Abstract:
A sensor, particularly for determining the oxygen content in exhaust gasses of internal combustion engines, includes sensor element which is fixed in a metallic housing and a sealing flange which is integrally formed on the housing and rests on a sealing seat which is formed on an exhaust system. The sealing flange has two ring elements which are integrally formed on the housing and each have an inclined sealing surface, a hollow space being formed between the two ring elements inside the housing.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a sensor, particularly for determining the oxygen content in exhaust gasses of internal combustion engines. 
     BACKGROUND INFORMATION 
     European Patent No. EP 624 791 (corresponding to U.S. Pat. No. 5,329,806) describes a gas sensor where a sensor element is fixed in a tubular, metallic housing in a gas-tight manner. At its lower part, the tubular housing has a lip facing radially outward which forms a sealing flange. The gas sensor is mounted in an opening of an exhaust system, the lip sitting on a sealing seat formed in the opening. A banjo bolt is led over the housing and screwed into a thread arranged in the opening, thereby joining the lip to the exhaust system in a gas-tight manner. Problematic in this design is, however, that the pressing or upsetting of the relatively thin-walled material of the housing can produce microcracks at the lip which can cause the leakiness of the housing. 
     SUMMARY OF THE INVENTION 
     The present invention has the advantage over the related art that the sealing flange is absolutely gas-tight, and the inclined sealing surfaces produce an absolutely gas-tight sealing seat at the exhaust pipe. Moreover, the hollow design of the sealing flange produces a spring effect which also supports the sealing effect. 
     It is particularly advantageous for the inclined sealing surfaces to be designed in an angle between 10° and 30°, preferably of 20°. Arranging the sealing flange behind the sealing arrangement for the sensor element, as viewed from the measuring gas side, has an advantageous effect on the installation of the sensor. In this manner, the sensor element can first be equipped with the ceramic parts of the sealing arrangement. The housing is then slipped over the sensor element equipped with the sealing arrangement. Furthermore, it is expedient to attach a connecting piece to the exhaust pipe, the connecting piece, at the end face, forming a sealing seat for the sealing flange. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a longitudinal cross section through a sensor mounted in an exhaust pipe. 
     FIG. 2 shows a detailed longitudinal cross section through the housing of the sensor according to FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     A sensor  10 , for example, an electrochemical oxygen sensor, is mounted in an exhaust pipe  11  and has a metallic housing  13 , in which a planar sensor element  15  having a section  17  on a measuring gas side and a section  18  on a connection side is arranged. 
     Housing  13  is a pipe element  20  which is open on both sides and has an end section  21  on connection side and an end section  22  on measuring gas side as well as an interior wall  23  and an exterior wall  24 . Moreover, pipe element  20  has a radially surrounding sealing flange  25  having an upper ring element  26  with a downward inclined upper sealing surface  26   a , and having a lower ring element  27  with an upward inclined lower sealing surface  27   a . The two sealing surfaces  26   a  and  27   a  run at an angle a of approximately 20° relative to a plane running at right angles to the center line of pipe element  20  (FIG.  2 ). Sealing flange  25  having ring elements  26 ,  27  running toward one another is designed in such a manner that a hollow space  29  forms inside housing  13  between ring elements  26 ,  27 . In this manner, the two ring elements  26 ,  27  can act as resilient legs whereby the sealing effect of sealing surfaces  26   a ,  27   a  is increased. In front of sealing flange  25 , as viewed from the measuring gas side, an annular surface  28  is integrally formed on interior wall  23 , the annular surface constituting a stop face for a sealing arrangement  30  which will be described later. Because of this design, sealing flange  25  is located behind sealing arrangement  30 , as viewed form the measuring gas side and is consequently relatively far away from exhaust pipe  11 . 
     To form sealing flange  25 , pipe element  20  is, for example, initially upset, a rounded bulge forming at pipe element  20  in the process. This bulge is subsequently processed, for example, by the manufacturing process of rotary kneading in such a manner that the two inclined sealing surfaces  26   a ,  27   a  are formed. However, one can also conceive other manufacturing processes by which sealing flange  25  can be manufactured efficiently, for example, by drawing and subsequently upsetting. 
     Sealing arrangement  30  mounted in housing  13  is composed, for example, of a molded ceramic part  31  on measuring gas side, a molded ceramic part  32  on connection side, and a sealing element  33  arranged in between. Molded ceramic parts  31  and  32  are composed, for example, of Al 2 O 3  and each have penetrations, which are not further described, for sensor element  15 . Sealing element  33  is composed, for example, of steatite and is inserted in a prepressed condition, having a penetration for sensor element  15 , as well. First, housing  13  is slid over sealing arrangement  30  until annular surface  28  strikes against molded ceramic part  32  on connection side. Subsequently, molded ceramic part  31  on measuring gas side is acted upon by a stamp on measuring gas side, using a pressure force rated such that prepressed sealing element  33  is squashed so that the power components press both against sensor element  15  and interior wall  23 . While the force is acting upon molded ceramic part  31  on measuring gas side, a contraction in area  35  running radially and facing inward is formed in pipe element  20  at end section  22  on measuring gas side. In this manner, ceramic part  31  on measuring gas side is kept in the pressing position with respect to sealing element  33 . 
     At end section  22  on measuring gas side, sensor element  15  protrudes from housing  13  and is surrounded there, for example, by a double protective tube  40 . Double protective tube  40  is inserted into end section  22  on measuring gas side, and there joined to housing  13  by a surrounding weld  41 . Double protective tube  40  has gas entrance and outlet apertures  41  for the exhaust gas/measuring gas. In the present exemplary embodiment, double protective tube  40  is formed in one piece. 
     End section  21  on connection side of housing  13  has a tapering section  45  with an opening  46 . Welded in opening  46  is, for example, a metallic jacketed tube  47 . Arranged in jacketed tube  47  are connecting cables  48  for sensor element  15 . Connecting cables  48  are connected to contacting pieces  49  which are contacted to terminals (not further shown), which are arranged at section  18  on connection side of sensor element  15 . Sensor element  15  can be contacted, for example, by clamping or by an integral connection. However, the cables may be brought out through opening  46  with the assistance of a temperature-resistant PTFE cable gland, as well. 
     For fasting sensor  10  in exhaust pipe  11 , an opening  60  is provided in exhaust pipe  11 , a cylindrical connecting piece  62  having a plane annular surface  63  and a threaded section  64  being welded into the opening. Lower sealing surface  27   a  of sealing flange  25  rests on annular surface  63 . A union nut  70  having an internal screw thread  71  and an internal annular surface  72  is led over housing  13 . Union nut  70  is screwed on connecting piece  62 , thereby pressing sealing flange  25  on annular surface  63 . Thus, annular surface  63  constitutes a sealing seat for sealing flange  25 . 
     For fasting sensor  10  in exhaust pipe  11 , however, other forms of fastening means are also possible, for example, fastening with the assistance of a banjo bolt having a thread on the outer surface which is screwed into an internal screw thread arranged on connecting piece  62 , the sealing seat for sealing flange  25  having to be designed with an additional annular surface inside connecting piece  62 . It is also conceivable to interposition an adaptor between connecting piece  62  and the banjo bolt, sensor  10  then, with sealing flange  25 , sitting on an annular surface of the adaptor, and the adaptor, with a further annular surface, resting on the annular surface of connecting piece  62 .