GB1581101A

GB1581101A - Wrench apparatus for tightening a nut and bolt assembly

Info

Publication number: GB1581101A
Application number: GB1490378A
Authority: GB
Original assignee: GKN Fasteners Ltd
Current assignee: GKN Fasteners Ltd
Priority date: 1978-04-15
Filing date: 1978-04-15
Publication date: 1980-12-10

Description

(54) WRENCH APPARATUS FOR TIGHTENING A NUT AND BOLT ASSEMBLY (71) We, GKN FASTENERS LIMITED, a British Company of P.O. Box 60, Heath Street, Smethwick, Warley, West Midlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a wrench apparatus for tightening a nut and bolt assembly.

The wrench apparatus which may be a wrench or wrench attachment, is intended for use in tightening a nut and bolt assembly including a load indicating nut, washer or bolt head of the type described and claimed in our prior Patent No, 1,370,792. Such a nut, washer or bolt head comprises a body (hereinafter referred to as the nut body) including a radially outwardly extending flange, the underside of which provides a continuous uninterrupted planar abutment engaging surface of annular form to provide uninterrupted engagement over an annular area with an abutment in the fastener assembly, the cross-section of the flange, taken in a radial plane, being such that there is provided an internal surface to the annular flange which takes the form of an annular groove of generally V-section with the apex thereof directed radially outwardly and the portion of the flange bounded by the one leg of this Vsection which is joined to the body is constructed and arranged so that, when the axial tensile load in the bolt shank reaches or exceeds a predetermined minimum value, plastic deformation of the metal of the flange takes place in shear in this one leg and the body moves in a direction towards the abutment against which it is being tightened so that a measurable reduction in the overall axial dimension of the nut, bolt head or washer occurs.

Thus, axial contraction of the body occurs due to plastic flow when a predetermined tension is achieved in the bolt shank of the fastener assembly.

Our prior Patent Application No. 7785/76 (Serial No. 1,578,724) describes and claims a method of tightening a nut and bolt assembly including a load indicating nut, bolt head or washer as set out above, and also a wrench for performing the method.

It is an object of the present invention to provide a load indicating nut wrench which is an improvement in or modification of that described and claimed in our co-pending British Patent Application No. 7785/76 (Serial No. 1578724).

Patent Application No. 7785/76 (Serial No.

1578724) describes and claims an apparatus in the form of a wrench or wrench attachment having a body with means to apply tightening torque to a nut when the body is rotated, characterised by detector means carried by the wrench body and having two relatively movable detector parts, at least one of which engages the body of the load indicating nut, and which detector parts are held in predetermined positions relative to one another determined by datum points of the assembly when the nut has been initially tightened (as therein defined) against the abutment surface, and a signal device carried by the wrench body and operatively associated with said detector means and which operates to produce a signal when there has occurred a change of predetermined value in the relative positioning of the datum points and hence of said two detector parts, consequent upon further tightening of the nut beyond said initial tightening. The datum points referred to will be on the nut, bolt head or washer, and on another portion of the assembly selected so that the relative movement of the datum points indicates the amount of axial contraction of the body of the nut bolt head or washer, due to the plastic flow referred to above.

According to the present invention there is provided a wrench or wrench attachment according to Claim 4 of British Patent Application No. 7785/76 (Serial No. 1578724) wherein movement of one of the detector parts causes movement of a movable abutment, bearing on one end of a resiliently biased pivoted lever, the remote end of which carries an electrical contact adapted to make or break an electric circuit via a second contact, in response to movement of the movable abutment, in order to provide said signal.

The movable abutment may constitute said one detector part and may be slidably mounted in the wrench or wrench attachment in alignment with the axis of the wrench.

The second electrical contact may be provided on a second lever pivoted adjacent the first lever and resiliently biased in the same sense of rotation, the first lever engaging the second lever and movement of the second lever under its bias being constrained by the first lever a stop being provided to limit movement of the second lever, whereby, when the second lever reaches the stop, further movement of the first lever causes separation of the first and second contacts and breaking of the electrical circuit.

The first and second levers may be pivoted about the same axis.

The position of the stop may be selectively adjustable.

The invention will now be described in more detail by way of example only with reference to the accompanying drawings in which: Figure 1 is an axial sectional view of a power driven wrench embodying the invention.

Figure 2 and Figure 3 illustrate diagrammatically the operation of a lever arrangement forming part of the invention shown in Figure 1.

Referring firstly to Figure 1 of the drawings, there is generally illustrated an electrically driven power wrench generally indicated at 10 having a final drive portion generally indicated at 11, having a rotational drive axis at right angles to the axis of the tool. The final drive is transmitted via bevel gearing 12.

A generally rectangular cross-section drive bar 13 is engageable within a standard socket 9 adapted to make driving contact with a nut (not shown) of a fastener assembly so that, on operation of the wrench, the nut can be tightened down on the fastener assembly.

The nut with which the apparatus is intended to be used is as described and claimed in our British Patent No. 1,370,792. This type of nut has the property of undergoing an axial reduction in length due to plastic flow when a predetermined load is exerted on the nut, for example when used in a fastener assembly in which the bolt tension exceeds apredetermined value.

The tool shown in Figure l enables the plastic flow condition to be detected in the nut when the fastener assembly is tightened up to the predetermined tensile load.

The final drive portion 11 of the tool is provided with a sleeve extension 14 which surrounds, in use, the standard socket and the nut received within it. When the tool is in use, the sleeve extension 14 is caused to bear on a surface of the workpiece surrounding the nut being tightened, this forming one of the datum points for measuring the axial shortening of the nut at the desired loading.

A cup member 15 bears on the top surface of the nut (not shown) during tightening.

This cup member is integrally secured to a rod 16 which extends upwardly through the drive bar 13 and bevel gearing 12 in such a manner that the tip of the rod extends into a secondary housing 17 mounted on top of the main housing 18 of the tool. A suitable collar and grub screw arrangement 19 holds the rod and cup member captive to the tool.

The extreme upper end of the rod 16 bears on the underside of a first lever 20 which is pivoted at 21. The end of the lever 20 remote from the rod 16 is spring urged upwardly and carries an isolated first electrical contact 22 which is electrically insulated from the lever 20.

A second lever 23 is pivotally mounted, also at the pivot 21 in the secondary housing 17.

This second lever is also spring biased upwardly in the same sense of rotation as the first lever 20. The lever 23 is forked at the pivot 21 and has a pair of limbs lying on either side of the lever 20. At the end remote from the pivot 21, the limbs join together to provide a second electrical contact 24, earthed to the casing of the tool. The contacts 22 and 24 are provided in a low voltage circuit and it will be appreicated that sepataion of these contacts will break the circuit.

The arrangement is such that the contacts are closed when the socket is engaging a nut except when axial compression of the nut occurs under plastic flow to a sufficient extent, whereupon the contacts separate and the electrical circuit is broken. This can be used to control the power input to the tool, cutting off further drive torque to the nut.

The way in which this happens is as follows: When the tension in the fastener assembly exceeds the predetermined value, plastic flow occurs in the nut and the cup member 15 which bears on the top surface of the nut tends to move downwardly relative to the sleeve extension 14 which is bearing on the workpiece. The rod 16 moves downwardly and allows the lever 20 also to move downwardly at the "rod" end, under its spring bias.

Since the lever is pivoted at 21, the end carrying the contact 22 tends to move upwardly. Initially, at least, the second lever 23 also moves upwardly in unison with the first lever since they are spring urged in the same sense of rotation and the two levers are in abutment. However, at a position which is predetermined by an adjustable set screw 25, the lever 23 cannot move further upwardly and the contacts 22 and 24 are separated, breaking the circuit. The set screw 25 can, of course, be positioned so that the circuit breaks at a chosen value of axial compression for the load indicating nut.

In order to prevent accidental damage to the switch mechanism 17, if the tool is carelessly handled, a cushioning stop 26 is provided directly in line with the rod 16 so as to prevent the rod 16 from being pushed excessively upwardly. This prevents the lever 24 from being forced downwardly into engagement with the main housing 18 of the tool, which could cause damage to the switch contacts 22 and 24.

It will be seen that the tool described above has various advantages as compared with the tool described and illustrated in the Parent Patent Application No. 7785/76 (Serial No.

1578724). In particular, the main components of the load indicating control system are housed in a relatively small capacity secondary housing which is mounted on the back of the tool, rather than being disposed axially in line with the final drive. This makes the tool easier to handle and reduces the amount of structural alteration which needs to be made to the tool to provide the load indicating facility.

Additionally, in our prior Patent Application, the electrical contact arrangement involved the use of brushes and slip rings, the position detecting parts of the device being housed within the rotating main drive body. In the tool described above, all the electrical circuitry is housed in a "clean" area away from the drive parts of the tool and no rotation of these electrical parts occurs. The only rotation which may occur is that of the rod 16 which may occur since the rod passes through the rotating drive formations at the final drive portion of the tool. However, even this can be prevented by simple rotation preventing formations.

The reduction in the number of moving parts and in particular in the number of rotating parts enables the tool to be more accurate in operation. Furthermore, the tool is readily adjusted to set the predetermined value of axial compression of the nut which will open the electrical circuit. This can be done readily by use of a screw driver on the set screw 25, without the need to remove the tool from the fastener assembly. The set screw 25 is locked against accidental rotation by any suitable means such as a frictional grip member.

WHAT WE CLAIM IS: 1. A wrench or wrench attachment according to Claim 4 of British Patent Application No. 7785/76 (Serial No. 1578724) wherein movement of one of the detector parts causes movement of a movable abutment, bearing on one end of a resiliently biased pivoted lever, the remote end of which carries an electrical contact, adapted to make or break an electrical circuit via a second contact in response to movement of the movable abutment, to provide said signal.

2. A wrench or attachment according to Claim 1 wherein the movable abutment constitutes said one detector part and is slidably mounted in the wrench or wrench attachment in alignment with the axis of the wrench.

3. A wrench or attachment according to Claim 1 wherein the second electrical contact is provided on a second lever, pivoted adjacent the first lever and resiliently biased in the same sense on rotation the first lever engaging the second lever and movement of the second lever under bias being constrained by the first lever, a stop being provided to limit movement of the second lever, whereby, when the second lever reaches the stop, further movement of the first lever causes separation of the first and second contacts and breaking of the electrical circuit.

4. A wrench or attachment according to Claim 3 wherein the first and second levers are pivoted about the same axis.

5. A wrench according to Claim 3 or Claim 4 wherein the position of the stop is selectively adjustable.

6. A wrench according to any preceeding claim provided with power drive means.

7. A wrench according to Claim 6 wherein the power drive means are electrically driven.

8. A wrench according to Claim 7 wherein the making and breaking of said electrical circuit respectively actuates and deactuates the drive of the tool.

9. A wrench substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

In order to prevent accidental damage to the switch mechanism 17, if the tool is carelessly handled, a cushioning stop 26 is provided directly in line with the rod 16 so as to prevent the rod 16 from being pushed excessively upwardly. This prevents the lever 24 from being forced downwardly into engagement with the main housing 18 of the tool, which could cause damage to the switch contacts 22 and 24.

It will be seen that the tool described above has various advantages as compared with the tool described and illustrated in the Parent Patent Application No. 7785/76 (Serial No.

1578724). In particular, the main components of the load indicating control system are housed in a relatively small capacity secondary housing which is mounted on the back of the tool, rather than being disposed axially in line with the final drive. This makes the tool easier to handle and reduces the amount of structural alteration which needs to be made to the tool to provide the load indicating facility.

Additionally, in our prior Patent Application, the electrical contact arrangement involved the use of brushes and slip rings, the position detecting parts of the device being housed within the rotating main drive body. In the tool described above, all the electrical circuitry is housed in a "clean" area away from the drive parts of the tool and no rotation of these electrical parts occurs. The only rotation which may occur is that of the rod 16 which may occur since the rod passes through the rotating drive formations at the final drive portion of the tool. However, even this can be prevented by simple rotation preventing formations.

The reduction in the number of moving parts and in particular in the number of rotating parts enables the tool to be more accurate in operation. Furthermore, the tool is readily adjusted to set the predetermined value of axial compression of the nut which will open the electrical circuit. This can be done readily by use of a screw driver on the set screw 25, without the need to remove the tool from the fastener assembly. The set screw 25 is locked against accidental rotation by any suitable means such as a frictional grip member.

WHAT WE CLAIM IS: 1. A wrench or wrench attachment according to Claim 4 of British Patent Application No. 7785/76 (Serial No. 1578724) wherein movement of one of the detector parts causes movement of a movable abutment, bearing on one end of a resiliently biased pivoted lever, the remote end of which carries an electrical contact, adapted to make or break an electrical circuit via a second contact in response to movement of the movable abutment, to provide said signal.
2. A wrench or attachment according to Claim 1 wherein the movable abutment constitutes said one detector part and is slidably mounted in the wrench or wrench attachment in alignment with the axis of the wrench.
3. A wrench or attachment according to Claim 1 wherein the second electrical contact is provided on a second lever, pivoted adjacent the first lever and resiliently biased in the same sense on rotation the first lever engaging the second lever and movement of the second lever under bias being constrained by the first lever, a stop being provided to limit movement of the second lever, whereby, when the second lever reaches the stop, further movement of the first lever causes separation of the first and second contacts and breaking of the electrical circuit.
4. A wrench or attachment according to Claim 3 wherein the first and second levers are pivoted about the same axis.
5. A wrench according to Claim 3 or Claim 4 wherein the position of the stop is selectively adjustable.
6. A wrench according to any preceeding claim provided with power drive means.
7. A wrench according to Claim 6 wherein the power drive means are electrically driven.
8. A wrench according to Claim 7 wherein the making and breaking of said electrical circuit respectively actuates and deactuates the drive of the tool.
9. A wrench substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.