U.S. patent number 3,662,843 [Application Number 05/006,820] was granted by the patent office on 1972-05-16 for impact tools.
This patent grant is currently assigned to General Dynamics Corporation. Invention is credited to Boyd A. Wise.
United States Patent |
3,662,843 |
Wise |
May 16, 1972 |
IMPACT TOOLS
Abstract
Impact tools are described which have an anvil system for
transmitting force pulses generated by the hammer to a load. The
anvil system includes an impact spring arrangement, the spring
being either mechanical or liquid. In one embodiment the spring has
a variable spring rate which changes under the duration of the
force pulses. In the other embodiment the spring is operative to
absorb the energy in the trailing end of the force pulse and return
it to the hammer. In this manner, force pulses are transmitted
which have a shape which may be efficiently utilized by the
load.
Inventors: |
Wise; Boyd A. (Webster,
NY) |
Assignee: |
General Dynamics Corporation
(N/A)
|
Family
ID: |
21722768 |
Appl.
No.: |
05/006,820 |
Filed: |
January 29, 1970 |
Current U.S.
Class: |
173/131; 173/211;
173/212 |
Current CPC
Class: |
B25D
9/12 (20130101); B25D 17/06 (20130101) |
Current International
Class: |
B25D
17/00 (20060101); B25D 17/06 (20060101); B25D
9/12 (20060101); B25D 9/00 (20060101); B25d
009/04 () |
Field of
Search: |
;173/128,131,133,139
;175/56 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; David H.
Claims
What is claimed is:
1. A tool for impacting a load which comprises
a. a hammer element
b. an anvil system adapted to receive force pulses from said hammer
element and to transfer said pulses to the load,
c. said anvil system including a spring member having a variable
spring rate which is variable in steps over the duration of each of
said force pulses.
2. The invention as set forth in claim 1 wherein said spring member
has a plurality of portions each providing a different spring rate
for said member.
3. The invention as set forth in claim 2 wherein said member is a
hydraulic spring having a plurality of active spring cavities of
different areas.
4. The invention as set forth in claim 2 wherein said spring member
is a rod having a plurality of portions of successively greater
diameter.
5. The invention as set forth in claim 2 wherein said spring member
is a rod with at least one cylinder surrounding said rod, one of
said rods and cylinder being slightly shorter than the other.
6. The invention as set forth in claim 1 wherein said anvil system
includes a piston and a shank, said piston being disposed between
said shank and said hammer, said piston comprising said spring
member.
7. The invention as set forth in claim 6 wherein said tool includes
a housing and wherein said spring member further comprises, said
piston having a plurality of portions of progressively larger
diameter at the end thereof adjacent said shank, said housing
having a cup shaped portion of progressively larger diameter, each
slightly larger than said piston portions, into which said end
portions of said piston enter when said piston is impacted by said
hammer, said shank extending into said housing portion of smallest
diameter, said housing being liquid filled in said cup shaped
portions thereof to define a variable spring rate liquid
spring.
8. The invention as set forth in claim 6 wherein said piston
comprises a rod of elastic material a plurality of cylinders of
elastic material encompassing and attached to said rod at the end
thereof adjacent said shank, said cylinders each being
progressively shorter than said rod so as to be successively
impacted by said hammer after said rod is impacted and deflects to
the length of each of said shorter cylinders.
9. The invention as set forth in claim 6 wherein said piston is an
elastic rod which extends into said shank said rod having portion
of progressively larger diameter so as to define an end and a
plurality of shoulders, said shank defining a plurality of stops
each spaced from each other a distance slightly greater than said
shoulders whereby the effective length of said rod is progressively
shortened as said piston enters said shank so that the spring rate
of said rod diminishes in steps with the motion of said piston into
said shank.
10. A tool impacting a load which comprises
a. a hammer element,
b. an anvil system adapted to receive force pulses from said hammer
element and to transfer said pulses to the load,
c. said anvil system including a spring member in the transmission
path of said force pulses to said load,
d. a housing in which said hammer and at least a portion of said
anvil system are disposed, and
e. means included in said housing for limiting the deflection of
said spring member to a predetermined deflection during the
application of said force pulse whereby a portion of said force
pulse energy is stored in said spring member of said anvil system
and is returned to said hammer after the period of said force
pulse.
11. The invention as set forth in claim 10 wherein said anvil
system includes a member movable in said housing toward and away
from said hammer, said spring member includes a liquid spring
defined by said housing and a portion of said anvil system member,
after said anvil system has moved a predetermined distance in a
direction away from said hammer.
12. The invention as set forth in claim 6 wherein said spring
member includes an elastic member, and means on said elastic member
for engaging said housing for limiting the movement thereof.
13. The invention as set forth in claim 10 wherein said spring
member includes a body defining a liquid spring, means for mounting
said body in said housing so that said liquid spring is movable a
predetermined distance upon impact of said anvil system by said
hammer said distance being less than the travel of said hammer
whereby a portion of the lagging end of said force pulse energy is
absorbed in said spring and the transmission of said portion to
said load is inhibited.
14. The invention as set forth in claim 10 wherein said anvil
system includes a piston and a shank, said piston being disposed
between said shank and said hammer, said piston having a reduced
diameter portion at the end thereof adjacent said shank, said
reduced diameter portion meeting the body of said piston at a
shoulder, said housing having a longitudinal opening in which said
shank and said reduced diameter portion are movably disposed with a
body of liquid therebetween which define a first liquid spring,
said housing having a cylindrical hole which enlarges the end of
said opening on the side thereof adjacent said piston should and is
substantially the same diameter as said piston body portion, said
opening and said shoulder being disposed in liquid filled cavity in
said housing so that said enlarged opening and shoulder define a
second liquid spring of stiffness much greater than said first
spring, said opening being of a length smaller than the length of
said reduced diameter piston portion.
15. The invention as set forth in claim 10 wherein said anvil
system includes a piston which provides said spring member, and a
shank, said piston being disposed between said hammer and said
shank, and means for limiting the travel of said shank under the
force applied thereto by said piston after said shank executes a
predetermined movement away from said hammer.
16. The invention as set forth in claim 15 wherein said housing
defines a liquid filled chamber between opposed ends of said shank
and said piston, said chamber being movable as said piston and
shank move until said shank reaches said limiting means said piston
and chamber providing a liquid spring.
17. The invention as set forth in claim 15 wherein said piston is
an elastic rod which is compressed between said hammer and said
shank.
18. The invention as set forth in claim 15 wherein said end of said
shank opposed to said piston has an opening therein for receiving
said piston with limited clearance, means providing a liquid filled
chamber in said housing in which said opposed ends of said piston
and shank and its openings are disposed, said opening and piston
when inserted therein providing a liquid spring.
Description
The present invention relates to impact tools and particularly to
an impact tool having an anvil system for the efficient transfer of
force pulses, generated upon the impact of a hammer, to a load.
The invention is especially suitable for use in percussive tools
such as drills for earth boring purposes. Other applications for
the invention will be found every where mechanical force pulses are
generated and must be transferred to a load.
The present invention is an improvement upon the anvil system
disclosed in my U.S. Pat. No. 3,382,932 issued May 14, 1968. That
patent describes an anvil system utilizing an elastic member which
has a stiffness or spring rate characteristic for shaping force
pulses developed by an impact generator and delivering those force
pulses to a load, especially the formation to be drilled. It is a
feature of this invention to provide an anvil system, which not
only affords a more precise shaping of the force pulses, but also
utilizes the energy in the pulse which may not be absorbed by the
load, so as to increase the efficiency of the generator which
initially produces the pulses.
It is an object of the present invention to provide an improved
anvil system for impact devices such as percussive tools.
It is a further object of the present invention to provide an
improved impact spring arrangement for shaping force pulses for
transmission to a load.
It is a further object of the present invention to provide an
improved impact spring which becomes progressively stiffer as force
is applied thereto so as to more accurately shape a force pulse
prior to transmission thereof to a load.
It is a still further object of the present invention to provide an
improved hydraulic impact spring.
It is a still further object of the present invention to provide an
improved variable spring rate impact spring which shapes mechanical
force pulses to provide greater energy in the portion of the pulse
which is adapted to perform useful work.
It is another object of the present invention to provide improved
impact devices such as percussive tools having higher
efficiency.
It is a still further object of the present invention to provide an
improved anvil system for impact devices which translates impact
force pulses into pulses for triangular shape having a controlled
rise time and a precipitous decay time.
It is still another object of the present invention to provide an
improved percussive tool in which effective use is made of impact
energy by returning a portion of such energy back to the force
pulse generator so as to conserve energy that would otherwise be
wasted and thus render the generator more efficient.
Briefly described, an impact tool embodying the invention includes
a hammer element which is vibrated so as to impact upon an anvil
system at least once during each cycle of vibration thereof. The
anvil system in some versions includes an impact spring having a
variable spring rate during the period of each of the pulses
generated when the anvil system is impacted. The spring member may
be a liquid or a mechanical spring. In order to increase the
efficiency of the system, the spring member may be effective to
have increased stiffness as a function of the duration of the force
pulse. Means may be included in the tool for limiting the
deflection of the spring member to a predetermined deflection
during the application of the force pulse. As the force pulse
continues, its energy is stored in the spring and is returned to
the hammer after the period of the force pulse delivered to the
drill steel or load.
The invention itself both as to its organization and method of
operation, as well as additional objects and advantages thereof,
will become more readily apparent from a reading of the following
description in connection with the accompanying drawings in
which:
FIG. 1 is a diagrammatic, fragmentary, sectional view of a portion
of an impact tool having an anvil system in accordance with an
embodiment of the invention;
FIG. 2 is a view similar to FIG. 1 illustrating another embodiment
of the invention;
FIG. 3 is still another view similar to FIG. 1 showing an impact
tool in accordance with still another embodiment of the
invention;
FIG. 4 is a pair of curves showing force pulses which are generated
by an anvil system both with and without the impact springs in
accordance with the embodiment of the invention shown in FIGS.
1-3;
FIG. 5 is a diagrammatic, fragmentary, sectional view of an impact
tool and anvil system which is effective both for pulse shaping and
for returning a portion of the pulse energy to the generator, the
system being provided in accordance with an embodiment of the
invention;
FIG. 6 shows curves of force pulses generated both with and without
the impact spring arrangement shown in FIG. 5;
FIG. 7 is a schematic diagram of the equivalent circuit of the tool
shown in FIG. 5;
FIG. 8 is a view similar to FIG. 5 of a portion of an impact tool
in accordance with another embodiment of the invention;
FIG. 9 is a curve of force pulses generated by the device shown in
FIG. 8;
FIG. 10 is a view similar to FIG. 5 of a portion of an impact tool
in accordance with still another embodiment of the invention;
and
FIG. 11 is another view similar to FIG. 5 of a portion of an impact
tool in accordance with still another embodiment of the
invention.
Referring more particularly to FIG. 1, there is shown an impact
tool of the percussive type having a housing 10, including a force
pulse generator 12, the hammer 14 of which is shown in FIG. 1. The
hammer oscillates axially and repeatedly impacts an anvil system 16
including piston 18 and a shank 20. The shank may be mounted on a
bearing 22 and may be connected to a drill steel (not shown) which
in turn may be connected to a drill bit. The force pulse generator
may be of the hydroacoustic type as described in my above
referenced patent. The anvil system is configured to provide a
variable spring rate liquid spring 24 which shapes the force pulses
produced when the hammer impacts the piston.
The housing 10 has a first cavity 26 which may be liquid filled
through porting means of the type described in my above referenced
patent. The housing also has a second cavity 28 which communicates
with a bore 30. A reduced diameter end 32 of the shank 20 is
disposed in the bore 30. Seals for the purpose of confining the
liquid, such as hydraulic oil, in the cavities 28 and 26 and
preventing it from seeping through the open end of the bore 30 are
not shown to simplify the illustration. Thus, bearing surfaces 34
are provided in the housing for guiding the piston 18. The end of
the piston 18 which is adjacent to the shank 20 has a pair of
reduced diameter portions 36 and 38. The portion 36 is adapted to
enter the bore, suitable clearance being provided, so as to confine
the liquid therein and form a first liquid spring 40. The bore has
an enlargedportion 42 approximately the same diameter as the
portion 38 of the piston. When the piston moves to the right, the
shoulder 44 traps liquid in the opening 42 and defines a second
liquid spring 46. The opening 42 is further enlarged to provide an
opening 48 of approximately the same diameter as the diameter of
the piston. Thus the shoulder 50, when it enters the opening 48,
confines the liquid therein and defines a third liquid spring 52.
Prior to impact, the shoulders 44 and 50 are clear of the openings
so that when the first liquid spring is effective, force is
transferred via the liquid spring 40 to the shank 20 and thence to
the load. As the piston moves further to the right, the other
liquid springs are brought into play. By making the length of the
second portion 38 longer than the first portion 36, the third
liquid spring will be effective after the first the first and
second liquid springs become effective.
The area of the shoulders which define the liquid springs determine
the stiffness as a function of the movement of the piston (viz. the
deflections of the spring). The spring stiffens with deflection.
The spring rate, which is a function of the square of the area of
the shoulders and inversely of the length of the spring is
desirably increased in the progression 1:4:16, as each of the
liquid springs 40, 46 and 52 are brought into play. Thus, if the
spring cavity lengths are equal, the area of the shoulders 44
should be equal to the area of the end of the piston portion 36 and
the area of the shoulder 50 three times the area of the end of the
piston portion 36. Translated into diameters, the diameter of the
shoulder 44 should be approximately 1.414 (the square root of two)
times the diameter of the end of the portion 36 while the area of
the shoulder 50 is 1.414 times the diameter of the shoulder 44.
FIG. 2 shows an impact tool similar to that shown in FIG. 1
utilizing a variable spring rate mechanical spring in its anvil
system 60. The force pulse generator includes a hammer 62 and the
anvil system includes a shank 64 and a piston 66 guided in the
housing 68 for movement as the hammer impacts the left end thereof.
The piston 66 is made up of a rod 70 of elastic material such as
steel. The end of the rod 70 has a stepped flange 72 which abuts
the shank 64. Two cylinders of elastic material 74 and 76 are
attached at the flange. The inner cylinder is shorter than the rod
70 so that the rod extends further towards the hammer. The outer
cylinder 76 is still shorter than the inner cylinder 74.
In operation, the hammer first impacts the rod 70, drives it
against the shank and causes it to deflect longitudinally. After
some deflection, the hammer reaches the end of the inner cylinder
74 which thereupon deflects. The spring rate of the inner cylinder
and the rods are then cumulative and the total spring rate of the
piston increases. With further deflection between the rod and inner
cylinders 70 and 74, the hammer reaches the end of the outer
cylinder, which thereupon deflects and adds its spring rate and
stiffness to the total effective spring rate and stiffness of the
piston. Thus the stiffness of the spring rate of the piston is
variable and increases in steps.
Referring to FIG. 3, the housing 80 of the tool includes a pulse
generator, which may be of the type heretofore described, having a
hammer 82. The anvil system 84 includes a shank 86 which is
longitudinally movable in a bore 88 in the housing 80. The piston
90 is disposed within the bore 92 in the shank 86. The piston has
three portions 94, 96 and 98 of different diameters. Prior to
impact, clearances of progressively greater lengths D.sub.1,
D.sub.2 and D.sub.3 are defined between the end 100 of the portion
92 and the shoulders 102 and 104 of the portions 96 and 98. The
piston 90 is a mechanical spring made of elastic material such as
steel. At the beginning of the force pulse, the end 100 is first
brought into contact with the end 106 of the bore 92. Then the
entire piston length is effective in determining the stiffness and
spring rate of the piston. When the portion 94 deflects so that the
shoulder 102 abuts the end of the opening 108 in the shank 86, the
effective length of the spring is the length of the portions 96 and
98. Further deflection of the piston brings the shoulder 104 into
contact with the end 110 of the shank 86. Then only the length of
the portion 98 is effective as the impact spring provided by the
piston 90. Since the spring rate and the stiffness increase as the
effective length of the piston spring 90 decreases, the stiffness
increases stepwise with deflection of the impact spring provided by
the piston 90.
FIG. 4 shows by the solid line curve the shape of the force pulse
which is produced by means of the impact spring anvil arrangement
shown in FIGS. 1-3. The dash line curves illustrate the effect of a
constant spring rate impact spring. It will be noted that the
maximum force of the spring is increased and that a larger portion
of the energy is contained in the leading or early part of the
pulse. As was explained in my above referenced patent, this shape
force pulse is more effective since it is more effectively absorbed
by the load as useful work and decreases reflections of energy back
up the drill steel. Such reflections may cause the drill steel to
fracture and, at a minimum, reduces the life of the drill steel by
increasing fatigue thereof.
FIG. 5 illustrates an impact tool wherein the anvil system provides
a deflection switch which not only improves the force pulse shape
but also increases the overall effectiveness of the drill by
returning energy, which is not adapted to perform useful work at
the load, back to the force pulse generator.
As in the tools illustrated in FIGS. 1-3 the tool is contained in a
housing 120 which also contains a force pulse generator which may
be of the type described in my above referenced patent. The force
pulse generator includes a hammer 122 which cyclically impacts an
anvil system 124 including a piston 126 and a shank 128. The shank
128 is movable from left to right in a bore 130 in the housing 120
and may be connected via a drill steel to a drill bit. The piston
126 has a reduced diameter portion 132, the end 134 of which is
disposed in the bore. Liquid is contained between the ends 136 of
the shank 128 and the end 130 of the reduced diameter portion 132
of the piston 126. The ends 134 and 136 and the confined liquid
therebetween define a first liquid spring 140.
The bore 130 is enlarged to define a cylindrical cup 142 which
opens into a liquid filled cavity 144 in the housing 120. Normally
a shoulder 146 of the piston 126 (before impact) is clear of the
cup 142. It is only after a deflection D of the first liquid spring
140 that the shoulder 146 enters the cup 142 and defines a second
liquid spring 148. The second liquid spring is defined between the
housing and the piston. Thus any deflection beyond D of the piston
126 the second spring 148 absorbs the force pulse and substantially
little of it is transferred to the first liquid spring and thence
to the shank 128. Since both spring 140 and 148 bear on the piston
and thence the hammer, the motion of the hammer is reversed in a
shorter time than would occur in the absence of the second spring
148. Once the motion of the hammer is reversed, energy is extracted
from both springs, including energy that otherwise would have been
imparted to the drill steel by spring 140.
The shape of the force pulse provided by the combination of the
first and second liquid springs 140 and 148 is enclosed by the
shaded area in FIG. 6. If the first liquid spring 140 were used,
the force pulse would not taper off abruptly at its lagging end but
would continue on as shown by the dash line. Immediately following
the cut-off time t.sub.D, which takes place when the shoulder 146
enters the cup 142, the force that is transmitted to the shank
drops sharply. The energy in the lagging portion of the pulse is
returned to the piston and drives the piston to the left towards
the hammer. This occurs when the hammer is moving away to the
right. The left hand end 152 of the piston may contact the hammer
or the liquid in the cavity 154 provides a medium for a transfer of
the force stored in the second liquid spring back to the hammer.
This additional energy is used in the operation of the force pulse
generator and reduces the energy demanded thereby from its own
power supply such as they hydraulic power supply described in my
above referenced patent.
FIG. 7 illustrates the equivalent circuit of the tool shown in FIG.
5. The impact energy for the force pulse is developed as a velocity
component (viz. current) through the inductance L presented by the
mass of the hammer 122. This stored kinetic energy is effectively
applied to the capacitance C.sub.1 of the first liquid spring and
to the drill steel in parallel with it when the switch S.sub.1
opens, which takes place on hammer to piston contact. The switch
S.sub.2 normally short-circuits the capacitance C.sub.2 presented
by the second liquid spring 148, inasmuch as the shoulder 146 does
not initially enter the cup 142. When the shoulder enters the cup
S.sub.2 opens and the total capacitance seen by the hammer
decreases. The amount of energy available in C.sub.1 is transmitted
in part to the transmission line .rho.cS represented by the shank
128 and the drill steel, and in part to the piston 126 and hammer
122, as the motion of the hammer is reversed. The foreshortening of
the trailing edge of the pulse then results and the force is no
longer transferred to the load, represented by the capacitance
C.sub.I. Rather the energy is stored in C.sub.2 and is returned to
the hammer, as the direction of the velocity V is reversed.
FIG. 8 illustrates another embodiment of the impact tool, this time
utilizing only a single liquid spring.
A housing 160 has a cavity 162 which may be liquid filled. A hammer
164 of a force pulse generator is mounted in the housing and
impacts an anvil system 166 including a piston 168 and a shank 170.
The shank is journaled for longitudinal motion in a bore 172 in the
housing 160. A shoe 174 which has a bell shaped opening 176 is
attached by screws 178 to the bottom 180 of the cavity 162. The
shoe has a bore 182 in which the left end 184 of the shank is
journaled. The shank also has an enlarged base 186 which is
disposed in the cavity 176. The shoulder 188 of the base is
separated from the end 180 of the cavity 162 by a preset gap D.
Liquid enters the cavity 176 in the shoe 174 via openings 190. The
space in the bore 182 between the ends 184 of the shank 170 and the
end 192 of the piston 168 is also liquid filled, and defines a
liquid spring 194.
In operation, when the hammer impacts, force is transferred via the
liquid spring 194 to the shank 170 until the shank moves the preset
gap distance D. The liquid spring then can not transfer any more
energy to the shank since the movement of the shank 170 is limited
by the stop provided by the end 180 of the cavity 162. Energy is
then stored in the liquid spring and is returned to the hammer 164
at the end of the force pulse. The shape of the force pulse has a
rising leading edge and a sharply dropping lagging end as shown in
FIG. 9.
FIG. 10 shows an impact tool having a housing 200, a force pulse
generator including a hammer 202 and an anvil system 204 made up of
a piston 206 having a section 208 of elastic material such as
spring steel which functions as a mechanical spring. The anvil
system 204 also includes a shank 210 having a base 212, the rear
shoulder 214 of which is disposed in a cavity 216. The rear end 218
of the cavity 216 is separated the shoulder 214 by a preset gap D.
The mechanical spring then acts in a manner similar to the liquid
spring 194 shown in FIG. 8. It will deflect until the shank moves
the preset gap distance D. The energy is stored in the spring
piston 206 and returned to the hammer at the end of the force
pulse.
FIG. 11 shows an impact tool also having a force pulse generator of
the type heretofore described with a hammer 220 which impacts an
anvil system 222 including a piston 224 journalled for longitudinal
motion in a bore 226 in a housing 228. The anvil system also
includes a shank 230 which is also mounted in a bore 232 in the
housing 228 and may move longitudinally. The shank 230 has an
enlarged portion 234 disposed in a liquid filled cavity 236 in the
housing 228. The enlarged portion has an axial blind hole 240
extending from the end 242 which is adjacent to the end 244 of a
reduced diameter portion 246 of the piston 224. When the end 244
enters the hole 240, it defines a liquid spring 248 with the liquid
contained in the hole 240. The rear end 250 of the enlarged portion
234 of the shank 230 separated from the rear wall 254 of the cavity
236 by a preset gap D.
The tool operates in a manner similar to that described in
connection with FIG. 8 except that the liquid spring 248 is a part
of the shank 230 itself.
From the foregoing description, it will be apparent that there has
been provided an improved impact tool especially suitable for use
in a percussive drill for earth boring applications. Other
applications of the tool and variations and modifications of the
herein described embodiments within the scope of the invention will
undoubtedly suggest themselves to those skilled in the art.
Accordingly, the foregoing descriptions should be taken as
illustrative and not in any limiting sense.
* * * * *