Abstract:
An attachment structure for use with a standalone control unit. The control unit includes a threaded insert located in an enclosed cavity which allows screws to be used for grounding of an EMI/RFI board, along with creating a sealed, enclosed pocket. The attachment structure allows for grounding of the PCB to the sheet metal base plate without creating a leak path to the outside of the control unit. This ground approach encapsulates the screw to prevent the formation of a leak path.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/870,464 filed Aug. 27, 2013. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to an attachment structure for use with a standalone control unit having a sealed enclosure. 
       BACKGROUND OF THE INVENTION 
       [0003]    Various types of control units are generally known. Some types of control units are standalone, and are designed to withstand operating in harsh environments. Standalone controllers use an aluminum sheet metal base plate to attach and provide a rigid support for a printed circuit board (PCB). A cover or housing is placed and sealed over a rigidizer creating a sealed PCB enclosure. It is difficult to ground the PCB for electromagnetic interface (EMI) and radio frequency interface (RFI) purposes because typical methods of using a screw create a leak path in the base plate. In addition, exposed screw threads through the bottom of the sheet metal base plate increase the risk of handling damage from the exposed screw threads. 
         [0004]    Transmission control units (TCU) that are sealed and use an aluminum sheet metal base plate require a method of grounding the PCB to the base plate for EMI/RFI control. Any holes or screws in the base plate create a leak path which occurs typically during thermal cycles. 
         [0005]    Accordingly, there exists a need for a standalone control unit which provides for a connection between a PCB and a base plate, and is also encapsulated and provides a proper seal. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is an attachment structure for use with a standalone control unit. A threaded insert in an enclosed cavity allows screws to be used for EMI/RFI board grounding along with creating a sealed, enclosed pocket. 
         [0007]    The attachment structure of the present invention allows for grounding of the PCB to the sheet metal base plate without creating a leak path to the outside. The attachment structure is suitable for electrical grounding, and is not limited to use with grounding an EMI/RFI board. This grounding approach encapsulates the screw to prevent the formation of a leak path. 
         [0008]    In one embodiment, the present invention is a transmission control unit having an attachment structure, which includes a base plate, a material layer disposed on at least a portion of a top surface of the base plate, and a printed circuit board at least partially disposed on the material layer. 
         [0009]    A cavity is formed as part of the base plate, and an insert is located in the cavity such that at least a portion of the printed circuit board is supported by the insert. A screw is inserted through an aperture of the printed circuit board and an aperture of the insert, connecting the printed circuit board and the insert to the base plate. At least one protrusion is formed as part of the base plate in proximity to the insert, and at least one recess is formed as part of the insert, such that the protrusion extends into the recess to connect the insert to the base plate. 
         [0010]    The cavity includes at least one side wall, and a bottom wall connected to the side wall. The protrusion is formed as part of the side wall. 
         [0011]    There is also an axis, and the insert is non-circular, such that as the fastener is inserted through the insert and rotated, the insert is prevented from rotating about the axis and remains stationary relative to the base plate. At least part of the cavity is shaped to correspond to the shape of the insert, preventing rotation of the insert about the axis as the screw is inserted through the aperture of the insert and the aperture of the printed circuit board. At least a portion of the screw is substantially parallel to the axis. 
         [0012]    The base plate is made of a metal material, such as aluminum, but it is within the scope of the invention that other types of metal may be used, such as, but not limited to, steel or copper. 
         [0013]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0015]      FIG. 1  is a sectional side view of an attachment structure for a standalone control unit, according to embodiments of the present invention; and 
           [0016]      FIG. 2  is a sectional side view of an insert attached to a base plate, which is used as part of an attachment structure for a standalone control unit, according to embodiments of the present invention; 
           [0017]      FIG. 3  is an exploded sectional side view of an insert and a base plate, prior to undergoing a swaging process, which are used as part of an attachment structure for a standalone control unit, according to embodiments of the present invention; 
           [0018]      FIG. 4  is an exploded sectional side view of an insert shown separately from a base plate, after undergoing a swaging process, which are used as part of an attachment structure for a standalone control unit, according to embodiments of the present invention; and 
           [0019]      FIG. 5  is an exploded view of an insert and a base plate, prior to undergoing a swaging process, which are used as part of an attachment structure for a standalone control unit, according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0021]    A section of a transmission control unit (TCU) having an attachment structure according to the present invention is shown in the Figures generally at  10 . The TCU  10  includes a printed circuit board (PCB)  12 , an insert  14 , and a base plate  16 . Also included is a fastener  18 , which in this embodiment is a threaded screw, but it is within the scope of the invention that other types of fasteners may be used. 
         [0022]    The screw  18  extends through a first aperture  20  formed as part of the PCB  12 , and a second aperture  22  formed as part of the insert  14 . There is an axis  44  which also extends through the first aperture  20  and the second aperture  22 , and is substantially perpendicular to the PCB  12 . The threaded portion of the screw  18  is inserted through the apertures  20 , 22  along the axis  44 . The screw  18  is substantially parallel to the axis  44 . The second aperture  22  is threaded and receives the screw  18  to secure the connection between the screw  18 , the PCB  12 , and the insert  14 . 
         [0023]    The insert  14  is also connected to the base plate  16  through the use of a retention feature, shown generally at  30 . The base plate  16  includes a cavity, shown generally at  24 , the insert  14  is located in the cavity  24 , and the screw  18  partially extends into the cavity  24 . The cavity  24  includes sidewalls  26  and a bottom wall  28 . Integrally formed as part of the sidewalls  26  is a protrusion  32   a,  which is part of the retention feature  30  and circumscribes the sidewalls  26 . The protrusion  32   a  extends into a recess  32   b  formed as part of the insert  14 . The recess  32   b  circumscribes the insert  14 , best shown in  FIGS. 1-2 , and  4 , and is also part of the retention feature  30 . The protrusion  32   a  is formed by a swaging process, and produces an interference fit between the protrusion  32   a  and the recess  32   b,  connecting the protrusion  32   a  and the recess  32   b,  and therefore properly positioning the insert  14  in the recess  32   b  relative to the base plate  16 . The retention feature prevents the insert  14  from being removed from the cavity  24 , and more specifically, from being pulled out of the cavity  24  due to the pulling force applied to the insert  14  as the screw  18  is inserted into the apertures  20 , 22 . 
         [0024]    The thickness of the insert  14  is such that the PCB  12  is not in contact with the base plate  16 , but rather the thickness and positioning of the insert  14  locates the inner surface  40  of the PCB  12  at a distance  34  away from the top surface  46  the base plate  16 . The distance  34  in this embodiment ranges from 0.13 mm to 0.30 mm, but it is within the scope of the invention that other distances may be used. 
         [0025]    Located between the PCB  12  and the base plate  16  is a material layer  42 . The material layer  42  is of a thickness approximately equal to the distance  34  between the inner surface  40  of the PCB  12  and the top surface  46  of the base plate  16 . The material layer  42  is made of a thermal interface material which performs the functions of transferring heat away from the PCB  12 , and the thermal interface material provides a dielectric isolation function. 
         [0026]    The cavity  24  is formed as part of the base plate  16  such that the inner surface  36  of the bottom wall  28  is located at a distance  38  from the outer surface  48  of the insert  14 . The location of the insert  14  is also such that the outer surface  48  of the insert  14  is also about the same distance  34  away from the top surface  46  of the base plate  16  as the lower surface  40  of the PCB  12 . This ensures that the outer surface  48  of the insert  14  is in alignment with the outer surface  50  of the material layer  42 , and therefore the PCB  12  is properly supported by the material layer  42  and the insert  14 . The cavity  24  formed as part of the base plate  16  seals and encloses the entire area around the screw  18  and the insert  14 , ensuring there is no leak path where liquid or other debris may enter the TCU  10 . 
         [0027]    During assembly, the insert  14  is placed into the cavity  24 , and the protrusion  32   a  is formed by the swaging process, as previously described, such that the protrusion  32   a  fits into the recess  32   b.  The insert  14  is a non-circular shape, and in this embodiment, the insert  14  is hexagonal in shape as shown in  FIGS. 4-5 , but it is within the scope of the invention that the insert may be other shapes as well, such as, but not limited to, triangular, rectangular, heptangular, and the like. The cavity  24 , or at least the portion of the cavity  24  surrounding the insert  14 , is of a shape that corresponds to the shape of the insert  14 , which in this embodiment is hexagonal. After the insert  14  is placed in the cavity  24 , and the swaging process is completed, the screw  18  is inserted through the first aperture  20  and is rotated, which then moves the screw  18  through the second aperture  22  of the insert  14 . The hexagonal shape of the insert  14  and the corresponding hexagonal shape of the cavity  24  prevents the insert  14  from being rotated about the axis  44  relative to the base plate  16  as the screw  18  is inserted into the second aperture  22  and rotated. 
         [0028]    Once the screw  18  is in place, the PCB  12  is connected to and positioned correctly relative to the base plate  16 . The shape of the base plate  16 , and more specifically the shape of the sidewall  26  and the bottom wall  28  creates the sealed cavity  24 , and therefore prevents the existence of a leak path around the screw  18  and insert  14 . 
         [0029]    While it has been shown that the attachment structure of the present invention may be used with a TCU, it is within the scope of the invention that the attachment structure may be used with any other type of standalone controller, such as an electronic control unit, or the like. Furthermore, the base plate  16  shown in the drawings is made of aluminum, but it is within the scope of the invention that other types of materials may be used, such as steel, copper, or the like. The attachment structure of the present invention is also not limited to use with EMI/RFI board grounding, but it is within the scope of the invention that the attachment structure may be used to provide electrical grounding as well. 
         [0030]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.