Abstract:
A water-resistant switching device has an elastomeric body overmoulded to one part of the casing. The elastomeric body has a rib which co-operates with a hooked flange portion to define a space for receiving a hooked flange of another part of the casing to provide a watertight seal.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a water-resistant switching device and more particularly but not exclusively to an entry transmitter for a vehicle including such a switching device. 
     It is increasingly a requirement to provide electrical switching capable of being operated under damp conditions, for example in the open air when it is raining. In the case of entry transmitters for vehicles, which commonly use radio frequency or infra-red transmitters to operate entry systems for the corresponding vehicle, manufacturers are seeking increasing levels of waterproofing with current requirements ranging from 0.3 to 6 metres. 
     Prior art techniques to provide waterproofing in water-resistant switching devices include the use of an “O” ring seal, with pressure on the seal being maintained by, for example screws an overall elastomer keypad with the edge of the keypad crushed between two plastic elements and maintained there by clips, or by overmoulding the seal with elastomer. 
     These techniques have a number of defects, including the relatively high cost and difficulty of assembling when using screws and metal inserts, and the likelihood of plastic clips failing over long durations and high temperatures. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least partially mitigate the difficulties of the prior art. 
     According to a first aspect of the present invention there is provided a water-resistant switching device having a casing, the casing having first and second parts, said first part having a base wall and a peripheral edge wall, said device further comprising an elastomeric body extending along said base wall and forming an upstanding rib portion, wherein said rib portion is spaced from and co-operates with a portion disposed on the inside of side peripheral edge wall to receive a counterpart flange portion of the second part of said casing. 
     Preferably said counterpart flange portion has a thickness greater than said spacing, whereby when said counterpart flange portion of said second casing part is engaged with said portion, said rib portion resiliently grips said counterpart flange portion. 
     Conveniently said portion is part of said elastomeric body and forms an inwardly-directed flange portion from said peripheral edge wall, and said counterpart flange portion has an outwardly-directed lip for co-operation with said inwardly-directed flange portion. 
     Conveniently said portion is part of the peripheral edge wall and forms an inwardly-directed flange portion from said peripheral edge wall, and said counterpart flange portion has an outwardly-directed lip for co-operation with said inwardly-directed flange portion. 
     Conveniently said elastomeric body is secured to said first part of said casing. 
     Advantageously said elastomeric body is secured by overmoulding. 
     Conveniently said casing contains a circuit device, and said first part of said casing is an operating member for said circuit device. 
     Advantageously said casing contains a battery, and said first part of said casing is removable for changing said battery. 
     According to a second aspect of the present invention there is provided an entry transmitter for a vehicle comprising a water-resistant switching device according to the first aspect of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the present invention will now be described with reference to the accompanying drawings, in which: 
     FIG. 1 shows a first vehicle entry transmitter of the prior art; 
     FIG. 2 shows a second vehicle entry transmitter of the prior art; 
     FIG. 3 shows a third vehicle entry transmitter of the prior art; 
     FIG. 4 shows a partial cross-section through a vehicle entry transmitter in accordance with a first embodiment of the present invention; 
     FIG. 5 shows a partial cross-section through the cap of the transmitter in FIG. 4, and 
     FIG. 6 shows a partial cross-section of another embodiment of the invention. 
     In the various figures like reference numerals indicate like parts. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIG. 1 which shows a cross section through a portion of a first vehicle entry transmitter, a body portion  10  extends to define a cavity within which there is disposed a circuit element  11 . 
     A part  12  of rigid plastics is disposed to cover an opening  13  in the body  10  for access to replace battery  14 . An O ring  15  is disposed between two concentric upstanding portions  16 ,  17  around the periphery of the opening  13  to afford waterproofing of the device. Screws  18  maintain an inward bias against the O ring so that waterproofing is maintained, and these are secured into threaded metal inserts  19 . 
     Although this arrangement can provide a good waterproofing performance, it is expensive to implement, because of the cost of the screws and metal inserts to secure the screws and secondly because of the labour costs involved in assembly. 
     Referring now to FIG. 2 an elastomeric operating member  22 , has a button  28  projecting through a hole in the cap  23 . A lower portion  24  of the entry device body defines, in co-operation with the operating member  22 , a cavity within which the circuit member  11  is disposed. The lower portion  24  has an upstanding peripheral lip  25 . The cap  23  is retained in position against the lip  25  by the clipping action of a shaped flange portion  29  against the lip  25 . The elastomeric operating member  22  extends into a gap formed between a lower wall portion  26  of the cap and an upper wall portion  27  of the lower portion  24 . To aid retention of the elastomeric portion, either of the walls  26  or  27  can be provided with a barb portion  28 . 
     Referring now to FIG. 3, a third vehicle entry transmitter has a body formed of two parts  31 ,  32  of which the lower  32  has an upstanding peripheral flange  33  with an inwardly-projecting lip portion  34  for clippingly engaging with a corresponding portion  35  of the upper part  31  to form a case. An elastomeric operating member  36  in the form of an elastomeric button protrudes through a hole of the upper part  31  and has a downward protrusion  37  for operating the circuit device  11 . The button  36  extends along the inner wall of the upper part  31  and is overmoulded to that wall to form a seal therewith. The lower part  32  of the case has a further upstanding rib  38  which, when the two parts are clipped together, is urged against an end face  39  of the elastomer to retain it in place. 
     Referring now to FIG. 4, the casing of a vehicle entry transmitter according to an embodiment of the invention comprises a lower part  41  and an upper part  42 . Both of these parts are made of hard plastics. The lower part  41 , has an upstanding flange portion  43  spaced from the peripheral edge of the part with an outwardly-directed lip portion  44  at the distal end thereof. 
     The upper part  42 , or first casing part, is a generally cup-shaped body having a generally planar base portion  45  and a peripheral side wall  46 . An elastomeric body  47  extends along the inner wall of the upper part  42  and has an upstanding rib portion  48  extending from the base wall  45 . A portion  50  disposed on the inside of the peripheral edge wall  46  is spaced from and co-operates with the rib portion  48  to receive the upstanding flange portion  43  of the lower part  41 , or second part of the casing. In this embodiment, the portion  50  is part of the elastomeric body  47  and is made of the same material. This elastomeric body  47  can also be used to form buttons through a hole in the upper part  42  (not shown in the figures). 
     The portion  50  of the elastomeric body extends in an end region thereof to an inwardly-directed flange  51  so that the outwardly-directed lip portion  44  can be clipped into engagement with the upper part  42  and retained there by engagement between the lip portion  44  and the flange portion  51 . 
     By comparison of FIG.  4  and FIG. 5, it will be seen that the spacing between the rib portion  48  and the portion  50  is less than the width of the flange portion  43  with its lip portion  44 , so that when the flange portion  43  of the lower part  41  is engaged with the portion  50  of the elastomeric body, the rib portion  48  resiliently grips the flange portion  43 . 
     Referring now to FIG. 6, it is shown another embodiment of the invention where the portion  50  is part of the peripheral edge wall  46  of the upper part  42  and is in the same material hard plastic. The elastomeric body  47  extends along the base wall  45  and presents an upstanding rib portion  48 . The other characteristics of this embodiment are the same as those describe in the context of FIG. 4 : the portion  50  forms an inwardly-directed flange portion  51  from said peripheral edge wall  46 , and said counterpart flange portion  43  has an outwardly-directed lip  44  for co-operation with said inwardly-directed flange portion  51 . 
     The elastomeric body  47  is overmoulded onto the hard plastics upper part  42  for a secure holding. 
     The hard plastics material of the upper part  42  is nonetheless sufficiently flexible that pressure in the unsupported region of the base  45  causes it to distort inwardly to engage the circuit for operation thereof. 
     It is possible to unclip the upper part  42  to provide access to the battery  14 , for example to change the battery. 
     In an alternative embodiment the upper part  42  does not form an operating member, but is merely a casing part, removable for battery access. 
     The device of the invention is advantageous in that a simple clip-together assembly is afforded. 
     Although the invention has been described in the context of a vehicle entry transmitter, it is clear that other low voltage switching devices could use the same concept. Such devices include, for example, pagers and mobile phones and also external switching devices such as interphones and security locks.