Such an anti-theft device to be detachably fitted on a king pin which is mounted on a semi-trailer of an articulated vehicle is known from DE-C-4425513. The prior art anti-theft device comprises a locking mechanism including a lock and a locking element including a movable locking cylinder, which is actuated by said lock. When a key is turned in said lock, the locking cylinder moves into a first coupling element which is present in said king pin in the form of an annular notch, as a result of which the king pin and the anti-theft device will interlock in axial direction. The king pin is thus covered and a detached semi-trailer cannot simply be taken along by unauthorized persons by means of a tractive unit of the articulated vehicle. One drawback of the prior art anti-theft device is the fact that the locking mechanism, which includes moving parts, is mechanically relatively vulnerable to sabotage.

The object of the invention is to provide an anti-theft device which includes fewer parts that are easily sabotaged.

In order to accomplish that objective, the anti-theft device according to the invention is characterized in that the anti-theft device comprises a second, rigid coupling element provided in said cavity, which is to be brought into engagement with said first coupling element.

The advantage of the anti-theft device according to the invention is that the rigid second coupling element in the cavity of the anti-theft device is directly coupled to the first coupling element on the king pin, so that axial movement is prevented without any movable parts being involved. As a result of this, the relative mechanical vulnerability and the susceptibility to sabotage are also reduced, which makes the anti-theft device according to the invention more vandal-proof

whilst reducing the number of parts that are needed.

One embodiment of the anti-theft device according to the invention is characterized in that the first and the second coupling element are complementary to each other, as a result of which the anti-theft device in question is easy to manufacture, using generally known methods, such as turning, sawing, drilling, milling, casting, etc.

Another embodiment of the anti-theft device according to the invention, which leads to an anti-theft device according to the invention which can be used universally in a large variety of embodiments thereof, is characterized in that the first and the second coupling elements are in the form of one or more ring-shaped or sector-shaped notches and/or cams.

In a special embodiment, the anti-theft device according to the invention comprises a lock provided with a key for interlocking the king pin and the anti-theft device, wherein more in particular the anti-theft device and the lock are so constructed that they can be separated.

The advantage of this special embodiment is that the risk of the lock and the anti-theft device becoming clogged with dirt, grease, sand and the like is very small, since it has become easier to remove dirt and impurities from the removable lock, the anti-theft device and the cavity or cavities of the anti-theft device. Yet another embodiment of the anti-theft device is characterized in that the anti-theft device is so constructed that the first and the second coupling element, which remain in engagement with each other, secure the anti- theft device and the king pin against axial movement when the lock is positioned in the anti-theft device.

The advantage of this embodiment is that a minimum number of parts are required in the solid anti-theft device, wherein the lock, which will be a common but very solid lock, will or will not provide said locking function, depending, respectively, on whether it is present in the anti-theft device or not.

A uniform and simple manufacturing method is ensured by an embodiment of the anti-theft device which is characterized

in that the anti-theft device and the second coupling element are made of the same metallic material, for example by means of a casting process.

The invention and its concomitant advantages will now be explained in more detail with reference to the accompanying drawing, wherein parts corresponding to each other are indicated by the same numerals in the various figures. In the drawing : Figure 1 shows a king pin which is known per se and which is intended for use with the anti-theft device according to the invention ; Figure 2 a cross-sectional view of a possible embodiment of the anti-theft device according to the invention ; Figure 3 is a bottom plan view of the anti-theft device of Figure 2 ; Figure 4 is a right-hand view of the anti-theft device of Figure 3 ; Figures 5A-5D show a few possible embodiments of coupling elements for use in the anti-theft device according to the invention ; and Figure 6 is a partial sectional view of the anti-theft device of Figure 2, showing a king pin in locked condition.

Figure 1 shows a king pin which is usually mounted on a semi-trailer (not shown) of an articulated vehicle or truck, which kin pin 1 can be coupled to a turntable which is mounted on a tractive unit of the articulated vehicle. In the detached condition of the semi-trailer, the king pin 1 is protected by means of an anti-theft device 2 as shown in Figure 2.

The anti-theft device 2 which is shown in Figure 2 is provided with a cavity 2, into which the king pin can be inserted. King pin 1 includes a first coupling element 4, in the form of an annular notch 4. 1 in Figure 1, which expands towards the end of king pin 1 into a widening cam or shoulder 4. 2. Cavity 3 in anti-theft device 2 is fitted with a fixedly or rigidly disposed second coupling element 5, which extends into cavity 3. When the anti-theft device 2 is placed round

king pin 1, the anti-theft device 2 will be moved sideways, to the right in Figure 2, and subsequently it can be moved back to the left behind cam 4. 2 so as to bring the first and the second coupling element 4 and 5 into engagement with each other. In practice the two coupling elements 4 and 5 will be at least partially complementary to each other so as to interlock properly and prevent axial movement of the anti- theft device 2 and the king pin 1 relative to each other. The anti-theft device 2 is provided with a lock cavity 6 which is in communication with cavity 3, in which cavity 6 a lock S will be present, which can usually be operated by means of a key SL. When lock S is fixedly disposed in anti-theft device 2, key SL and lock S must be turned upon insertion of king pin 1 into cavity 3 so as to allow lateral movement of the anti- theft device 2 with respect to king pin 1 in order to cause coupling elements 4 and 5 to interlock. After the key has been turned, the lock will prevent said lateral movement and provide the locking engagement of anti-theft device 2 on king pin 1. When on the other hand lock S can be removed from lock cavity 6 in an alternative embodiment, which is advantageous in practice in that fouling of cavities 3,6 or of the lock will occur less easily or that any dirt can be simply removed, the mere presence of such a detachable lock already suffices to prevent lateral movement of the anti-theft device 2 with respect to king pin 1, thus effecting a proper locking engagement. The lock which is inserted in lock cavity 6 functions to fill said cavity in that case, as a result of which the anti-theft device is securely locked on king pin 1.

In that case, it suffices to simply fit lock S with a lip in such a manner that the lock can no longer be pulled out of lock cavity 6 when key SL is turned in lock S, which can be easily achieved in a mechanically solid manner. This has a positive effect as regards the solidity of the anti-theft device 2 as a whole, while the number of necessary and/or movable parts is minimized. An example of a suitable detachable lock is to be found in EP-A-0 617 184. Also alternative locks, for example numeric locks or locks not

having a mechanical key but an electrical/code key can be used, of course. Also radiographically operated locks are possible.

The specific configuration of the two coupling elements 4 and 5 can be varied as desired. Usually, the rigid second coupling element 5 will be so configured that it also fits on usual prior art king pins 1. Figures 5A, 5B, 5C and 5D schematically show a few possible embodiments of coupling elements 4 and 5. All these coupling elements are ring-shaped or sector-shaped notches and/or cams.

Figures 3 and 6, wherein the anti-theft device 2 is shown, illustrate in particular the manner in which the second coupling element 5 is configured as a sector-shaped cam, which can be brought into engagement with cam 4. 2 of Figure 1. A thickening 7 is provided on the outer side of anti-theft device 2, which can be formed integrally therewith from the material of which the anti-theft device 2 is made, if desired, which thickening 7 will disappear under an elastic, usually rubbery substance 8 and which forms an additional precaution against a hole being drilled to lock cavity 6. The fact is that the presence of said thickening will cause a drill to slide off during drilling. The anti-theft device 1 is, preferably integrally, formed of a cast steel, which is not easy to drill into and which has a high shearing strength. An example of a suitable cast steel is nodular cast steel, such as nodular cast steel GGG40, which meets the DIN 1693 standard. The rubbery substance is a hard, ductile, poreless, grease and oil resistant rubber, for example 93% Shore rubber or NPR, about 75% SH nitrile rubber. The rubbery substance 8 is intended in particular to prevent the turntable and a king pin receiving mechanism on the tractive unit from being damaged when said tractive unit attempts to hitch to king pin 1 while the anti-theft device is still present thereon.

Substance 8 may be circumferentially bevelled so as to provide some clearance for the anti-theft device 2 when said anti- theft device is moved over king pin 1. Substance 8 furthermore screens the underlying bolts by means of which the king pin 1

is secured to the semi-trailer.

Figure 4 shows in particular that the lock cavity 6 includes flattened wall portions 10, two in the illustrated embodiment, which ensure that the lock will not turn along in lock cavity 6 when the key is being turned. From Figure 4 it can also be derived for this embodiment that the aforesaid lip of the lock can slip behind edge 11 of wall portion 10 so as to prevent the lock from being removed without using a key.