GB2082711A

GB2082711A - Tamper resistant arrangement

Info

Publication number: GB2082711A
Application number: GB8123718A
Authority: GB
Original assignee: Rolls Royce Motors Ltd
Current assignee: Bentley Motors Ltd
Priority date: 1980-08-02
Filing date: 1981-08-03
Publication date: 1982-03-10
Also published as: GB2082711B

Abstract

A tamper resistant fixing comprises a hexagonal headed screwthreaded bolt 4, a cylindrical distance piece 5, a cap 12 and a circlip 11.The cap 12 is made of a hardened material, defines an internal groove 14 and has an internal diameter slightly greater than the external diameter of the distance piece. The distance piece is formed with an external groove 10 which accommodates the circlip 11. After two parts have been fixed together by the bolt in a desired relative position, with the distance piece clamped between one of the parts and the head of the bolt 4, the cap 12 is pushed over the bolt head and distance piece until the circlip 11 springs into the groove 14 to lock the cap on. The bolt 4 may be replaced by a screwthreaded stud and associated nut. The bolt or stud itself may be hardened. The cap 12 may be flanged to prevent access to the fixing. The distance piece may be made integral with the bolt head. A bolt and nut may replace the bolt 4 in which case the distance piece is sandwiched between one part to be fixed and the nut and the head of the bolt is welded to the other part. Another tamper resistant arrangement described is an adjustable stop. <IMAGE>

Description

SPECIFICATION A tamper resistant arrangement The present invention relates to a tamper resistant arrangement such as a fixing or an adjustment.

Tamper-resistant fixing bolts are well known. In an example of one such bolt an attempt to remove the bolt results in complete destruction of the bolt.

In other fixing arrangements releasing the fixing is possible but not without leaving tell tale signs that the fixing has been tampered with. Examples of this type of fixing are described in British Patent Specifications numbers 1,409,502, 1,41 8;530, 1,526,428 and 2,014,680. These arrangements are not suitable, however, where it is necessary to prevent or at least greatly inhibit unauthorised release of a fixing. Such a requirement is now preferred in many applications, particularly, although not exclusively, in the automobile field. It may for example be necessary to prevent or greatly inhibit the altering of a setting on carburettors and/or distributors of internal combustion engines where the fixing bolts may be required to work in slotted holes for in that way maintenance of preset emission levels of combustion products are more easily achieved.

According to the present invention, there is provided a tamper resistant arrangement comprising a rotatable member, a locking member, a distance piece associated with the rotatable member and grooved to accommodate the locking member, and a protective cap also grooved to partially accommodate the locking member, the cap being shaped internally so that it can be pushed over the rotatable member and distance piece to prevent access thereto and the groove therein being disposed so that, when so pushed, the groove is axially aligned with the groove in the distance piece whereby the cap is axially locked with respect to the distance piece by the locking member.

A preferred embodiment of the invention may comprise any one or more of the following advantageous features: (a) The tamper resistant arrangement is a fixing for fixing two parts together and the rotatable member is a fixing device which may be rotated so as to tighten the fixing and the distance piece is disposed in use between the fixing device and the parts to be fixed together, (b) The fixing device of (a) is a screwthreaded bolt, (c) The fixing device of (a) comprises a screwthreaded stud and a nut which engages the stud enabling it to be rotated, (d) The fixing device of (a) comprises a screwthreaded bolt and complementary screwthreaded nut which engages the bolt, the head of the bolt being disposed in use on the side of the parts fixed together remote from the nut, (e) The head of the bolt of (d) is welded in use to one of the parts fixed together, (f) Where one of the parts to be fixed together has slotted holes for adjustment purposes, the distance piece is formed with a spigot remote from the means for enabling the fixing device to be turned so that when the fixing device is tightened down, the spigot is forced to deform locally a relatively soft part which is to be fixed to prevent subsequent movement of this part in the direction of the slot relative to the part to which it is to be fixed, (g) Where one of the parts to be fixed has a slotted hole, the periphery of the open end of the cap is flanged to prevent or inhibit access for a lever to its open end via an open portion of the slot, (h) The fixing device is made of a hardened metal, (i) The cap is made of a hardened metal, (j) The rotatable member comprises a screwthreaded bolt and the distance piece is disposed between two internally screwthreaded nuts located on the bolt the bolt being formed so that it can be rotated relative to and moved axially of the nut to provide an adjustable stop, (k) The bolt of (j) is slotted at its end remote from the top end to provide for adjustment thereof, (I) One of the nuts of (j) or (k) is externally formed for fixing the arrangement onto another body, (m) The external formation of (I) comprises screwthreads, (n) The said another body of (I) is made of an electrically insulating material, whereby to provide for electrically insulating the arrangement from an external body to which it may be fixed, (o) The insulating material of (n) is nylon, (p) A further member of electrically conductive material is disposed between the said another body and the said one nut to provide an electrical connection to circuitry external to the arrangement, (q) The distance piece is made of hardened metal, (r) The locking member is a preferably rectangular section circlip which is first forced into the groove in the distance piece on pushing on the cap and then allowed to spring back out partially into the groove in the cap to effect locking of the cap with respect to the distance piece, (s) The periphery of the open end of the cap and the ends of the distance piece are chamfered to facilitate assembly of the fixing.

In order that the invention may be more cleariy understood, several embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows one form of tamper resistant fixing in section in which the fixing device is a bolt, Figure 2 shows another form of tamper resistant fixing in section in which the main fixing device is a threaded stud provided with a complementary nut, Figure 3 shows an alternative fixing in section to that shown in Figure 1 where the base of the bolt is accessible, Figure 4 shows an alternative fixing in section to that shown in Figure 2 where the base of the stud is accessible and is welded to one of the parts being fixed together and may be used where this part is too thin to be threaded, Figure 5 is a sectional view of a modification of the embodiment of Figure 3, Figure 6 is a sectional view of a modification of the embodiment of Figure 4, Figure 7 is a plan view of the fixing of the type shown in Figure 1 used to fix the position of a distributor relative to the engine block of an internal combustion engine, Figure 8 is a sectional view of a modification of the fixing of Figure 6, Figure 9 shows a partial view in partial section of a fixing of the type shown in Figure 5 employed to connect a distributor to the engine block of an internal combustion engine, and Figure 10 shows a tamper resistant arrangement which provides an adjustable stop.

Referring to Figures 1 and 7, a first plate 1 is shown fixed to a second plate 2 by means of a tamper resistant fixing indicated generally by the reference numeral 3. This fixing 3 comprises a hexagonal headed screwthreaded bolt 4 under the head of which an annular distance piece 5 is retained. The bolt 4 is inserted through a hole or slot 6 in plate 1 and then screwed into a complementary screwthreaded bore 7 formed in plate 2 so that the distance piece 5 is clamped between the outer face of the plate 1 and the undersurface of the head of the bolt 4.

The distance piece 5 is cylindrical and is chamfered at opposite axial ends 8 and 9 in order to facilitate the fitting of a circlip 11. Strictly speaking of course only chamfering at axial end 9 is necessary. Substantially mid-way between these ends the piece 5 is formed with a circumferential groove 10. This groove 10 accepts a locking ring in the form of a rectangular section circlip 11. The internal diameter of the groove 10 and that of the circlip 11 are such that in its unstressed state the circlip 11 has an outside diameter greater than that of the distance piece and rests loosely in the groove 10 and does not resiliently grip the base of the groove. A cylindrical cap 12 is provided which has an internal diameter slightly greater than the external diameter of the distance piece 5.The internal periphery of the open end of the cap 12 is chamfered at 13 and the cap is provided with an internal groove 14. When the fixing device is tightened, the axial position of this groove 14 is at a distance slightly less than the axial distance of the groove 10 from the end of the distance piece 5 remote from the head of the bolt 4 in order to ensure engagement of the circlip in the cap. The cap 12 is made from a hardened metal.

Referring specifically to Figure 7, plate 2 is fixed directly to the block 1 6 of an internal combustion engine. Plate 1, to which the engine distributor 1 7 is fixed, is then adjusted to the correct angular position relative to the plate 2 to set the engine timing and fixed in this position by means of the tamper resistant fixing 3 described above. After the bolt 4 is finally tightened after checking the adjustment, the cap 12 is pushed over the head of the bolt 4. The chamfered end 1 3 rides over the circlip 11 pushing the circlip into the groove 10 against its own natural resilience. When the groove 14 is aligned with the groove 10, the circlip 11 springs back into the groove 14 thus locking the cap in position over the bolt 4.To increase the security of the cap 12 by preventing access to the bolt, through the slot 6, the cap can be provided with a flange around the periphery of its open end. Such a flange, which preferably should cover the slot 6 in either extreme position of the plate 1 relative to the plate 2, is indicated in dotted line in Figure 7 and identified with the reference numeral 1 8.

Figure 2 illustrates an embodiment similar in every respect to the embodiment of Figure 1 except that the bolt 4 is replaced by a stud 24 which is threaded at both ends and which has a hexagonal nut 204 screwed onto it at its head end to provide the equivalent of the hexagonal head of the bolt 4. Parts equivalent to parts of the embodiment of Figure 1 bear the same reference numerals prefixed with the numeral 2.

Figure 3 illustrates a further embodiment similar in every respect to the embodiment of Figure 1 except that the bolt (here referenced 34) is screwed into an open as opposed to a blind bore formed in the plate 32. Parts equivalent to parts of the embodiment of Figure 1 bear the same reference numerals prefixed with numeral 3. In addition to the cap 312, the bolt 34 itself is made of a hardened material to inhibit drilling out of the bolt 34, or possibly drilling, tapping and turning, from the underside of the plate 32.

The embodiment of Figure 4 is similar in most respects to the embodiment of Figure 2 except that because plate 42 is thin the stud (here referenced 44) fits through an open, as opposed to a blind, bore in the plate 42 and carries a flange 415 which is welded at 416 to the undersurface of plate 42. Parts equivalent to parts of the embodiment of Figure 2 bear the same reference numerals but with the prefix numeral 2 replaced by numeral 4. The welding of the flange 41 5 of the stud 44 to the plate 42 means that the stud 44 cannot be made of a hardened metal.

The embodiments of Figures 5 and 6 are respectively equivalent to the embodiments of Figures 3 and 4 except that the upper plate referenced 51 in Figure 5 and 61 in Figure 6 is made of a soft metal such as aluminium and the distance piece referenced 55 in Figure 5 and 65 in Figure 6 is provided with a spigot (518 in Figure 5 and 618 in Figure 6) which is pushed into the aluminium when the corresponding bolt or nut is tightened. Alternatively a hardened distance piece may be used with a mild steel upper plate. In this way forcible adjustment of the slotted plate 51 or 61 relative to the fixed plate 52 or 62 is prevented. Parts of the Figure 5 embodiment equivalent to those of the Figure 3 embodiment bear the same reference numerals but with the prefix numeral 3 replaced by a prefix numeral 6.

Parts of the Figure 6 embodiment equivalent to those of the Figure 4 embodiment bear the same reference numerals but with the prefix numeral 4 replaced by prefix numeral 6.

Referring to Figure 8, a modified form of the Figure 6 fixing is shown in which, effectively the nut 604 and distance piece 65 are combined in a single nut/piece member 85. Thus the groove 810 (equivalent to groove 610 of the Figure 6 embodiment) is formed tn the nut/piece member 85. To accommodate this member 85 the interior of the cap 812 is differently chamfered at 81 3. In ail other respects, this fixing is the same as the Figure 6 fixing and equivalent parts are given the same reference numerals with the reference numeral prefix 6 replaced by the reference numeral prefix 8.

Figure 9 shows a detailed sectional view of a distributor 817 fixed to the engine block 820 of an internal combustion engine utilising fixings of the type shown in Figure 5. These fixings 53 connect a plate 51, to which the distributor 81 7 is mounted, to a plate 52. The plate 51 is slotted and the fixing 53 extends through the slot so that the position of the plate 51 can be adjusted relative to the plate 51 before the fixings 53 are tightened. The slot, which is not well shown in Figure 9, is referenced 6 in Figure 7.

Figure 10 discloses a tamper resistant arrangement which provides an adjusting device for, for example, a throttle lever of an internal combustion engine. In this arrangement, an externally screwthreaded bolt 104 provides a rotatable adjustment member which is slotted at 1020 at its head end and substantially hemispherically formed at its other end 1021. This bolt 104 extends in turn through a complementary internally screwthreaded locknut 1004, a distance piece 105 and a further complementary internally screwthreaded nut 1044. The nut 1044, which is made of brass and includes an integral flange 1 045, is externally screwthreaded and screwed into an annulus 1046 made of nylon or other suitable electrically insulating material.A washer 1047 of electrically conductive material is sandwiched between the nylon annulus and the flange and provides an electrical connection to external electrical circuitry (not shown). The distance piece 105 is the same as the distance piece 5 of the Figure 1 embodiment. It defines a circumferential groove 1010 substantially midway between its ends which accepts a locking ring 1011 in the form of a rectangular section circlip.

The internal diameter of the groove 1010 and that of the circlip 1011 are such that in its unstressed state the circlip 1011 has an outside diameter greater than that of the distance piece and rests loosely in the groove 1010 and does not resiliently grip the base of the groove. A cylindrical cap 1012 of hardened metal is provided which has an internal diameter slightly greater than the external diameter of the distance piece 105. The internal periphery of the open end of the cap 101 2 is chamfered at 101 3 and the cap is provided with an internal groove 1014.

The hemispherical end 1021 of the bolt 104 provides an adjustable position stop in this case for the throttle lever 1050 of an internal combustion engine. In this position shown the lever is in the idle position and through its contact with the electrical conductive bolt provides an electrical signal at the flange 1045 indicative of that fact. This signal may be used, for example, to control the fuel flow to the engine. After adjusting the position of the stop to that desired, using a screwdriver in the slotted head 1020, the cap 1012 is pushed progressively over the bolt 104 until the circlip 1011 locates in the groove 1014 to lock the cap in position in the distance piece 1 05. Further unauthorised access to the bolt 104 is thereby prevented or inhibited. If desired the flange 1045 may have an integral shroud to prevent or inhibit access to the end 1021 of the bolt. Such a shroud is shown in dotted outline in Figure 10. The entire arrangement is located via the annulus 1046 in an apertured lug 1060 forming an integral part of the internal combustion engine.

It will be appreciated that the above embodiments have been described by way of example only and that many variations are possible without departing from the scope of the invention. For instance a nut and bolt each fitted with a locking device may be used.

Claims

1. A tamper resistant arrangement comprising a rotatable member, a locking member, a distance piece associated with the rotatable member and grooved to accommodate the locking member, and a protective cap also grooved to partially accommodate the locking member, the cap being shaped internally so that it can be pushed over the rotatable member and distance piece to prevent access thereto and the groove therein being disposed so that, when so pushed, the groove is axially aligned with the groove in the distance piece whereby the cap is axially locked with respect to the distance piece by the locking member.

2. A tamper resistant arrangement as claimed in Claim 1, which is a fixing for fixing two parts together, in which the rotatable member is a fixing device which may be rotated so as to tighten the fixing and the distance piece is disposed in use between the fixing device and the parts to be fixed together.

3. A tamper resistant arrangement as claimed in Claim 2, in which the fixing device is a screwthreaded bolt.

4. A tamper resistant arrangement as claimed in Claim 2, in which the fixing device comprises a screwthreaded stud and a nut which engages the stud enabling it to be rotated.

5. A tamper resistant arrangement as claimed in Claim 2, in which the fixing device comprises a screwthreaded bolt and complementary screwthreaded nut which engages the bolt, the head of the bolt being disposed in use on the side of the parts fixed together remote from the nut.

6. A tamper resistant arrangement as claimed in Claim 5, in which the head of the bolt is welded in use to one of the parts fixed together.

7. A tamper resistant arrangement as claimed in any of Claims 2 to 6, in which, where one of the parts to be fixed together has slotted holes for adjustment purposes, the distance piece is formed with a spigot remote from the means for enabling the fixing device to be turned so that when the fixing device is tightened down, the spigot is forced to deform locally a relatively soft part which is to be fixed to prevent subsequent movement of this part in the direction of the slot relative to the part to which it is to be fixed.

8. A tamper resistant arrangement as claimed in any of Claims 2 to 7, in which, where one of the parts to be fixed has a slotted hole, the periphery of the open end of the cap is flanged to prevent or inhibit access for a lever to its open end via an open portion of the slot.

9. A tamper resistant arrangement as claimed in any of Claims 2 to 8, in which the fixing device and cap are made of hardened metal.

10. A tamper resistant arrangement as claimed in Claim 1, in which the rotatable member comprises a screwthreaded bolt and the distance piece is disposed between two internally screwthreaded nuts located on the bolt the bolt being formed so that it can be rotated relative to and moved axially of the nuts to provide an adjustable stop.

11. A tamper resistant arrangement as claimed in Claim 10, in which the bolt is slotted at its end remote from the stop end to provide for adjustment thereof.

12. A tamper resistant arrangement as claimed in Claim 10 or 11, in which one of the nuts is externally formed for fixing the arrangement onto another body.

13. A tamper resistant arrangement as claimed in Claim 12, in which the external formation comprises screwthreads.

14. A tamper resistant arrangement as claimed in Claim 12, in which the said another body is made of an electrically insulating material, whereby to provide for electrically insulating the arrangement from an external body to which it may be fixed.

15. A tamper resistant arrangement as claimedin Claim 14, in which the insulating material is nylon.

1 6. A tamper resistant arrangement as claimed in Claim 14 or 15, in which a further member of electrically conductive material is disposed between the said another body and the said one nut to provide an electrical connection to circuitry external to the arrangement.

1 7. A tamper resistant arrangement as claimed in any preceding claim, in which the distance piece is made of hardened metal.

1 8. A tamper resistant arrangement as claimed in any preceding claim, in which the locking member is a preferably rectangular section circlip which is first forced into the groove in the distance piece on pushing on the cap and then allowed to spring back out partially into the groove in the cap to effect locking of the cap with respect to the distance piece.

19. A tamper resistant arrangement as claimed in any preceding claim, in which the periphery of the open end of the cap and the ends of the distance piece are chamfered to facilitate assembly of the fixing.

20. A tamper resistant arrangement substantially as hereinbefore described with reference to Figures 1 and 7 or Figure 2, or Figure 3, or Figure 4, or Figures 5 and 9 or Figures 6 and 8 or Figure 10 of the accompanying drawings.