Unattended trailer hitch lock

A trailer hitch lock provides a finned, external shell around a centrally-disposed lock assembly. The material of the shell, its distribution of fins, and the fin dimensions all cooperate to defeat a destructive attack on the lock by a portable angle grinder.

FIELD OF THE INVENTION

The present invention relates to a trailer hitch lock that prevents the theft of boats, lawn care equipment, and snowmobiles that are carried on a trailer but that may be parked and unattended for extended periods of time.

BACKGROUND OF THE INVENTION

A multitude of vehicles and equipment are carried on a trailer that connects to a towing vehicle with a ball hitch system. In such a system, the towing vehicle has a ball hitch mounted at the rear of the vehicle. The trailer has a forward trailer tongue with a semi-spherical receiver that fits over the rounded top of the ball on the towing vehicle. To aid in guiding the ball into the receiver and to reinforce the receiver, the bottom of the receiver often has a coupling, such as a flared flange. Once in position over the ball, the receiver is secured by an armature that is extended around the lower part of the ball by rotating an external handle down and toward the hitch. Such a system has been used for decades and is prevalent in a wide variety of towed vehicles, equipment, cargo, and mobile homes.

A similar system with a square-shaped hollow receiver tube is shown in U.S. Pat. No. 4,807,899 and US Publication 2015/0258866.

Trailers and their cargo are often parked in a place where it is convenient for the owner to pull in and disconnect the trailer. A dolly wheel and crank are often used to adjust the height of the connection frame to remain level. If left unprotected, however, there is little that prevents a thief from connecting to the unprotected receiver and pulling off. A trailer hitch lock secures the receiver from connecting to an unauthorized ball hitch.

Conventional trailer hitch lock systems engage the semi-spherical opening of the receiver with an obstruction that blocks access by an unauthorized vehicle. See U.S. Pat. Nos. 3,233,913; 5,222,755; and 5,743,549.

One type of locking system has an engagement lip that engages the receiver's flared flange and includes an insert into the receiver portion of the trailer hitch. See, U.S. Pat. Nos. 7,040,646; 7,204,508; 7,909,351; 8,020,885; and 9,701,169 (locking ball insert) and US published application nos. 2006/0163842 (flared flange lock), 2006/0208458, and 2006/0284398 (flange lock with “2” armature).

Despite the advances in lock designs that are found in the prior art, trailers continue to be stolen by thieves wielding battery-powered angle grinders. These thieves attack the very material of the lock and can cut through the vulnerable points in minutes. When the trailer is unattended, theft by grinder attack is a very real possibility.

It would be advantageous to provide a trailer lock exhibiting an enhanced resistance to angle grinder attacks.

Conventional trailer locks also typically have an exposed locking mechanism that makes the system vulnerable to moisture and rusting of crucial parts. There are few things more frustrating to a boat owner than going to great lengths to secure the trailer against theft only to have the lock become rusted shut so as to prevent access by its owner.

It would be desirable to have a trailer lock that was also protected against moisture infiltration and rusting or degradation of crucial mechanisms needed to remove the trailer lock.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a trailer hitch lock that would protect the locked hitch from theft and destructive attack by an angle grinder.

It is also an object of the invention to have a trailer hitch lock that was protected from internal rusting due to moisture.

In accordance with the above and other objectives of the invention that will become apparent from the description herein, a trailer hitch lock according to the invention comprises: (a) a hardened core that includes a locking mechanism operably movable vertically from a first unlocked position into a second locked position, and (b) a grinder resistant shell surrounding said core that is shaped to engage a flared lip of a trailer hitch receiver and is characterized by a plurality of radially extending fins that are made from a soft material that clogs coarse aluminum oxide grit of a cutting disc. Optional additional features include one or more moisture-resistant seals around key movable parts to provide resistance to moisture infiltration and a freely rotating ring around the locking mechanism that foils drill-based attacks on the locking mechanism.

The trailer hitch of the invention provides an effective locking system for an unattended trailer that resists destructive attack with an angle grinder, whether battery-powered or AC-powered. Such additional security is enhanced with an anti-drill ring that hinders a direct, drill-based attack on the locking assembly and enhanced moisture resistance with seals at key junctures.

DETAILED DESCRIPTION

A first embodiment of a trailer hitch lock according to the invention is conveniently described with reference to the attached figures.

As shown inFIG.1, the grinder-resistant trailer hitch lock according to the invention includes a lock assembly1that fits within a vertically-oriented, central chamber within a grinder-resistant shell2. Lock assembly1includes: (a) lock body3that houses lock mechanism4and (b) threaded end cap5that seals keyhole6from dirt and moisture.

The present hitch lock is installed onto a trailer's hitch receiver101by slipping slot10of shell2onto the coupling member of a hitch receiver via channel101so that lock assembly1becomes positioned below the recess that would receive the semispherical ball of the hitch connection and is thereby positioned to extend vertically up and into the hollow receiver portion. A key is inserted into keyhole6to push lock assembly1upwardly and into that recess. The coupling member can take the form of a radial flange, cast sleeve coupler, sleeve lock, or ring but is conveniently described with reference to a conventional hitch flange.

The Locking Assembly

Lock mechanism4is disposed within shell2. Shell2has an upper chamber23with a trailer slot10that receives a trailer hitch receiver in channel101between upper shoulder19and lower shoulder20. Middle chamber18is where the hitch receiver is engaged by lock mechanism4. Lower chamber17is where lock mechanism4retracts when unlocked and withdrawn from middle chamber18. Collectively, upper chamber23, middle chamber18, and lower chamber17form lock channel24.

The lock operates when lock mechanism4is pushed upwardly into middle chamber18. As the key turns locking cam16, first and second arms11,12are driven radially outwardly by contact with locking cam16as the key turns lock mechanism4and cam16. When in the locked position (FIG.1), the cam blocks radial retraction of first and second arms11,12. When the key is turned to the unlocked position, cam16is turned so as to allow locking arms11,12to radially retract and lock mechanism4may then be lowered into lower chamber17. Once first and second locking arms11,12are retracted, the whole lock body3can move down into lower chamber17. These steps secure the lock over the hitch coupling and obstruct access to the hitch recess until the lock is removed.

As shown inFIGS.1-3, locking ring15is secured in position in middle chamber18with opposing set screws30that can only be accessed when the lock is in the unlocked position and lock assembly1is removed. The lock body slider set screws30can be advanced to extend into vertical groove31formed in shell2to limit the travel of lock body3. Retaining ring set screws32secure locking ring15within middle chamber18of shell2. Set screws32are accessible only when lock body3is in its lowest position thus makes the manufacturing process easier because it allows the locking ring15to be securely fastened into shell2without requiring any post-machining of shell2. Additionally, having the set screws accessible only from middle chamber18does not expose externally-accessible fasteners that could represent a potential security weak point.

Lock mechanism4is secured within lock body3with lock housing set screw25that extends radially inward from lock body3into a threaded opening26in lock mechanism4. Lock mechanism set screw27secures tumblers28within lock mechanism4.

Sealing rings are used at junctions to help prevent moisture from intruding into lock assembly. For example,FIGS.1-3show an upper seal21in the form of a U-cup seal around the base of locking cam16and a lower O-ring22at the junction between the lock body and its cap.

The bottom lock opening of the lock assembly is protected from a drill attach with anti-drilling ring7. As shown inFIG.4, freely rotating anti-drill ring7is held in position against shoulders8of lock mechanism4. Anti-drill ring7has a tapered central opening71of a depth sufficient to allow a key to pass through the central opening9and engage lock mechanism4. The tapering angle72of the inner walls of opening9are, however, smaller than the typical angle of a drill bit. Most drills are ground to an angle of about 118° so any opening angle that is substantially less, e.g., an angle72within the range of 75° to 100°, will cause the drill bit to engage the tapering sidewalls and spin freely without cutting effect. A drill bit100of sufficiently small diameter to pass through opening9may grind away internal parts of the lock but cannot extend to the peripheral tumblers so as to drill out the lock as a whole and disengage the internal mechanism that locks the assembly into an obstructing position within the hitch receiver.

Threaded end cap5is then screwed into the threaded bore37at the bottom of lock body3. This protects lock assembly4from fouling by water, dirt, grit, and the like.

The Outer Shell

Surrounding locking assembly1is a grinder-resistant shell2. Shell2interferes with, and preferably prevents, destructive attack against the lock assembly1by an angle grinder disc. This shell2can be made of a relatively softer metal that clogs the grit of a grinding wheel or it can be made from a relatively hard metal that is not readily cut, ground, or scored by typical grinding wheel grit. Shell2can be cast as a single, unitary piece (FIG.1) or formed in separate parts that are joined together (FIG.5).

Permanent mold casting is the preferred process to make the grinder resistant shell2of the present invention.

A second embodiment of the invention is shown inFIG.5which shows the use of a three-piece shell. This design uses a hardened steel core coupler33sandwiched between a top shell piece34and a bottom shell piece35that are joined together around core coupler33. Top shell piece34and bottom shell piece35may be solid or exhibit internal fins (not shown) in the same manner as discussed above.

The top and bottom shell pieces34,35may be made of a material that is relatively softer than the grit of an angle grinder wheel to clog the grit to reduce the grinder's cutting efficiency and thereby drain the tool's battery with little cutting to show for the efforts. Conversely, the top and bottom shell pieces34,35may also be made of a material that is hard and relatively hard to scratch with a typical carborundum cutting disk.

A wide variety of metal joining methods can be used to join the top and bottom shell pieces34,35, such as, thermoset adhesives such as epoxy, mechanical fasteners such as rivets, and fusion methods such as welding. Welding is preferred.

Once positioned and secured to each other, the three-piece shell is preferably greater than 35 mm, preferably 37-55 mm, and even more preferably 40-50 mm in thickness from any direction that is accessible once the lock is installed on a trailer hitch. A typical angle grinder disc penetrates about 35 mm so a shell thickness that is greater than this depth will act as a visual and functional deterrent in the decision of whether to attempt to attack this lock.

A third embodiment of a lock according to the invention is shown inFIG.6. In this embodiment, the cast shell40surrounds the locking core41and middle section42of the coupler. Preferably, the cast shell40is made from steel or aluminum. This embodiment allows cast shells of ever greater diameter to defeat even the largest of portable grinder disks while also eliminating the need for lock assembly. This shell can be hollow or internally finned.

Shell2protects lock assembly1from destructive attack with a series of 7-15 vertical ribs43. In the exposed side of the lock (as shown inFIGS.2,3,7, and8), ribs43extend between upper horizontal support44, central horizontal support45and lower horizontal support46. On the side that faces the trailer (FIG.3), some of ribs43only extend between a lower central support47and lower horizontal support46so as to leave slot10unobstructed and able to receive the hitch coupling in channel101. Ribs43may, or may not, extend to a surface on the bottom or top of the rib.

Outer shell2is preferably made from a material that is relatively softer than the metal of the lock assembly1and is preferably chosen to clog the aluminum oxide grinding wheels most commonly used. Suitable materials include aluminum, aluminum alloys, aluminum-containing polymeric composites, and brass. Aluminum and its alloys are preferred. It is also useful, however, to make outer shell2from a material or metal that is relatively hard to cut or scratch with the grit on a conventional grinder.

Die casting is a cheaper and faster process for casting aluminum parts. Die cast parts are also too porous to weld.

The preferred alloys that are suitable shell materials have a copper content less than 0.5%. It is essential that the copper content of the alloys is low in order for it to be welded in a commercially viable process. The main purpose of copper in aluminum alloys is to increase the alloys reactivity to heat treatment, however, increased copper also decreases weldability and reduces corrosion resistance. Table 1 below identifies some of the suitable aluminum alloys for use in the shell of the invention. The values indicate maximum limits unless shown as a range or a minimum.

Table 2 lists the hardness of suitable alloys.

Preferred materials for the shell are weldable aluminum alloys having a Knoop hardness of at least 50, and more preferably a Knoop hardness within the range of 70-140.

The radial thickness of fins23and horizontal supports24,25,26,27should be sufficient to exceed the reach of a typical battery-operated angle grinder disk. Such disks can typically cut to a depth of about 35 mm so fins23should extend at least 35 mm from the outer surface of the hardened lock assembly1. Preferably, fins23extend radially away from the outer surface of lock assembly1by a distance within the range of 36-100 mm, more preferably a distance within the range of 40-75 mm.

Similarly, fins43should be spaced around the lock so that a grinder blade must engage at least two, and preferably three of the fins as it cuts toward the lock assembly. The additional material hastens the rate of clogging of the coarse blade grit as well as the drain on the battery as the user presses harder to continue to see the same rate of cut but with an even more dull disk.

Surprisingly, the presence of horizontal supports introduces an extra level of difficulty when a thief attempts to defeat the lock of the present invention. Compared to a planar cut test through just a set of only vertical fins, the connection of the horizontal members with all of the fins requires the attacker to make twice the number of cuts to remove any singular fin. Additionally, the distribution of the fins around the surface (e.g., a radial fin-to-fin distribution angle within the range of 30-40°, preferably an angle of about 36° fin-to-fin distribution) limits the advantage of removing any singular fin when attacking with an angle grinder. Instead, the attacker must remove at least two neighboring fins to gain any sort of geometric advantage with an angle grinder disc. As noted above, this accelerates the clogging actions on the disk and increases the battery drain of the device.

The external fins are preferably straight although it is within the scope of the invention to provide fins that are non-straight, e.g., exhibiting a wavy pattern or which are not at right angles relative to an adjacent fin.

It is understood however that the description above is intended to describe preferred embodiments and is not intended to limit the scope of the appended claims.