U.S. patent number 3,595,133 [Application Number 04/838,237] was granted by the patent office on 1971-07-27 for transducer for producing mechanical oscillations.
This patent grant is currently assigned to National Research Development Corporation. Invention is credited to Keith Foster.
United States Patent |
3,595,133 |
Foster |
July 27, 1971 |
TRANSDUCER FOR PRODUCING MECHANICAL OSCILLATIONS
Abstract
A transducer for converting fluid pressure oscillations into
mechanical oscillations usable as a rock breaking tool comprises a
differential area piston sliding in a cylinder having two chambers
therein. One chamber is connected to the oscillating pressure fluid
source, and a valve arrangement including a fluid storage space
ensures that the pressure in the storage space is greater than the
algebraic mean pressure in the first chamber. A position control
valve prevents slow drift or rapid excessive movements of the
piston.
Inventors: |
Foster; Keith (Birmingham,
EN) |
Assignee: |
National Research Development
Corporation (London, EN)
|
Family
ID: |
10325666 |
Appl.
No.: |
04/838,237 |
Filed: |
July 1, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Jul 2, 1968 [GB] |
|
|
31606/68 |
|
Current U.S.
Class: |
91/10; 92/84;
92/85R; 92/10; 92/85B; 173/DIG.4 |
Current CPC
Class: |
B25D
9/06 (20130101); B06B 1/183 (20130101); Y10S
173/04 (20130101) |
Current International
Class: |
B25D
9/06 (20060101); B06B 1/18 (20060101); B25D
9/00 (20060101); F15b 015/22 () |
Field of
Search: |
;91/390 ;92/8,9,10 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schwadron; Martin P.
Assistant Examiner: Cohen; Irwin C.
Claims
I claim:
1. A transducer for converting fluid pressure oscillations into
mechanical oscillations comprising a piston member having first and
second opposing faces and a cylinder member mounted for relative
oscillatory movement, the said first and second opposing faces of
the piston member respectively bounding first and second chambers
in the cylinder member, means to connect at least the first chamber
to a respective source of oscillating pressure fluid to cause said
relative oscillatory movement, a valve assembly within the cylinder
member, the valve assembly comprising a storage space, a flow
regulator valve connecting the first chamber to the storage space,
means to bias the regulator valve to maintain the fluid pressure in
the storage space greater than the algebraic mean pressure in the
first chamber, and a position control valve within the cylinder
member and engageable by the piston member, the position control
valve being adapted upon relative movement in one sense in excess
of a predetermined amount, to cause the storage space to be
connected to the second chamber, to oppose the said relative
movement in excess of a predetermined amount.
2. A transducer as claimed in claim 1 wherein the position control
valve is adapted upon further relative movement in said one sense
to connect the second chamber to the first chamber.
3. A transducer as claimed in claim 2 wherein the position control
valve is adapted to connect the second chamber to the first chamber
via the storage space, bypassing the flow regulator valve.
4. A transducer as claimed in claim 3 wherein there are two ports,
and the position control valve is adapted to be moved axially when
engaged by the piston member, and has an axially extending surface
provided with two axially spaced lands including a first land
cooperating with a first port to connect the storage chamber to the
second chamber upon said relative movement in excess of a
predetermined amount, a second land cooperating with a second port
to connect the storage space to the first chamber upon said further
relative movement, whilst the second chamber is connected to the
storage space.
5. A transducer as claimed in claim 4 wherein the said surface of
the position control valve bounds the storage space.
6. A transducer as claimed in claim 4 wherein a spring is provided
to oppose said axial movement of the position control valve.
7. A transducer as claimed in claim 2 wherein the position control
valve is adapted, upon said further relative movement, to connect
the first chamber to a relatively low pressure port.
8. A transducer as claimed in claim 4 wherein the position control
valve has a third land which cooperates with the relatively low
pressure port.
9. A transducer as claimed in claim 1 wherein at least two axially
spaced-apart bearings are provided slidably to support the piston
member in the cylinder member, a said bearing permitting the piston
member freedom of movement to accommodate malalignment between said
bearings.
10. A transducer as claimed in claim 9 wherein said bearing
comprises an annular bearing pad in which the piston member is
supported, and which has limited freedom of movement radially of
the axis of the piston member.
11. A transducer as claimed in claim 9 wherein the said bearing
supports one end of the piston member, the piston member being
hollow at said end, the said bearing comprising a spigot which
slidably engages said hollow end, the spigot being universally
mounted from the cylinder member.
12. A transducer as claimed in claim 1 wherein there is provided a
shock absorber device, the piston member consisting of at least two
portions connected together by said shock absorbing device.
13. A transducer as claimed in claim 12 wherein the shock absorbing
device comprises a dashpot.
14. A transducer as claimed in claim 12 wherein the piston member
comprises two relatively movable coaxial elements, one inside the
other, connected together by the shock absorbing device.
15. A transducer as claimed in claim 13 wherein the dashpot is
defined by an axially extending cavity formed in the inner piston
element which is adapted to contain pressure fluid, there being a
plunger carried by the outer piston element which plunger is
disposed in said cavity for damped axial movement therein.
16. A transducer as claimed in claim 1 wherein a vibration damping
device connects a portion of the cylinder member with the remainder
thereof, the said portion slidably supporting an end of the piston
member.
Description
This invention relates to a transducer for producing mechanical
oscillations.
The present invention provides a transducer for converting fluid
pressure oscillations into mechanical oscillations comprising a
piston member and a cylinder member mounted for relative
oscillatory movement, first and second opposing faces of the piston
member respectively bounding first and second chambers in the
cylinder member, means to connect at least the first chamber to a
respective source of oscillating pressure fluid to cause said
relative oscillatory movement, a valve assembly within the cylinder
member, the valve assembly comprising a storage space, a flow
regulator valve connecting the first chamber to the storage space
and biassed to maintain the fluid pressure in the storage space
greater than the algebraic mean pressure in the first chamber, and
a position control valve within the cylinder member and engageable
by the piston member, the position control valve being adapted upon
relative movement in one sense in excess of a predetermined amount,
to cause the storage space to be connected to the second chamber,
to oppose the said relative movement in excess of a predetermined
amount.
Preferably, the position control valve is adapted upon further
relative movement in said one sense to connect the second chamber
to the first chamber.
The position control valve may be adapted to connect the second
chamber to the first chamber via the storage space, bypassing the
flow regulator valve.
The position control valve may be adapted to be moved axially when
engaged by the piston member, and has an axially extending surface
provided with two axially spaced lands, a first land cooperating
with a first port to connect the storage space to the second
chamber upon said relative movement in excess of a predetermined
amount, a second land cooperating with a second port to connect the
storage chamber to the first chamber upon said further relative
movement, whilst the second chamber is connected to the storage
chamber.
The surface of the position control valve may bound the storage
chamber.
A spring may be provided to oppose said axial movement of the
position control valve.
The position control valve may be adapted, upon said further
relative movement, to connect the first chamber to a relatively low
pressure port.
Thus, the position control valve may have a third land which
cooperates with the relatively low pressure port.
The piston member may be slidably supported in the cylinder member
in at least two axially spaced-apart bearings, a said bearing
permitting the piston member freedom of movement to accommodate
malalignment between said bearings.
Said bearing may comprise an annular bearing pad in which the
piston member is supported, and which has limited freedom of
movement radially of the axis of the piston member.
Said bearing may support one end of the piston member, the piston
member being hollow at said end, the said bearing comprising a
spigot which slidably engages said hollow end, the spigot being
universally mounted from the cylinder member.
The piston member may consist of at least two portions connected
together by a shock absorbing device.
The shock absorbing device may comprise a dashpot.
The piston member may comprise two relatively moveable coaxial
elements, one inside the other, connected together by the shock
absorbing device.
The dashpot may comprise an axially extending cavity in the inner
piston element which is adapted to contain pressure fluid, the
outer piston element carrying a plunger which is disposed in said
cavity for damped axial movement therein.
An end of the piston member may be slidably supported in a portion
of the cylinder member which is connected to the remainder of the
cylinder member via a vibration damping device.
In another aspect, although not so restricted, the invention
provides a rock breaking tool comprising a transducer as set forth
above and a rock breaking bit arranged to receive impact blows from
the piston member.
The rock breaking bit may be slidably mounted in said portion of
the cylinder member.
The invention will be described, merely by way of example, with
reference to the accompanying drawings, in which:
FIG. 1 is a part-sectional, part-elevational view of a transducer
in accordance with the present invention,
FIG. 2 is a sectional view taken along the line A-A of FIG. 1,
FIGS. 3, 4 and 5 are sectional views showing details of FIG. 1 on
an enlarged scale,
FIG. 6 shows in section an alternative form of the structure of
FIG. 3, and
FIGS. 7 and 8 show sectional views of alternative forms of part of
the structure of FIG. 1.
The terms "left" and "right" as used hereinafter refer to
directions as seen in the drawings.
Referring to the drawings, there is shown a transducer 10 adapted
to be driven by fluid pressure oscillations to produce mechanical
oscillations in accordance with the present invention, embodied in
a rock breaking tool. The transducer 10 includes a double-acting
piston member generally indicated at 11 mounted in a cylinder
member generally indicated at 12 for relative sliding movement
therewith.
Within the cylinder member 12 are first and second chambers 13 and
14, each of which is adapted to contain pressure fluid. The
chambers 13 and 14 are each adapted to be connected to a source of
pressure fluid of cyclically varying pressure to cause relative
oscillatory motion between the piston member 11 and the cylinder
member 12, the pressure variations in the two chambers being
arranged to be 180.degree. out of phase.
The piston member 11 comprises an outer hollow annular working
piston element 16 and an inner element or rod 17 which is a coaxial
sliding fit inside the piston element 16. A large mass 18 is
connected to the rod 17, and is arranged to apply impact blows to a
rock breaking bit 19. The piston element 17 and the piston element
16 are connected at their respective left-hand ends by a small
movement shock absorbing dashpot device 54, described hereafter.
This manner of connecting together the two elements of the piston
member 11 is designed to reduce the Euler load imposed on a long
piston at impact, such as would occur when the transducer of the
present invention is incorporated into a 1,000 ft.-lb. hammer to be
mounted on a digger to give blows at a rate of approximately 10
blows per second, with a mass of 200 lbs.
The left-hand end of the piston member 11 is supported in a bearing
80 which may be an annular sintered bronze bearing pad, or which
may be as described hereafter with reference to FIG. 7.
The piston element 16 is provided with a raised land 20 having two
oppositely tapering working surfaces 21, 22. The surface 21 bounds
the chamber 13 and is subjected to the cyclically varying pressures
therein in operation, while the surface 22, which has a smaller
area than the surface 21, bounds the chamber 14.
The chambers 13 and 14 are axially separated by a valve assembly
generally indicated at 25 and located internally of the cylinder
member 12. The valve assembly 25 includes a flow regulator valve 26
of the nonreturn type, an axially moveable position control valve
27 (see FIG. 3), as well as a storage space 28. In addition to
these elements, the valve assembly 25 includes a wall member 29 and
a fixed structural body 30.
The nonreturn valve 26 communicates with the chamber 13 via a bore
31 in the wall 29, and it communicates with a storage space 28 via
a bore 33 in the body 30. The storage space 28 may be placed into
communication with the right-hand chamber 14 via a port 35 in the
body 30.
The position control valve 27 is generally cylindrical in shape,
with its left-hand end abutting the wall 29. The valve 27 has an
axially extending surface which bounds the storage chamber 28 and
is provided, adjacent its right-hand end, with a first land 32
which is in sliding engagement with the port 35 in the body 30,
which constitutes a first port. The left-hand end of the axially
extending surface of the valve 27 is provided with a second land 36
which cooperates with a second port 30a in the structural member
30. It will be noted that the lands 32, 36 are axially spaced. The
right-hand end of the valve 27 is provided with a radially inwardly
extending flange 37 which is engageable with the hollow piston
element 16. In fact, as can be seen in FIG. 3, the piston element
16 is provided with a shoulder 39 to abut the flange 37 so as to
axially move the valve 27 when the piston member 12 moves rightward
in excess of a predetermined amount. A spring 39a urges the valve
27 leftward towards the wall 29.
The right-hand end of the chamber 14 is bounded by an inwardly
extending flange 40 of the cylinder member 12, and a bearing pad
40a in the flange 40 through which the piston member passes is
sealed by way of sealing elements 41.
To the right of the flange 40 the cylinder member 12 has a portion
45 of reduced radial cross section within which slides the mass 18,
with an annular sintered bronze bearing pad 43 therebetween. The
portion 45 is itself slidably mounted in the remainder of the
cylinder member 12 and is radially spaced therefrom to provide an
annular space 46 wherein a shock absorbing, vibration damping
device is provided. Said annular space 46 is filled with oil and
the vibration damping device (FIG. 4) comprises a radially
outwardly extending flange 47 on the cylinder portion 45 which is
provided with a bore 48.
A spring loaded valve 49 seats against the left-hand end of the
bore 48 and is provided with one or more small orifices to permit
restricted flow through the valve 49. A spring 51 urges the
cylinder portion leftward relative to the remainder of the piston
portion. In operation, should the piston member move excessively
far to the right, e.g. due to the tool 19 breaking through into
relatively soft material, the mass 18 will strike the right-hand
end of the portion 45, forcing it rightward against the spring 51.
The valve 49 lifts under the action of the increased oil pressure
in the space 46 to allow oil to flow through the bore 48 to permit
this movement. When the piston member 11 retracts, the valve 49
closes and the portion 45 moves leftward under the action of the
spring 51 in a heavily damped manner, due to the dashpot effect of
the small orifices on the return flow of the oil in the space
46.
The small movement dashpot device 54 (FIG. 5) consists of an
axially extending cavity 56 in the inner piston element 17 which
contains oil, the outer piston element 16 carrying by means of a
threaded bush 58 a plunger 60, which has a threaded spigot 62
engaging the threaded bush 58 and secured thereto by a locknut. The
plunger 60 is disposed in the cavity 56 and has at intervals around
its periphery axially extending grooves 64 which permit a
restricted flow of oil from one side of the plunger 60 to the
other. A plug 66 closes the left-hand end of the cavity 56. The
grooves 64 permit a small degree of heavily damped relative axial
movement between the piston elements 16, 17. Only a small degree of
relative movement may be required to sufficiently reduce the Euler
load on the relatively long piston elements 16, 17 to a
satisfactory figure. The elasticity of the oil in the cavity 56
assists in this respect. Vents 68, 70 prevent air compression in
enclosed spaces in the dashpot device 54.
In operation, the chambers 13, 14 are each connected to a
respective source of oscillating pressure fluid causing the piston
member 11 to perform oscillatory sliding motion relative to the
cylinder member 12, the pressure variations in said chambers being
arranged to be 180.degree. out of phase with each other. However,
owing to the unequal areas of the surfaces 21 and 22 of the hollow
outer piston element 16, the piston will normally drift to the
right and makeup fluid will be introduced only into the left-hand
chamber 13. Excessive drift to the right is, however, prevented by
the provision of the shoulder 39 on the element 16. When the piston
member 11 moves in excess of a predetermined amount, the shoulder
39 will engage the flange 37 of the position control valve 27,
thereby causing the land 32 of the valve to be displaced relative
to the port 35 to permit communication between the storage space 28
and the right-hand chamber 14 via the bore 35. During this time,
however, the land 36 of the valve 27 still closes the port 30a. The
nonreturn valve 26 is biassed in such a way that it will only open
at the peaks of the pressure oscillations in the chamber 13 and
thus only this peak pressure will pass from the chamber 13 to the
storage space 28 via the bores 31, the valve 26 and the bore 33. In
this way, the storage space 28 will be charged up with high
pressure fluid and this high pressure fluid will pass to the
right-hand chamber 14 when the land 32 opens the port 35. When this
happens, the pressure level in the chamber 14 will be raised
quickly and will oppose the rightward drift of the piston
member.
It will be appreciated that the function of the flow regulator
nonreturn valve 26 is to maintain the pressure in the storage space
28 above the algebraic mean pressure in the left-hand chamber 13.
Consequently, the flow regulator valve 26 need not be a true
nonreturn valve; some reverse flow from the storage chamber 28 to
the left-hand chamber is permissible provided the pressure in the
chamber 28 is suitably maintained.
If there should be further rightward movement of the piston member
11, e.g. a too sudden and extreme drift to the right, as may occur
when the tool 19 "breaks through," the position control valve 27
will open fully, that is to say, the land 36 will open the port 30a
and direct communication will be established between the chamber 13
and the chamber 14, via the space 28, bypassing the nonreturn valve
26. Thus, the oscillating pressure difference between the two
chambers is greatly reduced and the reciprocating motion of the
piston member 11 will come to a rapid stop. The difference in the
areas of the faces 21, 22 promotes the cessation of the
reciprocating motion because, once the pressure difference between
the chambers 13, 14 is reduced, the piston member tends to drift
further to the right. Restarting of the transducer may be effected
by forcing the piston member mechanically leftward until the ports
30a, 35 are closed, whereafter reciprocating motion will
recommence.
FIG. 6 shows an alternative form of the valve assembly 25.
Corresponding parts in FIGS. 3 and 6 carry the same reference
numerals, and will not be described again.
In FIG. 6 the position control valve 27 is provided with a third
land 72 which cooperates with a port 74 which is connected via a
low pressure return line 76 to the source of pressure fluid
oscillations which is connected to the chamber 13. The spacing of
the lands 36, 32, 72 is such that upon the aforementioned further
relative rightward movement, the land 72 uncovers the port 74 and
connects the chamber 13 to the low pressure return line 74 via a
vent 77 and the space in which the spring 39a is located. The flow
of pressure fluid from the first chamber 13 to the return line,
indicated by the arrows 78, permits the pressure difference between
the chambers 13, 14 to be more quickly reduced upon the further
relative movement, whereby to more quickly stop the oscillatory
movement of the piston member 11. The flow of fluid via the land 72
and port 74 also has a cooling effect, since relatively hot fluid
leaves the transducer via the return line.
The axial spacing of the lands 36, 32, 72 and their respective
ports is preferably such that the port 35 is opened at an earlier
stage of the further rightward movement than is the port 74. It
will be appreciated that the port 35 is shown ghosted in FIG. 6 so
as to indicate that it does not connect with the return line 76. A
vent similar to that at 77 is provided in the FIG. 3 embodiment to
avoid unwanted fluid compression in the space containing the spring
39a.
It will be appreciated that the transducer need not be double
acting; the chamber 14 may be a closed chamber constituting a fluid
spring. Also leftward drift of the piston member 11 may be
controlled by a dump port which is uncovered by the piston member
upon excessive leftward movement to vent the chamber 14 to a return
line such as 76.
An alternative form of the bearing 80 is shown in FIG. 7. Again,
previously referenced parts carry the same numerals. The bearing
comprises an annular sintered bronze bearing pad 82 supported in a
radial wall 83 of the cylinder member 12 and axially located by two
keep plates 86, 88. A bore 90 in the wall 83 in which the pad 82 is
disposed is of larger diameter than the pad 82, to permit it
limited radial freedom of movement. O-rings 92 seal the pad 82
against fluid leakage from the chamber 13. A return line 94 which
may be branched off the line 76 of FIG. 6 connects via the radial
clearance between the pad 82 and the bore 90 with a leakage
collecting groove 96 in the bearing pad 82. Since the return line
94, although at a low pressure compared to that in the chamber 13,
may still carry a pressure of (say) 100 ft.-lb./in..sup.2, the
pressure in the said radial clearance imparts a degree of
resilience to the bearing. The radial freedom of movement of the
pad 82 permits any malalignment between this pad and the pads 40a,
43 to be accommodated.
A further alternative form of the bearing is shown in FIG. 8. In
this embodiment, the piston member 11, instead of being in two
pieces, joined by a shock absorber, is in one piece.
The working face 21 of the piston member is formed by the annular
end face of the left-hand end of the piston member 11, which is
hollow. A spigot 97 slidably engages the hollow left-hand end 98,
and this spigot is universally mounted from the cylinder member 12
via a spherical seat 100 and a split clamp ring 102. The seat 100
and clamp ring 102 permits the spigot 97 freedom to pivot slightly
during movement of the piston member 11 to accommodate malalignment
between the spigot 97 and the bearing pads 40a, 43. A return line
104 collects leakage, and a vent 106 provided with a filter 108
prevents undesirable air compression in the interior of the hollow
end 98 of the piston member 11.
* * * * *