consisting of the support, the conductors and the resistive wire may be coated with an insulating surface coating. The insulating surface coating can ensure or participate in the fixing of the conductors and the resistive wire on the support 4. If the support 4 is made of a suitable material, it can also be shaped by thermoforming, after fixing the conductors and the resistive wire, in order to take a substantially tubular form.

According to other variants of the invention, the conductors 1, 2 and the resistive wire enter into the constitution of an interlaced structure. According to the embodiment of the invention presented in FIG. 2, the conductors 1, 2 and the resistive wire 3 form part of a woven structure. The woven structure has, in known manner, warp threads 5 and weft threads 6.

The first conductor 1 and the second conductor 2 may each constitute a warp. They can also be interlaced in a fabric along warp yarns 5. The resistive thread 3 may constitute weft threads. Preferably, between each passage of the resistive wire as a weft yarn, a predefined number of weft yarns 6 is interposed. This is for example obtained by weaving the interlaced structure of the device according to this variant of the invention with the aid of FIG. a weaving loom of the double framer type. The resistive wire 3 can also be interwoven in a fabric along weft threads 6.

The woven structure, comprising the conductors and the resistive wire may be coated with an insulating surface coating on one or the other of its faces, or preferably on both sides. The flat fabric strip, obtained after weaving and incorporating the conductors 1, 2, and the resistive wire 3, can integrate weft son of thermoformable material, so as to be shaped by thermoforming. Suitable materials for constituting the thermoformable yarns include, in particular, the following polymers: polypropylene, polyester, polyamide, phenylene polysulfide or polyetheretherketone. It is thus possible to adopt the device a substantially tubular shape, adapted to the cladding of a pipe to be heated. Diagram 3a schematically shows a heating device according to a variant of the invention, shaped by thermoforming to be adapted to the cladding of a conduit. The initially planar structure is rolled on itself so as to take a substantially tubular shape. As previously mentioned, such a shape can be obtained starting from a device as shown in Figure 1, whose support is made of thermoformable material. Such a shape can also be obtained for a woven device, whose son of frames are thermoformable. FIG. 3b shows, in a diagrammatic view in three dimensions, an assembly comprising a heating device sheathing a pipe to be heated and said pipe. In the example shown here, the heating device is shaped by thermoforming, and tends to wind it on itself in the absence of external stress. Thus, the heating device placed around the duct, the inner wall of the tubular heating device tends to match the outer wall of the duct to be heated. According to the embodiment of the invention shown in FIG. 4, the conductors 1, 2 and the resistive wire 3 constitute a braided structure. Tubular braided structures are known and commonly used for cladding pipes, generally for their mechanical protection. These braided sheaths are obtained by braiding a generally large number of threads, using a braid loom (also called lace loom). A braid loom has a number of bobbins disposed at the periphery of a circular table. By judiciously positioning cans respectively containing the first filamentary conductor 1, the second filiform conductor 2, and the resistive wire 3, it is possible to obtain a braid having an adequate distribution of its elements, for example as shown schematically in FIG. The wires 1, 2 are integrated in the braid. They form two "parallel" propellers, with the same dextral or sinistral orientation, the first conductor 1 and the second conductor 2 never crossing each other and remaining preferably equidistant from each other. In other words, the conductors 1, 2 preferably have a relative spacing e constant. The conductors 1, 2 can thus form a double helix. The resistive wire 3 is integrated into the braid so as to form a helix of opposite orientation, dextral if the conductors 1, 2 form helices and senestres sinister if the conductors 1, 2 form dextral helices. Thus, the resistive wire 3 crosses successively the first conductor 1 and the second conductor 2, and so on, forming between them several resistive links 31, 32. In the example shown in FIG. 4, the device comprises a second resistive wire 3 'integrated in the braid. Preferably, it is of the same type and has the same resistivity as the resistive wire 3. It then preferably forms a helix parallel to the helix formed by the resistive wire 3, so as to intersect the conductors 1, 2 forming between them resistive bonds of the same characteristics as those formed by the resistive wire 3. It is possible to increase the number of resistive wires beyond two, for example by employing three, four or five resistive wires, to improve the homogeneity of the heating. Conductors 1, 2, forming a double helix, allow the formation, or resistive son 3, 3 'of resistive links of the same length, which allows the same heat energy to be obtained by each resistive link. If the helices formed by the conductors 1, 2 on the one hand, and the resistive wire 3 on the other hand, have a regular pitch, the heat energy generated per linear meter of heating braid is substantially constant. The braided structure comprising the conductors and the resistive wire may be coated with an insulating surface coating on the outer and / or inner face of the tubular structure formed.

Whatever the embodiment of the invention in question, the conductors 1, 2 are preferably arranged so as to extend longitudinally, that is to say in the direction of the length of the heating device. The conductors 1, 2 thus extend over a given length of duct once the latter has been sheathed by the heating device according to the invention.

If the device has a tubular shape, by shaping a flat structure or because it implements a braided tubular structure, the conductors 1, 2 extend, substantially straight or helically, along the tubular sheath thus formed. Whatever the embodiment of the invention in question, the first and second conductors 1, 2 may be provided with electrical connectors for their easy connection to a voltage source, for example a battery or a voltage generator. One of the advantages of the invention with respect to known devices lies in the fact that the electrical connection can be made at the same end of the device, without having to close the electrical circuit at the opposite end or to provide additional electrical circuit. It is thus particularly possible to produce a device according to the invention having a significant length, typically by producing it in "continuous". It can then be cut to the length required for the intended application. When a potential difference is imposed between the first conductor 1 and the second conductor 2, the resistive links behave as resistors in parallel with each other. The heating power dissipated by the resistive links depends, in a known manner, on their resistance and the potential difference applied. The potential difference can advantageously be controlled to control the heating obtained. A possible regulation mode is a so-called chopped regulation, consisting of alternating over time phases in which a voltage difference is established between the conductors, which are heating phases, with phases in which the voltage between the conductors is zero , which are phases of no heating. Such a regulation is shown diagrammatically in the form of a graph in FIG. 5. The abscissa is the time in seconds, the ordinate is the voltage imposed between the first conductor 1 and the second conductor 2. The voltage Uref corresponds at a reference voltage, depending on the application considered. For an automotive application, Uref 20 can be of the order of 12 volts, which corresponds to the nominal voltage of the automotive batteries commonly used. The alternation between heating periods and periods of absence of heating according to the previously mentioned driving mode, or any other form of voltage regulation, may for example be slaved to a control of the temperature of the fluid in the heated pipe, or a temperature control of said pipe. The voltage regulation can also be applied according to a predefined control law, for example a temporal law. In the context of an application of the invention to the heating of a duct made of plastic material, for example polyamide, control of the heating can make it possible to avoid degradation by overheating of the duct. The invention thus developed allows the heating of a conduit provided for the transport of a fluid, especially in applications where the fluid is likely to freeze, or requires heating, and this with a simple implementation. According to the variant of the invention in question, it has one or more of the following advantages: a simple electrical connection, in particular because it can be achieved by the same end of the device, without having to add an electrical connection for closing the circuit; a homogeneous distribution of the heating obtained, and in particular a homogeneous heating over the entire length of the heating device; - An ease of obtaining, because the device can be manufactured by simple adaptations of known methods (weaving, braiding); - a possibility of adaptation in retrofit.

Claims (15)

REVENDICATIONS1. Heating device adapted to the sheathing of a conduit for conveying a fluid, characterized in that it comprises a first filamentary electric conductor (1), a second filamentary electric conductor (2), and a resistive wire (3) crossing multiple times said first conductor (1) and said second conductor (2) so as to form between said first and second conductors (1, 2) several resistive links (31, 32), an electrical contact being established at each intersection between the resistive wire (3) and one of said first and second conductors (1, 2). 2. Heating device according to claim 1, wherein the first conductor (1) and the second conductor (2) have a relative spacing (e) substantially constant. 3. Heating device according to claim 1 or claim 2, wherein the resistive links (31, 32) are regularly spaced along the conductors (1, 2). 4. Heating device according to any one of the preceding claims, wherein the conductors (1, 2) and the resistive wire (3) are devoid of electrical insulating sheathing. 5. Heating device according to any one of the preceding claims, wherein the resistive wire (3) and / or the conductors (1, 2) are of the mono-filament type. 6. Heating device according to any one of claims 1 to 4, wherein the resistive wire (3) and / or the conductors (1, 2) are of the multi-filament type. 7. Heating device according to any one of claims 1 to 6, wherein the conductors (1, 2) and the resistive wire (3) are fixed on a support (4) flexible adapted to the cladding of a conduit. 8. Heating device according to any one of claims 1 to 6, wherein the conductors (1, 2) and the resistive wire (3) are in the constitution of an interlaced structure. Heating device according to claim 8, wherein the interwoven structure is woven and comprises warp threads (5) and weft threads (6), said first and second conductors (1, 2) being interwoven along warp threads (5) or constituting warp threads. Heating device according to claim 8 or claim 9, wherein the interwoven structure is woven and comprises warp threads (5) and weft threads (6), the resistive thread (3) being interwoven along weft threads (6) or constituting weft threads. 11. Heating device according to any one of claims 7 to 10, said device having a substantially tubular shape obtained by thermoforming. 12. Device according to claim 8, wherein the interlaced structure is braided in tubular form, the first and second conductors (1, 2) being intertwined so as to form two helices of the same orientation, the resistive wire (3) being interwoven with so as to form a propeller of opposite orientation. 13. Heating device according to claim 12, comprising a plurality of resistive wires (3, 3 ') respectively forming several helices of the same orientation. 14. Heating device according to any one of the preceding claims, wherein the device comprises a surface coating electrically insulating the conductors (1, 2) and the resistive wire (3) of the external environment. 15. An assembly comprising a fluid transport duct of a motor vehicle and a heating device according to any one of the preceding claims, encasing said duct, said duct being chosen from a duct of a washer fluid circuit, a conduit of a recirculation circuit to the inlet of the crankcase gases, or a transport duct of a liquid reductant for the catalytic reduction of the nitrogen oxides.