US3599730A - Pressure fluid operated percussion tool - Google Patents

Abstract

In a down-the-hole percussion drill, the exhaust power fluid is used as a flushing fluid during drilling. When the drill is suspended off bottom, the drill bit and with it the hammer piston drops into an exceptional forward position so that drilling ceases automatically and an uninterrupted blowing with fluid starts under full line pressure. The passages for supplying fluid for providing the power strokes of the hammer piston during drilling are used for conveying air for this blowing.

Description

United States Patent [72] Inventors Per Janne Olov Luthman [56] References Cited it}??? h k. N k K 1 UNITED STATES PATENTS a l u am as ima 1, ac a; ar Augus Valdemar Magnusson, Klinten; gggggl); 3/ 1959 Nlorrlson 173/78 Robe" Maumz Sandblom Alvs. 4 1 H961 Paulson T 173/135 J0, lrger ml/gr". Nam a Qweden 3,l91,693 6/1965 l.1ncoln.. 173/78 a t I pp NH 3,113,024 7/1965 ((lcary 173/78 I22] Filed Jun. 7, I970 I I'rimury lz'xamim'r -Jzimes Av Lcppink [45] Patented Aug. 17, 1971 Alturney- Munson & Fiddler [73] Assignee Atlas Copco Aktienbolag Na'cka, Sweden [54] FLUID OPERATED PERCUSSION ABSTRACT: In a down-the-hole percussion drill, theexhaust 17 Cl 6 D power fluid is used as a flushing fluid during drilling. When the aims, rawlng lg V drill is suspended off bottom, the drill bit and with it the [52] US. Cl 173/73, hammer piston drops into an exceptional forward position so i 173/78, 173/137 that drilling ceases automatically and an uninterrupted blow- [51] Int. Cl EZlb 1/00, ing with fluid starts under full line pressure. The passages for E21b 5/00 supplying fluid for providing the power strokes of the hammer [50] Field of Search 173/73, 78, piston during drilling are used for conveying air for this blow- 135,137; 175/92 ing.

23 721 20 i i x l7 -5; 60 e. i =1J 63, 59 sit a 0- tfl 1 W l 3 27 22 6 9 7 41 ff U 3 -70 IJ 6 E i -5 5 54 R? A I A? 45 65kg //0 O ,4 I 7 l N O Ill L PRESSURE FLUID OPERATED PERCUSSION TOOL This invention relates to pressure fluid operated percussion tools and more particularly to pneumatically operated percussive down-the-hole rock drills, so-called because the are adapted to be inserted into the hole being drilled. Usually, the exhaust fluid is used as a flushing fluid during drilling. It is, however, sometimes desirable that drilling be interrupted and a continuous increased flow of flushing fluid under full line pressure be provided to cleanse the bore hole from earth cutting. In a prior form of a down-the-hole drill, passages are used which are utilized exclusively for this uninterrupted flow. Since the major diameter of a down-the-hole drill is limited, these passages will reduce the area available for the hammer piston of the drill, and the percussion effect of the drill will be reduced. In another prior form, the passages for supplying fluid to provide the return strokes of the hammer piston are used also for such a continuous flow. Usually, these passages are long and have sharp knees and do not permit such a large flow as do the passages for providing the power strokes of the hammer piston. If the passages for providing the return strokes are widened, the area available for the hammer piston will be reduced.

'by way of example. In the drawings:

. FIG. la, 1b and 1c are to be seen together as longitudinal section on the lines lI in the FIGS. 2 and 3 of a down-the hole drill, FIG. la being the upper (rear) portion of the drill, FIG. lb being the middle portion, and FIG. lc being the lower (forward) portion. I 7

FIG. 2 is a cross section on the lines 2-2 in the FIGS. Ib and FIG. 3 is a cross section on the line 3-3 in FIGS. 1b and 4.

FIG. 4 is a longitudinal section of the medium portion taken partly on the line 4-4 in FIG. 3 and partly on theline 44 in FIG. 2.

The down-the-hole drill illustrated in the figures has a housing generally indicated with 10. A backhead ll of the housing is adapted to be screwed onto the lower end of a nonillustrated drill pipe. During drilling, the drill pipe transmits rotation and axial pressure to the drill and also supplies the drill with compressed air. The interior of the backhead 11 forms a portion of anair inlet passage 12 in which a spring biased one-way valve 13 is disposed. Downstream of thevalve 13, there is anannular strainer 14 and avalve assembly 15 with an annular valving element orvalve 16. Thisvalve 16 has two annular end surfaces l7 and 18. The interior of thevalve 16 is supplied with compressed air through a portion of theair inlet passage 12 in an upper seat member 19 which has an annular seat 20. When thevalve 16 is in its lower position (FIG. lb) with itsend surface 18 against anannular seat 21 on alower seat member 22, compressed air is supplied to an annular air-distributingchamber 23 and fromthere to a number ofpassages 24, 25 When thevalve 16 is in its upper position with theend surface 17 against the seat as illustrated in FIG. 4, compressed air is supplied to an annularair distributing chamber 26 and from there to a number ofpassages 27. Atubular liner 28 forms part of thehousing 10 and seals against a tubular outer housing member orcasing 29 so that longitudinal grooves in theliner 28 form a number of passages among which are thepassages 24, 25.

At the forward downwardly end of the drill there is a drill bit 30 (FIG. 1c). Thedrill bit 30 has asplined portion 31 on itsshank 32 cooperating with a splined portion of abit holding sleeve 33 so that rotation between thebit 30 and thehousing 10 is prevented, but axial movement, permitted. Thedrill bit 30 is slidable between a retracted drilling position in which an annular shoulder of the drill bit abuts the forward end surface of thesleeve 33 and a forward position in which aflange 35 on theshank 32 abuts asplit retainer ring 36. Thebit 30 has a centrallongitudinal bore 37 into which anexhaust tube 38 extends with its forward end with a sliding fit to provide a passage from the exhaust tube to the bore in the bit. Flushingpassages 39 lead from thebore 37 to the forward end of thebit 30. Theexhaust tube 38 has a flangedmember 40 at its upper end and is fastened by means of this flange member which is clamped between twoelastic rings 41.

Ahammer piston 42 with anaxial bore 43 is reciprocable in theliner 28 and divides the workingcylinder 44, 45formed by the linerinto aforward working chamber 44 in front of thehammer piston 42 and arear working chamber 45 has the back of thehammer piston 42. Thehammer piston 42 has a forwardstriking surface 46 with which it strikes the end surface 47the anvil surface of theshank 32. AT each end, thehammer piston 42 has acylindrical surface 48, 49 in a sliding fit with theliner 28. Between these twosliding surfaces 48, 49, the external diameter of thehammer piston 42 is preferably about 0.2 mm less than the diameter at thesliding surfaces 48, 49. There are also two deeperannular grooves 50, 51 in the piston. Although, in the figures, theentire bore 43 in the piston is shown in a sliding fit with theexhaust tube 38, the

middle portion of the hammer piston may have an internal diameter slightly larger than the internal diameter of the end portions.

There are forward 52 and rear 53 exhaust ports in theexhaust tube 38 so disposed that thehammer piston 42 opens therear ports 53 to exhaust air from therear working chamber 45 when in forward positions but shuts these ports off in other positions, and opens theforward ports 52 to exhaust air from theforward working chamber 44 when in rear positions but shuts these ports off when in other positions.

Thepassages 27 lead into the rear (upper) end of theexhaust tube 38, andsupply ports 54 connect the interior of theexhaust tube 38 with therear working chamber 45. Thevalve 16 and thesupply ports 54 are bypassed bynarrow passages 72, 73 which ensures starting in case thehammer piston 42 covers thesupply ports 54 before starting as may be the case when drilling upward directed holes. Thelower seat member 22 extends into theexhaust tube 38 and has aportion 55 which shuts off thetube 38 between thesupply ports 54 and therear exhaust ports 53. Thepassages 24, 25 lead toports 56, 57, 58 in the forward portion of the linear 28. The twopassages 24 lead to start ports 56 and toconnection ports 57 and thepassages 25 lead tomain ports 58.

Thevalve 16 has a flange with twopiston surfaces 59, 60. Theflange 59, 60 divides achamber 63, 64, in which it slides with a sliding fit, into afirst control chamber 63 and asecond control chamber 64. Acontrol port 65 and a control passage 66 (illustrated in a section in FIG. lb and schematically by dotted lines in FIG. 4) connect theupper control chamber 64 with therear working chamber 45 when thehammer piston 42 holds thiscontrol port 65 open. Anothercontrol port 67 and another control passage 68 (illustrated in a section in FIG. 4 and schematically by dotted lines in FIG. lb) connect thelower control chamber 63 with a forward workingchamber 44 when thehammer piston 42 holds thiscontrol port 67 open.

Thecontrol chamber 63 is vented to theexhaust tube 38 by means of a venting passage 69 (illustrated in a section in FIG. 4 and schematically by dotted lines in FIG. lb) and acentral passage 70 in the extended portion of thelower seat member 22. Thecontrol chamber 64 is vented by means of a similar venting passage 71 (illustrated in a cross section in FIG. 3 and schematically by dotted lines in FIGS. lb, 4) and thepassage 70. The ventingpassages 69, 71 are narrower than the control ports and passages 65-68. Thelower seat member 22 is extended below theexhaust ports 53, and some suction in thepassage 70 will result from the air exhausted through theseports 53. If this extension of theseat member 22 is omitted,

this exhaust air may have a detrimental effect on the venting of thecontrol chambers 63, 64. Direct venting of thecontrol chambers 63, 64 to the outside of thecasing 29 is avoided because mud and dirt would easily clog in the venting passage and because, when the drive air is off and the drill is in a water filled hole, water and mud would completely fill the drill notwithstanding the one-way valve 13 is closed. The ventingpassage 69 is used also for venting the space between theliner 28 and the smaller diametered middle portion of thehammer piston 42 by means of aport 74. This venting is essential for the operation when there are increased clearance gaps between the slidingsurfaces 48, 49 and theliner 28 because of wear.

In operation, the drill is suspended at the end of the nonillustrated drill pipe and air is supplied to the backhead ll of the drill through the drill pipe. During drilling, the drill is rotated by means of external rotation means rotating the drill pipe, and axial pressure is supplied to the drill so that the drill bit is pressed against the bottom of the hole. The drill bit is, therefore, in its retracted position -the drilling position as illustrated in the figures 1b, 1c.

In FIG. lb, the hammer piston is illustrated at the moment of a power stroke (forward stroke) when it strikes theanvil surface 47 of thebit 30. Thehammer piston 42 rebounds and, thus, thebit 30 limits the power stroke of the hammer piston. Thevalve 16 has the position illustrated in FIG. lb and compressed air is supplied through thepassages 24, 25 and theports 56, 57, 58 into theforward working chamber 44 so as to returnhammer piston 42.

As will be described, thevalve 16 remains in its position until thehammer piston 42 uncovers thecontrol port 67 during its return stroke and compressed air is supplied from the forward workingchamber 44 to thecontrol chamber 63 so that the air pressure upon thepiston surface 59 moves the valve into the position illustrated in FIG. 4.

The high pressure in thecontrol passage 68 is of short duration because just after thecontrol port 67 has been uncovered, theexhaust ports 52 are also uncovered by the hammer piston. Because of the air pressure upon theend surface 18, however, thevalve 16 remains in its position of FIG. 4 until thecontrol port 65 is uncovered during the following power stroke. Compressed air is now, at this stage of the return stroke, supplied to therear working chamber 45 through thepassages 27 and theinlet ports 54. However, thehammer piston 42 proceeds in its return movement because of its momentum until it covers theinlet ports 54 and the air in the closed cushion chamber, now formed at the rear of thehammer piston 42, stops the hammer piston and urges it forwards because of the stored energy. Theport 54 is again uncovered, and the compressed air supplied to therear working chamber 45 accelerates the hammer piston.

Before thehammer piston 42 strucks the bit, it uncovers thecontrol port 65, and the high pressure from therear working chamber 45, transmitted through thecontrol passage 66 to thecontrol chamber 64, influences thepiston surface 60 to shift thevalve 16 into the position illustrated in FIG. I.

The pressure rise in thecontrol chamber 64 is very short lasting because the hammer piston also uncovers theexhaust ports 53, but, when thevalve 16 once has shifted into this position, it remains there because of the air pressure upon theend surface 17 until there is another pressure pulse through thecontrol passage 68.

Whenever during drilling, the drill is raised off the bottom of the borehole or the bit advances much faster than the drill pipe, thebit 30 drops until theretainer ring 36 prevents additional downward movement. When thebit 30 drops, thehammer piston 42 tends to overtravel its normal forward stroke limit which is defined by theanvil surface 47 of thebit 30 in the retracted position. When the hammer overtravels, thegroove 51 will be in communication with thecontrol port 67 at the same time as thegroove 50 is in communication with the connection ports 57 (FIG. 4) Since thevalve 16 shortly before has taken up its position of FIG. 1 when theport 65 was uncovered, there is compressed air in thepassages 24, and the twogrooves 50, 51 and the clearance space in between the grooves transmit compressed air from thepassages 24 to thecontrol passage 68, and so thevalve 16 shifts back to the position of FIG. 4. Now, compressed air blows through thepassages 27, theports 54, therear working chamber 45, the

ports 53, theexhaust tube 38, thepassage 37 in the bit, and

theflushing passages 39. Since thecontrol port 65 is uncovered, the air pressure in the rear working chamber now tends to shift thevalve 16. However, as soon as thevalve 16 moves only a little from its seat 20, compressed air is supplied to thepassages 24 and from there via thegrooves 50, 51 in the hammer piston to thecontrol passage 68, and thevalve 16 returns to its seat 20. This movement of the valve 11 will take place for instance once every second. Thus, there is an uninterrupted hard air blow which cleanses the bore hole from cuttings and mud.

When thebit 30 is again pressed towards its retracted position, theconnection ports 57 are closed off by theforward sliding surface 49 of the hammer piston. Thus, the air pressure in thepassage 66 from therear working chamber 45 shifts the valve into the position of FIG. 1b. Then, when the start ports 56 into theforward working chamber 44 are uncovered, air is supplied to thischamber 44 and the hammer piston returns; that is to say, drilling restarts automatically.

Theconnection ports 57 may be disposed at the same height as thecontrol port 67. In this case the slidingsurface 49 extends to thegroove 51, and thegroove 50 is omitted.

An increased flushing may be desirable for drilling in soft rocks. For this purpose, abypass passage 75 may be provided in thelower seat member 22 as illustrated by dashed lines in FIG. 4.

It is to be understood that the invention may be varied in many other ways within the scope of the claims.

WE CLAIM:

1. In a pressure fluid operated percussion tool, an elongated hollow housing, means for connecting said housing at its rear end to a source of pressure fluid, a fluid-distributing valve assembly at said rear end of the housing, a hollow member of the housing forming a working cylinder for the pressure fluid, a hammer piston reciprocable in said working cylinder under the influence of said pressure fluid, a rear working chamber in the working cylinder at the back of said hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, means in the forward end of said housing for receiving and retaining an anvil and bit means but permitting the anvil and bit means to move axially between a forward and a retracted position, said hammer piston being arranged to strike the rear end of the anvil and bit means when the anvil and bit means is in the retracted position, a first exhaust passage means from the forward working chamber connected with passage means for conveying fluid to the forward end of the anvil and bit means, said first exhaust passage means being open when the hammer piston is in rear positions but closed when the hammer piston is in forward positions, second exhaust passage means from the rear working chamber connected with said passage means for conveying fluid to the forward end of the anvil and bit means, said second exhaust passage means being open when the hammer piston is in forward positions but closed when the hammer piston is in rear positions, first distributing passage means leading from the valve assembly to the rear working chamber, second distributing passage means leading from said valve assembly to said forward working chamber, a valving element of said valve assembly having a first position in which it supplies pressure fluid to said first distributing passage means and a second position in which it supplies pressure fluid to said second distributing passage means, a piston surface element disposed in a control chamber and adapted to urge the valving element into said first position when said control chamber is pressurized, and means adapted to connect the control chamber with the second distributing passage means when the hammer piston overtravels its normal forward stroke limiting position when the anvil and bit means is in its forward position so that said control chamber is pressurized by fluid from said second distributing passage means when said overtravel has taken place and the valve member supplies a flow of fluid directly into said second exhaust passage means through said first distributing passage means and said rear working chamber 2. A tool as claimed in claim 1 in which said means adapted to connect said control chamber with said second distributing passage means comprises a control passage having an-orifice into the working cylinder, an orifice of said second distributing passage means into the working cylinder, and a recess in said hammer piston adapted to provide a passage between said two orifices when the hammer piston is in said position forwardly of its normal forward stroke limiting position.

3. A tool as claimed inclaim 2 in which said recess in the hammer piston comprises two annular grooves connected by means of an annular clearance gap between the jammer piston and said hollow member.

4. A tool as claimed in claim 1 in which said control chamber is continuously vented through a venting passage which is restricted compared with said means adapted to connect the control chamber with said second distributing passage means.

5. A drill as claimed in claim 1 in which a one-way valve is arranged in said inlet passage which is supplied with pressure fluid from the drill pipe at the rear end of the housing.

6. A pressure fluid operated percussion tool comprising an elongated hollow housing, means for connecting saidhousing at its rear end to a source of pressure fluid, a pressure fluid distributing valve assembly at the rear end of the housing, a hollow member in the housing forming a working cylinder for the pressure fluid, a hammer piston with a longitudinal channel reciprocable in the working cylinder under the influence of the pressure fluid, a rear working chamber in the working cylinder at the back of the hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, means in the forward end of said housing for receiving and retaining a shank means of a drill bit but permitting said shank means to move axially between a forward and a retracted position, said hammer piston being arranged to strike the shank means when the shank is in the retracted position but overtravel to a forward flushing position when the shank is in the forward position, an exhaust tube closed at its rear end portion extending through the hammer piston with a sliding fit to the channel in the piston and into a channel in said shank means so as to provide a fluid passage for conveying flushing fluid to the forward end of the bit, hammer pistoncontrolled exhaust ports in said tube leading from the rear working chamber into the tube and from the forward working chamber into the tube, first passage means from the valve as sembly to said rear working chamber, second passage means assembly positioned externally of the working cylinder and leading from said valve to said forward Working chamber, said exhaust ports from the rear working chamber being open when the piston is in a forward position but closed when the piston is in rear positions and said exhaust ports from the working chamber being open when the piston is in a rear position but closed when the piston is in forward positions, and a valving element of the valve assembly having a first position in which it supplies pressure fluid to said first passage means and a second position in which it supplies pressure fluid to said second passage means, said tool being characterized by the combination that a control part in the hollow member opening into the working cylinder is connected with a piston surface of the valving element through a control passage means, said piston surface being adapted to urge the valving element into said first position when influenced by pressure fluid from the control port, said control port being disposed so as to be closed by the piston at the forward portion of the forward strokes during drilling but open to a recess in the piston when the piston is in its forward flushing position, and a port in the hollow member connecting said second passage means and the working cylinder being disposed so as to be open to said recess when the piston is in its flushing position.

7. A tool as claimed in claim 6 in which said control passage means is continuously vented through a venting passage which is restricted compared with the control passage means.

8. A tool as claimed in claim 7 in which said venting passage ends in the exhaust tube.

9. A pressure fluid operated down-the-hole percussion drill including an elongated hollow housing adapted for removable attachment to the forward end of a drill pipe, an inlet passage at the rear end of the housing supplied with pressure fluid from the drill pipe, a liner in the housing forming a working cylinder for the pressure fluid, a hammer piston having a cen tral longitudinal channel reciprocable in said working cylinder under the influence of said pressure fluid, a rear working chamber in the working cylinder at the back of the hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, means in the forward end of said housing for receiving and retaining the shank means of a drill bit but permitting said shank means to move axially between a forward and a retracted position, said hammer piston being arranged to strike the shank means when the shank is in a retracted position but overtravel to a forward flushing position when the shank is in the forward position, an exhaust tube extending through the hammer piston with a sliding fit to said channel in the hammer piston and into a channel in said shank means so as to provide a fluid passage for conveying flushing fluid to the forward end of the bit, first exhaust port means in said exhaust tube leading from the rear working chamber into the tube and positioned to be uncovered by the piston when the piston is in forward positions but covered when the piston is in rear positions, second exhaust port means in the exhaust tube leading from the forward working chamber into the tube and positioned to be uncovered by the piston when the piston is in rear positions but covered when the piston is in forward positions, inlet port means in the exhaust tube at the back of said first exhaust ports leading from the interior of the tube into the rear working chamber, said exhaust tube being closed by a closing member at a location between the first exhaust ports and said inlet ports, means forming a cylindrical valve chamber and including two opposed valve seats, an annular distributing valve reciprocable in said valve chamber between a first position against one of the seats in which it opens the first distributing passage means from the interior of the valve to the interior of the exhaust tube at the rear of said closing member and a second position against the other of the seats in which it opens a second distributing passage means from the interior of the valve to the forward working chamber, the interior of said valve being continuously supplied with pressure fluid from said inlet passage, a first valve throwing surface on the distributing valvev disposed in a first control chamber and activated by pressure fluid in the first control chamber for moving the valve to the first position, a second valve throwing surface on the distributing valve disposed in a second control chamber and activated by pressure fluid in said second control chamber for moving the valve to its second position, a first control passage between said first control chamber, and a first hammer piston-controlled control port in the liner opening into the forward working chamber, a second control passage between said second control chamber and a second hammer piston-controlled central port in the liner opening into the rear working chamber, said tool being characterized by the combination that said first hammer piston-controlled control port is disposed so as to be closed by the hammer piston at the forward portion of the forward strokes thereof during drilling but open to a recess in the hammer piston when said hammer piston is in its forward flushing position and a port in the liner connecting said second passage means, the working cylinder being disposed so as to be open to said recess in the hammer piston when the piston is in its forward flushing position.

10. A drill as claimed in claim 9 in which said control chambers are vented through venting passages which are restricted compared with said control passages and said control ports.

11. A drill as claimed in claim 9 in which said control chambers are vented to the exhaust tube by means of venting passages.

12. A drill as claimed in claim 11 in which said venting passages are connected to a passage through said closing member, which passage extends as a pipelike element to end forwardly of said rear exhaust ports,

13. A drill as claimed in claim 9 in which said valve throwing surfaces are the opposed piston surfaces of an annular flange of the valve.

14. in a pressure fluid operated down-the-hole percussion drill, an elongated housing adapted to be removably attached to the forward end of a drill pipe, an inlet passage at the rear end of the housing supplied with pressure fluid from the drill pipe, a one-way valve in said inlet passage, a hollow member in the housing forming a working cylinder for the pressure fluid, means in the forward end of the housing for receiving and retaining an anvil and drill bit means, a hammer piston reciprocable in said working cylinder under the influence of the pressure fluid, a rear working chamber in the working cylinder at the back of the hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, an exhaust passage adapted to be in communication with said rear working chamber when the piston is in forward positions and in communication with the forward working chamber when the piston is in rear positions, means forming a cylindrical valve chamber and including two opposed valve seats, an annular distributing valve reciprocable in said valve chamber between a first position against one of the seats in which it opens the first distributing passage means from the interior of the valve to the rear working chamber and a second position against the other of the seats in which it opens the second distributing passage means from the interior of the valve to the forward working chamber, the interior of said valve being continuously supplied with pressure fluid from said inlet passage, a first valve throwing surface on the distributing valve disposed in a first control chamber and activated by pressure fluid in said first control chamber to move the valve to its first position, a second valve throwing surface on the distributing valve disposed in a second control chamber and activated by pressure fluid in said second control chamber to move the valve to its second position, a first control passage between said first control chamber and a first hammer pistoncontrolled control port in the hollow member open into the forward working chamber, a second control passage between said second control chamber and a second hammer pistoncontrolled control port in the hollow member open into the rear working cylinder, a venting passage from said first control chamber venting to said exhaust passage, and a venting passage from said second control chamber communicating with the exhaust passage.

15. A drill as claimed inclaim 14 in which said venting passages are restricted compared with the control passages and control ports.

16. In a pressure fluid operated down-the-hole percussion drill, an elongated hollow housing adapted for removable attachment to the forward end ofa drill pipe, an inlet passage at the rear end of the housing supplied with pressure fluid from the drill pipe, a liner in the housing forming a working cylinder for the pressure fluid, a hammer piston with a central longitudinal channel reciprocable in said working cylinder under the influence of said pressure fluid, a rear working chamber in the working cylinder at the back of said hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, means in the forward end of said housing for receiving and retaining a shank means of a drill bit, said hammer piston being arranged to strike said shank means, an exhaust tube extending through said hammer piston with a sliding fit to said channel in the hammer piston and into a channel in said shank means so as to provide a fluid passage for conveying flushing fluid to the forward end of the bit, first exhaust port means in said exhaust tube leading from the rear working chamber into the tube and positioned to be uncovered by the piston when the piston is in its forward positions but covered when the piston is in its rear positions,

second exhaust port means in the exhaust tube leading from the forward wor ing chamber into the tube and posltloned to be uncovered by the piston when the piston is in rear positions but covered when the piston is in forward positions, inlet port means in the exhaust tube at the back of said first exhaust ports leading from the interior of the tube into the rear working chamber, an element extending into the exhaust tube from the rear end thereof and ending forwardly of said rear exhaust ports, a closing element on said element blocking the exhaust tube at a location between the first exhaust ports and said inlet ports, a longitudinal passage through said element, means forming a cylindrical valve chamber and including two opposed valve seats, an annular distributing valve reciprocable in said valve chamber between a first position against one of the seats in which it opens first distributing passage means from the interior of the valve to the interior of the exhaust tube at the rear of said closing member and a second position against the other of the seats in which it opens second distributing passage means from the interior of the valve to the forward working chamber, the interior of said valve being continuously supplied with pressure fluid from said inlet passage, a first valve throwing surface on the distributing valve disposed in a first control chamber and activated by pressure fluid in said first control chamber for moving the valve to its first position, a second valve throwing surface on the distributing valve disposed in a second control chamber and activated by pressure fluid in said second control chamber for moving the valve to its second position, a first control passage between said first control chamber and a first hammer piston-controlled control port in the liner opening into the forward working chamber, a second control passage between the second control chamber and a second hammer piston-controlled port in the liner opening into the rear working chamber, a venting passage from said first control chamber, and a venting passage from said second control chamber, said venting passages being connected to said longitudinal passages in the element which extends into the exhaust tube.

17. A drill according to claim 16 wherein said venting passages are restricted in comparison with the control passages and the control ports.

Claims (16)

1. In a pressure fluid operated percussion tool, an elongated hollow housing, means for connecting said housing at its rear end to a source of pressure fluid, a fluid-distributing valve assembly at said rear end of the housing, a hollow member of the housing forming a working cylinder for the pressure fluid, a hammer piston reciprocable in said working cylinder under the influence of said pressure fluid, a rear working chamber in the working cylinder at the back of said hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, means in the forward end of said housing for receiving and retaining an anvil and bit means but permitting the anvil and bit means to move axially between a forward and a retracted position, said hammer piston being arranged to strike the rear end of the anvil and bit means when the anvil and bit means is in the retracted position, a first exhaust passage means from the forward working chamber connected with passage means for conveying fluid to the forward end of the anvil and bit means, said first exhaust passage means being open when the hammer piston is in rear positions but closed when the hammer piston is in forward positions, second exhaust passage means from the rear working chamber connected with said passage means for conveying fluid to the forward end of the anvil and bit means, said second exhaust passage means being open when the hammer piston is in forward positions but closed when the hammer piston is in rear positions, first distributing passage means leading from the valve assembly to the rear working chamber, second distributing passage means leading from said valve assembly to said forward working chamber, a valving element of said valve assembly having a first position in which it supplies pressure fluid to said first distributing passage means and a second position in which it supplies pressure fluid to said second distributing passage means, a piston surface element disposed in a control chamber and adapted to urge the valving element into said first position when said control chamber is pressurized, and means adapted to connect the control chamber with the second distributing passage means when the hammer piston overtravels its normal forward stroke limiting position when the anvil and bit means is in its forward position so that said control chamber is pressurized by fluid from said second distributing passage means when said overtravel has taken place and the valve member supplies a flow of fluid directly into said second exhaust passage means through said first distributing passage means and said rear working chamber

2. A tool as claimed in claim 1 in which said means adapted to connect said control chamber with said second distributing passage means comprises a control passage having an orifice into the working cylinder, an orifice of said second distributing passage means into the working cylinder, and a recess in said hammer piston adapted to provide a passage between said two orifices when the hammer piston is in said position forwardly of its normal forward stroke limiting position.

3. A tool as claimed in claim 2 in which said recess in the hammer piston comprises two annular grooves connected by means of an annular clearance gap between the jammer piston and said hollow member.

4. A tool as claimed in claim 1 in which said control chamber is continuously vented through a venting passage which is restricted compared with said means adapted to connect the control chamber with said second distributing passage means.

5. A drill as claimed in claim 1 in which a one-way valve is arranged in said inlet passage which is supplied with pressure fluid from the drill pipe at the rear end of the housing.

6. A pressure fluid operated percussion tool comprising an elongated hollow housing, means for connecting said housing at its rear end to a source of pressure fluid, a pressure fluid distributing valve assembly at the rear end of the housing, a hollow member in the housing forming a working cylinder for the pressure fluid, a hammer piston with a longitudinal channel reciprocable in the working cylinder under the influence of the pressure fluid, a rear working chamber in the working cylinder at the back of the hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, means in the forward end of said housing for receiving and retaining a shank means of a drill bit but permitting said shank means to move axially between a forward and a retracted position, said hammer piston being arranged to strike the shank means when the shank is in the retracted position but overtravel to a forward flushing position when the shank is in the forward position, an exhaust tube closed at its rear end portion extending through the hammer piston with a sliding fit to the channel in the piston and into a channel in said shank means so as to provide a fluid passage for conveying flushing fluid to the forward end of the bit, hammer piston-controlled exhaust ports in said tube leading from the rear working chamber into the tube and from the forward working chamber into the tube, first passage means from the valve assembly to said rear working chamber, second passage means assembly positioned externally of the working cylinder and leading from said valve to said forward working chamber, said exhaust ports from the rear working chamber being open when the piston is in a forward position but closed when the piston is in rear positions and said exhaust ports from the working chamber being open when the piston is in a rear position but closed when the piston is in forward positions, and a valving element of the valve assembly having a first position in which it supplies pressure fluid to said first passage means and a second position in which it supplies pressure fluid to said second passage means, said tool being characterized by the combination that a control part in the hollow member opening into the working cylinder is connected with a piston surface of the valving element through a control passage means, said piston surface being adapted to urge the valving element into said first position when influenced by pressure fluid from the control port, said control port being disposed so as to be closed by the piston at the forward portion of the forward strokes during drilling but open to a recess in the piston when the piston is in its forward flushing position, and a port in the hollow member connecting said second passage means and the working cylinder being disposed so as to be open to said recess when the piston is in its flushing position.

7. A tool as claimed in claim 6 in which said control passage means is continuously vented through a venting passage which is restricted compared with the control passage means.

8. A tool as claimed in claim 7 in which said venting passage ends in the exhaust tube.

9. A pressure fluid operated down-the-hole percussion drill including an elongated hollow housing adapted for removable attachment to the forward end of a drill pipe, an inlet passage at the rear end of the housing supplied with pressure fluid from the drill pipe, a liner in the housing forming a working cylinder for the pressure fluid, a hammer piston having a central longitudinal channel reciprocable in said working cylinder under the influence of said pressure fluid, a rear working chamber in the working cylinder at the back of the hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, means in the forward end of said housing for receiving and retaining the shank means of a drill bit but permitting said shank means to move axially between a forward and a retracted position, said hammer piston being arranged to strike the shank means when the shank is in a retracted position but overtravel to a forward flushing position when the shank is in the forward position, an exhaust tube exTending through the hammer piston with a sliding fit to said channel in the hammer piston and into a channel in said shank means so as to provide a fluid passage for conveying flushing fluid to the forward end of the bit, first exhaust port means in said exhaust tube leading from the rear working chamber into the tube and positioned to be uncovered by the piston when the piston is in forward positions but covered when the piston is in rear positions, second exhaust port means in the exhaust tube leading from the forward working chamber into the tube and positioned to be uncovered by the piston when the piston is in rear positions but covered when the piston is in forward positions, inlet port means in the exhaust tube at the back of said first exhaust ports leading from the interior of the tube into the rear working chamber, said exhaust tube being closed by a closing member at a location between the first exhaust ports and said inlet ports, means forming a cylindrical valve chamber and including two opposed valve seats, an annular distributing valve reciprocable in said valve chamber between a first position against one of the seats in which it opens the first distributing passage means from the interior of the valve to the interior of the exhaust tube at the rear of said closing member and a second position against the other of the seats in which it opens a second distributing passage means from the interior of the valve to the forward working chamber, the interior of said valve being continuously supplied with pressure fluid from said inlet passage, a first valve throwing surface on the distributing valve disposed in a first control chamber and activated by pressure fluid in the first control chamber for moving the valve to the first position, a second valve throwing surface on the distributing valve disposed in a second control chamber and activated by pressure fluid in said second control chamber for moving the valve to its second position, a first control passage between said first control chamber, and a first hammer piston-controlled control port in the liner opening into the forward working chamber, a second control passage between said second control chamber and a second hammer piston-controlled central port in the liner opening into the rear working chamber, said tool being characterized by the combination that said first hammer piston-controlled control port is disposed so as to be closed by the hammer piston at the forward portion of the forward strokes thereof during drilling but open to a recess in the hammer piston when said hammer piston is in its forward flushing position and a port in the liner connecting said second passage means, the working cylinder being disposed so as to be open to said recess in the hammer piston when the piston is in its forward flushing position.

10. A drill as claimed in claim 9 in which said control chambers are vented through venting passages which are restricted compared with said control passages and said control ports.

11. A drill as claimed in claim 9 in which said control chambers are vented to the exhaust tube by means of venting passages.

12. A drill as claimed in claim 11 in which said venting passages are connected to a passage through said closing member, which passage extends as a pipelike element to end forwardly of said rear exhaust ports.

13. A drill as claimed in claim 9 in which said valve throwing surfaces are the opposed piston surfaces of an annular flange of the valve.

14. In a pressure fluid operated down-the-hole percussion drill, an elongated housing adapted to be removably attached to the forward end of a drill pipe, an inlet passage at the rear end of the housing supplied with pressure fluid from the drill pipe, a one-way valve in said inlet passage, a hollow member in the housing forming a working cylinder for the pressure fluid, means in the forward end of the housing for receiving and retaining an anvil and drill bit means, a hammer piston reciprocable in said working cylinder under the Influence of the pressure fluid, a rear working chamber in the working cylinder at the back of the hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, an exhaust passage adapted to be in communication with said rear working chamber when the piston is in forward positions and in communication with the forward working chamber when the piston is in rear positions, means forming a cylindrical valve chamber and including two opposed valve seats, an annular distributing valve reciprocable in said valve chamber between a first position against one of the seats in which it opens the first distributing passage means from the interior of the valve to the rear working chamber and a second position against the other of the seats in which it opens the second distributing passage means from the interior of the valve to the forward working chamber, the interior of said valve being continuously supplied with pressure fluid from said inlet passage, a first valve throwing surface on the distributing valve disposed in a first control chamber and activated by pressure fluid in said first control chamber to move the valve to its first position, a second valve throwing surface on the distributing valve disposed in a second control chamber and activated by pressure fluid in said second control chamber to move the valve to its second position, a first control passage between said first control chamber and a first hammer piston-controlled control port in the hollow member open into the forward working chamber, a second control passage between said second control chamber and a second hammer piston-controlled control port in the hollow member open into the rear working cylinder, a venting passage from said first control chamber venting to said exhaust passage, and a venting passage from said second control chamber communicating with the exhaust passage.

15. A drill as claimed in claim 14 in which said venting passages are restricted compared with the control passages and control ports. 16. In a pressure fluid operated down-the-hole percussion drill, an elongated hollow housing adapted for removable attachment to the forward end of a drill pipe, an inlet passage at the rear end of the housing supplied with pressure fluid from the drill pipe, a liner in the housing forming a working cylinder for the pressure fluid, a hammer piston with a central longitudinal channel reciprocable in said working cylinder under the influence of said pressure fluid, a rear working chamber in the working cylinder at the back of said hammer piston, a forward working chamber in the working cylinder in front of the hammer piston, means in the forward end of said housing for receiving and retaining a shank means of a drill bit, said hammer piston being arranged to strike said shank means, an exhaust tube extending through said hammer piston with a sliding fit to said channel in the hammer piston and into a channel in said shank means so as to provide a fluid passage for conveying flushing fluid to the forward end of the bit, first exhaust port means in said exhaust tube leading from the rear working chamber into the tube and positioned to be uncovered by the piston when the piston is in its forward positions but covered when the piston is in its rear positions, second exhaust port means in the exhaust tube leading from the forward working chamber into the tube and positioned to be uncovered by the piston when the piston is in rear positions but covered when the piston is in forward positions, inlet port means in the exhaust tube at the back of said first exhaust ports leading from the interior of the tube into the rear working chamber, an element extending into the exhaust tube from the rear end thereof and ending forwardly of said rear exhaust ports, a closing element on said element blocking the exhaust tube at a location between the first exhaust ports and said inlet ports, a longitudinal passage through said element, means forming a cylindrical valve chamber and including Two opposed valve seats, an annular distributing valve reciprocable in said valve chamber between a first position against one of the seats in which it opens first distributing passage means from the interior of the valve to the interior of the exhaust tube at the rear of said closing member and a second position against the other of the seats in which it opens second distributing passage means from the interior of the valve to the forward working chamber, the interior of said valve being continuously supplied with pressure fluid from said inlet passage, a first valve throwing surface on the distributing valve disposed in a first control chamber and activated by pressure fluid in said first control chamber for moving the valve to its first position, a second valve throwing surface on the distributing valve disposed in a second control chamber and activated by pressure fluid in said second control chamber for moving the valve to its second position, a first control passage between said first control chamber and a first hammer piston-controlled control port in the liner opening into the forward working chamber, a second control passage between the second control chamber and a second hammer piston-controlled port in the liner opening into the rear working chamber, a venting passage from said first control chamber, and a venting passage from said second control chamber, said venting passages being connected to said longitudinal passages in the element which extends into the exhaust tube.

17. A drill according to claim 16 wherein said venting passages are restricted in comparison with the control passages and the control ports.

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