Note: Descriptions are shown in the official language in which they were submitted.
The invention rela-tes to percussive tools ancl has particular, but
not e~clusive, reference to impact-type mineral mining machine heads.
Our Canadian Patent 937~835 (Dobson Park Industries limited, issued
December 4, 1973) discloses a mining head or other impact tool with control
valve gear, and in which an impact chisel or otller tool bit is driven on its
impact stroke by a compressible fluid that is compressed successively by a
pressure-fluid, preferably hydraulically, drive piston serving as, or driving,
a hammer for the impact chisel or other tool on working strokes driven by
expansion of the compressible fluid. It is an object of this invention to
make provision for a variable impacting rate for such a percussive tool either
to cope with desired working conditions or to compensate for the effects of
temperature on the compressible fluid.
Normally, the control valve gear is made responsive to relatively
low and high pressures, herein referred to as "control pressures", of the
compressible fluid in order to control the application and release, respect-
ively, of piston operating pressure-fluid.
According to the present invention, there is provided, in a percus-
sive *ool having a reciprocable piston driven on an impacting stroke of *he
tool by compressible fluid and, on a return stroke to compress that medium,
by pressure fluid supplied via control valve gear responsive at least to high
predetermined pressures of the compressible fluid, apparatus comprising means
for varying the operation of the control valve gear relative to actual attain-
ment of such predetermined pressures and presetting means operative to
establish a nominal tool operating rate and variable to change the actual
tool operating rate.
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This could be implemented using electrically triggered
control valve gear with electro-mechanical or electronic
determination of a desired time lag between achievement
of either or both of the predetermined high and low control
pressures in the compressible fluid. However, i-t is
preferred, particularly to meet intrinsic safety standards
required for mining equipment, to have the control valve
gear directly responsive -to compressible fluid pressures.
This may be achieved by providing a single unit in
a compressible fluid line and incorporating both a variable
flow restrictor and a reservoir or accumulator. If desired
such a unit could, of course, be mounted directly to a
compressible fluid port at the tool, or be mounted -to
or incorporated in the con-trol valve gear preferably
at a pressure responsive pilot valve means thereof. If
it is desired to control the impacting rate with reference
only -to one piston stroke, and thus with reference to
one only of the predetermined pressures, the restrictor/
reservoir unit may further include a one-way valve capable
of by passing the restrictor. ~he direction of permitted
flow through -the one-way valve will determine which of
the control pressure levels is modified in its application
to the pressure responsive control valve means~ ~ormally,
it is preferred to operate relative to initiating the
return stroke and the low con-trol pressure level in order
not to reduce impacting power, and make each working
cycle of subs-tantially constant length irrespective of
the actual rate of impacting. ~
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Preferably, in a combined restrictor, one-way valve
and reservoir or accumula-tor device, the one-way valve
selectively obstruc-ts a first branch passageway from a
compressible fluid supply passage -to a reservoir or
accumulator feed passage, and the restrictor is operative
on flow via a second branch passageway from -the
compressible fluid passage to -the reservoir or accumulator
feed passage via a clearance past or a port through
the one-way valve at least when the latter is in its flow
obstructing condition. This allows a particularly
convenient construction where the compressible fluid
flow passageway and reservoir or accumula-tor feed passageway
comprise parallel bores in a valve body, when the two
branch passageways may be formed as transverse bores
intersecting both of the first mentioned parallel bores,
preferably at different spacings therealong from the
positio~ of a bore of the reservoir or accumulator.
The nearest branch passageway to reservoir is preferably
counterbored to house and provide a sealing sea-t for
a spring biassed one way valve and being oversize
relative thereto at leas-t at its intersection with the
reservoir or accumulator feed passagee to allow communication
via the restrictorO Clearly, the other transverse bore
could house the restrictor to be operative relative to
that branch passageway at its intersection with the reservoir
or accumulator feed passage. Alternatively~ the restrictor
could be housed in a continua-tion of the reservoir or ~
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accumulator feed passage and be operative relative to
an orifice or step at or near the junction of that
passageway. A typical restrictor would comprise a tapered
member adjustable relative to a stepped seat to define
a variable annular flow cross-sectionA
In an alternative arrangement a variable flow restrictor
may be mounted to act relative to a bore directly communicating
with the compressible medium chamber of a percussive
tool of the type r~ferred to, and a communicating passageway,
usually a bore, to the main valve gear, usually a pilot
operating valve thereof. It is particularly convenient
for that communicating passageway to have at least a part
thereof of su~ficient cross-section to serve as a
reservoir. A one-way valve is conveniently mounted in
a similar bore directly communicating with the compressible
medium chamber with an interconnecting bore to the restrictor
bore. Both ends of such an interconnecting bore will
usually have a said communicating passageway to the main
valve gear, specifically a pilot valve. Conveniently,
restrictor and one-way valves have similar bodies and
are interchangeably mountable, say after the fashion
of spark plugs f`or internal combustion engines. Such
embodiments of the invention have particular advan-tage
by way of being integrally embodyable within a tool
body or rear part thereof`.
Embodiments of the invention will now be described,
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by way of example, witll referellce to the accompanying drawings, in which:-
Figure l is a diagrammatic repr0sentation of valve gear xlnd pressure-
fluid circwitry associated with an impact type mineral winning head shown
in simplified section;
Figure 2 is a section through a preerred unilary compressible fluid
pressure controlled device; and
Figure 3 is a diagrammatic generally sectional view of an arrange-
ment embodying the invention and integral with the rear tool body.
The mining head shown in Figure 1 is preferably of modular construc-
tion. In general terms, the head comprises a body 1~ housing, in a cylinderthereof, a drive piston 14 that is retractable from left to right of the
drawing by hydraulic pressure-fluid from a main valve 11 via annular passage
15 in order to compress a gaseous pressure-fluid in an end chamber 23. At its
forward end, the drive piston 14 has a hammer 28 for impact engagement with
a chisel tool bit 26 retained but slidable in the body 10 and shown only
partly in the drawing. The basic operation cycle requires piston drive
pressure fluid alternately to be applied to drive the piston to compress the
pressure-fluid in the chamber 14 until a predetermined high pressure is
achieved and to be released via the passage 15 so that the piston will be
driven to impact the tool by the energy stored in the compressed pressure-
fluid, reversal of piston driving pressure-fluid connections being made
for a further compression stroke on achievement of a predetermined low pres-
sure in the gaseous medium chamber 14.
The tool body and associated valve gear is preferably of modular
construction where a central body portion accommodates the drive piston
proper and provides the fluid access passage 14 from a main valve 11 that
is integral therewith or secured thereto. A gas chamber body part securable
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to the central part to complete the overall configuration of l~igure 1.
Pilot valve ~mcl accumulator units will then be securable to the main valve
bocly forwardly and rearwardly thereof, respectively but preferably inter-
changeably. Preferred accumulators operate directly on the main flow ancl
return for the piston drive pressure-fluid.
A diagra~matic representation of the control valve gear and pres-
sure-fluid circuitry associated with the mineral winning head for operating
purposes is also given in Figure 1. It will be seen that individual high
and low pressure pilot valve parts are shown separately at 32A and 32B
with both connected by gas lines 51 to the gas chamber 231 to respond7
differentially, to high and low pressures of the gas so as to constitute high
and
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low pressure gas opera-ted switches of predeter~i~ed or
preset characteristics say according to variable sprin~
ratings or settings. A hydraulic pilot start line 52
is shown connected to one port of the low pressure pilot
valve ~2B which has other ports connected to the cylinder
of one of the pilo-t pistons of the main valve ll via
line 53 and to a hydraulic drain pipe 56, respectively.
Drain connections 60, 61 are also shown -together with
intercoupling bored paths 62.
Hydraulic flow and return mains are shown at 30A
and 30B, respectively, connected to corresponding ports
of -the main valve ll and, via branch pipes, to ports of
the high pressure pilot valve 32A which has a further
port connected via a spring loaded shuttle valve device
54 to the cylinder of the other pilot piston of the main
valve via line 55. ~he device 54 also has a port connected i `
to a pilot reset line 57. s`
In describing operation, it is first assumed that
the piston ]4 is in its forward position and there is no
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pressure-fluid supplied to the head. On applying hydraulic
fluid pressure 9 the main valve pilo-t pistons will set to
positions corresponding to the states shown in Figure l,
if they are not already in such positions, due to
pressurisation of the pilo-t reset line 57. Hydraulic
pressure in the pilot start line 52 will act via the
low pressure pilot valve part 32B and the relevant main
valve pilot piston to cause the main valve to operate
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as described above to admit hydraulic fluid to retract
the piston 14 and compress the gas in the chamber 23.
Rislng gas pressure will act first to cancel the
low pressure pilot valve par-t 32B and lock the piston 14,
and then to op0rate the o-ther pilot valve part 33~ to
switch the main valve position to allow exhaustion of
hydraulic fluid as -the piston 14 is driven on its
impact stroke by the compressed gas. Subsequent cycles
will be self-starting for as long as hydraulic pressure
is applied over lines 30A and 52.
If desired, a controlled pressure non-return air
line branch can be connected to the front end of the
piston 14 to impose a higher than atmospheric pressure
and give both an air pump action and dirt ingress pro-tection.
Connections 6~ and 64 are shown directly to accumulators
for the main flow and return lines immediately adjacent
to the maln valve llo
~ he compressible fluid pressure lines 51 are shown
as incorporating a uni-tary or integral control devlce or
means 65 incorporating a reservoir 66 and a flow restriction
device 67 which is preferably bridged by a one-way valve
68 to ensure -that it is only the initiation of -the return
or compression stroke of the piston 14 that is modified.
If the one-way valve was reversed, it would operate to
delay initiation of the drive stroke, but that might
alter the impact power characteristics. If the one-
way valve is omitted, both stokes would be delayed.
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Figure 2 shows a preferred construction of the de~ice
65 where a body 70 has two parallel bores 71 æLd 72
both intersected by cross bores 73 and 7~ he bore
71 serves as a compressible fluid supply passage from
the gas chamber 23, and the bore 72 serves as a supply
passage to the reservoir 66 formed as a much larger
bore 75 from which a fluid pressure line are taken to
the pilot valve gear. Seals are shown at the ends of
these bores to facilitate connections thereto.
The transverse bore 73 is disposed between the
transverse bore 74 and the reserYoir 66, and is counterbored
to accommodate a one-way valve device 68 having a spring
loaded actuator 76 equipped with a seal 77 for closing
the bore 73 against fluid flow from the supply bore 71 for
low excess pressures therein compared with the pressure
in the reservoir 66. ~he bore 72 is also shown as being
counterbored to house a pressure-fluid flow restrictor 67
with a threaded adJuster 78 for varying the extension
of a tapered end 79 through an annular step 80 and thus the
annular flow section for pressure-~luid between -the
compressible fluid supply bore 71 and the reservoir supply
bore 72 via the transverse bore 74. ~he counterboring
of the transverse bore 7~ is such as to provide a clearance
chamber 81 about the actuator of the one-way valve 68,
and so provide clear passage for fluid between the
restrictor and the reservoir.
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The transverse bore 74 is also shown as being counterbored
and plugged at 82, though it will be appreciated that the
restrictor could be mounted in such a counterbore and
be operative relative to an orifice or stepped seat of
that transverse bore 74.
In operation, the illustrated device will allow
unrestricted built-up of pressure through the device
via the one-way valve until the pressure on the reservoir
side rises to within a prede-termined amount of the
pressure in the feed bore 71 related to the bias of
the one-way valve. ~his will normally be at or above the
high pressure control valve operation level at which the
piston drive stroke is initiated by switching from pressure
fluid supply to pressure fluid return for the passage 15.
~he drive stroke will produce a rapid drop of pressure
in the gas chamber 23 and thus the feed bore 71, and
release of -the previously built-up pressure on the
reservoir side of the one-way valve will be necessaril~
via the restrictor, and will take a substantially
constant time to drop to the low pressure control level
at which a compression or return s-troke of -the piston
1~ is initiated.
It will be appreciated -that the unit illustrated
in Flgure 2 could be attached -to or even formed integral
with the gas chamber or the pilot control valve gear.
Figure 3 shows a control arrangement wherein a
rear tool body part 87 defining the compressible medium
chamber 23 is drilled at 88 and 89 to mount restrictor
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and one-way valves 67 and 68 having similar external
body configurations. A communicating bore 90 extends
between the bores 88 and 89 and the valve~; control
compressible medium access to that bore 90 from the
chamber 23. Interconnecting bores 91 and 92 to a .
pilot valve of the main valve gear are shown extending
through the body part 87 generally at right angles to
-the interconnecting bore 90 and connected at opposite
ends thereof by further bores 93 and 94, respectively,
that are preferably inclined into the plane of the drawing
to aid flow. ~he interconnecting bores 91 and 92 are
larger than the bores 90, 93 and 94 at least over a
substantial part of their length and so are capable
of serving as the above-mentioned reservoir or
accumulator 66.
The bores 88 and 89 are clearly equivalent to the
branch passageways 7~ and 74 of Figure 2 and there will
be a clearance about the one-way valve so that both
enlarged comrnunicating passages 91 and 92 serve in
providing said reservoir capability~
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