Abstract:
An electronic package includes a circuit board and a capsule layer encasing the circuit board and forming an immersible electronic module. A housing receives the electronic module and forms a protective shell around the electronic module.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates generally to electronic packages, and, more particularly, to sealed electronic packages for use in rugged environmental conditions. 
   The proliferation of electronic devices in modern vehicles creates a number of manufacturing challenges in packaging the electronic devices to adequately protect electronic components and ensure reliable operation thereof. Especially for electronic packages which are mounted on the exterior of a vehicle, providing adequate protection for electronics can become a daunting task. 
   For example, electronic monitoring of brake wear for trucks, buses, and larger vehicles has become desirable to ensure proper performance of the vehicle and to comply with applicable regulations. By sensing an operating condition of the brakes for the vehicle or trailer, a warning signal may be provided to an operator of the vehicle, such as through a dashboard light or indicator, that one or more of the vehicle brakes should be serviced. Unacceptable or dangerous operating conditions may therefore be avoided, and inconvenient physical inspection of the brakes need not be as frequent. 
   To correctly monitor the condition of the brakes, the electronics and sensing mechanisms must be located underneath the vehicle near the brakes themselves, and are therefore exposed to varying temperature, pressure and moisture conditions, as well as exposed to a variety of engine fluids, lubricants, grease, brake fluids, debris, gravel, roadway composition coatings and by-products. Electronic components must therefore be carefully packaged to withstand such a harsh operating environment and reliably operate. 
   One known approach for protecting electronics from harsh environments is to contain the electronic components within a housing, and then fill or pack the housing with a silicon potting compound to insulate electronic components from adverse environmental conditions. The silicon potting compound, however, tends to result in bulky electronic packages. In one application for a brake wear monitor system, the housing of the electronic package must have a slim profile on the order of 0.5 inches or less. Achieving a profile such as this with silicon potting compounds is problematic. A suitable alternative to silicon potting compounds to protect electronic sensor packages is desirable. 
   BRIEF DESCRIPTION OF THE INVENTION 
   According to an exemplary embodiment, an electronic package comprises a circuit board and a capsule layer encasing the circuit board, thereby forming an immersible electronic module. A housing receives the electronic module and forms a protective shell around the electronic module. 
   Optionally, the capsule layer comprises a melt processsible rubber, and the housing comprises a longitudinal axis. An elongated opening extends transverse to the longitudinal axis in the housing for adjusting a position of the housing. The housing includes a mounting stud and at least one indicator bar. 
   According to another exemplary embodiment, an electronic package is provided. The package comprises an electronic assembly overmolded with a capsule layer, and the electronic assembly is configured to output a signal in response to a condition of a monitored object. A housing having a bore therein is configured to receive the overmolded electronic assembly, and one of the capsule layer and the housing comprises a latch configured to engage the other of the capsule layer and the housing. 
   According to another exemplary embodiment, a method of packaging an electronic assembly subject to a severe operating environment is provided. The method comprises encapsulating the electronic assembly to form an electronic module, fitting the enscapsulated electronic assembly into a housing shell, and securing the encapsulated module to the housing shell. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a brake assembly including an electronic brake stroke monitor formed in accordance with an exemplary embodiment of the present invention. 
       FIG. 2  is an exploded view of the brake stroke monitor shown in  FIG. 1 . 
       FIG. 3  is a perspective view partly broken away of a sensor module for the monitor shown in  FIGS. 1 and 2 . 
       FIG. 4  is another perspective view partly broken away of the sensor module shown in  FIG. 2 . 
       FIG. 5  is an assembly view of the brake stroke monitor shown in  FIG. 2 . 
       FIG. 6  is a top plan view of the brake assembly in a first position relative to the brake stroke monitor. 
       FIG. 7  is top plan view of the brake assembly in a second position relative to the brake stroke monitor. 
       FIG. 8  is top plan view of the brake assembly in a third position relative to the brake stroke monitor. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a sealed electronic monitor  10  formed in accordance with an exemplary embodiment of the present invention. The electronic monitor  10 , as explained below, is adapted for reliable monitoring of a brake assembly  12  despite an extreme or severe operating environment. While the invention is described in the context of a vehicle braking system monitor, it is to be understood that the following description is provided for illustrative purposes only, and is not intended to limit the invention to any particular use or application, such as with the brake assembly  12 . Rather, it is understood that the principles described below with respect to packaging of the electronics is applicable to other instances of electronic installations in extreme conditions and demanding operating environments, whether in a vehicle or otherwise. 
   The electronic monitor  10  is mounted proximate the brake assembly  12  upon a bracket  14  having an attachment portion  16  at one end. The attachment portion  16  has a opening therethrough (not shown in  FIG. 1 ) which allows the bracket  14  to be attached to a chamber mounting bracket  24  which supports a brake chamber  26  of the brake assembly  12 . The brake chamber  26  includes a clevis assembly  28  having a clevis pin  30  and a brake arm  29 . 
   The brake assembly  12  is a spring-assisted assembly of a known type that is commonly employed for braking of trucks, buses, and towed vehicles such as trailers. In normal braking operation, the brake arm  29  actuates the chamber  26  to apply and release brake pads (not shown) in response to an operator directed delivery and exhaust of a compressed fluid, such as air. 
   As the vehicle&#39;s brakes are applied over time, the brake pads are worn away, resulting in an increase in the stroke of the brake arm  29  needed to apply the necessary braking force. The stroke of the brake arm  29  can also change if the brakes are out of adjustment. Thus, the length of travel of the brake arm  29  is an indicator of brake wear or improper brake adjustment. 
   The stroke of the brake arm  29  is sensed by the electronic monitor  10  via movement of the clevis pin  30 , which moves with the brake arm  29  during use. When the pin  30  travels a specified distance, corresponding to a predetermined brake wear condition, a signal is sent from the electronic monitor  10  to a remote location, such as an indicator positioned on the vehicle dashboard. An unacceptable brake condition may therefore be identified and the operator may respond accordingly. 
   The electronic monitor  10  is mounted a predetermined distance, such as about 0.25 inches in an exemplary embodiment, from the clevis pin  30 . The electronic monitor  10  is oriented generally parallel to the clevis assembly  28  such that when the brake assembly  12  is in a fully released position, the clevis pin  30  sits at a predetermined location with respect to the electronic package  10 . When the brake assembly  12  is applied, the clevis pin  30  moves in a direction parallel to the monitor  10 , and by sensing the amount of movement of the clevis pin  30 , the brake stroke may be determined as acceptable or unacceptable as described below. 
     FIG. 2  is an exploded view of a brake stroke monitor assembly  40  including the bracket  14 , a sensor module  42 , and a module housing  44 . The sensor module  42  and the module housing  44  collectively form an electronic package for the monitor  10  (shown in  FIG. 1 ). 
   The mounting bracket  14  includes the attachment portion  16  including at least one opening  46  therethrough for mounting the attachment portion  16  to the mounting bracket  24  (shown in  FIG. 1 ) of the brake assembly  12  (shown in  FIG. 1 ) with a known fastener (not shown in  FIG. 2 ). The opening  46  is elongated to provide flexibility in positioning of the bracket  14  with respect to the brake assembly  12 . 
   A positioner portion  48  extends from the attachment portion  16  at substantially a right angle thereto, and the positioner portion  48  includes an elongated slot  50  therein which permits attachment of the sensor module  42  and the module housing  44  to the positioner portion  48 . While an exemplary bracket  14  is illustrated, it is understood that a variety of differently shaped and configured brackets may also be used in further and/or alternative embodiments of the invention. 
   The sensor module  42  includes an electronic assembly (not shown in  FIG. 2 ) which is embedded in a protective capsule layer  52 . In an illustrative embodiment, the capsule layer  52  is a low durometer, low temperature processing material applied to the electronic assembly in a known overmolding process into a generally rectangular form completely surrounding and in intimate contact with the components of the electronic assembly. A suitable material for the capsule layer  52  is an Alcryn® melt processsible rubber commercially available from Advanced Polymer Alloys of Wilmington Del., thereby providing a relatively soft and compressible protective casing for the electronic assembly. With such a material, a mold temperature of about 300° F. may be obtained, and by gating the mold appropriately so that the material does not directly impact the electronic assembly during molding, the electronic components are not damaged by the overmolding operation. When the electronic assembly is encapsulated in the capsule layer  52  to form the sensor module  42 , a slimmer profile is produced in comparison to modules having silicon potting compounds, and the sensor module  42  is completely immersible while providing a watertight enclosure for the electronic assembly. Additionally, enscapsulation of the sensor module  42  is less expensive than packing a housing with a silicon potting compound. 
   While one suitable material for the capsule layer  52  has been identified, it is understood that other known materials having similar properties and characteristics may likewise be employed in alternative embodiments to encapsulate the electronics of the sensor module  42 . 
   A cable  54  exits the sensor module at one corner thereof at approximately a 45° angle with respect to the longitudinal axis  55  of the sensor module  42 . In the illustrated embodiment, the cable  54  includes three conductors  56 , each of which are soldered to the electronic assembly within the overmolded capsule layer  52 . A portion  58  of the cable  54  stemming from the sensor module  42  is also overmolded with the capsule layer  52  to provide a strain relief to the cable exit and to prevent the conductors  56  from being separated from the electronic assembly. The cable  54  is coupled to an indicator or alarm (not shown) which alerts an operator to the status of the brake assembly  12  (shown in  FIG. 1 ). 
   It is understood that in further and/or alternative embodiments greater or fewer conductors  56  may be provided in the cable  54 , and that the cable  54  may exit the sensor module in an another location or another orientation with respect to the sensor module  42 . 
   The module housing  44  is separately fabricated from the sensor module  42  and forms a comparatively hard shell, thin walled enclosure for the sensor module  42 . A latch protrusion  43  is formed on one end of the sensor module  42  which engages a latch aperture  45  in the corresponding end of the module housing  44 . The sensor module  42  and the module housing  44  may therefore be securely engaged or locked to one another. 
   In an exemplary embodiment, the module housing  42  is fabricated from a material which is chemically compatible with the capsule layer  52 , and in one embodiment the module housing  42  is fabricated from magnesium according to a known thixo-molding process to form a non-magnetic enclosure for the sensor module  42 . Alternatively, the module housing  44  may be fabricated according to a known molding operation with a high strength plastic, such as Minlon® mineral-reinforced nylon resin available from E. I. du Pont de Nemours and Company. It is further contemplated that other known suitable materials may be employed in the fabrication of the module housing  44 . 
   The module housing  44  includes a substantially hollow interior or bore  60  which is shaped and dimensioned to receive and accept the encapsulated sensor module  42  when inserted therein with press-fit engagement Collectively, the encapsulated sensor module  42  and the module housing  44  provide a secure packaging for the electronics which may capable withstand severe environmental conditions encountered when mounted underneath a vehicle in proximity to the brake assembly  12  (shown in  FIG. 1 ). The sensor module  42  provides a moisture proof, sealed enclosure which is chemically resistant to fluids and moisture encountered during use, while the module housing  44  provides an impact resistant enclosure about the sensor module  42 . 
   A number of indicator slots  62  are formed into a top  64  and opposite sides  66  of the module housing  44 . A number of U-shaped indicator bars  68  may be coupled to the indicator slots  62  with snap-fit engagement such that the indicator bars are substantially flush with the top and side surfaces  64  and  66  of the module housing  44 . The plastic indicator bars  68  may be color-coded or otherwise distinguished from the module housing  44  to visibly indicate the brake stroke condition by observation of the location of the clevis pin  30  (shown in  FIG. 1 ) with respect to the indicator bars  68 . As such, the module housing  44  provides local visual indication of brake wear while the sensor module  42  provides remote indication of brake wear. 
   The indicator bars  68  may be selectively employed in designated indicator slots  62  to represent a plurality of acceptable brake stroke ranges between a selected pair of indicator bars  28 , and thus a single module housing  44  may be used with a variety of different vehicles and braking systems. While four indicator bars are illustrated in  FIG. 2 , it is understood that greater or fewer numbers of indicators bars could be used to visibly indicate greater or fewer ranges of brake stroke. 
   The module housing  44  is fabricated with a molded-in-place threaded stud  70  in an exemplary embodiment, and an elongated opening  72  oriented transverse to the longitudinal axis  55  of the module housing  44 . The threaded stud  70  is inserted through the slot  50  in the positioner portion  48  of the mounting bracket  14 , and a lock washer  74  and nut  76  are fastened to the stud  70  to securely couple the module housing  44  to the positioner portion  48 . A positioning bolt  78  is inserted through the opening  72  in the module housing  44  and also through the slot  50  in the positioner portion  48  of the mounting bracket  14 . A lock washer  80  and nut  82  are fastened to the positioning bolt  78  to securely couple the module housing  44  to the positioner portion  48  on an end of the module housing  44 . 
   By varying the location of the positioning bolt  78  in the transverse opening  72  in the module housing  44 , the longitudinal axis  55  of the module housing  44  may be positioned at an angle with respect to a longitudinal axis  84  of the positioner portion  48  of the mounting bracket  14 . The mounting bracket  14  therefore need not be precisely positioned on the brake assembly  12  (shown in  FIG. 1 ). Rather, the position of the module housing  44  may be readily adjusted for precise positioning of the module housing  44 , and hence the position of the sensor module  42 , with respect to the clevis pin  30  (shown in  FIG. 1 ). Installation of the brake monitor  10  (shown in  FIG. 1 ) is therefore simplified. 
     FIG. 3  is a perspective view partly broken away of the sensor module  42  illustrating an electronic assembly  100  inside the capsule layer  52 . The electronic assembly  100  includes a printed circuit board  102  and a number of sensors  104  mounted to the board  102 . In an exemplary embodiment the sensors  104  are hall effect sensors and the printed circuit board  102  includes circuitry for monitoring the voltage output of the sensors  104 . As the clevis pin  30  (shown in  FIG. 1 ) moves in front of the sensor module, the voltage output from the sensors varies, thereby reflecting a relative position of the clevis pin  30  with respect to the sensors  104 . In various alternative embodiments, other types of sensors and components may be employed in lieu of hall effect sensors to monitor the movement of the clevis pin  30 . 
   As also seen in  FIG. 3 , the conductors  56  of the cable  54  are terminated to the printed circuit board  102 . An output signal from the printed circuit board  102  may therefore be transmitted to a remote location through the cable  54 . 
     FIG. 4  is another perspective view partly broken away of the sensor module  42  illustrating an opposite side of the electronic assembly  100  inside the capsule layer  52 . A magnetic plate  110  is located behind the printed circuit board  102  within the capsule layer  52 . The magnetic plate  110  creates a magnetic field in the vicinity of the sensor module  42 . As the clevis pin  30  (shown in  FIG. 1 ) moves within the magnetic field, voltage changes are induced in the sensors  104  (shown in  FIG. 3 ). The printed circuit board  102  outputs signals through the conductors  56  in the cable  54  when the sensor outputs indicate a predetermined length of travel of the clevis pin  30 . 
     FIG. 5  is an assembled view of the brake stroke monitor assembly  40 . The sensor module  42  (shown in  FIGS. 2–4 ) is inserted into the module housing  44 , and the module housing  44  is mounted to the positioner portion  48  of the bracket  14  via the positioning bolt  78 , the stud  70  and associated fasteners. Indicator bars  68  (shown in  FIG. 2 ) may be snapped into the indicator slots  62  as desired for visual indication of the brake stroke. The attachment portion  16  of the bracket  14  may then be mounted to the brake assembly  12  (shown in  FIG. 1 ) and positioned such that the clevis pin  30  is positioned adjacent the top  64  of the module housing  44 . The positioning bolt  78  may be adjusted so that the longitudinal axis  55  of the module housing  44  is substantially aligned with an axis of motion of the clevis pin  30 . As the clevis pin  30  moves in a direction parallel to the longitudinal axis  55  of the module housing  44 , the output voltage of the sensors  104  (shown in  FIG. 3 ) in the sensor module  42  indicates the position of the pins  30  relative to the module housing  44 . When the brake stroke length reaches a predetermined threshold, such as a length greater than a longitudinal distance between a selected pair of the indicator bars (shown in  FIG. 2 ), the sensor module  42  outputs a signal through the cable  54  to alert the vehicle operator of the brake condition. 
     FIG. 6–8  illustrate the brake monitor  10  at different stages or conditions of the brake assembly  12 . Initially, the clevis pin  30  is orientated at a full brake position with respect to the module housing  44  at a location approximately corresponding to a first indicator bar  68  of the module housing  44 . At this stage of operation, the brake pads are worn little, if any, and the brake stroke is relatively small. The sensors  104  (shown in  FIG. 3 ) of the sensor module  42  (shown in  FIGS. 2–4 ) produce no output, and it may be visually observed that the brakes are in good operating condition with the clevis pin  30  substantially aligned with the first indicating bar  68 . 
   Over time, and as the brake assembly  12  is used, the brake pads wear and the brake stroke increases as illustrated in  FIG. 7 . The clevis pin  30  moves closer to a second indicator bar  120  that is located a predetermined distance from the first indicator bar  68  on the sensor housing, which also coincides with an acceptable brake stroke for the vehicle on which the brake monitor  10  is installed. At this stage of operation, the brake pads are moderately worn and the brake stroke is larger, but still within acceptable limits. The sensors  104  (shown in  FIG. 3 ) of the sensor module  42  (shown in  FIGS. 2–4 ) produce no output, and it may be visually observed that the brake assembly  12  is in an acceptable operating condition with the clevis pin  30  located between the first and second indicating bars  68  and  120 . 
   As the brake assembly  12  continues to be applied, the brake pads wear and the brake stroke increases further as illustrated in  FIG. 8 . When the brakes become severely worn, the clevis pin  30  moves beyond the second indicator bar  120 . At this stage of operation, the brake pads are unacceptably worn. The sensors  104  (shown in  FIG. 3 ) of the sensor module  42  (shown in  FIGS. 2–4 ) produce an output signal to warn the operator that the brake assembly  12  is in an unacceptable operating condition and that the brake assembly  12  should be serviced as soon as possible. 
   Packaging of the electronics of the break wear monitor  10  as described above ensures reliable operation of the monitor  10  despite the severe operating environment which the monitor  10  is subjected to in use near the brake assembly  12  located exterior and underneath the vehicle. Secure packaging is provided having a lower profile and lower cost than as compared to conventional electronic packages having a silicon potting compound. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.