THIS INVENTION relates to an improved drilling rig and more particularly to drilling rigs of the percussion type.

It has been known to employ percussion drilling apparatus for sinking test bores and the like wherein a weighted drilling tool or hammer is suspended from a mast by a wire cable which is reciprocated by a so-called walking beam mechanism to raise and lower the drilling tool so that a bore may be sunk. Such mechanism normally includes a pivotally mounted beam which is reciprocated about the pivotal axis by a cam or crank drive arrangement. The walking beam also includes a sheave about which the supporting wire cable passes and as the walking beam reciprocates the* tool is driven up and down as desired and as the bore is sunk the supporting wire cable is fed out from a storage spool mounted on the drilling appar¬ atus so that the drilling tool may be allowed to project further into the ground in which the bore is to be formed. This type of apparatus suffers the disadvantage that the drive arrangement for the walking beam is normally complicated and has a large number of moving parts which are susceptible to wear and require constant maintenance.

The present invention has been devised to overcome the above disadvantages of the prior art by providing a drilling rig which employs a simplified drive mechanism and which also enables the drilling tool to be driven up and driven down or to be driven up and allowed to free-fall depending upon the application. It is also an object of the present invention to provide a drilling rig which is easily transportable and which will be reliable and efficient in use and economical- to manufacture. Other objects and advantages will herein¬ after become apparent.

With the above and other objects in view,

this invention resides broadly in a drilling rig of the type including an upstanding mast assembly, a tool suspended from said mast assembly by a cable, and drive means associated with said cable and adapted to cause said tool to be reciprocated for drilling purposes; characterised in that said drive means includes a drive mechanism, a crank arm and a guide sheave mounted on said crank arm and adapted to receive said cable there- around, said crank arm being operatively associated with said driving mechanism in such manner that said crank arm may be driven through the full cycle of rotation thereof to raise and lower said tool or driven for only part of its cycle such that said tool is raised by said crank arm but allowed to free fall for drilling purposes. In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein:- Fig. 1 is a diagrammatic side view of the drilling apparatus according to the present invention;

Figs. 2 and 3 illustrate respective side and end elevational views of the components of the drive mechanism of the apparatus according to the present invention; and

Fig. 4 is a diagrammatic side view of the drilling apparatus with the mast in its folded position.

Referring to Fig. 1, the drilling apparatus 10 of the present invention comprises a mobile support frame assembly 11 mounted on wheels and supporting thereon a mast assembly 12 and a drive mechanism 13. The support frame assembly 11 includes a front wall 14 and a rear wall 15 which is braced to the main

body of the support frame by a bracing member 16.

The mast assembly 12 comprises two pivotally inter¬ connected upper and lower mast sections 17 and 18 respectively which are locked into- alignment with each other during the drilling operation and the lower mast section 18 is pivotally connected at 19 to the top of the rear wall 15. The lower section 18 also includes a foot member 20 at its lower end thereof which contacts the ground to support the mast assembly in its operative position and to further stabilise the support frame assembly during operation of the drilling rig, screw down feet members 21 may be provided adjacent the front wall 14. The top of the upper section 17 includes a guide sheave 22 over which a cable 23 passes for supporting a weighted drilling tool 24 and "the cable 23 also extends downwardly on the opposite side of the mast assembly 12 to return about a guide sheave 25 on the drive mechanism 13 to a storage spool 26. According to the present invention the guide sheave 25 is mounted on a crank arm 27 which. is supported on a shaft 28 engageable by a dog clutch assembly with a driven shaft which, in operation, is rotated at a constant speed by a motor mounted on the support frame 11. It will be seen that as the cra k arm 27 rotates the guide sheave 25 will move in a circular path about the shaft 28 so that the supporting cable 23 will be cyclically raised and loxered to cause the drilling tool 24 to be reciprocated.

A feature of the present invention is that the dog clutch assembly connecting the shaft 28 with the driven shaft may provide a positive connection there¬ between so that the tool 24 is driven up and driven down, or alternatively, it may provide a lost motion connection whereby the engagement between the shaft 28 and the driven

shaft during each revolution is effected only during lifting of the tool 24 whereas for the remainder of the cycle after the guide sheave 25 has passed over- centre it may free-wheel independently of the driven shaft to allow the tool free-fall. One example of such a dog clutch assembly is illustrated in Figs. 2 and 3 wherein a drive plate or disc 29 is connected to a driven shaft 30 and has a diametrically extending drive bar 31 extending thereacross which is adapted to be engaged by opposite dogs 32 of a co-operating fork member 33 which is connected to the shaft 28 on which is mounted the crank 27. The drive plate 29 is also provided with recesses 3- which may positively .accom- - modate the drive dogs 3 to provide a positive connection between the shaft 28 and the driven shaft 30 for the continuous drive-up/drive-down mode. In operation, the fork mechanism and drive plate are axially moved into engagement with each other so that the dogs 32 may be driven for 180 by the drive bar 30 for raising of the tool whilst in the second 180° of revolution the drive dogs will not be driven but will free-wheel under the action of the weight of the drive tool during the free fall driving stroke of the tool, here a full cycle of positive drive connection is required, further relative axial movement between the fork mechanism and drive plate enables the dogs 32 to be inserted into the recesses 34 and to be driven for the full cycle of rotation so that the tool is positively driven up and down. The free fall of the drilling tool allows a particularly efficient boring action to be achieved. This is due to the fact that when the tool is in a raised position, the cable is in tension and a twist develops therein. Vhen the tension is achieved as when

the tool is at the bottom of its stroke after free falling, the cable tends to untwist causing a corres¬ ponding rotation of the drilling tool and thus a rotary drilling action is superimposed on the percussive action. As- shown in Fig. 4, the mast assembly 12 may be pivoted about point 19 and folded onto the supporting frame 11 for transporting purposes. To facilitate the folding, there is provided at the hinge connection 35 between upper and lower mast sections 17 and 18, a counter lever 36 which has a sheave at its outer end which may be connected to the cable 23 to enable the mast to be lowered by actuation of the feed spool 26. The drilling apparatus is so designed that the .upper mast section 17 may be folded onto the lower mast section 18 and the whole mast assembly pivoted about point 19 so as to be disposed on the top of the front and rear walls of the support frame 11. When the mast assembly 12 is in this position the counter lever 36 is adapted to be provided with a hitch at its free end to provide a towing connection to a towing vehicle. Thus, the apparatus may be made extremely compact and may be quickly and easily assembled and disassembled and moved from one site to another.

While the above has been given by way of illus- trative example of the present invention, all modi ications and variations as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as herein defined by the appended claims.

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