Patent Publication Number: US-7214101-B1

Title: Electrical socket with dependent shutter

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an electrical socket for use with an electrical plug. In particular it relates to an electrical socket comprising means for preventing incorrect insertion of a single plug pin of an electrical plug into the socket. 
   A plug for use with the socket typically comprises two (Live and Neutral) or three (Live, Neutral &amp; Ground) plug pins. The plug may have different configurations depending on the standards used in each country for electricity supply outlets. For example, in continental Europe the use of Live (L) and Neutral (N) pins only is standard whilst in the United Kingdom three pins are used so as to include a Ground (G) pin otherwise known as an earth pin as well as the L and N pins. 
   The socket of the present invention may be embodied in a mains socket as found fixedly located in walls or may be embodied as part of an extension cable or as part of a travel adaptor or similar transportable device. 
   The plug pins are electrically connected to the socket by inserting the plug pins into receptacles formed in the socket. Each plug pin receptacle comprises an electrical contact which permits an electrical connection to be formed between the plug and the socket when the plug pin is inserted into the receptacle. 
   For safety, it is known in some sockets to provide a shutter that shuts off or covers the socket receptacles when there is no electrical plug being connected to the socket. This is provided to prevent potential electrocution by the insertion of foreign bodies into the receptacles and thereby making contact with, especially, the electrical contact of the Live plug pin receptacle. 
   An example is a United Kingdom three pin socket. When an electrical plug is inserted into this type of socket, a shutter in the receptacles is activated by the G pin of the electrical plug to move the shutter to expose the L and N receptacles. The G pin is longer than the L and N pins and thus comes into contact with the shutter before the L and N pins when the plug is being inserted into the socket. When the G pin is connected and the shutter is pushed to open, the L and N pins can then be connected to the corresponding receptacles. The shutter cannot be opened by inserting just the L and N pins. A disadvantage is that this type of safety mechanism cannot be used with sockets having only two pins as there is no G pin on the corresponding electric plug which can be used to trigger the shutter. 
   Sockets without such a shutter have a potential danger of single pin miss-insertion.  FIG. 1  shows just the L pin of a three pin plug  101  being inserted to one of the receptacles  102  on prior art socket  103  which does not contain a safety shutter, leaving its N pin  104  and G pin  105  hanging outside the socket  106 . The exposed N pin  104  may carry an electric current and cause safety issues if the plug  107  is connected to an electrical outlet in this condition. 
   As noted above, two-pin sockets cannot use a shutter that is triggered by a G pin. To avoid the danger of single pin insertion, German sockets (which are of the two-pin type) for Schuko plugs are made with receptacles on a surface which are recessed into the body of the socket. The recess is deep enough in relation to the length of the plug pins so that making electric connection is impossible if the plug and pins are not inserted into the socket with the pins and receptacles correctly aligned. This solution can work for mains electric sockets where the size, in particular the depth, of the socket is not of high importance. 
   Another way to avoid single pin insertion is to make the socket to have the distance between the receptacles and the edge of the socket larger than the distance between the pins of the plug. In this way the housing of the socket itself prevents only one pin being inserted into a receptacle. However, especially for travel adaptors there is a wish to minimise the size of the adaptor and this solution results in a large socket which is not suitable for travelling. Also, design of such a socket requires knowledge of the spacing of the pins on all plugs in different countries that might be used with the adaptor. 
   There is therefore a need for an electric socket which can operate safely so as to avoid single-pin insertion and be suitable for use with two and three pin designs of sockets and be suitable for use in mains sockets, extension cables and travel adaptors. 
   SUMMARY OF THE INVENTION 
   Accordingly the present invention provides a socket for an electric plug of the type comprising a first pin and a second pin, the socket comprising a housing, a first pin receptacle formed in the housing, a second pin receptacle formed in the housing, and a shutter mechanism, 
   the first pin receptacle containing a first contact for making electrical contact with a pin of an electric plug, 
   the second pin receptacle containing a second contact for making electrical contact with a pin of an electric plug, 
   the shutter mechanism comprising a first shield element and a second shield element, the first and second shield elements being joined together by a flexible member, the first and second shield elements each comprising a detent, 
   the shutter mechanism being mounted within the housing so as to be slidingly movable along an axis of sliding movement between a first position and a second position and also so as to be rotatable about an axis perpendicular to the axis of sliding movement, 
   wherein in the first position the first shield element closes off the first pin receptacle and the second shield element closes off the second pin receptacle preventing insertion of a pin of an electric plug into either the first pin receptacle or the second pin receptacle, 
   wherein in the second position the shutter mechanism reveals the first pin receptacle and the second pin receptacle allowing insertion of a first pin of an electric plug into the first pin receptacle so as to contact the first contact and a second pin of an electric plug into the second pin receptacle so as to contact the second contact, 
   the shutter mechanism comprising a biasing means for biasing the shutter mechanism into the first position, 
   wherein insertion of only a single pin into the first or second pin receptacle so as to contact the first or second shield element causes the shutter mechanism to rotate about the axis perpendicular to the axis of sliding movement bringing the detent of either the first or second shield element into engagement with the housing preventing movement of the shutter mechanism into the second position, 
   wherein insertion of a first pin into the first pin receptacle to contact the first shield element at the same time as a second pin into the second pin receptacle to contact the second shield element causes the flexible member to flex and the first and second shield elements to rotate about the axis perpendicular to the axis of sliding movement in opposite senses, thereby freeing the detents of the first shield element and the second shield element from the housing and allowing sliding movement of the shutter mechanism into the second position. 
   The first and second shield elements may each comprise a slanted surface against which, in use, pins of an electric plug may be pressed to move the shutter mechanism. 
   The first shield element may comprise an inwardly facing side face and the second shield element comprises an inwardly facing side face, wherein the inwardly facing side faces of the first and second shield elements face each other, wherein the detents of the first and second shield elements project from the inwardly facing side faces of the respective shield element. 
   The housing may comprise a centrally located projection comprising a first abutment surface for engaging the detent of the first shield element and a second abutment surface for engaging the detent of the second shield element. 
   The socket may comprise rail members for guiding sliding movement of the shutter mechanism. 
   The shutter mechanism may be symmetric about the flexible member. 
   The shutter mechanism may be formed as a single piece. 
   The socket may be a mains socket, a socket of an extension cable, or a part of an electrical adaptor. The electrical adaptor may also comprise a plug portion. 
   The socket may further comprise a third pin receptacle. 
   Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1 , shows a perspective view of a prior art socket with a single pin of an electric plug inserted therein; 
       FIG. 2  shows a perspective view of a socket according to the present invention, embodied as part of an adaptor; 
       FIG. 3  shows a perspective view of the socket of  FIG. 2  with some parts omitted to show internal portions, with a shutter mechanism of the socket in a first position; 
       FIG. 4  shows a perspective view of the socket of  FIG. 2  with some parts omitted to show internal portions, with the shutter mechanism of the socket in a second position; 
       FIG. 5  shows a perspective view of the socket of  FIG. 2  in cross-section; and 
       FIGS. 6   a  to  6   c  show schematically the operation of the shutter mechanism of the socket of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The illustrated embodiment provides an electrical adaptor  1  as shown in  FIG. 2  comprising a plug part  2  and a socket  3 . On plug part  2  are L and N pins  4  and  5 . On socket  3  are universal L and N receptacles  6  and  7 , and universal G pin receptacles  8  and  9 . Within the body of the socket  3  a shutter mechanism  10  is provided for selectively opening and closing the L and N receptacles  6  and  7  as will be described below. 
     FIG. 3  shows the shutter mechanism  10  in the closed position.  FIG. 4  shows the shutter mechanism  10  in the open position. 
   As shown in  FIG. 5  the L and N pins  4  and  5  are internally electrically connected to contact plates  11  and  12 , inside plug  2 , for connection to the plug pins inserted through universal L and N receptacles  6  and  7  on socket  3 . 
   As seen most clearly in  FIGS. 3 and 4 , the shutter mechanism comprises two shield elements  16 ,  17  joined together by means of a flexible member  15  in the form of a bridge. On bridge  15  a downwardly expending rod  19  is provided which holds in place one end of a spring  18  which extends between the bridge  15  and a bottom surface of the housing of the socket  3  so as to bias the shutter mechanism  10  into the closed position as shown in  FIG. 3 . The shield elements  16 ,  17  each comprise a slanted surface directed away from rod  19  so as to be directed generally towards an upper portion of the socket  3  in the orientation shown in  FIG. 3 . In the closed position shown in  FIG. 3  the slanted surfaces  16 ,  17  overly and close off the receptacles  6 ,  7 . The shield elements each comprise a detent  20 ,  22  formed towards an upper edge of the shield element on an inwardly facing side face of the shield elements  16 ,  17  as shown in  FIGS. 3 and 6   a . The housing of the socket  3  comprises two abutments  21 ,  23  formed on a centrally located projection. The abutments are on side faces of the projection facing towards the detents  20 ,  22 . 
   The shutter mechanism is slidably movable within the socket  3  along an axis of sliding movement. The sliding movement of the shutter mechanism is guided by rails  13 ,  14  formed as part of the socket housing. 
   It will be noted that the shutter mechanism is symmetric about the bridge  15 . 
   In use, when the slanted surfaces  16  and  17  of the shield elements are pressed at the same time by the L and N pins of any two or three pin plug, the shutter mechanism  10  is forced to slide to the open position as shown in  FIG. 4 , resulting in the spring  18  being compressed. Thus the L and N plug pins can be fully inserted into the electrical adaptor to make electrical connection. When the two or three pins plug is removed from the electrical adaptor, spring  18  will push shutter mechanism  10  to slide back to the closed position. 
   If only one pin is inserted into either receptacle  6  or  7 , the shutter mechanism  10  will not open and the pin cannot be inserted through to make electrical connection with the electric contact. As shown in  FIG. 6   b , when only the slanted surface  16 &#39;s side is being pushed by a single pin, shutter mechanism  10  starts turning about an axis perpendicular to the direction of sliding movement before it will slide. When the shutter mechanism  10  turns, detent  20  is engaged against abutment  21  of the socket  3 , stopping the shutter mechanism  10  from sliding. Thus, the shutter mechanism  10  does not open and single pin insertion is avoided. The effect is the same when a single pin is being inserted to the slanted surface  17 &#39;s side, because of the symmetrical construction. 
   When a plug is properly inserted, its L and N pins shall be inserted into the receptacles at more or less the same time. But if one is touching the slanted surface  16  or  17  earlier than the other, detent  20  or  22  as indicated in  FIG. 6   b  will engage against either abutment  21  or  23 , locking the shutter mechanism  10  in the closed position. Continued insertion of the plug will force both the L and N pins correspondingly against the slanted surfaces  16  and  17 . Once both shield elements  16 ,  17  are pressed by pins the shield elements will be forded to rotate in opposite senses about the axis of rotation as shown in  FIG. 6   c . This movement is accommodated by flexure of the flexible member of the bridge  15 . Consequently, both detents  20 ,  22  are disengaged from their respective abutments  21 ,  23  as the opposite rotation of the shield elements results in the distance between the detents  20 ,  22  becoming greater than the distance from edge to edge of the abutments  21 ,  23 . As shown in  FIG. 6   c , the shutter mechanism  10  will then be movable to the open position allowing the two plug pins to make electrical connection when fully inserted. 
   In the above embodiment the invention has been illustrated as part of a travel adaptor. It will be understood that the invention extends to all manner of electric sockets including, but not limited to, mains sockets and extension cable sockets.