GB2231293A

GB2231293A - Torque-indicating wrench

Info

Publication number: GB2231293A
Application number: GB9009326A
Authority: GB
Inventors: Terence Clifford Bullen
Original assignee: MHH ENG CO Ltd
Current assignee: MHH ENG CO Ltd
Priority date: 1989-04-28
Filing date: 1990-04-26
Publication date: 1990-11-14
Anticipated expiration: 2010-04-26
Also published as: GB8909865D0; GB2231293B; GB9009326D0

Abstract

The wrench includes a strain measuring dial gauge 34 with a master pointer 40 to give an indication of the torque being applied to the fastener by the wrench. A slave pointer 50 may be manually pre-set to an indication of a peak torque to be applied by the wrench and the slave pointer is arranged to be contacted by the master pointer 40 when the master pointer indicates a torque which corresponds to the peak torque. An electric circuit is completed by contact of the master pointer 40 with the slave pointer 50 and is arranged to cause the electric circuit to energise an indicator 53 and a buzzer 60 for at least a predetermined period of time which is independent of any lesser duration of contact of the master pointer 40 with the slave pointer 50. <IMAGE>

Description

"A Torque-Indicatinq Wrench" This invention relates to torque-indicating wrenches.

For the purposes of this specification, a wrench is a manually operable lever-like tool having a hub with a fastener-engaging bit or coupling for temporary attachment of a detachable fastener-engaging bit (for example, a hexagonal socket), the tool having a lever extending laterally from the hub and a manually engageable handle (or its functional equivalent) at or near the outer end of the lever, the wrench enabling a high turning moment or torque to be applied to a rotable fastener or other workpiece.

More effective use of a wrench may be made if the fastener-turning torque being delivered by the wrench is known with a reasonable degree of precision, as compared with the relatively haphazard estimation by the user of manual effort being applied. To this end, various forms of torque-indicating wrench have been proposed.

One such proposed form of torque-indicating wrench has the hub with its fastener-engaging bit (or the coupling therefor) mounted on the lever in a manner which allows at least limited rotation of the hub with respect to the lever, about a rotation axis substantially coincident with the axis about which the fastener is being rotated or tending to be rotated by use of the wrench. This relatively rotatable hub is coupled to the lever by an elastic link such that a momement manually produced on the lever results in a torque from the hub to the fastener or other workpiece along with a torque-dependent strain in the elastic link. A strain-measuring dial gauge coupled between the ends of the elastic link gives an indication of the torque.

More sophisticated guages can give a corresponding extension of function; for example, a slave pointer can be coaxially mounted over the strain-indicating master pointer to be driven round by the master pointer to the peak torque indication, where the slave pointer will remain as a form of torque-indication memory until reset. The pivotal mounting of such a slave pointer need only have a friction sufficient to hold the slave pointer against its own weight and minor extraneous disturbances, any higher friction causing unnecessary drag on the master pointer and probable erroneous torque indications in respect of both instantaneous torque and peak torque.

A proposal has been made to convert this conventional arrangement to an electrically powered indicating system by utilising the two pointers as electric switch contacts directly controlling a source of electric power for the indicator. However, tests have shown that good electrical contact between the two pointers requires that the pivotal mounting of the slave pointer have a friction so high that the slave pointer could no longer be driven by the master pointer. Hence, while the slave could be preset at a predetermined torque indication at which indication was to be given (electrically) that a predetermined torque had been achieved by the wrench, the slave pointer could no longer be moved by the master pointer to indicate (mechanically) that, in fact, some higher peak torque had been applied.

Moreover, vigilance in observing the indicator was necessary, since the pointer contact and hence indicator energisation could in practice be very brief even though a correct torque level had been achieved by the wrench.

Further, there was a tendency to arcing between the pointers, with long-term erosion of the contact regions.

According to the present invention there is provided a torque-indicating wrench, the wrench comprising a hub having a fastener coupling to enable a fastener to be coupled to the hub, a lever extending laterally from the hub and a manually engageable handle coupled to the lever, the hub being coupled to the lever by an elastic link such that a moment applied to the lever results in a torque being applied by the hub to the fastener with a torque-dependent strain in the elastic link, the wrench further comprising a strain-measuring dial gauge coupled to the elastic link and having a master pointer to give an indication of the torque being applied to the fastener by the hub, and a slave pointer capable of being manually presettable to an indication of a peak torque to be applied in next use of the wrench, the slave pointer being arranged when so preset so as to be contacted by the master pointer when the master pointer indicates a torque which corresponds to the peak torque, and an electric circuit comprising an electric subcircuit completed by contact of the master pointer with the slave pointer and arranged to cause the electric circuit to energise an indicator for at least a predetermined period of time which is substantially independent of any lesser duration of contact of the master pointer with the slave pointer.

The electric subcircuit is preferably such that arcing or sparking between the pointers, and erosion of their contact regions, is substantially obviated in use of the wrench.

Typically, the electric circuit further comprises a timing circuit such as a monostable circuit, which could be triggered by the completion of the electric subcircuit by mutual contact of the pointers. Alternatively, the timing circuit could be triggered by the breaking of the electric subcircuit upon separation of the pointers subsequent to completion of the subcircuit by mutual contact of the pointers, the timing circuit functioning when triggered to energise or to cause energisation of the indicator or indicators and to maintain energisation of the indicator or indicators until the timing circuit times out whereby the indicator or indicators remain energised in use for at least a predetermined period of time even if the pointers mutually contact for a lesser period of time.

Typically, the indicator comprises one or both of a visual indicator such as an electric lamp, and an audible indicator, such as an electrically operated buzzer or bleeper.

The wrench preferably includes both the lamp and the buzzer, the lamp serving to give a visible indication even if the ambient noise is such as to prevent the buzzer being clearly heard, while the buzzer enables an immediate audible recognition of the requisite torque being reached without the need for continuous visual observation of the wrench.

The mounting of the slave pointer preferably has a low enough friction that any increase in wrench torque following initial contact of the master pointer with the slave pointer allows the slave pointer to be driven by the master pointer to a substantially true indication of the actual peak torque delivered by the wrench to the fastener or another workpiece, the mounting of the slave pointer simultaneously being high enough to sustain the position of the slave pointer against unbalanced weight of the slave pointer and minor extraneous disturbances.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings wherein Fig. 1 is a view from above of one embodiment of torque-indicating wrench in accordance with the invention; Fig. 2 is a part-sectional side view of the wrench of Fig. 1; Fig. 3 is a part-sectional view from beneath of the wrench of Fig. 1; Fig. 4 is a sectional elevation of the torque-indicating part of a prior-art torque indicating wrench (to an enlarged scale relative to the wrench shown in Figs. 1, 2, and 3); and Fig. 5 is a sectional elevation of the torque-indicating part of the wrench of Fig. 1, to the same enlarged scale as Fig. 4.

Referring first to Figs. 1, 2, and 3, a torque-indicating wrench 10 in accordance with the invention comprises a hub 12 at one end of a wrench body 14. A lever 16 extends from the other end of the wrench body 14, and has a hand-grip 18 at its free end remote from the hub 12 to form a handle for operating the wrench 10. The hub 12 comprises a conventional double-ended square drive 20 to which selected fastener-engaging bits (not shown), hexagonal sockets for example, may be temporarily attached in use of the wrench 10.

The drive 20 incorporates a ratchet 22 which rotates with the drive 20 within the hub 12. In use, when the drive 20 is coupled to a fastener, the drive 20 is rotated in the direction of the arrow 21 by a pawl 24 when lever 16 of the wrench 10 is moved angularly in the same direction. When the lever 16 is moved angularly in the direction of the arrow 23, the drive 20 remains stationary due to slippage of the pawl 24 with respect to the ratchet 22. The pawl 24 is spring-loaded and is carried by a sub-arm 26 mounted within the wrench body 14 for rotation about the centre of the hub 12, i.e. the same rotation axis as the axis about which the drive 20 rotates in use of the wrench 10 to turn fasteners or other workpieces. The sub-arm 26 is coupled to the wrench body 14 by an elastic link constituted by a compression spring 28 held between low-friction fulcra 30.

A double-ended tie bolt 32 prevents the sub-arm 26 being forced out of the wrench body 14 while otherwise freely permitting the sub-arm 26 to rotate about the hub 12 within a limited range of angles, the svb-arm 26 and the wrench body 14 being elastically linked through the spring 28.

A dial guage 34 is mounted in the wrench body 14. The dial gauge 34 has a rack plunger 36 arranged to be depressed by the free end of the sub-arm 26. Thereby, the dial gauge 34 measures relative movement of the sub-arm 26 and the wrench body 14, thus effectively measuring changes in the length of the spring 28 since the ends of the spring 28 are connected respectively to the sub-arm 26 and to the the wrench body 14. Consequently, the reading on the dial gauge 34 is a measure of the torque arising from manual force on the handgrip 18 and being applied through the drive 20 to the fastener or the workpiece in use of the wrench 10.

The torque-indicating wrench 10 illustrated in Figs. 1, 2, and 3 is the same in many respects as a previously proposed torque-indicating wrench, but differs partly in the provision of a visual indicator lamp 38 and partly in the provision of certain features not readily susceptible of illustration, but which will be detailed below.

Turning now to Fig. 4, this illustrates a sectional elevation of a torque-indicating part of the above-mentioned previously proposed wrench; in particular, a vertical section of a dial gauge 134. A rack plunger 136 moves horizontally as viewed in Fig. 4 (in and out of the plane of drawing) to drive a dial spindle 138 about a vertical axis.

A master pointer 140 is secured to the top end of the dial spindle 138, and sweeps over an angularly calibrated dial face 142 similar to the dial face 42 illustrated in Fig. 1.

The dial face 142 is protected by a rigid transparent dial cover 144 fixed over the dial face 142. The centre of the dial cover 144 is fitted with a bush 146 which carries a short manually rotable shaft 148 coaxially with the dial spindle 138. The inner end of the shaft 148 carries a slave pointer 150 which can be manually swept over the dial face 142 generally above the. level of the master pointer 140.

The outer end of the slave pointer 150 is downcurved so that its tip crosses the path of the tip of the master pointer 140. The fit of the shaft 148 in the bush 146 is such that the slave pointer 150 is only just prevented from moving under its own weight or under minor extraneous disturbances; in particular, the slave pointer 150 can be rotated by contact with the master pointer 140 without introducing serious errors into the position of, and hence torque indication given by, the master pointer 140. Thus by manually gripping the outer end of the shaft 148 and turning the slave pointer 150 anticlockwise to a zero or near-zero torque indication, the slave pointer 150 will subsequently be driven clockwise by the master pointer 140 up to the indication of peak torque in concurrent use of the respective wrench.Thereafter, as the wrench torque declines to zero and the master pointer returns anticlockwise to a zero indication, the master pointer comes out of contact with the slave pointer, leaving the slave pointer indicating peak torque until manually reset.

As a further development, it has been suggested that if the slave pointer could be manually preset to a static position indicating a torque required to be delivered by the wrench in next use thereof, the subsequent contact of the master pointer with the preset slave pointer upon the preselected torque being achieved by the wrench could be arranged to complete an electrical circuit and so energise a visual indicator (for example, a lamp).

However, testing of such a proposed arrangement has disclosed certain practical problems and disadvantages, including the often momentary duration of pointer contact and hence of circuit completion. This results in an often momentary indication which may not be noticed by the operator. There is also the necessity of increasing the pivotal friction of the slave pointer to achieve a good electrical contact between the master and slave pointers.

This increased pivotal friction of the slave pointer prevents the slave pointer from being driven by the master pointer so as to give a reliably correct indication of the peak torque.

Fig. 5 illustrates some details of a preferred arrangement for overcoming the above-described problems. Fig. 5 shows part of the interior of the wrench 10 (Figs. 1, 2, and 3) to an enlarged scale. In Fig. 5 those parts which correspond to mechanically equivalent parts in Fig. 4 are given the same reference numerals, but without the prefix "lt'.

Essentially, the arrangement of Fig. 5 consists visibly of electrical connections to various components or assemblies, but most importantly also consists of an invisible reduction of the friction between the bush 46 and the shaft 48 below the level previously considered necessary for good electrical contact between the pointers.

In detail, an electrical connection 52 is made to the master pointer 40 through the electrically conductive wrench body 14 and body of the dial gauge 34. A small metal strip 54 is secured to the inside surface of the electrically insulating dial cover 44 to provide an electrical connection through the bush 46 and the shaft to the slave pointer 50. A multicore lead 56 connects with a 3-volt battery and electric control circuit (not illustrated) housed inside the remote end of the lever 16 and accessible through a removable end (not shown) of the hand-grip 18.

Set into the upper face of the outer end of the wrench body 14 is a visual indicator in the form of a lamp 58, angled away from the hub 12 and towards the hand-grip 18 to improve observability by the wrench operator. Also housed within the wrench body 14 is an audible indicator in the form of an electrically operated buzzer or bleeper 60. All the leads and components are interconnected as appropriate within a terminal block 62, or by any other suitable arrangement.

The electric control circuit contains an electronic amplifier or any other suitable device or arrangement in an electric subcircuit including the connection 52, the master pointer 40, the slave pointer 50, and the metal strip 54, arranged so that any contact between the pointers 40 and 50 completes the electric subcircuit. The current carried on completion of the subcircuit is sufficiently low that arcing between the pointers 40 and 50, and erosion of their contact areas, is eliminated.

The electric control circuit further contains a monostable circuit or any other suitable form of timing circuit which is triggered or otherwise responds to the completion of the electric subcircuit by initiation of contact between the pointers 40 and 50, to energise the lamp 58 and the buzzer or bleeper 60 or to cause the energisation of these and any other indicators. The monostable circuit or other timing circuit is such that when triggered, the indicators 58 and 60 remain energised until the monostable or other timing circuit times out, regardless of the brevity of the initial completion of the electric subcircuit. The monostable circuit period is preferably of the order of 2-3 seconds, such as to give visible and audible indications which are distinct and unambiguous.

The electric subcircuit, or the monostable circuit or the timing circuit can be arranged for the timed period of indicator energisation to commence when the electric subcircuit is broken by termination of contact between the pointers 40 and 50, the period from initiation to termination of pointer contact preferably being an untimed period of indicator energisation such that the indicators are energised immediately upon contact between the pointers.

While certain modifications and variations have been described above, the invention is not restricted thereto, and other modifications and variations can be adopted without departing from the scope of the invention.

Claims

1. A torque-indicating wrench comprising a hub having a fastener coupling to enable a fastener to be coupled to the hub, a lever extending laterally from the hub and a manually engageable handle coupled to the lever, the hub being coupled to the lever by an elastic link such that a moment applied to the lever results in a torque being applied by the hub to the fastener with a torque-dependent strain in the elastic link, the wrench further comprising a strain-measuring dial gauge coupled to the elastic link and having a master pointer to give an indication of the torque being applied to the fastener by the hub, and a slave pointer capable of being manually presettable to an indication of a peak torque to be applied in next use of the wrench, the slave pointer being arranged when so preset so as to be contacted by the master pointer when the master pointer indicates a torque which corresponds to the peak torque, and an electric circuit comprising an electric subcircuit completed by contact of the master pointer with the slave pointer and arranged to cause the electric circuit to energise an indicator for at least a predetermined period of time which is substantially independent of any lesser duration of contact of the master pointer with the slave pointer.

2. A torque-indicating wrench according to Claim 1, wherein the electric circuit further comprises a timing circuit which is triggered by the completion of the electric subcircuit by mutual contact of the slave and the master pointers.

3. A torque-indicating wrench according to Claim 2, wherein the timing circuit is a monostable circuit.

4. A torque-indicating wrench according to any of the preceding Claims, wherein the indicator comprises a visual indicator.

5. A torque-indicating wrench according to any of the preceding Claims, wherein the indicator comprises an audible indicator.

6. A torque-indicating wrench according to any of the preceding Claims, wherein the slave pointer is mounted such that there is a low frictional resistance to rotation of the slave pointer, such that any increase in wrench torque which follows initial contact of the master pointer with the slave pointer enables the slave pointer to be driven by the master pointer to a substantially true indication of the actual peak torque delivered by the wrench to the fastener.