Abstract:
An electronic control module includes a body portion, a printed circuit board positioned within the body portion, and a cap portion adapted to mate with the body portion. One of the body portion and the cap portion is formed with a groove and the other of the body portion and the cap portion is formed with a projection that is resiliently deformable upon entry into the groove to mechanically and sealingly couple the body portion and the cap portion. In some constructions, the projection is a U-shaped flange. In some constructions, the body portion and the cap portion are formed by molding a metal alloy from a thixotropic state.

Description:
BACKGROUND 
     The invention relates to electronic control modules, especially for vehicles, which include an electronic component inside a housing. More specifically, the invention relates to a housing for an electronic control module and a method of constructing an electronic control module with the housing. 
     SUMMARY 
     In one construction, the invention provides an electronic control module including a body portion, a printed circuit board positioned within the body portion, and a cap portion adapted to mate with the body portion. One of the body portion and the cap portion is formed with a groove and the other of the body portion and the cap portion is formed with a projection that is resiliently deformable upon entry into the groove to mechanically and sealingly couple the body portion and the cap portion. 
     In another construction, the invention provides a housing of an electronic control module, the housing including a first portion defining a cavity for an electronic component of the electronic control module, the first portion being thixomolded metal alloy and including a first connection portion, and a second portion being thixomolded metal alloy and including a second connection portion, the first portion and second portion being joined at the respective connection portions, substantially enclosing the electronic component, wherein the first connection portion includes one of an endless groove and an endless U-shaped flange formed integrally as part of the first portion, and the second connection portion includes the other of an endless groove and an endless U-shaped flange formed integrally as part of the second portion. 
     In yet another construction, the invention provides a method of constructing an electronic control module, the method comprising forming a first portion to include a cavity, the first portion being formed with one of a groove and a U-shaped flange, forming a second portion, the second portion being adapted to substantially close the cavity of the first portion and being formed with the other of a groove and a U-shaped flange, inserting an electrical component into the cavity, and mating the first portion and the second portion together by inserting the U-shaped flange into the groove. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an electronic control module embodying the invention; 
         FIG. 2  is an exploded assembly view of the electronic control module of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the electronic control module of  FIG. 1 ; 
         FIG. 4  is a detail cross-sectional view of a connection between portions of the electronic control module as shown in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of an alternate electronic control module embodying the invention; and 
         FIG. 6  is a front view of a body portion of the electronic control module of  FIG. 1 . 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an electronic control module (ECM)  20 . The ECM  20  includes an electrical component, such as a printed circuit board (PCB)  24 . The PCB  24  is electrically coupled with various sensors and controls of a vehicle (not shown). The vehicle is an off-road vehicle in some constructions, but the ECM  20  may be used in an automobile such as, a car or truck for on-road use in other constructions. Off-road vehicles may include not only dirt bikes, four-wheelers, etc., but also aircraft and watercraft including motorized boats and personal watercraft. The ECM  20  is in electrical communication with an engine of the vehicle to control certain operational characteristics of the engine, which may include but are not limited to air/fuel ratio, throttle response, ignition timing, etc. The ECM  20  also monitors operational characteristics of the engine and/or vehicle by receiving signals from various sensors (e.g., oxygen sensor, throttle position sensor, temperature sensor). The ECM  20  may interpret one or more of the signals in order to control one or more operational aspects of the engine and/or vehicle. 
     In addition to the electrical component (e.g., the PCB  24 ), the ECM  20  includes a housing assembly  28  and an interface portion  30  (i.e., PCB header). The housing assembly  28  includes a body portion  32  and a cover or cap portion  36 . The interface portion  30  can be considered a part of the housing assembly  28  and/or a part of the PCB  24 . The body portion  32  defies a cavity  38 , which receives the PCB  24 . As best shown in  FIG. 6 , the body portion  32  includes first datum features  39  and second datum features  40 ,  41 . The first datum features  39  provide a “hard stop” or abutment surface, which contacts the interface portion  30  when positioned fully into the cavity  38 . The second datum features  40 ,  41 , are discontinuous wall sections in the illustrated construction that fix the position of the PCB  24  within the cavity  38 . The second datum features  40 ,  41  pinch the PCB  24  and minimize fretting. 
     When the ECM  20  is assembled, the PCB  24  (already attached with the interface portion  30 ) is inserted into the cavity  38  until it contacts the second datum features  40 ,  41  and the interface portion  30  contacts the first datum features  39 . With the PCB  24  properly in place, the cap portion  36  is coupled to the body portion  32 . Although shown separately in the figures and described as such, the interface portion  30  and the cap portion  36  may be partially or fully integrated with each other in some constructions. For example, the cap portion  36  may incorporate some of the features of the interface portion  30 , or vice versa. In a fully integrated construction, the cap portion  36  and the interface portion  30  are not separate components, but are provided as a single piece. 
     The body portion  32  and the cap portion  36  are engageable with each other to substantially enclose the PCB  24 . Conductive pins  42 , which are electrically and mechanically coupled to the PCB  24 , have outer tips  42 A that protrude out through the interface portion  30 . One or more connectors (not shown), which can be coupled to the interface portion  30 , establish electrical communication between the PCB  24  and the various sensors and controls of the vehicle through the pins  42 . The pins  42  pass through individual openings  43  in the interface portion  30 . The interface portion  30  is secured to the PCB  24  and is mechanically retained by the cap portion  36 . In the illustrated construction, the pins  42  are arranged in two separate groups as they pass through the interface portion  30 , which is provided with two separate bosses  30 A and  30 B for establishing mechanical connections with two external connectors. 
     The interface portion  30  is formed with an O-ring groove  44  around a periphery thereof, the groove  44  opening radially outwardly. An O-ring  45  fits substantially within the O-ring groove  44  and is configured to contact an inner surface of the body portion  32  to make a seal between the interface portion  30  and the body portion  32  when the PCB  24  is inserted into the cavity  38 . The O-ring  45  inhibits dust, dirt, water, debris, etc. from entering the cavity  38  between the body portion  32  and the interface portion  30 . The cap portion  36  includes a peripheral retaining portion  46  that retains the interface portion  30  (and thus, the PCB  24 ) in position when the cap portion  36  is engaged with the body portion  32  to close the housing assembly  28 . 
     The openings  43  provide a substantially close-fitting and sealed arrangement around the pins  42  so that the outer tips  42 A of the pins  42  are accessible from outside the closed housing assembly  28 . The connection between the body portion  32  and the cap portion  36  is also substantially sealed and leak-free (e.g., to prevent entrance of debris and/or seepage of moisture from the surrounding atmosphere into the cavity  38 ). 
     Connection portions  48  and  52  are provided on the body portion  32  and the cap portion  36 , respectively, to enable the engagement of the body portion  32  with the cap portion  36  and to provide clamping pressure to the PCB  24 , which may be stabilized without constraining its thermal expansion. As illustrated in  FIGS. 2-4 , the connection portions  48  and  52  are endless and extend along respective peripheries of the body portion  32  and the cap portion  36 . In some constructions, the connection portions  48  and  52  have ends, and an additional sealing/coupling member may be incorporated to close a gap between the ends. In further constructions, such as an application where the PCB  24  need not be enclosed within the housing assembly  28  by a full peripheral connection, the connection portions  48  and  52  need not be endless and may instead form one or more separate connections having terminating ends. 
     The connection portion  48  on the body portion  32  includes a groove  56 , while the connection portion  52  on the cap portion  36  includes a U-shaped projection, or flange  60 . The groove  56  includes a first wall  56 A, a second wall  56 B, and a third wall  56 C. In the illustrated construction, the first and second walls  56 A and  56 B are substantially parallel and spaced apart, and the third wall  56 C is curved and extends between the first and second walls  56 A and  56 B. In other constructions, the groove  56  may have a different cross-sectional shape, such as first and second walls that are not parallel, a third wall that is not curved, etc. 
     As best shown in  FIGS. 3 and 4 , the flange  60  includes two engaging portions, specifically a first leg  62  and a second leg  64 , and a hinge portion  66  connecting the first and second legs  62 ,  64  around the entire periphery. The first and second legs  62  and  64  are spaced a first distance apart, but resilient flexure at the hinge portion  66  allows the first and second legs  62  and  64  to be squeezed together, reducing the distance therebetween. Therefore, when the first and second legs  62  and  64  are compressed, the hinge portion  66  becomes stressed and exerts a reactive force biasing the legs  62  and  64  away from each other because the natural at-rest state of the flange  60  is with the first and second legs  62  and  64  spaced the first distance apart. The bias force provides increased friction between the flange  60  and the groove  56 , which resists the separation of the cap portion  36  from the body portion  32 . Thus, fasteners of any kind that are separate from the body portion  32  and the cap portion  36  are not necessary and need not be incorporated. 
     The flange  60  and groove  56  are self-fastening and self-sealing by simply inserting the flange  60  into the groove  56  around the mutual periphery. Even in a construction where the flange  60  and groove  56  are not endless, the connection(s) therebetween may be self-fastening and self-sealing. Sealing components or compounds separate from the body portion  32  and the cap portion  36  are not necessary and need not be incorporated. Effectively, two peripheral seals are formed: one between the first leg  62  and the first wall  56 A of the groove  56  and another between the second leg  64  and the second wall  56 B of the groove  56 . Because the hinge portion  66  does not hilly fill the groove  56  in the depth dimension, a gap is formed between the first and second peripheral seals. Therefore, the peripheral seals are separated and in series with one another, and any dust, dirt, water, debris, etc. that might reach the cavity  38  must make its way through both peripheral seals. 
     In some constructions, such as an ECM  20  for use on a watercraft or other especially harsh applications, a sealant and/or adhesive material may be inserted between the flange  60  and the groove  56  and between the peripheral retaining portion  46  and the interface portion  30 . Specifically, in one construction, peripheral beads of sealant/adhesive material are dispensed onto the third wall  56 C of the groove  56  and onto the front of the interface portion  30 . Therefore, additional seals and additional fixing strength are present between the body portion  32  and the cap portion  36  and also between the cap portion  36  and the interface portion  30 . Such additional seals and fixing strength are included as a redundancy for the connection between the flange  60  and the groove  56 , which provides ample sealing and mechanical coupling performance without separate sealing/adhesive material and without separate fasteners. 
     The elimination of fasteners and seals reduces component and assembly costs for the ECM  20  while providing comparable or better performance in terms of structure robustness (vibration, temperature, and impact), dissipation of heat from electronics, and resistance to fluid intrusion when compared against conventional constructions using die-cast, stamped, or plastic injection-molded housings with adhesives, sealants, thermal greases, and/or thermal interface pads separating the housing pieces. The elimination of either one of fasteners and intermediate seals provides some of the same advantages to a lesser degree. 
       FIG. 5  illustrates an ECM  20 ′ having a housing assembly  28 ′ in which a body portion  32 ′ is provided with a U-shaped flange  60 ′, and a cap portion  36 ′ is provided with a groove  56 ′. The ECM  20 ′ is otherwise identical to the ECM  20  and thus, does not change the application or usefulness as compared with the ECM  20 . Aside from being provided on opposite portions of the housing assembly  28 ′ as compared to the housing assembly  28 , the flange  60 ′ and the groove  56 ′ are dimensionally similar to the flange  60  and the groove  56 , respectively. Therefore, the flange  60 ′ and the groove  56 ′ provide the same mutual engagement and functionality as described above with reference to the ECM  20 , and further features of the ECM  20  described below are equally applicable to the ECM  20 ′. 
     Returning now to  FIGS. 1-4 , the housing assembly  28 , including the body portion  32  and the cap portion  36 , is formed by molding a metal alloy while in a thixotropic material state. The metal alloy can be a magnesium alloy, such as AZ91D. Such molding is referred to as thixomolding, resulting in thixomolded parts, both terms being tradenames of Thixomat, Inc. of Ann Arbor, Mich. Thixomolding equipment and processes are described in further detail in U.S. Pat. Nos. 4,964,455; 5,711,366; 5,819,839; 5,836,372; 5,878,804; 5,983,978; 5,996,679; 6,059,012; 6,736,188; and 7,028,746, all of which are hereby incorporated by reference. In an alternate construction, a metal heat sink is insert-molded or over-molded with thermal plastic resin or elastomer. 
     The body portion  32 , which is not in direct contact with any heat-generating elements (e.g. elements that conduct electric current) of the PCB  24 , is a good thermal conductor. The cavity  38  is formed to closely surround the PCB  24  to eliminate the need for venting and to limit the interior air volume and the resistance to heat transfer. Heat from the PCB  24  is absorbed by the body portion  32  through conduction, convection, and radiation, and transferred efficiently to the surrounding atmosphere by convection. Because of the nature of the groove  56  and flange  60  interface, even in a construction where a sealant/adhesive material is inserted between the third wall  56 C and the hinge portion  66 , the body portion  32  and the cap portion  36  remain in direct contact with each other. Therefore, heat transferred from the PCB  24  to the body portion  32  can be further conducted from the body portion  32  to the cap portion  36 . Thus, the cap portion  36  provides additional thermal capacitance and, through convection with the surrounding atmosphere, additional heat sinking ability. Typically, intermediate seals and/or adhesives that completely disconnect housing components are especially limiting to heat transfer between the housing components. The engagement between the flange  60  and the groove  56  ensures that the body portion  32  and the cap portion  36  are not completely separated from each other by a seal and, or adhesive. 
     The body portion  32  is additionally formed with fins or ribs  74 . The ribs  74  enhance the ability of the housing assembly  28  to transfer heat to the surrounding atmosphere by convection. The ribs  74  also provide stiffness to the body portion  32 , which can prevent or flatten a warped PCB  24 . Alternately, another intricate pattern may be formed in the body portion  32  and/or cap portion  36 , such as a honeycomb pattern. The ribs  74  are easily formed in the thixomolding process, much like injection molding of plastic. The shape of the body portion  32  would be simple to form by injection molding of plastic, which can make complex shapes quite readily. However, forming the body portion  32  and the cap portion  36  from a metal alloy allows for better heat transfer and reduced electromagnetic emission as compared to plastic. The thixomolding process enables the housing assembly  28  to have the above-mentioned benefits of a metal alloy while being formed with the ribs  74  and other intricately-shaped features, which cannot be manufactured with similar precision with conventional metal forming operations. If the application for the ECM  20  permits, the housing assembly  28  may alternately be formed by die-casting aluminum, stamping aluminum or steel, metal injection-molding, hot die-casting, impact extrusion and injection-molding plastic, among other processes. 
     The cavity  38  may be coated with a dielectric material to electrically isolate the PCB  24  from the body portion  32 . The thixomolding process, especially with magnesium alloy, results in a low surface porosity, which is suitable for coating. The dielectric coating on the body portion  32  may be black in color to increase the radiation aspect of the thermal transfer from the PCB  24 . In some constructions, the cap portion  36  is electrically isolated from the PCB  24  by the body portion  32  and the interface portion  30  and need not be coated with the dielectric material. The cap portion  36  is also exposed to less heat from the PCB  24  as compared to the body portion  32 . In some constructions, the dielectric coating improves the adhesion of a thixomolded component to a plastic resin when a thixomolded part is used as the insert in an insert-molded or over-molded plastic housing assembly and/or component. The dielectric coating on the body portion  32  may include but is not limited to one of epoxy, polyester, epoxy/polyester blend, e-coating, powder coating, paint, and ink. 
     Various features of the invention are set forth in the following claims.