CA1053118A - Hammer - Google Patents

Abstract

HAMMER
Abstract of the Disclosure A hydraulically operable hammer and more particularly a hydraulically operable hammer having improved cycling of a hammer piston reciprocable therewithin.

Description

This inven-tion relates to a hydraulic drive for actuating a tool.
It is well kno~n in the art of rock drills to provide a drill assembly with a fluid actuat~d hammer comprised of a linear pexcussion motor of the valveless distribution type wherein a hammer piston is self excited for rapid linear reciprocatlon to repetitively impact a s~riking member for the purpose of drilling rock or other hard formations.
Although such drills have generally served the purposes intended, they have nonetheless been subject to various deficiencies for example, some such drills have been subject to unduly inefEicient transfer of mechanical energy Erom the hammer to the striking member. Some prior hammers have been extremely sensitive to small chanyes in such parameters as fluid supply pressure or temperature, or location of the striking member impact end, and have '~ thus been impractical for reliable day-to-day field use.
, Fluid cavitation of hydraulic fluid passing from a high pressure to a low pressure state has been a further problem i~ in many prior art hydraulic hammers. Other hammers have , ~ been very difficult to start. Still other hammers have been of bulky and cumbersome desiyn, and excessively difficult and expensive to manufacture.
These and o-ther shortcomings of prior hammers are alleviated by the instant invention according to which , ~ there is provided an improved and simplified hydraulic hammer of the valveless or self-actuating type.
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~ ni~r~]l.y, tlle object-s of thi~ Lnventlo~ arP ~o provide:
~a) a hydraulically operable self~portin~ hammer Qf compact and simplified design;
(b) a~ i~proved operating cyc.le for a hydra~llically operable hammer;
(c~ a hammer having improved and simplified startup characteristics;
(d) a hamme~ piston having a longer useful life than 1~ ordinarily obtainable;
(e) a hammer having improved efficiency of ~mpact energy transfer;
(f) a hammer having i~proved means to preclude pre~sure and fluid accumulations within portions thereof not intended to contain such pressure and fluid accumulations.
;:: Broadly speakin.g, therefore, the presen~ invention provides a method of moving an elongated impact piston through a work output stroke within an elongated bore of a body member in whlch the bore contains hydraulic fluid and t~e pis~on has an intermediate portion of the bore whereby piston actuating and piston return chambers are formed with.in the bore on opposite sides of the head por~ion comprising, moving the piston through an initial portion of such a work output stroke by admittlng pressurized hydraulic fluid to the actuatin~ chamber throughout the initial portion while simultaneously pressurizing fluid in : a clos~d volume in continuous hydraulic communication with the actuating chamber and dîscharging hydraulic fluid from the return chamber at a contrDlled rate, discontinuing the admitting and ~ A ~

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movillLJ tl~e pi~ton tll~o~lgl~ srl interme~lat~ portion of such ~ ~ork o~ltpUt ~troke i~n~idiately ~ubsequent to the initial portion by ~he hydraulic fluid in ~he closed volume and the actu~ting chamber while siin~ltaneously diicharglng hydraulic fluid from the return chamber at a controlled rate and moving the piston through a final portion o.f such a work output stroke immediately subsequent to the int~rmediate portion by the hydraulic Eluid in the closed volume and the actuating chamber whlle simultaneollsly discharging hydraulic fluid from tlhe actuating chamber and discontinuing the discha~ging of the return chamber.
The above method may be carried out by utilizing a hyd~aulic drive for ac~uating a tool comprising: a body ~ember having an elonga~ed bore therein with a central longitudinal axis and with one end of the bore being adapted to receive at least a portion of an actuatable tool structure internally thereof; and elon~ated piston axially reciprocal within the bore to deliver impact blows to such a ~ool; the bore having an axially inter-mediate chamber section of greater cross-sectional extent than the cross-sectional extent o~ the sections of the bore axially intermediate head section; the head section having a central portion with a finite axially extending outer surface closely slidably received within the chamber section to define chamber portions within the chamber section on axially opposite sides of the central portion of the he~d section which chamber por~ions vary inversely in volume as the piston reciprocates, first passageway mea~s in the body member having axially spaced fluid inlet port means i~ communication with the bore a~ially outwardly of the chamber section, respectively; the piston having formed axially spaced means cooperable with the port means, respectively, :' A

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for c;~lecrive admis i~n of hydrc~ulic fluid t~ the chamb~r portio~s al~er~ately to reciprocate the piston; second passageway means in the bo~y member having a discharge port means with an axial extent in communication with the ~h~mber section; the outer .' surface b~ing cooper~ble with the axial extent of the discharge ; port l~eans to con~rol ~he discharge of hydraulic fluid from the ......
chamber portions; and the piston having formed portions at the ~ ., ends of the axially extending ou~er sur~ace of a configuration to :,, control the rate of flow of such discharge.
These and other objects and advantages of the instant invention are more fully specified in the following descriptio~
with re~rence to the accompanying figures in wh~ch:
Fig. 1 is a perspective view of a rock drill including hydraulically actuated hammer means constructed according to the ' principles of this invent~on;
s Fig. 2 is an axial section of the drill shown in Fig. 1 : and taken on line 2--2 of Fig. 3;
Fig. 3 is a ~ransverse section taken on line 3--3 of ~ig. 2 and appears orl the same sheet as Fig. 1~
; 20 Fig. 4 is a fragmentary portion of the hammer means ~; of Fig. 1 showing the hammer piston in detail; and Fig. 5 is a diagram of the relationship between hydraulic fluid pressure on the piston head and piston posi~ion in its stroke.
In Fig. 1 a hydraulically actuated rock drill assembly 10 comprises a percussion head or motor portion 12 coaxially engaging a forward yoke portio~ 14. Suitably dis-like back head and front head members 16 and 18 coa~ially engage the rearward Pnd of percussion head 12 and the forward end of yoke 3a . ~' ' ' -:~
' ~ ' . ' 14, respectively. S~curing means such as a plurality of longitudinally extendiny side rods 20 rigidly clamp the here-inabove identified drill por-tions together to form the ~ unitary drill assembly 10. ~rill 10 is reversibly feedably .. 5 mounted on an elongated feed frame 22, which frame 22 is in -turn adjustably carried by any suitable mobile base such as a crawler frame and ar-ticulated boom assembly (not shown), and is supplied with motive fluid by suitable fluid hoses 24 communicating with drill 10 to actuate -the drill 10 as hereinbelow described.
The yoke portion 14 (Fig. 2) comprises a generally annular yoke housing 28 having a generally annularl elon-gated chuck member 30 axially rotatably carried therewithin as by roller bearings 32. Chuck member 30 includes a plurality of circumferentially spaced gear teeth 34 coaxially encompassing an axially intermediate external peripheral portion thereof for engagement with a driving gear train (not shown) carried within housing 28 for rocation of chuck 30 as described hereinbelow~
The chuck 30 carries coaxially therewithin an elongated annular rear bushing member 38 and an elongated annular drive member 40 forwardly adjacent bushing 38.
Bushing 38 and drive member 40 are coaxially aligned with an annular forward bushing 46 secured within an inner 25 peripheral portion 48 of front head 18 as by a nut 50 coaxially threadably engaging front head 18 whereby an elongated, generally cylindrical striking bar 4~ extending coaxially within chuck member 30 and front head 18 has , - . . ' - ; .
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its axlally opposed end portions longitudinally slidably suppor-ted within inner peripheral portions 44 and 45 of bushings 38 and 46, respectively. An externally splined intermediate .
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:~r~35~118 por-tion 5~ of strlking bar 42 ex-tending intermediate the respec-tive supported end portions thereof is engageable within a cooperably splined i.nterna.l peripheral portion 56 of drive member 40, and drive member 40 is non-rotatably splined to chuck 30 as at 58~ Accordingly, striking bar 42 is axially rotatable as by a suitable rotation motor such as a pressure fluid actuated motor 36 which receives motive fluid through suitable supply lines (not shown) to drive the chuck and striking bar assembly in coaxial rotation through the above-mentioned gear train.
As indicated hereinabove striking bar 42 is axially slidable within chuck 30. In its extreme rearward - position (Fig. 2) defined by abutment of cooperably formed, respective end portions 62, 66 of striking bar intermediate portion 54 and bushing 38, a rearwardmost end or impact surface 63 of striking bar 42 i5 positio.ned adjacent the forward end of percussion head 12 to receive impact blows therefrom. Inasmuch as the hereinabove described yoke portion 14 forms no part of the present invention and is well known to those versed in the relevant arts, further detailed description thereof is omitted herefrom.
Percussion head 12 (FigsO 2 and 3) comprises an elongated formed member or cylinder 72 such as a machined st.eel casting, and an elongated cylindrical shell 74 coaxially rigidly encompassing cylinder 72 and axially coextensive therewith. Percussion head 12 has a plurality of chambers 76A through 76D, hereinafter collectively identified as chambers 76, and preferably formed as a - ~

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plurality of axially spaced and aligned annular cavities 78 extending radially inwardly of the exterior periphery of cylinder 72 whereby an adjacent inner periphery 80 of shell 74 forms the radially outermost wall of the chambe~s 76. The chambers 76 are axially spaced apart by intervening ~ .
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radially outwardly extendin~ ~artitions 82, each having an outer annular perlphery 84 which sealin~ engages the inner periphery 80 of shell 74 to preclude fluîd communication between adjacent chambers 76. Okher radially outwardly extending partitions 82 are formed adjacent the forward and rearward axial end portions of cylinder 72 to sealingly engage respectiVe axlal end portions of periphery 80 thereby defining the outer or end walls of the end chambers 76A and 76D, respectively.
Shell 74 and cylinder 72 axe prefexably assembled by a shrink fitt~n~ process as by being initially formed for an interference fit therebetween at ambient tempera ture. For assembly the shell 74 is heated and/or the cylinder 72 cooled to thermally produce a diametrical cleaxance therebetween. After as$emb1y the shell 74 and cylinder 72 equalize to ambient temperature to diminish the diametrical clearance therebetween and proyide a continuous~ fluid tight face seal as described without recourse to known elastomeric sealing members and the like.
Cylindex 72 has an elQngated annular liner assembly 9Q retained within a stepped coaxial throu~h bore 92 thereof and comprising an elongated member or sleeve 94 and an elongated buffex ring 102 coaxially disposed within a xearward end pexlpheral portion 100 of sleeye 94. The coaxially communicating innex peripheries of buffer ring lQ2 and sleeye 94 define ;~ a co~xial through bore 88 wherein an elongated, stepped ' ~ :, `, ' `
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CyllrlClriCa 1 piStOII 70 is axially reciprocably disposed.
Bore 88 has respec-tive axially spaced forward and rearward bearing portions 96, 104 which slidably support -therewithin respective axially spaced forward and rearward stem portions 98, 98' of piston 70. An enlarged diameter intermediate portion 106 of the bore 88 extending intermediate the respective bearing portions 96, 104 has disposed therewithin a generally ~ ~5~8 sreppecl cylindrical :intermedi~te or head portion 108 of piston 70. Respective variable volume upstroke and downstroke piston driving chambers llG, 112 are formed adjacent respective forward and rearward ends of piston head 108 by axially spaced annular peripheral clearance spaces between the head 108 and bore portion 106. Piston 70 is cooperable with bore ~8 to provide for porting of pressurized motive fluid alternately to and from driving chambers 110, 112 for self~excitation of the piston 70 as described hereinbelow.
Bac~head 16 is rigidly clamped by sid~ rods 20 adjacent the rearward end of percussi.on head 12 in compressive axial engagement with suitably formed bearing surface portions of percussion head 12, for example coaxial bearing annuli 114 and 116 formed by rearwardly facing axial end portions of the cylinder 72 and shell 74, respec-: tively. Backhead 16 similarly engages the rearward end 118 . of buffer ring 102 which, in turn has a forward end portion ; 120 thereof, axially engaging a cooperable, annular, rear-wardly facing shoulder 122 formed upon the inner periphery of sleeve 94. Sleeve 94 seats within a rearward end portion of bore 92 by engagement of cooperably axially abutting shoulder portions formed on respective adjacent peripheral portions thereof as at 124 whereby the applied clamping forces of side rods 20 serve to rigidly seat liner assembly 90 within bore 92. The sleeve 94 and buffer ring 102 furthermore are non-rotatably affixed with respect to each other and cylinder 72 as by suitable keys or shear . ~ -7-~ .
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pins (not shown) fit-tecl in-to cooperably formed keyways.
The drilling apparatus 10 further comprises a flushing fluid means generally indicated at 11 and com-prising a tube 126 disposed withln suitably formed delivery passageways - . . . . .
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extending coax.Lall.y wll:h:Lrl backhead l6~ pi~ton 70 and ~triklng bar ~2, and :lncluding ~ flu~d inlet 128 ln backhP~d 16 fo~
dlrecting ~lushing fluid such ~9 air or ~ater thereinto for cleaning detritus from ~he bore hole. A full descrlptlon of the flushing fluid means 11 may be ~ound in copending Canadian applica~ion Serial No. 262,864, fll~d October 6~ 1976 which is assigned to ~he same asslgnee as the inst~nt invention.
Drilling apparat~s 10 has fluid supply mean9 as follows for delivery of mo~ive fluld to ac~uate pis~on 70. A motive fluid inlet connection 130 extends radially through shell 74 for communicatlng an external source of motive fluid flow such as a con~tant flow pump 132 via a fluid line.l34 into chamber 76A
which. ls of a volume to provide a reservoir of pressurized motive fluid for deliuery to the upstroke and downs~roke driving chambers 110, 112. When motive fluid is supplied to the respective driving chambers 110~ 112 the fluid response is s~pplied primarily by the chamber 76A whereby the percussion head 12 need not depend directly on pump 132 for immediate fluid flow reqponse and large pressure fluctuations in the supply line 134 are thus avoided. During inlet deadband cycle portions ~to be - described hereinbelow) when all fluid inlets to ~he chambers 110, 112 are closed, pump 132 recharges chamber 7~A for the next f1uid inlet opening. Cha~lber 76A communicates by means of a plurality of circumferentially spaced and generally radially extending bores 134 with a downstroke inlet annulus 136 extending radially outwardly of bore portion 104 axially rearwardly of the bore portion 106. The radial bores 134 are intersected by a respectlve plurality of axially extending passagæs 138 in cylinder 72 which in turn communlcate via another plurality of radially ex~end-P~ .
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ing bor~s l40 with an upstLolce inl~t annulu~ 2 extending radlally outwardly of bore ' . ~
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portion 96 axially forwardly of bore portion ]06 whereby fluld communication between chamber 76A and the respective inlet annuli 136, 142 is constan-tly maintained. Similarly, the annular chamhers 76s and 76D are in continuolls fluid communication with the downstroke and upstroke driving chambers 112, 110 via axially spaced pluralities of circumferentially spaced and ~enerally radially extending ~ores 144, 146, respectively~ to provide respective down-stxoke and upstroke fluid energy accumulators for storing and releasing fluid pressure energy as described herein below, and the remaining chamber 76C communicates vla a similarly disposed plurality of radially extending bores 148 with an exhaust annulus 150 extending radially outwardly of bore portion 106 intermediate the axial ends thereof.
The volume of chambers 110 and 112 and the associated chambers 76D, 76B is variable by movement oE piston 70 alternately into and out of the chambers 110, 112. The percent volume variation is quite small, for example in the range of a fraction of 1% to approximately 5% in view of the limited compressibility of hydraulic fluids. The limits of percent volume variation may vary depending upon the particular fluid to be used. The respective pluralities of radial bores 144, 145 and 148 are circumferentially spaced intermediate the axial passages 138 (Fig. 3) to provide proper fluid flow as described.
Preferably, all of the respective pluralities of radially extending bores 144, 146 and 148 are spaced evenly about the circumference of cylinder 72 whereby the fluid ~ _g_ .. ... . . . .

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flow therethrouyh to and from bore 88 produces no net side loading or -torque upon the piston 70. Accordingly, piston 70 may readily be rota-ted by an externally applied xotational impetus supplied for example by the rotating striking bar 42 during contact thereof with piston 70 at impact. Rotation of piston 70 within liner assembly 90 induces rotary viscous shear forces to provide a hydro-dynamic lubricant film between the relatively rotating elements thereby improving the efficacy of piston lubrica-tion to reduce wear and friction during piston reciproca-tion. Additionally, the absence of torque and side loading on piston 70 as described permits continuing piston rotation during cycle portions between impact.
To the extent that piston 70 is rotating concomitantly with striking bar 42 as each impact is initiated, the wear factor attr~butable to relative ~ns~

ro~atlon between sucl~ impacting members during contact will be reduced. An exhaust outlet connection 152 communicates radially through shell 74 with exhaust chamber 76C and has a fluid line 154 connected thereto whereby exhaust fluid may be directed to a suitable fluid reservoir 156~
secause piston 70 (Fig. 4) is symmetrical about its medial transverse plane P P, only one axial half portion of the illustrated pistonr i.e., the upstroke half, will b~ described. The remaining piston half portiGn, i.e. the downstroke half, is the mirror image of the upstroke half.
The reference characters applied to the downstroke half are primed characters -to correspond to the hereinbelow described parts of the upstroke half of piston 70. The head portion 108 of piston 70 comprises a central, axially extending annul.ar land 158 axially slidable within bore portion 106 in cooperation with exhaust annulus 150 to provide exhaust porting or valving during piston recip-rocation. A land 162 is formed with its largest diameter end portion 160, which is smaller than the diameter of land 158, located adjacent the axial end of land 158 and tapers radially and inwardly therefrom along its axial extent at a taper angle with respect to the central longi-tudinal axis of piston 70 in the range of about 5 to about 15, preferable 10, to provide controlled porting of exhaust fluid by uniformly increasing the outflow of pressure fluid to exhaust as the exhaust annulus 150 opens. Land 162 thereby reduces the possibility of . .

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undesirable flui~ cavitation which might occur as a result of uncontrolled fluid pressure release to the exhaust.
Additionally, the taper on land 162 tends to promote non-turbulent flow of pressurized fluid from the respective driving chambers 110, 112 to the exhaust as pis-ton head 108 alternately moves into each chamber 110, 112 during reciprocation, thereby reducing the tendency -lOA-, .

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of the fluid within chambers 110, 112 to retard piston movement ~hereinto.
Axially spaced from the outer axial end of land 162 is an annular land 166 cooperable with an annular cavity 168 formed adjacent the intexface of bore portions 106 and 96 to provide a fluid cushion in the event of excess piston overtravel during reciprocation. Extending axially intermediate the axially adjacent ends of lands 162 and 166 is an intervening portion 164 which may be formed with a uniform or a tapering diameter, depending upon the respective diameters of the portions of lands 162 and 166 joined thereb~. Land 166 extends axially outwardly to terminate adjacent the stem portion 98. A radially inwardly extending annular inlet groove 170 is formed in stem portion 98 intermediate the axial ends thereof for providing fluid inlet porting or valving dur.ing piston reciprocation in cooperation with inlet annulus 142. The stem portion axially inward (or rearward) of groove 170 functions primarily as an inlet valve seat in cooperation with the respective portion of bore porti.on 96. The portion of stem 98 axially outward (or Eorward) of groove 170 is cooperable with the remainder of bore portion 96 for slidably supporting the piston 70 within bore 88. With the symmet:rical piston 70 as described, the drill 10 may be assembled with either end of the piston 70 forward whereby an extended piston life is obtainable by reversing the piston 70 when the impact end thereof :-:

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becomes worn after lenythy service. rrO this encl, the bore portions 104 and 96 are arranged to engage equal axial lengths of the respective piston stem 98', 98 thereby ensuring the development of symmetrical wear patterns on the respective piston stem portions. That is, the axial lenyths of bore portions 104 and 96 are proportioned with respect to the stroke of piston 70 to ensure that respectively axially opposed llA-' . ' ,C
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i~' .' ` ' ' ' ~ ' ' " ' ' ' , ' . ' t:ip por-~ions 13, 15 of respective stems 98, 98~ are never slidably engaged within respective bore por-tions ~6, 104 during piston reciprocation (Fig. 2~. Accordingly, after extended use the tip portions 13, 15 will have a larger diameter than the respective slidably supported stem portions 98, 98' which will have sustained measurable wear, and symmetrically located annular ledges (not shown) will thus have been developed therebetween whereby piston 70 may be reversed in its bore even after ext~nded use without risk of mechanical interference between such annular ledges and the axially outward extremi.ties of the bore portions 104, 96.
Drill 10 includes a percussion case draining means 172 (Figs. 2 and 3) employed in conjunction with annular wiper seals 174 encompassing piston stem portions 98, 98' intermediate the axial ends of each respective bore portion 96, 104. Limited fluid leakage past wipers 174 gradually accumulates adjacent the piston end portions as in cavity 176 and therefore, such cavities as 176 are sui~ably vented to preclude such fluid accumulations.
In conjunction with each seal 174 an annular drain cavity 178 is formed in each bore portion 96, 104 axially inwardly of the respective seals 174 for containing any fluid which leaks axially outward along the periphery of the stem portions 98, 98' from the respective chambers 110, 112. Such fluid leakage is drained from each of the annuli 178 via one or more generally radially extending `' , :

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passages 180 to an axially extendlng passage 182 in cylinder 72. Passage 182 communicates with an annular drain cavity 184 which extends radially inward and outward of bearing annulus 114 intermediate cylinder 72 and backhead 16, and includes at least one radially extending slot 186 communicating radially across annulus 114 between the radially inward and outward portions thereo~.
Cavity 184 is isolated from the radially in~ardly acljacent cavi-ty :L76 by the axial face seal 118 between backhead 16 and buffer ring 102. A drain connection 188 is prov:ided in backhead 16 for communicating a fluid drain 1.ine 190 from reservoir 156 into cavity 184 whereby a Eluid flow path is established for dissipating fluid pressure and directing fluid leakage away from the axi.ally inner sides of seals 174.
In general, fluid leakage in drill 110 could cause dangerously high pressures therewithin, for example on backhead 16, thereby precipitating catastrophic failure of the front or back heads 18, 16 or side rods 20. Accord-ingly, the inclusion of annular cavity 184 in the drain path as described precludes any pressure buildup there-within by venting cavity 184 to reservoir 56 as part of the percussion case drain means 172. A similar provision may be utilized to preclude pressure buildup in the yoke housing 28 or between portions of the cylinder 72 and yoke 14.
The radial drain passage 180 communicating with the forward drain annulus 178 includes an axially elongated annular cavity 192 formed radially intermediate the liner 94 and cylinder 72 wherein fluid may accumulate to he tapped off for lubricating various portions of the drill.
For example, a network of passages 194 (Fiy. 2) communicates 25 from annulus 192 through cylinder 72, yoke housing 28 and .
front head 18 to deliver fluid leakage from annulus 192 ~ -13-,, ~

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for lubrication of relatively rota-table forward end portions of -the chuck 30 and front head 18.
A our way, open center valve 196 (Fig. 2) is interposed in fluid lines 134, 154 between the drill 10 and the pump 132 and reservoix 156 for cvntrolling motive fluid Elow to the drill 10. Valve 196 ls selectively operable to a pos~tlon A to connect pump 132 to inlet 130 and e~haust outlet 152 to reservoir 156, or to a position C for connecting pump 132 to exhaust outlet 152 and inlet connection 130 to reservoir 156 for a purpose to be described hereinbelow. Valve 196 addit.ionally provides for a third position B (not necessarily intexmediate the positions A and C) ~herein motive fluid flows ~reely ~rom pum.p 132 to all ports oE valve 196 and back to reseryoir 156 to equalize the fluid pressures in the drill i`nlet and exhaust chambers 76A, 76C. The position B provides a neutral or idle operating mode fox such purposes as purging of air or impurities $rom the fluid in dXill 10.
Operation of drill lQ is illustrated in Fig. 5 by the relationship of fluid pre$sure in the driving cha~bers 110, 112 and the respectiVe energy accumulators 76D, 76B to piston position in its reciprocal travel. As piston 70 reciprocates .. . .
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within bore 88 tl~e upst.roke and downstroke inlet grooves 170, 170' alternately communicate respective inlet annuli 142, 136 with respec-tive upstroke and downstroke chambers 110, 112 and the associated accumulators 76D, 76B (hereinafter ; 5 referred to respectively as the "upstroke side" and the "downstroke slde" of the piston) to act upon the differential areas formed by the diameter differential between land 158 and respective stems 98, 98'. Likewise, during piston reciprocation land 158 alternately communicates axially opposed end portions of exhaust annulus 150 with the up-stroke and downstroke sides of piston 70 to intermittently exhaust pressurized fluid therefrom. For illustrative clarity the piston displacement scale in Fig. 5 is greatly extended over the actual stroke of the piston in the described embodiment, which is a very short stroke on the order of 5/8". Furthermore, the illustrated range of presswre values may be varied widely and is therefore not to be considered a limitation on the invention described.
Drill 10 is of the valveless or self-exciting type wherein grooves 170, 170' and land 158 of piston 70 cooperate with respective annuli 142, 136 and 150 to valve motive fluid to and from the upstroke side and downstroke side of the piston 70 in response to the position of piston 70 in its stroke. The respective inlet and exhaust ports thus formed provide fluid flow rate control over a con~
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state as indicated by continuously variable flow resistances Rl through R~ in Fiy. 4. By virtue of peripheral clearances between piston 70 and bore 88 adjacent the respective i.nlet and exhaust ports a degree of fluid flow is maintained even when -the ports are "closed" as at Rl for example.
A balanced or equilibrium pis-ton posikion illustrated as being to the upstroke side of the midstroke position (Fig. 4) ~,, ii3~

is defined for the piston 70 wh~reat the upstroke and down-stroke sides of piston head 108 are subjected to equal and opposite motive fluid forcesO In terms of the indicated flow resistance the balanced position of piston 70 is defined as that position for which Rl/R2 equals R3/R4.
That is, the ratio oE inlet pressure drop to exhaust pressure drop on the downstroke sids of piston head 108 is equal to the ratio of inlet pressure drop to exhaust pressure drop on the upstroke side. In other words, the total pressure drop from inlet chamber 76A to exhaust chamber 76C is proportioned identically between the respective inlet and exhaust ports for both the upstroke side and the downstroke side of the piston. Since the total pressure drop from chamber 76A to chamher 76C is the same for any path therebetween, and since such pressure is identically pro-portioned between the respective inlet and exhaust ports on both the upstroke and downstroke sides of the piston head 108, the net effective pressure acting on either side of the piston head 108 will be equal for the balanced ~ 20 piston position. There is no general requirement for ;- equality among any of the flow resistances Rl through R~
at piston equilibrium so long as the indicated ratios hold.
~; For example, assume hypothetically that R3 exceeds Rl and R4 exceeds R2 at the piston equilibrium position. It ~ollows then that ~3 ~ R4 exceeds Rl -~ R2 (the total flow resistance from inlet 76A to exhaust 76C is greater for the downstroke side than for the upstroke side) and thus ~ -15-':.' . , - ' ~ ' . .
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a larger propo.r-tion of -the~ total flui~ flow from inle-t to exhaust will pass through -the ups-tro]ce side. Never theless, so long as the pis-ton 70 resides at the equilibrium position such that Rl/R2 equals R3/R4, equal net effective pressures will act on each side of the piston head 108 in spite of the unequal flows, and the piston 70 thus will not be urged in either the upstroke or the downstroke direction by fluid pressure.

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The above-describecl relati.onsh,ip of flow resistance is not dependent upon -the particular dimensions or form of plston 70 and lin~r assembly 90. In general the various porting land and cJroove widths, circumferential clearances, port spacing, taper angles and the like may be varied to provide the described flow resistance relation~
ships to deEine a suitable piston equilibrium pos.ition.
An additional requirement that R4 not be equal to R2 for the equilibrium position provides for simplified drill startup as hereinbelow described. For initial opera-tion, pump 132 is providing fluid at the full flow rate fo.~ the neutral operating mode with valve 196 in the B
position whereby fluid circulates freely from pump 132 through valve 196 and back to reservoir 156, and addition-ally to both the inlet and exhaust chambers 76A, 76C tocompletely flood all fluid flow passages and equalize fluid pressure throughout drill 10. To begin piscon reciprocation valve 196 is shifted from the B position to either the A or C position to port full motive fluid flow through drill 10. In the A position chamber 76A is pressurized by pump 132 and chamber 76C is exhausted to reservoir 156 whereby the piston 70, which in general will not reside at the hereinabove defined equilibrium position, will be urged toward its equilibrium position by the inlet-to-exhaust pressure differential. As an example, assume that the piston 70 .initially is positioned in the upstroke direction from its equilibrium position with valve 196 in 16_ ~.
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: ~ ' the A pOSitiOll. It follows that Rl and R2 axe greater (ports more fully closed) and R2 and R3 are less (ports more fully open) than when piston 70 is at equilibrium.
Accordingly, Rl/R2 will be greater than R3/R (the proportion of total pressure drop through the upstroke side inlet exceeds the proportion of total pressure drop through the downstroke side inlet) whereby a ~r 1 6P-`'' :; ::

net unopposed fluicl pressure component acts on -the down-s-troke side to urge piston 70 in the down~troke direction toward its equilibrium posi-tion. Similar considerations apply if piston 70 initially resides downstroke from its balanced position whereat Rl/R2 is less than R3/R~ and an unopposed fluid pressure component thus acts on the upstroke side to urge piston 70 toward the equilibrium position. In either case as the piston 70 approaches equilibrium, the ratios Rl/R and R3/R4 approach equality and the net unopposed fluid pressure component acting on piston head 108 approaches zero.
From the above analysis it will be clear that if piston 70 overtravels its equilibrium position from either direction under the impetus of an unopposed fluid pressure component, an oppositely directed fluid pressure component will be established to urge piston 70 back toward the equilibrium position. Such repetitive piston overtravel of the equilibrium position alternately in the upstroke ~nd downstroke dixections constitutes -the normal self-exciting piston reciprocation mode. Therefore~ when valve196 is placed in the A position piston 70 may immediately begin self-excited reciprocation, in which case drill startup is completed, or may come to rest at the equilibrium position. Should this occur drill startup may be effected by shifting valve 196 -to the C position to pressurize exhaust chamber 76C and connect inlet chamber 76A to reservoir 156. Inasmuch as R2 and R4 are not equal at Y

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the equilibrium position as hereinabove mentioned (in this case R4 exceeds R2~, the initial fluid pressuXe surge from chamber 76C will more readily pressuri~e the upstroke side of piston head 108 thereby ur~in~
piston 70 further upstroke and away ~rom equilibrium , -17A-~.~, .

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, Wit)l chamber 76C pressuriæed and chambers 76A
exhaus-ked, the condition Rl/~2 equals R3/R~ for piston equilibrium st.ill applies. However, in this case it is a very precarious equilibrium wherein any deviation of piston 70 from equilibrium results in a net unopposed fluid pressure component in the di.rection of such deviation which increases with increasing devia-tion to urge the piston fuxther from equilibrium. Accordingly, with valve 196 in the C position the initial pressure surge from chamber 76C urges piston 70 in the upstroke direction such that Rl/R2 increases and R3/R~ decreases, and an unopposed fluid pressure component thus develops on the upstroke side to urge the piston from equilibrium. As the piston 70 deviates from equilibrium the upstroke fluid pressure component increases to urge piston 70 to the full upstroke position at which point Rl/R2 greatly exceeds R3/R~.
Accordingly, upon shifting valve 196 back to the A position a large unopposed fluid pressure component will act upon the downstroke side to urge piston 70 toward and past equilibrium whereby self-excited piston reciprocation is established as hereinabove described.
Once having been started the piston 70 will continue in self-excited reciprocation according to the cycle depicted in Fig. 5. Piston 70 begins its downward stroke from the full upstroke position 200 (left ordinate of Fig. 5) whereat the downstroke side is fully open to inlet chamber 76A.

.~ -18-:

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and is pr~ssurized tu near peak inlet pressure, 2500 psi for exarnple. The ups-troke side is open to exhaust chamber 76C and is a-t the exhaus-t back pressure, for example 200 psi as shown at 202. Exhaust back pressure is maintained by the various flow restric-tions between annulus 150 and reservoir 156, for example the changing cross sectional shape of the exhaust passages 148, the length of fluid line 154 and so forth. The exhaust back pressure in con~unction with the hereinabove described piston tapers 160 prevents cavitation of pressurized fluid flowing to exhaust by maintaining a positive exhaust path Eluid pxessure at all times. As piston 70 begins to accelerate toward impact (to the right in Fig. 5) pressure on the downstroke side begins to fall along line 204 as the moving piston head 108 vacates chamber 112 to increase the volume théreof. Simultaneously the accelerating piston decreases the volume of chamber 110; however, because the exhaust remains open to the upstroke side during this cycle portion the fluid pressure in chambers 110 and 76D does not significantly increas~e, but remains essentially constant as indicated by line 206. As piston 70 reaches point 208 on line 204 in its downstroke the rearward edge of groove 170' passes the forward edge o~

annulus 136 and the inlet to the downstroke side closes (R3 increases substantially). Thereafter the continued operation of pump 132 charges inlet chamber 76A up to peak pressure along line 210 during an inlet deadband -19- ~
. ~ .
, . .

' : -" ' ~ ": ` ', ' portion of the cycle while the piston continues to accelera-te under the irnpe-tus of fluid pressure energy stored on the downstroke side in chambers 112 and 76B.
Because the volume of chamber 112 continues to increase as piston head 108 vacates it, the pressure of fluid therein and in communicating chamber 76B con-tinues to drop along line 212. Simultaneously the fluid pressure on the upstroke side of the piston (chambers 110 and 76D) begins to rise ~19A-.. . . . .

. :,.
- '.

along line 214 as the volume of chamber 1.10 continues to decrease before -the encroaching piston head 108 and the exhaust area open to the upstroke side clecreases (flow resistance R2 increases).
At point 216 on line 212 land 158 is centered on annulus 150 ~R4 equals ~2j and thus upon further piston movement the exhaust chamber 76C is opened to the down-stroke side and simultaneollsly closed to the upstroke side of piston head 108. Accordingly, the fluid pressure on the downstroke side drops rapidly along lrine 218 to the exhaust back pressure as the remaining fluid energy in chambers 112 and 76B is exhausted to chamber 76C. The indicated exhaus-t back pressure, although only a fraction of the peak driving pressure, continues driving the piston toward impact. Also substantially simultaneously with or very shortly after 216 in the cycle as at 216' the inlet deadband cycle portion ends as cham~er 76A is opened to the upstroke side to charge inlet fluid pressure energy into chambers 110 and 76D whereupon the pressure in chamber 76A drops from its peak value 220 and subsequently equalizes with the upstroke side pressure at 222. As the volume of chamber 110 further decreases and charging of fluid into the upstroke side continues the fluid pressure in the upstroke side rises along line 224 toward its peak value as the piston impacts upon the striking bar 42, indicated at 226 on the right ordinate of the Fig. 5.

. ~ -20-~ : ' The axia]. position o~ piston 70 at impac-t is not a fixed parameter of -the drill but may be varied over a compara-tively broad range of loca-tions because during the piston downstroke, chamber 76D absorbs much of the energy input generated by piston head 108 movement into chamber 110 and the pressu.re fluid inflow from chamber 76A thereby reducing the net fluid pressure resistance to further piston downstroke travel. Such fluid pressure resistance, if not reduced, would otherwise dissipate . ; ~ ' ,,:
` ' ` ' ' a signific~nt paxt of the piston kinetic eneXgy be~ore impact and render the drill substantially more sensitive to impact point locat.ion. Storage of fluid pressure energy in chamber 76D during the piston downstroke also provides an extended dwell time or contact period between piston 70 and stxiking bar 42 during ir~pact ~or more efficient impact energy transmission, and additionally provides an initial store of energy ~or accelerating the piston in the upstroke direction a~ter impact~
As the cycle continues, the piston rebounds from striking bar 42 and begins to accelerate toward its full upstroke position under the impetus of the ~luid energy in chamber 76D and simultaneously supplied from chamber 76A through the opPn inlet to the upstroke side.
As piston head 108 vacates chambex 110 to increase the volume thereof the pressure therein dxops along line 228 to point 230 whereupon the inlet to the upstroke side closes~ Substantially simultaneously or lf desired very shortly therea~ter as at 230', exhaust chamber 76C is opened to the upstroke side and closed to the downstroke side, and accordingly the upstxoke side pressure drops shaxply along line 232 as the Xemaining fluicl energy in chambers 110 and 76D is exhausted. Chambers 112 and 76B which have been gxadually pressurized along line 234 to point 230' during the upstroke are further pressurized along line 236 as the piston head lQ8 encroaches upon chamber 112 through the inlet deadband cycle portion. Also during the inlet deadband portion inlet chamber 76A is again ~ ~ -21-.. :

~4~

pressurized by flow :Erom pump 132 along line 238 to peak inlet pressure at 240. As tile piston reaches point 209 in its upstroke, which is -the end of the inlet dead-band portion, the pressure :Eluid inlet opens to the down-stroke side to once again charge pressure ~luid t.hereintofrom chamber 76A, the pressure in which Ealls o~ alon~
line 242 and equalizes with the `
';
.

~5~

downstrc~)ke side pressure which continues increasing along line 244. Fluid pressure on the upstroke side, which remains open to exhaust chamber 76C, continues to decrease along line 232 to the exhaus-t back pressure as the piston 70 travels to the full upstroke position. Under the impetus of fluid pressure accumulated within chambers 76A, 110 and 76B, the piston decel~rates to a stop at the full upstroke position thereof with peak inlet pressure refusing further upstroke movement as indicated at 200, and immediately accelerates toward another impact to begin another cycle.
The explanation hereinabove of piston startup and cycling represents the inventor's best understanding of some of the applicable theoretical considerations and is not to be construed as the complete, final or authori tative explanation of the physical laws governing operation of this invention.
The description hereinabove discloses an improved hammer for a rock drilling apparatus of simplified and compact design, and having means to easily start piston reciprocation from a neutral position thereof, and to prevent fluid cavitation, and an improved self-exciting hammer piston cycle which provides for improved impact energy transfer efficiency. The invention additionally provides among other novel features, means for draining leakage from closed cavities which could otherwise become dangerously pressurized.

~ -22-,~ ' . , ' .
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~ . , .

5~
Notwithstandin~ -the disclosure of a particular p-eferred embodiment of the invention, it i5 to be under~
stood -that -the invention is suscep-tib.Le of various alternative embodiments and numerous modifications without departing from the broad spiri-t and scope thereof.
For example: the yoke por-tion and fluid circuit means may ~ake any of various suitable forms; the relative sizes of the various accumula~or chambers may be varied ~5;3~

as by packing portions thereof with arcuate pla-tes (not shown); the piston may comprise any of a wide variety Q~
reversible or non-reversible symmetrical or asymmetrical designs, and particularly reversible asymmetrical designs wherein reversing the piston in its bore provides a modified operating cycle; various alternative porting arrangements offering mod;fied operating cycles within the scope of the invention may be employed such as a cycle including a short positive exhaust deadband portion during which chamber 76C is isolated from both the upstroke and downstroke sides o~ piston head 108, or a short ne~ative deadband portion durin~ which chamher 76C is open to both the upstroke and downstroke si:des; the upstroke si.de and downstroke side piston differential axeas are not necessarily equal; and the like. These and other embodiments and modifications having been env~.sioned and anticipated by the invento.r, the invention should be intexpreted broadly and limited only by the scope of the claims appended ~ hereto.
'-~
JSB:as ;~ D-7206 . -23-?

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A hydraulic drive for actuating a tool comprising:
a body member having an elongated bore therein with a central longitudinal axis and with one end of said bore being adapted to receive at least a portion of an actuatable tool structure internally thereof; and elongated piston axially reciprocal within said bore to deliver impact blows to such a tool; said bore having an axially intermediate chamber section of greater cross-sectional extent than the cross-sectional extent of the sections of said bore axially outwardly thereof; said piston having a formed axially intermediate head section; said head section having a central portion with a finite axially extending outer surface closely slidably received within said chamber section to define chamber portions within said chamber section on axially opposite.
sides of said central portion of said head section which chamber portions vary inversely in volume as said piston reciprocates, first passageway means in said body member having axially spaced fluid inlet port means in communication with said bore axially outwardly of said chamber section, respectively; said piston having formed axially spaced means cooperable with said port means, respectively, for selective admission of hydraulic fluid to said chamber portions alternately to reciprocate said piston; second passageway means in said body member having a discharge port means with an axial extent in communication with said chamber section;
said outer surface being cooperable with said axial extent of said discharge port means to control the discharge of hydraulic fluid from said chamber portions, and said piston having formed portions at the ends of said axially extending outer surface of a configuration to control the rate of flow of such discharge.

2. A hydraulic drive as set forth in claim 1 wherein said formed portions are identical in configuration.

3. A hydraulic drive as set forth in claim 2 wherein said formed portions are tapered at an angle with respect to the central longitudinal axis of said piston.

4. A hydraulic drive as set forth in claim 3 wherein said taper is in the range of 5 to 15 degrees.

5. A hydraulic drive as set forth in claim 1 wherein said configuration is of a form to maintain a pressure within the fluid in said chamber portions during such discharge.

6. A method of moving an elongated impact piston through a work output stroke within an elongated bore of a body member in which said bore contains hydraulic fluid and said piston has an intermediate portion of said bore whereby piston actuating and piston return chambers are formed within said bore on opposite sides of the head portion comprising, moving said piston through an initial portion of such a work output stroke by admitting pressurized hydraulic fluid to said actuating chamber throughout said initial portion while simultaneously pressurizing fluid in a closed volume in continuous hydraulic communication with said actuating chamber and discharging hydraulic fluid from said return chamber at a controlled rate, discontinuing said admitting and moving said piston through an intermediate portion of such a work output stroke immediately subsequent to said initial portion by the hydraulic fluid in said closed volume and said actuating chamber while simultaneously discharging hydraulic fluid from said return chamber at a controlled rate and moving said piston through a final portion of such a work output stroke immediately subsequent to said intermediate portion by the hydraulic fluid in said closed volume and said actuating chamber while simultaneously discharging hydraulic fluid from said actuating chamber and discontinuing said discharging of said return chamber.

7. The method as specified in claim 6 including admitting pressurized hydraulic fluid to said return chamber throughout said final portion while simultaneously pressurizing hydraulic fluid in another closed volume in continuous hydraulic communication with said return chamber, moving said piston through an initial portion of a return stroke immediately subsequent to said final portion of such a work output stroke by continuing the admitting of pressurized hydraulic fluid to said return chamber and said another closed volume throughout said initial portion of such a return stroke while simultaneously discharging hydraulic fluid from said actuating chamber at a controlled rate, dis-continuing said last mentioned admitting and moving said piston through an immediate portion of such a return stroke immediately subsequent to said initial portion of such a return stroke by the hydraulic fluid in said another closed volume and said return chamber while simultaneously discharging hydraulic fluid from said actuating chamber at a controlled rate, and moving said piston through a final portion of such a return stroke immediately subsequent to said intermediate portion of such a return stroke by the hydraulic fluid in said another closed volume and said return chamber while simultaneously discharging hydraulic fluid from said return chamber and admitting pressurized hydraulic fluid to said actuating chamber.