U.S. patent number 3,803,840 [Application Number 05/317,853] was granted by the patent office on 1974-04-16 for power driver device.
This patent grant is currently assigned to Illinois Tool Works Inc.. Invention is credited to Jan Toczycki.
United States Patent |
3,803,840 |
Toczycki |
April 16, 1974 |
POWER DRIVER DEVICE
Abstract
A pressure fluid power driving device for driving studs, nails
or the like having a gas chamber including an accumulator piston
movable against the force of the gas in the chamber by the action
of a noncompressible fluid against the accumulator piston. The
invention further relates to the use of noncompressible fluid
acting at a first, relatively low pressure to force a brake spool
to carry a ram upwardly into sealing engagement with a seat
element. The ram is propelled downwardly with great velocity when
noncompressible fluid at a second, relatively high pressure, enters
the cylinder to urge the accumulator piston against the bias of the
compressed gas until a predetermined pressure level is achieved
within the cylinder wherein an automatic pressure relief valve
system breaks the seal between the top of the drive piston and the
seating element allowing the full force of the compressed gas to
act on the upper surface of the drive piston through the
noncompressible fluid.
Inventors: |
Toczycki; Jan (Chicago,
IL) |
Assignee: |
Illinois Tool Works Inc.
(Chicago, IL)
|
Family
ID: |
23235540 |
Appl.
No.: |
05/317,853 |
Filed: |
December 22, 1972 |
Current U.S.
Class: |
60/371;
227/130 |
Current CPC
Class: |
B25C
1/048 (20130101); B25C 1/00 (20130101); B25C
1/005 (20130101); B25C 5/1627 (20130101) |
Current International
Class: |
B25C
5/00 (20060101); B25C 5/16 (20060101); B25C
1/00 (20060101); F15b 001/02 () |
Field of
Search: |
;60/371,412
;227/130 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Geoghegan; Edgar W.
Assistant Examiner: Woods; William F.
Attorney, Agent or Firm: Beart; Robert W. Buckman; Thomas
W.
Claims
I claim:
1. A power device including a body having a bore, a drive piston
having an enlarged head portion mounted in the bore for
reciprocating movement therein, an accumulator piston mounted
adjacent the bore for limited reciprocating movement independent of
the drive piston, means for biasing the accumulator piston
downwardly toward the drive piston, stationary stop means in the
bore adapted to limit the downward movement of the accumulator
piston, stationary seat means mounted in the bore adapted to
sealingly contact the upper surface of the enlarged head portion,
means to urge the drive piston upwardly into sealing contact with
the seat means, means for introducing a noncompressible power fluid
into the bore to urge the accumulator piston upwardly against the
force of the biasing means, adjustable pressure relief valve means
associated with the seat means and providing a passage from the
bore through the seat means to the top of the head portion when a
predetermined pressure has been built up in the bore, wherein the
power fluid acting on the top of the head through the passage
breaks the sealing contact between the seat and head and allows the
force of the biasing means, through the power fluid, to urge the
drive piston downwardly with great velocity.
2. A device of the type claimed in claim 1, wherein a brake means
encircles the drive piston and is adapted to limit the downward
extension of the drive piston as it is driving under the force of
the biasing means and also serves to cushion the drive piston when
it reaches its extended position.
3. A device of the type claimed in claim 1, wherein the means
urging the drive piston into sealing contact includes a
non-compressible power fluid which enters the bore and acts on the
lower surface of the head portion to force it into contact with the
seat means.
4. A device of the type claimed in claim 2, wherein a brake spool
encircles the drive piston and the means for urging the drive
piston upwardly includes a noncompressible power fluid which enters
the bore in such a position to contact the lower surface of the
brake spool wherein the brake spool carries the drive piston
upwardly into seating position.
5. A device of the type described in claim 1, wherein the upper
surface of the enlarged head portion is recessed to form an open
ended chamber having side walls and a bottom wall and the seat
means includes a projection dimensioned to sealingly engage the
recessed head portion.
6. A device of the type described in claim 1, wherein the body
includes a passage means adjacent the seat means to allow
non-compressible power fluid to urge the accumulator piston against
the force of the biasing means.
7. A device of the type described in claim 1, wherein the seat
means is mounted at the uppermost portion of the bore and extends
axially downwardly a short distance and having a terminal portion
which includes a sealing projection, the seat means including an
axially direct port means at the sealing projection and a radially
directed port means spaced axially above the sealing projection,
said port means each communicating with a valve seat, a valve
member associated with the valve seat and maintained therein
against the force of an adjustable biasing means, wherein the
radially directed port means provides communication with the
axially directed port means and the sealing projection when the
pressure in the bore exceeds the predetermined pressure level of
the adjustable valve biasing means.
8. A power device including a body having a main cylinder, a drive
piston reciprocably movable in said main cylinder, said piston
having an end portion extendable outwardly from one extremity of
the main cylinder through a seal means, said piston including an
enlarged head portion at the opposite end thereof, stationary seat
means in the body adjacent the other extremity of the cylinder for
sealingly engaging the head portion of the drive piston, an
accumulator chamber mounted adjacent the seat means, an accumulator
piston slidably mounted within the accumulator chamber, compression
means in the accumulator chamber to bias the accumulator toward a
fixed stop means at one extremity of the chamber, the stop means
restricting movement of the accumulator piston toward the main
cylinder, means introducing noncompressible power fluid at
different pressure levels to the main cylinder, relief valve means
associated with the seat means providing fluid communication
between the main cylinder and the sealed face of the head portion
at a predetermined pressure level after the head of the drive
piston has been moved into sealing engagement with the seat means,
wherein noncompressible power fluid may be introduced into the main
cylinder at one pressure level to force the drive piston to move to
a retracted position in sealing contact with the seat means and
thereafter allow noncompressible power fluid to enter the main
clyinder at a second, higher pressure level to force the
accumulator piston to move against the bias of the compression
means and also break the seal between the drive piston and the seat
means allowing the compression means to move the drive piston from
the retracted position to an extended position.
9. A power device in accordance with claim 8, which includes a cap
member mounted at one extremity of the main cylinder and forming
the accumulator chamber.
10. A power device in accordance with claim 9, which includes a
post mounted in the cap and extending downwardly into the
accumulator chamber generally along the axis of the accumulator
chamber and main cylinder, the free extremity of said post forming
the seat means, said post also including the relief valve means
providing communication, at a predetermined pressure level, between
the main cylinder and the seat means.
11. A power device in accordance with claim 9, wherein the
accumulator piston is slidably mounted around a post extending
axially of the accumulator chamber.
12. A device in accordance with claim 8, which includes a brake
spool mounted around the drive piston for reciprocating movement
within the main cylinder.
13. A device in accordance with claim 12, including a shock spool
mounted at the lowermost extremity of the main clyinder, said shock
spool having a central aperture adapted to receive the shank
portion of the drive piston, port means in said aperture providing
fluid communication with a reservoir, whereby noncompressible fluid
trapped beneath the brake spool will be forced into the
reservoir.
14. A device in accordance with claim 13, wherein the shock spool
includes an annular recess on its inner periphery communicating
through the port means with an annular recess formed on the outer
periphery of the shock spool.
15. A device in accordance with claim 8, wherein the enlarged head
portion of the drive piston is provided with a recess defined by an
upstanding sidewall portion, said seat means being provided with a
complementary protuberance adapted to at least partially fill the
recess in sealing arrangement therewith, said seat means also being
provided with passage means for releasing power fluid which may
become trapped in said recess.
16. A device in accordance with claim 15, wherein the passage means
includes port means communicating with an annular recess axially
spaced from the protuberance, a resilient sealing member mounted in
said annular recess to serve as a check valve for the exiting power
fluid.
17. A power driving tool including a cylinder portion having a
drive piston reciprocably mounted therein, the drive piston
extending through a brake spool also adapted for reciprocable
movement within the cylinder, a stationary seat means positioned at
one extremity of the cylinder and adapted to sealingly engage an
enlarged head portion of the drive piston, an accumulator chamber
operatively mounted adjacent the seat means and having an
accumulator piston slidably mounted therein, compression means in
the accumulator chamber acting on one face of the accumulator
piston to bias it toward the main cylinder, first means for
introducing noncompressible power fluid at a given pressure into
said cylinder to move said brake spool and drive piston toward the
seat means and force the drive piston into sealing contact with the
seat means to hold the drive piston in a retracted position, second
means for introducing noncompressible power fluid at a second,
higher pressure into the main cylinder to force the accumulator
piston to move against the bias of the compression means and urge
the brake downwardly in the main cylinder, relief valve means
associated with the seat means to allow the noncompressible power
fluid to contact the sealed surface of the head portion of the
drive piston thus breaking the seal between the head portion and
seat means at a predetermined pressure and allowing the compression
means to move the drive piston rapidly from a retracted position to
an extended position to drive a fastener associated with the
tool.
18. A driving tool in accordance with claim 17, wherein the drive
piston includes an intermediate portion and a terminal hammer
portion, the intermediate portion having a diameter which is less
than the diameter of the head portion.
19. A driving tool in accordance with claim 18, wherein the
terminal portion is generally cylindrical and is of a smaller
diameter than the diameter of the intermediate portion.
20. A driving tool in accordance with claim 18, wherein the
terminal portion is a generally flat, blade-like member.
21. A driving tool in accordance with claim 18, wherein the drive
piston includes a counterbore extending downward a substantial
distance into the intermediate portion.
22. A method of producing driving energy of the type required to
drive a fastener, including the steps of moving a drive ram having
an enlarged head in one direction in a bore through the
introduction of power fluid into the bore at a first pressure
through a first port to position the ram in seated position on a
stationary seat member in the bore, feeding a fastener beneath the
ram after the ram has been seated, introducing a power fluid
through a second port at a second pressure which is greater than
said first pressure while the head of the ram is seated on said
seat member to move a piston against a bias, and which is
sufficient to open a relief valve to provide communication between
the bore and the seated surface of the enlarged head of the ram to
expose the head of the ram to the power fluid and force of the bias
against the piston thereby driving the ram downwardly to contact
and drive the fastener.
Description
BACKGROUND OF THE INVENTION
Power devices having power reservoirs in which a compressible
fliud, such as gas, is maintained under pressure and is employed to
impart movement ot a noncompressible driving fluid which in turn
actuates a suitable driving means, such as a drive piston or
hammer, are known and are typified by the power devices disclosed
in U.S. Pat. Nos. 2,867,086 and 3,150,488. Other examples of such
devices may be seen in U.S. Pat. Nos. 3,636,707 and 3,667,222.
The prior art devices suffer from certain common inherent
limitations that prevent them from being commercially acceptable.
For example, the prior art devices have been found to experience a
large amount of oil leakage from the main power fluid cylinder to
the gas chamber. Since the tools in the prior art are primarily
displacement sensitive tools, that is, they normally fire when the
drive piston has been retracted a predetermined distance into the
cylinder, oil leakage into the chamber prevents the tool from
firing at predictable, constant energy levels. In addition, the
relatively long strokes necessitated by the prior art generate
substantial heat within the system which also has an effect on the
energy level at which the tool will fire. Since the prior art tools
normally operate by retracting the drive piston against the
pressure in the gas chamber, the indexing of a fastener beneath the
ram must be done quickly or the ram will be energized before the
fastener is correctly positioned, thus creating hazardous and
unpredictable firing conditions.
SUMMARY OF THE INVENTION
This invention relates to a power driving device having a gas
chamber in which a compressible gas is maintained under pressure,
an accumulator piston is movable against the bias of this
compressed gas to further compress the gas. A drive piston or ram
is reciprocally retracted into a cylinder by the introduction of a
noncompressible fliud acting on a brake spool which carries the
drive piston upwardly into seating and sealed arrangement with a
seating element. The drive piston remains in this retracted
position to allow the indexing of fasteners beneath the drive
piston and until compressible fluid is introduced into the cylinder
at a second, higher pressure. When the relatively high pressure
noncompressible fluid compresses the gas, through the movement of
the accumulator piston, to such an extent that the total pressure
built up in the system reaches a predetermined level, a pressure
relief valve system allows the upper surface of the drive piston to
be exposed to the pressure of the power fluid. The compressed gas,
acting through the power fluid as a linkage mechanism, thereafter
imparts drive movement to the drive piston, forcing it downwardly
in the cylinder at a relatively high velocity.
Additional features of the invention relate to a brake mechanism
which first acts to retract the drive piston into a retracted and
idling mode and, thereafter, returns to a position in the cylinder
for slowing the drive piston down and cushioning the shock of the
drive piston as it reaches the extended position.
It is an object of this invention, therefore, to provide a power
driving tool in which a compressible fluid, such as gas, is
employed to drive a ram, through noncompressible fluid as a linkage
between the compressible gas and the upper surface of the ram, at
constant energy levels.
A further object of the invention is to provide a power driving
tool in which the drive piston is maintained in a retracted
position in a cylinder to allow accurate placement of fasteners
beneath the ram prior to the introduction of noncompressible fluid
to build up pressure in the cylinder to a predetermined pressure
level.
Further features of the invention will become apparent to those
skilled in the art when the specification is read in conjunction
with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation in partial section of one embodiment of
the invention with the drive piston in extended position.
FIG. 2 is a front elevation view of the invention as shown in FIG.
1 taken along line 2--2 of FIG. 1.
FIG. 3 is a front elevation view similar to FIG. 2 showing the
brake spool and drive piston in a completely retracted
position.
FIG. 4 is a front elevation view similar to FIG. 3 showing the
drive piston in a completely retracted position as pressure is
built up in the gas chamber.
FIG. 5 is an enlarged end view of a fitting used to connect the gas
chamber to the main cylinder.
FIG. 6 is a sectional view of the fitting taken along line 6--6 of
FIG. 5.
FIG. 7 is an enlarged sectional view taken across the device, as in
line 7--7 of FIG. 4, and showing the pressure relief valve
system.
FIG. 8 is an enlarged view of the seating element sealingly
engaging the head of the drive piston as shown generally in FIGS. 3
and 4.
FIG. 9 is a partial sectional view of an alternate embodiment of a
brake spool for use with the present invention.
FIG. 10 is a fragmentary side elevation view in partial section of
an alternate embodiment of the invention.
FIG. 11 is a view of the embodiment shown in FIG. 10 but with the
drive piston in retracted position as pressure is built up in the
gas chamber.
FIG. 12 is a side elevation view of a second embodiment of a
pressure relief valve system for use with the embodiments of the
invention shown in FIGS. 10 and 11.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings wherein similar parts are designated
by similar numerals, the invention contemplates a new and improved
portable power tool device with a cylindrical body including a bore
therein and in which is mounted a drive piston or ram and a
centrally apertured brake spool surrounding the ram. A stationary
seating element is located adjacent the upper extremity of the bore
and which is adapted to sealingly engage the upper surface of the
drive piston when the drive piston is in a fully retracted
position. Also located adjacent the upper extremity of the bore is
a reservoir or chamber in which a compressible fluid, such as gas,
is maintained under pressure. An accumulator piston is mounted in
this chamber for movement against the bias of the compressed
gas.
The device operates by introducing power fluid at a first,
relatively low pressure, to force the brake spool upwardly,
carrying the drive piston with it, into seating engagement with the
seating element. With the low pressure fluid in the cylinder, the
drive piston remains in the idling mode until such time as the
operator of the power device desires to drive a fastener into a
workpiece. At that time, compressible fluid is introduced into the
cylinder at a relatively high pressure which first forces the brake
spool down to the opposite extremity of the bore while maintaining
the drive piston sealed against the seat member in a retracted
position. As the high pressure oil continues to be pumped into the
cylinder, it forces the accumulator piston to move against the bias
of the compressed gas, thus, building up the pressure within the
cylinder. Upon reaching a certain predetermined pressure in the
cylinder, a pressure relief valve opens to permit fluid
communication between the power fluid in the clyinder and the upper
surface of the sealed drive piston. When this occurs, the full
force of the compressible fluid acts through the noncompressible
fluid to rapidly extend the drive piston, with great velocity, to
drive a fastener which has been indexed beneath the ram.
The power driving device 10 thus includes a cylindrical body
portion 12 having a central pass through bore 14. The bore 14 is
provided with a counterbore 16 at the upper extremity thereof and a
lower counterbore 18. The body 12 is provided, at the upper end,
with an external threaded portion for connection with mating
threads on the lower cylinder wall portion 42 of a connection
fitting element 40. The connection fitting 40 includes a disc
shaped body 43, essentially traversing the counterbore 16. The disc
shaped body 43 includes a plurality of apertures 49 providing fluid
communication between the upper face 46 of the disc shaped body and
the lower face 47 of the body. A radially extending bore 45 is
provided in the disc shaped body which extends from the central
axis of the bore 14 to the outer periphery of the connection
fitting 40. Radial port 50 allows communication between one of the
apertures 49 and the radial bore 45 for purposes best set forth
hereinafter. The lower face of the body 47 includes an annular boss
48 extending generally axially of the bore of the device. This
annular boss 48 threadingly engages a generally cylindrical seat
element 52. A pass through port 53 extends generally axially of the
seat element and permits communication with a cyilndrical
projection 54 on the seat element and port 51 in the connection
element. The function of cylindrical projection 54 is best set
forth hereinafter.
The upper cylindrical wall 41 of the fitting 40 is threadingly
mounted to a cap 20. The bore 22 formed in this cap 20 functions as
a chamber for compressible fluid, such as gas. Such compressible
fluid is introduced into this chamber through a valve member 24.
Positioned within bore 22 in the gas chamber is a free floating
piston 26. The piston 26 includes an annular recess 28 designed to
accommodate a seal 29. The piston 26 rests on a stop, such as the
upper surface 46 of the connection fitting, but is free to move
upwardly in the bore 22 against the pressure of the compressible
fluid.
Positioned within the central bore 14 is power drive piston 30
which includes a generally cylindrical central portion 32 and an
enlarged upper end portion 36 which is connected to the central
portion by a tapered, frustoconical portion 37. At the opposite end
of the central portion 32 is provided a generally cylindrical
section of a diameter less than the diameter of central portion and
serving as a hammer portion 34. Attention is drawn to the
configuration of the upper surface of the end portion 36 as shown
most clearly in FIG. 8. This upper end surface is provided with a
recess 38 which includes side wall portions 39. It should also be
noted that the outer diameter of the cylindrical projection 54 is
complementary to the inner diameter of the recess on the head and
provides a sealed cooperation between the seating element 52 and
the drive piston 30 for purposes which will be set forth
hereinafter.
Located within the bore 14 and free to reciprocate therein is a
brake mechanism 60. This brake mechanism 60 surrounds the drive
piston 30 by the provision of a central bore 62 which accommodates
the central portion 32 of the drive piston. This central bore 62 is
enlarged slightly at the upper portion of the brake with a
counterbore 64. Tapered wall portions 66 connect the counterbore 64
to the central bore 62 and, as will be pointed out in detail
hereinafter, the surfaces forming the counterbore and tapered
surfaces 64 and 66 are complementary to the external surfaces
forming the upper end portion 36 and tapered portion 37 on the
drive piston.
Located complementary within the lower counterbore 18 and also
surrounding the drive piston 30 is a shock spool element 80. As
shown in FIG. 2, the brake 60 rests on the upper surface 81 of the
shock spool. For purposes which will be set forth hereinafter, the
shock spool is provided with an outer annular recess 83 and a pair
of inner annular recesses 84. A plurality of radial ports 85
enables fluid to communicate between the outer recess and the inner
recesses. Generally axially extending ports 73 afford communication
between the outer annular recess and the upper face 81 of the
spool.
At the lower end of the body 12, directly beneath the shock spool
80, is mounted a seal body member 90. Centrally located bore 92
extends through the body member to accommodate the central portion
32 of the drive piston 30. Counterbore 94 in the upper portion of
the body 90 accommodates an annular seal which is adapted for
sliding engagement with the drive piston 30. An O-ring sealing
member 97 is positioned in an annular recess 96 in the counterbore
18.
A nosepiece assembly 91 is attached, preferably removably, to the
lower extremity of the seal body 90. This nosepiece may be designed
to particularly accommodate various fastener configurations and is
merely representative of one design acceptable for use with the
power device of the invention.
A feed mechanism 210 may be provided to automatically index
fasteners 300 beneath the hammer of the drive piston. A hydraulic
line 211 permits noncompressible power fluid entry into a cylinder
216 through port 214. The power fluid acts against the relatively
large surface area of the head of the piston 218 to force it to
move to the left, as shown in FIG. 1, against the bias of spring
220. A rod-like extension 222 is attached to the piston 218 and is
fixedly mounted to a carriage 224 for slidable movement on a track
226. The carriage is provided with a finger 228 having a tip
portion 229 adapted to be accepted in a collated strip member with
indexable or notch-like grooves. When power fluid is introduced
into the cylinder, the piston moves to the left, moving the
carriage with it. The finger 229 will have engaged an aperture in a
collated strip to move a fastener beneath the path of the ram or
drive piston 30. When the oil pressure is released, the spring
member 220 forces the piston to the right as shown in FIG. 1 moving
the carriage and finger member with it to position the tip of the
finger into the next notch in a collated strip. It should be
understood that the feed mechanism shown in FIG. 1 is merely
representative of a mechanism which may be used with the invention
and forms no part of the invention. Feed mechanism such as that
shown in U.S. Pat. No. 3,661,313 could be adapted for use with the
instant invention.
Turning to FIGS. 1-4, the operational stages of the invention will
be described with particular emphasis on the various functional
characteristics of the elements recited above. Since an important
aspect of the invention is the use of noncompressible power fluid
pumped into the system at two pressure levels, the device must be
connected with a pump capable of such a dual pressure level
operation. Such a pump is not shown and, accordingly, does not form
part of this invention in and of itself since a number of
acceptable pumping devices are commercially available and known in
the art.
The device shown in FIGS. 1 and 2 describes the power drive piston
30 in a fully extended position and represents the mode of the
device immediately after it has driven an associated fastener 300.
At this point noncompressible fluid, such as oil, is pumped into
the cylinder through low pressure line 200 and enters the cylinder
through a port 206. The fluid communication provided by port 73 in
the shock spool allows the noncompressible power fluid to act on
the lower face 68 of the brake spool to carry the drive piston
upwardly in the bore 14 until the enlarged head 36 engages the
fixed seating element 52. The complementary sealing surfaces
provided by the cylindrical projection 54 on the seating element
and the recess and side wall portions 38 and 39 in the upper
surface of the drive piston allows the power fluid to seal the
piston against the seating element. As shown in FIG. 3 and in more
detail in FIG. 8, this seal exists as a result of the
cross-sectional area of the top edges of side walls of enlarged
head portion 36 being substantially less than the surface area of
the lower face on the brake spool.
The position of the device shown in FIG. 3 is the idling position
of the tool and it should be apparent that this mode allows the ram
to be held in a cocked position to facilitate indexing of fasteners
beneath the hammer and for proper positioning of the entire
device.
To cause the operation of the power device to perform work, such as
the driving of a nail, at high velocity, the high pressure level of
a two-stage pump is activated through conventional switching means,
such as by a trigger 112 in handle 116 serviced by electric lines
117. Hydraulic line 202 allows entry into the system of power fluid
at a higher pressure than that pumped used in the mode described in
relation with FIGS. 1 and 2. Passageway 208 allows this power fluid
to enter the bore 14 through port 204, which is located above the
upper surface of the brake spool 60. At this point, the brake spool
is forced down under the pressure of the power fluid to its
position shown in FIG. 4. However, since the surface area defined
by the frustoconical portion 37 on the drive piston is greater than
the cross-sectional area of the upper edges 35, any fluid pressure
which is exerted on the drive piston tends to hold it in tight
sealed engagement with the seating element. As the noncompressible
fluid is continued to be pumped into the bore through the port 204,
it acts on the lower surface of the accumulator piston 26 through
the apertures 49 in the connection fitting 40. As is apparent in
FIG. 4, the continued pressure of the noncompressible fluid forces
the accumulator piston upwardly against the bias of the
compressible gas in the chamber 22. The compressed gas in the
chamber normally may have a pressure of approximately 2,000 psi.
Upon further compression by the accumulator piston 26, it may
attain a pressure of a still higher value of 4,000 psi.
Pressure relief valve system 101 housed in the connection fitting
will allow the drive piston to drive fasteners at a predetermined
pressure level within the bore 14. Upon the attainment of such a
predetermined pressure level, power fluid enters bore 45 in the
fitting 40 through radially extending port 50. As will be seen from
FIG. 7, bore 45 is provided with a conically shaped valve element
102 having an axially extending stem 103. Also mounted in the bore
is a rod member 106 having an annular flange 107 adapted to engage
an adjustment screw 108. A compression spring 105 surrounds the rod
106 and stem 103 to bias the valve into seating and sealing
engagement with a seat 104. This precludes fluid from entering the
bore 45 until the pressure in the bore 14 exceeds the designed
force of the spring 105. It is important to note that this force
which the valve is held into engagement with the seat 104 may be
adjusted external of the cylinder by manipulation of the adjustment
screw 108.
Upon the attainment of the pressure sufficient to open the valve
102, power fluid is then free to communicate, through axial port 53
in the seating element, with the recess in the head of the drive
piston. This communication effectively allows the drive piston to
be urged away from the drive piston and the seating element,
breaking the seal there between. Once this seal is broken, the
pressure of the power fluid is now exerted across the whole
cross-sectional area of the upper end portion 36 on the drive
piston and as a result the drive piston is moved forcibly and with
great velocity downward due to the force exerted by the high
pressure power fluid plus the force of the compressed gas in the
gas chamber. Since the power fluid is noncompressible, it serves as
a linkage and transfer means for the force being exerted by the
compressed gas, through the power fluid, against the enlarged head
portion 36 of the drive piston 30.
The drive piston rapidly extends to the position shown generally in
FIG. 1. The brake spool 60 is configured to trap over fluid between
the counterbore 64 and associated tapered surface 66 and the
frustoconical surface 37 of the drive piston, thus slowing the
drive piston down as it approaches the end of its power stroke and
cushioning the shock of the engagement between head 36 and the
brake 60. It will be appreciated that the high energy power stroke
will produce surges of oil to be forced downwardly in the bore 14
under great pressure. To decrease this surge of power fluid and its
action on seals 95 and 97 in the lower body 90, the shock spool has
been positioned in lower counterbore 18. As power fluid is forced
downwardly through the shock spool between the internal surface of
the bore 87 in the shock spool and the central portion 32 of the
drive piston, it may be released to the low pressure return line
202 through inner annular recess 84 and the plurality of radial
ports 85 communicating between these inner annular recesses and an
outer annular recess 83. Thus the substantial surge of power fluid
and its action on the lower seals is decreased.
Due to the configuration of the upper seal surface of the recess 38
in the drive piston 30, it is possible that power fluid may become
trapped within this recess and tend to prohibit effective sealing
engagement between the drive piston and the seating element. For
this purpose, a bleed valve system is provided in the seating
element. Attention is drawn to FIG. 8 which shows a radial port 55
extending from the centrally located axial port 53 providing fluid
communication with a recess accommodating a ball valve 56. This
ball valve is resiliently seated at a predetermined force through
the use of an annular resilient seal 57. It should be apparent that
any oil trapped in the recess 38 will be forced out through the
radial port 55, however due to the ball valve 56 and seal 57 power
fluid may not enter the recess from the main cylinder.
A modification of the invention is shown in FIGS. 10-12 wherein the
use of similar numerals with the addition of the suffix a are
intended to designate similar elements or components. The power
device design 10a is particularly effective to provide a driving
tool which is compact in size and which is particularly designed to
generate a high velocity in the drive piston 30a.
The essential distinction between device 10 and device 10a resides
in the provision of an accumulator piston 26a having a central bore
127 and which includes an annular boss 128 and annular flange 129.
The annular flange includes both an inner and outer annular recess
125 to accommodate sealing O-rings. The accumulator piston 26a is
retained and slidably mounted on a post element 140. Thus, the
piston 26a is free to move in a telescoping fashion relative to the
post 140 and within the gas chamber 22a. The telescoping motion of
the accumulator piston 26a is due to the urging of a high pressure
noncompressible fluid forcing the accumulator piston upwardly as
shown in FIG. 11 against the bias of a compressible fluid in the
gas chamber 22a. In this embodiment the accumulator piston is
restrained from movement into the bore 14a of the cylindrical body
12a by the upper counterbore 16a functioning as an abutment surface
in a manner similar to the upper surface of the fitting 40 in the
embodiments of FIGS. 1-4.
The device 10a is provided with a pressure relief valve system to
allow the drive piston to be actuated upon the pressure in the
cylinder reaching a predetermined level. Post 140 includes an axial
port 142 and a series of counterbores 144, 145 and 146. Positioned
within the counterbore 145 is a cup-like bearing member having an
aperture at the lower surface thereof to permit a valve rod 152 to
reciprocate therethrough. The valve rod includes an integral head
156 and a rod portion 160 extending upwardly from the head. A
spring member 158 is mounted around the rod 160 and is supported by
the head portion at one extremity of the spring and impinges an
adjustment screw member 162 at the other extremity. Valve rod 152
is positioned in counterbore 146 for slidable movement therein. A
suitable seal is positioned within counterbore 144. At the lower
extremity of this rod 152 is provided a conical valve surface
element 154 which sealingly engages the seat portion 150 against
the normal bias of the spring 158. Radial port 165 provides fluid
communication between the bore 14a and the counterbore 146 and with
the shoulder 167 formed at the juncture extremity of rod 152 and
valve 154. As the pressure in the cylinder is increased, in a
manner similar to the process described relative to FIGS. 1-4, the
power fluid will exert a force on the shoulder 167 until the
pressure in the cylinder overcomes the predetermined force of the
spring 158. At this point, fluid communication is provided between
the bore 14a and the recess 38a in the drive piston. At this
instant the seal is broken between the head of the drive piston and
the complementary projection 143 in the post 140. Once the seal has
been broken, the full force of the compressed gas acting through
the linkage of the power fluid propels the drive piston rapidly
downwardly to drive an associated fastener.
It should be noted that hammer portion 34a is a blade-like
extension providing a fastener contacting cross-sectional area of a
generally rectangular configuration to better accommodate
staple-like fasteners.
Attention is directed to the bore 131 provided in drive piston 30a.
This decreases the mass of the drive piston while retaining the
effective area which may be subjected to power fluid pressure.
Thus, the velocity of the ram may be substantially increased as a
result of this design.
Attention is also directed to FIG. 12 wherein an alternate
embodiment of the post assembly 140 and pressure valve system is
described. Assembly 240 is provided with an axial bore 242 having
counterbore portion 244. An annular body 270 is slidably mounted in
counterbore 244. Body 270 includes a recess 272 which accommodates
an O-ring seal 274. The body also includes a projection 275 which
extends axially of body 270 in the counterbore 244 and which is
surrounded by the upper portion of a compression spring 258.
Slidably mounted in the counterbore 243 is a conical valve member
254 having a projection 255 extending toward and generally along
the same axis as the projection 275. Compression spring 258
surrounds projection 255 and retains the valve in sealing
engagement within the seat surface 250 until such time as the power
fluid in the cylinder reaches a predetermined pressure greater than
the force exerted by the spring 258. At this instant the power
fluid, through port 238 and axial port 242, forces the valve member
upwardly allowing fluid communication to longitudinally extending
port 232. In this manner the power fluid contacts the recess 38a,
breaking the seal between the post 240 and the head 36a of the
piston 30a. The breaking of this seal allows full force of the
power fluid to rapidly propel the drive piston.
In the event the accumulation of oil within the cavity 131 and
recess 38a prevents sealing engagement with the post means, a
one-way bleed valve system is provided. The oil trapped in recess
38a may be forced into radially directed ports 234 and out into the
bore 14a through the one-way valve system provided by an annular
resilient seal 236.
The operation of driving device 10a is similar to the operation of
device 10 in that low pressure power fluid is pumped into bore 14a
through port 206a and also through the shock spool 80a. The lower
pressure power fluid thus forces the brake spool 60a to carry the
drive piston 30a up in the bore into seating engagement with a post
140. This position is shown in FIG. 10 and, as is described
relative to the embodiments shown in FIGS. 1-4, shows the power
driving device in an idling position.
When the tool is to be actuated, the oil pump is switched to the
high pressure mode and oil at a relatively high pressure enters the
bore 14a through port 204a and, by virture of a longitudinal recess
119 in the bore, it is permitted to both impinge the lower surface
of the accumulator 26a and the upper surface of the brake 60a.
Under this relatively high pressure power fluid, the brake spool is
forced downwardly to rest against the upper surface of the shock
spool 80a while the accumulator piston is forced to move up against
the bias of the compressed gas in the accumulator chamber 22a, as
shown in FIG. 11. When the pressure of power fluid reaches a
certain predetermined level, the pressure relief valve system
described above allows the seal to be broken between the drive
piston and the post 140 thus subjecting the full force of power
fluid on the upper relatively large surface area of the drive
piston 30a, thus driving the piston rapidly downwardly.
FIG. 9 shows an alternate detail of a brake spool which may be used
with either of the embodiments of this invention. The spool 70 has
a central pass through bore 72 to accommodate the central portion
32 of the drive piston 30. Counterbores 74 and 75 and frustoconical
portions 76 and 77 act together to cushion the shock of the
engagement of the head of the drive piston 36 and the brake 70.
However, due to the plurality of differeing volumetric capacities
in the head of the brake spool created by the counterbores 74 and
75 and tapered surfaces 76 and 77, the drive piston is allowed to
transmit high energy levels toward the end of its driving stroke,
rather than initiating retardation early in the drive stroke.
A further feature of the brake spool 70 is the provision of a
plurality of circumferentially spaced ports 73 extending generally
along the axis of the brake. An equal plurality of radially
directed ports 71 are connected with the axial ports to permit
fluid communication between the lower surface of the brake 70 and
annular recess 79 which accommodates a resilient O-ring seal 78
around the periphery of the brake. Thus, when the driving tool is
in the idling position, as shown in FIGS. 3 and 10, low pressure
fluid is allowed to circulate through ports 71 and 73 and through
the one-way valve system 79 to effectively cool the system when the
tool is in the idling mode.
It will now be apparent that the power driving device illustrated
and described performs work due to the expansion of compressed gas
in a power accumulator or gas chamber. The pressured gas introduced
in the gas chamber may be initially of a relatively large value,
for example 2,000 psi, and compression of the gas in the chamber
due to the movement of an accumulator piston 26 by a
non-compressible power fluid, causes it to attain a pressure of a
still higher value approximately 4,000 psi. Thus, the energy stored
in the compressed gas is employed to drive a piston 30 using the
non-compressible power fluid as a linkage between the drive piston
and the accumulator piston. The power driving tool utilizes
compressible power fluid at two distinct pressure levels. Power
fluid at a first relatively low pressure is used to retract the
drive piston by forcing the brake spool to carry the drive piston
up into seating and sealing engagement with a stationary member.
The drive piston is retained in the idling mode by the relatively
low pressure compressible fluid until such time as the operator of
the tool desires to drive a fastener. At that time noncompressible
fluid is pumped into the bore 14 forcing the brake spool down in
readiness to accept and cushion the drive piston while the drive
piston remains in sealing engagement with the seat element.
Pressure is built up in the system by increased entry of the
compressible fluid which forces the accumulator piston to move
against the bias of the compressed gas. A further significant
feature of the invention is the provision of an adjustable pressure
relief valve system which allows the drive piston to be actuated to
release energy at a certain predetermined and repeatable pressure
level. Thus, the energy level which fasteners are driven will be
constant and neither the change in temperature within the system
nor the leakage of oil within the gas chamber will affect the
energy level at which the piston is driven.
It will be apparent to those skilled in the art that an economical,
compact, high velocity, high force is provided which drives
fasteners at a predictable energy level and in such a manner that
collated fasteners may be indexed beneath the driving ram in a
safe, efficient manner. Where all the invention has been described
in conjunction with specific embodiments thereof, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art in light of the foregoing
description. Accordingly, it is intended to embrace all such
alternatives, modifications and variations as fall within the
spirit and broad scope of the appended claims.
* * * * *