Abstract:
A connecting lead for a sensor, in particular for a sensor for determining a physical property of a measured gas, e.g. for determining the temperature or oxygen content in the exhaust gas of internal combustion engines, is described, said sensor comprising a sheathing tube, at least two electrical conductors extending in the sheathing tube, and an insulating arrangement that insulates the electrical conductors from one another and from the sheathing tube. To allow the use of unsheathed bare metal wires as electrical conductors, and avoid short circuits on the one hand between the metal wires and on the other hand between the metal wires and the sheathing tube, especially upon bending of the metal tube during installation, the insulating arrangement has a plurality of insulating elements, braced against one another, that have at least two through holes through each of which one electrical conductor is guided.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a connecting lead for a sensor, in particular for a sensor for determining a physical property of a measured gas, in particular for determining the oxygen content or temperature in the exhaust gas of internal combustion engines.  
       BACKGROUND INFORMATION  
       [0002]     In sensors that are used as exhaust gas lambda probes in the exhaust gas fittings of internal combustion engines in motor vehicles, upon installation the sheathing tube is bent largely at a right angle in order to make contact with the connecting lead, i.e. to allow connection to the electrical system of the motor vehicle. In order reliably to rule out a short-circuit of the electrical conductors, the electrical conductors are electrically insulated from one another and from the sheathing tube.  
         [0003]     In a known connecting lead for a sensor of this kind (German Patent No. 195 23 911), the electrical conductors are sheathed in a high-strength electrical insulation, e.g. glass filament, and four or five sheathed electrical conductors are received, with the highest possible packing density, in a sheathing tube made of a temperature-resistant metal, e.g. CrNi or NiCr alloys. At the connection end, the electrical conductors are welded onto crimp sleeves in which the ends of connecting cables leading to a connector plug are caulked. The crimp sleeves are encapsulated, together with one end of the sheathing tube and the end region of the connecting cable, in a sealing element made, for example, of PTFE. To allow the sheathing tube to be bent without damage, care must be taken that the sheathed electrical conductors have sufficient looseness within the sheathing tube to compensate for the changes, during bending of the metal tube, in the lengths of the electrical conductors inside the sheathing tube.  
         [0004]     In a heat-resistant connecting lead for an exhaust gas lambda probe that is also known (European Published Patent Application No. 0 843 321), a pair of bare electrical conductors made of nickel wire, and a pair of aeration tubes made of stainless steel, extend inside the stainless-steel sheathing tube. The electrical insulation is made up of a magnesium powder that is introduced into the metal tube in such a way that the two pairs of electrical conductors and aeration tubes are disposed, diametrically opposite one another, at the four corners of a square, and are completely insulated by the magnesium powder from one another and from the sheathing tube. A connecting lead of this kind cannot be bent upon installation.  
       SUMMARY OF THE INVENTION  
       [0005]     The connecting lead according to the present invention has the advantage that the electrical conductors are guided by the insulating disks at a defined spacing from one another and from the sheathing tube, and bare wires can therefore be used as electrical conductors, without the sheathing (made of high-temperature-resistant material) that is very expensive to manufacture. The process of manufacturing the connecting lead can be configured in very simple and inexpensive fashion, since the insulating elements merely need to be threaded onto the conductors, and the threaded-on unit can then easily be pulled into the sheathing tube.  
         [0006]     According to a preferred embodiment of the invention, the insulating elements are braced directly against one another in one element subregion and have, in the other element subregion remaining in the bracing plane, a clearance from one another that increases toward the element periphery. This spacing can be achieved by beveling or rounding the insulating elements. This geometry of the insulating elements guarantees the bendability of the connecting lead, since as the sheathing tube is bent, the insulating elements can assume an acute-angle incidence to one another because of the space present in the subregion, and thus allow curved guidance of the sheathing tube. As the sheathing tube is bent, the distances between the electrical conductors on the one hand, and between the electrical conductors and the sheathing tube on the other hand, are kept constant, and a short-circuit due to contact between the bare wires is avoided.  
         [0007]     According to a preferred embodiment of the invention, the insulating elements are embodied as disks whose at least one disk surface are beveled toward the disk center in one subregion, and rest against one another with their flat disk surface region. The partial beveling of the insulating disks can be performed on each disk surface, or on one of the two disk surfaces. Instead of a bevel, a rounding can also be performed in such a way that a rounding radius joins the one disk surface to the other.  
         [0008]     According to an advantageous embodiment of the invention, the through holes in each insulating disk are disposed in such a way that their hole axes lie next to one another on one diameter line. As a result, all the electrical conductors extend in a neutral zone of the sheathing tube, so that their lengths, clamped in place at the tube ends, are not modified upon bending.  
         [0009]     According to an advantageous embodiment of the invention, the insulating disks each have a through opening, the through openings in the insulating disks resting against one another being mutually aligned. Guided through the through holes is a preferably round spring rod that is retained in axially nondisplaceable fashion in the sheathing tube. Retention is accomplished by axial bracing of the spring rod in the region of the tube ends. The spring rod places the insulating disks under stress after the sheathing tube has been bent, so that vibrations of the insulating disks during vehicle operation, which might cause breakage of the insulating disks, are prevented.  
         [0010]     According to a preferred embodiment of the invention, the two outer ones of the insulating disks lying against one another are braced axially in the sheathing tube. The bracing is accomplished at the connection end of the sheathing tube by a seal element made of electrically insulating material and pressed into the sheathing tube, and bracing at the sensor end of the sheathing tube is accomplished by an insulating element that braces against the sheathing tube. The insulating element is in turn braced against at least one end disk, made of electrically insulating material, that closes off the sensor end of the sheathing tube. The insulating element and the at least one end disk are located in that part of the sheathing tube that is not bent but remains straight. The at least one end disk defines the desired connection pattern of the electrical conductors for the sensor element; and the insulating element creates, with its through orifices, the transition from the disposition, which deviates spatially from the connection pattern, of the through holes for the electrical conductors in the insulating disks. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a longitudinal section of a connecting lead for a sensor, in the state as delivered.  
         [0012]      FIG. 2  is a side view, partially sectioned, of the connecting lead in  FIG. 1  after final installation.  
         [0013]      FIG. 3  is a side view of an insulating disk in the connecting lead in  FIGS. 1 and 2 .  
         [0014]      FIG. 4  is a plan view of the insulating disk in the direction of arrow IV in  FIG. 3 .  
         [0015]      FIG. 5  is a perspective view of the insulating disk in  FIGS. 3 and 4 .  
         [0016]      FIG. 6  is a side view of an insulating element in the connecting lead in  FIGS. 1 and 2 .  
         [0017]      FIG. 7  is a plan view of the insulating element in the direction of arrow VII in  FIG. 6 .  
         [0018]      FIG. 8  is a perspective depiction of the insulating element in  FIGS. 6 and 7 .  
         [0019]      FIG. 9  is a side view of an end disk of the connecting lead in  FIGS. 1 and 2 .  
         [0020]      FIG. 10  is a plan view of the end disk in the direction of arrow X in  FIG. 9 .  
         [0021]      FIG. 11  is a perspective depiction of the end disk in  FIGS. 9 and 10 . 
     
    
     DETAILED DESCRIPTION  
       [0022]     The connecting lead depicted in  FIGS. 1 and 2  for a sensor, in particular for a sensor for determining a physical property of a measured gas, such as the temperature or oxygen concentration in the exhaust gas of internal combustion engines of motor vehicles, serves to join the sensor element (not depicted here), exposed to the measured exhaust gas, to a connector plug (not depicted here) for connecting the sensor to a control unit in the electrical system of the motor vehicle. Connecting lead  11  has a sheathing tube  13  made of high-temperature-resistant metal and, in the exemplary embodiment, a total of five electrical conductors  14  that extend in the interior of sheathing tube  13  between a sensor end  11  and a connector end  12  of sheathing tube  13 . Electrical conductors  14  are embodied as bare, high-temperature-resistant wires. In order to avoid short circuits on the one hand between electrical conductors  14  and on the other hand between electrical conductors  14  and sheathing tube  13 , electrical conductors  14  are guided in insulating means that prevent electrical conductors  14  from coming into mutual contact or into contact with sheathing tube  13  even in the context of a bending of sheathing tube  13  that occurs during installation, as depicted in  FIG. 2 . Provided for this purpose are a plurality of insulating elements, braced against one another, that are embodied in the exemplary embodiment as insulating disks  15  but can also have a different geometric shape. Insulating disks  15  rest with their disk surfaces  151 ,  152  ( FIG. 3 ) against one another and are partially braced with their peripheral surfaces  154  ( FIG. 3 ) against sheathing tube  13 . Insulating disks  15  have mutually aligned through holes  16  ( FIG. 3 ), and one of electrical conductors  14  is guided through each mutually aligned through hole  16 .  
         [0023]      FIGS. 3 through 5  depict an insulating disk  15  in a side view, plan view, and perspective view. The two mutually parallel disk surfaces  151 ,  152  are beveled at an acute angle toward disk center  153  in the lower surface region so that there results on each disk surface  151 ,  152 , as is evident in  FIG. 1 , a region that extends parallel to the disk center, hereinafter referred to as parallel surface  151   b ,  152   b , and a region proceeding at an obtuse angle therefrom, hereinafter called oblique surface  151   a ,  152   a . The mutually facing oblique surfaces  151   a ,  152   a  of two adjacent insulating disks  15  enclose an acute angle between them, whereas parallel surfaces  151   b  and  152   b  rest in planar fashion against one another. Each insulating disk  15  rests with its peripheral surface  154  against the inner wall of sheathing tube  13 . Peripheral surface  154  possesses a flat surface portion  154   a  extending in chord-like fashion. Placed on one diameter line extending parallel to this flat surface portion  154   a  are hole axes  161  of five equidistantly disposed through holes  16 . Their number corresponds to the number of electrical conductors  14  to be guided in sheathing tube  13 , that number being arbitrary and depending on the connection requirements of the sensor element. At a radial distance from this diameter line, a round through opening  17  is introduced in the region of parallel surfaces  151   b ,  152   b . As is evident from  FIGS. 3 and 5  and also from  FIGS. 1 and 2 , each insulating disk  15  has a concave indentation  18  on disk surface  151  and a convex protrusion  19  on disk surface  152 . Indentation  19  and protrusion  19  respectively surround the entrance openings and exit openings of through holes  16 . Indentations  18  and protrusions  19  are matched to one another in terms of shape in such a way that indentations  18  and protrusions  19  of insulating disks  15  that rest against one another engage conformingly into one another (cf.  FIGS. 1 and 2 ).  
         [0024]     As is evident from  FIGS. 1 and 2 , in the exemplary embodiment of the connecting lead described here, a total of fourteen insulating disks  15  are serially arranged and retained in axially nondisplaceable fashion in sheathing tube  13  in the manner described. The number of insulating disks  15  depends on the length of sheathing tube  13 . A round spring rod  20  is guided through the mutually aligned through openings  17  and is likewise retained nondisplaceably in the axial direction in sheathing tube  13 . One of the five electrical conductors  14 , of which only one is visible in  FIGS. 1 and 2 , is guided through each of the mutually aligned through holes  16  in insulating disks  15 .  
         [0025]     Disposed at sensor end  11  of measurement tube  13 , specifically in the portion of sheathing tube  13  that is not bent during installation but remains straight, are an insulating element  21  and two end disks  22 , resting against one another, that constitute the sensor-end bracing for the series of insulating disks  15 . Sheathing tube  13  is crimped over at the end onto the outer end disk  22 .  
         [0026]      FIGS. 9 through 11  show an enlarged depiction of end disk  22 . It is round in shape, and is braced with its peripheral surface  224  against the inner wall of sheathing tube  13 . It possesses five through holes  23 , corresponding to the number of electrical conductors  14  and having the same diameter as through holes  16  in insulating disks  15 , and are disposed in accordance with the connection pattern of electrical conductors  14  defined by the sensor element. In the exemplary embodiment of  FIGS. 9 through 11 , the connection pattern is approximately U-shaped, three through holes  23  being located in the crosspiece of the U and one through hole  23  in each limb of the U. A different connection pattern is of course possible, for example with three through holes  23  lying on one of two parallel lines that are equidistant from the diameter line. Disk surfaces  221  and  222  of end disk  22  are flat and parallel to one another. Once again a concave indentation  24  is present on disk surface  221 , and a geometrically identical convex protrusion  25  on disk surface  222 , each respectively surrounding the entrance openings and exit openings of through holes  23 .  
         [0027]     Insulating element  21 , made of high-temperature-resistant electrical insulating material, is depicted in  FIGS. 6 through 8 . Through holes  26  are introduced into insulating element  21  in such a way that their entrance openings, located in end surface  211  of insulating element  21 , are located congruently with the exit openings on disk surfaces  152  of insulating disks  15 , and their exit openings disposed on end surface  212  are located congruently with the hole pattern of through holes  23  in end disk  22 . In addition, an axial through orifice  31  is introduced into insulating element  21  in such a way that it aligns with through openings  17  in insulating disks  15 . Axial through orifice  31  has a diameter identical to that of through openings  17 , and serves for the passage of spring rod  20 . A concave indentation  27  is once again recessed into end surface  211  of insulating element  21  in such a way that it can conformingly receive convex protrusion  19  of an insulating disk  15 . Projecting on end surface  212  is a convex protrusion  28  which is configured so that it is conformingly insertable into concave indentation  24  of an end disk  22 .  
         [0028]     Near connection end  12  of sheathing tube  13 , electrical conductors  14  are each joined to an electrical connecting cable  29  by ultrasonic welding. Connecting cables  29 , of which only one is visible in  FIGS. 1 and 2 , are connected to a connector plug (not depicted here). At this connector end  12  of sheathing tube  13 , the series of insulating disks  15  is braced by a seal element  30  pressed into end  12  of sheathing tube  13 . This seal element  30  has on its periphery circumferential sealing lips  301 , axially spaced apart from one another, that press against the inner wall of sheathing tube  13  and ensure a sufficient sealing effect. Spring rod  20 , guided through the through openings  17  in insulating disks  15  and through axial through orifice  31  in insulating element  21 , is braced at one end against seal element  30  and at the other end against end disk  22  resting against insulating element  21 .  
         [0029]     Upon assembly of the connecting lead, the individual electrical conductors  14  are threaded through the mutually aligned through holes  16  in insulating disks  15 , through the through orifices  26  in insulating element  21 , and through the through holes  23  in the two end disks  22 , and protrude at sensor end  11  of sheathing tube  13  so that contact can be appropriately made to them from the sensor element. A protective cap  32 , indicated with dashed lines in  FIG. 1 , can be slid onto sensor end  11  of sheathing tube  13  as a transport protector, protecting the protruding ends of electrical conductors  14  from damage. At connector end  12  of sheathing tube  13 , seal element  30 , which surrounds the connector ends of electrical conductors  14  and the connecting cables  29  contacted thereto, is pressed into sheathing tube  13 ; sheathing tube  13  is then rolled over in this region so that a positive and nonpositive join is produced between sheathing tube  13  and seal element  30 .  
         [0030]     Upon installation of the sensor, the connecting lead is bent at a right angle in the direction of arrow  33  in  FIG. 1  so that it assumes the shape depicted in  FIG. 2 . This bending is possible because of the geometry of insulating disks  15  described above, since the latter are fitted together like the vertebrae of a spinal column. The mutually facing oblique surfaces  151   a  and  152   a  of adjacent insulating disks  15  permit such bending because they rest against one another not in planar fashion but with an acute-angled space left open, and come into contact against one another only after metal tube  13  has been correspondingly curved.  
         [0031]     The configuration of the insulating elements is not limited to the geometric conformation of insulating disks  15 . For example, insulating disks  15  can also, in the subregion of their disk surfaces, be beveled on only one of the sides facing away from one another or can be rounded on one or both sides. All that is important for the subsequent bending of sheathing tube  13  is that the insulating elements, braced against one another in one subregion, not touch one another in the other subregion within the bracing plane but rather have a clearance from one another that increases toward the outer periphery of the insulating elements. This clearance can be brought about by beveling or rounding on one or both sides. The insulating elements can, however, also be embodied as spheres that rest against one another at a single point, or as spherical caps that are serially arranged in the same direction, so that the one spherical shell is always braced in single-point fashion against the plane of the next spherical cap.