FIELD OF THE INVENTION This invention relates to a trailer security device suitable for use on any trailer, including caravans and light domestic and commercial luggage or goods trailers. More particularly, but not exclusively, the invention is concerned with trailers that may not have their own braking system.

BACKGROUND TO THE INVENTION The security of trailers has attracted much attention in the past in view of the ease with which an entire trailer, together with its contents, can so easily be attached to a towing vehicle of an unauthorized person with the result that the rightful owner is deprived thereof.

Many different expedients have been proposed in order to overcome this difficulty. In the case of trailers having their own braking system, various expedients have been proposed whereby the brakes can be locked in the applied condition in order to inhibit, and generally effectively prevent, the trailer from being towed.

Another type of expedient that has been proposed is that of wheel clamps and similar arrangements that can be applied to the wheel of a trailer, or for the matter any vehicle, in order to prevent the trailer from being towed.

Typically such wheel clamps consists of different components, very often in the form of one or more chocks, that must be applied to the vehicle wheel and removed therefrom each time that they are brought into operation. This is normally a dirty, troublesome, and very often tiring operation that is regarded by many as totally undesirable and generally requires that one at

least wash one's hands following an installation or removal of such a clamp thereby adding to the inconvenience.

An extremely common type of trailer coupling for coupling a drawbar to a generally part-spherical towing ball is a coupling having a part-spherical socket in a fixed coupling member and a cooperating pivotally mounted keeper member usually fitted with a handle and being spring loaded to a position in which it effectively closes the entrance aperture to the part spherical socket in its operative position towards which it is spring biased. A spring loaded locking pin is generally provided for locking the keeper member in its functional operative position. The simplest type of security device applied to trailer couplings of this general type has been the provision of holes in the fixed coupling member and an overlapping region of the keeper member with the holes being aligned in the operative position of the keeper member. The shackle of a long shackled padlock can be passed through the aligned holes to lock the coupling so that the keeper member cannot be operated to either attach or release the coupling to or from a towing ball associated with a vehicle towing bar.

The problem of this simple expedient is that padlocks are relatively simple to break open or otherwise render ineffective. Also, it does not prevent the trailer from being towed away in any event but only from being attached by means of the coupling.

OBJECT OF THE INVENTION It is an object of this invention to provide a trailer security device that overcomes, at least some extent, one or more drawbacks of the existing devices.

SUMMARY OF THE INVENTION In accordance with one aspect of the invention there is provided a trailer security device comprising a coupling assembly wherein a fixed coupling member provides an attachment formation for attachment to a towing formation on a motor vehicle, a keeper member movably associated with the fixed coupling member and movable between two positions, one in which engagement or release of the attachment formation relative to a towing formation is enabled, and one in which such engagement or release is denied, a locking member movable between an operative position in which movement of the keeper member relative to the fixed coupling member is effectively prevented and an inoperative position in, which such movement is enabled, and a lock assembly for locking the locking member selectively in either the operative or the inoperative position.

Further features of the invention provide for the locking member to be movable between the operative and inoperative positions by means of an operating member, typically a lever ; for the locking member to be coupled by mechanical transmission means to a wheel locking unit including a locking element associated with a wheel hub of the trailer and wherein the locking element is movable between an operative position in which it is urged towards a cooperating formation in the wheel hub such that rotation of the wheel hub is prevented when the locking element engages in the cooperating formation and an inoperative position in which the locking element is withdrawn from cooperating association with the formation on the wheel hub, the arrangement being such that the locking element is in its operative position relative to the hub when the locking member is in its inoperative position relative to the keeper member and the locking element is in its inoperative position relative to the hub when the locking member is in its operative position relative to the keeper member; and for the mechanical transmission means to be a control cable having an axially movable rigidly flexible inner transmission cable and a rigidly flexible outer sheath.

Still further features of the invention provide for the attachment formation of the fixed coupling member to be a part-spherical socket for cooperation with a generally part-spherical towing ball ; for the keeper member to be pivotally attached to the fixed coupling member; for the fixed coupling member to have an integral base bolted onto a drawbar of the trailer ; and for the locking member to be an axially movable locking pin.

In accordance with a second aspect of the invention there is provided a security accessory including a housing adapted to be associated with an existing coupling member so as to form part of a trailer security device as defined above, the housing having associated therewith said locking member and said lock assembly.

Further features of this aspect of the invention provide for the security accessory to have an axially movable carrier member carrying the locking member and wherein the carrier member is movable generally axially and is generally coaxial with the locking member so as to be movable between positions corresponding to the locking member being operative and inoperative; and for the carrier member to be attached, or to be a attachable, to mechanical transmission means associated with a wheel locking unit forming part of the accessory and being adapted for attachment to an existing trailer.

In order that the above and other features of the invention may become more apparent one embodiment of security device according to the invention will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:- Figure 1 illustrates schematically the general application of one embodiment of the invention to a trailer ; Figure 2 is a sectional elevation of a coupling assembly according to the invention and showing the locking member in its operative position; Figure 3 is a sectional elevation the same as Figure 2 but showing the locking member in its inoperative position; Figure 4 is a schematic cross-section through the housing only and taken along line IV-IV in Figure 2; Figure 5 is an exploded view illustrating schematically the various components of the accessory; and, Figure 6 is a schematic section taken through a wheel locking unit of the security device.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS Broadly, and as illustrated in Figure 1, the security device in this embodiment of the invention assumes the form of a housing (1) for association with an existing trailer coupling assembly (2) of the type adapted for cooperation with a part-spherical towing ball of the type in quite common usage. The housing is connected, by way of a control cable (3) of the type having an inner axially movable transmission member and an outer sheath, with a wheel locking unit (4) of a trailer, indicated by numeral (5). The trailer in this case is a light duty

luggage or goods trailer having a single pair of wheels (6) that do not have any brakes.

Referring now more particularly to Figures 2 to 5 of the drawings, the existing trailer coupling assembly (2) comprises a fixed coupling member (7) having a base (8) that is bolted to the drawbar (9) of the trailer. The fixed coupling member has an integral, part-spherical socket (10) for cooperation with the well-known part-spherical towing ball of a conventional towing bar (not shown).

A keeper member (11) having an integral handle (12) is attached to the fixed coupling member by means of a pivot (13) positioned towards the front (14) of the coupling. The functional part (15) of the keeper member is located lowermost and rearwards and forms part of the composite part-spherical socket that receives the part-spherical towing ball in use.

The movement of the keeper member is illustrated clearly in Figure 3 in dotted lines in which the upward and rearwards movement of the keeper member as it rotates to a limited extent about the pivot (13) from its operative position to its inoperative position is shown. With the keeper member in the latter position the socket can be installed on a towing ball whereas in the in the normal operative position of the keeper member a towing ball is either held captive within the socket or prevented from being introduced thereto past the entrance (16) to the socket.

The fixed coupling member has a passage (17) opposite an elevated upper region of the keeper member and in registration with a locking recess (18) in keeper member in its operative position. This passage normally receives a spring loaded locking pin for retaining the keeper member in its operative position unless the locking pin is withdrawn and held manually against the spring action. This locking pin is removed and discarded for the purposes of this invention.

In this embodiment of the invention in which the expedient is applied by way of an accessory, the accessory has a housing (19) bolted to the base (8) by means of bolts (20) attaching the base to the drawbar. The housing has a carrier (21) from which a locking pin (22) extends into the passage (17) of the fixed coupling member and in alignment with the locking recess (18) in the keeper member in its operative position.

The carrier (21) is movable coaxially with the pin (22) in the passage. An operating lever (23) extends transverse to the carrier (21) and is pivotally attached to the carrier so as to be able to move it axially between two terminal positions. The first terminal position is illustrated in Figure 2 and is one in which the locking pin (22) is engaged in the locking recess (18) in the keeper member. The second terminal position is illustrated in Figure 3 and is one in which the locking pin (22) is withdrawn from the locking recess (18).

It will therefore be understood that, with the locking pin engaged in the locking recess as illustrated in Figure 2, the coupling cannot be attached to, or released from, a towing ball. However, with the locking pin withdrawn from the locking recess as illustrated in Figure 3, the coupling cannot be properly attached to a towing ball because the socket cannot be locked in its closed condition.

The carrier has attached to its end opposite the locking pin (22) the inner cable (24) of a control cable (25) of the type having an outer sheath as indicated above.

The other end of the control cable is attached to a wheel unit generally indicated by numeral (26) in Figure 6. The wheel unit has an axially movable locking element in the form of a locking stud (27) that is attached to a follower (28) movable in unison with the inner cable (24) and coaxially in a guide (29) within a wheel unit housing (30). The attachment is by way of a compression spring (31) and a flexible tie (32) the purpose of which is described below.

The wheel hub (33) has a hole (34) therein that lies in the path of the locking stud (27) so that, when the stud is urged towards the hub, it will automatically snap into engagement with the hole when the wheel rotates to a position in which the two are in registration.

The follower (28) is attached to the inner cable (24) of the control cable (25) so that the follower will move in response to movement of the carrier (21).

The arrangement is such that rearwards movement of the operating lever (23) withdraws the locking pin (22) from the locking recess (18) in the keeper member and simultaneously imposes a thrust on the follower (28) so that the locking stud is urged towards the wheel hub (33). In the event that the stud is not in registration with the hole (34) the compression spring will become compressed with the flexible tie (32) giving way to enable this to take place.

The locking stud will then be urged against the surface of the hub and in the event that the wheel is rotated it will immediately snap into engagement with the hole (34) to prevent further rotational movement of the wheel when the hole reaches alignment with it.

On the other hand, with the operating lever (23) in its forward position, as illustrated in Figure 2, the locking stud is withdrawn from the hole and indeed from the entire surface of the hub and the locking pin (22) is engaged in the in locking recess (18) in the keeper member.

It will therefore be understood that, with the security device in the latter position towing of the trailer is allowed to take place freely and the keeper member is locked in its operative position to prevent withdrawal of the towing ball from the socket. With the security device in the latter position, ie with the locking pin withdrawn and the locking stud (27) urged into engagement with the wheel hub, excellent security is afforded in that the coupling cannot be effectively attached to a towing ball and the trailer wheel will lock immediately an attempt is made to tow it.

Finally, the carrier member is provided with two spaced holes (35) that cooperate selectively with a key operated lock (36) fixed to the wall of the housing (19) as shown in Figure 4. The lock can conveniently be of the type in which a tumbler cylinder unit (37) is spring loaded to an outer position (indicated in dotted lines) and has a peg (38) for engagement selectively in one or other of the holes (35) when it is in its inner locked position. The carrier member and operating member can thus be releasably locked in either of the positions described above according to requirements. As stated above, in the former position, the trailer is effectively locked to the vehicle and the trailer can be towed freely. In the latter position the trailer cannot be effectively attached to a towing vehicle and the trailer wheel will lock immediately tearing his attempted.

It will be understood that the embodiment of the invention described above can be fitted to an existing trailer and, in such a case, supply of the security device may take place in the form of an accessory kit comprising the housing and associated parts; the control cable ; and the wheel unit housing. It is, however, envisaged that the security device provided by this invention will be highly effective as an original installation in a trailer and in such a case appropriate modifications will be made.

The embodiment of the invention described above can be varied in many ways without departing from the scope hereof, the described embodiment simply being illustrative of the principles of the invention.