Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
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Down-the-hole drills are generally known in the
art. One such drill has been shown and described in
U.S. Patent No. 4,084,646 issued to Ewald H. Kurt and
assigned to Ingersoll-Rand Company.
OBJECT OF THE INVENTION
An object of the invention is to increase the
effective volume in front of the impact piston without
increasing the diameter of the drill.
A further object of this invention is to reduce
the effective back pressure developed on the impact
piston of a down-the-hole drill in order to improve
its deep hole work output.
Yet a further object of this invention is to
provide an impact piston with a reduced diameter
section forming an accumulator of pressure fluid which
~, travels with the piston without biasing the piston in
` directions of travel.
, Another object of the present invention is to
`` provide a down-the-hole drill with increased work
output at higher back pressures experienced in deep
holes without increasing the diameter of the drill.
These and other objects are obtained in a
percussive drill apparatus of the valveless type
comprising:
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a casing; a backhead disposed at the back end of
~- the casing adapted to connect the drill apparatus to a
drill
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string and a source of pressure fluid; a distributor
~; disposed within the casing towards the back end of the
casing; a percussive member disposed at the front end of
the casing to form a chamber having a back end disposed
towards the distributor and a front end disposed towards
the percussive member between the distributor and the
percussive member within the casing; a cylinder sleeve
disposed in the chamber toward the back end of the
chamber; a first pressure fluid passage formed be~ween th2
casing and the cylinder sleeve to connect the prsssure
fluid source to the chamber; a piston disposed in the
chamber to reciprocate axially therein and impart a blow
on the percussive member; the piston being in sliding
contact with the cylinder sleeve adjacent the back end of
: the chamber and in sliding contact with the casing
adjacent the front end of the chamber; a means for
continuously applying pressure fluid to a selected portion
of the back end of the piston to thereby provide a
, continued driving force on the piston towards the front
end of the chamber; a means for alternately supplying and
exhausting pressure fluid to a selected portion of one
`~, side of the piston disposed towards the back end of the
-' chamber and to a selected portion of the other side of the
piston disposed towards the front end of the chamber to
~1 thereby reciprocate the piston; the means for alternately
.~i supplying and exhausting pressure fluid to the back side
of the piston includes a second pressure fluid passage
~' extending from the fixst pressure fluid passage along the
:.. ;j interior of the sleeve and the exterior of the piston;
I The improvement comprising:
A means ~or accumulating additional pressure fluid in
~'l a portion of the piston dispersed towards the front end;
.~ and a means for communicating the means for accumulating
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additional pressure fluid with the first pressure fluid
passage.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal section of the center por-
tion of a pneumatic down-the-hole rock drill according to
; the prior art.
FIG. 2 is a longitudinal section of the center por-
tion of a pneumatic down-the-hole rock drill according to
the present invention.
FIG. 3 is a cross sectional view o~ the prior art
rock drill taken at section 3-3 shown on FIG. 1.
FIG. 4 is a cross sectional view of the rock drill
'1 according to the prior art taken at section 4-4.
FIG. 5 is a cross sectional view of the rock drill
according to the present invention taken at section 5-5.
1 FIG. 6 is a cross sectional view of the rock drill
3 according to the present invention taken at section 6-6.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
The drawings are numbered to correspond with similar
parts in U.S. Patent No. 4,048,646 for easy identification
and comparison. However, for purposes oX understanding
this invention it is necessary to know that, in a
conventional down hole drill and similar reciprocating
hammer devices driven by a pressurized gas, when the
pressure fluid enters the area in front of the piston on
iks down stroke it restrains the piston. If~this occurs
prior to piston impact as it does in the referenced
patent, it reduces the maximum obtainable impact.
In the referenced valveless design some overlap or
early introduction of pressure fluid in the frontal area
is required for the cycles to operate effectively and the
present invention is directed at reducing the restxaining
effect prior to impact. I have determined that one way
this may be accomplished is to effectively increase the
volume associated with the frontal area of the impact
1l piston. Since this volume must be pressurized a greater
; flow of pressure fluid is required to effect the same back
~`i pressure~ Since the flow of pressure fluid is to some
degree restricted by limitation of design in down-the-hole
drills this results in an effective time delay in reaching
full pressure below the piston. The delay results in in
creased piston impact while retaining the overlap required
for the cycle to operate. The above is particularly ef-
fective where as in a deep hole, the exhaust back pressure
is substantial and the frontal area pressure is therefore
already relatively high.
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Referring to FIG. 1 a rock drill longitudinal sectionis shown to illustrate the concerned parts of a
down-the-hole pneumatic drill according to U.S. Patent No.
4,048,646.
Briefly, in this pneumatic drill the air passes
through the drilled ports 63 in the cylinder sleeve 50
into an annular passageway 52 between the outside diameter
of the cylinder sleeve 50 and the inside of the casing 6.
From here the air moves forward into chamber 64
between the piston outside surface and the casing 6 in-
side diameter. This is an '1air reservoir space" because
there is always pressure fluid in this chamber and it is
from here that the air passes either to the upper chamber
68 of the piston or the lower chamber 69 of the piston.
With the piston in its lower position (shown in FIG. 1
which it would attain before the air is turned on, the air
passes into the lower chamber 69, exerting a ~orce on the
lower impact imparting surface 40 of the piston 30,
driving it upwards towards its one or inlet end. The air
continues to feed into the lower chamber 69 or Vl and is
trapped between the piston 30, the bit 8, the casing 6 and
a spacer ring 13 until the lower sealing surface 37 of the
casing, that is, until edge 86 contacts shoulder 87. When
this occurs, air is shut off to the lower chamber 69. The
piston continues to move upwards, however, by virtue of
its velocity and expansion of the air in the lower cham-
ber. As the piston rises, the lower sealing surface of
the axial bore 42 of piston 30 pulls off the end of the
exhaust tube 23. At this point, the air in the lower
chamber 69 exhausts into the drill bit ~3 and out into the
exhaust bore 67.
While this is going on at the lower end of the
piston, other events are occurring at the upper end. The
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first is that the upper chamber 68 is sealed off as the
sealing surface 43 of the piston axial bore engages the
lower end of the enlarged head 66 of the exhaust rod 65 of
the distributor. Shortly thereafter, pressure fluid is
admitted, via axial porting slots 33, into the upper chamber
68 as edge 88 of the piston slots 36 uncover the shoulder
89 of the undercut 80 inside the cylinder sleeve 50. The
air entering the upper chamber 68 first stops the piston
on its upwards travel (about an inch from hitting the
distributor) and then reverses the piston travel, pushing
it forward at increasiny velocity~ The pressure fluid
flow to the upper chamber 68 is shut off as edge 88 of the
piston slots 36 cover the shoulder 89 of the undercut 80.
From this point on, the piston is driven by expanding
pressure fluid. When sealing surface 43 loses contact
with enlarged head 66 of the distributor exhaust rod, air
in the upper chamber 68 is exhausted through the piston
30, into the exhaust tube 23 and out the bit 8 as the
piston continues to move towards its impact on other end,
edge 86 of the lower sealing surface 39 of the piston 30
loses contact with the shoulder 87 of internal surface 39
of the casing again at which point air re-enters the lower
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chamber 69. Shortly thereafter, the piston 30 impacts
against the bit 8. The piston rebounds somewhat. This,
plus the air re-entering the lower chamber, starts the next
cycle.
As can be appreciated by one skilled in the art once
the adge of the lower sealing surface 39 loses contact
with the shoulder 87 and air begins to enter the lower
chamber, the piston 30 begins to loose velocity as a
result of the force of such air action on the lower impact
surface 40 of the piston. This results in energy loss and
it is therefor desirable to minimize the pressure
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developed in chamber 69.
The pressure build up in chamber 69 has been sub-
stantially reduced by the presen~ invention. As shown in
Figure 2 the piston 30 is provided with a substantial cir-
cumferential undercut 100 which forms a substantial volume
V2 for the accumulation of pressure fluid. Shoulder 34 of
the prior art device has been extended outward to form an
upper circumferential sealing surface 101 of the same
diameter as lower circumferential sealing surface 39.
`; The casing internal fluted lonitudinal passages 102
have been extended to perform the same function, at shoul-
der 87' in cooperation with edge 86' of upper sealing
~' surface 101, as edge 86 performed with shoulder 87 in the
prior art and at the approximate same point in cycle
timing.
' Figures 3 and 6 compare the cross sections taken at
;~ sections 3-3 and 6-6 respectively in Figures 1 and 2.
Figures 4 and 5 compare the cross sections through the
piston at sections 4-4 and 5-5 respectively in Figures 1
and 2. These clearly show the reduced piston diameter in
'l Figure 5 which forms volume V2.
It can now be appreciated by one skilled in the art
that, once the upper sealing surface 101 loses contact
with shoulder 87', in order for pressure to build up the
pressure fluid or air must fill both volume Vl and V2.
With a given available flow of air the total pressure
build up is time delayed thereby subtantially reducing the
retarding force on the piston and dramatically increasing
the impact of the piston on the bit.
The results have been most impressive particularly in
deep holes where the back pressure or exhaust already
reduces piston impact and where the slightly increased air
flow resulting ~or the increased front end volume is of
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benefit air cleaning the hole.
Having described my invention numerous modifications
will now occur to one skilled in the art and I do not wish
to be limited in the scope of my invention except as
claimed.
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