U.S. patent number 3,796,050 [Application Number 05/254,482] was granted by the patent office on 1974-03-12 for high energy rate actuator.
This patent grant is currently assigned to Foster-Miller Associates. Invention is credited to Allan T. Fisk, Andrew C. Harvey.
United States Patent |
3,796,050 |
Fisk , et al. |
March 12, 1974 |
HIGH ENERGY RATE ACTUATOR
Abstract
An hydraulic actuator including a cylinder, a sleeve slidable in
the cylinder, and a piston slidable in the sleeve with an impacting
end extending out of the cylinder. A first chamber formed in the
cylinder surrounds the impact end of the piston, and energy storage
means is provided in the housing at the other end, which energy
storage means is in communication with the sleeve and piston. A
collar is carried on the piston having one face exposed to the
pressure on the first chamber and having a second opposed face
which in part defines a second chamber. Means are connected to the
first chamber for increasing the pressure therein to retract the
sleeve and piston in unison so as to develop stored energy in the
energy storage means, and means are provided for equalizing the
pressures on opposite faces of the collar as the piston and sleeve
retract to release the stored energy to drive the piston in a power
stroke in the direction of the impacting end and also causing the
stored energy to drive the sleeve in the same direction. The second
chamber is constantly open to the atmosphere.
Inventors: |
Fisk; Allan T. (Newton Center,
MA), Harvey; Andrew C. (Waltham, MA) |
Assignee: |
Foster-Miller Associates
(Waltham, MA)
|
Family
ID: |
22964464 |
Appl.
No.: |
05/254,482 |
Filed: |
May 18, 1972 |
Current U.S.
Class: |
60/371; 60/413;
92/134 |
Current CPC
Class: |
F16H
43/00 (20130101); B21J 7/28 (20130101); B21J
7/24 (20130101); F03C 1/00 (20130101); B25D
9/145 (20130101) |
Current International
Class: |
B21J
7/00 (20060101); B21J 7/24 (20060101); B21J
7/28 (20060101); B25D 9/14 (20060101); F16H
43/00 (20060101); B25D 9/00 (20060101); F03C
1/00 (20060101); B30b 001/30 () |
Field of
Search: |
;60/369,371,413
;91/47,49,422,234 ;92/134 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Geoghegan; Edgar W.
Attorney, Agent or Firm: Wolf, Greenfield & Sacks
Claims
What is claimed is:
1. An hydraulic actuator comprising
a cylinder,
a sleeve slidable within the cylinder and forming a seal with the
inner surface of the cylinder at one end thereof,
a piston slidable in and forming a seal with the sleeve at said one
end and having an impacting end extending out the other end of the
cylinder,
a first chamber in the cylinder at said other end defined in part
by said other end of the cylinder and the other end of the sleeve
and surrounding the impacting end of said piston,
a sealed gas filled second chamber at said one end of the cylinder
and defined in part by the adjacent ends of the sleeve and
piston,
a collar carried on the piston and having a face which is exposed
to the first chamber,
means connected to the first chamber for increasing the pressure
therein to retract the sleeve and piston in unison in the direction
of the sealed chamber to develop stored energy in the sealed
chamber by the compression of the gas therein,
a second face on the collar of the piston opposed to the first
recited face and a third chamber defined in part by the second
face, said third chamber being constantly open to the atmosphere,
and
means for equalizing the pressures on the opposite faces of the
collar as the piston and sleeve move toward the sealed second
chamber to cause the pressure in the sealed chamber to drive the
piston rapidly in a power stroke in the direction of the impacting
end of said piston, said last-mentioned means causing the pressure
in the first chamber to drop sharply and thereby permitting the
pressure in the sealed chamber to drive the sleeve in the direction
of said first chamber.
2. An hydraulic actuator as described in claim 1 further
characterized by
said means for equalizing the pressure in the second chamber being
a fluid duct bypassing the collar when the piston and sleeve are
retracted beyond a predetermined position within the houing.
3. An hydraulic actuator as described in claim 1 further
characterized by
said means for equalizing the pressure in the second chamber being
a stop provided in the housing for physically limiting the extent
the piston may be retracted in the housing.
4. An hydraulic actuator as described in claim 2 further
characterized by
said fluid duct being formed in the inner surface of the
housing.
5. An hydraulic actuator as described in claim 1 further
characterized by
the inner diameter of the cylinder at said one end which defines
the sealed chamber being smaller than the diameter of the other end
of the cylinder which defines the first chamber,
the end of the sleeve in part defining the first chamber forming a
sliding seal with the inner surface of said other end of said
cylinder.
6. An hydraulic actuator as described in claim 1 further
characterized by
said sleeve in part defining said third chamber and forming a valve
with the collar separating the third chamber from the first chamber
as the sleeve and piston retract in unison in the housing,
said valve opening to connect the first and third chambers when the
sleeve and piston move relative to one another.
7. An hydraulic actuator as described in claim 6 further
characterized by
a relatively large constantly open port in the sleeve communicating
with the third chamber and connecting the third chamber to the
atmosphere.
8. An hydraulic actuator as described in claim 5 further
characterized by
said sleeve in part defining said third chamber and forming a valve
with the collar separating the third chamber from the first chamber
as the sleeve and piston retract in unison in the housing,
said valve opening to connect the first and third chambers when the
sleeve and piston move relative to one another.
9. An hydraulic actuator as described in claim 8 further
characterized by
a relatively constantly open port in the sleeve communicating with
the third chamber and connecting the third chamber to the
atmosphere.
10. An hydraulic actuator as described in claim 6 further
characterized by
the area of the end of the piston exposed in the sealed chamber
being substantially equal to the area of the impact end of the
piston extending out of the chamber.
11. An hydraulic actuator as described in claim 6 further
characterized by
the area of the end of the piston exposed to the sealed chamber
being greater than the area of the impact end of the piston
extending out of the chamber.
12. An hydraulic actuator as described in claim 6 further
characterized by
the area of the end of the piston exposed to the sealed chamber
being smaller than the area of the impact end of the piston
extending out of the chamber.
13. An hydraulic actuator comprising
a cylinder,
a sleeve slidable within the cylinder,
a piston slidable in the sleeve and having an impacting end
extending out of the cylinder,
a first chamber in the cylinder defined in part by said cylinder
and sleeve and surrounding the impacting end of said piston,
energy storage means in the housing associated with the remote end
of the piston,
a collar carried on the piston and having a face which is exposed
to the first chamber,
means connected to the first chamber for increasing the pressure
therein to retract the sleeve and piston in unison in the direction
of the energy storage means to develope stored energy in said
means,
a second face on the collar of the piston opposed to the first
recited face and another chamber defined in part by the second
face, said other chamber being constantly open to the atmosphere,
and
means for equalizing the pressures on the opposite faces of the
collar as the piston and sleeve retract to permit the stored energy
to drive the piston rapidly in a power stroke in the direction of
the impacting end of said piston, said last mentioned means causing
the pressure in the first chamber to drop sharply and thereby
permitting the stored energy to drive the sleeve in the direction
of said first chamber.
14. An hydraulic actuator as described in claim 13 further
characterized by
said sleeve in part defining said other chamber and forming a valve
with the collar separating the other chamber from the first chamber
as the sleeve and piston retract in unison in the housing,
said valve opening to connect the first and other chambers when the
sleeve and piston move relative to one another.
15. An hydraulic actuator as described in claim 14 further
characterized by
a relatively large constantly open port in the sleeve communicating
with the other chamber and connecting the other chamber to the
atmosphere.
Description
BACKGROUND OF THE INVENTION
This application relates to high velocity hydraulic actuators and
more particularly comprises an improvement over the actuator
disclosed in application Ser. No. 91,651 filed Nov. 23, 1970, now
abandoned assigned to Foster-Miller Associates, Inc.
The actuator of the present invention is suitable for use in many
applications including rock drills, pavement breakers, punch
presses, forging hammers, nail drivers, etc. The actuator may be
operated either as a single or repetitive cycle device.
High velocity actuators normally deliver very high instantaneous
power during the power stroke. However, high velocities are not
compatible with conventional "steady flow" hydraulic systems for
reasons both of excessive fluid velocity losses and very high
instantaneous power. Consequently, actuators are designed to store
energy at modest power levels to be released at a high rate during
the power stroke.
Prior to the invention disclosed in application Ser. No. 91,651,
supra, actuator design was very complex. The complex designs are
particularly detrimental in those applications which require an
impact as the useful power output, because the complex designs are
not readily capable of withstanding the very substantial shocks
which are imposed on the systems in those applications. The
invention disclosed in application Ser. No. 91,651 represents a
substantial improvement over the prior complex designs for it
reduces the number of moving parts essentially to three; namely, a
piston, sleeve, and valve, and it accepts a constant flow rate as
the motivating force so as to enable the actuator to be powered by
commonly available fixed displacement power supplies.
Nevertheless, the design of the actuator shown in the earlier
application Ser. No. 91,651, now abandoned had certain
disadvantages. For example, in that system the exhaust flow of
motivating fluid fluctuates from zero to some high value during
each cycle. The high value may be as much as several times the
normal in-flow rate, depending upon the cycle rate of the actuator.
Furthermore, the central valve forming part of the preferred
embodiment of the actuator of that application represents a
potential source of maintenance problems, particularly because it
must cycle once for every cycle of the piston-sleeve assembly.
One important object of the present invention is to provide an
actuator with a very simple mechanical operation, which permits
energy storage in a compressed gas and quick release of that energy
without excessive fluid velocities or pressure surges.
Consequently, the simple mechanical configuration is conducive to
the adoption of simple, rugged piston and sleeve shapes suitable
for impacting service.
Another important object of this invention is to provide a high
velocity actuator which is free of external control valves that are
potential sources of maintenance problems.
BRIEF FIGURE DESCRIPTION
FIG. 1 is a cross section view of an actuator constructed in
accordance with this invention and schematically shown connected to
a hydraulic control circuit;
FIGS. 2-7 are schematic drawings of the actuator of FIG. 1
sequentially illustrating the positions of the various parts of the
actuator during a single cycle; and
FIGS. 8-14 are schematic drawings, some fragmented, of other
embodiments of this invention.
DETAILED DESCRIPTION
The actuator assembly shown in FIG. 1 essentially includes three
parts, namely, housing 10, sleeve 12, and piston 14. For
simplicity, piston rings and other forms of seals which may be
utilized have been omitted in the drawing. Housing 10 and sleeve 12
are shown to have upper diameters smaller than their lower
diameters, unlike the embodiments illustrated in earlier
application Ser. No. 91,651. However, this particular arrangement
is not essential to the operation of this invention, and the
diameters may be uniform throughout.
Housing 10 includes an inlet 16 adjacent its bottom wall 18, and an
exhaust port 20 approximately centrally located between the top 22
and bottom 18 of the cylinder. Cylinder top wall 22 defines with
the top of sleeve 12 and piston 14 an enclosed gas chamber 24. Top
wall 22 of the housing is fitted with a check valve 26 used to
charge the chamber 24 with gas.
The upper cylindrical portion 30 and lower cylindrical portion 32
which together define the housing 10 are joined at their inner
surfaces by frustoconical section 34, which with sleeve 12 defines
an annular hydraulic volume 36 in constant communication with the
port 20. The upper smaller diameter portion 38 of sleeve 12 is
joined to lower cylindrical portion 40 of the sleeve by
frustoconical section 42, which in turn defines with the piston a
second annular hydraulic volume 44. Hydraulic volumes 36 and 44 are
in constant communication with one another through the ports 46
formed in frustoconical section 42 of sleeve 12.
Piston 14 as shown in the drawing is essentially rod shaped but
includes a collar 48 of greater diameter than either the upper
portion 50 or lower portion 52 of the piston.
A chamfered seat 54 is formed in the lower end of sleeve 12, that
serves as a valve seat for the beveled edge 56 of collar 48 which
mates with it. When the sleeve and piston are in the position shown
in FIG. 1, volume 44 is sealed from the lower chamber 58 formed in
housing 10 about the lower end 52 of the piston.
Sleeve 12 slides freely in housing 10, and piston 14 slides freely
in the sleeve, and a sliding seal exists between upper cylindrical
portion 38 of the sleeve and upper portion 30 of the housing.
Similarly, a sliding seal is effected between upper portion 50 of
the piston and the inner surface of the upper portion 38 of the
sleeve.
To assist in understanding the description of the operation of the
actuator which follows, certain areas of the sleeve and piston have
been labeled with letters which are used in the equations below.
Thus, in FIG. 1, area A represents the upper end of piston 14, B
represents the area of the upper end of sleeve 12, C represents the
area of the collar 48 exposed to the pressure chamber 58, D
represents the area of the lower end of sleeve 12 exposed to the
pressure chamber 58, and E represents the area of the exposed end
of piston 14.
In FIGS. 2-7, the operating cycle of the actuator of FIG. 1 is
illustrated. In describing this operation it is assumed that the
inlet 16 is connected to a constant source of flow as may typically
be established by a gear pump. And at all times during the cycle,
the discharge port 20 is open to the atmosphere.
In FIG. 2 the pressure P.sub.58 (pressure in chamber 58) drives
piston 14 and sleeve 12 upwardly against the gas pressure P.sub.24
in chamber 24 by acting on area C of collar 48 and area D of sleeve
12. Thus the piston and sleeve combination move upwardly in
unison.
To assure that the piston and sleeve are held together the
following inequalities must be established.
[1] P.sub.58 C > P.sub.24 A and
[2] P.sub.24 B > P.sub.58 D
Because in the embodiment shown area C is larger than area A and
area B is greater than area D, the proper relationship is provided
so as to insure the joint travel of the piston and sleeve as
suggested in FIG. 2.
The piston-sleeve combination rises as a single body as flow into
chamber 58 continues as suggested in FIG. 2 while the relationships
set forth in equations 1 and 2 are maintained. As joint upward
travel of piston and sleeve continues, relief passages 60 formed on
the inner surface of cylindrical portion 32 of the housing 10 are
exposed by the lower end of sleeve 12 to the chamber 58. When this
occurs, volumes 44 and 36 are placed in communication with the
chamber 58 and the valve seat 54 and collar 48 are bypassed. This
results in the equalization of the pressures on the opposite side
of the collar 48 acting on areas C and C.sup.1. When the pressures
on opposite sides of the collar 48 are balanced, then the pressure
P.sub.24 on area A creates an unbalance, and the piston is driven
downwardly, breaking the seal at 54, 56 and free flow is
established from chamber 58 through volume 44, passages 46, volume
36, to discharge port 20. Downward travel of the piston is impeded
only slightly by flow of hydraulic fluid in the chamber 58 about
collar 48 through annular area D. Consequently downward movement of
the piston is very rapid, with the accelerating force approximately
equal to P.sub.24 A.
With the seal at the valve seat 54 broken, the pressure drop across
collar 48 from area C to C.sup.1 instantaneously becomes zero. If
the cross sectional areas A and E of the upper and lower portions
of the piston are equal, downward motion of the piston does not
displace fluid, and the piston moves downwardly until stopped by
some useful impact as suggested in FIG. 5. With the piston and
sleeve separated, the hydraulic fluid in chamber 58 is free to
exhaust through volume 44, passages 46, volume 36, to discharge
port 20. Consequently the pressure 58 is sharply reduced, assuming
a fixed inlet flow. If volume 44, passages 46, volume 36 and port
20 are large, the gas pressure in chamber 24 acting on area B will
rapidly drive the sleeve 12 down as shown in FIG. 6. The descent
rate of the sleeve depends on the restriction of those passages and
volumes. The sleeve descends, passing the relief passages 60 until
a seal is again formed at the valve seat 54 as suggested in FIG.
7.
The sleeve is able to form a seal at valve seat 54 to close off
flow at that area because of the force relationships expressed in
equations [1] and [2] above. That is, the downward force on the
sleeve closes the valve seat until the pressure in chamber 58
(P.sub.58) rises sufficiently to create an upward force on the
piston and sleeve areas C and D causing the piston and sleeve to
rise again as a unit in the manner suggested in FIG. 2.
In FIG. 1 the system which includes the actuator is suggested
schematically. A pump 70 is shown connected to inlet duct 16 for
providing a constant inlet flow to the chamber 58. The pump is
shown supplied by a reservoir 72 which in turn is connected to
discharge duct 20. The actuator may be shut off by shunting the
housing 10 as suggested by line 74 in the system, which contains an
on-off valve 76.
The present invention is susceptible to several modifications. Some
of these are suggested in FIGS. 8 to 14 described below.
In FIG. 8, a flexible membrane 80 is shown extending across the
chamber 24 so as to positively seal that chamber. Consequently,
hydraulic fluid may act on the top of the sleeve and piston through
the diaphragm, and a positive seal is provided to prevent any loss
of the fluid in chamber 24.
FIG. 9 shows another embodiment of the invention wherein the
reciprocating motion of the piston 84 is employed to power a
self-contained compressor which feeds the gas chamber 86 so as to
maintain the pressure in the chamber above some minimum level. In
accordance with this embodiment, housing 88 is provided with an
upper extension 90 having a bore 92 which slidably receives the
upper end of piston rod 94 carried by the piston 84. The upper end
of the bore 92 is closed by adjustable plug 96, and a port 98 is
provided in the extension in communication with the bore.
As the piston 84 moves downwardly during the power stroke, air
flows into bore 92 through inlet port 98 when the upper end of rod
94 drops below the port, and when piston 84 moves upwardly and rod
94 again closes port 98 the entrapped air in the bore is compressed
and ultimately discharges through the check valve 100 located in
exhaust port 102.
A second bore 104 closed at its outer end communicates directly
with chamber 86, and a check valve 106 in the bore controls flow
from the bore 104 to the chamber 86. When the pressure in chamber
86 falls below a selected value, the check valve 106 will open to
permit air to pass into chamber 86. This will occur only when the
piston and sleeve are at the bottom of their stroke. Consequently,
pressure in the chamber 86 is maintained at a minimum predetermined
value corresponding to the maximum pressure within the bore 92.
Plug 96 may be adjustable to vary the volume of the bore 92 so as
to adjust the predetermined minimum pressure value for chamber
86.
When starting the actuator, it may be necessary to cycle the device
a few times to achieve the desired pressure level. The variable
bore volume 92 provided by plug 96 may be adjusted to limit the
peak pressure within the compressor which, in turn, and in
cooperation with check valves 100 and 106 become the minimum gas
pressure in chamber 86.
In FIG. 10 yet another modification is shown. In this embodiment,
the diameter A' of upper piston 110 is greater than the diameter E'
of lower piston portion 111. Consequently, when the piston descends
during the power stroke, it must displace fluid in chamber 58, and
this tends to be accommodated by an upward acceleration of the
sleeve. As a result, sleeve descent is delayed, which counteracts
piston recoil effects.
In FIG. 11 another embodiment of the invention is shown wherein the
cross sectional area A" is smaller than the cross sectional area E"
of the lower end of the piston (an arrangement opposite to that
shown in FIG. 10). In this configuration, as the piston 114
descends during the power stroke, the negative change in volume of
the piston in chamber 58 tends to draw fluid into the chamber,
which is accommodated by a downward acceleration of sleeve 12 until
piston 114 stops. This configuration results in a shorter cycle
time than would otherwise exist.
In FIG. 12 still another embodiment is shown. In accordance with
this embodiment, the relief passages 60 are omitted, and a stop 116
is provided in the chamber 24 of housing 10 to arrest upward
movement of the piston during the retraction portion of the cycle.
It will be apparent that when the piston retracts to a position
wherein it engages stop 116 as shown in FIG. 12, continued inflow
of hydraulic fluid into chamber 58 will cause the sleeve to
continue to rise and unseat collar 48 from valve seat 54.
Consequently, when the seal is broken, the piston will immediately
fire in the power stroke of the cycle in accordance with the
teachings of the other embodiments.
The embodiment of FIG. 13 includes means for controlling the
descent rate of sleeve 12 which accordingly controls the cycle time
of the actuator. In accordance with this embodiment, the upper end
122 of piston 124 is somewhat elongated, and a partition 126 is
provided in chamber 128 in sealing engagement with the piston
extension. Sleeve 12 defines a volume 130 about the piston below
the partition 126.
A diaphragm 132 is also shown in FIG. 13 extending across chamber
128 in the manner of the embodiment shown in FIG. 8. However, that
diaphragm is not essential to the operation of the device, but
merely assures a positive seal in the chamber.
As piston 124 and sleeve 12 move upwardly together in housing 120,
fluid in volume 130 is free to flow into chamber 128 below
diaphragm 132 through ducts 134 and 136 connected by check valve
138 which is free flowing in only the direction indicated by its
arrow. After the piston is fired in the manner described in
connection with FIG. 1, sleeve 12 is restricted in its downward
motion because fluid can enter the volume 130 only through the
orifice 140 which also joins ducts 134 and 136. By adjusting the
orifice size, the velocity of the sleeve in its downward travel may
be varied.
Further control of sleeve descent may be achieved by the addition
of a duct 142 which joins the volume 130 somewhat below the top of
sleeve 12 when in its retracted position. That is, when the sleeve
12 is in its uppermost position, the duct 142 is closed so as to
bar flow from chamber 128 below diaphragm 132 to the volume 130
through it. However, when the sleeve descends in its downward
stroke and uncovers the duct 142, the orifice 140 is bypassed and
flow is allowed freely from chamber 128 below diaphragm 132 to
volume 130. Thus, the sleeve descent rate will increase after duct
142 is uncovered by the upper end of the sleeve.
Referring again to FIG. 13, yet another means of achieving a delay
of sleeve descent is suggested. In accordance with this embodiment,
the duct 142 may be eliminated as well as orifice 140. In the
absence of orifice 140 and duct 142, the descent of sleeve 12 would
be delayed until the top of piston extension 122 passed below the
point 144. When the piston drops below that point, free
communication is established between chamber 128 below diaphragm
132 and volume 130, and sleeve descent would thereupon be
unrestricted as in the embodiment of FIG. 1.
In FIG. 14 yet another modification is shown. In accordance with
this embodiment, the constant flow actuation is replaced by an
alternating power supply in the form of a reciprocating pump 150.
The pump is connected to chamber 58 by duct 152, and the discharge
port 20 is connected to reservoir 72 which in turn is connected to
duct 152 through check valve 154. The check valve limits flow only
in the direction from the reservoir to the duct as suggested by its
arrow.
In accordance with this embodiment, displacement of the pump in a
direction to drive fluid into chamber 58 is sufficient to cock the
piston-sleeve assembly, and the excess fluid present in chamber 58
during the compression stroke of the piston is discharged through
port 20 after the piston 14 has fired and separated from sleeve 12.
The flow in duct 152 may oscillate back and forth between the pump
and chamber 58 as the pump reciprocates. If desired, a check valve
(not shown) may be inserted in duct 152 to permit flow only in one
direction, namely, from pump 150 to chamber 58.
It will be appreciated that in all embodiments where the two ends
of the piston are of the same diameter, the piston may be made
precisely symmetrical so as to permit reversing the piston to
double its life. It will also be appreciated that the frequency of
the cycle may be controlled by providing throttling valves in the
discharge port or by introducing restrictions in the passages 46.
Alternatively, frequency may be controlled by providing means for
varying the inlet flow rate to chamber 58 from the pump.
It will be appreciated that the actuator disclosed in this present
application is of simple design capable of producing high impact
velocities. In each embodiment the velocity is achieved by
initially compressing a gas or some other energy storage means and
then applying that force of stored energy to the piston without
requiring rapid liquid displacement. The actuator lends itself to a
variety of control techniques as suggested above, and it may be
operated to provide fully automatic, continuous operation,
semi-automatic operation, or single blow operation.
It will also be appreciated that the foregoing description is
intended merely to be illustrative of the invention and that other
embodiments may occur to those skilled in the art. Therefore, it is
not intended to limit the breadth of this invention to the
embodiments illustrated and described. Rather, it is intended that
the scope of this invention be determined by the appended claims
and their equivalents.
* * * * *