GB2142968A - Safety padlock - Google Patents

Abstract

A padlock comprising a housing 2 and a hook 1 resiliently biassed towards an unlocked position and retained in a locked position by a resiliently biassed retainer 3 mounted in the housing 2 and engageable with the hook 1. A rotor 4 mounted in the housing 2 has a truncated conical frustum 41 of predetermined angle which is received in a complementary cavity 61 in the key 6 such that on turning the key 6 the rotor 4 is frictionally driven by the engagement of the frustrum 41 in the cavity 61 to retract the retainer to release the hook 1. <IMAGE>

Description

SPECIFICATION Safety padlock This invention relates to a safety padlock.

Nowadays, none of the existing types of locks used in padlocks can be said to be "unpickable".

Generally, existing locks fall into three categories, namely combination locks, pin-tumbler locks, and warded locks. Ordinary combination locks present no problem to an adroit picker, and complex forms of coded combination are required to prevent unauthorised unlocking, and this substantially increases the cost. Warded locks are also easy to pick.

Accordingly, pin-tumbler cylinder locks dominate the market.

However, the pin-tumbler lock is comparatively complicated to manufacture. Also the design and production of pin-tumblers is specialised work and very time consuming. Furthermore the assembly of pin-tumbler locks demands a high level of precision while the loading of the corresponding spring is similarly complicated. Consequently, the assembly of a pin-tumbler lock is a labour intensive operation.

Accordingly, it is the main object of this invention to provide a padlock which equals the cylinder lock with respect to its anti-picking function while being structurally less complicated, thereby permitting easier assembly and therefore lower cost of production.

According to the present invention a padlock with a key comprises a housing, a hook having a long leg and a short leg and being movable between a locked position and an unlocked position, stopping means in the housing engageable with the short leg to retain the hook in the locked position, resilient means to bias the stopping means into engagement with the short leg, a rotor mounted in the housing with its axis extending vertically, the rotor being rotatable about its axis only, the stopping means being movable to a second position where it permits upward movement of the short leg, the rotor being rotatable to a predetermined position to retain the stopping means in its second position, an opening in the lower side of the housing to allow the key to engage the lower part of the rotor, the lower part of the rotor defining a conical frustum of predetermined angle tapering towards its free end and the key having a cavity in its tip complementary to the frustum and the key cavity and rotor frustum being dimensioned so that the rotor is frictionally driven by the key.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings wherein Figure 1 is an exploded view of a padlock according to the present invention; Figure 2 is a perspective view, partly in section, to show the internal arrangement of the components of the padlock shown in Figure 1; Figures 3A and 3B are side views, partly in section showing the padlock in its locked and unlocked positions respectively; and Figures 4A and 4D show the engagement of the rotorfrustum in key openings having different taper angles.

The padlock shown in Figures 1 to 3 of the accompanying drawings comprises four main parts, namely a hook 1, a housing 2, a retainer 3 and a rotor 4.

The hook 1 is of generally U-shape having one leg longer than the other leg and is provided with an annular groove 11' at the end of the long leg and a rebate 11" at the end of the short leg. A spring 5a acting on the long leg of the hook resiliently biasses the latter to its unlocked position when the padlock is opened.

The retainer 3 has a wedge-shaped tip 32 engageable with the rebate 11" to lock the padlock and a recess 31 in which a stop pin 43 eccentrically mounted on the upper end of the rotor is received to restrict the horizontal motion of the retainer as described later. A spring 5 acting on the retainer 3 resiliently biasses the latter towards the short leg of the hook.

The rotor 4 is provided with an annular groove 42 around its waist and the lower end defines a frustum 41 of predetermined angle tapering towards its free end. The tip end of a key 5 for the padlock is provided with a cavity 61 complementary to the frustum 41.

Pins 22', 22" located in corresponding apertures 21 21" in the housing engage the grooves 11', 42 respectively to retain the hook and rotor. The width of groove 11' is greater than the diameter of the pin 22' to allow the hook to rise high enough to rotate about the long leg when the padlock is opened and to be depressed iow enough to engage the tip 32 of the retainer 3 in the rebate 11" of the short leg when the padlock is closed. The width of groove 42 corresponds to the diameter of the pin 43 to allow the rotor to rotate about its own axis but prevent axial motion thereof.

In use, starting from the position shown in Figure 3A, one only needs to insert the key 6 to engage the frustum 41 and rotate the key. The rotor 6 is frictionally driven about its own axis thereby causing pin 43 to move the retainer 3 away from the short leg of the hook against the resilient biassing of the spring 5 until the position shown in Figure 3B is reached where the tip 32 is disengaged from the rebate 11" and the hook 1 is released and raised to its unlocked position under the action of spring 5a.

However, since spring 5 is always urging the retainer 3 towards the short leg the position shown in Figure 3B is an unstable one and the retainer tends to return to the position shown in Figure 3A when the key is removed through the hook is now in the unlocked position. If the hook is subsequently depressed to return it to its locked position the free end of the short leg engages the inclined surface of the tip 32 causing the retainer to retract allowing further entry of the short leg until the rebate 11" aligns with the retainer whereupon the tip is urged into the rebate to retain the hook in the locked position.

Referring now to Figures 4A through 4D, these show that only a key having a cavity complementary to the frustum of the rotor will open the padlock.

Thus, as shown in Figure 4A if the degree of taper of the cavity does not coincide with that of the frustum, linear contact only is obtained, i.e. the contact is confined to the circle dx around the edge of the cavity. Such contact is insufficient to provide the required friction to rotate the rotor and retract the retainer against the action of spring 5. In other words the key only rotates freely around the frustum. In actual fact the key and frustum are not ideal rigid bodies and allow a very slight deformation so that the contact is not linear as shown in Figure 4A but a narrow band dx as shown in Figure 4B. However since the elastic modulus of the key and lock, generally made of metal, is very great, the strain is very small. Consequently the contact band of Figure 4B is also insufficient to provide the required friction to rotate the rotor.Even if the degree of taper of the key matches that of the frustum the contact to provide the required friction to rotate the rotor may still not be obtained. Thus if the cavity of the key is large than the frustum no contact is possible, while if the cavity is smaller than the frustum only a limited length ofthefrustum is allowed to enter the cavity (Figure 4C) and the contact area dx is still insufficient to provide the required friction to rotate the rotor.

Only when the right key is inserted (Figure 4D) is there enough contact area to provide the required friction to rotate the rotor.

This invention has several advantages over the known padlocks. No "skeletal key" can be applied to such a padlock. It is structurally simple and can be manufactured easily at reasonably low cost. The demand for accuracy is not critical except for that of the frustum of the rotor and its corresponding key. It is simple irr use. The key can be inserted into the lock without alignment and can thus be opened in the dark much more easily than are other kinds of locks.

After having opened the padlock the key need not be retained in the lock and can be removed. The cylindrical key shank is structurally much stronger than the conventional keys (mostly flat) which are susceptible to fracture. The degree of tapering and thickness can be standardised. The user only has to memorise the data of the padlock so that he can immediately have another suitable one when he loses his key.

Claims (5)

1. A padlock with a key comprises a housing, a hook having a long leg and a short leg and being movable between a locked position and an unlocked position, stopping means in the housing engageable with the short leg to retain the hook in the locked position, resilient means to bias the stopping means into engagement with the short leg, a rotor mounted in the housing with its axis extending vertically, the rotor being rotatable about its axis only, the stopping means being movable to a second position where it permits upward movement of the short leg, the rotor being rotatable to a predetermined position to retain the stopping means in its second position, an opening in the lower side of the housing to allow the key to engage the lower part of the rotor, the lower part of the rotor defining a conical frustum of predetermined angle tapering towards its free end and the key having a cavity in its tip complementary to the frustum and the key cavity and rotor frustum being dimensioned so that the rotor is frictionally driven by the key.

2. A padlock according to claim 1 wherein the short leg has a rebate in which the tip end of the stopping means is received.

3. A padlock according to claim 2 wherein the tip end is wedge-shaped, defining a slope inclined towards the free end thereof.

4. A padlock according to any one of the preceding claims wherein the upper end of the rotor is provided with an eccentric pin engageable with the stopping means to move the stopping means to and retain it in its second position.

5. A padlock with a key substantially as hereinbefore described with reference to Figures 1 to 3 and 4D of the accompanying drawings.