Abstract:
An electrode system, particularly for installation in an exhaust line, has a holding body made of an insulating material, on which at least one operating electrode is positioned. The holding body has a heating device for facilitating easy cleaning in the installed position.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an electrode system, particularly for installation in an exhaust line, and a method for cleaning an electrode system.  
         BACKGROUND INFORMATION  
         [0002]    An electrode system of the type initially described may be implemented, for example, as a carbon black sensor which may be used for installation in an exhaust system of a diesel engine.  
           [0003]    A conventional electrode system may be constructed in such a manner that it includes a holding body made of a ceramic material, on which at least one operating electrode is positioned, which may be used, for example, for induction measurements of charged particles of exhaust of a diesel engine. The holding body may penetrate a socket, which may be implemented as a socket of a spark plug. The socket may be screwed into a corresponding thread which may be implemented in a wall of a pipe of an exhaust system. The electrode bushing may be connectable, at a region lying outside the pipe, to an analysis and/or control device via appropriately designed terminals.  
           [0004]    Furthermore, particles such as carbon black particles may be capable of being electrically charged using an electrode. The charge of the particles may then be given off again at an electrode having a suitable polarity and/or a suitable shape, such as that of a Faraday cup. It may be required to use electrodes which are sufficiently well insulated.  
           [0005]    It may be required, particularly if an electrode system of the type initially described is used continuously in a pipe of an exhaust system, to maintain the insulation resistance of the holding body between the electrode and the pipe and therefore to check it regularly using an electrical measurement. The electrically charged particles may precipitate on the holding body and thus may reduce its insulation resistance.  
           [0006]    For this reason, it may be required to clean the holding body, which cleaning is conventionally performed in a chemical or mechanical manner.  
         SUMMARY OF THE INVENTION  
         [0007]    An electrode system according to the present invention provides a holding body implemented with a heating device so that it may be cleaned easily in the installed position.  
           [0008]    In an electrode system according to the present invention, it may be only required to activate the heating device, so that particles, such as carbon black particles, which may have precipitated in a holding body projecting into a testing or measuring volume, may be combusted.  
           [0009]    The heating device may also be kept at a temperature level at which no particles may accumulate on the holding body.  
           [0010]    An electrode system according to the present invention may be suitable for installation in an exhaust system of a motor vehicle having a diesel engine. However, it may also, for example, be used in other types of exhaust lines, for example those of an oil heater.  
           [0011]    The operating electrode may be used, for example, for measuring the carbon black concentration in exhaust of a diesel engine.  
           [0012]    The heating device itself may be shielded against particles that may precipitate on the electrode system so that its efficiency may not be impaired by these particles. For example, the heating device may be embedded in the holding body, which may be manufactured from a ceramic.  
           [0013]    Alternatively, the heating device may be positioned in a hollow space of the holding body which is open on a side lying outside the testing and/or measuring volume. The heating device may be inserted into the holding body from this side.  
           [0014]    The holding body may, for example, be implemented in a rod or tube shape and may have an essentially rectangular, round, or otherwise suitable cross section.  
           [0015]    An exemplary embodiment of the electrode system according to the present invention may include a device for measuring an insulation resistance of the holding body. A device of this type, which may be configured for measuring an impedance and/or a resistance or a capacitance, may be positioned on or in the holding body inside the testing volume and may be used for detecting particle accumulations on the holding body. Using the measuring device, a point in time may be determined at which the heating device may be activated so that particles precipitated on the holding body break away or at which the temperature of the holding body may be elevated in such a manner that no particles accumulate there.  
           [0016]    Through the combination of the heating device and the device for measuring the insulation resistance, accumulations of charged particles on the holding body may be detected and appropriate cleaning steps may then be initiated. A testing and cleaning routine of this type may run automatically.  
           [0017]    The device for measuring the impedance may be implemented in such a manner that it includes a testing electrode which is located between a first holding body end, on which the at least one operating electrode is positioned, and an attachment region.  
           [0018]    In this manner, it may be ensured that the insulation resistance may be measured in the region of the holding body which lies between the operating electrode and the attachment region, which may be metallic, and which may be attached in the operating state, for example, to a pipe of an exhaust system. The attachment arrangement may be connected to ground.  
           [0019]    An electrode system according to the present invention may include a socket for attachment to an exhaust system. The socket, which may be manufactured from metal, may, for example, be implemented as a spark plug socket, so that it may be penetrated by the holding body and may have a thread to be screwed into a corresponding thread of a wall of a pipe.  
           [0020]    In an exemplary embodiment, the operating electrode may, for example, include at least one grid which may be used for charging carbon black particles.  
           [0021]    In a further exemplary embodiment, the operating electrode may also be implemented in a cup shape. An exemplary embodiment of the operating electrode of this type, which may essentially correspond to a Faraday cup, may be suitable for charge measurement.  
           [0022]    The present invention also provides an exemplary method for cleaning an electrode system, which has a holding body made of an insulating material on which at least one operating electrode is implemented. In this exemplary method, particles precipitated on the holding body may be removed by heating the holding body using a heating device. The holding body may, for example, be heated continuously or periodically. The heating device may be operated as a function of the insulation resistance of the holding body, in such a manner that the temperature of the heating device is elevated as the insulation resistance of the holding body falls.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 shows a schematic illustration of a pipe of an exhaust system of a diesel engine having an electrode system according to an exemplary embodiment of the present invention.  
         [0024]    [0024]FIG. 2 shows a more detailed schematic illustration of the electrode system shown in FIG. 1.  
         [0025]    [0025]FIG. 3 shows a schematic projection of a holding body of the electrode system shown in FIG. 1.  
         [0026]    [0026]FIG. 4 shows a cross-sectional view of a section through the holding body along line IV-IV in FIG. 3.  
         [0027]    [0027]FIG. 5 shows a cross-sectional view of a section through the holding body along line V-V in FIG. 3.  
         [0028]    [0028]FIG. 6 shows a cross-sectional view of a section through the holding body along line VI-VI in FIG. 3.  
         [0029]    [0029]FIG. 7 shows an electrode system having a protective cap.  
         [0030]    [0030]FIG. 8 shows a longitudinal cross-sectional view of an electrode system in the shape of a hollow cone.  
         [0031]    [0031]FIG. 9 shows an electrode system in the shape of a hollow cone having a grid electrode.  
         [0032]    [0032]FIG. 10 shows a Faraday cup of an electrode system. 
     
    
     DETAILED DESCRIPTION  
       [0033]    In FIG. 1, an exhaust pipe  1  of an exhaust system of a diesel engine is illustrated, into which an electrode system  2  is screwed in the radial direction. Electrode system  2 , which is illustrated in more detail in FIGS.  2  to  6 , has a socket  3 , made of a metallic material, which is implemented having an external thread  8  which engages in a corresponding internal thread of exhaust pipe  1 .  
         [0034]    Socket  3  is penetrated by a holding body  4 , which is made of a ceramic and insulating material. Holding body  4  is essentially rod-shaped in this case and has a rectangular cross-section. One end  9  of holding body  4  projects into exhaust pipe  1 .  
         [0035]    Four operating electrodes  5  are implemented on end  9  of holding body  4 , which are used for measuring carbon black particles in exhaust flowing through exhaust pipe  1 . Electrodes  5  are each connected to a terminal  7  via bushings  6  embedded in holding body  4 . Electrode terminals  7 , of which there are therefore five, are connectable to analysis and/or control electronics.  
         [0036]    Furthermore, embedded in ceramic holding body  4  is an essentially axially oriented heating element  13 , which is provided with two terminals  14  and  15 , which lie outside exhaust pipe  1  and via which heating element  13  is connectable to a voltage source, which is not shown.  
         [0037]    Furthermore, a testing electrode  16  is positioned on holding body  4  which is used for measuring the insulation resistance of holding body  4 . Testing electrode  16 , which surrounds holding body  4 , is connected via a bushing  17  to terminal  18 , which lies outside exhaust pipe  1 . Terminal  18  is in turn connected to a resistance measuring instrument  19 , whose second input is connected to a terminal  10  which is implemented on socket  3 . Therefore, the insulation resistance of ceramic holding body  4  between testing electrode  16  and socket  3  may be measured using measuring instrument  19 .  
         [0038]    The insulation resistance of holding body  4  in the region lying between testing electrode  16  and socket  3  may, however, also be determined in a further exemplary embodiment via a capacitance measurement.  
         [0039]    Multiple testing electrodes may be used.  
         [0040]    Electrode system  2  illustrated in FIGS.  1  to  6  may operate in the manner described in the following.  
         [0041]    Operating electrodes  5  of electrode system  2  are used for measuring carbon black particles in exhaust flowing through exhaust pipe  1 . The measurement may, for example, be an induction measurement of charged carbon black particles which flow past electrode system  2 . If electrically charged particles precipitate in the region of holding body  4  lying between testing electrode  16  and socket  3 , the electrical resistance of this region may be reduced. This insulation resistance is measured using measuring instrument  19 . As soon as the insulation resistance has fallen below a predefined threshold value, a voltage source connected to heating element  13  via terminals  14  and  15  is activated, so that ceramic holding body  4  is heated, due to which its surface is burned free of the carbon black particles.  
         [0042]    An alternative exemplary embodiment of an electrode system  20  is illustrated in FIG. 7. The design of electrode system  20  may largely correspond to that of the electrode system shown in FIGS.  1  to  6 . Electrode system  20 , however, has only one operating electrode  5 , which is connected to a terminal  7  via a bushing, which is not shown here.  
         [0043]    A testing electrode  16  is connected to a terminal  18 , and a heating element embedded in holding body  4  is provided with terminals  14  and  15 . Terminal  7  of operating electrode  5 , terminal  16  of testing electrode  16 , and terminals  14  and  15  of the heating element are each connected to a line  22 . Lines  22  are initially guided into a cover cap  23 , which forms a tight hermetic seal, and then run into a cable strand  21 , which adjoins cover cap  23  on the side facing away from holding body  4 . Cable strand  21  leads to an electronic measuring and control device.  
         [0044]    In FIG. 8, an electrode system  30  is illustrated which is implemented having a holding body  31  which essentially has the shape of a rounded hollow cone and includes an attachment arrangement for attachment to an exhaust system.  
         [0045]    An operating electrode  5 , which is connected to a terminal  7 , indicated only schematically, for a measurement and/or control device, via a bushing  6 , running in holding body  31 , which is shaped like a hollow cone, is implemented on the tip of ceramic holding body  31 . The attachment arrangement lies on the end of electrode system  30  facing away from operating electrode  5 .  
         [0046]    In addition, an essentially annular testing electrode  16 , which is connected via a bushing  17  in holding body  31 , which is shaped like a hollow cone, to a terminal  18 , also only shown schematically, for a measuring instrument, is implemented on the circumference of holding body  31 , which has a hollow  32 .  
         [0047]    Furthermore, a heating device for holding body  31  is also positioned inside hollow  32 .  
         [0048]    In FIG. 9, an electrode system  40 , whose configuration may essentially correspond to that of the electrode system shown in FIG. 8, is illustrated in simplified form. However, in electrode system  40 , a grid-shaped electrode  42  for charging carbon black particles is implemented on the tip of a ceramic holding body  41 .  
         [0049]    Furthermore, a heating element  43  having two terminals  14  and  15 , which is insertable into the hollow of holding body  41 , which is shaped like a hollow cone, in the direction of an arrow F and is used for heating holding body  41 , is schematically illustrated in FIG. 9.  
         [0050]    In FIG. 10, a cup-shaped electrode  50  is illustrated which is used as a Faraday cup for charge measurement of carbon black particles and is attachable to a holding body of an electrode system, for example to the holding body shown in FIG. 9, in place of the grid.  
         [0051]    The mode of operation of the electrode systems shown in FIGS.  7  to  10  may essentially correspond to that of the electrode system shown in FIGS.  1  to  6 .