Abstract:
A device provided in an exhaust system of an internal combustion engine in order to detect exhaust gas temperature. The device includes an oxygen sensor which has a sense element outboard of a heater element. The oxygen sensor is further designed to incorporate a temperature sensing element on the outboard of the sense element. The temperature sensing element optimizes the detection of the exhaust gas temperature, thereby providing efficient operation of the engine.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a device for detecting the exhaust gas temperature of an internal combustion engine, and more particularly to an oxygen sensor located within the exhaust system which has an exhaust gas temperature sensing element deposited on the outside surface of the oxygen sensor. 
     BACKGROUND 
     In order to reduce the environmental damage that occurs due to the amount of emissions produced by automobiles, there have been strong legislative movements to require automobile producers to effectively monitor the performance of their engines. Although the monitoring and reduction of automotive emissions is a primary concern, so is the performance of the engine. With the intention of achieving optimal engine performance, a variety of approaches have been taken by automobile manufacturers in the attempt to maximize the efficiency of an engine, while producing as few emissions as possible. 
     One type of exhaust monitoring system incorporates an oxygen sensor. The oxygen sensor is located within the exhaust system of an automobile and is designed to detect an air/fuel ratio which is critical in the performance of a combustion engine. A specific mixture of air and fuel, otherwise known as the “perfect ratio”, is required to have the most favorable performance from an engine, while reducing the amount of pollutants produced. 
     If there is less air than the perfect ratio, fuel will be left over after combustion, resulting in what is known as a rich mixture. A rich mixture results in increased pollution due to the unburned fuel that is left following combustion. In contrast to the rich mixture, a lean mixture is obtained when there is an excess of oxygen in the air/fuel mixture. A lean mixture tends to produce more nitrogen oxide pollutants, resulting in poor engine performance and may ultimately cause damage to the engine. 
     In addition to monitoring the amount of oxygen present in the exhaust system, the temperature of the exhaust system must also be monitored in order to optimize engine performance. The overheating of the catalytic converter results in an increase in temperature of the exhaust gas system. This temperature increase in the exhaust gas system increases the amount of pollutants which are emitted into the environment. 
     With the purpose of monitoring the temperature of the exhaust system, different approaches have been taken to incorporate a temperature sensing element within the exhaust system. For example, temperature sensors have been placed as a discrete component within the exhaust system. However, this approach has certain drawbacks due to increased costs and the potential of breaking. 
     In order to overcome this drawback, another prior art approach incorporates a temperature sensing element within the oxygen sensor. In this approach, a temperature sensing element is printed on the heater element of the oxygen sensor. Although this approach is more popular than a separate temperature sensor, there are problems associated with it as well. For example, the existing heater element within the oxygen sensor is insulated from fluctuations in the exhaust gas temperature by the oxygen sensor&#39;s O 2  sensing element. Therefore, inaccurate readings are obtained from the temperature sensing element due to its location on the heater element. A time delay results from the exhaust gas passing over the oxygen sensor onto the heating element, wherein the prior art exhaust gas temperature sensing element is located. Therefore any response by the electronic control unit is outdated, due to the delay in time. 
     SUMMARY OF THE INVENTION 
     The present invention incorporates the use of a temperature sensing element with an oxygen sensor, but alters the placement of the temperature sensing element on the oxygen sensor. The change in location of the temperature sensing element allows for real-time feedback which can be useful in determining temperature conditions in the exhaust environment. This may include detecting misfires, changes in catalyst temperatures, as well as conditions during wide-open-throttle closed loop control. 
     More specifically, one object of the present invention is to incorporate a temperature sensing element on the outside of the oxygen sensor&#39;s sense element, which results in maximizing the reading capability of the temperature sensing element. The present invention thereby overcomes the problems associated with the prior art, and optimizes the amount of real-time feedback obtained from the temperature sensing element. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a first embodiment oxygen sensor incorporating the teachings of the present invention; 
     FIG. 2 is a partially cut-away, perspective view of the oxygen sensor of FIG. 1; and 
     FIG. 3 is a perspective view of a second embodiment oxygen sensor incorporating the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, an oxygen sensor  10  having a heater element  12  and a sense element  14  is illustrated. The particular embodiment of the oxygen sensor  10  in FIG. 1 has a cylindrical, cup-shaped outer shell  16  including an elongated, cylindrical internal bore or cavity  18  formed therein. The oxygen sensor  10  is primarily comprised of ceramic, although additional materials and components may by added, as is known in the art. 
     The outer shell  16  of the oxygen sensor  10  houses the heater element  12  generally within the internal cavity  18 . The outer shell  16  is formed of materials including some that, as described below, form the sense element  14 . The sense element  14  is located adjacent to the heater element  12 . That is, the interior side of the sense element  14  (i.e., the inboard surface of the sense element  14  adjacent the internal cavity  18 ) is disposed adjacent the outboard or exterior side of the heater element  12 . The sense element  14  includes zirconia oxide which reacts with oxygen and works in conjunction with the remaining components of the oxygen sensor  10  to send feedback to an electronic control unit (not shown). 
     As stated previously, the temperature sensing element  20  is deposited on the outboard or exterior surface of the sense element  14  of the oxygen sensor  10 . The temperature sensing element  20  preferably comprises a resistive circuit. The circuit  20  is designed to have fluctuating resistance, dependent upon the temperature of its surroundings, in this case, the exhaust gas. 
     The function of the resistive circuit  20  is to allow the electronic control unit to monitor the resistance of the circuit  20  as it changes with the temperature of the exhaust gas in a real time manner. This real time manner is made possible due to the present invention&#39;s placement of the resistive circuit  20  on the exterior surface of the sense element  14 . In particular, the resistive circuit  20  is spaced apart from the heater element  12  by (at least) the sense element  14 . 
     With particular reference to FIG. 2, another view of the sense element  14 , as well as additional exterior components of the oxygen sensor  10 , are illustrated. A plurality of laminated protective coatings  22  are located adjacent to the sense element  14 . The protective coatings  22  are applied to the outboard or exterior surface of the sense element  14  in order to isolate the resistive circuit  20  from the sense element  14  and heater element  20  (FIG.  1 ). By isolating the resistive circuit  20 , an accurate temperature reading may be obtained and the resistive circuit  20  is protected from most types of potential damage. 
     As shown in FIG. 2, two protective coating layers  22   a  and  22   b  are interposed between the sense element  14  and the resistive circuit  20 . The application of the protective layers  22  is not limited to this specific quantity and may vary according to the design of the oxygen sensor  10  or its particular application. A particular type of protective layer is preferably categorized as a spinel coating. The spinel coatings  22  are applied by a plasma spray technique. A ceramic material is preferably used as the basis for the composition of the layer  22 , although under application conditions this ceramic material is transformed in a glass-like material, in both appearance and performance. 
     The resistive circuit  20  is deposited on the outboard of the sense element  14 , following the initial application of protective layers  22 . The application of resistive circuit  20  is preferably accomplished by printing a resistive ink on exterior surface of the sense element  14  or protective layer  22 . The resistive ink is preferably applied in the form of a zigzag pattern. Following the printing of the resistive circuit  20 , an additional protective coating  22   c  is applied, using the same techniques as described previously. That is, the protective layer  22   c  is disposed over the resistive circuit  20  so as to sandwich it between the protective layer  22   c  and the protective layer  22   b.    
     In addition to the protective layers  22 , feedback circuitry  24  is incorporated within the oxygen sensor  10  to communicate with the electronic control unit. Electronic leads  24  from the resistive circuit  20  run up the sense element  14  and terminate within the interior of the sensor  10 . Furthermore, multiple wires (not shown) minimum one, possibly two, are added to the sensor ( 10 ) to transport the circuit signal from the leads  24  to the electronic control unit. 
     An alternate embodiment of the present invention is illustrated in FIG. 3. A planar sensor  26 , which has the same integral features as described previously in the first sensor embodiment, is an alternative design of the oxygen sensor  10 . The planar sensor  26  resembles the configuration of an IC chip, wherein the respective layers are built upon one another. As in the previous embodiment of the sensor, the planar sensor  26  includes a heater element  12   a , a sense element  14   a  adjacent the heater element  12   a  and a resistive circuit  20   a  printed on the exterior surface of the sense element  14   a  opposite the heater element  12   a . As with the first embodiment, the resistive circuit  20   a  is preferably sandwiched between two protective layers  22   b  and  22   c  outboard of the sense element  14   a . The main difference between the two embodiments is not in the components or in the functional capabilities, but in the manufacturing methods. 
     An additional feature of the present invention is the ability of the oxygen sensor  10  to be integrated with DaimlerChrysler&#39;s Next Generation Controller (NGC) in contrast to the Electronic Control Unit (ECU). The development of the NGC has resulted in a further integrated and highly responsive control unit. More specifically, by designing the oxygen sensor  10  to have the capacity to be applied with the NGC, the temperature of exhaust gas will be monitored and controlled to specific temperature levels and controller response times. 
     In general, the above disclosed invention provides an increase capability and more accurate means to monitoring the exhaust temperature system of an automobile. The integration of the resistive circuit  20  on the exterior surface of the sense element  14 , will provide additional information regarding temperature regulation within an internal combustion engine. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.