CA1097185A - Switching mechanisms - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention provides a hydraulically driven reciprocatory tool comprising a piston with a shoulder reciprocable within a cylinder, the space within the cylinder on one side of the shoulder being maintained at high pressure, and the space on the other side of the shoulder being maintained at low pressure. The piston is driven against a constant bias force by means of pressure fluid by means of which a driving force is cyclically applied to the piston under the control of a shuttle valve.
The shuttle valve position is controlled by the axial position of the piston in the cylinder as sensed via the pressure of fluid in a signal line connecting the shuttle valve with first and second ports in the cylinder wall. The signal line has non-return valves for preventing flow of fluid from the shuttle valve to the first port, and from the second port to the shuttle valve. The driving force is applied to the piston via a duct in part of the cylinder body which projects into a recess in the piston. The projecting part can form a sliding seal with the recess to form a fluid tight enclosure in which the pressure of driving fluid can bear cyclically on the end of the blind bore. Alternatively the driving pressure fluid can act cyclically on a rod piston slideable in the duct within the projecting port so that the rod bears on the end of the blind bore, Preferably each non-return valve has associated therewith a variable throttle in the signal line, and according to a further preferred feature, means are provided for the controllable flow of fluid to or from the signal line.

Description

J~ q ~L~397~ 5 This invention relates to devices in whic.h a piston within a cylinder can be caused -to execute reciprocatol~ motion by an alternating different-ial pressure actinO on ths opposed faces of -the piston.
In ~ny applications of devices employing reciprocating pistons~ for example hydraulic hammers~ it is desirable t~ have as long a piston s-troke as possible within the limit deter~ined b~ the overall leng-th of the device.
In known pressure ~onsed reciprocatory devlces in which the position of the p;s-ton controls the operation o$ ~alve gear w~ioh in turn controls flow of the fluid to, and hence acceleration of, the piston, the length of tn~
c~linder iæ extendedin.length beyond that of a simple ram by the presence of pressure sensing grooves in the oylinder casing to allow communication of pressure within the oylinder~ at appropriate instants in the cycle~ to the valve gear. Such known devicos either havec~lind2rs uhich are undesirably long or have a relatively short piston stroke1 and this neoessitates a high reaction foroe for a ~iven impact foroe.
This inven-tion seeks to provide a reoiprocatory -tool which pro~ides a piston which oan reoiprocate with a stroke leng~h which is longer for a given oylinder length than the kno~n pressure sensed reciprocatory devices.
Preferred embodiments of tool according to the pre~ent invention seek to provide a stroke length of the piston ~rhioh oan ~e varied, The pre~ent in~ention provides a reoiprocato~J devioR oomprising:
a. A piston and a body defining a cylinder ..within whioh the piston oan reciprocate along an axis, the piston having a shoulder in fluid-tight oontact with the oylinder and the cylinder defining first and seoond ports spaoed from one another in the axial direction;
b. a first fluid enclosura capable of being maintained at a ralativel~- high pressure on one side of the Ehoulder and a second

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~951 7~85i fluid enclosure oapable of being m~intained at a relatively low pressure on the other side of the shoulder, each enclosure being defined by the pi6ton and cylinder~ the arrangcment of ports and shoulder being such tha-t each of the ports can communicate, at one relative position of the piston and cylinder, with the first fluid enolosure only~ and at a different rela~ive position of the piston and oylinder, with the second fluid enol~s~ra only;
o. a signal line i-n fluid Co~mu?liCatiO~. with the first port -through a fir6t fluid pa~sage which inoludes a non-return valve arranged to prevent flow of fluid along the passage to the first port~ and being in fluid communioation with the seoond po.rt through a seoond fluid pasæage whioh includes a non-return valve arranged to prevent flow of fluid along ~e passage a~ay from the seoond port; ~nd d. a main oontrol valve having a ~upply inlet for oonneotion to a ` high pressure fluid source ~nd a supply outlet for draining fluid at low pressure~ and a drive oonneotion isolated in flui.d tight manner from the first and seoond enolosure~, the 6aid n~n oontrol valve having a signal input to whioh the signal line is connected and being actuable by ohanges in fluid pressure in the sign~l line to connect alternately . the~suppl~Y inlet and the supply.outlet to the drive oonneotion;
e.~ ~he piston ha~ng a blind bore into which a part of the body projects~ the said projecting part of the bodg having a duot through ~hioh the force generated by the prasenoe of high pressure fluid in the drive oonnection oan be transmitted to act on the end of the blind . borc.
In use of the invention, the piston is biased to move in one direction in the cylinder by the aotion of relatively high fluid pressure in the first

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~luid enclosure~ and relatively low fluid pressure is present in the æecond fluid enclosure. Forces ara æpplied to the end of the blind bore by tho action of the main control val~e, which forces are ~lternately greater and less than the bias force o~ the relatively high pressure in the first fluid enclosure on the shoulder.
During US9 of the in~ention, the pressure ~rithin the cylinder adjacent to '~he cylinder w~ll is constantly high on one side of the sho~lder atld lo~ on the o-ther. TheprPssurised fluidfrom themaincontrolval~e, whichprovide~ theforcefordri~ingthepi~ton againstthebiased pressure on one side of the shoulder~ is necessarily isolat~d from the oylinder wall.
qhe force on the end surface of the blind bore can be applied by feeding Pluidat high pressure into a third fluid-tight enolGsure sealed by a seal bet~seen the cylindrical sur~ace of the lind bore and the projecting part of the body. Altel~atively~ foroe can be applied b~y a rod piston slideable in the blind bore whioh can be urged QntO the end sur~ace by ~luid pressure in the drive connection oP the main oontrol valve. So that the piston oan be driven against the bias force by fluid at the sarna ~ressure as the bias fluid pressure in the first fluid enclosure on the ~ide of the shoulder, the arsa of the end wall of the blind bore (or o~ the ~d piston as appropriate) acted on by the fluid pressure is arranged to be consid~rably greater th~n the area ~f ~he side of the shoulder.
The effective function of the two ports iæ to detect in which part of the cylinder the shoulder is located at any given instant~ and they are pre~erably located close to opposite ends of the cylinder. While it is convenient to use t~e relatiYely high hydroætatic pressure of fluid present in the first fluid enclosure to bias the piston to move in o~e direction, it is envisaged that other means of so biasing the piston could ~ .

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be used. For example, a compression spring located bet~een the body and an amlular surface of the piston could be used.
By way of example, embodiments of the invention will now be described with re~erence to thc accompanying drawings, in which:
Fig 1 (a) tO (d~ is a 4-part schematic diagram of a hydraulio piston in a cylinder (cut away)~ each part of which illustr&tes respectively the pattern of flui~ press~re at a particular instant in the cyclic motion of the piaton, Fig 2 is an axial section illustrating one way of supplying pressurised flv.id to the end surface of the blind bore of the piston illustrated in Fig 1 thereby to apply foroe to the piston;
Fig 3 i8 an axial section illustr&t:Lng an alternative method by which force is transmitted from the hydraulic fluid to the end surface of the blind bore in the piston;
~ig ~ i~ an c~xial section oP an anvll for uae with the apparatus shown in Fig 2 or 3; and Fig 5 is a schematic diagram of part of a hydraulic circuit which can be included in the appar~tus shown in Fig 1~ ;
Fig 1 (a) to (d) shows a reciprocatory device comprising a dri~ing piston 6 and a bcdy 4 defining a cylinder 2. The drivin~ pi.ston 6 ~s reciprocable within the cylinder 2 between a retracted position, Shown in Fig 1 (a) in which a rear face 3 of the piston is close to a rear enddp of the oylinder 2, and a fo~ard position, shown in Fig 1 ~) at which a fol~ard end 5 of the piston 6 strikes the rear end of a tool bit 7. Fig 1 (b) and (d) shoN the piston 6 at intermediate positions between the ~ul1y retr~cted and the fully forward posi-tiona. Piston 6 has a shoulder Z of enlarged diameter ~hich is in fluid--tight contact with the cylindrical ~ 5 ,,.,.. ,.. ~.. - . ~,~

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7~L~5 surface of the cylinder. This shoulder 1 of the piston 6 may be termed the "Crown" or "head" of the piston.
A shuttle valve 8 constituting a main control valve is arranged to connect either a low pressure fluid supply line 9 or a high pressure fluid supply line 10 to a drive connection line 11 and hence to a projecting part of the body in the form of a tube or snout 12 extending forward parallel to the axis of the cylinder 2 from the rear end of the cylinder. The line 11 merges into a duct in the form of a bore extending through the tube or snout 12. The shuttle valve 8 is biased in such a way as to connect the low pressure fluid supply line 9 to line 11 by subjecting it to the high pressure in fluid supply line 10 fed through a duct 14 to a signal port 13 communicat-ing with a small shuttle face. The shuttle valve 8 is controlled and actuated by the presence or absence of high pressure H in a signal line 16 extending from a signal port 15, communicating with a large shuttle face.
The signal line 16 is connected to a first fluid passage 31 ending in a first port 28 and including a first non-return valve 25. It is also connected to a second fluid passage 32 ending in a second port 29 and including a second non-return valve 26. The non-return valves 25 and 26 permit, respectively, flow of fluid out of the cylinder through the port 28 which is located in the cylinder wall close to its rear end, and flow into the cylinder 2 through the port 29 which is located near its forward end.
The cylinder 2 is provided with a port 17 at its forward end perma-nently connected to the high pressure fluid supply line 10 through a duct 18 so that a first fluid enclosure 33 in the interior of the cylinder and forward of the shoulder 1 can be maintained at a high pressure H. A port 19 at the rear end of the cylinder 2 is connected to the low pressure of the fluid supply line 9 through a duct 20 including a non-return valve 30 which permits flow ,~
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7~5 of the fluid from the cylinder to the line 9 but not in the other direction~
and which hence maintains the interior of the cylinder in a seco-nd fluld enclo~ure 34, rearward of the piston 6 and out~ide the tube 12 at low pressure L.
It iB necessary to isolate fluid flow between the shuttle valve 8 a-nd the duct within the -tube 12~ which fluid drives the piston ~or~rd, fro that par-t of the volume within the cylinder which i~ otl-tside the tubo 12.
Figures 2 and 3 respeG-tively illustrate two methods by-~hich thi~ ~ay be done. In the embodiment illustrated in Fig 2, the tube or snout 12 extends into a blind bore 21 in the piaton 6~ the end portion 22 of -the tube 12 having a aeal with the c~lindrical surface of the bore 21. A third fluid-tight enolos~re is thtls formed between the projeoting part of the body and the end surf_ce of the blind bore. ~n the embodiment illuatrated in Fiæ 3, the bore of th~ tube 12 oontains a rod piston 23 slideable within the bore of the tube and in sealing oontact wi.th it, and the rod piston 23 oan be urged against the ~nd surfaoe 24 of the blind bore 21 by th~ applioa-tion to it of fluid presatlre.
qhe effeotive area of the driven rear face of the piston 6 is, in Figure ~1 the area of the end surface 24 of the bore 21. In Fig 3, it i~
the cross sectional a~ea of thc rod piston 23 acted on ~y fluid. In both cases this area is arranged to be approximately twice the effeotive area of an annular for~rd face 27 of the ahoulder 1 between the piston 6 and the cylinder wall~ so that the piston 6 can be driven forward or baokwards depending on ~hether the bore in the tube 12 is in communication with the high presaure Muid supply line 10 or the low pressure fluid supply line 9.
In this respeot in particular Figs 2 and 3 are not to scale~
The ~pparatus sho~ in Fig 1, which may include the embodiment of ~. .

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~7~5 Fig 2 or of Fig 3~ operates a,s foll,ows,. At the ~,on*igura,t,ion illustrated in Fig la in ~ihich the piston 6 i8 in the,retraoted-position~ fluid at high pressure communicates with the signal line 16 through duct 18, port 17, first fluid enclosure ~3, pcrt 28 and non~return valve 25~ so that the shuttle valve 8 is i~ a position con,nec-ting-the,h,igh pressure fluid supply line 10 to the d,uct w~thin tube 12.. Fl-~uid.at hi~s-~ressure ~ present in the first flu;.d enclosur~ 33 acts on the a.nnular for~ard face 27 of the shoulder 1 at al~ positions of piston 6. ~he piston 6 will thus be accelerated forward as the pressure on the effective area of its,rear face e~er-ts a greater force tha,n the sa~e~ high pressure acting on -its effective smaller front face 27. ~7hon tho piston 6 m,oves f~o~rd ,to Qover and pass the port 28 (Fig lb), direct communication between the,high pressure supply and the signal line 16 is brolcen bllt~ since fl.~lid can only lea~ ver~ slowly from the supply line 16~ the shuttle valva 8 c&nnot switch ~ntil the shoulder 1 passes the port 29 (Fig 1c). After $hi.~, ,f.luid flows fro~ tho si~nal line 16 into -the second fluid enclosure 34 beh.ind the shoulder 1, ~Jhich enolosure 3~ is in constant comml~lication ,with $he 10W pressure ~luid supply line 9 through duct 20. On reduction $o ,l~ow pres,sure of the pressure in signal line 16 and hence at signal port 15, -the sh,uttle ~alve 8 switches under the action of high pressure fl,uid in its na~row bore Rignal port 13 so that the fluid dr&~ns from tube 12 yia -the l-in~ 11 to the low pressure fluid supply line 9~ initiating a retracti,on of the pieton 6 under the action of the high pressure fluid acting via line 18 and port 17 on its annular forward face 27.
During retraction of the piston (Fig 1d)~ ~Jhen the piston 6 is between ports 28 and 29~ high pressure ~luid cannot enter the si~nal line 16 throu~h the non-ret~rn valve 26, so that the ~-uttle valve 8 does not switch until Ihe shoulder 1 passes port 28. A~ tShis inst~nt (Fig 1a)~

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high pressure fluid H enteræ the signal line 16 from the first fluid enclosure 33 and passes through non-return valve 25 to switch the shuttle valve 8 al1d hence in-itiate another advance of the piston.
It will be seen that reciprocation of the piston 6 will continue until the supply of high pressure hydraulic fluid to it is discontinued, and that the len~th of cylinder additional to that of the stroke of the piston is no more than that occupied by the thiclmess of the shoulder 1.
Fig 4 ~hows an anvil 40 t~lhich encloses a head 41 of a hammer piston.
A hammer piston can be the piston 6 o* the a~paratus shown in the preceding ~igures. As the ha~er piston is caused to reciprocate then opposed faces of its head 41 strike interior surfaces ~2 and 43 of anvil 40 alternately.
The scale of Fi~ 4 i8 not the æame as that of Figs 1 to 3~
Fig 5 shows a part of a hydraulic circuit, denoted generally by reference 50, which can be included in signal line 16 o~ Fig 1- It comprises a branch 51 of the signal line 16, the brc~nch leadin~ to a modifier valve 52 which haæ high and 10tJ pressure hydraulic fluid lines 53 and 54 respcctively. ~he modifier valve 52 is capable of ~dmitting a controlled flow of hydraulic fluid into -the branch 51 from high pressure line 53 or of allowing a controlled flow of fluid out~of branch 51 throu~
low pressure line 54.
Signal line 16 has a loop 55 which includes first and second non-return valves 57 and 56 respectively. First and second variable throttles 58 and 59 respectively are provided adjacent the non-return valves 57 and 56. ~he ar ~3gement is æuch that the first variable throttle 5~ throttles only flow ~rom the port 28 to the valve 8, and the second variable throttle 59 throttles only flow from the valve 8 to the second port 29. ~he same effect can be achieved by locating the throttle 58 adjacent to the non-return val~e 25 _ g _ ~7~S

and throttle 5~ adjacen-t thc non-return valve 26~
me modifier valve 52 funotions as follo~rs~ As shot~n above~ the stroke of the piston 6 ~s.nor~lly such as to carry its shoulder 1 alternateiy beyond ports 28 and 29. ~nis is beca~se the shoulder musttravel the full length of the cylinder 2 before the fluid press~e in the signal line 16 can ohange enough to ~7itch the shuttle valve 8. However, where the modif`ier valve 52 allo~ls fluicl to flow either in-to or o~t o* the signal line 16 along the b~anch~51 then the pressure in the si~al lirP can ohange sufficiently to swi-tch the shuttle valve 8 before the shoulder 1 has travelled the -full len~th of the c~linder 2. r~hus the shoulder 1 can oscillate between and end of the cylinder 2 and a point between the ends of the cylinder, which point oan be varied by varying tha flot~--throl~h the modifier valveO
~le variable -throttles 58 and 59 function similarly to one another.
When shoulder 1 moves to a position whioh allows high pressure fluid to enter the signal line 16 then if the variable throttle 58 restrio-ts the flow of fluid along the line 16 there is a delay before the preEsure of the shuttle valve 8 builds up sufficiently to switch the valve. The piston 6 can thus be mad.e to t'~it'~ at one en~ of its stroke for a period fixed by the degree of throttling o~ the variable throttle 5~. The operation of the variable throttle 59 is similar in that it delays the flot~ of ~luid away from the shuttle valve ~ and through the port 29 so causing the piston 6 to "t~ait" at the other end of its strolce. ~he modifier valve 52 and the ~ariable throttles j8 and 59 can be used in comb~ation to provide a wide variation of piston movements. ~he shuttle valve 8 can be replaced by a non-inverting valve substantiall~ as`~ scribed and sho~m in West German Offenlegungs Schrif-t No 26 31 301.

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Claims (9)

I Claim:-

1. A reciprocatory device comprising:-a. a piston and a body defining a cylinder within which the piston can reciprocate along an axis, the piston having a shoulder in fluid-tight contact with the cylinder, and the cylinder defining first and second ports spaced from one another in the axial direction;
b. a first fluid enclosure capable of being maintained at a relatively high pressure on one side of the shoulder and a second fluid enclosure capable of being maintained at a relatively low pressure on the other side of the shoulder, each enclosure being defined by the piston and cylinder, the arrangement of ports and shoulder being such that each of the ports can communicate, at one relative position of the piston and cylinder, with the first fluid enclosure only, and at a different relative position of the piston and cylinder, with the second fluid enclosure only;
c. a signal line in fluid communication with the first port through a first-fluid passage which includes a non-return valve arranged to prevent flow of fluid along the passage to the first port, and being in fluid communication with the second port through a second fluid passage which includes a non-return valve arranged to prevent flow of fluid along the passage away from the second port; and d. a main control valve having a supply inlet for connection to a high pressure fluid source and a supply outlet for draining fluid at low pressure, and a drive connection isolated in fluid tight manner from the first and second enclosures, the said main control valve having a signal input to which the signal line is connected and being actuable by changes in fluid pressure in the signal line to connect alternately the supply inlet and the supply outlet to the drive connection;

e. the piston having a blind bore into which a part of the body projects the said projecting part of the body having a duct through which the force generated by the presence of high pressure fluid in the drive connec-tion can be transmitted to act on the end of the blind bore.

2. A reciprocatory device as claimed in claim 1 wherein the exterior of the projecting part of the body forms a sliding seal with the cylindrical surface of the blind bore, whereby there is formed a third fluid-tight enclosure between the body and the end surface of the blind bore, said third enclosure communicating with the drive connection through the duct in the projecting part.

3. A reciprocatory device as claimed in claim 1 wherein the duct is cylindrical and a rod piston slideable therein can bear on the end of the blind bore.

4. A reciprocatory device as claimed in any one of the preceding claims including a first variable throttle located in the fluid connection between the first port and the main control valve.

5. A reciprocatory device as claimed in any one of claims 1 to 3 including a first variable throttle located in the fluid connection between the first port and the main control valve in a position such that it throttles only fluid flow from the first port towards the main control valve.

6. A reciprocatory device as claimed in any one of claims 1 to 3 including a second variable throttle located in the fluid connection between the first port and the main control valve.

7. A reciprocatory device as claimed in any one of claims 1 to 3 including a second variable throttle located in the fluid connection between the first port and the main control valve in a position such that it throttles only fluid flow towards the second port and away from the control valve.

8. A reciprocatory device as claimed in any one of claims 1 to 3 wherein the signal line has a branch to a modifier valve which can permit a controlled flow of fluid out of the signal line along the branch.

9. A reciprocatory device as claimed in any one of claims 1 to 3 wherein the signal line has a branch to a modifier valve which can receive a supply of fluid at high pressure and can permit a controlled flow of such fluid along the branch and into the signal line.