Security device for trailer coupling pin

The coupling pin of the trailer of a tractor-trailer rig is provided with a theft prevention device for preventing the unauthorized coupling of unattended trailers. The device includes a truncated conical housing having a cylindrical sleeve which is secured to the inner base of the cone and is adapted to receive the coupling pin. The coupling pin is held within the sleeve by means of a pair of opposed, spring-biased locking jaws which normally protrude through a pair of opposed slots in the sleeve. In order to engage the reduced diameter portion of the coupling pin. The locking jaws are mounted on a pair of U-brackets. The brackets carry a pair of camming surfaces which are engaged by the wing cams of a key-operated lock. The lock is preferably recessed within the housing so that it cannot be sheared off during use. The invention has the additional utility of serving as a safety device for preventing the movement of a trailer during unloading operations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to devices for preventing the unauthorized coupling 
of tractors to unattended trailers. 
2. Description of the Prior Art 
It is well known that the trailers of tractor-trailer rigs are often parked 
in isolated spots or left unattended. In recent years there has been an 
increasing problem with the hijacking of such vehicles by unauthorized 
persons. Aside from the theft prevention problem, there is a further 
safety problem associated with the naked exposure of coupling pins at 
loading docks and the like. In these instances it is possible for a 
tractor to be coupled to a trailer while such trailer is being unloaded by 
means of a forklift or the like. In such instances severe injury has been 
inflicted on persons who were unloading a trailer when it was mistakenly 
pulled away from the dock area. 
Thus, there is an acute need in the trucking industry for a simple, safe 
and reliable device for rendering trailers of tractor-trailder rigs 
insusceptible to coupling with unauthorized vehicles. 
SUMMARY OF THE INVENTION 
In accordance with the present invention there is provided a device which a 
single operator may lock in place over the coupling pin of the trailer of 
a tractor-trailer rig thereby preventing unauthorized coupling to such 
trailer. In a preferred embodiment the device of the present invention 
includes a truncated conical housing having a solid base and made from a 
high chrome alloy steel. A cylindrical sleeve member is welded to the 
inside of the base of the cone and extends upwardly therein for 
substantially the height of the cone. The sleeve has an inside diameter 
slightly greater than the outside diameter of a conventional coupling pin 
so that it may slidably receive the coupling pin. The sleeve is provided 
with a pair of opposed recesses which receive a pair of spring-biased jaw 
elements whch extend through the wall of the sleeve and engage the reduced 
diameter portion of the coupling pin to lock the pin in place. The jaw 
elements are secured to a pair of pivotally mounted U-shaped carriers 
which are normally spring biased so as to urge the jaw elements inwardly 
through the sleeve recesses. The carriers include camming surfaces which 
are adapted to engage a wing cam operable by means of a lock. 
In operation, the device may be slid onto the coupling pin whereby the jaw 
elements automatically retract and then lock within the reduced diameter 
portion of the coupling pin. Once locked in place, the device may be 
removed only by means of an authorized person having a key. If an 
unauthorized tractor backs into engagement with a trailer carrying the 
device, the coupling pin mating element of the tractor will simply slide 
along the outer surface of the cone thereby raising the cone and coupling 
pin and preventing any damage to the trailer. 
A primary feature of the invention is the provision of an anti-theft device 
for preventing the unauthorized taking of an unattended trailer. 
A further feature of the invention is the provision of a device which may 
be secured to the coupling pin of a trailer while it is being unloaded at 
a dock to prevent the removal of the trailer. 
Another feature of the invention is the provision of a relatively simple, 
safe and reliable security device which may be secured in place and 
removed by a single operator. 
Yet another feature of the invention is the provision of a lock-on cover 
for a coupling pin that will prevent damage to the trailer if an 
unauthorized coupling is attempted.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings and in particular to FIG. 1, there is shown a 
coupling pin 10 of the type normally attached to and downwardly projecting 
from the front portion of the trailer of a tractor-trailer rig. The 
coupling pin is substantially cylindrical and includes a reduced diameter 
portion 12. 
The device for securement over the coupling pin to serve as a lock-on cover 
is generally designated by the reference numeral 20. Device 20 includes a 
truncated conical housing 22 which comprises a sloped wall portion 24 and 
a flat base portion 26. Housing 20 is made from a material which will 
resist relatively high impacts, and in a preferred embodiment, the housing 
is made from a high chrome alloy steel. 
A cylindrical sleeve 30 is welded to the inside of base 26 and extends 
substantially the entire height of device 20. Sleeve 30 has an inside 
diameter slightly larger than the outside diameter of coupling pin 10 and 
is adapted to receive the coupling pin therein after it passes through a 
cover 31. As shown in FIG. 1, cover 31 is a flat sheet member which 
includes a central opening 32 for passing the coupling pin and four holes 
34 which align with holes 36 in boss elements 38 for securement of the 
cover to the cone by means of fasteners (not shown). 
The lock assembly 39 for locking coupling pin 10 within sleeve 30 will now 
be described in detail with reference to FIGS. 1-4. Sleeve 30 includes a 
pair of opposed horizontal slots 40, 41 which are adapted to receive a 
pair of jaw elements 42 and 44 respectively. Jaw elements 42, 44 include 
sloping cam surfaces 46, 47 the function of which will be explained in 
detail below. Elements 42, 44 are secured by welding or the like to a pair 
of jaw carriers 50, 52 whch are pivotally mounted on a U-bracket 54 by 
means of a retainer pin 56. The rear face 60 of U-bracket 54 is secured by 
welding or the like to the exterior surface of sleeve 30 so that carriers 
50, 52 substantially surround sleeve 30. Carriers 50, 52 are spring biased 
inwardly by means of a pair of coil springs 64, 66. Springs 64, 66 are 
received within bosses 68, 70 on the carriers and within bosses 72, 74 on 
the inners surface of cone 22. 
Springs 64, 66 normally urge jaw elements 42, 44 to the locked position 
illustrated in FIG. 2. With lock assembly 39 in the position shown in FIG. 
2 the device 20 may be lifted into engagement with a coupling pin whereby 
the pin slides within sleeve 30 until it engages cam surfaces 46, 47, 
thereby forcing the jaw elements outwardly against the bias of springs 64, 
66. When the coupling pin is fully inserted into sleeve 30 the jaw 
elements 42, 44 are urged into the reduced diameter portion 12 of the 
coupling pin thereby locking the device 20 to the pin 10. 
With reference to FIGS. 3 and 4 the unlocking of device 20 will now be 
described. Lock assembly 39 includes a tubular key-operated lock 80 whch 
is operable to rotate a wing cam 82 having wing elements 84, 85. Wings 84, 
85 are adapted to engage a pair of cam surfaces 86, 88 which are, in turn, 
secured to pivotally mounted carriers 50, 52. Thus, upon actuation of lock 
80 and the turning of wing cam 82 (in a clockwise direction as illustrated 
by the arrows in FIG. 4), cam surfaces 86, 88 are urged outwardly against 
the bias of springs 64, 66 to the position illustrated in FIG. 3 where jaw 
elements 42, 44 are fully withdrawn from recesses 40, 41. In this position 
the device 20 may be removed from coupling pin 10 thereby exposing the 
coupling pin for authorized coupling with a tractor. 
In the preferred embodiment the cone, cylindrical sleeve and jaw elements 
are made from a high chrome alloy steel. In the alternative, these 
elements have been made from a conventional mild steel; however, any 
suitable impact resistent material may be used. Although the carriers 50, 
52 have been illustrated as together forming a rectangle, the carriers may 
be curved on a radius at the corners or otherwise formed so that they may 
be easily stamped. In the preferred embodiment the inside diameter of 
sleeve 30 has been found to be optimized at 27/8 inches with slots having 
a height of approximately 11/2 inches.