Abstract:
A sealing device encloses a range of a base area and/or a cover area of a sensor element, which is accessible through an opening developed in a housing. Because of this, a seal may be achieved between the measured gas region and the reference gas region of the gas sensor, that is constructed using comparatively few individual parts, and, accordingly, also requires fewer method steps in its manufacture and assembly.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a gas sensor, especially for determining the oxygen content in exhaust gases of internal combustion. 
   BACKGROUND INFORMATION 
   Two such gas sensors may be seen in two German Patent Application Nos. DE 41 26 378 and DE 198 03 334 that originate from the same applicant. These two gas sensors are constructed from a plurality of individual parts, that have to be fit together with a corresponding expenditure. The manufacturing costs for such gas sensors are, consequently, among other things, besides being a function of the number of component parts, also a function of the required number of manufacturing steps. 
   SUMMARY OF THE INVENTION 
   Therefore, the present invention is based on the object of reducing the cost of manufacturing such gas sensors. The present invention relates to a gas sensor, especially for determining the oxygen content in exhaust gases of internal combustion engines. A crux of the present invention is that a seal encloses a range of a surface, preferably a base area or a cover area of the sensor element, which is accessible through an opening developed in the housing. 
   Because of such a sealing design, it is possible, using only one sealing element, to separate a large planar region of the sensor element from the measured gas region of the gas sensor. The seal, in this context, may be established together with the sensor element, in both a sealing and a fixing manner, in a single method step, by compression molding of the housing. To accomplish this, neither additional fixing elements nor further method steps are required for their production or for mounting them. 
   An additional advantage of this sealing device is that this sensor region is easily accessible for carrying out additional processing steps, even after sealing takes place, which may be attributed especially to the fact that the opening in the housing is designed transversely to the longitudinal extension of the sensor element. Thus, the sensor element may be contacted, for instance, on the inside, directly at the printed circuit traces, the type of contacting even being freely selectable within the scope of the given connecting possibilities. Contact surfaces situated at the surface of the sensor element, that were required up to this time, for the connecting wires leading to the outside, the so-called contact pads, may consequently be omitted. 
   In such a design, it is also possible to situate the seal about several connecting contacts, in common, of the sensor element and/or about one or more connecting contacts individually. An additional cost reduction comes about by doing without separately developed sealing elements, particularly if these sealing elements are situated at the sensor element using a single additional method step in producing the sensor element that is preferably constructed in a planar manner. 
   In order to be able to automate even better the production sequence when assembling the gas sensor, in one advantageous refinement it may be provided that the seal is developed in several parts, so that a sensor fixing element is situated between a part of the seal on the sensor side and a part of the seal that is on the housing side. Therewith it is possible, for example, to situate the seal in the housing together with this sensor fixing element, and, if necessary, to already wire the contact elements of the connecting lines, so that the entire unit may be prefabricated, and has subsequently still only to be automatically equipped with the sensor element and compression molded. 
   In this case it is particularly advantageous if a positioning aid and/or a fixing aid is situated on the seal. If the seal is additionally developed electrically or insulating with respect to heat technology, this has a further positive effect on the fixing and contacting of the sensor element in the housing. Especially at high temperatures, at which various alloys become electrically conductive, interferences in the transmission of electrical signals may be reduced or even completely avoided by using insulatingly fixed contacts. 
   However, besides the embodiment of the seal that is directly printed onto the sensor element, it may also be advantageous to provide such a device as a separately developed insertion part. This is particularly of advantage if additional positioning and/or fixing elements are provided for the sensor element in the housing. In that case, for example, a sealing element developed as a separate part may be inserted between such a positioning element and/or fixing element and the housing. Of course, it is also possible to develop the seal in common with the positioning and/or fixing element as one unit, which, in turn, again has a positive effect on the method sequence during assembly. 
   Preferably, the seal is made of a ductile material, so that it is able to take up the forces occurring during the compression molding of the housing, and, at the same time, fix the sensor element in a sealing manner. 
   It is regarded as being particularly preferred if the seal, or at least a part of the seal, is made of fused material. Thus, a gas-tight connection may be developed between a metallic and a ceramic substrate, such as the one according to the technical teaching of German Patent Application No. DE 101 35 235, in order to connect the sensor element that is, as a rule, made of ceramic to a metallic housing in a gas-tight manner. In this case, no additional sealing elements are required, and the fixing of the sensor element is done without any deformation whatsoever of the adjacent material regions. This is possible especially when using a laser beam, which heats mutually bordering materials possibly with, or even without additionally required solder glass and fuses them with each other. 
   Using a seal developed in such a way, additional method steps may be omitted, such as those for manufacturing, storing and assembling sealing and/or fixing elements that are thereby omitted. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a top view, at an angle, showing a housing, pulled apart in an exploded manner, of a gas sensor having a sensor element that is to be fitted into it, and a sealing device according to the present invention. 
       FIG. 2  shows a sensor element having a sealing device according to the present invention. 
       FIGS. 2   a ,  2   b  and  2   c  show an enlarged representation of the sealing region from  FIG. 2  ( FIG. 2   a ) and specific embodiments modified from these ( FIGS. 2   b ,  2   c ). 
       FIG. 3  shows a cut out sectional representation through a housing having a sensor element set into it and a seal according to the present invention. 
       FIG. 4  shows a specific embodiment modified from  FIG. 3 . 
       FIG. 5  shows a top view, at an angle, showing a sensor element housing pulled apart in an exploded manner, having a sensor element that is to be fitted into it, as well as various elements of the sealing device according to the present invention. 
       FIG. 6  shows a specific embodiment as in  FIG. 1 , however, having an additionally situated positioning and/or fixing element. 
       FIG. 7  shows a gas sensor housing prepared for accommodating a sensor element. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a top view, at an angle, onto a gas sensor having components  2  to  4  that are shown pulled apart in an exploded manner. For an improved representation of the individual details, housing parts  2   a  through  2   c  are also shown in an exploded manner. 
   Housing part  2   a  has an opening  2 . 1  in its wall that is directed upwards, which makes possible access to inner space  2 . 5  of housing  2 . On the inside of this wall, and around opening  2 . 1 , a sealing region  2 . 2  is defined for the sealing device according to the present invention. For the flexible use of the housing, an additional opening  2 . 3  is developed at the wall of housing part  2   a  lying opposite the first opening, to which, according to the present invention, a corresponding sealing region  2 . 4  is assigned. 
   At a sensor element  3 , situated in front of housing  2 , a seal  4  mounted on the former is shown. When sensor element  3  is fixed, this sealing device is pressed against sealing region  2 . 2  on the inside of housing  2 , so that there is created a gas-tight separation between the measured gas region and the reference gas region of the gas sensor. Additional fixing elements may be provided for fixing sensor element  3  in housing  2 , which, however, have not been shown here, for simplicity&#39;s sake. 
   Seal  4 , situated at sensor element  3 , consequently separates a region of a base area and/or cover area of the sensor element from the remaining part of the sensor element that is exposed to the measuring gas. It forms the sensor element part, that is assigned to the reference region of the gas sensor, which is accessible via opening  2 . 1  that is developed transversely to the longitudinal extension of the sensor element, even after the sensor element is fixed. Consequently, the seal encloses several connecting contacts  3 . 2 , which are developed in common in contact region  3 . 1 . For the separation of an individual contact, for instance, in this case, a sealing crosspiece  4   a  is shown between adjoining sections of seal  4  that run in the longitudinal direction. 
   Various modifications of this specific embodiment of the sealing device according to the present invention are shown in  FIGS. 2 through 2   c .  FIG. 2  shows a sensor element  3  having a first specific embodiment of a seal  4  according to the present invention, without an additional sealing crosspiece  4   a .  FIG. 2   a  shows an enlarged cutout A from the illustration in  FIG. 2 . In this case, it may be recognized that contact  3 . 2   a  has, in addition, an access to the reference gas channel on the inside of the sensor element. 
     FIG. 2   b  has a specific embodiment modified from the latter, which, in addition, has a hole-like positioning aid and/or fixing aid  3 . 4 . This, together with a further element that engages in the opening, may form an ensurance against loss for the sensor element. Because of this, even if there is a possibly abating clamping effect of the housing on the sensor element, the sensor element is no longer able to slip out of it. 
   This makes it increasingly certain that equipment positioned downstream in the exhaust gas plant, such as a catalyst, is protected from damage due to a lost sensor element. 
     FIG. 2   c  shows another specific embodiment of a sealing device according to the present invention on a sensor element  3  in a cutout-like, enlarged illustration. In this case, seal  4  is made up of three separately developed sealing elements  4   b , that are in each case situated around a connecting contact  3 . 2 . For this specific embodiment, the housing has correspondingly developed openings, which also make possible access to the contacts. 
     FIG. 3  shows the sectioned representation of a housing part  2 , a sensor element situated in it, and a seal  4 , according to the present invention, of a gas sensor  1 . 
   From the base area or the cover area of sensor element  3 , a connecting contact  3 . 2  extends through opening  2 . 1 , all the way through the housing, to the outside. It is located in the region of the gas sensor that is on the reference gas side, and that is separated from the region of the measuring gas side by seal  4  in the housing. Reference gas channel  3 . 5  also opens out in the area of opening  2 . 1 . 
   In order to attain a clean pressure distribution during the compression molding of the housing for the fixing of sensor element  3 , a seal  4  is also situated between the back side of the sensor element and the inner side of housing  2  that is assigned to it. Because of that, point-by-point occurring force applications may be distributed over such large areas that they are not problematical for the ceramic sensor element. 
     FIG. 4  shows a partial cutout of yet another specific embodiment of a gas sensor in a sectional illustration, which corresponds to the specific embodiment in  FIG. 5 . It is different from the specific embodiments up to now in that, between seal  4  and housing  2  there is situated additionally a sensor fixing element  5 . An additional seal  4 . 1  is shown for sealing between this sensor fixing element  5  and housing  2 , and situated between the two. 
   It may be advantageous for the assembly of the gas sensor that sensor fixing element  5  is situated together with additional seal  4 . 1  in housing  2 . Furthermore, as shown in  FIG. 7 , contact elements of the electrical lines leading to the outside may additionally be pre-positioned through opening  2 . 1 . Of course, to do this, additional gas sensor elements are required, using which, cable harness  7  may be correspondingly connected to housing  2 , so that finally only sensor element  3  has still to be inserted into the housing that has been thus prepared, and compression molded. Opening  5 . 1  in sensor fixing element  5  corresponds, as far as size is concerned, to opening  2 . 1  in the housing, and encloses contact region  3 . 1  of sensor element  3 , so that the latter is separated from the measuring gas region in a gas-tight manner. 
     FIG. 6  shows a specific embodiment of the gas sensor, which builds up on the specific embodiment of  FIG. 1 , and which is broadened by the elements additionally shown in  FIGS. 4 and 5 . The installation of sensor element  3  in housing  2 , as has been explained, takes place by prefabricating the entire accommodation unit housing  2 , sensor fixing element  5  and contacts  6  together with cable harness  7  that is attached to them. Subsequently, only sensor element  3  has still to be pushed into the remaining opening of sensor fixing element  5  positioned on the inside of the housing, and fixed in a gas-tight manner by compression molding of the housing. 
   In this case, sensor fixing element  5  is to be assigned functionally to seal  4 , since that is also developed in a gas-tight manner. Consequently, seal  4  is developed as a plurality of parts, and has a positioning aid and/or a fixing aid together with the collar that is situated in seal  4 . 1  and extends into opening  2 . 1 . For sealing from the housing, seal  4 . 1  lies on top of sealing region  5 . 2 . In order to be able, using the same housing, to accommodate a sensor element that has corresponding connectors also at the opposite base area, both the housing and sensor fixing element  5  are preferably developed in a symmetrical fashion. 
     FIG. 7  shows a prefabricated, assembled housing  2  having sensor element fixing  5  inserted into it and cable harness  7  connected to contacts  6 . It only has to be still equipped with sensor element  3  and compression molded for fixing the latter. 
   LIST OF REFERENCE NUMERALS 
   
       
         1  gas sensor 
         2  housing 
         3  sensor element 
         4  seal 
         5  sensor fixing element 
         6  contacts 
         7  cable harness 
         2 . 1  opening 
         2 . 2  sealing region 
         2 . 3  opening 
         2 . 4  sealing region 
         2 . 5  innerspace 
         3 . 1  contact region 
         3 . 2  connecting contact 
         3 . 3  measured gas electrode 
         3 . 4  positioning aid 
         3 . 5  reference gas channel 
         4 . 1  seal 
         4 . 2   
         4 . 3  seal 
         4 . 4   
         4 . 5   
         4   a  sealing crosspiece 
         4   b  seal 
         5 . 1  opening 
         5 . 2  sealing region 
         5 . 3   
         5 . 4  sealing region 
         5 . 5  positioning aid and/or fixing aid