Abstract:
A module is mounted to a object with a fastener and a special washer. The fastener engages the object through a mounting opening in mounting portion of a module case. The washer has a first portion extending obliquely outward and downward to be deformed between the fastener head and an electrically non-conducting surface of the mounting portion and thus increase a mounting force on the module with mounting advancement of the fastener. The washer has a second portion extending axially into the internal opening to contact an electrically conducting insert therein and thus create a series electrical circuit from the typically grounded object through the fastener, washer and insert to a detecting circuit, which verifies that the module is securely mounted with a predetermined mounting force.

Description:
TECHNICAL FIELD  
       [0001]     The technical field of this invention is module assemblies.  
       BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to modules adapted for secure mounting and retention on an object. An example of such an assembly is an electronic sensor and/or control module including an accelerometer and acceleration signal processing apparatus designed to sense the acceleration of the object for the control of a system on the basis of the sensed and processed acceleration signal. Such modules are, for example, mounted on vehicle members in vehicle seat occupant sensing and/or characterization systems for controlling the deployment of passive vehicle restraint devices such as airbags in a vehicle crash. A module used in this manner may include apparatus for sensing vertical acceleration of a seat occupant in an occupant weight sensing system to assist in determining to what extent an indicated occupant weight is actually due to the downward force exerted by a tightly cinched seat belt. Such modules may also, or alternatively, be mounted on vehicle body members for sensing their horizontal accelerations and/or to provide a crash sensing signal.  
         [0003]     If a nodule including an accelerometer in such a system is not securely fixed to the object on which it is mounted, the accelerometer may not share the true acceleration of the object, particularly in high accelerations; and the output acceleration signal may thus not accurately represent the acceleration of the object. A system for detecting a secure mounting of the module provides a higher degree of confidence in the reliability of such an accelerometer signal.  
         [0004]     In a prior art publication, Research Disclosures No. 453067, published January 2002, an apparatus is described as shown in  FIG. 1-3  herein. A case  10  of a module has a main portion  14  and one or more mounting portions  12 . A fastener  20  is shown as a bolt having a head  22  and a cylindrical, threaded shank  24 . Shank  24  is inserted through a mounting opening  11  in mounting portion  12  and threadably engages an aligned opening  17  in object  18 , which may be a member of a vehicle. Head  22  provides an interface for a torque generating tool to threadably advance shank  24  into object  18 . Case  10  is made of an electrically non-conducting material such as a thermoplastic resin, and object  18  is made of an electrically conducting material such as steel or aluminum. An electrically conducting insert  26  is molded into case  10  but projects out of and lays on an upper surface  19  of mounting portion  12  around the mounting opening  11 . Electrically conducting insert  26  is prevented from lateral contact with shank  24  of fastener  20 , if necessary by an insulating sleeve, not shown.  
         [0005]     Electrically conducting insert  26  further contacts an additional fastener  28 , which secures one end of a circuit board  16  to case  10  within its main portion  14 . An electronic circuit includes a circuit trace  36 , shown only schematically in  FIG. 3  but preferably provided on the underside of circuit board  16 , with a portion of the circuit trace surrounding an opening in circuit board  16  through which fastener  28  projects. Fastener  28 , in its securely fastening position, contacts both the circuit trace  36 , through its head on the underside of circuit board  16 , and electrically conductive insert  26 , for example through a stepped diameter portion of its shank as shown, to provide electrical contact between insert  26  and circuit trace  36 . For this reason, fastener  28  is shown schematically as a switch  28  connecting conductors  26  and  36  in the circuit diagram of  FIG. 3 .  
         [0006]     An electrically conducting washer  30  is provided with fastener  20 . This washer surrounds shank  24  directly underneath head  22  and has a frustro-conical shape. As seen in  FIG. 1 , wherein the apparatus is shown before case  10  is securely fastened to object  18 , washer  30  is undistorted: with an outer circumferential edge contacting surface  19  of mounting portion  12  radially outside electrically conducting insert  26  so that it is not in electrical contact therewith. In torqued advancement of fastener  20  downward through mounting portion  12  into object  18 , head  22  of fastener  20  provides a downward force on the inner edge of washer  30  to progressively distort washer  30  in a flattening manner until the washer physically and electrically contacts the exposed portion of electrically conducting insert  26 , as shown in  FIG. 2 . This contact establishes a series electrical circuit from object  18 , through fastener  20  and washer  30  to electrically conducting insert  26 , and continuing through fastener  28  to circuit trace  36  on circuit board  16 .  FIG. 3  shows this arrangement schematically, with a circuit trace representing object  18  being connected to circuit trace  36  in series through (1) a switch representing fastener  20  and washer  30 , (2) a circuit trace representing electrically conducting insert  26 , and (3) a switch representing fastener  28 . Object  18  is typically grounded to the vehicle chassis; and circuit board  16  further includes other electrical components providing a ground detection circuit, in which a resistor R 2 , circuit trace  36  and the two switches ( 20 , 30  and  28 ) described above are connected in series between a voltage reference VREF and ground (object  18 ), while a resistor R 1  is connected between circuit trace  36  and an input of a microcomputer  40  programmed with an algorithm to detect by the presented input voltage whether both of the switches are closed.  
         [0007]     The operation of the arrangement is based on the fact that a secure mounting of case  10  of the module on object  18  requires a specified clamping force exerted by one or more of the fasteners  20  on its respective mounting portion  12 ; and achievement of each specified clamping force may be inferred from the distortion of the respective washer to contact the respective electrically conductive insert  26  and thus effectively “close” switch  20 , 30  (providing switch  28  is also “closed”).  
         [0008]     But this prior art arrangement has a disadvantage, in that a normal, flat washer may be substituted for the frustro-conical washer, particularly in a repair or replacement activity. Electrical contact in such case may be achieved between fastener  20  and washer  30  with a minimal clamping force that does not guarantee a secure mounting of the module, and the design specifications on which the validity of the accelerometer signal would no longer apply. It would be desirable to modify this prior art arrangement to prevent such an occurrence.  
       SUMMARY OF THE INVENTION  
       [0009]     The invention is a module assembly having a case with at least one electrically non-conducting mounting portion having an internal wall defining a mounting opening therethrough. The mounting portion also contains an electrically conducting insert extending partly into the mounting opening internally of the mounting portion and adapted for connection to an electric potential detecting circuit.  
         [0010]     The assembly also includes an electrically conducting fastener comprising a head and a shank. At least one portion of the internal wall of the mounting portion is adapted for guiding the shank through the mounting opening into mounting engagement with an object with no contact between the shank and the electrically conducting insert.  
         [0011]     The assembly further includes an electrically conducting washer surrounding the shank adjacent its head. The washer has at least one first portion extending obliquely outward and away from the head of the fastener to be deformed between the head of the washer and a surface of the mounting portion and thereby exert a mounting force on the case as the fastener is advanced through the mounting opening into engagement with the object. The first portion of the washer may, be generally frustro-conical in shape and may comprise a plurality of obliquely, radially extending spokes joined at their outer ends in an annular member.  
         [0012]     The washer also has at least one second portion projecting from the first portion adjacent the head of the fastener axially away from the head and adjacent the shank into the mounting opening. The second portion of the washer may, for example, be in the form of a cylindrical member around the shank of the fastener; but, whatever its specific shape, it is adapted to engage the electrically conducting insert within the mounting opening in the same advancement of the shank when the mounting force exerted on the case by the deformed washer reaches a predetermined value. The second portion of the washer may be retained on a non-threaded portion of the shank of the fastener between the head of the fastener and a threaded portion thereof. The engagement of the second portion of the washer with the electrically conducting insert completes a series circuit from the electrically conducting insert through the washer and the fastener to the object at the reference potential to signals the achievement of the predetermined mounting force when the object is maintained at a predetermined reference potential and the electrically conducting insert is connected to a potential detecting circuit. Since the electrically conducting insert can be contacted by the washer only within the internal opening of the non-conducting mounting portion of the case, a substitute flat washer outside the mounting portion of the case will not be able to contact the electrically conducting insert for generation of the validating signal.  
         [0013]     The invention provides an advantage in any application in which confirmation of the secure mounting of a module on an object is desired. Such applications abound throughout industry and technology and are not limited to movable objects such as vehicles or modules with sensors. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0015]      FIG. 1  is a sectional view of a module assembly of the prior art before secure mounting on an object.  
         [0016]      FIG. 2  is a sectional view of a module assembly of the prior art after secure mounting on an object.  
         [0017]      FIG. 3  is a schematic view of a secure mounting detection apparatus for use with the prior art arrangement of  FIGS. 1 and 2  and the arrangement of  FIG. 4-6 .  
         [0018]      FIG. 4  is a sectional view of a preferred embodiment of a module assembly according to this invention before secure mounting on an object.  
         [0019]      FIG. 5  is a sectional view of the embodiment of  FIG. 4  after secure mounting on an object.  
         [0020]      FIG. 6  is an enlarged view of a portion of  FIG. 5 .  
         [0021]      FIG. 7-9  show perspective views of three suggested embodiments of washers for use in the module assembly of this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     Referring to  FIG. 4 , a case  50  of the module assembly has a main portion  54  and one or more mounting portions  52 , which may be in the form of brackets extending from main portion  54 . In one example, there may be three such mounting portions  52 , with two of the mounting portions extending from one side near two corners of the case and one extending from the opposite side. A fastener  60  is shown as a bolt having a head  62  and a shank  64 ,  65  projecting from head  62  and preferably cylindrical in shape. In this embodiment, portion  64  of the shank is threaded, and portion  65  thereof, which separates portion  64  from head  62 , may be unthreaded and of slightly smaller diameter than the threads of portion  64 , for reasons to be explained below. Shank  64 ,  65  is inserted through a mounting opening  100  in mounting portion  52  and is adapted, by threaded portion  64 , for engagement with an internal wall  81  defining an aligned opening into an object  58  that is physically located on a side of the mounting portion opposite head  62  of fastener  60 . Case  50  is thus adapted to be attached to object  58  by means of fastener  60  and, preferably, by similar fasteners associated with the other mounting portions  52 . Head  62  preferably provides an interface, such as a standard hex head, for a torque generating tool to threadably advance shank  64 ,  65  through mounting portion  52  into object  58 . With each mounting portion  52  firmly affixed to object  58  by its respective fastener, case  50  and its contents, including any accelerometers within, will share in accelerations and other movements of object  58 , which may for example be part of, or attached to, a vehicle.  
         [0023]     Case  50  is made of an electrically non-conducting material such as a thermoplastic resin; and object  58  is made of an electrically conducting material such as steel or aluminum. Object  58  is connected to a reference electrical potential: for example, vehicle chassis ground in the case of a vehicle member. An electrically conducting insert  66 , preferably made of an electrically conducting metal such as steel, aluminum or copper, is molded into case  50  and extends into mounting opening  100  below an upper surface  59  of the mounting portion  52  surrounding opening  100  (directional references such “up” and “down” in this description refer to relative directions in the drawings of this document and are not meant to limit the mounting orientation of the module). Electrically conducting insert  66  is prevented from direct contact with shank  64 ,  65  of fastener  60 , for example with a non-conducting sleeve or in a manner to be described below. Electrically conducting insert  66  further contacts an additional fastener  68  that secures one end of a circuit board  56  to main portion  54  of case  50  internally and is simultaneously connected thereby to one or more circuit traces on the circuit board, for example in the same manner as described for the prior art embodiment of  FIG. 1-3 .  
         [0024]     An electrically conducting washer  70  is provided along with fastener  60 . Washer  70  has an inner portion  72  that is preferably cylindrically tubular and one or more outer portions  74  that extend obliquely outward from an end  75  of inner portion  72  that is closest to head  62  of fastener  60 , the oblique direction being intermediate a radially horizontal direction and an axial direction toward the opposite end  76  of inner portion  72  (away from head  62  of fastener  60 ). This washer surrounds the upper region  65  of shank  64 ,  65 , with inner portion  72  conforming to and preferably being carried on axial region  65  of shank  64 ,  65 , beneath and adjacent head  62 . In the embodiment shown, axial region  65  of the shank, adjacent head  62 , is smaller in outer diameter than axial region  64  of the shank. This is preferred so as to allow permanent retention of washer  70  on axial region  65  of the shank before and during attachment of case  50  to object  58  and may be produced by rolling the threads on the shank after the washer is slipped onto the shank.  
         [0025]     In the embodiment described, fastener  60  is prevented from contacting electrically conducting insert  66  directly in the following manner. Mounting opening  100  is defined by an inner wall that is stepped in two distinct axial portions  102  and  104  having different diameters. The larger diameter axial portion  102  (the upper axial portion in  FIG. 6 ) is located closer to surface  59  and is provided with a first diameter that permits insertion of fastener  60  and inner portion  72  of washer  70  without hindrance. The smaller diameter axial portion  104  (the lower axial portion in  FIG. 6 ) is located on the opposite axial side of larger diameter axial portion  102  from surface  59 ; and its diameter is preferably designed to receive and retain portion  64  of fastener  60  in a predetermined axial alignment and orientation. The electrically conducting insert is preferably located axially so as to extend into opening  100  from the larger diameter axial portion  102  adjacent and above the boundary between axial portions  102  and  104 , so that it may be contacted axially by (lower) end  76  of inner portion  72  of washer  70 . But no part of electrically conducting insert  66  enters a circularly cylindrical space in axial portion  102  of mounting opening  1100  defined by an upward extension of the smaller diameter of axial portion  104  of mounting opening  100  or otherwise approaches that circularly cylindrical space sufficiently closely as to allow contact with fastener  60  when the latter is retained in smaller diameter axial portion  104 . This may be preferably be facilitated by ensuring that electrically conducting insert  66  is spaced outwardly by a specified margin from a cylinder defined by the smaller diameter axial portion  104 . Alternative and/or equivalent arrangements for preventing such electrical contact will be apparent to those skilled in the art.  
         [0026]      FIG. 4  shows the apparatus with shank  64 ,  65  of fastener  60  inserted though mounting opening  100  and partially advanced into opening  81  in object  58 ; but no outer portion  74  of washer  70  yet contacts upper surface  59  of mounting portion  52 . In this position, outer portion(s)  74  of washer  70  are not distorted from their pre-installed shape relative to inner portion  72 ; and end  76  of the latter is not in contact with electrically conducting insert  66 . As fastener  60  is advanced further through mounting opening  100  into object  58 , the outer portion(s)  74  of washer  70  will eventually contact upper surface  59  of mounting portion  52 , as shown in  FIG. 5 , and begin to distort. In the embodiment shown, the distortion will include at least a flattening reduction in the oblique angle of outer portion(s)  74  from the horizontal. With this distortion, the outer portion(s)  74  of washer  70  will begin to exert a retaining force on mounting portion  52  with respect to object  58 ; and this force will generally increase with the growing distortion as fastener  60  is further advanced into object  58 .  
         [0027]     Finally, as shown in  FIG. 5 , fastener  60  has been advanced axially into object  58  to the point where end  76  of inner portion  72  makes contact with electrically conducting insert  66  within mounting opening  100 . Fastener  60  is designed so that, when this point is reached, the retaining force provided to mounting portion  52  relative to object  58  has grown to at least a predetermined minimum desired mounting force required to hold mounting portion  52  in firm contact against object  58  according to predetermined specifications. The physical contact between fastener  60  and electrically conducting insert  66  establishes an electrical grounding circuit from vehicle ground through object  58 , fastener  60 , washer  70 , electrically conducting insert  66 , fastener  68  and circuit trace  36  to a detecting circuit on circuit board  56 , which may be the prior art circuit shown in  FIG. 3  applied to the apparatus of  FIG. 4-6  in the same manner as it is shown applied to the prior art apparatus of  FIGS. 1 and 2 . The detecting circuit signals, based on detection of the contact, that the desired mounting force has been achieved; and the advance of the fastener may be terminated.  
         [0028]     If, on the other hand, a standard, flat washer is used with a standard bolt with the circuit of  FIG. 3  applied to the apparatus of the invention, the required contact between the washer and the electrically conducting insert cannot be achieved, since the conducting insert is internal to the mounting portion of the case and the washer requires a portion such as inner portion  72  projecting into the mounting opening in order to make the contact. Thus, the problem of the prior art arrangement is eliminated.  
         [0029]     But the advantage of this invention is not limited to the initial mounting of the module in the factory environment. In use, the circuit of  FIG. 3  continues to monitor the contact between washer  70  and electrically conducting insert  66 . If the retaining force on the module loosens sufficiently that this contact is broken, even intermittently, this fact will be detected; and a warning can be provided that the module is no longer reliably retained. Of course, if the module is re-mounted or removed and replaced in service, the detection of sufficient force for reliable mounting will be provided automatically in the service just as it was in the initial mounting in the factory environment.  
         [0030]      FIG. 7-9  show several possible embodiments of washer  70 , with similar reference numerals indicating similar portions of the washer. Each has an inner portion  72  comprising a circular cylinder with a lower end  76  and an upper end  75  that may be extended outwardly in a circular flange  77 . Outer portions  74  of the washer are shown as spokes  78  and are joined in an annular portion  79  at their radially outward ends. The differences between the embodiments lie in the orientation and shape of the spokes of outer portions  74 . Spokes  78  of outer portions  74  in  FIG. 7 , looking downward on the washer, are straight and project essentially tangentially from flange  77 . Spokes  78  of outer portions  74  in  FIG. 8 , looking downward on the washer, are straight and project radially from flange  77 . Spokes  78  of outer portions  74  in  FIG. 9 , looking downward on the washer, project from flange  77  initially radially but are bent in an acute angle from the radial before joining circular portion  79 . Of course, in each case, spokes  78  of outer portions  74  are angled downwardly as previously described, to descend from flange  77  at the upper end  75  of washer  70  to circular portion  79  in a plane spaced downwardly from flange  77 . Of course, essentially equivalent variations of the embodiments shown will occur to those of ordinary skill in the art and are meant to be included in the washers of the invention.