Abstract:
A gas sensor apparatus and method of forming the same generally includes a gas sensor element comprising a heater and a plurality of electrodes. A ceramic substrate can be provided for supporting the electrodes on one side of the ceramic substrate and the heater on the opposite side of the ceramic substrate. The gas sensor element is preferably embedded in the ceramic substrate. The ceramic substrate also possesses a substantially circular shape in order to prevent a breakage of the gas sensor element, avoid thermal loss, and permit the gas sensor apparatus to withstand mechanical shock and high vibrations while occupying a minimal package space.

Description:
PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 11/710,068, filed Feb. 23, 2007, now abandoned, entitled “GAS SENSOR APPARATUS FOR AUTOMOTIVE EXHAUST GAS APPLICATIONS”, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments are generally related to sensor methods and systems. Embodiments are also related to gas sensors. Embodiments are additionally related to gas sensor packaging devices, systems and methods of forming the same. 
     BACKGROUND 
     Sensors are often utilized in association with internal combustion engines to measure operating parameters and constituents of a resulting feed stream. For example, an exhaust gas sensor in a control system of an internal combustion engine can be used to measure the parameter of air/fuel ratio, CO, CO 2 , NO x , etc. It is important to determine the gas concentration of exhaust gas in order to control the emission of an automotive engine. A control system can then use this information to control the engine parameters and thereby allow for minimum emissions. 
     An engine controller can then employ the air/fuel ratio information to control the feed stream that flows through the engine and into an after treatment device, such as a catalytic converter. A properly controlled gas feed stream is important for the complete operation of the exhaust after treatment and during light-off and steady-state warmed-up operations of the utilized control system. 
     Construction of a current sensor element can take place in the context of a planar-type (e.g., thin and long ceramic) substrate, which protrudes externally from the gas sensor housing for measuring gas concentration. Since the configuration is planar and thinner, the possibility of breakage due to vibration and mechanical shock is very high 
     It is known that the control of burning associated with an internal combustion engine is a function of the concentration of air-fuel ratio contained in exhaust gases. The concentration of the NO x  and the air-fuel ratio is effective in providing energy savings and emission control capabilities. In gas sensor configurations suitable for measuring the concentration of oxygen or other gases like CO, NOx, CO2, etc., in exhaust gases, a solid electrolyte body constructed from zirconia or metal oxide semiconductor (MOS) based gas sensors can be utilized. This type of gas sensor, however, in order to be effective, must be reduced in size, while maintaining efficient production costs and improving its durability and reliability. These factors are difficult to achieve. 
     In order to sense gas concentration, such as O2, NOx etc., a gas sensor element should be operated at high temperature. For example, a zirconia sensor for measuring oxygen, should be maintained at 650 deg C. An electric power circuit controls the temperature of the sensor element. Designing the sensor element with small size is important in order to reduce power required to maintain the sensor at this temperature. 
     It is believed that a solution to overcoming these problems involves the implementation of an improved sensor apparatus, which can be efficiently fabricated at a low cost for automotive exhaust gas applications. 
     BRIEF SUMMARY 
     The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
     It is, therefore, one aspect of the present invention to provide for an improved gas sensor apparatus and method. 
     It is another aspect of the present invention to provide for a gas sensor apparatus that avoids breakage of the utilized sensor element. 
     It is another aspect of the present invention to provide for a gas sensor packaging apparatus in which thermal loss is minimized. 
     It is further aspect of the present invention to provide for a gas sensor apparatus that operates with a reduced operating power. 
     The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A gas sensor apparatus and method of forming the same are disclosed herein. The gas sensor apparatus generally includes a gas sensor element comprising a heater and a plurality of electrodes. Additionally, a ceramic substrate can be provided for supporting the plurality of electrodes on one side of the ceramic substrate and the heater on an opposite side of the ceramic substrate. The gas sensor element is preferably embedded in the ceramic substrate. The ceramic substrate also possesses a substantially circular shape in order to prevent a breakage of the gas sensor element, avoid thermal loss, and permit the gas sensor apparatus to withstand mechanical shock and high vibrations while occupying a minimal packaging space. 
     The gas sensor apparatus also includes a plurality of contact terminals connected to the ceramic substrate in order to provide at least one electrical connection to the gas sensor apparatus. A metallic housing can also be provided, which surrounds and protects the gas sensor element, the heater element and the ceramic substrate. The gas the sensor element additionally includes a holding end portion located and secured in the metallic housing and a sensing end portion exposed to exhaust gases thereof. The heater can be provided in the form of a plurality of platinum heater elements, while electrodes are preferably formed from platinum. The sensing side of the substrate can include two platinum electrodes over which a sensing material can be coated, such as metal oxide semiconductor (MOS), or upon which a zirconia element can be attached. 
     The gas sensor element also includes at least one platinum conductive pad. The plurality of contact terminals can be resistance-welded to the ceramic substrate. The heater also maintains the temperature of the gas sensor element. Additionally, the metallic housing can be configured to include an outer baffle and an inner baffle provided in the metallic housing, thereby covering a gas exposed portion of the gas sensor element. The inner baffle forms a cup-like groove towards the gas sensor element. Additionally, an embossed feature can be provided, which assists a flow of gas flow near the gas sensor element. 
     The disclosed gas sensor apparatus is based on an innovative packaging design that avoid breakage of the sensor element, while the substrate shape can be circular with one side constituting a heater side and the other side functioning as sensor side. The contact pads can be screen-printed, while the contact terminals can be resistance-welded or any other suitable joining process to one or more of the contact pads. To minimize thermal loss, the substrate has a minimum contact surface with the housing and can be designed for less operating power. The sensor occupies less space as the sensor element size is minimized according to such a design. The circular ceramic substrate generally includes a platinum heater on one side (i.e., the heater side) and platinum electrodes on the other side, which provide for printing sensing material, such as a metal oxide semiconductor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein. 
         FIG. 1  illustrates a front view of gas sensor apparatus, which can be implemented in accordance with a preferred embodiment; 
         FIG. 2A  illustrates a longitudinal cross-sectional view of the gas sensor apparatus depicted in  FIG. 1 , which can be implemented in accordance with a preferred embodiment; 
         FIG. 2B  illustrates a longitudinal cross-sectional view of the gas sensor apparatus depicted in  FIGS. 1-2A , which can be implemented in accordance with a preferred embodiment; 
         FIG. 3  illustrates exploded view of the gas sensor apparatus as depicted in  FIGS. 1-2 , which can be implemented in accordance with an alternative embodiment; 
         FIG. 4  illustrates a schematic drawing for top, front and bottom views of a sensor element, which can be implemented in accordance with an alternative embodiment; 
         FIG. 5  illustrates a sectional view of improved gas flow of the gas sensor apparatus, which can be implemented in accordance with a preferred embodiment; 
         FIG. 6  illustrates a high level flow chart of operations depicting an improved method of gas flow to the sensor element, which can be implemented in accordance with a preferred embodiment; 
         FIG. 7A  illustrates a front view of a pipe-gas sensor apparatus assembly employed to determine the gas content such as NOx, O2, CO, CO2, etc., of exhaust gas generated by an internal combustion engine, which can be implemented in accordance with an alternative embodiment; and 
         FIG. 7B  illustrates a side view taken along line  7 B- 7 B of  FIG. 7A  of a pipe-gas sensor assembly, which can be utilized to determine the gas content of exhaust gas generated by an internal combustion engine, which can be implemented in accordance with an alternative embodiment. 
     
    
    
     DESCRIPTION 
     The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof. 
       FIG. 1  illustrates a side view of a gas sensor apparatus  100 , which can be implemented in accordance with a preferred embodiment.  FIG. 2A  illustrates a longitudinal cross-sectional view of the gas sensor apparatus  100  as depicted in  FIG. 1 , in accordance with a preferred embodiment. The gas sensor apparatus  100  generally includes an embossing  102 , a laser welding  103 , a collar  104 , and a welding  105 . The gas sensor apparatus  100  includes a crimping  101  to seal the cable  201  as depicted in  FIG. 2A , and an embossing  102  to retain a ceramic insulator  205  as also depicted in  FIG. 2A  and laser welding  103  of a rear cover  202  with a main shell  206  as further depicted in  FIG. 2A . The gas sensor apparatus  100  also includes a collar  104  located in a portion of the main shell  206  as indicated in  FIG. 2A  and a welding  105  of an outer baffle  211  as depicted in  FIG. 2A  with the main shell  206 . 
     The gas sensor apparatus  100  shown in  FIG. 2A  can be utilized to determine the gas content of exhaust gas generated by an internal combustion engine. The gas sensor apparatus  100  includes a connecting cable  201  associated with a rear cover  202 , a sleeve  203  a metallic wire  214  to cable crimping  204  (shown in  FIG. 2   b ). Note that the sleeve  203  can be formed from, for example, TEFLON. A sensor element  209  can be held by an inner ceramic holder  208  and an outer ceramic holder  210  maintained within the main shell  206 . A ceramic insulator  205  and a ceramic potting  207  can also be provided. The sensor element  209  is generally surrounded by an outer baffle  211  and an inner baffle  212  in the region  213  where the sensor element  209  is exposed to the exhaust gases. 
       FIG. 2B  illustrates a longitudinal sectional view of the gas sensor apparatus  100  depicted in  FIGS. 1-2A , which can be implemented in accordance with a preferred embodiment. Note that in the embodiment disclosed herein, four metallic wires  214  are indicated. It can be appreciated, however, that this number may vary; that is, fewer or more metallic wires  214  may be utilized depending upon design considerations. The longitudinal sectional view depicted in  FIG. 2B  of the gas sensor apparatus  100  illustrates the metallic wires  214  with cable crimping  204  and joined with substrate  215 . 
       FIG. 3  illustrates an exploded view of the gas sensor apparatus  100 , which can be implemented in accordance with an alternative embodiment. The gas sensor apparatus  100  depicted in  FIG. 1  includes a TEFLON sleeve  203 , a connecting cable  201 , a metallic wire  214  to cable crimping  204 , a rear cover  202 , a ceramic insulator  205 , a main shell  206 , and a ceramic potting  207 . The gas sensor apparatus  300  also includes a sensor element  209  with an inner ceramic holder  208  and an outer ceramic holder  210 . The TEFLON sleeve  203  provides a grease-free connection to the connecting cable  201  which is tied tightly with the metallic wires  214  that are encapsulated within a rear cover  202 . The outer ceramic holder  210  and inner ceramic holder  208  hold the sensor element  209  embedded within the ceramic substrate  401  as depicted in  FIG. 4 . 
     The ceramic insulator  205  and ceramic potting  207  provides thermal insulation to the sensor element  209 . The gas sensor apparatus  100  additionally includes outer baffle  211  and inner baffle  212  which act as a protective shield for the sensor element  209  in a region  213  where the sensor element  209  is exposed to exhaust gases. The sensor element  209 , ceramic insulator  205 , ceramic potting  207 , inner ceramic holder  208  and outer ceramic holder  210  are enclosed within a main shell  206  which prevents the sensor element  209  from breakage. Note that in  FIGS. 2A and 3 , identical or similar parts or elements are generally indicated by identical reference numerals. Thus, the reference numerals  201 ,  202 ,  203 , 204 ,  205 ,  206 ,  207 ,  208 ,  209 ,  210 ,  211 , and  212  as depicted in  FIG. 2A  refer to the same components in  FIG. 3 . 
       FIG. 4  illustrates a schematic side view of a sensing component  400  and a sensor element  209 , which can be implemented in accordance with an alternative embodiment. As indicated in  FIG. 4 , the sensor element  209  can be embedded in a substrate  401  having a side platinum conductive coating  402  to take the sensing electrode to the rear side. To avoid breakage of the sensor element  209 , the substrate  401  can be preferably formed in a circular shape in which one side of the substrate  401  constitutes the heater side  403  and the other or opposite side of the substrate  401  functions as the sensor side  404 . The substrate  401  can be configured, for example, from materials such as aluminum oxide. Sensing component  400  can be adapted for use with the gas sensor apparatus  100  described herein, depending upon design considerations. 
     The sensor side  404  can include a sensing material  405 , which can be, for example, a metal oxide semiconductor coated via screen-printing or attaching a sensing element over the substrate. The sensor side  404  includes sensing side electrodes  406  for measuring sensor signal and platinum electrode  407  held in ceramic substrate  401 . The heater side  403  generally includes a platinum heater  408  that maintains a temperature approximately &gt;650° C. for sensor element  209  and electrodes  409  for connecting wires. The sensor element  209  can be suspended in order to minimize heat transfer between the sensor element  209  and the gas sensor packaging  100 . Such a structure has the advantage that the platinum heater element  408  provides heat to the sensor element  209  over an area that results in essentially uniform, balanced thermal conditions and which counteract the tendency of the sensor element  209  to fracture. 
       FIG. 5  illustrates a sectional view of improved gas sensor apparatus  100 , including a gas flow to the sensor element  209 , in accordance with a preferred embodiment. Note that in  FIGS. 2 and 5  identical or similar parts or elements are generally indicated by identical reference numerals. Thus, the reference numerals  209 ,  211  and  212  as depicted in  FIG. 2  refer to the same components in  FIG. 5 . The gas sensor element  209  includes a gas-exposed portion. The gas sensor apparatus  100  maintains the gas sensor element  209  and includes an outer baffle  211  and an inner baffle  212  so as to shield the gas-exposed portion of the sensing element  209 . The inner baffle  212  forms a cup-like groove  213  towards the gas sensor element  209 . Reference numerals  501  and  505  represent inlet holes formed in the outer and inner baffles and reference numeral  506  represents a single outlet of inner baffle. Gas enters through inlet  501  of outer baffle  211  and enters through inlets  505  of inner baffle  212 . The gas flows and hits the embossed feature  503  of inner baffle  212  and flows upward to gas sensor element  209 . Gas exits through outlet  506  of inner baffle. 
       FIG. 6  illustrates a high-level flow chart of operations depicting logical operational steps of a method  600  for forming the improved gas sensor apparatus  100 , in accordance with a preferred embodiment. Note that the method  600  illustrated in  FIG. 6  can be followed to construct the gas sensor apparatus described previously. As indicated at block  601 , the process begins. Thereafter, as depicted at block  602 , the metallic housing contains an inner baffle and an outer baffle to cover the gas exposed portion of sensor element. The inner baffle can be configured as indicated next at block  603  to contain a cup-like groove  213  ( FIG. 5 ) extending inward. Thereafter, as depicted at block  604 , the flow of gas through the inner baffle can be provided. As depicted at block  605 , the embossed feature described earlier can be provided to assist the gas flow near the sensor element. The process can then terminate as indicated at block  606 . 
       FIG. 7A  illustrates a front view of a pipe-gas sensor apparatus  700  employed to determine the NO x  content of exhaust gas generated by an internal combustion engine, which can be implemented in accordance with an alternative embodiment. The gas sensor apparatus  100  can be mounted on an exhaust pipe  701 . The pipe holder  702  is designed to hold the gas sensor apparatus  100  on the exhaust pipe  701 . An outer nut  703  of the screw joining the gas sensor apparatus  100  to the pipe holder  702  is also illustrated in the view. 
       FIG. 7B  illustrates a side view A  700  of pipe-gas sensor assembly, which can be utilized to determine the gas content of exhaust gas generated by an internal combustion engine, which can be implemented in accordance with an alternative embodiment. Note that in  FIGS. 7A and 7B , identical or similar parts or elements are generally indicated by identical reference numerals. Thus, the reference numerals  100 ,  701 , and  702  as depicted in  FIG. 7A  refer to the same components in  FIG. 7B . Note that in  FIGS. 1-7 , identical or similar parts or elements are indicated by identical reference numerals. Thus, the  FIG. 7  illustration also generally contains the gas sensor apparatus  100  which is described above with respect to  FIGS. 1-7 . 
     It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, it can be appreciated that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.