FIELD OF THE INVENTION

The present invention relates broadly to a torque multiplier and relates particularly, though not exclusively, to a torque multiplier for tensioning a strata support cable or tendon. The invention also relates to a method of tensioning a strata support cable or tendon using a torque multiplier.

BACKGROUND OF THE INVENTION

In underground mining and strata control, bolting is generally recognised as the primary support system. Bolting involves grouting of a rock bolt hole formed in the strata of an underground mine. The bolt is tensioned so that the strata surrounding the bolthole is held in compression. This technique has been extended to cables or tendons where a barrel and wedge fitting is attached to the cable and is tensioned using hydraulically actuated equipment. These prior art arrangements suffer from at least the following drawbacks: i) the cables and tendons require relatively heavy tensioning units to achieve high tension loads; and ii) existing designs are large and very heavy to handle and when necessary to be held overhead creating additional occupational health and safety hazards. SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a torque multiplier comprising:

an input shaft and an input gear connected to and coaxial with one another; a secondary shaft together with a pair of coaxial multiplier gears connected thereto, one of the multiplier gears arranged to mesh with the input gear; and

an output shaft and an output gear connected to and coaxial with one another, the output gear arranged to mesh with the other of the multiplier gears, the input shaft coaxially aligned with and rotationally coupled to the output shaft via axial support means which allow the input shaft and the output shaft to rotate relative to one another whilst supporting one another.

Preferably the axial support means allow the input and output shafts to rotate relative to one another at different rotational speeds. Preferably the axial support means includes a shaft connected to and axially extending from the input gear, and an associated bearing connected to and extending from the output gear. More preferably the axial support means includes one or a pair of co-operating bearing bushes located intermediate the journal shaft and the associated bearing. Alternatively the axial support means includes a plurality of circumferentially disposed balls or roller bearings located within a bearing race formed by an annular groove within each of the shaft and the associated bearing,

respectively.

Preferably the torque multiplier also comprises a torque multiplier housing arranged to rotationally locate the input and output shafts together with the secondary shaft, and configured to contain the input and output gears together with the intermeshed multiplier gears. More preferably the multiplier housing includes an open-ended casing having each of its ends enclosed by respective of a pair of casing end caps. Even more preferably the casing end caps rotationally located the input and output shafts together with the secondary shaft. Preferably the torque multiplier further comprises a rotational anchor connected to the multiplier housing and adapted to co-operate with a drill motor for coupling to the input shaft for its rotation. More preferably the rotational anchor includes a reaction arm which is retractably received within a locating hole on the drill or drive motor.

Preferably the torque multiplier is designed to provide an increase in torque of around two times.

Generally the torque multiplier is used together with a dolly and drill motor for tensioning a strata support cable or tendon at loads of up to 20 tonne. BRIEF DESCRIPTION OF THE DRAWINGS

In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a torque multiplier will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 are perspective views of an embodiment of a torque multiplier according to the invention;

Figure 2 is an exploded view of the torque multiplier of figure 1 ;

Figure 3 is a schematic illustration of a torque multiplier adapted to couple with a drill motor; and Figure 4 is a schematic illustration of the torque multiplier of figure 3 showing the internal gears.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As best shown in figures 1 and 2 there is a torque multiplier 10 comprising an input shaft 12 together with its input gear 14, a secondary shaft 16 together with its associated pair of multiplier gears 18 and 20 respectively, and an output shaft 22 together with its associated output gear 24. The input gear 14 meshes with the multiplier gear 18 which in turn drives the other multiplier gear 20 which meshes with the output gear 24. The gear ratios of this example are designed to achieve an increase in torque of around two times from the input shaft 12 to the output shaft 22. Importantly, the input shaft 12 and the output shaft 22 are coaxially aligned and rotationally coupled to one another via axial support means designated generally as 26. The axial support means 26 of this embodiment is in the form of a shaft 28 and a bearing 30 which allows the input shaft 12 and the output shaft 22 to rotate at different rotational speeds or revolutions per minute (RPM) whilst supporting one another to prevent gear separation. The shaft 28 is connected to and axially extending from the input gear 14. The bearing 30 is connected to and axially extending from the output gear 24. In its simplest form the shaft 28 is a tolerance fit within the bearing 30 with a suitable lubricant reducing friction between the mating rotating surfaces. The axial support means serves at least the following functions: It allows the input and output shafts 12 and 22 together with their associated gears 14 and 24, respectively, to co-operate in supporting one another about their common axis of rotation;

2. Both sides of the input gear 14 are supported from axial displacement

relative to the secondary shaft 16 and its associated multiplier gear 18 to prevent their separation; and

Both sides of the output gear 24 are supported from axial displacement relative to the secondary shaft 16 and its associated multiplier gear 20 to prevent their separation. The axial support means may also include one or a pair of co-operating bearing bushes (not shown) located intermediate the shaft 28 and the bearing 30. In an alternative embodiment (not illustrated) the axial support means includes a plurality of circumferentially disposed balls or roller bearings located within a bearing race formed by an annular groove within each of the shaft 28 and the bearing 30, respectively. As best shown in figures 3 and 4 the torque multiplier 10 is housed within a torque multiplier housing designated generally as 40. The torque multiplier housing 40 includes an open-ended casing 42 having each of its ends enclosed by respective of a pair of casing end caps 44 and 46. The torque multiplier housing 40 is designed to:

1 . Rotationally locate the input and output shafts 12 and 22 together with the secondary shaft 16; and

2. Contain the input and output gears 14 and 24 together with the intermeshed multiplier gears 18 and 20.

The input shaft 12 includes a plug 48 designed to be engaged by a chuck of a drive motor of a drill rig (not shown). The input shaft 12 and its associated plug 48 extend through an input shaft opening 50 provided in one of the casing end caps 46. The output shaft 22 includes a socket fitting 52 adapted to engage a dolly for tensioning of a strata support cable or tendon (neither shown). The output shaft 22 together with its socket fitting 52 extends through an output shaft opening 54 provided in the other of the end caps 44. The secondary shaft 16 is supported at each of its respective ends via a journal bearing 56 and 58 provided in the respective end caps 44 and 46. The torque multiplier housing 40 thus axially supports the input and output shafts 12 and 22 together with the secondary shaft 16 for rotational movement and effective intermeshing of the input and output gears 14 and 24 together with the pair of multiplier gears 18 and 20. As best shown in figure 3 the torque multiplier 10 also comprises a rotational anchor or reaction arm 60 connected to the multiplier housing 40. The reaction arm 60 is in this embodiment adapted to engage a locating hole on the drive motor of the drill rig. The locating hole is formed within a flange protruding from the drilling rig assembly (not shown) and the reaction arm 60 is retractably received within the locating hole for rotational anchorage of the torque multiplier 10 during its operation in tensioning of the cable support strata or tendon (not shown).

The torque multiplier 10 is intended for tightening cable bolts or tendons that are designed to resist an unwinding reaction after the tensioning process. This unwinding problem is generally not inherent with solid steel rock bolts. The torque multiplier 10 of this embodiment has been developed to prevent twisting forces on the drilling rig assembly by anchoring the reaction arm 60 of the torque multiplier 10 to the motor driving unit or vice versa.

Now that a preferred embodiment of the present invention has been described in some detail it will be apparent to those skilled in the art that the torque multiplier has the following advantages:

1 . It provides torque multiplication at relatively low ratios with a simplified gear train;

2 The axial support means allows varied rotational speeds for the input and output shafts whilst supporting one another to prevent gear separation;

3 The input and output gears remain meshed with their co-operating

secondary gears;

4 The likelihood of damage to intermeshed gears is reduced with consistent axial alignment of the intermeshed gears, particular under high torque conditions. Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. For example, the torque multiplier may include additional gears of a more complicated gear train provided the input and output shafts are self-supporting. The torque multiplier housing may also vary from that described depending on the application which need not be limited to tensioning strata support cables or tendons.

All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.