- 1 - POWER TOOLS

Field of the invention

This invention relates to torque wrenches. In particular it is concerned with a torque wrench which is 5 hydraulically-operated by a piston and cylinder device and also includes a ratchet mechanism.

Successive operations of the piston and cylinder device allied to operation of the ratchet on the return stroke of the latter enable a nut or bolt to be tightened (or 10 untightened) without removing the tool from the nut (or bolt) and without need for manual re-setting between successive power strokes of the piston and cylinder.

Discussion of the prior art

Many forms of hydraulic torque wrench incorporating a 15 ratchet are known. For example European patent specification Number 62195A shows a wrench in which a form of. knee joint linkage is used to transmit pressure from a s piston in one part of the wrench to another part of the wrench, so that relative movement takes place between the 20 two parts, thereby turning a nut(or bolt) - engaging socket. A similar knee joint is used in association with a pawl and ratchet mechanism, to facilitate the return of the two wrentch parts to their starting point, for the next power stroke of the piston and cylinder device.

Object of the invention

It is an object of the invention to produce a ratchet-type hydraulic torque wrench of relatively simple construction.

Brief discussion of the invention

According, to this invention, a hydraulic torque wrench of the kind comprising two parts which are relatively movable about: a common axis of rotation with an associated ratchet and pawl mechanism, under the influence of a piston and cylinder device, is characterised in that the piston and cylinder device includes a hollow piston having a slot defined in a sidewall thereof and a distal portion of one of said relatively movable parts projects through said slot and through a corresponding slot in the cylinder into the hollow piston, to which it is operably connected only through a linkage between the piston at one end and said distal portion at the other end.

"Operably connected" means for present purposes that the linkage is not necessarily positively attached to the piston, for example by a pin, or to the distal portion, or to both of these. In some embodiments it may be more convenient to have no such positive connection between the linkage and the piston. For example, the otherwise free end of the linkage may be located within a recess or hollow in the piston. Operably-connected means in this case that the linkage can exert positive pressure in only one direction. For practical purposes this may be all that is actually necessary.

The hollow piston may be of unitary construction, closed at both ends. The return stoke of the piston and cylinder (prior to the next power stroke) may in this case be accomplished by applying hydraulic pressure to that end of the piston opposite to the end operably connected to the linkage.

However, it is also possible for that one end just mentioned to be open. In this case, a second independant and oppositely-directed piston may be provided in back-to-back relation to the first piston. The oppositely- directed piston may be constructed to apply pressure directly against the open end of the first piston, to cause the latter to make the return stroke. Alternatively, the oppositely directed piston may be operably connected to the same distal portion of one of the movable parts only through a linkage operably connected to the second piston at one end and to the distal portion at the other end.

Description of preferred embodiments

Figure 1 of the accompanying drawings illustrates the features of a torque wrench constructed in accordance with the invention. The drawing is a side elevation, partly in section, from which aspects not directly relevant to the invention have either been omitted, or are not shown in great detail.

A wrench body (1) with hydraulic fluid connectors (2) and a carrying handle (3) contains a pawl foot (4) and ratchet wheel (5), the latter driving a socket tool (6). The socket (6) is accessible through the wrench body? the pawl foot (4) is spring biassed in conventional manner (7) into wedging engagement with the ratchet wheel (5), with the aid of a cam surface (8) constituted by one side of an opening in a relatively movable member (9) located inside the wrench body (1). The member (9) has a distal portion (10). The body (1) also contains a piston (11) in a cylinder (12) .

The piston is hollow, with a piston head (13), (14) at each end. The piston is in two parts (15), (16) united by a screw-threaded connection (17). Annular seals (18) are

provided adjacent each piston head; each of the two fluid connectors (2) communicates with its own respective end of the cylinder (12) .

Both the piston and the cylinder have slots machined in them (not explicity shown, but in the region 19) to allow the distal portion (10) to project into the hollow piston. The free end of the distal portion has one end of a linkage (20) pivotally, attached to it. The opposite end of the linkage is connected to the inside of the piston head (13), by a pivot pin,. (21).

In use, pressure applied to the piston head (13) causes the piston to move to the right. This in turn moves the linkage (20) and with it the distal portion (10). The latter causes the member (9) to rotate clockwise about the axis of the socket (6). This movement, plus the action of the cam surface (8) and spring (7), wedges the pawl foot (4) into engagement with the ratchet wheel (5) so the latter turns with the member (9), forcing the socket (6) to do likewise, provided that the body (1) is not also free to rotate about the same axis. Normally this is accomplished by ensuring that there is engagement between the body and a fixed abutment on the hardware associated with the nut (or bolt) on which the socket is seated and which is to be tightened, or released by use of the wrench.

For example, the regions (22) or (23) of the body (1) may be abutted against the next nut in a series which are to be tightened (or released) .

After the completion of the first piston stroke, the fluid pressure, or at least some of it, can be applied at the other end of the cylinder, to piston head (13). This then moves to the left in the figure, causing the distal portion (10) to do the same. This rotates the member (9)

anti-clockwise; this in turn releases the pawl foot (4) from the cam surface (8) so that only the spring (7) holds it against the ratchet wheel. Provided that the nut (or bolt) engaged in the socket (6) is not actually loose, the pawl foot (4) will lift off the ratchet wheel allowing the member (9) to return to its starting position. The operation is repeated as desired.

It will be appreciated that the same tool can be used for both clockwise* and anti-clockwise rotation of a nut/bolt, by simply turning the tool over.

Figure 2 of the accompanying drawings shows a further embodiment of the invention. In this version, two separate pistons, 40 and 41 are provided and there are two linkages 42, 43 corresponding to the single linkage 20 of Figure 1. However, these linkages are pivotally connected to the distal portion 10 of the common member 9. (It should be noted that common reference numerals have been used in both figures, as far as possible), ^*

Because of the symmetrical construction, it is not necessary to secure the linkages 42, 43 to their respective pistons 40 and 41. The operable connection is in each case provided by co-operating ball (44,45) and socket (46,47) joints. The operation of this tool is otherwise generally similar to that of the first embodiment; it need not be described further here.

Figure 3 of the accompanying drawings illustrates a modification of the two piston arrangement shown in Figure 2. For ease of understanding, only the linkages 42, 43 are shown, on an enlarged scale. In order to urge the linkages towards one another and into contact with the actuator (10, in Figure 2) a coil spring 50 is provided. The spring extends into bores 51, 52 in the respective linkages and the

ends of the spring are retained by set screws 53, 54 respectively, so that the spring is under tension. The linkages are thus biassed towards one another and against th actuator 10. Whilst only one spring has been shown, it will be appreciated that a second spring diametrically opposite t the first one will usually be used, to ensure that the biassing: force is symmetrically disposed about the common axis of: the linkages.