FIELD OF THE INVENTION

The invention relates to a drill hammer of the "down-the-hole" type, which is operated with pressured air as its working fluid.

BACKGROUND OF THE INVENTION

Drill hammers of this general kind are well known. The components are designed to achieve the working mechanism of the drill hammer, which inter alia requires switching of supply air between a drive chamber and a return chamber to reciprocate a piston to impact a drill bit.

Drill hammers are made with mechanisms (involving working areas and fluid flow paths) that fail to optimize the space available within the diameter of a hole to be drilled (as determined by the bit diameter). The components are often unnecessarily complicated and suffer from losses in efficiency or blow energy generated by a reciprocating piston.

OBJECT OF THE INVENTION

It is an object of the invention to provide a drill hammer of the kind referred to which has increased reciprocating piston stroke and/or speed over drill hammers with similar arrangements of components that do not employ the features of the invention.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a down-the-hole drill hammer that includes:

a reciprocating piston having a piston head with a piston stem extending from the piston head and providing an impacting face;

a control rod supported from a back-head which withdraws from an axial bore in the piston to exhaust a drive chamber;

a piston stem bush from which the piston stem is withdrawn to exhaust a return chamber;

the piston head providing a drive stroke working area on a face opposite the piston stem around the axial bore and a return stroke working area on an inward annular step around the piston stem;

with a first lateral shoulder provided on the piston head adjacent the drive stroke working area and a second lateral shoulder provided on the piston head adjacent the return stroke working area;

the first shoulder and the second shoulder being of substantially the same diameter;

a longitudinal air distribution passage provided on the piston head between the first shoulder and second shoulder;

with the distribution passage configured to provide substantially balanced, opposed working areas for pressurized working fluid within the distribution passage. The invention further provides for a drill hammer as defined in which: the piston head is slidably engaged and reciprocates within a constant diameter bore of the drill hammer provided between a lifting port through which working fluid is supplied to the return chamber and a delivery port through which working fluid is supplied to the drive chamber, with the distribution passage located over a supply port provided between the lifting port and delivery port; and the constant diameter bore is provided by a longitudinally flat portion of a wear sleeve and a longitudinally flat region of a cylindrical skirt that extends from a back-head, with the supply port provided between a free end of the cylindrical skirt and the longitudinally flat portion of the wear sleeve. Further features of the invention provide for a drill hammer as defined in which: the distribution passage is provided by radially spaced apart longitudinal grooves with the balanced, opposed working areas provided at opposite ends of the longitudinal grooves; the first shoulder and second shoulder are provided by annular regions on the piston head; the grooves are provided uniformly with the first shoulder and second shoulder formed provided adjacent opposite ends of the grooves; and the grooves are machined into a uniform diameter land providing the piston head and its shoulders.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent from the following description of one embodiment, made by way of example, with reference to the accompanying drawings:

Figures 1A & 1 B which show a cross-sectional side view of a pneumatic drill hammer separated between top and bottom ends.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figures 1A & 1 B, a down-the-hole drill hammer 1 in accordance with the invention is shown.

The drill hammer 1 is provided with a reciprocating piston 2 comprising a piston head 3 with a piston stem 4. The piston head 3 provides a drive stroke working area on an annular face 6 opposite the piston stem 4. (The face 6 is formed around an axial piston bore 7 that extends through the piston 2.) A return stroke working area 8 is provided on an inward annular step 9 around the piston stem 4.

A first lateral shoulder 10 is provided adjacent the annular face 6 and a second lateral shoulder 11 adjacent the inward step 9. In accordance with the invention, the first shoulder 10 and the second shoulder 11 are the same diameter and the piston head 3 includes a longitudinal air distribution passage 12 between the two shoulders 10 and 11. More specifically, the distribution passage 12 is provided by radially spaced apart longitudinal grooves 13. The grooves 13 are provided uniformly with the first shoulder 10 and second shoulder 1 1 formed at opposite ends of the grooves 13.

The piston 2 of the drill hammer 1 is configured to cooperate with a control rod 14 supported by a back-head 15 and a piston stem bush 16 to provide the required working fluid supply and exhaust cycle, to and from a drive chamber 17 and a return chamber 18, for reciprocation of the piston 2 and intermittent impact of a drill bit 19. The piston head 3 is formed from a uniform diameter land which has the grooves 13 machined into it to provide the two shoulders 10 and 1 1 at opposite ends.

The grooves 13 are located over a supply port 20 formed over a recess in the wear sleeve 22 adjacent a free end 21.1 of a cylindrical skirt 21 provided as an integral extension of the back-head 15. As the piston 2 reciprocates, the grooves 13 are brought into communication with the drive chamber 17 and return chamber 18, respectively. (There is also an annular recess 23 machined between the grooves 13 that corresponds to the supply port 20 when the piston 2 is in a forward position as shown in the drawings.)

A longitudinally flat portion 24 of the wear sleeve 22 between the supply port 20 and a lifting port 25 is provided with a constant diameter and no cutouts or recesses as this portion 24 of the wear sleeve 22 is bridged by the grooves 13 when air is supplied to the return chamber 18 (via the lifting port 25). The lifting port 25 is provided as an annular recess in the wear sleeve 22. A longitudinally flat region 26 inside the free end 21.1 of the cylindrical skirt 21 is provided with the same diameter as the longitudinally flat portion 24 of the wear sleeve 22 to accommodate the piston head 3 with an outward step providing a delivery port 27 provided to communicate with the grooves 13 for supply of air to the drive chamber 17.

The drill hammer 1 of the current invention is absent the usual step between a lower large and upper small diameter on the head of a piston. The head 3 of the piston 2 is instead provided along a single diameter (before it steps down to a reduced diameter piston stem 4), save for the air distribution passage 12. Also, the air distribution passage 12 is provided within the piston head diameter (instead of a cutout or recess formed into a wear sleeve). During the drive stroke of a piston with a step as referred to, the pressure on the step adds together with the pressure on the area of the rear face of the piston and assists in giving the piston its speed in the impact stroke to strike the bit. However, despite the anticipated effects of extra blow energy delivered by the increased working area, the air pressure, which continuously acts on this step (between the two piston head diameters), has been found to have a negative overall effect on the performance of the hammer. When the piston is moving up and away from a drill bit, it has pressure acting on this step which provides a braking force, which acts against the upward speed of the piston and has also been found to restrict the stroke in the upward direction, especially after the lifting port has closed and the piston is travelling on its own inertia.

In the current embodiment, the distribution passage 12 is configured to provide substantially balanced, opposed working areas for pressurized working fluid, adjacent opposite top 28 and bottom 29 ends inside the grooves 13, adjacent the first shoulder 10 and the second shoulder 1 1 , respectively.

The piston head 3 is slidably engaged and reciprocates within a constant diameter bore 52 of the drill hammer provided between a lifting port 25 and delivery port 27. In this embodiment, the constant diameter bore 52 is provided by the longitudinally flat portion 24 of the wear sleeve 22 and the longitudinally flat region 26 of the cylindrical skirt 21.

During operation, pressurized air enters the back head 15 at an inlet 30 and pushes a check valve 31 down against a spring 32. (The check valve 31 is biased to close against a check valve seat 33 by the spring 32.) With the check valve 31 open, compressed air passes through ports 34 into cutout 35 in the wear sleeve 22. The pressurized air accumulates at annular supply port 20 between the piston 2, cylindrical skirt 21 of the back-head 15, and the wear sleeve 22. From supply port 20, the compressed air flows via distribution passage grooves 13 through the lifting port 25 in the wear sleeve 22, around the second shoulder 11 , and into a return chamber 18. The pressure in the return chamber 18 acts on return stroke working area 8 and urges the piston 2 to move in an upward direction toward the drive chamber 17. Free end 36 on the control rod 14 enters and slidingly seals at first point 37 in the piston bore 7 thereby sealing off the drive chamber 17. With the upward movement of the piston 2, the bottom end 29 of the air distribution grooves 13 move past and shut off flow through lifting port 25. The compressed air stops flowing into return chamber 18 from the air distribution grooves 13.

The piston 2 continues upwards and an end 38 on the piston stem 4 pulls out past second point 39 in the piston stem bush 16 and allows the return chamber 18 to exhaust through a bit bore 40 of the drill bit 19 and out of bit ports 41 in the bit face, to the atmosphere.

A top end 28 of the air distribution grooves 13 now passes into communication with the delivery port 27 provided at an outward step 27.1 in the cylindrical skirt 21 of the back- head 15 and compressed air from supply port 20 flows via air distribution grooves 13 into the drive chamber 17. The compressed air in the drive chamber 17 acts on the drive stroke working area 5 of the annular face 6 and accelerates the piston 2 back towards striking the bit 19.

In the interim, first point 37 in the piston bore 7 has pulled passed the free end 36 of the control rod 14 and the spent air from drive chamber 17 exhausts down the bore 7 of the piston, through the bit bore 40 and bit ports 41 to the atmosphere. The lifting port 25 will once again be opened by the position of the second shoulder 11 and the cycle repeats.

When the hammer 1 is lifted from the drill face (at the bottom of the hole), the bit 19 drops forward against bit retaining rings 42 and inward step 43 on the piston stem 4 passes over third point 44 on the piston stem bush 16 allowing the return chamber 18 to become vented to the atmosphere through an undercut recess 45 that locates across a throat 46 of the piston stem bush 16 and via passages 46 in the piston stem bush 16, 47 in the bit retaining rings 42, and 48 and 49 in a chuck 50, causing the piston 2 to stop cycling. The piston 2 drops forward, following the bit 19, and the piston head 3 disengages from inside the cylindrical skirt 21 allowing compressed air from supply port 20 to flow through piston bore 7, and out of the drill hammer 1 through bit bore 40 and bit ports 41 in a full flush mode into the atmosphere. As soon as the hammer 1 is lowered onto the rock face again, the bit 19 and piston 2 are pushed back the piston 2 starts cycling again.

In the illustrated embodiment of the invention, the back head 15 is shown in one piece with its cylindrical skirt 21 but it could be provided in two parts: a back head with spanner flats as one piece and a suitably configured cylindrical skirt as a separate piece or insert. Such a two-part construction is commonly used. Furthermore, a cylindrical skirt may be provided as a sleeve to extend for part of the way or up to the vicinity of the piston stem bush 16 (in the case of the latter, the entire piston will be inside this extended cylinder). In such an embodiment, a greater or the full extent of a constant diameter bore in the drill hammer for the reciprocating piston head may be provided by the inside of the cylindrical skirt.

The hammer drill of the invention has a piston that avoids the presence of a working area on a step in a fluid distribution chamber (or passage) that would be constantly subjected to working fluid pressure resulting in a force that limits the return stroke. The invention instead has an increased size drive stroke working area on the back end of the piston. The use of the available diameter in the wear sleeve is efficient with the fluid distribution passages along the piston placing the supply port in communication with the return port and delivery port, respectively.

A person skilled in the art will appreciate that a number of variations may be made to the features of the described embodiment without departing from the scope of the present invention.