This invention relates to a padlock for securement of possession, more specifically, to a padlock having tamper evident feature.

BACKGROUND OF THE INVENTION

The padlock is a convenient lock used to secure possession from unauthorised manipulation or theft. In many applications, a padlock is provided with a tamper evident feature to provide evidence that a iocked possession has been tampered with. Most tamper-evident padlocks as used on airline trolleys or luggage consist of a lock body, a hasp, and a locking key (also known as a disposable seal). This type of padlock frees the user of need to carry a key, an advantage which eliminates possibility of loss of the key. Compared to padlock with number combination codes, the user needs not memorise the code or worry about jammed dials.

US 71 18144 B2 discloses a tamper-evident padlock and padlock combination. The padlock has a moulded plastic lock body which includes an open-ended passage and an opening spaced from the passage, There is also a hasp which has first and second spaced apart legs. An end of the first leg can be located in the passage through a first end thereof whiie the end of the second leg can be located simultaneously in the opening. The end of the first leg in the passage can then be engaged by a breakable seal which is inserted into the passage through the opposite end of the passage, in order to lock the hasp relative to the lock body. The padlock combination comprises the padlock and the seal in combination.

A drawback of the above-mentioned invention is that any pul!lng force exerted on the hasp transfers directly to the frangible portion of the seal, which at times causes accidental breakage of the seal, resulting in removal of the hasp from its Iocked position.

US 7370892 B2 discloses a security seal which has housing and a hasp moveable relative to the housing in a first direction between a Iocked position and an unlocked position. The hasp, in the locked position, is !ockable to the housing by a disposable seai. The housing has an opening to ailow the insertion of the disposable seal in a second direction different from the first direction. The hasp includes a first locking element engageable, in the locked position, with a second, matching Socking element of the disposable sea! to prevent movement of the hasp in the first direction toward the unlocked position and withdrawal of the disposable seal in the second direction. The hasp is attached to the housing so as to be both slidable and pivotabfe relative to the housing. The above-mentioned invention improves on the previous invention by employing a sea! transversely. Nevertheless, accidental breakage of the sea! still occurs occasionally, when the pulling force exceeds strength of the heads of the insertion portion of the seal.

SUMMARY OF THE INVENTION

According to the invention, the drawbacks of the prior padlocks are overcome by a padlock which comprises a generally U-shaped hasp, a lock body, and a locking key. The hasp has one leg longer than the other. Said longer leg has an end portion wider than the rest of the hasp. The wider portion has an elongate slot which extends parallel to the leg, and a recess which opens sideways towards the shorter leg. The lock body, the interior of which has a first blind passage towards one side of the body for receiving the wider portion of the hasp and has a peg for engagement with the slot in the wider portion, a second blind passage for receiving the shorter leg, a third passage for receiving a locking key which has a chamfered end, and a transverse passage for receiving a spring loaded locking pin. The arrangement is such that the hasp can be moved between a locked position in which the locking pin is engaged in the recess in the wider portion, and an unlocked position in which the locking pin extends into the third passage under the Influence of the spring . The locking key comprises a shaft which has an undercut chamfered end that when inserted into the third passage engages the chamfered end of the locking pin, and forces it into the transverse passage to enter the recess in the wider portion, after which the locking pin springs back to engage under the undercut to prevent removal of the key, Said key has a frangible end portion of the shaft to ho!d the key in position until the end portion is broken off.

Preferably, the longer leg has a protrusion disposed on the side opposite the edge of the wider portion; said protrusion hinders intrusion to the interior of the lock body when the hasp is in the locked position,

Advantageously, the first passage is defined by a generally P-shaped depression which has the head portion of the P shape trimmed to a!lovv the hasp to rotate about the peg.

The invention also discloses a method for locking the padlock. The method comprises a step of inserting the shaft of the locking key into the third passage via an opening of the third passage disposed on an end of the lock body opposite the hasp, such that the chamfered end of the shaft engages the chamfered end of the locking pin, and forces it into the transverse passage to enter the recess in the wider portion , after which the locking pin springs back to engage under the undercut to prevent removal of the key.

Furthermore, the invention discloses a method for unlocking the padlock. The method comprises steps of: tearing along the frangible end portion of the shaft of the locking key, and breaking off the tab portion and the transverse portion of the key; and pushing the shaft and the undercut head through the passage to release the locking pin.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of one form of a padlock according to the invention, in which a hasp is in a locked position and a locking key is disengaged from a through passage of a lock body;

Fig. 2 is a partially exploded view of the padlock shown in Fig. 1 ;

5 Fig. 3 is a front view of the padlock shown in Fig. 1 with a lock cover removed and the hasp in a locked position; and

Fig. 4 is a front view of the padlock shown in Fig. 1 with the lock cover removed, the hasp In the locked position, and a shaft of the locking key residing in the through passage in the lock body. t o As shown in the drawings, a padlock comprises a lock body that is formed by two parts 1 a, 1 b. The lock body 1 has a first blind passage 9 disposed in proximity to one edge, a second b\m ^' 0 passage 1 1 parallel to the passage 9, at about the middle of the Sock body 1 , a through passage 12 disposed in proximity to an opposing edge of the lock body 1 , and a

15 transverse passage 15 extending from the first passage 9 to the through passage 12 without intersecting the second passage 1 1. A generally U- shaped hasp 2 has one leg 3 longer than the other 5. The longer leg 3 has on one side a portion 4 wider than the rest of the hasp 2. The wider portion 4 has an elongate slot 8 which extends parallel to the leg 3, and a recess 0 7 which opens sideways towards the shorter leg 5. The longer leg 3 has a protrusion 24 disposed on the side opposite the edge of the wider portion 4 to prevent access to the interior of the lock body 1 when the hasp 2 is in the locked position. The first passage 9 receives the wider portion 4 of the hasp 2 and has a peg 10 for engagement with the slot 6 In the wider 5 portion 4; the first passage 9 is defined by a generally P-shaped depression having the head portion of the P shape trimmed to allow the hasp 2 to rotate about the peg 10. The second passage 1 1 receives the shorter ieg 5, and the transverse passage 15 receives a spring-loaded locking pin 1 7. 0 The locking pin 17 is moveable between a locked position In which it engages the recess 7 of the wider portion 4 of the longer ieg 3, and an unlocked position in which a chamfered end 21 protrudes into the third passage 12. The locking pin 1 ? comprises the chamfered end 21 , a rod portion 26 around which a spring 18 is loaded, and a collar 27 disposed between the chamfered end 21 and the rod portion 26. The collar 27 acts as a stopper to prevent the rod portion 26 from extending into the through passage 12, while allowing the chamfered end 21 to protrude perpendicularly into the through passage 12 by force exerted by the spring 18.

The Iocking key 13 comprises a shaft 19 which has a chamfered end 14. The chamfered end 14 has an undercut point 20. The shaft 19 also has a frangible end portion 22. A tab portion 23 is connected to the shaft 19 by a transverse portion 27 disposed perpendicularly between the shaft 19 and the tab portion 23. The tab portion 23 has on one of its surface a ridge (not shown in the figure) protruding towards the shaft 19. The ridge is mated to a groove 28 in cover 1 a of the lock body 1 , which guides the insertion of the shaft 19 into the through passage 12.

The hasp 2 is made of spring steel plated with nickel, and the lock body 1 is made of A8S (acrylonitriie-butadiene-styrene) which has an excellent cold resistance, i.e. as low as -10°C. From experiments, the spring 18 (as that loaded on the locking pin 17} is found to be able to sustain a considerable weight for as long as two weeks without experiencing permanent loss of resilience. A tensile test shows that the hasp 2 as locked by the locking key 13 is able to withstand a force as high as 83 kilogram-force. In terms of durability, the padlock is capable of being locked and unlocked for as many as five hundred times before it fails to function as it should.

To Sock the padlock, the shaft 19 of the Iocking key 13 is inserted into the third passage 12 via an open end of the third passage 12 disposed on an end of the iock body 1 opposite the hasp 2, such that the undercut head 14 of the shaft 19 engages the chamfered end 21 of the locking pin 17 and forces it into the transverse passage 15 to enter the recess 7 in the wider portion 4 after which the focKing pin 17 springs back to engage under the undercut 20 to prevent removal of the key 13.

To uniock the padlock, the shaft 19 of the locking key 13 is torn along the frangible end portion 22 of the key 13 is broken off, so that the shaft 19 and the undercut head 14 can be pushed through the passage 12 to release the locking pin 17,

As shown in Fig. 1 and 2, laser print may be made on a smaller part 29 of the tab portion 23, and a corresponding laser print may be made on a larger part 30 of the tab portion 23. During use, the smaller part 29 is broken off along a frangible portion 31 and kept by user for identification during redemption of his or her locked possession.