TECHNICAL FIELD OF INVENTION 
       [0001]    The invention relates to an evaporative emission device for preventing discharge of fuel vapors from the fuel system of a motor vehicle, more particularly to a coupling for attaching an evaporative emission device to a motor vehicle, and more particularly to a latch for preventing separation of the evaporative emission device from the motor vehicle, and even more particularly to such a latch which can accommodate manufacturing variations of the coupling. 
       BACKGROUND OF INVENTION 
       [0002]    Motor vehicles are typically equipped with evaporative emission devices in order to prevent the fuel system of the motor vehicle from discharging fuel vapors to the atmosphere which can result in air pollution. Evaporative emission devices are mounted to the motor vehicle and typically include a housing containing activated carbon. A conduit is included for providing fluid communication between the evaporative emission and a volume of the fuel tank that does not contain fuel. Fuel vapors are absorbed by the activated carbon while air is allowed to be purged from the evaporative emission device. When the internal combustion engine of the motor vehicle is running, the fuel vapors absorbed by the activated carbon may be purged from the evaporative emission device and consumed by the internal combustion engine. 
         [0003]    One known coupling for attaching the evaporative emission device to the motor vehicle is commonly referred to as a dovetail coupling. In a dovetail coupling, a housing of the evaporative emission device includes a pair of converging rails forming a male portion of the coupling. The motor vehicle includes a mounting surface with a pair of matching converging tracks forming a female portion of the coupling. The converging tracks are sized to slidably receive the converging rails therewithin. When the evaporative emission device is assembled to the motor vehicle, the converging rails are slid into the converging tracks to a predetermined seated position. In order prevent the evaporative emission canister from decoupling from the motor vehicle during operation of the motor vehicle, the coupling also includes an aperture formed in the mounting surface of the motor vehicle in order to receive a latch formed on the housing of the evaporative emission device. However, prior art dovetail couplings do not substantially prevent relative movement between the evaporative emission device and the motor vehicle throughout the tolerance range to which the coupling may be manufactured. This relative movement may result in objectionable noise and possible damage to the coupling. Additionally, prior art dovetail couplings may not permit the latch to be received within the aperture throughout the tolerance range to which the coupling may be manufactured. This condition prevents the evaporative emission device from being properly secured to the motor vehicle. 
         [0004]    What is needed is a coupling with a latch received in an aperture that will substantially prevent relative movement between an evaporative emission device and a motor vehicle throughout the tolerance range to which the coupling may be manufactured. What is also needed is a coupling with a latch that will be received within an aperture throughout the tolerance range to which the coupling may be manufactured. 
       SUMMARY OF THE INVENTION 
       [0005]    Briefly described, a coupling is provided for attaching an evaporative emission device having a housing to a mounting surface of a motor vehicle. The coupling includes a pair of tracks fixed to one of the housing and the mounting surface. The coupling also includes a pair of matching rails fixed to the other of the housing and the mounting surface. The rails are sized to slide within the tracks until reaching a predetermined seated position within the rails. An aperture is fixed to one of the housing and the mounting surface. The aperture includes a shoulder with a manufacturing tolerance defined about a nominal location at the predetermined seated position. A resilient latch is fixed to the other of the housing and the mounting surface and located so as to snap into the aperture at the predetermined seated position. The latch includes an inclined engaging surface to engage the shoulder over the entire tolerance range of the shoulder. 
         [0006]    Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    This invention will be further described with reference to the accompanying drawings in which: 
           [0008]      FIG. 1A  is an isometric view of a prior art evaporative emission device and coupling for attaching the evaporative emission device to a motor vehicle; 
           [0009]      FIG. 1B  is an enlarged isometric view of a latch of the coupling of  FIG. 1A ; 
           [0010]      FIG. 2A  is an isometric view of an evaporative emission device and coupling in accordance with the present invention for attaching the evaporative emission device to a motor vehicle; 
           [0011]      FIG. 2B  is an enlarged isometric view of a latch of the coupling of  FIG. 2A ; 
           [0012]      FIG. 3A  is a an isometric view of a second embodiment of an evaporative emission device and coupling in accordance with the present invention for attaching the evaporative emission device to a motor vehicle; 
           [0013]      FIG. 3B  is an enlarged isometric view of a latch of the coupling of  FIG. 3A ; 
           [0014]      FIG. 4A  is an enlarged elevation view of the latch of the prior art coupling of  FIGS. 1A and 1B  after the evaporative emission device has been attached to the motor vehicle; 
           [0015]      FIG. 4B  is an enlarged elevation view of a latch of the coupling of  FIGS. 2A and 2B  after the evaporative emission device has been attached to the motor vehicle; and 
           [0016]      FIG. 4C  is an enlarged elevation view of a latch of the coupling of  FIGS. 3A and 3B  after the evaporative emission device has been attached to the motor vehicle. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0017]    Referring to  FIGS. 1A ,  1 B, and  4 A, a prior art coupling  10  for attaching evaporative emission device  12  to motor vehicle  14  is shown. Coupling  10  includes receiving member  16  fixed to mounting surface  18  of motor vehicle  14 . Mounting surface  18  may be, for example, a fuel tank or a chassis member. Receiving member  16  includes a pair of converging tracks  20  defining a female dovetail portion of coupling  10  which may be made of a thermoplastic, for example, polypropylene. Alternatively, receiving member  16  may be made of metal, for example, steel. 
         [0018]    Coupling  10  also includes insertion member  22  fixed to housing  24  of evaporative emission device  12 . Insertion member  22  may be integrally molded as one piece with housing  24  which may be made of a thermoplastic such as nylon. Alternatively, insertion member  22  may be made separate from housing  24  and subsequently joined to housing  24  by known methods such as welding, adhesives, or mechanical fasteners such as rivets or screws. Insertion member  22  includes a pair of matching converging rails  26  defining a male dovetail portion of coupling  10 . Rails  26  are sized to slide within tracks  20  when insertion member  22  is inserted into receiving member  16  along insertion axis  28  in a first direction indicated by arrow  30 . 
         [0019]    Receiving member  16  includes stop surface  32  which connects tracks  20  to each other and defines a predetermined seated position for insertion member  22 . Insertion member  22  is insertable into receiving member  16  until insertion member  22  abuts stop surface  32 , thereby stopping at the predetermined seated position. 
         [0020]    Coupling  10  is provided with retention member  34  for retaining insertion member  22  within receiving member  16 . Retention member  34  includes aperture  36  formed in receiving member  16 . Retention member  34  also includes latch  38  which is fixed to insertion member  22  and which is insertable into aperture  36  when insertion member  22  is inserted to the predetermined seated position within receiving member  16 . Latch  38  flexes out of the way resiliently in order to allow insertion member  22  to be inserted within receiving member  16 . Latch  38  then snaps into aperture  36  when insertion member  22  reaches the predetermined seated position and latch  38  is aligned with aperture  36 . Shoulder  40  of aperture  36  acts against engaging surface  42  of latch  38  in order to prevent removal of insertion member  22  from receiving member  16  along insertion axis  28  in a second direction indicated by arrow  44  which is opposite to the first direction indicated by arrow  30 . Shoulder  40  is substantially coplanar with engaging surface  42 , however, some incidental mismatch may occur. 
         [0021]    Now referring to  FIG. 4A , an enlarged elevation view of latch  38  positioned within aperture  36  is shown such that shoulder  40  is positioned at a nominal position with respect to engaging surface  42  when insertion member  22  is seated against stop surface  32  at the predetermined seated position. The nominal position of shoulder  40  with respect to engaging surface  42  is most desirable because latch  38  is allowed to snap freely into aperture  36  while substantially preventing movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28 . This nominal position is represented by nominal line  46 . However, variations in manufacturing receiving member  16  and insertion member  22  allow the position of shoulder  40  to vary with respect to engaging surface  42 . The minimum location of shoulder  40  with respect to engaging surface  42  is represented by minimum line  48  while the maximum location of shoulder  40  with respect to engaging surface  42  is represented by maximum line  50 . As can be seen, a condition in which shoulder  40  is located at minimum line  48  fails to allow latch  38  to snap into aperture  36 . As can also be seen, a condition in which shoulder  40  is located at maximum line  50  provides a gap between shoulder  40  and engaging surface  42 , thereby allowing evaporative emission device  12  to move an undesirable magnitude relative to motor vehicle  14  along insertion axis  28 . 
         [0022]    In accordance with a preferred embodiment of this invention and referring to  FIGS. 2A ,  2 B, and  4 B, coupling  110  is shown. Elements of coupling  110  that are substantially the same as elements of coupling  10  will use the same reference numbers while elements of coupling  110  that are not substantially the same as elements of coupling  10  will use one-hundred series numbers. 
         [0023]    Still referring to  FIGS. 2A ,  2 B, and  4 B, coupling  110  is similar to coupling  10  with the exception of retention member  134 . Retention member  134  is similar to retention member  34  in that aperture  36  is formed in receiving member  16 . However, retention member  134  differs from retention member  34  in that latch  138  includes inclined engaging surface  160  for accommodating variations in manufacturing receiving member  16  and insertion member  22  which allow the position of shoulder  40  to vary with respect to latch  138 . Inclined engaging surface  160  includes a plurality of steps that define a plurality of engaging surfaces  142   a,    142   b,    142   c.  Each engaging surface  142   a ,  142   b,    142   c  is spaced a unique distance away from stop surface  32  when insertion member  22  is inserted within receiving member  16  to the predetermined seated position. 
         [0024]    Now referring to  FIG. 4B , an enlarged elevation view of latch  138  is shown positioned within aperture  36  such that shoulder  40  is positioned at a nominal position with respect to latch  138  when insertion member  22  is seated against stop surface  32  at the predetermined seated position. As can be seen, latch  138  is allowed to snap freely into aperture  36  while substantially preventing movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28  due to the close fit between shoulder  40  and engaging surface  42   b.  However, even when manufacturing variations allow the position of shoulder  40  to vary with respect to engaging surface  142   b  from the minimum location represented by minimum line  48  to the maximum location represented by line  50 , latch  138  is allowed to snap freely into aperture  36  while substantially preventing movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28 . This results from engagement surface  142   a  being positioned at minimum line  48  and from engagement surface  142   c  being positioned at maximum line  50 . While the axial distance between each engagement surface  142   a,    142   b,    142   c  may still allow for some movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28 , the magnitude of movement allowed by latch  138  of coupling  110  is greatly reduced compared to the magnitude of movement allowed by latch  38  of coupling  10 . Furthermore, the number of engagement surfaces and the distance between each engagement surface can be designed to allow for an acceptable magnitude of movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28 , thereby substantially preventing movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28 . Shoulder  40  is substantially coplanar with each engaging surface  142   a,    142   b,    142   c,  however, some incidental mismatch may occur. The coplanar mismatch may be especially evident when engaging surface  142   a  or engaging surface  142   b  is abutted with shoulder  40 . This is due to latch  238  remaining partially flexed when either engaging surface  142   a  or engaging surface  142   b  is abutted with shoulder  40 . 
         [0025]    In accordance with a second embodiment of this invention and referring to  FIGS. 3A ,  3 B, and  4 C, coupling  210  is shown. Elements of coupling  210  that are substantially the same as elements of couplings  10 ,  110  will use the same reference numbers while elements of coupling  210  that are not substantially the same as elements of couplings  10 ,  110  will use two-hundred series numbers. 
         [0026]    Still referring to  FIGS. 3A ,  3 B, and  4 C, coupling  210  is similar to coupling  110  with the exception of retention member  234 . Retention member  234  is similar to retention member  134  in that aperture  36  is formed in receiving member  16 . However, retention member  234  differs from retention member  134  in that latch  238  includes inclined engaging surface  260  for accommodating variations in manufacturing receiving member  16  and insertion member  22  which allow the position of shoulder  40  with respect to latch  138  to vary. Rather than including a plurality of steps defining a plurality of engaging surfaces  142   a,    142   b,    142   c  as in inclined engaging surface  160 , inclined engaging surface  260  includes tapered engaging surface  242  which is substantially planar and which is inclined to shoulder  40 . 
         [0027]    Now referring to  FIG. 4C , an enlarged elevation view of latch  238  is shown positioned within aperture  36  such that shoulder  40  is positioned at a nominal position with respect to latch  238  when insertion member  22  is seated against stop surface  32  at the predetermined seated position. As can be seen, latch  238  is allowed to snap freely into aperture  36  while substantially preventing movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28 . However, even when manufacturing variations allow the position of shoulder  40  to vary with respect to tapered engaging surface  242  from the minimum location represented by minimum line  48  to the maximum location represented by line  50 , latch  238  is allowed to snap freely into aperture  36  while substantially preventing movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28 . This results from the upper-most and lower-most portions of tapered engaging surface  242  being located between the minimum location of shoulder  40  with respect to engaging surface  42  and the maximum location of shoulder  40  with respect to engaging surface  42 . The same force that causes latch  238  to snap into aperture  36  after flexing out of the way in order to allow insertion member  22  to be inserted within receiving member  16  also urges tapered engaging surface  242  tightly against corner  52  of aperture  36 . With tapered engaging surface  242  pressed tightly against corner  52 , movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28  is substantially prevented. Furthermore, tapered engaging surface  242  substantially prevents movement between evaporative emission device  12  and motor vehicle  14  along insertion axis  28  when shoulder  40  of aperture  36  is manufactured to fall at any location between the minimum location represented by minimum line  48  and the maximum location represented by maximum line  50 . 
         [0028]    Corner  52  may interface particularly well with tapered engaging surface  242  when aperture  36  is formed in metal. This is because the sharp nature of corner  52  may “bite” into the softer tapered engaging surface  242 , thereby assisting to prevent movement. However, if aperture  36  is formed in plastic, shoulder  40  may be formed at an angle (not shown) which substantially matches the angle of inclined engaging surface  242 . This allows a surface contact between the shoulder and the inclined engaging surface rather than a line contact as shown in  FIG. 4C . Similarly, forming the shoulder at an angle which substantially matches the angle of inclined engaging surface  242  may also be used when the aperture is formed in metal. 
         [0029]    While the coupling has been described in terms of converging tracks and matching converging rails sized to slide within the converging tracks, it should be understood that other arrangements also fall within the scope of this invention. Another non-limiting example is parallel tracks and matching parallel rails sized to slide within the parallel tracks. 
         [0030]    While the receiving member has been described as being fixed to the motor vehicle, it should now be understood that the receiving member may instead be fixed to the housing of the evaporative emission device. Similarly, when the receiving member is fixed to the evaporative emission device, the insertion member may be fixed to the motor vehicle rather than the housing of the evaporative emission device. 
         [0031]    While the aperture of the retention member has been described as being formed in the receiving member, it should now be understood that the aperture may instead be formed any member fixed in relation to one of the receiving member and the insertion member. Similarly, the latch may be fixed to any member fixed in relation to the other of the receiving member and the insertion member. 
         [0032]    While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.
A coupling is provided for attaching an evaporative emission device having a housing to a mounting surface of a motor vehicle. The coupling includes a pair of tracks fixed the mounting surface and a pair of matching rails fixed to the housing. The rails are sized to slide within the tracks until reaching a predetermined seated position within the rails. An aperture is fixed to the mounting surface and includes a shoulder with a manufacturing tolerance defined about a nominal location at the predetermined seated position. A resilient latch is formed on the housing and located so as to snap into the aperture at the predetermined seated position. The latch includes a inclined engaging surface to engage the shoulder over the entire tolerance range of the shoulder.