GB2235268A - Anti-tamper nuts and bolts - Google Patents

Abstract

A locking nut (or bolt) for securing motor vehicle wheels, comprises a screw-threaded fastening part 12 mating with a driving part 14 which is engageable by a spanner, Allen key or screwdriver. The driving part 14 is formed with pins 26 projecting from an annular flange 22, and the fastening part 12 is provided with recesses 28 lying on an annular recess 24. The axial pressure needed to maintain the two parts 12, 14 in engagement while exerting torque, is reduced. <IMAGE>

Description

TITLE: Locking Nuts and Bolts Field of the Invention The invention relates to security screw-threaded fastening members such as nuts or bolts in which the head is removable from the screw-threaded fastening portion. The invention is particularly but not exclusively concerned with the provision of locking wheel nuts and bolts for motor vehicles.

Background of the Invention Locking wheel nuts and bolts for motor vehicles are well known, for example from GB 2006371 and GB 1250110. The known principle of construction is that each nut or bolt is formed in 2 parts, namely a screw-threaded fastening part which has no head thereon for engagement by, for example, a spanner; and a removable headed part having a surface shape that is engageable by that spanner. The two separable parts can be placed into mating engagement by moving the headed part axially against the fastening part, so as to bring an array of axial pins or a particular pattern of projecting lobes on the headed part into engagement with co-operating recesses in the unfastening part.The pattern of the size and distribution of the pins or lobes and recesses provides for security, in that only a headed part with pins or lobes that match the apertures in the fastening part can be used to transfer rotational torque to the fastening part.

There is a disadvantage in the use of such locking wheel nuts. As torque is applied to the headed part, there is a tendency for the headed part to move axially away from the fastening part so that the mating engagement is lost. To resist this, considerable axial pressure must be applied when tightening or unfastening the wheel nuts. It has been proposed to provide the headed part with a cylindrical flange portion completely surrounding the array of pins or lobes, and to provide the fastening part with a peripheral rebate to accept that flange. In that way, the flange to a certain extent maintains the two parts of the fastening in axial alignment and reduces the axial pressure needed to maintain the two parts in engagement during fastening or unfastening.

Where the mating engagement is provided by an annular array of projecting pins, it has also been proposed to provide a similar cylindrical flange projection internally of the annular array of pins. Although this solution has helped to a certain extent in reducing the axial pressure needed to maintain the two parts in engagement during fastening and unfastening, it is not a total solution and the original problem still remains.

When the mating engagement between the two separable parts of the wheel nuts or bolts is provided by an array of axial pins, there is a further disadvantage in that if excessive torque is applied either to fasten or to unfasten the wheel nut or bolt, the pins can shear in the plane of abutment of the two separable parts of the wheel nut or bolt. There is therefore a tendency to err on the side of caution and fasten the nuts or bolts to less than their optimum tightness, and not only does this introduce the risk of the wheel nut or bolt working loose during use of the vehicle, but also an under -tightened locking wheel nut or bolt can be removed using a headed part with only one axial pin, which of course will mate with any combination of axial holes in the corresponding fastening part.Alternatively an under-tightened wheel nut or bolt can sometimes be removed by inserting the point of a punch into the outer end of one of the recesses in the fastening part, and striking the punch with a hammer at a small angle to the plane of the wheel, so as to provide an impact torque to release the nut or bolt. Alternatively an under -tightened nut or bolt can sometimes be removed using a plumber's wrench to grip the cylindrical outside of the fastening part.

It is an object of the invention to overcome some or all of the above disadvantages.

Suo-ary of the Invention The invention provides a screw-threaded fastening member formed in two parts, namely an unheaded screw-threaded fastening part and a removable headed part having a surface shape engageable by a screwdriver, key or spanner for rotation thereof, with an array of twoor more axial pins arranged on a circle around the headed part being engageable in a cooperating array of pin recesses arranged on a circle around the fastening part to enable rotational torque to be transferred through the pins from the headed part to the fastening part; wherein the headed part is formed with a cylindrical flange outstanding from an end face thereof, receivable in a cylindrical recess in an end face of the fastening part, and the axes of the pins and pin recesses are on circles lying between the radial inner and outer walls of the cylindrical flange and cylindrical recess respectively.

The advantages of the particular disposition of the pins and flange in the fastening member of the invention are substantial, and not such as would immediately become apparent from a consideration of the above problems alone. The torque transmission from the headed part to the fastening part is extremely good, with very much less axial pressure needed on the spanner or brace to keep the two parts in engagement than was the case with the prior proposed wheel locking nuts and bolts.It is thought that this might be because of the engagement between both the radial outer and inner faces of the cylindrical flange with the corresponding faces of the cylindrical recess, which serve to maintain much better alignment of the two parts than with prior art proposals in which the flange engaged only an outwardly or only an inwardly facing cylindrical surface of a recessed housing in the fastening part. Furthermore, using the fastening member of the invention substantially greater torques can be transferred without aausing shearing of the pin members. It is thought that this might be because the torque transfer is not concentrated on a single plane of shear.If the axial pins extend from the headed part for an axial extent greater than the axial length of the cylindrical flange1 then there is torque transfer providing a potential shear line in the plane of the end face of the cylindrical flange. However this is not necessarily the sole plane of torque transfer. If the diameter of the pins is greater than the radial thickness of the wall of the cylindrical flange, then a significant amount of torque transfer takes place over the axial length of the flange itself, which reduces the tendency for the pins to shear.Indeed although a conventional wheel locking nut or bolt with an annular array of four locating pins to key the headed part to the locking part has been tested and found capable of withstanding only 80 lbs (36 kg) of torque before the headed part requires axial pressure to prevent it from jumping out from engagement with the fastening part, a locking nut or bolt according to the invention with a similar array of pins can withstand a torque of up to 200 lbs (91 kg) without any axial pressure being needed to keep the two parts in engagement. Similar test to destruction have shown a comparable increase in the total torque carrying capacity of essentially the same pins. This gives rise to the possibility that the hardened or tempered steel pins of the prior art locking nuts and bolts can be replaced by less expensive pins in the fastening members of the invention. The user can therefore tighten the locking nuts or bolts of the invention to a greater extent than with the prior proposed nuts and bolts, in reasonable confidence that the pins will not shear. The fastening portion is therefore not as likely to work free in use, as it can be fastened to full recommended bolt tightness. It will therefore be correspondingly more difficult to remove without the proper headed member. This added security is enhanced, however, by the fact that the location of the axial recesses for receiving the pins in an array spanning the cylindrical recess for receiving the cylindrical flange means that it is correspondingly more difficult to place a punch at a shallow angle to remove the fastening members by means of a hammer and punch.Also, a suitable choice of materials and dimensions can insure that the fastening members cannot easily be removed by means of a plumber's wrench. A relatively thin band of material is provided between the outer cylindrical surface of the fastening member and the cylindrical recess therein for receiving the cylindrical flange of the headed member, and this narrow band of material would bend and throw off the plumber's wrench if any attempt were made to remove the fastening part by gripping it around the outside.

An additional advantage of the fastening member of the invention is that the radial width of the cylindrical flange can be varied form one headed to another, so as to provide an additional variable in the relative dimensions and contours of the two cooperating parts, for additional security purposes.

Although the invention is of particular relevance to wheel locking nuts and bolts for motor vehicles, that is not the only end use. The locking nuts and bolts may be used to secure any potentially removable components from equipment normally left unguarded. For example, hammers and buckets from building site excavating equipment can be secured in place using the locking members of the invention, and locking nuts according to the invention can be used on the transom bolts on boats to secure outboard engines in position while the boats are left unattended either on a trailer or in the water.

DRAWINGS Figure 1 is an axial section through the two parts of a fastening member according to the invention; Figure 2 is an end view of the locking part only of Figure 1, viewed in the direction of the arrow A of Figure 1; and Figures 3 and 4 are perspective views of the two parts of Figure 1, after complete separation.

In the drawings, the screw threaded fastening member illustrated is a locking nut indicated generally as 10 for a motor car wheel. The nut comprises a fastening part 12 and a headed part 14, of which the fastening part 12 is formed with an internally screw-threaded bore 16 and a conical bearing face 18. It will be appreciated that the shape and identity of the screw threaded part 16 and the bearing face 18 are dictated by the motor vehicle and the motor vehicle wheel with which the fastening member is to be used. For example, some vehicles require a conical bearing face 18, whereas others would require the bearing face to be planar.

Some vehicles require wheel nuts in which the screw-threaded portion 16 is an internally threaded bore as in Figure 1. Others require wheel bolts in which the screw-threaded portins is an externally threaded bolt portion. All such features are therefore dictated by the cooperating part with which the fastening member has to engage, and form no part of the invention.

Similarly the headed part 14 is illustrated in Figure 3 as having a hexagonal head 20 which in use would be engaged by spanner or wheel brace. Equally the headed portion 14 could be provided with a screwdriver slot or with a hexagonal recess for an Allen key, for actuation by a cooperating torque-imparting member. Conventionally, wheel nuts for motor vehicles are provided with hexagonal heads as illustrated in Figure 3.

Oatstanding from an end face of the headed member 14 is a cylindrical flange 22 which engages in a cylindrical recess 24 in-the anchorage member 12. The flange 22 and recess 24 are made to reasonably accurate tolerances, so that when the headed part 14 is pushed onto the anchorage part 12 in the direction of the arrow A the cylindrical surfaces of the flange and recess are in engagement to prevent twisting of the headed member relative to the anchorage member.

An array of four blind bores is formed into the headed member 14, each bore being centered on a line midway between the outer and inner cylindrical faces of the flange 22. Into each bore is fitted an axial pin 26 which is a friction fit in the bore. Each pin 26 is aligned with a corresponding recess 28 in the fastening portion 12. The bores 28 are deeper than the recess 24, and the pins 26 extend from an end face 30 of the headed member 14 by more than the axial extent of the cylindrical flange 22, so that when the headed member 14 is moved in the direction of the arrow A into engagement with the anchorage member 12 the pins 26 are fully received in the bores 28, and the flange 22 is fully received in the recess 24. When torque is applied to the hexagonal head 20, there is little tendency for the headed part 14 to twist and jump out of its engagement with the anchorage part 12.Furthermore the torque transfer between the two parts is not confined to a single plane, so that the tendency for the pins to shear is reduced.

It will be apparent from Figure 4 that there is only a limited opportunity for inserting a punch at a low angle into the outer extremity of the bores 28 in order to obtain an impact torque and effect unauthorised removal of the nut 12. Also because the outer wall portion 32 between the outer periphery of the anchorage part 12 and the annular recess 24 is relatively thin, any attempt to grip the anchorage part of the wheel nut by means of a wrench around its outer circular periphery would result in bending of that outer portion 32, providing a surface which would cause the wrench to slip off.

In the case of a wheel nut as illustrated in the drawings, or a wheel bolt for similar use on motor vehicles, it is desirable to cover the outer exposed face of the anchorage part 12 with a decorative plastics cap. Some users may prefer the decorative plastics cap to have a hexagonal head matching that of the other wheel nuts or bolts on the vehicle, for aesthetic purposes. This does however carry with it the risk that a potential thief could remove one or more of the other wheel nuts before encountering the locking nut, and then leave the wheel in an unsafe condition. Other users may therefore prefer the decorative plastics cap to have a distinctive colour or appearance. Either way, such a decorative cap or cover is preferably secured by having a cylindrical flange which engages either the internal or the external cylindrical surface of the groove 24. This gives rise to the possibility of having a single sized decorative cap which would fit two alternative sizes of wheel nut or wheel bolt, engaging the smaller of those two sizes by engagement with the outer cylindrical surface of the recess 24, and engaging the larger at the inner cylindrical surface.

Claims (6)

CLAIMS:

1. A screw-threaded fastening member formed in two parts, namely an unheaded screw-threaded fastening part and a removable headed part having a surface shape engageable by a screwdriver, key or spanner for rotation thereof, with an array of two or mobs axial pins arranged on a circle around the headed part being engageable in a co-operating array of pin recesses arranged on a circle around the fastening part to enable rotational torque to be transferred through the pins from the headed part to the fastening part; wherein the headed part is formed with a cylindrical flange oustanding from an end face thereof, receivable in a cylindrical recess in an end face of the fastening part, and the axes of the pins and pin recesses are on circles lying between the radial inner and outer walls of the cylindrical flange and cylindrical recess respectively.

2. A screw-threaded fastening member according to claim 1, wherein the pins outstand from the end face of the headed part by an axial length greater than the axial length of the cylindrical flange.

3. A fastening member according to claim 1 or claim 2, wherein the pins are of a diameter greater than the wall-to-wall thickness of the cylindrical flange.

4. A fastening member according to any preceding claim, wherein the cylindrical recess in the fastening part is formed sufficiently close to the outside wall of the fastening part that the outer wall is weakened and will collapse inwardly on attempted gripping of the fastening part by a gripping wrench.

5. A fastening member according to any preceding claim, being a wheel locking nut or bolt for a motor vehicle.

6. A fastening member substantially as described herein with reference to the drawings.