Note: Descriptions are shown in the official language in which they were submitted.
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~ ~EG~PRDCATING PERCUSSIVE DEVICE
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The present mvention relates to hydraulically or pneumatically
actuated reciprocating devices, and in particular to percussive
devices such as rock drills.
United Kingdom patents GB 1526048 and GB Z157220 describe such
devices having preferred embodiment6 in the form of rock drills and
other percussive tools such as impactors (e.g. pav mg-breakers).
Such devioes oomprise a cylinder containing a double-actiny piston
having recessed portions which co-operate with a cont~ol port formed
in the cylinder wall. miS port leads to a controlling val~e
arrangement which controls the reciprocation of the piston. This
reciprocating motion is then imparted to a drill rod or shank
adaptor axially aligned ~ith the piston. The above two patents, GB
1526048 and ~B 2157220, relate specifically to such devices in which
the fre~uency of reciprocation may be varied.
In the case of rock drills and similar rotary percussive tools,
~e drill rod or shank adaptor is caused to rotate by gearing linked
to a driving motor. The gearing is arranged to allow some degree of
axial mov~ment of the drill rod, the generation of rotary moti~n is
thus independent of the percussive mechanism. ~-
In use, there is an optimum position of the drill rod relative
to the stroke of the hammer piston, such that the piston strikes the
drill xod just prior to the end of the piston power stroke.
Achieving this optimum positioning will result in maximlm transfer
of energy to the drill bit with increased penetration rates and
minimised reflected or wasted energy which can cause excessive wear
of the drill bit and damage to the rock drill oomponent6.
Because of the wear of the strike faces which can occur in use
together with the build up of tolerances w~lich affect the strike
position, wide variations in strike position from one mach:ine to
another oan result. We have appreciated that a mechanism i6
reguired to maintain the optimum 6trike position and oo~pensate for
it6 possible variation depending on piston power, rock oonditions
and thrust levels.
In acoordance with the present invention there is provided a
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hydraulic or pneumatic percussive devi oe oompri~ing a dbuble-acting
piston which executes~reciprocal motion and a t~ol ~r tool holder
executing limuted reciprocal mction due t~ the pisto~ striking the
said tool or holder near the end of the pi6ton pawer 6tr~ke wherein
a spool valve i6 provided which in resp~nse to the axial thrust
acting on the tool or holder applies a greater or lesser fluid
pressure t~ the tool or holder to maintain a substantially oDnstant
position thereof relative to the piston stroke.
Thus, when drilling, thrust levels will vary depen~ing on rock
conditions and piston power which will vary the forces on the tool.
During mLment6 of increased force the tool will tend to nnve
backwards (into the drill). By increasing the fluid pressure on the
tool or taol holder, the position of the tcol or tool holder
relative to the device (and hence the piston stroke) i~ maintained
substantially oonstant. With a corresponding drop in pressure which
occurs when drilling forces are reduced, the device maintains the
optimIm strike position.
In a further preferred embodiment, the ~ystem is adjustable, to
o~pe with drilling different types of rock, varying piston power,
and varying thrust levels.
The invention will now be further described by way of example
and with reference to the acooTpaning drawings in which:
Fig. 1 shows a sectioned part-assembly of a percussive rock
drill,
Fig. 2 is an enlarged view of the spool valve ass~i~bly of
I ~'ig.1,
', Fig. 3 shows a variable sleeve position control used in
conjunction with the 6pool ~alve of Fig. 2,
Fig. 4 shows diagrammatic representations of the hydraulic
circuits for the 6pool vaive of Fig.2, with (Fig. 4A) or without
(Fig. 4B) the control valve of Fig.3.
; The 6truckure and operation of the drill i6 similar ~a that ofour earlier application (GB 2157220) and, where appropriate, the
Bame reference numeral6 have been u6ed.
Referring initially to Fig. 1, the drill oomprise6 a hammer
pi~ton 60 at it6 left h~nd end for imparting blows to a drill rod
(n~t shown) retained by a Bhank adaptor 90 at it~ right h~nd end.
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The shank adaptor 90 and drill rod are caused to rot~te hy neans of
the engagement of 6pl~ned portion 86 with an internally splin~d
61eeve 88B ~*~ch m turn engages via dsgs 92B a gear 90B which
incorporates an insert 90D. The gear is rDtated by a pinion 93B
which iB oQnnected to a motor output shaft 94B via splines 200. Ihe
pinion is supported in bearings 201 and the motor output shaft 94B
is limited in axial movement by stop 203. The gear 90B is
supported in bearings 204 and 205 which are housed in housings 206
and 207. The rotation is ind~pendent of the percussive me~hanism.
During drilling the drill steel with its bit is thrust in to
the rock and the action of percussion and rotation causes it to
drill a hole. The reaction from the thrust and drilling forces i~
resi6ted by the gear 90B due to its contact, by way of the insert
90D, with the shank adaptor 90. The reaction is then normally
absorbed in a thrust bearing situated between the gear 90B and
housing 206 (as in GB 2157220A).
qb optimise the strike position and hence the effectiveness of
the percussive action the g~r 90B is in the form of a piston 90C at
the left hand side which ves in a cavity 208 counterbored into
housing 206. me allowable axial movement of the gear 90B is
limited in its forward direction (right hand) by a thrust bearing
209 and in its rearward direction (left hand) by the rear wall of
the cavity 208.
lo sense and control the axial movement of the gear 90B (and
hence the shank adaptor 90) a spool 210 housed in a sleeve 211 is
provided in the rear wall of the cavity 208 (see Fig.2).
Pressurised fluid either from a high pressure cavity within the
machine or from an external source enters passage 212 at the rear
(left hand) end of the spool 210. A central hole 210A through the
spool 210 emerges at the right hand end via a smaller choke hole
210B in a hydrostatically balanced pad 210C. The balance is such
that contact is maintained between the pad 210C and the pi~ton 90C
irrespective of the po6ition of the gear 90B. Connected to the
central hole 210A are holes 213 which connect to a fir6t reoess 214
on the out6ide of spool 210. A ~econd re oess 215 on the outside of
the 6pool 210 i~ 6eparated from the firet by a land 216.
Holes 218 in eleeve 211 connect to recess 218A. ThiB in turn
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connects to a passage way which links up with the tanX/return llne
of the rock drill (not shown~. HDle6 219 in Rleeve 211 connect to
recess 219A and to axial holes 219B which emerge into cavity 208.
In operation pressuri6ed fluid antering passage 212 forces the
6pool 210 with its hydrostatic pad 210C into contact with piston
90C. In the position 6hown the gear 90~ ~nd hence the shank 9~ are
in the optim~m 6trike position. The position is maintamied by 5
virtue of the positional relationship between land 216 and hole 219 1 -
metering sufficient fluid into or out of cavity 208 to maintain the
required pressure acting on area al, to resist the forward thrust of
the machine.
The condition of over thrusting or encountexing greater
resistance to penetration will cause ~he shank 90 and gear 90B t~
move into the drill (to the left of Fig. 2) taking spool 210 with
it. Now land 216 opens hole 219 and hence connects recess 214 andi
hole 213 (which are pressurised) to cavity 208 via recess 219A and
axial holes 219B. This raises the pressure in cavity 208 to oounter
the additional forces, and causes the gear 90B and shank 90 to m~ve
~orward towards the designed strike position.
Conversely during under-thrusting conditions or sudden
increased penetration into a fissure or 60fter rock the gear 90B and
shank 90 will move forward ~to the right of Fig. 2). Pressure on
the end of the spool at 212 will cause the spool to follow the gear
hence connecting hole 219 to the tank/return line via recess 215,
hole 218 and recess 218A. Pressure in cavity 208 is now r~duced and
the gear 90B and shank 90 return to their correct strike position by
virtue of the normal feed force from the thrusting mechanism.
The combination of the available pressure and area al of the
piston section 90C of gear 90B ensures more than ample reaction
force to counter any thrust levels likely to be encountered during
drilling. The nett effect is optimum performance with reduced wear
and hence increased relia'oility.
The sleeve 211 can be made movable (left or right) thereby
altering the metering position of the spool 21~ and hence the ~trike
position. Moving the sleeve forward (right) will cause the
effective ~trike position of shank 90 to move forward. MbvLng the
~leeve to the left will cause the strike po~ition to move to the
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left. The ~trike position can ~e retarded or advancsd to 6uit the
dynamics of the hammer pi~ton an~ ~he type of rock being drilled.
The ~leeve 211 ~an be moved hydrauli~ally, pneumatically,
mechanically or by any oo~b mationO
Gne suitable method of axially m~ving the sleeve 211 is 6hL~n
in Fig. 3. Pressure in cavity 220 acts on an area a2 of the sleeve
211 and is resisted by the foroe from spring 221. Increasiny the
pressure mDves the sleeve 211 to the right until a balanoed
sib~ation is maintained and a new strike position achiev0d.
Fig. ~A illustra~es the hydraulic (or pneumatic) ~ystem of such
a drill having a nDvable sleeve: Fig. 4B illustrates the
oorresponding system for a fixed sleeve.
Although the invention has been described with particular
reference tD percussive rock drills, it will be understood that
possible applioationa a~re not so limited.
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