Patent Publication Number: US-2009238547-A1

Title: Heatable fluid line with a heating power which can be set

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to German Utility Model Application No. DE 20 2008 003 908.8, filed Mar. 19, 2008, the content of which is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a heatable fluid line having a heating line comprising a conduit and an electrical heating element which is arranged, in particular, on the circumference of the conduit, a particular heating power being able to be set. 
     BACKGROUND OF THE INVENTION 
     An example of a fluid line is disclosed in EP 1 764 541. In the case of this heatable fluid line, at least one electrical heating conductor and at least two electrical supply lines are arranged on the circumference of the conduit such that they run in the longitudinal direction of the conduit, the heating conductor being alternately electrically connected to one of the two power supply lines, to be precise alternately to the positive pole and negative pole of the supply voltage. In this case, the connecting points are at equal distances behind one another, as seen in the longitudinal direction of the conduit. The electrical heating conductor is connected to the supply lines by means of soldering, welding or crimping, for example. As a result of this configuration, the fluid line has a constant heating power per unit length. This makes it possible to prefabricate the fluid line in long lengths and to cut it to any desired length, each length of line which has been cut to length having the same heating power per unit length. However, this known fluid line has the disadvantage that relatively high material costs are produced since, in addition to the electrical heating conductor or conductors, at least two supply lines have to be respectively concomitantly provided. An increased outlay in terms of production also results during production on account of the necessary alternating connecting points between the heating conductor and the supply lines. Each heatable fluid line which has been prefabricated in such a manner has a defined heating power per unit length. However, if different heating powers per unit length are required for different applications, it is necessary to prefabricate different heatable fluid lines with the respectively required heating powers per unit length, with the result that it is necessary to stockpile or store the prefabricated fluid lines. This also results in increased production costs. 
     SUMMARY 
     The present invention is based on the object of avoiding the above disadvantages and providing a heatable fluid line in which the desired heating power per unit length can be adapted to the respective application before the fluid line is installed, but it is still possible to prefabricate the fluid lines in any desired length. 
     According to the invention, this object is achieved by virtue of the fact that the heating element comprises at least three heating conductors which are electrically insulated from one another and run along the longitudinal direction of the conduit, and the ends of the electrical heating conductors are connected to one another and can be connected to an electrical supply voltage in such a manner that a plurality of heating conductors are connected in series and/or in parallel such that, for a particular supply voltage, the heating power of the fluid line is determined by the total electrical resistance of the electrical heating conductors. After the fluid line according to the invention has been cut to length, the present invention makes it possible for the available electrical heating conductors to be connected in any desired manner such that a total electrical resistance which is suitable for the required heating power is set. 
     The present invention also relates to a heating line for use in a fluid line according to the invention. In the case of such a heating line according to the invention, four metal wires, which are provided with electrical insulation, are advantageously arranged as electrical heating conductors on the circumference of the conduit in the longitudinal direction. Arranging four electrical heating conductors on the circumference of the conduit results in twenty six different possible circuits as a parallel and/or series connection of the individual electrical heating conductors, with the result that twenty six different total electrical resistance values can be set, as a result of which there is a wide range of variation in the heating power which can be respectively achieved. It is within the scope of the invention to also produce the electrical heating conductors from bands with an electrically conductive coating or to produce the heating conductors using individual electrically conductive layers which are in the form of strips and are applied to the conduit. The electrical heating conductors may also be integrated inside the wall of the conduit. The electrical heating conductors may also run inside the conduit, for example in the form of a twisted conductor bundle. 
     According to the invention, the wide range of variation in the adaptability of the fluid line according to the invention to a wide variety of heating powers is also improved by virtue of at least one of the heating conductors, preferably all of the heating conductors, having an electrical resistance per unit length which differs from the electrical resistance per unit length of the other heating conductors. The electrical resistance of the individual heating conductors per unit length can be changed, on the one hand, by means of an appropriate selection of materials and/or by changing the conductor cross section. In the event of the individual electrical heating conductors having different resistances, it is expedient if corresponding color coding of the heating conductors is provided. 
     Further advantageous embodiments of the invention are contained in the subclaims and are explained in more detail using the exemplary embodiments which are illustrated in the accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  shows a first embodiment of a fluid line according to the invention, 
         FIG. 2  shows a basic illustration of another embodiment of a heating line according to the invention for use in a fluid line as shown in  FIG. 1 , 
         FIG. 3  shows a basic view of an alternative embodiment of a heating line according to the invention for use in a fluid line as shown in  FIG. 1 , 
         FIG. 4  shows a calculation table for determining the total electrical resistance of a fluid line according to the invention having four electrical heating conductors per conduit. 
     
    
    
     In the different figures, the same parts are always provided with the same reference symbols. 
     DETAILED DESCRIPTION OF THE INVENTION  
     As illustrated in  FIG. 1 , a heatable fluid line according to the invention comprises a heating line  1  comprising a conduit  2 , on the circumference of which an electrical heating element, which comprises four individual electrical heating conductors  3 ,  4 ,  5 ,  6  in the exemplary embodiment illustrated, is arranged. In the exemplary embodiment illustrated, the heating conductors  3 ,  4 ,  5 ,  6  are formed from individual electrical resistance wires. These individual resistance wires each have an electrical resistance R 3 , R 4 , R 5 , R 6  which is dependent on the electrical resistivity of the wire material and on the diameter of the wire and on the total length of the resistance wire wound around the conduit  2 . In the exemplary embodiment illustrated, the heating conductors  3 ,  4 ,  5 ,  6  are wound around the conduit  2  in the form of a spiral parallel to one another and with a constant pitch. The individual heating conductors  3 ,  4 ,  5 ,  6  can be wound around the conduit  2  by machine, for example. This allows continuous winding. As also illustrated, the heating conductors  3 ,  4 ,  5 ,  6  may be surrounded by an external protective layer  7  and this external protective layer  7  may be produced from a wound adhesive tape or from an extruded layer or from a plastic shrink tube. This external protective layer  7  forms external protection against damage and moisture. In addition, the fluid line  1  according to the invention is preferably surrounded by an external protective sleeve  8  which is preferably formed by a corrugated pipe or a protective tube. In the exemplary embodiment illustrated, the external protective sleeve  8  is illustrated in the form of a corrugated pipe. A circumferential air gap is preferably present between the external protective sleeve  8  and the protective layer  7 . 
     The electrical heating conductors  3 ,  4 ,  5 ,  6  are preferably composed of metal but may likewise be produced from carbon material. 
       FIG. 2  illustrates another embodiment of a heating line according to the invention. In this embodiment, the electrical heating conductors  3 ,  4 ,  5 ,  6  are arranged on the circumference of the conduit  2  such that they run in the longitudinal direction of the conduit  2  and parallel to the longitudinal axis of the latter. For the rest, the structure of the fluid line according to the invention with the heating line  1  illustrated in  FIG. 2  corresponds to that shown in  FIG. 1 . 
       FIG. 3  shows an alternative embodiment with regard to the arrangement of, for example, three heating conductors  3 ,  4 ,  5  on the circumference of the conduit  2  for the purpose of forming a heating line  1 . In this case, the heating conductors  3 ,  4 ,  5  run in meandering fashion on the circumference of the conduit  2  in the longitudinal direction of the latter. 
     In the exemplary embodiments illustrated, three or four heating conductors  3 ,  4 ,  5 ,  6  are respectively arranged on the circumference of the conduit  2 . However, it is also within the scope of the invention to arrange a larger number of heating conductors on the circumference of the conduit  2 . The heating conductors may have the same electrical resistance or else have a respectively different electrical resistance. As already stated, the electrical resistance of the heating conductors is determined, on the one hand, by the selection of materials and, on the other hand, by the length and cross section of the individual heating conductors. If the individual heating conductors have a different electrical resistance, it is expedient if the individual heating conductors have corresponding color coding such that a visual check is possible and it is possible to discern which of the individual heating conductors have the same electrical resistance or a different electrical resistance. 
     The inventive design of the heating line  1  or fluid line enables continuous manufacture, with the result that cost-effective production and storage is possible. 
     So that a fluid flowing through the conduit  2  when in use is heated with a desired heating power, it is necessary for the fluid line according to the invention to be able to generate a particular heating power. This heating power is dependent on the available supply voltage which, for example in a motor vehicle, comprises a vehicle electrical system voltage of 12 volts DC. This heating power is also dependent on the electrical resistance of the individual heating conductors and the total electrical resistance of the heating conductors. Depending on the medium to be respectively heated, it is necessary for a particular heating power to always be able to be generated per unit length of the fluid line according to the invention. For this purpose, the invention now provides for the ends of the individual heating conductors  3 ,  4 ,  5 ,  6  to be connected to one another and to the supply voltage in such a manner that the individual heating conductors are connected in series and/or in parallel such that, for the predefined supply voltage, the heating power of the fluid line is determined by the total electrical resistance of all heating conductors. 
       FIG. 4  uses a table to illustrate, for example, how resistance cascading is possible, in the case of a four-conductor concept, that is to say the presence of four heating conductors  3 ,  4 ,  5 ,  6  which are wound around the conduit  2  in the form of a spiral with a constant pitch, by connecting the individual heating conductors  3 ,  4 ,  5 ,  6  in parallel and/or in series. In this exemplary embodiment, the heating conductor  3  has a resistance R 3  of 20 ohms, the heating conductor  4  has a resistance R 4  of 13 ohms, the heating conductor  5  has a resistance R 5  of 10 ohms and the heating conductor  6  has a resistance R 6  of 3 ohms. The pitch of the spiral winding of the individual heating conductors  3 ,  4 ,  5 ,  6  is 30°, from which a length factor per m of 1.178 is calculated. The resistance R 3 , R 4 , R 5 , R 6  per m of the individual heating conductors  3 ,  4 ,  5 ,  6 , which is dictated by the material and diameter, is 16.978 ohms in the heating conductor  3 , 11.036 ohms in the heating conductor  4 , 8.489 ohms in the heating conductor  5  and 2.547 ohms in the heating conductor  6 . The table illustrates the individual possible ways of connecting the individual heating conductors  3 ,  4 ,  5 ,  6 , p being used to indicate a parallel connection of the heating conductors  3 ,  4 ,  5 ,  6  and + being used to indicate a series connection of the individual heating conductors  3 ,  4 ,  5 ,  6 . A combination p 1 -p 1  or p 2 -p 2  indicates which resistances are connected in parallel with one another. As emerges from the table, twenty six different combinations are possible, with the result that twenty six different total resistances can be set by connecting the individual heating conductors  3 ,  4 ,  5 ,  6  of the heating conductors  3 ,  4 ,  5 ,  6  in parallel and/or in series. In this case, provision is likewise made for individual heating conductors of the heating conductors  3 ,  4 ,  5 ,  6  not to be connected to the supply voltage at all, which is expressed in the illustrated table by no entry in the associated field. The smallest resistance value of the overall circuit results when the heating conductors  3 ,  4 ,  5  are connected in parallel with one another and the heating conductor  6  is connected in series with this parallel connection of the three heating conductors, and the highest resistance of the heating conductors  3 ,  4 ,  5 ,  6  results when all heating conductors are connected in series with one another. The end of the series and/or parallel circuit comprising the individual heating conductors  3 ,  4 ,  5 ,  6  is respectively connected to the supply voltage by means of appropriate connecting lines. In this respect, it may likewise be expedient if, in addition to the heating conductors  3 ,  4 ,  5 ,  6 , at least one electrical connecting line for the voltage supply is provided in the fluid line according to the invention such that it runs along the pipeline  2 . This electrical connecting line is surrounded by electrical insulation. 
     According to the invention, it is thus possible to prefabricate a fluid line according to the invention which is provided with standardized winding of individual heating conductors  3 ,  4 ,  5 ,  6 , and it is possible to set the necessary heating power on the basis of the desired length of the fluid line by means of appropriate instructions for connecting the individual heating conductors  3 ,  4 ,  5 ,  6 . The same heating power can also always be set in this manner for each unit length which has been cut to length. 
     The present invention is not restricted to the exemplary embodiments illustrated and described but rather also comprises all embodiments which have the same effect in the sense of the invention. Furthermore, the invention has hitherto not yet been restricted to the combination of features defined in the respective independent claim either but rather may also be defined by any other desired combination of particular features of all the individual features disclosed as a whole. This means that, in principle, virtually any individual feature of the respective independent claim may be omitted or may be replaced with at least one individual feature disclosed at another point in the application. In this respect, the claims should be understood as merely a first attempt at formulating an invention.