Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION ~
This invention pertains to the art of rock drilling with .
pressure fluid actuated percussion type drills wherein repeated
impact blows are transmitted through a drill stem comprising one - -
or more elongated rods or tubes coupled end to end and connected
to a percussion bit which penetrates a rock formation by localized
fracture and crushing of the rock structure.
It has been observed in pursuing the present invention that a
rock formation of a particular hardness or compressive strength
can be penetrated with the aforementioned type of drilling most
efficiently, that is the greatest rate of hole formation for a
given rate of energy input to the rock drill proper, at a parti-
cular impact blow energy value taking into consideration the con-
figuration and size (diameter) of the percussion bit. An impact
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~03782~
blow which has a low energy value will deflect the rock forma-
tion but not sufficiently to cause substantial fracture and
breaking up of the rock structure. Accordingly, since most
rock formations exhibit a stiffness characteristic and undergo
elastic deflection when subjected to impacts a major portlon of
the energy of an impact blow imparted to the rock may be reflected
back through the bit and the drill stem or dissipated into the rock
formation without effecting very much rock fracture. Operation of -
a percussion drill at a hammer blow energy which is too low will
result in very slow penetration or hole formation and an early
failure of the drill stem components as well as substantial loss
of the energy or power consumed in operating the drill.
Conversely, it is believed that if the impact blow energy is
too high that penetration of the bit and breaking of the -rock will
15 occur but that at least some elastic compressive deflection of the ;-~
drill stem and bit caused by the impacting of the hammer cannot be
transmitted substantially to the rock formation once initial break-
ing and penetration has taken place because the bit will not remain
in firm contact with the unbroken rock. Therefore, at least some
of the impact blow energy cannot be transmitted to the rock forma-
tion and instead causes cyclical compression and elongation of the
drill stem which is undesirable. If the impact blow energy is too
high for a particular type of rock being drilled early fatigue
failures of the drill stem components and bit is also experienced
and energy is wasted.
It has been further observed that a rock formation of a par-
ticular compressive strength (as measured by uniaxial loading of
a finite sample) requires a certain energy value to break out or
remove a unit volume of rock by percussion drilling. It follows
then that in percussion drilling of circular cross section holes
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with bits which have a fixed ratio of cutting edge length to bit
diameter it would be desirable to maintain a fixed value of impact
energy per uhit of bit diameter for drilling holes of various sizes
in a given type of rock. Accordingly, depending on hole size the
total impact blow energy imparted to the bit by the hammer should
be adjusted to provide the requisite blow energy for a given hoIe
size which will be the most efficient or yield the greatest pene-
tration rate for the power input to the drill proper.
In pursuing the present invention it has been determined that
a percussion drill motor operated by hydraulic pressure fluid and
capable of imparting to the drill stem and bit impact blows of
variable intensity or energy value may be advantageous for drilling
in different types of rock in the most efficient manner. Moreover,
such a drill may also be used to drill more efficiently a range of --
hole sizes within the working limits of the drill system in regard
to the impact blow energy delivered to the drill stem and bit and
total power input to the drill which will not materially reduce ~
the useful life of the drill or the drill stem components. -
Percussion type rock drills are known which are capable of -
being controlled to deliver variable impact blow energy and blow
frequency. Prior art drills are generally characterized by control ~`
~ devices which require direct access to the rock drill unit itself
to effect a change in hammer stroke length and blow frequency.
Prior art hammer stroke length and blow frequency controls are
also generally characterized by devices which provide for a finite r~
number of different drilll operating frequencies and hammer stroke
lengths none of which might be the most effective for drilling a
particular type of rock in accordance with the foregoing observa-
tions. - ~-
Furthermore, in known drills of the type which operate on ~-
hydraulic pressure fluid supplied by a conventional motor driven ~
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pump the changes in fluid flow rate and supply pressure caused
by changes in hammer stroke length or blow frequency do not permit
operation of the drill unit at a substantially constant rate of
hydraulic power input to the drill itself. Accordingly, the
improvements in drill penetration rate for a particular type of
rock or hole size which could be achieved with changing the impact
blow energy are not realized because the necessary changes in fluid
flow and pressure cannot be accomplished to provide a substantially
constant hydraulic power input to the drill percussion mechanism.
SUMMARY OF THE INVENTION
The present invention provides an improved pressure fluid
actuated percussion rock drill system wherein the impact blow
energy delivered fro~ the piston hammer to the drill stem and bit ,
may be varied to thereby achieve the maximum rate of rock removal
for a particular type of rock being drilled and for a particular
bit size and configuration.
The rock drill system of the present invention includes a
hydraulic pressure fluid actuated percussion drill which includes
means for changing the impact blow energy to substantially any value 1
between and including high and low limits whereby the greatest pene-
tration rate of the drill may be easily selected without predeter-
_ mination of the requisite impact blow energy setting for the type
of rock or the size hole being drilled.
In accordance with the present invention there is provided a
hydraulic pressure fluid operated rock drill which includes meansfor changing the hammer impact blow energy to substantially any
selected value within the drill operating limits, which means may
be operated at a remote location with respect to the drill proper
and while the drill is in operation. A preferred embodiment of
the drill comprises a percussion mechanism including a piston
` hammer which is reciprocated by intermittent valving of pressure
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fluid to one of a pair of opposed pressure surfaces formed on
the piston hammer. Impact blow energy is varied by changing the
hammer stroke length and hammer~velocity at impact of the drill
stem through control of the movement of a pressure fluid distrib-
uting valve which supplies pressure fluid to effect oscillation
of the hammer. Stepless control of valve movement with respect- -
to the hammer position provides for infinitely variable hammer
blow energy between the high and low limits which are defined in
part by the particular-size and configuration of the percussion -
10 mechanism itself. ~-
The rock drill system of the present invention is also adapted
for remote control of the hammer impact blow energy by the drill
operator. Selection of the maximum drilling rate may be determined
- by the drill operator or attendant by changing the pressure setting
of a fluid control circuit until the maximum drilling rate is ob-
served. Moreover, the mechanism provided for remote control of
the drill impact blow may be easily adapted to -an automatic control
system for producing the maximum drilling rate.
The present invention further provides for a hydraulic per-- ,
20 cussion rock drill system in which a substantially constant rate '' '
of energy is supplied to the drill proper in the form of hydraulic
_ fluid at variable pressures and flow rates whereby the drill may
be operated with the same fluid power input to the drill regardless
of the hammer lmpact blow energy setting of the drill. By providing
a hydraulic rock drill sy~tem which includes a variable impact blow
rock drill in combination with a source of hydraulic pressure fluid
which is automatically controlled to provide substantially constant
fluid power at various combinations of pressure and flow rate to the
drill proper the drill may be operated at the most effective drilling
rate for most types of rock formations and drill hole diameters.
In a preferred embodiment of the present invention the source of
constant hydraulic fluid power is a variable displacement pump of
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the so-called "constant power" type. However, any combi~ation
of pump and prime mover may be used which is adapted to
automatically provide hydraulic pressure fluid at various
combinations of pressure and flow rate which will produce
substantially constant fluid power input to the rock drill.
According to one broad aspect, the invention relates -
to a hydraulic rock drill system comprising: a source of
hydraulic pressure fluid; a hydraulic pressure fluid actuated
percussion rock drill operable to be in communication with said
source and including; a. a casing having a cylindrical bore;
b. an impact receiving member; c. a pressure fluid reciprocable
piston hammer disposed in said bore and responsive to
pressure fluid acting thereon to transmit impact blows to
said impact receiving member; d. a distributing valve for
controlling the flow of pressure fluid to and from said bore to
effect reciprocation of said hammer, said distributing valve
being operable to control the movement of said hammer to vary
the impact blow energy transmitted to said impact receiving
member by said hammer; and, said source of pressure fluid
includes means for providing pressure fluid to said rock drill
at variable pressure and flow rate in accordance with the
variation of impact blow energy transmitted to said impact
receiving member by said hammer and whereby the fluid power
input to said rock drill remains substantially constant.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side elevation of a portable drillinq unit
including the rock drill system of the present invention~
Fig. 2 is a longitudinal section view of a hydraulic
precussion rock drill in accordance with the present invention;
Fig. 3 is a schematic illustrating the control circuit
of the rock drill system of the present invention; ;
6~
Fig. 4 is a gr~pQ3i~ ~ustrating the basic performance
characteristic of the hydraulic fluid pump of Fig. 3; and,
Figs. 5 and 6 illustrate an alternate embodiment of the
mechanism for changing the stroke length of the drill piston
hammer.
DEscRIpTIoN OF THE PREFERRE~ BMBODIMENTS - - :
The rock drill system of the present invention may be
adapted to various types of drilling apparatus. A typical drill
rig which is suited for use of the improved rock drill system
is illustrated in Fig. 1 and generally designated by the
numeral 10. The drill rig 10 includes a self-propelled wheel
type undercarriage 12 upon which is mounted a movable boom 14.
A rock drill feed support 16 is pivotally supported on the
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distal end of the boom 14. Suitable mechanism such as r~
hydraulic cylinder type linear actuators 18, 20, and 22 are
operable to position the feed support so that holes may be
drilled in various directions. A hydraul~c percussion rock
drill 24 is slidably disposed on the feed support 16 and is- ~ ~ ~
connected to suitable mechanism, not shown, for advancing and -
retracting a percussion drill stem 26 and bit 28 with respect
to the feed ~
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~037821
support 16. The drill stem 26 may be made up of one or more
elongated hollow rods or tubes and suitably coupled to a member
disposed in the drill 24 which is adapted to transmit impact blows
to the drill stem. The bit 28, coupled to the drill stem 26, may
- 5- be of a conventional percussion type provided with a plurality of
hard metaI inserts which are wedge shaped to provide cutting edges
for impacting the rock surface. Suitable guides 30 and 32 are pro-
vided on the feed support 16 for guiding the drill stem 26 in a
known way.
Hydraulic pressure fluid is supplied to and conducted from
the drill 24 by flexible conduits or hoses which are in circuit
with control valves and other attendant devices including a reser-
voir disposed on the undercarriage 12. The hoses are suitably
supported by a flexible boot 34. Hydraulic fluid at variable
pressure and flow rate is supplied to operate the drill 24 by a
pump 36 which is driven by an electric motor 38 mounted on the
undercarriage 12. The motor 38 is also drivingly connected to a
second pump 40 for supplying hydraulic fluid to opPrate the actu-
ators 18, 20, and 22 and the feed mechanism for the drill 24. The
operation of the drill rig 10 including the drill 24 is controlled
by an operator person from a control station 42 on the undercarriage
- 12.
Referring to Fig. 2 the drill 24 is shown in a longitudinal
side elevation, partially sectioned, to illustrate details of the
percussion mechanism. The drill 24 is mounted on a slide 44 which
is adapted to be slidably disposed on the feed support 16. The
drill 24 is characterized by a main casing formed in two separable
parts 46 and 48 which are held in assembly between end covers 50
and 52 by suitable elongated bolts 54, one shown. The casing part `~
48 rotatably supports an impact blow receiving member`56 which is
coupled to the drill stem 26 shown in Fig. 1 in a well known manner.
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The member 56 includes a transverse face 58 which is disposed to
receive repeated impact blows from an elongated piston hammer 66
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to be described hereinbelow. A rotary motor 60 mounted on the -
end cover 52 is drivingly connected to the member 56 through an
elongated drive shaft 62 and suitable speed reduction gearing
disposed within the casing part 48. The member 56 is~rotatably
driven by the motor 60 for rotating the drill stem and bit.
The casing part 46 includes a longitudinal cylindrical bore
64 in which is reciprocably disposed the piston hammer 66. The
hammer 66 is characterized by two oppositely facing transverse
- pressure surfaces 68 and 70 and an annular channel 72, shown in
Fig. 3 also. The area of pressure surface 70 is greater than the
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area of surface 68. The hammer 66 is supported by two spaced apart
bearings 74 and 76 disposed in the casing part 46 and including ~-
suitable end seals.
The drill 24 also includes two gas charged flexible diaphragm
type accumulators 78 and-80-.- The accumulator 78 includes a chamber -
82 which is in communication with a source of high pressure hydrau~
lic 1uid by way of suitable conduits within the casing part--46.~
; 20 The accumulator 80 is characterized by a chamber 84 which is in ~`
communication with a low pressure return line 88, shown schematically
~ in Fig. 3. The positions of the accumulators 78 and 80 with respect
to the hydra~lic fluid flow circuit of the drill 24 are also shown
in Fig. 3.
The casing part 46 includes spaced apart annular grooves 90, ~,
92, 94, 96, and 98 which ~pen into the bore 64. A passage 100 ,
leads from the accumulator chamber 82 to the groove 90 and communi-
cates high pressure hydraulic fluid into the bore 64 to act con- -
tinuously against the pressure surface 68 when the drill is in
30 operation. When the hammer 66 is in the impact position shown in ;
Fig. 2, the annular channel 72 in the hammer also communicates
high pressure fluid to the groove 92.
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1037t~2~
The drill 24 further includes a pressure actuated fluid
distributing valve 102 disposed in a transverse bore 104 in the
casing part 46 and between the accumulators 78 and 80. The valve
102 comprises a hollow cylindrical spool which is disposed to be
hydraulically actuated to conduct pressure fluid to and from the
- groove 98 and the portion of the bore 64 in communication therewith
and which is also in communication with the pressure surface 70.
When high pressure fluid i5 conducted to the groove 38 a pressure
force acting on the surface 70 causes hammer 66 to accelerate to
deliver an impact blow to the member 56. When the groove 98 is
vented to the low pressure return line 88 through the valve 102
the fluid pressure acting on surface 68 returns the hammer to a
position whereby high pressure fluid is again conducted to the
groove 98 upon actuation of the valve.
The operation of the valve 102 and hammer 66 together with
means for varying the impact blow energy transmitted by the hammer
to the member 56 will now be described in detail with reference to
Fig. 3. Although the valve 102 is mounted in the drill 24 for
- movement in a direction transverse to the disposition and move-
ment of the hammer the valve is shown in Fig. 3 in schematic form
in longitudinal section to facilitate an understandinq of its
operation. Fig. 3 also illustrates the mechanism for changing the
working stroke and impact blow energy of the hammer 66 which mech-
anism is disposed in a portion 106 of the casing part 46 also shown ;~
in Fig. 2.
The valve 102 includes transverse pressure surfaces 108 and
110 which may be acted onlby high pressure fluid to move the valve
to the position shown in Fig. 3. The total area of surfaces 108
and 110 is greater than the area of an oppositely facing pressure
surface 112. However, the area of pressure surface 112 is greater
than the area of pressure surface 110. High pressure fluid at the
supply pressure to the drill is conducted to the valve through a
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10378Zl
conduit 114 and through passages 116 and the hollow interior 118
to act continuously on the surfaces 110 and 112. Accordingly,
the valve 102 is moved to a position in the bore 104 opposite to
the position shown in Fig. 3 when there is insufficient pressure
S acting on surface 108 which together with the pressure acting on -
surface 110 can overcome the force caused by pressure on surface~
112. Circumferential grooves 120, and 122 cooperate with an `
annular recess 124 on the valve 102 to conduct pressure fluid
from supply conduit 114 to the groove 98 to act on the surface 70 ~
10 when the valve is shifted to the position opposite that shown in -
Fig. 3. In the position of the valve 102 shown in Fig. 3 grooves
122 and 126 in the bore 104 are placed in communication with each
other by way of the recess 124 and pressure fluid is discharged
from the chamber formed by the groove 98 to the low pressure return
15 line 88. The groove 90 in the bore 64 is continuously in communi-
cation with high pressure fluid supplied by way of groove 120 sur-
rounding the valve 102 and the groove 96 in the bore 64 is continu-
ously in communication with the low pressure return line 88 by way
of the groove 126.
As shown in Fig. 3 the portion 106 of the casing part 46 in- ,
cludes a bore 130 in which is disposed means for controlling the ,
shifting of the valve 102 from the position shown to the position
in which pressure fluid is conducted to the groove 98. The control
of shifting of the valve 102 to introduce pressure fluid to groove
25 98 has the effect of changing the length of the impact stroke of ~?s -
the hammer 66 and the impact velocity as well. Accordingly, the -
impact blow energy may be controlled by changing the hammer stroke
length with the drill 24 in combination with the drill system shown
in Fig. 3.
The bore 130 contains a two-piece plug 132 having a passage
134 in communication with the groove 94 by way of a conduit 95.
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1037821
A seat is formed at one end of the passage 134 against which is
disposed a movable valve closure member 136 having a transverse
pressure surface 138. The groove 96 ~in the casing part 46 is in
communication with an enlarged bore 140 in which the closure member
is disposed. The bore 140 also contains a piston 142 and a coil
spring 144 interposed between the piston and the closure member 136.
Hydraulic fluid is supplied by way of a conduit 146 to act on the
piston 142 for biasing the closure member 136 in the seated or
closed position shown in Fig. 3.
The pressure of the fluid supplied to the piston 142 may be
varied by a pressure regulator 150 having an operating member in
the form of a pressure adjusting control knob 152. The pressure
regulator 150 receives high pressure fluid from the discharge
conduit 114 of the hydraulic pump 36 which ~lso supplies hydraulic
fluid to reciprocate the hammer 66. The pressure regulator 150 is
advantageously disposed at the control station 42 for adjustment i~
by the drill operator at will. The regulator 150 is of a well known
type which provides a reduced pressure of a constant value depending
on the setting of the operating or adjusting member 152. The par-
ticular regulator shown in Fig. 3 is a model QWA3-165 manufactured
by Double A Products Co., Manchester, Michigan, U.S.A.
_ The basic operation of the drill system of the present inven-
tion will now be described with reference to both Figs. 2 and 3.
When the hammer 66 reaches the impact position shown in Fig. 2 the
groove 92 is placed in communication with groove 90 by way of 3
channel 72 in the hammer and high pressure fluid is conducted to 7" ., '
a chamber 154 to act on pressure surface 102 which will shift the
valve 102 to the position shown in Fig. 3. In the position shown
in Fig. 3 the pressure surface 70 on the hammer 66 is exposed to `~
the low pressure in the return line 88. Accordingly, high pressure
fluid acting continuously on the surface 68 moves the hammer to
the right, viewing Figs. 2 and 3. As the hammer 66 moves through
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10378Zl
the return stroke the valve 102 is held in the position shown
in Fig. 3 by pressure fluid trapped in the chamber 154 and conduit '
158 as the channel 72 on the hammer moves out of communication with '
groove 90.
As the hammer 66 continues moving to the right on the return ~, ~
stroke the channel 72 moves into commu,nication with the groove 94--- '~',-
and the pressure of the fluid in the chamber 154 and conduit 158 '
is transmitted to act on the surface 138 of closure member 136.
The fluid pressure acting on surface 112 of the valve 102 will ;
cause the valve to commence movement to shift to the left, viewing
Fig. 3, when the fluid pressure acting on the surface 138 increases
sufficiently to open the closure member 136. When the valve 102
has shifted to place the high pressure supply conduit 114 in com- ''
munication with the groove 98 high pressure f-luid will act on sur- -
face 70 causing the hammer to be brought to rest and-then accel-
erated in the opposite direction (to the left) on the impact stroke. '
Just prior to impacting the member 56, the channel -72 will come into
communication with the groove 90 and high pressure fluid will again '-
be transmitted to chamber 154 causing the valve 102 to shift to the '~ '
20 position shown in Fig. 3. - ~ -
As may be appreciated from the foregoing description by adjust-
_ ing the pressure of fluid acting on the piston 142, which controls
the compression of spring 144, movement of the closure member 136
to relieve the pressure in chamber 154 can be controlled and shifting ~', , '
of the valve 102 can be varied with respect to the position of the
hammer 66. When the pressure acting on the piston 142 is increased
to the supply pressure the closure member 136 will not open and the ~ ,
valve 102 will be shifted only after the channel 72 in the hammer ',
places the grooves 92 and 96 in communication with each other, '
which will result in the maximum hammer stroke length and greater
velocity at impact. Accordingly, a substantially stepless control
of the stroke length of and the impact blow energy delivered by the ~
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1037~
hammer may be obtained by the timing of the shifting of the valve
102. If the valve 102 is shifted very soon upon commencing com-
munication of the groove 92 with the groove 94 the hammer stroke
length will be short and the hammer velocity at impact reduced.
5 Therefore, the impact blow energy will be relatively low also.
When the hammer stroke is short the total time to complete one
cycle of oscillation is less and the frequency of oscillation and
impact may be increased. Conversely, when the hammer stroke is
relatively great the impact frequency will decrease. However, the
10 total energy rate transmitted to the drill stem and bit may remain
substantially constant and the impact energy per blow of the hammer -
66 may be controlled to provide the greatest penetration rate in
accordance with the type of rock and the bit.
It has been observed with hydraulic pressure fluid operated
15 percussion drills of the general type described herein and parti- -
cularly also characterized by a shiftable valve for effecting ?
oscillation of the piston hammer that when the drill is operated
at progressively shorter hammer stroke lengths the resistance to
flow of working fluid through the drill increa-ses relative to the
20 flow conditions at the longer stroke lengths operation. This ~ ~
results in a higher operating pressure for a given input flow rate -`
_ of working fluid. Therefore, in order to provide for operation of ~ ~
the drill at the maximum allowable power and prevent imparting too ; -
high an input power to the drill it is desirable to adjust the l -
25 flow and pressure of the hydraulic working fluid to maintain a
constant rate of fluid energy input to the drill proper.
It has been determined in pursuing the present invention that
operator controlled adjustment of the fluid flow rate to the drill
when changing the hammer stroke length is difficult and very time `
30 consuming and often does not result in improved drilling rates.
Such is the case because upon changing the stroke length it is
necessary to hunt for the combination of fluid pressure and flow -
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1037~21
rate which will produce the desired power input to the drill
which will result in the faster drilling rate which was sought
by changing the hammer impact blow energy. Accordingly, it is
highly desirable to hàve a source of pressure fluid which is
automatically controlled to provide constant fluid power input
to the drill proper regardless of the change in hammer stroke _
length.
With the rock drill system of Fig. 3 the input flui~ power
to the drill is controlled to be substantially constant by a par-
ticular type of variable displacement hydraulic pump which includescontrols which automatically adjust the flow rate in accordance
with changes in discharge pressure which will occur as the stroke
length of the drill hammer is adjusted. Although various types
of pumps and controls therefor can be adapted to automatically
15 supply fluid at a substantially constant power the pump 36, shown :`
in Fig. 3, is of a type manufactured by New York Air Brake Co.,
Watertown, N.Y. under-the----trademark Dynapower--and--is speci-fically
designated as a model 45, phase--IV equipped-with a cons-tant horse-- -- -
- power control mechanism disposed on the pump and generally designated
by the numeral 37.
Referring to Fig. 4, the graph illustrates the basic per-
formance characteristic of the pump 36. The abscissa of the graph
is designated V and~represents increasing output fluid volume flow
of the pump 36. The ordinate is designated P and represents in- ~-
creasing discharge fluid pressure. The line 168 represents a line
of substantially constant fluid horsepower delivered by the pump 36.
The pump 36 may operate a~ any point on the line between the point ~ -
of maximum volume displacement 170 and the point of maximum pres-
sure 172 as controlled by the inbuilt control 37 provided for the
particular pump specified herein.
In the schematic control circuit of Fig. 3 conventional com-
ponents such as heat exchangers, the pump replenishing circuit,
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~37~2~
and drain lines from the pump 36, and control valve 150 have
been omitted for the sake of clarity and conciseness. Pressure
fluid is discharged from the pump 36 by way of conduit 114 which
supplies the drill 24 and the control valve 150. Fluid discharged
from the drill 24 is returned to the pump by way of return line 88
--- which is maintained at a low pressure relative to the discharge
pressure of the pump.
An alternate embodiment of the mechanism for controlling the
movement of the fluid distributing valve 102 is shown in Figs. 5
and 6. Fig. 6 is a longitudinal section view taken generally in
the same plane as the view of the drill shown in Fig. 3. The em-
bodiment of Figs. 5 and 6 includes a casing part 174 which is
, ` - . .
similar to the casing part 46 in substantially all respects except
as herein noted. The casing part 174 includes a plurality of
15 passages 175 which open into the bore 64 between the annular re- ~-
cesses 92 and 96. The passages 175 are arranged in a staggered ~--
pattern with respect to the longitudinal axis of the bore 64. -
The~embodiment of Figs. 5 and 6 also includes a casing ~ ~ -
portion 178 which is removably fastened to the casing part 174 and ,~
includes a stepped bore 180 which is closed at opposite ends by
threaded plugs 181 and 184. The removable casing portion 178 also ;~
includes a plurality of passages 176 which open into the bore 180
and which are aligned with the respective passages 175. In Fig. 5
certain components are omitted and part of the casing portion 178
is broken away to show the staggered relationship of the passages
175-176. As shown in Figs. 5 and 6 the groove 96 is in communi- ~;
' cation with the bore 180land the passages 175-176. A stepped
; piston 182 is disposed in the bore 180 and is biased into the
position shown in Fig. 6 by a coil spring 185. The piston 182
includes an integral projection 183 which limits movement of the
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piston toward the plug 181 and guides the spring 185. The piston
182 also includes a transverse face 186 on the end of the piston
opposite the-projection 183. The conduit 146 leading from the
regulator 150 is connected to conduct pressure fluid to act
against the piston face 186.
In response to the introduction of pressure fluid to act
against the piston face 186 at variable pressure as controlled
by the pressure regulator 150 the piston 182 may be moved to
cover one or more of the passages 175-176 thereby controlling ~-
the communication of pressure fluid in chamber 154 and conduit 158
to the groove 96 in accordance with the position of the control
edge 73 on the piston hammer 66. The passages 175-176 are posi- ,~
tioned in such a pattern that the embodiment of Figs. 5 and 6
also provides for substantially stepless control of the hammer ' '
stroke length and impact blow energy. The advantage of the embodi-
ment of Figs. 5 and 6 for controlling the movement of the valve 102 ~-
~is that the-onset of movement of the valve is delayed and the total
time for shifting of the valve, once movement is,initiated, is '~
somewhat faster than the embodiment of Fig.-3. Faster movement ~-
of the valve 102 tends to prevent leakage of high pressure fluid
from the groove 120 across the groove 122 and to the low pressure'
_ groove 126 in the valve. Moreover, faster shifting of the valve
102 from the position shown in Fig. 3 may also tend to increase ,'
the energy stored in the accumulator 78 which is absorbed during
the phase of arresting the movement of the hammer 66 during its
return s~roke.
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