Abstract:
A resistor assembly, comprising: a housing body having a recess defined by a peripheral edge; a pair of channels disposed in the peripheral edge, the pair of channels extending from the recess and through the peripheral edge; a trim resistor element disposed in the recess, the trim resistor element comprising a nonconductive support surface, a pair of conductive pads disposed on the nonconductive support surface, the pair of conductive pads being disposed in a spaced relationship on the nonconductive support surface, and a trimable resistive film disposed on the nonconductive support surface, the trimable resistive film being in electrical communication with each of the pair of conductive pads at separate locations to provide a conductive path between the pair of conductive pads through the trimable resistive film; a pair of lead wires, each lead wire comprising an electrically insulative sheath disposed about a metallic wire, each lead wire further comprising a terminal section formed of an exposed metallic wire stripped of the electrically insulative sheath, wherein each wire is arranged with the housing body such that the insulative sheath is received in one of the pair of channels and the terminal section extends into the recess to make electrical contact with a respective one of the pair of conductive pads; a housing top fixed to the housing body, the housing top having a first top portion and a second top portion, the first top portion overlying a portion of the pair of lead wires and clamping the electrically insulated sheath within a respective one of the pair of channels and the terminal section against a respective one of the pair of conductive pads, the housing top further comprising a second top portion, the second top portion having an opening defined by a perimeter, the opening overlying and exposing the trimable resistive element and the perimeter overlying a portion of the trim resistive element to retain the resistive element within the recess.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part (CIP) of U.S. patent application Ser. No. 10/472,409, attorney docket no. DP-304209 filed Sep. 17, 2003, which is a National Stage Entry of PCT/US02/07449, which claims priority to U.S. Provisional Application 60/277,037, filed Mar. 19, 2001 the contents each of which are incorporated herein by reference thereto. 
     
    
     BACKGROUND  
       [0002]     Some exhaust sensors need a compensation resistor to tell the electronics how to compensate for part-to-part variability in the sensor itself. There are two ways to do this, first using a discrete fixed resistor. A fixed value resistor requires a very large collection of resistors in which the manufacturer must pick a resistor that is closest in value to the required resistance. This will almost never allow for a perfect match and requires many different part numbers. The second way of compensation is to use a trim resistor, which requires a laser to burn a resistive surface until the exact resistance is achieved. This requires only one part number and perfectly matches the desired resistance. The current method of attaching trim resistors to sensors is to integrate the trim resistor into the off end connector. While this is compact, it is not flexible to customers needs if they wish to use a different connector.  
       SUMMARY OF THE INVENTION  
       [0003]     A resistor assembly, comprising: a housing body having a recess defined by a peripheral edge; a pair of channels disposed in the peripheral edge, the pair of channels extending from the recess and through the peripheral edge; a trim resistor element disposed in the recess, the trim resistor element comprising a nonconductive support surface, a pair of conductive pads disposed on the nonconductive support surface, the pair of conductive pads being disposed in a spaced relationship on the nonconductive support surface, and a trimable resistive film disposed on the nonconductive support surface, the trimable resistive film being in electrical communication with each of the pair of conductive pads at separate locations to provide a conductive path between the pair of conductive pads through the trimable resistive film; a pair of lead wires, each lead wire comprising an electrically insulative sheath disposed about a metallic wire, each lead wire further comprising a terminal section formed of an exposed metallic wire stripped of the electrically insulative sheath, wherein each wire is arranged with the housing body such that the insulative sheath is received in one of the pair of channels and the terminal section extends into the recess to make electrical contact with a respective one of the pair of conductive pads; a housing top fixed to the housing body, the housing top having a first top portion and a second top portion, the first top portion overlying a portion of the pair of lead wires and clamping the electrically insulated sheath within a respective one of the pair of channels and the terminal section against a respective one of the pair of conductive pads, the housing top further comprising a second top portion, the second top portion having an opening defined by a perimeter, the opening overlying and exposing the trimable resistive element and the perimeter overlying a portion of the trim resistive element to retain the resistive element within the recess. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     The present invention will now be described, by way of an example, with references to the accompanying drawings, wherein like elements are numbered alike in the several figures in which:  
         [0005]      FIG. 1  shows an exploded perspective view of an independently housed trim resistor in accordance with an exemplary embodiment;  
         [0006]      FIG. 2  shows a perspective view of an independently housed trim resistor in accordance with an exemplary embodiment;  
         [0007]      FIG. 2A  is a view along lines  2 A- 2 A of  FIG. 2 ;  
         [0008]      FIG. 2B  is a view along lines  2 B- 2 B of  FIG. 2 ;  
         [0009]      FIG. 3  shows a top down view of a trim resistor in accordance with an exemplary embodiment;  
         [0010]      FIG. 4  shows a block diagram describing a method for fabricating an independently housed trim resistor in accordance with an exemplary embodiment;  
         [0011]      FIG. 5  shows a cross sectional view of an example of an independently housed trim resistor disposed within a sensor wire sheath in accordance with an exemplary embodiment;  
         [0012]      FIG. 6  shows an example of a final sensor assembly which employs an independently housed trim resistor in accordance with an exemplary embodiment; and  
         [0013]      FIG. 7  is another perspective view of trim resistor assembly constructed in accordance with exemplary embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0014]     Referring now to the figures, an independently housed trim resistor  1  is provided that advantageously allows for a wide range of devices to employ a trim resistor by providing a novel trim resistor design that can be used with a variety of circuit connectors inexpensively and effectively.  
         [0015]     Referring to the drawings,  FIG. 1  and  FIG. 2  show independently housed trim resistor  1  having a resistor housing  2 , a trim resistor element  4  and a plurality of lead wires including a first lead wire  6  and a second lead wire  8  in accordance with an exemplary embodiment. In one embodiment, resistor housing  2  preferably includes a housing top  10  and a housing body  12 , wherein housing body  12  defines a resistor cavity or receiving area  14  for receiving and containing trim resistor element  4  therein. A portion of a periphery of the resistor cavity is defined by a peripheral wall  11  and an end wall portion  15  of the housing body as illustrated, the housing body comprises a first body portion and a second body portion, the first body portion including wall portion  15  and the second body portion including peripheral wall  11 .  
         [0016]     Referring to  FIG. 3 , a trim resistor element  4  is shown in accordance with an exemplary embodiment. Trim resistor element  4  preferably includes a trimable resistive element or trimable resistive film  16  comprising an electrically conductive material and a plurality of conductive pads  18  for example, a first pad  20  and a second pad  22 , which are shown in the Figures, wherein the first pad and the second pad are in electrical communication with resistive element  16  by for example overlapping a portion of the conductive material of the conductive pads with separate portions of the resistive element to provide a pair of overlapping areas  17  and  19 . In accordance with an exemplary embodiment, the resistive element provides an electrical resistance between first pad  20  and second pad  22 .  
         [0017]     As illustrated, the resistor element has a longitudinal axis  21  parallel to the channels of the housing body, and a lateral axis  33  perpendicular to the longitudinal axis. In accordance with an exemplary embodiment, the conductive pads extend from the lateral axis in a first direction towards the pair of channels and the trimable resistive film extends from the lateral axis in a second direction away from the channel, wherein the pair of conductive pads each contact the trimable resistive film at the lateral axis. In accordance with an exemplary embodiment and as discussed herein the pair of conductive pads each underlie or overlie the trimable resistive film at the lateral axis. As illustrated, the conductive pads are positioned on the non-conductive substrate in a parallel spaced relationship with respect to each other.  
         [0018]     In accordance with an exemplary embodiment, trimable resistive element  16 , first pad  20  and second pad  22  are preferably disposed so as to create an open area  28  adjacent to resistive element  16 . In addition, housing top  10  preferably includes a trim opening  24  disposed so as to allow communication with resistive element  16  and open area  28 . Moreover, resistor housing  2  preferably includes a pair of openings or channels  26  disposed in end wall portion  15  and depending on the configuration of the housing, a pair of complimentary channels are disposed in a lower surface of housing top  10 .  
         [0019]     Channels  26  are configured to provide a path from an outer periphery of the housing body and the housing top into resistor cavity  14  such that the lead wires can be terminated with plurality of conductive pads  18 . In accordance with an exemplary embodiment the channels are disposed in a parallel, spaced relationship wherein a first one of the conductive pads is disposed proximate to one of the pair of channels and a second one of the conductive pads is disposed proximate to the other one of the pair of channels.  
         [0020]     In addition, a portion or first top portion  23  of housing top  10  is configured to secure the lead wires between housing top  10  and housing body  12  as well as providing a sufficient force or compressive force to the wire so that an electrical termination of the conductive cores of the lead wires is provided to the conductive pads. As illustrated, portion  23  is configured to have a step or feature  25  configured to cooperate with a complimentary step or feature  27  lower portion  12  wherein a compressive force is applied by a lower portion of upper housing portion  10  to un-insulated portions of the lead wires to ensure electrical contact is made once upper portion  10  is secured to lower portion  12 . As illustrated, feature or step  27  is created by wall portion  15  having a height greater than wall portion  11 . Of course, other configurations of housing top and housing body capable of providing the necessary compressive force (e.g., lead wire termination) are contemplated to be within the scope of exemplary embodiments of the present invention.  
         [0021]     It is also understood, that in an alternative exemplary embodiment a temporary initial electrical connection may be made by a terminal contacting the conductive pad or a tack weld or spot weld, which is permanently secured thereto by the force of the housing top.  
         [0022]     First lead wire  6  and second lead wire  8  preferably include a conductive core  30  and a protective sheath  32  encasing conductive core  30 . In accordance with an exemplary embodiment, first lead wire  6  is preferably disposed such that conductive core  30  is in electrical communication with first pad  20  and second lead wire  8  is preferably disposed such that conductive core  30  is in electrical communication with second pad  22 .  
         [0023]     In accordance with an exemplary embodiment, first lead wire  6  and second lead wire  8  may be any wire suitable to the desired end purpose.  
         [0024]     In accordance with an exemplary embodiment, housing top  10  is preferably non-movably associated with housing body  12  so as to secure the trim element in the resistor cavity or receiving area  14 .  
         [0025]     In addition, trimable resistive element  16  is applied to provide a layer of trimable resistive film that is preferably removably associated with trim resistor element  4 .  
         [0026]     Referring to the figures, a method for fabricating an independently housed trim resistor  1  as described hereinabove is illustrated and discussed. In accordance with an exemplary embodiment, a first lead wire  6 , a second lead wire  8 , a trim resistor element  4  having a trimable resistive element  16  and a plurality of conductive pads  18  disposed thereon and a resistor housing  2  having a housing top  10  and a housing body  12  are obtained as shown in step  100 . In accordance with an exemplary embodiment, resistor housing  2  preferably includes a pair of openings or channel openings  26  disposed so as to allow the lead wires to be in electrical communication with the conductive pads  18 . In addition, housing top  10  preferably includes a trim opening  24 , which allows direct contact with the resistive element when the trim element is retained within the resistor cavity by portion  23  and peripheral portion or second top portion  29  of housing top  10 .  
         [0027]     First lead wire  6  and second lead wire  8  are then arranged so as to be communicated with conductive pads  20  and  22  via a respective opening or channel  26  extending into resistor cavity  14 , wherein first lead wire  6  is communicated with first pad  20  and second lead wire  8  is communicated with second pad  22 , as shown in step  102 . Trim resistor element  4  is then arranged so as to be disposed within resistor cavity  14  such that resistive element  16  is directed away from housing body  12  and housing top  10  is then arranged to cover trim a portion of resistor element  4  and enclose resistor cavity  14 , also as shown in step  102 .  
         [0028]     In accordance with an exemplary embodiment, housing top  10  is preferably disposed relative to trim resistor element  4  and housing body  12  so as to allow communication with resistive element  16  via trim opening  24 . Also, housing top  10  is preferably disposed relative to housing body  12  so as to cause first lead wire  6  and second lead wire  8  to be compressingly and non-movably associated with plurality of conductive pads  18 . Moreover, housing top  10  is configured and preferably arranged relative to housing body  12  so as to non-movably contain trim resistor element  4  within resistor cavity  14 . In accordance with an exemplary embodiment a depth of the resistor cavity and a width or height of the trim resistor element positions a top surface of the trim element proximate to a top surface of peripheral wall  11 . In addition, a perimeter portion  29  of the housing top is configured to define opening  24 , while also providing a means for securing the trim resistor therein when housing top is secured to housing body  12 . In other words, perimeter portion  29  has a larger width than peripheral wall or perimeter portion  11  of housing body  12  that defines resistor cavity  14 , such that a portion of perimeter portion  29  will make contact with a portion of the resistor element when it is disposed in the resistor cavity.  
         [0029]     Once all of the components of independently housed trim resistor  1  have been arranged as shown in step  102 , housing top  10  is then connected to housing body  12  as shown in step  104 . In accordance with an exemplary embodiment, housing top  10  and housing body  12  are formed out of non-conductive plastic and housing top  10  is preferably ultrasonically welded to housing body  12  so as to create a seal between housing top  10  and housing body  12 . One non-limiting example of the plastic material for the housing top and housing body is Valox plastic.  
         [0030]     In addition, housing top  10  is preferably ultrasonically welded to housing body  12  so as to create a seal between first lead wire  6  and resistor housing  2  and between second lead wire  8  and resistor housing  2 . In accordance with an exemplary embodiment, the plastic housing itself seals around the insulation of the wires, a portion of the trim element, and the plastic of the complimentary housing portions to create a hermetic seal about the un-insulated wires and the conductive pads they make contact with. As used herein and in an exemplary embodiment, hermetic seal is defined as fluid leakage being &lt;0.5 cc/min at an external pressure of 7-7.5 psi. Of course, ranges above and below the aforementioned ranges are contemplated to within the scope of exemplary embodiments of the present invention.  
         [0031]     In another exemplary embodiment and after the wires are sealed between housing top  10  and housing body  12  (e.g., within channels  26 ) and the un-insulated portions are sealed in electrical contact with conductive pads  20  and  22  (e.g., pressure exerted from housing top portion  23 ) the hermetic seal about the lead wires (conductive and non-conductive portions) is further provided by the sealant disposed in cavity  24 , which provides a seal between the interior perimeter of opening  24  and the resistor element making contact with the interior perimeter.  
         [0032]     Although housing top  10  is preferably connected to housing body  12  via ultrasonic welding, housing top  10  may be connected to housing body  12  using any method suitable to the desired end purpose (e.g., securing the lead wires therebetween and in one exemplary embodiment hermetically sealing the wires therein). In accordance with an exemplary embodiment the connection process will provide a high normal force crimp on the bare wire of first lead wire  6  and second lead wire  8  so that electrical connection is made with the conductive pads of the trim resistor element  4 .  
         [0033]     Once housing top  10  has been connected to housing body  12  as shown in step  104 , resistive element  16  is adjusted (e.g., removing portions of the resistive element  16  so as to change the resistance between first pad  20  and second pad  22  by for example, extending the length of the conductive path of the resistive element between pad  20  and pad  22  as well as reducing the width of the conductive path between pad  20  and  22 ) so as to achieve a desired resistance between first pad  20  and second pad  22 , as shown in step  106 . In accordance with an exemplary embodiment, resistive element  16  is preferably adjusted via laser trimming. This is preferably done by communicating a laser beam with a predetermined starting position within open area  28  of trim resistor element  4  via trim opening  24 . In accordance with an exemplary embodiment, the laser would preferably find its proper starting location by finding the predetermined starting position disposed somewhere within open area  28  of trim resistor element  4 . However, the laser may find its proper starting location by locating two edges that are ninety degrees apart from each other or by finding the top and either the right or left edge of resistive element  16 . In accordance with an exemplary embodiment, the laser will make a series of passes over the trimable resistive element by for example, in an “I”, “L”, “J” or hook patterns, which can be inverted, wherein the desired amount of the resistive film of the resistive element is removed to provide an electrical conduit or path between the conductive pads, which has a known resistive value. Of course, any configuration is contemplated (e.g., zigzag) as long as there is a conductive path between the conductive pads.  
         [0034]     Once the laser has been communicated with the predetermined starting position, the laser beam then removes a portion of resistive element  16  by cutting into resistive element  16  until a desired resistance is achieved between first pad  20  and second pad  22 . In accordance with an exemplary embodiment, additional laser cuts may be used to further refine the resistance by for example, removing portions of the resistive element.  
         [0035]     Once the desired resistance has been achieved, and since trim opening  24  is located above resistive element  16 , an adhesive coating or sealant  31  may be applied to housing top  10  so to create a protective seal to the area within trim opening  24 . In accordance with an exemplary embodiment adhesive coating or sealant  31  may be any adhesive coating having non-conductive properties capable of bonding to resistor housing  2  so as to form a watertight seal, such as an acrylic encapsulate.  FIG. 7  illustrates sealant  31  disposed in opening  24  after the desired resistance is achieved. Sealant may be clear or opaque or any combination thereof.  
         [0036]      FIG. 2A  illustrates a view along lines  2 A- 2 A of  FIG. 2 . As illustrated, housing top  10  is secured to housing bottom  12  wherein trim element  4  is retained in cavity  14  by a peripheral wall portion  29 , which is wider than peripheral wall portion  11  and upper housing portion  23 , which overlays a portion of the pair of lead wires clamping the electrically insulated sheath within a respective one of the pair of channels and the terminal section against a respective one of the pair of conductive pads.  
         [0037]     In addition, opening  24  overlays and exposes the trimable resistive element disposed on a surface of the non-conductive substrate of the trim element, allowing for direct contact and removal of a portion of the trimable resistive element as well as applying a sealant thereto after a portion of the trimable resistive element has been removed to provide the desired resistance.  
         [0038]      FIG. 2B  illustrates a view along lines  2 B- 2 B of  FIG. 2 . As illustrated, housing top  10  is secured to housing bottom  12  wherein trim element  4  is retained in cavity  14  by a peripheral wall portion  29 , which is wider than peripheral wall portion  11  and upper housing portion  23 , is configured to overlay and seal a portion of the pair of lead wires within a respective one of the pair of channels as well as provide a direct contact force to the terminal section such that an electrical contact is made against a respective one of the pair of conductive pads.  
         [0039]     In accordance with exemplary embodiments, trim opening  24  and trimable resistive element  16 , conductive pads  20  and  22  are configured such that only a portion of the trimable resistive element is accessible for trimming via opening  24  or alternatively a portion of conductive pads  20  and  22  are also accessible via opening  24  and thereafter are sealed by sealant  31  or alternatively no portion of the conductive pads are accessible and all of the trimable resistive element is accessible or any combinations of the foregoing are contemplated wherein desired resistances are achieved by removing a portion of the trimable resistive element.  
         [0040]     In accordance with an exemplary embodiment, the resistance of resistive element  16  may be measured via a passive trim approach or via an active trim approach. One type of passive trim measurement approach, which may or may not be performed during the lasing process, measures the resistance of resistive element  16  by probing either first pad  20  and second pad  22  and/or first lead wire  6  and second lead wire  8 , using any resistance measurement device suitable to the desired end purpose. If the resistance is being measured during the lasing process, the laser will terminate lasing once a desired resistance is achieved. If the resistance is not being measured during the lasing process, the resistance will be measured following a laser cut. If the resistance is not as desired, the lasing processes will be repeated until a desired resistance is achieved. Another type of passive trim measurement approach would be to calculate, using the property characteristics of resistive element  16 , how much of the resistive element  16  must be removed in order to achieve a desired resistance. Once this is calculated, the laser may be precisely controlled to remove the calculated quantity.  
         [0041]     In accordance with an exemplary embodiment, under an active trim measurement approach, which also may or may not be performed during the lasing process, independently housed trim resistor  1  is connected to a desired device, such as a sensor. A known condition is applied to the input of the device and the output of the device is monitored. The resistance of resistive element  16  is then adjusted, as discussed hereinabove, until a desired output of the device is achieved.  
         [0042]     In accordance with an exemplary embodiment, although resistance of resistive element  16  is explained hereinabove as being adjusted using a laser, the resistance of resistive element  16  may be adjusted using any suitable adjustment method or device, such as sandblasting, high pressure air or water cutting. In addition, the laser used to adjust resistive element  16  may be any laser that abates material.  
         [0043]     In accordance with an exemplary embodiment, wire terminations may be applied to first lead wire  6  and second lead wire  8  so as to allow independently housed trim resistor  1  to be communicated with external devices, such as wide range sensors. Independently housed trim resistor  1  may then be secured using any suitable retention method, such as tape or inserting independently housed trim resistor  1  into a wire protection sheath along with other device wires as shown in  FIG. 5  and  FIG. 6 .  
         [0044]     In accordance with an exemplary embodiment, trim resistor element  4  preferably comprises a ceramic substrate of non-conductive materials. However, trim resistor element  4  may be constructed of any material suitable to the desired end purpose.  
         [0045]     In accordance with an exemplary embodiment, resistive element  16  is preferably constructed of printed resistor ink, such as ruthenium oxide, which is applied via silk screening, printing or any other suitable process to provide the desired amount of trimable resistive film on the nonconductive surface of the resistor element. However, resistive element  16  may be constructed of any resistive material suitable to the desired end purpose.  
         [0046]     In accordance with an exemplary embodiment, first pad  20  and second pad  22  are preferably constructed using a conductive ink constructed of a conductive material, such as palladium. However, first pad  20  and second pad  22  may be constructed of any conductive material that resists oxidation and that is suitable to the desired end purpose.  
         [0047]     As discussed herein, one non-limiting example of the trimable resistive film is a ruthenium oxide disposed on a non-conductive surface of the trim resistor element by for example, in an ink form, wherein the trim resistor element comprises a ceramic substrate such as AlO 2  and the trimable resistive film is in electrical communication with a plurality of conductive pads disposed on the non-conductive surface of the ceramic substrate. One non-limiting example of the conductive pads are areas of conductive ink such as palladium, which are configured to overlap a portion of the conductive ink comprising the trimable resistive film providing overlapping areas, which comprise electrical contact points between the conductive pads and the trimable resistive film.  
         [0048]     In addition, the periphery of trim opening  24  will provide a means for retaining the sealing material therein until it has cured (e.g., a liquid sealing material is disposed into trim opening  24  making direct contact with the trimable resistive film).  
         [0049]     As illustrated, electrical communication is provided to at least two separate areas of the conductive ink of the trimable resistive film. The electrical communication in one exemplary embodiment being at the locations where the conductive ink of the resistive film overlaps with the conductive ink of the contact pads. Of course, and in accordance with exemplary embodiment of the present invention, numerous other configurations for providing electrical communication with the resistive film are contemplated.  
         [0050]     While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.