Abstract:
A pressure-sensitive locking device comprises a housing ( 2,20 ) having an opening therein, and an insertable member ( 1,21 ) adapted to be inserted into the opening whereupon it can enter into locking engagement with a locking member ( 4,36 ) in the housing. The locking member ( 4,36 ) is cooperable with pressure-sensitive means ( 7,28 ) in the housing to effect disengagement between the locking member ( 4,36 ) and the insertable member ( 1,21 ) upon a reduction of pressure.

Description:
FIELD OF THE INVENTION 
     This invention relates to a locking device, and more particularly to a locking device which is automatically engageable or disengageable upon a change in pressure. 
     BACKGROUND OF THE INVENTION 
     A particular application for such a locking device is as a security seal for use on passenger aircraft. The device can be used to seal the containers used for the in-flight distribution of perishable and non-perishable goods. The theft of goods from containers costs airlines vast sums of money each year. Although containers are sealed when they leave the warehouse, it is necessary for the seals to be easily removable by hand as it is quite impractical for cabin crews to carry special seal removal tools on the aircraft. We have found that these problems can be solved by a locking device which is pressure-sensitive; the device thus being actuated by the reduced pressure during flight. 
     SUMMARY OF THE INVENTION 
     The present invention thus provides a pressure-sensitive locking device comprising a housing having an opening therein, an insertable member adapted to be inserted into the housing through the opening, and a locking member in the housing, the locking member being biased towards engagement with the insertable member so that the locking member is lockably engageable with the insertable member upon insertion of the insertable member into the housing, and the locking member being cooperable with pressure-sensitive means pressure-sensitive arrangement in the housing to effect disengagement of the locking member from the insertable member upon a reduction of pressure. 
     In a preferred embodiment, the locking member is resiliently biased towards the insertable member when inserted in the housing so as to be in locking engagement therewith under normal atmospheric pressure. When the pressure is reduced, for example when an aircraft achieves a predetermined altitude, the pressure-sensitive means effects disengagement of the locking member from the insertable member, whereupon the insertable member can be withdrawn from the housing. 
     The opening in the housing preferably communicates with a channel, and the insertable member is preferably elongate and adapted to be slidingly inserted lengthwise through the opening into the channel. 
     The locking device can serve both as a barrier seal and as an indicative seal. The elongate member can be shaped so as to engage with a hasp or other securing device of an aircraft goods container. Alternatively, the elongate member can be U or J-shaped whereby the limbs can be inserted in two channels in the housing and lockable in one or both such channels, the device then being usable in the same way as a padlock. The locking device preferably includes an additional disposable locking element which engages with the elongate member in the locked position, and which has to be physically broken to permit withdrawal of the elongate member from the channel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic representation, partly in cross-section, of a locking device according to a first embodiment of the invention, the device being shown in the locked condition; 
     FIG. 2 is a view corresponding to FIG. 1 but with the device unlocked; 
     FIG. 3 is an exploded perspective view of a locking device according to a second embodiment of the invention; 
     FIG. 4 is an end view of a disposable locking element used in the second embodiment; 
     FIG. 5 is a plan view of the second embodiment when ready to be locked; 
     FIG. 6 is a plan view of the second embodiment in the locked position, and partly cutaway to show internal details; 
     FIG. 7 is a view of a combined capsule and locking member used in the second embodiment; 
     FIG. 8 is a side view corresponding to FIG. 7; 
     FIG. 9 is a partial end view corresponding to FIGS. 7 and 8; 
     FIG. 10 is a part-sectional side view showing the operation of the combined capsule and locking member of the second embodiment in the locked condition; 
     FIG. 11 corresponds to FIG.  10  and shows the device unlocked by a reduction in air pressure; 
     FIG. 12 corresponds to FIGS. 10 and 11 and shows the operation of a secondary locking member to prevent unauthorised or accidental “shock” opening; 
     FIGS. 13 and 14 are diagrammatic plan views showing a modification of the second embodiment; and 
     FIGS. 15 and 16 are sectional views corresponding respectively to FIGS.  13  and  14 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIGS. 1 and 2, there is shown a housing  2  with a channel  9  defined therein. An elongate member in the form of a bar  1  of cylindrical section is able to slide within the channel. The bar  1  has a tapered head and immediately behind this a groove  3 . A locking member  4  is provided within the housing and is rotatable about an axis  10 . One end of the locking member has an enlarged head shaped so as to engage with the groove  3  of the bar  1 . An opposite end of the locking member  4  is engaged with one end of a helical spring  8 , the other end of which is mounted in the housing  2 . The spring  8  resiliently biases the locking member  4  into locking engagement with the groove  3  of the bar  1 . When the bar  1  is initially inserted into the channel  9 , the tapered head of the bar slides past a sloping surface of the head of the locking member  4 , thereby deflecting the locking member against its spring bias, and then the locking member snaps into engagement with the groove  3 . The locking engagement between the locking member  4  and the groove  3  prevents withdrawal of the bar  1  from the channel  9 . 
     Also provided within the housing is a pressure-sensitive means in the form of a capsule  7  which communicates with a tube  6  but is otherwise air-tight. The capsule  7  has concertina-like flexible side walls to permit expansion and contraction. An elongated sliding element  5  with rounded ends is provided in a transverse channel  11  which adjoins the channel  9 . Before insertion of the bar  1 , one end of the sliding element  11  projects slightly into the channel  9 . As the bar  1  is inserted, it deflects the sliding element  5  to one side so that it slides further into the transverse channel  11 . This causes the opposite end of the sliding element  5  to press against the side of the tube  6 , which is of flexible material. The tube  6  is thereby sealed at this point, with the result that the capsule  7  is completely air-tight. 
     As the pressure is reduced, for example, as an aircraft increases altitude, the pressure of the air enclosed within the capsule  7  becomes greater than that of the surrounding air, with the result that the capsule expands, as shown in FIG.  2 . An end of the capsule  7  abuts against a rounded contact point on the locking piece  4 , intermediate the axis  10  and contact point of the spring  8 . Expansion of the capsule  7 , as shown in FIG. 2, thus causes the locking piece  4  to pivot about the axis  10 , whereby the head of the locking piece  4  becomes disengaged from the groove  3  in the bar  1 . The bar  1  can then be freely withdrawn from the channel  9 . Once the bar  1  has been withdrawn, the sliding element  5  ceases to be pressed against the tube  6 , and the natural resilience of the tube  6  pushes the sliding element  5  back towards the channel  9 . Air can therefore pass from within the capsule  7  and out through the tube  6 , thereby equalising the pressures inside and outside the capsule  7 . The spring  8  will then cause pivoting of the locking piece  4  about the axis  10 , so that the head of the locking piece  4  once more projects into the channel  9 . If the bar  1  is then reinserted into the channel  9 , it will again engage with the head of the locking piece  4  to effect locking. Once this position has been reached, and without any further reduction in pressure, unlocking of the device can only be achieved by destruction of parts thereof, for example by cutting the bar  1 . If desired, a special tool could be designed to disengage the locking piece  4  from the bar  1 , although such an arrangement would be inherently less secure. 
     The locking device described above is typically used to seal a goods container, for example a drinks trolley, for use on an aircraft. The trolley is filled at the warehouse and then locked with the locking device. If the trolley is to be inspected by authorised personnel while still on the ground, the locking device is opened by cutting the bar, and the trolley is then locked with a new locking device. The locking device can thus only be opened on the ground by destroying at least part of it, and thus any interference with the trolley is readily apparent to an inspector. Once on the aircraft, above a designated altitude, the locking device is automatically unlocked by the reduced pressure. The trolley can then be used in the normal way, and after use it can be relocked with the same locking device. Thereafter, the locking device can again only be unlocked by destruction of at least part of it, which would be done by authorised personnel. Again, any unauthorised interference would be readily apparent to an inspector. 
     Referring now to FIGS. 3 to  12 , a second embodiment of the invention is described. The locking device shown includes a housing  20 , an insertable member in the form of a flat bar  21  and a disposable locking element  22 . The housing has a hinged guide member  23 , pivoted to an end portion  24  of the housing. The guide member  23  is able to pivot between an open position (FIG. 5) and a closed position (FIG.  6 ). The guide member  23  has an opening  25  for receiving the bar  21 , and in the closed position the opening  25 , which extends through the guide member, is in register with openings at opposing ends of the main body of the housing  20 , so as to effectively form a channel through the housing. 
     The bar  21  is J-shaped. An end portion of the longer limb can be pre-placed in the opening  25  of the guide member  23 , with the guide member in the open position as shown in FIG.  5 . In order to effect locking, as described in more detail below, the guide member  23  is then rotated to the closed position (FIG. 6) and the longer limb of the bar  21  is then fully inserted in the channel of the housing  20 , the end portion of the longer limb projecting slightly from the other side of the housing (FIG.  6 ). The shorter limb of the bar  21  is received in an opening  26  in a side wall of the housing, and in the locked position travels to a short extent through the opening into the interior of the housing (FIG.  6 ). The fit of the end of the longer limb of the bar  21  in the opening  25  is sufficiently close that the bar  21  can be held by the guide member  23 , as shown in FIG. 5, but does not impede further insertion of the bar  21  through the opening  25  until the bar reaches the locked position, as shown in FIG.  6 . 
     Inside the housing  20  is a locking member  27  which incorporates a pressure-sensitive device in the form of a sealed capsule  28 . The capsule  28  is in the form of a shallow cylindrical cup, one end of which is sealed by an elastomeric membrane  29 . The cup and the membrane define a closed space. A short extension piece  30  to one side of the capsule terminates in a transverse hinge member  31  which cooperates with a hinge support  32  inside and at one end of the housing  20 . Extending from the opposite side of the capsule  28 , but slightly offset from the extension piece  30 , is an arm  33 . On the underside of the arm, close to the capsule  28 , there is formed a cylindrical cup  34  for receiving an end of a helical spring  35 , the other end of the spring being mounted on an internal wall of the housing. By virtue of the hinge  31  and the spring  35 , the arm  33  of the locking member is biased away from the internal wall of the housing on which the spring  35  is mounted. Also on the underside of the arm  33 , but closer to its free end, there is an integral locking piece  36  in the form of a ridge having a sloping ramp  37  at one side (FIG.  9 ). 
     The bar  21  has a rectangular slot  38  towards the end of its longer limb. As the bar  21  is inserted into the housing, the leading edge of its longer limb passes under the arm  33  of the locking member. The leading edge first strikes the ramp  37  of the locking piece  36 , and rides up the ramp, thereby pressing the arm  33  against the bias of the spring  35 . On further insertion, the locking piece  36  becomes level with the slot  38  in the bar  21 , and at this point the spring  35  causes the arm  33  with its integral locking piece  36  to snap into engagement with the slot  38 . Attempted withdrawal of the bar  21  is prevented by engagement between the end of the locking piece  36 , opposite to the ramp  37 , with the trailing end (on extraction) of the slot  38 . 
     In this position, the bar  21  is securely locked in the housing  20 . With this arrangement, there is a risk that a sharp blow to one side of the housing, closest to the underside of the arm  33 , could momentarily deflect the arm against the spring  35 , which would permit the bar  21  to be withdrawn (referred to herein as “shock opening”). Such a blow could be inflicted deliberately in an attempt to interfere with the locking device, or by accident. In order to overcome this problem, there is provided a secondary locking member  39  (FIGS. 10 to  12 ). The secondary locking member  39  is shaped similarly to the locking member  27  except that it does not have the capsule  28 . The secondary locking member  39  has at one end a hinge member  40  which is mounted inside the housing close to the hinge member  31  of the locking member  27 . Close to its opposite end, there is an integral upstanding locking piece  41 , similar to the locking piece  36  but without a ramp. As shown in FIG. 10, the secondary locking member  39  normally lies alongside an internal wall of the housing, with the locking piece  41  close to but not actually engaged with the slot  38  of the bar  21 . In this position, if a sharp blow is applied to the housing wall adjacent the secondary locking member, the locking member  27  may be momentarily deflected out of engagement with the slot  38 , as shown in FIG.  12 . However, such a blow will deflect the secondary locking member  39  in the same direction, and this will be into locking engagement between the locking piece  41  and the slot  38 . The slot  38  is designed to be sufficiently wide that both locking pieces  36  and  41 , which are offset from each other, can be accommodated. When the effect of the sharp blow has subsided, the spring  35  returns the locking member  27  and locking piece  36  into engagement with the slot  38  of the bar  21 , and the arrangement is again as shown in FIG.  10 . 
     When the locking device is in the locked position (FIG. 10) a predetermined reduction in ambient pressure will cause it to be unlocked. When the ambient pressure is reduced, the pressure of the air enclosed in the sealed capsule  27  causes the elastomeric membrane  29  to expand outwardly. This membrane abuts against the surface of the secondary locking member  39 , which in turn abuts against the internal surface of the housing. The result is that the locking member  27 , by virtue of its hinge  31 , is pressed against the bias of the spring  35 , and the locking piece  36  is raised out of engagement with the slot  38 , as shown in FIG.  11 . The locking device is then unlocked, and the bar  21  can be withdrawn. The elastomeric grade of the membrane  29  can be adapted to provide locking devices which will be unlocked over a range of predetermined pressure changes. 
     The locking device includes a supplementary security seal in the form of a disposable locking element  22  (FIGS.  3  and  4 ). The disposable locking element  22  includes a head part  42  in the form of a flat tab, and upstanding on one side thereof a plug part  43  and a locking post  44 . The disposable locking element  22  cooperates with the guide member  23  (which is part of the housing  20 ) and the bar  21  in the following manner. 
     The bar  21  has a circular hole  45  in its longer limb spaced from the trailing end (on insertion) of the slot  38 . The guide member  23  has a corresponding through hole  46  whereby, when the bar  21  is locked in the housing  20 , the holes  45  and  46  are in register and can receive the locking post  44  of the disposable locking element  22 . The guide member  23  has a hollow interior, with an opening  47  spaced to one side of the hole  46 . The plug part  43  of the disposable locking element is in the form of a resilient barb. The plug part  43  passes through the opening  47  as the locking post  44  is inserted through the holes  46  and  45 . As the plug part  43  passes through the opening  47 , the barb is resiliently deflected to one side, but as soon as it is inside the guide member  23 , the barb resiliently returns to its original dimensions, and resists withdrawal. In this position, the bar  21 , as well as being locked by the locking member  27  inside the housing, is additionally locked by the locking post  44 . Thus, even when a reduction in pressure has caused the locking member  27  to disengage from the bar  21 , the disposable locking element  22  must additionally be released in order to withdraw the bar  21 . 
     The head part  42  incorporates a tear line which separates the parts of the head part respectively attached to the plug part  43  and the locking post  44 . Thus, by manual manipulation, which is assisted by a pull tab  48 , the disposable locking element can be split into two parts. The locking post  44  can then be freely withdrawn, permitting release of the bar  21 . The plug part  43  remains inside the guide member  23  but the guide member  23  can now be freely rotated to the open position, thereby releasing the plug part. The disposable locking element  22  can be marked for security purposes, such as with a serial number or bar code. If desired, the locking device can be relocked using a new disposable locking element. 
     FIGS. 13 to  16  illustrate a modification of the second embodiment of the invention (FIGS. 3 to  12 ). Instead of the secondary locking member  39  (which is absent in FIGS. 13 to  16 ), shock opening is prevented by modifying an internal chamber  49  in the housing and allowing a loose fit of the hinge  31 . The loose fit permits a small amount of sideways movement of the arm  33 , whereby the bar  21  can be pushed slightly beyond its normal locking position (FIGS. 13 and 15) to an extended position (FIGS.  14  and  16 ). The effect of this can be seen by comparing FIG. 15, which is a section on the line XV—XV of FIG. 13, with FIG. 16, which is a similar section corresponding to FIG.  14 . The chamber  49  is provided with a step  50  near the point of entry of the bar  21 . The step  50  is dimensioned such that the thickness of the arm  33  can just fit between the step  50  and the bar  21 . Thus, in the normal locking position shown in FIGS. 13 and 15, the step  50  prevents shock opening. Shock opening can only be achieved if the bar  21  is pulled away from the housing simultaneously with applying the shock, and in this position the step  50  prevents movement of the arm  33  to take the locking piece  36  out of engagement with the bar  21 . 
     When a fall in pressure permits normal opening (in the manner already described), the disposable locking element  22  is first extracted. The bar  21  can then be pushed into the extended position (FIGS.  14  and  16 ), where the holes  45  and  46  are now slightly out of register. The arm  33  is now moved off the step  50 . The spring  35  will cause it to remain in engagement with the bar  21  (as shown in FIGS.  14  and  16 ). However, if the pressure has fallen sufficiently, the expansion of the capsule  28  will cause the arm  33  to move out of engagement with the bar  21 . The bar  21  can then be pulled out of the housing as described above. 
     There may be a need to inspect a container locked by the locking device while still on the ground. In this case, an authorised official will break the disposable locking element  22  and cut the bar  21  in its longer limb, on the trailing side (relative to insertion) of the hole  45 . The leading end of the longer limb, which projects from the other side of the housing, can then be pulled, and the residual part of the bar  21  withdrawn from the housing. This is possible because the ramp  37  of the locking piece  36  will cooperate with the trailing end of the slot  38 , whereby the locking member  27  is moved out of engagement with the residual part of the bar  21 . The device is then relocked with a new bar  21  and new disposable locking element  22 . 
     It is sometimes desirable for containers on aircraft to be openable while the aircraft is still on the ground, for example if there is a flight delay. This can be accommodated according to the present invention by modifying some locking devices so that the slot  38  is absent in the bar  21 . The device is then not locked by the pressure-sensitive locking member  27 , but is only locked by the disposable locking element  22 . In a typical situation, a limited number of containers of the aircraft would be locked in this way, the remaining containers being locked in the full pressure-sensitive manner as described above. 
     A container on an aircraft may be locked by the device according to the invention by cooperation between the bar  21  and a hasp or other securing device on the container. Alternatively, a cable may be provided with loops at its end. The cable is then used to secure a container door in the closed position and the loops are held by the bar  21  which acts in the manner of a padlock.