GB2130737A

GB2130737A - Clamping tension indicator

Info

Publication number: GB2130737A
Application number: GB08329924A
Authority: GB
Inventors: Maurice David Chattaway
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-11-13
Filing date: 1983-11-09
Publication date: 1984-06-06
Also published as: GB8329924D0

Abstract

A device for indicating unacceptable reduction in tension in a clamping device comprises an indicating member 15, 16 clamped between components 12, 14 of the clamping device. The indicating member is adapted to be released on reduction of the clamping force below a predetermined level for movement in a plane at right angles to the direction of the clamping force to an indicating position in which an indicating portion 16 provides a visual indication that the clamping force is insufficient. The indicator may be hidden when under tension and be released to move radially and/or circumferentially of the clamping device. <IMAGE>

Description

SPECIFICATION Clamping tension indicator This invention relates to means for indicating the state of tension of clamping devices.

Many situations arise in which it is desirable to have some means of indicating whether a desired degree of tension has been maintained in a clamping device. In the fixing of wheels to vehicles a plurality of nuts and studs are used to secure the wheels in position. During use these fastenings are subjected to substantial centrifugal forces and can work loose resulting in possible detachment of the wheel from the vehicle. Bridges, pressure vessels and other structures commonly incorporate fastening devices, maintenance of tension in which is critical for safety reasons. There is therefore a requirement in various clamping situations for early warning in the event of clamping devices becoming insufficiently tensioned or loose.

It is an object of the present invention to provide a tension indicating device of simple and effective construction which may be used in situations of the kind referred to above.

According to the invention there is provided a device for indicating unacceptable reduction in tension of a clamping device, and comprising an indicating member at least a portion of which is adapted to be directly clamped between a component of the clamping device and the clamped structure, and which is adapted to be released on reduction of said clamping force below a predetermined level for movement in a plane at right angles to the direction of the clamping force to an indicating position in which an indicating portion thereof provides a visual indication that the clamping force is insufficient.

The clamping device will generally comprise a threaded bolt or stud and a nut engageable therewith, the indicating device being adapted to be clamped between the nut or the head of the bolt and the surface of a clamped structure.

Said indicating member may comprise a washer having an enlarged hole therethrough and incorporating spring means adapted to urge the washer to an eccentric indicating position when the clamping force falls below said predetermined level.

Alternatively the indicating device may comprise a projection or "flag" maintained in a non-indicating position by spring means when said clamping force is above said predetermined level and movable in said plane to an alternative indicating position on reduction of the clamping force below the predetermined level.

Said spring means may comprise a spring washer arranged to move axially clear of said indicating device to release same on reduction of said clamping force. Alternatively said spring washer may be arranged to move clear of and release said indicating device by radial contraction on reduction of said clamping force.

Advantageously the indicating device comprises a unitary structure incorporating a spring washer and an indicating member mounted on a two-part collar capable of axial contraction and expansion when subjected to a clamping force. In this way the device may be interposed between clamping elements of any desired clamping device to enable a visual indication of the degree of clamping to be obtained.

In one embodiment applicable to the clamping of vehicle wheels, a device according to the invention may be mounted on each of the wheel studs between the wheel and the associated wheel nut whereby to afford a visual indication when any one or more of the wheel nuts becomes loose to an unacceptable degree.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a part-sectional end view showing one form of device according to the invention for use in detecting loose vehicle wheel nuts; Fig. 2 is a diagrammatic front view showing three adjacent vehicle wheel nuts, two of which are fitted with devices according to Fig. 1; Fig. 3 is a part-sectional perspective view of a modified form of device for use in detecting loose vehicle wheel nuts; Fig. 4 is a part-sectional perspective view of an alternative form of device; Fig. 5 is a fragmentary part-sectional view showing parts of the device of Fig. 4 in an indicating position; Figs. 6A and 6B are fragmentary crosssectional views showing an alternative form of device similar to that shown in Figs. 1 and 2 in alternative positions of use;; Fig. 6C shows a form of conical washer which may be used with the embodiment shown in Figs.

6A and 6B; and Fig. 7 is a fragmentary cross-section through a unitary indicating device according to the invention suitable for use in a variety of different situations.

Referring to Figs. 1 and 2, a vehicle wheel 10 is secured to studs 11 on the wheel hub (not shown) by means of nuts 1 2 threadedly engageable with the studs 11. Interposed between each nut 1 2 and the wheel 10 is a conical washer 13 having a rigidly projecting flange 14 defining a peripheral recess accommodating one end of an indicating member or flag 1 5 and the other end of which projects generally radially from the assembly towards the adjacent wheel nut 12 and carries at its free end a reflector 1 6. A disc spring 1 7 is interposed between the indicating member 1 5 and a flange 1 2A on the nut 12 such that when the latter is tightened on the stud 11 the disc spring is compressed and flattened and clamps the flat 1 5 tightly preventing it from rotating about the axis of the stud 11.

In the event the nut 12 becomes loosened during use, the disc spring 1 7 will be released to a point where the clamping force on the indicator or flag 1 5 is reduced or removed and the latter will rotate about the axis of the stud 11 under gravity or under the centrifugal forces which are applied when the vehicle wheel rotates. The reflector 1 6 will therefore move into an indicating position clear of the adjacent wheel nuts, thereby providing a visual indication to the driver of the vehicle that the associated wheel nut has become loosened to an unacceptable degree.

Fig. 2 shows three adjacent wheel nuts two of which are fitted with indicating devices 1 5. The devices are shown in full lines in the normal position adopted when the wheel nuts are sufficiently tight and one device is also shown in broken lines at 1 SA in the position adopted in the event the centre wheel nut should become insufficiently tight. The components may be designed such that the indicating device will permit a slight degree of slackening of the wheel nut before moving to its indicating position but will move to that position as soon as the clamping force reduces below a predetermined level indicative of undue reduction in clamping force and loosening of the wheel nut with resultant danger of detachment of the wheel from the vehicle.

In Fig. 2 the wheel nuts are shown fitted with enlarged diameter washers 1 8 behind which the reflectors 1 6 locate when the indicators 1 5 are in their normal position so that in such a position the reflectors are not visible. Loosening of any one or more of the wheel nuts is therefore immediately apparent since the associated reflector or reflectors will appear from behind the washers 1 8 of adjacent wheel nuts to give a visual indication of unacceptable reduction in the clamping force.

Fig. 3 shows a modified arrangement generally similar in construction to that shown in Figs. 1 and 2. However in this instance the outer edge of the spring washer 1 7 is located in an inwardly opening peripheral recess 1 9 in the indicating member 1 5 and is of a diameter such that when the washer is compressed following clamping of the device to the desired degree, the outer edge of the washer frictionally engages the recess in the indicating member and thereby retains it in its normal position.If the clamping force falls below a predetermined level the release of the disc spring causes it to contract slightly in a radial direction thereby reducing or removing the frictional force between the spring and the indicating member and permitting the latter to rotate to its indicating position under the influence of gravity or of the centrifugal forces imparted during rotation of the vehicle wheels.

Figs. 4 and 5 illustrate a modified form of device in which the indicator comprises a washer 20 having a central hole 21 which is enlarged relative to the diameter of the stud 11. A pair of flexible ears 22 project into the hole 21 and are deformable under manual pressure to locate the washer in a position centralised relative to the stud 11. The remaining components of the device are similar to those described with reference to Fig. 1 and the nut 12 is tightened with the washer in its depressed position, thereby clamping it against movement. In the event the clamping force drops below a predetermined level the disc spring 1 7 will release the washer and the resilient lugs 22 then urge the washer into an eccentric position illustrated in Fig. 5 which is readily visible and thereby gives an indication that the wheel nut is not sufficiently tight.

The lugs 22 could be replaced by a ieaf spring or other deformable means enabling the washer to be arranged concentrically when the device is clamped but to move to a radially eccentric position when the clamping force drops below a predetermined level. This form of device does not rely on centrifugal or gravitational force to move the indicating member to its indicating position and may therefore be used with static fastening devices such as those employed on pressure vessels, bridges or other static structures where safety requires that an early indication of loosening of clamping devices should be given.

Figs. 6A and 6B illustrate a further modification in which the wheel nut 1 2 is provided with a ring 25 having chamfered faces 25A directed towards the wheel 10 and a conical spring 26 is interposed between the wheel and the ring 25. The indicator 1 5 is provided with an inturned foot portion 15A clamped between the outer portion of the disc spring 26 and the chamfered faces 25A on the ring 25. The arrangement functions in a manner similar to Fig. 1 , the indicator 1 5 being tightly clamped against rotational movement when the nut is tightened, as shown in Fig. 6A, but being released by outward expansion of the conical spring 26 when the clamping force falls below a predetermined level. Fig. 6B shows the components in a slack condition prior to clamping.

Advantageously the cone spring 26 takes the form shown in Fig. 6C having radially directed slots 27 formed at its outer and inner peripheries which facilitate expansion and contraction of the spring under the applied clamping forces and improve the action of the device.

Fig. 7 shows an alternative form of device comprising a unitary component which may be fitted between the clamping components of existing clamping devices. For this purpose the component comprises a collar having inner and outer annular components 30A and 30B which engage with one another and are capable of relative sliding movement in a direction axially of the clamping device. In Fig. 7 the device is shown as comprising a bolt 11 and nut 12 acting on a clamped structure 10. A disc washer 31 is engaged between the components 30A and 30B of the device and the component 30A is provided with a recess 32 at its outer periphery in which an indicating member or flag 33 is received. When the nut is tightened the parts 30A and 30B move axially towards one another and deform the washer 31 into engagement with the indicating device 33. If the clamping force is released the parts 30A and 30B start to move apart, thereby reducing the clamping force on the washer 31.

When the clamping force falls below a predetermined level the washer 31 releases the indicating device 33 and permits it to move to its indicating position warning that the device is insufficiently tight. The indicating member 33 may comprise either end of a flag device of the kind shown in Figs. 1 and 2 or a spring urged eccentric washer of the kind shown in Figs. 4 and 5 dependent on the situation in which the device is to be used. Devices of this kind may thus be used in static as well as dynamic situations and with various different forms of indicator dependent on requirements.

The indicating devices described above have a number of advantages compared with similar previously proposed devices. By virtue of the fact that the indicator moves in a plane at right angles to the axis of the clamping device, a visual indication is given without components projecting into positions in which they might be dangerous.

Some devices proposed previously have incorporated indicators which project axially of the clamping device when in their indicating position.

Such devices are not suitable for use with vehicle wheel nuts as the axially projecting indicators would be dangerous to adjacent persons or vehicles. The arrangements according to the present invention indicate by virtue of movements in planes generally parallel to that of the vehicle wheel and do not therefore introduce an additional safety hazard. A further advantage arises from the fact that the devices described may be used both in dyanmic and static situations since only in certain instances is reliance placed upon gravitational or centrifugal forces to move the indicating device between its two positions.

Various modifications may be made without departing from the invention. For example the conical washer described with reference to Fig. 6C may have radially-directed slots on its outer or inner peripheries and not necessarily both. The device shown in and described with reference to Figs. 1 and 2 may be provided with urging means tending to move the flag into the indicating position. The urging means may be a resilient body or spring, and is especially useful where the device is not used on rotating bodies or in applications where the force of gravity is of no assistance. Moreover, although reference has been made primarily to the fastening of vehicle wheel nuts and to static situations such as bridges and pressure vessels, devices according to the invention can be used in a wide variety of other situations where early visual warning of slackening of fastening devices is required.

Claims

1. A device for indicating unacceptable reduction in tension of a clamping device and comprising an indicating member at least a portion of which is adapted be directly clamped between a component of the clamping device and the clamped structure, and which is adapted to be released on reduction of said clamping force below a predetermined level for movement in a plane at right angles to the direction of the clamping force to an indicating position in which an indicating portion thereof provides a visual indication that the clamping force is insufficient.

2. A device as claimed in claim 1, in which the clamping device comprises a threaded element having a head, and a nut engageable with the threaded element, the indicating member being adapted to be clamped between the nut or the head of the threaded element and the surface of a clamped structure.

3. A device as claimed in claim 1 or claim 2, in which the indicating device comprises a washer having an enlarged hole therethrough and incorporating spring means adapted to urge the washer to an eccentric indicating position when the clamping force falls below said predetermined level.

4. A device as claimed in claim 1 or claim 2 in which the indicating device comprises a projection or "flag" maintained in a non-indicating position by spring means when said clamping force is above said predetermined level and movable in said plane to an alternative indicating position on reduction of the clamping force below the predetermined level.

5. A device as claimed in claim 3 or 4, in which said spring means comprises a spring washer arranged to move axially clear of said indicating device to release same on reduction of said clamping force.

6. A device as claimed in claim 3 or 4, in which said spring means comprises a spring washer arranged to move clear of and release said indicating device by radial contraction on reduction of said clamping force.

7. A device as claimed in any preceding claim, in which the indicating device comprises a unitary structure incorporating a spring washer and an indicating member mounted on a two-part collar capable of axial contraction and expansion when subjected to a clamping force.

8. A device as claimed in any of claims 5, 6 or 7, in which said spring washer is a conical washer which undergoes both radial and axial movement in response to reduction of said clamping force.

9. A device as claimed in claim 8, wherein said conical washer is provided with radially directed slots at its outer and/or inner peripheries.

10. A device as claimed in any preceding claim, in which the indicating portion of said indicating member is rendered reflective.

11. A device for indicating unacceptable reduction in tension of a clamping device substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

12. A device for indicating unacceptable reduction in tension of a clamping device substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

13. A device for indicating unacceptable reduction in tension of a clamping device substantially as hereinbefore described with reference to Figs. 4 and 5 of the accompanying drawings.

1 4. A device for indicating unacceptable reduction in tension of a clamping device substantially as hereinbefore described with reference to Figs. 6A, 6B and 6C of the accompanying drawings.

1 5. A device for indicating unacceptable reduction in tension of a clamping device substantially as hereinbefore described with reference to Fig. 7 of the accompanying drawings.

16. A vehicle wheel assembly incorporating at least one device according to any preceding claim.

1 7. A vehicle wheel assembly comprising a hub, a plurality of studs carried by said hub, a wheel removably mounted on said studs and clamped to said hub by clamping nuts threadedly engaged with said studs, and a device according to any preceding claim interposed between the wheel and each of said clamping nuts.

1 8. A vehicle wheel assembly according to claim 1 6 or 17, wherein the indicating device associated with each of said devices for indicating reduction in tension comprises a projection angularly movable around the axis of the associated stud and having an indicating portion extending radially therefrom and of a length substantially equal to the distance between adjacent wheel studs, each of said studs incorporating a flanged member serving to conceal the indicating portion of the adjacent indicating member when the latter is in its nonindicating position.

19. A vehicle incorporating a wheel assembly according to any of claims 1 6 to 1 8.

20. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.